Geology of the Northern Pennine Orefield Volume I—Tyne to Stainmore Economic memoir covering the areas of 1:50 000 and one-inch geological sheets 19 and 25, and parts of 13, 24, 26, 31, 32 (England and Wales)

By K. C. Dunham

Bibliographic reference: Dunham, K C. 1990. Geology of the Northern Pennine Orefield, Volume 1 Tyne to Stainmore (2nd edition). Economic Memoir of the British Geological Survey, sheets 19 and 25 and parts of 13, 24, 26, 31, 32 (England and Wales).

Geology of the Northern Pennine Orefield Volume 1 Tyne to Stainmore

K C Dunham

Second edition. Economic memoir covering the areas of 1:50 000 and one-inch geological sheets 19 and 25, and parts of 13, 24, 26, 31, 32 (England and Wales)

London: HMSO, 1990.  © Crown copyright 1990 ISBN 0 11 884471 7

First edition 1948. Second edition published 1990

Author: Sir Kingsley Dunham, DSc, SD, FRS, FEng, FIMM Charleycroft, Quarryheads Lane, Durham DH1 3DY

Other publications of the Survey dealing with this district and adjoining districts

Books

Maps

Preface to the second edition

By 1977 the second printing of this Economic Memoir had been sold out. Consideration was given to the issuing of an appendix to Volume 2, then under preparation, summarising the wealth of new information which had become available during 40 years of lively mining activity, but this was rejected in favour of a revised second edition. This has been written, during his retirement at Durham, by Sir Kingsley Dunham. The later stages of the work have come under the supervision of Mr D H Land (Programme Manager, Northern England). The scientific editing has been carried out by Mr B Young at the Newcastle office of the British Geological Survey.

During the past four decades, lead ore production has continued but only one mine has been worked for this ore alone, the greater part having been a by-product of the working of fluorspar and barium minerals. Fluorspar production has quadrupled and barytes output has doubled during the period. Gratitude is expressed to the following operating companies for access to their properties and records: Athole G Allen (Stockton) Ltd, British Steel Corporation, Consolidated Gold Fields Ltd, Laporte Industries Ltd, the Owners of Settlingstones Mine Ltd, Swiss Aluminium (UK) Ltd, Vieille Montagne Zinc Co., Weardale Lead Co. Ltd, Weardale Minerals Ltd, and Weardale Mining and Processing Ltd. The author wishes to express his indebtedness for their help during this second period of investigation to Mr J A Hill, Mr D A Greenwood, Mr J D Willson, Mr A Treloar Jr, Mr P G L Vipan, Mr A Carstairs, Dr G A L Johnson, Dr B L Hodge, Professor A C Dunham, Dr F W Smith, Mr J R Foster-Smith, Mr W Wardrop, Mr H Green, Mr D W Strutt. Logging of certain important boreholes on behalf of the British Geological Survey was carried out by Mr I C Burgess and Dr A A Wilson. Wardell Armstrong and Co. are thanked for their aid with some aspects of the statistical data. The Northumbrian Water Authority, through their Engineering Consultants Babtie Shaw and Morton generously permitted the examination of mineralised intersections before the concrete lining of the Tyne-Tees tunnel system took place; Mr D A C Mills collaborated.

F G Larminie OBE Director. British Geological Survey, Keyworth Nottingham NG12 5GG 20 March 1990

Preface to the first edition

The area covered by this economic memoir includes parts of that shown on Old Series one-inch sheets 102, 103 and 106, which were published between 1881 and 1893. The relevant portions of these were surveyed on the six-inch scale by D Burns, W Gunn, C T Clough, H Howell, J R Dakyns, H Miller and J G Goodchild between 1869 and 1881. Of the 38 six-inch full sheets covering the Northern Pennine Orefield, all but 11 were published. No decriptive memoirs were, however, issued. The occurrence of the barytes, witherite, fluorspar, lead, zinc and iron ores of the field were described in Volumes II, IV, IX, XXV and XXVI of the Special Reports on the Mineral Resources of Great Britain by R G Carruthers, T Eastwood, R L Sherlock, Stanley Smith and D A Wray.

During the years 1939–1943, primarily for war purposes, the mineral deposits were re-investigated by Dr K C Dunham, under the superintendence of Mr T Eastwood; Dr J R Earp assisting for a short period in 1941. In the course of this work, the mapping of the veins was revised, all exploratory levels and crosscuts were inserted on the six-inch maps, and all available mine-sections were reduced to the common scale of 200 ft to an inch. Revision of the geological mapping was undertaken only where necessary for better understanding of the mineral deposits.

Petrographic investigations in connection with the work were made by Dr J Phemister, Petrographer, and Dr Dunham. Twenty-five new analyses of rocks and minerals were made by Mr C O Harvey and Mr G A Sergeant of the Chemical Laboratory, with spectrographic determinations by Mr H K Whalley and Mr J A C MacClelland of the Government Laboratory. Apart from corals, which were determined by Dr Stanley Smith, the faunal identifications mentioned were made by Dr C J Stubblefield of the Palaeontological Department. Mr Eastwood has edited the memoir.

We are grateful to Dr J A Smythe of Kings College, Newcastle, for permission to quote analyses of Pennine minerals made by him. The willing co-operation of all mine-owners and operators and their staffs made possible the investigation; we are indebted to them for placing mining and chemical information at our disposal without reserve. Particular mention may be made of the Weardale Lead Co. Ltd, the Vieille Montagne Zinc Co., the Weardale Steel, Coal and Coke Co. Ltd, Fluorspar Ltd, Wrentnall Baryte Co., Athole G Allen (Stockton) Ltd, B Laporte and Co., the Owners of Settlingstones Mine Ltd, Holmside and South Moor Colliery Co. Ltd, and the New Brancepeth Coal Co. Permission has been granted by the Non-ferrous Minerals Development Control and Home Ore Department (Iron and Steel Control) of the Ministry of Supply to quote information gained in the course of investigations undertaken in connection with operations in the field controlled by them.

W F P McLintock Director,Geological Survey Office, Exhibition Road South Kensington London SW7 4 October 1948

Notes

Unpublished maps are available for public reference in manuscript form at offices of the British Geological Survey.

Throughout this memoir National Grid references are given in square brackets. Most lie in 100 000 m square NY: the index letters in these cases are omitted. Where a site lies in another 100 000 m square the appropriate index letters are included.

Summary of the geology

The northern one-third of the Backbone of England, that ridge of hilly country known since last century as the English Pennines, consists of a double fault-block with the Pass of Stainmore between the two halves. The northern half or Alston Block is host to a great majority of the deposits of lead ore and associated minerals described in this volume; those from the Pass southward to the Craven country form the subject of Volume 2. A small part of the Northumberland Trough as far as the Roman Wall is included here, for the Wall delimits exactly the metalliferous mining field. Lead may indeed have been produced here by the Roman occupiers, but definite evidence begins in the 12th century with the records of the great monasteries and the Norman Kings who founded them. By the mid-17th century, most of the veins had been discovered, and from this time to the early years of the present century, two large companies dominated the mines, The Governor and Company for the Smelting of Lead with Sea Coal and Pit Coal (the London Lead Company) and the W Beaumont Company. The heyday of lead mining seemed to be over with the demise of these concerns but at least one major discovery of lead ore remainded to be made. Meanwhile fluorspar, witherite and barytes, minerals that accompany the galena, all became industrially important. The 20th century has witnessed the development here of major sources of these minerals, and lead has continued to be won as a by-product. From a restricted area of the field, zinc ore has also been mined. The deposits occur in fissure veins which form a geometrical pattern cutting rocks ranging from the Asbian through the Brigantian to the Pendleian stage of the Carboniferous system in an area of about 1700 km2; the incidence of orebodies is a little less than one per km2. A few related deposits reach the Westphalian rocks of the Durham Coalfield. The intrusive Whin dolerite sills which occur throughout the orefield also act as wallrocks for some of the veins.

The Dales of the South Tyne, Derwent, Wear and Tees, with their tributaries have been sculptured during erosion to reveal the run of the low-dipping hard members of the rock sequence. The whole block was uplifted to the west along one of Britain's largest faults, forming an escarpment facing the Vale of Eden. Here, as in the dales country, the remains of a long-standing mining industry give character to the attractive fellside landscape.

So far, this northern half of the orefield has contributed over 4 million tonnes of lead ore, one-third of a million tonnes of zinc ore, more than 2 million tonnes of fluorspar, 1 million tonnes of witherite and nearly 1.5 million tonnes of barytes to United Kingdom mineral output.

Chapter 1 introduction

Geography

The mining of lead ores has for many generations been one of the principal occupations of the scanty population of the fell and dale country extending southwards from the Tyne Valley to the Craven district, here described as the Northern Pennine Orefield. The field as a whole covers nearly 1500 square miles (4000 km2) including parts of the counties of Cumbria, Northumberland, Durham and Yorkshire. It is divided into two complementary parts by the Stainmore gap, between Barnard Castle and Brough; the present volume deals with the northern half (Figure 1). This forms a single physiographic unit which may be regarded in the simplest terms as a plateau, uplifted along its western margin, tilted to the east and dissected by rivers. On the west the Pennine Escarpment, crowned by the triple peaks of Cross Fell, Little Dun Fell and Great Dun Fell (respectively 2930, 2761 and 2780 ft (893, 842, 847 m) above sea level), forms a natural boundary with the fertile lowlands of the Vale of Eden. To the N the orefield, as developed up to the present, terminates about 5 miles (8 km) S of the main E–W valley of the Tyne, but an isolated group of deposits lying between the river and the Roman Wall to the N is included among those described. The saddle of Stainmore Forest forms the southern margin of the area, separating it from the Yorkshire Dales country, described in Volume 2. The eastern boundary is not well defined; the main mineralised area lies among the high fells, but some related deposits, described here, have been found farther E in the Durham coalfield.

The western escarpment is drained by youthful streams discharging into the River Eden to the W, but over the remainder of the area, the drainage is to the E. The three principal rivers of NE England, Tyne, Wear and Tees, rise within sight of Cross Fell. The South Tyne and its tributaries, the East and West Allen, flow northwards until they reach the main E–W valley. The Derwent drains to the NE, the Wear to the E and the Tees to the SE. The bottoms of the main valleys are at 750 to 900 ft (230 to 274 m) above sea level, while the watersheds between reach average altitudes of about 2000 ft (600 m). The fells have broad, flat tops and their convex side-slopes are sculptured into prominent features indicating the alternation of resistant and nonresistant beds in the gently dipping rock formations. In the bottoms of the broader valleys trains of rounded mounds of glacial drift are found, and there are several instances of heavy drift-cover piled up on the E-facing slopes of the N–S valleys. In the main, however, the higher slopes are free from drift but the flat tops of the fells are covered with hill-peat, usually deeply eroded into 'haggs'.

The population is restricted to the valleys, each main valley having a district centre. Alston, Allendale Town, St John's Chapel, Stanhope, Wolsingham and Middle-inTeesdale are the principal towns of the main area, while the escarpment is within easy reach of Appleby and Penrith. Geological occupations other than metalliferous mining include the quarrying of limestone, dolerite, sand and ganister, and the mining of coal; these industries do not, however, come within the scope of the present account. Agriculture is practised in the valleys and sheep-farming on the fells, but none of these occupations is able to support a large population and the area is likely to remain essentially rural, in contrast to the great industrial area of E Durham and S Northumberland. The traditional Dales miner worked in a partnership of six to ten men, taking bargains (in effect piecework contracts) from the owners (Hunt, 1984). He was a smallholder as well, and up to quite recent times work at the mines was restricted during the seasons of haymaking and harvest (Bowes and Roberts, 1983).

The main valleys were formerly served by branch railway lines with termini at Alston (South Tyne Valley), Allendale Town (East Allen), Wearhead (Weardale) and Middletonin-Teesdale, but these have now closed. The mines on the escarpment are within reach of the line in the Vale of Eden.

The detached Haydon Bridge district is near the Carlisle–Newcastle railway.

Many of the main roads of the district were made in the first case by the lead-mining companies of the past, particularly by the Beaumonts in Allendale and Weardale, and by the London Lead Company in Alston Moor and Teesdale. The past half-century has witnessed great improvements in the roads, and the valleys are now well served with good roads which also provide links over high passes, with adjacent valleys. The passes are liable to be closed for short periods in an average winter. Many of the mines are remote from the main roads, and in the past the ore from these was transported to the smelt-mills by pack-horse. Mines so situated which have been worked in recent years have been served either by aerial ropeway or by specially built roads for motor-lorry traffic. In Weardale, the iron ore worked during the nineteenth century was transported by means of a railway system, built by the Weardale Iron Company, which crossed the high fells north of Stanhope and was connected with the valleys by means of inclines. This has now been dismantled.

In 1983 the greater part of the region was designated an Area of Outstanding Natural Beauty by the Department of the Environment. Existing mining and quarrying operations, with the relevant planning permissions, will not be inhibited, but virgin developments may be affected. Meanwhile Durham County Council has encouraged the establishment of a lead mining centre around the great water-wheel at Killhope to commemorate mining and ore-dressing practices. A voluntary organisation, the Friends of Killhope, has been formed to assist in running this. Over the pass at Nenthead old mining and smelting remains are being preserved by Cumbria County Council to provide a second centre at Nenthead. Safe access to underground workings for visitors may eventually become possible at these centres. The old mining hamlet of Allenheads in being restored with aid from the Prince of Wales' Fund.

At the mines the chief and often the only source of power was hydraulic and the remains of water wheels, formerly used as prime movers for winding, pumping, dressing and smelting operations could until recently be seen. Only one, at Killhope, has been preserved. Steam power has been little used: at Hunstanworth it was tried but discarded in favour of the cheaper water power. There were some oil installations, but these have given place in most of the mines to electrification, made possible by the grid which has reached the escarpment and the principal valleys. A form of hydraulic mining known as 'hushing' was practised by the old miners, by which a torrent of water was allowed to rush over or along the course of a vein, making in the course of years a great excavation or 'hush'. Deep prospecting trenches were cut in the same way. Water from surface sources is available in adequate quantities for dressing operations. Underground the mines are not heavily watered, 80 to 100 gallons (350 to 500 litres) per minute being considered a substantial inflow even in a large mine.

Subdivision of the field

The results of the geological investigation of the northern half of the orefield are here presented in two main parts. The first covers the general description of the mineral deposits and their environment (Chapters 2 to 5), and in this the field is treated as far as possible as a whole. In the second, details of the individual deposits are summarised (Chapters 6 to 14) and here for descriptive purposes, the field is divided into nine areas, as shown on the sketch map (Figure 1). Of these the first seven constitute the main ore-mineral field and the boundaries between them are in general the watersheds between the principal valleys. In the main field, deposits occur throughout the whole exposed section of Carboniferous rocks. A detailed account of the stratigraphy, in so far as it affects the deposits, is therefore given for this region. The stratigraphy of the areas in the main Tyne Valley (8) and the Coalfield (9) in which isolated deposits occur is not treated in detail.

'New Series' colour-printed one-inch Geological Survey maps have been published for sheets 19 and 27; 1:50 000 maps for 13, 24, 25, 26 and 31, shown on (Figure 1). For the Primary six-inch geological survey, completed before 1895, six-inch maps published at that period cover almost the whole of areas 2 to 6, and parts of areas 1 and 7. The numbers of these, as well as the numbers of the unpublished maps are indicated in the detailed descriptions. No sheet memoirs were issued for the area during last century but these have now appeared for the revised sheets 13 (Frost and Holliday, 1980), 24 (Arthurton and Wadge, 1981), 31 (Burgess and Holliday, 1979) and 32 (Mills and Hull, 1976).

History of mining in outline

The Brigantes, the Iron Age tribe whose territory included at least part of the Northern Pennines, may well have been the first miners of the lead-silver ores. Tacitus reports the Roman general Agricola saying to his men that among the prizes of the invasion there would be gold, silver and other metals. The Brigantian leader, Venutius, is believed by some to have made his last stand against the Romans under Petillius Cerealis at Stanwick, between Stainmore and Dere Street in AD 74 and though the evidence is not conclusive, it is significant that the Romans were smelting lead at Greenhow near Pateley Bridge by AD 81 (Wheeler, 1954; Dobson, 1970; Jennings, 1967) leaving behind them two pigs of the metal stamped with the imprint of the emperor Domitian, and bearing the letters BRIG to identify the territory whence they came. However, although the Roman track known as the Maiden Way crosses the western escarpment and runs not far from the veins still exposed in the bed of the South Tyne near Alston, although remains including an altar and a ladle have been found in Upper Weardale, and although Hadrian's Wall marks in a striking way the northern limit beyond which no productive metalliferous veins have been found in England, there is still no proof of Roman mining within the region with which this volume deals. Raistrick and Jennings (1965, p.8) have indeed canvassed the possibility that the Castles near Hamsterley [NZ 103 331] was a penal settlement for prisoners of the Romans and the Roman practice of using prison labour in their mines elsewhere is well known; but the final links in the evidence are missing. Wallace (1890) has maintained that there was no settled population in Alston Moor until long after the Roman occupation.

During the Dark Ages mining and smelting of lead was almost certainly in progress in the North of England, for Bede, writing at Jarrow about 735 (Historica Ecclesiastica Gentis Anglorum III, xxv) mentions that Bishop Eadbert had covered the roof and oakensides of the church on Lindisfarne with sheets of lead. The nearest source might have been close to the already existing settlement of Hexham.

The first documentary evidence comes with the Normans, though not in Domesday Book; the fell country was either 'waste' or not mentioned; but a pipe roll, 31st Henry I, 1130, refers to the Carlisle Silver Mines which have been identified with Alston Moor or south Northumberland; coins of William Rufus found in an old drift on Browngill Vein lend substance to this.

Lawrence of Durham, monk and soon afterwards prior of the Benedictine monastery, was already writing in 1147 of his bishop's silver mines and it is likely that the bishops of Durham owned Weardale and its mineral rights from the foundation of the Palatinate in 1072. For later mediaeval mining, the authorities are Wallace (1890), Louis and Vellacott (1907), Smith (1923) and Raistrick and Jennings (1965). The earliest official document appears to be a charter of King Stephen granting the right to mine for silver to his nephew, Hugh de Puiset, Bishop of Durham. Puiset shortly afterwards granted a mine of iron at 'Rokehope' to the hospital of St Giles. In Pipe Roll 8, Richard I, 1196–97 there are references to the Bishop's Mint in Durham, from which he issued his own coinage. The mines may have been run under the direct control of the bishoprick or the abbey until 1379 when Bishop Thomas of Hatfield issued a 50-year lease, though still retaining the mines of 'Rykhope', Stanhope and Newlandside to himself. In 1391 there are references to 'Grenefeld' (Greenfield), 'Dawtrysheles' (probably Greenlaws, near Daddryshield), Toggythawaytegrove' and 'Blackden' (Blackdene) mines. In 1401 'Aldwoodeclough' (probably Allercleugh) Mine was mentioned in a lease; it was idle in 1426 as was Burnhope, but West Sedling delivered 25 loads of ore. In the Ecclesiastical Commissioners minerals accounts there are references to smelting at Wolsingham and 'Kughteslaw' in 1457. There is a Baal Hill Wood north of Wolsingham and the hill named Billing, near Eastgate probably also refers to the bole hill method of smelting with natural draught. However as early as 1429 smelting 'with a wheel' (that is, with bellows driven by water wheel) is mentioned and figures suggest that at that time it was more expensive than boling. It was not until the 17th century that all smelting was done in mechanised mills. A grant of 1475 mentions 'Shyldeyn' (Shildon) and Teccheroos' (Fletcheras) mines, respectively in Hunstanworth and Alston Moor. Although Wallace (1890) expressed the view that no extensive mining was done in the latter district before 1650, it is clear from the long list of mines named in the documents in the case of W Blackett v. Isaac Basire, Rector of Stanhope in 1666 that most of the Weardale deposits had been discovered by that time. To the early period, prior to the middle of the 17th century belong the bell pits, shallow shafts, a few adits, and notably the hydraulic hushes like Coldberry Gutter, where 2.5 mt of rock were removed by repeated sluicing of the hillsides. Both this excavation, and the Cowhorse Hush at the head of Weardale were already in existence before the two major operating companies discussed below began work. It is difficult to get any reliable idea of the output during the first five centuries of mining after the Norman conquest. Among the few figures, Durham records show the purchase of 330 loads of ore, yielding 60 fothersThe fother seems to have varied in amount in different parts of the Pennines. Here it was perhaps 22 cwt, since in 1429 the accounts show an entry of 3 fothers 174 stones. The total output of the Bishop's mines in that year may have been 35 t on this basis. of lead, when Wolsey was Bishop of Durham in 1523. It may well be that the whole field averaged little more than 100 t lead annually during these early centuries, when mining was probably intermittent. The bringing of German miners by Queen Elizabeth I to her mines in the Lake District, with knowledge of the construction of horse and water-driven equipment such as Agricola (G Bauer, 1556) described and illustrated, almost certainly improved practice in the Pennine fields; names such as Henrake (Heinrich) and Rowpotts (Rupert's) veins at Silverband, and Blaygill (Bleigill) suggest their influence. The industry probably began to grow in the 16th century, and reached more substantial production in the 17th.

The 18th century, however, witnessed the great development of lead mining and smelting in the Northern Pennines, two companies being mainly responsible in the country north of Stainmore. The London Lead Co., the historian of which is Dr Raistrick (1933, 1936, 1938; Raistrick and Jennings, 1965) acquired its first leases in Alston Moor soon after its formation in 1692. During the century which followed, its activities spread to the (former) Westmorland Pennines, to Weardale, to Teesdale and into the Derwent area. Meanwhile, the family concern founded at about the same time by Sir William Blackett and handed on through his successors to the Beaumont family (referred to hereafter as the Beaumont Co., though it was not in fact a limited company until the closing years of its activity) commenced work in the Allen-dales and shortly afterwards acquired most of the Weardale mines. For 200 years these two firms continued their operations, to the great benefit of the district. Hutchinson (1794) records that by 1772, over 7500 tons of lead were being shipped annually from the Tyne. A statistical study of the records of the two companies, preserved through the initiatives of Henry Louis and Arthur Raistrick in Newcastle (Dunham, 1944) shows that the period of maximum output was between the end of the Napoleonic Wars and 1880, the combined annual production of lead concentrates by the two companies averaging over 20 000 t. A number of small lead-mining companies referred to in the detailed description of the mines, were also active in the field at this time. The old mining works thus mainly belong to the 18th and 19th centuries; they include many long, well-engineered levels and crosscuts and a few deep shafts.

Throughout this memoir the following convention is adopted: where production is recorded in Imperial Tons the unit is retained: where metric Tonnes are recorded the abbreviation t is used.

The London Lead and Beaumont Cos., facing a rapidly falling price of lead and presumably having no belief in the future of lead mining in the region, surrendered their respective Alston Moor and Weardale leases in 1882 and 1884. The Weardale Lead Co. took over in Weardale, and was able to maintain a substantial output of lead concentrates until 1931. In 1924 this company also took over the last mines of the Beaumont Company in East Allendale. In Alston Moor zinc mining, started in a small way by the London Lead Co., became of first importance with its successor, the Nenthead and Tynedale Zinc Co. (Almond, 1977) which operated until 1906 when the Vieille Montagne Zinc Co. of Liege, Belgium, took over and continued production of zinc concentrates until 1921.

There were 28 lead smelt mills in the region (Raistrick, 1936; Clough, 1980) and the remains of their flues, in some cases as much as 0.9 miles (1.5 km) long, may be seen on the fell sides. The last of these, owned by the Weardale Lead Co. in Rookhope, closed in 1919, concentrates thereafter being shipped to the Tyne and elsewhere for smelting. Some zinc ore was smelted at the Greenwich Hospital's Langley smelter as early as 1817, and a zinc smelter near Milton was in operation from 1845 to 1896. The Vieille Montagne Co. normally shipped its concentrates to Belgium. As zinc production slowed down, this company had some success in underground exploration at its Nentsberry Mine, which remained a useful lead producer until 1938, yielding crude ore with up to 13.4 per cent PbS. Meanwhile during the present century the Weardale Lead Co. discovered the rich flats at their Boltsburn Mine, Rookhope, which up to its closure in 1931 yielded nearly 100 000 t of lead concentrates. Since the closure of the company's Allendale mines in 1943, only one orebody in the region has been worked exclusively for lead.

The mining of iron ore, though begun many centuries ago in Weardale and Teesdale, was of little importance until 1842 when the Weardale Iron Co. started to develop the industry. The important period lasted up to 1880, but some mining continued up to 1920, and there was a brief resumption during the second world war.

The decline of lead and iron mining has been to some extent offset by the development of the nonmetallic resources of the field. Witherite, for the production of which the Northern Pennines is unique in the world, was being worked in the Alston district as early as 1850. Between 1860 and 1870 two old lead mines in the Haydon Bridge area changed over to witherite production: Fallowfield and particularly Settling-stones had between them produced a large proportion of the world's supply of natural barium carbonate when operations came to an end in 1969. Three collieries, Ushaw Moor, Cragside and South Moor, also made useful contributions. Although prospecting has been continued, at present (1985) there is no longer any output of witherite. Barytes production reached substantial tonnages at Lunehead, Cabbish and Cowgreen mines and New Brancepeth Colliery between 1900 and 1921. The Second World War led to the revival of Cowgreen and the resumption of production at New Brancepeth, the former being regarded as exhausted by the time it was submerged beneath the Northumbrian Water Authority's reservoir in 1968, and production from the latter ceasing with the closure of the colliery in 1956. Meanwhile at Silverband (Cumbria) and at Closehouse in Lunedale, both former London Lead Co. properties, large and hitherto unworked barytes deposits were brought into production by Laporte Industries Ltd and Athole G Allen (Stockton) Ltd. Closehouse (now Closehouse Minerals Ltd) is at present the leading English producer. The mining of fluorspar, begun in 1882 by the Weardale Iron Co. at their Crawley Mine was largely developed by the Weardale Lead Co. There were exports to the USA up to 1930. The British Steel Corporation, through one of its constituent companies acquired considerable interests in fluorspar mining in Weardale and Derwent after the Second World War, and in 1964 Imperial Chemical Industries acquired a controlling interest in the Weardale Lead Co. to secure a source of high-grade spar. This interest was taken over in 1977 by Swiss Aluminium Mining (UK) Ltd, who were already developing the former Anglo-Austral mine in Weardale. The 1985 position is that the tonnage of ore being broken in the ten active mines of the region probably totals not much less than the output of crude ore at the peak of the London Lead and Beaumont production, but owing to mechanisation a very much smaller number of men are now employed. Large central processing plants built by Swiss Aluminium at Frosterley and by British Steel Corporation at Blackdene, both now owned by companies of the Minworth Group, make it possible to deal with substantially greater tonnages of crude fluorspar, and further prospecting and development will be needed. The driving of a deep 40 km-long aqueduct tunnel by the Northumbrian Water Authority to convey water from the Tyne to the Tees as part of the Kielder Project, situated E of the main fluorspar-producing area has not, however, given as much hope of extension in that direction as might have been expected.

In (Table 1) and (Table 2) the production record of the Tyne to Stainmore region to 1938 is reproduced, with minor amendments, from the first edition of this memoir, and additional statistics are given to bring the position up to 1985. It must be stated, however, that while reasonably complete official data were available for publication for the period 1848 to 1938, this has not been the case since then. The information has been collected from operators and owners of mineral rights and is published with their permissions. The general situation up to 1956 (Dunham, 1959) had already been summarised, and valuable additional data has come from Greenwood and Smith (1977); it must be noted, however, that the figures given by these authors for fluorspar production refer to crude mined ore from 1957 onwards whereas figures given in (Table 1) refer to sales of fluorspar of all grades after processing. In Weardale this has been derived from the treatment of nearly 3.7 mt of mined ore (including about 7.5 per cent stope fill from lead mining) plus an estimated 0.5 mt residues from previous lead and fluorspar mining. A rough estimate of the total quantity of calcium fluoride extracted is almost 2 mt.

In order to place the total output in (Table 1) and (Table 2) in geochemical perspective, it may be stated that they represent the mining, to date, in an area of approximately 1600 km2, through a rock thickness of about 0.5 km. The mass of rock, calculated at 2.6 t/m3 amounts roughly to 2.08 X 1012 t, thus the mined lead represents about 1.663 parts per million, zinc 0.09 ppm, fluorine 0.49 ppm, barium 0.73 ppm; these may be compared with the accepted crustal values, respectively 16, 80, 660 and 80 ppm in sedimentary rocks. Though very small compared with rock mass around them, the deposits to be described are very highly concentrated. This memoir attempts to trace how this may have come about.

References

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ALMOND, J K. 1977. The Nenthead and Tynedale Lead and Zinc Company Ltd, 1882–1896. Mem. Northern Mine Res. Soc., British Mining, No. 5, 26–40.

ARTHURTON, R S, and WADGE, A J. 1981. Geology of the country around Penrith. Mem. Geol. Surv. G.B. 177 pp.

BOWES, P, and ROBERTS, A. 1983. Farmer-miners of the High Pennines. Optima, Vol. 31, 200–220.

BURGESS, I C, and HoLLIDAy, D W. 1979. Geology of the country around Brough-Under-Stainmore. Mem. Geol. Surv. G.B. 131 pp.

CLOUGH, R T. 1980. Lead smelting mills of the Yorkshire Dales and Northern Pennines. 325 pp. (Keighley: Clough.)

DOBSON, B. 1970. Roman Durham. Trans. Arch. & Arch. Soc. of Durham and Northumberland, Vol. 2 (new series), 31–44.

DUNHAM, K C. 1944. The production of galena and associated minerals in the Northern Pennines; with comparative statistics for Great Britain. Trans. Inst. Min. Metall. , Vol. 53, 181–252.

DUNHAM, K C. 1959. Non-ferrous mining potentialities of the Northern Pennines. 115–148 in The future of non-ferrous mining in Great Britain and Ireland. (London: Institution of Mining and Metallurgy.)

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FROST, D V, and HOLLIDAY, D W. 1980. Geology of the country around Bellingham. Mem. Geol. Surv. G.B. 112 pp.

GREENWOOD, D A, and SMITH, F W. 1977. Fluorspar mining in the northern Pennines. Trans. Inst. Min. Metall., Vol. 86, B181–190.

HUNT, C J. 1984. The lead miners of the northern Pennines in the eighteenth and nineteenth centuries. 282 pp. (Newcastle upon Tyne: Davis.)

HUTCHINSON, W. 1794. The history and antiquities of the County Palatine of Durham. Vol. 3, 522 + 29 pp. (Hutchinson: Carlisle.)

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MILLS, D A C, and HULL, J H. 1976. Geology of the country around Barnard Castle. Mem. Geol. Surv. G.B. 385 pp.

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RAISTRICK, A R. 1936. Lead smelting in the North Pennines during the seventeenth and eighteenth centuries. Proc. Univ. Durham Philos. Soc. , Vol. 9, 164–170.

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RAISTRICK, A R. and JENNINGS, B. 1965. A history of lead mining in the Pennines. 347 pp. (London: Longmans.)

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Chapter 2 The country rock: Lower Palaeozoic foundation and sedimentary stratigraphy

Introduction

All the workable mineral deposits of the Northern Pennine field occur in country rocks of Carboniferous age, a majority being found in the Carboniferous Limestone Series or Dinantian, formerly called the 'Lead Measures'. The rocks of this series are remarkable for the constancy of succession which they exhibit over a wide area. There is little doubt that individual beds in the sequence had been recognised and named by the lead miners long before geology became a systematic science. The succession was worked out by Westgarth Forster, who epitomised the information derived from centuries of lead mining in his Treatise on a section of the strata from Newcastle-upon-Tyne to Cross Fell (first edition, 1809), providing a standard succession which more modern work has, for the most part, confirmed. The first general account of the geology of Northumberland and Durham, accompanied by a geological map, was due to Winch (1817, p.1). The area south of the Tees was described by Phillips (1836, p.54), who demonstrated the continuation of his Yoredale Beds of Wensleydale into the present area. In the meantime, at the mines of the Beaumont and London Lead Companies, particularly under the influence of Sopwith and Wallace, increasing attention was paid to the exact survey of details of wall-rock stratigraphy, with the result that excellent sections of all the important mines are in existence today. Both Sopwith (1833, p.85) and Wallace (1861, p.1) published accounts of the stratigraphy of Alston Moor, the latter emphasising variations from Forster's standard succession. In the primary six-inch geological survey the limestone and coal horizons were mapped with a few of the sandstone beds. The frequency of these horizons enables an accurate picture of the geological structure to be obtained, though there are certain gaps in the succession which could with advantage be filled in on the maps. Even without revision, however, the primary maps have provided a satisfactory basis for the present investigation.

Up to the beginning of the present century all stratigraphical work in the area had been based on the comparison of lithological horizons. The palaeontological approach may be said to have begun with Garwood (1907, p.70; 1912, p.449) and Stanley Smith (1910, p.591), who made zonal studies on the lines of Vaughan's work in the Bristol area, which have been carried further in Westmorland by Turner (1927, p.319). The Coal Measures of Northumberland and Durham have been zoned by Hopkins (1928, p.1; 1930, p.254). These investigations have revealed a number of key horizons useful for correlation purposes, but their main value lies in the comparisons with other areas which they make possible. More recent investigations are reported in the appropriate sections, below.

The Lower Palaeozoic foundation

The older Palaeozoic rocks upon which the Carboniferous of the northern part of the Northern Pennines rests are exposed in two areas. One, known as the Cross Fell Inlier, is a long narrow strip lying between the Carboniferous outcrop on the escarpment and the Outer Pennine Fault; the other occurs beneath Cronkley Scar in upper Teesdale. The Cross Fell Inlier, well known from the works of Buckland (1817), Goodchild (1889), Nicholson and Marr (1891) and others, has been revised in detail by Shotton (1935) and by the Geological Survey (Burgess and Wadge, 1974).

Numerous minor igneous intrusions, including felsite, rhyolite, lamprophyre and dolerite types, occur in the Cross Fell inlier. They have been described in detail by S N Hudson (1937, p.323). The relations between the rocks and the inlier are structurally complex, but for the present purpose the important point is that the basement beds of the Carboniferous all along the escarpment rest upon Skiddaw Slates. Marr (1921, p.64) made the interesting observation that the Coniston Limestone Series is found round the margins of the Pennine rigid block, always dipping away from the block (of which the present area forms the northern half). He drew the conclusion that a core of rocks older than the Coniston Limestone Series underlies the Carboniferous rocks of the Pennines.

This is borne out in the Cronkley Inlier of Teesdale, where almost unfossiliferous highly cleaved slates, tentatively classed as Pale Slates (Stockdale Shales) by Gunn and Clough (1878, p.27), but now shown by Johnson (1961) to belong to the Skiddaw Group, crop out together with lavas referred to the Borrowdale Volcanic Group. Dykes of lamprophyre trending ENE cut through the slates near Cronkley Pencil Mill [NY 8490 2956].

At Emma Pit, Crook the Roddymoor Borehole [NZ 1513 3634], 20 miles (20 km) ENE of the Cronkley Inlier, reached the base of the Carboniferous at (2827 ft) 861.8 m below surface and passed into slates which according to Woolacott (1923) corresponded with Skiddaw Slates. More recently the joint British Steel Corporation–Institute of Geological Sciences No. 1 Boring at Allenheads [NY 8604 4539] terminated in grey-green slates 1533 ft (467.5 m) below surface, beneath the base of the Carboniferous. It thus appears that the sedimentary rocks most likely to be encountered beneath the Carboniferous between Tyne and Stainmore would belong to the Skiddaw Group; no evidence to support the suggestion of 0 T Jones (1927, p.14) that Precambrian rocks might occur has been forthcoming. In the northern part of the escarpment the base of the Carboniferous rises from 1250 ft (381 m) above OD in Kirkland Beck to 1350 ft (411 in) in Crowdundle Beck; towards the SE it falls, reaching 1200 ft (366 m) in Rundle Beck below the Dufton mines, 1150 ft (351 m) above OD in High Cup Gill and 950 ft (290 m) in Hilton Beck. The Cronkley exposures reveal the base at 1300–1350 ft (396–411 m) above OD, while at Crook it is at 2276 ft (694 m) below OD, the fall from Cronkley to Crook being at the average rate of 180 ft per mile (34.3 m per km).

Weardale Granite

The presence of a stock or batholith of granitic of granodioritic composition, concealed beneath the Carboniferous rocks, was first suggested (Dunham, 1934, p.715) as a possible explanation of the zonation of the mineral deposits, but this was no more than a speculation based upon analogy with the orefield of Cornwall and Devon. The only other evidence that could have been held to support such a view at that stage was the incipient hornfelsing of the Skiddaw Slates of the Cronkley Inlier (Robinson, 1970) and the presence of garnet in the slates cut in the Crook borehole (Wollacott, 1923). A detailed gravity survey over the region by M H P Bott and D Masson Smith (1957), following a single traverse by J Hospers and P L Willmore (1953), revealed pronounced negative Bouguer anomalies, the form of which provided strong presumptive evidence for the existence at depth of a batholith with several cupolas, composed of rock less dense than those into which it was intruded. The minimum gravity values lay close to Rookhope, and here Bott (1960) calculated that the top of the postulated granite was probably not over 2000 ft (610 m) below surface. The Rookhope Borehole [NY 9374 4278] drilled in 1960–61 for the University of Durham with support from the former Department of Scientific and Industrial Research, entered granite directly beneath Carboniferous rocks at 1281 ft (390.5 m) below surface at 222 ft (67.7 m) below OD. There had been no sign of metamorphism in the Carboniferous rocks, and the granite surface was covered with a soil-like mudstone rich in quartz and white mica derived from the weathered upper part of the granite. The granite plainly predated the Carboniferous sediments (Dunham, Bott, Johnson and Hodge, 1961). The granite exhibits flat-lying foliation marked by micas and quartz eyes, consistent with its postulated position near the apex of a cupola. Petrographical examination (by A C Dunham, in Dunham, Dunham, Hodge and Johnson, 1965, pp.338–393) shows that it is a two mica, nonporphyritic rock composed of albite (about An12), potash feldspar ranging from orthoclase to maximum microcline, quartz, muscovite, biotite and minor amounts of magnetite-ilmenite, zircon and monazite (Plate 2). It contains segregations and veins of pegmatite and aplite, and a few tourmaline-bearing veins. Horizontal jointing perhaps representing relief jointing related to the surface exposed in Carboniferous time, is present in groups at intervals; and steeply inclined joints also occur. Muscovite is most abundant in the upper part of the 1369 ft (417 m) drilled through, the relative amount here appearing significantly greater than in most British Lower Palaeozoic granites. Age determinations on separated muscovite from the granite by M H Dodson and S Moorbath (1961) using Rb-Sr and K-Ar methods, and by F J Fitch and J Miller (1965) using K-Ar gave apparent ages ranging from 361 ± 7 to 392 ± 6 million years (Ma). Determination of 87Rb/86Sr and 67Sr/66Sr values for eight whole rock samples taken from depths varying from 1850 to 2551 ft (564 to 776 m) in the borehole enabled J G Holland and R St J Lambert (1970) to conclude that the geologic age of crystallisation was 410 ± 10 Ma, that final cooling of subjacent magma, with intrusion of aplites took place at 390 ± 8 Ma, but that hydrothermal activity continued to 365 ± 8 Ma causing down-dating of the muscovites. The almost gneissic texture of the upper part of the granite suggests that some measure of recrystallisation may have taken place after the initial stages of cooling. Holland and Lambert regard the initial 87Sr/86Sr of 0.706 deduced from their isochron as evidence that the Weardale granite is of mantle derivation, rather than from crustal anatexis.

The chemistry of the granite has been investigated in some detail, five full analyses being included in Dunham et al. (1965) and fifteen more in Holland (1967). A wide range of trace-element determinations were made in connexion with this work by Mrs M Kaye. Representative data are given in (Table 3), but the papers of Holland, and Holland and Lambert cited above should be consulted for a discussion of the petrogenetic significance of the results. Brown et al. (1987) have contributed six additional full analyses of the Weardale Granite with trace element determinations for 18 trace elements. Ranges of such elements of possible interest in connection with the overlying mineral deposits include: Ba 43–372 ppm; Sr 21–126 ppm; Pb 16–35 ppm; Y 8–15 ppm; La 3.9–19.2 ppm; Ce 8.8–45.8 ppm; Eu 0.3–0.7 ppm; Th 2.3–13 ppm; U 4.1–9.2 ppm. These authors conclude that the peraluminous nature of the granite may have resulted from its intrusion into relatively wet slates compared with the drier environment of the granite beneath the southern half of the orefield. The Weardale environment is supposed to have promoted early and prolonged hydrothermal activity in the intrusion.

It is concluded that the Lower Palaeozoic foundation of the northern half of the Northern Pennine orefield contains an extensive granitic batholith belonging to the 'Newer Granite' series of post-tectonic Caledonian intrusions. Bott (1967) has interpreted the gravity data to suggest that the long axis trends ENE, and that the area covered is of the order of 1250 km2, with major cupolas beneath Rookhope and Tynehead, and smaller protrusions under Upper Scordale, Burnhopefield and perhaps Cornsay. Seismic evidence enables the depth to the bottom of the batholith to be estimated at about 7.5 miles (12 km).

Carboniferous

Classification

In the first edition of this Memoir, the Carboniferous Limestone Series, the base of which rests uncomformably on the old foundation rocks, was described in four main divisions. The lowest or Basement Group included the basal Carboniferous conglomerates, and also, in the extreme south-western part of the area, south of the South Swindale Beck Fault, shales, sandstones and limestones representing the zones of Athyris glabristria (C1), Michelinia (C2) and Productus corrugato-hemisphericus (S) of Garwood (1912, p.534). N of the fault, no evidence has been found in the Basement Group of beds earlier in age than the Nematophyllum minus (S2) sub-zone. The three succeeding divisions corresponded with the three divisions of the Upper Bernician of Northumberland adopted in the Brampton Memoir (Trotter and Hollingworth, 1932, pp.16, 44) following the practice established in the Belford and Holy Island Memoir (Carruthers et al., 1927, pp.37, 38). In the first edition, these divisions were referred to as the Lower, Middle and Upper Limestone groups, without the use of the term Bernician. The Lower Limestone Group corresponded with Garwood's Lower Dibunophyllum (D1) subzone; extending from the non-sequence above the Bryozoa Band, which occurs near the bottom of the Melmerby Scar Limestone (Turner, 1927, pp.334, 357) up to the base of the Smiddy Limestone. This limestone, since it contains the Girvanella Band, marks the base of the D2 subzone (Turner, 1927, pp.347, 348) and was taken as the lowest bed of the Middle Limestone Group. The lower part of this group is definitely of D2 age, but there is a lack of agreement about the position of the top of the sub-zone. Garwood regarded the Orionastraea Band, represented in the present area by the Tynebottom and Single Post limestones (Turner, 1927, p.350) as probably marking the base of D3 as understood in Derbyshire (1924, p.255). Stanley Smith (1910, p.599) placed the Middle Limestone Group in D2-3, whereas in the Brampton Memoir (1932, p.44), where a summary of the various classifications may be found, the Middle Limestone Group was taken as D2, and the Upper Limestone Group referred to D3 or Dy in agreement with Stanley Smith. Hedley (1931) classified the beds of the Middle Limestone Group above the Single Post Limestone, together with the whole Upper Limestone Group as Yoredaleian, using a term which had already been suggested as a new major division of the Carboniferous (British Association Committee, 1926, p.256) for beds above D1.

The terms Yoredale and Yoredaleian had been far too widely used to admit exact definition. Originally introduced by Phillips (1836, p.37) to include the beds in Wensleydale from the Hardraw Scar Limestone up to the base of the Millstone Grit, there just above the Great Limestone, the term Yoredale Beds was used by the primary surveyors to cover measures with alternations of limestone, shale and sandstone wherever they were found overlying massive limestone in the North of England. In the present area, the series from the top of the Melmerby Scar Limestone up to the base of the Millstone Grit was so described. The term Yoredaleian has been used both in the zonal sense noted above, and also as a facies name (Hickling, 1931, p.222). It is not proposed to make further stratigraphical use of either term here but it may be noted that the Upper Limestone Group was taken in the first edition of this memoir (1948) to extend up to the base of the First or lowest grit of the Millstone Grit as mapped on Old Series Sheet 102 NE, this line corresponding with the top of the Yoredale Rocks of the Primary Survey. Traditionally, this line was also the division between the Lower and Upper Carboniferous. The same practice with regard to the Upper Limestone Group was continued on the partial revision of New Series Sheet 19 by R G Carruthers (published 1956) and of Sheet 25 by myself (published 1965), but on the former the Upper Carboniferous was assumed to commence at the top of the Great Limestone (the bottom member of the Upper Limestone Group) while on the latter the question was left open.

Research in stratigraphical palaeontology had, in fact, advanced by that time to the point where it was beginning to be possible to chose a position for the junction between the Lower and Upper Carboniferous corresponding with that recognised in adjacent parts of Europe, that is, the junction between the Dinantian and Namurian, palaeontologically defined by the division between the Goniatites (P2) and Eumorphoceras (E1) zones. Already by 1948 some indication of the likely position was beginning to emerge. From a reexamination of the cores from the Roddymoor boring at Crook, Sir James Stubblefield had identified Girtyoceras sp.(P2) from the shale overlying the Five Yard Limestone of Woolacott's correlation (1923, p.51). In a faulted area of shale and limestone near the escarpment, a band containing Cravenoceras sp intermediate between malhamense and cowlingense, associated with Eumorphoceras (Shotton, 1935, p.688; Shotton and Trotter, 1936, p.386) indicated either an E1 or a low E2 age for these beds, which Shotton considered to be just above the Great Limestone or near the Oakwood Limestone, ie in the lower part of the Upper Limestone Group. In the Tyne Valley the presence of Tylonautilus nodiferus (Armstrong) high in the Upper Limestone Group (Hedley, 1931, p.237) is taken as indicating an E2 age.

Correlations with localities outside the area, bearing on the classification of the Carboniferous, include (1) the correlation of the Jew Limestone of the present area with the Oxford Limestone of northern Northumberland, the shale above which at Rock Middlesteads Limekiln Quarry contains Beyrichoceratoides truncatum, identified by Stubblefield from a specimen in the Geological Survey collection; suggesting a low P age; (2) the probable equivalence of a limestone low in the Middle Limestone Group with the Budle Limestone of Northumberland, the shale overlying which contains Posidonia becheri and Goniatites crenistria' (Hedley, 1931, p.181), indicating a P1 age; (3) the correlation of the Jew Limestone, low in the Middle Limestone Group, with the Hardraw Scar Limestone of Wensleydale and the Lamellibranch Bed of Ingleborough (Turner, 1927, p.348). The Hardraw Scar Limestone overlies shales containing Goniatites sphaerico.striatus of P1, age (Bisat, 1945); (4) the correlation of the Great or Four Fathom Limestone of the present area with a limestone mapped as the Main Limestone on the summit of Fountains Fell on Sheet 50. A shale immediately beneath this limestone contains Eumorphoceras pseudobilingue (Hudson, 1941, p.269) E. tornquisti (O'Connor, 1964) and Cravenoceras leion (Arthurton et al., 1988) indicating an E1 age; (5) the correlation of the Mirk Fell Ironstone of Tan Hill, shales associated with which carry Cravenoceras cowlingense of low E2 age (Hudson, 1941) with a horizon high in the Upper Limestone Group; Carruthers (1938, p.252) suggested the Knuckton Shell Beds; Hudson preferred the Rookhope Shell Beds, but present ideas favour the Lower Felltop Limestone (Mills and Hull, 1976, p.28). From these considerations it appeared that the Middle Limestone Group was mainly of P age, while the few fossils obtained from the Upper Limestone Group were of E1 or E2 age. It had become clear, however, that goniatites, abundantly present in the Bowland Basin and Mid-Pennines, where W S Bisat's classic work (1924) forms the basis for their use as Carboniferous zone-fossils, are very rare N of the Craven faults. Nevertheless, collecting during the 1950s enabled the position of the Dinantian–Namurian boundary to be fixed as very close to the base of the Great Limestone, the most significant discoveries being G A L Johnson's find of Girtyoceras? costatum and G. cf. waitei or cf. shorrocksi in a thin shale separating the Four Fathom Limestone from the overlying cherts in the Mount Pleasant boring [NZ 034 152] near Barnard Castle indicating a position near the top of the P2 zone; and the collection of Cravenoceras leion (E1a) from shale above the Great Limestone at Greenleighton, Northumberland (Johnson, Hodge and Fairbain, 1962), who review other supporting discoveries, including that of Cravenoceras aff. malhamense from shale above the Little Limestone near Swinhope Mine [NY 826 466]. Eumorphoceras has been recorded from near the base of the sandstone above the Great Limestone at Brunton Bank, Northumberland (Johnson, 1986, p.45). The shale above the Great Limestone at Greenleighton may well be the equivalent of the upper part of the limestone itself in the present region. Thus the choice of the base of the limestone gives a boundary within a few metres of the absolute chronostratigraphic position, and since this is probably the best mapping line in the Carboniferous of the North of England, it has won general acceptance. Fully revised 1:50 000 geological maps issued more recently (24–Penrith, 1974; 31–Bough-under-Stainmore, 1974; 26–Wolsingham, 1977) all show the Lower Carboniferous (Dinantian)/Upper Carboniferous (Namurian and Silesian) boundary in this position as does one-inch sheet 32–Barnard Castle, 1969. This important development has led to the abondonment of the terms Lower, Middle and Upper Limestone Group. On the three 1:50 000 sheets mentioned, however, the terms Lower and Upper Alston Group have been introduced to replace the first two of the three former divisions. The old terms Carboniferous Limestone Series and Millstone Grit Series are retained on all these sheets, but to avoid confusion with the first edition of this memoir they will not be used here, since they are now synonymous respectively with Dinantian and Namurian: these chronostratigraphic terms will be used instead.

There remained the question of the upper limit of Namurian strata, and the position of the 'Millstone Grit' as mapped during the primary survey in the present region. To clarify this, the Institute of Geological Sciences drilled a borehole near Woodland [NZ 0910 2770] near the SE fringe of the part of the orefield covered by the present volume. The result enabled the internationally recognised chronostratigraphic stages with the Namurian and lowest Silesian to be placed in relation to the succession in the Northern Pennines (Hull, 1968; Mills and Hull, 1968) though with varying degrees of certainty. The key fossil Gastrioceras subcrenatum, the incoming of which defines the Namurian–Westphalian boundary, was unfortunately not found, but by means of indirect arguments it was possible to recognise the Quarter-burn Marine Band of the Barnard Castle area as defining this line. The effect is to bring the uppermost of the three grits (sandstones) of the 'Millstone Grit' as mapped during the primary survey into Westphalian A. The 'First Grit' was shown on goniatite evidence to belong to the R1 zone and thus to the Kinderscoutian stage; thus the 'Second Grit' is assigned in part to the Marsdenian, but mainly to the Yeadonian stage. The position of the Homoceras Zone (H) is less satisfactory. The highest record of Posidonia corrugata, which is known only from the Eumorphoceras (E) zone elsewhere, lies only 56 ft (17 m) below proved R1a beds. Hence the H zone, represented by the Chokierian and Alportian stages, must be very much attenuated, if it is present at all. The greater part of the Namurian section, including almost all the beds formerly classed in the Upper Limestone Group, belong to the Pendleian (E1) and Arnsbergian (E2) stages with the division between them near the position of the Lower Felltop Limestone.

Returning now to the Lower Carboniferous, it may be noted that of the two major divisions of the Dinantian–Tournaisian and Visean–beds belonging to the 'first-mentioned may continue eastward from Ravenstonedale into the Stainmore Trough, but this has not been proved; effectively, all the Lower Carboniferous rocks of the present region belong to the Visean. Recently the Stratigraphical Committee of the Geological Society of London (T N George, G A L Johnson, M Mitchell, J E Prentice, W H C Ramsbottom, G Sevastopulos and R B Wilson, 1967) has agreed upon stage names for the chronostratigraphic division of the Dinantian of the British Isles. While the Chadian, Arundian and Holkerian stages are represented in the marine upper part of the Basement Group of the extreme south-western part of the Tyne to Stainmore region, only the last-mentioned persists north of the South Swindale Beck Fault. The term Orton Group has been applied on sheets 24, 31 and 26 to the succession of marine strata up to the base of the Asbian Stage. This latter stage (corresponding with Gar-wood's DI zone) and the succeeding Brigantian Stage (including D2 of Garwood, but continued up to the base of the Great Limestone) are the important ones for the purpose of the present account and are represented respectively by the Lower and Upper Alston groups, already mentioned. In the Geological succession (inside front cover) the classification to be used here is set out.

Dinantian

Chadian, Arundian, Holkerian–Basement and Orton groups

The basement beds of the Carboniferous are exposed in deep valleys cut into the Escarpment and around the Cronkley Inlier. They have been proved in the Roddymoor, Rookhope and Allenheads No. 1 borings. In their normal development they include conglomerates, sandstones and shales, with a few bands of argillaceous limestone and, rarely, thin coals. In thickness they vary greatly and it is probable that they filled up broad hollows in the pre-Carboniferous floor; this is very well illustrated by Burgess and Wadge 1974, figs. 17 and 18, which also shows the variable lithology. An older and a newer Basement Series was recognised during the primary survey. The older type, which has been called the Polygenetic Conglomerate, contains a high proportion of pebbles foreign to the area, and exhibits dips up to 40° greater than those in the overlying Newer Series. The principal exposures of the older conglomerates lie east respectively of Gamblesby, Melmerby and Ousby Townhead. Wadge (1978) has suggested that these beds originated in fans, possibly derived from a fault-scarp lying to the W. Like some earlier authors, he regards their age as possibly Devonian. The lithology of these conglomerates and those of the normal Carboniferous Basement Group have been studied by J G Capewell (1956). The latter are often dominated by vein-quartz pebbles, but otherwise contain clasts of local origin. A Carboniferous age for these beds in Hilton Beck has been proved by Shotton (1935, p.643).

The Orton Group is regarded as commencing at the incoming of marine conditions in place of the continental environments in which the older and newer Basement Beds presumably originated. The base of the Group is markedly diachronous, and it appears that shallow-water marine conditions continued to alternate with nonmarine environments. Over the greater part of the exposed area there is no evidence of Carboniferous sedimentation earlier in age than the Holkerian, but particularly in the area S of the Swindale Beck Fault (the continuation of the Inner Pennine Fault) between Roman Fell [NY 754 203] and Hillbeck [NY 795 155] (near Brough), earlier beds have been shown by Garwood and Turner to be present. These have been investigated in stratigraphical and petrographical detail by Burgess and Harrison (1967); they include representatives of the Ravenstonedale Limestones (Chadian), Ashfell Sandstone (Arundian) and the Hillbeck Limestone (Holkerian), the last-mentioned continuing northward as the Dun Limestone of the Scordale and Dufton Fell mines. There is a drastic change of thickness across the fault, strikingly illustrated by Burgess and Harrison's fig. 2 and the contention in the first edition of this memoir (Dunham, 1948) that the fault acted as a contemporaneous hinge line, comparable with the Stublick and Craven faults is justified. The combined thickness of Basement and Orton groups S of the fault reaches nearly 1640 ft (500 m); immediately to the N where it is reduced to about 328 ft (100 m), the Chadian and Arundian stages are absent. Still farther N the Basement Group again thickens from a minimum of 246 ft (75 m) at High Cup Nick, 476 ft (145 m) at Crowdundle Beck, while below Melmerby Scar, 755 ft (230 m) has been attained (Shotton, 1935; Burgess and Wadge, 1974). Eastwards from the Escarpment, the limited evidence indicates that both groups thin considerably and may be absent. In the Cronkley Inlier, the maximum thickness is 131 ft (40 m), but at Falcon Clints and in Cowgreen mine only 66 ft (20 m) remain. Comparative sections of the Basement Group are shown in (Figure 2). Fossils indicating the Holkerian subzone are present (Johnson, 1970, p.35) so the Orton Group can be said to continue to here. At Rookhope, however, the boring showed that rocks with D, (Asbian) fossils continue to within 3 ft (1 m) of the top of the granite (Dunham et al., 1965, p.398). In the Roddymoor Borehole [NZ 1513 3634], on the other hand, it appears from the faunal list of Lee (1924) that both Orton and Basement groups are represented, to a total thickness of 269 ft (82 m).

Asbian–Lower Alston Group (formerly Lower Limestone Group)

By definition this group embraces the Lower Dibunophyllum subzone. In the southern part of the escarpment, the Bryozoa Band, which occurs on Long Fell near the bottom of the Melmerby Scar Limestone and at Scordale [NY 761 228] at the top of the Dun Limestone lies near to the base of the Asbian. Turner (1927, p.344) has recorded a break in sedimentation at the base of the D1 subzone, indicated by nodules of limestone enclosed in shale, in Scordale, near Melmerby and near Brough. This may be represented by the 'honeycomb limestone' of the Roddymoor Boring [NZ 1513 3634] (Woolacott, 1923, p.59) and by the peculiar nodular limestone (now highly metamorphosed) seen beneath the Melmerby Scar Limestone at Falcon Clints in Upper Teesdale [NY 824 281]. The group maintains a fairly steady thickness of 203 ft (62 m) except to the S of the Swindale Beck Fault, where this figure is nearly doubled in a short distance.

Melmerby Scar Limestone

This bed, the thickest individual limestone of the Carboniferous succession, consists of pale grey and grey limestone in massive posts separated by marl films or beds a few inches thick. Dark patches can be seen on freshly broken surfaces of the limestone. In all its characteristics this bed corresponds with the limestone typically found in the D1 subzone throughout the North-west Province of Garwood (1912, p.475). S of the Swindale Beck Fault its thickness is at least 351 ft (107 m), but this includes some beds referable to the S2 subzone for, according to Turner (1927, p.357) the base of D1 lies more and more above that of the limestone south of Roman Fell. N of the fault the thickness decreases sharply to 131 ft (40 m) and this order of thickness is maintained to the N along the escarpment. To the E exposures in Upper Teesdale and the workings at Cowgreen Mine [NY 811 308] revealed a thickness of 90 ft (27.4 m) above the Whin Sill (a thick sill of quartz-dolerite here intruded into the limestone), while 25 ft (7.6 m) of limestone below the Sill were also considered to form part of the Melmerby Scar Limestone. In the Roddymoor boring shale beds split up this limestone and the thickest individual bed measures only 42 ft (12.8 m). At Rookhope [NY 9374 4278] the limestone is also split by thick clastic intercalations and it could be argued that the tendency for massive Melmerby Scar Limestone to pass northward into two or three rhythmic units including elastics as well as limestone, displayed in the Brampton district (Trotter and Hollingworth, 1932, p.46) and in the Northumberland Basin, is also showing itself here.

Robinson Limestone

The upper part of the Asbian or Lower Alston Group consists, not of massive limestone, but of alternations of shale, sandstone and limestone. The lowest of the thinner limestones, named 'Robinson's Lime' on Forster's section (1809, p.42) is a light grey crinoidal bioclastic type, in appearance intermediate between the pale limestone typical of the Melmerby and Great Scar limestones and the darker grey rocks found at higher levels, particularly in the Brigantian. All the available evidence indicates that this limestone is persistent throughout the present region, but it is seen at surface only along the escarpment and in Upper Teesdale. In the southern region, S of Stainmore, it becomes united into the Great Scar Limestone. Sandstone usually predominates between the Melmerby Scar and Robinson limestones; at Cowgreen Mine, for example, a soft sandstone, increasing in thickness in the space of less than 984 ft (300 m) from 4 to 17.5 ft (1.2 to 6.1 m) occupies this position. The thickness of the limestone is normally 13 to 19.7 ft (4 to 6 m), but in Augill Beck, approaching the Stainmore Trough, it increases to 82 ft (25 m).

Birkdale Limestone

A dark grey limestone 1–3 m thick, separated from the top of the Robinson Limestone by 3.3–13 ft (1–4 m) of siltstone or sandstone, was found to be a persistent bed during the resurvey of sheets 31 and 24 (Burgess and Mitchell, 1976, p.626) where the rock commonly weathers red at the top. This is now recognised as the highest limestone of the Lower Alston Group; shale overlain by sandstone with a combined thickness around 26.2 ft (8 in) complete the section in this Group.

Brigantian–Upper Alston Group–(formerly Middle Limestone Group)

The alternating sequence of shale, sandstone and limestone had, as noted above, already commenced before the end of Asbian times, but the typical rhythmic series, corresponding with Phillips' Yoredale Beds is found in the Brigantian. The complete cycle, as Hudson (1924, p.125) and Brough (1929, p.116) have shown, consists of the following beds in upward succession: limestone, calcareous shale, ferruginous shale, sandy shale or shaly sandstone, sandstone, ganister or underclay, coal. The complete series, or cyclothem, or a close approximation to it is repeated at least eleven times in the Group.

Locally evidence may be found for small breaks in the succession during which erosion has taken place. Such breaks have been detected at the base of the sandstone, at the base of and on top of the limestone. The absence of particular beds may, in certain instances, be explicable by small unconformities of this type, but generally the amount of erosion which occurred was not great.

The individual cyclotherns of the Brigantian are described below and comparative sections are shown in (Figure 3). In each case the name of the limestone, which is regarded as the base of the rhythmic unit, is given first, followed by the name of the sandstone member of the cyclothem, if that bed is named.

Lithological characteristics

The limestones of the group are all dark blue-grey, fine grained and rather thin bedded. Several of them include beds of calcareous shale, notably the Scar Limestone. The succeeding calcareous shale is usually fossiliferous, but free from limestone nodules. This gives place to dark grey or black shales, the higher parts of which in places carry clay-ironstone nodules. Grey beds are widespread in the group, being found below the sandstone member, or in a few cases, taking its place. The sandstones are, with few exceptions, white or brown moderately micaceous rocks in which the quartz grains are subangular, averaging 0.1 to 0.3 mm diameter. The tops of the sandstones, or in certain cases, the whole bed (notably the Six Fathom Hazle of Weardale and the Nattrass Gill HazleHazle (also spelt Hazel, and generally pronounced Hazle) is a local term meaning, according to Forster (Nall's revision, 1983, p.55) sandstone, harder than freestone, but softer than girdle bed. The term sill is locally employed to denote a bed or stratum, not necessarily igneous; it is roost often applied to sandstones, but it 'is also used in Whin Sill, where it means 'hard bed' beneath Crook), may be highly siliceous and workable as ganister. The coal member of the cyclothern is seldom more than a few inches thick in the Upper Alston Group and may be represented by a smut. A few thin coals have, however, been worked in this group (Smith, 1912, pp.184–185).

Rough–Peghorn–Lower Smiddy Limestone

The incoming of the faunas which characterise the Brigantian almost, but not quite coincides with the position of the conveniently widespread band, the Girvanella Bed of Garwood. J S Turner (1927) established the position of this in the Smiddy Limestone of the Westmorland Pennines. During 1:2500 mapping of the Cowgreen mine-area in 1939–40, a 26 ft (7.8 m) limestone between the Robinson and Smiddy limestones was named the Peghorn Limestone from its type locality, now under the water of the Cowgreen Reservoir. In the original edition of this memoir this was equated with an un-named limestone in the same position in Forster's (1809) section, and with the Rough Limestone at the London Lead Company's Dufton mines. As the Smiddy Limestone at Cowgreen contained Osagia nodules the Peghorn Limestone was assigned to the Lower Limestone Group. However, Dr Johnson, in the course of his resurvey of the Moor House Reserve on behalf of the Nature Conservancy, was able to show that the Smiddy Limestone when followed northwards splits into two, the lower member being the Rough Limestone of Dufton Fell, and further that the Girvanella algal bed is contained in this member, renamed by him the Lower Smiddy Limestone (Johnson and Dunham, 1963, p.35). Johnson recognised a tripartite division of the limestone; a lower dark, crinoidal portion, a central, light-coloured fossiliferous limestone with an algal band at its base; and an upper 6.5 ft (2 m) bed of dark limestone with, in its centre a band of 'large Girvanella-bearing nodules ( = Osagia)'. This lithology was put to good use by Burgess and Mitchell (1976), who traced it from Westmorland to Durham and North Yorkshire, and found it in the borings for Cowgreen Reservoir. They further point out that the D2 fauna comes in at the base of the Peghorn Limestone, and that this line establishes the base of the Brigantian. (Figure 2) has been revised accordingly. In the Rookhope Borehole, as interpreted by Burgess and Mitchell (1976, pl. 5) sandstone has taken the place of the pale limestone. The Peghorn Limestone is separated from the Smiddy Limestone by 13–19.7 ft (4–6 m) of shale and sandstone. At Cowgreen a bluish silica-cemented sandstone, easily mistaken for limestone underground, directly underlies the Smiddy Limestone and was formerly worked nearby for ganister. A similar rock occurs in this position at Closehouse Mine [NY 850 227].

Smiddy = Upper Smiddy Limestone

(Of Johnson and Dunham, 1963) The limestone is dark grey, evenly bedded, and in every way typical of the limestones in the Brigantian succession save that in addition to corals and brachiopods, it contains scattered nodules with Girvanella and as exposed in Swindale Beck (Moor House) also contains two bands with more abundant Osagia. This underlines the fact, also noticed farther S in the Pennines, that in some places more than one band carries these algae, though the vertical range remains restricted. The recommendation of Burgess and Mitchell, quoted above, that the base of the Brigantian should be drawn at the bottom of the limestone containing the Girvanella Bed perhaps needs to be reinforced by adding the word 'Lowest' before 'limestone'.

With the Smiddy Limestone, cyclothemic sedimentation typical of the Yoredale facies in general and the Brigantian in particular has set in. The limestone ranges in thickness from 13 to 32.8 ft (4 to 10 m) and is overlain by very fossiliferous black or grey mudstone passing upward into mudstone of brackish-water origin, with sandy intercalations. Fine-grained light-coloured, silica-cemented sandstone follows, the Srniddy Ganister of Johnson and Dunham (1963), 26.2–52.5 ft (8–16 m) thick with in places a thin coal in shaly beds at the top. Faunal lists for this and the succeeding Brigantian cyclotherns based on collecting by Dr Johnson on the Moor House Reserve will be found in Johnson and Dunham, (1963, pp.35–44). Fossils occur in the lower part of the shale but not in the sandstone, except where it includes a thin limestone. The incomplete evidence in the neighbourhood of Cowgreen suggests that the proportion of shale to sandstone between the Srniddy and Lower Little Limestone is greater there, while beneath Crook this part of the section is mainly shale.

Grain Beck Limestone

On Sheet 31 a 8.2 ft (2.5 m) thick limestone, elsewhere mapped as the lower part of the Lower Little Limestone, has been separately mapped under this name (Burgess and Mitchell, 1976, p.38).

Lower Little Limestone

The streams cutting the escarpment and the exposures in the Cowgreen–Maizebeck area reveal that this limestone is 12–25 ft (3.7–7.6 m) thick. It is overlain by 24–30 ft (7.3–9 m) of beds in which sandstone, with shells, predominates. In the Roddyrnoor Boring the beds assigned to the Lower Little Limestone includes 47 ft (4.3 m) of limestone with interbedded calcareous shale, near the base of which at 2280 ft (695 m) below surface there is a layer crowded with Productus hemisphaericus (Lee, 1924, p.147) which resembles the P. hemisphaericus bed in the Hardrow Scar Limestone of Wensleydale (Hudson, 1924, p.131). This bed is one which may prove useful as an index horizon. The Lower Little Limestone is the lowest bed reached, on the footwall of the vein, in the deep sinking at Rampgill Mine, Nenthead [NY 782 435], and it is present in the Rookhope and Allenheads No. 1 boreholes see (Figure 4).

Jew Limestone

Like the beds below, the outcrop of this limestone is limited to the escarpment and the CowgreenMaizebeck area, but it was formerly visible in Burnhope (Weardale) on the site of the reservoir. Usually 25–30 ft (7.6–9 m) thick, its fauna includes Productus pugilis Phillips and Lonsdaleia floriformis (Martin), the latter form also being known in the Lower Little Limestone (Turner, 1927, p.348). This limestone was the lowest bed reached by No. 1 underground shaft at Rotherhope Fell Mine, near Alston [NY 700 427]. The overlying beds consist of shale followed by sandstone with several included shale partings and one or more thin limestones, the total thickness from top of the Jew Limestone to the base of the Tynebottorn Limestone varying from 70 to 100 ft (21 to 30 m). The Jew Limestone is transgressed by the intrusive Whin Sill at Camrnock Eals Mine, Weardale [NY 935 383]; it is above the Sill at Rookhope but in Allenheads No. 1 borehole [NY 8604 4539] it is faulted out by Old Vein.

Tynebottom Limestone and alternating beds

The Tynebottorn Limestone is so named because it crops out or closely underlies the bed of the South Tyne between Alston and Tynehead. This limestone is well exposed along the escarpment, also outcropping in a wide area W of the Burtreeford Disturbance in Teesdale, the Maizebeck and Troutbeck. In Weardale it is exposed in Burnhope and the limestone exposed on the S bank of the stream opposite Copt Hill Whin Quarry [NY 851 408] is considered to be the Tyne-bottom. The thickness of the limestone in Scordale is approximately 25 ft (7.6 m); at Dufton Mines, 27 ft (8.2 m); in the South Tyne valley about Alston 24 ft (7.3 m) is an average figure, decreasing to 22 ft (6.7 m) at Rotherhope Fell Mine. The Rampgill sinking proved 21.3 ft (6.5 m). In Teesdale both Greenhurth [NY 7838 3281] and Grasshill [NY 8123 3484] shafts proved 30 ft (9.1 m). In Weardale, Burtree Pasture Underground Shaft [NY 8603 4180] did not fully penetrate the bed. At Greenlaws Mine [NY 889 370] the greatest known thickness 48 ft (14.6 m), was proved, but this thickness is not maintained to the N at Slitt Shaft [NY 9058 3920], where only 34 ft (10.3 m) was recorded. The thickness at Roddyrnoor [NZ 1513 3634] was 38 ft (11.6 m). There is thus evidence of a small eastward increase in thickness in this bed. The upper 3–4 ft (0.9–1.2 m) of the limestone in the Alston area is very shaly.

The overlying beds, comprising shale (the 'Tynebottom Plate') succeeded by thin beds of fine-grained sandstone, sandy shale and shale many times repeated, are collectively known as the Alternating Beds. Probably they represent more than one complete cycle of rhythmic sedimentation.

The series usually includes two thin limestones, the Single Post, a mottled greyish white limestone, and the Cockle Shell, the latter bed characteristically full of giganteid productids. In some localities, for example at the Dufton Fell Mines, more than two such limestones are present. A third limestone, below the Single Post, has been named the Maize Beck Limestone by C T Clough on his field slip (Johnson and Dunham, 1963, p.39). These limestones are normally 3–6.5 ft (1–2 m) thick. There is, moreover, reason to suppose that where two limestones are found, they are not necessarily the same over the whole area. Proved thicknesses of the Alternating Beds are as follows: (Thickness data cited here where derived from specific shafts or borings have eight-figure grid references; where only six figures are given, the thickness applies to an appreciable area, for example to a whole mine section.)

Dufton Fell Mine [NY 715 276] 150 ft (46 m); Silverband Hush [NY 680 321] 150 ft (46 m); Cross Fell area [NY 687 343] 190 ft (58 m); Tynehead [NY 771 371] 130 ft (40 m); Rotherhope Fell Mine [NY 700 427] 190 ft (58 m); Rampgill UG Shaft [NY 7975 4417] 157 ft (48 m); Longcleugh No. 1 BH [NY 7686 5180] 173 ft (52 m); Allenheads No. 1 BH [NY 8604 4539] 165 ft (50 m); Burtree Pasture Shaft [NY 8603 4180] 130 ft (40 m); Rookhope BH [NY 9374 4278] (faulted) 94 ft (29 m); Slitt Shaft [NY 7058 3920] 138 ft (42 m); Greenlaws Mine [NY 888 370] 130 ft (40 m); Rigg BH [NY 9142 3896] 135 ft (42 m); Cammock Eals Mine [NY 935 383] 104 ft (32 m); Crawleyside BH [NY 9962 4010] 147 ft (45 m); Grasshill [NY 8123 3484] 130 ft (40 m); Ettersgill BHs [NY 890 290] 145 ft (44 m); Roddymoor BH [NZ 1513 3634] 110 ft (34 m).

There is thus a broad indication of diminishing thickness in an eastward or south-eastward direction, with a low at Cam-mock Eals perhaps extending to Rookhope, since the strata cut out by faulting in the Rookhope Borehole can hardly exceed 10 ft (3 m). Although Johnson, Nudds and Robinson (1980, p.6) found good correlation between the group between Cross Fell area and Ninebanks, 12 miles (19 km) to the NNE, lithological variation within the Alternating Beds is considerable, and no further analysis is therefore attempted.

Turner (1927, p.300) has recorded the diagnostic fossils Orionastraea placenta (McCoy) from the Tynebottorn Limestone and O. phillipsi (McCoy) from the Single Post. Orionastraea also has been recorded from Upper Teesdale at this horizon (Johnston and Dunham, 1963; Johnson, 1988).

Scar Limestone, Slaty or Low Brig Hazle

The Scar Limestone cyclothern is exposed high on the escarpment as well as in Teesdale and Alston Moor. In Weardale it appears in two inliers, one W of the Burtreeford Disturbance, the other extending from Blackdene eastwards to Billing. In the Alston Moor, escarpment and Weardale areas the thickness of the limestone is consistently about 30 ft (9 m); many mine sections in these areas show shale interbedded in the upper part of the limestone. In Teesdale the thickness diminishes, being (22.5 ft (6.9 m) in borings at Ettersgill. In the Roddymoor Boring, this limestone, split by the intruded Whin Sill, totals 30 ft (9.1 m), including 5 ft (1.5 m) of shale near the top. The Scar Limestone normally contains some chert nodules, as for example in the quarries near the former Alston Station [NY 717 467], a feature not common in the limestones of the area. It is succeeded by fossiliferous shale. The P2a goniatites Goniatites cf. granosus Portlock (Rayner, 1953) and Sudeticeras cf. splendens Bisat (Mitchell, 1957) have been found in shale above the Scar Limestone at Bowlees, Teesdale [NY 907 283]. This passes upwards into shale with ironstone nodules. From this there is an upward transition into sandstone in most sections, the sandstone being known in Weardale and Alston Moor, where it is thinly bedded and micaceous, as the Slaty Hazle, while in Teesdale, where it is more massive and siliceous, it is called the Low Brig Hazle. A 3 in (7.6 cm) coal was proved within this sandstone at Bur-tree Pasture Mine, coal and shale being recorded at about the same horizon at the Trough Head Mines in the Harwood Valley [NY 820 343]. Shale generally separates the Slaty Hazle from the overlying Five Yard Limestone. The variations in thickness in the Scar cyclothem are illustrated in (Table 4).

Five Yard Limestone, Six Fathom or High Brig Hazle

The limestone of this series, besides cropping out in areas in which the Scar Limestone is found, is the lowest limestone reached by mining operation in East Allendale (Area 4). The thickness suggested by its name is probably greater than the average for the present area. In the Roddymoor Boring a limestone 28 ft (8.5 m) thick, overlying calcareous shale with two thin limestones totalling 17.75 ft (5.4 m) thick have been assigned to this horizon (Woolacott, 1923, p.51). On the W side of Great Dun Fell the limestone yielded Sudeticeras newtonense Moore, (Johnson and Dunham, 1963, p.41) indicating the P21, subzone. The shale is succeeded by a siliceous massive fine-to medium-grained sandstone, the Six Fathom Hazle of Weardale, equivalent to the High Brig Hazle of Teesdale. This rock has been worked for ganister at Lanehead, near Westgate and also at Billing Hills in Weardale. (Geological Survey, 1920, p.61–64). The rock is a sandstone of average grain-size 0.1–0.2 mm consisting mainly of angular quartz grains with some mica and sericite. The cement, which is small in amount, is of silica (E11545)Numbers in brackets refer to rock-slices in the British Geological Survey collection.

The siliceous character of the bed is maintained in the exposures on the N side of Teesdale and on the escarpment. Its thickness is given in (Table 5).

A coal 8 in-1 ft 4 in (20–40 cm) thick, worked above the High Brig Hazle in the Langdon Beck area of Teesdale, and one of 7 in (18 cm) recorded at Bentyfield Mine, near Garrigill [NY 756 425], in the same position, may possibly be correlated with the Shilbottle Coal of Northumberland.

Three Yard Limestone, Nattrass Gill Hazle

The Three Yard Limestone though less often exposed at the surface than the thicker limestones may be followed without difficulty since it lies immediately above the strong feature formed by the Six Fathom Hazle. It is overlain by marine shale from which a goniatite of possible P2c age has been collected (Johnson et al., 1962); this passes upward into sandy shale and grey beds. The succeeding Nattrass Gill Hazle takes its name from a right bank tributary of the South Tyne, a mile (1.6 km) south of Alston. Here and in many other streams in Alston Moor, Teesdale and Upper Weardale the bed is well exposed. It varies from a thin-bedded pale grey or brownish sandstone with carbonaceous streaks, shaly in places, to a ganister. In the latter condition it was worked for silica-rock near Lanehead in Weardale. Here the rock is composed of angular quartz grains of 0.1–0.15 mm with a little white mica and some sericite derived from material present interstitially (E11544), (E11581). The Roddymoor Boring proved the greatest recorded thickness of this bed, 84 ft 6 in (25.8 m); this thickness is approached only in the eastern workings at Sedling Mine, Weardale. In Harwood and Upper Teesdale the Nattrass Gill Hazle is poorly developed, in some sections being almost wholly represented by grey beds. Proved thicknesses are given in (Table 6).

A coal seam 1 ft 6 in (0.46 m) thick on top of the Nattrass Gill Hazle has been mined on the eastern and western slopes of Park Fell, W of Alston [NY 700 460]. Elsewhere this horizon is generally marked by a bed of black carbonaceous shale.

Four Fathom Limestone, Quarry Hazle

Owing to its proximity to the Great Limestone, this cyclothem and the next one above it have been penetrated by mine workings in all parts of the field. The Four Fathom Limestone, sometimes spotted with Saccamina carteri is also unusual in carrying chert nodules. It is overlain by a thick shale, the lower part of which is very limy and fossiliferous. The shale becomes sandy and passes upwards into the Quarry Hazle, a medium-grained white or brown micaceous sandstone with carbonaceous streaks and plant impressions. These beds are exposed at the surface in all the main valleys except the Allendales and the Derwent. Thicknesses are given in (Table 7).

Iron Post Limestone, Tuft

The highest cyclothem of the (Brigantian Middle Limestone Group), directly beneath the Great Limestone, has at its base a thin limestone known in Alston Moor as the Iron Post, and elsewhere as Hewitson's Lime. The name Iron Post comes from the hardness of the bed, not from any ferruginous tendency. In some sections this horizon is not a limestone, but is represented by a few feet of highly fossiliferous shale overlying the Quarry Hazle. Although only a few feet thick, this marine horizon can be recognised over the whole area, except in a restricted belt running through Stanhopeburn Mine, Weardale [NY 986 413], and possibly continuing to the Cornish Hush Mine in Bollihope [NZ 000 335], where a thickening of the Tuft Sandstone normally found in the upper part of the cyclothem has obliterated the lower part of the series and united with the Quarry Hazle to form a sandstone reaching 95 ft (29 in) in thickness at Stanhopeburn Mine, with only 25 ft (7.6 m) of shale separating its base from the Four Fathom Limestone see (Figure 3), Section 9). Eastwards at Hope Level Mine [NY 991 397], the sandstone has thinned to about 40 ft, but the lower part of the Iron Post cyclothem has not reappeared. The thickness of beds here between Great and Four Fathom limestones is only 50 ft (15.2 m). Probably the sandstone fills a local erosion-hollow comparable with the 'washouts' commonly found in the Coal Measures. Local disconformity of the kind seen here, becomes of much greater importance in the Namurian.

At Carricks Mine, Wearhead [NY 861 380], borings from surface on Groveheads Vein East (GLE 3, 4, 5, 8) proved the

following average section:

ft in
Base of Great Limestone
Shale with thin coal 2 0.6
Tuft sandstone 16 4.9
Shale 40 12.2
Fossiliferous shale 1 0.3
Limestone 20 6.1
Sandstone 18 5.5
Shale - base not proved

Two possible interpretations may be considered: one is that the limestone is the Four Fathom, in which case the Iron Post Limestone and Quarry Hazle are absent; the other is that the Iron Post Limestone and accompanying cyclothem is nearly three times its normal thickness. The surface evidence is complicated by the fact that the primary surveyors mapped a thin limestone, exposed at only one place, 500 ft (152 m) NE of the mouth of Craig's Level [NY 8613 3794], between the Great and Four Fathom limestones. From the mine evidence this is now believed to be part of the Great Limestone, and this favours the first possibility. A nonsequence or unconformity in the shale above the limestone of the borehole sections would be required to explain the facts.

The Tuft or Water Sill varies lithologically from a fine-grained brown micaceous sandstone to a condition approaching coarse grit, thus differing from the normal sandstones of the Brigantian. Within the Tuft on Knock Fell [NY 720 300] in the south-western part of the area, a coal seam 14–18 in (35–46 cm) was formerly worked. A seam 8 in (20 cm) thick was discovered at Dun Fell Mine in recent borings, presumably the same seam as that worked round the summit of Meldon Hill [NY 770 290], N of the upper headwaters of Maize Beck. Elsewhere a smut is commonly found directly beneath the Great Limestone; it can be seen, for example, by the roadside a mile (1.6 km) E of the summit of Killhope Pass [NY 824 433].

Thickness variations in the Iron Post cyclothem are given in (Table 8).

Namurian

Pendleian (formerly lower part of Upper Limestone Group

The basal member of the Namurian is the Great Limestone, a thicker limestone than any in the Carboniferous of the area except the Melmerby Scar. For the purpose of the present investigation, the Great is the most important limestone. Above it, although the rhythmic alternations of shale–sandstone–coal- marine horizon can still be discerned, there is a gradual but striking change in conditions. The marine horizons are of interest only because of their value as index beds; they are represented by very thin limestones, marine shales or shelly sandstones. Over much of the area, shale predominates over sandstone in this group, but it will be shown that there are certain belts in which thick sandstones or grits are developed to the exclusion of shale. Coarse grits first appear a short distance above the Great Limestone.

Correlation in a series so variable is far less easy than in the two lower groups (Figure 4). Apart from four thin limestones and two sandstones (the Firestone and Grindstone sills) individual beds were not mapped during the primary survey. At Brampton Trotter and Hollingworth (1932, p.70, 71) recognised the value of the many marine bands in the series and they have been used effectively in the revision of Sheets 31 (Burgess and Holliday, 1979) and 32 (Mills and Hull, 1976). The Woodland Borehole [NZ 0910 2770] provides a standard section for the latter sheet. Carruthers (1937, p.236) has suggested that the absence of one of these, the Lower Felltop Limestone, over parts of the present area may be due to an unconformity which can be widely traced. Some support for this suggestion has been obtained, together with evidence of another and greater unconformity at a lower horizon, during the course of revision of mineralised areas around Hunstanworth, Stanhope and Middleton-in-Teesdale.

Attempts at correlation in the group have led to the application of the same name at different mines to beds of sandstone which are certainly not identical. This applies particularly to the terms Slate Sills, and Grit Sills, but to a less extent it is also true of the terms Firestone, White Sill, Pattinson Sill and Coal Sills. The marine horizons, all but one of which were recognised by Carruthers (1937, pl.xiii, section 1) in his standard section at Coalcleugh (West Allendale), provide index horizons, but unfortunately their fossil content has not so far proved to be sufficiently diagnostic to determine any individual bed. Use, therefore, has to be made of the associated strata, as Carruthers has suggested, and uncertainty must arise where variation is demonstrably so rapid. Sufficient is now known, however, to indicate those stratigraphical trends which have an important bearing on the potentialities of the orefield.

The beds hereafter described in subgroups mostly do not coincide with single cyclothems.

Great Limestone

This limestone resembles those of the Brigantian in being grey-blue, fine-grained and in breaking into posts varying from 6 ft (1.8 m) to a few inches thick. Fairbairn (1978) has demonstrated the remarkable persistence of individual named posts between Frosterley and Wearhead. The principal quarrying area, formerly an important source of ironworks flux and currently of roadstone and cement manufactures lies between Frosterley, where the limestone emerges from the bed of the Wear, and Stanhope. B L Hodge (1965) measured and assembled all available sections of the limestone bringing out gentle regional variations in an otherwise uniform pattern of thickness. The average for the Alston Block is near 65 ft (19.8 m), but this increases to 72 ft (22 m) in the Stanhope quarries. At Lunehead Mine, Teesdale [NY 846 205] the London Lead Co.'s mine section records a thickness of 102 ft (31 m) but investigation during the extraction of barytes have failed to confirm this high figure. The upper 14–15 ft (4.2–4.6 m) contain a number of interbedded shales (the Black Beds) a few inches up to 2 ft (0.6 m) thick. These, with the interbedded limestone posts, are collectively called the Tumbler Beds. Locally the shales are, however, absent. N of Sipton Shaft in East Allendale [NY 8468 4987], N of Mohopehead Mine in West Allendale [NY 759 500], and probably over much of the northern part of the area, the proportion of shale to limestone is greater. At Esp's Vein, Sipton Mine, East Allendale the section is: Limestone 10 ft (3.0 m); Shale with thin argillaceous limestones 17 ft (5.2 m); Limestone 38 ft (11.6 m) while in the Brampton area, the Tumbler Beds are 20–30 ft (6–9 m) thick, overlying 20 ft (6 m) of massive limestone (Trotter and Hollingworth, 1932, p.72). E of the main mineral field, the Great Limestone was proved in a boring at Lintz Ford, near Chopwell [NZ 1438 5743], to be 68 ft (20.7 m) thick including a bed of shale 11 ft 6 in (3.5 m) thick, 7 ft (2.1 m) below its summit; while at Crook 13 miles (21 km) to the south, the Roddymoor Boring proved 60 ft 8 in (18.5 m) of Great Limestone, without shale. These borings thus confirm the northward change in the upper part of the limestone. At Woodland the limestone is only 52 ft 11 in (16.1 m), with only a 4 in (10 cm) mudstone band 6 ft 5 in (1.96 m) below the top. (Mills and Hull, 1968, p.29).

In addition to these upper shaly layers, a few inches of shale are present in some sections 33–35 ft (10–11 m) above the base of the limestone and have been recorded (as a 'till bed') at Carricks Mine, [NY 861 380] as well as at Brandon Walls Mine, Rookhope [NY 947 412]. Elsewhere there is a limestone post 3–4 ins (7–10 cm) thick associated with shaly films. Still lower, a shaly horizon is found 15 ft (4.6 m) above the base. The posts lying below the Tumbler Beds and those lying directly below the two other shaly horizons are known respectively as the High, Middle and Low Flats of the Great Limestone. They have favoured replacement in the process of mineralisation (Chapter 5).

At or near the bottom of the High Flat, 20–25 ft (6.1–7.6 m) below the top of the limestone, a post rich in corals and brachiopods is found in Weardale, where it was worked under the name of Frosterley Marble. A similar bed 2 ft (0.6 m) thick was noted in Middle Tongue Beck, near Silverband Mine, 20 ft (6.1 m) below the top of the limestone. This richly fossiliferous layer may be of some use as a guide to approximate position within the limestone, since at other levels large fossils are not abundant. Johnson (1958) has nevertheless shown that in addition to the Frosterley biostrorne, which he has described in detail, there are two others: the Brunton Band, 17 ft (5.2 m) above the base, full of microscopical algae, and near the bottom of the limestone a band with Chaetetes.

Faunal lists for the Great Limestone will be found in the works of Stanley Smith (1910, p.621–623), Turner (1927, p.350, 351), Hill (1938), Johnson (1958) and Johnson and Dunham (1963); also for the Chaetetes Band in Fairbairn (1978). The common fossils included the corals Dibunophyllum bipartitum (McCoy), Lonsdaleia floriformis (Martin), Diphyphyllum lateseptatum McCoy, Aulophyllum fungites (Fleming) and Koninckophyllum magnificum, Thomson and Nicholson, together with latissimoid Producti.

Strata up to the Little Limestone; the Coal Sills

Considerable variation in detail in the shale and sandstone strata between the Great and Little Limestone occurs, with a marked influence upon the mineral veins in and below these beds. A typical section in the Alston Moor area is that recorded from the workings on High Raise Vein, Nentsberry Mine:

Little Limestone Thickness ft Thickness in Thickness m
Sandstones, White Hazle 7 2.1
Shale 5 4 1.6
Coal 10 10 0.25
Sandstone, High Coal Sill 12 3.7
Shale 8 2 2.5
Coal 4 0.1
Sandstone, Low Coal Sill 10 3.0
Shale 18 5.5
Great Limestone

With minor variations, this sequence holds for the mines of the Nenthead district and Middle Fell. Around Alston the coals increase to workable thickness, old workings continuing on the E side of the South Tyne Valley as far S as Garrigill Burn in the upper seam, while in the Nent Valley both seams were wrought as far E as Blagill. The names Low and High coals have been suggested for these two seams, while for the seam above the White Hazle and its equivalents the name Tynedale Coal is proposed, with Fourstones Coal for its upward split. There is a northward change from semianthracite at Alston to typical bituminous coal in the Tyne Valley (Trotter and Hollingworth, 1932, p.76, 77). The Tynedale Coal directly•beneath the Little Limestone, which is the main seam worked in the Haydon Bridge–Hexham district though it has not been found at Alston, is recorded at Ramshaw and Jemmy's Shafts at Hunstanworth, where it is about 1 ft (30 cm) thick. At Taylor's Shaft, Hunstanworth [NY 9658 4824], and in the north-eastern workings on Boltsburn Vein a coal is also found directly overlying the Great Limestone.

At Rampgill Mine [NY 781 435], NE of Nenthead, the Low Coal Sill disappears, thus giving a thick shale above the Great Limestone, which at Barneycraig Mine [NY 804 466] exceeds 40 ft (12 m). At Holmes Linn Shaft [NY 8419 5240] in East Allendale a thin Low Coal Sill, overlain by a 6 in (15 cm) coal reappears; the High Coal Sill here and at Esp's Vein, Sipton Mine, has increased to nearly 30 ft (9 m). At Allenheads and in Swinhope (Allendale) the section resembles that of Alston Moor. Similar conditions persist into Rookhope and the highest parts of Weardale. Between Sedling–where the 'Alston' section still holds good–and Blackdene a very striking change occurs, which may be illustrated by the following section at Levelgate Mine [NY 882 389]:

Thickness ft in m
Little Limestone
Shale 1 6 0.5
Sandstone, White Hazle 9 2.7
Shale 21 6.4
Sandstone 64 19.5
Great Limestone

Similar sections have been proved at the Blackdene and Middlehope mines. The thick sandstone probably occupies an erosion channel developed during the deposition of the High Coal Sill. It follows a sinuous course north-eastwards, for the Boltsburn Vein workings prove 'Alston' condition alternating with 'Blackdene' conditions. In the Hunstanworth mines, 2–3 miles (3–5 km) N of Boltsburn Mine, the section is again mainly sandstone except at the north-eastern end of the workings. The approximate course of this 'washout' is indicated on the index map on (Figure 5). The 'washout' can be followed by way of Harthope to the vicinity of Langdon Beck in Upper Teesdale. E of the belt of thick sandstone, the section again resembles that at Alston, though the coals are reduced to smuts. On the S side of the Wear Valley, the shafts at Carricks and Greenlaws mines show two, three or four thin sandstones interbedded with shales. In Teesdale the same applies at Ashgillhead and Flushiemere, but at Coldberry, and in the adjacent Bollihope Valley, there is again a thick sandstone, as the following sections (Table 9) at Skears Mine [NY 950 280] indicate.

Along the escarpment there is no good section, but the Coal Sills are present as far S as Hartside, and again around Cross Fell and the Dun Fells. A rise on Henrake Vein at Silverband Mine [NY 704 318] gave the following somewhat expanded version of the 'Alston' section:

Little Limestone ft in Thickness m
Soft brown feldspathic sandstone 4 1.2
Shale 1 6 0.45
Sandstone 6 0.15
Shale 1 0.3
White quartzite 6 1.8
Shale 3 6 1.07
Coal 3 0.08
Brown sandstone with plants 9 10 3
Shale 5 10 1.78
Brown and white quartzite 11 3.35
Shale 5 6 1.68
Sandstone 1 4 0.41
Shale 3 8 1.12
Coal 6 0.15
Grey micaceous sandstone 9 2.74
Sandstone and shale 6 1.8
Shale 19 5.8
Great Limestone

B L Hodge (1965) derived isopachytes for the beds between the Great and Little Limestone from 364 measured surface and subsurface sections throughout the orefield and adjacent areas, and from the distribution of thick sandstones such as those of Levelgate, Blackdene and Allercleugh was able to follow the course of a system of main distributary channels existing on the Namurian delta. The main channel runs S and SSW from Fallowfield, passing W of Blanchland to pass St John's Chapel and connect with High Hurth Edge [NY 865 313] near Langdon Beck, where it contains coarse pebbly sandstone. Thence it is believed to pass between Little Fell and the Lunehead mines to join up with exposures of pebbly grit at the head of the Pass of Stainmore near Barras. In the northern part of its course, SE-trending branches are given off, one connecting with the excellent exposures of the channel in Rogerley Quarry, near Stanhope [NZ 015 378]. Here the channel cuts through the High.Coal Sill Sandstone and the Low Coal, but definitely pre-dates the High Coal . (Hodge, 1965; Elliot, 1976).

The thickening of the White Hazel at Skears Mine, noted above, was found by Hodge to continue northwards to Cornish Hush [NZ 000 335], in Bollihope, and to occupy an area substantially wider than that of the palaeodistributary system lower in the cyclothem. He also noted that the sequences coarsen upwards in it, not downward as in the channels.

The sedimentology of a postulated delta lobe represented by 17 detailed sections in the area from the Stanhope quarries southward to Stainmore has been studied by T Elliott (1975), who has distinguished (a) a coastal plain phase of mudstones, (b) a progradational phase with coarsening-upward sequences representing repeated infillings of an interdistributary bay with levees, spits, splays and mouth bars, (c) an abandonment phase with coals and marine sediments, and (d) a post-abandonment phase in which pro-gradation was resumed, with one or more coarsening-upward sequences, the top one with thick, flat-bedded sandstone, interpreted as the remains of a transgressive offshore bar or island, enclosing a lagoon. Phase (b) corresponds with the sequence leading to the Low and High Coal Sills of the present account. Phase (c) with the High Coal and phase (d) with the sequence including the White Hazle, the belt of thickening of which (Figure 5) correponds with the barrier island, not with a distributary channel. This interpretation is acceptable but if Elliot's western lobe margin implies that the Alston and Weardale successions cannot be correlated, that is not acceptable since the former can be traced through subsurface and surface evidence in the Swinhope and Killhope valleys directly into the latter at Sedling and Burtree Pasture.

Data on the thickness of strata from the base of the Great Limestone to the base of the Little Limestone, with figures showing the relative proportions of sandstone and shale are summarised in (Table 10).

Strata from the Little Limestone to the Firestone Sill

The Little Limestone, normally fine-grained and hard, varies from 4–21 ft (1.2–6.4 m) thick, the maximum being at Harehope Gill Mine, near Frosterley. The average thickness is less than 10 ft (3 m). Shale usually succeeds the limestone, though at Middlehope and Fulwood a thin sandstone intervenes. The shale may vary in thickness from a few feet to over 80 ft (24 m), the maximum being recorded at Ramshaw Shaft, Hunstanworth [NY 9500 4722], but over much of the area a sandstone appears 10–30 ft (3–9 m) above the top of the Little Limestone. It has been the practice to call the first sandstone above the Little Limestone the Pattinson Sill, but comparison of sections strongly suggests that several different sandstones, present as lenticular bodies, have been so named. The Pattinson Sill of the Nenthead sections, lying 20–30 ft (6–9 m) above the limestone, is a hard medium- to fine-grained sandstone 5–15 ft (1.5–4.6 m) thick containing marine fossils and plant remains. This bed continues into the West Allen Valley (Carruthers, 1938, pl.xiii, section 1). It may be recognised at Allenheads and in Swinhopehead Shaft [NY 8250 4637]; Holmes Linn Shaft [NY 8419 5240] probably starts in it. In the Rookhope Mines, the name Pattinson Sill has been applied to the sandstone directly on top of the Little Limestone, though it may not be the same bed of that name farther W. At Hunstanworth the first substantial sandstone, again called the Pattinson Sill, lies 70–80 ft (21–24 m) above the Little Limestone. This bed is 30 ft (9 m) thick at Jeffries Shaft [NY 9602 4781], where it is overlain by 1 ft (0.3 m) of limestone. This sandstone probably corresponds with a higher bed of the Alston and Allenheads districts, there called the White SillNot to be confused with the White Hazle, which underlies the Little Limestone., and, retaining the term in its Nenthead usage, the Pattinson Sill is represented at Hunstanworth by thin sandstones and interbedded shales.

On the S side of Weardale, sections in Bollihope show a sandstone 24 ft (7.3 m) thick, 54 ft (16.5 m) above the Little Limestone. Closely similar conditions obtain at the Coldberry Mines [NY 941 290], N of Middleton-in-Teesdale. Traced from Bollihope eastwards to Harehope Gill, the thickness of shale separating this bed from the Little Limestone decreases to 24 ft (7.3 m). In all three localities it is named 'Tattinson Sill' on the mine section, but it is impossible to be certain that it is not wholly or in part the equivalent of the White Sill of Alston. Around Harehope Gill [NZ 032 352] it is overlain by shale containing marine beds, succeeded by shale which has been mined for the abundant clay-ironstone nodules contained in it. A collection from the marine shales on the dumps from these workings yielded: Camarotoechia pleurodon (Phillips), Cleiothyridina sp.,. Lingula sp., Productus concinnus? J Sowerby, P. (Eomarginifera) lobatus JSowerby, P. (Buxtonia?), Spirifer aff. bisulcatus J de Sowerby.

Farther E the Roddymoor Borehole showed four thin limestones in shales at what may be supposed to be an equivalent horizon, but no sandstone. These marine strata have been equated by Mills and Hull (1968, p.8) with the fossiliferous beds between 1117 ft 6 in and 1171 ft (340.6 and 357 m) in the Woodland Borehole, where the fauna includes Tylonautilus nodiferus 'early mut' of Stubblefield, characteristic of the upper part of the Pendleian (E1) stage.

The White Sill of Alston Moor, sometimes called the High Pattinson, is a sandstone 5–25 ft (1.5–7.6 m) thick separated from the Pattinson Sill proper by 20–40 ft (6–12 m) of shale. In some sections it is represented by 'girdle beds' (alternations of sandstone and shale) as at Wellhope Shaft [NY 7790 4661]. Overlying it is a shelly sandstone or marine shale. It is reasonable to regard the White Sill as the Alston equivalent of the Faraday House Sill of Turner (1935) in Westmorland, where the overlying marine band contained a first record of T. nautilus 'early mut' (Rowell and Scanlon, 1957, p.34). A sandstone in a similar position to the White Sill was proved in the Allenheads workings to be 30 ft (9 m) thick, and, as noted above, is believed to continue into the Derwent area as the so-called Pattinson Sill of Hunstanworth.

Shale varying from 5 to 50 ft (1.5 to 15 m) follows, succeeded by the Firestone Sill. This bed was mapped throughout the area during the primary survey. Its recognition depends upon the presence over a large part of the area of a persistent thin limestone, the Crag Limestone, overlying a coal which rests on top of the Firestone in most sections. The Firestone Sill presents two different types of lithology. In Alston Moor, along the Teesdale–Weardale watershed and around Middleton-in-Teesdale the bed is a coarse sandstone, in places approaching a grit; generally it has a pebbly top. On the north side of Weardale, in Rookhope and in the Derwent Valley, on the other hand, it is a hard brown or white siliceous medium-grained sandstone, on top of which a good ganister was formerly worked in Rookhope and in the Hunstanworth area. This ganister has been studied at Round Hill Quarry near Frosterly [NZ 0120 3835] and identified as an A2 (eluvial) horizon of a podzolic palaeosol (Percival, 1981; 1983). The section at Redburn Quarry [NY 926 435] (Geological Survey, 1920, pp.59, 60) and an account of the petrography of the rock have been published. The Firestone is recognised in the Cross Fell–Dun Fell outlier, where it is represented by about 20 ft (6 m) of medium-grained sandstone. The section in Dun Fell Hush reveals that here both White and Pattinson sills are unrepresented, but the shale between the Little Limestone and the Firestone, over 100 ft (30 m) thick, carries three marine bands, the uppermost with Cravenoceras sp (Johnson and Dunham, 1963, p.54). On the S side of Lunedale the southernmost exposures in the area reveal the Firestone as a coarse flaggy sandstone, overlain by the Crag Limestone. At Bentyfield Mine, Garrigill [NY 756 425], only 65 ft (2 m) of sandstone in the position of the Firestone are recorded; while in Hudeshope, above the Coldberry Mines, and also in the side valley of Snaisgill (Carruthers, 1938, p.241) it is represented by interbedded shale and sandstone. A similar passage into shale occurs in parts of Bollihope. In Hudeshope the Firestone reaches it maximum thickness of 65 ft (20 m) in the workings of Cold-berry Mines; only a mile (1.6 km) away it has almost completely thinned out or passed into shale. It is clear from adjacent sections both near Garrigill and near Middleton-in-Teesdale that the effect is a strictly local one. S of Snaisgill, for example, the Sill resumes it normal condition and may be followed through quarries on the N side of the Middleton-in-Teesdale to Barnard Castle Road. Other instances of local passage into shales-with-sandstones are found at Sedling Mine West [NY 860 411], at the Sunniside Mines [NZ 005 361], Frosterley and in the Roddymoor Borehole. Such instances are exceptional; over the remainder of the area the Firestone may be recognised in all appropriate sections. Variation in thickness in the series between the Little Limestone and the top of the Firestone Sill is greater than in the preceeding subgroups as in (Table 11).

These figures indicate that there is a marked thickening of the strata between the Little and Crag limestones from S to N. S of Cross Fell, in Teesdale and in Weardale between Frosterley and Crook, the thickness lies between 80 and 100 ft (24 and 30 m). The remainder of Weardale and Alston Moor shows thicknesses of 100–150 ft (30–45 m). In borings covering the range Lower Felltop Limestone to Great Limestone in Swinhope, East Allendale, described by Dunham and Johnson (1962), the interval (taking account of a desirable revision of the correlation to recognise the Crag Limestone at 93–95 ft, (28.3–29 m) depth in No. 4 boring is 155–160 ft, (47.2–48.7 m). Northwards, in the Derwent Valley several sections show thickness of 150–200 ft (46–61 m), as do two on the N side of the Nent Valley and one at Allenheads. Finally at Shildon, near Blanchland, the northernmost mine of the main area shows the maximum thickness, 224 ft (68.2 m). The thicknesses in the Woodland, Roddymoor and Lintz Ford borings are consistent with this view. The figure at Shildon may be compared with the thickness of the probable equivalent beds in the main Tyne Valley still farther N, 320 ft (97.5 m) at Fallowfield Mine.

Overlying the Firestone there is a coal which has been worked at Coalcleugh and Nenthead, where its thickness is 18 in (46 cm). This seam has been correlated with the Oakwood Coal of the Tyne (Smith, 1912).

Crag Limestone and Knucton Shell Beds

The Crag Limestone is present in the following parts of the area: in the Snaisgill, Hudeshope and Bollihope valleys, at Wiregill Mine, Great Eggleshope, in Bollihope, in Weardale from Stanhope to Wolsingham, in the Hunstanworth area and in Lunedale. The westernmost occurrence is at Barneycraig Mine [NY 804 467], West Allendale, but it may be noted that this limestone has not been recorded at Allenheads Mine [NY 860 454], though it is almost certain that this was the limestone found at a depth of 57–63 ft (17.4–19.2 m) below adit level in Studdon Dene Shaft [NY 8395 5440] on the Blackett Level. The occurrence in Barneycraig Mine is of some importance because the Firestone when followed southwestward through continuous workings into Rampgill Mine is overlain not by limestone but by 'Ironstone' (a ferruginous limy sandstone with shells) which takes the place of the Crag Limestone in the Alston Moor sections. The Crag horizon is thus a valuable index marker. It has been correlated with the Oakwood Limestone of the main Tyne Valley (the next limestone above the Little at Fallowfield). If this correlation is correct, then it would seem that in the Brampton area, the Firestone of Alston Moor splits into two thick beds of sandstone, separated by shale with a marine band. The two beds are called by Trotter and Hollingworth the Firestone Sill and Fiddler's Sill respectively (1932, pl. iii). It is generally agreed that the Crag Limestone continues into the Askrigg region (Dunham and Wilson, 1985) as the Crow Limestone. The Ten Fathom Grit beneath the limestone also splits into two beds over part of the area, the Uldale and Faraday House sills of Turner (1935).

Probably the best exposure of the Crag Limestone in the area is at Round Hill Ganister Quarry, 1 mile (1.6 km) SE of Stanhope Church. Here the bed is 6 ft (1.8 m) thick and overlies 1 ft 6 in (45 cm) of Banister. The fauna of the limestone here include Zaphrentis enniskilleni Edwards and Haime, Trepostomatous polyzoa, ?Athyris lamellosa (Leveille), cf. Brachythyris oxalis (Phillips), Chonetes sp., Cleiothyridina sp., Composita ambigua, Martinia sp., Phricodothyris sp., Productus (Krotovia) aculeatus (Martin), P. concinnus J Sowerby, P. (Echinoconchus) elegans McCoy, cf. P. (Dictyoclostus) muricatus Phillips, P. (Avonia) youngianus Davidson, Schuchertella sp., Spirifer aff. bisulcatus J de C Sowerby, S. cf. calcaratus McCoy, Limipecten dissimilis (Fleming).

It is also seen in Witton Gill Sike 1.5 miles (2.8 km) WNW of Stanhope Church where the following additional fauna was obtained: Crurithyris sp., Dielasma sp., Lingula squamiformis Phillips, Spiriferellina cf. perplicata (North), Coelonautilus subsulcatus (Phillips).

In Swinhope (Carruthers, 1937, p.240) 'lime plate' -limy fossiliferous shales with streaks of chert along the bedding-appear above the Crag Limestone. These beds may be regarded as the northern feather-edge of the Crow Cherts, extensively developed on Sheets 40 and 41 in Upper Swaledale. Similar beds are seen in the headwaters of Bollihope Burn, where the following section is exposed [NY 954 345]:

ft in Thickness m
Shelly sandstone (Knucton Shell Bed) 2 0.6
Shale 20 6.1
Lime Plate and limestone 8 6 2.6
Black shale 13 4
Crag Limestone 2 0.6
Shale 6 0.15
Shelly sandstone 3–6 0.07–0.15
Sandy micaceous shale 3 0.9
Ganister 3–6 0.07–0.15
Black shale 2 6 0.8
Coal 4 0.1
Coaly shale 1 6 0.46
Brownish medium-grained sandstone (Firestone)

Lime-plate is also seen in Coldberry Gutter and near Ravelin Mine. Above the Crag Limestone, except in the area where an unconformity to be described below has transgressed them, two beds of shelly sandstone interbedded with thick shale beds follow. The marine beds have been called the Knucton Shell Beds by Carruthers (1938, p.238). They are well developed at Coal Crag [NY 924 473], in Knucton Burn, north of Hunstanworth, and may be seen at Redgroves Hush [NY 740 449] near Alston, at Coalcleugh, in a branch of Sedling Burn as well as in most of the streams running from the watershed between Upper Teesdale and Weardale. A typical section is seen in Coldberry Gutter [NY 930289], the great opencast on Lodgesike Vein:

ft in Thickness m
Flaggy sandstone (Low Slate Sill) 15 4.6
Shale 8 2.4
Coarse sandstone 6 1.8
Shale 18 5.5
Sandstone with plants and shells 9 6 2.9
Shale 20 6.1
Shelly sandstone 9 0.2
Shale 13 4
Lime plate and limestone 6 1.8
Shale 15 4.6
Crag Limestone 2 0.6

The following fauna was collected from the Knucton Shell Beds in Great Eggleshope Burn, 3600 ft (1.1 km) NW of Wiregill Mine: Chonetes sp., Composita ambigua (J Sowerby), Derbyia sp., Lingula sp., Orthotetid, Productus (Krotovia) aculeatus (Martin), P. cf. concinnus J Sowerby, P. (Echinoconches) elegans McCoy, Spiriferellina insculpta (Phillips), ?Limipecten dissimilis (Fleming), Sanguinolites striato-granulatus Hind. Euphemites [Euphemus] sp., Glabrocingulum cf. armstrongi Grey-Thomas, Hypergonia?, Latischisma cf. globosa Grey-Thomas, Naticopsis sp., Worthenia sp., Cf. Yvania parva Grey-Thomas, Zygopleura sp., Orthocone nautiloid, Weberides [Phillipsia] mucronata (McCoy).

In Holebeck Gill, [NZ 051 365] SE of Frosterley, near the Sunniside Mines the following section is exposed:

ft in Thickness m
Brown sandstone (Low Slate Sill) 6 1.8
Sandy shale 6 1.8
Shelly sandstone 9 0.2
Sandy micaceous shale 1 0.3
Soft sandstone with plants and shells 1 0.3
Sandy shale 2 6 0.8
Shelly sandstone 1 0.3
Sandy micaceous shale 6 1.8
Limonitised limy fossiliferous sandstone 3 0.9

From the lowest bed of this section was obtained: Crinoid columnals up to 20 mm diameter, Fenestella sp., Chonetes sp., ?Composite ambigua (J Sowerby), Martinia.2, Productus concinnus J Sowerby (with tube-like front to trail), P. (Eomarginifera) lobatus J Sowerby, P. (Buxtonia) sp., P. (Linoproductus) sp., Spirifer cf trigonalis (Martin), Spiriferellina sp., Nuculana?, Pseudamusium?, Rhabdospira?, Orthocone nautiloid.

Of a total thickness of 70 ft (21.3 m) of shale and sandstone assigned to this group in Swinhope No. 4 borehole [NY 827 454], all but 10 ft (3 m) carried marine fossils. Dunham and Johnson (1962) give additional details of the fauna.

Slate Sills and Low Grit Sill: the Rogerley Channel

The next portion of the Upper Limestone Group comprises the High and Low Slate sills and interbedded shales of Westgarth Forster's section with their equivalents the Great Sill of Rookhopehead, the Low Grit Sill of Hunstanworth and the Freestone Sill of the London Lead Company's Bollihope Air Shaft. The Low Slate Sill of Bollihope and the Eggleshope mines is also considered to fall within the present subgroup. The top of the subgroup is taken at the base of the Rookhope Shell Beds of Carruthers (1938, pl.xiii). The base of the Low Slate or Grit Sill provides the clearest evidence of erosive wash-out relationships so far found in the Namurian of the area. Since this reaches its maximum in the neighbourhood of Rogerley Intake 1.5 miles (2.4 km) E of Stanhope, it is here called the Rogerley Channel. Evidence for this disconformity will be presented before the lithology of the subgroup is considered.

Throughout Alston Moor, the basal Low Slate Sill occurs at an average of 65 ft (19.8 m) above the Crag Limestone, overlying the Knucton Shell Beds as may be seen in the opencast on Redgrooves Vein on Middle Fell [NY 750 440]. At Coalcleugh the base is 83 ft (25.3 m) above the Crag Limestone, while at Collier Shaft, Allenheads [NY 8690 4530] it is recorded at 67 ft (20.4 m) above the top of the Firestone Sill. Corbetmea Shaft at Rookhopehead [NY 8772 4443] reveals 62 ft (18.9 m) of beds between the base of the Great Sill and the top of the Firestone. Both at Collier and Corbetmea Shaft an 'Ironstone' (a name usually applied by the miners to a ferruginous or 'famped' sandstone) is recorded in these beds, probably indicating the presence of at least one of the Knucton Shell Beds. In Upper Weardale the section in an eastern tributary of Sedling Burn and that at Burtree Pasture indicate the presence of Knucton Shell Beds below the Low Slate Sill. They can be seen on the S side of Weardale in Swinhope, Westernhope and at Bollihope Burn head. Red-way Rise on Boltsburn Vein showed the base of the Low Slate Sill 62 ft (18.8 m) above the Firestone Coal, while at Coal Crag, Knucton Burn at least 60 ft (18.3 m) of beds intervene between the base of the Low Grit Sill and the horizon of the Crag Limestone. Traced eastwards from the last-mentioned locality along Knucton Burn, these beds become progressively thinner. At the confluence with Little Knucton Burn [NY 943 488], the thickness remaining is only 24 ft (7.3 m), while 0.5 mile (0.8 km) NE, where the Linn-bank Vein crosses the gorge in which Knucton Burn runs, the coarse pebbly Low Grit Sill is separated by only 2 ft (0.6 m) of shale from the top of the Crag Limestone. The most reasonable explanation of these facts is that the base of the Low Grit Sill is strongly erosive. In Weardale the erosive base is more conclusively demonstrated. On the W side of the valley of Stanhopeburn, the base of the Low Slate Sill lies considerably above the Crag Limestone, as shown by Hopeburn Shaft on Boltsburn Vein (Figure 4), Section 7). On the E side, however, only a few feet of beds intervene. The grit of Crawley Edge rests almost directly on the Crag Limestone. The same is true in deep borings drilled from Dead Friars [NY 968 456] to test the north-eastward continuation of the Boltsburn deposits. At Round Hill Ganister Quarry, in Rogerley Intake, the base of the grit may be seen cutting out the shale and lime-plate above the Crag Limestone, then transgressing across the limestone, and finally, at the east end of the quarry, cutting out the Firestone Ganister. It is very likely that in Saugh Sike, 0.75 miles (1.2 km) N, it has cut out the whole of the Firestone Sill. The Round Hill exposures thus show the unconformity rising eastwards. In Rogerley Burn [NZ 019 378] the Knucton Shell Beds reappear. They have been mapped eastwards to Willowgreen Burn [NZ 040 373]. On the N of Weardale there is, therefore, a belt 2 miles (3.2 km) wide in which the Knucton Shell Beds are cut out. Towards the centre of the belt, the Crag Limestone is also cut out. The trend of the belt is N–S, for it may be recognised equally clearly on the S side of the dale, and farther S in Bollihope. The section at Bollihopehead, already quoted, shows one Knucton Shell Bed present. All along the side of Catterick Moss, the Yew Tree Grit rests on or transgresses the Crag Limestone. At Cornish Hush Mine in Hawkwood Burn [NZ 001 327], there is 6.5 ft (2 m) of shale between the base of the pebbly grit and the Crag Limestone. In Wager Burn [NZ 010 344], 1 mile (1.6 km) NE of Cornish Hush, 12 ft (3.7 m) of shale separate the grit and the Crag Limestone. The Knucton Shell Beds reappear in Fine Burn [NZ 022 347] and as noted above they are excellently developed farther E near the Sunniside Mines [NZ 051 351]. The width of the belt in which they are absent on the S side of Weardale is approximately 2.5 miles (4 km). The belt is believed to continue southward to Eggleshope mines; it lies E of the headwaters of Great Eggleshope, which expose the Knucton Beds.

It is suggested the, that a large-scale 'wash-out' of the Knucton Shell Beds and the shale 60–90 ft (18–27 m) thick associated with them, occurs in a belt 2–2.5 miles (3.2–4 km) wide which runs southwards from Blanchland and Hunstanworth through Dead Friars and Stanhope, nearly reaching Middleton-in-Teesdale. The course of the belt is shown in shading on the index map to (Figure 4) and on (Figure 5).

Within this belt, the lithology of the beds above the Rogerley Channel is markedly different from that on either side of it. In the Alston Moor area the section at Rampgill Mine shows two sandstones, the High and Low Slate Sills respectively 35 and 30 ft (10.7 and 9 m) thick, separated by 10 ft (3 m) of shale. Above the High Slate Sill the Rookhope Shell Beds are seen adjacent to the continuation of Rampgill Vein in Dowgang Hush [NY 775 430]. On Middle Fell, and adjacent to the Nent Valley, the thickness of beds between the base of the Low Slate Sill and the horizon of the lowest Rookhope Shell Bed is 75–90 ft (23–27 m), but here there may be three or even four beds of sandstone. At Coalcleugh a single sandstone 50 ft (15 m) thick represents these measures, while at Allenheads they are again split up by shales in Collier Shaft [NY 8690 4530], though there is a return to the single sandstone condition in the Great Sill at Corbetmea Shaft, Rookhopehead [NY 8772 4443]. In Burtree Pasture Mine [NY 860 413] two sandstones respectively 20 and 20–30 ft (6 and 6–9 m) thick were proved, separated by 40 ft (12 m) of sandy shale. The aggregate thickness of the subgroup increases eastwards, for at Hopeburn Shaft [NY 9564 4422] 130 ft of beds include a sandstone 60 ft (18 m) thick at the top with thinner sandstones below. In the streams running down from the Teesdale–Weardale watershed, there are at least two thick sandstones, gritty in places, separated by shales with ironstone nodules. A thin coal appears on top of the lower sandstone in Great Eggleshope, with marine strata above it. By contrast the shafts at Hunstanworth, within the 'wash-our belt, show the whole subgroup to be represented by grit, pebbly and conglomeratic at the base, varying from 150 to 200 ft (46 to 61 m) thick, with, in places, a parting of coaly shale. Near Stanhope the Crawleyside mines, and those on Catterick Moss reveal the same conditions. The Air Shaft [NZ 0014 3270] sunk by the London Lead Company to Cornish Hush deep level showed 178 ft (54.3 m) of grit and sandstone (the Freestone and Low Slate sills) including only a few thin beds of sandy shale near the top. E of the belt of thick grit, there is a return to conditions resembling those to the W of the belt, with two 'Slate Sills' separated by shale at Frosterley Intake, as well as between Fine Burn and Harvey Hill. At the Sunnyside Mines shale predominates in the subgroup, and three thin coals make their appearance. Farther east still, the Roddymoor Boring shows that the subgroup has passed wholly into shale with thin limestones.

On (Figure 4), the thick-grit belt, in which the Rogerley Channel has cut out the Knucton Shell Beds, is represented by sections 10–13; sections 14–16 lie E of the belt, the remainder W of it. The significant effect of these stratigraphical changes on the mineral deposits is discussed in Chapter 5.

Rookhope Shell Beds to Lower Felltop Limestone

A coal up to 8 in (20 cm) thick rests on top of the Low Grit Sill and in some places on the High Slate Sill. In Corbetmea Shaft [NY 8772 4443] a coal 4 in (10 cm) thick is regarded as the top of the subgroup discussed in the previous paragraph. A poor coal, possibly on the same horizon is exposed in Red-burn, Rookhope [NY 926 434]. Above this horizon is found a series of shales with shelly calcareous sandstones which Carruthers has named the Rookhope Shell Beds and Ironstone. They are exposed about Rookhopehead, where the trial level to Frazer's Hush [NY 890 444] was driven in one of them, also at Coalcleugh, in Sedling Burn, Middlehope Burn and Dowgang Hush, Nenthead. They are succeeded by flaggy sandstone, upon which rests the Lower Felltop Limestone, a fine-grained grey limestone varying from less than a foot (0.3 m) to 6 ft (2 m) thick. The thickness of the beds from the top of the High Slate Sill or Low Grit Sill to the top of the Lower Felltop Limestone has been measured in the following sections: Dowgang [NY 775 430], 65 ft (19.8 m); Middlecleugh [NY 789 425], 105 ft (32 m); Coalcleugh [NY 801 451], 65 ft (20 m); Swinhope No. 1 Borehole [NY 825 465], 70 ft (21.3 m); Rookhopehead [NY 890 444], 70 ft (21.3 m); Burtree Pasture Mine [NY 860 413], 70–75 ft (21.3–22.9 m). The Lower Felltop Limestone is exposed in many sections in Alston Moor. On the summit of Middle Fell, where it was formerly quarried for lime-burning, it is remarkable for the presence in it of the alga Girvanella, associated with brachiopods. The Lower Felltop horizon, or perhaps one of the Rookhope Shell Beds, may be represented by the thin limestone seen in Coldberry Gutter [NY 932 290] on the downthrow side of Lodgesike Vein. On the S side of Weardale, the Lower Felltop Limestone was formerly exposed at the N end of Catterick Moss. It is suggested also that the limestone mapped as the 'Telltop' from the Sunniside mines almost to Harperley on the S side of Weardale, which has been quarried extensively above Wolsingham, is in fact the Lower Felltop. At Sunniside, apart from the 10 ft (3 m) sandstone directly underlying the limestone, the remainder of the 143 ft (43.6 m) of beds down to the top of the High Slate Sill are entirely shale, with three thin coals, and fossiliferous strata representing the Rookhope Shell Beds near the bottom. The underlying sandstone is only 13 ft (4 m) thick, and the Roddymoor Borehole, still farther to the E, shows that while the Shell Beds have passed into limestone, the arenaceous members of the succession have almost disappeared.

Summarising the sedimentary history of the Pendleian stage in the Tyne to Stainmore region of the Northern Pennines, it is possible to recognise at the bottom a cyclothem similar in most respects to those so well displayed in the Brigantian, with the Great Limestone as its open-sea member, overlain by foredelta shale and deltaic sandstones in coarsening upward successions. Distributary channels can be identified, filled with coarse, in places current-bedded and pebbly, sandstone, fining upwards; the Coal Sills and White Hazle sandstone are medium- to fine-grained deposits probably formed respectively in interdistributary and barrier island-fringed lagoons. Instead of a single abandonment phase, as preposed by Elliot (1974, 1975), there appear to have been three, marked by the Low, High and Tynedale/Fourstones Coals and succeeding marine strata affecting different parts of the region, though in some places, as near Alston, overlapping. After the deposition of the Little Limestone the sections in some parts of the region suggest a single cyclothem with the Firestone as its arenaceous member, but over wide areas this is seen to divide into two or three separate rhythmic units, respectively the Pattinson, White Sill and Firestone units, each with marine strata above the sandstone. The succeeding group, beginning with the Crag Limestone contains cherty shales marginal to the substantial development of cherts in North Yorkshire, estuarine shales with clay ironstone nodules, the sandy Knucton Shell Beds, but no substantial arenaceous member in the normal sequence. The fine- to medium-grained Slate Sills follow, overlain by Rookhope Shell Beds, marine to estuarine shale, and finally by the flaggy sandstone beneath the Lower Felltop Limestone. The whole of this succession, down to the Crag Limestone, has been cut through by the major distributary channel containing the coarse sandstone of the Low Grit Sill sequences. The channel may well, as Mills and Hull (1976, p.36) suggest have acted as feeder for the transgressive Mirk Fell Ganister = Lower Howgate = Grassington Grit of the Stainmore to Craven half of the Northern Pennines.

Arnsbergian (formerly upper part of the Upper Limestone Group)

In North Yorkshire the base of the Arnsbergian Stage is precisely defined by discoveries of the E2a goniatite Cravenoceras cowlingense Bisat at Greenhow and Bolton Gill (Dunham and Stubblefield, 1945, p.238), around Pen Hill (Wilson and Thompson, 1959) and near Tan Hill (Hudson, 1941), in limestone or marine shale overlying the Grassington Grit and its equivalents, including Mirk Fell Ganister. This bed has been traced, in Sheet 31, into the sandstone underlying the Lower Felltop Limestone and as noted, this limestone is taken to mark the base of the Arnsbergian in the present region. It is regrettable, however, that the characteristic fauna has not yet been found in it, though the Coalcleugh Coal, mentioned below, carries plant spores thought to be of E2 age.

The Coalcleugh Beds and High Grit Sill

Over some parts of the present region the Lower Felltop Limestone is absent. The present distribution of the limestone and the way in which is appears and disappears, as proved for example by borings for ironstone at Rookhopehead [NY 885 445], is best explained by a disconformity or local facies change as Carruthers (1938, p.239) has suggested. The limestone is overlain by a variable sandstone series named the 'Transgression Beds' by Carruthers. To distinguish them from the beds connected with the Rogerley Channel, they are here called the Coalcleugh Beds. They comprise limonite-stained flaggy sandstones, with ganister in places, medium to coarse grained but rarely becoming grits. They are considered to be represented by ganister at the summit of the Harthope Pass between Weardale and Teesdale, where they have been extensively quarried. Percival (1981) has identified this quartz arenite as a storm-shallow marine sand bar, linked to a rise in sea level prior to the deposition of the Coalcleugh Marine Band. The rock here (E11510) is a nonfeldspathic quartzitic sandstone with a little mica, of grain size 0.1 mm and under. The worked thickness was 12 ft (3.7 m). Eastwards, this ganister appears to be represented in the headwaters of Swinhope by 3 ft (0.9 m) of quartzitic sandstone overlying 12 ft (3.7 m) of soft micaceous rubbly sandstone. In Frazer's Hush and the nearby ironstone opencasts at the head of Rookhope [NY 880 445], poor ganister is again present (though Carruthers regards this as lying underneath the plane of transgression) above the Lower Felltop Limestone. At Bur-tree Pasture Mine [NY 860 413] the sandstone correlated with the Coalcleugh Beds is 20–30 ft (6–9 m) thick. It is here suggested that in the Derwent Valley, these beds are represented by the High Grit Sill, and that the disconformity here has cut out the Lower Felltop Limestone and Rookhope Shell Beds. In support of this view it may be pointed out that when the High Grit Sill is followed up Beldon Burn, shale with a thin limestone appears between the base of the Sill and the top of the Low Grit Sill in a section 1000 ft (305 m) SE of Riddlehamhope House. In Allenheads No. 2 [NY 8715 4505] and in the Dead Friars borings [NY 9682 4480], the High Grit Sill must have cut out the Lower Felltop Limestone. In Bollihope the Coalcleugh Beds are considered to be represented by the sandstone named 'High Slate Sill' on the London Lead Co. section at Cornish Hush Air Shaft [NZ 0014 3270]. Here, and in the several sections in the Stanhope and Frosterley neighbourhood, the sandstones are medium to coarse and vary from 20 to 30 ft (6 to 9 m) thick.

Overlying the sandstone measures of the Coalcleugh Beds is the Coalcleugh Coal, worked along the summit of Killhope Pass [NY 800 432], on Nunnery Hill [NY 769 429] and along the fell side S of Coalcleugh [NY 801 451]. The most recent working was the Weardale Lead Co.'s Whetstone Mea Colliery [NY 841 470], where the thickness of the seam was 22 in (56 cm). It can be seen in the ironstone quarries near Rookhope head, where the section shown in (Table 12) may be seen.

The 1 ft (0.3 m) coal overlying the 60 ft (18.3 m) sandstone of Hopeburn Shaft, Boltsburn Mine [NY 9564 4422], is tentatively correlated with the Coalcleugh Coal, and it is suggested that the sandstone represents the Coalcleugh Beds resting on the High Slate Sill. The Lower Felltop Limestone is absent in this shaft section.

Coalcleugh Marine Beds, Hipple Sill

The 'shale with marine fossils' of the North Grain section (Table 12) is the representative of a marine horizon which initiates a series of beds reminiscent of a Brigantian cyclothem. Shale with ironstone nodules overlies the marine beds, passing upwards into sandy shale which is followed by micaceous flaggy sandstone. The sandstone is known as the Hipple Sill at the Hunstanworth Mines, and the Low Grindstone on the Killhope Law Ridge. At Allenheads the bed seems to have been mistaken for the Grindstone Sill proper when the Beaumont Co.'s general mine-section was drawn up, no doubt owing to confusion about the two Felltop Limestones. In most sections the Hipple Sill is followed by sandy shale or grey beds overlain by flagstones with plants. The flagstones pass into ganister at the top, on which rests a thin coal or smut. The whole thickness of the subgroup from the Coalcleugh Marine Beds to the base of the Upper Felltop Limestone, which overlies the coal, varies from 80–100 ft (24–30 m), but it is proved in very few sections. Of this thickness, about half is normally sandstone. Two recent provings showed, at Allenheads, 90 ft (27 m) and at Dead Friars, 110 ft (34 m) between the base of the Coalcleugh marine beds and the Upper Felltop Limestone.

The following fauna was obtained from the Coalcleugh Marine Beds of Groverake East Quarry [NY 900 441], north of Groverake Vein: Aff. Composita ambigua (J Sowerby), Orbiculoidea sp., Productus (Krotovia) aculeatus (Martin), P (Eomarginifera) lobatus J Sowerby, P (Buxtonia) sp., Grammatodon cf. reticulatus (McCoy), Limatulina scotica Hind, Nuculana attenuata (Fleming), Bucaniopsis cf. undatus (Fleming), Pleurotomariid indet, Straparolus sp.

Upper Felltop Limestone

The limestone, though it is rarely more than a few feet (1 m) thick, is widely present on the high fells between the dales, and is mapped in the Cross Fell–Dun Fell outlier. In some sections it appears to be replaced by ochre, or to use the local term, 'tamped'. In others it is a bluish slightly crinoidal limestone. The following fauna was collected from old ironstone trials near the collar of Hopeburn Shaft, at the head of Stanhope Burn [NY 9564 4422]: Aulophyllum fungites (Fleming), Dibunophyllum biparilium (McCoy), Crinoid stems up to 1 in (2 cm) in diameter, Polyzoa including Stenopora?, Chonetes sp. , Composita?, Diclasma sp., Productus (Krotovia) aculeatus (Martin), P. (Gigantella) latissimus J Sowerby, P. (Eomarginifera) longispinus J Sowerby, P. (Dictyoclostus) pinguis Muir-Wood, Phricodothyris sp. nov?, Amusium concentricum Hind, Bairdia sp. Aulophyllum fungites was also obtained from exposures at the head of East Whiteley Burn, 2.25 miles (3.6 km) N of Stanhope Church [NY 993 439].

The overlying beds, owing to their position high up on the fell sides, are poorly exposed at the surface. They are, however, penetrated by shafts at Sharnberry [NZ 005 314], Burtree Pasture [NY 8603 4180] and Hunstanworth Mines [NY 950 470] of which records are available. They are known to include marine beds extending from 11 to 27 ft (3.4 to 8.2 m) above the limestone in the Roddymoor Boring. Marine beds ('Cockle beds') 16 ft (4.9 m) thick were recorded in an equivalent position in Reed's and Jeffries shafts, Hunstanworth [NY 9601 4789] and [NY 9602 4781]; at Taylor's Shaft [NY 9658 4824] these had thinned, according to the records, to 2 ft (0.6 m). This marine horizon has been recognised in the stream east of Bell's Shaft, Sunnyside mines [NZ 0525 3527], and in the headwaters of Hudeshope and Great Eggleshope, where it is accompanied by a ganister and a thin coal. Probably the coal 2–3 ft (0.6–0.9 m) thick which underlies the ganister at Pit House, 1.75 miles (2.8 km) E of Stanhope [0198 3858] is at about the same horizon.

Up to 50 ft (15 m) of shale succeeds these beds, followed by the Grindstone Sill, a flaggy sandstone 30–50 ft (9–15 m) thick, which has been shown on the Old Series maps. This contains a lens of coarse grit on Bollihope Carrs [NY 962 355] and around the head of Swinhope [NY 885 333]. It is overlain by ganister which has been worked at Sandyford as well as near Townfield, Hunstanworth, [NY 951 484]. Probably the same bed occurs SE of Allenshield Farm, Blanchland, where it has been worked [NY 970 495].

Little is known about the beds which succeed the Grindstone Sill. They include, above Harthope, some greenish micaceous sandstones, with a thin coal, but it may be supposed that they are dominantly shaly. Their variation in thickness, with data for Upper Pendleian and earlier Arnsbergian strata is shown in (Table 13).

The Woodland Borehole [NZ 0910 2770] proved a limestone, interbedded with mudstone on top of the Grindstone Sill, a little over 4 ft (1.2 m) thick, containing a fauna of brachiopods (Mills and Hull, 1968, p.6); to this the name Grindstone Limestone was given. No outcrop of this bed had been found during the mineral resurvey of the region, but that is perhaps not surprising in view of the very poor exposure of these beds, usually found high on the fells, covered with peat haggs. The Dead Friars borings have now demonstrated that the Grindstone Limestone does indeed continue into the area. In the Woodland Borehole, the top of the Arnsbergian stage is taken at a thin limestone overlying shale containing Posidonia corrugate, 33 ft (10 m) above the top of the Grindstone Limestone, but it may be suggested that the line on Sheet 25 indicating the top of the Grindstone is the nearest mapping line to indicate the upper limit of strata of this stage.

Chokierian and Alportian (formerly uppermost beds of Upper Limestone Group)

Some 54 ft (16 m) of mudstone and shale, with two poor coals near the top, are assigned by Mills and Hull (1968, p.18) to the H1 and H2 zones, the upper limit being marked by the occurrence of Homoceras henkei H Schmidt indicating the commencement of the R1 zone. There is no direct faunal evidence that these stages are present in the region, and they are known to be thin in North Yorkshire. Evidence of their presence in a corresponding position in the outlier of high Namurian and Westphalian brought in by faulting at Stainmore (Owens and Burgess, 1965) is however provided by plant spores. Their occurrence has little practical significance in connection with the mineral deposits, but it is worth mentioning that recent work does not appear to support the postulate of an unconformity hereabouts, a suggestion that was formerly made to explain the small thickness or absence of some Namurian stages.

Kinderscoutian, Marsdenian, Yeadonian (lower two-thirds of former 'Millstone Grit' with some lower strata)

It was already well known before the first edition of this memoir was written that the 'Millstone Grit', mapped as three bands of coarse, often pebbly sandstone between the highest shale above the Grindstone Sill, and the horizon of the Tow Law Ganister or Ganister Clay Coal by the primary surveyors, could not be correlated satisfactorily with the Millstone Grit of its type area in the Mid-Pennines of Yorkshire and Lancashire. The three 'Millstone Grits' were therefore treated on a lithogical basis, without exact implication as to age. The Woodland Borehole [NZ 0910 2770], put down to settle the position of the Silesian/Namurian boundary and the stage boundaries, found, in addition to H. henkei, Reticuloceras sp.characteristic of the R1b zone in mudstone 46 ft (14 m) higher in the succesion, but below the base of the First Grit, which, though only 113 ft (34.5 m) thick, must correspond with the great thickness of the Shale Grit and Kinderscout Grits of Huddersfield. Marine fossiliferous mudstones, the Woodland Shell Beds, occur between this and the 'Second Grit', but contain no diagnostic fauna. However, the Quarterburn Marine Band on top of the 'Second Grit' is taken on indirect evidence discussed by Mills and Hull (1968, p.6) to be the equivalent of the Gastrioceras subcrenatum marine band, which occurs at its nearest point on the SW fringe of the region in the Stainmore Outlier. This marks the top of the Namurian and base of the Silesian, bringing the 'Third Grit' into Westphalian A.

Within the main part of the orefield, the Dead Friars borings starting below the top of the 'First Grit', passed through 52 ft 6 in (15.8 m) into the marine shales beneath.

The 'First Grit' was proved to be at least 40 ft (12 m) thick at Middlehope Head Air Shaft, Burtree Pasture Mine [NY 860 413]; at least 47 ft 6 in (14.5 m) thick at Sharnberry 'A' Shaft on the Weardale–Teesdale [NZ 0053 3143] watershed, and 57 ft (17.4 m) in full thickness at Taylor's Shaft, Hunstanworth [NY 9658 4824], where it is called the Rowton Well Sill. The thickness of the correlated basement grit at Crook is 70 ft (21.3 m). Where exposed the rock is a coarse pebbly grit, not markedly different from the Low Grit Sill of the Pendleian at Hunstanworth.

In the area between Stanhope and Blanchland, the Second Grit of the primary survey was worked in several quarries for moulding sand (Carruthers and Anderson, 1943, p.3). It is a coarse sand-rock with a kaolin cement, which has been found in a rotted condition not only at surface, but also at a considerable depth. At a higher horizon ganister has been worked near Edmondbyers Cross [NZ 003 447] and nearby on Horseshoe Hill. The horizon may be similar to that of the Castle Hill Quarry rock, and also that worked at West Butsfield [NZ 094 448], but proof of this is lacking.

Only one lead mine, Healeyfield [NZ 069 486], has penetrated the whole thickness of the 'Millstone Grit'. A section of this mine has been given by Winch (1817, p.59). Since this corresponds with the relevant part of Forster's section (1821, p.163), the source of the latter is clear. Forster applied the name 'Millstone Grit' only to a single bed of grit, 27 ft (8.2 m) thick, but in Nall's revision of Forster's Strata (1883, p.91) the term 'Millstone Grit Series' is applied to the beds of the Healeyfield succession. The section given by Forster and Winch, while not entirely consistent with that on a more recent longitudinal section of the mine (Mines Dept No. 2728) does not differ in essentials. The latter has been quoted by S Smith (1923, p.37) and is reproduced here on (Figure 6), Section 4. The correlation shown is based on the position of the 'famp' (No. 111 of Forster's section) which corresponds according to the primary survey with the position of the Upper Felltop Limestone in the Derwent Valley; it cannot be regarded as more than speculative. A ganister which has been worked at Castle Hill Quarry [NZ 047 495], W of the Healeyfield Vein, apparently occurs between the Dene Howl Firestone and the Healeyfield Firestone of the mine section (S Smith, 1923, p.37).

A rough correspondence between the beds at Healeyfield and those in the Crook boring (Figure 7), Section 2) may be noted. On the revised classification of this part of the Crook boring proposed by Mills and Hull in the light of experience at Woodland, Forster's (1809) 'Millstone Grit' bed probably lies between the Grindstone Sill and the base of the 'First Grit'.

Dinantian and Namurian

Note on the Haydon Bridge Area

In the forgoing description of the Brigantian and Pendleian stages of the Carboniferous, the stratigraphy of the rocks exposed in the metalliferous mines of the Haydon Bridge area (Area 8) has not been considered although these rocks belong to the two groups mentioned. This is because the area is detached from the main orefield and lies N of the Stublick hinge-faults, so that instead of being deposited on a stable shelf (the Alston Block of Trotter and Hollingworth, 1928, p.443) they were laid down in a more rapidly subsiding basin, the Northumberland Trough see (Figure 5) and (Figure 6). This is inferred from the increase in total thickness of this part of the succession by a factor of 2, and from certain stratigraphical changes. In (Figure 6) a full succession for the Haydon Bridge mines has been constructed by joining together the records of seven shafts and one underground borehole; in no case was there any ambiguity about the correlation from shaft to shaft, though of course minor local variations undoubtedly exist. From the Oakwood Coal, the correlative of the Crag Coal of the Alston Block, down to the Three Yard Limestone no problem of correlation arises; the successive cyclothems are immediately recognisable, the principal change being increased thickness of the clastic members coupled with some diminution in the limestones. Beneath this horizon, a tendency already heralded on the rigid blocks by the northward splitting of the Middle Limestone cyclothem of Askrigg into three or four cyclothems, the Scar, Cockleshell, Single Post and locally the Maizebeck of Teesdale and Alston. This effect is much more widely seen in the Northumberland Trough, and while it is clear that the generally cyclical style of sedimentation was maintained, the number of cycles increases three- or fourfold. This was recognised by the primary surveyors W Gunn and D Burns, who assigned letters rather than names to some of the limestones. The dilemma was apparent to Trotter and Hollingworth (1932, p.54) who found that by mapping through the Five Yard Limestone from the Alston Block, there was an unidentified limestone between this and the Three Yard Limestone. More recently the drilling of the Longcleugh borings [NY 772 520] (Johnson, Nudd and Robinson, 1980) showed very clearly that the next limestone below the Three Yard is not the Five Yard, the rest of the correlation with Alston plainly confirming this. During the resurvey of Sheet 13 (Bellingham) which includes near its southern margin part of the metalliferous area, this limestone was named the Redhouse Burn Limestone (Frost and Holliday, 1980, fig. 20) and it was shown to split into three minor cycles. Two such splits are present in the Leadbitter and Grindon Hill shafts [NY 8260 6612] and [NY 8346 6767] (Figure 6). Traditionally, the Eelwell Limestone of Sheet 13 has been regarded as equivalent to the Five Yard Limestone of Alston. This view was followed by G A L Johnson (1959) and though there has recently been some dissent (Holliday, Burgess and Frost, 1976; Frost and Holliday, 1980, fig. 15) the most recent assessment by Frost (1984) favours the correlation of the Scar Limestone of Alston with the next limestone below the Eelwell, the Shotto Wood. In (Figure 6) the traditional view is accordingly maintained. Frost further shows that a series of boreholes drilled during the past five years by Selection Trust (BP Minerals Limited) and by the British Geological Survey in the mining area give a consistent picture of the succession down to the Colwell and Dalla Bank limestones, which he takes to represent the Single Post horizon of Alston. At Settlingstones Mine [NY 844 683] the 12 ft (3.7 m) limestone beneath which the Whin Sill was intruded, mapped by the primary surveryors as the Scar, is now considered to be the Colwell (see p.265).

While the nomenclature and correlation of the thin limestones around Haydon Bridge may not be a matter of first importance in assessing the metalliferous potential, it seems likely that the repetition of thin cycles representing several advances and retreats of the elastic deltas into the limestone-depositing sea during a single cycle on the stable shelf to the south, do not create a sufficient thickness of hard strata to favour ore deposition beneath the Three Yard Limestone, except where hardened by the intrusion of the Whin Sill.

The resurveys of Johnson (1959) and of Sheet 13 failed to bring to light diagnostic faunas in the numerous fossiliferous horizons; thus (Figure 6) summarises the current status of correlation by lithological sequence.

Note on washouts, transgressions and distributary channels

The rocks of Yoredale and Millstone Grit facies described in this chapter accumulated within the ambience of a major delta system, probably larger in scale than most currently existing deltas. The limestones are interpreted as the sediments of foredelta seas; in most cases they were engulfed by mud swept over the delta top so that fossiliferous shale gives place upwards to unfossiliferous tidal flat or lagoonal shale. As the delta advanced, a coarsening-upward succession produced 'grey beds' (thin laminations of shale and sandstone) followed by shaly sandstone and medium-grained sandstones. If the sandbanks emerged above sea-level, swamps supporting a growth of coal-forming vegetation appeared. Features such as ripple marks, rill channels and minor current bedding suggest a tidal flat environment for some unfossiliferous shales and part of the sandstones. It is not surprising to find some evidence of disconformity, resulting from the excavation of distributary channels and also produced during the migration of barrier islands. The channels are readily recognised only by the cutting-out of marker horizons.

Channels have been mentioned in the foregoing pages in Brigantian, Pendleian and Arnsbergian strata. In the Brigantian, probably the most important case is the channelling by the Tuft Sandstone between Stotfield Burn (Rookhope) [NY 943 424] and Stanhope Burn [NY 986 413] (p.205) by which the calcareous and argillaceous parts of the Iron Post Cyclothem have been eliminated, producing thick sandstone from the base of the Great Limestone down to the base of the Quarry Hazle. At a lower horizon, the quartzite-filled channel at Settlingstones beneath the Dalla Bank Limestone, while of economic importance, is only one of many channel sandstones in the Northumbrian Trough brought to light during the resurvey of Sheet 13 (Bellingham). In the Namurian, two major channel systems were identified during the mineral resurvey, both with significant wallrock effects on the metalliferous deposits. In the Great Limestone Cyclothem a major channel crosses the orefield in a sinuous SSW course from near Blanchland to Barras in Stainmore. Parts of this system were recognised from mine records before but the full extent was unknown until B L Hodge mapped it (1965). The main channel-fill sandstone here reaches a maximum thickness of 120 ft (36.6 m) but probably averages 80 ft (24 m). Two sheet sandstones, the Low and High Coal Sill are considered to have formed in inter-distributary bays by flooding over levees, by crevassing or by accumulation of spits or bars. This channel is believed to have transported the sediment across the mainly mud-filled Northumberland trough in the neighbourhood of Fallowfield (Figure 5). The supply of sediment appears to have ceased temporarily at the time of formation of the swamps that produced the Low Coal and again when the High Coal abandonment occurred. The belt of thick sandstone in the White Hazle, lying SE of and roughly parallel to the channel system (Figure 5) is not interpreted as a palaeodistributory but, following Elliot (1975) as the remains of a barrier island which continued southward to join up with his section in Stainmore.

The most spectacular distributary so far described is however that recognised in the first edition of this Memoir (1948, p.36) as the Rogerley Transgression; the term Rogerley Channel is now preferred. The channel, which is 2 miles (3.2 km) wide at outcrop above Stanhope, is at least 250 ft (76 m) deep and can be followed, mainly from shaft and borehole records, from the Hunstanworth Mines of the Derwent valley along a curving but generally southward course 14 miles (22 km) to the mines NE of Middleton in Teesdale. Probably it continues through Eggleston and Cotherstone, though subsurface evidence here is lacking. However Burgess and Holliday (1978, fig. 32) illustrate washout channels cutting through the Tan Hill Coal, Mirk Fell Ironstone and beds down to the Upper Stonesdale Limestone ( = Rookhope Shell Beds) in Lower Baldersdale and Deepdale. In ground on Sheet 32 (Barnard Castle) described by Mills and Hull (1976) a corresponding channel-fill also cuts across the Knucton Shell Beds. As already noted, these latter authors further suggest that the continuation of the Rogerley Channel may have fed the sediment to the Mirk Fell Ganister, the Lower Howgate and Grassington Grits, which are the arenaceous beds resting on the intraPendleian unconformity of the Askrigg Block (Dunham and Wilson, 1985, p.19). In the northern part of the orefield, no section is known where the Lower Felltop Limestone occurs above the channel-fill and evidence suggests that the distributary continued to be active at least until the time of deposition of the Coalcleugh Coal. When it first came into existence is less clear, but in many sections a division of the fill between Low Grit Sill and High Grit Sill, with shale or even coal between the two, is recognised. The term Grit Sills, probably introduced by the Hunstanworth miners, covers the coarse and, in places, pebbly sandstones filling the channels; they contrast lithologically with the partly equivalent Slate Sills, fine- to medium-grained flaggy sandstones which may be considered to have resulted from flooding of interdistributary bays when levees along the channel were crevassed. These beds owe their name to their use as stone slabs used for local buildings.

If, as seems likely, the Rogerley Distributary continued to be filled with sediment up to the time of formation of the Coalcleugh Coal, the Coalcleugh Transgression Beds of Carruthers (1938) contribute to the upper part of the fill. However, they spread far more widely; the type locality is clearly not a distributary channel. No doubt the extreme variability of this group, from mixed soft sandstones and shales to Grit Sills facies, is the result of the various environments in which they were deposited. There is clear evidence that the base of this formation, outside the channel system, was a transgressive one; this is best illustrated by the way in which it repeatedly cuts out the Lower Felltop Limestone in Rookhope and Upper Weardale. This is, nevertheless, not the same horizon as the intra-Pendleian unconformity of the Askrigg Block. The beds are more likely to be correlatives of the Red Scar = Upper Howgate Ridge Grit and it is tempting to correlate the Coalcleugh Marine Beds with the Colsterdale Beds, and the coal with that of Tan Hill.

The inadequate exposure of the beds from the Upper Felltop Limestone up to the Quarterburn Marine Band on the high fells, and the paucity of subsurface information means that no data are available on possible distributaries during later Namurian time.

On (Figure 5) the courses of the known distributaries are plotted against isopachytes of the Pendleian stage rocks.

Westphalian

It is beyond the scope of the present memoir to describe the Coal Measures rocks that represent the Westphalian division of the Carboniferous System around the margins of the orefield. However, as a small number of related mineral deposits, some of them very productive, have been found in Silesian rocks, a brief note on their stratigraphical settings is included here. As already explained, the Namurian–Silesian boundary is now placed lower than the former Millstone Grit–Coal Measures boundary of the primary surveyors, as a result of the substitution of the Quarterburn Marine Band of Mills and Hull (1968) for the Ganister Clay Coal on top of the 'Third Grit' (Figure 7). The grit, perhaps represented at Healeyfield by the Healeyfield Firestone, is now classed as Westphalian A in age. The former classification which included the measures up to the Brockwell Coal in the Lower division of the Coal Measures has now been superseded by the Westphalian A stage, extending up to the Harvey Marine Band of the Durham Coalfield, and comprising the lenisulcatsa, communis and the lower half of the modiolaris non-marine lamellibranch zones. Mineral deposits occur in strata referred to this stage, and also in beds belonging to the succeeding Westphalian B stage, extending from the Harvey or Hopkins Marine Band, through the upper part of the modiolaris and the Lower similis-pulchra zones to the Ryhope or Mansfield Marine Band. Characteristically, the measures are dominated by mudstone and shale, but they include some substantial beds of sandstone, in some cases with hard, seat-earth tops or intercalations. Marine strata form only a minor part of the succession, much of which was formed on paralic coastal flats. Major coal seams are spaced at intervals of 50–150 ft (15–46 m) through the succession. Intensive mining having been in progress for three centuries or more, the coalfields flanking the Northern Pennine Orefield have been far more thoroughly investigated underground than the Namurian and Dinantian core of the field. It must be concluded that most of the introduced metalliferous and related deposits in the coalfield areas have been found by this time. (Figure 7) illustrates the stratigraphical sections of most interest from the point of view of mineralisation.

Boreholes that link the productive coal measures of Westphalian B and A with the underlying Namurian are not numerous. Smith and Francis (1967, p.33) in their memoir on Sheet 27 give sections of seven holes bored through Westphalian and reaching the 'Second Grit', but only one, at Ryal [NZ 3626 2968], was continued as far as the Upper Felltop Limestone. Scattered ocurrences of galena and sphalerite have been found in the southern part of the Durham coalfield, but not in workable amount (p.273); the relationship of these to the lower strata is unknown.

Permian rocks

Stratigraphical note

E and SE of the Northern Pennine Orefield, Permian rocks rest with marked unconformity upon the Westphalian and Namurian strata. Prior to the onset of sedimentation, probably in Upper Permian time, folding had produced the Durham Coalfield 'basin', and after ensuing erosion, a conspicuously reddened surface had been developed before the first Permian deposits arrived (Anderson and Dunham, 1953). The initial sediments were white or (at outcrop) yellow incoherent dune sands, driven before the advancing Zechstein Sea and filling up the modest irregularities in the land surface. An episode of euxinic black shale deposition followed, producing the carbonaceous dolomitic siltstone known as the Marl Slate. Unlike its probable equivalent the German Kupferschiefer, this is not known to contain workable metalliferous ground, but the concentration of lead in it exceeds by two orders of magnitude the normal local background (Deans, 1950; Hirst and Dunham, 1963; Smith and Francis, 1967, pp.103–106). The thickness of the bed is generally 2 ft (0.6 m) or less. In the Lower Magnesian Limestone which follows, Fowler (1943, p.41) showed that mineralisation was more widespread than had formerly been supposed, especially between Bishop Middleham and Cox-hoe, while Hirst and Smith (1974, p.B49) have given details of the occurrence of baryte, fluorite and associated minerals in the Ferryhill area, where the thickness varies between 160 and 220 ft (49 and 67 m). The overlying Middle Magnesian Limestone consists of a western lagoonal facies about 300 ft (91 m) thick, giving place to the E to the remains of a barrier reef at least 500 ft (150 m) thick, beyond which an evaporite facies is strongly developed beneath the North Sea and in North Yorkshire (Smith, 1970, p.73). Minerals of the Pennine suite have been found in small quantities in exposures and borings in the Middle Magnesian carbonate facies, (Fowler, 1983) but detailed examination of the evaporitic facies, mined for anhydrite and halite around the Tees Estuary, and for potash in North Yorkshire (Stewart, 1950, 1951a, 1951b; Armstrong, Dunham, Harvey, Sabine and Waters, 1951) failed to reveal even small amounts. The Upper Magnesian Limestone contains a few occurrences of baryte, fluorite and sphalerite (Smith and Francis, 1967, p.168) but again they have not been found in the evaporitic facies.

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Chapter 3 The country rock: igneous intrusions

Introduction

Igneous rocks assigned to three major periods of activity occur within the Northern Pennines. The earliest group, found among the Lower Palaeozoic rocks which underlie the Carboniferous, embraces the andesites, rhyolites and tuffs of the Borrowdale Volcanic Group, together with a suite of minor intrusions. Since these are not seen in relation to the mineral deposits of the field, they are not further described here. Of more immediate interest is the Weardale Granite, part of a batholith that underlies much of the orefield. However, this predates the mineralisation, having been intruded at the end of Lower Palaeozoic time. It is known to be cut by small veins related to the Red and Boltsburn veins at Rookhope, and could form the wallrock for deep orebodies. It has already been descibed with the foundation rocks (p.00).

The second major group embraces the quartz-dolerites of the Whin Sill, a series of connected or related sills or phacoliths intruded into the Carboniferous sediments. These are now known to be of Hercynian (Late Carboniferous–Early Permian) age. Dykes associated with these intrusions traverse the area. The third group comprises some members of an echelon of tholeiite dykes, collectively known as the Cleveland–Armathwaite dyke, the age of which is certainly post-Jurassic on geological evidence and has been dated as early Tertiary.

The Whin Sill

The practice among the lead miners of calling persistent beds in the stratigraphical succession 'sills' has already been noted. The Whin Sill was regarded by them from early times as a normal member of the succession, the name simply denoted 'hard bed'. It seems probable that the term now universally employed in geology to denote a concordant igneous intrusion, was derived from the present area. When the igneous origin of the formation began to be understood, it was at first regarded as a contemporaneous lava rather than as an intrusion, but its true nature, first suggested by Sedgwick (1827), was established by Tate (1870) and confirmed by Topley and Lebour (1877). The Geological Survey mapping of the area had by this time proved that, although in the Upper South Tyne valley the intrusion occurs more or less concordantly beneath the Tynebottom Limestone, elsewhere in the field it is found at different horizons, varying from a position low down in the Asbian Upper Orton Group up to the Four Fathom Limestone near the top of the Brigantian. To the NW, in the Brampton District, sills are found both in the Namurian and in the Westphalian Coal Measures. The changes in horizon take place along definite lines or belts, of which only a few correspond with major faults or disturbances. Between these belts there are broad stretches in which the intrusion occupies a nearly constant horizon. The identity in composition and structure of the sills justifies the practice of regarding the whole series as a single intrusion. At Rookhope and at Woodland in the present area two sills are known to be present vertically above one another. This situation is also known farther N in Northumberland. It is probable that the Whin Sill in this broad sense, is present over the whole of the Tyne to Stainmore orefield, except where it has been removed by denudation.

Horizon and thickness

The finest exposures are in Teesdale (Area 7) where there are continuous outcrops on the S side of the valley from the head south-eastwards to Middleton-in-Teesdale [NY 940 250] which was the centre of an important road-metal quarrying industry. In the large quarries around Middleton the thickness of the sill is not less than 140 ft (43 m), while two borings made at the Ettersgill zinc prospect [NY 882 300] during 1942 showed a full thickness of 221 ft 6 in (67.5 m) (ET/16) and 243 ft (74 m) (ET/11) respectively. From Middleton north-westwards to Langdon Beck [NY 853 311], the sill lies below the Single Post Limestone, intruded into the shales and sandstones of the 'Alternating Beds'. The Tynebottom Limestone lies underneath the sill, as may be seen in the well-known exposure at the High Force [NY 880 283] (Clough, 1876, p.446). Borings to the top of the sill at Ettersgill revealed that its depth below the base of the Single Post Limestone varied, in a small area, between 10 ft and 49 ft (3 and 15 m). Even in this area, therefore, where mapping suggests that the sill is at a more or less constant horizon below the Single Post Limestone, some transgression within the Alternating Beds has taken place.

Teesdale is crossed by a faulted monocline, known as the Burtreeford Disturbance, between Langdon Beck and the east end of Cronkley Scar [NY 853 285]. Along this line there is an abrupt change in the horizon of the sill from the position described to one below the Melmerby Scar Limestone west of the Disturbance. The facts suggest that the sill may have been intruded along a horizontal plane which cut through a pre-existing fold. West of the monocline, on Cronkley Fell, the sill is found at its lowest known horizon, 88 ft (26.8 m) below the Melmerby Scar Limestone. Clough (1880, p.435) has described the upward change in horizon to the Robinson Limestone which may be observed nearby. At Falcon Clints [NY 823 281] and at the Cowgreen mines [NY 811 303] the sill lies 90 ft (27.4 m) below the top of the Melmerby Scar Limestone, its thickness as proved on Winterhush Vein being 240 ft (73.1 m). S, W and N of this area there is a series of upward migrations. Between West Cowgreen and Dubbysike Mine [NY 795 320], probably close to the latter locality, the sill appears immediately below the Smiddy Limestone. It is in this position at Greenhurth Mine [NY 780 328] where the proved thickness is again 240 ft (73.1 m). On the right bank of the Tees, opposite Dubbysike, in Rowantree and Lodge Gill Sikes [NY 787 302] and [NY 782 301], sections described by Clough (1880, p.438) show that the sill is present above the Smiddy Limestone, but below the lower part of the Lower Little Limestone. An adjacent section in Cockle Sike [NY 792 298] shows only sedimentary beds between the Smiddy and Lower Little limestones. The remarkable feature of the sections is that the total thickness of rock between the two limestones is the same, whether the sill is present or not, so that the sill has apparently replaced an equivalent thickness of sedimentary strata. Upon this and similar field evidence, Clough built up a case for wholesale assimilation of sediments by the Whin magma, which, however, petrological and chemical evidence completely fails to support. It will moreover be evident from the sections given in (Figure 3) that the intrusion of the sill, where thick, was certainly not accompanied by a comparable thinning of the sediments. Smythe (1930, pp.139–144) has suggested a mechanical explanation of the facts first observed by Clough involving sideways movement of blocks of strata along bedding planes which is quite competent to explain the instances cited by him, though some doubt may be felt as to the general applicability over the whole area in view of the very large horizontal movements it would imply.

Similar upward changes in horizon are observed along the course of the Maizebeck. On the left bank of the Tees, the Whin may be seen to have transgressed across a marl bed in the Melmerby Scar Limestone (Clough, 1880,(Figure 1). The next exposures, in the Maizebeck around Birkdale Farm [NY 806 277] show the sill under the Smiddy Limestone. Near the old Maizebeck Trial Level [NY 7986 2687] there is an abrupt upward change to the Lower Little Limestone.

From field and mining evidence, a series of broad belts in which the sill is at a more or less constant horizon, separated by lines or zones of migration, may be discerned. These have been plotted on (Figure 8). It will be noted that there is a progressive series of upward steps away from the Burtreeford Monocline in a westward direction, the only exception being an apparent reversal in the neighbourhood of the Scordale Mines [NY 763 227] where the sill underlies the Smiddy Limestone (Horizon III). The position under the Lower Little Limestone (Horizon IV) is unrepresented on the escarpment, the position N of Scordale being under the Tynebottom Limestone (Horizon V). This belt, though evidence is lacking in the middle, almost certainly extends from High Cup Nick [NY 745 262] and Dufton Fell [NY 712 275] to the neighbourhood of Garrigill [NY 740 410]. It was within this belt that Forster's section was taken. Near the escarpment, an underground shaft at the Dufton Fell mines proved the thickness of the sill to be 72 ft (22 m). On the S side of the Great Sulphur Vein, exposures in the Tyne and Cash Burn suggest a thickness exceeding 100 ft (30 m), while at Rotherhope Fell Mine [NY 700 426], the proved thickness is 180 ft (55 m). W of Rotherhope Fell exposures in Smittergill [NY 674 388] both NE and SW of the Great Sulphur Vein show that the intrusion has risen to a position under the Single Post Limestone (Horizon VI), the same horizon as in Teesdale E of the Burtreeford Disturbance. Whin at this position is present on the escarpment, N of Middle Tongue Beck [NY 690 329] and Crowdundle Beck [NY 690 330], but here the belt is not extensive, migration up to the base of the Scar Limestone having taken place between Crowdundle and Kirk Dale. The Scar Limestone position is maintained northwards through Ousby Dale, where the sill is 65 ft (19.8 m) thick, to Loo Gill [NY 640 426]. In Gilderdale a higher horizon, under the Five Yard Limestone is apparently reached. To the N, in the Brampton District, the upward changes in horizon continue (Trotter and Hollingworth, 1928, pp.442–445), until at Midgeholme [NY 640 590], the highest known horizon of intrusion, in the Coal Measures, is attained. The higher belts of approximately constant horizon on the west side of the Burtreeford Disturbance appear to run roughly N–S. The deep underground shaft at Rampgill Mine [NY 7990 4225], Nenthead which was sunk to the Lower Little Limestone without encountering the Whin Sill, presumably lies within a belt in which the sill is at one of the lower horizons. At Longcleugh Mine, 5 miles (8 km) NNW of Rampgill a borehole [NY 7688 5175] has proved the second greatest thickness of the Great Whin Sill so far recorded, 266 ft (81 m) (Johnson, Nudd and Robinson, 1980, p.00). The sill is here at horizon V, under the Tynebottom Limestone. The impression is created of a belt of maximum thickness more or less paralleling the Burtreeford Disturbance (Figure 7). At Allenheads [NY 860 453], E of the monocline it is 233 ft (71 m) thick, at a similar horizon. However, at Blackdene Mine [NY 868 390], not in this belt, a thickness of 300 ft (90 m) was recorded near a small horizon change.

E of Rampgill, the Burtreeford Disturbance crosses Weardale near Wearhead. At Copt Hill [NY 851 408] quartz-dolerite is seen within the fold (Wager, 1929, pp. 235–236). Here the intrusion lies under the Single Post Limestone. Burtree Pasture underground shaft [NY 8603 4180], not far away, proved the sill at the same horizon, with a thickness of 241 ft (73.5 m). To the E there is a downward migration, for both at Greenlaws [NY 890 370] and Slitt Mines [NY 901 392], the sill was found beneath the Tynebottom Limestone. Recent development at Blackdene Mine (Greenwood and Smith, 1977, p.187) showed that the top of the sill breaks upward through the Single Post Limestone, before dropping to the Slitt and Greenlaws position. Farther E at Cammock Eals Mine [NY 935 383] it has descended still farther to a position under the Jew Limestone (IVA). This was found to be its horizon in the Rookhope Borehole [NY 9374 4278] (Dunham et al., 1965). Here the thickness is 192 ft 9 in (58.75 m), and here a second sill, 5 ft 10 in (1.78 m) thick is present within the Three Yard Limestone. In Weardale this small sill in the Three Yard Limestone is known as the Little Whin Sill; it increases in thickness eastwards from a few feet at Billing to 38 ft 6 in (11.7 m) at Greenfoot Quarry, Stanhope [NY 983 393]. Prior to the Rookhope drilling no deep sinking had ever been made in the area occupied by it, so that it was not known whether another main sill underlay it as was evidently assumed when it was named. The Little Whin Sill was recorded to the N of Stanhope in the western workings at Stanhopeburn Mine, which reached the Three Yard Limestone. In the Northumbrian Water Authority tunnel, what was probably a continuation was found in an upward transgression 8917 ft (2718 m) S of the River Wear portal. Ten miles (16 km) E of Stanhope, the Roddymoor Boring [NZ 1513 3635] proved 187 ft (57 m) of quartz-dolerite, intruded into the Scar Limestone, while in the Woodland Borehole [NZ 0908 2770] a 'Little Whin Sill', 7 ft 2 in (2.23 m) thick was found 50 ft (15.2 m) higher than in Weardale, while the top of the main sill was cut under the Three Yard Limestone.

Of all the migration in horizon so far discussed, only those which coincide with the Burtreeford Disturbance show any relation to previous faulting or folding. It is a remarkable fact, as Clough has pointed out, that horizon changes elsewhere were accomplished with little or no faulting or folding of the associated beds. There is, nevertheless, one other important example of the relation of the intrusion to major faulting within the area. This is found along the Lunedale fault-belt, on which Closehouse Mine [NY 850 227] is situated. On the E side of Fish Lake Valley, the main fault of the belt brings the Scar Limestone on the S opposite beds between the Smiddy and the Lower Little limestones on the N. N of the fault system, the Whin Sill, 100 ft (300 m) thick, lies at horizon IV, above the Smiddy Limestone. Within the main fault itself it forms a broad dyke, spreading out into a sill above the Low Brig Hazle on the S side of the fault. Plainly, the main fault at least was in existence at the time of the intrusion, though it is likely that there has been renewed movement on the fault of later date than the intrusion. Farther E along the Lunedale Faults the sill rises to a position under the Four Fathom Limestone (Horizon X) in Wemmergill [NY 907 226] on the S side of the fault, while on the N side it lies beneath the Scar Limestone. No dyke is known within the fault here.

In the Haydon Bridge district, the Whin Sill in the mineralised area is found beneath the limestone indicated as the Dallabank on the revised Sheet 13, probably close to the Tynebottom horizon of the main field. Between Settlingstones [NY 845 682] and Greenhead [NY 660 654], there is an upward change in horizon of nearly 300 ft (90 m), the sill at Cockmount Hill [NY 698 776] appearing beneath a limestone which Burns and Trotter have correlated with the Five Yard Limestone of the main field (Trotter and Hollingworth, 1932, pp.54, 119), but which Holliday et al. (1975) regarded as the Scar. The proved thickness of the sill in Winter's and Ellen's shafts [NY 8460 6855] and [NY 8500 6878] at Settlingstones Mine is 150 ft (45.7 m); in Frederick Shaft it is 158 ft (48.1 m). The smaller apparent thickness of 120 ft 6 in (36.7 m) in Old Engine Shaft is probably due to faulting. Stonecroft Pumping Shaft [NY 8545 6892] to the N proved 153 ft (46.6 m) of Whin Sill, at the same horizon as in the Settlingstones workings. At Cockmount Hill [NY 698 776] the thickness is 138 ft 9 in (42.3 m).

Petrography

The classic petrographic description by Teall (1884, p.640) has been followed by several important contributions in more recent years, including Holmes and Harwood's discussion of the petrology (1928, p.493), Smythe's exhaustive chemical study (1930, p.16) and an account of certain peculiar varieties by Tomkeieff (1929, p.100). The Ettersgill borings in 1942 led to the recognition of four macroscopic variants (described below), while the Rookhope boring, though it showed the main sill to be altered, provided good material for a detailed petrographical and geochemical study of the Little Whin Sill by A C Dunham and M J Kaye (1965, p.229) using advanced equipment. Their paper also contains a full list of references to the sills. Subsequently R K Harrison (1968, p.38) investigated the Little Sill and the upper 58 ft 8 in (17.9 m) of the Great Sill cored at Woodland [NZ 0908 2770]. In 1970 A C Dunham reviewed the state of knowledge of the sills beneath Durham County, and with V E H Strasser-King (1982) the late-Carboniferous intrusions of northern Britain.

The significant facts for the Northern Pennine Orefield are as follows:

Four normal types of quartz-dolerite may be recognised in the Whin Sill, the first three grading into one another: (1) Tachylitic marginal facies, a black very fine-grained rock in which crystals are generally not visible without the use of the microscope; (2) Fine-grained grey (or if weathered, greenish) dolerite, in which ferromagnesian minerals and feldspars are plainly discernible using a hand lens; (3) Medium-grained mottled dolerite, in which the principal constituents are visible to the naked eye; (4) Doleritepegmatite of two types, one grey, rich in large pyroxenes up to 2 cm long, the other a pink granophyric variety. The two types of pegmatite are frequently, though not always, asociated. The relation between the principal types where the sill is thick was well illustrated by a boring at Ettersgill (Table 14).

Types 3 and 4 are in general confined to the thicker sills of the area and their presence may be taken to indicate that the nearest intrusive contact is at least 30–50 ft (9.1–15.2 m) distant.

An estimate of the mineral composition of the intrusion, in round figures, based on the chemical work of Smythe and micrometric measurements by Holmes and Tomkeieff, may be made as follows: Pyroxene, 34 per cent; plagioclase feldspar, 46; hornblende, biotite, chlorite, 4.5; iron-titanium oxides, 8; quartz, orthoclase and micropegmatite, 5.5; calcite, pyrite, apatite, 2.

The plagioclase, occurring in lath-shaped crystals, is zoned, sometimes exhibiting cores as calcic as Ann, but varying down to albite on the outer margins. Holmes and Smythe, approaching the subject from different angles, agree that the feldspar contains orthoclase in solid solution and has a composition approximating to Or10Ab35An52. Phenocrysts of anorthite, approximating to An90 occur sporadically and show evidence of reaction. Phenocrysts of fresh olivine (Fa15) were detected by Dunham and Kaye in the lower part of the Little Sill, in amounts up to 2 per cent of the rock; pseudomorphs occur elsewhere, e.g. at Woodland. Four distinct pyroxenes have been recognised. The first to crystallise was a colourless to pale green slightly pleochroic rhombic pyroxene in which, according to Wager (1929, p.224), 2V = 65°, suggesting a composistion Fs35; Dunham and Kaye find a range from Fs23 to Fs27. Teall (1884, p.653) has applied the name bronzite to this mineral. Its place may be taken by a colourless or faintly green clinopyroxene which is nearly uniaxial. The third type, representing the bulk of the pyroxene present, is a grey-green or brown mineral with 2V approaching 50°, according to Holmes (1928, p.504). An analysis by Teall of a pyroxene of this type from Tynehead gave the following composition: silica , 48.41 per cent; alumina, 4.05; ferric oxide, 2.36; ferrous oxide, 15.08; manganous oxide, 0.37; lime, 15.98, magnesia, 12.14; water, 1.19; total, 99.58. Dunham and Kaye, from X-ray measurements, find a range of composition from Ca45Mg5iFe4 to Ca38Mg38Fe24 in the Little Sill and confirm that iron variation is greater still in the main sill.

Subcalcic augite with submicron-size exsolution of augite has also been found, presumably representing a metastable state (A C Dunham, personal communication). Green uralitic and brown hornblendes have developed from the pyroxenes by reaction, together with a little biotite. The iron-titanium oxide minerals occur in skeletal growths and massive grains. Average samples analysed by Smythe (1930, p.62) gave the composition: ferric oxide, 38.5 per cent; ferrous oxide, 29.6; manganous oxide, 1.0; titanium oxide, 30.9; the minerals are magnetite–ulvospinel intergrowths with ilmenite. Apatite and pyrite are the principal accessory minerals. The interstices between the minerals so far described are occupied by micropegmatite, an intimate intergrowth of quartz and alkali feldspar, or by separate developments of these minerals.

Type 1 (E20559)Numbers shown thus refer to the Geological Survey sliced rock collection. contains phenocrysts of plagioclase, averaging 0.2 mm long, with occasional pyroxenes, set in a groundmass consisting of minutely crystalline minerals, including innumerable grains of iron-titanium oxide averaging 0.001 mm diameter. In type 2 (E20548), (E20549), (E20557), (E20558) the typical doleritic texture is displayed, an intersertal or ophitic arrangement of plagioclase laths, pyroxenes and titanomagnetite, with quartz, alkali feldspar and micropegmatite in the interstices. The average grain-size ranges from 0.15–0.5 mm. The medium-grained variety (Type 3) (E20550), (E20551), (E20553), (E20554), (E20555) owes its mottled appearance to the presence of clinopyroxene and titano-magnetite grains and aggregates between 0.5 and 1.5 mm diameter which contrast with the feldspar laths surrounding them. Harrison (1968, p.46) notes that hypersthene and iron oxide minerals are somewhat more abundant in this type that in type 2. In the pegmatite, Type 4, the pyroxenes and feldspars may reach 2 cm in length but the average grain size in the commonest type is 2 or 3 mm (E20552).

For a discussion of the petrogenesis of the sills, reference should be made to the works of A C Dunham, M J Kaye and R K Harrison already cited. It is interesting to note that on a Si02/Na2O + K2O plot, the numerous analyses of the Whin dolerite fall between the acceptable fields for alkali and tholeiitic basalts respectively. No crystal settling can be demonstrated and over the huge area (at least 3000 square miles, (7680 square kilometres) the chemical composition varies remarkably little, though it is expressed by varying mineral assemblages at different levels in the sills. Trace-element contents include Pb 33 ppm, Cu 59, Zn 109, Ni 59 (M J Kaye) hardly differing from local background. The crystallisation of the Whin magma led to the concentration of its volatile constituents, with results which may be traced in the pegmatites and late-stage alterations. The doleritepegmatites presumably represent the results of local accumulations of volatiles at a comparatively early stage in the cooling history. Of later date, later than the early joint system, is the widespread chloritic alteration which has been studied in detail by Wager (1929, p.221). Minerals associated with this stage, which Wager attributes to gases which condensed in the joints to become hydrothermal solutions, include besides the chlorite (a diabantite of negative sign and refractive index between 1.60 and 1.61), bowlingite, calcite, pyrite, quartz, albite, anatase and sphene.

Smythe (1924, p.100; 1930, pp.111–116) has also demonstrated the occurrence of pectolite as a late-stage alteration product. It is noteworthy for the present purpose that although the Whin magma had a well-defined hydrothermal stage, the minerals generated at that stage did not include any of the important minerals of the metalliferous deposits of the area, but chalcopyrite, arsenopyrite, pyrrhotite and pyrite have been found in very small amounts.

The alteration of the quartz-dolerite adjacent to the mineral veins is considered in Chapter 5, where two of Smythe's analyses of the unaltered rock based on very carefully taken samples, are reproduced (p.85).

Metamorphism of sedimentary rocks

The rocks in contact with and adjacent to the intrusion have been metamorphosed to an extent which depended upon their susceptibility to heat and their permeability to solutions which emanated from the intrusion. To the thermal effects may be ascribed the baking of shale into 'whetstone', a smooth, porcellanous rock in which the bedding may be nearly or entirely obliterated. In other shales a spotting has been developed, and, in some instances, andalusite. Pure limestones have been completely recrystallised into marble, but Robinson (1970, p.120) makes the important point that marmorisation is hindered or prevented by the organic carbon content of the dark grey Brigantian limestones whereas pale limestones like the Melmerby Scar are totally recrystallised. Impure limestones have been converted into calcsilicate rocks. In addition it is clear from the work of Hutchings (1895, pp.121, 163; 1898, pp.69, 123) that in some places there has been a substantial addition of soda to the metamorphosed rocks, though the effect is a patchy one.

The extent of the metamorphism is illustrated by the Ettersgill borings, where shale is affected up to 44 ft (13.4 m) above the top of the intrusion, and down to 37 ft (11.3 m) below the base. A limestone at 36–40 ft (11–12 m) above the sill is not visibly marmorised, whereas another 14 ft (4.3 m) nearer the sill is completely recrystallised. At Falcon Clints (Hutchings, 1898, p.125) metamorphism is observed down to 83 ft (25.3 m) below the sill. The nearby workings at Cowgreen Mine [NY 811 303] showed the Melmerby Scar Limestone, 90 ft (27.4 m) thick above the sill, completely marmorised. Traces of the effect are discernible in the Robinson Limestone, at 100 ft (30 m) above the sill. At Rotherhope Fell Mine the Tynebottom Limestone, 22 ft (6.7 m) thick, rests directly on the sill and is thoroughly altered. Here at least 6 ft (1.8 m) of shale above the limestone is affected. Within the Great Sulphur vein-zone at Crossgill [NY 739 382], metamorphism due to the sill extends to 40 ft (12 m). above the top. The thickness of the 'whetstone' proved above the sill at Burtree Pasture was 46 ft (14 m), with at least 30 ft (9 m) of similar baked shale below the sill. At Rookhope (Dunham et al., 1965, p.403) spots in shale can be seen to 129 ft (39 m) above and 127 ft (38 m) below the Great Whin Sill.

The shales of the Asbian and Brigantian stages are generally grey or black, well-bedded rocks containing sharply angular grains of detrital quartz and usually some detrital mica. Metamorphism produces a smooth porcellanous rock in which the bedding is nearly obliterated and in which incipient development of clear spots, some of which contain andalusite, may be recognised under the microscope (E18535), (E18552), (E18552), (E185524), E20547). Recrystallised rutile occurs in these rocks. Probably there is some new development of mica and quartz during metamorphism. When the shales are limy, diopside may be produced.

Shaly limestones yield a more extensive suite of minerals under conditions of metamorphism. Examples from Falcon Glints (Bed No. 1 of Hutchings, 1898, p.125) show pale yellow to almost colourless garnets with refractive index 1.741 (probably grossularite), vesuvianite, diopside and chlorite with refractive index 1.645 (aphrosiderite near daphnite according to Winchell's tables) (E18537), (E18538), (E18539), (E18540), (E18541). Investigation of borehole cores from Cowgreen Reservoir site enabled Robinson (1970) to add wollastonite to this list of minerals, implying a temperature of 550° or more.

From Falcon Glints Hutchings (1898) described a remarkable shale containing dark chloritic nodules which he ascribed to metamorphism, but which Wager (1928, p.88) has since shown to have been original constituents of the shale. This rock is interesting because it shows without doubt the replacement of detrital quartz by newly developed white mica (E18543)–(E18544). From the same locality metamorphosed impure limestone or limy sandstone shows the development of soda-feldspar in good crystals, replacing quartz and calcite. The feldspar is probably an oligoclase (E18545)–(E18546). Both the development of soda-feldspar and sericite at the expense of quartz implies the addition of alkalis to the rock, and illustrates the process of metasomatism of which Hutchings' analyses provide suggestive evidence. The same effect was seen in the sandstone just above the sill collected from the Flank Level to the Horse Level at Cowgreen Mine (E18547), (E18548), (E18549). Wager (1929, p.91) has suggested that the soda-bearing solutions were the residuum of the hydrothermal solutions which produced the chloritic alteration of the Whin Sill adjacent to its early joints. Sericite extensively developed in the upper shaly part of the Tynebottom Limestone at Rotherhope Fell Mine (E18893), (E18894), (E18895), (E18896) should probably be ascribed to the metasomatic action of solutions from the Whin Sill rather than to the later mineralising solutions which produced the fluorite-quartz-galena replacements at this mine. Harbord (see Emeleus, 1974, p.267) found that sedimentary iron sulphide in the metamorphosed shales had been converted into marcasite and pyrrhotite, and that in some Teesdale examples, copper and zinc appeared to have been added from the Whin magma, forming chalcopyrite and sphalerite. The magma may have provided iron to form magnetite in Harwood (see p.75).

Whin Dykes

A series of dykes trending between NE and ENE occur within the area and have been attributed to the same period of intrusion as the Whin Sill. They have been described by Teall (1884, p.209) and Holmes and Harwood (1928, pp.511–528). The rock of which they are composed is for all practical purposes identical with Type 2 of the Whin Sill, tachylitic margins similar to Type 1 being developed at the side contacts. Owing to the more rapid cooling of the dyke-rocks, glassy mesostasis is generally commoner than in the sill, and many of the dyke-rocks may be described as tholeiites.

Haydon Bridge Dyke

The northernmost dyke of the present area, the Brunton dyke of Lebour (1886, p.89), crosses the River Allen 0.5 mile (0.8–km) SSE of Ridley Hall, at [NY 860 632] and runs in an average direction N 78°E along the N side of Morralee Wood. The trials for lead known as Morralee Mine [NY 805 636] were made along and near this dyke. To the E the dyke crosses and recrosses the South Tyne in the neighbourhood of Haydon Bridge [NY 850 650] and runs along the southern margin of the workings of Fourstones Colliery. It forms one member of the St Oswald's Chapel dyke-echelon of Holmes.

Dykes within the Stublick Fault-system

Trotter and Hollingworth (1932, pp.119–120) refer to the presence of a whin dyke in the coal workings along the line of the Stublick Fault, 3 furlongs (619 m) NE of Birch Trees [NY 690 585], and to a number of other dykes in the same neighbourhood. On the E side of the Haydon Bridge Area, other instances are found near the eastern end of the fault-system, 0.5 miles (0.8 km) SE of Dilston [NY 976 632] and at Thornbrough, 1.5 miles (2.4 km) ENE of Corbridge [NZ 004 604]. The fault is also mineralised at Corbridge (Smith, 1923, p.20).

Near Hartside Mine a dyke is exposed in Loo Gill [NY 640 428] and has been cut through in the deep crosscut level. Its direction is N 68°E and its width in the level is 20 ft (6.1 m). The rock (E19557) is a tholeiite resembling the Acklington type, composed of labradorite or andesine laths 0.1–0.5 mm long, colourless or yellow augite which is mostly in aggregates of interfering prismatic grains but is partly prismatic and subophitic to feldspar, grains of iron oxide, prismatic pseudomorphs of bowlingite after orthopyroxene and abundant glassy or devitrified mesostasis. A little granular quartz is associated here and there with the mesostasis.

Hett Dyke System

The members of this series include, from W to E, the two small dykes seen on the escarpment near Long Fell Mine [NY 768 197], the Connypot Dyke, seen in the headwaters of the Lune [NY 813 207], the Greengates dykes quarried 1.5 miles (2.4 km) SW of Middleton-in-Teesdale [NY 933 235], and the Hett Dyke proper, which runs from the Tees W of Middleton at [NY 990 258] to the Permian escarpment near Quarrington Hill, 4 miles (6.4 km) SE of Durham. The general course is N 70°E. Approximately two miles (3.2 km) N of this dyke in the eastern part of its course lies the Ludworth Dyke, first encountered in the workings of Oakenshaw [NZ 221 386] and Brandon collieries [NZ 228 390], the Busty Engine Plane from the latter having passed through the dyke, which is acompanied by witherite mineralisation, 7 furlongs (1.4 km) NNE of Brancepeth Castle.

Intrusion of the Sill

It was previously supposed that the feeders of the sill probably lay beneath the areas of maximum thickness, perhaps adjacent to the Burtreeford monocline but magnetometer surveys fail to support this. A more plausible view has been proposed by Francis (1982) namely that the feeders were the flanking dykes such as the Hett and Haydon Bridge dykes and that from these the dense basaltic magma followed bedding planes, at intervals breaking across them to maintain the downward flow under gravity. Thus the basin-shaped series of sills transgresses the gentle dome of the Alston Block (discussed in the next chapter).

Age of the Whin Sill and dykes

The occurrence of both sills and dykes of this suite in rocks of Middle Coal Measures age and their absence from the Permian suggests a post-Upper Carboniferous, pre-Permian age. Confirmation is obtained from two sources. Two pebbles of quartz-dolerite of Whin Sill type have been found in the Upper Brockrarn conglomerate (Holmes and Harwood, 1928, pp.532–533); Dunham, 1932, p.425). An absolute estimate of the age of the sill by the helium method by Dubey and Holmes (1929, p.477) gave a figure of 196 Ma as compared with 28 Ma for the Tertiary Cleveland Dyke, discussed below. Although these pioneer studies set the two suites in proper relative position, the absolute values are now known to be low. An investigation of Rookhope borehole material by F J Fitch and J A Miller (1967) gave a preferred late Silesian age of 295 Ma. Palaeornagnetic studies by K M Creer, E Irving and A E M Nairn (1959) reveal the interesting fact that the district lay in tropical latitudes at the time of crystallisation of the sills.

Cleveland Dyke System

The area is also crossed by several members of the well-known echelon of dykes collectively called the Cleveland–Armathwaite Dyke. The westernmost example in the area is exposed in the headwaters of Crossgill, [NY 733 369] 6 miles (9.6 km) S of Alston. It crosses Round Hill and is exposed in the South Tyne headwaters 0.25 mile (0.4 krn) NE of Calvert Fold [NY 757 365]. The second member is first seen in Ettersgill [NY 885 295]. Here some revision of the 6-inch map (Durham 39 NW) was necessary, for the dyke was shown by the primary surveyors passing to the S of the Whin Sill outcrop 0.5 mile (0.8 km) N of Dirt Pit Farm, whereas actually it may be seen cutting through the sill beneath the foot bridge at Outberry Bat [NY 8849 2955]. To the E the dyke is seen in Smithy Sike [NY 892 295], and again in Bow Lee Beck near Mirk Holm [NY 908 293], where it splits into two parts and includes a screen of sediments. Its probable eastward continuation is seen in Coldberry Gutter [NY 930 289] as a narow dyke along or near the line of the Lodgesike–Manorgill fault-vein. Two parallel branches of this dyke were met with in Red Grooves Level [NY 9237 2905], 95 ft (29 m) apart. A third unit of the echelon occurs E of Middleton-in-Teesdale, but it is not of interest in the present connection.

Age

The western part of the echelon cuts through the New Red Sandstone of the Vale of Eden, while the eastern portion cuts the Liassic rocks of NE Yorkshire. There is little doubt as to the Tertiary age of these intrusions which Holmes and Harwood (1929, p.3) believe to converge on the Mull dyke-swarm. Evans, Fitch and Miller (1973) using the K-Ar method find a minimum age 58.4 ± 1.1 Ma (late Palaeocene).

Petrography

In the field the rock of the Cleveland dyke is readily distinguished from the Whin Sill type by its porphyritic character, with evenly distributed small phenocrysts of plagioclase and pyroxene set in a dark, fine-grained groundrnass. Under the microscope (E18556), (E18557), (E18558), (E18559), (E18560), (E18561), the phenocrysts prove to be zoned plagioclase with the inner zones labradorite up to An65 (rarely anorthite), the outer zones oligoclase. The maximum size is 1.5 mm by 0.6 mm. The pyroxenes present include colourless enstatite, pigeonite and coloured augites. Rod-like iron oxides and tiny plagioclase and pyroxene microlites occur in a glassy mesostasis, which is in some places devitrified. In the Cleveland type the amount of pyroxene exceeds the amount of feldspar, in contrast with the Whin Sill type. Teall (1884, pp.209–227) gave a full description of the dyke and Holmes and Harwood (1929, pp.34–41), who refer to the rock as a tholeiite of Cleveland type, give chemical analyses. The most recent accounts are by H J Emeleus (1970, 1974).

References

CLOUGH, C T. 1876. The section at High Force, Teesdale. Q. J. Geol. Soc. London. Vol. 33, 466–471.

CLOUGH, C T. 1880. The Whin Sill of Teesdale as an assimilator of the surrounding Beds. Geol. Mag., Dec. 2, Vol. 32, 433–447. DUBEY, V S, and HOLMES, A. 1929. Estimates of the ages of the Whin Sill and Cleveland Dyke by the helium method. Nature, London, Vol. 124, 447.

CREER, K M, IRVING E, and NAIRN, A E M. 1959. Palaeomagnetism of the Great Whin Sill. Geophys. J. R. Astron. Soc., Vol. 2, 306–323.

DUNHAM, A C. 1970. Whin sills and dykes. 92–100 in Geology of Durham County. Trans. Nat. Hist. Soc. Northumberland, Durham and Newcastle upon Tyne, Vol. 41.

DUNHAM, A C. and KAYE, M J. 1965 The petrology of the Little Whin Sill, County Durham. Proc. Yorkshire Geol. Soc., Vol. 35, 229–276.

DUNHAM, A C. and STRASSER-KING, V E H. 1982. Late Carboniferous intrusions of northern Britain. 277–283 in Igneous rocks of the British Isles. SUTHERLAND, D S (editor). (New York: John Wiley.)

DUNHAM, K C. 1932. Quartz-dolerite pebbles (Whin Sill type) in the Upper Brockram. Geol. Mag., Vol 69, 425.

DUNHAM, K C. DUNHAM, A C, HODGE, B L, and JOHNSON, G A L. 1965. Granite beneath Visean sediments with mineralization at Rookhope, northern Pennines. Q. J. Geol. Soc. London, Vol. 121, 383–417.

EMELEUS, H J. 1970. Tertiary igneous intrusions. 101, 102 in Geology of Durham County. Trans. Nat. Hist. Soc. Northumberland, Durham and Newcastle upon Tyne, Vol. 41.

EMELEUS, H J. 1974. In The geology and mineral resources of Yorkshire. RAMSEY, D M, and HEMINGWAY, J E (editors). 405 pp. (Leeds: Yorkshire Geological Society.)

EVANS, A L, FITCH, F J, and MILLER, J A. 1973. Potassium-argon determinations on some British Tertiary igneous rocks. J. Geol. Soc. London, Vol. 129, 419–443.

FITCH, F J, and MILLER, J A. 1964. Radiometric comment on the age of the Whin Sill. P.372 in The Phaneroic time scale, item 176. Q. J. Geol. Soc. London, Vol. 120 suppl.

FRANCIS, E H. 1982. Magma and sediment I. Emplacement mechanism of late Carboniferous tholeiite sills in northern Britain. f. Geol. Soc. London, Vol. 139, 1–20.

GREENWOOD, D A, and SMITH, F W. 1977. Fluorspar mining in the northern Pennines.         Trans. Inst. Alin. Metall., Vol. 86, B181–190.

GUNN, W. Second edition by CARRUTHERS, R G, DINHAM, C H, BURNETT, G A, and MADEN, J. 1927. Geology of Belford, Holy Island and the Fame Islands. Mem. Geol. Surv. G.B., 110–124.

HARRISON, R K. 1968. Petrology of the Little and Great Whin Sills in the Woodland Borehole, Co. Durham. Bull. Geol. Surv. G. B. , No. 28, 38–54.

HOLLIDAY, D W, BURGESS, I C, and FROST, D V. 1975. A recorrelation of the Yoredale Limestones (Upper Visean) of the Alston Block with those of the Northumberland Trough. Proc. Yorkshire Geol. Soc., Vol. 40, 319–334.

HOLMES, A, and HARWOOD, H F. 1928. The age and composition of the Whin Sill and related dykes of the North of England. Mineral Mag., Vol. 21, 493–542.

HOLMES, A, and HARWOOD, H F. 1929. The tholeiite dykes of the North of England. Mineral Mag., Vol. 22, 1–52.

HUTCHINGS, T M. 1895. An interesting contact-rock with notes on contact metamorphism. Geol. Mag., Dec. 4, 121–133, 163–169.

JOHNSON, G A L, NUDDS, J R, and ROBINSON, D. 1980. Carboniferous stratigraphy and mineralisation at Ninebanks, West Allendale, Northumberland. Proc. Yorkshire Geol. Soc., Vol. 43, 1–16.

LEBOUR, G A. 1886. Outlines of the geology of Northumberland and Durham. (Newcastle upon Tyne: Lambert.)

ROBINSON, D. 1970. Metamorphic rocks. 119–123 in Geology of Durham County. Trans. Nat. Hist. Soc. Northumberland, Durham and Newcastle upon Tyne, Vol. 41.

SEDGWICK, J A. 1827. On the association of Trap Rocks with the Mountain Limestone Formation of High Teesdale. Camb. Philos. Trans. Vol. 3, 139–196.

SMYTHE, J A. 1924. Minerals of the North Country: Silicates. The Vasculum, Vol. 10, 100–103.

SMYTHE, J A. 1930. A chemical study of the Whin Sill. Trans. Nat. Hist. Soc. Northumberland, Durham and Newcastle, New Series, Vol. 30, 16–150.

TATE, G. 1870. On the basaltic rocks of Northumberland. Proc. Berwick Nat. Club, Vol. 6, 197–217.

TEALL, J J H. 1884. Petrological notes on some North-ofEngland dykes. Q. J. Geol. Soc. London, Vol. 40, 209–247.

TEALL, J J H. 1884. On the chemical and microscopical characters of the Whin Sill. Q. J. Geol. Soc. London. Vol. 40, 640–657.

TOMKIEFF, S I. 1929. A contribution to the petrology of the Whin Sill. Mineral Mag., Vol. 22, 100–120.

TOPLEY, W, and LEBOUR, G A. 1877. On the intrusive character of the Whin Sill of Northumberland. Q. J. Geol. Soc. London, Vol. 36, 406–425.

TROTTER, F M, and HOLLINGWORTH, S E. 1932. Geology of the Brampton District. Mem. Geol. Surv. G.B. 223 pp.

WAGER, L R. 1928. A metamorphosed nodular shale previously described as a "spotted" metamorphic rock. Geol. Mag., Vol. 65, 88–92.

WAGER, L R. 1929. Metasomatism in the Whin Sill of the north of England. Part I. Metasomatism by lead vein solutions. Geol. Mag., Vol. 66, 97–110.

WAGER, L R. 929. Metasomatism in the Whin Sill of the north of England. Part II. Hydrothermal alteration by juvenile solutions. Geol. Mag., Vol. 66, 221–228

Chapter 4 Structure

Three major periods of earth-movement have played their parts in the tectonic evolution of the orefield, deforming the rocks by fracturing and folding and so preparing the way for the mineralising solutions. After the mineral deposits were emplaced, there is evidence that further earth-movements occurred.

Grain of the foundation rocks

The Caledonian orogeny, of Siluro-Devonian date, has imparted to the Lower Palaeozoic rocks of the North of England a dominant ENE pattern of strong folds. Associated with these, cleavage was developed either parallel to the folding or, within limited areas, in a WNW direction. In the Cross Fell Inlier an analysis of the structure of the autochthonous Skiddaw Slates shows a dominant ENE strike (Shotton 1935, p.691). Three or, in places, four stages of the evolution of the folds, each with its associated cleavage, have now been recognised (Burgess and Wadge, 1974; Burgess and Holliday, 1979, p.76). In the Teesdale Inlier the cleavage again strikes ENE. It is probable that the older rocks forming the foundation of the orefield have a 'Caledonian' grain which has affected the response of the younger rocks to later movements. The form of the Weardale Granite (Bott, 1967) strongly suggests that it is a post-tectonic intrusion with respect to the Caledonian orogeny. Over much of the area, Lower Palaeozoic slaty rocks are believed to intervene between the top of the batholith and the pre-Carboniferous surface.

The Alston Block

The Northern Pennine Orefield as a whole, covers an area which as Kendall (1911, p.53), Marr (1921, p.63) and Versey (1927, pp.1–16) have shown, has maintained its morphological unity since the beginning of Carboniferous times. By comparison with the troughs of Carboniferous sedimentation to the N and S, the Carboniferous deposits are thin in this region, which may be regarded as a shelf area. A rhythmic rise and fall of the shelf relative to the sea-level of the time took place throughout the Carboniferous, perhaps accompanied by very gentle warping. Post-Carboniferous earth-movements produced strong folds in the troughs, but the shelf remained relatively stable, and suffered only gentle doming and tilting to the E. The orefield is divided into two fault-blocks by the E–W Stainmore depression, which is followed by the Cotherstone Syncline (Reading, 1957). The northern, western and southern margins of the northern half of the orefield (excluding Area 8) are marked by major structural features, the Stublick Fault-system, the Pennine Fault-system and the Stainmore Trough respectively. The region so defined has been called the Alston Block by Trotter and Hollingworth (1928, p.443). The eastern margin of this block is obscured by the cover of Permian rocks, but it certainly lies E of the Roddymoor boring. The boring at Harton [NZ 396 656] (Ridd, Walker and Jones, 1970) on the Durham coast, revealed a much thicker Carboniferous succession than on the Block, which is best interpreted as part of the Northumbrian Trough sequence. The northern hinge must therefore run ESE away from the Stublick Fault. On present ideas, therefore, the northern hinge lies far S of the Ninety-Fathom Fault.

During Carboniferous times the northern block must have been separated from the Northumbrian Trough to the N by a 'hinge' area, the position of which corresponds with the Stublick Fault-system. Similarly, as noted in Chapter 2, in early Lower Carboniferous times there was also a hinge line in the neighbourhood of the present Swindale Beck Fault. This is linked through the Closehouse–Lunedale Fault-system with the Lunedale–Staindrop, Eggleston–Woodland and Butterknowle faults which form a hinge-zone in the Barnard Castle area (Mills and Hull, 1976, p.159). S of this E–W to ENE feature, there is a rapid thickening of the Carboniferous sediments to as much as 11 500 ft (3.5 km) in the centre of the Stainmore Trough (Swinburn, 1975), compared with about 3200 ft (1 km) total thickness on the Block.

The principal tectonic features of the orefield are summarised on (Figure 9). The Pennine Fault-system, forming the western margin contains, according to Shotton (1935, pp.676–698) three principal groups of faults, of different ages (i) the NNW Inner Pennine Fault, downthrowing E (ii) a series of thrust faults, along which the overthrusting was directed ENE (iii) the Outer Pennine Fault, a great NNW system downthrowing W some thousands of feet, bringing the Lower Palaeozoic rocks of the inlier against New Red Sandstone of the Vale of Eden. The first two are assigned to Hercynian earth-movements, the latter to the Tertiary. Turner (1935, p.121) considers that the thrust-faults, together with an east-facing monocline which may be traced southwards from Swindale Beck, E of Roman Fell, are the northward continuation of the Dent system of overfolds and reverse faults. Although the Pennine Line may have been defined soon after the intrusion of the Weardale Granite as Burgess (1979) suggests, bringing in the younger Lower Palaeozoic strata on the W side of the Cross Fell Inlier, the Alston and Lake District blocks appear not to have been separated by a hinge until after Carboniferous times, when the line was reactivated (George, 1958). There is now evidence, somewhat differently interpreted by Bott (1974) and Burgess and Wadge (1974) that a western scarp was presented towards the Vale of Eden as early as Upper Permian times, implying renewed activity prior to Tertiary times.

The Stublick Fault-system comprises a belt of E–W to ENE faults now downthrowing N, extending from the neighbourhood of Castle Carrock [NY 540 550] eastwards to Thornbrough [NZ 014 653], near Corbridge. The 'Ninety Fathom Dyke', which runs from Acton Fell [NY 950 540] to the Northumbrian Coast near Tynemouth [NZ 353 700], has been regarded as the continuation, en echelon, of the Stublick Fault-system. If the dating of the Whin Sill and its dykes as

Hercynian is correct, it is certain that at least some of the faults in the Stublick system were in existence in Hercynian times, for dykes are found within them. It is possible, however, to argue from the downward change in horizon in the Whin Sill across this fault-belt in a northward direction that the downthrow at the time of intrusion of the sill was to the S, a conclusion which Trotter and Hollingworth (1928, p.446) support from other lines of evidence. The main movement on the Stublick and Ninety Fathom faults is, however, a downthrow N of 500–1750 ft (152–533 m). Since both faults affect Permo-Triassic strata, the age of the main movement is taken to be Tertiary, but it might well have begun earlier.

The Syncline which forms a structural and topographic depression between the two halves of Marr's Northumbrian Fault-Block, corresponds with an early Lower Carboniferous trough of sedimentation lying S of the Swindale Beck Fault and its eastward continuation. The maximum amplitude of the syncline is of the order of 1700 ft (518 m) (Reading, 1957) or 2100 ft (640 m) (Burgess and Holliday, 1979) as calculated from the Namurian rocks. These must be underlain by much thickened Visean strata. Along the N side of the syncline the Swindale Beck Fault downthrows N. The Lunedale faults throw S approximately 500 ft (152 m) at Closehouse Mine [NY 850 227], but here the main fault has on its upthrow side a belt of strata dipping very steeply to the N, suggesting a former downthrow in that direction. The main fault was certainly in existence before the intrusion of the Whin Sills, but there is evidence that it has moved again since that event. S of the Lunedale faults the beds dip towards the Cotherstone Syncline at an average rate of 800 ft (244 m) per mile (1.6 km). The Butterknowle and Wigglesworth faults both downthrow S. On the S sides of these faults there is an anticlinal fold. Magraw, Clarke and Smith (1963) established that both the Butterknowle Fault and the folding adjacent to it affect Permian and Coal Measures strata in the neighbourhood of Ferryhill, but displacement and fold amplitudes are substantially greater in the Carboniferous, proving renewal of movement.

The evidence of the marginal structures may be summarised as follow: (i) During Lower Carboniferous times hinge-lines along the present courses of the Stublick and Swindale Beck faults separated the stable block or shelf from adjacent, more rapidly sinking areas. (ii) The earliest faulting of Hercynian age depressed the block along its northern, western and southern margins, the northern and southern faults following the hinge lines, the western faults a reactivated zone in the basement. This took place before the intrusion of the Whin Sill. (iii) Compression directed ENE also probably in Hercynian times, produced overthrusts in and adjacent to the Cross Fell Inlier. (iv) In New Red Sandstone times and continuing intermittently to the Tertiary, the Alston Block was elevated by normal faulting along the Stublick, Outer Pennine and Lunedale–Butterknowle faults. This may have been preceded by compressive stress directed N–S, producing ENE folds near the southern margin.

The Teesdale Dome

Attention may now be turned to the structure of the block itself. This has been investigated by means of contours on the base of the Great Limestone, a method which had previously been employed, though in less detail, by Hickling (1931, p.331). For this key horizon underground there is abundant exact evidence of its height relative to OD from mine sections. It crops out in all the principal valleys. Key horizons below the Great, including the bases of the Scar, Single Post, Tynebottom and Smiddy limestones, and the top of the Melmerby Scar Limestone (sensu stricto) were used in the areas from which the Great has been removed by erosion. The levels recalculated from these are reasonably accurate owing to the numerous good shaft-sections in these measures. Above the Great Limestone, the Little and Upper Felltop limestones, the base of the 'Millstone Grit' and the Brockwell seam were employed, control for the latter two being obtained from the Chopwell and Roddymoor borings [NZ 1438 5743] and [NZ 1513 3635]. In these cases the error may be as great as 100 ft (30.5 m). The broad structure has previously been described by Versey (1927, pp.1–16) as the Teesdale Anticline. The contours suggest, however, that it is more satisfactory to regard it as a gentle asymmetric dome, truncated by the Pennine faults. The nearly flat top of the dome lies between Great Dun Fell, Mickle Fell and Cronkley Fell, with the key horizon at 2400–2500 ft (732–762 m) above OD. To the N and E the beds dip away at an average of 130 ft (40 m) per mile (1.6 km), the key horizon reaching 500 ft (152 m) below OD beneath the western edge of the Durham Coalfield. To the S, as already noted, the beds dip rapidly into the Stainmore Syncline. As the Pennine faults are approached, especially W of Cross Fell, the beds rise rapidly, the key horizon reaching 3000 ft (914 m) above OD. Presumably this feature is derived from the former eastern downthrow along this line.

The freshness of the fault-scarps of the Pennine and North Stublick faults, and of the feature made by the upturning of the beds towards the Lunedale Faults, leaves little room for doubt that the last elevation along these lines is not older than the Tertiary. Trotter (1929, p.161) has argued from the physiography that a peneplain which was developed over the area after an early-Tertiary uplift was subsequently elevated and folded into the Teesdale Anticline. On his argument, the age of the dome is late Tertiary. Since, however, the supposed peneplain at the crest of the dome is cutting across beds belonging to the Brigantian, while to the N, E and S it cuts successively across the Namurian, including the 'Millstone Grit' and the Westphalian, the view that the surface of the peneplain is even approximately parallel to the Great Limestone cannot be supported. Even if the existence of the peneplain be admitted it is clear that the measures had already been domed prior to its development. It is here suggested that although some additional warping may have taken place in Tertiary times, the dome was initiated at a much earlier period. The Durham Coalfield was gently folded into a basin prior to the deposition of the Permian. The Teesdale Dome is a structure of comparable dimensions and may well have originated during the Hercynian as the counterpart of the basin, providing a barrier, between the western and eastern areas of Permian sedimentation, which was perhaps planed down before Triassic times.

Burtreeford Disturbance

Extending across the area from N to S there is a major disturbance which has long been known to the lead miners as the Burtreeford 'Dyke'. Between Elphagreen in East Allendale [NY 844 485] and Hargill Beck in Lunedale [NY 870 242], the disturbance is an E-facing monocline. At Cowshill, where it crosses the Wear [NY 851 407], the eastward downthrow amounts to approximately 250 ft (76 m). To the north this effect is cancelled by a fault throwing west, but the uprise westwards is still shown, for example in the Top Level West from Gin Hill Shaft, Allenheads Mine [NY 846 453], which was driven through the disturbance. At Burtree Pasture Mine [NY 860 413] the Horse Level was also driven through the monocline to reach the Greenfield Vein, but unfortunately no records of the geology have survived. Copt Hill [NY 851 407] furnishes the best surface evidence; on the west side of the fold the lowest bed exposed is the Tynebottom Limestone. The succeeding beds, up to the Four Fathom Limestone are seen in less than 1000 ft (300 m) to the SE, dipping east at 30° to 50°. The Whin Sill appears between the Tynebottom and Single Post limestones as the pitching phacolith described by Wager (1929, p.234). In Black Cleugh [NY 845 400] the beds involved range from the Single Post Limestone to the Five Yard Limestone. Formerly an exposure in Burnhope [NY 839 387], now covered by the waters of the reservoir, showed some overfolding on the E side of the disturbance, with the Three Yard Limestone inverted and thrust over higher beds along a small eastward-directed thrust. The eastward displacement of the whole structure has increased here to approximately 500 ft (152 m). Inverted beds are seen again in West Grain [NY 842 383], a tributary of Burnhope, while at Pencil Cleugh [NY 842 341], at the head of Ireshopeburn, the Four Fathom limestone and associated beds are vertical. The next exposure to the S is in Drygill Sike [NY 845 323], 0.5 mile (0.8 km) NW of the Langdon Beck Hotel, where steeply dipping and contorted beds from the Tynebottom to the Scar Limestones are seen, the former limestone being replaced by limonite and baryte. There is no exposure where the monocline crosses Harwood Beck or the Tees. It passes to the E of White Force and continues into Hargill Beck, crossing poorly exposed ground. The change in level of the beds shows that the fold must continue southward to link up with the Lunedale faults, as shown on (Figure 9).

It is suggested that this monocline, a compression feature, belongs to the same movements as those which produced the thrusts in the Cross Fell Inlier. It has already been noted that the Burtreeford Disturbance was slightly earlier than, or contemporaneous with, the intrusion of the Whin Sill.

Faulting and minor folding

The regularity of the dip away from the crest of the Teesdale Dome to the N and E is broken by a number of faults, associated with which there is some minor folding. Only faults with displacements over 40 ft (12 m) are considered in this section; a few of these carry mineral deposits. The great majority of the mineral veins, described in the next section, occupy fissures with displacements of less than 40 ft (12 m). The results of a statistical analysis of the directions of the faults with over 40 ft (12 m) displacement are presented on (Figure 10). The marginal faults are included in this analysis, which indicates that the dominant direction of faulting was NW, spreading over a considerable angular range but with a maximum at N 25–35°W. Another maximum is reached in an E–W direction. Feebler faulting in an ENE direction, and a few faults trending nearly N–S are indicated.

The marginal belt close to the Pennine faults contains many subsidiary faults which account for a substantial proportion of the NNW group, together with some in the conjugate ENE direction. None of the NNW faults is mineralised, and only a few of the ENE faults, for example in the Hartside area, carry oreshoots. There is a possibility that many of the faults in this belt are later than the mineralisation, but the negative evidence is not, of course, conclusive. The complex faults of the Cross Fell Inlier also appear to be unmineralised.

The most striking of the NW faults within the orefield is one which extends from the neighbourhood of Middleton-inTeesdale to Park Fell, near Alston. This is known, from SE–NW, as the Teesdale Fault, the Harwood Fault, Sir John's Vein and the Park Fell Cross Vein. In the Brampton Sheet (one-inch New Series 18) it continues as the Faugh Cleugh Fault. It seems very probable that the courses of the Harwood Valley and of the Tees Valley between Langdon Beck and Middleton have been determined by this fault. The displacement is at its greatest in Teesdale, where the fault is in two parts with a total throw of about 330 ft (100 m) NE, producing the prominent scarp made by the Whin Sill along the SW side of the valley. The throw decreases towards the Burtreeford Disturbance and the course of the fault may be interrupted in the neighbourhood of Langdon Beck, but this cannot be taken as certain. W of the Disturbance the fault resumes with a displacement of about 300 ft (90 m) NE, but this gradually diminishes until the fault becomes the Sir John's Vein of Alston Moor, with only a few feet of throw. N of Blackburn, however, the displacement again increases. This fault is mineralised in Teesdale, Harwood and Alston Moor. In Harwood two branches are thrown off on the SW side which become the Teesdale and Winterhush veins of the Cowgreen mines. The latter vein has a maximum throw of 80 ft (24 m) E. Parallel to and SW of the Teesdale–Park Fell Fault, the Michaelly Sike Fault of the Brampton Sheet continues into the orefield across the head of Gilderdale. The throw is about 100 ft (30 in) SW where this fault crosses the Alston–Hartside main road [NY 678 423]. It may join up with the Rotherhope Fell West Cross Vein, which however throws 12 ft (3.7 m) NE. Also parallel to the Teesdale Fault is the strong belt of cross veins of the Nenthead District. Sections showing the effects of these have been published by Wallace (1861, Plate vii). They are ramifying faults trending NW, with which there is associated a synclinal area in the Nent valley and an anticline under the Nent–Wellhope watershed, the axes of the folds running parallel to the faults. (Figure 22) illustrates the relationship of these fractures by means of structure contours. The most important fault of the belt is Carr's Vein. At Loveladyshield Level [NY 7585 4608] this throws 252 ft (77 m) NE. At Nentsberry Haggs Level [NY 766 450] the displacement is 216 ft (66 m) NE. South of Brownley Hill Horse Level [NY 776 446] a series of branches are given off on the E side which unite south of Rampgill Vein to become Handsome Mea Cross Vein, throwing 95 ft (29 m) NE. The main fault continues under Nenthead village where another branch is given off on the E side, to become Smallcleugh Cross Vein, throwing 40–45 ft (12–14 m) SW. From here to the southernmost limit of mining development from Nenthead, the throw of Carr's Vein, steadily decreases. It is 83 ft (25.3 m) NE where it crosses Middlecleugh North vein, 40 ft (12 m) NE where it crosses Longcleugh Vein. West of Carr's Vein, Black Ashgill Cross Vein reaches a displacement of 40 ft (12 m) SW where it crosses Longcleugh Vein. Wellgill Cross Vein reaches 40 ft (12 m) NE in Brownley Hill Mine. The remaining NW faults and fissures of the belt have only small displacements.

Another belt of NW faults runs from the Killhope mines to the West Allen valley, on the NE side of the Nent–Wellhope Anticline. Of these the most important are the Coalcleugh East and West Cross Veins, which together form a fault-trough into which the beds are dropped down 90–130 ft (27–40 m). As far as is known, all the Nenthead and West Allen Cross veins or faults die out southwards before reaching the Burtreeford Disturbance, their courses being crossed by a number of NNE faults, including the Scraithhead Vein. These faults run parallel to the local direction of the Disturbance.

In Upper Weardale there are only two NW faults of consequence, the Swinhope Fault-belt and the Westernhope Old Vein. The former has a throw of only a few feet where first seen, in the workings on Ireshopeburn Vein in Barbary Mine [NY 864 385]. Crossing Groveheads Low Vein it takes the form of a monocline facing NE, but southwards from Groveheads High Vein it is a strong fault with a number of branches (described under Carricks Mine, Chapter 11). In Greenlaws Mine the workings on New Vein showed a down-throw of 60 ft (18 m) SW on this fault, a similar downthrow being revealed by the exposures at the head of Swinhope [NY 886 342]. This fault continues into Teesdale as the Flushiemere Great Cross Vein; it may be represented in Skears Mine by No. 2 Cross Vein, which downthrows SW 60–100 ft (18–30 m). The Westernhope Old Vein has little or no throw where it crosses Weardale below St John's Chapel, but on the W side of Swinhope its NE downthrow begins to be apparent. Where worked at the head of Westernhope [NY 917 343] the throw was 60 ft (18 m) NE. This fault may continue across the head of Hudeshope to join up with a fault which branches from the western end of the Eggleshope (California) Vein in Great Eggleshope.

In the Derwent area, a NW fault throwing 40 ft (12 in) SW terminated the westward workings at Beldon Mine [NY 928 495]. Farther E, the Healeyfield Fault trending NNW brings 'Millstone Grit' against Coal Measures at Healeyfield Mine [NZ 071 487], here downthrowing 152 ft (46.3 m) NE.

The second important direction of faulting and minor folding runs E–W parallel to the northern and southern margins of the Alston Block. The Great Sulphur Vein of Alston Moor belongs to the faults of this class. This vein, 8.5 miles (13.6 km) long, runs roughly E–W, but includes three NW sections in its course. It is essentially a faulted monocline; the total effect of which is a northward downthrow varying up to a maximum of nearly 600 ft (185 m) in Cashburn (Thompson, 1933, p.93), but averaging about 150 ft (45 m). The beds within the monocline dip at 25° to 30°N. In width it varies from 100 to 1200 ft (30–366 m), being strikingly wider where is crosses hilltops than in the valleys. There are fissures on both sides of the monocline, but these appear to be strongest on the N side; the displace ment effected by them is not great. At the western end the displacement is taken by a NE fault, throwing 200 ft (61 m) NW, which branches off the main lode 2 miles (3.2 km) E of the Outer Pennine Fault.

The Dun Fell Vein, parallel to and 4 miles (6.4 km) S of the Great Sulphur Vein has a maximum downthrow to the N of 164 ft (50 m) in Silverband Mine [NY 704 318]. This fault continues into the Cross Fell Inlier as the Crowdundle Fault of Shotton (1935, pp.675–676). He argues from its great throw in the Skiddaw Slates that it was already in existence before Carboniferous times. E of Dun Fell Mine the throw of this fault diminishes in the Carboniferous, until it is of little importance in Teesdale.

A belt of E–W and NE faults with associated folds carrying important mineral deposits commences NW of Middleton-in-Teesdale and may be traced into the Durham Coalfield. The western portion of this belt is first seen in Ettersgill where it is represented by the Lodgesike Fault, throwing 14–23 ft (4.3–7 m) S, and by the fissure which has been filled by a unit of the Cleveland dyke-echelon. The next exposure to the E is in Bow Lee Beck [NY 9086 2906], where the Lodgesike Fault brings the Scar Limestone against the High Brig Hazle, throwing approximately 100 ft (30 m) S. The dyke-fissure, in two parts, effects a southward displacement of 30 ft (9 m). Both fault and dyke converge in Red Grooves Mine and Coldberry Gutter Opencast to the E. An anticline, the presence of which is first suggested by dips of 10° and 15° on the N side of the Lodgesike Fault in Bow Lee Beck, is proved to accompany the fault in the Red Grooves Levels. The mapping of the Great Limestone in Hudeshope indicates that it has an amplitude of over 100 ft (30 m) there. E of Hudeshope the Lodgesike Vein changes direction to ENE, but it is probable that the anticline continues on its E–W course across the Namurian country towards Woodland. The throw of the Lodgesike Vein was proved to be 98 ft (29.9 m) SE in a rise connecting Marlbeck Low Level with Lodgesike Low Level. The vein continues into Manorgill Mine [NY 975 301], where it encounters the E–W Manorgill North Vein, which apparently carries the main throw on to the E. This may be traced across Great Eggleshope into the Dustygill Vein and thence through Flake Brig Vein into Sharnberry Vein. In this course there are several alternations between E–W and ENE. Sharnberry Vein is mapped as a main fault cutting through high Namurian between Teesdale and Weardale. It is joined in the neighbourhood of Shaftwell Head by the nearly E–W Eggleshope Vein which, with a throw of 84–98 ft (25.6–29.8 m) S, continues westward to Great Eggleshope, where it splits into several divergent minor faults. It is interesting to note that in California Level and elsewhere along this vein, the beds dip N at angles up to 40° into the fault, which is throwing S. The Sharnberry Vein has a proved throw of 105 ft (32 m) SE at '13' Shaft, Sharnberry Mine [NZ 0005 3099]. It has been mapped as far as Ashes Allotment [NZ 004 350] 0.75 mile (1.2 km) SE of the Sunniside Mine, where it makes a striking gap in the 'Millstone Grit' features. It is suggested that it continues across drift-covered ground to link up with the Tow Law Vein-fault of the Durham Coalfield. This had been traced as far E as High Bradley, where a mineral spring arises on its course at Bradley Spa [NZ 009 362]. The course of the fault through Stanley, Wooley, Esh, Ushaw Moor and New Brancepeth collieries reveals that it is a belt of fractures whose directions, as in Teesdale, alternate between E–W and NE. The displacement continues to be southward, the proved throw of the main fault from W to E being as follows: Opencast sites near Thornley [NZ 134 322] to [NZ 129 370], 96 ft (29.3 m); White Lea Drift [NZ 153 381], about 150 ft (45.7 m); north of Wooley Shafts [NZ 193 390], 210 ft (64.1 m); Esh Colliery, 182 ft (55.5 m); New Brancepeth Barytes Workings [NZ 235 429], 108 ft (33 m). Mineralisation has been found at intervals along this belt (Chapter 14, (Figure 45). The average hade of the fault where proved at New Brancepeth is 15°.

N of the Lodgesike–Sharnberry–Tow Law Fault-belt, a second fault-system extends eastwards from the orefield into the Coal Measures. This is the 'Great Spar Dyke' which commences at the Healeyfield Mine [NZ 068 486] and passes immediately N of Lanchester. At a distance of 0.75 mile (1.2 km) ENE of Lanchester the main fault, which down-throws 120 ft (36.6 m) N, gives off an ENE branch which carries the Morrison witherite oreshoot. The throw of this branch is 46 ft (14 m) N at the underground shaft [NZ 1792 4780] on this deposit, decreasing to zero 900 ft (274 m) NE of the shaft. A number of other small E–W faults cut through the Morrison Colliery area; some of them carry witherite.

Apart from the NE-trending members of the major fault-belts described above there are few faults in this direction with more than 40 ft (12 m) displacement. There are, however, a number of small folds in this direction which deserve mention. At St Peter's Mine, East Allendale [NY 852 488], an elongate dome with a maximum amplitude of 30 ft (9 m) lies on the S side of St Peter's Vein (Dunham, 1937b, fig. 3). On more or less the same ENE line a similar fold appears in the Devil's Water near Harwood Shield [NY 912 512]. Small sharp anticlines of similar dimensions follow the Riddlamhope valley for nearly a mile (1.6 km) SW from

Heatheryburn [NY 905 493], and the Knucton valley from Rosas Bower for 2.5 miles (4 km) to Gibraltar Banks [NY 941 490]. The Jeffries–Ramshaw veins at Hunstanworth run along the N side of a larger anticline well illustrated by the section of Whiteheaps Mine [NY 949 466] (Figure 35). Some sharp minor folds trending WNW are associated with the White Vein at this mine. In Alston Moor a flat-topped anticline of amplitude about 40 ft (12 m) accompanies Rotherhope Fell Vein.

All the faults described in this section are, as far as is known, steep normal faults. It must be concluded therefore that the effects of both tension and compression are discernible in each of the principal structural directions, NNW, E–W and ENE.

Vein fissures

The orefield is remarkable for the perfect conjugate pattern of vein-fissures which it exhibits. The major trend of the productive veins is ENE; the statistical analysis shows a strong maximum at N50–65°E. This set is traversed by cross veins, seldom strongly mineralised, and therefore less well known than the others, which trend N20–35°W. An additional set of cross veins trending N45–50°W intersects these at a small angle. The conjugate angle is bisected by a second set of productive veins, the so-called 'Quarter-Poine Veins, whose trend varies from E–W to N65°W. Individual veins in the productive directions may be traced for very long distances though in most cases they are not continuously mineralised. Thus among the ENE veins the Old Fall-Scarsyke–Boltsburn Vein is altogether 7.5 miles (12 km) long, while in the WNW group Slitt Vein is at least 12 miles (19.2 km) long. On the productive veins the displacement is rarely more than a few feet. As noted above the larger faults are seldom strongly mineralised, probably because they were already choked at the time of mineralisation with gouge from dragged-in shale. Small displacement on the other hand tended to produce clean-cut fissures, free from gouge, in the sandstones and limestones. The vein-fissures of small displacement responded in a characteristic way to the nature of the rocks they were traversing. In hard beds, including limestones and the more compact sandstones, the bade is found to be small, whereas when they pass into shale the hade increases up to 40 or 50°. The typical behaviour of a vein with small displacement is illustrated in (Figure 11). This effect was known to Forster (1821, pp.188–190), who remarks: "Whatever the inclination or hade may be, in the Stratum of Stone, it is generally more in the Stratum of Shiver or Plate, that is more from the perpendicular." In almost all cases, the increase in hade in the shale is accompanied by closing of the fissure. Leithart's analysis (1838, pl. VI) shows that this is to be expected if the faulting is normal; reverse faulting of small displacement would tend to produce open spaces in the highly hading parts of the vein. As a result of the response of the vein-fissures to the hardness of the beds traversed, channels for the passage of mineralising solutions were restricted to the hard beds. Since these beds are thin, the channels were of great length in comparison with their height. This is among the most important of the factors which have controlled the localisation of the oreshoots. The opening of the channels in the hard beds implies a tearing-apart of the walls and thus a general condition of tension perpendicular to the directions of the productive veins. It is suggested that this condition was provided by the formation of the regional dome, the upper layers of which were necessarily stretched relative to the lower layers. It would follow from this that the amount of opening in the hard beds should become gradually less as the veins are followed downwards. Mining experience in the district provides confirmation that this is in fact the case. In an ideal situation, the following approximate expression relates: W, the width of the opening in the hard bed to T, the throw of the fault and θ, the hade of the vein: W = T tan θ. The implication is that the hade in shale becomes greater as the width of the opening increases, as illustrated in (Figure 11) (see also Dunham, 1937a, p.519; 1988). It may be deduced that in its upward course the hade in shale will at some point become so great that the fissure dies out as a low-angle fault in shale. This may well explain the apparent disappearance of many veins above the Great Limestone which are at their best at that horizon. Similarly, there is a decrease in the hade of the vein as it is followed downwards through successive shale beds, and in the width of the opening produced in the hard beds. The effects so far described may be said to hold good up to a maximum throw of about 12 ft (3 m). Above that figure, the dragging of soft shale against the hard bed such as the Whin Sill may still produce a marked steepening of the vein as the accompanying section of Burtree Pasture Mine (Figure 12) shows. Even on large faults such as the Tow Law Vein at New Brancepeth, a small decrease in hade is noticeable in the harder strata.

On the 'Quarter-Point' veins, control of opening by varying bade, though it is well seen in some cases (for example, Stotfield Burn Mine [NY 944 424], Dunham, 1959, (Figure 5) may be less important than control by variations in strike. An analysis of the Red Vein (Dunham, Dunham, Hodge and Johnson, 1965) shows that it exhibits abrupt changes of strike between WNW (where it is usually barren) and nearly E–W (where it carried wide oreshoots). Opening thus controlled implies sinistral transcurrent movement and on the parallel Slitt Vein, Greenwood and Smith (1977, p.B187) have been able to demonstrate this very neatly by the strike-slip displacement of a vertical dolerite–'whetstone' contact of 88 ft (27 m). The widest openings up to 33 ft (10 m) are found on veins in the 'Quarter Point' direction.

Some of the NW and NNW fissures show the same response to hardness of the beds traversed as do the productive veins. Examples include the Dupont and Cox veins at Nentsberry Mine [NY 778 466], which are structurally in every respect similar to the ENE veins. In general, however, the tension perpendicular to the NW fissures seems to have been taken up by faulting of larger magnitude, as discussed in the previous section. Parallel to the larger NW faults many subsidiary fissures having little or no displacement were developed. These are seldom mineralised, but they are of some importance because the openings on the ENE and E–W veins apparently terminated or began at intersections with such minor fractures, which are now found to limit the oreshoots. Good examples are found in Weardale (Dunham, 1937a, fig. 37).

The age-relations between the productive veins and the cross fractures have been the subject of some dispute. Forster (1821, pp.209–210) quotes examples from the Nenthead district of the apparent sideways shift of ENE veins by NNW veins, and doubtfully invokes the Wernerian doctrine of vein intersections to suggest that the NNW fractures are of later formation. There are other examples in the field of sideways heave by Cross Veins, including a striking one in Burtree Pasture Mine [NY 860 413] and several at the Heights mines [NY 925 390]. Such examples are, nevertheless, the exception rather than the rule. There are, moreover, cases where the cross fracture not only terminated the oreshoot on an ENE vein, but also terminated the fissure itself. There are also cases of the apparent sideways shift of NNW fractures by ENE veins, for example in Brownley Hill [NY 776 446] and Nentberry mines [NY 766 450]. The evidence is, as Wallace (1861, pp.76–81) has pointed out, inconsistent. Wallace concluded that the NNW fractures were formed either anterior to or contemporaneously with the productive vein-fissures, and this conclusion is fully supported by the present investigation.

Minor folding of the strata adjacent to the vein-fissures in all three main directions is of widespread occurrence, though it is not universally present. Leithart (1838, p.9) has called the bending of the beds adjacent to the vein the 'bur' of the vein. A remarkable feature is that in many cases the adjacent beds dip towards the hangingwall of the vein, and away from the footwall, i.e. in the contrary direction to the drag effected by normal faulting. It appears that, as with the major faults, a small bend or fold was produced by compression, which was followed by tension giving rise to the normal fault. A similar association of minor folds and vein-fissures has been established in the Halkyn district by Schnellmann (1939).

Joints

A well-marked joint-system is seen in the limestone quarries of the area and may also be discerned in the harder beds of shale and sandstone. Underground the points persist in limestone to the greatest depth reached by mining, over 1000 ft (300 m) below surface, though beneath the water table they are normally tightly closed and are revealed only by the directional breaking of the rock in tunnelling operations. They do not vary more than a few degrees from vertical even in shale beds, a fact which emphasises that the mineral veins are not merely widened joints. Adjacent to the veins in limestone, however, joints may be mineralised for short distances, so that it appears that they were already in existence before mineralisation took place. Measurements of the directions of over 1000 joint faces exposed in the Great Limestone quarries around Stanhope and Frosterley (Dunham, 1933, pp.243–246) were employed to construct the frequency curve incorporated in (Figure 10). In the present work the joints are classified into 5° groups: they are not averaged according to the method employed in making the detailed curves in (Figure 2) and Figure 3) of Dunham (1933). This shows two well-defined peaks, a larger one corresponding with N20–25°W, a smaller one with N60–70°E. The master joint directions at Stanhope thus correspond with the directions of the conjugate vein-system of the area, the most abundant joints with the cross vein direction. Observations in other parts of the area suggest that similar joint-directions are widespread, though there are no exposures other than the Stanhope quarries which lend themselves to statistical investigation. It is suggested that the joint-system was among the earliest effects of the Hercynian orogeny, and that the presence of well-defined directions of weakness in the hard beds exercised a controlling influence on the directions of the mineral veins. The poor development of the E–W to WNW directions in the joint system is noteworthy. It is also to be noted that a number of E–W veins and faults swing round to ENE. Examples additional to those discussed above are provided by the Browngill and Bentyfield vein-systems, E of Garrigill.

Postmineralisation movements

Many of the productive veins show evidence of movement after mineralisation, in the form of more or less horizontally striated slickensides, accompanied by zones of breccciation or wholesale crushing of weak minerals such as fluorite which cut through the mineral bodies, generally in the same plane as the vein. Beautifuly polished surfaces on galena were formerly visible in the East Allendale mines; slickensides on fluorite, quartz and carbonates may be seen at any of the Weardale spar mines. A few examples of slickensided limonite have been found, suggesting that small movements have occurred since the orebodies have been brought within the zone of oxidation by erosion of the cover. Postrnineralisation movement, up to 10 ft (3 m) laterally, may in part explain the relation between the NNW veins and the ENE veins which 'heave' them at Nentsberry Mine. Few instances of postmineralisation faulting of larger scale have, however, been established in the field, though one example, at Settlingstones Mine [NY 844 683] is mentioned below; so the evidence is not sufficient to prove that such faulting is absent. On the whole, however, it appears that postmineralisation movements were of small magnitude.

Haydon Bridge area

This area lies N of the Alston Block, within the Northumbrian Trough, though at no great distance from the Stublick Faults. The principal direction of the productive veins is ENE. Thornbrough Vein, as already noted, occupies the end of the Stublick fault-system. Fallowfield Vein is a major fault downthrowing 180–275 ft (55–84m), swinging round from N 77°E to N 50°E. Settlingstones Vein follows an average course of N 50°E, but this is subject to the development of loops both on the small and the grand scale. The throw at Old Pump Shaft [NY 8500 6878] is 30 ft (9 m) SE while at Frederick Shaft [NY 8423 6825] it is 86 ft (26 m) SE. This vein is cut by many small cross fractures, two of which, both trending N 75°W, shift the vein sideways and have an important influence on the oreshoots.

In 1953 it was possible to demonstrate a sinistral movement of Settlingstones Main and South veins by Grindon Cross Vein of 105 ft (32 m) and to date this as late in the mineralising process (see p.265). Langley Barony Vein follows a sinuous NE course. It downthrows 42 ft (12.8 m) at Joicey Shaft [NY 8134 6659], 33 ft (10 m) at Leadbitter Shaft [NY 8260 6612]. The Stonecroft and Greyside veins trend E–W to WNW. The measures clip southward towards the Stublick Fault at 3° to 4° but there is also some gentle lateral folding in this area.

In (Table 15) an attempt is made to summarise the structural history of the orefield. Although periods of maximum stress leading to distortion or failure of the rocks may have been short, exact definition in time remains controversial in some case. Slow, mainly vertical movements in upward or downward directions continued over long periods of time.

Advances in the investigation of the structure of the north of England have made it possible to attempt a more comprehensive summary in this table as compared with that in the first edition of this memoir. For the Lower Palaeozoic rocks, fuller details will be found in Moseley (1972), Burgess and Wadge (1974), Burgess and Holliday (1979) and in a series of articles in the Geology of the Lake District (edited by F Moseley, 1978). In (Table 15) the impact of ideas about continental collision following plate movement is noted. In particular, the extension of the of the collision line causing the Caledonian orogeny, believed by W E A Phillips, C J Stillman and T Murphy (1976) to cross Ireland from the Shannon estuary to the E coast N of Navan, would take it through the Solway and ENE across Northumberland. On this concept, the northern Pennine block forms part of the south-eastern continent of pre-Caledonian times. A dextral strike-slip movement along this suture of as much as 1000 km is postulated by these authors but as yet its exact position beneath Northumberland has not been located, and no evidence has been found of posthumous movements of Carboniferous or later age along it. Thus although the two largest lead-zinc deposits in Ireland (Navan and Silvermines) are located in Lower Carboniferous rocks adjacent to it, there is little evidence to connect it with Pennine mineralisation, the foci of which lie 35 miles (56 km) to the SE of it. No doubt, however, the ENE grain of the Lower Palaeozic foundation was influenced by the closing of the Iapetus Ocean, and this direction continued to be important throughout Carboniferous and early Permian events.

Note is also taken in the table of the important point made by Burgess (1979) that the NNW Pennine fault-line became established after the intrusion of the Weardale Granite, and is the reason why the Ashgillian and Silurian rocks do not extend under the Carboniferous of the Pennines from the Inlier. A Devonian date can only tentatively be suggested for the initial movements, but it is clear that once established, the same line or zone moved again, though not aparently until the Hercynian movements affected it. The northern (Stublick) and southern (Swindale Beck–Lunedale–Butterknowle) hinge lines were on the other hand most effective during the earlier part of the Carboniferous. Reversals of movement on the Pennine and Lunedale lines near the time of intrusion of the Whin Sill are believed to account for the limitation of sill-intrusion to within the W and S margins of the Alston Block. Several important contributions have been made to the study of the joint-system in the Carboniferous and later rocks since 1948. Spears (1961) demonstrated that in Teesdale the jointing in the Whin Sill is not solely due to cooling, as previously thought, but reflects strongly the NNW and ENE sets also found in the sediments. Understandably, he argued for a post-Whin Sill age for the whole joint system, but the extensive statistical investigation in northern England carried out by Moseley and Ahmed (1967) showed that joints in similar directions also appear in Permian and Triassic rocks. They therefore concluded that jointing is a very early effect and that the directions, once established, continue to affect later formations after their emplacement. It is interesting, however, that the NNW set, at right angles to the grain of the foundation rocks, greatly predominates throughout both the Alston and Askrigg blocks (see also Dunham and Wilson, 1985), and the N–S set com- mon elsewhere in NW England is hardly represented. The view continues to be taken here that the earliest joints in the Carboniferous were due to shearing related to N-directed compression from the Hercynian movements, which are, after all, believed to have caused major transcurrent motion along the Great Glen Fault, still more remote from the Hercynian front, but no doubt later E-directed compression also played its part. Reading (1957) and Wells (1957) found that the joint directions in the Cotherstone syncline and Middleton Tyas-Sleightholme anticline respectively are not con- sistent with those in the blocks, no doubt because of the different tectonic regimes in those structures. Wells discussed the difficulty that experimental shearing of rocks, even under confining pressure, fails to produce two sets at right angles and pointed out that the ENE set in the Alston Block may really consist of two sets at a small angle. Even for such simple structures as joints, perpendicular to bedding, some intractable problems remain to be explained. During the formation of the vein-fractures, here considered to be due to the gentle doming of the block, wrench movements of limited magnitude in the 'Quarter Point' (WNW/E–W) direction must now be accepted. The growth of these fractures by curviform extensions, as suggested by R J Firman (1977), for the southern Pennine orefield, following the theoretical analysis of M A Chinnery (1963, 1966), was also effective here. Horizontal and vertical loops carrying subparallel oreshoots are characteristic of these veins, and evidence is now coming forward that oblique fractures, like those found in Riedels's (1929) experiments were opened in less competent formations. Sinistral wrenching, which may also have affected some ENE and NNW fractures is implied. There was a much later episode of sinistral wrenching when the Cleveland Dyke was intruded in the Palaeocene.

A computer analysis of vein outcrop directions as shown on the one-inch and 1:50 000 Geological Survey maps by J S Carter and J McM Moore (1978) using a programme which fitted trend-surface to each of the three main vein directions defined three zones crossing the orefield in an ENE direction and two running NNW in which there were minor changes of direction and increases in the number of veins. It was tentatively suggested that these might be due to sinistral strike-slip in faults in the foundation rock.

References

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BURGESS, I C, and HOLLIDAY, D W. 1979. Geology of the country around Brough-under-Stainmore. Mem. Geol. Surv. G.B. 131 pp.

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MILLS, D A C, and HULL, J H. 1976. Geology of the country around Barnard Castle. Mem. Geol. Surv. G.B. 385 pp.

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Chapter 5 Mineral deposits: general description

Form of oreshoots

The term 'oreshoot' is here defined as follows: 'a continuous body of ore which may be worked with profit or with hope of profit'. The term thus introduces both geological and economic factors. From this it follows that while the boundaries of an oreshoot may, in certain circumstances, correspond with the actual limits of mineralisation, in the greater number of instances the boundaries represent workable limits, within which the orebody is sufficiently wide and of sufficient grade to be exploited. Mineralised ground thus continues beyond the limits of many oreshoots.

In the Northern Pennine orefield, the oreshoots may be classified into two principal types (i) vein oreshoots, developed by mineralisation along fissures which seldom deviate more than 20° from the vertical where they carry orebodies (ii) metasornatic flats, owing their form to replacement of flat-lying favourable beds of limestone. Members of the second type are invariably associated with veins or fissures by which the mineralising fluids gained access to the limestone. The feeding veins may or may not themselves carry vein oreshoots adjacent to the flats. Metasornatism of limestone adjacent to vein oreshoots is invariably present to some degree, but in the majority of cases it has not produced workable flats, though, the width of the vein oreshoots in limestone is favourably influenced by the susceptibility of that rock to replacement. The essential distinction between the two types of oreshoot is thus one of attitude, the vein oreshoots being approximately vertical, the flats nearly horizontal. Both types are roughly tabular; among the vein oreshoots the height and length greatly exceed the width, while in the flats the thickness is normally much less than the horizontal dimensions. Individual vein-fissures may carry more than one vein oreshoot, or may have more than one flat associated with them, the ground between the oreshoots being poorly mineralised or unpayable.

Stratigraphical relations

Vein oreshoots

The production of laterally extensive channels of no great height, corresponding with the planes of coincidence of a vein fissure with hard beds in the wall-rock, and limited above and below by shales in which the fissure is virtually closed, has been discussed in Chapter 4. The filling of such channels with minerals has given rise to the commonest type of vein oreshoot in the field, a type which may be described, from its appearance in longitudinal section, as the 'ribbon' oreshoot. The principal physical control of such an orebody is clearly evident from a study of the wall-rock stratigraphy; the Northern Pennines provide some of the finest known examples of this type of control. The limestones and hard sandstones in the stratigraphical sucession are relatively thin beds. In the Brigantian and Lower Pendleian rocks where the greatest number of veins have been worked, the thickest limestone, the Great, averages only 60–70 ft (18–21 m), while the remaining limestones average less than 30 ft (9 m). Except in a restricted area, the sandstones seldom reach 50 ft (15 m) in thickness. The height of the oreshoots controlled by these beds is thus very small as compared with their length, which may reach 3000 ft (914 m) or more. Examples are illustrated in (Figure 23), (Figure 24 and (Figure 30).

Greater vertical dimensions are attained in the restricted area (Figure 4) in which, by the operation of the Rogerley and Coal Sills washouts, thick shale beds in the Pendleian sequence have been cut out and their places taken by grits and sandstones. At Hunstanworth, at Stanhope, in Bollihope and in the Eggleshope area of Teesdale, the Grit Sills give rise to individual oreshoots as much as 300 ft (91 m) high. The sandstone-filled washout here has had an important effect upon the mineralisation. A similar effect may be noted in three areas of thick Coal Sills sandstones. It can also be seen against Brigantian strata where, as at Stotfield Burn, the Tuft and Quarry Hazle sandstones have united into a single hard bed.

While a series of ribbon oreshoots may occur one above the other on a single vein, it is more usual to find oreshoots in only one or two favoured beds. Burtree Pasture Vein provides an outstanding example of a vein carrying many ore-shoots (Figure 30); here the shoots appear at progressively higher horizons towards the NE, an illustration of the relation called 'squinting' in Derbyshire. The oreshoot in the Whin Sill at the SW end of the vein apparently has a greater vertical than horizontal dimension. Such a condition, approaching that of a vertical pipe, is very rare in the present field. Probably it is due to the proximity of an emanative centre, from which, it is suggested, Breconsyke, Burtree Pasture, Sedling, Midge Pits and Copt Cleugh veins, all radiating from a small area, were fed. A similar oreshoot of substantial vertical dimensions was found on the Slitt Vein beneath the Middlehope valley (Figure 33) where it was followed downwards for over 500 ft (152 m). Here and also at Carnbokeels Mine, the presence of an emanative centre is suggested. It is considered that the mineralising solutions ascended by way of a few more or less vertical channels, cutting across the beds, and that on reaching the lateral channels in the hard beds of the Brigantian and Pendleian stages, they spread out, travelling great distances horizontally, but in places forcing their way up from one hard bed to the next. As will be shown in a later section, the mineralogical evidence is consistent with this view.

The restrictive effect of shale beds is less evident on veins with over 12 ft (4 m) displacement, and on veins where the width of opening has been exceptionally great, due to wrench movement. The best examples come from veins in the 'Quarter-Point' direction (E–W, WNW) where in places widths of 20–30 ft (6–9 m) of veinstuff are reached, unaided by replacement.

The physical response of the hard beds to fracturing is not the only factor determining the widths of oreshoots of the ribbon type. In limestones the channels are widened during mineralisation by solution and metasomatism. Thus, on the average, wider oreshoots may be expected in the limestones than in the sandstones. As indicated below, the Whin Sill is also chemically reactive, its early conversion during mineralisation into a carbonate-rock causing it to behave in certain respects like a limestone, wide oreshoots such as those at Closehouse, Setdiugstones, Cowgreen and Cambokeels mines being produced in it partly as a result of replacement.

Summing up, the following order of favourability to vein oreshoots may be recognised:

Favourable: limestone, dolerite, hard sandstone, hornfelsed shale. Unfavourable: soft sandstone, shale. The distribution of worked oreshoots in relation to the hard beds of the field is indicated by the statistical summary in (Table 16).

Although, being dependent upon accident of discovery, these figures have no absolute significance, they nevertheless point to a striking concentration of mineralisation in and near-the Great Limestone. Unfortunately complete data for an assessment of the production, horizon by horizon, of the oreshoots is not available, but the limited evidence suggests that the oreshoots in and near the Great Limestone were both larger and more productive on the average than those anywhere else in the succession, with two exceptions: (i) the Grit Sills oreshoots in the restricted areas mentioned above (ii) the Whin Sill oreshoots. It would, nevertheless, be quite wrong to conclude that the Great Limestone, Grit Sills and Whin Sill are the only possible bearing-beds. The table indicates that all the hard beds in the succession have carried some oreshoots. The range of mineralisation in each area, as indicated by the table, corresponds with the range of beds exposed at surface, or easily accessible from surface. That this is not due to any connexion between the present surface and the primary mineralisation, but merely to ease of discovery and exploitation, is shown by the fact that some of the most productive oreshoots in the field have been worked at depths varying from 400 to 1000 ft (122–305 m) below surface, as at Coalcleugh, Allenheads and Boltsburn.

The control of vein oreshoots by thin hard beds in the wall rock has led to a widespread impression that the veins die out downwards. Structurally, it is of course clear that this is not the case. Strong mineralisation is, however, in many instances restricted to a single hard bed, such as the Great Limestone. Trials at lower horizons in these instances generally reveal some mineralisation, but of poor grade, and there is little inducement to try more than one hard bed when poor results are obtained. Thus it is questionable whether any but the strongest veins have been adequately explored in depth. It should be emphasised that the oreshoots quite equally die out upwards above the favoured horizon or horizons. This fact may be regarded as more firmly established than the behaviour of the veins in depth, for access by means of levels from surface is generally easier at the higher horizons. Numerous illustrations of 'blind' oreshoots will be found in the figures accompanying the detailed descriptions of the veins.

Flats

Workable replacement deposits have been discovered in nine of the limestones of the Carboniferous succession. In (Table 17) a statistical analysis of the horizons of the flats is presented. In this, each connected run of flats is counted as one oreshoot.

The concentration of mineralisation at the horizon of the Great Limestone is once again strikingly indicated. The flats at this horizon are, moreover generally more extensive than those in the other limestones.

While it cannot be claimed that the reasons for the formation of metasomatic flats in preference to vein oreshoots are fully understood, certain geological facts appear to have some significance: (1) Flats are found only in association with veins accompanied by numerous diverging or sub-parallel 'leaders' (minor fissures), or in the neighbourhood of vein intersections. (Figure 14) illustrates the connection between the Tynebottom Limestone flats at Rotherhope Fell Mine and 'leaders' which diverge from the vein; (Figure 15) shows the formation of flats in the Great Limestone associated with the numerous vein-intersections at the E end of Allenheads Mine. (ii) There is some evidence that flats are formed in association with strongly mineralised veins in places where for some reason the formation of vein oreshoots was inhibited. At Boltsburn Mine, the stratigraphical variations in the beds between the Great and the Little Limestone appear to have provided a control. Where the Coal Sill Sandstone was thick, both the sandstone and the underlying Great Limestone carried vein oreshoots, but there were no flats. Where, however, the sandstone thinned, and thick shale intervened between the sandstone and limestone, vein oreshoots no longer occurred, or were feeble, but large flats were found in the limestone (Figure 31). Similarly, the extensive central flats at Rotherhope Fell occupy the ground between the two vein oreshoots, where the vein is constricted and poor. Another example is provided by the Rampgill–Barneycraig vein-system. Rampgill Vein, in Cumbria, carries a notable series of 'ribbon' vein oreshoots, at horizons from the Slate Sills down to the Slaty Hazle. After passing into the West Allen area, the vein oreshoots are very much reduced in extent, but a considerable run of flats, not found in Cumbria, accompanies the vein. At Allenheads, Henry's Vein carried large vein oreshoots between the Slate Sills and the Nattrass Gill Hazle, but as it approached the area of intersections illustrated in (Figure 15) the vein ceased to be productive except in the Great Limestone. Flats, which had been lacking adjacent to the vein oreshoots, now appeared. (iii) Some, but not all, flats occupy gentle anticlines. The most striking illustration is the St Peter's deposit, where the flats partly occurred in a small dome (Figure 27). At Rotherhope Fell the flats occur in a flat-topped anticline on the NW side of the vein. At the foremost workings of Gudhamgill Mine the Great Limestone flats occur in a gentle anticline which runs parallel to the main 'leader'. On the other hand, no such folding accompanied the important Boltsburn flats.

As noted in Chapter 2, three beds within the Great Limestone, known respectively as the High, Middle and Low Flats, were particularly favourable to metasornatism. It is not certain that the horizon of these is exactly the same over the whole field, but in mines such as St Peter's, east Allendale it can be demonstrated that exactly the same post, 2 ft 1 in (0.63 m) thick, is replaced throughout the deposit, which is confined to the High Flat. A comparison of the rock composing this bed with adjacent beds under the microscope failed to reveal any significant difference (E18565), (E18566), (E18567). More probably the reason for the restriction of replacement to this horizon is to be found in a thin shale layer above it. At Boltsburn separate replacements occurred in all the three favourable Flats, but in places the mineralisation was strong enough to link them up. Comparisons of the section at Boltsburn (Table 55) with the nearest published section (Heights) in Fairbairn's (1978) detailed measurements of the Great Limestone suggest that the High Flat corresponds with his Grey, Loggerheads and Top Crabby posts, the Middle with the Elsey and Cockle Shell posts, and the Low Flat with Kits Bastard. The Allenheads flats were mainly in the High Flat horizon, 3–6 ft (0.9–1.8 m) thick, but there were also small deposits in the Middle Flat post. Among the flats worked for iron ore in the Great Limestone in Weardale, those at the Heights Mine were confined to the High Flat, while those related to the Slitt Vein at Slitt Pasture and West Rigg mines were most extensive at the High Flat horizon, but extended to lower beds in the limestone adjacent to the main vein, producing thicknesses exceeding 30 ft (9.1 m). On the other hand, the important iron ore flats at Carricks Mine are in the bottom part of the limestone, 10–15 ft (3–4.6 m) thick. The beds involved would probably include Jins down to the Newcastle post of Fairbairn (1978). The best-known replacement of the Low Flat posts is the great Smallcleugh galena-ankerite deposit at Nenthead, which was extracted to a height of 15–16 ft (4.6–4.9 m) (Wallace, 1861). Flats connected with Rampgill, Scaleburn, Gudhamgill and Holyfield veins in the same area were mainly in the High Flat. At Silverband Mine (Cumbria) (area 1) extensive replacements worked for barytes are mainly at the bottom of the Great Limestone, 6–8 ft (1.8–2.4 m) thick, but adjacent to Dun Fell and Henrake veins higher beds in the limestone are mineralised, giving much greater thicknesses. In the Scar Limestone, three thin posts are said to have been selectively replaced by galena in the Ashgill Field flats (area 2). In the Tynebottom Limestone at Rotherhope Fell Mine, the greater part of the limestone is metasomatised near the main vein, but away from the vein only the upper part of the limestone is mineralised (Figure 14). Thin limestones such as the Lower Felltop and the Single Post are usually more or less completely replaced.

The galena-bearing portion of flats worked for this mineral did not necessarily occur immediately against the main vein with which they were associated. In the Boltsburn flats, up to 25 ft (7.6 m) of ankeritised limestone poor in galena separated the rich f1ats from the vein. At Rotherhope Fell silicified and ankeritised limestone lies between the flats and the vein. For this reason, flats may have been missed in some mines, as they were during the early history of Boltsburn Mine.

Primary minerals

Among the mineral constituents of the deposits, two classes may be distinguished. One class embraces those minerals which occur within the zone of circulating groundwaters, the oxidation zone, but which fail to occur at greater depths. These are referred to here as secondary minerals. The other class includes the original minerals of the deposits, persistent beyond the reach of surface or near-surface agencies. These primary minerals include the following.

Galena PbS

Galena is probably the only primary lead mineral present in the district apart from certain rare sulphosalts. It occurs in the veins as bands, generally coarsely crystalline. In the flats it may be disseminated through silicified, ankeritised or fluoritised limestone as tiny cubes, or it may form coarsely crystalline bands or masses. Its relations with associated minerals are seldom so intimate as to prevent the production of a good grade of concentrate by simple gravity processes. (Table 18) includes representative analyses of concentrates.

Microscopic examination of polished sections of the galena shows that both zinc and copper are present as separate minerals, sphalerite and chalcopyrite respectively. There is also no reason to suspect any chemical combination between the iron and lead, the iron being present as pyrite or marcasite, or in combination with the copper. On the other hand, silver is known to occur in solid solution in the galena and both antimony and bismuth are expected to occur in this state though these are also known to occur as separate sulphosalts. A spectrographic examination of a galena concentrate from Rotherhope Fell Mine (by J A C McClelland, Geological Survey analysis No. 1414, 1944) for other possible minor constituents gave largely negative results. The presence of copper, zinc, antimony and silver was confirmed, but gold, nickel, cobalt, vanadium, thorium and uranium were not detected. A doubtful trace of arsenic was recorded. The development of the electron microprobe since these early spectrographic investigations has made it possible to demonstrate that Ag, Co, Ni, Bi, Sb and As do in fact occur in a wide variety of separate mineral phases, though in very minor quantities. The results of Ixer, Vaugh, Stanley and others are referred to below.

Although not rich in silver, the galena mined in the northern Pennines has, since the commencement of operations by the London Lead and Beaumont companies, proved to be worth desilverising. In the period 1729–1870 some 5 450 000 oz of silver were recovered from 1 542 184 tons of lead concentrates, an average of 3.5 oz per ton of concentrates (Raistrick, 1936; Dunham, 1944). A more detailed statement of the distribution of silver values is given in (Table 19) and (Table 20). The first is based on the official statistics, and summarises the silver recovery from representative deposits. These figures are inevitably less than those which would have been obtained from representative assays, owing to losses in smelting and refining. The second table gives a number of assays, some of which Dr J A Smythe kindly made in connection with the present investigation.

These summaries reveal that the normal silver content of the galena in the Northern Pennine deposits varies between 4 and 8 oz per ton lead metal. Deposits with exceptionally high silver values occurring along the Sir John's Vein and its branch Stow Crag Vein in the neighbourhood of Tynehead (area 2) were worked at Leehouse Well, Stow Crag, Sir John's and Clargillhead mines, the average silver recovery being about 40 oz. It is probable that the float ore from a field called the Chesters near Tynehead, assayed by Dr Smythe, came from one of these nearby deposits. It is also interesting to note that the boulder of float galena mentioned by J Cameron Swan (in discussion of paper by Nall, 1904) as carrying over 90 oz of silver per ton (2511 ppm) is understood to have come from Cadger Well, at the head of the Harwood Valley, near the south-eastward continuation of Sir John's Vein. Comparable silver values are unknown elsewhere in the field. J C Swan (Nall, 1904, p.408) and others have suggested that in the early days of mining in the district, when the workings were near-surface, more highly argentiferous galena was commonly found. Some support for this view comes from the shallow, oxidised deposits of the Middle Fell district, Alston (Holyfield, Nattrass, Hudgill Burn, Galligill Sike, Grassfield) all of which showed silver values above the normalThere has been speculation that the large sum (for the 13th century) of £2154 mentioned in the Northumberland Piperoll of 1225 as royalty rent due on the Carlile Silver Mines indicates that very rich silver ore rather than galena was being mined near Alston. However, Wallace (Alston Moor, its pastoral people, its mines and miners, 1890, p.105) takes the view that this sum represented unpaid arrears, not an annual rent. The rent in the 12th century was £50 to £100, reasonable sums to represent 1/5th of the value of output of producting lead mines of the period.. It is nevertheless doubtful whether a satisfactory case can be made for supergene silver enrichment, for the variation could equally be a primary one. The generally high values in the Derwent district (including Burnhope, Healeyfield and Beldon, 18 oz per ton being reported from the latter) must almost certainly be ascribed to primary causes, much of the ore here having been worked below the oxidation zone. Similarly the relatively high silver content found by Dr Smythe in galena from the South Moor witherite vein can hardly be due to supergene enrichment.

Variation of silver values in individual deposits fails to indicate any general rule. At Rotherhope Fell Mine, the vein-galena (worked up to 1902) yielded an average of 6.8 oz per ton lead, more than twice that recovered from the galena in the Tynebottom Limestone flats. At Boltsburn the ore from the Great Limestone flats showed silver values which declined from a maximum of 8.2 oz per ton lead to 5.6 oz as the deposits were followed down-dip to the NE. On the other hand the Greenhurth oreshoot, Teesdale, showed a marked increase in silver content, from 5.3 oz per ton to 12.1 oz as it was followed downwards. The London Lead Co.'s operations in the Hudeshope- Eggleshope area of Teesdale also appear to have shown on the average a higher silver recovery with increasing depth of working. The value given for 1861–1875 in the official statistics for these mines is evidently an average one, since each individual deposit has exactly the same silver value assigned to it. It is nevertheless instructive to compare this with the much higher values obtained during the last ten years of the Company's operations.

Silver values below normal are generally found in the outlying parts of the field. In the detached Haydon Bridge area, the average is only 1–2 oz per ton lead. Similarly, scattered occurrences of galena in the Northumberland and Durham coalfield, show very low contents of silver, less than 1 oz per ton, according to information from Dr Smythe. To this the South Moor occurrence is an exception.

Adjacent to the post mineralisation slickensides in many deposits, granular galena is converted into a laminated variety known as 'steel ore', presumably as a result of stresses set up by the movements. It is a fact of general experience at the Allendale mines, confirmed by assays recorded above, that this type of galena is somewhat richer in silver than the normal variety. A similar condition has been noted at the Halkyn Mines, North Wales (B Smith, 1921; Schnellmann, 1940). The reason for this is not understood.

In the course of microscopic investigation D J Vaughan and R Ixer (1980) have found argentiferous tetrahedrite in specimens from Teesdale. Generally, however, the galena of the orefield carries no separate silver minerals. The silver is thus considered to be in solid solution in the galena, which as demonstrated by Guild (in Fairbanks, 1928), is able to hold up to 0.10 per cent of silver without the development of visible silver minerals. Nevertheless note must be taken of a remarkable specimen collected by Mr A W G Kingsbury, now in the British Museum (Natural History) mineral collection which upon microscopical and microprobe investigation by Ixer and Stanley (1987) proved to contain the silver minerals argentopyrite (AgFe2S3), sternbergite (its orthohombic polymorph), pyrargyrite (Ag3SbS3), stephanite (Ag5SbS4), acanthite (Ag2S) and un-named silver-iron sulphides. The specimen was collected from the disused Tynebottom Mine [NY 7893 4181]; but although this mine was worked for lead, the paragenesis in this specimen was with the Ni and Co arsenides chloanthite, rammelsbergite, safflorite and lollingite and with chalcopyrite rather than galena.

Sphalerite ZnS

Sphalerite is the only primary zinc mineral of the field. In the Nent and West Allen area, where it is abundantly present, it occurs as brown to dark brown crystalline bands in the veins and flats. Cavities contain crystals which are nearly black, with a high lustre. Throughout areas 1 to 7 the sphalerite is generally similar. In area 8, however, at Langley Barony and Stonecroft–Greyside Mines, a pale brown variety is found. Both varieties contain iron in solid solution; the analyses given below suggest that the lighter colour at Stonecroft is due to a smaller iron-content than at Nenthead. The colloform banded variety 'schalenblende' was found in a replacement flat in the Jew Limestone in the Rookhope Borehole. Similar banded sphalerite is abundant at Stonecroft Mine (area 8) and smaller amounts have also been observed at the nearby Greyside and Langley Barony Mines (B Young- personal communication). A small amount of cadmium is also present in solid solution; the free cadmium sulphide greenockite has been found as a secondary mineral at a few localities in Teesdale (p.90). A little mercury is also present, probably also in solid solution. Bishara (1966) found mercury contents of northern Pennine sphalerites to be generally below 50 ppm though up to 3500 ppm were found at Settlingstones. The free mercury sulphide, cinnabar, has been found only at Nattrass Mines (area 2) as an oxidation product of sphalerite (Young et al., 1989).

Analyses of sphalerite concentrates are shown in (Table 21).

Chalcopyrite CuFeS2

Chalcopyrite is present in small amounts throughout the field, but has been found in workable concentrations only in a few small veins in the Tynehead and Crossgill districts (area 2). It appears to be present in amounts somewhat greater than normal in the Groverake, Redburn and Stotfield Burn (west) workings on Red Vein, in Sedling Vein, and in the Barbary, Slitt and Merkiel workings of area 5. Bridges (quoted by Ixer, 1986), has found 600–290 ppm Sn in chalcopyrite from Redburn.

Cassiterite SnO2

Dr Ixer states (1986) that microscopic amounts of cassiterite have been observed by Mr Flowers in early quartz from the orefield.

Bismuthinite Bi2S3

Ixer (1986) has noted the occurrence of bismuthinite inclusions at Redburn Mine (area 5). Very small blades of bismuthinite are present in early quartzchalcopyrite veinstone at a number of localities e.g. Sir Johns Mine and Crossgill (area 2), Groverake and Cambokeels Mines (area 5) and Whiteheaps Mine (area 6) (B Young, personal communication).

Pyrrhotite Fex-1Sx.

Pyrrhotite occurs in some quantity in the Great Sulphur Vein (area 2). Preliminary examination of material from Sir John's Mine by Dr J H Jones (Fuel Research Coal Survey, Newcastle) in connection with an investigation of sources of sulphur ore revealed, in a magnetic sample, iron 45.2 per cent, sulphur 28.8, corresponding with the formula Fe8S9. A later examination of a quantitative magnetic separation which showed the material to contain approximately 7 per cent pyrrhotite, suggested that the composition is nearer to Fe6S7. In a gravity concentrate made by Messrs Huntingdon. Heberlein and Co. from a bulk sample from Crossgill, the amount of pyrrhotite present was found to represent approximately 8 per cent of the total sulphides. Only traces of nickel were found in tests by Dr Jones on Sir John's and Crossgill samples. Other records of pyrrhotite in the area are at Wynch Bridge (area 7) where a boring revealed the mineral in metamorphosed impure limestone (E19673), with pyrite at Calvert Mine (area 2), and with marcasite in quartz and fluorite near the horizon of the Tynebottom Limestone at Cambokeels Mine (area 5). Vaughan and Ixer (1985) have found it in White Whin at Closehouse (area 7). Small quantitites of pyrrhotite are present locally in the magnetite and niccolite-bearing rock at Lady's Rake Mine, area 7 (Young et al., 1985). All the occurrences so far could be attributed to the heat of the Whin Sill as must the conversion of syngenetic pyrite in shale above the Cockle Shell Limestone to pyrrhotite at Scoberry Bridge, Teesdale (N H Hardbord, p.239 in Dunham and Walkden, 1968). The low-temperature variety recorded by Sawkins, Dunham and Hirst (1964) from a fluorite vein in the Weardale granite, and the tiny inclusions in early chalcopyrite at Whiteheaps (area 6; Vaughan and Ixer, 1985) probably belong to the main mineralisation.

Pyrite FeS2

Pyrite, though generally present in small amount in the veins and replacements, is a major constituent of only one series of deposits, those associated with the Great Sulphur Vein. Diagenetic pyrite, in part as 'framboids' is widely present in the limestones and carbonaceous shales of the Brigantian and Pendleian.

Marcasite FeS2

Marcasite is also an important constituent of the Great Sulphur Vein. Here the massive sulphides consist of an intimate mixture of the three iron sulphides, among which polished surfaces show pyrrhotite to have been the earliest. This is replaced in part by pyrite. Marcasite, identified in polished sections by its birefringence, occurs in tiny anastomosing veinlets, replacing both pyrrhotite and pyrite. In small amounts marcasite also occurs in the Weardale fluorspar veins. At Sedling fluorspar mill, middlings on certain jigs consisted of a mixture of marcasite and siderite. At Levelgate Level, Weardale, massive marcasite occurs on the dumps, probably derived from Slitt Vein. The mineral is distinguished in hand specimens from pyrite by its bladed.or laminated form, and by its rapid alteration to iron sulphate under damp atmospheric conditions. Electron microprobe measurements by Ixer, Stanley and Vaughan in 1979 have revealed the presence of up to 8 weight per cent arsenic, 3 to 4 per cent cobalt and 1 per cent nickel in marcasite from the Tynebottom Mine (area 2). Ixer (1986) has also found bravoite (Ni, Fe, Co)S2 here.

Ullmannite NiSbS

Ullmannite was first described from the field by Spencer (1910), who discovered it in the barytewitherite vein at New Brancepeth Colliery (area 9). Russell (1927) recorded the species from Settlingstones Mine (area 8). At New Brancepeth the mineral occurred as a parallel intergrowth with galena and as large cubic crystals. Separated from this, Spencer found the nickel-content to be 27.87 per cent, and the antimony content over 52 per cent. Sulphur and a trace of iron were proved to be present and arsenic and cobalt absent. An examinaton of massive ullmannite from the same locality by Smythe (1947) gave, on analysis and recalculation to elimate galena, calcite, ferrous sulphate and insolubles–nickel 25.8 per cent; iron, 3.2; antimony, 54.7; arsenic, 1.0; sulphur, 15.3. Dr Smythe suggests that the arsenic in the mineral replaces antimony isomorphously, and that the iron bears a similar relationship to the nickel. Small amounts of ullmannite occur in the magnetite-niccolite ore at Lady's Rake Mine, Teesdale (area 7) (Young et al., 1985).

Niccolite NiAs

Niccolite was recorded by Russell (1927) from Settlingstones Mine (area 8), where it was found in a pipe-like deposit within the witherite vein, associated with sphalerite, galena and ullmannite. A second record is from the Dowscar Level of Hilton Mine (area 1) where Bridges (1978) found a small pocket in the baryte-fluorite-galena-quartz vein. Young et al. (1985) found niccolite associated with magnetite at Lady's Rake (area 7).

Arsenopyrite FeAsS

In 1953 small amounts of this mineral were found in brecciated Westphalian shale adjacent to the New Brancepeth baryte vein (area 9). Recently 'very minor' amounts have been found as inclusions associated with a tetrahedrite group mineral in sphalerite from Closehouse Mine by Vaughan and Ixer (1980).

Glaucodot (Co,Fe)AsS, Gersdorffite NiAsS etc.

The complex mineral assemblages from the Tynebottom Mine found by Ixer et al. (1979) has explained the record of erythrite Co3As2O8.H2O (Dunham, 1931) as a secondary mineral at this locality. The glaucodot, showing on microprobe analyses cobalt 19–24 per cent, nickel 1–6, iron 9–12 is stated to have grown on arsenical marcasite. It is surrounded by gersdorffite with nickel 17–24 per cent, cobalt 7–12, iron 1–6. A second specimen from Tynebottom in the Kingsbury Collection yielded to Ixer (1986) skutterudite (Co, Ni, Fe)As2, cobaltite CoAsS, niccolite and gersdorffite. The last-named mineral has also been recorded from Nenthead and from Teesdale as inclusions in chalcopyrite and galena by Vaughan and Ixer (1980). In the case of Teesdale the association also includes ullmannite, tetrahedrite and arsenopyrite. Gersdorffite has been reported in small amount associated with niccolite at Hilton Mine (Bridges, 1978) at Lady's Rake and Settlingstones Mines (Young et al., 1985). Bournonite Cu2S.2PbS.Sb2S3 was recorded by Vaughan and Ixer (1980) from Sir Johns Vein.

It must be emphasised that these interesting sulpharsenides and other sulphosalts ocur in very minor quantities and nowhere form workable ores. Ullrnannite and niccolite and gersdorffite have all been identified macroscopically, but the typical occurrence of the remainder is as very small inclusions in the ores. They show that the trace amounts of Sb, Bi, Ni, Co and As found in some analyses of galena and sphalerite may be due to the presence of separate minor mineral phases. It should be added, however, that, as Vaughan and Ixer found at Closehouse, massive galena may be quite free from such inclusions, while sphalerite may contain only tiny exsolved blebs of chalcopyrite.

Millerite NiS

The Sir Arthur Russell Collection at the British Museum (Natural History) contains this mineral from Cowgreen and Boltsburn mines (areas 7 and 5); also it has been recorded by J A Jones (1978) from the Scordale mines (area 1). It has also occasionally been found in shales in the Durham Coalfield (area 9) far remote from the mineralised districts. Sphalerite in very small amounts also occurs in this way; these trace occurrences may be the results of euxinic sedimentation or diagenetic processes. Among other millerite occurrences listed by Dearman and Jones (1967), those at Boltsburn and Cowgreen may belong to the Pennine suite.

Fluorite CaF2

Fluorite is the most abundant matrix mineral in areas 4, 5 and 6 and is present in many deposits in areas 2 and 7. In massive form it is generally white with streaks of purple or greenish coloration. Where, however, crystal faces have been able to develop freely, in vein vugs or the cavities of flats, beautiful coloured crystals are found, the shades including violet, bluish purple, bluish green, green and amber (Plate 1), (Frontispiece). Penetration-twinned cubes are common; untwinned crystals are very rare. Complete cubes up to 6 inches (15 cm) side are not uncommon in the flats; incompletely developed polysynthetic cubes up to 15 inches (38 cm) side have been observed. The cause of the colour of fluorite has not yet satisfactorily been explained. It has long been a controversial subject, but two possibilities, both of which may have operated in this district, may be considered: (1) the presence of impurities, particularly rare-earth elements substituting for fluorine and causing lattice defects with related colour centres; (2) the effect of radiation, which has been shown by McLaughlan and Evans (1968) to release colloidal calcium giving rise to a violet colour spectrally identical with that of Weardale fluorite (MacKenzie and Green, 1971). Respecting (1) J A C McClelland (in Dunham, 1952a, p.10) made quantitative spectrographic analyses of 12 specimens and mill-concentrates of coloured fluorite from the northern region of the orefield, showing yttrium contents ranging from 150 to 1200 ppm, lanthanum, not detected in five, present in the remainder; europium, 20 to 110; cerium generally less than 10, but reaching 300 in one sample; ytterbium, present in some. The subject has been followed up in greater detail by F W Smith (1974 a and b) using x-ray fluorescence methods on samples collected from different parts of fluorspar ore-shoots. His results show a range for yttrium from 102 to 888 ppm, and his mean yttrium figure for fluorite from the large Groverake oreshoot is 356 ppm, lanthanum 60, cerium 101. There is a strong suggestion that both colour and fluorescence are related to rare-earth content; comparative figures for the pale to colourless, nonfluorescent fluorite from the southern region of the Northern Pennines (Dunham and Wilson, 1985, p.92) and from the Derbyshire orefield obtained by McClelland (in Dunham, 1952) and Smith (personal communication) show rare-earth contents an order of magnitude less. Confirmation that there is a correlation between high colour and rare earth element-content comes from the work of Shepherd et al. (1982), who have shown, however, that the total 'REE-content is independent of ore fluid temperature and bulk geochemistry. Regarding the different shades exhibited, the data suggest that the amber yellow variety carries appreciably less rare earths than the mauve and green, and it is possible that there is some connection between the strong green variety and its europium content, but this requires further investigation. On the second possibility, it is known that the colour of Pennine fluorite can be destroyed by heating, and restored by exposure to radiation; but it should be noted that repeated tests by scintillometer of Pennine veins have failed to show any appreciable quantity of radioactive minerals. If radioactive elements were present in the mineralising solutions, they have not remained in mineral form; hypothesis (1) thus appears the more satisfactory. Of other trace elements in the fluorite, sodium may be present, reaching 170 ppm in the sample examined by MacKenzie and Green (1971), who also found 10–20 ppm strontium. McLelland's results show very small amounts of gadolinium in some samples.

Rare earth minerals

Ixer and Flowers (personal communication) have identified synchysite Ca, Ce, La, Nd (FCO3) in the early quartz-marcasite association and elsewhere in the fluorine zone. Monazite CePO4 and xenotime YPO4 have been found in minor amounts at Whiteheaps (area 6). Dr Ixer reports that the synchysite appears to be more abundant and widespread than the minor Co-Ni-AsSb minerals found recently; but the bulk of the yttrium seems to be combined in fluorite.

Quartz, chalcedony SiO2

Silica is an important constituent of the deposits of the present field, unlike the mineralised areas further S in the Pennines. In the veins, the commonest form is quartz, as milky bands or veinlets, and colourless pyramids where these have been free to develop. Chalcedony also occurs as bands in certain veins, its colour being pale brown, or pale shades of blue and grey, usually delicately banded. Good examples may be seen at the Groverake and Shildon mines (areas 5 and 6). An analysis of a specimen from the latter locality by Dr Smythe gave the following results: silica, 98.35 per cent; ferric oxide and alumina, 0.25; lime 0.1; water, 1.00; total, 99.70. Silicification of the wall-rock, especially where this is limestone, accompanies almost every vein. In the replacement deposits replacement of limestone by chalcedonic silica is common, imparting to the rock a black shiny appearance when freshly broken. Quartz, in microcrystalline condition is also found in the replaced rock. Quartz is the principal constituent of only two major veins in the area; the Great Sulphur Vein, and the Catterick Moss–Bollihope portion of the Slitt Vein (area 5). In the Winterhush Vein at Cowgreen Mine (area 7) it occurs in an unusual sugary form (E18389), possibly developed as a result of replacement of marble from the Melmerby Scar Limestone.

Magnetite, Fe3O4

The discovery of this mineral by Young et al. (1985) intergrown with niccolite, galena, sphalerite and chalcopyrite introduces to the northern Pennine paragenesis a mineral out of the traditional range. The three localities, in the Harwood Valley (area 7) are associated with the Teesdale fault-system (p.240), close to the Whin Sill and it is possible, as the authors hint, that metamorphism related to the sills was still in progress when the inflow of Pennine fluids began to arrive. Relatively high-temperature sulphide paragenesis recorded by Vaughan and Ixer (1980) in manifestly low-temperature settings like the Closehouse baryte deposit (area 7) may also bear some relation to heat emanating from the Whin intrusions.

Dolomite, ankerite, siderite (chalybite)

The northern part of the Northern Pennine field is remarkable for the abundance of carbonates of iron, magnesium, manganese and calcium which it displays. Previous investigators have generally considered dolomite to be among the commonest of the carbonates here, but the present investigation has shown that most of the minerals formerly classified as dolomite are in reality ankerites, belonging to the isomorphous series represented by the general formula (MgCO3. CaCO3).(FeCO3.CaCO3).(MnCO3.CaCO3) (CaCO3), in which the principal components are dolomite, ferrodolomite, mangandolomite, and calcite, in solid solution. It is now clear that ankerite is more abundant than any other mineral in the unoxidised metasomatic deposits, forming a mass of interlocked rhombs in which individual crystals can generally be distinguished without the use of a lens. In cavities the mineral appears as white rhombs with pearly lustre, exhibiting curved faces when the composition is near the dolomite end of the series, but flat faces when a substantial proportion of iron is present. Analyses of ankerites by Dr Smythe in (Table 22) are quoted from Smythe and Dunham (1947, p.62):

Many specimens of ankerite show a range in composition within the isomorphous series, with a corresponding range in refractive indices; and since the ankerites should properly be reagarded as a four-component system, it is not possible to deduce the exact composition from refractive index measurements. Subject, however, to an error which may amount to as much as 10 per cent, the content of ferroman–gandolomite may be deduced from the ordinary-ray refractive index, as illustrated in (Table 23) which gives determinations on specimens from a wide range of localities. This summary indicates the comparative rarity of ankerites near the dolomite end of the series. The iron- and manganese-content is of some interest since ankerite is the dominant mineral in many replacements of limestone from which, by oxidation, workable bodies of iron ore have been developed. In these, however, there is generally a substantial proportion of siderite.

The carbonates here classed as siderite are iron carbonates containing small quantities of manganese, magnesium and calcium carbonates in solid solution, as a result of which their ω-refractive indices average 1.840 as compared with 1.875 for pure ferrous carbonate. They are not, as the analyses in (Table 24) show, members of the ankerite series. Fresh siderite is white, but it is seldom if ever found completely unoxidised. In the primary deposits, it normally has a pale to honey-yellow colour. Crystallised in cavities, it almost invariably shows curved faces. By this characteristic, combined with the yellow colour, it may be distinguished from ankerite in unoxidized deposits. Very fine-grained siderite is the principal constituent of the primary (replacement) iron ore known as 'fine steel-grey ore' in the Weardale iron mines. A vein in which siderite was the principal constituent was formerly worked at Rispey Mine, Rookhope (area 5), the ore being known as 'white iron'. An intensive microprobe study of carbonates replacing the Tynebottom Limestone adjacent to Allenheads Old Vein (area 4), and from the vein itself opposite the position of Jew Limestone in Allenheads No. 1 borehole [NY 8604 4539] by A C Dunham and F Wilkinson (unpublished report, 1984) showed that siderite greatly predominates here, though ankerite and a little calcite are also present. The siderite is more than normally manganiferous, with Fe:Mn up to 82:18. Traces of sphalerite and chalcopyrite were the only associated sulphides.

Calcite CaCO3

Calcite, though not an abundant mineral in the deposits, is seldom absent. In cavities both 'nail-head' and scalenohedral crystals are found; large examples of the former were found at Rotherhope Fell Mine (area 2). Well-formed, and often colourless crystals were formerly common at Tynebottom Mine (area 2). At Boltsburn Mine (area 5) remarkable stalactites composed of chains of 'nail-head' crystals were found in cavities in the flats.

Aragonite CaCO3

Massive aragonite, with banded fibrous texture, occurs at the Crag Green mines, Alston (area 2) and at Yorkshire Silverband (area 7). In small amount its distribution in the deposits is widespread. A specimen of pale bluish green aragonite frpm Lunehead Mine (area 7), investigated by R J Friend and J P Allchin (unpublished paper read before the Mineralogical Society, March 1940), proved to contain strontium carbonate, 4.7 per cent; copper, 237 ppm; iron, 64 ppm. Gold and nickel were absent. The colour was considered to be due to the copper.

Baryte* BaSO4

BaryteIn this account the name baryte is used for the pure mineral; the name barytes for the commercial product from the mines, which is not, of course, pure baryte. Fluorite and fluorspar are respectively used in a similar way. is the most persistent gangue mineral in the peripheral areas of the field. Two types are common: (i ) a fibrous variety, often banded perpendicular to the fibres; this type is frequently coloured, in shades varying from milky white to flesh pink, the pink colour being due to the presence of very finely dispersed iron oxide particles (ii) a tabular crystalline variety, crystals up to a foot (0.3 m) long and several inches thick being by no means uncommon. The fibrous variety is generally coarser than the cawk of the Derbyshire field. Crystals of the tabular variety are normally milky white when found in veins; in the oxidation zone they are commonly found superficially stained with limonite but the iron oxide is seldom if ever dispersed through the crystals. In certain replacement deposits (e.g. Silverband, Dufton (area 1), Closehouse (area 7) large water-clear crystals are found. Small water-clear crystals have also been collected from cavities in veins. Some of the largest crystals ever discovered came from the Tynebottom Limestone flats at Dufton Fell Mine (area 1), including one weighing about 1 cwt (50 kg) (Brammal 1921). The normal forms present in the tabular crystals are (001) (102) and (102), with (110) as a subsidiary face. Where, however, baryte occurs in veins dominantly filled with witherite, as at Settlingstones (area 8) and South Moor (area 9), it exhibits a sharp pointed form which seems to be confined to this paragenesis, in which the dominant faces are (110), combined with (001). As regards composition, a feature of interest is the presence of strontium, as indicated by the following analyses in (Table 25).

The presence of strontium in analysis No. 6 is of particular significance since this determination was carried out on a single water-clear crystal. Celestite (SrSO4) has not been detected as a separate mineral in any of these deposits and it is presumed that the strontium is isomorphously present in the baryte. It is also possible, though not proved, that calcium sulphate may occur in solid solution in the baryte. Anhydrite has not been proved in the deposits, though gypsum is quite common in the oxidation zone where sulphate waters have attacked limestone; here, however, it is normally found as an efflorescence.

Witherite BaCO3

Witherite is a common mineral in the Northern Pennines; in this respect the field is unique in the world. It is the predominant mineral of the Settling-stones and Fallowfield deposits in area 8, and of the South Moor, Cragside and Ushaw Moor deposits in area 9. Important quantities also occur at Nentsberry and several other localities in the West Allen area (area 3). In the massive form, the colour is white to pale yellow; freshly broken surfaces exhibit a characteristic greasy lustre. Although the mineral belongs to the orthorhombic system it always forms pseudohexagonal crystals. Miers (1929) records bipyrarnids from Fallowfield and these are also abundant at Settlingstones, but the commonest forms obtainable in recent years are those showing pseudobasal pinacoids (as at Ushaw Moor) or pseudoprism faces (as at Nentsberry). That all these crystals are twins becomes evident if a section is cut approximately parallel to the pseudobasal pinacoid, for this shows that the crystal is made up of six segments of different orientation. Strontium occurs in witherite, probably in solid solution as strontium carbonate, the amount varying from 0.8 to 1.7 per cent strontium carbonate in examples analysed from the West Allen mines. A quantitative spectrographic analysis of a single crystal of pure witherite from South Moor by J A C McClelland (Geological Survey and Museum Lab. No. 1421; 1944) showed strontium, 0.35 per cent; calcium, 0.03; lead, 0.02–0.04.

Barytocalcite BaCO3.CaCO3

A remarkable deposit of the otherwise rare mineral barytocalcite occurs in Fistas Rake, Blagill mines (area 2), where it is said to compose the greater part of a vein which reaches up to 8 ft (2.4 m). An analysis of picked material from the dump is given in (Table 26). Although resembling witherite in its yellowish colour and greasy lustre, it may be distinguished by its slender prismatic crystals, sharply truncated by (121) faces. In the analysed example there is an excess of calcium carbonate of 4.2 per cent, probably present as calcite or aragonite. The mineral also occurs in First Sun Vein, Nentsberry Mine and was stated by Russell (personal communication) to be present at Settlingstones. In a review of the occurrence of the barium and barium-calcium carbonate minerals in the orefield, Young (1985a) lists nine new localities for barytocalcite, and states that it is a major constituent of veins at Blackpool Bridge, Heartycleugh, Scraithole (area 3), Clargill (area 2) and Stake Beck (area 7) mines.

Alstonite has the same composition as barytocalcite, but shows orthorhombic (pseudohexagonal) symmetry, whereas barytocalcite is monoclinic. Alstonite was first described from the Brownley Hill Mine under the name bromlite (Thomson, 1837); the specimen is said to have come from the Jug Vein. It has also been found at the Fallowfield, Settlingstones, Nentsberry (Young, 1985a) and New Brancepeth mines, the last-mentioned occurrence having been found by Spencer (1910, p.306), who gives the following analysis: baryta, 52.3 per cent; lime, 18.0; manganous oxide, 0.06; insol. in hydrochloric acid, 0.2; corresponding with barium carbonate, 67.3 per cent, calcium carbonate, 32.1 per cent. It is possible that either barytocalcite or alstonite is generally present in the witherite-bearing deposits.

Harmotome, (K2Ba)O.A12O35SiO2.5H2O

The barium zeolite was found by Sir Arthur Russel (personal communication), filling the interstices of the witherite mass at Settlingstones Mine (area 8); harmotome also occurs at the adjacent Stonecroft Mine. Young and Bridges (1984) add two more sites: Wellhope Shaft, Nentsberry (area 2) and Greyside Mines (area 8).

Strontianite SrCO3

Strontianite has so far been found only at Settlingstones Mine (Trestrail, 1931) as a yellowish or greenish fibrous mineral and at the adjacent Stonecroft Mine (area 8) as colourless to very pale green crystals in vugs (Young, 1985c). Wray (in Sherlock and Hollingworth, 1938) reports the mineral from Greenlaws Mine, Weardale (area 5) but doubt has been cast on this occurrence (Young, 1985a).

Clay minerals Smith and Hardy (1981) have recorded a variety of clay minerals from several deposits within the orefield: Kaolinite Al2Si2O5(OH)4 was found in a 4 cm-wide vein branching from the Middle Groverake Vein in the Firestone Sublevel at Groverake Mine, Rookhope (area 5). Turquoise-blue dickite fills cavities up to 1 cm across in calcite-galena-sphalerite veinstone on the dumps of Stonecroft Mine (area 8). A dark olive-green mineral coating vein minerals at Redburn and Cambokeels Mines, Weardale and in the North Wear Aqueduct Tunnel (area 5) has been identified as berthierine-chamosite. Pockets of a clay mineral occupying siderite-lined cavities in a borehole at Redburn Mine, Rookhope (area 5) were shown to be a chlorite of the cookeite type. Compact, fine-grained pale yellowish green muscovite occurs in brecciated vein fillings at Burtree Pasture, Redburn and Frazers Hush Mines in Weardale (area 5). At Closehouse Mine (area 7) bluish green coatings and veinlets in 'white whin' have been identified as barium-muscovite (R I Lawson, personal communication).

It must be added that it is not certain that all these clay minerals belong to the primary suite.

Hydrocarbons

J F W Johnston (1839) recorded from the witherite vein at Settlingstones (area 8) a hard to brittle, pale yellow to deep red resinous substance containing carbon 85.13 per cent, hydrogen 10.85, ash, 3.26, which showed pale green fluorescence. A hydrocarbon found in a cavity in the South Moor witherite vein (area 9), examined by Dr Smythe, proved to be soft, dark brown, to have no smell and to melt at 93°. On analysis this yielded carbon 84.25 per cent, hydrogen 13.57, loss 2.18. Both minerals approximate to the composition (CH2)n and are probably high molecular paraffins or olefines, or mixtures of both.

Very small grains of black brittle hydrocarbon occur in fine-grained quartz in a vein believed to be Boltsburn Vein in the Weardale Granite at a depth of 502 m in the Rookhope Borehole (Bath et al., 1986, p.39).

Traces of brownish black solid hydrocarbon have recently been found in calcite on the dumps of New Engine Shaft, Fallowfield Mine (area 8) (B Young, personal communication).

Distribution of primary minerals

It will already have become evident that the Northern Pennine deposits are by no means uniform in composition. They range from concentrations in which fluorite is the dominant mineral, through deposits with workable quantities of lead, zinc or iron ores to mineral bodies in which baryte or witherite predominates. There are, nevertheless, transitions linking all these types, so that it is reasonable to conclude that, with one possible exception (the Great Sulphur vein-system) the mineralisation of the field was a single unified process. The community of structural type in the deposits supports this conclusion.

The existence of a fringe of barium deposits peripheral to the field, with fluorite deposits in the central areas, was first noticed by Smythe (1922). A detailed study of the distribution of mineral species was the principal object of a previous investigation, the results of which appeared many years ago (Dunham, 1934; 1937). To these there is little to add so that it is only necessary to summarise here the conclusions reached. (Figure 16) shows the distribution of the principal matrix minerals in relation to the sulphides. The central part of the field, including most of areas 2, 4, 5 and 6, the southern part of area 3 and the northern part of area 7 contains deposits in which fluorite is the important matrix material. The fluorite area is surrounded by a narrow belt in which there are a few deposits carrying both fluorite and baryte, but in which a majority of the deposits contain neither of these minerals. The fringes of the field, areas 1, 8, 9 and southern part of area 7, together with the outer parts of the other areas, contain deposits dominated by barium minerals. There is, therefore, a crudely systematic distribution of matrix minerals. In the innermost parts of the fluorite zone, in Weardale, Alston Moor and at Hunstanworth, deposits composed largely of fluorite, and containing only minor quantities of sulphides are found. These are the main sources of the fluorspar production of the northern Pennines. The chalcopyrite occurrences at Tynehead (area 2) (where there was formerly a small production of copper ore), at Sedling, Barbary, Groverake, Slitt and Merkiel (area 5) occupy central positions in this innermost zone. Quartz is generally most abundant in the innermost part of the fluorite zone. Towards the outer part of the fluorite area, the most important galena deposits, including those of East Allendale, the great belt of deposits running through Nenthead and West Allendale, the Burtree Pasture, Boltsburn and Greenlaws deposits of Weardale and the Coldberry—Eggleshope—Sharnberry belt of northern Teesdale are found. Sphalerite, though present in small amounts in most of the deposits in the fluorite zone, becomes of practical importance only in the outermost part of this zone, increasing to a maximum in the intermediate zone, and dying out a short distance beyond the inner margin of the barium zone. It is, moreover, restricted to that part of the field lying west of the Burtreeford Disturbance, a fact noticed long ago by Forster (1821, p.270). The disturbance appears to divide the field into two parts to which the supply of zinc during mineralisation was very different. Sphalerite in workable amount east of the Burtreeford Disturbance has so far been found only in small deposits at Ettersgill and Wynch Bridge, Teesdale. In the zinc deposits of the western area, galena was coequal in importance with, or of greater importance than sphalerite. In the barium zone, galena persists farther than sphalerite, but it, too, decreases to insignificant amounts or disappears altogether, in the outermost parts of the zone, where the principal deposits worked for barium minerals occur. For example, at Cowgreen, Hartside, Closehoue and Lunehead very little galena is found, while this mineral was regarded as a rarity at Settlingstones, South Moor, Ushaw Moor and New Brancepeth. Within the barium zone, no rational relationship appears to exist in the distribution of baryte and witherite; the latter mineral is not necessarily found between limestone wall rocks. On the other hand, the ankerites appear to bear little relationship to the mineral zones, but to be confined to limestone replacement deposits or the vicinity of such deposits. Siderite also appears at all stages, though the most important concentrations are found in the area east of the Burtreeford Disturbance, in the fluorite zone. Aragonite is most generally associated with the intermediate and barium zones.

That the mineral variation from zone to zone takes place in a lateral rather than a vertical sense is a result of form of the channels along which the mineralising fluids moved. There are many instances of lateral variation in vein-contents; a few cases of vertical variation have been recorded by Forster (1883, pp.150, 151) and Dunham (1934, pp.700–703). Briefly, instances of upward transition from fluorite to baryte as the dominant gangue include the Brownley Hill, Rampgill, Middlecleugh Second Sun and Killhopehead veins, all of which contain fluorite in the Great Limestone and baryte in the Grit Sills or Grindstone. Among the sulphides, chalcopyrite is found in Sir John's Vein in the Tynebottorn and Scar limestones, but it gives place to galena in the Six Fathom and Slaty Hazles. Windybrae Vein carried chalcopyrite in the Scar Limestone, galena in the Great. The lower parts of some of the Nenthead oreshoots–on Rampgill, Middlecleugh and Longcleugh veins, for example–were apparently richer in sphalerite than the upper parts, where the values were mainly in lead.

The Great Sulphur Vein, and a few small veins related to it, appears to be unique in the field in carrying great quantities of quartz in an upper zone, and pyrrhotite, pyrite and marcasite, with a little chalcopyrite, in a lower zone (Thompson, 1933). Arguments have been advanced for regarding this vein as younger in age than the remainder of the Pennine veins (Dunham, 1934, p.711). The discovery, in the course of the 1941 investigation, of an apparent shift of the hangingwall of the Great Sulphur Vein by Sir John's Vein (in addition to the previously known fact that Sir John's Vein is itself shifted by the footwall of the Great Sulphur Vein) weakens the structural argument advanced. The acceptable alternative is to regard the mineralisation of the eastern half of this vein as representing the innermost zone of the Pennine suite. The presence of pyrite, pyrrhotite, quartz veinstone, of typical Great Sulphur Vein aspect, at Calvert Mine (area 2) and discoveries of early chalcopyrite and of pyrrhotite at depth in the eastern area, at Cambokeels Mine and in veins in the Weardale granite (area 5) lend credence to this view, as does the increase of SiO2 with depth at fluorspar mines such as Stotfield Burn p.205. In Weardale and Bollihope (area 5) the massive quartz filling of the Slitt Vein between Catterick Moss and Harehope Gill and the downward passage of the fluoritic Sharnberry Vein into massive quartz suggests conditions analogous with the Great Sulphur Vein W of Burtreeford. At Cambokeels Mine the fluorite oreshoots cut through early massive quartz, but a late phase of quartz is also present.

To illustrate the variation in composition among the deposits, an attempt has been made to estimate the composition of representative oreshoots, in (Table 28).

It should be emphasised that in the fluorite zone, visible baryte is absent; similarly, fluorite is not found in the baryte zone. Analyses reveal traces of these minerals outside their zones, which serve to reinforce the evidence of transition linking the mineralisation into a unified whole. Within the fluorite zone, the purple or green colour of the fluorite gives place to amber as the outer edge of the zone is approached (Dunham, 1937).

Texture and paragenesis in primary veins

The typical veins of the area exhibit a banded texture, paralleling the vein-walls. The bands normally consist of pure or nearly pure minerals, with crystal faces developed on that side of the band nearest the centre of the vein, indicating that the veins were ftlled from the walls inwards. Bands of matrix material, fluorite, quartz of baryte are generally continuous, but sulphide bands may consist of a broken chain of lenses, with gaps between them. This 'discontinuous banded texture' (Dunham, 1934) is probably due to the incomplete covering of the surface on which sulphides were being deposited before the deposition of the next band commenced. The symmetry of the banding is disturbed in many veins by the presence of inclusions of wall rock (Plate 3). In some instances, for example in the Winterhush Vein at Cowgreen, the bands surround and envelop such inclusion. In others reaction effects in the vicinity of the inclusion have prevented the formation of bands. A few veins exhibit chains of small cavities along their central axes, where filling was not quite complete, but in most instances these have been destroyed by postmineralisation movements, which produced slickensides accompanied by narrow belts of brecciated vein material. The postmineralisation movements were seldom if ever accompanied or followed by the deposition of new primary minerals. Many veins, however, show evidence of cracking and reopening prior to the formation of the postmineralisation slickensides. In the veinlets so produced, late quartz and carbonates have been noticed cutting across baryte at Cowgreen (E18390), fluorite at Stotfield Burn (E18429),  (E18430), (E18431), (E18432), (E18433) and Groverake (E18531)–(E18532). Both fluorite and baryte also contain inclusions of quartz of earlier or simultaneous deposition, which may be as small as 0.05 mm diameter. These have been described by Dr Phemister in reports on the relation of silica and baryte at Cowgreen, silica and fluorite at Stotfield Burn and Groverake. It appears that such inclusions are widely present in what appear to be pure bands of fluorite and fibrous baryte, though they represent only a small proportion of the total silica associated with these minerals. It follows, however, that fine grinding would be necessary before the silica could be completely eliminated.

The veins exhibit many repetitions of bands, followed by several minor phases of reopening. Under these circumstances, no general 'order of deposition' of minerals can be acceptable. It has, however, been shown that quartz, marcasite and chalcopyrite were generally 'early' sulphides, and that the crystallisation of fluorite was completed before the deposition of baryte in the few instances where these minerals are associated in this field (Dunham, 1934, p.709). Ixer (1986) has advocated the existence of three paragenetic assemblages as follows (the numbering is his): (1) early quartz-pyrrhotite, pyrite bladed marcasite; (2a) fluorite, galena, sphalerite, Co-Ni sulpharsenides and silver minerals; (2b) (fluorite), baryte, witherite, silver-poor galena, sphalerite, Ni-sulpharsenides and sulphantimonides; the only modification made here to this list is to place the fluorite of 2b in brackets as a reminder of its very infrequent association with the barium minerals in this field. Ixer (1986) comments that his assemblage 2b corresponds with the outer zone of the present study, but this is not correct; it corresponds with Zones III- V of (Table 27). He proceeds to give crystallisation-sequences of the various phases in these parageneses (using this term to mean no more than mineral associations). Having regard to the repetition of numerous bands as seen in-situ in the veins, though less easy to appreciate in material from dumps, and having regard to the accident of discovery implicit in the very minor phases, some doubt may be felt about accepting these orders as of more than local significance. The zonal assemblages are on the other hand, facts of geography whatever their explanation may be, and thus general to the northern orefield.

Metasomatic deposits and wall-rock alteration

In limestone

There is strong evidence that the earliest effect of the mineralising solutions upon the limestone wall-rocks of the channels along which they moved was the conversion of the limestone into ankerite-rock, with variable amounts of siderite and chalcedonic silica. The ankerite occurs as sharp idioblastic rhombs, sometimes in two or more generations. In material from the Middlehope mines, (area 5), (E18903–18096) it was possible to demonstrate by the use of the staining method devised by Hallimond (1925, p.39), in which a chip is treated with hydrogen peroxide before sectioning, that the cores of the ankerite rhombs consist of dolomite, the outer parts of ankerite.

Siderite and silica envelop the earlier ankerite, or fill the interstitial spaces between the rhombs. Ankeritised limestone of this type occupies the ground between Boltsburn Vein and the productive flats in the East Mine. A similar rock is found between the vein and the North Central flats at Rotherhope Fell Mine.(area 2), though here silica predominates over carbonates (E18900), (E18902). At Carricks Mine, Weardale, borings have proved large areas of ankeritised limestone of similar type, associated with Lowe's, Dawsons, and Far veins and Nos. 4 and 5 cross veins (E18822). It appears that alteration of this type provided an environment mainly unfavourable to replacement by fluids belonging to later phases of the mineralisation, carrying fluorine and lead. At Carricks Mine, these deposited their load above the Great Limestone, in the White Hazle and Little Limestone. At Boltsburn and Rotherhope Fell structural conditions caused them to break through the ankeritised belt, and attack the limestone beyond. The replacement flats produced contain bands of coarse galena and scattered cubes of galena in a matrix composed of fluorite, quartz, chalcedony, ankerite and siderite. An approximate estimate of the bulk composition of the Boltsburn deposit has been given above (analysis 3, (Table 28), showing that in the productive part of the flat, siderite is more abundant than ankerite. Under the microscope the ankerite rhombs are seen to be enveloped by fluorite, which in places shows idioblastic faces towards galena and the other minerals present. At Rotherhope, clear brownish chalcedony and cryptocrystalline quartz are more abundant than fluorite (E18886), (E18887), (E18888), (E18889), (E18890), (E18891), (E18892); galena cubes are surrounded by a 'halo' of quartz; sericite is present in the rock, in places fairly abundantly. Early carbonates include ankerite and siderite and in the cavities large calcite crystals were the last to crystallise. Horizontal or gently inclined banding is in places developed in the flats. At Rotherhope there were remarkable examples of bands of coarse fluorite alternating with black, fine-grained, fluoritised limestone. Here the banding was definitely at a small angle to the bedding of the limestone, as may be seen from a published photograph (Mine and Quarry Engineering, Vol. 3, 1938, p.44). Similar banding, between baryte and altered limestone, occurs in the flats at Silverband Mine (area 1). At Gudhamgill Mine, (area 2), the flats contain bands and masses of sphalerite, which is also scattered through the ankerite-quartz-fluorite matrix in tiny crystals. The replacement of limestone by the denser minerals of the metasomatic deposits, if it takes place in the proportions required for reaction relations, should lead to a substantial reduction in volume. This may take place in one of two ways (i) the metasomatic deposit may reproduce faithfully the bedding, joints and even fossils of the limestone, in which case the volume-change is taken up in the formation of cavities (Plate 2); or (ii) there may be an overall contraction, leading to the collapse and brecciation of the beds above the limestone. The first case applies to the Great Limestone flats which have been examined, and to the Tynebottom Limestone flats at Rotherhope Fell. The former texture of the rock, including bedding planes, stylolites, joints and some fossils, is faithfully reproduced in the deposit. Fossils replaced by quartz, fluorite, sericite and even galena have been found. Large cavities in these flats indicate decrease in volume of total mineral. The second case is exemplified in the Single Post Limestone flats at Ettersgill and Wynch Bridge, Teesdale. The normal thickness of the limestone, when unaltered, averages 6 ft (1.8 m) here; mineralisation has led to a reduction in thickness to 3–4 ft (0.9–1.2 m), accompanied by collapse of the overlying metamorphosed sandy shale, which now forms a breccia several feet thick on top of the mineralised limestone. A similar effect was seen in the Jew Limestone at Cambokeels Mine, Weardale (Plate 7). The collapse took place during mineralisation, the fragments in the breccia now being cemented by siderite and sphalerite. Cavities, other than very small ones, do not occur in these flats. A smaller-scale example was found in the 'Klondike' area at Boltsburn Mine, where Coal Sills sandstone had collapsed into the Great Limestone, the fragments being cemented by fluorite and galena. These replacements did not, therefore, take place on a strictly volume-for-volume basis such as Lindgren (1918) has contemplated.

The Tynebottom Limestone within the Great Sulphur Vein presents an example of very complete metasomatism. Of the original calcite of the limestone, less than 0.5 per cent remains, its place is taken by silica and iron sulphides. The alumina of the original rock remains, but it is mainly combined in newly formed sericite (E18487), (E18488), (E18489). Polished sections show that the iron sulphides owe their apparent tabular form to replacement of small slabs of argillaceous limestone, probably derived from the top bed of the limestone, which is considered to have collapsed during the metasomatism of the lower, more calcitic beds. Among the sulphides there is a sequence of replacements, pyrite replacing earlier pyrrhotite, marcasite replacing both minerals.

The analyses in (Table 29) illustrate the composition of representative metasomatised limestones. In all cases it may be taken that the original limestone contained at least 95 per cent calcium carbonate.

Most of the ordinary primary minerals known in the veins also occur replacing limestone. The formation of meta-somatic deposits is not restricted to any particular mineral zone (for example, an abundance of fluorine is not a necessary condition for extensive metasomatism). As might be expected, the carbonate-content of the metasomatic deposits is generally greater than that of the veins. Two minerals which do not, as far as is known, occur as vein-minerals, have been found in metasomatic deposits. One is sericite, mentioned above as occurring in the Tynebottom Limestone at Rotherhope and in the Great Sulphur Vein. The other is chlorite, of two different varieties (mean refractive indices 1.590 and 1.620 respectively), found in the metasomatised Single Post Limestone at Wynch Bridge.

In the cavities in the flats, successive crusts of primary minerals show that more or less pure minerals were deposited in succession. No standard 'order of crystallisation' holds, however, for there are many repetitions and reversals in succession, as repeated counts made while the Boltsburn flats were still accessible showed. Earlier minerals were in some cases redissolved during the process. Epimorphs, preserved in quartz or chalcedony reveal that at some stage fluorite, marcasite and other minerals were dissolved out. The crystal faces of galena, far below the oxidation zone, show pitting indicating a similar effect. The only general conclusion which can be safely be drawn from a study of the metasomatic limestone deposits is that there was an early phase of mineralisation during which ankerite, siderite and silica were introduced; a main phase during which sulphides, fluorite, baryte and carbonates were deposited, and a late phase characterised by deposition of calcite. Calcium and strontium were removed during the main phase. Ineson (1969) who has studied dispersion patterns of minor and trace elements in relation to veins traversing the Great limestone at Redburn, Ashes, Heights and Newlandside (area 5) finds that strontium is depleted in all cases from a normal background of 1750 ppm to near zero as the vein is approached, while zirconium increases from a background below 10 ppm to form an aureole with up to 100 ppm extending up to 16 ft (4.9 m) from the vein. The mineralogy of this latter effect has not yet been solved, but similar aureoles accompany veins in limestone in Derbyshire.

In quartz-dolerite

Adjacent to the veins, even the smallest examples, alteration of the dark, dense quartz-dolerite of the Whin Sill to a white, lighter rock, the 'White Whin' of the miners, has taken place. The composition of the altered rock has been investigated at Rotherhope Fell (Area 2) by Finlayson (1910b, pp.304–305), at Wynch Bridge (area 7) by Wager (1929a), at Force Burn (area 7) and Aglionby Beck (area 2) by Smythe (1930, pp.116–126). Two analyses, representing altered dolerite from two mines worked in the Whin Sill, Cowgreen (area 7) and Settling-stones (area 8), were made in connection with the present investigation, with results stated in (Table 30).

The alteration is expressed in profound mineral changes, producing rocks of the 'white trap' type, composed of secondary carbonates, kaolinite, micaceous clay minerals, anatase or leucoxene and residual quartz and apatite. Wager (1929, p.106), following the process stage by stage, has shown that at the outer margin of the 'White Whin', the alteration first becomes apparent in the conversion of the ferromagnesian minerals into carbonates with minute inclusions, probably anatase. Slight alteration only is sufficient to change the black dolerite to a pale grey colour, as shown by two samples from borings at Settlingstones analysed by Ineson (1972). Nearer the vein, the calcic cores of the plagioclases are attacked, while at a still more advanced stage, the process affects their alkalic margins and the orthoclase. The feldspars are replaced by kaolinite and clay micas but not as high as muscovite. The rock from Wynch Bridge analysed by Wager (Table 30), column 5) (E21724) represents the most advanced stage of the alteration at this locality. It is composed of carbonates, kaolinite, micaceous aggregate, anatase, apatite and quartz; no feldspar remains in it. The analysis, nevertheless, shows 10.3 per cent soda, which is tentatively assigned to paragonite by Wager in calculating the mineral composition of the rock. Although the validity of this species has now been established (Schaller and Stevens, 1941, p.541) it is clearly a very rare mineral, and in the light of recent work on clay micas, it is perhaps more probable that a mineral of the brammalite (sodium illite) type is present.

The Force Burn rock, analysed by Smythe (Table 30), column 6 represents a much less advanced state of alteration, in which most of the feldspar remains unaltered, though the pyroxenes have largely been converted into carbonates. The analysed material from Cowgreen and Settlingstones mines ((Table 30), columns 3 and 4, (E18885); (E20064)-(E20065), collected to represent the full width of the altered belt, may be regarded as intermediate between the Wynch Bridge and Force Burn rocks. The pyroxenes in them have been completely altered to ankerite, with calcite at Settlingstones. Kaolinite, identified by its optical properties and by the methylene green staining test (E20065B) has replaced the cores of the plagioclases, accompanied by a clay mica of higher birefringence, but both samples contain residual soda and potash feldspars, the maximum refractive index of the remaining plagioclase being 1.545. No satisfactory petrographical evidence of the new formation of alkali feldspar, such as Smythe (1930, p.119) considered on chemical grounds to have taken place at Force Burn, was found, and tests for zeolitic material and analcite were negative (E20065A). In a thorough investigation of 'White Whin' at Closehouse Mine, Ineson (1968) made eight new full analyses; an average, recalculated from 15.9 per cent alumina to 15.4 is quoted in (Table 30).

The foregoing examples of the alteration of the quartz-dolerite are qualitatively similar; but the altered rock from Rotherhope Fell, analysed and described by Finlayson (1910b, p.304), and that from Aglionby Beck (Smythe, 1930, p.118) show important petrographical and chemical differences. The Rotherhope Fell rock, reinvestigated from material collected in situ (E18883)–(E18884) contains substantial amounts of quartz and pyrite introduced from the vein, and some fluorite is also present. The addition of these constituents explain the low carbonate-content of what is nevertheless a very highly altered dolerite. At Aglionby Beck limonite, probably derived from the oxidation of pyrite, appears to have taken the place of the carbonates, and this rock may be regarded as an extreme example of the further alteration of 'White Whin' in the zone of oxidation.

Recalculation of the analyses in terms of mineral composition has been attempted by several different methods, but none has proved to be satisfactory. If potash and soda are allocated to muscovite and paragonite, the calculations show a substantial apparent increase in free silica as compared with the unaltered dolerite (compare Wager, 1929, p.102) which, except in the case of the Rotherhope Fell rock, appears to be inconsistent with the petrographical evidence. It appears likely, therefore, that the clay mica has a higher silica/alumina ratio than muscovite and in this respect, minerals of the illite type would be more likely. The identity of the clay minerals in the 'White Whin' investigated using X-ray methods by Ineson (1968) supports this view but indicates that kaolinite is also present. A remarkable altered dolerite from Settlingstones (Ineson, 1972, sample S3) containing 11.2 per cent potash must be richer in clay mica than average.

The chemical significance of the alteration process is not easy to assess by direct comparison of the analyses of the unaltered and altered dolerite, owing to the strong probability that volume changes accompany the process notwithstanding the objection to the procedure on grounds of analytical accuracy. Wager's method of comparing the analyses on the basis of constancy of alumina appears to be the most promising. The assumption that there has been no appreciable migration of aluminous material is reasonable in view of the absence of clay minerals from the veins in and above the Whin Sill, except where these occur in mechanically incorporated fragments of 'White Whin' or shale. (Table 31) shows the tonnages of the principal constituents in analysed 'White Whins' (in the formation of which surface agencies may be supposed to have played little or no part) which would be produced from 100 tons of average Whin Sill dolerite.

The comparison, though it emphasises that the alteration process in dolerite is as variable as that in limestone, nevertheless indicates certain definite tendencies. There are consistent gains in carbon dioxide, potash and combined water. In all instances except Rotherhope Fell marked losses in silica and iron are shown. Magnesia was lost in three cases: in all but one instance soda was lost. The apparently anomalous composition of the Rotherhope Fell rock is due to the fact that the mineralising solutions at this stage (Zone II) were depositing silica, and iron, as sulphide. In Zone III (Wynch Bridge) and Zone V (Force Burn, Cowgreen, Settlingstones) both silica and iron were being leached out. In some cases magnesia and lime, both liberated from the minerals in which they were originally combined, were leached out: in others they remained as carbonates or were augmented from the mineralising solutions. The formation of clay mica and kaolinite from the feldspars liberated soda if the alteration reached a sufficiently advanced stage but the production of the first-mentioned mineral involved the addition of potash. Comparison of trace element contents in fresh and altered dolerite at Closehouse (Ineson, 1968, p.380) show a gain in rubidium corresponding with the gain in potash, and addition of barium and zinc. There are partial losses of strontium, copper, nickel, chromium and vanadium.

It appears very probable that the 'White Whin' was itself susceptible to metasornatisrn during the later stages of the mineralisation. At Amber Hill Mine, Scordale, and at Closehouse Mine, small flats of baryte occur within the altered Sill. The great width of the Fish Lake deposit at Closehouse, between altered dolerite walls, strongly suggests replacement, as does the form of a remarkable swell in the Winterhush Vein orebody formerly visible on the 191 ft (58 m) Level South at Cowgreen. The Rotherhope Fell rock best illustrates this further stage in the alteration among the analysed examples, but considerably more advanced cases could be obtained.

Bearing on the chemical composition of the mineralising fluids, it may be suggested from the chemical evidence presented above that solutions reaching the Whin Sill were carrying carbon dioxide, water and potash, together with silica and iron in the inner zones of the field. On leaving the Sill they were relatively enriched in one or more of the following constituents: silica, iron, magnesia, soda. Wager (1929, p.105) has suggested that the iron minerals in the lead veins of Teesdale and Weardale owed their origin to the metasomatism taking place as the mineralising solutions traversed the Whin Sill. It is here suggested that this conception may be extended to include at least part of the silica and magnesia in the intermediate and outer zones of the mineral field. The great concentrations of ankerite, siderite and silica which are peculiar to the present area, and almost unknown in the West Yorkshire and Derbyshire Pennines may well owe their origin to material leached out of the Whin Sill, which is also restricted to the northern field. The evidence of the metasornatised limestones shows that these were early minerals; the inference may be drawn that the metasornatisrn of the Whin Sill was far advanced before deposition of metallic and associated minerals in the veins and flats commenced.

In sandstone

Metasomatism of sandstone adjacent to the mineral deposits is comparatively rare in the area, and no deposits of commercial importance have originated in this way. Small amounts of galena replacing sandstone of the Basement Group were noted at Lowfield Hush, Scordale, (area 1) associated with fluorite, baryte and quartz. Galena also replaces a sandstone near the horizon of the Felltop Limestone at Cobbler's Venture Trial (area 7). Silicification of sandstone accompanies the Great Sulphur Vein on a great scale. Specimens from the slopes of Noonstones (E19239), (E19240), (E19242), (E19243) show that the quartz of the sandstone was first completely recrystallised to granulite, growing round flakes of mica; then sheared and veined with quartz. Recrystallisation of quartz extending for a few mm was noted in grit adjacent to a baryte vein on Knitsley Fell (E18585) (area 5). Replacement of sandstone by sharp cubes of pyrite is common, but it is not certain that this is related to the mineralisation process.

In shale

Silicification is also the principal alteration to be observed in shale. Fragments of shale incorporated in the vein at Stotfield Burn Mine, Rookhope, were found to have been replaced by chalcedonic silica (E18430A). Within the Great Sulphur Vein, intensely silicified shales occur (E18490), (E18491), (E19250) containing, in addition to chalcedony, chlorite and sericite. Limy shale or shaly limestone from the Crossgill exposures of the vein contains rhornbs, perhaps formerly ankerite, now pseudomorphed by quartz. The limy shale at the top of the Tynebottom Limestone is replaced, at Rotherhope Fell Mine, by sericite, quartz and sphalerite. The thick 'Black Bed' shale at Esp's Vein, Sipton Mine, (area 4) carried small, perfect cubic metacrysts of galena. No workable deposit has, however, been produced as a result of metasomatism of shale.

Secondary processes

The oxidation zone

By secondary processes are meant those which have modified the mineral deposits since their primary emplacement. It is quite clear from the nature and distribution of the primary minerals discussed in the foregoing paragraphs that their deposition was in no way related to the present or to a former land surface. It is also reasonable to conclude that the primary mineralisation of the field was completed before erosion brought the deposits within reach of the circulating groundwaters. Their texture displays few affinities with the near-surface epithermal deposits of Lindgren and none with the fumarolic deposits poured out at the surface. Many of the primary minerals are, moreover, unstable within the zone of moving meteoric groundwaters, as will be shown

Above the permanent water table, lying, except in the valley bottoms, at some distance below the land surface, there is a zone in which meteoric waters move downwards or circulate. The waters, carrying oxygen and carbon dioxide, give rise to reactions mainly of an oxidising nature. Their zone of operation has thus become known to students of ore deposits as the oxidation zone. Here ferrous minerals are converted into hydrated ferric oxide; sulphides are replaced by sulphates, carbonates, hydrous silicates, hydrous oxides or chloro-phosphates; carbonates are converted into sulphates. (Table 32) briefly summarises the mineral changes observed in the oxidation zone.

In addition to the changes listed, there is evidence of the presence of phosphate in the waters of the oxidation zone, from the existence of pyromorphite as an alteration product of galena, and from the greater phosphorus-content of the limonitic iron ores as compared with the iron carbonate protores.

The secondary minerals are discussed below, but the stable primary minerals deserve a brief notice. They include baryte, quartz, chalcedony and fluorite. There is no evidence of any attack upon the first three under oxidation-zone conditions. It is presumed that the silica which is undoubtedly carried by the meteoric waters originates from some source other than the mineral deposits, for no evidence of attack on quartz or chalcedony can be found. Fluorite, from its existence in great bulk near the surface, might at first sight be regarded as completely stable, but examination of crystals faces and surfaces shows that these are in many instances strongly etched, a feature seldom found in primary fluorite below the oxidation zone. It appears, therefore, that a little fluorite is being or has been dissolved out by meteoric waters. No instance has been found of the deposition of fluorite as a secondary minerals, save one recorded by Watson (1900), who stated that fluorite, quartz and calcite crystals were found in a stalagmite covering fallen timber during the reopening of Old Fall Mine, Weardale. The fluorite may, however, have been mechanically incorporated in the stalagmite.

Sulphates are only produced when sulphides undergoing oxidation are present. The only stable sulphate is baryte, which always forms a capping to the witherite deposits when these contain substantial amounts of sulphides, or when sulphides (e.g. pyrite) are present in adjacent strata. The soluble zinc, iron, calcium and magnesium sulphates are normally found only as the products of post mine oxidation in the drier workings, as incrustations or efflorescences. Hydrozincite also occurs under these conditions.

The depth below the surface to which oxidation may extend has been determined at a number of mines. The best example is at Boltsburn West Level, (area 5) which is driven through a belt of flats extensively worked for limonitic iron ore. At 300 ft (91 m) below surface, cores of siderite and ankerite appear in the limonite. As depths greater than 325 ft (100 m) are reached, oxidation effects die out, fresh galena, siderite and ankerite, with fluorite, filling the vein and small flats. At Carricks Mine, Weardale, the flats associated with Groveheads Low and High Veins are almost completely oxidised to depths reaching 200 ft (61 m) below surface. The workings on Lowe's Vein, on the other hand, contain appreciable amounts of carbonates at 250 ft (76 m) below surface. At similar depths, Dawsons, No. 4 Cross Vein and Maddison's Vein all carried partly oxidised carbonate ores (analyses (Table 59), p.195). The Stotfield Burn and Stanhopeburn fluorspar mines on the Red Vein (area 5) both exhibit strong limonite-staining in the vein down to depths averaging 300 ft (91 m) below surface, beneath which this effect disappears completely. It is noticeable that the silica- content of the limonite-stained fluorspar is distinctly higher on the average than that of the unoxidised vein-filling below, which has been followed to 540 ft (165 m) below surface at Stanhopeburn. The witherite oreshoot at South Moor Colliery (area 9) had a baryte capping of secondary origin, the base of which varies from 125 to 150 ft (38 to 46 m) below ground surface. Witherite was proved down to 780 ft (238 m) below surface. At Settlingstones Mine (area 8) the oreshoot worked for witherite extended from 300 to 680 ft (91 to 207 m) below surface, but dies out upwards; it is not known to have a secondary capping. At Nentsberry Mine (area 2) unaltered witherite is present in the gangue of the veins, the depth of the workings varying from 200 to 400 ft (61 to 122 m). Both at Boltsburn East and Rotherhope Fell mines, the lead-bearing flats showed no indications of oxidation, the depth of the workings being from 350 to 875 ft (107 to 267 m) in the former and from 400 to 450 ft (122 to 137 m) below ground in the latter case. It may be concluded therefore that the oxidation zone, away from the valley bottoms, may reach as much as 300 ft (91 m) below surface. There is one instance of oxidation at much greater depths, at Silverband Mine (area 1) where Slope Vein, at a depth of 450 ft (137 m) below the summit of Great Dun Fell still gives evidence of this process. Here, however, the conditions, with steep slopes on both sides of the fell, are exceptional. At the valley bottoms, unoxidised vein-minerals should theoretically be found at the surface. There are several instances in which this is actually the case. The outcrop of Browngill Vein in the bed of the South Tyne near Garrigill (area 2) contains fresh galena and abundant unaltered marcasite. Unoxidised galena may also be seen in the Force Burn Vein and in several veins near Moor House (area 7) in the beds of streams. The outcrop of Old Moss Vein and a Great Limestone flat associated with it in the bed of Killhope Burn (area 5), contains both galena and sphalerite; siderite and ankerite are also present, but these have suffered some alteration to limonite, though the process is by no means as far advanced as in comparable deposits beneath the side slopes of the valleys. In the Esp's and St Peter's veins, (area 4) galena, only slightly oxidised, continued to the sub-boulder clay outcrop of the veins against the preglacial East Allen valley.

The analyses in (Table 33) illustrate partly and fully oxidised deposits, the protores from which they were derived having been similar in composition to those illustrated by analyses 4 and 5, (Table 29). The results emphasise that oxidation increases towards completeness away from the valley bottoms; analysis 2 represents material low down on the valley side, while analysis 3 is of material remote from the nearest stream.

The proximate mineral composition of an interesting example of altered quartz-dolerite adjacent to the Great Sulphur Vein at Aglionby Beck (area 2) is given in column 8 of (Table 30); here the carbonates have been replaced by limonite, probably derived in part from the oxidation of pyrite.

Postmineralisation solution effects

The circulation of meteoric waters carrying carbon dioxide in solution led not only to the chemical changes in the mineral deposits described above, but also to the formation of caverns in the limestones, the origin of which is independent of, and later than, the primary mineralisation. It is generally considered that the reactions which take place involve the formation of soluble calcium bicarbonate (Smythe, 1926) and that the process occurs only above the permanent water-table. The widespread distribution of such caverns is suggested by the numerous swallow-holes which follow the outcrops of, for example, the Great and Scar limestones. Underground they have been encountered in a number of mines. Sopwith (1833) has given a graphic description of the caverns at Ayleburn and Hudgill Burn mines (area 2). At Lunehead Mine (area 7) a series of caverns, apparently developed along joints in the Great Limestone trending WNW have cut through the baryte veins, which 'outcrop' on the cavern sides. Undissolved lumps of veinstuff were found on the floors of these caverns. Spectacular examples also occur at Silverband Mine (area 2) (Figure 17). In both cases it is quite clear that the cavernisation occurred at some date much later than the primary mineralisation. It appears, however, that the permanent water-table was at a lower level when the caverns were formed than is now the case, for both at Silverband, and in the upper part of the Melmerby Scar Limestones cutting through Greenhush Vein at Cowgreen (area 7), the caverns were full of water when tapped. The characteristic feature of the caverns is their smooth, or fluted water-worn sides. They are in every respect different from the metasomatic flats. The only new minerals formed in them are calcite, or in rare instances minerals characteristic of the oxidation-zone, such as cerussite and smithsonite.

Secondary minerals

Cerussite PbCO3 and anglesite PbSO4

Cerussite and anglesite are the common alteration-products of galena, forming a white coating to the grains and masses of the mineral, sufficient in many instances to protect it from further alteration. Only where there has been strong alteration, as on the NE slopes of middle Fell, near Alston, have considerable masses of secondary lead minerals been worked. The best-known locality was Hudgill Burn Mine, now closed. Polished sections of galena from the oxidation zone show that the attack proceeds from the cleavages (Dunham, 1937, fig. 11). Well-developed anglesite crystals have been found at Pike Law and Closehouse mines (area 7). Masses of cerussite crystals were formerly obtainable from the upper workings of Stanhope-burn and Redburn mines (area 5), but good examples are now rare and neither cerussite nor anglesite are of commercial importance in the field.

Pyromorphite PbCl(PO4)3

Pyromorphite has been found in small quantities at a number of localities. At Hard Rigg Edge (area 1) and Closehouse (area 7) well-developed green prismatic crystals are common. At Grasshill Common and Yorkshire Silverband (area 7) it is found in botryoidal or cellular masses. These and other localities have been reported by Young (1985b), who has shown that in all cases the composition approaches the pyromorphite end-member. The mineral is not found in workable concentrations.

Smithsonite ZnCO3

Smithsonite is the most abundant zinc mineral in the oxidation zone, the so-called 'dry bone' variety being the commonest, at many places surrounding cores of sphalerite, and locally pseudomorphing sphalerite crystals. More massive, green and yellow smithsonite was formerly obtained from Farnberry and Holyfield mines; a picked sample gave on assay: zinc, 25.63 per cent; lead, 0.07; sulphur, 0.04 (assay by Mineral Resources Laboratory, Imperial Institute, 1941).

Hemimorphite Zn4Si2O7(OH)2H2O

Hemimorphite is locally associated with smithsonite. Small colourless to brown radiating crystal aggregates occur at Swathbeck Mine (area 1), Bayle Hill, Nenthead Field and Nentsberry mines (area 2) and at the Ashgillhead and Foster's Hush workings (area 7) (B Young, personal communication).

Hydrozincite ZnCO3.3Zn(OH)2

Hydrozincite was found in white massive form at Hudgill Burn Mine (area 2); it is a common product of the oxidation of sphalerite in mine workings and in dumps.

Greenockite CdS

If cadmium is present in sufficient quantity in sphalerite, greenockite forms when the cadmium is released during oxidation. The new sulphide is easily recognisable by its yellow colour. The first edition record of it at Ashgillhead has now been confirmed. Greenockite has now been identified from Blagill Mine (area 2), Greenhurth, Reddycombe, Trough and Willyhole mines (area 7) and Stonecroft Mine (area 8) (Young et al., 1987).

Malachite Cu2CO3(OH)2 and azurite Cu3(CO3)2(OH)2

These common oxidation products, usually from chalcopyrite, are widespread even in the outer zones of the orefield, but in trace amounts only. Greater amounts have been found only in the small copper veins of Tynehead and Crossgill (area 2).

Native copper

Native copperwas formerly visible in a vein in Lower Magnesian Limestone at Raisby Hill Quarry (area 9). F W Smith (1973) has also described an occurrence from the oxidation zone at Groverake Mine Firestone Level, with ferricopiapite associated. Native copper has also been found in small amounts at Cornriggs, Sir Johns Mine (area 2) and Westernhope Mine (area 5) (B Young, personal communication).

Covellite CuS

Covellite CuSis occasionally found as coatings on other sulphides, in positions which suggest incipient copper secondary enrichment.

Rosasite (Cu,Zn)2(CO3)(OH)2

Rosasite (Cu,Zn)2(CO3)(OH)2 has been described by Young et al., 1985 from Closehous Mine (area 7) and West Pasture Mine (area 5) (Young and Francis, 1989).

Aurichalcite (Zn, Cu)5(OH)6(CO3)2

This hydroxycarbonate was probably first noticed in the orefield by Sir Arthur Russell at Hilton (personal communication). It has been recorded by Young et al. (1985) at Windy Brow, Greenhurth and Foster's Hush (area 7) and in addition has recently been found at Closehouse Mine (area 7).

Limonite Fe2O3xH2O

Limonite has proved to be the most important of the secondary minerals, the great bulk of the iron-ore production of the field having been of the 'brown hematite' type. The commonest primary source, or protore, of the limonite orebodies has been the metasomatic flats in the Lower Felltop, Little, Great and Scar limestones in which the primary iron minerals present were ankerite and siderite (Plate 5). The latter oxidises first, so that a stage may be recognised where the rock contains limonite pseudo-morphs after siderite associated with fresh ankerite. At a later stage the form of siderite is lost, but ankerite pseudomorphs may be recognised in the mass of limonite. At a still-more-advanced stage, these too disappear and bands of crystalline geothite appear in the otherwise amorphous limonite. Rarely, a little red hematite may be formed, but the hydrated oxide is normal. The combined water in the limonites of the field generally exceeds 1 molecule to 1 molecule ferric oxide, as shown in (Table 33) and 34, compiled from analyses of limonitic iron ores on the approximately correct assumption that all the combined water is in limonite and hydrous manganese oxides.

A comparison of the analyses of iron ores presented in the detailed descriptions of mines which follows shows that the carbonate ores are on the average less siliceous than the limonites. General experience shows that while 5–8 per cent of silica may be expected in carbonate ores, limonite ores seldom average below 15 per cent. The oxidation process is accompanied by removal of magnesia (which may perhaps be redeposited as secondary dolomite, though proof is lacking) and lime, but the increased silica content cannot be accounted for merely by residual concentration. New silica appears to be deposited as an intimate intergrowth of chalcedony with limonite. There is also, on the average, an increase in the phosphorus-content as oxidation proceeds.

Limonite is also produced from pyrrhotite, pyrite and marcasite. Limonite pseudomorphs after pyrite are fairly common. Epimorphs displaying the tabular form of marcasite are found; they may be coated with a film of sulphur, as at Harehope Gill Mine, Weardale.. Sulphur is liberated from marcasite on oxidation; it may be recollected that the Stokes method of determining pyrite and marcasite depends upon this property (Allen and Crenshaw, 1914).

Most of the limonites contain manganese as a subsidiary constituent, probably as psilomelane and pyrolusite. Manganese-contents of 3–5 per cent are normal; in a pocket of black-stained limonite discovered in Groveheads opencut, Carricks Mine (area 5), 13.6 per cent of manganese was recorded.

Psilomelane (probably H4Ba2Mn8O20)

Small amounts of black botryoidal psilomelane have been found on the dumps from workings on the Remmingtons Vein on the E side of Great Dunn Fell (area 1). Traces of pyrolusite (Mn02) may also be present. (B Young, personal communication).

Cinnabar HgS

Cinnabar HgS has been found in very small amount encrusting 'dry bone' Smithsonite at the Nattrass Mines (area 2) as an oxidation product of sphalerite (Young et al., 1989).

Baryte BaSO4

Secondary baryte, forming the capping of witherite deposits may readily be distinguished from the primary mineral by the fact that it occurs as very fine-grained banded incrustations or as an open mesh of tiny, ill-formed crystals, commonly associated with limonite.

Other sulphates

Secondary gypsum CaSO42H2O has been identified at the Hilton Mines (area 1) in limonite near pyrite undergoing oxidation, and as efflorescences at Brownley Hill and Smallcleugh (area 2), Boltsburn (area 5) and elsewhere.  Epsomite MgSO4.7H2O occurs in the ankerite-rich flats at Smallcleugh (area 2), together with melanterite FeSO4.7H2O. In material collected from the witherite workings at Ushaw Moor Colliery, Smythe (1933) identified goslarite ZnSO4.7H2O (containing nickel, manganese, iron and magnesia in solid solution), epsomite, and melanterite, both containing small amounts of the other sulphates. His account contains full analyses, the results of which indicate limited solubility-relations between the monocline melanterite and mallardite (MnSO4.7H2O) on the one hand, and the rhombic goslarite, epsomite and morenosite (NiSO4.7H2O) on the other. Chalcanthite CuSO4.5H2O of post-mine formation has been noted at Groverake Mine together with ferricopiapite Fe5(SO4)6O (OH).2OH2O (Smith, 1973). Linarite PbCu'SO4)(OH)2 has been observed at Smittergill Head (area 2) (Young, 1985) and at Tynebottom Mine (area 2) where it is commonly associated with a little brochantite Cu4(SO4)(OH)6, chrysocolla (Cu, Al)2H2Si2O5(OH)4.nH2O and rarely with traces of wroewolfeite Cu4(SO4)(OH)6.2H2O (Braithwaite, 1982). Bridges (1987, p.169) described serpierite Ca(Cu, Zn)4 (SO4)2(OH)2.3H2O and devilline CuCu4(SO4)2 (OH)6.3H2O as post-mine encrustations at Smallcleugh and Tynebottom mines (area 2).

Erythrite Co3(AsO4).8H2O

Erythrite Co3(AsO4).8H2O is common as a post-mine encrustation at Tynebottom Mine, Garrigill (Dunham, 1931). Traces of the mineral have also been noted at the nearby Rotherhope Fell Mine and on the dumps from an old copper trial in Crossgill (area 2) (B Young, personal communication).

Annabergite Ni3(AsO4)2.8H2O

Annabergite Ni3(AsO4)2.8H2O has been recorded as an encrustation on niccolite at Hilton Mine, Scordale (Bridges, 1978) and at Lady's Rake Mine, Teesdale (Young et al, 1985). Small specimens have also been obtained from Smallcleugh Mine, Nenthead though without obvious primary nickel minerals (Bridges, 1983).

Origin and age of the deposits

Historical

Westgarth Forster confined his classic treatise (1821, part II) to a factual description of the deposits. Sop-with (1833) likewise refrained from speculation as to their origin. Taylor (1834) emphasised the concentration of ores at particular stratigraphical horizons, confirming Forster's earlier observations, and urged that theories implying injection from below must be considered in the light of this phenomenon. Leithart (1838) suggested that the formation of veins and their filling was due to terrestrial electricity. His conception of the origin of the monomineralic bands in the veins (pp.81, 82) in terms of what would now be called 'plating-out' may yet prove to be justified. The first comprehensive genetic theory was, however, that of Wallace (1861) who, having described the structural and stratigraphical relations of the deposits, concluded that they were formed from downward-moving meteoric waters, and proposed five laws regulating the descent of water below the earth's surface. In these he related the quantity of water in circulation directly to (i) the nearness to surface; (ii) distance from watersheds; (iii) inclination of strata towards the hillsides; (iv) openings traversing the rocks; and related the quantity inversely to (a) steepness of slopes and (b) inclination of strata towards the hill-summits. Wallace believed that anticlines separated the Nent and West Allen valleys (justified by recent observations; see (Figure 20) and the Tyne and Wear valleys (not confirmed). In terms of these he explained the circulation of underground waters and the mineralisation of Alston Moor. His account, is mainly valuable now for the wealth of careful observation which it contains, including the recognition of the important part played by metasomatism, but it is also interesting as an exposition of the theory of 'lateral secretion' carried to its logical conclusions. It again emphasises the importance of the Great Limestone and adjacent strata as bearing-beds. In De Rance (1873) Wallace found a disciple. To the 'lateral secretion' hypothesis Goodchild (1889) provided an answer by demonstrating that the composition of the deposits is quite independent of the lithology of the rocks in which they occur. He concluded that the deposits were emplaced 'by the agency of thermal springs rising through pre-existing channels, under conditions of great pressure', during the cycle of Tertiary igneous activity. As evidence that mineralisation postdated the last major phase of tectonic activity, Goodchild pointed to the perfectly unbroken crystal faces of many of the minerals found in the veins. Phillips and Louis (1896) recorded that the Cleveland (Tertiary) dyke is of later formation than the Doukburn Vein, near Tynehead. Watson (1900) produced evidence of sphalerite, fluorite, quartz and calcite of recent formation, and on this basis supported the meteoric theory. Finlayson (1910a and b) in two notable papers classified the deposits as of Hercynian age and of gas–aqueous origin; but, in reply to Goodchild, postulated redistribution of the minerals by underground atmospheric waters. J D Kendall (1921) advocated a similar hypothesis.

Both authors were impressed by the limited vertical range of the deposits, as was Carruthers and Strahan (1923). More conclusive evidence that the primary mineralisation was brought about by hydrothermal solutions has in recent years been provided from two lines of approach (i) the variation in composition of the deposits, noted by Forster (1821, p.269), Goodchild, Smythe (1922) and Miss Sweet (1930) was worked out in detail by Dunham (1934), demonstrating mineral zoning on a broad scale, which pointed to mineralisation from a small number of emanative centres; (ii) the alteration of the Whin Sill dolerite, studied by Finlayson (1910a), Wager (1929) and Smythe (1930) provided evidence that the composition of the vein-solutions and their effect on the dolerite was quite different from that of normal meteoric waters, which are not capable of producing intense carbonate-sericite alteration. Hancox (1934) investigated the relations of baryte and witherite in the witherite veins, showing that witherite was developed by replacement of baryte. The occurrence of minerals of the Pennine suite in the Permian Magnesian Limestone of east Durham, already known through the investigations of Trechmann (1914, p.258) and Smythe (1922) has been shown to have quantitative significance by Fowler's discovery (1943) of widespread fluorite and baryte in the Lower Magnesian Limestone. From this and from tectonic arguments, Trotter (1944) assigned the deposits to the Tertiary. Trotter (1954) was the first to recognise the coincidence of the area in which Namurian coals have been devolatilised beyond his lower critical limit of 37.5 per cent volatiles with the three inner mineral zones of Dunham (1934) on the Alston Block. The conversion to high rank he ascribed to the combined effect of tectonic pressures associated with the thrusting along the Inner Pennine fault-system, and magmatic heat, of which he also regarded the northern Pennine ores as an expression. Semibituminous rank in the Westphalian coals was held to correspond in a general way with mineral zones IV and V (Dunham, 1934, plate 18). It was clear at this stage that no coincidence could be established between the Whin sills and the rank of the coals (save where quartz-dolerite intrusions were in physical contact with the seams, and equally that the mineral zones were in no way related to the heat of the sills.

The proving of the Weardale granite batholith, forecast by the gravity survey of Bott and Masson-Smith (1957) never- theless failed to provide evidence of a widespread source of magmatic heat beneath the Pennines in post-Carboniferous time, since the batholith was already being eroded when the first Carboniferous sediments were laid down. However, it became clear that the outer margin of the fluorite zone (III) corresponds closely with the margins of the batholith as deduced from the geophysical evidence except to the E of the orefield, where the principal bearing horizons disappear beneath younger, and generally unfavourable cover rocks. It was therefore suggested by Dunham et al. (1965) that the granite provided structural channel-ways for hot fluids rising from below; but it must be emphasised that the presence of hydrothermal solutions in the veins could not possibly bring about a general heating of the country rocks sufficient to explain the zoning of coal rank, in spite of the correlation of these zones with the buried granite.

Mineralisation temperatures

At this stage in the investigation it had become important to establish the absolute temperatures at which the minerals in the veins and flats were deposited. The initial work was undertaken by Sawkins (1966) using the fluid inclusion method, first proposed by H C Sorby in 1858, but neglected until the 1920s. In the Pennine orefields, fluorite is the most useful mineral for this purpose, since unbroken primary inclusions containing a liquid phase and a gas phase are nearly always present; the temperature of homogenisation plus a small correction for pressure at the time of formation yields the mineralisation temperature. Consistent and reproducible results are obtained, and the method has won wide acceptance. The inclusions are normally of microscopic dimensions, suitable for investigation in thin section on a heating stage. However, Rankin (1978) states that of 770 specimens of the mineral from northern England in the Main and Russell collections of the British Museum (Natural History) (almost all from the present area), 21 contain inclusions visible to the naked eye, ranging from 1 x 1 x 2 mm up to 24 x 17 x 4 mm. Sawkins also examined cavities in quartz, calcite and baryte; none was found in witherite. His adopted pressure correction was 11°C. (It should be noted that this was not the same as that adopted by Rogers (1978) in the Askrigg Orefield; he used + 8°C in Swaledale, + 15° in Wensleydale and Wharfedale (see Vol. 2, p.102). Sawkins' results on 650 inclusions in 70 samples from 30 representative localities showed 216–181°C on quartz from the Great Sulphur Vein in the central zone; a range from 177° in the central parts of the fluorine zone down to 110° near the margins, determined mainly on fluorites but also using some quartz; only one specimen (from Nentsberry, close to the margin between the fluorine and barium zones) showing two-phase cavities in baryte, indicating 126–129°, all the remaining barytes having liquid filling, indicating temperatures of 50°C and below; and a single instance of late calcite in the fluorine zone showing 78–84°C. No clear evidence that green fluorite forms at higher temperatures than purple was obtained, but the amber coloured variety characteristic of the outer margin of the zone or late in the sequence forms at the lowest recorded temperatures, along with some pale mauve varieties. More recently, F W Smith undertook detailed surveys of the fluorspar oreshoots accessible underground at the mines of the Weardale Lead Co. and British Steel Corporation. The overall ranges agree with those found by Sawkins, but using filling temperatures in the first-formed fluorite bands, it has been found possible to trace the flow of the solutions (Phillips and Smith, 1974) and to produce isotemperature lines for the large oreshoot at Groverake Mine (Greenwood and Smith, 1977, fig. 3) where a range in temperature from 194° to 133°C was observed. (Smith used a pressure correction of 29°C at the base of the Namurian, increasing at 0.015°C/m with depth). Temperatures along the Slitt Vein of Weardale proved to be on average lower than those recorded from fluorite on the Rookhope Red Vein system, on which Groverake Mine is situated (F W Smith, personal communication). At Cambokeels Mine where Slitt Vein has been developed in beds from the Scar Limestone down to the Whin Sill (p.212) Bailey (1977) investigated cross-sections of the unstressed South Lens on the 160 and 200 m levels taking serial samples from the wall to the centre of the vein. Against the wall, homogenisation temperatures in quartz showed initial values of 195–207°C. Fluorite temperatures showed an inward drop to 150° before rising again to 172–178°; there was then a fall to 150° at the vein centre. Two surges of fluorite mineralisation are thus clearly indicated, and it will be noted that these cross-sections show a range of filling temperatures equivalent to approximately the upper half of the total range found by Sawkins and Smith. It may be recalled, however, that Sawkins worked mainly on good crystals derived from the central cavities of veins, while at Groverake Smith sampled consistently 1 ft (0.30 m) from the vein wall.

If the geothermal gradient in the country rock was similar to that obtaining at present in the Rookhope boring, determined by Bott, Johnson, Mansfield and Wheildon (1973) as 34.5°C/km in Carboniferous sediments and Whin Sill to 426.7 m depth, and 31.1°C/km in the underlying granite, and assuming, following Trotter (1954), that 1.1 km of overlying sediments have been removed, the temperature at the base of the Carboniferous could hardly have been above 70°C, a figure of 250°C would not be reached at less than 5 km below the top of the granite. In that case, as Sawkins claimed, a marked difference in temperature between the mineralising fluids and the wallrocks would have existed at the time of mineralisation. The devolatisation of the Carboniferous coals, however suggests that this may not have been the case. A detailed investigation covering the orefield, by Creaney (1980) and of a wider area by Creaney, Allchurch and Jones (1979) in which the vitrinite reflectance method was applied to samples of coal and other carbonaceous rocks, showed that heat-flow prior to (and unrelated to) the intrusion of the Whin sills gave rise to general rock temperatures of 185°C at the level of the Great Limestone, around the concealed margins of the Weardale Granite; and further, that since the isoreflectance surface is domed over the granite, the heat flow must have been channelled through the granite. It is, of course, clear from the fluid inclusion data that the Brigantian and Namurian rocks had cooled below 185° soon after the onset of mineralisation occurred , but it is likely that the area of the fluorine zone was substantially above the temperature of 70°C. Phillips and Smith (1974, p.19) state that measurement of about 600 mean primary filling temperatures covering different stratigraphical horizons over a vertical range of above 1 km has established minimum formation temperatures at each horizon; these fall on a gradient equivalent to 75°C/km, which they suggest approximates to the geothermal gradient at the time of vein-filling. The figure appears reasonable for the decaying phase of a period of abnormally high heat flow such as the devolatilisation of the coals demands.

Heat flow through the Weardale Granite

The zonal pattern of the mineralisation centres upon the concealed cupolas of the Weardale Granite. The thermal history of the granite from late Stephanian time is relevant. Present heat flow through the granite was investigated by Bott et al. (1972), who found that in that part of the granite penetrated at Rookhope, the thermal gradient is 31°C/km, compared with 34.5°C/km in the overlying Asbian–Brigantian sedimentary rocks. The thermal conductivity of the granite (21 samples) was found to be 2.94 W/mK (Wheildon and Rollin, 1985, table 2.2). By implication, the conductivity of the Carboniferous section at Rookhope is 2.7 W/mK. These data indicate a present heat flow at Rookhope of 95.4 mW/m2 of which 42 per cent can be ascribed to the radioactive minerals of U + Th + K in the granite.

From 1980 to 1985, a series of studies of high heat-producing granites, started by Plant et al. (1980) led to the suggestion that granite plutons able to contribute extra heat to the regional flux and also having higher thermal conductivity than the rocks which they intrude may promote convection of mineralising fluids. This concept was applied specifically to the sub-Pennine granites by Brown et al. (1987) who list in full the several other contributions. While there is little doubt that radiogenic heat played its part there, a case may also be made in favour of a major heat flow event of limited duration in the history of the Northern Pennines.

The evidence comes from the devolatilisation of the Namurian coals between the Great and Little limestones to form semianthracites. Trotter (1954) noted that the area of coal metamorphism coincides roughly with the mineralised area of the Alston Block, and suggested a connection. Any hypothesis that requires the mineralising fluids to transport sufficient heat during convection to achieve this widespread and consistent alteration of the coals must be rejected. With a density of one vein or less per km2, sufficient fluid could not possibly be carried to raise the temperature of the whole rock mass through 150°C. Creaney (1980) found, from vitrinite reflectance studies that a temperature of at least 185° was required. This was in no way directly related to the intrusive Whin sills, which however cause coking of the coals near their contacts. Creaney's petrographic studies of the coke led him to claim that anthracitisation had already occurred prior to Whin intrusion at 293 Ma. The area of coal metamorphism coincides with the outline of the concealed Weardale pluton so closely that it cannot be accidental; it may therefore be concluded that heat flow through the granite raised the temperature at the level of the Great Limestone to at least 185°C by 293 Ma (Dunham, 1988a and b). It has been claimed (Brown et al., 1987) that the normal flux with its radiogenic component could bring this about as a result of the blanketing effect of the sedimentary cover above the granite. In Stephenian–Zechstein times the maximum thickness was 1.6 km plus any late Silesian sediments subsequently removed, making the total cover perhaps 2 km. The recent European Geothermal borehole at Soultz-sous-Forets, Alsace (Kappelmeyer and Gerard, 1989) may suggest a model. The borehole through Tertiary petroleum-bearing sediments, thin Jurassic and thick Trias, entered granite at 1.375 km in the core of an elaborate fold/fault structure. The temperature at the sediment/granite contact is 126°C, while 116°C at different depths in the Buntsandstein/Muschelkalk aquifer show that horizontal convection is taking place. At the bottom of the hole at 2 km, the temperature has only risen to 140°C. A modest heat flow of 80 mW/m in the granite, with a low gradient, provokes gradients as high as 100 c/km and heat flows of 150–200 mW/m2 in the sediments (K Rollin, in litt.). The sedimentary section at Soultz contains highly permeable members, and the probable thermal conductivity is low, less than 2 W/mK.

The model, though attractive, may not apply satisfactorily to the Weardale case. The required heat flow at the time of coal metamorphism may be estimated as at least 225 mW/m but the sedimentary section, both Dinantian and Namurian, cannot have been other than impermeable. Sharpness of contacts between dykes and vein fractures and the sediments shows that diagenesis was complete before Whin intrusion and mineralisation, and present thermal conductivities may differ little from those of 293 Ma. Heat transfer would be by conduction, virtually unaided by convection, and at the granite/sediment contact a heat flow of about 200 mW/m2 would be required. The radiogenic contribution to this would only be one fifth of the total. The model here preferred thus includes a major input of heat from the mantle, no doubt associated with fusion to produce the tholeiite magma which rose up widely separated fractures in the Upper Crust, from which the Whin sills were fed (Francis, 1982). The area of mantle fusion exceeded 4000 km2 extending from what is now Stainmore to the Fame Islands and the Midland Valley of Scotland. Its heat flow extended high into the Upper Crust in the present area because the thermally conductive Weardale Granite made this possible.

This Hercynian magmatic episode is not known to have produced granite on any scale beneath the Alston Block, but if the heat flow at the top of the granite at 293 Ma, quoted above, is correct the possibility that fusion temperatures in the lowest part of the granite were reached can hardly be ruled out. Above the Great Limestone the temperature gradient at this time must have been about 75°C/km until the episode ended and the rock temperatures began to fall. At this stage the elaborate fissure system which became the vein pattern originates, providing secondary permeability in the otherwise impermeable Carboniferous rocks. The way was now open for convective circulation, probably upward through the granite, but horizontally outward in the sediments (Dunham, 1988a, fig. 2). There is some evidence that mineralisation began while metamorphism adjacent to the Whin Sill in Teesdale was still in progress (p.75). The bulk of the mineral deposits were, however, emplaced after the ambient rock temperature over the granite had fallen to about 100°C. Into this environment flowed fluids initially at over 212°C. At present this temperature is predicted in the Weardale Granite at 7 km depth (British Geological Survey, 1988, fig. 9.1) but according to the model here outlined for the Stephanian–Zechstein interval, the necessary heat would be available at less than half this depth in the waning phase of the pre-293 Ma thermal event.

Nature of the mineralising solutions

There is general agreement that the deposits originated from aqueous solutions; melts of the minerals could not exist within the introduced mineral suite, the alteration of the Whin Sill indicates that abundant carbon dioxide and potassium were available in solutions reaching the sills and that sodium, iron, magnesium and at many places silica were contributed to the solutions by the alteration process. It can be stated categorically that meteoric waters circulating above the water table could not produce the primary deposits, for here the fugacity of oxygen is much too high, producing the highly oxidised secondary mineral suite (p.88). At or near the water table dissolved oxygen ceases to be available, and here secondary sulphides may form from other pre-existing sulphides, as in the secondary enrichment process. This process seems, however, to be of very little importance in the Pennine orefields. The deposits in the oxidation zone do indicate, however, that calcium, magnesium, iron, zinc, phosphorous and possibly small amounts of fluorine and barium undergo restricted movement above the water table. By far the commonest product of phreatic water is however calcite or aragonite.

Experience from the development of underground water supply, and more particularly from oil-well drilling has shown that with increasing depth below the water table there is a marked increase in salinity. Apart from those cases where contamination from inflow of sea water has occurred, this is due to at least three factors: (1) presence of connate or trapped sea water in buried sediments (2) solution of evaporites (3) repeated membrane filtration of migrating water through partly consolidated clays or shales. The concept that a limited zone of static water gives place at depths of only a few km to dry rock implied in the first edition of this memoir cannot be supported, for saline water is still present at the greatest depths, approaching 10 km, penetrated by drilling into permeable rocks. Data from White, Hem and Waring (1963) on the composition of subsurface waters show, as the plots in Dunham (1970, figs. 1–3) illustrate, that carbonate waters tend to coexist with or give place to sulphate waters down to about 650 m below the water table, but that beneath this, chloride waters greatly predominate, their concentrations reaching at least six times that of sea water. Sodium and potassium take over as the principal cations from calcium at depths generally less than 650 m.

This vast body of saline underground water, as Lindgren (1935) had already begun to recognise, cannot be neglected in any consideration of the origin of shallow, low-temperature mineralising fluids, and it is no surprise to find that the fluids trapped in the sealed inclusion cavities in the fluorite and other minerals of the orefield are, in fact, highly concentrated brines. Sawkins (1966) carried out freezing experiments indicating, for the fluorine and innermost zones, the equivalent of 6.9–23 weight per cent NaCl (compared with a total salinity in sea water of 3.43 per cent), substantially higher results being obtained on specimens from the outer barium zone. The ratio K/Na was found to decrease from 0.109 (average of six samples from the fluorine zone) through 0.091 in the intermediate zone to 0.032 (five samples from the barium zone).

Warm water has only rarely been encountered in the mines and only one partial analysis is available. This refers to a warm spring cut at the E end of the 240 m level at Cambokeels (Cammock Eals) Mine, Weardale (area 5), which carried: Ca 1750 ppm, Mg 75, Na 2500, K 40, Cl approximately 1700, Zn 0.6, Fe 0.4 (data from Weardale Minerals Ltd).

Most of the elements in the introduced minerals are virtually insoluble in pure water and have only very limited solubility in carbonated water. Hypersaline brine, on the other hand, is a much better solvent, probably mainly as a result of formation of chloride complexes by the metals.

Nriagu and Anderson (1970) found that chloride complexing is responsible for large solubilities of PbS in neutral to weakly acid concentrated brines; they concluded that it was unlikely to cause significant migration of copper at moderately low temperatures. The brine solutions are capable of carrying sulphur in sufficient quantity, and there is evidence that bisulphide complexing (e.g. Helgeson, 1969) also plays an important part. The fact that the solubility of some chloride complexes (e.g. ZnS-Cl) increase with falling temperature might present a difficulty if temperature is regarded as the principal control of precipitation, but H D Holland (personal communication) finds that this difficulty does not apply to the relevant fluorine complexes, and there is every likelihood that such complexes existed in the inner zones of the field during mineralisation. It is concluded that the aqueous fluids contained the following constituents at some stage in their primary courses (arranged in rough order of abundance): Cl-, Na+, Ca+, Mg+, K+, F-, S2-, HCO3, Ba+, Fe+, SO-4, Pb+ Zn+, Cu+, Mn+ with minor amounts of Ag+, Ni+, Co+, As-, Cd+, Rb+, Y+ and other rare-earth elements. The chemical evolution of such fluids is necessarily complicated, and it cannot yet be claimed that it is understood. However, Holland (1965), who has applied thermochemical data to the problem, has delineated fields in which the minerals of the Pennine suite could form at temperatures up to 250°C; to quote a single example, at that temperature, there is a field defined by log fO2 = -37 to -39.5, log fS2 = -13 to -14.2 where at fCO2 = 1 atmosphere and in the absence of silica, chalcopyrite, galena, blende, pyrite, siderite, calcite and witherite could coexist. As more experimentally determined thermodynamic data become available, it should eventually become possible to define closely the conditions in the multicomponent system represented by the solutions active during mineralisation.

In the Northumberland–Durham Coalfield, hypersaline brine feeders have been encountered at a number of different localities, generally in workings more than 1000 ft (305 m) below OD the compositions of which exhibit most of the characteristics of the brines here under discussion. Bedson (1877) first described brine from the Brockwell Seam at Redheugh Colliery, Gateshead, containing BaC12 1372 mg/1, CaCl2, 21058; MgC12, 3127; NaC1 59265; LiCl, 358. Anderson (1945) recorded ten other localities, with BaC12 ranging from 741 to 2676 mg/1. For many years until the 1940s, deep brine at Backworth Colliery, north of the Tyne, was pumped and used for the manufacture of blanc fixe. Edmunds (1975) selected, on the basis of the National Coal Board's file of 100 analyses of brines from their workings, 13 principal localities for sampling and detailed analytical study. Though a fairly wide range of compositions was found, mean figures show the characteristics suficiently well for the present purpose: Ca, 1849 mg;51; Mg, 387; Sr, 105; Na, 8964; K, 227; Li, 6.2; Rb, 0.34; Cs, 0.01; Fe, 20; Mn, 5.6; Ag, 0.004; As, 0.0013; Cd, 0.0016; Co, 0.026; Cr, 0.004, Cu, 0.017; Ni, 0.167; Pb, 0.023; Zn, 0.036; F, 0.2; Cl, 63670, Br, 121; I, 0.96; HCO3, 96. Of the thirteen samples, three carried appreciable sulphate and no barium; the remaining ten showed a range from 92 to 4180 mg/1, the highest figure being from Backworth. The total determined constituents indicate a salinity more than three times that of sea water. If they were evolved from sea water trapped in the Carboniferous sediments when they were flushed out, as Edmunds suggests, the processes being base exchange and reverse osmosis, they are enriched in calcium, lithium and the base metals relative to sea water, but (except for samples from the southern end of the coalfield, perhaps affected by Permian water) they are depleted in sodium, potassium and magnesium. Fluorine is depleted, iodine considerably enriched. If, as experience when they were first found showed, these chloride brines are allowed to mix with sulphate waters derived from solution of evaporites, or from the oxidation of pyrite, baryte is precipitated and it is possible that some of the small baryte deposits found in the Westphalian strata could have formed by some such process of natural mixing. The large witherite and baryte-witherite oreshoots in Area 9 are, however, very unlikely to have formed in this way. For the scattered baryte occurrences in the Ferryhill district, mainly in Lower Magnesian Limestone, Hirst and Smith (1974) have advocated mixing of Coal Measures chloride brines with sulphate in the Permian; but they recognise that the yellow fluorite, associated with the baryte, which formed at 104–107°C from fluids six times as saline as sea water, presents some difficulties.

In an endeavour to trace the source of the reduced sulphur species and the sulphate in the mineralising solutions of the orefields, Solomon, Rafter and Dunham (1971) investigated the isotopic composition of sulphur in 81 samples from the outer zones. Oxygen isotopes were also determined for the barytes, all the determinations being made by Dr Rafter at the Institute of Nuclear Sciences, Lower Hutt, New Zealand. The isotopic composition of sulphur in 26 anhydrites from the Durham Permian and elsewhere was also examined. Delta 34S values with respect to meteoritic sulphur were found to range from + 15.0 to - 5.9. Sphalerites from a vein, possibly connected with the Rookhope Red Vein cut in the Weardale granite gave the highest positive values, 15.0, 14.4; pyrrhotite nearby showed 14.0, 12.2, 11.7; chalcopyrite from the earliest phase of mineralisation at Groverake Mine gave a mean value of 10.3, while the results for galena ranged downwards from + 11.7 in the centre of the fluorine zones, to become mainly negative in the barium zones. Baryte, except where secondary after witherite, shows a more restricted range of delta 34S values from 17.0 to 22.2, oxygen values being equally steady. The mean value for sulphur in baryte proved to be twice that of anhydrite sulphur in the Permian except at Ferryhill, where the correlation was close. A Permian source for the brine, suggested by Davidson (1966) must thus be ruled out except for the Ferryhill area, but the sulphate in the outer zone baryte of the orefield could reasonably have come from Lower Carboniferous waters since the value is consistent with that in Lower Carboniferous anhydrite. Formation temperatures based on partition of sulphur isotopes between coexisting sphalerite and galena gave a reasonable agreement with fluid inclusion results in 7 out of 12 samples examined; in three cases the isotope temperature was appreciably higher, in two appreciably lower, and one impure sample from Killhope gave a very high, unacceptable result.

Comparing the Alston Block figures with those for the zoned lead-zinc-fluorite-baryte deposits in the Derbyshire Pennines (Robinson and Ineson, 1979) the delta 34S values there range from + 7 in the eastern zone, characterised by fluorite with baryte to -23 in the western calcite-baryte area; the values also decrease with time of deposition. On the other hand the baryte, mostly of the 'cawk' variety unknown in the northern Pennines, shows a very wide spread in both delta 34S of +23, to +4, and of delta 18O of +9 to -26. Between Derbyshire and the present field, 12 samples from Greenhow-Skyreholme at the southern margin of the Askrigg Block (Mitchell and Krouse, 1971) gave for sulphur in galena a very much more restricted spread of -0.6 to -3.8, averaging -2.2 ± 1.1, close to the Canon Diabola meteorite standard (CDT). However, the wider area of zoned mineralisation in the Askrigg Block has not yet been investigated for S isotopes.

The conclusion reached by Solomon et al. (1971) was that deep Carboniferous chloride-dominated formation waters were convected upward through the Weardale granite cupolas to become the primary mineralising fluids (see Dunham, 1988b, fig. 2) while much shallower SO4 water reached the outer zone by migrating up-dip, eventually leading to precipitation of baryte by mixing with the residual primary fluids. These are known to have carried the barium through the fluorite zone (Solomon, 1966). Support for this general concept has come from stable isotope investigations on inclusion fluids from quartz, fluorite and baryte by Shepherd et al. (1982) and particularly by Moore (1980), whose very full results unfortunately remain unpublished. One of the barium brines, from a spring in Eccles Colliery, was among the brines from the Durham undersea coalfield investigated for oxygen and hydrogen isotopes by Shepherd and Langley (1984). Though slightly enriched in deuterium compared with modern meteoric water, it is concluded that this brine is probably of fossil meteoric origin. At no stage has positive evidence either of juvenile or connate waters been found during the isotopic investigations. While it is recognised that both are probably no more than philosophical abstractions, mixing of trapped fossil sea water with meteoric water is not ruled out by the evidence.

In certain parts of Zone IV and V there is evidence of a strong flow of carbonate-rich water at a late stage in the mineralisation process. Hancox (1934) investigating the relationship of witherite and baryte at Nentsberry, produced strong evidence that the carbonate was formed by replacement of the sulphate. This surprising result was confirmed in 1954 at Settlingstones, in the area near the Grindon Cross Vein where the large witherite oreshoot gave place to banded baryte–galena in both the N and S veins (p.265). Here it is certain that the massive baryte was carbonatised to witherite, for the galena bands hang almost unsupported through cavities in the carbonate: the witherite contains tabular pseudomorphs, clearly after baryte. It is not conceivable that reaction could have been brought about by cold HCO3 groundwaters, but as yet no experimental or fluid inclusion evidence is available to show at what elevated temperature it took place.

Mine water containing barium carbonate has been recorded in the vicinity of the South Moor Witherite deposit, but this may merely be due to the solubility of the witherite in the local groundwaters. The concentration of barium is in no way comparable with that in the brines mentioned above.

Origin of the deposits

The following is a brief summary of the results of the Geological Survey investigation, and of later work already described mainly at the University of Durham, bearing upon the problem of the genesis of the ores:

i The deposits are restricted, for practical purposes, to hard beds in the stratigraphical succession. Although the greatest concentrations are in and near the Great Limestone, deposits have been found in almost every hard bed in a succession more than 3000 ft (914 m) thick. The restricted vertical range of individual oreshoots is clearly conditioned by local stratigraphical and tectonic factors, not, as had been suggested, by any relation to an ancient groundwater-level or land surface.

ii Owing to the stratigraphical control, the great majority of oreshoots pinch out both upwards and downwards. Their form, therefore, supplies no clue as to the upward or downward movement of the mineralising fluids. It may, however, be significant that oreshoots tend to be concentrated at the crests of anticlines, or on the upthrow sides of strong cross veins.

iii The relationships suggest that, in some instances at least, the solutions were under sufficient pressure to keep apart the walls of the veins.

iv In a few instances, oreshoots with considerable downward extensions, the bottoms of which have not been proved, are known; Burtree Pasture, Groverake, Slitt, Cam-mock Eals and Rotherhope Fell are examples. It is suggested that these correspond with the restricted channels up which the primary solutions rose. On reaching hard beds in which there were suitable openings (generally in the form of laterally extensive channels) the solutions spread out more or less horizontally.

v In conformity with this, mineral zoning proves to be more apparent in a lateral than a vertical sense. A similar lateral spread has been noted by Dines (1933) in the outer zones of the Cornish district. The innermost zone indicates the position of emanative centres, some of which correspond with the vertical channels mentioned above; in other cases, including Tynehead, Westernhope and Merkiel the channel has not yet been located or explored. No doubt other centres not yet revealed by erosion exist.

vi Prior to 293 Ma a heat-flow event created temperatures around 185°C which caused devolatilisation of the Namurian coals. Since the area affected corresponds in outline with that of the 410 Ma Weardale Granite beneath, it appears that the heat was transmitted by conduction though the granite, its source being a mantle hot-spot, or lower crustal magma, or both. Intrusion of quartz dolerite magma as sheets in the Carboniferous fed by widely spaced dykes now followed. Lead-zinc mineralisation began while contact metamorphism by the dolerite was still in progress, but the main phase of convective flow of mineralising fluids followed tectonism that produced the Teesdale dome and the associated pattern of vein fractures. Probably the convection was initially driven by residual heat from the hot-spot, but the country rock had cooled to below 100°C while the fluorite zone was formed in an area also reflecting the outline of the concealed granite.

At the emanative centres, fed through the granite, temperatures above 210°C were attained, but at the zone margins the temperature had dropped to about 100°C.

Deposition outwards from the centres to the edge of the fluorite zone was temperature controlled.

vii The position with regard to the formation of baryte and witherite is less satisfactory. No measureable fluid inclusions have been found in the carbonate, and for baryte a few results between 100 and 125°C have been obtained but much of the baryte gangue may have formed below 70°C. If this is correct, a rapid falling-off in temperature in zones IV and V is implied. The carbonatisation of baryte to form witherite in large bodies must however, have involved the activity of substantial volumes of HCO3-bearing water at elevated temperatures, probably at pH well below neutral.

viii In the sulphides, sulphur isotope ratios show wide-ranging changes in conformity with the lateral zonal pattern, from ä34SCDT = 16 in the centre to values near neutral at the fluorine/barium boundary, and with negative values down to–5.6 in zones IV and V. Sulphate sulphur in baryte, on the other hand, varies only a little around ä34S = 20, and ä18Osmow is equally consistent around 12. The data for baryte correspond with accepted values for Lower Carboniferous evaporites but, except at minor localities in the Lower Magnesian Limestone, are very different from values for Permian sedimentary sulphates.

ix The fluid trapped in primary inclusions in the minerals is a chloride brine with up to six times the salinity of sea water as indicated by freezing experiments. The mineralising waters were therefore hypersaline brines. The ratio K/Na falls concordantly with the lateral zoning from 0.9 to 0.3. Brines with average salinity about three times that of sea water remain trapped in various parts of the Westphalian strata of the adjacent Northumberland–Durham Coalfield until released by deep mining. Some of these contain as much as 4000 mg/1 barium. They are enriched in calcium but depleted in sodium and potassium if the solute composition is compared with that of sea water, and the metals lead, zinc, copper, cobalt and nickel, though present only in small fractions of a mg/1, are enriched relative to sea water.

x The primary mineral suite quartz, pyrrhotite, marcasite, chalcopyrite, galena, fluorite, sphalerite, siderite, ankerite, pyrite, baryte, witherite with minor sulpharsenides and sulphosalts and barium-calcium carbonates had been emplaced before erosion of superimcumbent strata brought some of the deposits into the region of vadose water above the water table. Phreatic caverns related to the present cycle of erosion cut through the deposits, and a normal suite of secondary minerals has been produced. Calcite and aragonite in part belong to the secondary suite, in part to the primary mineralisation.

The genetic implications of these data may now be examined. Primary mineralisation contemporaneous with Carboniferous sedimentation has not occurred in this orefield. All the stratified flat deposits in limestone are plainly related to crosscutting veins and feeders. Primary mineralisation by cold groundwaters can equally be ruled out. The old simple hypothesis based on analogy with the Cornubian orefield, of zoning relating to an intrusive granite supplying late hydro-thermal fluids still has its attractions, but received no support from the Rookhope Borehole. Hydrothermal fluids from crystallising granite may well be concentrated brines, as first shown by Sorby in 1858 in Cornwall and more recently by Holland (1972) on thermochemical grounds. The argument that enrichment of the brines involves a magmatic source is not accepted, for equilibrium with a granite wallrock, or solution of potash evaporites would have the same effect. The isotopic composition of the sulphide sulphur ranges too widely to make a mantle or igneous source likely, particularly in view of the relatively high positive delta 34ScDT values at the zonal centres. It is necessary to emphasise that the range is quite different from that found by Greig et al. (1971) for the Silvermines lead-zinc deposits in Tipperary, where the range is–8 to–31 per mille. The change in the present area from + 16 to–6 per mille may have some relation to reaction with limestone wallrocks, as proposed by Evans (1976) on the basis of the findings of Greig et al. (1971) but no support for juvenile origin of the hydrothermal waters is forthcoming from this source. Wallrock enrichment in zirconium led Ineson (1969) to suggest that this indicated a juvenile origin, but not enough is known about the migration of this element in solution to support or disprove this. The high levels of the trace element yttrium established by F W Smith's work on the fluorites of the orefield have led Russell and Smith (1979) to offer this as evidence that the large volumes of fluorine concentrated in the deposits were of magmatic origin; but they contemplate saline formation waters as the principal agents of mineralisation, with juvenile fluorine and rare-earth elements added to them.

The position is taken here that even if some elements in the geochemical assemblage were of juvenile origin, the mineralisation process cannot be explained without substantial mixing with saline waters already impregnating the country rocks. Sawkins (1966, p.399) considered that there was an uprise of juvenile fluids into the central zones 'as a manifestation of differentiation processes taking place in the mantle' but advocated mixing of these in the vicinity of the zone III/IV margin with calcium-barium chloride brines like those still existing in pockets in the Durham Coalfield. Solomon, Rafter and Dunham (1971) preferred, on the basis of the evidence of sulphur and oxygen isotopes, to postulate deep chloride brines of formation-water type as the principal mineralisers, but advocated mixing of these with shallow Carboniferous SO4 waters. Edmunds (1975) concluded that if Cl- brines similar to those in the coalfield became involved in convection in the Weardale Granite, they could form effective mineralising fluids, while his work also revealed SO4 brines which if mixed with the others would precipitate baryte.

It may now be concluded that sinking of the heavy brines to depths of 8 km or more to attain the required temperatures before being expelled upwards is no longer necessary. Creaney's work has shown that a much higher geothermal gradient than at present existed at the right time, in the Stephanian–Upper Permian interval. This may have been associated with a rejuvenation of the lower part of the Weardale Granite, but no petrographical evidence other than the mineralisation supports this view. It may merely point to high heat-flow associated, as Sawkin (1976) has suggested, with a mantle hot-spot or plume. That heat was available to drive a convective system is now clear; how much magmatic activity, other than the quartz-dolerites, was involved remains an open question. Brown et al. (1978) have argued against any involvement of magma at the time of mineralisation. As to the sources of the elements introduced into the veins, if granitic magmas were involved, they could have supplied some of them; leaching of the foundation slates and granite probably occurred, leaching of the Whin sills to provide iron magnesium, silicon and sodium certainly did occur, and the Carboniferous rocks may have provided a small part of the lead. Experimental work to demonstrate that leaching of the various rocks by hypersaline brine at the appropriate temperature and pressure are needed to prove that the observed assemblage of elements is indeed produced, and not an assemblage containing elements of no significance in the orefield.

The Pennine ores may be regarded as part of the worldwide Mississippi Valley–Alpine type, but a case has been made (Dunham, 1983) for associating them with the Illinois/ Kentucky and certain other fields in a special fluoritic subgroup. In this paper genetic models that have been proposed since Wallace's initial work are compared and assessed, taking into account the Askrigg and North Derbyshire orefield in addition to the present Alston Block area. Consanguity with the Mississippi Valley type is indicated by the way in which the lead isotope ratios 208/204:206/204 fall on the straight line characteristic of the type; the source of the Pennine fields was, however, less radiogenic than the average for the American Mid-West (Dunham, 1983, fig. 3).

Age of the deposits

Veins of the Pennine suite cut slatesof the Skiddaw Group (at Cowgreen), Weardale Granite, and Carboniferous rocks ranging through the full succession from the basement conglomerates up to Westphalian B. They cut and are certainly of later origin than the sills and dykes of the Whin suite, dated at 293 Ma. Fairly widespread but uneconomic disseminated deposits occur in Westphalian and Lower Magnesian Limestone rocks south of the Butterknowle Fault around Ferryhill. The fluorite, galena, sphalerite and chalcopyrite here were introduced during or after diagenetic dolomitisation of the limestone and though Permian brines were invloved, it is difficult to divorce this mineralisation completely (Hirst and Smith, 1974) from activity in the adjacent orefield, especially as the Butterknowle Fault links with the Lunedale system, a major channel of mineralisation. Scattered occurrences continue up to the Upper Magnesian Limestone (Smith and Francis, 1967) but none has been found in Upper Permian Marl or the succeeding Mesozoic formations. The Cleveland dyke (58 Ma) cuts through an oreshoot on Doukburn Vein (Phillips and Louis, 1896) but a unit of the Clevelend echelon near the Lodgesike Vein has been converted into 'white trap' (E18561)–(E18562). This last evidence is ambiguous, since this form of alteration can be produced by intrusion into carbonaceous shale (A C Dunham and Kaye, 1965; p.250).

Two attempts have been made to date the deposits from isotope ratios. Moorbath (1962) determined 204Pb/206Pb 204Pb/208Pb for galenas from Barbary, Sedling, Rotherhope and Settlingstones in the orefield, and Chilton and Thickley quarries in the Lower Magnesian Limestone. Model ages were calculated by means of the Holmes-Houtermans equation ranging from 260 to 310 Ma. Moorbath remarks (1962, p.318) 'there is… good agreement with the mean parameters of the Cornwall–Devon mineralisation. No reasonable doubt can remain that the two orefields (i.e. northern Pennines and Cornubia) are geochronologically and geochemically equivalent'. It is assumed that this statement remains substantially correct in spite of the different results obtained from the ratios concerned by Mitchell and Krouse (1971) who employed constants in their calculations to normalise Moorbath's data for Ivigtut, Greenland lead to Kanasewich and Slawson's (1964) figure for that locality. This enables worldwide comparisons to be made, but it reduced the model ages for the Alston orefield to the range 62–113 Ma. Mitchell and Krouse interpret these apparent ages as anomalous in relation to the geological evidence, and regard the leads as J-type as in other fields referable to the Mississippi Valley type. If however the comparison with Cornubia remains valid, the most likely age for the main surge of mineralisation would equate with the Stephanian–Upper Permian interval. The second attempt, (Dunham, Fitch, Ineson, Miller and Mitchell, 1968) which applied the omegatron method of Miller and Mitchell to determine 40Ar/39Ar ratios in the clay minerals of 'white whin' suggested that events subsequent to the main mineralisation took place at around 230 Ma and 170 Ma. The method has been criticised by Mitchell and Krouse on the grounds that loss of 40Ar must have occurred from these fine-grained minerals. That resurgence of mineralisation took place is more likely if formation waters played the dominant part assigned to them here. Measurements by Shepherd et al. (1982) of an Rb/Sr isochron on inclusion fluids gave 206 ± 9 Ma, a Triassic date.

The date open to the least dispute is one by T W Stern, J E T Home and S H U Bowie (Bowie, in litt.) based on U/Pb ratios for radioactive mineralisation in a veinlet at 1660 ft (506 m) in granite in the Rookhope Borehole, of 292 ± 20 Ma. Microscopic veinlets in little-altered Weardale Granite (J Parnell, in litt.) with minerals of the Pennine suite most probably originated at this time.

It is concluded that the balance of evidence favours a Hercynian age for the mineralisation, commencing soon after the cooling of the Whin sills, and continuing into Permian time. A later resurgence may have occurred but there is no evidence here of Tertiary mineralisation. Evidence of preStephanian mineralisation is equally lacking save for a minor indigenous phase, including molybdenite and tourmaline in the Devonian (410 Ma) Weardale Granite.

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Chapter 6 Mineral deposits. Details, Area 1 The Escarpment

Introductory note

The chapters which follow are devoted to descriptions, by areas, of the details of the mineral deposits, summarising the wealth of information which has been collected during the re-examination of the orefield. The deposits are described according to the vein along which they occur, or with which they are associated. As a general practice, the veins within an area are described from N to S or from NW to SE. In many instances a single vein has been wrought at several mines. In this event the mines are described from W to E, or from SW to NE. Where several veins have been worked at a single mine, they are as far as possible grouped together. After each mine the name of the owners at the time of the revised resurvey is inserted if the mine was working or temporarily idle. Disused mines are indicated as such. The economic product from each vein is shown on the right-hand side of the page. If there has been no production, or if potentially workable minerals are present, these are indicated in brackets. The six-inch sheet is shown on the left of the page beneath the name of the vein; where revised six-inch Standard maps on the metric grid are available for public reference, only the metric number is quoted, but if standards are available only on County sheets, the numbers of these are quoted.

Details, Area 1 The Escarpment

Area 1 forms a narrow strip, extending south-eastwards from the valley of Raven Beck, 10 miles 16 km NE of Penrith, through Cross Fell and the Dun Fells to Stainmore Forest, near Brough (Figure 18). It thus embraces the greater part of the steep, W-facing Pennine Escarpment. The Great Limestone and overlying beds are present in the area from Hartside Cross, on the Alston–Penrith road, northwards, and also in an outlier surrounding Cross Fell. The greater part of the Carboniferous outcrop, however, consists of rocks of the Basement Group, and the Asbian and Brigantian stages. These form the main part of the steep slope of the Escarpment. The foundation-rocks, of pre-Carboniferous age, make a series of characteristic conical-shaped hills, the Pikes, separated by low-lying ground, which occurs W of the main escarpment. Access to the mines of the area, owing to the rugged topography, is generally difficult, steep mountain roads or, formerly, aerial tramways being employed for transport. Railway transport is available at distances varying from 4 to 8 miles (6.4–12.9 km) from the mines, on the lines which follow the Vale of Eden. The area itself is unpopulated, but the three towns of Appleby, Penrith and Brough are within easy reach and there are besides, many small villages in the fertile Vale.

The mineral deposits all belong to the outer zones of the orefield, so that they are mainly of importance for barytes, at present the only product of the area. Small quantities of lead concentrates were obtained in the past, mainly from the mines of the London Lead Co. Iron ore is available on certain veins, but it is generally phosphoric and has been little worked.

Raven Beck Veins—Barytes

NY64SW; Cumberland 33SW

Three small veins are exposed in the headwaters of Raven Beck; (i) 2 miles (3.2 km) ENE of Renwick at [NY 6242 4468] a vein of pink baryte 1–2ft (0.3–0.6 m) wide trends about N33°W, through the Whin Sill, downthrowing 2 ft (0.6 m) NE. A zone of "white whin" 4 ft (1.2 m) wide accompanied the vein; no exploration has been done on this vein; (ii) 2000 ft (610 m) SW of the first vein a fault trending N75°E and downthrowing N crosses the Beck, accompanied by a sharp northward downfold of the beds; a shaft of unknown depth, marked "Copper Mine" on the 6-inch map [NY 6205 4420] has been sunk, probably at the horizon of the Tynebottom Limestone and associated beds, and some opencutting has been done, but apart from a little pyrite and ankerite, with traces of malachite staining, nothing of economic interest appears to have been found; (iii) strings trending N65°E cut through the Five Yard Limestone 1200 ft (366 m) E of the first vein at [NY 6279 4468]. Some of them carry up to 6 inches (0.15 m) of baryte but no trial has been made. There are also indications of baryte at the horizon of the Great Limestone. The area may justify further trials for barytes.

Rowton Beck Vein–Loo Gill No. 1 group

The above veins occur within the property of Hartside Mines (disused). The Loo Gill Veins were both developed at the horizons of the Great Limestone and Coal sills by the Hedworth Barium Co., a flat or wide pocket being obtained in the Great Limestone on the N side of No. 1 Vein near the head of Loo Gill. Some opencutting against a footwall of Nattrass Gill Hazle was done on No. 1 Vein in the bottom of the Gill, the course of which is determined by the vein in its upper reaches. In the 1940s, B Laporte Ltd continued driving the Harrison Adit, the portal of which is in Loo Gill at [NY 6422 4280], NW of Hartside Cross. The level, at approximately 1600 ft (488 m) above OD, commences at the bottom of the Nattrass Gill Hazle, and follows a general course about N10°W. At 200–220 ft (61–67 m) from the portal it passes through a whin dyke. At 960 ft (293 m) from the portal it reaches No. 2 Vein. Here a rise 115 ft (35 m) to surface revealed the top of Nattrass Gill Hazle 22 ft (7 m) above the level sole on the footwall SE of the vein; the vein is poor above the Four Fathom Limestone. A second rise on No. 2 Vein, 700 ft (213 m) to the SW, is 30 ft (9.1 m) up to surface and shows baryte 3 ft (0.9 m) wide in the Nattrass Gill Hazle. The developed length underground on No. 2 Vein is about 1000 ft (305 m), the width of the vein varying up to 4 ft (1.2 m). A stope 480 ft (146 m) long, reaching a maximum height of 60 ft (18 m) has been taken out in the Four Fathom Limestone and Nattrass Gill Hazle. On surface No. 2 Vein has been proved to carry a width of 4 ft (1.2 m) of baryte in the Slaty Hazle, 500 ft (152 m) NE of the confluence of Grainings Beck and Loo Gill. There are also traces of baryte in the Scar Limestone on the line of the vein in Loo Gill related to a branch which has been exposed in a stream E of Grainings Beck. Thus the possible mineralised length on present indications on No. 2 Vein exceeds 2000 ft (610 m) but much remains to be done to develop the vein. The Harrison Adit reached Daffenside Vein 1000 ft (305 m) NNW of No. 2 Vein, and exposes up to 3 ft (0.9 m) of baryte with the Four Fathom Limestone on the footwall.

Daffenside Vein was also worked by Hedworth Barium Co., by means of a level [NY 6394 4329] at 1695 ft (518 m) above OD 1 mile (1.6 km) NNE of Hartside Cross, between a Great Limestone foot-wall and a hangingwall of Coal Sills sandstone; these workings have collapsed. The total length of ground worked appears to have been about 350 ft (107 m); the condition of the vein in the forehead is unknown. At about 30 ft (9 m) above this level, an opencast trial in sandstone shows the vein split up into strings. Barytes, somewhat limonite-stained, was the only product. To the SW the fissure continues as a fault trending N35°E, as yet unexplored. A trial cutting [NY 6388 4304], on the W bank of Grainings Beck, 1100 ft (335 m) N of its confluence with Loo Gill, reveals 4 ft (1.2 m) of baryte in the Nattrass Gill Hazle. There are indications of baryte in the Great Limestone on the course of the Beck.

Loo Gill No. 1 Vein is exposed in the Gill near the mouth of the deep level, and is reached underground by a NE branch of the level. The vein is pockety, reaching a maximum width of about 4 ft (1.2 m). At 450 ft (137 m) ENE of the main level it is cut by a strong belt of NW fractures. The principal movement on this belt appears to have been sideways; since it contains dragged baryte it seems likely that it was of postmineralisation date. The facts suggest a shift of the No. 1 Vein E side N of nearly 40 ft (12 m), but more development will be necessary to make this certain. This vein, like No. 2 Vein, offers promise for north-eastward development from the Harrison Adit. At the head of Loo Gill the collapsed workings on the branch or flat on the N side of No. 1 Vein may be seen. Above the Great Limestone a level [NY 6446 4200], now run in, is said to have been carried 600 ft (183 m) north-eastwards in the main vein. Baryte mixed with shale occurs on the dump.

Some 700 ft (213 m) SE of Loo Gill No. 1 Vein, at [NY 6430 4262], a parallel fault throws about 90 ft (27.4 m) NW. A surface trial SSE of the portal of the Harrison Adit shows strings of baryte on this fault in sandstone, probably the Tuft.

Rowton Beck Vein, at [NY 633 432], the northernmost of the Hartside Group, has been developed by means of an opencut and two levels, all in the Nattrass Gill Hazle. The vein was worked by Hedworth Barium Co., widths up to 13 ft (4 m) of baryte being recorded. In more recent workings, the vein carried a large "horse" of sandstone. The baryte is coarse grained, with tiny bands of limonite and traces of galena and malachite. Harrison Adit extended 200 ft (61 m) NNW of Daffenside Vein appears not to have reached Rowton Beck Vein.

The ore from the Harrison Adit hoisted up the fellside by surface tramway, was lorried to Laporte's Silverband Mill for removal of sandstone from the otherwise good-quality baryte. However, the establishment by 1946 of substantial reserves of more-cheaply worked ore at Silverband led to the closure of the Hartside operations.

Separate figures for production from the Hartside mines are not available. 1940s production, mainly from development, reached about 2500 tons per year. If ever 1 m-wide barytes veins again become of interest, the Hartside Mines offer possibilities.

Mineralisation with baryte has been found over a vertical range of nearly 400 ft (122 m).

Gamblesby Fell Veins—Baryte

NY64SW; Cumberland 41NW

Immediately S of Hartside Cross, a series of faults trend N60°E, shifting the outcrop of the Great Limestone. At 300 ft (91 m) S of the Hartside Cafe [NY 6464 4182] one of these faults carries a few inches of baryte, accompanied by limonitic ironstone in the limestone. A little baryte is also seen in a shallow opencut on a string 150 ft (46 m) N of and parallel to this fault. At 600 ft (183 m) [NY 6472 4159] S of the Cafe, indications of baryte are again seen on a fault, here traversing the Four Fathom Limestone. At 1000 ft (305 m) E of Hartside Cross, the first-mentioned fault crosses the Alston–Penrith road: an opencut on the N side of the road shows limonitised limestone. The mineralisation here appears to be feeble, though considerable lengths of the faults, known to exist on geological evidence, remain untested.

Twotop Hill Veins—Iron ore

NY64SW, Cumberland 41NW

S of Twotop Hill the Scar Limestone is cut by two NE-trending faults which carry limonite. Locally the limestone has been replaced by limonitic iron ore which has been worked from an opencast at [NY 6362 4110]. Trials have also been made by shallow shafts and a level. Some 1640 ft (500 m) to the W a WNW-trending fault also carries iron ore; limonite is abundant on the dumps from a trial working at [NY 6293 4112] (Arthurton and Wadge, 1981).

Long Crags Vein—Iron ore

LY64SW; Cumberland 41SW

A NE-trending fault which cuts the Melmerby Scar, Robinson and Smiddy Limestones south of Long Crags contains limonitic iron ore [NY 6300 4005]. Several shafts and collapsed adits suggest that small flats may have been worked in the limestones though the date of the working and the amount of ore produced is unknown. (Arthurton and Wadge, 1981).

Knapside Vein—Lead ore

NY63NW, NE; Cumberland 41SW. Direction N58°E, throw approximately 200 ft (61 m) NW accompanied by a sharp downfold on the north side of the vein.

The Great Sulphur Vein (described under Alston Moor, p.130) dies out just inside the present area, but its throw is carried on by Knapside Vein, a SW branch. Knapside Mine (disused) consists of three levels; (i) at about 2020 ft (616 m) above OD, driven under the Lower Little Limestone at a location [NY 6441 3822] on the footwall side of the vein, possibly communicating with a shaft [NY 6464 3831] 800 ft (244 m) to the NE; (ii) at about 1950 ft (594 m) above OD, [NY 6439 3815] entering the vein from the S side as a crosscut; (iii) at about 1750 ft (533 m) above OD, [NY 6434 3795] running NNW through Basement Beds to reach the vein at 750 ft (229 m) from the portal. These workings are not accessible and no plan is in existence. The dumps show siliceous limonite and quartz, with a little galena. There are no records of production, but it is clear that only a small quanitity of ore was extracted and dressed.

On Hard Rigg Edge approximately 0.75 miles (1.2 km) NE of Knapside Mine, trials [NY 6552 3876] have been made on the vein in beds above the Single Post Limestone. The dumps show abundant quartz, some of which displays excellent pseudomorphs after cockscomb baryte and a cubic mineral, probably fluorite. Pyromorphite and goethite are also common, the latter occasionally pseudomorphing calcite. At 980 ft (299 m) NE of these workings a crosscut adit, the Foxfold level [NY 6579 3893] has been driven S for about 1410 ft (430 m) into the Whin Sill from near the junction of Knapside vein with the Great Sulphur Vein: the dumps consist mainly of dolerite blocks and show no mineralised material.

Parallel to, and 350 ft (107 m) SE of the Knapside Vein a small vein cuts through the Melmerby Scar Limestone, the base of which is here at 2000 ft (610 m) above OD. The vein is feebly mineralised with limonite, in places stained with malachite.

Ardale Head Vein—Iron ore

NY63NE; Cumberland 51 NE. Direction N60°E, throw 35 ft (11 m) NW.

This vein is mineralised from the Three Yard Limestone to the Little Limestone. It was worked at Ardale Head Mines (disused), situated at an altitude of over 2000 ft (610 m) above OD on Ousby Fell, 2 miles (3.2 km) NE of Kirkland. The vein follows more or less the course of Gregory's Sike, but it apparently dies out before reaching the main Ardale valley. Trials have however shown that it runs for at least a mile (1.6 km) NE from the 2202 ft (671.2 m) above OD spot height, to the outcrop of the Great Limestone on the E side of the fell.

Deposits related to this vein were probably tried in early times but the first recorded development for iron ore was done about 1887 by the Ousby Mining Co., and Messrs Bell and Partners. Eleven borings were put down, the records of which are on British Geological Survey files; these cannot however be sited.

At this time an adit level was driven, and a small opencut made. A report by the late Mr J D Kendall, dated 1887, was unfavourable largely because of the transport difficulties, which are great. During 1914–18 the Cargo Fleet Iron Co. prospected the deposits (Sherlock, 1919, p.14) but again they did not reach the stage of production. The ore was found to average 48 per cent iron and 7 to 8 per cent manganese. In 1940 further prospecting was done under Mr T S Durham's direction.

The deposits are replacements of limestone adjacent to the vein. The opencut at [NY 671 357] reveals limonite replacing the Great Limestone on the downthrow side of the vein. The 1887 development proved a thickness of 16–32 ft (5–10 m) of limonitic ore, over a width of 18–33 ft (5.5–10 m). One of the borings made at this time (No. 1) started above the limestone and presumably passed through the fault; on the assumption that the replacement did not involve diminution in thickness of the limestone, the record below indicates that the throw of the fault is about 35 ft (11 m):

All the ore, save 90 tons shipped in 1886, remains on the dump from this opencut. About 600 ft (183 m) SW of the opencut, [NY 6690 3565] an old adit mouth can be seen; the dump shows limonitic ironstone, which may have come from a replacement of the Four Fathom Limestone. Some 700 ft (213 m) SW of this adit mouth, a trial [NY 6674 3552] made by the side of the stream has revealed a thickness of about 6 ft (1.8 m) of ironstone, probably replacing the Three Yard Limestone. In addition to the replacements of these three limestones, shafts [NY 6775 3607] 2600 ft (792 m) NE of the open-cut show ironstone which may have come from bodies in the Little Limestone.

The ironstone is cavernous limonite containing an unusually high proportion of crystalline goethite and possibly some red hematite. The phosphorus-content is high. The only mineral known to be present apart from iron oxides is baryte, which occurs in small quanitities only. (Table 35) gives partial analyses of the ore.

A second NE vein has been proved about 300 ft (91 m) NW of the first vein; a boring possibly on this vein showed a thickness of 16 ft (5 m) of ironstone. A level has been driven on the vein above the Great Limestone at [NY 6703 3580]. At 1700 ft (518 m) SE of Ardale Head Vein a small vein carrying baryte and limonite has been tried by means of a shaft [NY 6735 3526] starting above the Great Limestone, and by opencuts [NY 6720 3520] above the Four Fathom Limestone.

Hunter's Vein—Lead ore

NY73SW; Westmorland 1. Direction N65°E, throw said to be 6 ft (1.8 m) SE; productive in the Great Limestone.

The workings, known as Hunter's Vein Mine (disused) [NY 709 337] lie on the NE slope of Little Dun Fell, and consist of an opencut in the Great Limestone and Coal Sills, a level in the Great Limestone at about 2250 ft (686 m) above OD and communicating shafts. The mine was worked by the London Lead Co., a new shaft being sunk in 1881 according to information recorded by C T Clough on the primary 6-inch map. The deposits consisted of small flats in the Limestone, carrying galena, purple and green fluorite, quartz and limonite. A productive flat 27 ft (8 m) below the top of the Limestone is recorded. The length of ground developed was about 900 ft (274 m). Trials SW of the workings in the shale below the Firestone were unsuccessful, but what may be the continuation of Hunter's Vein was proved by a level [NY 6955 3331] driven ESE under the Great Limestone from Crowdundle Beck at about 2280 ft (695 m) above OD, which cut an ENE vein throwing 6 ft (1.8 m) SE at 800 ft (244 m) from the portal. The veinstuff was chiefly limonite. Production records are incomplete; 116 tons of lead concentrates were produced in 1869–76.

Swathbeck Vein—Lead ore

NY73SW; Westmorland 5NE. Direction N60°E, throw small; productive in the Great Limestone.

Swathbeck Mine (disused) is situated half a mile (0.8 km) E of the summit of Little Dun Fell. The main developments include a hush, exposing the vein in the Great Limestone and Coal Sills [NY 7137 3300] and a level [NY 7140 3319] 1925 ft (587 m) long, of which the first 225 ft (69 m) is a crosscut, driven at the base of the Great Limestone. The London Lead Co. sections (Mines Dept. Plan No. 702) shows numerous rises from this level, but gives no details of the stopes, which are probably ancient. It is probable that a vein oreshoot, carrying galena, fluorite and limonite was worked. On the W slope of the Escarpment, the vein has been tried at Lord's Level [NY 7047 3247], driven on top of the Great Limestone from Middle Tongue Beck, and from a long crosscut which followed natural caverns, communicating with Silverband Mine (see(Figure 17). There is no veinstuff on Lord's Level dump, and the nature of the vein in the Great Limestone is not known. No production data are available.

–group

Dun Fell Vein–Loppysike Vein group

Dun Fell Vein may be regarded as the master vein of the series listed above. It extends from the Cross Fell Inlier, where (as the Crowdundle Fault) it separates ashy Milburn Beds on Grumply Hill from Ellergill Beds to the S. No mineralisation appears here. In the Carboniferous, the westernmost workings are on the S side of Middle Tongue Beck, 1 mile (1.6 km) ENE of its confluence with Crowdundle Beck. Here an opencut [NY 6948 3202] shows barytegalena mineralisation opposite the Jew Limestone on the footwall of the vein. At 1250 ft (381 m) farther E, Gilbert's or New Silverband Level [NY 6982 3215] (disused) runs S from the beckside at 1838 ft (560 m) above OD reaching at 290 ft (88 m) from the portal the hanging wall of the vein and proving a width of about 50 ft (15 m) of limonitic ore with a little baryte. The level is driven in sandstone and shale beneath the Scar Limestone; on the footwall of the vein the Tynebottom Limetstone is exposed, with the Whin Sill showing beneath it.

Near the portal of Gilbert's Level the Rowpotts Vein appears in the bed of Middle Tongue Beck, forming with Dun Fell Vein a fault-trough which may be traced in an easterly direction for about 2000 ft (610 m). Hushes follow both veins, revealing baryte in a limonite matrix opposite the outcrops of the limestones between the Scar and the Great, and strings of baryte in smashed sandstone, probably the Six Fathom Hazle, adjacent to Dun Fell Vein. Burn's Level on Dun Fell Vein at 2033 ft (620 m) above OD [NY 7019 3204] and Henrake Level at 2244 ft (684 m) were reopened in connection with Silverband Mine, the latter giving access to Great Limestone flats N of Dun Fell-Henrake Vein.

Under the northern slopes of Great Dun Fell, the Rowpotts Vein loses its throw, and the series of ENE veins listed above spring from the N side of Dun Fell Vein. This ground was worked from Silver-band Mine (disused) by B Laporte & Co. between 1939 and 1963. Silverband Low Level [NY 7031 3176] at (2286 ft (697 m) above OD, was driven by the London Lead Co. in the early part of the 19th century and was reopened to become the main working level for Laporte's barytes operations. It runs in a direction N45°E in the shale below the Nattrass Gill Hazle. At 650 ft (198 m) from the portal it passes through the Dun Fell Vein, here poorly mineralised, into the shale below the Tuft. At 730 ft (223 m) after passing through the Tuft, the base of the Great Limestone is encountered, dipping 30°N. The level then turns ENE and after a loop joins the Deed Vein, which is followed for 950 ft (290 m) in the Great Limestone, the dip of which now flattens. At 440 ft (134 m) ENE of the turn in the level, the north crosscut to Swathbeck Vein commences. This appears to have been made by widening a series of natural caverns which follow the joint-system in a direction N28°–34°W. The crosscut is 2100 ft (640 m) long, the only vein of note between Deed and Swathbeck veins being the feeble continuation of Rowpotts Vein. At 100 ft (30 m) ENE of this crosscut, No. 2 crosscut runs SSE through a similar series of caverns, cutting Henrake Vein at 340 ft (104 m) from Deed Vein, Slope Vein at 485 ft (148 m) and reaching Dun Fell Vein at 510 ft (155 m). No. 3 Crosscut commences from Deed Vein 1115 ft (340 m) ENE of the turn in the Low Level, running SSE and reaching Remmington North Vein at 100 ft (30 m), and Henrake Vein at 410 ft (125 m). The latter vein is followed for 70 ft (21 m) through a cavernous stretch known as the "jungle", after which the crosscut resumes its course, cutting Slope Vein at 40 ft (12 m) from Henrake, and Loppysike Vein at 70 ft (21 m). Three baryte-bearing ENE veins, Nos. 6, 7 and 8, were encountered at 165 ft (50 m) 280 (85 m) and 310 ft (95 m) SE respectively from Slope Vein. Between the second and third veins the top of the Great Limestone is in the level sole. At 370 ft (113 m) from Slope Vein, Dun Fell Vein was reached, with the Four Fathom Limestone on the footwall.

Silverband High Level at 2384 ft (727 m) above OD [NY 7048 3183] was driven by the London Lead Co. to command the Great Limestone on the footwall of Dun Fell Vein. It runs N67°E through shale and overlying Quarry Hazle to reach Dun Fell Vein at 340 ft (104 m) from the portal, continuing through the Great Limestone to reach Henrake Vein at 560 ft (171 m). The inclined road from which Slope Vein takes its name runs on that vein from its junction with Dun Fell Vein 280 ft (85 m) E of the main top level down to the Low Level at No. 3 Crosscut. The High Level drive in Dun Fell Veins runs 2800 ft (853 m) to the E reaching Dun Fell Hush.

The vein oreshoots on all the veins are essentially similar, consisting of coarse white baryte with galena in strings and narrow bands. Aragonite, calcite and sphalerite are present in very minor amounts. The galena values were evidently low, for the London Lead Co.'s sections show the stopes coloured red and yellow on all the veins but Remmington's South, on which small patches of blue are shownOn almost all the extant stope sections of the London Lead Co., recovery values are indicated by these colours: blue represents over 16 cwts lead concentrates per fathom stoped; red represents 10–16 cwts; yellow under 10 cwts.Recalculated on a basis on 2 cu. ft. (0.06 m3) of ore per ton, and a 3 ft (0.9 m) wide vein, blue represents over 9.0 per cent, red 5–9.0 per cent, yellow under 5.5 per cent. For veins of greater width the values are correspondingly lower.. Nor are the stopes extensive when they are compared with the great length of development done at this mine by the London Lead Co. Dun Fell Vein appears to have been worked from surface shafts before this company acquired the property in the early nineteenth century; subsequently a stope 1230 ft (375 m) long by 20 ft (6 m) high was worked against a Great Limestone footwall and another 450 ft (137 m) by 15 ft (4.6 m) against a Four Fathom Limestone footwall. The stoping on Deed Vein was 800 ft (244 m) long by 15 ft (4.6 m) average height, at about the horizon of the "high flat" of the Great Limestone. On Remmington's SouthVein, three oreshoots aggregating about 1000 ft (305 m) long by 30 ft (9 m) average height were worked, while on Slope Vein the length of stoped ground was 1500 ft (457 m) by an average height of about 35 ft (10.7 m). In these areas pillars rich in excellent quality barytes were left, but the developments by Laporte's clearly indicated that much of the workable ground on the veins was removed by the lead miners. Barytes stopes in vein oreshoots have, however, been worked on Henrake Vein between No. 2 and 3 crosscuts, 640 ft (195 m) long by 25 ft (7.6 m) average height, and on Slope Vein between Dun Fell Vein and No. 3 Crosscut. On Loppysike Vein stoping up to 12 ft (3.7 m) wide has been carried 700 ft (213 m) ENE from No. 3 Crosscut, but with small height.

Between the veins, extensive areas in which the Great Limestone has been replaced by baryte, almost free from sulphides, formed the mainstay of the barytes mining. The horizon most attacked was the bottom 6–10 ft (1.8–3 m) of the limestone, but adjacent to the veins, the replacement deposits thicken. This is particularly the case along the N side of Dun Fell Vein, where step-faulted segments of Great Limestone within the fracture belt appear to have been completely replaced by a mixture of baryte, silica and clay with some limonite. The baryte in places occurs in large, water-clear crystals, but there is always a high proportion of fine-grained baryte in the replacement ore in addition to these. The great replacement orebody following Dun Fell Vein, was found to represent the main ore-reserve of the mine. It extends downwards from the footwall position of the Great Limestone, exposed in Silverband High Level, where there are flats up to 20 ft (6 m) wide, to the Low Level; its vertical extent was not less than 100 ft (30 m), the continuity over this height was well proved. The width was variable, according to the position of the limestone segments and the distances between the fractures which constitute the fault. Widths exceeding 25 ft (7.6 m) were encountered during development from No. 8 Rise, and in the surface opencut. The full length of this remarkable replacement orebody from Henrake Adit to the fracture-belt E of the intersection of Dun Fell and No. 8 veins amounts to some 2500 ft (762 m). This structure was illustrated by contours on the base of the Great Limestone in Dunham (1959) and Johnson and Dunham (1963).

The average baryte content of the ore proved to be between 50 and 60 per cent, the matrix being mainly limonite and silica. Apophyses from this orebody follow all seven diverging ENE veins. Away from the Dun Fell vein-belt and the branch veins, the thickness of the replacement diminishes, but replaced limestone up to 6 ft (2 m) thick has been proved to extend at least 100 ft (30 m) from the nearest vein.

The compositions of samples taken at an early stage from the veins and flats are given in (Table 36). Some of these samples contain fluorine, but the former mines manager, Mr Sibson, stated that the only occurrence of fluorite visible to the naked eye so far noted was in the deepest workings of the mine, reached from the underground shaft.

Apart from a shoot in the Four Fathom Limestone on Dun Fell Vein, all the workable oreshoots, both for galena and baryte have occurred in the Great Limestone; this applies to both flats and veins. Above that horizon there is little hope of finding anything of value, because of the predominance of shale in the section (pp.27, 28). The eastward dip, at about 1 in 100, carries the Great Limestone below adit level E of No. 3 Crosscut on Slope and Loppysike vein; on Nos. 7 and 8 veins it is already below the sole of No. 3 Crosscut. As the vein oreshoots approached exhaustion for barytes, an underground shaft was sunk 112 ft (34 m) from No. 3 Crosscut on Slope Vein. This showed that the vein carries a width of 3.5 ft (1 m) of baryte in two parts, separated by replaced limestone, between a footwall of Four Fathom Limestone and a hangingwall of shale. A winze was carried 25 ft (8 m) deeper in the vein, but it appeared doubtful whether the mineral shoot is of workable dimensions. Postmineralisation caverns associated with Slope and Loppysike veins created pumping difficulties during the sinking, but eventually provided free drainage for the mine-bottom.

The level from the bottom of the shaft gave full access to the base of the Great Limestone on all the eastern veins. The barytes ore was still being extracted from the replacements associated with these when, in 1963, Laporte Industries decided to close the mine, not because it was exhausted (about 100 000 tons of crude ore were believed to remain) but because cheaper by-product barytes became available from the Company's operations near Eyam, Derbyshire.

Separate production figures for lead ore cover only the period 1863–1876, when 1007 tons of lead concentrates containing 75 per cent of lead, with 6.9 oz of silver per ton of lead ore were obtained. The figure of 15 oz of silver per ton given by Brammal (1921) is not 'ustified by these records. For the whole period 1821–1879, the London Lead Co. records of their mines on the Thanet-Tufton royalty show a total of 15 062 tons of lead concentrates. It may be estimated that about half of this total, or 7500 tons, came from Silverband, a poor return for the 17 500 ft (5.3 km) of drivage done by the company at this mine. There was a small production of barytes when the mine was reopened under Mr Brammal's direction in 1914–18. When Laporte's took over in 1939, an aerial ropeway 3.5 miles (5.6 m) long was installed to transport the crude ore from the mine to a mill at Milburn Grange, whence another ropeway conveyed the product to the railway. The production of dressed barytes, 1939–1963 amounted in round figures to 215 000 tons. The ropeways and mill were dismantled, and the property remained idle until the 1970s when Mr H Taylor acquired it, built a mill at the mine and removed the overburden from the Henrake–Dun Fell replacement ground as far east as High Level head see (Figure 17) producing about 75 000 tons. The rise of the fell and the eastward dip of the strata now prevent further opencast recovery eastward except from Dun Fell vein and any future for Silverband Mine must lie in reopening the deeper workings. In 1983 the property was taken over by Crag and Cutriss Ltd, who are excavating replacement ground N of Henrake Vein West, estimated to contain about 15 000 tons of barytes. They are also preparing to follow Dun Fell footwall ore as far eastward as opencut working will permit.

On the E side of Great Dun Fell, at the Dun Fell Mines (disused), important changes both in structure and mineralisation have occurred. Dun Fell Vein is in at least three branches, up to 80 ft (24 m) apart, between which the northward throw is distributed in a series of steps. At about 250 ft (76 m) N of the northernmost branch an E–W vein appears, downthrowing S; this is generally regarded as the continuation of Henrake Vein, though that vein as seen at Silverband throws N. The fault-trough structure, seen W of Silver-band is thus resumed to the E; ENE veins are no longer found at Dun Fell Mine. The change in mineralisation is the disappearance, for practical purpose, of baryte and galena, and the appearance of limonite in great quantity as a replacement of limestone. The limestones which appear at surface within the Dun Fell fault-zone, the Little, Great and Four Fathom are more or less completely converted into ironstone. In the trough between Dun Fell and Henrake veins, replacement has also been extensive, though here it is not complete; while adjacent to Henrake Vein limonitic bodies take the place of the Great Limestone.

The Dun Fell vein-system is exposed in a great opencut [NY 718 318], Dun Fell Hush, 0.5 mile (0.8 km) long and up to 50 ft (15 m) deep; a small hush [NY 720 319] reveals Henrake Vein. From the bottom end of Dun Fell Hush at 2301 ft (701 m) above OD, Dun Fell Low Level [NY 7203 3185] has been driven 2400 ft (732 m) following a sinuous course presumably designed to test the several branches of the vein. A shorter level [NY 7172 3186] commences at 2470 ft (753 m) above OD, while on Henrake Vein a level [NY 7229 3199], now collapsed, enters at 2226 ft (678 m) above OD. The area was thoroughly trenched and a boring programme was carried out 1941–1942 on behalf of Messrs Colvilles Ltd. The levels were in part reopened. The work revealed that a substantial tonnage of ironstone is present, in a series of stepped slices between the branches of Dun Fell Vein, and along Henrake Vein, but the structural conditions preclude easy or cheap workings. Moreover, though the iron and manganese content is higher than the average for iron ores in the district, the ironstone has proved to be phosphoric and the silica-content to exceed one-third of the metal content. On the footwall N side of Henrake Vein, the limonite is highly siliceous; the same is the case at the eastern end of the outcrop of the Great Limestone in the trough between Henrake and Dun Fell veins. The ironstone is soft and friable, and difficult to bore. The results of boring indicate, from the position of definitely identifiable beds above and below the Great Limestone, that this limestone was reduced in thickness during the process of replacement, and at its outcrop, the upper part is converted into a mixture of limonite, clay and shale, the last derived from the bed which normally overlies the limestone. The maximum continuous thickness of ironstone proved by boring does not exceed 25 ft (7.6 m). Average analyses of the iron ore are given in (Table 37). It is probable that iron ore was obtained at Dun Fell in ancient times, and smelted at the old mill in Knock Ore Gill, but the exact date of this work is not known, Present-day exploitation of the deposits would require the construction of an aerial ropeway several miles long. Access by the steep mountain road up Knock Ore Gill is possible, but difficult.

Dun Fell Vein continues for at least 2.5 miles (4 km) E of Dun Fell Mine, into the Teesdale area.

Loppysike Vein has been explored on the E side of Great Dun Fell from the Loppysike Level [NY 7213 3230] the mouth of which is 1550 ft (472 m) N of that of Dun Fell Low Level. It runs WNW as a crosscut beneath the Great Limestone, reaching the vein at 550 ft (168 m). The drift on the vein is only 150 ft (46 m) long. Baryte, limonite and small quanitities of witherite and galena occur on the dump. Cockscomb baryte and psilomelanc are seen on the shaft heaps NW of this level, presumably sunk to the continuations of the Remmington's veins.

Knock Ore Gill Veins—Barytes

NY73SW; Westmorland 5NE

On the E side of Knock Ore Gill at 1922 ft (586 m) above OD an ENE vein carrying baryte 2 ft (0.6 m) wide cuts through the Whin Sill, which here underlies the Tynebottom Limestone [NY 7100 3044]. There is also some baryte, limonite and galena in three small E-W faults which cut across The Heights to the NE [NY 718 305] as indicated by old shafts into the Great Limestone [NY 7197 3065] and sunk beneath the Scar Limestone [NY 7115 3050].

Dobson's Vein–Clovendock Vein group

The veins listed above were recently worked at the Threlkeld Side and Dutton Fell mines, by Sanbar Minerals Ltd. The mines lie respectively on the NW and SE sides of the valley of Rundale Beck, 3 miles (4.8 km) NE of Dufton. At Threlkeld Side Mine [NY 7120 2753] the principal level, at about 1500 ft (457 m) above OD, was driven in the Melmerby Scar Limestone, running 325 ft (99 m) N to Hard Ark Vein, then following this vein under the head of the valley for 1600 ft (488 m), to the junction with Barrow's Vein, which was followed for 1350 ft (411 m). At the forehead the level sole was 52 ft (15.8 m) below the top of the Melmerby Scar Limestone; a rise at this point was put up to the Smiddy Limestone, the base of which was 139 ft (42.4 m) above the level sole. At 50 ft (15.2 m) back from the forehead, a crosscut was put out N20°W, 625 ft (191 m) long, testing Hard Ark and Dobson's veins. The whole of this exploration in the Melmerby Scar Limestone appears to have been unsuccessful; no galena was got and very little baryte was found. Other levels at Threlkeld Side, all driven N, tested the top of the Melmerby Scar, the Robinson and Smiddy limestones; in addition, one, Threlkeld Low Level [NY 7122 2746] was driven 450 ft (137 m) in the shaly limestone of Holkerian age which underlies the Melmerby Scar Limestone. The only productive ground discovered seems to have been in the Smiddy Limestone, where small flats up to 6 ft (2 m) thick, carrying baryte in altered limestone are accessible. Dobson's Vein, tried from a level above the Smiddy Limestone, may have been productive in sump workings in that limestone.

On the SE side of the valley the veins cut through limestones higher in the succession, becoming productive in the Dufton Fell Mine. This mine according to information from Mr Alexander Reid, was to to some extent explored by Messrs B Laporte's in 1943, together with the Threlkeld Side Mines. The mine was developed by the London Lead Co. in the early part of the nineteenth century, but it is probable that the superficial workings date from a much earlier period. The lowest level is the continuation of Threlkeld Level at 1500 ft (457 m) above OD which has already been described. In the Robinson Limestone a level running N63°E passes through Hard Ark Vein (at portal [NY 7146 2763]), which is quite barren at this horizon. Dufton Low Level [NY 7154 2771], at about 1595 ft (486 m) gave access to Hard Ark and Barrow's veins below the Smiddy Limestone; the results again seem to have been poor. From a level at the foot of the hush on them, these veins were tested in the Lower Little Limestone, and a crosscut reached Gascoign's Vein. As the development here was not pursued it must be assumed that little was obtained. At about 1740 ft (530 m) above OD the London Lead Co. drove a flank level below the Jew Limestone, running 825 ft (252 m) at [NY 7176 2790] S58°E, to reach Barrow's Vein; a ramifying belt of small flats or leads was worked above this level. At Barrow's Vein this level turned to S38°E and continued through Gascoign's Vein, on which 600 ft (183 m) of ground was opened up in the Jew Limestone to White Rake. On this vein there was a rise up 20 ft (6 m), from which a crosscut continued S30°E at the base of the Jew Limestone, cutting Clovendock Vein at 550 ft (168 m) and continuing 750 ft (228 m) beyond this vein. It seems clear that some productive ground was got in the Jew Limestone, not only on the veins mentioned, but also on Dobson's Vein, which was entered at the foot of Dobson's Hush by a level at this horizon. The main productive horizon of the mine was, however, the Tynebottom Limestone. The principal means of access was by Atkinson's Level [NY 7194 2808], which starts from the SE side of the valley near the ruins of the London Lead Co.'s dressing floor, at about 1875 ft (571 m) above OD. This runs S40°E in sandy shale beds with a thin limestone, which lie between the Tynebottom Limestone and the Whin Sill, for 450 ft (137 m). It then cuts and follows a cross vein trending S27°E and downthrowing about 5 in (0.13 m) SW. About here there is a small change in horizon of the Whin Sill, cutting out all but 5 ft (1.5 m) of sandstone between the Sill and the Tynebottom Limestone. At 560 ft (171 m) and 620 ft (189 m) from the level mouth, two branches of Dobson's Vein were cut, throwing respectively 3 ft (1 m) and 6 ft (2 m) S. A rise on the S branch gives access to extensive workings on this vein in the Tynebottom Limestone, in which small flats, extending up to 30 ft (9 m) from the vein were worked over a length of 1750 ft (533 m) to the ENE of the level, and 300 ft (91 m) to the WSW. The cross vein was productive between the two branches of Dobson's Vein in the Tynebottom Limestone. At 270 ft (82 m) SSE of the rise the level reaches Hard Ark Vein, and at about 150 ft (46 m) SSE of this vein, Barrow's Vein. On both there were ramifying belts of small flats in the Tynebottom Limestone covering a length of ground similar to that developed on Dobson's Vein. Barrow's Sun Vein branches from Barrow's Vein about 600 ft (183 m) ENE of Atkinson's Level; flats on it were worked for about 400 ft (122 m) over a width not exceeding 12 ft (3.6 m). Atkinson's Level continues SSE, reaching White Rake at 1710 ft (521 m) from the portal, and communicates with a surface shaft. About 400 ft (122 m) NE of the shaft, at [NY 7222 2765] White Rake is intersected by Gascoign's Vein, which apparently shifts the Rake N side W some 200 ft (91.5 m). Flats were worked in the neighbourhood of the intersections. A small vein N of White Rake was discovered by a crosscut here, and named Bergatum Vein. At about 1750 ft (533 m) ENE of Atkinson's Level, Dobson's, Hard Ark and Barrow's Sun veins were found to be unproductive. A drive was, however, continued on Dobson's Vein to 2060 ft (628 m), and a crosscut put out, reaching Hard Ark Vein at 150 ft (46 m) S. The drift was continued 900 ft (274 m) on the hangingwall of this vein, with numerous crosscuts to the vein in the Tynebottom Limestone, but apparently with little result. A second crosscut was carried N to Dobson's Vein, but this was found to have changed direction to N65°E, and to have increased in throw to 27 ft (8.2 m) SE, faulting shale against the Tynebottom Limestone. At 550 ft (168 m) from the change in direction, a crosscut was driven 800 ft (244 m) SSE, proving that Hard Ark and Barrow's veins had split into a series of strings with only a few feet of aggregate displacement. At 1300 ft (396 m) from the change in direction on Dobson's Vein [NY 7330 2837] a shaft was sunk from surface, and the Tynebottom Limestone was tested by a sump. Crosscuts from here were carried 600 ft (183 m) NNW and 1750 ft (533 m) SSE, the second in the shale above the Tynebottom Limestone, without discovering anything of value. At 800 ft (244 m) ENE of the shaft, the drift on Dobson's Vein was suspended. The final exploration by the London Lead Co. was a level from the valley beneath the Scar Limestone [NY 7239 2822] at about 2040 ft (622 m) above OD, running S52°E in sandstone with thin shale beds (the Copper Hazle), reaching Dobson's Vein at 930 ft (283 m), Hard Ark Vein at 1080 ft (329 m), and Barrow's Sun Vein at 1290 ft (393 m). All three veins, though thoroughly tested, are completely barren, containing nothing but gouge. A sump communicates with the flats in the Tynebottom Limestone on Dobson's Vein.

Summing up, therefore, it appears that of the 600 ft (183 m) of beds explored at the Threlkeld Side and Dufton Fell mines, not more than three beds, the Tynebottom, Jew and Smiddy limestones, aggregating only about 70 ft (21 m) in thickness, carried workable lead orebodies, and the total length of workable ground did not exceed 3000 ft (914 m). W Wallace (in a document preserved at the Mines Dept) has recorded that it was terminated to the E at a cross vein. Separate production figures during the London Lead Co. period are available only from 1863 to the closing of the mine in 1873; 620 tons of lead concentrates containing 72 per cent of lead, with 6.9 oz of silver per ton of lead were obtained. The total production under the London Lead Co. was probably of the order of 7000 tons of lead concentrates. The mineralisation, mainly in small flats, consisted of galena, baryte and aragonite replacing limestone, associated near the surface with limonite and limonitic clay which may have been derived from ankeritised limestone. Baryte occurred in white opaque masses and in water-clear crystals; Brammal (1921, p.43) records the finding of a crystal weighing nearly 1 cwt, now in the Geological Museum collection. Dufton Fell was one of the first mines of the area to turn over to barytes production; it was worked from 1882 to 1897, yielding 9495 tons of barytes and 84 tons of lead concentrates. Some exploratory work was done during 1914–18, but this does not appear to have disclosed workable reserves of barytes. The present holders of the lease are reworking the extensive dumps, with recovery of about 200 tons per week of dressed barytes. Underground extraction, following open-casting, is contemplated when these have been exhausted.

Murton Fell Second North Vein–Dowscar Vein group

The master vein of this group is Murton Fell North Vein; it has been worked from the White Mines (disused), in Gasdale, 1.5 miles (2.4 km) N of Hilton village, continuously across Mell Fell to the Murton Mines (disused), a distance of about a mile (1.6 km) (Figure 19). Here it turns NE and continues into the Hilton Mines (disused), on the east side of Scordale, 2.5 miles (4 km) NE of Hilton, where it has been followed for a further 0.5 mile (0.8 km). At the White Mines the lowest level, [NY 7425 2263] at 1279 ft (390 m) above OD, is driven in dark shaly limestone and black shale, 90 ft (27 m) below the base of the Melmerby Scar Limestone. For a distance of 500 ft (152 m); a little pink baryte was found in the vein. Near the forehead a rise up 134.5 ft (41 m) communicated with the White Mines Top Level [NY 7440 2262] at 1414 ft (431 m) above OD near its mouth; this level runs 950 ft (290 m) E, in the Melmerby Scar Limestone. There was also an intermediate level between the two mentioned. A crosscut from the Top Level proved the Murton Fell Second North Vein, on which workings were carried 1300 ft (396 m) to the ENE. No stope sections of the White Mines remain, but it appears that some galena, in a baryte matrix, was obtained on both veins in the Melmerby Scar Limestone. In the Smiddy Limestone opencast workings suggest that good-quality baryte was present.

The levels from Murton Mines reached and overlap the foreheads of those from White Mines. The lowest level, Hardside Low Level [NY 7613 2271], commences 400 ft (122 m) E of the confluence of Great Augill and Scordale Beck at the base of the Melmerby Scar Limestone, at 1299 ft (396 m) above OD. It runs NW as a crosscut, meeting Murton Fell North Vein at 260 ft (79 m); the main level on this vein runs SW and W a distance of 4100 ft (1.29 km), the forehead being at 1365 ft (416 m) above OD; this level, like nearly all local workings is no longer accessible. The Horse Level [NY 75942259], commencing 800 ft (244 m) WSW of Low Level is driven in the sandstone between the Whin Sill and the Smiddy Limestone, first as a NW crosscut, reaching the vein at 180 ft (55 m), and continuing W for 4125 ft (1.3 km). John 's Level [NY 7565 2254], commencing 1750 ft (533 m) WSW of the Low Level mouth, is driven under the Lower Little Limestone for 1700 ft (518 m) E; rise workings extend 70 ft (21 m) above this level. In the absence of stope sections it is not possible to do more than point out that development on such an extensive scale would hardly have been pursued had there not been some return from this part of the vein. Galena in limonitised limestone may be seen in small quantity around the surface shaft dumps.

Mason's Hole Vein was also worked at Murton Mines. Mason's Hole is an ancient opencut on the NW side of the Scordale valley, over 1000 ft (305 m) long, from which lead ore was presumably obtained. At the NE end of the opencut, a belt of flats , developed at the top of the Melmerby Scar Limestone beneath metamorphosed shale and sandstone which separates the limestone from the Whin Sill, commences. These have been worked underground for a distance of 850 ft (260 m), the average width being about 60 ft (18 m), the maximum width 120 ft (37 m). Through the centre of the flats run two stringers which are taken to represent Mason's Hole Vein . The mineralisation consists of amber fluorite, quartz, white opaque baryte and galena; the flats are 4 ft (1.2 m) to 6 ft (1.8 m) thick, and contain many cavities. Access to the flats was by levels driven from the steep valley side, but the ore was brought out by rises communicating with a branch of Hardside Low Level [NY 7613 2271]. From Curly Level [NY 7605 2262], which commences 400 ft (122 m) SW of the Low Level mouth, a crosscut continues beyond the flats to reach Murton Fell North Vein, associated with which there is a flat known as the "Carbonate Shake" from which witherite has been produced . Flats associated with this vein have also been proved from a series of small levels W of the Low Level. Hilton Mines lie opposite Murton Mines, on the E side of Scordale. Here the continuations of the North and Mason's Holes Veins have been worked, together with several others lying to the south. An extensive belt of flats related to these veins (as shown on (Figure 19) has been wrought at the top of the Melmerby Scar Limestone. The mineralisation differs only from that on the Murton Side in the presence of less quartz and more baryte, in large white crystals which enclose idiom orphic amber fluorite. In addition Bridges, (1982, p .33) has recorded niccolite, associated with gersdorffite, millerite and annabergite in a pocket exposed in the Dow Scar High Level. North Vein has been tested at six levels; (a) the Horse Level [NY 76242281], 1250 ft (381 m) above OD, driven into the vein on the W side of the beck in limestone and shale of the Holkerian continuing east of Scordale Beck for 1250 ft (381 m); a stope 450 ft (137 m) by 70 ft (21 m), marked yellow (see p.1l0) on the London Lead Co.'s section was worked at the NE end of this level; (b) Wilson's Low Level [NY 7636 2293], 1326 ft (404 m) above OD, starts from the beck side in the Melmerby Scar Limestone, 90 ft (27 m) below the top, continuing 1140 ft (347 m); a stope 630 ft (192 m) was worked above this level; (c) a short level at 1396 ft (426 m) above OD gives access to the flats 10 ft (3 m) below the top of the Melmerby Scar Limestone; which continue for 750 ft (229 m), with an average width of 18 ft (5.5 m), up to 8 ft (2.4 m) thick; these are related to a shale parting in the limestone, not to the baked shale overlying the limestone; (d) a level driven in the base of the Smiddy Limestone in the roof, at 1472 ft (449 m) above OD which continues 1100 ft (335 m) and gives access to a stretch of poor stoped ground 400 ft (122 m) by 10 ft (3 m) at the eastern end; (e) Jacques Level [NY 7695 2302], 1670 ft (509 m) above OD, at the base of the Jew Limestone, 1690 ft (515 m) long, from which the only stope was 200 ft (61 m) by 6 ft (2 m) and said to be poor (f) Brown's Level [NY 7664 2338] which enters the vein as a crosscut from Little Augill at 1700 ft (518 m) above OD, under the Tynebottom Limestone; nothing was found here. It is clear from the extensive exploration done on this vein that east of Scordale, the productive ground is confined to the Melmerby Scar Limestone, over a maximum height not exceeding 120 ft (37 m). Along the small veins to the south, ramifying flats at the top of the Melmerby Scar Limestone, 2–6 ft (0.6–2 m) thick have been found; small stopes were worked lower down in the Melmerby Scar Limestone on the Middle and Dowscar veins, in which there appears to have been rather more fluorite than in the flats above.

The veins are exposed at surface in Gasdale and on the steep slopes of Scordale. On the western part of Murton Fell North vein, mineralisation extended from below the Melmerby Scar Limestone up to and perhaps above the Lower Little Limestone, whereas in Scordale it was confined to the Melmerby Scar Limestone. No flats were found where the mineralisation was extensive vertically, in the western area; in Scordale flats are found on all the veins. The Whin Sill, though tried by surface cuts and rises, is barren or only feebly mineralised.

The Hilton and Murton mines were worked by the London Lead Co. from 1824 to 1876, producing a total of 10 060 tons of lead concentrates. Hardshins Mine, presumably the western workings on Murton Fell North Vein, produced 876 tons of lead concentrates containing 71.0 per cent of lead, with 6.2 oz silver per ton of lead between 1861 and 1870. In the same period Hilton and Murton mines yielded 818 tons of lead concentrates containing 73.3 per cent lead with 5.9 oz of silver per ton of lead. The mines were reopened by the Scordale Mining Co. in 1896, 70 tons of witherite being produced in that year. This company continued to work until 1906, when the Brough Barytes Co. took over, continuing until 1912, when they were succeeded by Scordale Barytes Ltd. This firm ceased work after 1919, and their plant at Hilton (Wilson et al., 1922, p.47) has been dismantled. In 1930–39 a little work was done here by W Wharton. Recorded total production of barytes, 1896–1913 amounts to 7194 tons. The total output probably does not exceed 10 000 tons. Some reserves of barytes ore remain in the flats, and it cannot be supposed that the possibilities for further exploration at the top of the Melmerby Scar Limestone have been exhausted. The ore is, however, of rather low grade, owing to admixture of the fluorite and galena. Though no production of barytes was achieved, the mines in Scordale were held under lease by B Laporte Ltd until 1963, when the ruined buildings were blasted down. The area now falls within the Warcop firing range, and all but one adit mouth has been closed by the Army.

Amber Hill Veins—Barytes

NY72SE; Westmorland 10SW

At the head of Stow Gill, on the E side of Scordale, two prospecting levels [NY 7645 2250] and [NY 7641 2245] driven into the sandstone below the Smiddy Limestone were unsuccessful. To the SW, on Amber Hill [NY 762 222], trial levels have found two parallel veins, called Lowfield and Amber Hill, trending about N45°E, with which flats containing baryte, quartz and amber fluorite in the top part of the Melmerby Scar Limestone are associated. An E–W fault down-throwing N lies to the S of the workings. The veins may be the continuation of a NE fault which shifts the Scar Limestone on Whelpside Crag, at the head of Great Augill. There has been a small production of barytes, included in the Scordale Mines figure above.

Lowfield Vein

NY72SE; Westmorland 10SW

On the NW side of Scordale, 1.5 miles (2.4 km) ENE of Hilton, there is a large opencut called Lowfield Hush [NY 7525 2165], running more or less E–W, 700 ft (213 m) long. There is much drifted material, limestone and quartz dolerite, in the hush but there is also sandstone, part of the Basement Group, replaced by galena, baryte and amber fluorite.

Long Fell Veins—Barytes

NY71NE; Westmorland 16NW

"A" Vein, direction N70°E, probably small N throw; "B" Vein, direction N60°E; "C" Vein, direction N60°E; "D" Vein, direction N52°–60°E.

These veins were worked at the Long Fell Mines (disused) on the summit of Long Fell, 2 .25. miles (3.6 km) ESE of Hilton. The horizon of the workings is the Melmerby Scar Limestone, here 400 ft (122 m) thick, which forms the steep western face of the fell and makes an outcrop nearly 0.5 miles (0.8 km) wide on the top. The filling of the veins is nearly pure baryte, with traces of aragonite and occasional malachite stains; in places mixed with clay. They were virgin in 1914, when Long Fell Barytes Ltd commenced operations, as described by Wilson et al. (1922, pp.44–46). This company's operations continued until 1924; the plant had been dismantled and the aerial ropeway removed by 1939. W Wharton's operations commenced in that year, transport in the early stages being by 6-wheel lorry on crude and often very steep tracks across the fell. A road had been constructed from Hilton to the mines, by way of the western slope of Roman Fell by 1941.

Workings on "A" Vein commence about 300 ft (91 m) NE of the edge of the scarp slope of Long Fell [NY 7650 1969]. The vein has been opencut over a length of 90 ft (27 m), the average width being 2.5 ft (0.75 m). In the next 50 ft (15 m) the width of the vein at surface is only about 1 ft (0.3 m). It then increased to 2 ft (0.6 m) to 3.5 ft (1 m) and has been opencut for 180 ft (55 m); in this stretch. Mr Wharton sunk a shaft 75 ft (23 m) deep, with levels at 20 ft (6 m). At the shaft bottom the vein contained pockets up to 40 ft (12.2 m). An unworked gap of 90 ft (29 m) succeeds this stretch, followed by an opencut up to 6 ft (2 m) wide, 66 ft (20 m) long to the NE, 20 ft (6 m) deep in places. At the end of this cut the vein is apparently shifted E side S 3 ft (0.9 m) by a crosscourse, after which it becomes narrower for the next 125 ft (38 m). A worked stretch 20 ft (6 m) long, with baryte 1.5 ft (0.45 m) to 2 ft (0.6 m) wide in the NE forehead follows. A trial pit 120 ft (37 m) ahead again revealed the vein. In depth the vein was reached by a crosscut from the Long Fell Co.'s level on "B" vein, no longer accessible; it was tried by a N crosscut from the newer level on "B" vein at 1813 ft (553 m) above OD, but this lies SW of the known productive ground.

On "B" Vein the Long Fell Co.'s adit commenced near the scarp edge at 1900 ft (579 m) above OD [NY 7650 1960] and is said to have continued at least 600 ft (183 m) to the NE. From the adit mouth the first 210 ft (64 m) of the vein appears to have been poor, improving at the first shaft to widths of 6–8 ft (1.8–2.4 m). At 375 ft (114 m) from the portal a wide crosscourse cut through the vein, containing clay with pieces of baryte and purplish quartz-conglomerate resembling the Roman Fell Beds. Another crosscourse is said to cut through the vein at 600 ft (183 m) from the portal; in this vicinity a shaft has been sunk from surface. NE of the crosscourse the vein shows only 1–1.5 ft (0.3–0.5 m) of baryte at the surface to its junction with "A" Vein, 500 ft (152 m) ahead. A new level, at [NY 7646 1960] was driven on "B" Vein at 1813 ft (553 m) above OD from the escarpment revealing a small shale bed in the Melmerby Scar Limestone. The vein in the level roof varies up to 3.5 ft (1 m) wide. At 110 ft (34 m) from the portal a crosscut links up with "D" Vein Low Level, 700 ft (213 m) S. At 290 ft (88 m) a crosscut runs N to "A" vein, mentioned above. The advance of this level would give backs up to 200 ft (60 m) below surface, half of which are certainly virgin.

“C” Vein fails to reach the escarpment and was very little developed by the Long Fell Co. In the S crosscut from "B" Low Level it is represented by strings only. The westernmost working lies 630 ft (192 m) NE of this crosscut; here a shaft inclined NE at 78° was sunk and had reached 85 ft (26 m) in February 1944. A stretch of ground 500 ft (152 m) long had been developed to a depth of 70 ft (21 m) below surface NE of this shaft and some stoping done, the ore being hauled up a shaft 235 ft (72 m) NE of the first. The vein can be traced in trial pits at intervals for at least 1350 ft (411 m) NE of this ground.

“D” vein, on the other hand, was mainly developed by Long Fell Barytes Ltd. Two levels [NY 7670 1952], the higher 15 ft (4.6 m) above the lower, were driven in from the scarp edge; N of the outcrop of the quartz-dolerite dyke [NY 7670 1953]; the higher one had reached 530 ft (162 m) in 1921, the lower 350 ft (107 m). The superficial workings extend for about 1150 ft (350 m). Measured from the higher level mouth, the first 345 ft (105 m) was worked 2–7 ft (0.6–2.2 m) wide at surface. A crosscourse shifts the vein E side S 6 ft (2 m): workings continue for 105 ft (32 m) to a second crosscourse, shifting E side S 3 ft (0.9 m). A third crosscourse is encountered 165 ft (50 m) ahead; underground development is said not to have got beyond this point. The vein, and a parallel vein 10 ft (3 m) to the S however continue; more recent workings 170 ft (52 m) ahead showed 2 ft (0.6 m) of baryte.

As "D" Vein coverges south-eastwards upon the whin dyke mentioned above it splits into strings. S of the dyke a vein, formerly called "E" Vein, but now regarded as the continuation of "D" vein appears. Into this a level [NY 7664 1947] was driven at 1811 ft (552 m) above OD for about 270 ft (82 m). At about 165 ft (50 m) from the portal it meets the crosscut from "B" Low Level; this crosscut reveals no workable veins between "B" and "D" Veins. The dyke was not reached in "D" Low Level; the vein is about 1.5 ft (0.45 m) wide.

It will be clear from the foregoing that the veins at Long Fell are very pockety but with the reservation that the average width overall is probably small, there is little doubt that substantial reserves of barytes remain. The deepest workings are still at least 150 ft (46 m) above the base of the Melmerby Scar Limestone. The veins are known for much greater strike-lengths than have yet been explored.

The production of barytes by the Long Fell Co. amounted to about 23 000 tons. Production during World War II operations amounted to a total of about 8000 tons. A dressing plant to remove clay and fragments of country rock, was erected at Hilton; transport was by motor truck. When Long Fell became part of the target area of the Warcop firing range, blast walls were erected to protect the main adit, and funds were provided for the crosscuts mentioned above. However, by 1950 continued operation had become impossible and the mine was abandoned.

Carry Pots Veins—Barytes

NY71NE; Westmorland 16NW, NE

At the southern end of Long Fell the Carry Pots Fault cuts through the escarpment [NY 7700 1904], throwing the Melmerby Scar Limestone and underlying beds 100 ft (30 m) S. In the vicinity of Long Fell Pike the fault, with diminished throw, splits into a series of branches, several of which carry baryte. The northernmost one, trending N50°E, carried a pocket up to 9 ft (3 m) wide which was worked to a depth of 40 ft (12 m). A small production was obtained from these veins by Mr J T Bell about 1939; he also worked barytes from the supposed continuation of "D"Vein, NE of Long Fell on the E side of Tinside Rigg [NY 7733 1982]. A simple washing plant was in use in 1940 at the head of Warcop Scarth.

Middle Fell Veins—Barytes

NY71NE; Westmorland 16NE

On the top of Middle Fell, E of Warcop Scarth, a fault trending N30–50°E, downthrowing NW, carries baryte with a little galena in the Smiddy Limestone; in shallow workings which extend over a length of 600 ft (183 m). Three shafts, the southern one at [NY 7801 1858] sunk to the vein through the overlying shales also proved baryte. A trial 1350 ft (411 m) SW of the Smiddy Limestone workings showed 1 ft (0.3 m) of baryte in the Melmerby Scar Limestone; the vein dies out before reaching the steep western face of the fell. A parallel vein 400 ft (122 m) to the SE shows baryte up to 2 ft (0.6 m) wide in the Smiddy Limestone.

Key Scar Vein—Barytes

NY71NE; Westmorland 16NE

Near Hillbeck Wall End, 2 miles (3.2 km) NNW of Brough, trials have been made on a ramifying series of small veins trending between N80°E and N72°W in the Melmerby Scar Limestone at Key Scar [NY 7832 1716]. Pink baryte, with traces of galena and chalcopyrite is present on the dumps; the total length of ground explored is about 1800 ft (549 m). A trial has also been made on a N–S minor fault. The mineralisation appears to be feeble.

Carry Band Veins—Barytes

NY81NW; Westmorland 16SE

Trials have also been made on three nearly E–W veins on the N side of Carry Band [NY 802 164], 1.25 miles (2 km) NNE of Brough, in the Melmerby Scar Limestone and overlying shale. The middle vein shows baryte up to 1.5 ft (0.5 m) wide in the limestone; in the southern vein 2–2.5 ft (0.6–0.75 m) of baryte can be seen in a shallow opencut.

Augill Vein—Lead ore

NY81NW; Westmorland 17SW

The valley of Augill Beck is crossed, at a distance of 0.75 mile (1.2 km) NNE of the main Brough–Bowes Road, 1.25 miles (2 km) E of Brough, by a belt of steeply dipping strata which Turner (1935, p.131) has termed the "Dent Line", and which he regards as the northward continuation of the Dent Fault-system. In Augill the main fault associated with this belt, the Augill Vein, is an overthrust hading 50°SW and trending N70°W, along which sandstone and shales, of presumed Namurian age, are thrust against limestones of Asbian or earlier date. The lowest limestone adjacent to the fault, probably the Melmerby Scar, is overturned. It has been thoroughly dolomitised, and many tiny cracks in its have been filled with galena, pyrite, and pink baryte, the mineralisation extending as much as 50 ft (15 m) N of the fault. The low-grade orebody so produced has been worked opencast [NY 8219 1564], mainly on the NW side of the stream, and trial shafts have been sunk. Nothing is known about the continuity of the mineralisation away from the stream, but it is likely that similar geological conditions may persist for some distance. The broken ore was trammed to a crushing mill now in ruins 0.5 mile (0.8 km) NNE of the main road. A heap mainly consisting of dolomite cuttings remains. The period of the work is indicated by a return of 41 tons of lead concentrate in 1882–83.

Cabbish Vein and Parlour Vein

Both veins are branches of a fault having a small SE downthrow. They were worked at the Cabbish Mine (disused), near Peniston Green House, 0.5 mile (0.8 km) NE of North Stainmore church. The adit level, [NY 8377 1559], follows a winding NE course in the beds between the Great and Four Fathom limestones, at about 1100 ft (335 m) above OD; it has been walled up at the mouth and the underground workings were not examined during the resurvey. At 1150 ft (351 m) NE of the portal (direct distance) the SE end of the ground worked for barytes by the late Mr J G Reynoldson of Brough was reached. The total length of the stopes on the main vein was 1100 ft (335 m) (Mines Dept plan No. 8482), and the maximum height was 120 ft (37 m). The horizon of the workings was the Great Limestone, which dipped to the NE; the vein pinched in the overlying shale. Probably the height of the oreshoot was due to the fact that in this area the Great Limestone considerably exceeds its normal thickness as it enters the Stainmore Trough. The NE foreheads both on this vein and its branch, Parlour Vein, were abandoned in shale, due either to the eastward dip of the beds, to the effects of a cross-fault, or both. The workings were above adit level, except in the foremost 210 ft (64 m) of the main oreshoot, where an underground shaft 25 ft (7.6 m) deep gave access to understopes. It is not certain that the veins were ever adequately explored in limestone beyond the area in the shale.

The mine was developed for lead ore, 319 tons of concentrates being produced in 1854–64. It was reopened in 1905 for barytes, the production up to 1920 being 21 327 tons. Separate figures are not available up to 1930, when the mine was closed down, but the probable total production is of the order of 25 000 tons. A few tons of lead concentrates were picked from the barytes each year. Comparison of the output with the area of stoped ground suggests that the veins may have averaged 5 ft (1.5 m) in width.

References

ARTHURTON, R S, and WADGE, A J. 1981. Geology of the country around Penrith. Mem. Geol. Surv. G.B. 177pp.

BRAMMAL, V. 1921. The mining, manufacture and uses of barytes in the neighbourhood of Appleby, Westmorland. Trans. Inst. Min. Eng., Vol. 59, 42.

BRIDGES, T. 1982. An occurrence of nickel minerals in the Hilton Mine, Scordale, Cumbria. J. Russell Soc., Vol. 1, 33–39.

DUNHAM, K C. 1941. Iron ore deposits of the Northern Pennines. Geol. Surv. Wartime Pamph., No. 14.

DUNHAM, K C. 1959. Non-ferrous mining potentialities of the Northern Pennines. 115–148 in Future of non-ferrous mining in Great Britain and Ireland. (London: Institution of Mining & Metallurgy.)

JOHNSON, G A L, and DUNHAM, K C. 1963. The geology of Moor House. Mon. Nature Conservancy, No. 2. 182pp.

SHERLOCK, R. 1919. In sundry unbedded iron ores. Spec. Rep. Miner. Resour. Mem. Geol. Surv. G.B.,Vol. 9. 87pp.

TURNER, J S. 1935. Structural geology of Stainmore, Westmorland. Proc. Geol. Assoc., Vol. 46, 121.

WILSON, G V, EASTWOOD, T, POCOCK, R W, WRAY, D A, and ROBERTSON, T. 1922. Barytes and witherite (3rd edition). Spec. Rep. Miner. Resour. Mem. Geol. Surv. G.B., Vol. 2. 119pp.

Chapter 7 Mineral deposits. Details, Area 2 Alston Moor

The Alston Moor area covers the main South Tyne valley southwards from the neighbourhood of Alston, with the tributary valleys of Black Burn, Cross Gill, Ashgill and the Nent (Figure 20). The area lies almost wholly in the county of Cumbria. The lowest altitudes in the neighbourhood of Alston, are a little below 1000 ft (305 m) above OD, but most of the area lies between, 1000 and 2000 ft (305 and 610 m) above OD, and the fells which form the watersheds between the Tyne drainage and the Eden, Tees, Wear and Allen valleys reach heights exceeding 2000 ft (610 m) above OD. At surface the part of the area W of the South Tyne is occupied by rocks of Brigantian age. The Great Limestone and Namurian appears in the northern part of the area, in Gilderdale Forest, and continues south-east round Middle Fell and in the Nent valley; there is also an outlier of rocks of this age surrounding Cross Fell. In the South Tyne valley the Whin Sill is present directly below the Tynebottom Limestone; to the east it has not been proved, but there is reason to suppose that it lies at a much lower horizon; to the W of the South Tyne in the headwaters of Black Burn, it rises to the Single Post Limestone. The whole area contains mineral veins in abundance, but the most productive part lies in the Nenthead district, where the greatest concentration of lead-zinc deposits in the orefield and one of the greatest in Britain, has been worked. Alston Moor was formerly served by a branch line of the LNER terminating at Alston. The Nent and the E side of the South Tyne valleys are accessible by good roads from Alston, but much of the western part of the area is remote and not easily reached. The population, which is small, is confined to the valleys. Alston is the only town and forms a market centre; the principal villages are Nenthead in the Nent valley and Garrigill in the South Tyne valley. The area owes its development to its mineral wealth to a large degree, but at present it is mainly supported by sheep-farming on the fells, and agriculture in the valleys. Electricity is supplied by a grid-line which enters over the Hartside pass, and which extends as far as Nenthead. Almost the whole area formerly belonged to the Earl of Derwentwater, but at his attainder, following the 1715 rebellion, it passed to the Crown, and was assigned to the Commissioners of Greenwich Hospital. The present owners of the mineral royalties are their successor, The Catholic Trust.

For purposes of description it has been found convenient to divide the area into two subareas, the first comprising South Tynedale, Gilderdale, Black Burn and Crossgill valleys, including the western slopes of Middle Fell; the second the Nent Valley.

Subarea A South Tynedale

General description

Only in the northern and eastern parts of this subarea are there considerable stretches of Great Limestone and higher strata. The main South Tyne valley south of Alston and the two major western tributaries of Black Burn and Crossgill expose Brigantian rocks down to the Tynebottom Limestone, while in their upper reaches the Whin Sill makes its appearance, faulted up by the Great Sulphur Vein. In or about 1775 John Gilbert, part owner of mines on Middle Fell, proposed to the Receivers for the Commissioners of Greenwich Hospital the driving of an underground canal beneath the South Tyne from near Middle Craig ?[NY 725 842] to Lee House [NY 753 393] (Wilson, 1963). A shaft at Beldy Gin near Garrigiil (exact site not identified) when sunk to the required depth entered hard basalt and only 180–200 ft (55–61 m) of driving was done before the project was abandoned.

Ayle Burn Vein—Zinc ore

NY74NW, 75SW; Northumberland 104SW. Direction N75°E, throw 24 ft (7 m) NW, mineralised in Great Limestone and Tuft.

Ayle Burn Vein is the northernmost vein of Alston Moor, and lies just inside Northumberland. It was tried from a level starting from the N bank of Ayle Burn 150 ft (46 m) NE of the bridge on the Clargill–Ayle road [NY 7276 4978], at about 1090 ft (332 m) above OD, driven by the London Lead Co. about 1824. This runs 1225 ft (373 m) in a direction N21°W, cutting Ayle Burn Vein at 575 ft (175 m) from the portal. The vein carried blende and witherite in the Tuft sandstone; barytocalcite is also present on the dump. In the overlying Great Limestone a series of postmineralisation caverns, graphically described by Sopwith (1833, pp.64–67) have removed much of the possible mineralised ground, though a little galena is said to have been found. The base of the caverns, according to Sop-with, is 30 ft (9 m) above the level. The level continues, to cut at 1100 ft (335 m) from the portal a vein known as the Clay Vein; no record of its contents remains. The only record of production from Ayle Burn Vein is in 1894–96, when 122 tons of blende were obtained.

Clargill Vein

NY74NW; Cumberland 34NW. Direction N75–90°W, throw about 10 ft (3 m) N

This is a small fault which passes beneath Clargill Hall. It was tried from a level driven in the shale overlying the Great Limestone, the entrance to which is 1200 ft (366 m) NE of the Hall [NY 7290 4944]. The level must have been at least 900 ft (274 m) long as a crosscut, before reaching the vein; it is not now accessible. A little baryte and barytocalcite may be seen on the shale dump, but it is understood that the trial was unsuccessful.

Taylor's Groove Vein—Zinc ore, barytes

NY74NW; Cumberland 34NW. Direction N85°W, throw 7 ft (2 m) S, mineralised in Great Limestone.

The vein was developed by a level [NY 7219 4853] and shafts in the Great Limestone 1200 ft (366 m) NNE of Newshield. Wallace states that the lead deposits were poor, and did not repay the cost of extraction (1890, pp.185–186). Witherite, barytocalcite baryte and sphalerite occur on the small dumps; the production records show 168 tons of barytes in 1876–1886, and 176 tons of blende between 1893 and 1896.

Gilderdale Veins

NY64NE, SE; Cumberland 33SW, SE; Northumberland 106B,NW, NE (Old series)

The Gilderdale valley is crossed, 1 y4 miles (2 km) SW of the Alston–Brampton road, at [NY 6595 4580] by a NW fault which may be regarded as the continuation of Sir John's Vein, described below (p.129). This, with a small SW throw exposes the Whin Sill on the footwall side. Trials on the Northumberland side of Gilder-dale have revealed calcite, baryte and quartz with a little pyromorphite. At 120 ft (366 m) SW of this fault a second one crosses the valley, downthrowing NE, associated with a NE-facing monocline. Short levels driven NW between the Scar Limestone and Slaty Hazle reveal some limonitic mineralisation and malachite staining. Near the head of the valley, the NW Michaelly Sike Fault brings the Great Limestone into the valley bottom. A level [NY 6624 4427], starting 3.75 miles (6 km) SW of the Alston–Brampton road at 1440 ft (439 m) above OD has been driven at the base of the limestone a distance of 1500 ft (457 m) to the west; according to the primary survey map, this was partly driven on an E–W vein, but little mineralisation was found. Farther W, Daffenside Cleugh is cut by a number of NE smashes, possibly representing the continuation of the Hartside veins (pp.104–105), exposed in shales of the lower Namurian. These may some day repay exploration. The Michaelly Sike Fault carries a little baryte on the Northumberland side of Wold Gill at a high horizon in the Namurian, near Tom Smith's Stone, [NY 6572 4650] at 2071 ft (631 m) above OD. Baryte float is abundant in head deposits [NY 6518 4676] about 164 ft (50 m) above the Wolf Crag Grit. There is no record of production from any of these deposits. Access to them is difficult.

Horse Edge–Park veins—Iron ore (umber), barytes

NY64NE, SE; 74NW; Cumberland 33SE, 41NE. Direction N50°–55°E, throw about 10 ft (3 m) SE at Horse Edge; splitting into several branches throwing NW on Park Fell.

Horse Edge is a ridge [NY 685 446] on the SE side of the Gilderdale Valley, 2.75 miles (4.4 km) SW of Alston, capped by the Great Limestone. The Horse Edge Vein has been proved over a length of 1000 ft (305 m) by means of surface trenches on the SE side of the ridge. These appear to have been started as umber workings about 1886; they were reopened and extended in 1917–18, and again reopened and sampled for Home Ore Department, Ministry of Supply in 1941. The deposit here is a replacement of the Great Limestone by limonite, with which a little baryte and traces of galena are associated. The width in the trenches varied from 34 to 66 ft (10.4 to 20 m). The upper layer of the deposit was found to consist of umber, at least 10 ft (3 m) thick, overlain by boulder clay and peat 3–9 ft (1.1–2.9 m) thick. Beneath the umber layer hard limonitic ironstone occurs, but the junction between the layers is probably very irregular and a mixed zone exists. Sufficient data are not available to make possible an estimate of the relative quantities of umber and hard limonite present, but it is certain that a substantial tonnage of the former occurs. An estimate of tonnage at outcrop, based on a width of 30 ft (9.5 m) and 15 cu. ft per ton, gave 70 000 tons (Dunham, 1941). At the SW end of the outcrop, the deposit passes under the shale overlying the Great Limestone. It has been proved, 1250 ft (381 m) SW of this point, from an old level [NY 6792 4450] 820 ft (250 m) long, driven as a lead-prospect from the Gilderdale side of the ridge at the top of the Great Limestone. Hard ironstone is present in small quantity on the dump. The chemical composition of the Horse Edge deposit is illustrated by the analyses in (Table 38).

The umber is a brown clay-like substance, smooth to the touch in spite of its high silica-content, leaving a strong yellowish brown stain; its specific gravity is about 2.1. The mixed nature of the deposit makes it unsuitable for mining for iron ore. The south-summit of Horse Edge is traversed by several small veins which are regarded as belonging to the same vein-belt; they contain small quantities of limonite, baryte and galena and have been tried from levels driven from the NW side of the Edge, the principal one [NY 6807 4478] beginning 750 ft (229 m) NNE of the level mentioned in connexion with Horse Edge Vein.

North-east of Horse Edge, the vein-belt traverses beds below the Great Limestone and is crossed by the continuation of Sir John's Vein near the Maiden Way. On the SW side of Park Fell the belt re-enters the Great Limestone and here there are at least three separate veins. The middle one has yielded iron ore from a roughly circular flat, which appears to be exhausted. The south-eastern vein has been tried by a shaft about 25 ft (7.5 m) deep and levels. The ore on the dump is highly siliceous, as the analysis below shows. The proved width is said to have been 8 ft (2.4 m). On the NE side of the fell, iron ore has been worked at the Park Mines (disused) [NY 703 458] in Park Grove and Blackhouse Plantation. A considerable unworked stretch remains between the trials mentioned above and these mines, but it is impossible to say whether workable orebodies occur here. Baryte is present in greater quantity on the NE side of the fell, and a little was obtained here by Hedworth Barium Co. in 1916–18. Traces of witherite are also present at Park Mines.

Nearer Alston the Woodlands Level [NY 7150 4693] has proved the vein-belt from Hall Hill Plantation, W of the Railway Station, to the Alston–Brampton road. For the first several hundred feet this level ran through the boulder clay of a small drumlin. It was reopened by Hedworth Barium Co. in 1917–18 with the object of reaching flats containing iron ore and baryte in the Scar Limestone which were understood to have been left by the old miners. From information supplied by the late Mr C Heaps, the ironstone was found to be 12 ft (3.7 m) wide, in numerous flats close together.

E of the South Tyne the Park Veins were worked at the Manor House Mine (disused) in the Scar Limestone, the entrance to which [NY 7158 4701] was adjacent to the Railway Station. The deposits were limonitic replacements of the Scar Limestone. A description of this deposit has been given by Smith (1896, pp.17, 18). Probably the greater part of Alston Moor's output of 52 021 tons of iron ore between 1856 and 1875 came from here. The veins probably terminate against the Ayle Cross Vein, a small fault running N–S through Newshield.

Scarberry Hill Deposits

NY64SE; Cumberland 41NE

On the E side of Scarberry Hill the Great Limestone and associated strata are weakly mineralised with baryte and galena (Arthurton and Wadge, 1981). Trial shafts have been sunk at about [NY 6876 4385] and a level driven at [NY 6871 4367] in the beds above the limestone. No fault or vein has been mapped here with which the mineralisation may be associated though a connection with the Horse Edge Vein system to the north is possible.

Meathaw Hill Deposit NY64SE; Cumberland 41NE

Exposures of Great Limestone [NY 6772 4231] near the A686 road at Meathaw Hill show partial replacement of limestone by limonite. This mineralisation is probably associated with the northern continuation of the Rotherhope West Cross Vein.

Slote Vein to Fistas Rake (Blagill Old Vein)

The Blagill Mines (disused) at which these veins were worked lie on the southern spur of Newshield Moss, between the South Tyne and Nent valleys. Slote Vein, on which all the workings are very ancient, was reached by levels as follows (i) under the Great Limestone at about 1220 ft (372 m) OD, [NY 7240 4754] starting adjacent to the present Coatley Hill Limestone quarry; the dumps are obscured by quarry dumps (ii) in the shale above the Great Limestone, starting beside the Clargill–Blagill road 300 ft (91 m) [NY 7240 4754] N of High Spencycroft, and running 1000 ft (305 m) NNE as a crosscut to reach the vein (iii) Bunker Hill Level [NY 7256 4755], driven as a crosscut under the Little Limestone starting 600 ft (236 m) NE of High Spencycroft, reaching the vein at 775 ft (457 m), and continuing ENE for 1500 ft (457 m) on the vein. The dumps from these levels show a little witherite and much secondary baryte, probably developed by alteration of a barium carbonate, with limonite and a little galena. A vein carrying pyrite is stated to have intersected the Slote Vein at a small angle in a rise near the forehead of Bunker Hill Level. North of Slote Vein, a parallel string called Coatley Hill Vein has been tried from a level [NY 7202 4771] near the limestone quarry, while at the N end of Mounthooly Plantation a NW string called Copperbole Head Vein has also been tried from short levels [NY 7213 4791] in sandstone and shale of the Coal Sills. Thorngill Vein, called Lough Vein E of Blagill Burn, is the main vein of the group. Where cut in Bunker Hill Level, near its junction with Slote Vein, it was apparently unproductive. The western part of the vein was worked from Shop Level [NY 7345 4743], driven between the Little Limestone and the Pattinson Sill, starting 800 ft (244 m) NNW of Far Hilltop, at about 1400 ft (426 m) above OD, reaching the vein at 700 ft (213 m), and continuing W for 1750 ft (533 m) Blagill Green Level [NY 7322 4732], starting 1250 ft (381 m)WNW of Far Hilltop, reached the vein at 1350 ft (411 m), near the base of the Coal Sill sandstone. Here a sump was sunk into the Great Limestone, but apparently without success. The productive part of the vein apparently lay on either side of Blagill Burn; here there are large opencuts. The vein, exposed west of the Burn in the Great Limestone [NY 742 476], is 7 ft (2.1 m) wide, composed of limonite with a little sphalerite and traces of galena. Some iron ore was worked here, and also farther W, where the vein cuts through the Little Limestone, and gives off a SSW branch called Thorngill Sun Vein. The principal underground workings were Thorngill Top Level [NY 7462 4753], which explored the vein for 850 ft (259 m) in the Quarry Hazle, and Thorngill Low Level [NY 7395 4720], driven in the Nattrass Gill Hazle from the burn side, reaching the vein at 1400 ft (427 m), and continuing 1650 ft (503 m) westward on the vein. A rise near the forehead of the Low Level linked it to the Shop Level. Probably there are extensive scopes in this vein, but although plans of the levels are in existence (Mines Dept Nos. 4984, R10, and R393A) no stope section has been found.

E of Blagill Burn large opencasts 1750 ft (533 m) long reach up to the Firestone on Lough Vein; limonite again appears to have been the principal gangue mineral in the old lead workings. At 2200 ft (671 m) E of the burn, Lough Vein is intersected by Fistas Rake. This strong NE vein carried lead ore-shoots in the Great and Four Fathom limestones and in the Quarry Hazle, the gangue mineral being mainly barytocalcite with a little witherite and calcite. The vein is said to have been 9–10 ft (2.7–3 m), and to have had flats associated with it. The main levels were driven under the Great Limestone at about 1250 ft (381 m) above OD [NY 7413 4732], and beneath the Four Fathom Limestone from the side of Blagill Burn. Trials beneath the Four Fathom Limestone were not successful. The following analyses of ironstone from Thorngill Vein, and the barytocalcite on the dumps from Fistas Rake

The name Blagill is probably derived from Bleigill suggesting that German miners worked here: this may perhaps be connected with Wallace's statement (1891, p.109) that the Alston Moor mines were held under lease in 1359 to one Tilman of Cologne; much of the lead working here is certainly ancient. Production figures for lead concentrates, which are incomplete, and in the main represent no more than the last gleanings from these strong veins, are as follows: Thorngill West, 219 tons in 1849–63: Thorngill East, 206 tons in 1851–63; Blagill, 1192 tons in 1848–81. The silver content varied from 6 to 7 oz silver per ton of lead. The London Lead Co. minute books show that in the quarter ending June 1721, Thorngill Vein yielded 200 bings (80 tons) of ore, perhaps giving a glimpse of the mine in its heyday. Between 1876 and 1895 Blagill was a producer of "witherite", 1652 tons being obtained from Fistas Rake. It is significant that whereas in 1894–5 Blagill "witherite" was being sold, according to the Greenwich Hospital records, for 25/- to 35/-per ton, the witherite from Nentsberry, which came onto the market at about that time, realised 45/- to 100/- per ton. There is little doubt that Blagill "witherite" was actually barytocalcite, and that the availability of Nentsberry witherite closed the market to Blagill. Considerable reserves of barytocalcite may remain on Fistas Rake, should any market be found for a product containing as little as 50 per cent barium oxide.

Brownside Veins—Iron ore

NY74SW; Cumberland 33SE. Direction N52°E, branching to N75°E, throw not known.

The main vein crosses the low road from Alston to Garrigill 1 miles (2.4 km) S of the town 900 ft (274 m) SE of Gill House. On the W side of the road a small plantation has grown over the subsidence [NY 7102 4434] caused by the working of a flat of ironstone in the Scar Limestone. The vein which branches near the road, has been followed SW from a level whose mouth [NY 7137 4465] can be seen near the South Tyne. It is not known whether any ironstone remains unworked in this mine, and there is no plan. As shown by the analysis quoted below the ore remaining on the dump near the river is very siliceous.

Nest Veins—Iron ore

NY74SW; Cumberland 34SW

Two veins running N74°E, one running N60°E productive in Scar Limestone.

The Nest Mines (disused) [NY 718 443] on the E bank of the S Tyne, 1.5 miles (2.4 km) S of Alston were, next to Manor House Mine, the most important iron-ore producers in Alston Moor. Three ENE veins are known, the southern pair, with throws of 18 ft (5.5 m) S and 15 ft (4.6 m) N respectively, making a fault trough. Low Nest Level [NY 7170 4445] at about 965 ft (294 m) above OD gave access to the orebodies, which were flats in the Scar Limestone; no plan remains. Some large pieces of iron ore left on the dumps proved to be limonite boxworks, with cores of unreplaced limestone. The limonite is hard and dense, some greasy hematite being present. The analysis quoted in (Table 41) refers to this material and is not necessarily representative of the composition of the whole orebody worked here.

High Nest Mine [NY 7169 4431], 1000 ft (305 m) SW of High Nest, is an old opencast working in a flat in the Scar Limestone. There is no detailed plan of these mines, but an old general plan of Alston Moor (in the possession of the Mines Department) shows a level driven SE from the waterfall in Nattrass Gill to cut these veins below the Five Yard Limestone. the level is shown dotted on the plan and it is not certain that it was completed. The veins may represent the SW continuations of some of the veins worked near Nattrass, on Middle Fell, but no correlation can definitely be made. No separate production figures are available. Access is by a poor road which leaves the Alston–Middleton main road 1.5 miles (2.4 km) S of Alston, running to High Nest Farm.

Bayle Hill Vein and Middle Fell Cross Vein

The old Bayle Hill Mines (disused) lie at the end of Potter's Lane on Middle Fell, 0.75 mile (1.2 km) SE of Alston. Here Bayle Hill Vein is crossed by Middle Fell Cross Vein. Both veins have been wrought opencast [NY 7285 4565] and by short levels [NY 7269 4581] and [NY 7277 4565] in the Great Limestone. The veinstuff consists of smithsonite (calamine), presumably an oxidation product of sphalerite, and calcite, with some aragonite. Between 1877 and 1890 387 tons of calamine were sold from Bayle Hill; the mine also probably contributed to the total of 2335 tons of oxidised zinc ore raised in Alston Moor between 1854 and 1871.

Bayle Hill Vein has also been tried from a level [NY 7445 4665] driven on Hudgill Cross Vein from the side of the Nent, 1750 ft (533 m) WSW of Foreshield. Very coarse sphalerite associated with siderite on the dump probably came from the workings in the Six Fathom Hazle on the cross Vein (Sopwith, 1829, pl. 11) rather than from the trial on Bayle Hill Vein, which was made by a sump to the same horizon. Wallace (1861) on his map shows the vein as poor except at the intersection with the Cross Vein. On the NE side of the Nent, shafts near Foreshield and Cocklake failed to find anything of value in it.

The northern slopes of Middle Fell are thickly covered with boulder clay. The level on Hudgill Burn Cross Vein referred to above was driven in clay for the first 965 ft (294 m). Four prospecting levels [NY 7355 4576], [NY 7353 4600], [NY 7405 4618] and [NY 7438 4608] driven southwards from the S side of the Alston–Nenthead road, three of which were over 1500 ft (457 m) long, passed through boulder clay. None of these found anything of value, though a little ankerite is seen on the dump of one of them [NY 7405 4618], driven at the horizon of the Four Fathom Limestone, starting 1700 ft (518 m) ESE of High Skelgill. The old general plan of Alston Moor shows that the two levels from Skelgill Burn, one above and the other below the Great Limestone, cut several weak veins.

S of Bayle Hill Vein the primary map shows three small parallel veins, High Bayle Hill, Farnberry Field and Limekiln veins, but no surface evidence of these now remains.

Farnberry Old Vein—Zinc ore (calamine)

NY74NW, SW; Cumberland 34SW. Direction N52°E; productive in the Great Limestone.

Farnberry Mine (disused) is entered by means of a crosscut north at the base of the Great Limestone [NY 7319 4493], reaching the vein at 675 ft (206 m); workings extend to 450 ft (137 m) NE in the vein. A trial from a level driven 1500 ft (457 m) SE in the coal and overlying shale above the High Coal Sill, which reached Farnberry Vein near its forehead appears to have been unsuccessful. The dumps are mingled with those from Holyfield Mine (below).

Holyfield Old Vein and Holyfield Sun(Quaker Vein)

Both veins were worked at Holyfield Mine (disused), 1.5 miles (2.4 km) SE of Alston. The Old Vein was developed from a level [NY 7320 4491] starting 500 ft (152 m) E of Nattrass, above the Great Limestone from which the oreshoot, 1250 ft (381 m) long, in the limestone was worked by means of sumps. The Sun Vein was reached from a level driven below the limestone, starting close to Farnberry Level; the total worked length was 2350 ft (716 m). A section by Sopwith (1829, pl. 1) shows a vein-stope commencing 1250 ft (381 m) from the level mouth, 750 ft by 30 ft (299 by 9 m), in the bottom part of the limestone, succeeded to the NE by a stope 500 ft by 35 ft (152 by 10.6 m) in the upper part of the limestone. The second stope commences where an E–W "swinning" vein or string cuts through the main vein. From the same point northeastwards, flats extending 20–30 ft (6–9 m) from the vein on the NW side were worked at the horizon of the Middle Flat, 15–25 ft (4.6–7.6 m) above the base of the limestone, for a total length of 800 ft (244 m). One plan of the mine (Mines Dept No. 396A) shows similar though smaller flats associated with the Old Vein. On the Sun Vein small flats were also found at the High Flat horizon, 46 ft (14 m) above the base of the limestone. Three trials were made of beds above the Great Limestone; nothing of value was found. The underlying beds are not known to have been tested. The mineralisation consisted of galena, cerussite, smithsonite (calamine) with aragonite and calcite. Wallace (1861, p.199) notes the extensive alteration which has affected the zinc deposits here, and remarks that in some instances joints in the limestone have been filled with secondary calamine. This mineral is common on the dumps, in spite of the fact that the mine was worked for it and the dumps picked over between 1850 and 1870. A picked sample gave the following assay: zinc, 25.63 per cent; lead, 0.07; sulphur, 0.04 (Analysts, Mineral Resources Laboratories, Imperial Institute, 1941). Production of lead concentrates was as follows: 1793–1865, 8387 tons; no separate figures for calamine are available, but the mine probably contributed to the Alston Moor total.

Nattrass Old Vein, Millican's Vein and Nattrass Redgroves Vein

These veins were worked at the old Nattrass Mines (disused), 0.5 mile (0.8 km) E of the bridge over Nattrass Gill on the Alston–Middleton main road. The principal working is a great opencast, Redgroves Hush [NY 740 449], on Redgroves Vein, in which the vein was worked in the sandstones, sandy shales and shales between the Firestone and the Low Grit. Underground workings were reached from Nattrass Level [NY 7349 4482], driven in the shale above the Great Limestone; abundant limestone, both limonitised and unaltered on the dump indicates that there must have been sump-workings in the Great, but no plan is extant. The gangue minerals were quartz and calcite; some secondary zinc minerals were probably obtained here. Young et al (1989, p.389) record small quantities of cinnabar in association with smithsonite from the dump of Nattrass Level. The total length of worked ground extends 3000 ft (914 m) NE of the level mouth. A trial level [NY 7318 4473] beneath the Great Limestone from the side of Nattrass Gill appears to have had little success. The mine was being worked in the eighteenth century before the Greenwich Hospital took over the royalty (Wallace, 1890, App. II); the production of 227 tons of lead concentrates in 1850–68 no doubt represents the last gleanings before abandonment.

Flow Edge Vein—Lead ore

NY74SW; Cumberland 34SW Direction N70°E

The Flow Edge Mine (disused) was entered by a level [NY 7360 4442] starting 3000 ft (914 m) SE of Nattrass Gill Bridge, driven in the shale above the Great Limestone. According to Wallace's map (1861) a rich oreshoot about 900 ft (274 m) long was found probably in the Great Limestone. The gangue minerals included quartz and aragonite; a little sphalerite is present on the dump. A trial above the Firestone, from surface, was unsuccessful. For the years 1790–1859 recorded production amounted to 5363 tons of lead concentrates. A weak parallel string called Flow Edge Sun Vein occurs 300 ft (91 m) SE of Flow Edge Vein, and has been tested above the Great Limestone.

Birchy Bank Veins

NY64SE; Cumberland 41NE, SE

Between the junctions of Rowgill Beck and Smittergill Burn with Black Burn five veins have been tested at or near the horizon of the Scar Limestone, all trending NE. High Birchy Bank Vein, the second vein N of Smittergill, throws N bringing the Scar Limestone into contact with the Five Yard; the remainder have only small throws. The mineralisation, as revealed by short levels, shafts and a hush [NY 6848 4100] on the E bank of Black Burn is similar in all five veins consisting mainly of quartz with marcasite and pyrite: galena and fluorite are found locally e.g. [NY 6856 4116]. These veins may be regarded as part of the Great Sulphur Vein suite, described below.

Smittergill Hill Vein? = Victoria Vein—Lead ore

NY64SE, NE; Cumberland 41SE, NE. Direction N55–60°E. Throw about 50 ft (15 m) SE as it crosses Smittergill (from geophysical measurement); decreasing rapidly to NE. Victoria Vein throws 9 ft (2.7 m) SE in Rotherhope Fell Mine, and is mineralised in Scar Limestone.

Smittergill Hill Vein crosses Black Burn 328 ft (100 m) N of the junction with Smittergill Burn. On the E side of Black Burn the vein has been worked in beds ranging from the Copper Hazel up to the Five Yard Limestone, from numerous shallow shafts and a short cross-cut level at [NY 6853 4051]. The dumps from these workings show quartz, fluorite and galena. Victoria Vein, formerly worked at Rotherhope Fell Mine (below) may be the NE continuation of this vein; it carried fluorite, ankerite and galena in the Scar Limestone, and was worked SW of Blackburn Level. To the NE a drift was driven from Blackburn Level 116 ft (35 m) by the Vielle Montagne Zinc Co. and two rises were opened, proving only traces of galena and sphalerite in the Alternating Beds and Scar Limestone. A vertical diamond borehole from Blackburn Level, starting 7 ft (2.1 m) N of the vein entered vein-breccia at 68 ft (21 m), containing quartz, and calcite with a little galena and sphalerite, and reached the Tynebottom Limestone from 81 to 94 ft (24.7 to 28.7 m) below the level. The limestone was strongly silicified with associated ankerite and calcite, but no galena. In view of the strongly mineralised flats in the Tynebottom Limestone on Rotherhope Fell Vein to the SE, Victoria Vein may be worthy of a further trial at this horizon, in spite of the failure of the first boring.

Smittergill Hill Sun Vein = Rotherhope Fell Vein = Rotherhope Cleugh Sun Vein = Crag Green North Vein = Dowpot Sike Vein—Lead ore, fluorspar

NY64SE, 74SW; Cumberland 41SE, NE, NW; 34SW. Direction N65°E, with a short stretch at N45°E. Throw decreases from 180 ft (55 m) SE in Smittergill, Vs mile (0.8 km) SW of confluence with Black Burn to 100 ft (30 m) S at Black Burn, according to geophysical measurements; proved throw in Rotherhope Fell Mine, 40 ft (12.2 m) SE west of West Cross Vein, 35 ft (10.7 m) SE at central flats, 24 ft (7.3 m) SE at No. 1 Underground Shaft: decreasing NE, small or zero at Crag Green.

The Rotherhope Fell Vein may be regarded as the most important channel of mineralisation in the western part of Alston Moor. It is unique in carrying substantial oreshoots in the middle part of the Brigantian and in the Whin Sill, which at Rotherhope Mine directly underlies the Tynebottom Limestone. The south-western stretch of the vein, which is believed to follow the Smittergill valley from the Great Sulphur Vein to Black Burn, has not been prospected, but the presence of a fault of some magnitude beneath the valley was established by means of a magnetometer survey (Hallimond and Eyles, 1949) carried out in conjunction with the present investigation. The vein has been tried by opencut immediately NE of Black Burn [NY 6865 4033] at about the level of the Scar Limestone where it carries only feeble quartz mineralisation. It is exposed in Smittergill Burn on the SE side of a small inlier of Whin Sill [NY 6834 4005] where' it carries tabular epimorphs in quartz after pyrite and marcasite, a feature characteristic of the Great Sulphur Vein suite. In the stream some 1640 ft (500 m) to the SW the vein is exposed and is seen to comprise quartz up to 13 ft (4 m) wide with inclusions of altered sedimentary wall-rock. The vein probably extends to the SW to merge with the Great Sulphur Vein. At 3600 ft (1097 m) NE of Black Burn, the Rotherhope West Cross Vein (throw 12 ft (3.7 m) E) cuts through the vein, shifting it about 80 ft (24 m) E side S; the direction of Rotherhope Fell Vein changes to N80°E, 400 ft (122 m) SW of the cross vein, but resumes its normal direction immediately NE of the intersection.

Here the oreshoots of Rotherhope Fell Mine (disused) commence. There are two principal vein-shoots, both of which have been productive against beds ranging downwards from the Five Yard Limestone to the Whin Sill. The western oreshoot is approximately 1000 ft (305 m) long with a maximum vertical extent of nearly 400 ft (122 m). The workings in the Whin Sill on this shoot revealed its width as 8–10 ft (2.4–3 m). A stretch of ground barren or poor in the beds above the Tynebottom Limestone separates the western from the eastern vein-shoot which has a maximum length of 2100 ft by 400 ft (640 by 122 m) average height, the height in one place exceeding 500 ft (152 m). In the Whin Sill on this shoot the vein was 17–20 ft (5.2–6 m) wide. Another cross vein passes through the vein within this oreshoot, but its exact location is now uncertain. According to an old plan (Mines Dept No. R.120E) the throw on the cross vein is about 40 ft (12 m) E but there are reasons for doubting the accuracy of this figure. Between the two vein-shoots, flats are developed in the Tynebottom Limestone related to strings diverging from the vein (Figure 14), p.67). These are strongest on the footwall (N) side of the vein, where they extend over 300 ft (91 m) from the vein, but they are also present on the hangingwall side. Adjacent to the leader nearest the vein more or less the full thickness of the Tynebottom Limestone, excepting the top shaly bed, 3 ft 6 in (1.5 m) thick, has been replaced. Away from the vein the mineralised thickness diminishes to 8 ft (2.4 m) and then to 5 ft (1.5 m), the mineralised portion being the limestone immediately below the shaly top bed. The grade of lead ore obtainable was better where the flat was thin. In 1942–43 diamond borings both SW and NE of the rich footwall flat showed that the limestone is not mineralised on either side of the central area between the two vein-shoots. Another flat was, however, discovered W of the West Cross Vein, on the hangingwall side of the vein. The only workable flat-ground in the Tynebottom Limestone so far found adjacent to the vein-oreshoots is situated near the centre of the eastern shoot, where a large number of leaders were found on the N side of the vein.

Rotherhope Fell Vein was probably originally prospected from an adit driven SW on the vein from Rotherhope Cleugh [NY 7074 4120] under the Three Yard Limestone at 1210 ft (368 m) above OD. The main development was, however, by long crosscut-levels from the north. Middle Level [NY 6971 4199], giving access to the workings in and above the Scar Limestone starts at 1250 ft (381 m) above OD, and runs SSE, reaching Victoria Vein at 1140 ft (347 m) and Rotherhope Vein at 2350 ft (716 m). This level was latterly used only as a tailrace for water from hydraulic machinery. The Blackburn Level [NY 6993 4264], formerly the working entrance to the mine, was engineered by Smeaton and started from the south bank of the burn, 0.75 mile (1.2 km) SW of Blackburn Bridge on the low road from Alston to Garrigill, at 1035 ft (315 m) above OD. It runs S2°E to Victoria Vein at 2900 ft (884 m) then turns SSE and reaches the main vein at 4200 ft (1280 m). This level is driven through a broad syncline, of amplitude about 50 ft (15 m), in the Alternating Beds at or above the horizon of the Single Post Limestone. The Rotherhope Vein is accompanied by a flat-topped anticline of about 40 ft (12 m) amplitude, underneath which flats lie, when they are present. Two underground shafts have been sunk near the point where Blackburn Level reaches the main vein: No. 1 is 370 ft (113 m) deep, and No. 2 is 120 ft (36.5 m) deep. No 1 shaft tested the vein down to the footwall position of the Jew Limestone, where the vein was 8 ft (2.4 m) wide, but carried only poor lead values. The main working level from the shaft was at 120 ft (36.5 m) and there was a short level at 250 ft (76.2 m), at the base of the Whin Sill. Blackburn Level continues 1500 ft (457 m) NE of No. 1 Shaft on the vein, but this part of the level was not recently accessible. To the SW the level reaches the West Cross Vein at 2850 ft (869 m), from No. 1 shaft, and has been driven through and about 1000 ft (305 m) beyond the cross vein. The central footwall flats were reached by a 1 in 3 incline from Blackburn Level, which was continued into the hangingwall flats. The vein-workings in the Whin Sill on the western oreshoot were reached from No. 3 underground shaft, 2060 ft (628 m) SW of No. 1, 140 ft (42.7 m) deep.

The minerals in the vein include, in order of abundance, fluorite, quartz, galena, carbonates, pyrite, marcasite and a little sphalerite. Traces of chalcopyrite are present. There is definite evidence of downward increase of quartz relative to fluorite, as shown by the composition of the tailings dumps from Middle and Blackburn levels (Table 42).

Within the flats the same minerals are present, but silica, mainly as chalcedony, greatly predominates over all the rest, as the analysis quoted on p.83 shows. Traces of erythrite have been found locally. A description of the characteristics of the metasomatised Tynebottom Limestone has already been given. The average galena-content of both vein and flats has probably not exceeded 8 per cent, though the outer part of the central footwall flat considerably exceeded this figure in 1940–41. The mine has not, therefore, been very successful in spite of the substantial oreshoots and has had long periods of difficulty. It was equipped with a modern jig and table mill, of capacity about 6 tons feed per hour, worked by water-turbine, but with stand-by oil engines. Compressed air was supplied by a hydraulic system, and by electric compressors installed underground. Production figures are fairly complete; the total yield of lead concentrates from 1827 to 1938 was 60 076 tons, of which 14 471 tons were produced by the Vieille Montagne Co. since 1913; between 1939 and 1947 some 4720 tons were produced. The mill produced concentrates of excellent grade, exceeding 80 per cent lead. The average silver content is 2 to 3 oz silver per ton of lead. Fluorspar has been produced by hand-picking veinstuff; 894 tons are recorded between 1906 and 1914. The grand total of 14 100 tons of product fluorspar is recorded from Rotherhope Fell Mine. Preparations were made for milling Middle Level tailings during the 1914 war, but apparently these did not come to fruition. During the 1939–45 war there was a small output from the vein, and from the milling of tailings at Nentsberry. Analyses above illustrate the grade obtained during tests on Middle Level material. Extraction of lead ore from the flats continued until 1948, the yearly output of concentrates obtained being about 1000 tons. The Vieille Montagne Co.'s properties were then taken over by Anglo-Austral Mines, a subsidiary of Imperial Smelting Corporation, and Rotherhope Fell Mine was closed down and dismantled. Subsequently some fluorspar was produced by a small firm with a plant near Alston Station; and since 1974 Middle Level tailings have been lorried to Frosterly (Weardale) for treatment. The possibility cannot be dismissed that ground workable for lead and fluorspar remains in the mine below Blackburn Level, or that new oreshoots might be found in the Whin Sill below Smittergill or towards Crag Green.

The ground S of Rotherhope Fell Vein has been prospected by means of a series of levels driven S or SSE. Middle Level was extended 1150 ft (35 m) SSE of the vein, cutting "Rotherhope New Vein" (throw 1 4 ft (0.45 m) NW) near the forehead. Apparently this vein was not productive. High Level [NY 6986 4157], starting from Middle Gill at 1340 ft (408 m) above OD passed through Rotherhope Fell Vein at 700 ft (213 m) above the top of the eastern oreshoot, cut the New Vein at 1875 ft (572 m) and continued to 4300 ft (1311 m), cutting another small vein. This trial was at about the horizon of the Three Yard Limestone and Six Fathom Hazle.

The productive ground on Rotherhope Fell Vein ceases before Rotherhope Cleugh is reached, and for the remainder of its course as Crag Green North Vein and as Dowpot Sike Vein it has been poor at all the horizons tried, including the Scar, Four Fathom and Great limestones. Smyth (1856, p. 17) states that NE of the Tyne the Crag Green Vein carried brown iron ore 16 to 20 ft (4.9 to 6.1 m) wide in the Scar Limestone but from the position of the working it seems that this was probably not on the main vein, but on a SW branch, or perhaps even on Guttergill Vein. At Crag Green the vein was reached by a crosscut level under the Great Limestone [NY 7291 4360] running ESE from the Alston–Middleton road near the second milestone from Alston. The vein may be seen at the S end of Howhill Quarry [NY 7296 4336], as a limonitised smash, without sulphides, in the Great Limestone. Dowpot Sike [NY 739 443], farther to the NE, is an old opencut on the vein in the sandstone and shales above the Great Limestone. A little galena was found here in the vein and in strings branching off it; none was got in the limestone below. Altogether 1662 tons of lead concentrates were raised from the Dowpot Sike portion of the vein and from the adjacent Guttergill Vein (described below) in 1848–1887.

Weatherall Mea Vein; Greencastle Veins

NY64SE,74SW; Cumberland 41SE

SE of Rotherhope Fell Vein in Black Burn there is a series of NE veins which step down the beds in a SE direction. These carry quartz, with marcasite and pyrite, or with the tabular epimorphs left by the weathering-out of these minerals. Greencastle Vein is exposed in Black Burn [NY 6894 3962] where it is 10 ft (3 m) wide and composed of quartz, pyrite and marcasite. A Level [NY 6902 3969] on it shows quartz, with no trace of sulphides other than those of iron. Quartz veining in the Scar Limestone in Swarth Beck [NY 6878 3956] may represent the extension of the vein to the SW. A vein, parallel to Greencastle Vein, is exposed in Black Burn [NY 6910 3959] where it is seen to be 6.5 ft (2 m) wide composed of quartz and pyrite. The veins show as ribs of quartz where they cross the limestones on the east side of the valley. Above the Great Limestone Greencastle Vein carries some fluorite 600 ft (183 m) N of the Tarn. Charlton's Level [NY 7022 4097], driven S from Red Sike, starting at about 1475 ft (450 m) above OD, 1.25 miles (2 km) S of Rotherhope Fell Mine, tested all the Greencastle Veins between the Four Fathom and Great limestones, without success. Cleugh Head Level [NY 7065 4060) at 1500 ft (457 m) above OD, driven 3000 ft (914 m) SSE from Rotherhope Cleugh under the Great Limestone was equally unsuccessful, while Rotherhope Fell High Level [NY 6996 4157], which reached Greencastle Tarn Vein at its forehead, found nothing worth working. Stone Currack Level [NY 7118 4034], starting 1900 ft (579 m) ESE of Cleugh Head Level above the Great Limestone was also unsuccessful. This very extensive series of underground levels may be regarded as having very thoroughly explored the horizons accessible to adits on Rotherhope Fell for a N and S distance of 2 miles (3.2 km); they represent a total of 18 725 ft (5.7 km) of drivage. The only payable vein discovered was Rotherhope Fell Vein; among the only possibilities which remain on the other veins is that there may be flats in the Tynebottom Limestone associated with some of them.

Guttergill Vein, Crag Green Middle Vein and Crag Green Sun Vein

Guttergill Vein was worked by means of a crosscut from Crag Green North Vein, leaving that vein 350 ft (107 m) NE of the point where the adit level [NY 7291 4360] starting by the second milestone on the Alston–Middleton road joins that vein. The small production obtained from the Great Limestone is included with that of Dowpot Sike, given above. The Crag Green Middle and Sun veins appear to have been stronger veins, and from them the bulk of the production of Crag Green Mine (disused) was obtained. The main access-level [NY 7322 4299] was on the Sun Vein, starting on the NE side of the Alston–Garrigill road, 1200 ft (365 m) SE of Howhill House, driven in the shale below the Tuft. This reached the vein at 225 ft (69 m), and continued 3100 ft (914 m) in the Sun Vein in a NE direction, the vein curving round from N55°E to N80°E as it approached Old Groves Cross Vein. At 1450 ft (442 m) from the level mouth, the vein having been poor up to this point, a cross vein, believed by Wallace (1861) to be the southward continuation of the Ayle Cross Vein, was cut; the Sun Vein beyond it became productive in the Great Limestone, the oreshoot continuing to Old Groves Cross Vein. Here the vein was lost; drives in both directions on the cross vein failed to locate it. A crosscut from this level starting 1600 ft (488 m) from the level mouth ran 825 ft (25 m) NNW to the Middle Vein, which also carried an oreshoot in the Great Limestone between Ayle and Old Groves Cross veins, and which was likewise lost NE of the latter cross vein. The gangue minerals included massive aragonite, purple fluorite and quartz, with limonite replacing an iron carbonate. The production of galena amounted to 5604 tons in 1792–1812; there are no records between 1813 and 1849; 80 tons were obtained between 1850 and 1862. A trial of the Sun Vein in the Scar Limestone was unsuccessful, and there is no reason to expect any extension of the oreshoots, long since worked out, at this mine. To the NE of Old Groves Cross Vein there is, however, a large virgin area untried apart from short drives on the cross vein. A stratigraphically lower test of the Crag Green veins beside the Tyne at [NY 7258 4290] appears to have had little success.

Black Sike Vein and Fletcheras Vein

These two veins together form a fault-trough on the SW side of Old Groves Cross Vein, which, however, dies out before the outcrop of the Great Limestone is reached. The most productive ground was in the Firestone, on Fletcheras Vein; there is a great spread of tailings [NY 744 433] from ancient hand-dressing of lead ore on the hillside above the outcrop of this sandstone, containing quartz, siderite and limonite. The Firestone oreshoot lay on the NE side of Old Groves Cross Vein; it was worked by shallow whimsey shafts, and drained by a long level in the shale under the Firestone [NY 7433 4319], driven from the E. In the Great Limestone, Fletcheras Vein was explored from High Hundybridge Level (disused) [NY 7387 4285] at about 1410 ft (430 m) above OD, which starts in the Tuft, in the plantation 400 ft (122 m) S of High Hundybridge House. A notable amount of sphalerite, much of it in sandstone, is present in the tailings on the substantial dumps from this level. The level reaches Old Groves Cross Vein at 2100 ft (640 m) from the portal; here it turns NW on the cross vein, cutting Black Sike Vein on the SW side at 150 ft (46 m), and what was supposed to be the same vein on the NE side at 225 ft (69 m). The forehead stands 525 ft (160 m) NW of Fletcheras Vein. To the SE a drift on the cross vein links up with the Hundybridge and Cowper Dyke Heads workings, described below. The production of lead concentrates from Fletcheras Vein in 1778–1878 amounted to 3172 tons; Black Sike Vein yielded 452 tons in 1850–68.

Hundybridge Vein and Cowper Dyke Heads Vein

Cowper Dyke Heads Mine (disused) is entered by a level [NY 7409 4260] under the Quarry Hazle, the portal of which is 1000 ft (305 m) SE of High Hundybridge Level, 0.75 mile (1.2 km) NNW of Garrigill village green. This is driven directly on Cowper Dyke Heads Vein, reaching Old Groves Cross Vein at 2150 ft (655 m) where a shaft communicates with the surface. The vein, according to Wallace (1861, p.201) contained little lead ore SW of the cross vein. To the NE the vein is said to be weak, not more than a few inches in width, containing a little galena but not enough to pay the cost of extraction. At Old Groves Shaft [NY 7465 4295], where Cowper Dyke Heads Vein joins the cross vein, there is a connection along the cross vein to High Hundybridge Level. At 250 ft (76 m) NW of the shaft, a small fault called Crafty Vein, throwing 4 ft (1.2 m) NW was cut and tried. At 800 ft (244 m) NW of the shaft the Hundybridge Vein is encountered. The productive ground on this lay to the NE of the cross vein; to the SW the vein is split up and poor. Two oreshoots, respectively 800 (244 m) and 600 ft (183 m) long, separated by 350 ft (107 m) of barren ground were worked in the Great Limestone; access to these was from a crosscut at Cowper Dyke Heads level, driven from Old Groves shaft. The forehead of this level in Hundybridge Vein stands 2250 ft (686 m) NE of Old Groves Cross Vein, 15 ft (4.6 m) below the base of the Great Limestone. Hundybridge Vein was tried in the Firestone from a long crosscut adit [NY 7498 4288] at 1620 ft (494 m) above OD, starting 1400 ft (427 m) N of the bridge over Garrigill Burn on the Alston-Middleton road. The trial was unsuccessful. Wallace (1861, p.144) remarks that the Cowper Dyke. Heads veins were plentifully mineralised with calcite and fluorite in the Great Limestone, and figures a cross-section of one of them (Plate 6), (Figure 1). The occurrence of coarse fluorite on the dumps from Cowper Dyke Heads Level bears out this statement. Possibly some reserves of fluorspar remain here; but the exact location of the portions of the veins carrying this mineral is not known. The production of lead concentrates in 1848–1872 from Cowper Dyke Heads Mine amounted to 840 tons. A little work, in search of zinc ore, was done during the Vieille Montague Zinc Co.'s tenure of the royalty.

Cowper Dyke Heads Sun Vein—Lead ore (Fluorspar)

NY74SE; Cumberland 41NW. Direction N63°E

On the NE side of Old Groves Cross Vein, approximately 1100 ft (335 m) SE of the course of Cowper Dyke Head Vein, a small vein has been prospected by means of a crosscut adit [NY 7519 4264] starting 750 ft (229 m) NE of Garrigill Burn Bridge on top of the Great Limestone at 1495 ft (456 m) above OD. Sumps were probably sunk into the Great Limestone on the vein; the dump from the level contains limestone, with coarse purple fluorite, sphalerite, pyrite, quartz and limonite.

Old Groves Cross Vein Lead ore

NY74SW, SE; Cumberland 34SW, 42NW. Direction N45°W, throw not certainly known; may be small displacement to NE.

A number of references to this cross vein have been made in the foregoing account of the veins on the western slope of Middle Fell. N of Garrigill Burn, the vein was worked at Whitesike Mine (disused) froma level [NY 7510 4252] at 1425 ft (434 m) above OD, the portal of which is 300 ft (91 m) ENE of Garrigill Burn Bridge. This runs under the Great Limestone for 2150 ft (655 m) to Old Groves Shaft. From it, an oreshoot 1100 ft (335 m) long was worked in the Great Limestone, according to Wallace (1861). From Old Groves Shaft north-westward to a point 525 ft (160 m) beyond the intersection with Fletcheras Vein, the main development was at the horizon of High Hundybridge Level; the vein was unproductive throughout this stretch. After an untried gap of 210 ft (64 m), the drift from Crag Green Sun Vein has tested the Cross Vein for 725 ft (221 m); another untried gap of 500 ft (152 m) separates this drift from that connected with the workings on Crag Green Middle Vein. Nothing is known of the character of the cross vein in these drifts. After a gap of 550 ft (168 m), a short level [NY 7362 4418] from surface, starting from Guttergill and passing through Dowpot Sike Vein, tested the cross vein. It is not known N of this point.

South of Garrigill Burn, the Browngill or Whitesike Level [NY 7519 4249] at 1430 ft (435 m) above OD, the main entrance to the Whitesike Mine workings on Browngill and Browngill Sun veins, was driven on Old Groves Cross Vein at the base of the Great Limestone. A series of shafts continue 1100 ft (335 m) SE of Browngill Sun Vein on what is presumably the course of the cross vein, but show no veinstuff on the dumps. A trial was also made on the cross vein beneath Garrigill Burn and to the SE from a level in the Nattrass Gill Hazle at 1265 ft (386 m) above OD. There is no reason to think that much lead ore was obtained from any of these workings.

The NE veins of Whitesike Mine, including Taylor Sike, Bentyfield Sun, Thortergill Sike, Browngill and Browngill Sun, together with the continuation of Browngill Vein west of the S Tyne will be described with the Nent Area (Subarea 2) because they belong geologically to the great mineralised belt of Nenthead. It may be noted that this belt of veins originates in the area between Garrigill and the Rotherhope Fell Vein, upon which they converge; the belt grows in importance in its north-eastward course from Garrigill, reaching a maximum at the head of the Nent Valley.

Middle Sike Vein, Wellhopeknot Vein and Potato Garth Vein

The westernmost working is on the W bank of Crossgill, where a short level [NY 7384 3946] has revealed quartz with pyrite and marcasite; to the SW the vein probably converges on the Great Sulphur Vein, which contains similar minerals. There are no workings between Cross Gill and the Tyne Valley, but on the W side of the latter, levels [NY 7554 4009] which tested the vein in and below the Scar Limestone were unsuccessful. In the bottom of the valley, however, a belt of leaders given off from the S side of the vein produced flats in the Tynebottom Limestone, 600 ft (183 m) long, and up to 20 ft (6.1 m) wide, known as Nursery Nook flats. On the E side of the South Tyne, the Ashgill Field Mines (disused) [NY 758 405], worked Ashgillfield Vein; here crossed by Potato Garth Vein. From the intersection southwards a large flat, 400 ft (122 m) long by 150 ft (46 m) wide was found in the Scar Limestone, one of the few instances of metasomatism at this horizon. The Wellhopeknot Vein, continuing Ashgillfield Vein NE of the intersection, also carried a belt of flats at the same horizon, 400 ft (122 m) long. The flats are said to have carried up to 2 in (5 cms) of galena at three different horizons in the limestone. Between the large flat, and Ashgill Burn, extending along the N side of Potato. Garth Vein the limestone is stated by Wallace (1861, pl. XV) to have been replaced by clay. Another flat is shown by Wallace SE of the junction between the Windshaw Bridge Cross Vein, and Ashgillfield Vein, 875 ft (267 m) NE of the Tyne; this is not indicated on the existing plans of the mine (preserved at the North of England Institute of Mining Engineers, Newcastle). Access to the flats was by way of levels [NY 7558 4033], [NY 7585 4046], [NY 7089 4046] driven 19 ft (5.8 m) below the base of the Scar Limestone, beneath Ashgill Force. A level [NY 7560 4013] was also driven NE from the Tyne on Ashgillfield Vein in the shale above the Tynebottom Limestone. The mineralisation in the flats consisted of purple fluorite, quartz, chalcedony, and carbonates accompanying galena. Separate production figures are not available; Priorsdale Royalty produced 2976 tons of lead concentrates under the London Lead Co. between 1818 and 1882; the bulk of which probably came from Ashgill Field mines.

Wellhopeknot Vein continues NE along the N side of the Ashgill Valley; there are old opencast and underground workings in the Four Fathom and Great limestones, but little seems to have been got.

Crossgill Copper Vein—Copper ore

NY73NW; Cumberland 42SW

In Crossgill, 1.75 miles (2.8 km) SSW of its confluence with the Tyne, a NE vein has been tried on both sides of the burn by short levels [NY 7392 3886] in the Copper Hazle sandstone. Quartz veinstuff with iron sulphides, a little chalcopyrite and some malachite is seen on the dumps. Traces of erythrite have also been found (B Young, personal communication).

Little Gill Vein—Lead ore

NY73NE; Cumberland 42SE. Direction N65°E, throw at NE end of Little Gill workings, 1 ft (0.3 m) N.

The vein crosses Little Gill 1 mile (1.6 km) S of its confluence with Ashgill Burn. In the Great Limestone little or no mineralisation was found; the oreshoot lay NE of the Gill, in the Pattinson and Firestone sandstones. The workings at Little Gill Mine (disused) comprise a level [NY 7782 3953] driven under the Great Limestone from Little Gill Force, which reaches the vein at 500 ft (152 m), and continues to 2000 ft (610 m) on the vein; a level [NY 7808 3952] 2875 ft (576 m) long driven NE in the shale above the Little Limestone, from which the Pattinson and Firestone workings were reached by rises; and an opencut [NY 7820 3957] in the Firestone. The galena was accompanied by quartz, siderite, limonite and a little sphalerite. The vein is stated on the London Lead Co.'s plan (1846) to have been very weak at the forehead. The levels were apparently reopened about 1820; a sump dated 1774, sunk to the Great Limestone 1200 ft (366 m) ahead of the Force Level forehead was found at this time. In the Tyne valley a trial [NY 7677 3908] was made on the vein in the Great Limestone 1750 ft (533 m) SE of the 6th milestone on the Alston–Middleton road, but without success.

Hard Sike Vein—Lead ore

NY73NE; Cumberland 42SE

Some 2000 ft (610 m) SE of Little Gill Vein the course of another vein crossing the Gill is marked by a line of shafts trending N60°E. A level [NY 7801 3898], now closed, was driven into the vein above the Great Limestone. Mineralisation appears to have been similar to that on Little Gill Vein; both veins were weak. Cerussite was noted on the dumps.

Windy Brae Veins—Lead and copper ore

NY73NE; Cumberland 42SE

On Windy Brow, the western slope of Yad Moss, a number of feeble veins have been worked. Hole Pasture Vein, trending N60°E, was tried in the Great Limestone from a level at [NY 7691 3864], and was also reached by a long crosscut at about the same horizon from the Little Gill Vein trial. A little fluorite, quartz, limonite and galena was found. At 1000 ft (305 m) SE of this vein small opencuts [NY 7698 3832] have been made on the probable continuation of Hard Sike Vein, here known as Copper Slitts Vein. Quartz, chalcopyrite, ankerite and limonite, accompanied by malachite and traces of azurite occur in the spoil. Windy Brow North Vein, trending N65°E, was worked in the Great Limestone from a level [NY 7700 3820] 350 ft (107 m) SE of Copper Slitts, for a length of 675 ft (206 m) but appears to have yielded little ore. A level [NY 7610 3806] from the W bank of the Tyne at Dorthgillfoot followed Windy Brow Vein, here containing much calcite and quartz, through the shale above the Tynebottom Limestone, to Sir John's Vein. Windy Brae Vein, the main vein of the group, runs N75–90°E, and throws 21 ft (6.4 m) S. The lowest working was a level under the Scar Limestone, in the Copper Hazle [NY 7642 3810] 600 ft (183 m) ENE of Tynehead Farm; the dump shows quartz, ankerite, pyrite and a little chalcopyrite. In the Great Limestone, the vein was worked for a length of 700 ft (213 m) from an adit [NY 7701 3812], galena with a little fluorite being obtained; these workings were terminated by a cross vein. The vein, however, continues to the E after an apparent shift of about 50 ft (15 m), E side S, the eastern portion being reached by a level [NY 7704 3795] driven ENE from Ladygill Bridge. Windy Brow yielded 799 tons of lead concentrates between 1779 and 1855. Two levels were driven in Little Gill S of Hard Sike Vein in an attempt to find the Windy Brow Veins, one [NY 7810 3881] 750 ft (229 m) long, under the White Hazle, and the other [NY 7827 3862], 2000 ft (610 m) long, starting directly beneath the Firestone and ending 36 ft (11 m) below that bed; both ran SSE. The London Lead Co.'s 1846 plan shows a series of weak strings cutting through the levels, but nothing workable was found. A note in the London Lead Co.'s minute books for June 1821 reads: 'Windyfree: where the company has got 1000 bings of ore is being driven this summer in hope of testing the great flat'.

Stow Crag Vein—Lead ore

NY73NE; Cumberland 42SW. Direction N8°W, productive in Tynebottom Limestone

The workings of Stow Crag Mine (disused) extending northwards for 1500 ft (457 m) from the confluence of Dorthgill and the South Tyne, comprise shallow shafts and opencuts [NY 7602 3834], along the west bank of the river. The ore consisted of galena in a quartz gangue; 2186 tons of concentrates were obtained between 1811 and 1871. The galena from this vein was exceptionally rich in silver; 311 tons of lead concentrates obtained between 1855 and 1871 contained 69.1 per cent of lead, the silver yield averaging 38.5 oz of silver per ton of lead. This was confirmed by a determination made by Dr Smythe in 1939 on galena from the adjacent field called "Chesters" [NY 7607 3837], probably left from dressing of Stow Crag ore which contained 75.55 oz of silver per ton of lead. A drift driven S from a shaft [NY 7596 3910] 1000 ft (305 m) N of Hole House for 875 ft (267 m), in the shale above the Tynebottom Limestone, and in the limestone was not successful in finding a northward extension of the Stow Crag oreshoot. The name 'Chesters' raises the question of whether the Romans discovered and worked this vein. They were familiar with the desilverisation of lead and their road across the fells is only a few miles distant.

Scar End Vein = Leehouse Well Cross Vein = Sir John's Vein—Copper ore, lead ore

NY73NE, NW, 74SW; Cumberland 42NW, SW, SE; 52NE Direction N40–50°W, throw, NW of Tynehead, 0–20 ft (0–6 m) NE; to SE of Tynehead, said to change to SW; productive horizons, Six Fathom Hazle down to Tynebottom Limestone.

Sir John's Vein forms part of a line of NW faulting which, as described in Chapter 4, extends from Middleton-in-Teesdale through the Harwood valley and continues north of Alston Moor into the area of the Brampton sheet. The northward continuation is described above under Gilderdale and Horse Edge; the southern or Teesdale portion is described below under Lady's Rake and Park End.

The vein crosses Rotherhope Fell Vein 700 ft (213 m) SSE of Slaggieburn House; a level on top of the Scar Limestone has been driven and a shaft sunk near the intersection [NY 7175 4256]. A few tons of copper ore were obtained here in 1861–65. In Dry Burn, 0.5 mile (0.8 km) to the SE, Sir John's Vein is is in two parallel portions, 50–60 ft (15–18 m) apart, the SW one being exposed in the Scar Limestone, where it carries quartz, ankerite and specks of chalcopyrite. A level [NY 7220 4190] driven SE on the other proved similar mineralisation with a little galena; this level may have proved the intersections of Sir John's vein with the westward continuations of Bentyfield and Browngill veins (described below) but this is not certain. The next working of Sir John's Vein is Scar Ends Level (disused) [NY 7410 3997], starting from the N bank of Cross Gill, 34 mile (1.2 km) SW of Crossgill Bridge, in the Copper Hazle sandstone beneath the Scar Limestone. The vein contains quartz, ankerite, pyrite and chalcopyrite; 81 tons of copper concentrates were obtained in 1824–26. A more recent trial, in which some work has been done since 1920, is a level [NY 7414 3993] driven SE from the opposite bank of the burn, in the Copper Hazle. Similar mineralisation was found. The Leehouse Well Mine (disused) reached Sir John's Vein by means of crosscut adits, one [NY 7535 3921] starting 500 ft (152 m) WSW of Tynehead school, in the Slaty Hazle, reaching the vein at 900 ft (274 m); the other [NY 7559 3936] commencing 300 ft (91 m) ENE of the School, reaching the vein at 1850 ft (564 m) in the Copper Hazle. In the period 1823–1834, 640 tons of copper concentrates were obtained here from a stretch of ground 700 ft (213 m) long. In the same period 327 tons of lead concentrates were obtained. In the nearby Mid Leehouse Well allotment a shaft sunk in 1912 directly on the vein, by Mr H Millican, gave access to a drift at 48 ft (14.6 m) depth in the Six Fathom Hazle which found a good pocket of lead ore, 42 ft (12.8 m) long, containing quartz, fluorite, carbonates, galena and traces of chalcopyrite. The shaft was reopened in 1920–21 to the natural water level, 27 ft (8.2 m) deep and some ore was obtained from the Six Fathom Hazle. The total yield from Mid Leehouse Well Mine was about 100 tons of lead concentrates. As noted in Chapter 5, there is evidence of zonal transition from lead to copper here; the Six Fathom and Slaty Hazle workings carrying lead ore, the workings in and below the Scar Limestone carrying copper ore.

The vein is exposed in Pettergill [NY 7586 3825], 1500 ft (457 m) NW of Tynehead Farm, where it contains ankerite, quartz, pyrite and chalcopyrite. From Pettergill a level [NY 7589 3838] forming part of Stow Crag Mine (disused) reached the vein as a crosscut under the Copper Hazle, while another level [NY 7610 3806] from the W bank of the Tyne near Dorthgillfoot followed Windy Brow Vein through the shale above the Tynebottom Limestone to Sir John's Vein. From these workings, 856 tons of copper ore were obtained between 1823 and 1836, and 20 tons between 1870 and 1871. It is possible that some of the lead production recorded above under Stow Crag Vein may have come from Sir John's Vein.

In Sir, John's Mine (disused) the vein was followed from the E bank of the Tyne to and beyond its intersection with the Great Sulphur Vein, and proved on the S side of that vein. This mine was reopened during 1941 for the Non-Ferrous Ores Committee (Ministry of Supply) to obtain access to the Great Sulphur Vein. The main level [NY 7616 3782], at 1380 ft (421 m) above OD, is driven through boulder clay into the thin sandstones and shales of the Alternating Beds. It follows Sir John's Vein for the first 400 ft (122 m), then continues parallel to it on the SW side for 890 ft (271 m) until the Great Sulphur Vein is reached. The vein, as far as it is exposed in this level, is pinched. A crosscut driven ENE 130 ft (40 m) N of the Great Sulphur Vein reached Sir John's Vein at 80 ft (24 m) and the presence of rises here suggests that there may have been workings at a higher horizon. Although the Great Sulphur Vein appears to shift the vein, S side E, the detailed relations in the crosscut strongly suggest that the N Wall of the Sulphur Vein is in fact shifted a few feet by Sir John's Vein, E side S. The main level was continued through the Sulphur Vein; it was not reopened south of the footwall of this vein and it is not clear from the old plan (Mines Dept No. R136 C) whether Sir John's Vein was found here in the Whin Sill. Middle Level, driven from Sidehead Sike has collapsed and its course is not recorded on the plan. High Level [NY 7633 3755], driven at 1558 ft (475 m) above OD from Sidehead Sike at about the horizon of the Slaty Hazle is also inaccessible, but the plan shows that it passed through the Great Sulphur Vein, continuing S about 700 ft (213 m) in Sir John's Vein. Apparently a little lead was worked from this level; 158 tons of concentrates are recorded in 1850–59. The recovery of silver amounted to 40 oz of silver per ton of lead.

S of the Great Sulphur Vein, Sir John's Vein and two branch veins known respectively as Clargillhead and Baxter's were worked at Clargillhead and Hiddenhole mines (disused). The veins were reached from levels [NY 7800 3723] and [NY 7715 3658] driven into the W bank of Clargill Burn in the Scar Limestone; probably the oreshoots were no more than small pockets. Quartz and silicified limestone, with a little galena remain on the dumps. Like the Stow Crag and Sir John's Mine workings, the galena was exceptionally rich in silver here; from 18 tons of concentrates produced between 1856 and 1867, the yield was 43 oz of silver per ton of lead.

Considerable stretches of Sir John's Vein remain unexplored and nothing is known about its behaviour in depth save that a shaft [NY 7615 3786] sunk near the entrance to Sir John's Low Level, presumably to the Tynebottom Limestone, found only quartz, ankerite and calcite with traces of chalcopyrite. As, however, small copper and lead oreshoots are of little interest under present conditions, it cannot be said to offer an attractive prospect.

Aglionby Beck Vein—Iron ore

NY63NE; Cumberland 41SW Direction N46°E

Near the head of Aglionby Beck a NE-trending fault, probably connected with the Great Sulphur Vein suite, cuts quartz dolerite of the Whin Sill, here below the Scar Limestone. Adjacent to the fault the dolerite is locally replaced by limonite, (an analysis of which has been published by Smythe, 1930, p.118; see (Table 30), p.85). An attempt was made to work the deposit opencast [NY 6529 3904] and a tramway was constructed to Hartside Cross, 1.75 miles (2.8 km) distant, but the venture was not a success.

Great Sulphur "Vein"—Quartz, pyrites

NY63NW, NE; Cumberland 41SW, SE, 52NE. Direction E–W, with short stretches trending WNW; aggregate throw 120 to 600 ft (37 to 183 m) N.

The Great Sulphur "Vein", properly described as a lode, is unique among the veins of the orefield. Its total length is nine miles from Knapside Hill [NY 6454 3890] on the Escarpment, overlooking Melmerby Scar, to Darngill Bridge [NY 7745 3709], 7 miles (12 km) S of Alston on the Middleton-in-Teesdale road. Structurally it is a N-facing monocline, with, for at least part of its course, a strong shear-belt developed on the N side. The width of the structure, apparently decreases downwards; it is narrower in the valley-bottoms than on the adjacent fell tops. The greatest width is over 1200 ft (365 m), on Noonstones Hill [NY 749 381], the least, 108 ft (33 m) in Black Burn [NY 700 389]. The dominant introduced mineral throughout is quartz, mainly present as a replacement of limestone, shale and sandstone within the lode, but making a few shoots of massive vein-quartz which stand out as ribs. At the lowest exposed levels, at about the horizon of the Tynebottom Limestone, there is what may be presumed to be a continuous zone of sulphides, containing pyrrhotite, pyrite and marcasite with in places a little chalcopyrite. These minerals occur as tabular masses within the quartz, their form being due, as shown in Chapter 5, to replacement of tabular fragments of country rock. Although tried at many points, the lode has yielded little of economic value.

Between Aglionby Beck and the Maiden Way the SW branch known as Knapside Vein (described on p.105) is given off. Farther east the Smittergill Head Mine (disused) worked an oreshoot on the footwall of the lode from an opencut on the E side of Gale Sike [NY 6720 3895], and from a shaft [NY 6739 3896] 150 ft (46 m) deep sunk beside Rowting Beck. The total length of ground worked or tried was 1525 ft (465 m), the horizon of the beds on the footwall being, according to the mine section (Mines Dept No. R10 D) the Jew and Lower Little limestones. As, however, the Whin Sill, which crops out on the footwall side, is here above the Tynebottom Limestone, it appears more likely that the limestones here were the Tynebottom and Jew. Galena was obtained, the accompanying minerals being sphalerite in coarse crystals, pyrite, pyrrhotite, marcasite, quartz, purple fluorite and carbonates. Some pyromorphite and traces of malachite, linarite and cerussite occur on the dumps from the opencast workings at Gale Sike. The production of lead ore, 1851–63, amounted to 393 tons, the recovery of silver in 1859 being 3 oz silver per ton lead. Assays of tailings (by Messrs Michie and Davidson, Newcastle, 1942) gave the following results: Coarse tailings, calcium fluoride, 52.7 per cent, silica 29.6; Fine tailings, calcium fluoride, 39.4 per cent, silica 31.7 per cent. As noted above (p.125), it is probable that the SW continuation of Rotherhope Fell Vein joins the Great Sulphur Vein close to Smittergill Head, a fact which may have some connection with the presence of fluorite, galena and sphalerite in the lode here. These minerals are not known to be present in it elsewhere.

To the N of Smittergill Head Mine, tributaries of the Smittergill Burn expose sandstones of the Copper Hazle in which quartz veins are numerous for up to 330 ft (100 m) from the vein. Arthurton and Wadge, (1981) have noted numerous large blocks of vein quartz from the Great Sulphur Vein on the hillside [e.g. 6774 3903 to 6807 3911] to the S of the burn.

In Swarth Beck [NY 6863 3915], 0.75 mile (1.2 km) E of Smittergill Head Mine, an exposure of the vein shows a mass of quartz dolerite up to 3 ft (1 m) across enclosed in vein-quartz (Arthurton and Wadge, 1981). Small outcrops [NY 6877 3914] to [NY 6908 3914] of vein-quartz with sandstone inclusions may be seen between here and Blackburn.

In the head waters of Blackburn the vein is exposed [NY 6977 3892] with the Whin Sill on the footwall. The vein itself consists of much broken quartz-veined sandstone. Although ribs of quartz are seen, there is no sign of the sulphide zone here. On Pikeman Hill [NY 727 386] branches are given off to the NW and SW. Between the mountain track from Garrigill to the Cash Well Mines and Duffergill Burn, a quarry [NY 6285 3856] for silica-stone was opened in a quartz shoot during 1939–40, but the cost of transport and the variable character of the product prohibited successful working.

Sulphides are exposed where the lode crosses Cross Gill, and here the two-fold character of the structure becomes apparent. The northern part of the lode, at least 100 ft (305 m) wide, consists of E–W fractures; in one of these a vein-like shoot, 6–11 ft (1.8–3.4 m) wide, is exposed on the E side of the Gill [NY 7395 3828]. A channel sample taken by Mr J D Wilson (Information on Cross Gill and Sir John's Mine is quoted from reports prepared in collaboration with Dr G A Schnellmann and Mr J D Willson for the Non-ferrous Ores Committee (Ministry of Supply), by permission.) assayed 18.25 per cent sulphur; a full analysis is quoted below. The southern part of the lode is monoclinal in form and exposes the Tynebottom Limestone, replaced in a patchy manner by quartz, sericite and iron sulphides. Near the N wall of the lode, there is an open shaft [NY 7396 3832] of unknown depth; another old shaft has been sunk close to the stream at 1511 ft (461 m) above OD on the quartz-sulphide shoot described above. A drainage level over 1000 ft (305 m) long driven S under the Scar Limestone (portal at [NY 7396 3866]) presumably reaches these shafts. Wallace (1890, p.143) remarks: "About the year 1814 or 1815, the Commissioners of Greenwich Hospital commenced to make trials for the discovery of copper ores in the Great Sulphur Vein, where it crosses Crossgill Burn. After a level was made to the vein under the Scar Limestone, a sump was sunk to a considerable depth in the vein. Not succeeding in their attempt to discover copper, the mine was abandoned. Their works were reopened by Messrs Cookson & Co., Newcastle, to raise sulphur pyrites. An hydraulic engine was placed in the Commissioners' shop; sulphur, however, could not be raised profitably, and the mines were only worked for a short period".

On the western slope of Noonstones the best exposures of the upper quartz zone of the vein, free from sulphides, are seen. Here the monoclinal nature of the structure is plainly apparent; beds such as the Six Fathom Hazle can be traced across the full width, dipping N at about 20°. Near the summit [NY 7482 3802] of the hill a series of vein-quartz shoots striking N10°E can be followed across the lode, one of them being continuous for 1200 ft (366 m) and up to 20 ft (6 m) wide. The lode is covered with glacial drift on the E side of the Noonstones. It is, however, partly exposed where it crosses the Tyne [NY 7602 3752]. Here the top of the Whin Sill is some 30 ft (9 m) below the base of the Tynebottom Limestone; the limestone is not so highly mineralised as in Crossgill or in Sir John's Mine, where the limestone is directly underlain by quartz-dolerite.

In Sir John's Mine (disused) the N wall of the Great Sulphur Vein is encountered 1290 ft (393 m) from the mouth of the main level [NY 7616 3782] which enters, as described above, on the course of Sir John's Vein. The structure of the Great Sulphur Vein here is illustrated by the accompanying diagram (Figure 21). The northern part consists of a sheared zone, containing nearly vertical fractures striking N70°W cutting a replacement breccia of highly silicified shale. Sulphur values in the breccia average less than 1 per cent, silica over 90 per cent. The southern part, or bedded zone, is interpreted as a replacement of the Tynebottom Limestone, 20 ft (6 m) thick, dipping N at 40°, by quartz and iron sulphides. The whole replacement averages 9.5 per cent sulphur, and the best 5 ft (1.5 m) contains 24.7 per cent sulphur, analysis 1 below. The Whin Sill underneath the metasomatised limestone is converted into white whin, carrying pyrite in the upper 6 ft (1.8 m). Detailed analyses of sulphur ores and concentrates from the lode are given in (Table 43).

At 1600 ft (488 m) E of the Sir John's Mine exposure, the lode is seen in Clargill Burn [NY 7694 3738], where beds at and above the horizon of the Scar Limestone dip N. The mineralisation is mainly quartz. A fault striking N20°E, throwing about 15 ft (4.6 m) SE with associated strong quartz veining crosses the lode. E of Clargill the lode begins to split into divergent strings, some of which are exposed about Darngill Bridge [NY 7745 3709], before dying.

The Great Sulphur Vein probably contains a large tonnage of iron sulphides at and near the horizon of the Tynebottom Limestone, particularly where this is directly underlain by the Whin Sill. Being associated'with a quartz gangue which makes up at least half the ore, these could hardly hope to compete with massive sulphides from abroad. There is also a lack of attractive ancillary metals, such as copper and gold. An attempt to work for gold was made at Sir John's Mine and until recently the remains of the crusher and gold pan were still to be seen near the mine entrance: the attempt was quite unsuccessful.

Cashburn Vein; Cornriggs Vein—Copper ore

NY73NW; Cumberland 51NE, 52NW

These two small veins, trending N60°E, cross the headwaters of Cash Burn respectively 0.75 mile (1.2 km) and 1 mile (1.6 km) S of the Great Sulphur Vein. Cash Burn Vein, tried over a length of 1200 ft (366 m) in the Scar Limestone and overlying beds, proved to contain mainly quartz with traces of copper minerals [NY 7130 3768]. Cornriggs Vein, reached by a level [NY 7154 3720] in the Slaty Hazle and tried from small shafts in an old hush between [NY 7168 3720] and [NY 7186 3728] contained quartz and malachite with traces of azurite.

Katelock Little Vein and West Cross Fell Vein, West Cross Fell North Vein

The Cross Fell veins commence on the NE shoulder of Cross Fell, continuing to a distance of 3 miles (4.8 km) to Cross Gill. Attempts to fmd them N and NW of the screes were made at Yad Stone [NY 6824 3533] and West levels [NY 6902 3538], above the Great Limestone; the latter level cut a fault throwing 42 ft (12.8 m) S, 870 ft (265 m) S of the portal, but neither found workable deposits. In the headwaters of Black Burn exploratory hushes in the Three Yard Limestone at [NY 6901 3600] show traces of azurite though no veins can be traced here (Arthurton and Wadge, 1981). The mineralised ground appears to commence at Long Katelock Level (disused), the portal of which [NY 6960 3551] is 4600 ft (1.4 km) NE of the summit currock on Cross Fell. This level runs SSE in the shale above the Great Limestone, cutting Katelock Little Vein at 325 ft (99 m), and reaching West Cross Fell North Vein at 1075 ft (328 m) from the mouth. Some ore was got in the Low and High Coal Sills sandstones on the former vein from this level. An E–W branch-vein from the North Vein provides a link with West Cross Fell Vein, the main vein of the group. The principal workings at the SW end of the vein were those of Slatesike Mine (disused); here a series of crosscut-adits [NY 7060 3529] and [NY 7070 3524] reached the vein at and above the Little Limestone, but found little ore; and a level 2825 ft (861 m) long was driven to the vein beneath the Great Limestone from Slate Sike [NY 7130 3491]. An oreshoot in the Great Limestone and Coal Sills 650 ft (198 m) long is recorded. Fluorite, quartz, siderite and limonite, with traces of galena occur on the dumps from the latter level; a note on the map in Geological Survey records by C E De Rance states that "brown haematite" 4 ft (1.2 m) thick was found when Slatesike Mine was last worked. A gap of about 700 ft (213 m) separates these workings from those of Cashwell Mine (disused) to the NE. Here there were four principal adit levels: Cross Fell High Level [NY 7110 3584], 850 ft (259 m) long, commanding the High Coal Sill; Little's Level [NY 7160 3610], at about 2175 ft (663 m) above OD, 2600 ft (792 m) long, in the shale below the Great Limestone; Mill Level [NY 7168 3644], reaching the vein as a crosscut 1025 ft (312 m) long running due S from Cash Burn, and continuing 1900 ft (579 m) SW on the vein, in the Nattrass Gill Hazle; and Cashwell Level [NY 7170 3674], a straight crosscut adit running SSE, reaching the vein at 1700 ft (518 m) from the portal in the shale below the Six Fathom Hazle. The only recorded oreshoot at the higher horizons was one 600 ft (183 m) long in the Great Limestone and Coal Sills, near the fore-end of Little's Level; but the considerable amount of veinstuff scattered from surface shafts and opencuts along the vein suggests that there were probably others. From the head of Cashwell Level [NY 7195 3629], an engine shaft was sunk to the Copper Hazle sandstone; here an oreshoot 1425 ft (434 m) long was worked in the Scar Limestone. In the overlying beds up to the Five Yard Limestone, the shoot was 825 ft (251 m) long, with a suggestion of pitch to the SW. Exploration of the Scar Limestone was continued 700 ft (213 m) SW and 1500 ft (457 m) NE of the oreshoot, without success, though some ore was found in the Slaty Hazle over a length of about 250 ft (76 m). At 1500 ft (457 m) NE of the engine shaft mentioned, a second shaft [NY 7233 3650] was sunk and from here explorations in the Copper Hazle and in the shale above the Tynebottom Limestone were carried out, apparently without success, though no definite record of the condition of the vein has been obtained.

North-eastwards the vein continues into the ancient Doukburn Mine (disused), on the W side of Cross Gill, where levels [NY 7304 3682], [NY 7337 3710] and [NY 7337 3717] reached the vein in the Nattrass Gill Hazle and in the Scar Limestone. A member of the Cleveland dyke-system cuts through the vein in the workings of this mine; Wallace (1861, p.57) records that "No trace of the vein was found in the dyke; but after the latter was cut through, the former was found in its proper position or bearing.

The Cross Fell or Cashwell Vein is strongly mineralised with fluorite, especially at Cashwell Mine; other minerals present include quartz, carbonates, and sphalerite. The lead was obtained as galena. Production of lead concentrates was as follows: Long Katelock, 1854–1868, 237 tons: Slatesike, 1811–1870, 5172 tons; Katelock and Slatesike, 1871–1880, 83 tons; Cashwell and Doukburn, 1848–1911, 7700 tons. Total from Cross Fell Veins, 1811–1911, 13 192 tons. Silver recoveries, based on figures for 1856–65, were: Long Katelock, 7.3 oz silver per ton of lead. Slatesike, 9.0 oz, Cashwell and Doukburn 6.4 oz. The lead was smelted at a smelt-mill at the head of Cash Burn. Cashwell Mine was in operation until about 1921, and some fluorspar has been obtained from the dumps since that date. Were it not for the remote situation of this mine, it might well offer an interesting prospect for fluorspar.

Crossgill Head Vein—Lead ore

NY73NW; Cumberland 52NW

At the Head of Cross Gill, at about 2000 ft (610 m) OD, a N–S vein appears to have influenced the direction of the stream. Shallow workings (between [NY 7310 3643] and [NY 7296 3589]) in the Five Yard Limestone and Slaty Hazle revealed the presence of purple fluorite, quartz, limonite and galena; 8 tons of lead ore were obtained between 1811 and 1855.

Broad Mea Vein and Green Banks Vein

  • Broad Mea Vein—Lead ore NY73NW; Cumberland 52NW
  • Green Banks Vein NY73NW; Cumberland 52NW

    • On the W side of the Round Hill outlier of Great Limestone, between Crossgill Head and the Tyne, a little lead ore has been won from shallow shafts between [NY 7363 3609] and [NY 7405 3625] in the ENE Broad Mea Vein; 55 tons are recorded for 1811–55. The NE Green Banks Vein, which may be the continuation, or a branch of Broad Mea Vein, was tried from levels at the head of Josh's Hush [NY 7484 3673] on the NE side of Round Hill, where it carried quartz, purple fluorite and galena incrusted with cerussite.

    Allen's Cleugh Vein—Lead ore

    NY73NE; Cumberland 52NW, NE. Direction N40–50°W, throw 80–90 ft (24–27 m) SW.

    The Allen's Cleugh Fault may be regarded as a branch of the Teesdale Vein, running between Crook Burn and the Great Sulphur Vein on Noonstones. It has been tried from levels in the Alternating Beds near Cocklake [NY 7573 3722] and in Allen's Cleugh [NY 7650 3635], and from a level [NY 7590 3690] in the Whin Sill starting 650 ft (198 m) S of the old Tynehead Smelt Mill, running 850 ft (259 m) SE. A little galena, strongly sheared into "steel ore" is seen on the dumps of the level in Allen's Cleugh. The record of 31 tons of lead concentrates between 1811 and 1855, from "Allen's Hills" may have come from here.

    Calvert Vein—Lead ore (fluorspar)

    NY73NE, NW; Cumberland 52NW. Direction N50–60°E; may have small NW throw; mineralised in Scar Limestone, Five Yards Limestone.

    Calvert Vein is probably the NE continuation of Hunter's Vein (p.108). A trial [NY 7348 3480] at Fall Crag on the N bank of the Tees, 2 miles (3.2 km) W of Trout Beck foot revealed some galena with traces of sphalerite in the Scar Limestone. The principal workings were, however, at the Calvert Mine (disused) at Tynehead. A level [NY 7518 3599] 0.5 mile (0.8 km) SSW of Tynehead Smelt Mill gave access to the vein in the Scar Limestone immediately SW of the Tynehead unit of the Cleveland tholeiite dyke-system; there is no evidence that this level penetrated the dyke. These workings appear to have been poor. The main level was driven, in the shale below the Slaty Hazle and approximately following the course of Calvert Burn, as a crosscut. As no plan of the mine exists it is not known how far the workings here were carried, nor is it certain at what horizons the ore was obtained. Quartz, purple fluorite, marcasite, sphalerite and galena are present on the dump together with numerous blocks of pyrite-pyrrhotite-quartz veinstone closely resembling material from the Great Sulphur Vein. At the time of the primary survey a shaft [NY 7402 3535] on the vein 3400 ft (1036 m) SW of Calvert Burn was laddered and in use, this may give some indication of the length of ground explored. A little ore seems to have been won from an opencut [NY 7531 3641] in the Six Fathom Hazle near Calvertfold. The production of lead concentrates between 1811 and 1870, when the mine closed, was 1985 tons. Silver recovery between 1854 and 1870 was 7.7 oz silver per ton of lead.

    Tynehead Veins—Lead ore (fluorspar)

    NY73NE, SE; Cumberland 52NW

    In the gap which leads from the head of the South Tyne to the Tees a series of NE veins have been worked on the E side of the valley. The workings are in the Alternating Beds and Scar Limestone; the mineralisation of all the veins is essentially similar, consisting of coarse quartz and purple fluorite, with small quantities of galena and traces of sphalerite. The Dosey Vein has been explored from a level [NY 7540 3567] in the Single Post Limestone, 1 mile (1.6 km) S of Tynehead Smelt Mill; the length of the workings on the vein is said to be 400 ft (122 m). Tyne Bogs Vein was worked for a similar length from a level [NY 7536 3553] 500 ft (152 m) farther S. There were also workings from surface shafts on both veins; 1219 tons of lead concentrates were obtained between 1811 and 1870; silver recovery in the period 1855–1868 was 8.1 oz silver per ton of lead. Bowman's Spring Vein, 500 ft (152 m) SE of Tyne Bogs Vein, has been tried in the Scar Limestone from a surface shaft [NY 7561 3544]. Middle Tynegreen Vein, worked from a level [NY 7528 3502] beneath the Single Post Limestone has 2100 ft (640 m) of workings on it, but seems to have yielded only small quantities of ore. Far Tynegreen Vein, entered by means of an adit [NY 7531 3473] in the shale above the Tynebottom Limestone 3100 ft (945 m) S of Dosey Level, was also tried for over 2000 ft (610 m) to the north-east of the portal. Ladies Vein was worked from a level [NY 7537 3450] in the top part of the Tynebottom Limestone, and from a whimsey shaft in the Scar Limestone; the records of production show about 165 tons between 1811 and 1865; silver recoveries were 7.4 oz silver per ton of lead. The Tynehead veins were not discovered on the W side of the valley, owing to the thick mantle of drift there, but there is little evidence of them in the Tees, apart from Far Tynegreen and Ladies veins. The former vein yielded some ore from shafts on the S side of the river, 0.75 mile (1.2 km) NW of Troutbeck Level (p.230). An attempt has been made to obtain fluorspar from dumps at Tynehead. Some spar is said to remain underground on Calvert and Dosey veins but a trial by Athole G Allen Ltd on the former failed to disclose workable quantities.

    Subarea B The Nent Valley

    General description

    In this area some of the most productive deposits of the orefield have been worked. Many of them were first discovered in the higher beds, above the Great Limestone, which crop out on the valley sides. According to Wallace (manuscript notes accompanying the plan of Scaleburn Mine, Mines Dept. No. R274) many of the deposits had been worked at these horizons by 1735, but the Great Limestone had been little explored. The discovery by Sir Walter Blackett of very rich deposits in the limestone on High Coalcleugh Vein in West Allendale lent impetus to development in this bed in the Nent Valley, where it has proved to carry prolific mineralisation. Development was commenced by the royalty owners, the Lords Commissioners of Greenwich Hospital, but shortly after 1735 the lease of several of the principal mines passed to the London Lead Co. to whom the exploitation of the area about Nenthead was largely due. The mines lower down the valley were developed by smaller companies. Under these companies the veins of the Nent valley were worked from a few centralised points.

    The accompanying map (Figure 22) illustrates the structure of this part of ore field. A belt of strong ramifying NW faults and veins follows the course of the valley; here the structure is broadly synclinal. On either side of the valley NE veins are developed. Under the ridge between the Nent and West Allen valleys there is a gentle anticline, the axis of which runs NW; the maximum mineralisation on the NE veins appears to coincide with the crest of this anticline. These veins generally fail to carry workable orebodies where they pass under the valley, but on the NE slopes of Middle Fell rich deposits have been worked. The valley has been explored in depth by means of the Nentforce Level which runs from Alston to Nenthead, a total distance of almost 5 miles (7.95 km) starting at the waterfall from which it takes its name [NY 7198 4677] and ending at Brewery Shaft [NY 7830 4351] on Scaleburn Vein. This, the first of the major drainage-cum-exploration projects in the northern Pennines, was financed by the Commissioners of Greenwich Hospital and commenced in 1776 under the direction of their two Receivers, Nicholas Walton and John Smeaton; the latter became very celebrated as an engineer, but it is probable that Walton had more direct influence on the work here. According to Wallace (1890) the proposal to drive underground canals may have come from John Gilbert of Bridgewater Canal fame, a shareholder in mines on Middle Fell. When Forster wrote in 1821, the level was approaching Nentsberry Haggs Engine Shaft [NY 7557 4804] where water wheel-driven pumping enabled a drift to be driven northward to meet the tunnel at 890 ft (271 m) above OD. A second drift was being driven S at 1035 ft (315 m) above OD. From the commencement of driving, it had been decided to keep the tunnel dead flat, and soon it was planned to use boats for underground transport. Thus the level was driven at a minimum cross section of 9 x 9 ft. (2.74 m2). It had been completed to Nentsberry, 3.4 miles (5.4 km) from the portal by the time Sopwith (1833) described the works, but it is not certain that boats were used beyond Lovelady Shield. At the portal, [NY 7198 4677] now obscured by quarrying operations in the Scar Limestone, the level started in the shale beneath the limestone. Before the commencement of the drive, a group of local experts had reported (Public Records Office, Kew, ADH 275/203) on the strata exposed between Nent Force and Middle Cleugh Deep Level at Nenthead, above which the Great Limestone is seen, concluding that "the regular rise of the strata is such that nothing above, or where a level should be taken out under Nent Scarr or Force, should interfere with the prosecution of the said level". Though it is not specifically mentioned, the question at issue was probably whether the Whin Sill would be encountered, in view of the difficulty experienced with a shaft for the proposed South Tyne Level at Garrigill (p.120). Some of the original records of the drivage may have been destroyed in the fire at the Nenthead mine office in 1930, but these cannot have been seen by Stanley Smith (1923, p.71) since he states that the main drive was replaced at Lovelady Shield by a drift 35 fms (64 m) higher up "in beds above the Four Fathom Limestone". The latter part of the statement is obviously incorrect, but in the absence of evidence to the contrary, the termination of the deep drive at Lovelady Shield Shaft was accepted in the first edition of this memoir, and this error was perpetuated in the section illustrating Lord Wilson's (1963) historical account of Nentforce Level. Underground investigation by the Norpex mine exploration group at Nentsberry (Wilkinson, 1981) have shown that the deep level did indeed reach this 350 ft ((107 m) shaft, as suggested by Forster. The stratigraphical information in (Table 44) is taken from a copy of the original section (Public Record Office, Kew, ADH75/203), showing the shafts sunk for ventilation between the portal and Nentsberry.

    A waterblast shaft (Jockey's) 485 ft (148 m) from the portal passed through 23 ft (7 m) of Scar Limestone to reach the level which, from the portal to Nentsberry was driven in the so-called Alternating Beds between the Scar and Tynebottom limestones. There is a slow rise of less than 1° towards the E, except that as Lovelady Shield Shaft is approached a gentle monoclinal rise at 6° occurs, extending 450 ft (137 m) beyond the shaft before the slow rise is resumed. A sandstone rises into the drive but dips down again before Nentsberry Haggs Shaft is reached. This lowest horizon cut in the tunnel could be about 50 ft (15 m) above the Tynebottom Limestone. If the Whin Sill is still in its South Tyne position here, this would be about 85 ft (26 m) above the top of the sill. A sample of black fossiliferous shale provided by Mr Wilkinson of Norpex from within 10 ft (3 m) of the bottom of Nentsberry Shaft resembles the Tynebottom Plate, but shows no sign of metamorphism; as however, metamorphism can rarely be detected more than 70 ft (21 m) above the intrusion, this cannot be taken to indicate that the sill has migrated to a lower stratigraphic horizon. It must however do so before Nenthead is reached (p.48).

    Because of the increasing cost of the ventilation shafts, the deep drive was not continued beyond Nentsberry Haggs Shaft; a drive at 1035 ft (315 m) above OD in shale on top of the Scar Limestone took its place, for most of its course holding this position in spite of a more rapid rise in the beds beginning 900 ft (274 m) S of the shaft. At 20 900 ft (6.3 km) from the portal the level passed through the Cowshill Cross Vein, throwing perhaps 30 ft (9 m) SW. The next shaft is at Wellgill [NY 7772 4432], 22 260 ft (6.78 km) from the portal; this shaft is 213 ft (64.9 m) deep with the following section: Alluvium and shale, 90 ft (27.4 m), Three Yard Limestone 15 ft (1.4 m), Six Fathom Hazle 54 ft (16.5 m), Shale 6 ft (1.8 m) Five Yard Limestone, 12 ft (3.7 m), Slaty Hazle 24 ft (7.3 m) Shale 12 ft (3.7 m), making the level sole about 1060 ft (323 m) above OD. The drive was continued, passing through Scaleburn Vein, to reach Rampgill Vein at 26 055 ft (7.94 km) from the portal. This completed, in the year 1839 the Commissioner's project. Neither of the two veins, the most important at Nenthead, offered any promise in the beds between the Scar and Five Yard limestones. Later the lessors, the London Lead Co., drove on Scaleburn Vein and, by way of Carr's Vein, linked up with the NE part of Rampgill vein as far as Low Whimsey (Figure 23) but productive ground was not found. A sump connected Rampgill Horse Level, 450 ft (137 m) from its portal, with these deep workings at 1103 ft (336 m) above OD, no doubt to ventilate them. When the Vieille Montague Zinc Co. took over, the sump was enlarged and carried up to surface to become Brewery Shaft [NY 7830 4351]. Underground here turbine generators to supply electricity to the large Rampgill Mill were installed early in the century, and hydraulic compressors which were still supplying air to the centre of Nentsberry Mine, more than 2 miles (3.2km) distant, during the 1930's. Drainage through Nentforce Level still functions. It must nevertheless be said that this great project failed in its purposes. In spite of encouraging stratigraphical results from the shafts, indicating hard strata formed by the Six Fathom Hazle, Five Yard Limestone and Slaty Hazle of up to 97 ft (30 m) thickness, and in spite of the abnormally thick Scar Limestone (50 ft (15 m) instead of the normal 30 ft (9 m), the only new oreshoot opened up by the project was on Hudgill Burn-foot Cross Vein, for which a special shaft was sunk at [NY 7432 4686]; this yielded only 4000 bings (1600 tons) of lead concentrates. An ENE fracture cut at 3750 ft (1143 m) from the portal may have been the continuation of Fistas Rake from Blagill (p.122) but it was not considered worth driving on. The primary geological survey records seven intersections between Gossip Gate and Water Green shafts, and nine NE-trending fractures between Foreshield and Lovelady Shield, the latter perhaps representing the Hudgill Burn veins, but none was developed, though a connexion was made to that mine. Beyond Foreshield the level had entered the essentially synclinal valley and this was unfortunate, for even the most productive veins found in the flanking gentle anticlines were barren here. The level contributed very little to the drainage of the Nenthead mines, very little ore having been found beneath the several Horse Levels listed below. It might have been considered, under modern conditions, as a possible starting place for trials of the Nenthead veins in the Whin Sill; but since the Rampgill Underground Shaft (p.143) and borings at Longcleugh Mine, West Allendale (p.152) suggest that the sill may be at a very low stratigraphical horizon here, this project is unlikely to attract high priority.

    The work of Smeaton at Nentforce and also at Rotherhope Fell, and that of Sir Walter Blackett in West Allendale had the important effect of leading to the general adoption into local mining practice of the driving of properly engineered horse levels (Sopwith 1833, p.118), by which the ore was brought to surface in wagons. (Table 45) summarises the principal examples in the Nent Valley.

    These levels were commenced in the late eighteenth and early nineteenth century. The first three in the table were commenced by the smaller firms; Rampgill, Smallcleugh and Capleclough were the work of the London Lead Co. The centralisation of underground transport led to the establishment of centralised dressing floors, in contrast with the older practice of dressing the ore as close as possible to the whimsey shaft or opencut from which it was obtained. This led to great improvements in methods of treatment. At Nenthead two dressing floors for lead concentrates were built by the London Lead Co., one serving Smallcleugh Level and the higher levels on Rampgill and adjacent veins, the other, in Nenthead village, serving Rampgill and Capleclough levels. Zinc concentrates were extracted at a plant near Wellgill: There were also dressing floors at Hudgill Burn, Nentsberry and Bloomsberry. In 1882 the London Lead Co. surrendered its Nenthead leases, which passed to the Nenthead and Tynedale Zinc Co., who operated the Rampgill dressing floor, mainly for zinc concentrates (Almond, 1977). This firm was succeeded in 1896 by the Vieille Montagne Zinc Co, who in 1908 replaced the old dressing floor with a large gravity mill by Krupp, in its time the most up-to-date of its kind (described by Smith, 1923, pp.89–92), which produced both lead and zinc concentrates. The presence of abundant ankerite and siderite in the ores rendered them difficult to dress for zinc by gravity methods, and the grade of concentrates obtained averaged only about 40 per cent zinc. This mill continued work until 1921. All these dressing operations at Nenthead led to the accumulation of large gravel-tailings heaps at Smallcleugh, opposite Hillersdon Terrace (from the old Rampgill washery) and adjacent to the newer mill. A sampl ing campaign, carried out on these dumps in collaboration with Mr Amos Treloar in 1940 on behalf of the Non-ferrous Ores Committee (Ministry of Supply) indicated a total tonnage of 615 000 with 0.4 per cent lead and 3.5 per cent zinc.

    The average amount of zinc metal present in the oxidised state, i.e., as hydroxide, carbonate or silicate was of the order of 1 per cent; probably nearly half the lead was in this condition. In 1942–43 a flotation plant, with capacity for treating up to 1000 tons of gravel per day, was erected within the earlier mill buildings by Non-ferrous Minerals Development Ltd for the production of zinc concentrates for war purposes; it has been described by Mr E W O Dawson (1947). The recovery of zinc concentrates was of the order of 3.3 per cent by weight of the input. Lead concentrates representing about 0.25 per cent of the feed were obtained. The gravel contained 50–60 per cent of silica and 25–30 per cent of ankerite and siderite, with fluorite, baryte, witherite, limestone, sandstone and shale, and an appreciable amount of organic matter which necessitated special treatment in the mill. The operation, which yielded altogether 19 941 tons of zinc concentrates containing 56.2 per cent zinc and 1355 tons of lead concentrates containing 73.1 per cent came to an end in 1946. In addition to the old tailings heaps, there are large scattered dumps of coarse rock, many of which contain sphalerite. The zinc plant was dismantled, but Anglo-Austral Mines Ltd subsequently erected a flotation plant in the existing building with daily capacity of up to 50 tons, to produce fluorspar. This operated until 1960, mainly on ore from Cammock Eals Mine (area 5). At the end an attempt was made to separate fluorspar from the Rampgill Firestone Level tailings but this was uneconomic and the plant was sold to the Rampgill Mill Co. for lead-zinc recovery from local dumps, but this lasted only until 1963 when the plant was dismantled (Houston, 1963, Critchley, 1984).

    The records in (Table 46), though incomplete, serve to give an indication of the quantities of lead and zinc concentrates obtained from the Nent subarea.

    The figures emphasize the change-over from lead to zinc production during the nineteenth and early twentieth centuries. The Nent valley mines produced three-quarters of the lead concentrates won in Alston Moor. Previous to 1796, 335 384 tons of lead concentrates had been mined in Alston Moor during the period commencing 1666. If the Nent Valley produced a similar proportion of the total prior to 1796 as it did in later years, it may be estimated that the total yield of the Nent mines was of the order of 600 000 tons. Since 1921 the only active mines have been Nentsberry, and for a short period, Brownley Hill. The principal workings from both mines in this period have been in the West Allen area of Northumberland, though the ore was brought out through Cumbria; very little ore has been obtained in the area here under description. In addition to the notable historical accounts by Raistrick listed in Chapter 1, more recent writings on Nenthead by Jackson (1969) and Critchley (1984) may be consulted.

    Hudgill Burn Veins—Lead ore

    NY74SW, SE, NE, NW; Cumberland 34SW

    The romantic circumstances leading to the discovery by John and Jacob Wilson of the rich group of veins worked at Hudgill Burn Mine (disused) in 1812–14 have been related by Sopwith (1833, pp.122–124). There are two principal veins, trending E–W, the Hudgill Burn Old Vein, and Galligill Well Vein. Between these there is a complex series of linked ENE and E–W veins, the Sun veins. The whole complex is reminiscent of the "horse-tail" structure developed in the Butte district, Montana. The veins are unique in the orefield not only for their structure, but for the abundance of cerussite in them. Wallace (1861, p.197) states: "Where the richest deposits were found in the Great Limestone, very thick clay beds form the surface of the country; and near the outcropping of this stratum of limestone with these clay beds, by driving levels on the line of the veins, detached masses of rock were found containing much sulphide of lead, which was found changed into a carbonate of lead, where placed in actual contact with the clay; the central part of the masses, however, remained a sulphide". The oreshoots were short, probably seldom exceeding 600 ft (182 m) in length; they were, however, 10–12 ft (3–3.7 m) wide, in places reaching 20 ft (6 m) (Sopwith, 1833, p.124). The ore was sufficiently decomposed to be workable entirely by the pick, without blasting. A small flat was found on the N side of Third Sun Vein. The oreshoots appear to have been confined to the Great Limestone; trials from the London Lead Co.'s Eden Braes Level [NY 7605 4539], which starts at 1185 ft (361 m) above OD from the W bank of the Nent, 1400 ft (427 m) SSE of Nenthall, and runs SW beneath the Nattrass Gill Hazle, were not successful; nor were explorations at the horizon of the Firestone. The oreshoots all died out to the W, more or less beneath the line of outcrop of the Firestone, where a natural cavern (a description of which is quoted by Sopwith 1833, pp.69–74) ran south-eastwards across the lines of the Sun veins.

    The Burn or Horse Level [NY 7506 4547] starts mile (0.5 km) N of the vein-complex and runs SSW sending off two branches to give access to the veins. A third branch was driven to prospect the ground for 2000 ft (610 m) to the NNW, but without success. The horizon of the level is the shale below the Tuft; it is no longer accessible. The extensive dumps suggest that gangue minerals were not abundant, but quartz, aragonite, ankerite, siderite and calcite were present, together with hydrozincite, smithsonite and cerrussite. At least 100 000 tons of tailings remain from dressing; a sample taken from superficial pits assaying 3.31 per cent lead, 4.88 zinc, 0.16 sulphur (assay by Mineral Resources Laboratory, Imperial Institute, 1940), indicated the advanced state of oxidation of the remaining ore minerals.

    Hudgill Burn North Vein branches W from Old Vein where that is reached by the west branch of Horse Level and appears to be the continuation of Redgroves Vein of Middle Fell, while the Middle Vein, a SW branch of the Old Vein, may be the continuation of Dowpot Sike Vein. Since unworked stretches at least 1600 ft (488 m) long in the Great Limestone separate both veins from their supposed continuations it must be presumed that the foreheads on both sides of Middle Fell on these veins were unpromising, though no record remains.

    Hudgill Burn Mine worked from 1814 to 1870, producing a total of 54 642 tons of lead concentrates. The ore was richer in silver than the average for the Nent mines; in 1854–70 the recovery amounted to 13.0 oz silver per ton of lead; the grade of lead concentrates produced in the same period averaged 71.5 per cent of lead.

    Galligill Sike Veins—Lead ore

    NY74SE; Cumberland 34SW

    Two veins, known as Galligill Sike Middle Vein, and, 150 ft (46 m) to the SE, the more important Galligill Sike Vein, trend N55°E along the NW side of Galligill Burn, SW of Nettle Hall on the eastern slope of Middle Fell. The main entrance to Galligill Sike Mine (disused) was a level [NY 7585 4448] driven into Galligill Sike Middle Vein at the base of the Great Limestone from which crosscuts extended to the main vein. There was also a level [NY 7574 4430] driven at the horizon of a coal, probably that above the High Coal Sill, into both veins. In the Great Limestone a belt of small flats was worked on the SE side of the main vein, following leaders in the High Flat. This belt extended 700 ft (213 m) SW from the intersection of the main vein with a weak cross vein which was also cut in Hudgill Burn Mine. At Galligill Sike there were also vein oreshoots, but the available information leaves some doubt as to whether these were worked on the Middle Vein or the main vein (Mines Dept Plan No. R10 A). The Great Limestone carried an oreshoot 725 ft (221 m) long, extending SW to a point beneath the outcrop of the Firestone; at higher levels oreshoots in the Coal Sills sandstones, Little Limestone and Pattinson Sill, covering a total length of 1175 ft (358 m), extended farther SW than did the mineralised ground in the Great Limestone. The total production from 1848 to 1891 amounted to 1538 tons of lead concentrates; silver recovery between 1854 and 1870 was equivalent to 11.7 oz silver per ton of lead.

    A trial in the Four Fathom Limestone by means of a sump on the main vein yielded a little ore, but was not apparently considered worth pursuing; the veins must be regarded as exhausted as far as development has proceeded. It may be noted, however, that these two veins are the probable continuations of Black Sike and Fletcheras veins and that nearly 3000 ft (914 m) of virgin ground remains on their courses beneath the summit of Middle Fell.

    Nentsberry Green and Nentsberry Haggs veins—Lead ore

    NY74NE; Cumberland 34SW, SE

    At Nentsberry, on the NE side of the Nent Valley, a series of five feebly mineralised NE veins, which have been worked from short levels [NY 7619 4550], [NY 7623 4536], [NY 7646 4541] and [NY 7650 4514] starting near the Nenthead–Alston road, may represent the continuations of some of the Hudgill Burn and Galligill Sike veins. The minerals present include galena, sphalerite, smithsonite, quartz, siderite, ankerite and limonite. According to Wallace (1861, p.213) the only vein which contained much ore was the Nentsberry Haggs (Sun) Vein, upon which the Nentsberry Haggs Horse Level [NY 7661 4503] (p.138) is driven for the first part of its course. Narrow stopes in the Nattrass Gill Hazle and Four Fathom Limestone, extending as far NE as the intersection with Cowhill Cross Vein, 1230 ft (375 m) from the portal, can be seen above the level; the vein throws 3 (1.07 m) NW. At 1180 ft (360 m) from the portal there is a sump on the vein, believed to communicate with a branch from Nentforce Level. Wallace remarks that ore was got down to the Three Yard Limestone in this vein.

    High Raise Vein—Lead and zinc ore, witherite

    NY74NE; Cumberland 34SE. Direction N52°E, throw (in Cumbria) 7–10 ft (2–3 m) NW; productive in upper part of Great Limestone. Continues into West Allen area (p.154).

    Sun Vein

    Same direction, 875 ft (267 m) to SE.

    The Nentsberry Haggs and Nentsberry Greens veins terminate against the major fault known as Carr's Vein, which here has a throw of 200 ft (61 m) NE. At 550 ft (168 m) NE of Carr's Vein in Nentsberry Haggs Horse Level, another strong cross vein, Wellgill Vein, throwing 30 ft (9 m) SW, is cut. There is productive ground on the NE side of the cross vein, and two veins have been worked from the Horse Level within Cumbria. The Sun Vein lies approximately 1000 ft (305 m) NW of the point where the Horse Level reaches Wellgill Vein; it is reached by a crosscut beneath the Quarry Hazle which forms part of the Horse Level, diverging northwards from Wellgill Vein. The level continues NNW to High Raise Vein. The workings on both these veins form part of Nentsberry Mine (disused), the major part of which lies in Northumberland, and is described under the West Allen Area (p.155).

    The Sun Vein is mineralised in the Great Limestone, especially in the upper part of the limestone, where it carries sphalerite, galena, ankerite, with baryte and a little witherite. A length of 900 ft (274 m) has been developed in Cumbria and by means of a drift, connected with the Horse Level by two rises, about 30 ft (9 m) above the base of the Great Limestone; the ground above the level has been extracted in part only, yielding ore containing 6–8 per cent lead sulphide and 10–12 per cent zinc sulphide. The vein is essentially a fracture belt up to 10 ft (3 m) wide along which the orebody has developed by partial replacement of the limestone. A length of 1700 ft (518 m) remains unworked between the Cumbria workings and those in Northumberland, where the vein is called Second Sun Vein.

    The original workings on High Raise Vein (according to a report by John Leathart, dated 1842) were from High Raise Low Level [NY 7649 4583], which starts beneath the Quarry Hazle from Brown Gill, 2300 ft (701 m) E of Nenthall. After passing through Carr's Vein this level ran near the bottom of the Pattinson Sill until, after passing through Wellgill Vein, it was at the horizon of the coal above the High Coal Sill. In 1842 the forehead of this level, on High Raise Vein, was standing 564 ft (172 m) NE of Wellgill Vein; at 480 ft (146 m), owing to the rise NE of the beds towards the anticline which lies between the Nent and Wellhope valleys, the level reached the coal above the Low Coal Sill. Sumps to 42–48 ft (12.8–14.6 m) below this level, reaching the upper part of the Great Limestone, proved a vein 5–7 ft (1.5–2.1 m) wide which, according to Leathart, contained "a blackish and brown rider, black jack, and some pearl and quartz spar". By 1852 (according to a report by Jacob Walton) the Nentsberry Horse Level had been advanced to

    High Raise Vein, and connection had been made to High Raise Level by means of rises. Walton states that the vein in the Great Limestone proved to be 2–6 ft (0.6–1.8m) wide, containing "black or brownish iron rider, a little quartz, carbonate of lime, sulphate of barytes, and a large quantity of black jack, with lead ore exceedingly variable in quantity, in some places a mere trace and in others a rich bunch (but these have been few and far between)". Most of the ground was unpayable; the best horizon appears to have been the Tumbler Beds of the Great Limestone on the footwall side, where ore was developed 6–9 ft (1.8–2.7 m) in vertical height, over a length of 1200 ft (366 m). Later developments, under the Nentsberry Mining Co., and their successors the Lugdale Chemical Co., revealed that parts of the vein were rich in witherite. The main mineral was witherite with some baryte from 1250 to 2450 ft (381 to 747 m) NE of Wellgill Vein. It proved, however, to be very intimately mixed with sphalerite, and chemical methods of separation were employed for a time. During their tenure of the mine the Vieille Montagne Zinc Co's operations on High Raise Vein were entirely in Northumberland. The production of minerals up to 1912, mostly if not entirely from the Cumbria workings, amounted to 1366 tons of lead concentrates, 10 939 tons of zinc concentrates, and 1600 tons of witherite, production of lead commencing in 1852, zinc in 1875 and witherite in 1894.

    Grassfield Vein—Lead and zinc ore

    NY74SE; Cumberland 34SW, SE. Direction N53°E; productive in Great and Four Fathom limestones.

    The main level [NY 7673 4460] at Grassfield Mine (disused) starts midway between Grassfield and Hayring beneath the Great Limestone, at 1332 ft (406 m) above OD, reaching Grassfield Vein at 625 ft (191 m). Information on the workings of this mine is scanty; the only plan is the general plan of Alston Moor workings (Mines Dept). This indicates that the main workings on the vein extended 2100 ft (640 m) SW, as far as West Cross Vein, the presumed continuation of the Nunnery Cross Vein, against which Grassfield Vein appears to have terminated. According to Wallace (1861, p.212) the Four Fathom Limestone carried an oreshoot, which did not, however, extend down into the Nattrass Gill Hazle, nor into the Slaty Hazle, in which a trial was made from Nentforce Level. The Four Fathom Limestone was reached from two levels, one [NY 7648 4496] starting opposite Nentsberry Mill at 1225 ft (373 m) above OD, the other [NY 7691 4482] starting 500 ft (152 m) ESE of Nentsberry Bridge. It appears probable that the oreshoots lay between Sike Cross Vein and West Cross Vein; the Sike Cross Vein also contained ore in the Great Limestone and was worked from this mine. The minerals present, as evidenced by the dumps from the levels, included quartz, ankerite, limonite, sphalerite, smithsonite and galena. A drift SE in the West Cross Vein in the Great Limestone attempted to find the SW continuation of Grassfield Vein, or to pick up some of the veins (including Hundybridge) worked on the W side of Middle Fell at Cowper Dyke Heads Mine, but apparently without success. A report by Isaac Walton dated 1852 states that the West Cross Vein itself was a poor vein, containing a mere trace of lead ore, in clay, limonite and calcite. The production from Grassfield Mine from 1803 to 1385 amounted to 14 834 tons of lead concentrates, with 96 tons of zinc concentrates in 1872–77. Recovery of silver during the ten years ending 1864 was equivalent to 17.8 oz silver per ton of lead.

    Brownley Hill Veins—Lead and zinc ore

    NY74SE, NE; Cumberland 34SE. Direction N45°E, changing to N65°E; productive in Great Limestone.

    Grassfield Vein, as noted above, is unproductive beneath the Nent Valley where it is cut by Nentforce Level. NE of the level it does not appear to have been tried between the valley bottom and Wellgill Cross Veins, but on the NE side of that cross vein there is a group of NE veins, including Brownley Hill North Vein, Brownley Hill Vein, North Middle Vein, Middle Vein and Sun Vein, one of which may be regarded as the continuation of the Grassfield Vein. Brownley Hill Mine (disused), which worked these veins, was entered by means of two levels from Gudham Gill, one, the Bloomsberry Horse Level [NY 7762 4465], driven through Carr's Vein and Wellgill Vein to the Gudhamgill Burn Cross Vein, along which a drift gave access to the Brownley Hill veins in the Great Limestone; the other, the Brownley Hill High Level [NY 7788 4993] driven in the sandstones and shales between the Great and Little Limestones, passing through the Burn Cross Vein and continuing NNW to Brownley Hill Vein. The mine workings are very extensive; the High Level, as well as the Horse Level, connects with all the veins. Although a good plan is in existence, unfortunately no longitudinal sections have been preserved. It is not, therefore, possible to be certain whether any ore was worked above the Great Limestone, but it is clear that this limestone was again the main bearing horizon. Brownley Hill Vein and North Vein run parallel for 2000 ft (610 m) from Wellgill Cross Vein; the Moss Cross Vein is then encountered, and the veins change direction to N65°E, uniting before they reach the county boundary 1500 ft (457 m) from Moss Cross Vein. In Northumberland the vein continues as Scraithole Vein of the West Allen Area (p.156). Between Moss Cross Vein and the boundary two more NW veins have been proved on the SE side of Brownley Hill Vein, known respectively as High Cross Vein and West High Cross Vein. The three cross veins have all been extensively worked in the Great Limestone. The remaining NE veins are important near the Burn Cross Vein only, and die out before reaching Moss Cross Vein. One of them, Middle Vein, is of interest because a substantial flat was related to it, extending between Wellgill and Gudhamgill Burn Cross veins in the lower part of the Great Limestone.

    The principal minerals were galena, sphalerite, quartz, chalcedony and (according to Forster, 1821, p.289) fluorite in the Great Limestone workings. As the mine was developed northeastward, barium minerals, not present in the workings near the Burn Cross Vein, came in. Shafts, for example at [NY 7827 4572] on the main vein near the county boundary, found coarse white baryte: an old level, probably in Slate Sills sandstone, was reopened during the 1950s by Mr E Richardson revealing pink baryte. At lower levels there are said to have been some barium carbonate minerals, including alstonite, for which this is the type locality. It is now known from underground investigations that this mineral came from the High Cross Vein in the Great Limestone (Young et al., in press). Statistics of production are incomplete for this mine; the production of lead concentrates from 1848 to the closing of the mine in 1886 amounted to 14 732 tons; 1197 tons of zinc concentrates were obtained between 1872 and 1876. Silver recovery between 1854 and 1884 amounted to 5 oz silver per ton of lead (Smith 1923, p.85).

    The plan of Brownley Hill Mine gives the impression that the ground has been very thoroughly explored at the horizons of the two principal levels. A crosscut from the High Level runs E for 2350 ft (716 m) from the end of the workings in the Sun Vein; from this drift a cross vein known as Jug Vein, possibly the continuation en echelon of West High Cross Vein, was worked. It is not known whether trials were made below the horizon of the Great Limestone at this mine.

    Bentyfield Veins = Greengill Veins = Gudhamgill Vein—Lead and zinc ore

    NY74SE, NE; Cumberland 42NW, NE, 34SE. Direction N45° to 65°E, throw in Gudhamgill workings, 9 ft (2.7 m) NW.

    The Bentyfield Veins are believed to be the NE continuation of a fault known as High Scar or Great Vein west of the Tyne near Garrigill, which throws at least 30 ft (9 m) NE, but which in trials from Dry Burn [NY 7219 4166] has proved to be unmineralised. East of the Tyne the throw diminishes but is taken up by the parallel Browngill Vein, as Wallace (1861, p.62) has pointed out. A level [NY 7435 4205] has been driven on the fault, starting near Low Houses Bridge, Garrigill, for a distance of 1930 ft (588 m) ENE at the base of the Scar Limestone, but without finding ore. East of the Alston–Middleton road, the direction changes from ENE to NE and from here to the Tyne–Nent watershed the vein is known as Bentyfield Vein. The main development at Bentyfield Mine (disused) was a level [NY 7555 4255] driven on the top of the Great Limestone from Garrigill Burn at about 1505 ft (459 m) above OD following a branch known as Taylor Sike Vein for 925 ft (282 m) then joining the main Bentyfield Vein and continuing in it for 1700 ft (518 m). Ore-bearing ground in the Great Limestone, Coal Sills and Little Limestone covered a length of 1250 ft (381 m) and was worked from this level. The minerals present include quartz, purple fluorite, galena and sphalerite; the tailings are mingled with those from Whitesike Mine (described below). The Bentyfield Mine was worked partly by the London Lead Co. and partly by the Alston Moor Mining Co.; it yielded, between 1848 and 1882, 4868 tons of lead concentrates; 40 tons of zinc concentrates are recorded for the year 1874. Silver production between 1854 and 1875 indicates a recovery of 7.6oz silver per ton of lead.

    At the watershed the vein was unproductive for about 600 ft (183 m) but to the NE an oreshoot, worked in very early times, was found near the surface in the Slate Sills, at Greengill Mine (disused). This oreshoot appears to have terminated against the Nunnery Cross Vein; it was explored in the Firestone Sill by means of a long level [NY 7669 4392] driven from the N, patchy ore-bearing ground being found at this level. NE of Nunnery Cross Vein, the vein is in two branches, which were worked in and above the Firestone, but with poor results. It is probable that a branch level from Grassfield Horse Level, driven along Sike Cross Vein, reached the Greengill Vein in the Great Limestone. Wallace (1861, p.194) says, of this trial "little is now known respecting its contents, except that no lead ore was raised, and that the extensive works made in it incurred a very considerable loss of capital". Sike Cross Vein joins Black Ashgill Cross Vein at the NE end of Greengill Hush [NY 7699 4376]; the latter vein is apparently shifted 130 ft (40 m) S side W by Greengill Vein.

    A length of 6000 ft (1.8 km) of unproductive ground on the vein occurs NE of the inter-section with Black Ashgill Cross Vein, continuing beyond Gudhamgill Burn Cross Vein into the workings of Gudhamgill Mine (disused); This mine was developed in common with Brownley Hill Mine, from the Bloomsberry Horse Level [NY 7762 4465], a branch of which extends SE along Gudhamgill Burn Cross Vein from the levelhead, reaching Gudhamgill Vein at 1650 ft (503 m) in the Tuft at 1342 ft (409 m) above OD. The bearing ground on this vein commences at the intersection with Jug Vein, 1250 ft (381 m) NE of the Burn Cross Vein, and continues up to and beyond the county boundary. The vein bifurcates shortly before reaching the boundary. Up to the split, the oreshoot is 2550 ft (777 m) long in the Great Limestone; over most of this length it has been stoped the full height of the limestone, while in a stretch 500 ft (152 m) long stopes have been carried up to the Little Limestone. Beneath the Great Limestone the Tuft and underlying shale are barren, but there is an oreshoot in the Quarry Hazle 1450 ft (442 m) long, commencing 1000 ft (305 m) NE of Jug Vein intersection. This was worked above the Horse Level, the beds having risen NE from Burn Cross Vein towards the crest of the NentWellhope anticline. At 1220 ft (372 m) NE of Jug Vein, an underground shaft was sunk to the Five Yard Limestone. A small oreshoot was found in and above the Four Fathom Limestone. 750 ft (229 m) long by an average height of less than 20 ft (6 m); beneath this horizon no workable ground was discovered. In addition to the vein ore-shoots, extensive flats accompany the Gudhamgill Vein in the Great Limestone. These commence 700 ft (65 m) NE of Jug Vein, their beginning possibly corresponding with the intersection of a weak NW leader tried in Brownley Hill Mine. The larger flats were found on the footwall side of the vein, extending as much as 300 ft (91 m) from it; on this side of the vein they occur at the High Flat horizon, but smaller flats on the hangingwall side of the vein include some in the Low Flat position. One of the footwall flats examined during 1940 proved to have been developed in a small E–W anticline, along the crest of which there was a belt of small mineralised leaders, diverging from the vein.

    The mineralisation in the flats consists of a fine-grained replacement of limestone by sphalerite with wedge-shaped masses of galena. Vugs containing amber fluorite, sphalerite, galena and quartz are common. In 1917, in an unpublished report to the Ministry of Munitions by J G Cunningham, the yield from the flats was estimated to be 0–1 ton galena and 0.5–1 ton sphalerite per fathom: Work by the Veille Montagne Zinc Co. in the 1930s realized an average yield of 4 per cent lead sulphide and up to about 7 per cent zinc sulphide. Throughout the Gudhamgill oreshoots sphalerite appears to have exceeded galena in amount, an unusual occurrence in the Northern Pennine field. The production of the mine under the London Lead Co. during the years 1848–1882 amounted to 3596 tons of lead concentrates, but this figure gives no adequate idea of the yield of the oreshoots here. Silver recovery was 7 oz silver per ton of lead (Smith, 1923, p.84). No separate figures are available for the output under the Vielle Montagne Co., but the yield is included in the general figures given on p.139.

    A short oreshoot was worked in the Pattinson Sill, but trials in the Firestone were unsuccessful. The ground may be said to have been adequately explored in Cumbria, but a substantial length of virgin ground lies ahead of the well-mineralised foreheads now standing in the flats within Northumberland.

    Dowgang Vein–Scaleburn Vein—Lead and zinc ore

    NY74SE Cumberland 42NE, 34SE. Direction N60°E, changing to N35°E; throw about 10 ft (3 m) SE at Dowgang Hush; 15 ft (4.6 m) NW near Rampgill Cross Vein; 6 ft (1.8 m) SE in Scaleburn workings.

    The great Dowgang Hush [NY 776 431], WSW of Nenthead village, is a man-made valley, the purpose of which was to work lead ore which occurred in the Slate Sills on Dowgang Vein. Possibly this vein may be a branch from the Browngill vein-system, but the connection has never been established SW of Nunnery Hill. In the hush, Brigal Burn Vein, which farther to the NE becomes Rampgill Vein, branches from Dowgang Vein. Underground developments at Dowgang Mine (disused) were reached from Dowgang Shaft [NY 7761 4316], sunk at the junction of the hush with the small valley of Dowgang Burn; the underground workings were drained by means of a branch of Capleclough Horse Level [NY 7761 4316]. No information is obtainable about the oreshoots on Dowgang Vein, save that, according to Wallace (1861, p.193) rich lead ore was obtained in the Slate Sills, Firestone, Litte Limestone, "and even as low as the upper part of the Great Limestone" but, except on the E side of Black Ashgill Cross Vein, the quantity was so small that it scarcely repaid the cost of extraction. Small oreshoots were found on an E–W branch of Dowgang Vein near the shaft, and also on Dowgang North Vein, lying 200 ft (61 m) to the NW of the main vein at the shaft. In the belt of strong cross veins between Cowhill and Patterdale Cross Veins (illustrated on the section of Rampgill Mine (Figure 17), no ore was obtained from the NE vein. NE of Patterdale Vein, the vein, now known as Scaleburn Vein, was probably productive in the Firestone. The main bearing ground, however, began in the neighbourhood of the shaft 500 ft (152 m) NE of Patterdale Vein. In the 680 ft (207 m) NE to Scaleburn Whimsey Shaft there were stopes from the top of the Great Limestone to the Little Limestone, as well as in the Pattinson Sill. From Scaleburn Whimsey an irregular series of vein-stopes were worked to the county boundary in the Great Limestone; in the same area small flats at the High Flat horizon were found on both sides of the vein. A little ore seems to have been won from the Little Limestone, Pattinson, Firestone and Slate sills in parts of this ground but the stopes were very small. The vein continues into West Allendale as the Low Coalcleugh Vein (p.158). The main access to Scaleburn Mine (disused) was by way of Rampgill Horse Level [NY 7818 4350] at 1432 ft (436 m) above OD; this was continued almost to the county boundary, but gave only a partial command of the Great Limestone. Sublevels above this ran on top of the Great Limestone, and above the Little Limestone. There was also a level from surface driven above the Firestone. An extra 100 ft (30 m) of depth was added to this mine by the driving-up of Bloomsberry Level, following the course of Rampgill Cross Vein. This gave access to the Quarry Hazle, where oreshoots aggregating about 450 ft (137 m) in length and averaging 25 ft (7.6 m) high were worked. A sump to the Four Fathom Limestone, sunk, according to Wallace (MS accompanying Scaleburn Mine Plan, Mines Dept No. R274), beneath rich ground in the Quarry Hazle proved this limestone to be barren.

    Scaleburn Vein was approaching exhaustion before the middle of last century; the available separate records, for the period 1848–1882, show only 2277 tons of lead concentrates, containing 73 per cent lead, from which the silver recovery was 7 oz silver per ton of lead. The vein was not reworked during the period of zinc production and is considered to be exhausted. The gangue minerals present on the shaft heaps along the vein include purple fluorite, quartz, and carbonates but there is no reason to believe that workable fluorite bodies remain.

    Brigal Burn–Rampgill Vein and Rampgill Sun Vein

    Brigal Burn Vein diverges from Dowgang Vein near the head of Dowgang Hush, close to the intersection with Black Ashgill Cross Vein. Here a small flat in the Great Limestone was worked between Brigal Burn Vein and the cross vein. No section remains showing the stopes in Dowgang Mine on Brigal Burn Vein, but information from Wallace suggests that workable ground extended 1350 ft (411 m) NE of the Black Ashgill intersection, between the Firestone and the base of the Great Limestone. This ground was reached by a branch of Capleclough Horse Level, but it is likely that much of it was exhausted from surface shafts before the driving of that level in the early years of last century. The production from Dowgang Mine (including Brigal Burn and the Dowgang veins) was 3791 tons of lead concentrates between 1848 and 1882, with 530 tons of zinc concentrates between 1872 and 1888.

    Like the other NE veins of the district, the Rampgill Vein is barren where it passes through the belt of cross veins between Cowhill and Smallcleugh Great, in spite of the presence of the Great Limestone in an easily accessible position. The bearing ground commences NE of the Great Cross Vein, in the vicinity of Firestone Bridge on the Nenthead–Cowshill main road, and extends continuously to the county boundary. The disposition and shape of the oreshoots are illustrated by (Figure 23). The highest productive horizon was the Slate Sill, here a sandstone 72 ft (22 m) thick with a median shale parting. Beneath the Slate Sill there was barren ground down to the well-mineralised Firestone. The White Sill, Pattinson Sill, Little Limestone, Coal Sills, Great Limestone, Quarry Hazle and Four Fathom Limestone all carried oreshoots, mostly of the ribbon type; generally, however, the vein was not productive where shale formed both walls. There were three main periods of working in Rampgill Mine (disused). The first period, up to 1745, saw the discovery of the vein and its exploitation in the Slate Sills, Firestone, White Sill and Pattinson, mainly from surface whimseys. In 1745–46 the London Lead Co. acquired the mine (after the Commissioners of Greenwich Hospital had made a disappointing trial in the Great Limestone near the Engine Shaft). The ground opened up by the London Lead Co. from the Pattinson Sill to the bottom of the Great Limestone, proved to be the richest ever worked in Alston Moor. There were two main levels one driven from Firestone Bridge [NY 7876 4350] to command the Firestone Sill, the other the Rampgill Horse Level, [NY 7818 4350] commenced shortly before 1800. Nentforce Level was driven up to the Engine Shaft [NY 7896 4361] in this period, but the appearance of the vein in the Three Yard Limestone here was not such as to encourage further extension. The London Lead Co. mine-section (preserved at the North of England Institute of Mining Engineers, Newcastle) shows that the base of the Great Limestone was the bottom limit of workings by this company, though the Engine Shaft, and a sump 2100 ft (640 m) NE of it, had tested the measures down to the Four Fathom Limestone. The third period of working began in 1896 with the Veille Montagne Zinc Co. who first reworked a length of ground in the north-eastern part of the mine for zinc ore. Subsequently they sank a vertical underground shaft from the Horse Level, 200 ft (61 m) SW of the county boundary, 380 ft (116 m) deep, reaching the base of the Scar Limestone in a crosscut to the hangingwall of the vein. From this shaft oreshoots were exploited in the Quarry Hazle, the Four Fathom Limestone, and the Slaty Hazle. From the Scar Limestone an inclined shaft on the vein was carried down to the footwall position of the Lower Little Limestone. Geological evidence indicates that the vein splits up in its downward course, to a greater extent than was realized at the time the exploration was done (vide Smith, 1923, p1.13, which is a reproduction of the section made then). No further oreshoots were found by this sinking; the vein carried carbonates only.

    The extensive vein oreshoots terminate at the Bounder End Cross Vein, near the county boundary, but the vein continues into West Allendale as the Whitewood Vein (p.158). Associated with Bounder End Cross Vein there were extensive flats at the High Flat horizon of the Great Limestone; these are the forerunners on the great belt of flats which in West Allendale take the place of the vein-oreshoots of Rampgill Vein.

    Rampgill Sun Vein, a smaller vein SE of Rampgill Vein, carried small oreshoots in the Great Limestone between Smallcleugh Cross Vein and the Great or Handsome Mea Cross Vein, and also in the vicinity of Rampgill Cross Vein, along which the workings were connected with those on Rampgill Vein. Farther NE there was another connection to the Sun Vein starting near the Underground Shaft; very patchy oreshoots were found in the Great Limestone. This vein was of little importance in Cumbria, but its supposed continuation in Northumberland, the Barney Craig Vein, produced the most highly mineralised deposits in the West Allen Area.

    The mineral assemblage in the Rampgill veins included quartz, siderite, ankerite and calcite; purple fluorite was present in abundance in the workings from Firestone Level, but in the Great Limestone Wallace (1861, p.143) states that it was rarely met with in considerable quantities. He states, however, that "at some former period it must have been plentifully deposited in the veins of the district, since casts of its crystals in quartz are by no means uncommon, even in veins where not the smallest particle of the substance can now be found". Wallace (1861, p.149) also states that barytocalcite was found in Rampgill Vein at the horizon of the Grindstone Sill, but no trace of this mineral was found at lower levels. No workings in the Grindstone are shown on the mine sections, and it has not been possible to confirm this observation. The ore minerals at Rampgill were galena, from which silver was recovered at the rate of 7 oz silver per ton of lead (Smith, 1923, p.84) and sphalerite. Wallace estimated the total production of lead concentrates from Rampgill Vein up to 1861 as 120 000 tons (1861, p.103). Separate records are available only for the period 1848–1882, when 10 562 tons were obtained. No separate figures for zinc concentrates are available, but this vein made a substantial contribution to the Nenthead grand total. Some fluorspar was produced by jigging material from the dumps from Firestone Level at Nentsberry mill, but no mining for this mineral has been done.

    Dryburn Washpool–Browngill–Archer's Vein Lead and zinc ore

    NY74SW; Cumberland 42NW, NE. Direction N65–90°E, changing to N45°W on Archer's Vein; throw: W of Tyne, small; E of Tyne, increases to 42 ft (13 m) N near Bunkershill; about 60 ft (18 m) N at head of Whitesike Level; 70 ft (21 m) N near Longholehead Whimsey, 55 ft (17 m) NE on Archer's Vein.

    There is good reason to regard the Browngill Vein as one of the principal channels of mineralisation in the district. At surface, however, its western portion, known as Dryburn Washpool Vein, is only feebly mineralised in the Scar Limestone in Dryburn [NY 7219 4143] nothing workable having been found between Dry Burn and High Redwing. On the W bank of the Tyne, N of Garrigill, the Tynebottom Mine (disused) worked flats in the Tynebottom Limestone related to this vein in the vicinity of its intersection with Windshaw Bridge vein, a cross vein running N 55° W. The flats extended for a distance of 800 ft (244 m) WSW along Dryburn Washpool Vein from the intersection with Windshaw Bridge Vein; they also continued along the latter vein for about 800 ft (244 m) SE. The average width appears to have been about 20 ft (6 m) but at the intersection, this increased to 50 ft (15 m). The mineralisation was similar to that found in the Tynebottom Limestone at

    Rotherhope Fell Mine; the limestone is replaced by chalcedony and quartz, with disseminated crystals of galena, marcasite and pyrite. Quartz, purple fluorite, ankerite and calcite occur in vugs. A small quantity of glaucodot (Ixer, Stanley and Vaughan, 1979) has been found in the ore, oxidation of which has led to the deposition of erythrite in pink stalacites of postmine origin. A suite of silver-bearing sulphosalts of cobalt and arsenic has been described by Ixer and Stanley (1987) from specimens collected at Tynebottom Mine by A W G Kingsbury. These seem to have been minor constituents only of the lead ore. A statement by Wallace (1861, p.136) suggests that the extent of the flats at Tynebottom is considerably greater than the extent of the workings, the lead ore not being so plentifully diffused through the mass as to repay the cost of mining. East of the intersection with Windshaw Bridge Vein, the flats are either not present, or are of too low grade to work. The vein, accompanied by much-altered Tynebottom Limestone, may be seen crossing the South Tyne 1100 ft (335 m) NNW of Garrigill church; here it contains galena with much marcasite, the limestone being replaced by fine-grained silica with disseminated sulphides. A small anticline here accompanies the vein. The principal mine developments were from an adit [NY 7394 4183] starting 600 ft NNW of the vein. This did not command the Tynebottom Limestone throughout the mine, and pumping was necessary, surface pumps working in a shaft [NY 7412 4171] 300 ft (90 m) SSE of Garrigill School being used. The workings on the vein were continued beneath and extended 900 ft (274 m) E of the river, but without discovering further flats. Trials made in the Whin Sill found only carbonates in the vein, but the returns suggest that the vein yielded some ore in the Tynebottom Limestone E of the river. The mine was worked by the Earl of Carlisle and Co. from 1771–1798, and by the London Lead Co. 1798–1873; the total production was 11 529 tons of lead concentrates.

    E of the Tyne, Browngill Vein was proved to be unproductive in the Alternating Beds where it was reached by a crosscut from the level [NY 7435 4205] on Bentyfield Vein which starts close to Low Houses Bridge, Garrigill. The crosscut reached Browngill Vein at Bunkershill Shaft [NY 7487 4191], and continued in the vein for 1900 ft (579 m) to the NE at about 1135 ft (346 m) above OD. The vein appears to have been barren up to its intersection with OldGroves Cross Vein 4000 ft (1219 m) ENE of Garrigill church, E of which a long stretch of mineralised ground commenced. The principal development here was the Whitesike or Browngill Low Level [NY 7519 4248] from Whitesike Mine (disused), driven SE from Garrigill Burn beneath the Great Limestone on Old Groves Cross Vein at 1430 ft (436 m) above OD, reaching the vein at 2200 ft (671 m) from the portal. Clay Level [NY 7538 4229] at 1530 ft (466 m) above OD and Colonel's Level [NY 7562 4252] at 1510 ft (460 m) above OD gave access to the vein in the shale above the Great Limestone. There was also a trial in the Nattrass Gill Hazle from a level [NY 7482 4237] starting at 1285 ft (392 m) above OD in Shieldhill Plantation. Exact details are lacking, but it is clear that a considerable amount of ground has been stoped here, probably in and above the Great Limestone. The tailings heap, now crossed by the Alston–Middleton road, contains not less than 60 000 tons of gravel including fluorite, quartz, siderite, a little sphalerite and rock fragments; a sample from superficial pits assayed 1.89 per cent lead, zinc 1.32 (assay by Mineral Resources Laboratory, Imperial Institute, 1940). The vein may be followed to the E by the line of large old whimsey shafts over Flinty Fell. A level [NY 7628 4246] at 1745 ft (532 m) above OD from Brown Gill showed that it was still partly mineralised in the Low Slate Sill, but a higher level [NY 7658 4231] starting near the bend in the Garrigill–Nenthead hill road, 4500 ft (1372 m) E of Whitesike Level mouth, at about 1820 ft (553 m) above OD found little above the Slate Sill horizon. The Whitesike workings extended as far E as Longholehead Whimsey [NY 7710 4225], 2000 ft (610 m) E of the bend in the road mentioned above. Probably much of the work on Browngill Vein in this stretch is ancient, and was carried on from the surface shafts. The production of lead concentrates, between 1848 and 1882 under the London Lead Co. amounted to 7322 tons. This figure may include some ore obtained from Thortergill Syke Vein, a small vein worked from Whitesike Mine in the Great Limestone, 400 ft (122 m) N of Browngill vein; as well as from Browngill Sun Vein, a loop-vein about Yi mile (1.2 km) long which branches from the S side of Browngill Vein near Longholehead Whimsey, downthrowing 12 ft (3.7 m) N. Browngill Sun Vein contained coarse quartz, with purple fluorite; it is doubtful whether much ground was worked on this vein after the "surface whimsey" period. Silver recovered from the Browngill ore during 1861–1870 was equivalent to 7.0 oz. silver per ton of lead, which may be compared with the figure of 6.9 oz. for Tynebottom during the same period.

    The workings from Nenthead join those of Whitesike Mine in the vicinity of Longholehead Whimsey. The principal level from Nenthead was Capleclough Horse Level [NY 7811 4349] (disused), driven by the London Lead Co. at 1500 ft (457 m) above OD. This company's stapes, however, bottomed 120 ft (37 m) above this horse level, being confined to the beds above the Great Limestone on the footwall side of the vein. A length of 2200 ft (671 m), with an average height of 50 ft (15 m), was stoped out by them. The lower ground accessible from the horse level probably contained too much sphalerite and too little galena to be of interest to the London Lead Co., but this was subsequently stoped by the Vieille Montagne Zinc Co., over a total length exceeding 3000 ft (914 m), with an average height of about 60 ft (18 m) (Figure 24). The oreshoot worked here thus extended on the footwall from the Little Limestone down to the Quarry Hazle, and on the hangingwall from the Pattinson Sill down to the Great Limestone. It is presumed that there was a definite downward increase in sphalerite content within the shoot.

    Although precise data are lacking, it is thought that the beds bordering the vein in the Whitesike workings lie almost flat relative to the plane of the vein. From Longholehead Whimsey for a distance of about 1000 ft (305 m) eastwards, there was a marked rise in the beds on both sides of the vein; thus Whitesike Level forehead  is at the base of the Great Limestone on the hangingwall side at 1457 ft (444 m) above OD, while 1000 ft (305 m) to the E the base has risen to 1496 ft (456 m) above OD. Still farther E the dip again flattens. Meanwhile as the vein approaches Black Ashgill Cross Vein it takes a sharp turn to the SE, after which it is known as Archer's Vein, almost paralleling the cross vein. From Archer's Vein an E–W branch is given off which passes through the cross vein, and then splits into what becomes the Capleclough, Middlecleugh and Longcleugh veins, described below. The whole structure closely resembles a Butte "horsetail".

    The lead concentrates recorded for Capleclough Mine for the period 1848–1882 probably came from the workings on Browngill and Archer's Vein described above; the total amounts to 6819 tons. No separate figures are available for workings under the Vieille Montagne Zinc Co.

    Capleclough Vein–Longcleugh Vein group

    The veins listed above may be regarded as originating from the eastward splitting of the Browngill Vein. The principal cross veins which traverse them, E of Black Ashgill Cross Vein, are Cowhill, Carr's, Smallcleugh and the Great cross veins. From Black Ashgill Vein the measures rise steadily to Carr's Vein, which throws them down to the east. They are again elevated between Smallcleugh and the Great cross veins, as a horst. The oreshoots bear a striking relation to the structure; the principal bearing-ground is found on the W side of Carr's Vein, in the upfaulted area. In the trough E of Carr's Vein little has been found on any of the veins. The Smallcleugh horst carried an important belt of flats, related to the cross veins rather than the NE veins. East of Great Cross Vein, in downfaulted ground, little has been found, though here exploration is not so complete as it is to the W.

    The three horse levels, Capleclough [NY 7811 4349], Rampgill [NY 7818 4350] and Smallcleugh [NY 7877 4298] all reached this valuable complex of veins. Capleclough Level, at 1490–1495 ft (454–456 m) above OD gave access to North Vein, Second Sun and Longcleugh veins beneath the Quarry Hazle. Rampgill Level, entering along Smallcleugh Cross Vein, commanded the Great Limestone in and on either side of the Smallcleugh horst, at about the same altitude. Smallcleugh Level, at 1610–1620 ft (491–494 m) above OD, gave a partial command of the limestone in the upfaulted areas, but was above the limestone in the Carr's-Smallcleugh trough, and also E of the Great Cross Vein. In addition to these levels a fourth, Middlecleugh Upper Level [NY 7895 4251], was driven from Middle Cleugh 350 ft (107 m) S of its junction with Long Cleugh Burn, under the Firestone in the ground between Carr's and Smallcleugh cross veins, with branches on all the principal veins. This level, at 1720–1740 ft (524–530 m) above OD, was above the horizon of the principal oreshoots, and was probably driven for ventilation. West of Carr's Vein it was below the Little Limestone or the Pattinson Sill.

    On Capleclough Vein the Great Limestone is immediately above Capleclough Horse Level between the point where the vein diverges from Archer's Vein and Black Ashgill Cross Vein; an oreshoot in the limestone here was worked by the Vieille Montagne Zinc Co. for zinc. Black Ashgill Vein throws 40 ft (12.5 m) W here; zinc stopes continued for 850 ft (259 m) E of the cross vein in the Great Limestone; some lead ore had previously been obtained from the Little Limestone in this stretch by the London Lead Co. At approximately 1000 ft (305 m) E of Black Ashgill Cross Vein, Middlecleugh North Vein branches from the S side of Capleclough Vein; the intersection with Longcleugh Vein may lie closer to Black Ashgill Vein but its exact position is not certain. Little is known about the workings on Capleclough Vein E of where North Vein leaves it, save that the vein follows more or less the course of Old Carr's Burn and has been worked in two branches from surface shafts at about [NY 784 421]. It was apparently not considered worthy of development from Capleclough Horse Level.

    Middlecleugh North Vein appears to have been discovered at surface. It was worked from numerous shallow shafts in the Firestone at about [NY 789 421]; fluorite is very abundant on the dumps from the nearby washing-places. The length of the Firestone oreshoot was 2000 ft (610 m), the full thickness of the bed (35 ft (10.7 m) being mineralised. The oreshoot terminates eastwards against Carr's Vein. Oreshoots at the Pattinson, Little Limestone and Coal Sills horizons also terminated there. In the Great Limestone, the full thickness was stoped out over a length of 1150 ft (351 m), while in the Quarry Hazle an oreshoot 350 ft (107 m) long, terminating against the footwall of Carr's Vein, was wrought. This was the lowest worked horizon. A length of 450 ft (137 m), was stoped in the Great Limestone east of Carr's Vein. All the stoping so far described was for lead ore, under the London Lead Co. and earlier operators. Zinc workings by the Vieille Montagne Zinc Co. were confined to a length of 340 ft by 30 ft (104 by 9 m) high in the Great Limestone adjacent to Capleclough Vein-intersection. Approximately 2300 ft (701 m) of virgin ground lies between the forehead of Capleclough Horse Level and Carr's Vein on the North Vein, commanding the Four Fathom Limestone for much of the distance. The east foreheads of the Vieille Montagne Co.'s workings are, however, said to have been poor, though the vein was 5–8 ft (1.5–2.4 m) wide in the Great Limestone.

    Middlecleugh Vein was worked from Smallcleugh Horse Level, and also, W of Cowhill Cross Vein, from Capleclough Horse Level; no scope section is, however, available.

    First Sun Vein is only known to exist east of Carr's Vein; to the west it probably unites with Second Sun Vein. A little ore may have been obtained from sumps below Smallcleugh Level into the Great Limestone, but no stopes are indicated on the London Lead Co.'s section. A trial at Rampgill Horse Level was unsuccessful.

    Second Sun Vein was productive for 2800 ft (853 m) from Carr's Vein. Here the development, at Middlecleugh Upper, Smallcleugh and Capleclough levels, together with connecting rises, seems to have been done by the London Lead Co., but the stoping recorded was all the work of the Vieille Montagne Zinc Co. The horizons of the oreshoots were the Great Limestone and the Quarry Hazle; a trial of the Four Fathom Limestone adjacent to Cowhill Cross Vein was not successful. After passing through Longcleugh Vein, Second Sun Vein terminates 1150 ft (351 m) to the W against the "New" Cross Vein, discovered by the Vieille Montagne Co.

    Longcleugh Vein carried the largest oreshoot of the group, extending 1650 ft (503 m) W of Carr's Vein, continuously mineralised from the Little Limestone down to the base of the Great Limestone, and in the eastern part reaching down to beds below the Quarry Hazle, giving a maximum height of 220 ft (67 m), and an average of about 150 ft (46 m). West of this oreshoot, some zinc ore was obtained in the lower part of the Great Limestone between the intersection with Second Sun Vein and Capleclough Vein.

    Both Second Sun and Longcleugh veins were explored E of Great Cross Vein. A length of 300 ft (91 m) on the latter yielded ore in the Firestone; no stopes are shown on Second Sun Vein, though the extent of the workings suggest that the vein must have been well developed. Second Sun Vein may continue NE to become the Killhopehead Vein; if this is the case, 3500 ft (183 m) of unexplored ground remains between the workings, but it is clear that the foreheads at both ends were poor and not encouraging.

    The records give the production from Longcleugh as 27 971 tons of lead concentrates in 1848–1882; for the same period the yield from Middlecleugh was 6334 tons. Silver recovery in both cases was equivalent to 7 oz silver per ton of lead.

    Minor NE Veins at Nenthead

    NY74SE, NE; Cumberland 42NE.

    The Nenthead Fields Vein and North Vein were tried from levels [NY 7788 4374] and [NY 7772 4388] driven beneath the Great Limestone, west of Rampgill tailings dump at 1430 ft (436 m) above OD the small dumps show quartz, limonite, galena, cerussite, smithsonite and a little hemimorphite; the veins are said to have been only feebly mineralised. Cowhill Vein was worked SW of Cowhill Cross Vein, 1425 ft (434 m) SE of Brigal Burn Vein. It was reached by the Cowhill Level [NY 7847 4316], running SSW from the Nent, beneath the Great Limestone. A small oreshoot was worked in the Great Limestone. Crosscuts S discovered the feeble vein called Cowslitts Vein. Cowhill Level continued to cut Hangingshaw Vein farther SSW, but this vein was not productive where cut. It became productive (according to Wallace, 1861, map) NE of Cowhill Cross Vein in the Great Limestone, the oreshoot extending to Carr's Vein. No stope section of the workings remains. What may be the continuation of the same vein was worked NE of the Great Vein where a level [NY 7888 4336] from the Rampgill Burn gave access to a small oreshoot in the Firestone. Rampgill Horse Level was driven to this vein on the E side of Great Vein, but no ore was found in a rise from this level to the Great Limestone.

    Nenthead Cross Veins—Lead ore

    NY74SE, NE, NW; Cumberland 34SW, SE, 42NW, NE

    Numerous references have been made above, in describing the E–W and ENE veins, to intersections with NW veins. These have a greater development, and are more often mineralised in this area than in any other part of the orefield, but the oreshoots on them are generally restricted to the near vicinity of the ENE veins, which evidently acted as feeders. The following is a summary of the information available with regard to the cross veins:

    Black Ashgill Cross Vein is known to extend from the Nent, 1750 ft (533 m) E of Foreshield, to the headwaters of Ash Gill. A level [NY 7445 4665], driven SE from the bank of the Nent was mentioned above in connection with Bayle Hill Vein (p.123). A small oreshoot, 285 by 20–30 ft (87 by 6–9 m), was worked beneath the level from sumps, the first of which was 725 ft (221 m) from the portal. Coarse sphalerite, with siderite and a little galena occurs on the dump. The level was continued in the Three Yard Limestone for 2000 ft (610 m) passing through strong E–W intersections from 1350 to 1500 ft (411 to 457 m). The existing section (Sopwith, 1829, pl.II) shows many sumps sunk to the top of the Five Yard Limestone, connecting with a subdrift at this horizon, but no more stoping appears to have been done. At Hudgill Burn Mine a level was driven SW from Loveladyshield Shaft on Nentforce Level, connecting with a shaft [NY 7529 4584] on Black Ashgill Vein 1700 ft (518 m) W of Nenthall. It is assumed that the drift was at the original horizon of Nentforce Level in the Alternating Beds beneath the Scar Limestone. No details remain but this trial is understood to have been unsuccessful. There is no evidence that the drive tested the Hudgill Burn veins in depth. The cross vein here splits into two branches. The western branch , known as Jacob Teesdale's Cross Vein was tried for a length of 1125 ft (343 m) from Eden Braes Level [NY 7605 4539] at 1185 ft (361 m) above OD which cut the vein 1500 ft (457 m) SW of the portal. The eastern branch, regarded as the continuation of the main Black Ashgill Vein, was cut 900 ft (274 m) from the portal of Eden Braes Level, and drives on it total 850 ft (259 m) in length. The Eden Braes workings were beneath and in the Nattrass Gill Hazle; a sump was sunk to the Three Yard Limestone on Black Ashgill Vein. Quartz and sphalerite occur in small quantity on the dump. The western branch continues SE to become the West Cross Vein of Grassfield Mine, here uniting with a weak cross vein proved in Hudgill Burn and Galligill Sike mines. Farther SE it is believed to be continuous with the Nunnery Cross Vein of Greenhill and Dowgang mines, on which there are no known workings. The main Black Ashgill Vein continues through Grassfield Vein, downthrowing (according to the primary 6-inch map) 60 ft (18 m) SW. It is shifted S side SW 175 ft (53 m) by Greenhill Vein, beyond which it has been explored for 2600 ft (792 m) SE by a branch of Capleclough Horse Level from Dowgang Mine, which communicated with the level on Nenthead Fields North Vein. An oreshoot, 1000 ft (305 m) long was worked in the Great Limestone NW of Dowgang North Vein. In this stretch Greengill Cross Vein runs parallel 350 ft (107 m) SW as does Nenthead Fields Cross Vein 450 ft (137 m) NE. According to Wallace the latter cross vein was mineralised in the Great Limestone for 1250 ft (381 m) SE of its intersection with Nenthead Fields North Vein. A small flat in the Great Limestone was worked in Dowgang Mine at the intersection of Black Ashgill Vein with Brigal Burn Vein. At 1450 ft (442 m) SE of this intersection, the main Capleclough Horse Level entered the vein, continuing in it for 1850 ft (564 m) SE in the Tuft to Capleclough Vein. The throw of Black Ashgill Vein here is 40 ft (12 m) SW. At 1400 ft (427 m) SE of Caplecleugh Vein a strong branch is given off south-south-eastward from the vein, throwing NE. Both the main vein and the branch were explored from Wellhopeknot Mine (disused), entered by a level [NY 7805 4143] driven in the shale above the Great Limestone. An oreshoot 950 ft (290 m) long was worked in the Great Limestone on the main vein from this level.

    Sike Cross Vein, a NNW branch of Black Ashgill Vein, was worked in the Great Limestone between Grassfield and Greengill veins, but no stope section remains. Access was by Grassfield Main Level [NY 7673 4460] Cowhill Cross Vein or Fault is first known in Nentsberry Haggs Horse Level [NY 7661 4503], where it appears to be converging north- wards upon Carr's Vein. This level cuts it at 1220 ft (372 m) from the portal; the throw is 45 ft (14 m) SW, the hade 450; the fault is not mineralised. No information is available with regard to the in- tersections with Grassfield, Greengill and the Dowgang veins, but the fault was cut by Capleclough Horse Level [NY 7811 4349] at the point where this level reaches Brigal Burn Vein. Farther SE Cowhill Level [NY 7847 4316] tested the vein for a short distance; here the downthrow has probably diminished to 20–30 ft (6–9 m) SW. Its effect is apparent in Old Carr's Burn [NY 7865 4227], where it brings the Firestone into the burn on the W side of the fault. Between Mid- dlecleugh North Vein and Longcleugh Vein Wallace (1861, pl.VIII) gives the throw as 7 ft (2.1 m) SW, increasing SE of Longcleugh Vein to 14–18 ft (4.3–5.5 m). It is probable, though not certain, that the south-eastward increase of throw continues. Smallcleugh Horse Level was driven on Cowhill Vein between Longcleugh Vein and Middlecleugh Vein in the Great Limestone, but no stoping is recorded. A branch level was also continued 2070 ft (631 m) SE of Longcleugh Vein. Here a rich oreshoot which extended 1000 ft (305 m) SE from Longcleugh Vein was worked in the Great Limestone to an average height of 40 ft (12 m). A branch of Middlecleugh Upper Level was driven 1270 ft (387 m) on this part of the vein in the sandstones and shales between the Great and Little limestones but no ore was found; the level communicated with Baron's Shaft [NY 7923 4141], 335 ft (102 m) deep from surface, near its forehead. Cowslitts Cross Vein lies between Cowhill and Carr's veins, NW of Old Carr's Burn and was reached by levels [NY 7887 4289] and [NY 7870 4287] driven in the shale above the Great Limestone W of Smallcleugh Horse Level portal; an oreshoot 700 ft (213 m) long was worked from sumps into the limestone. Carr's Vein is the most powerful fault of the series. At the NW end of its course it is split up into three branches, from W to E known as Blagill Moss Cross Vein which throws 24 ft (7.3 m) NE at Loveladyshield Level, terminating the oreshoots on Lough Vein and Fistas Rake, North Grain Cross Vein, and Carr's Vein. Foreshield Level passed through all three branches, but apparently found no ore; details of the geology are not available. Loveladyshield Level, [NY 7591 4614] starting in the shale below the Nattrass Gill Hazle, passed into the Great Limestone NE of Carr's Vein, the throw here being 252 ft (76.8 m) NE. At Nentsberry Haggs Horse Level, Carr's Vein is exposed 1920–1940 ft (585–591 m) from the portal; the throw here is 200 ft (61 m), the hade 350; Sopwith (1832) has described the distortion of the adjacent strata. No mineralisation is present, but a small accommodation fracture called Brownley Hill East Cross Vein, 30 ft (9 m) to the NE has been stoped in the Great Limestone (here immediately above the level roof) to a small extent. In the neighbourhood of Wellgill two branches are given off from the E side of Carr's, which become respectively the Smallcleugh and Handsome Mea Great cross veins (described below). The relations of Carr's Vein and adjacent cross veins in Rampgill Horse Level are illustrated in (Figure 23). The vein crosses the Nent Near the ruins of the old Smallcleugh dressing floor [NY 7869 4298]; here a parallel string, called Force Vein, is exposed in the Great Limestone, where it carries a little galena and fluorite. Immediately south of Old Carr's Burn a flat in the Great Limestone worked on the W side of the vein, was reached by way of the level [NY 7882 4247] to Cowslitt's Cross Vein. The flat is supposed to have been formed where strings resulting from the splitting-up of Capleclough vein impinged upon Carr's Vein. At the intersection with Middlecleugh North vein, the throw of Carr's Vein was found to be 80 ft (29 m) NE, a similar throw being recorded where the vein crossed Second Sun Vein. To the SE Carr's Vein splits into at least three subparallel veins, associated with which, on both sides of Longcleugh Vein, there were flats in the Low Flat horizon of the Great Limestone. The middle branch, called South End Vein, was explored to a distance of 2050 ft (625 m) SE of Longcleugh Vein, small oreshoots on the vein in the Great Limestone being worked to a distance of 1270 ft (387 m) SE of Longcleugh Vein; access was by Smallcleugh Horse Level, [NY 7877 4290] which commanded the limestone on the footwall side. The Carr's and Hangingshaw workings of the London Lead Co. (probably including Cowslitts and Cowhill veins) yielded 10 548 tons of lead concentrates between 1848 and 1882; in addition there is a record of 294 tons from an independent working on "Carr's Vein West of Nent" the exact site of which has not been established.

    Smallcleugh Cross Vein, branching from Carr's Vein and diverging eastwards, takes part in the Middlecleugh fault-trough to which reference has already been made. In spite of its throw of 48–60 ft (14.6–18.3 m) SW this vein was apparently mineralised betwen Hangingshaw Whimsey, 1600 ft (488 m) SE of the Smelt Mill, and its intersection with Middlecleugh First Sun Vein, the oreshoot being worked in the Great Limestone on the hangingwall side from sumps on Smallcleugh Horse Level, and from a sublevel driven from Hangingshaw Whimsey. Rampgill Horse Level, driven at about the horizon of the Quarry Hazle on the hangingwall, was extended through this ground after it had been worked out, and is not connected with the workings.

    Handsome Mea Great Cross Vein throwing as much as 96 ft (29 m) NE formed in conjunction with Smallcleugh Cross Vein an upfaulted tract or horst, in which the Handsome Mea or Smallcleugh flats are situated, extending over a total length of 3600 ft (1.1 km). These deposits have been admirably illustrated by Wallace (1861, pl,XIV), who estimated that not less than 5 000 000 cu ft (3.5 x 106m3) of limestone underwent metasomatism during their formation. They appear to be related to numerous small strings or leaders which traverse the horst. Their hardness was due to the replacement of the limestone by ankerite, which may be seen on the walls of the excavations which remain, with siderite and fine-grained silica (Plate 3). Their horizon is that of the Low Flat of the Great Limestone; access was obtained by means of crosscuts from Smallcleugh Horse Level; there was also a connection at the northern end of the flats to Rampgill Horse Level, by way of a rise on Great Cross Vein communicating with the workings of Hangingshaw East End Vein. According to Wallace, the Handsome Mea flats were discovered in 1796 (MS notes on Smallcleugh Mine Plan, Mines Dept No. R143 C); the recorded figure of 4999 tons of lead concentrates for the period 1848–1882 probably represents only a fraction of the total yield of these extensive deposits. The silver recovery was equivalent to 7 oz silver per ton of lead according to the published records, but this figure may merely represent an average for the London Lead Co.'s Nenthead mines, for Cameron Swan (in discussion on Nall, 1904) states that the Handsome Mea galena was nonargentiferous.

    The horst between Smallcleugh and Great Cross veins which exceeds 700 ft (213 m) at the widest part, narrows southwards to 130 ft (40 m) at Longcleugh Vein. Flats continue 150 ft (46 m) SE of Longcleugh Vein, beyond which no exploration has been done; the condition of the foreheads here is not known. Geological evidence in the Wellhope Valley (Weardale), 1 mile (1.6 km) SE, strongly suggests that a narrow horst between two cross veins which are in line with the continuations of the Smallcleugh and Great cross veins exists. This has not been explored in the Great Limestone in Wellhope, though a shaft was sunk to the Little Limestone by the Weardale Lead Co. during the closing years of last century.

    The Fairhill, Patterdale and Gilgil Cross veins are known only in the workings of Scaleburn and Rampgill mines (Figure 23); they are not known to be mineralised.

    Wellgill Cross Vein was probably reached by Foreshield Level [NY 7513 4698] at its northern end, but no record remains of its condition. At Loveladyshield Level, [NY 7591 4614] the main adit terminated at Wellgill Vein, here throwing 42 ft (12.8 m) SW. From the level head drifts were driven 570 ft (174 m) NW and 2100 ft (640 m) SE on the vein, probably in the hope of intersecting ENE veins. One such vein was discovered, 1025 ft (312 m) SE of the level head, throwing 4–6 ft (1.2–1.8 m) NW, but little ore seems to have been obtained either from this or from Wellgill Vein. Nentsberry Haggs Horse Level [NY 7651 4503] (p.137) follows Wellgill vein for 2700 ft (823 m) NW from the level head (ending within 250 ft (76 m) of the forehead from Loveladyshield) and 2600 ft (792 m) SE. The level is in the shale below the Quarry Hazle on the footwall side of the vein, with the Great Limestone on the hangingwall. Some stoping has been done in Wellgill Vein, but no record of the exact extent of the stopes, nor of their contents, remains. At 2050 ft (625 m) SE of Haggs level head the Horse Level communicates with the Gin Underground Shaft from Bloomsberry Horse Level. Haggs Level is here at 1285 ft (392 m) above OD, Bloomsberry Level at 1.340 ft (408 m) above OD. Gin Shaft is 600 ft (183 m) NW of the head of Bloomsberry adit; the level continues 700 ft (213 m) NW of the shaft, commanding the Great Limestone on the footwall of Wellgill vein; the throw of the vein is 32 ft (9.8 m) SW in this level. South-east of Bloomsberry Level head the Horse Level follows Wellgill Cross Vein for 650 ft (198 m) to the point where it merges with Gudhamgill Burn Cross Vein. The vein is only feebly mineralised in the Bloomsberry workings, but a flat formed at its junction with Brownley Hill Middle Vein was worked from the Low Flat horizon of the Great Limestone up to the Black Bed.

    Gudhamgill Burn Cross Vein cuts through the Brownley Hill Veins as a fault throwing 4 ft (1.2 m) SW. After joining Wellgill Vein it is followed by Bloomsberry Horse Level to its junction with Gudhamgill Vein. A branch of the horse level continues along this cross vein for about 650 ft (198 m) thereafter turning ESE and reaching Rampgill Cross Vein. The Burn Cross Vein is considered to be represented by a fault throwing 42 ft (12.8 m) S in a WSW crosscut which was driven from Rampgill Cross Vein starting 900 ft (274 m) NW of Scaleburn Vein. Farther SE this fault probably forms part of the Great Vein of Rampgill Mine (Figure 23); it may ultimately converge upon Handsome Mea Great Cross Vein.

    Bloomsberry Horse Level followed Rampgill Cross Vein, throwing 5 ft (1.5 m) SW south-eastwards to Scaleburn Vein, where it terminates at 1350 ft (411 m) above OD. Orebearing ground was worked in the Great Limestone for a distance of 1000 ft (305 m) NW of Scaleburn Vein on Rampgill Cross Vein: access being obtained both by Bloomsberry Level and from sumps from a branch 'of Rampgill Horse Level, here at 1438–1465 ft (438–447 m) above OD. Between Scaleburn and Rampgill veins, an oreshoot on the cross vein was worked for a total length of 310 ft (94 m) in the Great Limestone. S of Rampgill Vein, Rampgill Horse Level [NY 7818 4350] commands the Great Limestone on the cross vein, and an oreshoot in this bed was worked for 1050 ft (320 m) from Rampgill Vein. A little ore was also got in the Coal Sills and Little Limestone from a rise 150 ft (46 m) SE of Rampgill Vein.

    The cross veins of Brownley Hill Mine (Moss, West High, High and Jug veins) all yielded ore in the Great Limestone, but the dimensions of oreshoots are not known. Bounder End Cross Vein in Rampgill Mine is an insignificant fracture, but it was accompanied by a rich belt of flats in the Great Limestone on both sides of Ramp-gill Vein.

    References

    ALMOND, J K. 1971. The Nenthead and Tynedale Lead & Zinc Company Ltd., 1882–1896. Mem. Northern Mine Res. Soc., 26–40.

    ARTHURTON, R S and WADGE, A J. 1981. Geology of the country around Penrith. Mem. Geol. Surv. G.B. 177pp.

    CARRUTHERS, R G, and POCOCK, R W. 1922. Fluorspar [3rd edition]. Spec. Rep. Miner. Resour. Mem. Geol. Surv. G. B. , Vol. 4. 42pp.

    CRITCHLEY, M F. 1984. The history and working of the Nenthead mines, Cumbria. Bull. Peak District Mines Hist. Soc., Vol. 9, 1–50.

    DAWSON, E W O. 1947. War-time treatment of lead-zinc dumps situated at Nenthead, Cumberland. Trans. Inst. Min. Metall., Vol. 56, 587–606.

    DUNHAM, K C. 1941. Iron ore deposits of the Northern Pennines. Geol. Surv. Wartime Pamph., No.14

    DUNHAM, K C. 1952. Fluorspar (4th edition). Spec. Rep. Miner. Resour. Mem. Geol. Surv. G.B., Vol. 4. 144pp.

    FORSTER, W. 1821. A treatise on a section of the strata from Newcastle-upon-Tyne to the Mountain of Cross Fell, in Cumberland; with remarks on mineral veins in general (2nd edition]. (Alston: W. Forster.)

    HALLIMOND, A F, and EYLES, V. 1949. A magnetic survey in Cumberland; the results of an investigation of faults in the Whin Sill at Smittergill Burn, Alston. Mining Mag., Vol. 80, 329–333.

    HOUSTON, W J. 1963. Rampgill Mill. Mine and Quarry Eng., Vol. 29, 75–78.

    IXER, R A, and STANLEY, C J. 1987. A silver-nickel-cobalt mineral association at Tynebottom Mine, Garrigill, Near Alston, Cumbria. Proc. Yorkshire Geol. Soc., Vol. 46, 133–139.

    IXER, R A, STANLEY, C J, and VAUGHAN, D J. 1979. Cobalt, nickel and iron-bearing sulpharsenides from the north of England. Mineral. Mag., Vol. 43, 389–395.

    JACKSON, P. 1969. Some preliminary notes on the mining region of Alston Moor. Mem. N. Cavern & Mines Res. Soc., 41–53.

    MOORE, J M. 1982. Mineral zonation near the granitic batholiths of south-west and northern England and some geothermal analogues. 229–242 in Metallization associated with acid magrnatism. EVANS, A M (editor). (Chichester: John Wiley.)

    NALL, W. 1904. The Alston mines. Trans. Inst. Min. Eng., Vol. 24, 392–404.

    SHERLOCK, R L. 1919. Sundry unbedded iron ores. Spec. Rep. Miner. Resour. Mem. Geol. Surv. G. B. , Vol. 9. 87pp.

    SMITH, S. 1923. Lead and zinc ores of Northumberland and Alston Moor. Spec. Rep. Miner. Resour. Mem. Geol. Surv. G.B. Vol. 25. 110pp.

    SMYTH, W W. 1856. Iron ores of Great Britain, Part I. Mem. Geol. Surv. G.B.

    SMYTHE, J A. 1930. A chemical study of the Whin Sill. Trans. Nat. Hist. Soc. Northumberland, Durham and Newcastle, Vol. 7, 16–150.

    SOPWITH, T. 1829. Geological sections of Holyfield, Hudgill Cross Vein and Silver Band Lead Mines in Alston Moor and Teesdale. (Newcastle: E Walker.)

    SOPWITH, T. 1832. On the application of isometric projection to geological plans and sections, with descriptive notices of the mining district at Nentsberry in the County of Cumberland. Trans. Nat. Hist. Soc. Northumberland, Durham & Newcastle upon Tyne, Vol. 1, 280–288.

    SOPWITH, T. 1833. An account of the mining districts of Alston Moor, Weardale & Teesdale. 183pp. (Alnwick: W Davidson.)

    THOMPSON, L M. 1933. The Great Sulphur Vein of Alston Moor. K C Dunham (editor). Proc. Univ. Durham Philos. Soc., Vol. 9, 91–98.

    WALLACE, W. 1861. The laws which regulate the deposition of lead in veins; illustrated by an examination of the geological structure of the mining districts of Alston Moor. 258pp. (London: E Stanford.)

    WALLACE, W. 1890. Alston Moor, its pastoral people, its mines and miners. 213pp. (Newcastle: Mawson, Swan & Morgan.)

    WILKINSON, B P. 1981. Nentforce Level-a preliminary report by Norpex. Northern Mines Res. Soc., Newsletter for February.

    WILSON, G V, EASTWOOD, T, POCOCK, R W, WRAY, D A, and ROBERTSON, T. 1922. Barytes and witherite (3rd edition). Spec. Rep. Miner. Resour. Mem. Geol. Sun,. G. B. , Vol. 2. 119pp.

    WILSON, P N. 1963. The Nent Force Level. Trans. Cumberland & Westmoreland Antiguan & Archaeol. Soc., Vol. 63. 253–280.

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    Chapter 8 Mineral deposits

    Details, area 3 West Allandale

    From the hamlet of Ninebanks southwards to the head of the West Allen valley, as well as in Wellhope and the valley of the tributary Mohope Burn, there are numerous remains of former mining operations for lead (Figure 25). Outcrops of the Great Limestone form inliers in the valleys, the sides of which are formed of members of the Pendleian Stage. The principal mines were situated at Carrshield and Coalcleugh, where the continuations of the Brownley Hill, Gudhamgill. Scaleburn and Rampgill veins of the Nent valley were worked for lead by the Blacketts aid Beaumonts and reworked, mainly for zinc by the Vieille Montagne Zinc Co. A zinc–witherite oreshoot has been further explored during 1977–81 by Mineral Industries Ltd at Scraithhole Mine. Farther N, under Wellhope, the workings on High Raise Vein had been extended from the Nent Valley, and an important group of new veins were discovered during 1925–30 by the Vielle Montange Zinc Co. Most of the ore from these has been taken out through the Nentsberry Haggs Horse Level into Cumbria. Still farther N the Heartycleugh and Mohopehead mines in Wellhope were worked by the Beaumonts; Longcleugh and Ouston mines lie beyond the limits of their estate and were explored by smaller concerns; Longcleugh Mine was reopened in 1970–71 by Ferguson Wild and Co. Ltd to search for workable witherite but without success. The workings on the small veins S of Ninebanks on the E bank of the West Allen probably date from the sixteenth century (Smith 1923, p.55). The West Allen valley is provided with good roads, one of which leads from Coalcleugh to Allendale Town, 9 miles (14.5 kms) distant. The Wellhope valley is not accessible by road above the hamlet of Keirsleywell Row.

    As in the Alston Moor area, the principal productive veins trend ENE, but there is also a set of powerful NW fractures, some of which are mineralised. The Wellhope valley has been very systematically explored by means of N–S or NW levels and cross cuts, driven either below or immediately above the Great Limestone. In the Upper West Allen valley, the portion S of Carrshield has been thoroughly explored, but there is a gap between Carrshield and Bates Hill in which little has been done. Some fluorspar was produced from High Coalcleugh during the 1950s.

    Ouston Vein

    NY75SE Northumberland 106 NE (Old Series)

    An ENE vein has been explored by means of a level [NY 7752 5311] driven on top of the Great Limestone, starting 750 ft (229 m). NW of Ouston, 0.5 mile (0.8 km) W of Ninebanks. Sumps may have been sunk into the limestone, but no plan is available. A little baryte and galena occur on the shale dump.

    Crooked Bridge Veins—(Witherite)

    NY75SE Northumberland 106 NE (Old Series).

    Two ENE veins, proved by boring in the Great Limestone; throws not known.

    G A L Johnson, J R Nudds and D Robinson (1980) in summarising the geological results of exploration by Ferguson, Wild and Co. in search of the source of the dump of good quality witherite near Longcleugh level mouth (analysis No. 1, (Table 47) state that when it proved impossible to account for this in Longcleugh Mine, an old adit [NY 7724 5206] on the N side of the burn opposite Longcleugh level was reopened and found to be accessible for 748 ft (228 m), running straight in Great Limestone. Three underground borings, drilled near the blockage at the N end, proved broken ground in the limestone ahead of the fall, and found two narrow veins, approximately 197 ft (60 m) apart, carrying calcite and witherite. These were believed to be the source of the witherite on the dump, but they were not made accessible. The Crooked Bridge veins may also have been cut by workings in the Little Limestone Coal from an adit at [NY 7711 5222].

    Longcleugh North–Keirsleywell Row Cross Veins group

    Two main fractures, with minor faults between; direction at W end of Longcleugh workings, N15°W, but changing northward to N–S, southward to N25°W. Total displacement across the belt perhaps 20 ft (6 m)

    The veins were worked from Longcleugh Mine (disused), which should not be confused with the mine of that name at Nenthead. The Horse Level was driven from the S bank of Whitewalls Burn at [NY 7729 5197], at 900 ft (274 m) above OD in the Great Limestone. At approximately 260 ft (79 m) from the portal it cut the Middle Vein, turned and continued on this for 1800 ft (549 m) approximately to the WSW to reach the East Cross Vein; the other ENE veins were explored from drives in the Cross Vein and from crosscuts. Smith (1923, p.65) reproduces a note on an old plan dated May 30th 1846, and initialled 'G.H.' to the effect that no vein or string running in an east-and-west (i.e. ENE) direction ever produced ore in sufficient quantity to pay, except Walton's Vein, which in a drift 6 x 6 ft (1.8 X 1.8 m) produced as estimated 16 bings (6.4 tons) per 6 ft (1.8 m) advance. The note adds that nearly 1300 bings (520 tons) were obtained from cross strings. During the 1970–71 reopening, details about which have been given by Johnston, Nudds and Robinson (1980), the Horse Level was cleared to 1000 ft (305 m) WSW of the level head; Middle vein contained discontinuous pockets of mineralisation with calcite and witherite but insufficient to extract. The level was not cleared to the cross veins, but access to these was gained from a surface shaft [NY 7685 5175], revealing that flats about 40 ft (12 m) wide and at least 295 ft (90 m) long had been worked for galena in the vicinity of the intersections of Middle and Lee's veins with the East Cross Vein. Both the ENE veins were seen but they were 'narrow and contain calcite gangue with some barytocalcite and witherite'. Access to the ground W of the cross vein was not gained, and Walton's Vein was not seen. The observations lend confirmation to the note quoted by Smith. The stratigraphical position here is unfavourable to the formation of vein oreshoots in the Great Limestone by reasons of the passage of the upper part of the limestone into shale (leaving little more than 36 ft (11 m) thickness) in combination with fractures having displacements up to 43 ft (13 m). The northward deterioration of the limestone as compared with the main mineral field of Nenthead or Upper Weardale is as evident here as it is in the northern part of the Blacken Level (p.161) or in the Haydon Bridge area (Chapter 13).

    In addition to two vertical boreholes from surface, one of which cored the full succession down to and through the Great Whin Sill, here beneath the Jew Limestone, see (Figure 3), Ferguson Wild and Co. drilled eight underground boreholes, of which the most interesting was an inclined hole from the crosscut at 1000 ft (305 m) W in the Horse Level, which intersected Lee's Vein in the upper part of the Scar Limestone, and Longcleugh South Vein in the Tynebottom Limestone. The latter intersection showed a wide shatter zone, but only calcite was found in the two veins. Johnson et al. conclude that sulphide and barium mineralisation does not continue in depth. It will be noted that although the stratigraphical position of the Whin Sill was established, no test of the veins at this, the principal host to economic mineralisation, including witherite, in the Haydon Bridge district was made; but it must be admitted that intersections intermediate between the Great Limestone and the Sill gave no encouragement.

    The total output of lead concentrates is not known, but, the last five years of mining up to 1853 yielded 284 tons from Whitefield Mine, probably Longcleugh, but possibly including Ouston. West of the Keirsleywell Row Cross Veins, some small old shaft heaps suggest the presence of at least two veins running nearer to E–W than the Longcleugh group. They are believed to have been penetrated by a level beneath the Little Limestone at [NY 7649 5183] possibly driven to search for the Little Limestone Coal though no mineralised material is present on the dump. Although Longcleugh Horse Level penetrated beyond Keirsleywell Row East Cross Vein, it is not known whether it gave access to these veins in the Great Limestone, or what they contained. Still farther west, another cross vein, apparently of small displacement only, was explored by a level driven southward from Whitewalls Burn at [NY 7631 5189], also above the Great Limestone: again no mineralised material can be seen here today. It is assumed that all these western workings date from the early part of last century.

    Keirsleywell Row Veins—Lead ore (Barytes)

    NY75SE Northumberland 106 NE (Old Series). Direction N67°E; two parallel veins, 150 ft (46 m) apart, forming a fault trough 9 ft (2.7 m) deep

    The workings on these veins probably predated the period of operations under the Beaumonts, which commenced in 1729. Commencing about 1816 Keirsleywell Level (disused) [NY 7741 5154] was driven into North Vein in the Great Limestone, and was continued in the vein or along its N side for a distance of about 1400 ft (427 m) at approximately 970 ft (296 m) above OD. At 1600 ft (488 m) from the portal, Keirsleywell Row East Cross Vein was encountered, downthrowing 30 ft (9 m) SW. At a further 250 ft (76 m) SW, the West Cross Vein, throwing 11 ft (3.4 m) NE was cut. The level was continued 900 ft (274 m) farther, cutting another strong fault at 260 ft (79 m), with an unspecified but considerable SW downthrow. Close to the forehead of the level, crosscuts NW and SE failed to find ENE veins. The westerly downthrow of the beds would bring the level considerably above the Great Limestone at this end; that horizon has thus not been adequately tested W of the belt of cross veins. At approximately 1000 ft (305 m) from the portal of Keirsleywell Row Level, a crosscut was driven 2800 ft (853 m) S passing through the South Vein at 150 ft (46 m). Owing to the rise of the strata in this direction, this crosscut must encounter successively lower beds. At 1900 ft (579 m) beyond the South Vein it cut a small ENE vein near Peatgap, on which some exploratory work was done. A weak ENE vein, named the Bates Hill Vein on the primary survey map, and tested by a shallow shaft [NY 7848 5154] near Bates Hill in the West Allen Valley, is nearly on the same line as this. The crosscut then turned SW and reached Mohopehead Sun Vein (described below) 1700 ft (568 m) from the turn. The extensive explorations at Keisleywell Row yielded only 597 tons of lead concentrates in the period 1816–1830, 1847–1853. Apart from galena the mineralisation in the Keirsley Row Veins included baryte, witherite, some of which appears to be pseudomorphous after baryte, and traces of barytocalcite. Coarse baryte is present on the old shaft heaps along the Keirsleywell Row Veins; an analysis of a picked sample is given in the table below (analysis No. 2).

    Stag Rake Veins

    NY75SE Northumberland 106 NE (Old Series)

    Stag Rake Vein is mapped on the primary survey map as crossing the West Allen just south of its junction with Mohope Burn. The only sign of its presence is a group of three grassed-over bell shaft heaps W of Malakoff Bridge [NY 7799 5178], [NY 7803 5180] and [NY 7809 5181]. East of the Allen, as indicated by an adit at [NY 7833 5195], the vein is cut by the West Allen Great Cross Vein (the northward continuation of Coalcleugh East Cross Vein, described below), which throws 96 ft (29 m) W here. On the E side of the cross vein there is a series of ENE step faults, which were discovered by the driving of Ninebanks or Blackpool Bridge Level (disused) [NY 7831 5222]. The level gave off a N crosscut 500 ft (152 m) long; the main drive starts, probably on Longcleugh South Vein, above the Great Limestone south of Ninebanks Parsonage at about 880 ft (268 m) above OD. It runs eastwards through the Great Cross Vein, which throws 96 ft (29 m) W, into beds which are probably beneath the limestone. At about 350 ft (107 m) from the portal it turns SSE and at a further 750 ft (229 m) from the turn cut a fault throwing 43 ft (13 m) SE; 200 ft (61 m) farther ahead another throwing 35 ft (11 m) NW was encountered. Both were explored, but neither appears to have proved productive. At 200 ft (61 m) beyond the second fault a third, throwing 4 ft (1.2 m) SE was cut and proved by driving 550 ft (168 m) ENE. The plan of the Coalcleugh group of mines in the Beaumont records dated 1863 shows the forehead of the level about 200 ft (61 m) SSE of the third fault. Smith (1923, p.67) states that the level continued half a mile to Greenleycleugh North Vein, but it has not been possible to confirm this statement. The continuation appears unlikely since the Great Limestone outcrops before reaching Greenleycleugh. The dump from the level shows only traces of veinstuff, with baryte, barytocalcite and calcite. No production is recorded. This ambitious prospect was well placed to test the faults cut by rising into the Great Limestone, and it must be assumed that they were barren.

    Greenleycleugh Veins—(Barytes)

    NY75SE Northumberland 106 NE (Old Series)

    Two small veins trending ENE have been tried near Greenleycleugh, 1 mile (1.6 km) S of Ninebanks on the E bank of the West Allen. The N vein is exposed in a level [NY 7860 5106] near the base of the Four Fathom Limestone; it is 3 ft (0.9 m) wide, filled with a breccia of limestone fragments cemented by ankerite and coarse calcite. The S vein has also been tried by a short level [NY 7872 5084] driven in shale beneath the Four Fathom Limestone without success. Shafts into the Nattrass Gill Hazle close to the river [NY 7865 5081] show fairly abundant coarse baryte, an analysis of which is given below (No. 3). Some strings of baryte can be seen crossing the river nearby.

    Mohophead Veins—Lead ore

    NY75SE, 74NE, Northumberland 106 SE (Old Series). Direction North Vein N 65°E, throw 4 ft (1.2 m) NW; Sun Vein N 60 to 65°E, throw 3 to 5 ft (0.9 to 1.5 m) SE

    Mohopehead Mine (disused), situated in Scabby Cleugh, worked Sun Vein. The main level [NY 7594 4999] at 1086 ft (331 m) above OD, runs 725 ft (221 m) WNW, the first 225 ft (69 m) being through boulder clay, the remainder at or a little below the base of the Great Limestone, with a sump connection at that distance to the Keirsleywell Level (described above); here at about 1040 ft (317 m) above OD, at the base of the Quarry Hazle. The Mohopehead Level continues NW cutting Sun Vein at 350 ft (107 m) from the sump, and North Vein at 800 ft (244 m). The workings on the Sun Vein extend 2850 ft (869 m) SW from the Level. The base of the Great Limestone rises from 1089 ft (332 m) above OD on the foot-wall of the vein where it is cut by the main adit level, to 1127 ft (344 m) near the SW forehead; the level itself is thus in the Tuft and underlying shale. The stopes were confined to the Great Limestone.

    Cross veins were encountered at 560 ft (171 m) SW of the Mohopehead Level head (throwing 4 ft (1.2 m) SW), 1130 ft (344 m) (throwing 3 ft (0.9 m) SW and shifting the Sun Vein 40 ft (12 m) E side N) and at 2750 ft (838 m) (throwing 3 ft (0.9 m) SW). North Vein was tried from a crosscut on the second cross vein, but little work was done on it; it was also unproductive where cut by the main adit. A crosscut from Sun Vein west of the third cross vein failed tc find the North Vein; presumably Sun Vein also became impoverished here. The gangue minerals included witherite and barytocalcite, with secondary baryte and some calcite (analysis No. 4, (Table 47). The total production lead concentrates, from 1729 to 1878, amounted to 4200 tons.

    Heartycleugh Veins—Lead ore

    NY74NE, Northumberland 106 NE (Old Series). Main Vein, direction N60 to 65°E; Cross Vein, direction N30 to 45°W.

    The main level at Heartycleugh Mine (disused) [NY 7715 4909], driven in the early years of the nineteenth century, runs 500 ft (152 m) SW, under the Great Limestone at about 1180 ft (360 m) above OD, to reach the main vein, along which it turns cutting the cross vein at about 1000 ft (305 m) from the level head. Branches on either side of the cross vein unite with it to the SE of the main vein. The eastern branch of the cross vein is shown on the primary 6 inch map as shifted S side E by the main vein; the Beaumont general plan dated 1863, suggests that the shift was N side E. The cross vein and its western branch pass directly through the main vein. Workings, presumably in the Great Limestone, were continued 2000 ft (610 m) NW and 2400 ft (732 m) SE of the main vein on the cross vein and at the latter point encounter two intersecting veins running slightly E of N. Little is known about the contents of any of these veins. The gangue material on the dump is mainly coarse calcite with ankerite; witherite and barytocalcite are present in small amounts, with secondary baryte (analysis No. 5, (Table 47). Barytocalcite with traces of chalocopyrite, is the main mineral present on the dump of an old shaft [NY 7703 4892] on Heartycleugh Vein about 660 ft (201 m) SSW of the level portal.

    The ENE vein was also worked on the E side of Wellhope Burn at Hesleywell Hush, where the dump from a short level [NY 7765 4929] in the Great Limestone shows witherite (analysis No. 6, (Table 47) with some sphalerite and traces of barytocalcite. A level [NY 7753 4955] was driven to the vein under the Four Fathom Limestone, starting 1000 ft (305 m) N of the Hush, and running 1200 ft (366 m) SE. No veinstuff is present on the dump.

    Between 1808 and 1815 the reported production of lead concentrates from Heartycleugh, included with that from Wellhope (head) Mine in the Beaumont accounts was 3335 tons. From 1816 to 1831 Heartcleugh yielded 1171 tons; Hesleywell yielded 64 tons between 1823 and 1828. The total yield from the Heartycleugh workings was probably of the order of 3500 tons.

    Farney Cleugh Vein—(Witherite)

    NY74NE, Northumberland 106 SE (Old Series)

    East of West Allen Great Cross Vein, a small E–W vein has been tried in the upper part of the Great Limestone near the head of Farney Cleugh [NY 7912 4912] 2 miles (3.61 km) S of Ninebanks. A small quantity of witherite, with baryte, is present on the dump (analysis No. 7, (Table 47).

    Treloar Vein–Robson Vein group

    The nine veins listed above carry the oreshoots formerly worked at Nentsberry Mine (disused) which were discovered by the Vieille Montange Zinc Co. during the years between the wars. These veins were the most important group of deposits discovered in the orefield during the period. The veins form an almost rectilinear pattern of intersecting ENE and WNW fissures. Two of the four ENE veins, High Raise and Second Sun, are known in Cumbria, the workings from the Nent Valley having been described on p.140. When the Vieille Montagne Co. took over the mine in 1913–14, the workings on High Raise Vein had already advanced into Northumberland. The continuation of these workings led to the discovery of the intersecting Sincay, Cox and Dupont veins, and from these the parallel ENE veins were found. E of Wellhope it was found that three of the ENE veins had been located by the old miners of the Beaumont period. Wellhope Low Level [NY 7796 4791] driven in the shale above the Great Limestone, starts on the E bank of Wellhope Burn 3 miles (4.8 km) S of Ninebanks church and runs at least 4500 ft (1372 m) beneath the burn in a SSE direction. First and Second Sun veins and Treloar vein had been cut in this level; on the first there was a sump to the bottom of the Great Limestone and the vein had also been opened out in the Low Coal Sill. There was also a sump to the bottom of the Great Limestone on Treloar Vein. The First Sun and Treloar veins had, however, proved to contain mainly witherite and sphalerite and it appears likely that the workings were abandoned before the beginning of the ninteenth century, leaving intact the substantial lead oreshoots lying to the SE.

    The known oreshoots are confined to the Great Limestone; most of them to that part, about 45 ft (13.7 m) thick, which lies beneath the Black Bed. No true flats have been found but it is nevertheless probable that a considerable amount of replacement of limestone occurred in the formation of the wide vein-shoots along First Sun Vein. In one instance only, on First Sun Vein, the oreshoot carried a short distance into the shale above the Great Limestone. Most of the veins have been seen in the Quarry Hazle but none has proved to be productive there. No trial had been made below this horizon until 1948, when Anglo-Austral Mining Co. had taken over. They deepened Coes Sump near the junction of Cox and Treloar veins, and a sump near the junction of Liverick and First Sun veins to the Four Fathom Limestone. According to reports by the late W R Jones, mineralisation was found but it was not payable at 1950 metal prices, and the mine was abandoned without advancing further any of the workings. A circumstantial account of what was done at this period, based on Anglo-Austral Co. archives, has been published by M F Critchley (1984).

    The mineralisation of the vein-complex affords a striking instance of mineral zoning in a lateral sense. In the region of the intersections of the ENE veins with Sincay, Cox, Dupont and Liverick veins all the veins carried good lead orebodies, containing coarse galena with subsidiary sphalerite and pyrite in a gangue dominated by ankerite and quartz, but with some barium spars. In three directions–NE, SE and SW–away from the intersections, the veins became progressively poorer in galena, while baryte and/or witherite appeared in quantity. Large crystals of barytocalcite are present locally in Second Sun Vein and a few specimens of alstonite were obtained by Sir Arthur Russell in 1931 from Cox's Vein, S of its intersection with this vein (Young, 1985). A few crystals of harmotome have recently been found, associated with barytocalcite, on the dumps at Wellhope Shaft [NY 7790 4661] (Young and Bridges, 1984). To the NW mineralisation on all the veins dies out rapidly beyond the ends of the rich lead shoots, and though the barium minerals are present, they are not in quantity. Dupont Vein, which has been followed farther than the others in this direction, contains large calcite crystals in open, loughy ground, with occasional spots of galena, small crystals of ankerite and patches of witherite. The wide bodies of barium spars on the ENE veins carry good zinc values for considerable distances beyond the zone of high lead values. High Raise Vein in Cumberland, as already noted, was filled with material of this sort, but yielded little lead ore. It passed into the payable lead zone in Northumberland; NE of Liverick Vein it again contains barium and zinc minerals.

    The average width of the lead oreshoots on all the veins was 6–7 ft (1.8–2.1 m). On Sincay Vein the maximum width reached was 20 ft (6.1 m), near the point where this vein split into strings. Dupont Vein reached a maximum width of 12 ft (3.7 m). First Sun Vein, in the zinc-barium zone, is probably as much as 20 ft (6.1 m) wide in places. The length of ground stoped out in the Great Limestone on each vein is summarised as follows: Treloar Vein, 1130 ft (344 m); High Raise 1550 ft (472 m); First Sun, 1820 ft (555 m); Second Sun, 1925 ft (587 m); Sincay, 1480 ft (451 m); Cox, 1620 ft (493 m); Dupont, 2350 ft (716 m); Liverick, 1550 ft (472 m); Robson, nil. The average stope height overall is about 30 ft (9 m). It will be evident that these ribbon-like oreshoots, owing to their small height, produce a relatively poor yield per fathom of development. Almost the whole of the above stoping has been done in the zone of rich lead values; there is no doubt that these have, from the economic point of view, proved to be sufficiently high to offset the relatively high development costs. In the period 1923–1938, a total of 277 657 tons of crude ore were extracted from the oreshoots, which yielded a total of 33 998 tons of lead concentrates containing 80 per cent of lead. This represents a recovery of 12.2 per cent lead sulphide over the whole period, with 18.5 per cent for the best single year. Almost the whole of the ore was treated at the Nentsberry Mill, near the mouth of Nentsberry Haggs Horse Level [NY 7661 4503], which had a capacity of about 4 tons per hour, and was equipped with standard crushers, rolls, jigs and tables. An excellent lead concentrate was obtained here, but the zinc-witherite mixture proved to be very difficult to separate, owing to the small difference in specific gravity of the minerals. For this reason very little stoping has been done in the zinc-witherite zone. Development has, however, revealed that mixed ore of this type persists ENE of the lead zone for at least 1250 ft (381 m) on Treloar Vein, and for 3200 ft (975 m) on First Sun Vein. Mixed zinc-lead ore also remains in place in the stretch between the workings in Cumbria and those in Northumberland on Second Sun Vein, the distance being 1700 ft (518 m). A sampling campaign carried out by engineers of the Nonferrous Minerals Development ControlUnpublished reports to the Non-ferrous Minerals Development Control (Ministry of Supply). Nentsberry Mine and Nenthead Dumps, by James Jackson, 1942. Nentsberry Mine. Calculation of ore reserves by H R Middleton and J M Stowell, 1942. Additional data from this report has been published by Critchley (1984) p.28.) during 1942 gave the following average assay for the ore remaining on Treloar, First Sun, and a short accessible stretch of Second Sun Vein: 8.75 per cent of zinc, 1.5 lead, 13 barium carbonate contained in a total of 54 000 tons. So far as is known this ore is still in place. Possible ore remaining on First Sun East, and Second Sun West could easily reach as much again. The ENE foreheads on Treloar and on First Sun veins are still in ore, though the Horse Level on the latter vein has almost reached the top of the Great Limestone owing to the northerly dip of the beds. It is probable that Second Sun Vein joins First Sun near the forehead, but the connection has not been established. There are also subsidiary veins linking Treloar and First Sun veins which have not been explored. The average widths of Treloar, First Sun and Second Sun veins as established during the sampling campaign were: 5 ft (1.5 m), at least 8 ft (2.4 m), and 5 ft (1.5 m). It follows, therefore, that a moderate tonnage of zinc ore remains in place at this mine, and that the prospects for further development in the Great Limestone have not been exhausted.

    Witherite is most abundant on Treloar Vein, where a stope 66 ft (20 m) long contained, according to the sampling, 33 per cent barium carbonate. Hand picking of the witherite from another stope on this vein, E of Liverick Vein, yielded a good quality mineral, as the assay quoted below indicates. Much of the witherite in the mine especially on Second Sun Vein, is however, intimately intergrown with sphalerite. At one time some of the jig-middlings from treatment of the mixed ore was shipped for treatment to a chemical plant outside the district. An analysis of a representative sample of the middlings is quoted in (Table 48). The residue left after removal of the soluble barium salt was rich in zinc, but could not be regarded as a good quality zinc concentrate. Flotation appears to be the only solution to the problem of treating the mixed ore here. The zinc can undoubtedly be recovered, but the problem of separating witherite from other carbonates such as calcite and ankerite has not, to the writer's knowledge, yet been solved.

    The main entrance to Nentsberry Mine was by way of Nentsberry Haggs Horse Level [NY 7661 4503], which starts at 1251 ft (381 m) above OD from the side of the Alston–Nenthead road, 1 mile (1.6 km) NW of Nenthead. The level passes through the Nent Valley cross veins and follows High Raise Vein into Northumberland, in the shale below the Quarry Hazle. The level is now seriously blocked by falls. Wellhope Shaft [NY 7790 4661] was sunk in 1925 close to the intersection of High Raise Vein with Dupont Vein to provide an alternative means of transport for the ore. The shaft is 416 ft (127 m) deep to the Horse Level, here at 1311 ft (400 m) above OD and was equipped with an electric hoist; an aerial ropeway was erected from the shaft to Rampgill Mill, but owing to technical difficulties this never functioned satisfactorily and was soon dismantled. From the shaft branches of the Horse Level run respectively 2200 ft (671 m) NW on Dupont Vein, and 3900 ft (1189m) NE, following first High Raise and then First Sun Vein. The Great Limestone lies entirely above the Horse Level, except on the eastern part of First Sun Vein. The workings are reached by means of rises; sublevels have been driven near the base of the Great Limestone on all the veins. Horizons above the Great Limestone proved unproductive in the old workings from Wellhope Low Level, described above; two old surface levels [NY 7816 4665] and [NY 7831 4692] which reached First Sun Vein below the Firestone also appear to have yielded nothing. In 1940 a trial in the Firestone from Wellhope Shaft found Cox and Dupont veins united at 107 ft (32.6 m) NE of the shaft, with a throw equal to the thickness of the Firestone (28 ft (8.5 m); a little pyrite was the only mineralisation found. The prospect in the beds above the Great Limestone is not, therefore, hopeful. In 1983 a trial was made by Ashover Consolidated Mines Ltd, on behalf of Industrial Minerals Ltd, which led to the reopening of Wellhope Shaft; it proved to have about 16 ft (5 m) of water in the bottom, making access to the Horse Level, and thus to First Sun Vein, impossible. However, access was gained to the sublevels near the base of the Great Limestone worked north of First Sun Vein, and unextracted pillars of high-grade lead ore were noted. However, the principal resource of Nentsberry Mine is its zinc-witherite ore, as mentioned above, on Treloar, First Sun and Second Sun veins. These could be fully unwatered by driving an adit on the projected line of First Sun Vein from the West Allen valley at 1250 ft above OD (381 m), on the base of the Great Limestone. The distance, all in virgin ground, is about 3650 ft. (1.1 km) and this would only be worth doing if the vein can be found and followed in productive ground. The W slope of the West Allen Valley may, like that of the East Allen (p.161) be mantled with thick boulder clay.

    The production of Nentsberry Mine during the period 1913–1938 amounted to 39 251 tons of lead concentrates, almost the whole of which came from the workings in the West Allen area, and 4152 tons of zinc concentrates. The silver content of the lead concentrates was equivalent to 6.5 oz. silver per ton of lead.

    Wellhopehead = Scraithole Vein—Lead and zinc ore (Barytes)

    NY84NE, 84NW; Northumberland 110 NE, 111 NW (Old Series) Direction N58°E, throw 1 ft 2 in. (0.4 m) SE

    This vein is the continuation of the Brownley Hill Vein of the Nent Valley, and in it Wellhopehead and Coke shafts [NY 7849 4586] and [NY 7875 4607] probably sunk into the Slate Sills, found coarse baryte; the mineral is abundant on the dumps. Wellhopehead Mine (disused), situated at the head of the valley, 3.75 miles (6 km) S of Ninebanks church, reached the vein by Wellhope Top Level [NY 7838 4653], a drive of 1875 ft (572 m) SE beneath the Firestone at 1607 ft (490 m) above OD. Baryte, witherite (partly altered to baryte) and a little sphalerite occur on the dumps. The mine section shows no stopes above this level, but surface shafts and dumps suggest that ground was extracted here, the working probably being ancient. Beneath the Wellhope Top Level a drift known as the Middle Level extends 1670 ft (509 m) NW from the vein in the shale beneath the Pattinson Sill. As this level falls from 1520ft to 1515 ft (463 to 462 m) above OD in a NW direction, it was presumably driven from the NW, and although no plan now exists showing the connection, it is suggested that it started from a rise from Wellhope Low Level (described under Nentsberry Mine, above). It is possible that the Low Level may have been driven up to Wellhopehead Vein, for the vein-section shows a drift at 1440 ft (439 m) above OD, in the shale above the Great Limestone; on the other hand this may have been worked from a sump which connects it with Middle Level. From this drift a series of sumps gave access to a belt of small flats on the downthrow side of the vein, 950 ft (290 m) long, up to 30 ft (9 m) wide, which were worked in the High Flat horizon of the Great Limestone. These extend ENE from the intersections of Top and Middle levels with the vein. Ground WSW of this point appears to have been left intact by the Beaumont Co., and here an extension of Brownley Hill Horse Level by the Vieille Montagne Zinc Co. from Nenthead gave access to a zinc-ore stope in the limestone 500 ft (152 m) long, decreasing in height from 50 to 10 ft (15 to 3 m) in an ENE direction. The north-eastward extension of the vein, known as Scraithole Vein, was worked from Scraithole Mine (disused) at Carr-shield. The Low Level [NY 8032 4694] runs WSW from the West Allen, on the footwall side of a fault, throwing 20–25 ft (6–7.6 m) SE, known as Barneycraig Low Vein at 1308 ft (399 m) above OD, in the shale below the Tuft. At 910 ft (277 m) from the portal, Coalcleugh East Cross Vein with a throw of 80 ft (24 m) SW was cut. The beds rose towards the footwall of this fault, bringing the quarry Hazle into the level which runs NW in the fault for 100 ft (30 m), then turns WSW in Scraithole Vein, in the middle of the Great Limestone. From 555 to 850 ft (169 to 259 m) from the turn a belt of small faults representing the breaking-up of Coalcleugh West Cross Vein, throwing in general to the NE, was cut through. For the next 1040 ft (317 m) the level is mainly in the Quarry Hazle, with the beds rising westward. A second belt of cross veins, 450 ft (137 m) wide is then encountered; the general effect is to produce a fault trough, the largest throw being 45 ft (13.7 m) on the eastern fault. The level continues beyond this belt for 1700 ft (518 m) to a rise communicating with the NE end of the flats mentioned above. Only one stope in the Great Limestone, 150 ft (46 m) long, is shown on the vein section in the Beaumont records, and this was confirmed by the reopening of the mine by Mr E Richardson during the 1970s, but the vein is strong, 4–8 ft. (1.2–2.4 m) wide in the Great Limestone, continuing down into the underlying sandstone (Plate 4). The mineralisation is similar to that already discussed (p.155) in the Nentsberry Sun Veins with witherite and sphalerite closely intergrown. Young (1985) notes that barytocalcite commonly lines vugs in the witherite.

    Evidently this orebody was too refractory to interest the Vieille Montagne Co. Development by Industrial Minerals Ltd led to an estimate of tonnage of 35 000 with 11 per cent Zn, 10 per cent BaCO3, 8.4 per cent BaSO4, 2 per cent Pb, and a possible total tonnage of twice this figure.

    A small gravity plant was erected. However, separation of the sphalerite and witherite by chemical methods again proved uneconomic and this company ceased operation in 1981. The work done underground included reopening as far as the Dodd crosscut to Gudhamgill flats (described below) and some rising and driving in Great Limestone on Scraithole Vein. Middle Level [NY 7998 4683] at 1459 ft (136 m) above OD explored the vein in the White Sill in the first fault-trough, and in the Pattinson Sill between the fault-troughs; while High Level [NY 7979 4682] at 1527 ft (465 m) above OD, which enters from the north as a crossscut, tried the vein in the White Sill between the troughs. Production records confirm the impression that Scraithole Vein was only poorly mineralised with galena; 950 tons were obtained in 1826–1828 and 1861–1878. From the Wellhopehead portion of the vein, 3564 tons were produced between 1763 and 1807, and from 1808–1815, when included with that of Heartycleugh, 3335 tons were obtained. The total production from the vein by the Beaumont Co. was thus probably of the order of 6000 tons of lead concentrates. None of the cross veins was found to be mineralised.

    A possiblity which appeared to remain was that the baryte, which appears to be present in some abundance in the Slate Sills, might be workable around the Coke Shafts [NY 7875 4607] where one 1000 ton dump carries 73 per cent BaSO4, 7.1 per cent Zn but no BaCO3. There are other bell-pit heaps nearby but attempts to reach these by bulldozer were unsucessful.

    Gudamgill Vein—Lead and zinc ore

    NY74NE Northumberland 110 NE (Old Series)

    From Scraithole Low Level at 4550 ft (1387 m) from the portal a crosscut known as Dodd Level was driven due S to test the continuation of the Gudhamgill Vein of Nenthead in the present area. A sump near the start of the level may have tested Scraithole Vein in the Four Fathom Limestone, but without sucess. The crosscut sole was the top of the thin Iron Post Limestone, which overlies the Quarry Hazle; this rose from 1344 ft (410 m) above OD adjacent to Scraithole Vein to 1392 ft (424 m) above OD where it encountered Gudhamgill Vein, 3000 ft (914 m) to the S. The vein was found to be split up into three branches the N and S branches throwing respectively 1 ft 4 in (0.4 m) and 2 ft 6 in (0.76 m) NW. A stope 720 ft (219 m) long, and about 10 ft (3 m) high at the Middle Flat horizon of the Great Limestone was worked on the S branch from rises; possibly the production recorded form Scraithole Mine for 1861–78 came from here. These workings were reopened and extensive flats were discovered when the Vielle Montagne Zinc Co., advanced Bloomsberry Horse Level into this ground. A report during the first world warUnpublished report to the Ministry of Munitions: Nenthead Mines by G Cunningham, 1917 gave the dimensions of the flat at the Middle Flat horizon as 210 ft by 30 ft by 6 ft (64 by 9 by 1.8 m), yielding 1 ton zinc sulphide and 0.5 ton lead sulphide per fathom. A flat 25 ft (7.6 m) wide, 10 ft (3 m) thick associated with the N branch of the vein yielded 1 ton zinc sulphide and 1 ton lead sulphide per fathom. A little work, done in this ground as recently as 1938 yielded ore containing 4 per cent lead sulphide, 7 per cent zinc sulphide. Approximately a mile (1.6 km) of virgin ground lies ahead of the foreheads of these workings, but it may be noted that the S branch was not found in a drift from Coalcleugh Mine following the Little Cross Vein (below) in the Great Limestone, which might have been expected to cross the line of the S branch about 2600 ft (792 m) ahead of the forehead of Bloomsberry Horse Level.

    Low Coalcleugh Vein–New Vein group

    The earliest workings at the Coalcleugh Mines (disused) were from surface shafts sunk to Low Coalcleugh Vein SW of the hamlet of Coalcleugh [NY 801 451]. Later a prospecting level, Coalcleugh Level [NY 8015 4518] driven SSE in the shale above the Firestone, discovered High Coalcleugh Vein 2500 ft (762 m) from the portal at 1715 ft (523 m) above OD. Some ore was obtained from the Slate Sills on both Low and High veins, but information as to the full extent of the stopes has not been preserved. If those in the stretch SW of the Coalcleugh level head shown on the Beaumont mine-section are typical, they were not extensive. The level was reopened in the 1950s by Mr Amos Treloar Jr, yielding some good fluorspar from ground in the Slate Sills previously slit for galena. The High Vein was also worked in the Firestone and lower beds from shafts sunk below Coalcleugh Level communicating with the Galloway Level on top of the Great Limestone at 1520 ft (463 m) above OD. Evidently the veins appeared sufficiently promising to warrant a thoroughly planned scheme for development in the Great Limestone. In about 1760 the Barneycraig Horse Level (disused) [NY 8039 4672] was commenced. This starts beneath the Great Limestone at 1321 ft (403 m) above OD from the E bank of the West Allen, 0.5 mile (0.8 km) S of Carrshield village. It runs straight for 3600 ft (1097 m) S25°E; a branch is then given off to the SW, leading to the Low Coalcleugh Vein and carried to within 695 ft (212 m) of the county boundary, while the main level continues S41°E for 2900 ft (884 m), giving access to the workings on Barneycraig Vein. These workings came into production between 1808 and 1823. They proved remarkable for the rich belt of Great Limestone flats associated with Whitewood and Barneycraig veins, and the cross veins which intersect them.

    The arrangement of veins, flats and cross veins worked at Barneycraig Mine is shown in (Figure 22). Flats in the Great Limestone, related to diverging or subparallel strings were found in association with Low Coalcleugh Vein for a distance of 3400 ft (1036 m) SW of Coalcleugh West Cross Vein, against which the vein apparently terminates. No vein stopes are indicated on the Beaumont section of this vein, but the dumps from surface shafts with their quartz, fluorite, sphalerite and carbonate suggest that the vein was well mineralised, probably in the sandstones above the Great Limestone, SW of the belt of flats. This ground was worked out from Low, Middle and High Whimseys before the driving of the Horse Level. The cross veins recorded in the Low Coalcleugh workings include one throwing 17 ft (5.2 m) SW, cut 2250 ft (686 m) from the main Barneycraig adit, and Little Cross Vein, throw 10 ft (3 m) NE, a further 500 it (152 m) NE. The first-mentioned cross vein is considered to be continuous with the eastern fault of the second fault-trough cut in the Scraithole workings. A fault-trough between Coalcleugh East and West cross veins lies between the main adit and workings on Low Coalcleugh Vein. The beds bend down towards the West Cross Vein at 30°, the combined displacement of the monocline and fault being about 100 ft (30 m) NE. A series of small faults cut the beds in the trough; the East Cross Vein throws 140 ft (42.7 m) SW. Although the main adit lies east of East Cross Vein, it failed to find any continuation of Low Coalcleugh Vein.

    The direct continuation of Rampgill Vein of Nenthead in Barneycraig Mine is known as Whitewood Vein. For the first 2500 ft (762 m.) of its course in Northumberland with a throw of 12 ft (3.7 m), this vein hades N, the horizontal distance between the workings in the Firestone and those in the Great Limestone being over 150 ft (46 m), indicating a low hade. At about 2500 ft (762 m) the hade and presumably the throw, is in the reverse direction. At 3200 ft (975m) the vein apparently dies out against Killhope Cross String. E of the Coalcleugh fault-trough, however, a vein in a corresponding position has been worked for 1800 ft (549 m) NE. Flats were associated with the vein in the 1100 ft (335 m) NE from the county boundary; the remaining stretch to Killhope Cross String appears to have been poor. Extensive flats were again found associated with the vein in the Great Limestone NE of the Coalcleugh East Cross Vein. These form part of a remarkable series of flats which extend along the foot wall of the East Cross Vein for a distance of 850 ft (259 m) NW of Whitewood Vein, to join up with the Engine Strings, a series of weak ENE veins. To the SW the flats join up with those along Barneycraig Vein. Part of this ground has been illustrated by Smith (1923, pl. 14).

    It is very likely that the main flow of mineralising solutions from Rampgill Vein did not, however, follow Whitewood Vein. A short distance east of the county boundary, an E–W vein, known as Hardshins String, is given off from Whitewood Vein. This forms a link to the curviform Barneycraig Vein, which like Whitewood Vein, usually hades NW at a low angle. A belt of flats approximately a mile (1.6 km) long is associated with Barneycraig Vein, with the subsidiary Sun Vein to the SE, and with the numerous cross veins which traverse them. The whole belt terminates against West Cross Vein. In the fault-trough between the Coalcleugh cross veins, into which the two faults throw 112 ft (34 m) and 128 ft (39 m) respectively, it is understood that no mineralisation was found in Pump Sump, a trial below the Horse Level. The flats are, however, resumed in strength NE of East Cross Vein; they continue along Barneycraig Vein to the limit of its workings, 2100 ft (640 m) NE of the East Cross Vein and persist in the Swinhope workings (described below under East Allendale). The Horse Level, except where it crosses the fault-trough, runs in beds between the base of the Great Limestone and the shale beneath the Quarry Hazle. This represented the lowest level worked by the Beaumont Co., except between the Pumpsump Cross Vein and West Cross Vein, where trials, apparently unsuccessful, were made to the Four Fathom Limestone on Barneycraig Vein; and within the fault-trough, where the Great Limestone was probably (but not certainly) tried. Very little stoping on the vein was done by the Beaumonts, though a little ore was got from horizons between the Great Limestone and Pattinson Sill NNE of East Cross Vein. The main production, however, came from the flats. The mine was regarded as exhaused for lead ore by 1880. It was, however, reopened for zinc ore by the Vieille Montagne Zinc Co., who advanced their workings from Rampgill Underground Shaft and connected them with Barneycraig Horse Level. A total length of 2400 ft. (732 m) was stoped out, the horizons worked being the lower part of the Great Limestone, the Quarry Hazle and the Four Fathom Limestone. In 1917, in an unpublished report to the Minstry of Munitions Nenthead Mines by J G Cunningham, the Barneycraig vein in the Four Fathom Limestone was reported to be 4 ft. (1.2 m) wide, yielding 3 tons of sphalerite per fathom. A stope at the horizon of the Middle Flat of the Great Limestone on Hardshins Vein was estimated to carry 2 tons per fathom. Zinc ore was obtained not only from virgin ground on the veins left by the Beaumont miners because of its high zinc-content, but also from old fill in stopes and flats. It was noted in 1917 that much of the ground on Barneycraig Vein and flats had not then been re-examined for material of this type. As the operation closed down in 1921, it is probable that some zinc ore still remains; not more than one third of the total length of the Barneycraig workings had then been reworked by the Vieille Montagne Co., according to records available in 1940.

    The flats are not now accessible and data on their exact horizon and mineralogy are scanty. Smith (1923, p.76) states that they reach thicknesses up to 30 ft (9 m) in which lenses of ore and spar alternate with dolomitized limestone. From an inspection of the tailings at Barneycriag Mill, it appears that the minerals replacing the limestone included, in addition to galena and sphalerite, abundant ankerite, with siderite, quartz and subordinate amounts of fluorite. Barium minerals are absent.

    Complete details of production from the Coalcleugh and Barneycraig veins are available in the accounts of the Beaumont Co. from 1729. They are summarised in (Table 49).

    The silver recovered under the Vielle Montagne Co. was equivalent to 8 oz silver per ton of lead; no separate figures have been obtained for the earlier operations. Between 1874 and 1880, during the Beaumont operations, 311 tons of zinc concentrates were obtained. The main period of zinc mining was,however between 1899 and 1920 when, 56 231 tons of concentrates were obtained. Post-Second War treatment of old jig tailings by flotation added an estimated 3500 tons.

    Exploration during the later years of the Beaumont operations revealed New Vein, approximately 900 ft (274 m) SE of Barneycraig Vein; it was tried from a crosscut known as Bellingham Level, and also from a SSE drift following Little Cross Vein, but little appears to have been obtained from it. The main Horse Level on the east side of East Cross Vein was continued 750 ft (229 m) SE of Barneycraig Vein, but not far enough to explore the ground beneath Killhope Law and Middlehope Moor to the SE, which, in view of the numerous veins known on the west side of the Coalcleugh Cross Veins at the Killhope mines, appeared to offer one of the most promising virgin areas remaining in the orefield. It was prospected during 1955 to 1957 by way of Swinhope Horse Level [NY 8315 4712] (described below pp.165–166), from which a crosscut commanding the Great Limestone had already been commenced by the Beaumont Co. before the abandonment of Swinhope Mine. A new and longer crosscut was driven but without success.

    References

    CRITCHLEY, M F. 1984. The history and working of the Nenthead mines, Cumbria. Bull. Peak District Mines Hist. Soc., Vol. 9, 1–50.

    JOHNSON, G A L, NUDDS, J L, and ROBINSON, D. 1980. Carboniferous stratigraphy and mineralization at Ninebanks, West Allendale, Northumberland. Proc. Yorks. Geol. Soc., Vol. 43, 1–16.

    SMITH, S. 1923. Lead & zinc ores of Northumberland and Alston Moor. Spec. Miner Resour. Mem. Geol. Surv. G.B., Vol. 25. 110pp.

    YOUNG, B. 1985. The distribution of barytocalcite and alstonite in the Northern Pennine Orefield. Proc. Yorkshire Geol. Soc., Vol. 45, 199–206.

    YOUNG, B. and BRIDGES, T F. 1984. Harmotome in Northumberland. Trans. Nat. Hist. Soc. Northumbria, Vol. 52, 24–26.

    Chapter 9 mineral deposits

    Details, Area 4 East Allendale

    Mining in the East Allen valley commenced near its head with the finding, probably in the Firestone Sill west of the present village of Allenheads, of a series of lead veins, the development of which led to the discovery of the most productive single mine of the orefield, for Allenheads Mine, under the Blacketts and Beaumonts, yielded nearly 260 000 tons of lead concentrates between 1729 and 1896, when it was closed (Figure 26). From Allenheads village the valley runs nearly due N 7 miles (12 km) to Allendale Town. A continuation of the Barneycraig Vein of West Allendale was worked in Swinhope, an important side valley about 2 miles (3.2 km) below Allenheads. East Allendale is served by a good road which runs along the eastern side of the river and continues over Burtree Fell into Weardale. From Allenheads roads branch to Nenthead, through Coalcleugh and to Rookhope.

    The rocks exposed on the sides of the valley between Allenheads and Allendale Town belong to the Pendleian stage of the Namurian while the high fells which separate the valley from the headwater streams of the Derwent system to the E are capped by outliers of "Millstone Grit' facies which postdate the Pendleian. Along the western side of the valley runs the northward continuation of the Burtreeford Disturbance, here consisting of a monocline facing E, associated with a fault downthrowing W; the effect of the disturbance is indicated on the structure-contour map, (Figure 9), p.55. Swinhope Mine lies W of the disturbance; all the remaining mines described in this chapter are to the E of it. The western slopes of the valley are covered with glacial deposits. The mining developments have indicated that the old preglacial valley has been filled to a depth exceeding 100 ft (30 m) with boulder clay, sand and gravel. The present river follows the E side of this infilling, "solid" rocks being exposed on the E bank. Against the glacial fill the Great Limestone crops out for a distance of 4 miles (6.4 km) and it is probable that in preglacial times beds a little lower in the succession were exposed in the valley bottom. The Great Limestone is now exposed at surface only near Allenheads, and on the western side of the valley where it is rising towards the Burtreeford Disturbance. Here the subsidiary Elphagreen Fault runs parallel to the disturbance, downthrowing 20–30 ft (6–9 m) W.

    The success of Allenheads Lead Mine led the Company in 1855 to commence the construction of a long adit known as Blackett Level, designed to drain and explore the valley from Allendale Town to Allenheads. At this time Thomas Sopwith, FRS was General Manager, and T J Bewick (one of the founders of Bewick, Moreing and Co.) was employed as engineer. The level was driven simultaneously from the portal [NY 8375 5602] at Allendale Town and from shafts at Studdon Dene [NY 8395 5440], Holmes Linn [NY 8419 5240], and Sipton [NY 8468 4987]. Up to 1903, when the main drive was suspended, a total of 4.68 miles (7.54 km) had been completed. The forehead stands 400 ft (122 m) NW of St Peter's Church, Spartylea. At Brackenhill, 3175 ft (968 m) ahead of the forehead another shaft [NY 8503 4761] had been sunk, but here difficulty was experienced with water, the influx reaching the figure, exceptional for the district, of 300–400 gallons per minute according to a report by Bewick dated 1859. The total cost up to 1896 was approximately £120 000 (not £250 000 as stated by Smith, 1923, p. 56). An excellent record of the geology of the tunnel exists, and the portion from Sipton Shaft, 4000 ft (1.2 km) S to St Peter's Vein, and 3000 ft (914 m) N to Esp's Vein was open for inspection during the 1939–41 investigation. A generalised section has already been published (Smith, 1923, pl. 9) but some additional details are sum- marised here. From the portal, the level runs through boulder clay for 780 ft (238 m), the thickness of the glacial deposits here being at least 110 ft (34 m). "Solid' rock is then entered, the beds dipping to the N at an average of 3°. The succession passed through up to Studdon Shaft, 5300 ft (1.6 km) from the portal, is summarised in (Table 50).

    It is suggested that the lowest of these sandstones is the Firestone, and that the limestone overlying it in Studdon Shaft, passing into limy sandstone before the level cuts the corresponding horizon 2200 ft (671m) to the N, is the Crag. From 1710 to 2220 ft (521 to 677 m) from the portal a series of sixteen faults, none of them throwing more than 4 ft (1.2 m), were cut through in the 11 ft (3.4 m) sandstone and the shale underlying it. The trend of the faults was E-W to ENE; none was mineralised except with calcite, pyrite and "spar" and no trial to more favourable horizons below was made. The sandstones in the upper part of the sequence presumably represent the Slate Sills or Low Grit, though beds as high as the Coalcleugh Transgression Beds may perhaps be present. From 390 to 590 ft (119 to 180 m) S of Studdon Shaft a belt of strong faults, associated with steep northward dips is encountered. Calcite, pyrite and traces of galena are recorded. At 590 ft (180 m) S of the shaft the following sequence commences: limestone 3–4 ft (0.9–1.2 m); shale 4 ft (1.2 m); sandstone, 4 ft (1.2 m); shale, 10 ft (3 m); sandstone, 13 ft (4 m); shale, 21–29 ft (6.4–8.8 m); Little Limestone, 7 ft (2.1 m); the dip being between 2 and 3°N. The primary surveyors appear to have regarded the thin limestone here as the same as that cut in Studdon Shaft, but it is hard to believe that the underlying 45 ft (13.7 m) sandstone has split up in so short a distance. Their view implies that the faults throw S. It is suggested as an alternative that the second limestone overlies the Pattinson Sill, and that the faults, which hade N, also throw in that direction. A similar view appears to have been adopted by Smith (1923, pl. 9). At 9380 ft (2.86 km) from the portal the Little Limestone appears in the level sole. From 9720 to 10 000 ft (2.96 to 3.05 km) another belt of small faults occurs, the southernmost having an estimated throw of 39 ft (12 m) N. Some "spar" was recorded here but the exact nature of the mineral is not known, and no trial has been made. At 10 830 ft (3.3 km) the top bed of the Great Limestone, overlying a thick "Black Bed" (shale), is in the sole. A series of NNE and E–W joints in the limestone is recorded. Holmes Linn Shaft [NY 8419 5240] is at 11 958 ft (3.65 km) from the portal, and at 430 ft (131 m). S of this shaft the base of the Great Limestone rises above the level roof. The Tuft, 3 ft (0.9 m) thick, is underlain by 7 ft (2.1 m) of shale, below which the Quarry Hazle appears. At 1542 ft (470 m) S of Holmes Linn Shaft, the first vein carrying galena, Whintings Vein, was cut. From 2612 to 3450 ft (796 to 1052 m) S of the Shaft, the level cuts through the Four Fathom Limestone. Esp's Vein was cut in the Nattrass Gill Hazle at 5442 ft (1.66 km) S of Holmes Linn Shaft. Sipton Shaft [NY 8468 4987] 8471 ft (2.58 km) S of Holmes Linn Shaft, is 339 ft (103.5 m) deep, sunk through 108 ft (33 m) of boulder clay, the "solid" section including beds from the Quarry Hazle down to the top of the Five Yard Limestone. At 130 ft (40 m) N of this shaft the Sipton Vein, throwing approximately 50 ft (15 m) N was cut in Blackett Level; this brings the Five Yard Limestone and overlying shale on the south against the interbedded shale and sandstone beneath the Nattrass Gill Hazle on the N; from this fault northwards to Esp's Vein the dip of the beds is very small. A small vein 800 ft (244 m) N of Sipton Shaft, throwing 6 in (15 cm) SE was tried by a rise to the Four Fathom Limestone without success. Smith's Vein, 2140 ft (199 m) N of Sipton Shaft also represented in Blackett Level by small strings carrying sphalerite and carbonates, yielded some ore from the Great Limestone during 1930s development work. S of Sipton Shaft there is little change in the stratigraphical horizon of the level to its forehead, S of St Peter's Vein. A small fault trending NE and throwing 4 ft (1.2 m) SE was cut 300 ft (91 m) S of Sipton Shaft; St Peter's Vein passes through the level 4000 ft (1.22 km) S of the Shaft, with a subsidiary vein 425 ft (130 m) N of it.

    Esp's and St Peter's veins were extensively developed, and proved very productive; Whinting's, Smith and Sipton veins have received some attention. The possibilities of the ground opened up by Blackett Level are, however, by no means exhausted. The general scheme of exploration southwards towards Allenheads was continued by the Weardale Lead Co., who drove a crosscut in the Great Limestone 2475 ft (754 m) S from St Peter's Vein. Blackett Level is at 678 ft (207 m) above OD at the portal; 687 ft (209 m) above OD at Studdon Shaft; 698 ft (213 m) above OD at Holmes Linn Shaft; 707 ft (215 m) above OD at Sipton Shaft and 713 ft (217 m) above OD at the forehead. (Figure 9) (p.55) shows that in a considerable area E of East Allendale the Great Limestone could be drained from Blackett Level. In addition, the two groups of small faults cut by the level in the Pendleian strata may prove worth exploring in the Great Limestone below the level.

    Allenheads Mine was reopened during the 1970s to search for fluorspar but no workable deposit was found and the mine closed in 1981.

    Whinting's Vein—Lead ore

    NY85SW; Northumberland 107 NW, NE (Old Series) Direction N25–30°W, throw 6–9 ft (1.8–2.7 m SW)

    From Blackett Level during 1875–1882 drifts were made 200 ft (61 m) NW and 1440 ft (439 m) SE in Whinting's Vein, in the Quarry Hazle and underlying shale. In the SE drift the vein is recorded as having been 2–5 ft (0.6–1.5 m) wide, with good walls, filled with broken sandstone cemented with siderite, quartz, fluorite and, in places small quantities of galena. Pyrite was abundant locally. A rise was put up to the Great Limestone 40 ft (12 m) SE of Blacken Level, and connected with a sinking from a short surface drift. Here the vein was decribed thus:Allendale Mine Reports, 1875; quoted from a summary by Mr J A Hill, which has been of great value in preparing the present account of the Allendale Mines. "cherry limestone and weak strings about 18 in (0.46 m) wide, perpendicular in limestone but nearly horizontal in the plate (shale) in the limestone". The width later improved to 3 ft (1 m) and some ore was raised (included with Allenheads production) but this vein was never a serious producer.

    Esp's Vein—Lead ore

    NY85SW Northumberland 107 NW, NE (Old Series). Direction N45–55°E, throw 4 ft (1.2 m) NE of Blackett Level, changing to 2–6 ft (0.6–2 m) SE, W of Blackett Level.

    Although this vein was discovered during the construction of Blacken Level 3029 ft (923 m) N of Sipton Shaft, and recorded in 1871 as 3 ft (0.9 m) wide "ridery substance, intermixed with a little coarse spar and black jack, some specks of ore", it was not brought into production until shortly before 1914. A continuous oreshoot in the Four Fathom Limestone was worked 675 ft (206 m) NE and 200 ft (61 m) SW of Blackett Level; over a length of 575 ft (175 m) ore extended 30 ft (9 m) above the top of the limestone, into the shale below the Quarry Hazle. The upward extension ceased a short distance SW of Blackett Level, but flats then appeared in the Four Fathom Limestone, continuing for over 400 ft (122 m), in places 20 ft (6 m) wide. Adjacent to the flats the vein is less than 1 ft (0.3 m) wide, elsewhere to the NE it averaged 4 ft (1.2 m) wide, with fluorite (mainly green), quartz, coarse bands of galena and a little sphalerite, siderite and pyrite. Above this Four Fathom Limestone oreshoot, the vein became barren from the Quarry Hazle up to the base of the Great Limestone. The development of the Great Limestone was carried out by the Weardale Lead Co. after 1923, on a vein 20–35 ft (6–10.7 m) SE of the Four Fathom position, believed, but not proved, to be Esp's. It proved to carry a rich oreshoot 1300 ft (396 m) long, averaging 30–35 ft (9–10.7 m) high and 6 ft (1.8 m) or more wide, associated with small flats at both the High and Middle Flat horizons, in places extending as much as 30 ft (9 m) from the vein. Parts of the Great Limestone ground have yielded crude ore containing at least 25 per cent lead sulphide, with fluorite, quartz, siderite and traces of sphalerite. Ore ends at the thick shale in the upper part of the Great Limestone, though a stringer in the shale carrying baryte has been noted. Trials from Plantation Drift [NY 8439 5067] which, with a connecting rise provided ventilation from surface, show the vein to be barren in the Little Limestone and White Hazle. A strong slickenside cheek was noted both in the Great Limestone and Four Fathom Limestone workings, adjacent to which galena has been sheared into "steel ore". Smith (1923, p.58) quotes this analysis by T E Hull of Esp's "steel ore": lead sulphide, 87.00 per cent; ferrous sulphide 9.46; antimony sulphide 0.62: calcium fluoride, 1.60: insol., 0.84. The concentrates from Sipton Mine contained a small proportion of antimony. As a rule, "steel ore" is richer in silver than the normal galena (see p.71).

    A strong cross vein passes through Esp's Vein 550 ft (168 m) NE of the main Blackett Level, at that horizon trending N–S; the same vein was encountered 40 ft (12 m) farther NE in the Great Limestone. At both horizons this cross vein appears to have an adverse effect upon the oreshoots, for they pinch out within 200 ft (61 m) NE of it. Crosscuts have been put out both NW and SE but oreshoots have not been found farther NE. The line of Whinting's Vein lies about 950 ft (290 m) ahead of the forehead of the drift from Blackett Level.

    The Great Limestone oreshoot terminated 850 ft (259 m) SW of Blackett Level against the boulder clay filling the old East Allen valley. As the boulder clay was approached, limonite became more abundant in the ore, but the galena was not greatly oxidised. The sub level at the base of the Great Limestone was continued 275 ft (84 m) SW in boulder clay without locating the W side of the wash, but the erosion channel does not reach the Four Fathom Limestone. After proving by means of a boring in 1942, 450 ft (37 m) SW of the eastern margin of the wash, that the Great Limestone is again present and carries galena, the Weardale Lead Co. drove forward the SW drift from Blackett Level and put up an inclined rise. The vein was found in the Great Limestone. Development here revealed good patches in the vein, but values did not appear to be so high as those obtained E of the washout, and they cut out before reaching the Burtreeford Disturbance.

    The ore from Esp's was worked by the Weardale Lead Co. from Sipton Mine (disused). The ore was transported by battery loco haulage along Blackett Level, and raised at Sipton Shaft [NY 8468 4987] where the last hydraulic hoisting engine in the Pennines operated up to the time of closing of the mine in 1946. The ore was treated in a conventional gravity mill with ore from St Peter's Vein, described below. Recorded production of lead concentrates from the two veins 1923–1938, was 21 765 tons, to which an estimated 11 000 tons is added for 1939–1945. In 1982 approximately 15 000 tons of tailings with an estimated calcium fluoride content of at least 25 per cent remained but these had been removed by 1988 save for a few thousand tons of fines, probably from previous treatment.

    Smith's Vein—Lead ore

    NY85SW; Northumberland 107 NE (Old Series) Direction N50°E, throw 2–3 ft (0.6–0.9 m) NW

    This vein was cut in Blackett Level 875 ft (267 m) S of Esp's Vein, where in the shales and sandstones below the Nattrass Gill Hazle it consists of two main leaders, 50.5 ft (1.7 m) apart, both carrying sphalerite and quartz. From a rise put up to the Great Limestone in 1936–37, small flats at the High Flat horizon were found. Development proceeded 350 ft (107 m) SW and 150 ft (46 m) NE of the line of Blackett Level, but work was suspended owing to ventilation difficulties. The flats are 2–2 ft (0.6–0.76 m) thick, with coarse galena, fluorite, siderite and quartz; the maximum width worked was about 10 ft (3 m). At the NE end of the workings, the vein is split into two parts, the flats following the southern branch. It was anticipated that the outcrop of the Great Limestone against the boulder clay in the old valley would terminate the workings southwestwards, but the vein may exist W of the wash.

    Sipton or Four Fathom Vein—Lead ore

    NY84NW, NE; Northumberland 107 SE (Old Series). Direction N75°W, throw in Blackett Level approximately 50 ft (15 m) NE

    The vein was cut in Blackett Level 130 ft (40 m) N of Sipton Shaft. It is here in two parts, the southern part 2 0.5 ft (0.76 m) wide of sandy fluorite, sandstone and shale gouge, separated by 40 ft (12 m) of barren ground from the northern part which is 5 ft (1.5 m) wide, chiefly gouge, hading S. The fault may be followed at surface on the east side of the valley, where it produced a considerable shift in the feature of a sandstone mapped as the Grindstone Sill on the primary 6-inch maps on the W slope of Tedham Moss. The fault continues eastward into the Derwent headwaters.

    Exploration was done from Sipton Shaft (disused) [NY 8468 4987] in 1859–63 when a crosscut driven S5°E at a depth of 176 ft (53.6 m) from surface, in shale above the Four Fathom Limestone, cut at 103 ft (31.4 m) from the shaft a vein trending N70°E, 2–5 in (5–13 cm) wide, containing fluorite, quartz, calcite, pyrite and spots of galena. A small parallel vein had been noted during the sinking of the shaft. A rise was put up to the Quarry Hazle, but the vein proved to be not more than 10 in (0.25 m) wide, with fluorite and spots of galena. A drift along the vein at 180 ft (55 m) NE from the crosscut converged upon the first part of the Sipton Vein, the Quarry Hazle appearing on the N side. At 308 ft (94 m) the second part of the Sipton Vein was cut, and the drift was turned on this vein. At first the shale above the Quarry Hazle formed the N wall, but as the drift proceeded eastward higher beds appeared, the base of the Great Limestone being reached at about 300 ft (91 m) from the turn. In this stretch many strings in different directions, some carrying fluorite and galena, were found and in places a well-defined fault, filled with gouge. The drift was continued to 440 ft (134m) from the turn in a direction S75°E and a rise, known as 'Hunter Shields', was made to the upper part of the Great Limestone, indicating that much of the N downthrow attributed to Sipton Vein in the Great Limestone was due to a monoclinal fold. The rise was carried up on a cross vein throwing 1.5 ft (0.45 m) W, which was 2 0.5 ft (0.76 m) wide, of spar with spots of galena at the rise top 85 ft (26 m) above the drift. From the rise top a drift at 947 ft (289 m) OD was carried S in the cross vein, with the intention of cutting the main fracture of Sipton Vein. As, however, the place of this had been taken by a fold, it was never found, but the drift starting at the Black Bed, came into lower and lower horizons in the limestone, cut by many small strings, some of them mineralised. At 44 ft (13 m) from the rise top a branch drift, driven for 495 ft (151 m) S50°E, cut a mass of strings, some containing galena and fluorite, trending between N–S and NE–SW. Some signs of flats were noted but nothing worth extracting was found, and exploration was abandoned in 1867 owing to bad ventilation conditions. Shortly before the Weardale Lead Co. took over Sipton Mine in 1923, the old crosscut and drift were opened as far as the bottom of Hunter Shields' rise and a branch drift was driven into the N side of the Sipton Vein, N of the rise. Again the work was hampered by lack of ventilation, and it was not resumed by the Weardale Co.

    E of Sipton Mine, Siptonhead Level (disused) [NY 8515 4997] driven on the N side of Sipton Vein in 1788–1807 starts at the W end of Sipton Cleugh and runs S80°E in the shale on top of the Firestone, i.e. about 205 ft (62 m) above the Great Limestone. At 144 ft (44 m) from the level mouth there is a crosscut driven to test a fault, throwing 6 ft (1.8 m) N, seen near the mouth, the direction of which proved to be N65°E. A sump of 36 ft (11 m) at the end of the crosscut, into the Firestone, proved a few pieces of galena in the vein, but a great quantity of water, probably from the adjacent stream, prevented further work. At 378 ft (115 m) from the main level mouth a poor string, not thought worthy of further trial, was cut. Another was seen at 522 ft (159 m), a rise being put up on it to the first sandstone above the level, probably one of the Knucton Shell Beds. No ore was found and no better results were obtained in a flank level driven along the string for 140 ft (43 m). At 1302 ft (397 m) from the portal three small strings cross the level and a rise was put up into sandstone without finding ore. At 1602 ft (488 m) a string was cut containing small pieces of ore; the contemporary report, by W Crawhall, states "for 15 fathoms or upwards from here, every joint in the sill had small particles of ore in them, similar to sludge ore ... being dashed against a wall". The mineralised belt starting at 1602 ft (488 m) is supposed to represent a vein found in 1744 on the fellside to the NE, from which about 2 cwts of galena were obtained. The level was continued to 1980 ft (604 m) from the portal without cutting further veins or strings. It does indicate, however, that there are at least two NE veins, slightly mineralised even in the unfavourable beds tried from Siptonhead Level, north of the Sipton Vein. Since these would probably converge upon Sip-ton Vein ahead of the existing exploration drifts on that vein, a further trial of this ground in the Great Limestone appears to be justified.

    Before Sipton mine closed a short drift had been driven WSW on the Sipton Vein from Blackett Level, at and above the horizon of the Five Yard Limestone. Small quantities of galena were found, but no payable orebody has yet been discovered on this vein. However, in view of the importance of veins in this direction as fluorspar producers it may well merit prospecting further afield in the future. Sipton Vein could represent the continuation for example, of the White Vein of Hunstanworth (p.223) if its average course remains S73°E; but it must be noted that on the revision of Sheet 19, Carruthers adopted a more easterly course, towards Halleywell.

    St Peter's Vein—Lead ore

    Northumberland 107 SE (Old Series). Direction N65°E, with a short stretch at N85°E, throw 2–5 ft (0.6–1.5 m) NW at SW end of workings, increasing to 28–30 ft (8.5–9 m) NW 1500 (457 m) NE of St Peter's Shaft; decreasing farther NE

    This vein, worked until 1946 at St Peter's Mine (disused) by the Weardale Lead Co., was discovered in Blackett Level, 3950 ft (1.2 km) S of Sipton Shaft, and was the southernmost vein discovered by the level, the forehead of which lies only 300 ft (91 m) farther S. It was first developed, during the last years of the Beaumont Co. by means of a flank level from Blackett Level running SE through the vein and the S-facing monocline which accompanies it, and turning E. At 460 ft (140 m) E of Blackett Level the flank level communicates by a 100 ft (30 m) rise with the 54-Fathom Level of the mine at 812 ft (247 m) above OD. From the foot of this rise a crosscut to test the vein in the Three Yard Limestone, found fluorite, but without payable lead values. Similar conditions were found in a trial from the 54-fathom level at the horizon of the Four Fathom Limestone. The ore-bearing ground on St Peter's Vein was proved to be confined to the Great Limestone. To make possible the working of this ground, a shaft [NY 8515 4876] was sunk from the side of the Allendale Town–Allenheads road, 1000 ft (305 m) SSE of Spartylea. The shaft is vertical and is 318 ft (97 m) deep to the 54-Fathom level. Ore from the mine was tipped into a bin at the shaft head, whence it was conveyed by motor truck to Sipton Mill for treatment.

    At 540 and 680 ft (165 and 207 m) SW of St Peter's Shaft, the top and bottom respectively of the Great Limestone are in contact with boulder clay filling the old Allen valley, thereby terminating the oreshoots on St Peter's Vein; it is probable that the limestone has been eroded on the course of the vein for at least 3500 ft (1067 m) SW, beneath the side valley of Swinhope Burn. It is brought in again by the Burtreeford Fault, and the Swinhope or Williams Vein may represent the SW continuation of St Peter's Vein in it.

    The total length of the ore-bearing ground proved on St Peter's Vein in the Great Limestone amounts to 3400 ft (1036 m). Both vein-oreshoots and flats are present. The flats occur at the High Flat horizon, the stratigraphy of the upper part of the limestone being as follows: limestone with shale beds, 17 ft (5.2 m); Limestone in posts of: 1 ft 5 in (0.43 m); 1 ft (0.3 m); 9 in (0.23 m); 1 ft 8 in (0.51 m); and the High Flat posts, 1 ft 6 in (0.46 m) and 7 in (18 cm). The replacements occur in the high flat posts, but may extend up into the "Twenty-inch" bed overlying it. There is a very pronounced smooth bedding plane at the base of the overlying "Nine-inch" post, with traces of shales; this forms the roof of most of the workings. This excellent and persistent datum was used to construct the accompanying structure-contour plan (Figure 27) of St Peter's Mine, the levelling being the work of Mr J A Hill, which shows the relation between the steep monocline and the vein. The monocline lies S of the vein in the vicinity of the shaft, and together with the vein, produces an elongate domal structure enclosing substantial flats. Two flats cut through the monocline and diverge from the vein to the SW following minor strings. To the NE, the monocline converges upon the vein, and apparently dies out where the throw of the vein to the N increases, and a belt of small faults appears on the NW side of the vein. These are accompanied by substantial flats, some of which have yielded crude ore containing as much as 25 per cent lead sulphide. The throw of the small faults is generally to the NW, but both their throw and that of the main vein gradually diminish, until only a few inches of displacement, apparently unaccompanied by folding, remain in the vicinity of the NE foreheads. Here, too, the mineralisation died out. It should, nevertheless, be noted that near Harwood Shield in the Devil's Water there is a SE-facing monocline associated with a vein containing fluorite in the Firestone, which lies on or near the line of St Peter's Vein, approximately 3.5 miles (5.6 km) ahead of the St Peter's foreheads. It can hardly be said therefore that the possibilities of the St Peter's structure are yet exhausted, though the immediate ore-reserves have been extracted.

    The minerals of St Peter's Vein and flats included coarse galena, small quantities of sphalerite and pyrite, in a gangue of green or purple fluorite, with quartz, ankerite, siderite and calcite. All these minerals entered into replacement relationships with the limestone.

    The oreshoots were worked from a series of sublevels which, owing to the general dip of the measures, were at successively lower horizons towards the NE. Internal hoisting of the ore did not, however, prove necessary, owing to the 54 fathom level, which even at the NE end of the mine is still 60 ft (18 m) below the flats.

    From St Peter's Mine crosscuts have been driven 1100 ft (335 m) NNW and 2475 ft (754 m) SSE in the Great Limestone. The former proved a gentle anticline 350 ft (107 m) wide N of the vein, with small mineralised fissures on both flanks; the latter cut a small vein, with feebly mineralised flats 460 ft (140 m) S of the main vein, but not as was expected the two small veins found in an old hush at the head of Ellershope.

    Swinhope North Vein and Williams(Swinhope Vein)

    Williams Vein is the continuation, in the Swinhope side valley of East Allendale, of the Barneycraig Vein of the West Allen Area and as noted above perhaps of St Peter's Vein beyond the Burtreeford Disturbance. The vein was worked from Swinhope Mine (disused), the main entrance to which is a horse level [NY 8315 4712] starting at about 1262 ft (385 m) above OD from the S bank of Swinhope Burn. This reaches the vein with the Little Limestone on the foot-wall at 425 ft (130 m) from the portal, and follows it SW. The coal above the High Coal Sill is passed through at 1070 ft (326 m) that above the Low Coal Sill at 1570 ft (479 m), and the top of the Great Limestone is reached at 2020 ft (616 m) from the portal. Throughout this stretch, and up to 2820 ft (860 m) from the portal, the vein was barren. For the remainder of the distance, 4500 ft (1372 m) to the West Allen boundary, the vein was productive in the Great Limestone, where it varied from 1 to 5 ft (0.45 to 1.5 m) wide, and also carried small oreshoots in the Coal Sills sandstones, the Little Limestone and the Pattinson Sill. At the High Flat horizon of the Great Limestone there were small flats on both sides of the vein. The contemporary reports repeatedly refer to the abundant "black jack" (sphalerite) present in the vein and flats; galena, pyrite, quartz, siderite and limonite were also present, but fluorite was rare or absent. The mineral assemblage did not, therefore, resemble that in St Peter's Vein.

    Prior to the driving of the horse level, the ore from Williams Vein was won from a whimsey shaft [NY 8250 4637] at Swinhopehead which was later reached by the level 3320 ft (1012 m) SW of the portal. Crosscuts at Swinhopehead proved North Vein, at about 200 ft (61 m) NW of Williams Vein. North Vein was reported to have been 2–5 ft (0.6–1.5 m) wide, with flats at the High Flat horizon, strongly mineralised with sphalerite, but poor in galena. The workings were abandoned as unpayable. It was presumed that both on Williams Vein and North Vein some reserves of zinc ore remained, as neither of these veins had been reworked for sphalerite. There is no separate record of production from this mine under the Beaumonts or the Vielle Montagne Zinc Co. and there is very little evidence of ore-dressing around the site. It is possible that ore from Williams Vein and the flats was transported though the underground connection to Barneycraig, to be treated at Coalcleugh dressing floors. The limited stoping on North Vein was probably the work of the Vielle Montagne Co., since this vein is only of interest for its zinc value. Smith (1923, p.64) remarks that that company kept a few men in the mine, but it had not become a major producer before zinc production from Carshield was brought to an end.

    From Swinhope horse level exploratory crosscuts were driven 1200 ft (366 m) NW and 1080 ft (329 m) SE at 5000 ft (1524 m) from the level mouth. Neither found workable veins. The SE drive, which is in the Quarry Hazle, was in a position to command a large area of virgin Great Limestone between the Barneycraig East and Swinhope workings, the Coalcleugh East Cross Vein and the Burtreeford Disturbance, an area that could be regarded as one of the most important areas remaining in the field (Dunham, 1944). The only exploration done within it consisted (in addition to the crosscut mentioned above) of the Deepcleugh Level [approx 8226 4625] driven 1650 ft (503 m) SE from Swinhope valley in the shale beneath the Firestone, Doctor's Hush, which covers the ground from Killhope Law to the Coalcleugh- Allenheads road (which is said to have uncovered a strong vein 1600 ft (488 m) S of the road) and a short level [NY 8345 4555] running SW on top of the Firestone at the head of the Middlehope Valley. The last three trials were at horizons too high to yield decisive results; the crosscut from the horse level was not advanced far enough to reach promising ground.

    The mine was reopened in 1951–52 by Mr Amos Treloar Jr on behalf of the zinc oxide manufacturers Durham Chemicals Ltd. Track was installed in the horse level, and 4540 tons of development ore from North and Williams veins were shipped to Birtley for treatment in a small flotation plant. The yield is stated to have been 4 per cent Pb and 8 per cent Zn, but transport of untreated ore over this long distance proved uneconomic.

    In 1955 New Consolidated Gold Fields Ltd. took over the mine with the object of prospecting the large area of virgin Great Limestone lying between Barneycraig-Williams Vein, the Killhope Vein complex and Allenheads Mine. Four fully cored boreholes were drilled to establish the exact position of the Great Limestone in the project area (sites are given on (Figure 22). The stratigraphical results of the borings have been published (Dunham and Johnson, 1962). Subsequent consideration suggests that the highest marine band in No. 1 borehole (and not the second) is the equivalent of the Crag Limestone.

    The horse level being too narrow for modern mine cars, a new access to the mine was made in the form of a 32° incline from Swinhope Head [NY 8249 4651] holing into the crosscut from the horse level to North Vein at 245 ft (74.7 m) having passed through the following succession: peat and head 5 ft (1.5 m); sandy shale 15 ft (4.6 m); black shale 11.5 ft (3.5 m); Little Limestone 9 ft (2.7 m); sandstone and shale, 5 ft, (1.5 m); shale 10.5 ft, (3.2 m); coal 0.66 ft, (0.2 m); High Coal Sill sandstone, 4 ft (1.2 m); shale, 17 ft, (5.2 m); coal 0.5 ft; (0.15 m); Low Coal Sill 4 ft, (1.2 m); limy shale 11 ft, (3.4 m); Great Limestone to 35 ft, (10.7 m) with a mineralised flat related to North Vein 17 ft; (5.2 m) below the top of the limestone.

    From the S side of the horse level, opposite the north crosscut, an exploratory drive holding the base of the Great Limestone approximately on strike as far as possible near the roof of the drive, much of which was therefore in Tuft sandstone, was driven a total distance of 7523 ft (2.293 km). Its direction swings round from S18°E eventually to S37°E see (Figure 22). Veins trending ENE were intersected at the following distances from the point of origin: No. 1, 120 ft (37 m); this proved to be a branch vein leaving Williams Vein 410 ft (125 m) to the E; No. 2, 390 ft (119 m); the 6040 Vein 6037 ft (1.840 km); the 6300 Vein 6299 ft (1.920 km) and the 7330 Vein 7329 ft (2.234 km). NNW-trending cross fractures cut at 4304 ft (1.312 km) and 4825 ft (1.471 km) released considerable quantities of water but were unmineralised. The disappointing feature of this effort at exploration in the traditional manner in the orefield, by a long drive commanding the Great Limestone was the absence of veins between those closely associated with Williams Vein and the group nearly 2 km farther S which, as (Figure 22) shows, must be regarded as the equivalents of the Killhope complex. Evidently no major vein-system lies beneath the Weardale/Nent–West Allen/East Allen watershead.

    Systematic channel sampling of the four northern veins may be summarised thus:-

    These figures are obtained from averaging channel samples taken at 6 ft (1.8 m) intervals over the lengths stated, and an arbitrary figure of 36 ft (10.9 m) is taken as the effective height of mineralisation in the limestone. In practice, however, it is clear that the veins are mainly the result of replacement of the limestone related to near-vertical fracturing, but also affected by favourable levels such as the High Flat. The tonnage derived from these figures should be regarded as probable rather than proved, and it must be made clear that the total of about 23 000 tons greatly underestimates the tonnage of mineralised ground because the width is much greater than the sampling of these relatively high-grade streaks indicates. An attempt on Williams Vein at 1560 ft (475 m) W of the point of origin of the South Crosscut to assess the real position by means of three oblique upward diamond borings gave results that could be interpreted as showing, over a mineralised height of 47 ft (14.3 m), an extractable width of 13.5 ft (4.1 m) carrying 0.76 per cent Pb, 5.23 Zn (yielding 65 tons per foot) or over a width of 39 ft (11.9 m) 0.41 per cent Pb and 2.36 Zn (185 tons per foot). Williams Vein was worked for lead by the Beaumont miners between 1815 and 1872, producing 23 829 tons of lead concentrates. While it is probable that the Vieille Montagne Zinc Co. looked over this area, their reworking for zinc did not extend from Barneycraig Mine into it. Thus from the Barneycraig/Swinhope boundary eastward to the point where No. 1 Vein joins Williams Vein is 4100 ft (1.25 km) which could contain, on the lower grade basis, 4100 ft (1.25 km) x 185 = 758 500 tons of rock potentially containing 32 500 tons 55 per cent zinc concentrate and 4000 tons 75 per cent lead concentrate. E of this the Williams orebody passes below drainage level and has been tested by only two winzes that were not pumped out during 1955–59; so over 5000 ft (1.5 km) remain before the Burtreeford Disturbance is encountered. Thes figures are given merely to indicate that potential remains for large-scale, low grade extraction but they must be regarded as in no higher category than speculative reserves. It must also be made clear that ground of this kind is difficult to estimate accurately. It would be more attractive had it not been previously "high-graded" for lead, but this objection probably does not apply to the eastern extension below drainage level.

    The minerals in the Williams group of veins comprise, in probable order of abundance, ankerite, quartz, sphalerite, siderite, galena, pyrite and calcite. These same minerals reappear in the southern group of veins, but with the addition of fluorite, though not in major quantity. These southern deposits are again very wide in the limestone; the 6040 Vein proved to be accompanied by a width of 52 ft (15.8 m) of mineralised ground at the High Flat horizon, while the corresponding width on the 6300 Vein was 40 ft (12.2 m). Unfortunately, however, the metal values in the limited ground exposed are very poor. The two best samples on 6040 gave 0.5 Pb, 6.2 Zn; and 0.7 Pb, 1.5 Zn. Bearing ground seen in the High Flat gave 6.6 Pb, 2.6 Zn. The 6040 showed a strong and persistent fracture throughout the 380 ft (115.8 m) of developed ground, and the 6300 throwing 12 ft (3.7 m) N, appeared more persistent still. Surprisingly, in view of the fact that these veins were intersected at least 500 ft (152 m) below surface, the minerals are extensively oxidised and particularly in the case of zinc this may well have led to loss of values. The northern group of veins, though much nearer to the surface, are almost free from oxidation. When the 6040 Vein was first cut, a very strong flow of water issued from it, and the 6300 was also heavily watered, the flow from these veins continuing for over two months. A reservoir of groundwater at some higher level had evidently been tapped and it is possible that the exceptionally deep oxidation zone was connected with this.

    The last vein, the 7330, was cut in shale below the Tuft and followed up into the Great Limestone where a single rise showed disseminated sphalerite in the limestone, but with only a little galena. Oxidation was again apparent. At 7408 ft (2.258 km) the top of the Iron Post Limestone rises into the crosscut and at the ultimate forehead at 7531 ft (2.295 km) it stands 3 ft (0.9 m) above the sole. As (Figure 22) shows, the possible continuation of the Killhope veins has probably been covered, and equally the lines of Allenheads Old, Diana and associated veins have been crossed with no corresponding discovery. The New Consolidated Gold Fields project was therefore abandoned in 1960.

    In 1960 the possibility arose of a joint venture between The Owners of Settlingstones Mine Ltd, and the Weardale Lead Co. Ltd to extract the proved higher grade ore for milling, and to continue development if the result was encouraging. In the event, arrangements were made for ore to be treated at the small flotation plant of Mineral Recovery Ltd, which was completing its work of recovering the zinc from Barneycraig jig tailings at Carrshield. Some 2400 tons were treated, the indicated head grades (allowing for 80 per cent recovery of sulphides) were 6.1 Pb, 5.0 Zn. A test shipment of 129 tons of ore milled in the efficient gravity plant at Settlingstones contained 11.1 Pb, 5.4 Zn, but it became evident that small-scale operation at Swinhope could not be made profitable, and the mine closed in 1960. Since then the Gold Fields incline has been closed and the site has been used by British Steel Corporation for dumping waste from the reopening of Allenheads Mine.

    On the north side of Swinhope, the Struther Sike Level [NY 8259 4675] was driven during 1825–1829 and extended during 1874–1878 in the hope of finding Low Coalcleugh Vein. The level, which was below and in the Pattinson Sill, cut several strings but no strong vein was found.

    Vein Mean width Ft Mean width(m) Length Ft Length(m) Horizon Pb Zn tons Indicated
    North 4.75 (1.4) 580 (176.8) Low in Great Lst 0.4 8.6 8265
    Williams 3.14 (1.0) 380 (115.8) Wide at Low Flat 4.5 5.14 3588
    No. 1 3.66 (1.1) 560 (170.7) Low in Great Lst 10.1 8.8 5980
    No. 2 2.95 (0.9) 570 (173.7) Great Lst near 6.95 6.77 5052

    Allenheads Old Vein–Victoria Vein group

    The group of veins listed above occurs at the head of the East Allen valley, or under the adjacent Rookhope valley; all were worked from Allenheads Mine (disused) [NY 860 454] the most productive single lead mine of the orefield. The general relations of the veins have been figured by Smith (1923, pl. 12). The Old Vein follows a more or less E–W course through Allenheads Village, where the main Gin Hill shafts are situated [NY 8602 4534]. Mills and Bretton veins are NE flyers from the N side of Old Vein; Diana Vein is a southern loop which, east of East End Shaft [NY 8654 4526] unites with Old Vein to form Wentworth Vein. There are several unnamed flyers associated with these veins. In the vicinity of the Northumberland–Durham boundary, a series of NE veins, including Coronation, Grindstone, Henry's and Henrietta, converge upon the E–W vein system, which is also traversed by three cross veins. As elsewhere, there are cases of the apparent displacement of NE veins by cross veins, and also cases of the displacement of cross veins by NE veins. At the western end of the workings on Old Vein the Burtreeford Disturbance was encountered; the Top Level at 1270 ft (387 m) was driven through it, with cross cuts N and S, but the continuation of Old Vein was not found. Middlehopehead [NY 8345 4555] and Deepcleugh levels [NY 8226 4625] (mentioned above pp.165 and 166) were driven to find the continuation of the vein, but they, too, were unsuccessful. As all of these trials were in beds considerably above the Great Limestone, the problem of the continuation of this vein cannot be said to have been finally settled, but having regard to the Gold Fields crosscut (p.166), it is most probable that it does in fact terminate against the Burtreeford Disturbance.

    The ore bodies at Allenheads included vein-shoots extending from the Slate Sills down to the Four Fathom Limestone and a great development of flats, particularly at the eastern end of the mine (Figure 15), p.68), where there are numerous vein-intersections. It is noticeable that substantial vein-shoots above the Great Limestone seldom occur where there are flats in that limestone. The minerals in both the veins and flats included galena, purple and green fluorite, quartz, siderite, ankerite and calcite. Only small amounts of sphalerite were found; pyrite was occasionally recorded. In spite of the great extent of the workings, there is no evidence of any considerable variation in the mineral content of the deposits, except near the surface, where the normal oxidation products were present.

    The principal shafts and workings levels on Old Vein are shown in relation to the geology in (Figure 28). The earliest workings [NY 859 453] probably dating back to the sixteenth century, were situated west of Allenheads village where oreshoots were found in the Firestone Sill near the surface. By the end of the eighteenth century, Gin Hill main shaft [NY 8602 4534] had been sunk to the Four Fathom Limestone and the level at that horizon had been driven; the workings westward had already penetrated the Burtreeford Disturbance, while to the E they had been advanced beyond East End Whimsey [NY 8654 4526]. Old Vein (proper) was, therefore, approaching exhaustion before the beginning of last century; the records remaining from last century refer mainly to the flats at the W end which follow diverging strings, to reworking of old ground above the Great Limestone and to trials below that horizon. W of the village, the vein in the Firestone was 6 ft (2 m) wide, and contained abundant fluorite, as the great spread of tailings from hand dressing operations around New Whimsey [NY 8586 4536], Wet Shaft [NY 8573 4538] and Craigshield Whimsey [NY 8569 4532] testifies. Some of these tailings have since been treated for fluorspar at Sipton Mill and elsewhere. In the White Sill the width recorded was only 1–1.5 ft (0.3–0.45 m). In the Little Limestone widths up to 4 ft (1.2 m) were noted, similar widths being recorded from the Great Limestone. In the Quarry Hazle the vein was only 1–2 ft (0.3–0.6 m) wide, filled with spar but containing little ore. In the Four Fathom Limestone a report states that the vein contained rider (altered rock) with spots of galena. Gin Hill shaft was deepened to the footwall position of the Six Fathom Hazle; both in this bed and in the Nattrass Gill Hazle the vein was found to be "strait and ridery, without spar and very little ore". No record remains of the exact distribution of vein-stopes on Old Vein. The most important belt of flats in the western part of the mine occurred on the north side of Old Vein, adjacent to its intersection with Elpha Green Fault (here throwing nearly 60 ft (18 m) W) and with the weak Mills Vein. These were at the High Flat horizon, and were worked from Flat and Coe shafts [NY 8505 4534] and [NY 8515 4523], adjacent to West End Burn. Smaller "runs" of flats followed intersecting strings near Old [NY 8539 4533] and Craigshield Whimseys. The flats are described as having been 3–6 ft (1–1.8 m) high, with 4–6 in (10–15 cms) of galena next to the "band stone", a post which may perhaps correspond with the "Twenty-inch" post at St Peter's Mine (p.164). Small flats were also worked at the Middle Flat horizon near Craigshield and New Whimseys.

    Mills Vein was tried by an adit level [NY 8572 4569] starting in the shale below the Firestone, 1525 ft (465 m) NW of Gin Hill Shaft. At 280 ft (85 m) from the mouth the base of the Firestone comes into the level: the vein is said to contain a little fluorite here. At 430 ft (131 m) driving on the vein ceased, but one branch was driven SSE to Craigshield Shaft, while another continued NW cutting some small strings. There remains untried a length of 1500 ft (457 m) of Mills Vein SW of this level, but workings from Bent and Little Shafts apparently found little in it. Mills Level was reopened by Ferguson, Wild and Company prior to their operations at Stanhopeburn (p.207) but they failed to find workable amounts of fluorspar, (Johnson, personal communication).

    Bretton Vein branches from Old Vein about 400 ft (122 m) W of Craigshield Shaft, and workings on it continue for 2400 ft (732 m) ENE but little is known about them save that in that direction the vein is understood ultimately to split up into strings. A small flat was worked on the S side of the vein, N of Gin Hill Shaft.

    Diana Vein was first discovered in 1792 in the shale beneath the High Coal Sill, but it was not explored in the Great Limestone until 1806 when it proved to be associated with a productive belt of flats. The total length worked amounted to approximately 3000 ft (914 m), there being a gap of some 200 ft (61 m) in the workings SW of Gin Hill Shaft. The vein was 1–2 ft (0.45–0.6 m) wide, and was accompanied by a series of subparallel strings. The flats resembled those elsewhere in the mine, but are stated to have been hard, perhaps due to silicification of the limestone.

    Diana Vein joins Old Vein about 200 ft (61 m) E of Knopley Shaft [NY 8628 4528] but from here to East End Whimsey there are several ENE strings on the S side of Old Vein, some of them associated with flats at the Middle Flat horizon. The eastward prolongation, known as Wentworth Vein continued to be important for the flats associated with it for 800 ft (244 m) E of East End Whimsey. These, however, terminated where a strong string, tested in the Great Limestone for 820 ft (250 m) SW reached the main vein. The succeeding 800 ft (244 m) E appears to have been poor, though wide and sparry; but the intersection with the NE continuation of Coronation Vein brought in another ramifying belt of flats, continuing to the West Cross Vein, which caused an apparent shift of Wentworth Vein, E side S 150 ft (46 m). In the next 1000 ft (305 m) E, the vein is recorded as variable in character, with some fairly good lengths, some very poor; flats, probably related to the intersection with Grindstone Vein, were worked on its S side. The relations between Wentworth Vein, East Cross Vein, Victoria Vein and the large associated flats at the east end of the workings are illustrated on (Figure 15). The only important trial in depth on Wentworth Vein was made from the pump sump below Low Underground Shaft [NY 8682 4529], where in a drift 180 ft (55 m) long in the Four Fathom Limestone the vein was found to be very poor.

    The veins lying south of the main E–W system were discovered and exploited from a series of four important crosscuts–Allercleugh, Plantation, Kearton's and Currey's–all driven in shale above the Great Limestone. Fawside Adit Level, portal: [NY 8603 4546], driven in the shale above the Firestone served as the main outlet for the mine in the last 100 years of its life; from it two underground shafts. Low Shaft on Wentworth Vein, and High Shaft on Henry's Vein, communicated with the principal workings beneath. The adit level continued SE of Henry's Vein beneath the headwaters of the Rookhope valley.

    Coronation Vein was discovered in Allercleugh Crosscut in 1822, 2055 ft (626 m) SSE of Craigshield Shaft, from which this crosscut starts at 1179 ft (360 m) above OD in the shale between the Coal Sills sandstones, reaching the shale above the Great Limestone farther S. In these shales it was 9 in (23 cm) wide, with spots of galena.

    In the Great Limestone it was found to be accompanied on the south side by a rich belt of flats, which in places reached an overall width of 150 ft (46 m), and which was worked for a length of 1400 ft (427 m)–W Crawhall's reports (dated 1824–1840) contain the following description of part of these flats; "This in all probability proved the richest length that was ever opened at Allenheads as a flat grove. I have seen this flat partially excavated several fathoms in length and 6 or 8 fathoms (11 or 15 m) in width, 14 ft (4.3 m) high, the sides and a portion of the roof appearing almost all ore, the High and Middle Flat were all in one, chiefly filled with ore and tumbling limestone, some of which would contain 0.5 cubic yard with a layer of ore on the lower side 3 or 4 in (8 or 10 cm) thick and many solid lumps of pure ore upwards of 1 cwt ... cavities after cavities were broke into, full or ore ..." These flats yielded a total of 7163 tons of lead concentrates between 1824 and 1840, when they were virtually exhausted, having extended 900 ft (274 m) ENE and 500 ft (152 m) WSW of Allercleugh Cross cut. Stoping of the vein was continued E of the flats at intervals for 2300 ft (701 m), the workings ultimately being connected to Kearton's Crosscut. The vein is described as being 6 in–2 ft (0.15–0.6 m) wide in the Great Limestone, containing spar and, in places, workable ore. A trial in the Quarry Hazle showed the vein to be 4–12 in (10–30 cm) wide, "hard grey spar without galena". E of Kearton's Crosscut there is an unworked length of 650 ft (198 m) succeeded by about 500 ft (152 m) of workings leading to the intersection with Wentworth Vein, where extensive flats were developed on the SE side of Coronation Vein, and the S side of Wentworth.

    Allercleugh Crosscut proved two more strings, respectively 220 and 286 ft (67 and 87 m) S of Coronation Vein, throwing 2 ft (0.6 m) N and 1.667 ft (0.5 m) N. The first, called Bell's String, was tested in the Great Limestone by a crosscut from Coronation flats; it yielded about 100 tons of concentrates from 450 ft (137 m) of workings. The second was not tried. At 600 ft (183 m) S of Coronation Vein the Allercleugh Crosscut was connected to surface by means of Plantation Shafts [NY 8580 4456], situated beside the Allenheads–Cowshill road, 3000 ft (914 m) SSW of the village. The crosscut continues 930 ft (283 m) S of the shaft, proving another small vein at 300 ft (91 m). Sumps to the Great Limestone proved the vein to be heavily watered. Plantation Shaft was sunk beneath Allercleugh Crosscut to 19 ft (5.9 m) below the top of the limestone, and a crosscut there driven S33°E reached Captain's Vein at 315 ft (96 m). The vein proved to be "burnt and strong, with occasional knots of ore", but unpayable. Crawhall (mine reports, 1830) remarked: "this place should not be lost sight of when the lead trade improves, being worthy of further pursuit". Nothing further, however, appears to have been done. The crosscut, known as Plantation Crosscut, was continued on a straight course, reaching Henry's Vein at 3830 ft (1.167 km) from Plantation Shaft. The following beds were passed through, the distances being measured from the shaft: top of Great Limestone in Level sole, 1250 ft (381 m); top of Low Coal Sill (1.75 ft (0.53 m) thick) in sole, 2090 ft (637 m); shale (with thin coal which reaches sole at 3230 ft (985 m) to Henry's Vein.

    Grindstone Vein was not found in Plantation Crosscut; the workings on it begin at Kearton's Crosscut–driven from Knopley or Peter's Level (on Old Vein) in a direction S11°E, starting at 1133 ft (345 m) above OD and reaching Henry's Vein, 3000 ft (914 m) from Old Vein, at 1168 ft (356 m) above OD. The horizon of the crosscut is the shale above the Great Limestone; the top of the limestone appeared in the sole of the crosscut from 900 to 1045 ft (274 to 319 m), 1212 to 1285 ft (369 to 392 m) and 2345 to 2750 ft (715 to 838 m) from Old Vein, possibly indicating minor undulations in the strata. The NE turning from Kearton's Crosscut to Grindstone Vein occurs 1690 ft (515 m) S of Old Vein; the vein was tried from numerous sumps into the Great Limestone, but it does not appear to have been continuously stoped; the width varied from 1.5 to 3 ft (0.4 to 0.9 m). In the Low Coal Sill 1–2 ft (0.3–0.6 m) of poor vein was found. The best part of the Grindstone Vein workings lay on either side of West Cross Vein, where there were ramifying flats. At Fawside Level horizon a drift on Grindstone Vein in the shale above the Firestone served as a link between the two branches of the adit, one of which follows Wentworth Vein eastward from Low Underground Shaft, the other turning SE towards High Shaft. A trial in the Firestone and a rise into the Low Slate Sill on the vein seem not be have succeeded. The drift in the shale above the Firestone on Grindstone Vein lies 200 ft (61 m) SE of the corresponding drift in the Great Limestone; the vein evidently has a low hade above the limestone.

    Henry's Vein, destined to be the mainstay of the mine for the last 70 years of its life, was cut prior to 1796 in Fawside Level, about 600 ft (183 m) SE of Grindstone Vein, but it was not thought worth developing until 1825, when a drift above the Great Limestone on West Cross Vein reached it. A trial in the limestone revealed a well-mineralised vein, and immediately steps were taken to sink High Underground Shaft [NY 8244 4449] from Fawside Level, which became the principal means of access to the vein. At Allenheads a total length of 8650 ft (2.637 km) was worked on Henry's Vein. The Allendale workings terminate within 300 ft (91 m) of those from Weardale, where the vein is known as Breconsike Vein (p.180). A discrepancy in the apparent position of the vein between these workings is probably due to a shift caused by the presence in the gap of Burtree Pasture West Cross Vein. The vein closely follows the Northumberland-Durham boundary. Unlike the remainder of the Allenheads veins, the oreshoots on Henry's Vein are large vein-shoots; flats only occur at the NE end of the workings in the vicinity of intersections with the cross veins and with Wentworth Vein, where vein-shoots above the Great Limestone are strikingly absent. The distribution of stoped ground is shown on the accompanying section (Figure 28). The range of strata involved is from the High Slate Sill down to the Three Yard Limestone. There is a suggestion that the oreshoot as a whole pitches gently NE, but it is not certain that the possibilities of the vein in depth beneath the Quarry Hazle Level have been exhausted at the SW end. Where the vein was productive in the High Slate Sill, it reached in places the remarkable width of over 20 ft (6.1 m). In the Firestone it averaged about 8 ft (2.4 m) but reached 12 ft (3.7 m) in places; in the White Sill it varied from 3 to 10 ft (0.9 to 3 m) wide; in the Pattinson Sill it was narrower but more productive. Widths up to 7 ft (2.1 m) were recorded in the Little Limestone, while in the Great Limestone 6–8 ft (1.8–2.4 m) widths were common, though in parts the width was less. Lower beds showed widths as follows: Quarry Hazle, 2–8 ft (0.6–2.4 m); Four Fathom Limestone, 3–5 ft (0.9–1.5 m); Nattrass Gill Hazle, 2–9 ft (0.6–2.7 m); Three Yard Limestone, 3–7 ft (0.9–2.1 m). NE of west Cross Vein, the flats shown in (Figure 15) were mainly at the High Flat horizon, and were worked to a height of 5.5–6 ft (1.7–1.8 m). They terminate in a remarkable way against Victoria Vein and in spite of crosscutting on the E side of this vein 220 ft (67 m) N and 430 ft (131 m) SE of Henry's Vein, the only continuation found was a belt of small leaders in the High Flats, the E forehead of which showed, when it was abandoned in 1852, “8 ft (2.4 m) wide, 5.5 ft (1.7 m) high of rider with several strongish strings in it, together with poor brangles of ore, very slow to work". It is worth noting in connection with this exploration that the water level beneath the Great Limestone was never driven as far E as East Cross Vein. During the exploration of the NE end of the mine, therefore, hand pumping as well as hand hoisting of the ore to Peter's Level (normal in the Allenheads system of working flats from levels driven in the shale above the limestone) would make the work slow and expensive. It must be concluded that this end of the mine has not been adequately explored; nevertheless, it is quite possible that the two converging vein-systems do in fact die out here. It is however, a possibility that the Beldon-Shildon veins of the Derwent area (pp.222–223) represent a prolongation of Henry's Vein. There is an untested gap of 4 miles (6.4 km) NE of the Allenheads foreheads.

    Trials on Henrietta Vein, SE of Henry's Vein, extend over a length of nearly 1500 ft (457 m), but the vein, first cut in a SE crosscut from High Shaft in the shale above the Great Limestone, proved to be only 1.5–3 ft (0.46–0.9 m) wide in the limestone, with poor values. The crosscut was continued more or less beneath Fawside Level, and at 1250 ft (381 m) SE of Henrietta Vein cut Great Vein. This also proved to be poor when explored in the Great Limestone; it varied from 6 in to 4 ft (0.15 to 1.2 m) wide, with spar, altered limestone and poor galena values. It was worked over a length of 600 ft (183 m), but not continuously. A little ore was raised from the Low Coal Sill.

    Fawside Level continues 3380 ft (1.03 km) SE of High Underground Shaft; at 2260 ft (689 m) Corbetmea Shaft [NY 8772 4443] communicates with the surface at the head of Rookhope. Small veins SE of this shaft are described under Frazer's Hush (p.199).

    The Beaumont operations at Allenheads had come to an end before fluorspar became a saleable commodity, but a substantial quantity of fluorite-bearing waste had been brought to surface from shafts such as Craigshield, Old Whimsey and Bent, situated on the Old Vein-system west of Allenheads Village. As already noted, the Weardale Lead Co. treated some material to recover fluorspar during the 1940s, and after their surrender of the East Allendale Lease, more was removed by G Ridley & Co., who are also said to have obtained some production from underground, presumably from the Firestone workings. The main tailings dump from the dressing of 200 years or more of lead mining at Allenheads, lying N of the village and E of the river where it probably forms, in part, a foundation for the Allenheads–Allendale Town road, contains no more than a few per cent of fluorite, and the records of working in the flats which provided the bulk of the production prior to the discovery of Henry's Vein do not suggest that much spar was present in them. As already indicated, a majority of records of the veins in the E–W belt show narrow widths; less than 3 ft (1 m) at virtually every intersection. There is no evidence that any subtantial veinstopes exist in this ground save in the Firestone. In the case of Henry's Vein, which reaches substantial widths from the Great Limestone upwards, it can only be said that if fluorite was a major constituent it must have been left behind, unextracted or as stope fill. This situation was believed to exist on Burtree Pasture Vein in Weardale where it has recently been proved to be so (p.181). At Allenheads it was known that the records show that some of the stopes had been 'quoted with deads' (Dunham, 1952, p.63). The village tailings dump, already mentioned, is estimated to contain, at 17.5 cu ft/ton ( = density 2.75) some 170 000 tons. Where the heap can be reached in the plantation covering it, the contents are largely silicified limestone, with little fluorite. Dressing underground, with waste storage in old workings must have been practiced. No evidence could, however, be obtained that the fill was sufficiently rich in fluorite to merit extraction, without unwatering the mine. On the failings heaps fluorite is abundant only W of the village, and not on the main village dump.

    In 1969–70 the British Steel Corporation began the reopening of the property under the name Beaumont Mine in the hope of establishing a major new source of fluorspar. A boring [NY 8604 4539], Allenheads No. 1, was put down in the mine yard to establish the position of the Whin Sill, and with the collaboration of the Institute of Geological Sciences, this was continued to prove the base of the Carboniferous (Burgess, 1971) see (Figure 3) and (Figure 4).

    The boring passed through what is believed to be the downward extension of Old Vein from 1085 to 1100 ft (331 to 335 m), in and below the Tynebottom Limestone, but only siderite and ankerite were present in the filling. Pumps were installed in one of the Gin Hill shafts to dewater this extensive mine from the Hough Water Level (portal at [NY 8509 4666]) at 1180 ft (360 m) above OD eventually to the Three Yard Limestone position at about 860 ft (262 m) above OD. No attempt was made to use the old levels of the mine which were judged to be too small for modern practice. A new haulage incline portal at [NY 8650 4531] was sunk from a site 150 ft (46 m) NE of the shafts in a direction S73°E, dipping at 14°; when suspended in 1979, this was 3025 ft (922 m) long and having passed through strata from the top of the Firestone to the Three Yard Limestone, stands at 835 ft (255 m) above OD. A small parallel access incline was carried down to the upper beds of the Great Limestone on the footwall side of Old Vein at 1100 ft (335 m) above OD. From here a drive was carried directly towards High Underground Shaft until at about 2600 ft (792 m) it was turned SSW to parallel the hangingwall of Henry's Vein. Three crosscuts into the old stopes in the upper part of the Great Limestone revealed that the fill largely consists of shale here, though with some lumps of fluorite. An incline at 6° starting near High Underground Shaft was carried down to 973 ft (297 m) above OD in a SW direction, entering the Nattrass Gill Hazle; a crosscut through Henry's Vein here is said to have been poor, but this intersection lies beyond the south-western end of the worked oreshoot and did not reached below the large southern mineralised area where vein-widths were greatest. When the mine was closed in 1981, therefore, the area most likely to contain residual ore or backfill with fluorite had not been tested, but three trials on the northern oreshoot on Henry's Vein had proved unsuccessful see (Figure 28).

    From the bottom of the access incline a new level was driven westward cutting Diana Vein, connecting with the Gin Hill shafts and thereafter continuing on the footwall side of the Old Vein to a point 475 ft (145 m) WSW of Craigshield Shaft. Access was gained from this to a series of old flat workings in the High Flat horizon of the Great Limestone, none of which proved to contain any fill, or much evidence of metasomatic mineralisation remaining, save near the incline where greenish purple fluorite crystals and coarse massive galena were still to be seen. The vein-intersections of Diana and Old veins and various leaders are all uniformly narrow and though fluorite is present in them, it is not workable. From the end of this level at 1124 ft (343 m) above OD an incline was carried down at 7° to 975 ft (297 m) above OD reaching the Three Yard Limestone. A branch tested Mills Vein, but both this and Old Vein in the strata below the Great Limestone remained too narrow to be workable. All the evidence thus confirms the narrow widths of the vein in the Old-Diana-Wentworth system already known from the mine records. A crosscut from the main drift towards Collier Shaft [NY 8690 4530] tested the unworked stretch between Old and Wentworth veins, also without success. Thus in spite of its 'quarter-point' direction, it appears that this system, which yielded an important part of Allenheads lead production has no potential as a fluorspar producer save perhaps at the western end where some resources, not reached by recent exploration, may remain in beds above the Great Limestone.

    As it stands in 1983 with the equipment intact, the question may be asked whether this once-great mine can have any future. If it is decided that it merits pumping out again, four possibilities could be considered: (a) to ascertain whether workable low-grade lead ore remains in the pillars between the extensively worked flats; (b) to complete the original objective by exposing the southern oreshoot on Henry's Vein, a task that would require 2200 ft (671 m) of drifting from the SW face of the incline plus some hundreds of metres of rising; (c) Henry's Vein could be tested at lower horizons (for example, the Whin Sill which would be expected to lie approximately 510–745 ft (155–227 m) below the new main drift near High Underground Shaft) by underground borings and if productive could be reached by extending the haulage incline to about 350 ft (107 m) above OD; (d) if extensions either of Henry's Vein or Wentworth Vein could be located by boring from surface E or NE of the present eastern forehead of the mine [NY 8769 4540], access to this ground would require at least 3300 ft (1.005 km) of new driving from the present forehead of the haulage incline, but it would give access to the large virgin area between Allenheads and Hunstanworth. No certain outcome could be guaranteed for any of these projects and each could make substantial demands on risk capital.

    The only remaining proved lead ore is a small block at the SW end of the workings on Henry's Vein between the Hazle and Horse levels, left when the W B Company closed down.

    The total production of lead concentrates from Allenheads mines during the period 1729–1795 was 55 785 tons; from 1800–1896, when the mine closed, it amounted to 200 032 tons (including a very small tonnage of slimes ore from Coalcleugh during 1865–1878. It may be estimated that the production during 1896–99 was 4000 tons; the records for these years are missing. The grand total is thus approximately 260 000 tons. The only separate data available for silver recovery are for 1882–1896 (Smith, 1923, p. 68) when the yield was 5 oz of silver per ton lead. The overall recovery for the Beaumont mines for 1729–1870, to which Allenheads contributed approximately one quarter of the total ore produced, was 2.8 oz per ton lead concentrates (not per ton lead) (Dunham, 1944, p.190). No exact figure is available for recovery of fluorspar from the surface dumps west of the village; a figure of 10 000 tons included here is a nominal one.

    References

    BURGESS, I C. 1971. Synopses of logs of Allenheads No. 1 Borehole ([NY 8604 4539]; OD 406.76 m) and No. 2 Borehole ([NY 8715 4505]; 536.45 m OD). Ann. Rep. Inst. Geol. Sci. for 1970, 33.

    DUNHAM, K C. 1944. The production of galena and associated minerals in the Northern Pennines, with comparative statistics for Great Britain. Trans. Inst. MM. Metall. , Vol. 53, 181–252.

    DUNHAM, K C. 1952. Fluorspar (4th edition). Spec. Rep. Miner. Resour. Mem. Geol. Surv. G.B., Vol. 4. 141pp.

    DUNHAM, K C. and JOHNSON, G A L. 1962. Subsurface data on the Namurian strata of Allenheads, South Northumberland. Proc. Yorkshire Geol. Soc., Vol. 33, 235–254.

    SMITH, S. 1923. Lead & zinc ores of Northumberland and Alston Moor. Spec. Rep. Miner. Resour. Mem. Geol. Suro. G.B., Vol. 25. 110pp.

    Chapter 10 Mineral deposits

    Details, Area 5 Weardale

    The metalliferous area of Weardale extends eastwards front the pass of Killhope for a distance of 21 miles (33.6 km) to Harperley, 3 miles (4.8 km) W of Crook, embracing in addition to the main Wear Valley side valleys both to the N and S, among which those of Sedling, Middlehope, Rookhope, Stanhope and Waskerley to the N, and Wellhope, Burnhope, Ireshope, Swinhope, Westernhope and Bollihope to the S are the most important (Figure 29). From Killhope to Harperley the river falls from 2000 to 350 ft (610 to 107 m) above OD. On the S side of the area the average height of the fells forming the watershed with Teesdale exceeds 2000 ft (610 m) above OD. The main valley, up to Wearhead, is more populated than the areas so far described, but the side valleys are in many cases almost uninhabited. The main road from Crook enters the dale near Harperley and runs, mainly N of the river, to Killhope, continuing through Nenthead to Alston. It is joined by roads from Tow Law and Lanchester at Wolsingham, and crossed by the N–S route from the Derwent country to Teesdale at Stanhope. From Eastgate there is a minor road up the Rookhope valley to Allenheads. Two unconnected railways served the dale. A branch line of BR (goods only) from Bishop Auckland terminates at Eastgate while another which entered the valley by an incline from Waskerley, terminated at Stanhope but has now long been dismantled. Stanhope and Frosterley were centres for an extensive limestone quarrying industry which supplied the blast furnaces of north-eastern England. Higher up the dale mining has given place to sheep farming as the principal occupation.

    In mediaeval times the greater part of the area formed the hunting-forest of the Bishops Palatine of Durham. From then the ownership of the mineral royalities has devolved upon the Church Commissioners. The Blackett-Beaumont family, who held the greater part of the Durham Bishopric royalty in Weardale from 1696 to 1882, developed and exploited a majority of the lead mines though many of them had been discovered prior to 1696. No record of the tonnage produced up to 1729 has been obtained. From 1729 to 1817, the Beaumont Co.'s mines yielded a grand total of 249 138 tons of lead concentrates. After 1817 details for the inividual mines are available and are given below. The London Lead Co. operated mines at Ireshopeburn, Middlehope, Stanhope and in Bollihope. Iron mining is an ancient occupation in the dale, but its systematic development began about 1842 with the Weardale Iron Co. The mining of fluorspar, which began in the closing years of last century, was first developed by the Weardale Iron Co. and by the Weardale Lead Co., who succeeded to the Beaumont Co.'s lead mines in 1883. Very little zinc ore and only minor quantities of barytes have been obtained from the area.

    The lower part of the dale, between Harperley and Frosterley is cut entirely in Namurian strata, with the Millstone Grit facies forming Harperley Banks, where a few small baryte veins have been worked. The Great Limestone first appears in the river bed at Frosterley, where the quarries were from the 13th century, the source of the coral bands worked as Frosterley 'marble' first used in the Nine Altars Chapel of Durham Cathedral. The westward rise of the beds along the main axis of the half-dome of the Alston Block is steeper than the rise of the river bed, and from Frosterley westward to beyond Stanhope, more than 14 miles (22 km) of quarry face have exposed the Great Limestone on the valley sides. The main part of the dale exposes strata from the Scar Limestone of the Brigantian up to high Namurian.

    Since 1948, considerable changes in the fortunes of the mining industry have occurred. The mining of iron ore ceased at the end of the World War II, and the Weardale Iron Company has gone out of existence. On the other hand, fluorspar production has greatly increased in quantity and improved in quality during the past 75 years. The Weardale Lead Co. continued production, being taken over in 1962 by Imperial Chemical Industries Ltd, who in turn sold out to Swiss Aluminium Mining Co. (UK) in 1977. This concern had been prospecting in Bollihope from 1972, and had acquired the former Fluorspar Ltd property at Stanhopeburn, and through Messrs Brown and Maddison, the Cambokeels (Cammock Eals) Mine worked in the early 1950s by Anglo-Austral Mines (a subsidiary of Imperial Smelting Corporation). Through Weardale Lead Co. the newly discovered oreshoot at Redburn Mine, and the reopened Burtree Pasture Mine came into their possession and to centralise and improve treatment, they erected in Broadwood Quarry, Frosterley a flotation mill with capacity to produce 50–100 000 tonnes high-grade fluorspar per year. This came on stream in 1978. Meanwhile in 1952 the United Steels Co. had acquired the Blackdene Mine to supply their need for metallurgical grade fluorspar, and this mine, together with the Groverake and Whiteheaps mines of Blanchland Fluor Mines (Colvilles) Ltd came under the British Steel Corporation upon its formation. The desire for high quality fluorspar for steel-making led to the erection at Blackdene of a flotation mill capable of producing at least 50 000 tonnes of fluorspar briquettes per annum.

    The world recession of the 1980s led to great difficulties both for SAMUK and BSC and the upshot has been that their plants and mines have been acquired by subsisiary companies of Minworth Ltd, a privately owned company, with headquarters in Derbyshire. In 1989 production is continuing at the Frosterley plant which is in full operation.

    Details of the results of prospecting and mine development since 1948 are given under the mine descriptions that follow. There has, however, been another enterprise in Weardale with some bearing on the metalliferous mining situation. This has been the driving of the three aqueduct tunnels connecting the Tyne with the Wear and the Tees as part of the major Kielder development of the Northumbrian Water Authority. The three tunnels have a total length of 20 miles (32 km) in hard rock and cross the half-dome in a general direction from N to S, mainly in Namurian and Brigantian strata. The geological results have been discussed by P Carter and D A C Mills (1976) (site investigations) and T P Davies, P G Carter and D A C Mills (1981) (drivages); engineering properties of the rocks involved were studied in an experimental mine by W H Ward, D J Coats and P Tedd (1977). When driving was complete, but before concreting of the walls of the 3.5 m diameter tunnels the writer was enabled, through the kindness of Babtie, Shaw and Morton, the consulting engineers, and by permission of the Northumbrian Water Authority, to examine the mineralisation exposed on the walls.

    The tunnel system crosses the Derwent drainage (Area 6) and ends in Teesdale (Area 7). The schedule of mineralised structures encountered is however given in (Table 51).

    The Kielder Aqueduct Tunnel System includes three drives, the courses of which are shown on (Figure 29). The northern section, from Letch House to the N side of the Derwent Valley near Edmondbyers passed through Westphalian strata from the Top Busty Coal to the base, and entered high Namurian strata, but though a number of faults were cut, no mineralisation was encountered and this section is not considered further here. The Derwent–Wear tunnel runs for 8.31 miles (13.3 km) from the Derwent Portal [NZ 0405 5073] near Edmondbyers to the North Wear Portal at [NZ 0121 3768], between Stanhope and Frosterley. The sole rises from 608 ft (185 m) above OD to 643 ft (196 m) above OD at Waskerley air shaft [NZ 0296 4439] and falls to 604 ft (184 m) above OD (196 m) above OD at the North Wear Portal. The strata traversed in this tunnel range from a little above the base of the Durham Millstone Grit at the Derwent Portal to the Nattrass Gill Hazle at North Wear; the base of the Great Limestone, calculated from stratigraphical sections and the site investigation boreholes, rises from 150 ft (46 m) below OD to over 760 ft (232 m) at North Wear, the difference representing the amplitude of the transect of the half-dome. The South Wear to Tees Tunnel starts at [NZ 0117 3705] and ends near Eggleston at [NZ 0016 2269], the levels being 558 ft (170 m) above OD, rising to 601 ft (183 m) at Sharnberry Air Shaft [NZ 0098 3074] then falling to 575 ft (175 m) above OD at the Tees portal. In this stretch, 9 miles (14.4 km) long, the calculated base of Great Limestone falls from 770 ft (235 m) above OD at South Wear to 387 ft (118 m) before being swept upward in the Egglestone fault system, only to be dropped down to about 150 ft (46 m) above OD in an anticlinal structure at the S end of the tunnel. Longitudinal sections, both anticipated as a result of site investigations and proved by the drivage are given by Davies, Carter and Mills (1981).

    Of the 26 mineralised intersections, only one (the Swandale Vein) could be regarded as of near-economic grade. It is, of course, true that many of the structures were cut in unfavourable strata but it must nevertheless be regarded as disapponting that White Vein (in Grit Sills sandstone), Red, Slitt and Sharnberry veins (in Great Limestone) made such poor showings, for these are the four major channels of the orefield. It is, however, salutary to recall that only a minor proportion of the length of any such channel carries payable ore. The most completely explored so far is the Red Vein of Rookhope-Stanhope, and no more than 35 per cent of the length of this structure can be regarded as productive, even at the most favourable stratigraphic horizons.

    In (Table 51) distances are measured N and S of the Wear Portals.

    The Whitefield's Vein–Himer's or Hindmarch's Vein group

    The group of veins worked at the old Killhope Mines (disused) geologically form part of the great vein-complex of Nenthead and West Allen see (Figure 22). They lie on the W side of the Coalcleugh West Cross Vein, some of them perhaps representing the continuation of veins from Middlecleugh Mine to the SW. Near the head of Killhope the Great Limestone forms the floor of the valley; here many of the veins were discovered and worked at outcrop. The outcrop of Old Moss Vein (analysis, (Table 52) may still be examined in the banks of the burn [NY 8201 4335]. Of the eleven NE veins, seven have been worked underground, the principal access level being Park Level, the portal of which is situated 3000 ft (914 m) WNW of Gold Hill, on the S side of Killhope Burn at 1518 ft (463 m) above OD [NY 8258 4308]. The remains of the Beaumont Co.'s dressing plant, with a large water wheel, may be seen adjacent to the level mouth. The wheel and mill are now preserved as the Killhope Lead-mining Centre, under the auspices of Durham County Council. Park Level runs 2750 ft (838'm) N75°W from its mouth, starting in the shale beneath the Quarry Hazle immediately west of Coalcleugh West Cross Vein. The base of the Quarry Hazle comes into the level roof at 340 ft (104 m) and into the sole at 660 ft (201 m), the level remaining in sandstone to Vicker's Shaft [NY 8175 4329] which communicates with surface 2710 ft (826 m) from the portal. Near Vicker's Shaft an underground shaft 120 ft (36.6 m) deep gave access to the Nattrass Gill Level in the shale below the Nattrass Gill Hazle, from which Old Moss and Middle Grove veins were worked in the beds beneath the Great Limestone. A branch of Park Level followed Trent Vein northwards to Killhopehead Vein, while a short rise near Vicker's Shaft communicated with the Old Water Level at 1535 ft (468 m) above OD, which follows a sinuous course to Killhopehead Shaft 2600 ft (792 m) W, on the vein of that name.

    The oreshoots on the Killhope veins include small vein-shoots at horizons ranging downwards from the Firestone to the Nattrass Gill Hazle. The width of the opencuts in the Great Limestone, and information from contemporary reports indicates that small flats in the Great Limestone were associated with some of the veins, but no flat workings appear on the existing plansThe plans of the Beaumont and Weardale Lead Co.'s mines in Weardale are preserved in the County Record Office, Aykley Heads. There is also a remarkable collection of agent's reports on the various operations. Gratitude is expressed to the Directors of the Weardale Lead Co. for making possible the systematic extraction of the information contained in these plans and reports, while they were still at that Company's offices at Wearhead and Rookhope.

    The minerals present in the veins, besides galena, include siderite, quartz, pyrite, purple fluorite, ankerite and calcite. Sphalerite is fairly abundant in places; its presence in quantity serves to identify these deposits with those of Nenthead and West Allen rather than with those normal to the Weardale area east of the Burtreeford Disturbance. During the 1950's, zinc concentrates were recovered from the dumps by means of a portable flotation plant.

    Hindmarch's Vein was worked opencast in the Great Limestone SW of Killhope Burn [NY 8250 4309]. Underground it was cut by Park Level 365 ft (1 1 1 m) from the portal; a branch from the level was carried 2000 ft (610 m) SW along the vein in the shale below the Quarry Hazle. Above this there were workings in the Quarry Hazle, and some ore was got in the Great Limestone 1450–1750 ft (442–533 m) of the point where Park Level crosses the vein. Little is known about the vein save that a report dated 1863 states that it had deteriorated from a moderate vein, 1.5–2.5 ft (0.46–0.76m) wide, to a clay joint only 4 in (10 cm) wide in the lower part of the limestone. It does not appear to have been worked since that date.

    Hazely Vein was also worked in a surface hush [NY 8234 4315]. J Graham's rise on this vein, starting 950 ft (290 m) from the portal of Park Level, was carried up 45 ft (13.7 m), but no drifting appears to have been done from it, so that it may be presumed to have been unpayable in the Quarry Hazle. Bell's Vein, also a small vein in the Great Limestone, yielded nothing when tried by a rise 25 ft (7.6 m) up from Park Level at 1180 ft (360 m) from the portal.

    Middle Grove Vein, also worked at surface [NY 8210 4320], was cut by Park Level 1685 ft (514 m) from the portal, in the Quarry Hazle. Branch drifts which were carried along it 460 ft (140 m) NE and 875 ft (267 m) SW yielded some ore from workings in small flats in the Great Limestone. Development from the Nattrass Gill Level at 1403 ft (428 m) above OD revealed two oreshoots, respectively 350 and 520 ft (107 and 158 m) long in the Nattrass Gill Hazle and Four Fathom Limestone, separated by 140 ft (43 m) of barren ground, where a small cross vein called Roddam's String passes through. The Nattrass Gill Level cut Coalcleugh West Cross Vein at 1240 ft (378 m) NE of Park Level; the level passed out of the Nattrass Gill Hazle into the Great Limestone, indicating a displacement of 130–110 ft (39.6–42.7 m). It is doubtful whether Middlegrove Vein was located E of the cross vein, though some drifting to the NW and SE was done.

    Surface workings on Old Moss Vein [NY 8195 4328] were mainly above the Great Limestone; the exposure of the vein in Killhope Burn [NY 8201 4335] is probably at the horizon of the High Flat (Analysis 1, (Table 52)). In Park Level, which cut this vein at 2365 ft (721 m), the vein was 10 in–1 ft 4 in (0.25–0.41 m) wide, very rich in galena in the Quarry Hazle, but attempts to understope at this horizon were disappointing. SW of Park Level the vein in the Great Limestone was so poor as to be barely traceable. From Nattrass Gill Level a drift 800 ft (244 m) NE on Old Moss Vein is reported to have shown the vein 2–3 ft (0.6–0.9 m) wide in the sandstone including 4–6 in (10–15 cm) galena, but only 1 ft (0.3 m) wide in the overlying Four Fathom Limestone. Coalcleugh West Cross Vein was not reached in this drift.

    Tweed Vein in the Quarry Hazle was 9 in–1 ft 6 in (0.23–0.46 m) wide, in places rich in galena; it was worked for a length of 250 ft (76 m) from Park Level. in the Great Limestone a trial showed a considerable strength of altered rock, which was however, very hard and poor in galena. The vein was not considered worth working from the Nattrass Gill Level.

    Levelgrove Vein, 325 ft (99 m) NE of Vicker's Shaft was 4–6 in (10–15 cm) wide with a little galena in the shale below the Tuft. In the Great Limestone old workings were found in 1866–1868, the report stating "the flats here seem to have been wrought to a considerable extent, especially on the north side". This vein was not payable where tested in the Nattrass Gill Hazle.

    Silversides and Burngrove veins do not appear to have been worked during the recorded period of Beaumont operations, i.e. after 1800. Burngrove Shaft [NY 8130 4322] midway between the two veins, was presumably sunk to the old water level: there is abundant veinstuff with limonite, carbonate, fluorite and some galena on the dumps from this and other shafts in the vicinity.

    Trent Cross Vein was cut in Park Level 2560 ft (780 m) from the portal and a branch level from Park Level followed this vein for part of its course, reaching the base of the Great Limestone about 850 ft (260 m) N of the main Park Level. The cross vein is reported in 1868 to have been an open joint in the limestone, with the walls slightly altered to limonite. At 1300 ft (396 m) N of Park main level, the branch level turned away from Trent Vein and continued 550 ft (168 m) NW to reach Killhopehead Vein. This vein was first worked from whimseys near Killhope Burn [NY 8100 4323]. No information remains as to the extent of the stopes in the 1600 ft (488 m) NE of the burn. In the later period of Beaumont operatons, two stopes in the Great Limestone, respectively 640 and 700 ft (195 and 213 m) long, in places reaching the full height of the limestone were worked; the vein varied from 3 to 9 ft (0.9 to 2.7 m). In 1875 one forehead was yielding 5.6 tons of galena per fathom. A little ore was also got from the High Coal Sill. A short distance SW of the intersection with Trent Vein the Killhopehead vein split into two. Under the Weardale Lead Co. both were tried; the southern branch, after 400 ft (122 m) of barren ground had been driven through, yielded a stope in the Great Limestone 480 ft (146 m) long. At 220 ft (67 m) NE of the end of this stope, Coalcleugh West Cross Vein was cut at the horizon of Park Level (here at 1529 ft (142 m) above OD). The fault is reported to have been a clean break 2 ft (0.6 m) wide, filled with gouge, with the Low Coal Sill sandstone on the footwall, and a firm, regularly bedded sandstone, believed to be the Firestone on the hangingwall. A drive of 110 ft (34 m) SSE in the fault cut a NE vein, described as 3 ft (0.9 m) wide, calcite and sandstone, and heavily watered. This was followed for 150 ft (46 m) NE, but ventilation difficulties led to the abandonment of the trial, though spots of galena had been found. Coalcleugh East Cross Vein was not reached. In 1885 an underground shaft 165 ft (50 m) deep was sunk on Killhopehead Vein, starting 240 ft (73 m) SW of the point where the Trent branch of Park Level reaches the vein. A section of the shaft is given in (Figure 12), p.60. The vein proved to be productive in the Quarry Hazle, where it varied from 1.5 to 8 ft (0.46 to 2.4 m) wide, with galena in a fluorite matrix, the yield varying from 2 to 5 tons lead sulphide per fathom. A continuous oreshoot 1420 ft by 30 ft (433 by 9 m) was worked beneath the two Great Limestone oreshoots extracted by the Beaumont Co.: an oreshoot 400 ft (122 m) long underlay the easternmost Great Limestone oreshoot. The vein was also tested by a drift in the upper part of the Nattrass Gill Hazle and Four Fathom Limestone, but here, though its width in places reached 8 ft (2.4 m), it was mineralised with sphalerite, siderite and pyrite, with so little galena that it was not worth workings. In the north-eastern part of Killhopehead Vein there is evidence of old workings in the Firestone. The dumps [NY 8155 4374] show a little baryte with limonite.

    Whitefield's Vein diverges westward from the N side of Killhopehead Vein. It was worked at surface in the Firestone in an opencut [NY 8080 4334] 700 ft (213 m) long, but little veinstuff remains there now. Trials made from crosscuts from High Gin Shaft [NY 8108 4330] 425 ft (130 m) NE of Killhope Burn, and from Killhopehead Cross Vein, the latter in the Great Limestone, were unsuccessful, possibly because the ground had already been worked out. A little ore was recovered from the sole of old workings in the High Flat.

    Reports on Killhopehead Vein make numerous references to the great width of "rider" (probably limonitised limestone) and iron carbonate which accompany the vein. In one place a width of 18 ft (5.5 m) of this material was worked because there were spots of galena in it. Siderite is a major primary constituent of all the Killhope veins. Near the surface this is converted into limonite, which but for its contamination with sulphides, would have been valuable as an iron ore.

    The production of lead concentrates at Killhope by the Beaumont Co., from 1818–1883, amounted to 31 213 tons; the Weardale Lead Co. obtained 9041 tons between 1884 and 1916; total production recorded is thus 40 254 tons for the Killhope Mines. The mines are known, however, to have been active for at least 150 years prior to the period of the records and it is likely that at least 60 000 tons have been mined here. Flotation treatment of 1575 tons of gravel tailings during the late 1950s yielded 180 tons of zinc concentrates.

    The north-eastward continuation of the Killhope veins, beyond the Coalcleugh East Cross Vein remained untested until the driving of the Consolidated Gold Fields crosscut from Swinhope Mine (p.166). Four veins cut in this tunnel between 1.84 and 2.23 km may be considered to represent the Killhope complex, but values in all four were uneconomic in the Great Limestone.

    Snodberry Vein—Iron ore

    NY84SW; Durham 22 NE

    This small NE vein is believed to run on the S side of Snodberry Cleugh, crossing Killhope Burn 1300 ft (396 m) W of Gold Hill. Nothing is known of its history save that Mr J V Peart of Gold Hill obtained some iron ore from a flat in the Great Limestone related to it in 1906–1907; this is stated to be exhausted. Near the main road, 650 ft (198 m) NW of Snodberry Bridge, approximately 3 miles (4.8 km) NW of Wearhead station, in 1940 a deposit of limonite had recently been opened by by Mr Peart [NY 8294 4294]. The deposit crops out between the road and the Burn over a length of at least 60 ft (18 m), but its full width and strike remain to be proved; it has replaced the Great Limestone, probably adjacent to part of the Coalcleugh East Cross Vein, which is here splitting up.

    Analyses of iron ore for Snodberry and Killhope are given in (Table 52).

    Cowhorse Vein—Lead ore

    NY84SW; Durham 22 NW, NE. Direction N85°W–N80°E, throw small, variable.

    Half-a-mile (0.8 km) S of the Killhope Mines, on the W side of Killhope Burn lies the great opencut known as Cowhorse Hush [NY 8222 4224] to [NY 8327 4242], from which lead ore was obtained from Cowhorse Vein in beds ranging from the top of the Great Limestone down to the Four Fathom Limestone. Underground, Cowhorse Mine (disused) was developed by the Beaumont Co. between 1854 and 1876. The principal or Low Level [NY 8344 4215] runs WNW starting from Killhope Burn at 1400 ft (427 m) above OD. It cuts the Coalcleugh East Cross Vein at 435 ft (133 m) and passes from the shale beneath the Six Fathom Hazle to the shale beneath the Nattrass Gill Hazle. At 1525 ft (465 m) it cuts the Coalcleugh West Cross Vein and passes from the Nattrass Gill Hazle into the Three Yard Limestone, reaching Cowhorse Vein at 1800 ft (549 m). The limestone and the beds immediately above it may have yielded some ore as there are numerous short rises from the level after it reaches the vein, but no details of stoping remain. At 1870 ft (570 m) W from the point where the level reaches the vein, a strong cross vein, downthrowing about 70 ft (21 m) SW is cut. The average hade of this so-called Trent Vein is about 50°; in the Great Limestone it splits up into a series of three step-faults. Low Level terminates 220 ft (67 m) W of the Trent Vein, with the base of the Four Fathom Limestone in the roof. From the head of the opencut Top Level [NY 8253 4219] starts at 1590 ft (485 m) above OD, running on top of the Quarry Hazle to reach Trent Vein at 520–560 ft (158–171 m). The Quarry Hazle is unusually thick at Cowhorse Mine, reaching 50 ft (15.2 m). The position of the opencut suggests that it carried ore, but a trial in the 400 ft (122 m) E of Trent Vein was not successful, the vein proving to be "only a cheek". In the Four Fathom Limestone it was 3 ft (0.9 m) wide, mostly altered rock with a little spar, yielding Y2 bing lead sulphide per shift (probably about 1.5 per cent). W of Trent Vein, however, exploration of the Great Limestone from a rise above the Low Level revealed a belt of small leaders diverging from both sides of the vein with which small but productive flats at the High Flat horizon, 48–52 ft (14.6–15.8 m) above the base of the limestone were associated. From the same rise Middle Level was driven at 1530 ft (466 m) above OD in the shale below the Tuft. At 840–870 ft (256–265 m) W of the rise this level cut the strong West Cross Vein, throwing 100 ft (30 m) NE and from a rise following it a level was driven farther west in the lower part of the Great Limestone at 1680 ft (572 m) above OD. The High Flat horizon does not appear to have been tried here; the forehead of the drift in the limestone stands 460 ft (140 m) W of the second cross vein. Cuthbert's Level, [NY 8246 4203] in shale above Great Limestone, provided ventilation E of the cross vein. The displacements of West and Trent veins are lost before reaching the Trent Cross Vein of Killhope presumably by virgation. The minerals present at Cowhorse included fluorite, quartz, carbonates and galena, with limonite near outcrop. The production from 1854 to 1876 amounted to 2474 tons of lead concentrates. The very large hush suggests greater output in past centuries.

    Puddingthorn Vein—Lead ore

    NY84SW; Durham 22 NE

    This small vein pursues an irregular course averaging N35°E heading SE. There is evidence of ancient workings in the Coal Sills sandstones [NY 8396 4269] and a small overgrown opencut in the Great Limestone [NY 8382 4242]. The Beaumont Co. drove a level [NY 8358 4219] starting at 1506 ft (459 m) above OD opposite Cowhorse Level, to test the vein in the Nattrass Gill Hazle, and a little galena in a fluorite matrix was obtained from rise-workings yielding 157 tons of concentrates in 1851–60.

    Wellheads Veins: Bowmans Vein—Lead ore

    NY84SW; Durham 22 NW, NE

    From an ancient opencast, Wellheads Hush [NY 8238 4028]–[NY 8266 4048], high up on the S side of the Wellhope valley (not to be confused with the West Allendale Wellhope) 1.5 miles (2.4 km) SW of Lanehead, lead ore was worked from three converging NE veins near their intersection with the continuation S of Cowhorse West Cross Vein.

    The minerals included galena, sphalerite, amber fluorite, aragonite, calcite, siderite, cerussite and limonite. Bowman's Vein, the easternmost of the group, downthrows at least 50 ft (15 m) NW. Nearer the valley bottom old workings [NY 8335 4125] suggest that some ore was obtained between the Six Fathom and Slaty Hazles. No work has been done on these veins since 1831; the Beaumont accounts record 484 tons of concentrates for the period 1825–31. Kirkstead Level [NY 8201 4065] 2000 ft (610 m) W of Wellheads Hush, was driven 800 ft (244 m) S in the Tuft as a prospect: a small NE vein cut near the forehead was tested up to the Little Limestone, but proved disappointing. Nearer the head of the Wellhope valley, prospecting levels were driven 2200 ft (671 m) N and NW, [NY 8107 4102] and 1525 ft (465 m) S [NY 8099 4098] from the valley bottom beneath the Great Limestone; neither level proved any veins. Still farther west, two NNW faults bounding a horst cross the valley: they probably represent the continuation of some of the Nenthead cross veins, perhaps the Smallcleugh and Great Cross veins. A shaft [NY 8030 4091] sunk in the horst north of the burn by the Weardale Lead Co. late last century reached the Little Limestone, and other steeply dipping beds, but the trial was given up before decisive results had been obtained.

    Guinea Grove Vein—Lead ore

    NY84SW, SE; Durham 22 NE Direction N45°E

    The workings at Guinea Grove Mine (disused) consist of an opencut in the Great Limestone [NY 8470 4265], and two flank adit levels driven on top of the Four Fathom Limestone [NY 8488 4241] and on top of the

    Three Yard Limestone [NY 8473 4220] respectively, from Heathery Cleugh, north of Lanehead. The vein has been proved for a length of about 2500 ft (762 m) but no plan or section of the workings remains; the exact position of the oreshoots is not known. The Beaumont accounts record a production of 3087 tons of lead concentrates between 1818 and 1857, when the mine was abandoned.

    Claypath Vein and Greenfield Vein

  • Claypath Vein—Lead ore NY84SW, SE; Durham 22 NE. Direction N45°E
  • Greenfield Vein—Lead ore NY 84 SW, SE; Durham 22 NE. Direction N80–85°E; throw about 24 ft (7.3 m) S; near Greenfield Bridge gives off Greenfield North String, trending N65°E.

    • Claypath Vein is a small vein worked in the Great Limestone in the headwaters of Heathery Cleugh NE of [NY 8512 4244]. Greenfield Vein and its branch have been worked from the Four Fathom Limestone up to the Little Limestone in superficial workings and shallow shafts which extend 2000 ft (610 m) ENE from Greenfield Bridge [NY 8499 4200], on the Cowshill–Allenheads road; the vein has also been tried in beds ranging down to the Slaty Hazle in a hush WSW of the bridge. The minerals present include coarse purple and amber fluorite, quartz, galena and limonite; the exact position of the stoped ground is not known. At greater depth, an extension of Burtree Pasture Horse Level was driven NW from Greenfield Sump on Breconsike Vein, through the Burtreeford Disturbance, to reach Greenfield Vein; but this trial, at about 1350 ft (411 m) above OD probably in the Six Fathom Hazle, was unsuccessful. The combined production from Claypath and Greenfield veins from 1823–1859 was 695 tons of lead concentrates.

    Burnhope Veins—Lead ore

    NY 83 NW; Durham 22 SW, SE

    In the Burnhope valley, on the W side of the Burtreeford Disturbance, the lowest beds in Weardale are exposed. Two ENE veins have been worked in beds beneath the Tynebottom Limestone. The eastern one crosses Burnhope Burn near the foot of Whae Sike [NY 8339 3863], close to the head of Burnhope Reservoir. During the construction of the reservoir in 1931–33 workings from an adit on the north side of the valley were reopened in order to make certain that water would not be likely to escape through them. The vein, in the shale and sandstone beneath the Jew Limestone proved to be up to 2 ft (0.6 m) wide, containing purple and green fluorite, galena, sphalerite, siderite and limonite. Similar minerals occur on the dumps SW of the burn [NY 8328 3860]. Higher up the valley, 1.5 miles (2.4 km) W of Burnhope Dam, the second vein was worked in Milburn's Hush SW of [NY 8262 3874] in the sandstone between the Tynebottom and Jew limestones. Chalcopyrite is present in addition to galena and sphalerite. All these workings are very ancient; they antedate the period of detailed records of Beaumont operations.

    On the N side of the Burnhope valley, a prospecting level known as Poppet Level [NY 8141 3947] was driven in the shale above the Great Limestone, starting 0.5 mile (0.8 km) NNW of the junction of Sally Grain and Scraith Burn, for a total length of 1825 ft (556 m). Nothing is known of it save that a Beaumont plan shows a WNW vein 100 ft (30 m) from the forehead. Sally Grain Level [NY 8119 3911], starting 1800 ft (549 m) NW of the junction of the streams in the shale beneath the Nattrass Gill Hazle at 1641 ft (500 m) above OD ran NNW and cut a small ENE vein 450 ft (137 m) from the portal. The drive was carried in this for 325 ft (99 m) ENE; a rise near the forehead proved the Nattrass Gill Hazle to be 20 ft (6 m) thick, and entered the Four Fathom Limestone at 1706 ft (520 m) above OD. The vein did not prove to be payable.

    Some prospecting for fluorspar was carried on in the Burnhope Valley in the 1970s by British Steel Corporation, but without finding workable ore.

    Scraith Head Vein—Lead ore

    NY 83 NW, 73 NE; Durham 22 SW, 30 NW. Direction N18–35°E; throw on Yad Moss, about 20 ft (6 m) NW; on White Edge, 24 ft (7.3 m) SE.

    Scraith Head Vein occupies a persistent fault which has been followed from Yad Moss, near the Teesdale–South Tyne watershed, for 3 miles (4.8 km) northwards across the headwaters of Burnhope to Lamb's Head. The reversal of throw is at the head of Scraith Burn. Here it was worked from the ancient Scraith Head Mine (disused) from levels beneath the Firestone [NY 7941 3714] and beneath the Great Limestone [NY 7976 3753]. In the Great Limestone a total length of 2100 ft (640 m) was worked, but although a good plan remains, no scope section was kept. Bottom Level [NY 8021 3786] starts 1900 ft (579 m) NE of the portal of the other level, as a crosscut, through boulder clay and Three Yard Limestone reaching the vein at 800 ft (244 m) NW of its mouth. The vein does not appear to have been very productive at this horizon, except possibly beneath the oreshoot worked at higher levels. The minerals present include purple fluorite, quartz, siderite, calcite and limonite. Production amounted to 7705 tons of lead concentrates from 1818 to 1847. South of Scraith Head Mine, a trial was made on the vein from a crosscut from the London Lead Co.'s Ashgillhead prospecting level (p.239), and still farther south an old level from Crookburn Beck found little in the vein beneath the Four Fathom Limestone. N of Scraith Head, opencast trials at Green Slit [NY 801 390] in the Sally Grain Valley were equally unsuccessful. N of the Bottom Level head, the fault changes to a more northerly direction; a level at [NY 8037 3861] found nothing, and the Poppet Level driven NW from [NY 8141 3947] at 1850 ft (564 m) failed to reach the vein.

    Lodgegill Vein and Scaud Hill Vein

    Lodgegill Vein runs for part of its course along the boundary between Weardale and Teesdale, continuing SW into the latter area as Ashgillhead North Vein. The main or adit level of Lodgegill Mine (disused), [NY 8020 3749] 0.5 mile (0.8 km) E of Scraith Head Mine, under the Great Limestone at about 1920 ft (585 m) above OD, runs 2050 ft (625 m) SE to reach Lodgegill Vein and continues 250 ft (76 m) farther to Scaud Hill Vein. Owing to the southward rise of the beds, the horizon of this level on Lodgegill Vein is probably the Quarry Hazle. The total length of ground worked on Lodgegill Vein is about 2800 ft (853 m); no details of the stopes remain. It is known from records that ore was obtained from the High and Low Coal Sills, here combined as a single bed 33 ft (10 m) thick, and from the Great Limestone, from which the sandstone is separated by 11 ft (3 m) of shale. The vein is recorded as 2–3 ft (0.6–0.9 m) wide in the sandstone and the upper part of the limestone, diminishing downwards. Workings on Lodgegill Vein terminated north-eastwards against a vein running more or less E–W, possibly the continuation of the small Dry Sike Vein, known adjacent to Scraith Head Vein. Scaud Hill Vein, worked for a length of about 1300 ft (396 m), yielded some ore from sumps below the adit level, presumably in the Four Fathom Limestone; one of them is marked 'very rich' on the plan. No systematic exploitation of the Four Fathom Limestone appears, however, to have been done. Lodgegill Mine appears to have been the most productive of the remotely situated mines in the Burnhope headwaters, yielding 11 306 tons of galena between 1846 and 1871, when it closed. The associated minerals were purple fluorite, quartz, aragonite, calcite, siderite and limonite.

    North Langtae Head Vein and South Langtae Head Vein

    North Langtae Head Vein is the continuation of the Ashgillhead Vein of Teesdale (p.238), while South Vein also continues into that area. Langtae Head Mine (disused) is situated at the head of East Langtae Burn, at about 2000 ft (610 m) above OD. It consists of an adit level [NY 8178 3682] driven S under the Great Limestone which reached North Vein at 1100 ft (325 m) and South Vein at 1450 ft (442 m) from the portal. On North Vein the workings shown on the existing plan extend 1200 ft (366 m) W, 700 ft (213 m) E of the level head, but there are the remains of even more extensive old workings from surface shafts [NY 8165 3651] of much earlier date than the adit. Almost directly above the level head, North Vein is exposed at surface [NY 8184 3650], where it contains purple fluorite and quartz cementing sandstone fragments. Farther E, aragonite is abundant on the old shaft heaps, with minor amounts of baryte. A total of 2002 tons of lead concentrates were obtained from Langtae Head Level between 1818 and 1860, but it is likely that much of the ore in these veins was removed prior to that date.

    All the deposits in Weardale west of the Burtree Disturbance have now been described; attention may be turned to the more important area E of the Disturbance.

    Breckonsike Vein—Lead ore, fluorspar

    NY 84 SE; Durham 22 NE. Direction N15–30°E, throw 4–6 ft (1.2–1.8 m) NW.

    N of Cowshill, Breckonsike Vein cuts through, or forms part of the Burtreeford monoclinal disturbance. Within an area lying 500–2500 ft (152–762 m) N of the village, Burtree Pasture, Coptcleugh and Sedling veins converge upon Breckonsike Vein. Here the Great Limestone, exposed at the surface dipping E, has been converted into a deposit of limonite which reaches a maximum width of 700 ft (213 m). Iron ore had been worked here since Elizabethan times (Eggleston, 1882), but the greater part of the deposit was exhausted as the Queensberry Ironstone Workings (disused) [NY 859 413] of the Weardale Iron Co. during the middle years of the last century. These workings are now overgrown. There is no record of galena production from them. The lead-fluorite oreshoot on Breckonsike Vein begins approximately 1 mile (1.6 km) N of Cowshill, where the vein diverges eastward from the Burtreeford monocline. The earliest workings were opencast in beds from the base of the Low Slate Sill to the top of the High Grit. The Lower Felltop Limestone, present beneath the High Grit is converted into ankerite and siderite, in which spherulitic masses of sphalerite occur. There were also old workings from whimsey shafts. Coarse purple and green fluorite are abundant on the heaps, with quartz, carbonates, galena and sphalerite. A sample of fluorspar from the heaps assayed 88.4 per cent calcium fluoride, 5.05 silica (Assay by Mineral Resources Laboratory, Imperial Institute, 1941). Some 280 tons of spar were picked from these heaps by Mr J A Proud in 1929–30, but the inaccessible situation makes transport difficult. The workings of Breckonsike Mine (disused) consist of a level driven NW in the shale above the Firestone from Sedling Burn [NY 8602 4185] which reaches the vein at about 1050 ft (320 m) from the portal and continues a further 1750 ft (533 m) to the NE in the vein. This level was reopened in the 1940s as a trial for fluorspar by Messrs R C Conway. Deeper workings were reached from Burtree Pasture Mine (disused), the Horse Level (portal [NY 8603 4133]) of which reached Breckonsike Vein at 1360 ft (415 m) above OD in the shale below the Tuft, and continued in the vein for 3750 ft (1143 m) NE. The top of the Great Limestone reached the sole of this level 2830 ft (862 m) NE of the point where the level turned on the vein. Workings below Horse Level were drained to 1245 ft (379 m) OD by means of Burtree Pasture Water Level [NY 8573 4075]. No record remains of stoping here. Mine reports dated 1874 state that the vein varied from 5 to 13 ft (1.5 to 4 m) wide, "coarse spar". But when Swiss Aluminium Mining (UK) recently reopened the Great Limestone workings to 1512 ft (461 m) N of the crosscut, only a short length near the northern end showed these widths. From the Horse Level an underground shaft known as Greenfield Sump went down to 1010 ft (308 m) above OD with a connection to the Breckonsike Low Level, at 1100 ft (335 m) above OD. At the sump bottom in the Alternating Beds, the vein is recorded as 5 ft (1.5 m) wide, coarse spar. The lowest trial was from the N extension of Milburn's Level of Burtree Pasture Mine, which cut the vein in the top part of the Whin Sill at 920 ft (280 m) above OD; here it consisted, according to a report dated 1867, of spar threads only. In the Whetstone Bed above, it was, however, 7 ft (2.1 m) wide, with 2 ft (0.6 m) of gouge on the N side, then 2–5 ft (0.6–1.5 m) of spar with galena; then 2 ft (0.6 m) spar. From the horizon of Milburn's Level on this vein, only small stopes are shown on the section; possibly lead values were too low to make the vein payable. The reports consistently refer, however, to substantial widths of spar and it is likely that a considerable reserve of fluorspar remains in this mine, especially below the water level. To investigate this possibility, the Weardale Lead Co. in 1970 drilled three inclined boreholes from the W side of the vein. No. 1 sited at [NY 8563 4213] started at 1748 ft (533 m) above OD and was directed S 65°E at 63° inclination. According to the log by Mr I C Burgess, this began in the Low Grit (or Slate) Sill sandstone, reaching the base of the Great Limestone at 1345 ft (410 m) above OD. At 1298 ft (396 m) above OD a fault, assumed to downthrow W, cut out the beds between the Quarry Hazle and the Three Yard Limestone, the probable displacement being about 105 ft (32 m); the limestone was veined with fluorite and pyrite. A small fault also cut and brecciated the Scar Limestone, with introduction of ankerite and a little galena. The Single Post Limestone, also mineralised with ankerite, fluorite and galena in vugs was cut at 958 ft (292 m) above OD, and the top of the Whin Sill was found 70 ft (21.3 m) below this. The dolerite proved to be patchily altered to white whin, and Breckensike Vein was proved about 8 ft (2.4 m) wide with ankerite, quartz, fluorite and pyrite between altered dolerite walls. Borehole No. 2 was drilled from [NY 8574 4235] at 1778 m (542 ft) above OD. The base of the Great Limestone was cut at 1280 ft (390 m) and the full normal sequence of lower Pendleian and upper Brigantian strata was present here, with the Whin Sill occupying a position similar to that in No. 1 bore, with its top at 808 ft (246 m) above OD. Some 70 ft (21 m) thickness of the dolerite was drilled through and the whole may have ended against the vein, but only calcite and ankerite were found, against little altered dolerite. The test appears to–been indecisive. Hole No. 3 at [NY 8589 4265] from 1883 ft (574 m) above OD, inclined at 62° ESE, showed, according to Mr Burgess, the beds inclined at 45° to the core from the Lower Felltop Limestone down to the Great Limestone at 1313 ft (400 m) above OD, thereafter at 30° (i.e. horizontal). The higher dips in the upper beds may be related to the Burtreeford Disturbance. This borehole finished at 957 ft (292 m) rod length, at about 1059 ft (323 m) above OD in the Slaty Hazle without apparently having penetrated the vein.

    Breckonsike Vein continues into Allenheads Mine as Henry's Vein (p.170). The production of galena from the Weardale workings amounted to 5852 tons between 1836 and 1878, when this part of Burtree Pasture Mine was closed.

    Burtree Pasture Vein—Lead ore, fluorspar

    NY 84 SE; Durham 22 NE, 23, NW 16 SW. Direction N55–65°E, throw near Burtree Pasture Underground Shaft, 34 ft (10.4 m) NW, decreasing SW to 16 ft (4.9 m) and NE beneath Broadmea Slit, to 7 ft (2.1 m) NW.

    Burtree Pasture Vein, the principal vein of Burtree Pasture Mine (disused) has been, to date, Weardale's greatest producer of lead ore, with an estimated total production of at least 175 000 tons of concentrates. Its oreshoots cover a vertical range of strata of more than 1250 ft (381 m) from the base of the Whin Sill up to the sandstone beneath the Upper Felltop Limestone. (Figure 30) shows the distribution of the stopes worked out by the Beaumont Co. during the nineteenth century. It should be noted, however, that there is good reason to believe that substantial areas were stoped at an earlier stage in the SW part of the vein, between Milburn's Level and the Horse Level, but surface evidence strongly suggests that the oreshoots did not extend as high as Broadmea Slit Hush, where no veinstuff is to be seen. Thus there is a progressive NE rise in the top, as well as the bottom of the zone of oreshoots, away from the supposed emanative centre at Sedling. A section of the vein at the Underground Shaft [NY 8603 4180] is shown in (Figure 13), p.61. The width of the vein at the various horizons being worked during the period 1861–1882 is shown in (Table 53), based on averages of T Rumney's mine reports for that period. The width stated for the Great Limestone applies to the NE workings.

    In the south-west, in ancient workings recently reopened (as described below) widths ranged from 1 to 10 ft (0.3 to 3 m), but at the end of the new drift the vein, now in the upper part of the limestone, showed a marked decrease of hade and almost cut out. Small flats, particularly at the High Flat horizon, extended up to 9 ft (2.7 m) from the vein. Purple fluorite, quartz, siderite, ankerite and calcite were the principal gangue minerals among which fluorite was the most abundant. In the upper part of the Whin Sill there was a considerable concentration of quartz in the vein, but lower down in the Whin Drift and the Whin Level, this gave place to fluorite, up to 5 ft (1.5 m) wide, in which galena values were generally poor, but in which some sphalerite occurred. The deepest trial, a sump sunk to the Tynebottom Limestone on the hanging-wall of the vein 120 ft (37 m) E of the Underground Shaft showed the vein to be only a few inches wide. No drifting was done. It is possible that had fluorspar been a saleable product at the time of the deep workings at Burtree Pasture, their extent might have been very different.

    Two cross veins cut through Burtree Pasture Vein. Great Cross Vein, cut in the Horse Level 3500 ft (1066 m) NE of the Underground Shaft, and at Milburn's Level a further 40 ft (12 m) NE shifts Burtree Pasture Vein NE side SE 115 ft (35 m) at Broadmea Slit Level, 75 ft (23 m) at the Horse Level and 50 ft (15 m) at Milburn's Level. At 1110 ft (338 m) NE of Great Cross Vein, Little Cross Vein is cut in the Horse Level. Great Cross Vein throws 18 ft (5.5 m) NE, Little Cross Vein 5 ft (1.5 m). Neither was mineralised.

    The total lateral extent of the ground worked for lead ore on Burtree Pasture Vein amounted to 9600 ft (2.93 km), the stopes terminating about 1 mile (1.6 km) SW of Rookhope Burn. In the vicinity of the outcrop of the vein on the W side of the Rookhope Valley, however, an extensive flat of limonitic iron ore, replacing the Lower Felltop Limestone and presumably related to the vein, was worked by the Weardale Iron Co. at West Groverake opencast [NY 891 436]. The ironstone extended 500 ft on both sides of the vein, the thickness being 3–4 ft (0.9–1.2 m). To the SE, the ore was probably cut out by the unconformable overstep of the Coalcleugh Transgression Beds; to the N it passed into limestone before being overstepped. Underground the ironstone was mined W of the face of the quarry for a length of 600 ft (182 m) along the N side of the vein, the width being 150 ft (46 m), thickness 4.25–5.5 ft (1.3–1.7 m). Access was by way of Gowland's Level [NY 8910 4361] at 1605 ft (489 m) OD which was continued SW to join, by means of a sump, Burtree Pasture Horse Level. It may be noted that the Lower Felltop Limestone was not discovered in the Burtree Pasture lead workings, even where the oreshoots reached the appropriate horizon; it is assumed that it was cut out by unconformity here, as in parts of Rookhope.

    Still farther NE Burtree Pasture Vein converges upon the Red Vein, and is said to have been cut, though not in a productive condition, in Groverake Mine (p.203). It has not been located beyond Red Vein, but it may be remarked that on the same general line 3 miles (4.8 km) NE, the highly productive Ramshaw-Jeffries oreshoots of Hunstanworth commence.

    Burtree Pasture Vein yielded 147 324 tons of lead concentrates between 1818 and 1883, but this figure represents only part of the Beaumont period of operation. Under Weardale Lead Co., the vein yielded 1076 tons before the closing of the mine in 1890.

    In the 1970s Weardale Lead Co. reopened the mine for fluorspar; contractors cleared the underground shaft to Kellot's Level, 343 ft (105 m) below Horse Level but were unable to reach the bottom of the shaft. Garget's Level at 1127 ft (344 m) above OD was tested, showing the vein up to 7 ft (2.1 m) wide, with fluorite on the walls and in pillars, but with much shaly fill in the Nattrass Gill Hazle. The spar was not economically recoverable. After the takeover by Swiss Aluminium Mining (UK) in 1977 an incline was sunk from the Horse Level 500 ft (152 m) and was driven NE to command the Great Limestone. In 900 ft (274 m) of drivage running of old stopes and removal of fluorspar from walls and pillars yielded 47 200 tons of crude spar averaging 45 per cent CaF2 but production ceased on economic grounds in 1981. Ambitious plans were made for the connection of the incline to surface and its continuation to below the Whin Sill. Including dumps the output of fluorspar probably reaches 100 000 tons and a large reserve in fill may exist as well as in virgin vein below Donaldson's Level at 800 ft (244 m) above OD see (Figure 13) and (Figure 30). This major project, which would also provide access to Sedling and other veins in depth, must await economic conditions more favourable than those obtaining in 1985.

    Coptcleugh Vein = Wolfcleugh Old Vein—Lead ore, fluorspar

    NY 84 SE, 94 SW; Durham 22 NE, 23 NW, 16SW. Direction N67°E, throw 19 ft (5.8 m) SE at Wolfcleugh.

    The Horse Level of Burtree Pasture Mine commences on the right bank of Sedling Burn at [NY 8603 4133], in the shale above the Great Limestone. At 300 ft (91 m) from the portal a small vein was discovered which has been worked for a total length of 1200 ft (366 m) in the Great Limestone, by means of sumps. The vein is here called Coptcleugh Vein, but it is very probable that it is the continuation of Wolfcleugh Old Vein of Rookhope, the nearest workings on which lie 1.75 miles (2.8 km) NE. Coptcleugh Vein was reported to be 4–5 ft (1.2–1.5 m) wide in the limestone, composed of spar, hard to drive (mine report, 1870). Small flats were associated with it NE of the Horse Level. The workings, drained by Burtree Pasture Water Level, at 1220 ft (372 m) above OD were reopened by Weardale Lead Co. in 1948, but the vein was found to be unpayable.

    The workings at Wolfcleugh in Rookhope are mostly of ancient date. Some galena in a fluorite matrix, must have been obtained from superficial workings and shallow shafts from the Firestone up to the Slate Sills. Little was done here in the recorded period of Beaumont operations; only 325 tons of galena, obtained between 1818 and 1846, are mentioned. Reopened by the Weardale Lead Co. in 1901, Wolfcleugh Mine (disused) yielded 3400 tons of fluorspar and 1639 tons of lead concentrates up to 1912 when it was abandoned as unpayable. During this period the workings were extended down to the Great Limestone from two shafts on the S bank of Rookhope Burn, 2.25 miles (3.6 km) W of Rookhope village. One of the shafts, the Pumping Shaft, [NY 9019 4324] was carried down to the base of the Nattrass Gill Hazle on the footwall. The vein is nearly vertical in the hard beds, but inclined in the shales (for section see Carruthers 1923, p.9). The mine is drained by the Tailrace Water Level, (portal at [NY 9162 4271]) which also served Groverake (p.199) and Rispey (p.184) mines. The main level, in the Tuft, was however below the water level, at 35 fathoms (1113 ft (339 m) above OD); there was also a sublevel at 1160 ft (354 m) above OD. From these, small stopes extending at intervals over a length of 2240 ft (683 m) SW of the shafts were worked. When the mine was reopened and re-equipped by the Weardale Lead Co. during the 1950s the workings were extended 210 ft (64 m) but the vein was too patchy to be payable. The attraction of driving through to Coptcleugh is the possibility that extensive flats, like those of Boltsburn (p.190) might be found. The vein is said to have averaged 6 ft (1.8 m) wide, mainly fluorite with galena, quartz, siderite and a little marcasite. There was also a small working in the Quarry Hazle from the 43-Fathom level (1066 ft (325 m) above OD). A trial in the Four Fathom Limestone at 999 ft (305 m) above OD was not successful. An attempt to work the vein in the Firestone from a surface level [NY 9000 4317] was also unsuccessful. On the NE side of the burn the vein was worked in ancient times in Thorney Slit, [NY 904 434], but it appears to peter out in this direction. Reserves of galena and fluorspar most probably remain on the unworked portion of this vein between Sedling Burn and Rookhope but improved values would be needed if they are to be worked.

    Wolfcleugh New Veins—Lead ore

    NY93SW; Durham 16SW, 23NW

    Two veins which can hardly be considered to be connected are named Wolfcleugh New Vein. One apparently diverges from the north side of the Old Vein about 660 ft (201 m) SE of the Wolfcleugh shafts in a direction N85°W. It is not recorded on the Weardale Lead Co.'s plans and sections, and it is presumed that it was not found or noticed in the Great Limestone workings. It can, however, be followed readily from a line of superficial workings and shafts, the dumps from which show abundant coarse fluorite. On the NE side of the valley, a second vein, parallel to and 650 ft SE of Old Vein, has been worked from Greenwell's Level (disused) [NY 9069 4304] which starts 1700 ft (578 m) ESE of Wolfcleugh shafts at 1265 ft (386 m) above OD in the Little Limestone. This level reaches the vein 850 ft (259 m) from the portal and follows it for 2200 ft (671 m) NE then diverges southward. The junction of New Vein and Red Vein was not reached. In Hawk Sike, however, NE of Red Vein, a fault, down SE repeats the full thickness of the Low Slate Sill and still farther NE shifts the outcrop of the Upper Felltop Limestone, as proved by ironstone explorations made by the Weardale Iron Co. It is probable that this fault corresponds with one cut in the Beaumont Co.'s Hawk Sike prospecting level [NY 9215 4367] in the shale below the Firestone, at 1835 ft (559 m) NNW of the mouth. The fault has not been prospected at favourable horizons north of Rookhope, but what may well be its continuation in the Hunstanworth district, the Florence Vein (p.227) has been proved to carry fluorite, galena and sphalerite at the horizon of the Felltop Limestone. The only recorded production from the Wolfcleugh New Vein (Greenwell's Level) is for the period 1818–1846, when 325 tons of lead concentrates were produced; in the same period 1152 fathoms (2.1 km) of dead development were done here. It appears, therefore, that in the stretch tried from Greenwell's Level, the vein was poor. Nothing is known, save their position, of the two small veins, Kittle Stirrups Young and Old veins, shown on the Iron Co.'s plan 250 and 125 ft (76 and 38 m) SE of Wolfcleugh New Vein. These small veins were probably found in Tailrace water level or Greenwell's Level, but it is uncertain which.

    Rispey Vein—Iron and lead ore

    NY94SW; Durham 23 NW, NE, 16 SW. Direction N60°E, throw 9 ft (2.7 m) SE

    Although an old lead mine, Rispey Mine (disused) was important mainly as the principal source of iron carbonate ores in the district. The vein was worked from a shaft [NY 9109 4280], 200 ft (61 m) deep on the south side of Rookhope Burn, 1.5 miles (2.4 km) W of Rookhope village, which was sunk to the shale below the Quarry Hazle. Iron ore was got from both the Little and Great limestones, the main level, commanding the latter, extending 1432 ft (436 m) SW and 252 ft (77 m) NE of the shaft. In the Great Limestone the average width of iron ore was 24 ft (7.3 m), of which about 2 ft (0.6 m) was pure white iron carbonate, the remainder "grey iron", probably mainly siderite but containing some ankerite. The reports state that 1 cubic fathom of this material yielded 20 tons of iron ore. An analysis is quoted by Sherlock (1919, p.5). Limonite was found in a cross vein 1098 ft (335 m) SW of the shaft, probably the continuation of Heights Cross Vein, along which oxidising waters had evidently obtained access to the siderite. During its best period the mine yielded 200 tons of mixed white and grey carbonate and 30 tons of white carbonate per week. It is now considered to be exhausted. Production of galena, obtained as a by-product in the ironstone operations, amounted to 407 tons between 1853 and 1857. On the north side of the valley old shafts mark the course of the vein for a mile (1.6 km) to Red Burn. Some of the dumps show a little fluorite. The Rispeysike levels [NY 9163 4285] and [NY 9164 4286] reached the vein in this stretch, in the Coal Sills sandstones. Mill Level [NY 9242 4302] near Rookhope Smelt Mill in the shale above the Great Limestone, also tested Rispey and Red Veins near their junction, but nothing of value was found. Development by the Weardale Lead Co. in the late 1960s (p.204) confirmed that this is in a barren section of Red Vein. The heaps from the shafts along Rispey Vein NE of Red Vein show black shale only.

    Scarsike Veins (Rookhope)—Lead ore

    NY94SW; Durham 23 NW

    At distances of 650 and 1150 ft (198 and 351 m) SE respectively of Rispey Vein the Little Scarsike and Scarsike veins of Rookhope occur. In the adjacent Middlehope valley there is also a vein called Scarsike Vein, but this forms part of the Old Fall-Boltsburn vein-system, and has no connection with the Rookhope Scarsike veins. Tailrace Water-level, portal at [NY 9162 4271] which, drained the Rookhope valley up to Groverake Mine near its head, commences as a drive 1125 ft (343 m) SW on Scarsike Vein, beneath the Little Limestone; it then turns NW and continues as a crosscut via Rispey Engine and Wolfcleugh shafts to Groverake. At its mouth it is at 1195 ft (364 m) above OD; at Wolfcleugh Pumping Shaft, 1215 ft (370 m) above OD; at Groverake Whimsey Shaft, 1234 ft (376 m) above OD. The total length is 9175 ft (2.8 km). At present the level is understood to be partially blocked between Wolfcleugh and Groverake mines.

    Little is known about the Scarsike veins, save that their positions are shown by old shafts with heaps containing purple fluorite, siderite and limonite on the south side of the valley. The Weardale Iron Co.'s records for 1851–53 state that a crosscut was driven to Scarsike Vein from Rispey, but its exact position is not known unless Tailrace Level is meant. Scarsike Vein, tried in the Great Limestone, proved to be 2 ft (0.6 m) wide at the horizon of the Low Flat, "moderately good for lead ore". The Iron Co. also drove a level from surface [NY 9131 4270] on Scarsike Little Vein in the Little Limestone, but without finding much iron ore. Neither of the veins is mentioned in the Beaumont records.

    At 1550 ft (472 m) ENE of Tailrace Level mouth, a level driven south from the bank of Rookhope Burn [NY 9206 4288] at 600 ft (183 m) cut a small vein called Straitlegs Vein, which was tried, presumably without success for a length of 250 ft (76 m). The vein was tested when Redburn incline was sunk on Red Vein (p.204) and found to be 2 ft (0.6 m) wide, with fluorite, siderite and a little galena, in the Great Limestone.

    Yearncleugh Veins—Lead ore

    NY84SE; Durham 23 NW

    In Middlehope valley, 1400 ft (427 m) NW of Middlehope Bottom, a NE vein has been worked from a level [NY 8918 4100] in the shale above the Great Limestone, starting from the south bank of the stream. The length of the workings, as indicated by surface shafts, is about 600 ft (183 m). Quartz, purple fluorite and galena occur on the level dump. At 1300 ft (396 m) farther up the valley there is an arched level [NY 8882 4115] which apparently runs WNW with similar minerals on the dumps. An old plan formerly in the Weardale Lead Co.'s collection shows a vein running nearly E -W worked in the Great Limestone from a shaft or sump here. In Yearncleugh 2000 ft (610 m) W of this level mouth, a third level [NY 8820 4110], driven beneath the Low Slate Sill, followed an E–W vein. Purple fluorite and quartz occur on the dump. At the head of Middlehope, a level known as Middlehopehead Grove [NY 8799 4203] has been driven on a NW fault which downthrows at least 20 ft (6.1 m) SW. It is not known whether this level, which is in the shale above the Firestone, was driven far enough to reach the line of Wolfcleugh Vein, but no veinstuff can be found on the dump. Between 1818 and 1827, 112 tons of lead concentrates were obtained from the Yearncleugh workings. There is no record of working since 1827, save for fluorspar picked from the heaps.

    Wearhead Vein—Iron and lead ore

    NY83NE; Durham 22SE

    On the hillside NE of Wearhead village large opencast workings [NY 861 397], some of them on the Slitt Vein, others on the Wearhead Vein which intersects it, extend from the Three Yard to the Great Limestone. One 350 ft (107 m) long and 100 ft (30 m) wide in the Great Limestone worked iron ore from a flat on the SE side of Wearhead Vein. Monthly average iron-contents of the ore produced between 1884 and 1888 varied from 31.3 to 38.1 per cent. From the face of the opencut near the Black Dene-Cowshill Road, a level [NY 8626 3982] driven along the vein was reopened and extended by the Weardale Lead Co. in 1929–1930. The vein continued for 400 ft (122 m) NE of the road, a little galena being obtained from small flats on the N side. It was cut off by a cross vein. The mouth of this level, known as Sparke's Pasture Level, has now collapsed but in 1941 a shaft communicating with it was reopened. It was found that the ironstone flat on the S side of the vein continues between the road and the cross vein, and a sample taken along a 66 ft (20 m) crosscut through the flat assayed 33.3 per cent iron, 23.9 silica. An average from samples taken at 30 ft (9.1 m) intervals on the S side of the drift on the vein gave 27.6 per cent iron, 37.0 silica (Assays by L C W Birkett, Weardale Steel, Coal and Coke Co.). The deposit appears, therefore, to be of too low a grade for present-day mining. The only reservation which should be made is that the ground sampled was wholly in the upper part of the limestone; the Black Bed at the shaft is 17 ft (5.2 m) above the level sole; 400 ft (122 m) NE it is 3 ft (0.9 m) above the sole. Thus the workings do not penetrate the lower beds of the limestone, which from experience elsewhere in Weardale are the most favourable for ironstone flats. The vein contains quartz, purple fluorite, galena, siderite and ankerite, the latter two mainly oxidised to limonite.

    Rogers Vein—Lead ore

    NY83NE; Durham 22SE, 23SW

    This small vein, trending N65°E, was worked N of Slitt Vein from Elmford Mine (disused). A crosscut from Elmford Level [NY 8676 3968] reached the vein 0.5 mile (0.8 km) E of the level mouth, in the upper part of the Great Limestone at 1274 ft (388 m) above OD. Small oreshoots were worked in the upper part of the limestone and the thick Coal Sills sandstone, where the vein was 6 in–1 ft 6in (0.15–0.45 m) wide, of fluorite and galena. The vein was not found in Silverdikes Level, in the shale beneath the Firestone. A crosscut from Blackdene 'North Slitt' workings in the Six Fathom Hazle failed to show any improvement with depth.

    Blackdene & Silverdykes Veins—Lead ore, fluorspar

    NY83NE; Durham 22SE, 23SW, NW. Direction N60–65°E. Blackdene Vein (S of Slitt Vein) hades SE; Silverdykes, on approximately the same line N of Slitt, hades NW.

    The ore-bearing ground on Blackdene Vein lies beneath the NE slope of the main Wear valley between West Blackdene village and New House Moor. On the S side of the valley, the vein was tried from Rigg Level driven NW along a cross vein throwing 3 ft (0.9 m) NE from Ireshopeburn Mine (disused). Rigg Level, which leaves Ireshopeburn Horse Level 2630 ft (802 m) SW of the portal (situated close to the confluence of Ireshope Burn and the Wear at [NY 8687 3877]), is driven in the shale beneath the Slaty Hazle, reaching Blackdene Vein 915 ft (279 m) from Ireshopeburn Vein. A rise showed the vein to be 1–1 ft 6 in (0.3–0.45 m) wide in the Slaty Hazle and Five Yard Limestone, and composed of spar threads, siderite and rock and only traces of galena. In a drive of 160 ft (49 m) SW from the rise, holding the base of the Five Yard Limestone in the roof, the vein did not improve.

    N of the river, Blackdene Vein was extensively worked by the Beaumonts for lead, following earlier opencut and bellpit workings of possible mediaeval date. The principal underground levels of the WB period were: Silverdykes crosscut adit, driven from [NY 8794 3946] at 1477 ft (450 m) above OD in shale below the Firestone; Elmford Wagon Level, driven through from Slitt Vein at about 1270 ft (380 m) above OD, commanding the Great Limestone and unusually thick (70 ft + , (21 m + ) Low Coal Sill sandstone above it; the Blackdene Level which enters as an oblique crosscut from [NY 8676 3899] at 1048 ft (319 m) above OD in the Six Fathom Hazle. The last-mentioned working reaches the vein some 600 ft (183 m) from the portal; from this point it was driven along the vein before continuing westward in Slitt Vein as Elmford Low Level, the linkage being by way of Ridley's Crosscut leaving Blackdene Level at 2550 ft (777 m) from the portal; this crosscut links with New Sedling Level and served as the main drain for the Sedling workings. The Beaumont period thus saw extensive developments on Blackdene Vein, and for the period 1818–1861 the mine was credited with the production of 14 198 tons of lead concentrates (including some from Elmford in 1824–1832). This production could well have involved mining 200 000 tons of ore, much of which most probably came from the two upper levels. The miners of the time would avoid bringing any more of this out of the mine than necessary. The principal gangue mineral is purple fluorite, and between 1906 and 1939 Messrs Hinchcliff's worked some fluorspar from the vein in connexion with their Elmford operations; the records however show 4623 tons produced but there must be doubt about this figure. The old workings in the Great Limestone and Coal Sill are said to have varied between 3 and 14 ft (0.9 and 4.3 m) wide. From surface, Allercleugh Level communicated with the blind SW end of Elmford Wagon Level, 20 ft (6.1 m) above it, and from here and from a drift in the Coal Sill, good quality fluorspar was worked by Mr J V Peart in 1936–1939 from old workings; collapse to surface 450 ft (138 m) inbye occurred after 3754 tons had been produced. It is possible that fluorite increases downward relative to galena on Blackdene Vein. Four sumps below Blackdene Level, representing the deepest workings of the Beaumont period showed spar with little galena. One of them, 1366 ft (416 m) from the portal revealed up to 7 ft (2.1 m) of fluorite in the Five Yard Limestone. On the basis of these facts, attention was directed to the potential of this vein, in the first edition of this Memoir (1948, p.226).

    In 1949 The United Steel Companies Ltd acquired Blackdene Mine (disused) and put in hand a vigorous programme of exploration and development. By 1951 two of the sumps had been pumped out, and by 1954 many of the workings above Blackdene Level had been investigated. Although some production was obtained from old stopes in and above the Three Yard Limestone, the conclusion was reached that the virgin ground beneath the level offered the best possibility for sustained production. Principal developments were at 40, 95, 145 and 190 ft (12, 29, 44 and 58 m) below Blackdene Level, served by a series of vertical shafts and by four main inclines. The stratigraphic range of the workings is from the Three Yard Limestone down to the Alternating Beds beneath the Scar Limestone, a section here containing less soft shale and more hard strata than is normal in the orefield. In the event the oreshoot proved to be more continuous than some fluorspar bodies in the district, a total length of 2800 ft (853 m), almost reaching the intersection with Slitt Vein. An indication of vein-widths is given by the following data, based on systematic measurements made during extraction: (a) SW of Ridley's Crosscut (roughly the SW half of the oreshoot), 40 ft (12 m) random (the local term for horizon), 2.7 ft (0.8 m) average of 53 measurements; stoped ground between 40 and 190 ft (12 and 58 m), 4.7 ft (1.4 m) (58), 190 ft (58 m) random, 2.4 ft (0.7 m) (51); (b) NE part of oreshoot, 40 ft (12 m) random, 4.1 ft (1.2 m) (46), 40–145 ft (12–44 m) random stopes and support, 4.8 ft (1.5 m) (171), 190 ft (58 m) random, 2.3 ft (0.7 m) (74). The vein is shifted by a cross fault, along which Ridley's crosscut is driven to the NNW, 130 ft (40 m), NE side NW; the movement possibly postdates the main mineralisation. The vein widths quoted illustrate the tendency of the orebody to pinch both upward and downward, though old stopes in the Three Yard Limestone above Blackdene Level were noted. The oreshoot was regarded as stoped out by 1973, save that good ground had been left as support for Blackdene Level above the 40 random, and beneath No. 3 Incline. Before this stage was reached, a new main haulage level, accessed by means of a 1 in 7.2 incline from surface had been driven 29 ft (8.8 m) below the 190 random. The vein having deteriorated in the Alternating Beds beneath the Single Post Limestone, it was not followed all the way. The main purpose of this level was to facilitate the extraction of ore from Slitt Vein which was developed E of Blackdene Vein from it; only one short block of workable ground was found between the 190 random and the Main Haulage Level. As far NW as the foot of No. 3 Incline the top of the Whin Sill lies about 25 ft (7.6 m) below the haulage level; it then transgresses across the Single Post and Cockleshell limestones to intrude beneath the Scar Limestone, but after 520 ft (158 m) the intrusive level drops though the sill reappears in the Haulage Level on Slitt Vein. On Blackdene Vein three tests of the vein in the sill were made by means of inclines, and attempts were made to establish a working 270 ft (82 m) random but this was found not to be feasible since the vein-width averaged less than 1 ft (0.3 m). No. 2 Incline was carried to the base of the sill almost beneath the bottom of No. 3 Incline, 400 ft (122 m) NE of Ridley's Crosscut; the thickness of the sill established here, 288 ft (87.8 m) is the greatest yet proved in the orefield. Since however, the measurement coincides with the upward transgression of the upper surface, this thickness may not be maintained. The trials here appear sufficient to discourage further exploration in depth on Blackdene Vein, but Slitt Vein has been found to carry workable ore in the sill. The Blackdene oreshoot is nearly vertical throughout, and the vein continues at a steep angle to surface as far NE as the Ridley's Shaft. From here, the Elmford and Silverdykes levels diverge increasingly towards the NW, and before reaching the intersection with Slitt Vein, Blackdene Vein has an average inclination of about 70°SE, though no doubt in steps as in (Figure 11); the veins in Blackdene Mine present good illustrations of the tendency, anticipated theoretically, for the fractures to steepen with depth.

    The Blackdene oreshoot pinched as it approached Slitt Vein and both veins appear on present evidence to be constricted when they meet. The complex intersection area is further discussed below in connexion with Slitt and Dick's veins, but here it remains to consider Silverdykes Vein. Surface mapping based on the line of old shafts suggests that this vein is the direct continuation of Blackdene Vein north of the Slitt intersection, but underground evidence shows that the dip, 65–70°NW on average, is opposite to that of Blackdene Vein, and the veins do not exactly coincide. Silverdykes Vein has been worked in former times from Silverdykes adit [NY 8794 3946] in the Pattinson Sill ('Girdle Beds' on the Beaumont section, above the Little Limestone) and perhaps in the Firestone; outlines of stopes in the Great Limestone and extending down to the upper part of the Four Fathom Limestone are also shown. The Four Fathom Limestone workings were connected by means of a sump with an extension of Blackdene Level, but this level has been blocked by falls south of Slitt Vein and was not accessible during the Steel Co.'s operations. However, the plans of the three upper levels are shown in Beaumont records; the NE direction is maintained to within about 320 ft (97.5 m) of the N side of Slitt Vein but there is then a swing, in two stages, to a more northerly direction as the intersection is approached, as if Silverdykes Vein had been dragged off course by dextral movement on Slitt Vein. This explanation cannot however be maintained, since there is positive evidence on Slitt Vein of 88.5 ft (27 m) of sinistral movement (Greenwood and Smith, 1977, p.B187). Further, as noted above, Silverdykes Vein dips NW. From rises above the Main Haulage Level, a 200 ft (61 m) random level was driven in search of Silverdykes Vein in the Alternating Beds, which revealed, at about 310 ft (94 m) from Slitt Vein on strike, the vein 6 in (0.15 m) wide of quartz and siderite, with two accompanying strings of siderite. A rise into the Scar Limestone revealed disseminated fluoritic mineralisation over a width of 20 ft (6.1 m) containing a vein-channel 20 in (0.5 m) wide. Further development of the 200 ft (61 m) level disclosed an oreshoot 500 ft (152 m) long reaching a maximum height above rail of 90 ft (27 m) with vein widths up to 6 ft (1.8 m). This lies below the stoped ground in the Great and Four Fathom Limestones already mentioned; at the latter horizon the Beaumont agent's reports mention vein widths up to 3.5 ft (1.1 m). At the NE forehead of the 200 level, the vein is split and unworkable. The old workings higher up however suggest that it may continue 1600 ft (488 m) further to intersect Bleaklaws Cross Vein, since a drift at about 1225 ft (373 m) above OD, forming part of the elaborate system of levels from

    Levelgate Mine, was driven 1470 ft (448 m) from the cross vein on the Silverdykes course and linked with the level in the Four Fathom Limestone by a rise. At the horizon of the Great Limestone some stoping was done above the SW part of the drift from Levelgate. At the time of writing (1985) 7000 t of crude ore have been extracted from the Silverdykes oreshoot and there appears to be scope for further exploration.

    Blackdene passed, with United Steel, into the British Steel Corporation and was one of the Corporation's principal sources of metallurgical fluorspar. According to Greenwood and Smith (1977) output of crude fluorspar had reached 213 395 tons by 1976; production since then has raised this total to over 300 000 t ( = 288 360 tons) of which perhaps half has come from the Blackdene oreshoot.

    The minerals present include fluorite (predominant), galena (over 5 per cent on average), quartz (a few per cent, less than the normal silica-content for the district) and carbonates including ankerite, siderite and calcite. The iron carbonates tend to appear near the fringes of the oreshoot. Up to 1979 gravity separation was employed to produce a good grade of gravel metallurgical spar, but since then an all-flotation treatment was employed, producing briquettes with 92 per cent CaF2 and better. The difficulties experienced by the steel industry led in May 1982 to the sale of the Blackdene plant and the mines associated with it to Weardale Mining & Processing Ltd, a subsidiary of the Minworth Group. Production continued until 1987.

    Dick's Vein—Lead ore

    NY83NE; Durham 23SW, NW Direction N75–85°E, inclined S.

    At the time of the primary geological survey about 1875, surface mapping and consultation of the Beaumont plans led to the conclusion that Slitt Vein is shifted by Blackdene Vein E side S about 200 It (61 m). This interpretation appears on the published geological maps and was accepted in the first edition of this Memoir (1948) but the subsequent development of Blackdene Mine has shown that it is incorrect. The supposed Slitt Vein diverged from the E side of Blackdene Vein at about 1200 ft (366 m) NE of Ridley's crosscut; it follows an ENE course for nearly 1000 ft (305 m) before turning to the E–W course normal hereabouts, the previous trend continuing as a weak vein called Dick's. The driving of the 200 ft (61 m) Level from Blackdene Main Haulage has shown that Blackdene Vein effects little if any shift on Slitt Vein which continues virtually uninterrupted from the W. Thus the ENE vein as a whole must be regarded as Dick's Vein. The developments on it included Slitt Wagon Level (1234 ft, (376 m above OD), Coal Sills Drift (1303 ft, (397 m) and about 280 ft (85 m) of drivage from Silverdykes adit, here at 1480 ft (451 m) above OD. Small flats seem to have been worked near the junction with Slitt Vein, but there are few rise workings and production cannot have been large. A trial from the 40 random at 1010 ft (308 m) above OD was negative, offering no inducement for fluorspar development in depth, and the vein fracture, cut in the South Slitt 200 Level attracted no interest.

    Ireshopeburn Vein and Richard's Vein

    The total length of this system of veins is over 6 miles (9.6 km), carrying a series of apparently disconnected oreshoots. SW of the Wear, Ireshopeburn Vein was worked at Ireshopeburn or Barbary Mine (disused) near Ireshope village. The earliest workings, by the London Lead Co., exploited the vein down to the Old Water Level at 1060 ft (323 m) above OD, about 80 ft (24 m) below surface; the oreshoot was in beds between the Slaty Hazle and the Three Yard Limestone. Early in the nineteenth century the mine passed to the Beaumonts, who drove the Horse Level [NY 8687 3877] at 1025 ft (312 m) above OD, starting in the shale beneath the Six Fathom Hazle, but reaching, owing to the southwards rise of the beds, the Scar Limestone. The vein is recorded as 3–5 ft (0.9–1.5 m) wide in the limestone, containing spar but poor for ore. A total of 2226 tons of galena were produced between 1818 and 1872, when the mine closed. It was reopened during the present century by Messrs Blackwells for fluorspar. The workings were extended below the Horse Level into virgin ground by means of two inclines. The earlier one [NY 8590 3833], starting from the left bank of Ireshope Burn 0.5 mile (0.8 km) SW of the village was carried down to 1000 ft (305 m) above OD, understoping from a subsidiary incline reaching 977 ft (298 m) OD. The length of ground worked from this incline was 2140 ft (652 m). To the SW the oreshoot pinched after passing through a NW cross vein, while at the NE end of the ground worked here, Swinhope Cross Vein caused a temporary "nip". Fluorite was, however, found to be present farther north-east; the second incline [NY 8648 3860] commencing 600 ft (183 m) SW of Ireshopeburn Bridge, and reaching 927 ft (283 m) above OD, gave access to 1290 ft (393 m) of additional ground. The oreshoot was in the Scar Limestone and underlying Alternating Beds and the vein, 4–8 ft (1.2–2.4 m) wide, contained, in addition to massive fluorite, a little galena, chalcopyrite and siderite. The spar produced was of unusually good quality for the district, averaging only 5 per cent silica. Much of it was shipped to the USA. The total production, from 1905 to 1934, when the mine was abandoned, was 80 716 tons of fluorspar and 1676 tons of lead concentrates.

    Barbary Mine east incline was reopened by Weardale Lead Co. in 1953–54. After reconditioning it was continued from the existing bottom at 927 ft (283 m) above OD to establish a new level, known as the 34-Fathom, at 887 ft (270 m) above OD. During operations that lasted until 1959, this level was driven 3206 ft (977 m) to the WSW. The new sinking was entirely in the Alternating Beds, but the top of the Whin Sill rose into the level 490 ft (149 m) from the incline foot, and except between 2806 ft (855 m), where a cross-fault downthrowing SW carried it below the level, and 3030 ft (924 m) where it returned, it was continuously exposed in the lower part of the drive. Throughout the 34 Fathom Level the vein proved to be split up into ramifying branches with the total displacement rarely exceeding 1 ft (0.3 m) and with widths of fluorite measurable in inches or cm only; save that between 980 and 1640 ft (299 and 500 m) it was more collected and a shallow sump showed a width of 3.5 ft (1 m) 10 ft (3 m) below the level. Investigation of the ground, as much as 80 ft (24 m) high, up to the bottom of the Blackwell's stopes was more favourable, and showed that the statement reproduced in the first edition of this memoirs that the oreshoot had been exhausted, was incorrect. In the 10–20 ft (3–6 m) of metamorphosed shale ('whetstone') above the sill the vein was for the most part unworkable, but above this a total length of 1940 ft (591 m) of new stoping ground was obtained, with an average vertical dimension of about 50 ft (15 m), the yield suggesting a mean vein width near 4 ft (1.2 m).

    The Swinhope Cross Vein, cut at 710–729 ft (216–222 m) from the incline foot, proved to dip at about 75°NE, and to consist of three fractures with intervening rock, the widest being on the foot-wall, 1.5 ft (0.45 m) across. Each contained gouge and brecciated fluorite, chalcedony and pyrite. No doubt some postmineralisation movement had taken place, displacing Ireshopeburn Vein W side N less than a drift width. Immediately SW of the cross vein a rise was put up to dewater the Blackwell workings through boreholes, 5.3 million gallons of water being pumped as a result. The late Mr H Green supplied the following description of the block of ground 830 ft (253 m) long extracted SW of Swinhope Cross Vein: "This block of fluorspar was split into two separate qualities, the upper half being good uncontaminated fluorspar with a low galena content, and the lower half, poor fluorspar contaminated with ankerite but richer in galena (3–4 per cent). There was a band of shale dividing the upper and lower sections, giving a lateral thrust to the south of the upper portion, from 0 to 26 ft (7.9 m) and back to zero at the SW end of the block. The galena content rose to 6–7 per cent here in the lower portion." At this point a second cross vein was cut and 100 ft (30 m) of dead drivage followed, but mineralisation reappeared and continued erratically for another 1140 ft (347 m), vein-width in the lower portion being reduced to 2 ft (0.6 m) and largely ankerite. At the end of this block, rises were put up to the 19-Fathom level, and the SW forehead of the Blackwell stopes was found to carry fluorite ore 5–7 ft (1.5–2 m) wide. This heading was advanced 70 ft (21 m) before the vein split up into diverging branches. Entry was also gained to workings in the Five Yard Limestone and Six Fathom Hazle, above the Horse or Gin Level, where the branching vein was seen to be cut by a cross vein. There was evidence in subsequent workings that the branches would reunite and in the ultimate forehead in the Scar Limestone, this had happened, with the vein up to 4 ft (1.2 m) but cavernous and contaminated with iron carbonates. It was nevertheless by no means dead after 520 ft (158 m) of driving in virgin ground in the Scar Limestone. Ahead, surface mapping by A C Dunham showed that about 5750 ft (1.75 km) of ground on the line of the vein remained, unexplored save for 12 old shallow shafts; two, one into the Four Fathom and the other into the Great Limestones have fluorite among the spoil, the rest only shale. The line is assumed to terminate at the Burtreeford Disturbance.

    In the Whin Sill the vein was tested by continuing the E incline 73 ft (22 m), the vein here comprising mainly ankerite; and by sinking a second incline below the 34 Fathom level at 490 ft (149 m) SW, leading to the 45 Fathom Level at 828 ft (252 m) above OD; this was productive only in the 50 ft (15 m) W of Swinhope Cross Vein; a total of 400 ft (122 m) was driven. The mine closed in 1959, having produced 36 865 tons of crude ore, yielding 18 918 tons of fluorspar and 887 tons of lead concentrates.

    NE of the Wear, the vein, here known as Lodgefield Vein, was prospected in the Scar Limestone and Alternating Beds at Lodgefield Shaft (disused) [NY 8716 3887], near New House, 157 ft (48 m) deep to the bottom level, which was driven 701 ft (214 m) N. Some fluorite was found, one 21 ft (6 m) length averaging 3 ft (0.9 m) wide but the rest was 2 ft (0.6 m) or less; ankerite was abundant, with a little galena. During prospecting in 1926–28, 212 tons of spar were obtained. Workings on Lodgefield Vein at higher horizons are ancient; old pits and opencasts which extend from Lodgefield Shaft up to the Little Limestone at [NY 8780 3927] show purple fluorite. At 3650 ft (1113 m) NE of Lodgefield Shaft, Levelgate Level (disused) [NY 8817 3890] reached the vein at about 1200 ft (366 m) above OD. This commences 1000 ft (305 m) N of East Black Dene as a crosscut beneath the Quarry Hazle, reaching Old Fall Vein (described below) at 1000 ft (305 m), Lodgefield Vein at 1800 ft (549 m) N of the portal. No record of the condition of Lodgefield Vein here has been found, but Levelgate Level followed it to its intersection with Slitt Vein, 1550 ft (472 m) NE from the level head. North of Slitt Vein the Lodgefield Vein appears to have been tried by means of a rise on Bleaklaws Cross Vein from Levelgate Level, but no drifting was done. An untried gap of 2000 ft (610 m) follows, the next working being from Douks Level (disused) [NY 9022 4026] which reaches the vein in the shale beneath the Tuft from Middlehope at about 1180 ft (360 m) OD. The mine reports for 1861 state that the vein was 3 in (8 cm) wide in the shale, but in the Great Limestone it was 2–3 ft (0.6–0.9 m) wide, consisting of spar with ore 9 in (0.23 m), the remainder altered limestone. Douks Level reaches Lodgefield Vein by way of Longsike Vein; Lodgefield Vein was worked for 1150 ft (351 m) SW of Longsike but was not followed across the valley NE of Longsike Vein. In the London Lead Co.'s Middlehope Mine (disused) [NY 9044 4011] a vein called Richard's Vein corresponds in position with Lodgefield Vein but little is known of it save that after the company had given up the mine some of the NE workings on it were reopened for iron ore by the Weardale Iron Co. In the Rookhope valley the Fulwood North and Fulwood veins may be taken to represent the continuation of the same vein-system. The North Vein yielded some lead ore in the Coalcleugh Beds in a gangue of quartz, limonite and fluorite near the 1573 and 1674 ft (479 and 510 m) above OD spot heights on the Rookhope–Westgate road. It was also fairly extensively worked near the head of Linzgarth Cleugh [NY 923 424]. Fulwood Vein, parallel and 275 ft (84 m) SE of Fulwood North Vein, throws 2 ft 6 in (0.76 m) NW where cut by the Fulwood crosscut from Boltsburn West Level at [NY 9250 4236] and is 1–5 ft (0.3–1.5 m) wide in the Great Limestone, with fluorite, siderite and small amounts of galena. A trial on it in the 1930s was abandoned as unpayable. An analysis of siderite from this vein is quoted below (Table 24), p.77). At Low Fulwood Mine (disused) [NY 9340 4292] W of Rookhope village, flats in the Great Limestone yielded limonitic ironstone over a length of 800 ft (244 m), averaging 40 ft (12 m) wide. These terminate NE against the Red Vein, N of which Fulwood Vein has not been found.

    Old Fall Vein, Middlehope Vein and Scarsike New Vein

    The Old Fall-Boltsburn vein-system is known to continue for a distance of 7 miles (12 km) from the S side of the Wear near Weardale House, through Middlehope and Rookhope to the N side of the valley of Stanhope Burn. S of the Wear it carried a small lead oreshoot in beds ranging from the Three Yard down to the Five Yard Limestone which was worked from the Earnwell Level, a SE crosscut from the horse level at Ireshopeburn Mine (disused). N of the Wear the Old Fall [NY 8760 3865] and Levelgate levels (both disused) [NY 8817 3890] gave access to lead workings ranging from the Six Fathom Hazle up to the Firestone. Sunnyside Opencut (disused) [NY 878 390] worked a small ironstone flat in the Great Limestone related to the vein. On the SW side of Middlehope the vein was worked from Douks Level (above p.187) (disused) [NY 9022 4026] but there is an unworked stretch of about 1650 ft (503 m) between the forehead here and the nearest workings from Levelgate Mine. At Middlehope Mine (disused) [NY 9044 4011] on the NE slope of the valley, the London Lead Co. worked an oreshoot over 4000 ft (1.2 km) long which occurred in beds extending from the base of the Great Limestone up to the Little Limestone, and there was a small shoot in the Quarry Hazle. Scarsike New Vein intersects the main vein in the Middle-hope workings. After the period of lead working, Weardale Iron Co. took over the mine and extracted substantial quantities of partly oxidised ironstone from flats related to the Scarsike veins in the Great Limestone. Between the NE forehead on Scarsike Vein and the SW forehead of Boltsburn West Level (disused) (portal at [NY 9365 4283]) 1700 ft (518 m) of ground remain untested. The first 4200 ft (13 kms) of the West Level workings were developed by the Iron Co., and extensive flats of limonite were worked in the Great Limestone. At about 4200 ft (1.3 km) the bottom of the oxidation zone was reached and farther SW the workings passed into ground with unoxidised siderite and ankerite, too poor to work for ironstone. In 1930–42 the Weardale Lead Co. extended the workings on the vein towards Middlehope, obtaining lead ore from small stopes in the Great Limestone and Coal Sills. NE of Rookhope Burn the Boltsburn Mine (disused) worked deposits which proved to be, next to Burtree Pasture Mine, the richest lead-bearing ground in the Weardale Area. The initial development here was done by the Beaumont Co. but in their time the vein, though it yielded satisfactory oreshoots in the Great Limestone and Coal Sills, was never outstandingly rich. It fell to the Weardale Lead Co. during the closing years of last century to discover the great belt of flats which extend over 2 miles (3.2 km) NE of Rookhope village in the Great Limestone. These maintained the mine until 1932, making it for many years the leading British kad mine. Owing, however, to the northward dip of the strata ((Figure 31) the productive bed at Boltsburn had to be reached by a succession of underground shafts and levels. Thus although ore was still present in the NE foreheads, the mine was abandoned because of the high cost of transport.

    Earnwell Level starts from Ireshopeburn Horse Level 235 ft (72 m) from its mouth and runs SSE, reaching Old Fall Vein at 875 ft (267 m) in the Five Yard Limestone at Dobson's Shaft [NY 8688 3849]. The oreshoot here was worked for 650 ft (198 m) SW, the maximum height being 100 ft (30 m). The vein is reported to have been 1–3 ft (0.3–0.9 m) wide with galena in a spar matrix pinching SW to 8 in (0.2 m). At 250 ft (76 m) SW of the end of the oreshoot, a cross vein throwing 3 ft (0.9 m) NE was cut, containing 2 ft (0.6 m) of spar and altered rock, but no ore. NE of Earnwell Level, old workings were encountered and it appears that part of the ground in the Six Fathom Hazle had also been removed via surface shafts prior to the driving of Earnwell Level. No attempt was made to test the vein at greater depth here.

    N of the Wear, a shaft [NY 8733 3871] was sunk 600 ft (183 m) SSE of New House 143 ft (43.6 m), through the Scar Limestone on a narrow unpayable vein, containing fluorite, ankerite and a little galena. Old Fall Level [NY 8760 3865] in the Six Fathom Hazle at 1010 ft (308 m) above OD starts as a crosscut near Middle Black Dene, reaching the vein at 530 ft (162 m) N of the portal, and continues on it for 2500 ft (762 m): the old plan shows many rises above it, but no details of the horizon of the stopes are extant. Sunnyside Opencut [NY 878 390], 3/4 mile (1.2 km) NW of St John's Chapel, contained a small but good quality flat of limonite replacing the Great Limestone an analysis is quoted in (Table 54). At 1500 ft (457 m) NE of the opencut, Levelgate Level enters Old Fall Vein as a crosscut, turning on and continuing in it 2100 ft (640 m) to Slitt Vein and 400 ft (122 m) farther to Bleaklaws Cross Vein. The level is in the shale immediately below the Quarry Hazle, the base of which is in the roof. Rises communicate with workings in the Great Limestone. Some of these were reopened during 1921–25 by the Weardale Lead Co., but the vein, with a throw of 2 in (5 cm) NW, proved to be narrow and poor. Surface shafts in this stretch are not numerous but some starting just above the Little Limestone show some purple fluorite on the heaps, while the heap from a shaft [NY 8854 3953] starting above the Firestone near the head of Levelgate Sike is abundantly supplied with this mineral, accompanied by siderite.

    At Douks Level [NY 9022 4026] the drift on Old Fall Vein is in the Tuft; the mine report for 1863 states that in the SW forehead the vein is barely traceable, while in the overlying Great Limestone it is 9 in–1 ft 6 in (0.23–0.45 m) wide between the base of the limestone and the Middle Flat, but very hard and poor in ore; above this it had been worked out 2–3 ft (0.6–0.9 m) wide. It deteriorates SW and it seems unlikely that the prospects are good in the unworked stretch between Levelgate and Douks levels.

    The main entrance to Middlehope Mine (disused) was the Governor and Company's Level [NY 9044 4011], starting in the Tuft from the left bank of the burn at 1174 ft (358 m) OD, 1.5 miles (2.4 km) N of Westgate, reaching the Great Limestone at about 500 ft (152 m) N from the portal and Scarsike Vein at 2175 ft (663 m). At 1200 ft (366 m) ENE of the level head, Scarsike New Vein cuts through the main vein; which is in two subparallel branches 50–150 ft (15–46 m) apart. At 900 ft (274 m) ENE of the intersection, Middlehope Shield Cross Vein, throwing 7 ft (2.1 m) SW, cuts through the veins. Owing to the presence of a single sandstone, 71 ft (22 m) thick representing the Coal Sills, the oreshoot has an unusually great vertical extent, in places reaching 175 ft (53 m). This sandstone appears to have carried more consistent lead mineralisation than the Great Limestone. The minerals present in the vein included fluorite, quartz, ankerite, siderite and galena. In the Great Limestone flat replacements rich in siderite and ankerite, partly oxidised to limonite, were extensively worked for iron ore; as they were not worked during the period of lead mining at Middlehope, it must be presumed that the galena-content of them was very small. They yielded iron ore which contained, on monthly averages for the years 1884–89, 30.7–38.2 per cent iron. Separate figures for the production of iron ore are not available. The London Lead Co. produced, between 1816 and 1847, 15 720 tons of lead concentrates, but mine reports for 1806 and 1820 make it clear that the mine had been extensively worked before 1816. Later, the Beaumont Co. extended their White's Level (described below) along Middlehope Shield Cross Vein, reaching the Scarsike veins, and continuing the level 2800 ft (853 m) NNW on the main vein along the cross vein as a prospecting level in the Great Limestone. Richard's Vein, part of the Lodgefield–Fulwood vein-system, 600 ft (183 m) NW of Scarsike main vein, was worked from this level. A trial was also made by the Beaumont Co. from Company's Level to the Four Fathom Limestone, near the intersection of the Scarsike main and New veins. This proved the throw of the main vein to be 6.5 ft (2 m) SE. The vein was 4.5 ft (1.4 m) wide, consisting of stone mixed with hard spar and "only moderate in ore", not payable (mine reports, 1861) An ore-shoot about 150 ft (46 m) long had previously been worked here in the Quarry Hazle.

    Boltsburn West Level (disused) [NY 9365 4283] starts from the SE bank of Rookhope Burn on the Boltsburn Vein at 1090 ft (332 m) above OD in the upper part of the Great Limestone. At 170 ft (52 m) from the portal Red Vein cuts through Boltsburn Vein, accompanied by large ironstone flats. Boltsburn Vein in the next 2000 ft (610 m) SE appears to have been poor, though there may have been some stoping from a lower level from surface at 1050 ft (320 m) above OD. Extensive ironstone flats then appear, related to Boltsburn Vein and to a small vein which intersects it from the SE called Paterson's Vein on the Iron Co.'s plans. An analysis of a composite sample taken from the pillars in these flats, in which about 12 000 tons of iron ore is estimated to remain, is quoted in (Table 54). At 3500 ft (1.066 km) from the adit mouth Stony Hill Shaft [NY 9275 4217] communicates with surface through beds from the Low Slate Sill to the Great Limestone and a crosscut on the top of the Great Limestone connects with the old Fulwood Mine to the NNW. At 400 ft (122 m) SW of Stony Hill Shaft a second drive follows a small cross vein, downthrowing 1.5 ft (0.46 m) SW, to the Fulwood veins. This was extended to Fulwood North Vein, but without finding payable ground. The ironstone flats cease about 900 ft (274 m) SW of Stony Hill Shaft. The vein, now containing siderite, fluorite, quartz and galena continues. The ground opened up here between 1932 and 1940 by the Weardale Lead Co. revealed the vein 1–3 'A ft (0.3–1.1 m) wide in the Great Limestone and Coal Sills sandstone, but part of the ground proved to be below economic grade, and no substantial lead-bearing flats were discovered. The throw of the vein is 1 ft 3 in- 3 ft 5 in (0.38–1.04 m) SE. It may be noted that throughout the SW part of the mine, the Coal Sills sandstone rests directly on top of the Great Limestone. The shales normally present in the upper part of the limestone appear to be absent, either due to dying out or to unconformity between the sandstone and the limestone. At Stony Hill Shaft the sandstone is thin and shaly; farther SW it is massive and hard, increasing to 30 ft (9.1 m) thick in the westernmost rise, and it seems very probable that the conditions were not favourable for flat formation. For about 0.5 mile (0.8 km) NE of Stony Hill Shaft the limestone was more or less sealed above with shale. North of Rookhope Burn, however, thick sandstone appears again and it is suggested that for this reason the first part of Boltsburn East Mine contained vein-oreshoots without flats. The first appearance of the great belt of flats coincides approximately with the advent of shale in the lower part of the beds between the Great and Little limestones; farther NE the Coal Sills sandstone thins rapidly.

    In West Level at 5020 ft (1.53 km) SW of the portal, a branch or string leaves the vein on the north side; as the adjacent rock is strongly mineralised with siderite, two crosscuts were put out to test the possibility that a workable flat exists here, but the siderite continued for a few feet only.

    The workings of Boltsburn Mine (disused) proper lie NE of Rookhope Burn (Figure 31). The Horse or East Level, driven by the Beaumont Co., starts near the former mine offices at 1058 ft (322 m) above OD [NY 9376 4289] and continues 5800 ft (1.768 km) NE, beginning near the top of the Great Limestone and finishing above the Little Limestone. The upper part of the mineralised ground in the Coal Sills and a short stretch where an oreshoot occurred in the Little Limestone and Pattinson Sill was worked from this level. The main working level, Watts Level, was, however, driven from Boltsburn Engine Shaft [NY 9368 4279] on the SW side of Rookhope Burn, starting 179 ft (54.6 m) below the shaft collar at 908 ft (277 m) above OD, and 81 ft (24.7 m) below the base of the Great Limestone. Watts Level continues 10 950 ft (3.338 km) NE, passing through the Great, and ending above the Little Limestone. From this four underground shafts were sunk, at 4730 ft (1.442 km) (Fairless' Sump); 6170 ft (1.881 km) (No. 1 Shaft); 8175 ft (2.492 km) (No. 2 Shaft); and 9825 ft (2.995 km) (No. 3 Shaft); these giving access to successively lower levels driven to command the Great Limestone. From the bottom level of No. 3 Shaft, at 770 ft (235 m) above OD, and 1800 ft (549 m) NE of it, a fifth underground shaft was sunk shortly before the mine closed. Ventilation was effected by means of Redway rise, near Fairless' Sump, which communicated with Redway Level [NY 9450 4362], driven at 1376 ft (419 m) above OD in the shale below the Low Slate Sill; and Hopeburn Shaft [NY 9564 4422], a rise to surface on the SE side of the Stanhope Burn valley, 8000 ft (2.438 km) NE of Boltsburn Engine Shaft.

    The vein oreshoot in the Coal Sills sandstone continued from Rookhope almost to Hopeburn Shaft, though it was not continuously workable. Widths of oreshoots were as follows: in the Little Limestone 1.5–3 ft (0.46–0.9 m); in the Coal Sills sandstone 1–4 ft (0.3–1.2 m); in the Great Limestone, where workable 1–5 ft (0.46–1.5 m). In the Quarry Hazle the vein was only 6–9 in (0.15–0.22 m) wide, though galena was present in places. At Fairless Sump it was 1–1.5 ft (0.3–0.46 m) wide in the Four Fathom Limestone, reported in 1869 as "moderate for ore", but it did not prove to be workable at this horizon.

    In the vicinity of Redway Rise the belt of flats first appears; it continues almost without interruption to the foreheads of the mine 7700 ft (2.347 km) to the NE. After the Great Limestone flats appeared, the vein was often poor and unpayable. The galena-bearing portion of the flats was not normally found directly in contact with the vein; a belt of ankeritised limestone, 10–20 ft (3–6 m) wide, usually separated this from the vein. Probably this explains the fact that the vein-workings had been advanced far beyond the beginning of the flat-ground before the flats were discovered. Small mineralised joints or flyers from the vein, called leaders, run from the vein through the ankeritised limestone to the flats, and were the principal means by which the flats were found. The three flat horizons within the limestone were all mineralised, but the greatest concentration was at the High Flat. The section of the limestone supplied by Mr Tom Maddison is summarised in (Table 55).

    Although the replacements were normally confined to the flat horizons, in places mineralisation was continuous between them. Galena was present as coarse bands and as crystals disseminated through the altered limestone. Cavities within the flats were remarkable for the beauty of the purple fluorite crystals–sometimes 6 in (15 cm) along the cube-edge-developed in them (Plate 1). Specimens from Boltsburn have found their way into mineralogical collections throughout the world (King, 1982). Other minerals present included siderite, in pale brown curved crystals; ankerite (formerly incorrectly identified as dolomite) in white or yellowish rhombs; quartz; "nail-head" calcite; sphalerite; pyrite and, very rarely, chalcopyrite. The whole of the Boltsburn East flat-workings lay beneath the zone of oxidation. The many repetitions of incrusting minerals within the cavities has already been mentioned (p.82); there is no semblance of a "standard" order of deposition. In places the flats extended as much as 200 ft (61 m) from the vein, but the average width was of the order of 75 ft (23 m), including the belt of unproductive ground adjacent to the vein.

    A number of small cross-veins traverse Boltsburn Vein NE of Rookhope Burn. One, 3250 ft (991 m) NE of Boltsburn Engine Shaft, is a NNW fault throwing 5 ft (1.5 m) E; this was followed for 710 ft (216 m) NNW but was apparently not productive; it shifted Boltsburn Vein a few feet E side SE. Another crossed at 7000 ft (2.134 km) and a third, at 8540 ft (2.603 km), was followed for 1450 ft (442 m) NNW by a drive at the bottom of the Great Limestone, beneath the headwaters of Stanhopeburn, where there is some evidence of old workings [NY 957 446] for limonitic iron-ore in the Upper Felltop Limestone near the course of the cross vein. Workable orebodies were not, however, found in the Great Limestone. Two others at 10 450 and 10 500 (3.185 and 3.2 km) (throw 3 ft (0.9 m) NE) are believed to represent the Burntshieldhaugh Cross Vein of the Derwent field (p.222). It is notable that there is no tendency for the flats here to follow the cross veins away from the main vein, such as was found at Barneycraig Mine.

    The production of the Boltsburn mines, from the beginning of the detailed Beaumont records to 1940 is given in (Table 56).

    The average value of the ore mined is indicated by the following figures supplied by the Weardale Lead Co: in the period 1901–1931, 513 609 tons of ore were mined. (The actual figures for ore mined are recorded in the Company's books in shifts and waggons. The approximate relationship upon which the total tonnage mined is based is 8 waggons equals 1 shift; 1 shift equals 5.5 tons); the recovery of lead concentrates, averaging 77 per cent lead, amounted to 89 320 tons or 17.4 per cent. The best year recorded was 1908, when 15 549 tons of ore mined yielded 3869 tons of concentrates, or 24.8 per cent.

    In Boltsburn East Mine, the silver content of the galena in the earlier workings in the flats averaged 7.5–8.25 oz silver per ton of lead; this gradually decreased to 5.6 oz as the workings advanced to the NE. Fluorspar was mainly obtained from the vein, but a supply of high-quality fluorspar for optical purposes was obtained from large crystals from the cavities in the flats. If the carefully taken sample of gravel tailings remaining in 1943 from gravity treatment of Boltsburn crude ore (used in the calculation of the proximate composition of the orebody, analysis 3, (Table 29) was representative, over 100 000 tons of fluorite must have been present in the residues from the 1901–1931 period. It may be estimated roughly that half this tonnage was recovered after flotation was installed at Boltsburn Mill in the 1960s. For a short while after the closure of Redburn Mine in 1981, and at the time of writing (1983) Boltsburn flotation tailings were included in the feed for the Broadwood plant of Weardale Minerals Ltd.

    The fact that the rich lead deposit of Boltsburn was not exhausted when the deep workings were allowed to flood in 1932 has led at intervals to consideration of possible reopening; Watt's Level was, in fact, kept pumped out by means of the water-wheel-driven pumps in the Engine Shaft until the 1950s. The facts about the NE end of the workings, as examined by the writer in 1931, are that at the forehead of the main level at 770 ft (235 m) above OD, the High Flat horizon had dipped beneath the level, but the flats, where last worked 100 ft (30 m) back were still strongly developed and unchanged in mineralogy, up to nearly 100 ft (30 m) wide on the N side of the vein. The forehead of the level from the fifth underground shaft, at approximately 725 ft (221 m) above OD beneath these workings, was near the bottom of the Great Limestone. The vein was 0.76 m wide, inclination 70°, filled with fluorite and quartz, a minor amount of siderite, with two small bunches of galena on the NW side and a central leader with galena and sphalerite. This description of the vein could apply almost anywhere throughout the rich flat-bearing ground.

    The most recent consideration of the problem was in 1979 by Swiss Aluminium Mining (UK) Ltd, to whom we are indebted for the following details. In 1972–73, Acmin Exploration (UK) Ltd drilled four inclined deep boreholes, from two sites near Dead Friars, adjacent to the Stanhope- Hunstanworth road. Nos. 1 and 2 were sited at 1533 ft (467 m) above OD at [NY 9682 4480], aimed to intersect the Boltsburn mineralised zone 360 ft (110 m) ahead of the NE forehead of the mine. No. 1 hole was inclined at 70° but steepened to 79° before it was completed, under the Three Yard Limestone, here beneath the Little Whin Sill, at 1130 ft (344.4 m). Minor fractures with galena, sphalerite and quartz were noted in shale beneath the Hipple Sill, in the High and Low Grit Sills, and in the Firestone. Fluorite first appeared in the Little Limestone and was also present in the Great Limestone, which was not, however, strongly mineralised. Flat-type mineralisation was however found, with the usual assemblage, in the Four Fathom Limestone, and mineralised breccia in and adjacent to the Three Yard Limestone was considered to represent the vein-channel. No. 2 borehole was accordingly drilled in the same NNW direction, but at a starting inclination of 62°; this increased to 78° before the hole was completed beneath the Great Limestone at 697 ft (212 m) above OD. Here the vein-channel was cut in shale above the Great Limestone, and the drilling of a deflection into the N side flats gave positive results (Table 57).

    Though two samples gave assays better than the run-of-mine at Boltsburn, the lead content of most samples was appreciably lower; on the other hand, the values were apparently distributed through a much greater thickness of limestone than in the worked ground. The last set of figures above gives a weighted average for the full thickness of this formation below the 'black beds'. Though not too much weight must be placed on one promising intersection, it might be thought possible that the Boltsburn flats continue 500 ft (152 m) beyond the 1932 foreheads. A report by J G Cunningham to the Ministry of Munitions in 1917 stated that 1000 ft (305 m) of advance of the 18 Fathom Level at Boltsburn were calculated to yield 11 500 tons PbS and this figure is conservative against the whole history of the flat workings, which yielded 12 750 tons PbS per 1000 ft (305 m) advance of the development.

    The Boltsburn Vein, as interpreted in Acmin Nos. 1 and 2 boreholes is steeper than might be expected and appears to dip SE at about 87°. At surface the fault was believed to have been located by the SE downthrow of a small coal seam above the First Millstone Grit in a trench at 170 ft (52 m) NNW of the first borehole site, but subsequent trenches farther NE failed to prove a continuation, though a shift of a small coal seam in the same sense was interpreted as due to facies change rather than structure. Two further deep boreholes were drilled from [NY 9704 4498], starting at 1564.5 ft (476.9 m) above OD. No. 3, directed N31°W started at 66° inclination and had increased to 71° before reaching the Tuft at 890 ft (271 m) true depth below surface (674 ft (205 m) above OD). Breccia considered to be the Boltsburn Vein was cut at rod-length 391.5–410.5 ft (119.3–125.1 m) in mudstone within the Grit Sills. Associated gouge contained carbonate veinlets and there was a trace of chalcopyrite and a little pyrite; but strong mineralisation has nowhere been found on this vein, under these conditions. The Great Limestone was virtually unmineralised. No. 4 hole, in the same direction and from the same site was inclined at 75°, increasing to 81° in depth. Veinlets in which witherite was identified were found at rod-length 264 and 269 ft (80 and 82 m) above the Upper Felltop Limestone, but the fault-zone proper was found at 500–506 ft (152–154 m), where it cut through and brecciated beds at the top of the Low Slate Sill. Fracture-linings include sphalerite, pyrite and quartz. Joining up the intersections in Nos. 3 and 4 boreholes suggests that the inclination of the fault has decreased here to 70°SE, a more normal inclination among ENE veins in this district. If this inclination is maintained consistently with depth (which probably it is not) the Great Limestone, where intersected by No. 4 borehole could be as much as 170 ft (52 m) from the 'vein' at the High Flat horizon, and thus beyond the normal range of metasomatism. The Limestone was in fact unmineralised apart from the calcite veins found anywhere in this rock, some authigenic pyrite and one small vein of dolomite or ankerite close to the bottom, which for practical purposes was level with the base in No. 3 borehole. Regrettably, at this stage the exploration was abandoned as expensive, time-consuming and difficult to control because of deviation of the holes from the vertical. This trial, which has important implications for the future of the mining district, is further discussed on p.283.

    Apart from the reclamation of the access from Boltsburn Engine Shaft which is very unlikely ever to be attempted, two principal methods of reaching the NE end of the old workings have been under discussion. One involves a new shaft or incline from Dead Friars, where a vertical depth of 900–1000 ft (274–305 m) below surface would need to be attained. The site is exposed and remote from services. An attractive alternative would be the reopening of the old Harehope Gill Mine [NZ 0097 4846], the development of which to the SE along Swandale Vein towards the promising intersection in the Northumbrian Water Authority tunnel (p.176) would cross the line of Boltsburn Vein about 3.5 miles (5.6 km) NE of the Ac-min Nos. 3 and 4 boreholes. Hereabouts, from the evidence of the tunnel, the base of the Great Limestone might be at about 300 ft (91 m) above OD, but evidence of the continuity of the mineralised zone would be needed. The only point where prospecting, probably in ancient times, seems to have been done was at Eudon Groove Shop [NY 9831 4593] near the direct line of Boltsburn Vein and approximately 1 mile (1.6 km) NE of No. 4 borehole. It is not known whether the vein fracture was found, but one borehole of a group of five 200 ft (61 m) holes around [NY 990 460] cut a fault gouge beneath 1st Millstone Grit, approximately 1000 ft (305 m) SE of the most probable line of the vein; the remainder found no structure.

    Lodgesike Vein (Weardale)—Lead ore

    NY83NW, NE; Durham 22SE. Direction N85–90°E, throw 5 ft (1.5 m) S

    This vein should not be confused with the important vein of the same name in Teesdale. It lies W of the Ireshope Burn, where it was worked at Lodge Sike Mine (disused). The main levels were Hemsley's Level [NY 8497 3733], reaching the vein in the Nattrass Gill Hazle after passing through boulder clay; Wham Level [NY 8482 3717] above the Four Fathom Limestone, and Lodgesike Level [NY 8454 3718] in the shale above the Great Limestone: the last two being crosscut adits from the SE. The minerals present include siderite, limonite, purple and almost colourless fluorite and galena. Mine reports for 1862 state that in the Great Limestone a crosscut passed through "strong rider of bad quality" 36 ft (11 m) wide at the horizon of the High Flat; this suggests limonitised limestone, such as is found in the ironstone flats at the nearby Carricks Mine (below). In Hemsley's Level the vein was 2.5 ft (0.76 m) wide in the Four Fathom Limestone, but carrying only traces of galena. The production for the years 1838–71 amounted to 1532 tons of lead concentrates. The mine has not been worked for iron ore. The crosscut Lodgesike Level was continued 950 ft (290 m) N of the vein, mainly in the shale above the Great Limestone, but in the limestone where passing through a small anticline; it was driven in a fruitless search for Ireshopeburn Vein. Attempts to find the Lodgesike Vein in the Great Limestone east of Ireshope Burn were unsuccessful, but at Gravelheads Green Opencut (disused) [NY 8523 3727] a flat of limonite iron ore was worked, probably related to a cross vein throwing about 15 ft (4.6 m) NE, which passes through the burn 200 ft (61 m) NE of Hemsley's Level mouth. Quartz and skins of baryte, with traces of galena, were associated with the limonite.

    Broadsike Vein—Lead ore

    NY83NW; Durham 22 SE Direction N85°E

    Broadsike Levels (disused) lie nearly 0.5 mile (0.8 km) SW of Hemsley's Level, on the W bank of Ireshope Burn; one [NY 8449 3683] is driven into the vein beneath the Great Limestone, the other [NY 8438 3684] is in the shale above the limestone. The vein, reported as 6–9 in (15–25 cm) wide in the upper part of the Great Limestone, had small workable flats 2.5 ft (0.76 m) thick on the south side, containing clay with "balls of ore". In the White Hazle the vein was 1 ft (0.3 m) wide with clay, soft sandstone and "balls of ore". To the W, as at Lodgesike Mine, the rapid rise of the beds towards the Burtreeford Disturbance terminated the workings. A total of 680 tons of lead concentrates were obtained in 1834–1856. Limonite (Table 58) with siderite, galena and a little sphalerite is present on the dumps.

    Groveheads Low Vein–Far Vein group

    The veins of this group are mainly of importance for the iron ores associated with them in flats in the Great Limestone. These were last worked during World War II at the only surviving ironstone mine of the district, Carricks Mine (disused). The veins occur at the head of the Ireshope valley where they were discovered in hushes and first worked from levels at the horizon of the Little Limestone in Deepcleugh [NY 8443 3628]. In 1848–62 the Beaumont Co. drove Glints Level [NY 8445 3668] at the base of the Great Limestone from Clints Crags, 1930 ft in length, but the veins there proved to be disappointing for lead ore. The dumps suggest, however, that they were accompanied by strong sideritic mineralisation though they have not been worked for iron ore.

    The Clints iron ore is only partly oxidised and is essentially a carbonate ore (Table 58). No estimate of the size of the orebodies is possible, as the workings are not accessible.

    Carricks Mine (disused) [NY 861 380], is situated 0.5 mile (0.8 km) SW of the village of Ireshopeburn. The Groveheads Veins were probably discovered at surface; their courses are marked by surface hushes and shallow shafts. The mine was developed for lead ore by the Beaumont Co. Their earliest level was Groveheads Level, [NY 8580 3781] driven near the top of the Great Limestone from Groveheads Sike, cutting the two Groveheads Veins not far from their intersection. From it, small ramifying flats at the High Flat horizon were worked for lead ore on the N side of the High Vein. Craig's Level, [NY 8613 3794] which became the principal entrance to Carricks Mine, was commenced by the Beaumont Co. from Cold Knuckles in 1863; it runs 4050 ft (1.234 km) S4°E and by 1878 had been driven a further 2408 ft (734 km) S19°E. The Weardale Lead Co. subsequently extended it an additional 260 ft (79 m), the total length now being 6718 ft (2.05 km). The level starts near the base of the Great Limestone; after passing through Low Vein, the level enters the Tuft, and from Jingler Vein it is in the shale beneath the Tuft. S of Dawson's Vein the base of the Great Limestone is near the level roof, but farther S the limestone rises again, and the level probably ends in the Quarry Hazle, though it was not accessible S of Far Vein when examined in 1941.

    The veins listed above were cut in succession by Craig's Level; (Figure 32) shows their relations. The NE and E–W veins are traversed by the cross veins, which probably represent the splitting-up of the strong Swinhope Cross Vein known in the Swinhope Valley and Greenlaws Mine, farther to the SE. Lead ore was obtained from the Low Vein in the Coal Sills; from flats at the High Flat horizon associated with High Vein; from a vein-oreshoot 565 ft (172 m) long by 20 ft (6.1 m) average height by 1.5–2 ft (0.46–0.6 m) average width in the Little Limestone and "Pattinson Sill" (a sandstone immediately overlying the limestone) on Carr's Vein, with which were also associated small flats at the High Flat horizon of the Great Limestone; and from Dawson's Vein, which in the Little Limestone and associated beds carried a vein-shoot totalling 1850 ft (564 m) long and averaging 25 ft (7.6 m) high, the vein being 6–15 in (15–28 cm) wide, rich in galena. Production of galena from 1828–1879 was 5709 tons. The very meagre result for the considerable amount of exploration done here was due to the fact that almost all the veins proved to be poor in galena; but most of them were strongly mineralised in the Great Limestone with iron ore, limonite in the shallower workings, carbonate ores in the deeper places. The iron ore deposits here are thus of Bilbao type. The iron ore proved to be concentrated mainly in the bottom 10–20 ft (3–6 m) of the limestone; in places it extended as much as 200 ft (61 m) from the feeding vein. Iron ore has been obtained from the following veins in Carrick's Mine: Low, High, Lowe's, Dawson's, Maddison's, Far, and Nos. 4 and 5 cross veins. West of the junction of High and Low veins a flat of limonite, here at the High Flat horizon was formerly worked by the Weardale Iron Co. This terminates against the Quarry Cross Vein downthrowing NE. Borings have shown that ore is present in the lower part of the limestone in the trough between this cross vein and No. 4 Cross Vein.

    The mineral-assemblage in the veins of Carrick's Mine is as follows: siderite, ankerite, quartz, fluorite, dolomite, calcite, galena, limonite. Ankerite and siderite are the main primary constituents of the replacement bodies; upon oxidation, limonite is produced, and some additional silica and phosphorus appears to be introduced. Dolomite, also replacing limestone, appears to be particularly associated with Nos. 4, 5 and Quarry cross veins. The main source of limonite ore in the 1940–46 workings was a substantial extension, beneath water level, of the Low Vein flat E of Craig's Level. This has been worked as far E as No. 2 Cross Vein; boring proved the flat to continue still farther E, but unfortunately directly under a boulder clay cover which introduced serious mining difficulties. Carbonate ore, partly oxidised, has been obtained from Lowe's Vein and from small subparallel veinlets (Risdale, Race's and an unnamed one). Boring revealed an orebody estimated to contain about 100 000 tons S of Far vein. On the S side of this orebody fluorite was found in some quantity, possibly indicating the proximity of another vein not yet identified.

    E of Carrick's Mine, the older Rowantree Mine (disused) [NY 870 374] worked flats no longer accessible in the Great Limestone. The relation of these to the Carrick's workings is shown in (Figure 32). The largest flats, lying N of Rowantree Vein, appear to be related to a belt of ENE fractures which are unrepresented in Carrick's Mine W of No. 2 Cross Vein.

    There is little doubt that considerable opportunities remain in the Carrick's Mine area and in the ground SE of Craig's Level for the development of further iron ore deposits of the type indicated above. Similar deposits are, for example, probably present in the upper reaches of Langdon Beck (see p.242).

    Analyses of iron ores from Carricks are given in (Table 59).

    Incomplete records of production in the official statistics give a total of 342 703 tons of iron ore from Carrick's Mine between 1888 and 1919, when shipments ceased; from 1880–1920, 1059 tons of galena were obtained. The mine was reopened in 1940–41 on behalf of the Ministry of Supply, and produced up to 1000 tons of iron ore weekly until 1942. Total output of Bilbao-type iron ore from Carrick's Mine thus exceeds 0.5 million tons.

    Sidehead Quarry Vein—Iron ore

    NY83NE; Durham 23 SW

    During 1942 a vein of limonite trending N60°E was discovered at the Sidehead Limestone Quarry (disused) [NY 8895 3875] 0.5 mile (0.8 km) NNE of St John's Chapel Station. The vein appears to be 12–14 ft (3.7–4.3 m) wide at the top of the limestone; a crosscut about 10 ft (3 m) below the top revealed a width of 5 ft (1.5 m). In 1942 the vein was known over a length of 125 ft (38 m). An arithmetical average of samples representing (i) the top exposure (ii) the crosscut (iii) pieces of ore from the vein near the bottom of the limestone gave the following result: iron, 45.0 per cent; silica, 11.6; sulphur, 0.055; phosphorus pentoxide, 0.06; lead, 0.12 (dried; analysis by Pattinson and Stead, Middlesbrough, 1942). The vein appears to be on approximately the same line as the belt of ENE fissures cut in the northern part of Rowantree Mine.

    Bleaklaws Cross Vein—Lead ore

    NY83NE, 84SE; Durham 23SW, NW. Direction N25°W

    This vein has been followed a distance of 2450 ft (747 m) SSE from Slitt Vein by a branch of Levelgate Level (p.186), on which, at 2000 ft (610 m), a shaft [NY 8903 3906] connects with surface; the shaft dump shows quartz, calcite, purple fluorite, galena, with limestone replaced by ankerite and limonite. Blealdaws Shaft [NY 8907 3887], 600 ft (183 m) S, is connected with the end of the branch level by a crosscut 200 ft (61 m) long. N of Slitt Vein, Blealdaws Cross Vein has been followed by Levelgate Level at 1215 ft (370 m) OD from the end of the Levelgate workings on Old Fall Vein to Sedling Vein, 2130 ft (649 m) a crosscut continues through the Quarry Hazle to Longsike Vein.

    Middlehope Cross Vein, Shield Close Vein and Middlehope Shield Vein

    White's Level [NY 9058 3976] formed the main entrance to the Beaumont Co.'s Middlehope Mine (disused). This runs NE from the bank of Middlehope Burn 1 mile (1.6 km) N of Westgate, probably in the shale beneath the Quarry Hazle. The level mouth has collapsed. At 650 ft (198 m) it cut Shield Close Vein, flats related to which were worked from rises above a branch level for a length of 1300 ft (396 m) in the Great Limestone. Iron ore appears to have been obtained from the same flats, by way of an intersecting NE string called Dawson's Vein, on which a level [NY 9088 3965] was driven by the Iron Co. from surface. At 2060 ft (628 m) from the portal White's Level enters the Great Limestone; at 2700 ft (823 m) Middlehope Shield Vein was cut and followed eastwards for 400 ft (122 m), but no record of the condition of this vein remains. The level then turned on to Middlehope Cross Vein, which was followed northwards for approximately a mile (1.6 km), and in the first 900 ft (274 m), small flats in the Great Limestone were worked on the E side. As noted above (p.189) the level on the cross vein gave access to the old London Lead Co.'s workings on Scarsike Vein, and also to workings on Richard's Vein. The total production by the Beaumont Co. from the Middlehope Mine amounted to 15 831 tons of lead concentrates between 1818 and 1864 when operations ceased.

    The absence of any veins which might be regarded as equivalent to the NE veins of Carricks Mine in the White's Level workings is noteworthy.

    Thorny Brow Vein—Lead ore

    NY94SW, SE; Durham 23NE. Direction N55°E, probable downthrow SE

    This vein is known only in Rookhope where a shaft has been sunk on it on the E bank of the burn [NY 9450 4148], 3400 ft (1.036 km) S of Rookhope church. Ancient workings in the Great Limestone are said to have yielded ironstone on both sides of the burn, but no details are available. The shaft–collar at 980 ft (299 m) above OD–is sunk to the Low Level at 807 ft (246 m) above OD which commands the Three Yard Limestone; a sump continues to 770 ft (235 m) above OD. The Low Level [NY 9461 4140] was driven 1700 ft (518 m) NE; no stopes are shown on the section. A rise at the forehead communicated with small workings in the Nattrass Gill Hazle and Four Fathom Limestone, while a sump was sunk 32 ft (10 m) to the Three Yard Limestone, which owing to the dip NE had there passed beneath the Low Level. Coarse purple fluorite, with quartz, siderite, and a little galena and sphalerite occur on the dump. The only record of production is 257 tons of galena obtained by the Beaumont Co. in 1836–42. The continuation of Thorny Brown Vein is considered to have been cut at the western end of Stotfield Burn Mine (p.205).

    Greenlaws West Vein and Greenlaws East Vein

    Greenlaws Mine The account of this mine is summarised from a report by Dr J R Earp, dated 1941, based on plans, sections and records of the Beaumont and Weardale Lead Co.(disused), the workings of which lie S of St John's Chapel, exploited the two Greenlaws Veins. The West Vein was probably discovered first, and worked in Greenlaws Hush [NY 882 367] in the Great Limestone and from shallow shafts. The vein, which can only be regarded as weak, carries very small oreshoots in the Great Limestone, and in the Slaty Hazle. The East Vein, on the other hand, was strongly mineralised and yielded ore at horizons ranging from the Little Limestone down to the Tynebottom Limestone from patchy vein-oreshoots extending over a total length of 2 miles (3.2 km). (Figure 30) illustrates the relation of these to the principal working levels. Development of East Vein appears to have begun about 1850; by 1860 it was making a serious contribution to Weardale production. This represents the last substantial discovery by the Beaumont Co.; it was only partially exploited when the Weardale Lead Co. took over in 1884; production ceased, apart from small quantities obtained by tributers, in 1897.

    Two major cross veins cut the Greenlaws veins. The Swinhope Cross Vein, referred to in connection with Carricks Mine, was encountered near the SE end of the workings on both veins. Its throw at West Vein is 21 ft (6.4 m) NE; at East Vein 40 ft (12 m) NE. Smaller faults, presumably flyers, were cut on both veins. Western-hope Cross Vein, a broad confused belt of fracturing, cuts the two veins in the vicinity of the outcrop of the Four Fathom Limestone in Daddry Shield Burn [NY 8883 3696]. Neither cross vein carried workable lead mineralisation at Greenlaws, though a little ore was produced from a S flyer of Swinhope Vein. There is a record that the strongest unit, Westernhope Cross Vein, which cuts the East Vein about 1600 ft (488 m) SW of Quarry Level head, was 5–6 ft (1.5–1.8 m) wide, mainly composed of coarse fluorite in the Scar Limestone; this has not been worked. The cross vein shifts East Vein NE side 5 ft (1.5 m) NW.

    The principal levels on Greenlaws West Vein were (i) Birksike Level [NY 8700 3608], a crosscut from Harthope Burn in the shale probably beneath the High Coal Sill, reaching the vein at 515 ft (157 m) S34°E; (ii) Dent's Level, [NY 8821 3672] starting from Greenlaws Hush at 1410 ft (430 m) above OD in the Great Limestone, about 2700 ft (823 m) long on the vein; (iii) Dent's Low Level, [NY 8935 3761] starting from the W bank of Daddryshield Burn, driven in and below the Slaty Hazle for 1425 ft (434 m). There is an unworked gap of about 800 ft (244 m) between the end of the workings from Low Level and the mouth of Dent's Level. The vein is reported as 2 ft (0.6 m) wide in the Great Limestone, composed of fluorite, "rider" and a moderate admixture of galena. Calcite, aragonite and sphalerite are also present on the dumps. In the Slaty Hazle the average width was 1.5 ft (0.46 m) while in the Scar Limestone widths up to 3 ft (0.9 m) were reported, but no stoping was done.

    The highest exploration on the East Vein was in the Firestone, [NY 8839 3616] but here no workable ground was found. Jackson's or Watt's Level [NY 8865 3671], at 1380 ft (421 m) above OD, starting one mile (1.6 km) SSW of Daddry Shield Bridge, commanded the Great Limestone and gave access to the oreshoot there and in the beds up to the Little Limestone. The Tuft and Quarry Hazle, with their associated shales, produced generally poor ground on the vein, but a strong belt of mineralisation accompanied the Four Fathom Limestone and Nattrass Gill Hazle, while another extended from the Three Yard Limestone down to the Scar Limestone, in places continuing to the Single Post Limestone. Below this a trial to the top of the Whin Sill showed some mineralisation in the vein in the Tynebottom Limestone, but results here were disappointing. The Whin Sill can hardly be said to have been satisfactorily tested, but the exploration done evidently suggested downward impoverishment of the vein. Vein widths throughout the oreshoots varied from 1 to 8 ft (0.3 to 2.4 m); the width in the Tynebottom Limestone (which is exceptionally thick here) was 2 ft (0.6 m). The mineral suite included amber fluorite, quartz, siderite, galena, calcite, with minor amounts of pyrite and sphalerite. At the horizon of the Middle Level [NY 8887 3695] (beneath the Four Fathom Limestone at 1218 ft (371 m above OD), D A Wray, (in Sherlock 1918, p.58) recorded strontianite though Young (1985, p.762) has cast doubt on the authenticity of this. The vein had an average hade to the NW of 15° between the Little Limestone and Nattrass Gill Hazle. Above the Little Limestone the hade in shales was greater.

    Greenlaws East Vein carried, in addition to the vein-shoots illustrated in (Figure 30) (p.182), a belt of small flats at the High Flat horizon, 15 ft (4.6 m) below the top of the Great Limestone, which extended for 1000 ft (305 m) along both sides of the vein. These flats were 3–4 ft (0.9–1.2 m) thick, but were workable only for 5–10 ft (1.5–3 m) on either side of small leaders subparallel to the vein. Such leaders were encountered as far as 120 ft (37 m) from the vein. The flats were composed of altered limestone, with cavities containing fluorite and galena crystals, and clay. The altered limestone contained ankerite and siderite, converted to limonite near the surface, but no iron-mining has been done on this vein. Flats 2–6 ft (0.6–1.8 m) thick were also found in the upper part of the Scar Limestone, extending 6–10 ft (1.8–3 m) from the vein, containing siderite, coarse fluorite and some galena. The yield from these was poor, and they were not extensively worked. They are, however, unique in Weardale.

    East Vein, NE of and near Swinhope Cross Vein, was poor at all horizons. SW of the cross vein, however, ore was found in the Great Limestone and Coal Sills and worked as far as the first subsidiary cross vein; the latter was about 3 ft (0.9 m) wide, and yielded some ore. About 120 ft (37 m) SW of it a second belt of flyers shifted the East Vein SW side SE; the vein is reported as narrow and poor in the forehead of a drift in the Great Limestone. Neither this drift nor the main Jackson's Level (here in the Quarry Hazle) was driven clear of the cross veins or flyers; uncertainty, therefore exists as to whether the vein was finally impoverished at the cross veins. Virgin ground exists for over a mile (1.6 km) SW of these foreheads, but in Langdon Beck where the next workings on or near the line of the vein occur, there are numerous small, rather poor veins rather than a single strong vein. This virgin ground could be reached by extending Craig's Level SE from Carrick's Mine for there is very little change in the level of the Great Limestone between the two mines.

    Recorded production of lead concentrates from Greenlaws Mine is as follows: 1818–1883 (Beaumont Co.), 27 643 tons; 1884–1907 (Weardale Lead Co.), 15 210 tons; total 1818–1907, 42 853 tons.

    In the 1940s an unsuccessful attempt was made by Mr J Adamson to reopen Quarry Level, [NY 8941 3762] the lowest adit on the East Vein, which runs as a crosscut at the base of the Slaty Hazle from the right bank of Daddryshield Burn at 990 ft (302 m) above OD to the vein, with the object of working fluorspar. Spar may remain in Westernhope Cross Vein, but there seems little hope of substantial quantities from backfill in old lead stopes on East or West Greenlaws veins. Their presumed continuations in Langdon Beck (p.242) indicate a fanning-out into weak structures.

    Heights North Vein–Heights West Cross Vein group

    Heights North Vein possibly represents the continuation of Greenlaws West Vein, but there is no evidence of its existence between Dent's Low Level at Greenlaws Mine, and the Slitt Vein. North of Slitt Vein the group of veins listed above was worked at Heights Mine (disused) [NY 921 392]. The South Vein and probably the West Cross Vein were discovered at outcrop in the Great Limestone; both are still visible at surface. The veins were chiefly important for the flats associated with them at the High Flat horizon. Some lead ore was obtained from these by the Beaumont Co., but their main value lay in limonitic ironstone. The flats were worked by the Weardale Iron Co.; they were associated with Heights North, South and West Cross veins, as well as with Coulthard's String, a small vein 150 ft (46 m) NW of the North Vein. North Vein appears to be shifted 117 ft (36 m) NE side NW by East Cross Vein, though the apparent shift may merely represent a transfer of productivity to Coulthard's string NE of the cross vein. The flats averaged 7–8 ft (2.1–2.4 m) thick. From 1850, when ironstone mining commenced, to 1863 a total of 141 491 tons of iron ore were mined. The excavations produced were estimated by the Weardale Iron Co. as follows (data from MS records of the Company, dated 1863):

    Greenlaws or Heights North Vein 37516 cubic yards (28,683 m3)
    Coulthard's String 4158 cubic yards ( 3179 m3)
    West Cross Vein 54432 cubic yards (41616 m3)
    Heights South Vein 19826 cubic yards (15158 m3)
    Total 115 932 cubic yards (88 637 m3)

    The mining method adopted was to drive levels from the surface on the line of each vein, to command the High Flat. A main heading was carried on for exploration out of which bords were turned 6 yards (5.5 m) wide, a pillar 3 yards (2.7 m) wide being left between the bords. The bords were driven to the edge of the flat, and the pillars then recovered. Iron mining at Heights continued until 1867–68; West Cross Vein was explored for 800 ft (244 m) NW of Coulthard's String, and North Vein was tried E of East Cross Vein, but neither exploration proved very successful. A trial of South Vein from Park Burn Level [NY 9217 3860] (p.212) in the Nattrass Gill Hazle and Four Fathom Limestone also failed.

    Both veins are today exposed in the Great Limestone in Heights Quarry. South Vein has been left as an unworked pillar in the western part of the quarry [NY 9240 3900]. The vein is here up to 6 ft (1.8 m) wide consisting of bands of coarse quartz and purple fluorite with limonite and a little galena, calcite and aragonite; the adjacent limestone has been replaced for at least 6 ft (1.8 m) on the N side of the vein by ankerite and siderite, now largely oxidised to limonite. South Vein is also exposed along the northern face of the eastern section of the quarry where it carries abundant purple fluorite and limonite [NY 9272 3904]. Limonite-rich flats are associated with the vein here; purple and green fluorite commonly line vugs in these flats. The Heights workings have provided many well-crystallised specimens of green fluorite. West Cross Vein is also exposed in the centre of the quarry [NY 9255 3900]. The filling resembles that of the South Vein, consisting of bands of fluorite, quartz, limonite and a little galena. some strings of fluorite, quartz and calcite, apparently branching from West Cross Vein were seen in the top of the limestone in recent excavations a short distance to the N of this. The mineralisation and the unstable ground conditions associated with the old underground workings in both veins have imposed limits on quarry development.

    Heights North Vein (on the orthodox interpretation of the shift by East Cross Vein) continues NE. In 1861–67 the Beaumont Co. drove Northgate Level [NY 9351 4200], a crosscut-adit, to the vein from Sunderland Cleugh, in the upper part of the Great Limestone. Flats, up to 15 ft (4.6 m) wide from the vein, were found to contain "rider" 6–8 ft (1.8–2.4 m) thick, but they were poor in galena. Some iron ore was subsequently obtained from them. To the SW the workings joined up with those from Heights Mine, NE they extended 1500 ft (457 m) from the level head. Farther north-east, some iron ore seems to have been obtained from the old Hangingwalls Mine (disused) [NY 9417 4073] on the same vein, on the W side of the Rookhope valley, but no details are available. At Brandon Walls Mine (disused) a shaft [NY 9465 4111] E of Rookhope Burn reached the base of the Scar Limestone. The vein yielded galena in a matrix of fluorite, siderite and quartz for a length of 1150 ft (351 m) in the Three Yard Limestone and Six Fathom Hazle; after an unproductive stretch 300 ft (91 m) long, another small oreshoot, extending in the Six Fathom Hazle 550 ft (168 m) NE to the forhead of the mine, was worked; 2800 ft (853 m) ahead exploratory levels from Stanhopeburn Mine found Brandon Walls Vein to be represented by small strings only. In the Great Limestone, iron ore was obtained from a surface adit [NY 9476 4118], with which a winding shaft [NY 9487 4125] near the Rookhope–Bewdley road communicated. The total yield of lead concentrates recorded from Heights and Brandon Walls Mines was as follows: Heights Mine, 1847–69 (including Northgate), 7470 tons; Heights Limestone Quarry, 1901–18, 39 tons; Brandon Walls Mine, 1850–86, 1354 tons. The average silver recovery from Brandon Walls ore was 6 oz silver per ton of lead.

    Captain's Cleugh Vein—Iron and lead ore

    NY94SW, SE; Durham 23NE Direction N80°E.

    The main level of Captain's Cleugh Mine (disused) [NY 9497 4095] starts from Brandon Cleugh, 500 ft (152 m) SE of Brandon Walls Farm. Iron ore was worked from replacements at the High Flat horizon of the Great Limestone, the top of which is 2.5–4 ft (0.76–1.2 m) below the Black Bed here. The flats averaged 6 ft (1.8 m) thick but in places ore extended 20 ft (6 m) down into the limestone. At 900 ft (274 m) from the adit mouth the vein splits, the mineralisation following an ENE branch for 820 ft (250 m) to the forehead; on this branch a shaft [NY 9530 4106] communicates with surface. No separate record of iron ore production remains; 241 tons of lead concentrates are recorded for 1850–58, from which 5.3 oz silver per ton of lead were recovered. The probable eastward continuation of Captain's Cleugh Vein was cut under Reahope Burn in a crosscut from Stanhopeburn Mine, but the vein was not workable.

    Swinhope Cross Vein—Lead ore

    NY83SE; Durham 31NW. Direction N43°W, throw at Swinhopehead Mine, 65 ft (20 m) NE.

    The splitting-up of this cross vein in the Ireshopeburn and Carricks mines has already been described and its effect upon the Greenlaws Veins; has been mentioned. At Carricks and Greenlaws the main fault is not mineralised, but orebodies are associated with flyers from it. At Swinhopehead Mine (disused) [NY 8874 3418] some lead ore was got from the main fault. This crosses the headwaters of Swinhope Burn (Weardale) about 0.75 mile (1.2 km) SW of Swinhope Bridge on the Newbiggin–Westgate road. A crosscut level enters the vein from the downthrow side in the Great Limestone. Coarse, rather siliceous fluorspar is present on the heaps. The vein is intersected N of the stream by a small E–W vein, less than 1 ft (0.3 m) wide where exposed in an opencut [NY 8856 3424] in the limestone, W of the main vein. The Beaumont records state the Swinhope Vein was about 3.75 ft (1.1 m) wide "free spar thinly mixed with ore". At the intersection with the E–W vein, the width increased to 12 ft (3.7 m), mostly coarse spar. The only record of production is 326 tons of galena in 1823–46. A trial for fluorspar was made by G G Blackwell and Son in 1905–06, but no production is recorded.

    Westernhope Old Vein–Westernhope Great Vein group

    Westernhope Old Vein runs more or less parallel to Swinhope Cross Vein and has already been mentioned in connexion with Greenlaws East Vein. It was worked from the western headwaters of Westernhope Burn at the remote Westernhope Old Mine (disused). There are extensive opencuts extending through the Great Limestone up to the Coal Sills sandstones. Martindale's Level [NY 9176 3433] from the bottom of the opencut was being used to rework old ground on the vein in 1861. The main level [NY 9196 3450] driven from the downthrow side, reached the vein beneath the Great Limestone; it extended 1800 ft (549 m) NW and 2575 ft (785 m) SE of West Grain, across the head of Wolf Cleugh. Trials were made to the Four Fathom Limestone, but no reacord of the results has been found. Both in West Grain and in Wolf Cleugh there are extensive heaps, containing coarse fluorite and quartz in approximately equal quantities, with small amounts of sulphides, including galena and chalcopyrite.

    Robinson's Vein has been worked on the W side of the valley only from a level [NY 9210 3515] 1100 ft (335 m) long in the Great Limestone. Purple and amber fluorite, limonitised limestone and galena are present on the dump. Records state that in the forehead the vein is only 10 in (0.25 m) wide "of bad quality".

    The eastern headwater of Westernhope Burn, Ash Cleugh, is the site of Westernhope New Mine (disused). The principal level here [NY 9297 3472] was driven E through one of the Ash Hill veins to reach, at 500 ft (152 m), Great Vein, which runs along the E side of the Swinhope valley. A branch continued along this vein to reach Gowland's Vein at about 1600 ft (488 m) SE. All the veins here are associated with extensive ankeritisation in the Great Limestone (analysis, (Table 22). The other minerals include purple and amber fluorite, quartz and galena. T Rumney's mine report, dated 1861, states of the veins in Ash Hill Cleugh that they are "altogether very weak veins and I do not know of anything that is worthy of further trial...". There is, however, an unconfirmed report that a substantial quantity of fluorite remains in Great Vein.

    The Westernhope Mines produced 3146 tons of lead concentrates in 1818–61. The only production of fluorspar so far has been 157 tons from the dumps, transported by tractor. Some hundreds, possibly thousands, of tons remain, but the mines are not accessible by road.

    Red Vein—Lead ore, iron ore, fluorspar

    NY84SE, 94SW, SE, 93NE, NZ04SW; Durham 16SW, SE, 23NE, 24NW. Direction N65–80°W, throw; approximately 14 ft (4.3 m) NE at North Grain; small SW throw after union with Groverake Vein; 6–7 ft (1.8–2.1 m) NE at Stotfield Burn Mine; 16 ft (4.8 m) SW at Beaumont Sump, Stanhopeburn Mine; small NE throw at Hope Level.

    Greencleugh Vein and Groverake Vein

    Greencleugh Vein—Lead ore, iron ore, fluorspar

    NY84SE; Durham 16SW. Direction N80°W–N80°E ?small throw

    Groverake Vein—Lead, ore, iron ore, fluorspar

    NY84SE; Durham 16SW. Direction E–W, throw 18 ft (5.5 m) S at Groverake Shafts

    Red Vein is the northernmost of the three great "Quarter-point" veins of Weardale, the other two being Sedling-Longsike Vein and Slitt Vein. All three have the following characteristics in common (i) the oreshoots on them are spread over a considerable vertical range of strata (ii) they carry wide bodies in which fluorite is the principal mineral, lead values being generally low. Extensive ironstone deposits are associated with both Red and Slitt veins (iii) they are productive when the direction is nearest to E–W, but turn barren where it changes to WNW (Dunham et al., 1965); (iv) transcurrent movement has predominated on them (Greenwood and Smith, 1977).

    Red Vein extends from the head of Rookhope nearly 9 miles (14 km) ESE. The principal mines associated with it include the group of ironstone opencuts and mines at Rookhopehead; Red-burn, Stotfield Burn, Stanhopeburn and Hope Level mines (Figure 33). The extent of ground workable for fluorspar on the vein has proved to be 39.6 per cent of its total known strike length. At Rookhopehead what is believed to be Red Vein is exposed in shale in North Grain [NY 8824 4496], 400 ft (122 m) S of the bridge which carries the Allenheads- Rookhope road over the stream. The vein is not mineralised in the shale, though a chalybeate spring rises from the fracture. Immediately to the S, a flat of limonitic ironstone replacing the Lower Felltop Limestone has been worked [NY 883 449] in upfaulted ground between Red Vein and a small parallel fault 280 ft (85 m) SW which throws about 6 ft (1.8 m) SW. N of the road, 3500 ft (1.07 m) ESE of North Grain ironstone quarry, a small opencut [NY 8930 4452] tested the vein at the horizon of the Coalcleugh Beds, without success. The nearby Bashamere North Level [NY 8905 4441] in the Low Grit Sill, is said to have found strings of fluorite only.

    Greencleugh Vein, regarded as a branch of Red Vein, may be traced from South Grain, where it crops out close to Corbetmea Shaft [NY 8772 4444], the air shaft to Fawside Level (Allenheads Mine; see p.171), through a series of great opencasts known as Frazer's Hushes [NY 881 445]. The original hushing was probably done in search of lead ore; a little fluorspar has been obtained from the tailings remaining from dressing of lead ores. In the middle of the last century, Weardale Iron Co. opened up an exceptionally extensive flat of limonitic ironstone, which had replaced the Lower Felltop Limestone on both sides of Greencleugh Vein. This was 1300 ft (396 m) long and up to 700 ft (213 m) wide, the thickness of the ore being 3–5.5 ft (0.9–1.7 m). A SW branch from Greencleugh Vein at 1925 ft (587 m) E of Corbetmea Shaft probably contributed to the mineralisation of the flat, and ironstone has been worked along it underground SW of the face of the opencut for 600 ft (183 m), the average width being 150 ft (46 m). The Beaumont reports for 1863 state that this branch in the Felltop Limestone was 8 ft (2.4 m) wide, and consisted of a 2 ft (0.6 m) middle rib of ironstone in spar; the throw is given as 5–8 ft (1.5–2.4 m). Greencleugh Vein is reported to have been 3–5 ft (0.9–1.5 m) wide, of the same quality. Some stoping was done in the sandstone beneath the Felltop Limestone by the Beaumont Co., the vein being 1–2 ft (0.3–0.6 m) wide "nice spar, quick in ore". W of the ironstone workings, Greencleugh Vein was tried in 1939–40 by Mr J W Philipson. In a surface cut the vein was 2 ft (0.6 m) wide; a dip shaft [NY 8778 4442] showed that in depth it increases in width; at 35 ft (11 m) deep, probably in the Hippie Sill, the width is said to have been 10 ft (3 m). The vein contains purple and green fluorite, with some galena and sphalerite; a sample of lump fluorspar taken in 1941 assayed 95.9 per cent calcium fluoride, 2.91 silica (assay by Mineral Resources Laboratory, Imperial Institute, 1941). At greater depth, both Greencleugh Vein and its branch vein were explored from the Fawside Level of Allenheads Mine at 1370 ft (418 m) above OD. Neither was found to contain more than traces of mineralisation in the level, which is driven in the shale above the Firestone. The records state that a rise put up on Greencleugh Vein from a crosscut from Corbetmea Shaft reached the lower 5 ft (1.5 m) of the Great (or Low Grit) Sill, but found the vein pinched. It is likely that the vein is affected by a strong cross vein met in the crosscut and also in Fawside Level. The branch vein, tried by a rise which penetrated 20 ft (6 m) into the Great Sill, carried 8–10 in (20–25 cm) of fluorite with sphalerite. Exploratory work at Rookhopehead Mine (disused) [NY 8859 4457] by Border Minerals Co. consisted of the driving of a level from the S bank of Rookhope Burn, starting 2850 ft (869 m) ENE of Corbetmea Shaft, which passed through boulder clay into shale with one of the Rookhope Shell Beds exposed in the bottom part and reached Greencleugh Vein at 500 ft (152 m) from the portal. This was 16 in (0.4 m) wide where cut, increasing in a 12 ft (3.7 m) winze into sandstone to 2 ft (0.6 m), mineralised with fluorite, quartz, galena and sphalerite.

    This trial was abandoned in 1944, but in the 1970s Weardale Lead Co. began a programme of deep drilling of Greencleugh Vein which was continued by Swiss Aluminium (UK) Ltd (SAMUK) after their takeover. Altogether eight inclined holes were drilled, of which five found ore, the deepest intersection being 80 ft (24.4 m) below the base of the Great Limestone. Before SAMUK ceased operations they had driven an incline drift known as Frazer's Hush Mine from [NY 8900 4435] at 1420 ft (433 m) above OD down westward to reach the middle of the Great Limestone at 1110 ft (338 m) above OD. Weardale Minerals Ltd then acquired the property, which has now (1989) become the company's principal mine. The 60-Fathom Level from Groverake Mine (described below) has been driven up under the Great Limestone to connect with Greencleugh Vein, revealing an oreshoot 1000 ft (300 m) long lying E of the boreholes and Samuk incline. Extraction of well-mineralised ground westward from the incline is also proceeding.

    Red, Greencleugh and Groverake veins come together in a triple junction (on surface approximately [NY 9002 4445]) and according to the primary geological survey, the barren continuation of Burtree Pasture Vein also continues to this junction, which is within the workings of Groverake Mine (Weardale Mining and Processing Ltd) [NY 896 442] (Plate 5). Operations here probably predate the Beaumonts, since Groverake Vein outcropped in high Pendleian strata on the hillside east of the Allenheads- Rookhope Road. The Beaumont Co. drove adits and sank two main shafts from the valley bottom; their records mention widths of 7–12 ft (2–3.7 m) in the Great Limestone, average widths of 10 ft (3 m) in the sandstone above the Firestone and the fact that at this horizon, the walls were seldom reached; a test in one place showed a width of 34 ft (10.4 m) from wall to wall; the filling was 'chiefly fluorspar, coarse and glassy, on the whole very thinly mixed with (lead) ore'. Towards the end of their tenancy, the Beaumont Co. built a mill at Rispey, about a mile (1.6 km) SE, to which the crude ore was trammed for dressing. Gravel tailings here, sampled in 1941, were found to carry CaF2 73.77; SiO2 17.5, Pb 0.72, Zn 0.18 per cent (Assay by Imperial Institute). Output of lead concentrates in the Beaumont years, 1819–1883 amounted to only 6489 tons. The Weardale Lead Co. in its earlier years continued operations, obtaining 18 061 tons between 1884 and 1916. Fluorspar was also mined, but inadequate treatment plant prevented adequate removal of silica, and the total output by Weardale Lead Co., and its successors J W Philipson, Allenheads Mining Co., and Billing Ganister Co. 1901–1940 totalled only 31 817 tons. It remained for modern operations dating from World War II, by Blanchland Fluor Mines Ltd (a subsidiary of Colvilles Ltd) and eventually by British Steel Corporation (BSC) to make this mine the leading fluorspar producer of the orefield. In the middle of the 19th century, Groverake also contributed a substantial tonnage of iron ore, from flats in the Lower Felltop Limestone both N and S of the vein. Weardale Iron Co. worked these opencast and by underground pillar-and-stall methods.

    Red Vein (sensu stricto) was tested NW from the triple junction and SE of the junction yielded some stoped ground above the 50-Fathom level containing highly comminuted veinstuff, interpreted as due to postmineralisation movement. It should be added that while it may be the case that Red, Groverake and Greencleugh veins come together near the surface, in depth they diverge owing to their differing attitudes; Red Vein dips steeply NE, Greencleugh less steeply NNE, while Groverake Vein dips S. The main eastward continuation of Greencleugh Vein was picked up when Rake Level, in the Grit Sills group was redeveloped over a length of 1300 ft (396 m) and to heights varying up to 120 ft (37 m). Tested on the 50-Fathom Level in the Great Limestone, where its junction with Red Vein lies approximately 500 ft (152 m) WNW of Groverake Vein, it did not prove to be workable. The redevelopment of the mine has also led to the conclusion, according to Greenwood and Smith (1977, p.B184) that while Burtree Pasture Vein does not impinge on the triple junction near surface, it can be followed through the workings, where its intersection with Groverake Vein plunges at about 45°W.

    The principal producer at this mine has, however, been Groverake Vein itself. The oreshoot, one of the largest in the northern Pennines, is 4350 ft (1.326 km) long and the maximum worked height reaches 700 ft (213 m) in wallrocks ranging down from the Lower Felltop Limestone to the base of the Nattrass Gill Hazle. Exploration has already begun to go deeper. The oreshoot is at its most consistent in the Great Limestone, which is mineralised over virtually the whole length of the shoot. Greenwood and Smith (1977) record that in a 2297 ft (700 m) length the average width was 12.5 ft (3.8 m) and a maximum of 20 ft (6.1 m) was reached. The former lead miners had slit the vein near the footwall to extract galena, their workings being less than 3 ft (1 m) in average width. The filling of the vein consisted of (i) an early phase of quartz with some massive chalcopyrite (ii) galena, mainly near the N wall, associated with ankerite, siderite and some fluorite (virgin stretches of this were seen in the western part of the mine); (iii) the main filling of green and purple coarse fluorite with some interbanding of quartz and chalcedony; (iv) late transgressive quartz, chalcedony and carbonates. It is not clear whether (ii) was in effect an assymetric band produced by later reopening to introduce the main surge (iii) but that is perhaps more probable than late-stage introduction of (ii). Above the limestone, through the thin sandstones and shales up to and above the Little Limestone, the continuity of mineral was less complete but there were still workable channels through to the higher beds. From the Firestone upward, continuity was again remarkable, a fact attributed by Greenwood (personal communication) to hardening of the shales by early wallrock silicification. There is another factor that also probably played its part. No detailed record of the strata from the sandstone beneath the Lower Felltop Limestone down to the Firestone exists, but it was noted that only a short distance above the latter, coarse grit was seen and it may be suggested that this great oreshoot has in fact developed against a washout channel of the Grit Sills, mainly filled with sandstone, comparable with the conditions at Hunstanworth (Chapter 11). This part of the Rogerley palaeoriver probably continued, becoming shallower towards the head of the Rookhope Valley for at Corbetmea and Frazer's Hush there is still a sandstone, the Great ( = Low Grit) Sill, of 58–60 ft (17.7–18.3 m), too thick to be part of the normal Slate Sills stratigraphy as recorded at Allenheads. In the Firestone and overlying beds, Groverake Vein was found to have split into two or three linked branches and of these, the lead miners had only worked in the northern one. An important part of the large output from the mine under British Steel Corporation (BSC) came from these workings, and running ground was still being extracted via Rake Level when the mine was put on care and maintenance at the end of their tenancy. Further substantial tonnages have been won during the retreat stage of Rake Level, albeit of somewhat diluted ore.

    The state of development at the time BSC took over is outlined on the section forming fig. 5 in Dunham (1952, p.33). Wallace's Level [NY 8989 4416] close to 1600 ft (488 m) above OD remained from the ironstone workings where the vein had been recorded as 8 ft (2.4 m) wide in the Lower Felltop Limestone, and a sublevel at 1645 ft (501 m) above OD had given access to the highest workings. The next adit was Rake Level [NY 8956 4413] starting from the mine yard at 1411 ft (430 m) above OD and this had been driven well beyond the eastern termination of the oreshoot, to where the trend changed from E–W to ESE. The Drawing or No. 1 Shaft [NY 8950 4410], in the hangingwall, had been sunk to the 50-Fathom Level at 1106 ft (337 m) above OD, while the Whimsey or No. 2 Shaft [NY 8953 4412], was down to the 80-Fathom Level at 960 ft (293 m) above OD. The outline of the oreshoot has not been greatly enlarged during the redevelopment, but it has been filled out and much fluorspar has been won from veins previously slit and branches previously unworked. This process has been facilitated by the driving of a new incline, the Firestone incline, to give access to the Firestone Sill at 1318 ft (402 m) above OD; an additional in-bye incline became necessary to keep control of this bed as it dipped gently E. Redevelopment of the Rake Level was also essential to enable extraction of the upper ground. In depth, the Quarry Hazle, unfavourable in the vicinity of the shafts because shale beds were present in it, became a good wallrock 500 ft (152 m) to the E and was stoped to the point on the 60-Fathom Level where much of this formation had dipped beneath the level. An incline has been sunk to reach the block ahead, where the vein is still 12–14 ft (3.7–4.3 m) wide; this block was the last reserve extracted before operations in this part of the mine ceased. The 80-Fathom Level was extended to work a block 900 ft (274 m) long lying either side of the shafts in the Nattrass Gill Hazle, but at about 600 ft (183 m) E of No. 1 Shaft the vein which had thus far stood almost vertically below its position in the 60-Fathom Level, began to hade over to the S, and alternate between E–W and ESE, with an adverse effect on the mineralisation; this condition continued 650 ft (198 m) to the forehead. No. 2 Shaft has now been sunk to the Three Yard Limestone at the 90-Fathom Level, 897 ft (273 m) above OD, but this was done to provide water standage, though lenticular ore occurrences have been found. An incline dipping E has been started from the 80-Fathom Level E of No. 1 Shaft and had reached the 95-Fathom horizon at the time operations ceased. It will give access first to the ground between Three Yard and Scar limestones that proved so favourable at Blackdene Mine but it was designed to go the the Whin Sill. The present company has drilled a vertical borehole from a footwall crosscut, 944 ft (287 m) E of the shaft, proving the top of the sill beneath the Tynebottom Limestone, 374 ft (114 m) below the 80 Level. Unfortunately the beds from the Six Fathom Hazle to the Tynebottom Limestone are more shaly than at Blackdene and an inclined hole showed the vein to be siliceous and split up in and near the Scar Limestone. To reach the Whin Sill the existing incline would require about 2500 ft (762 m) of additional drivage at the existing dip, and would be beneath the eastern end of the oreshoot when this point was reached. More economical methods of testing the vein in the sill are likely to be devised. The strong vertical element in Greenwood and Smith's temperature and yttrium measurements which suggest a vertical feeder at Groverake nevertheless make the test one of great significance.

    Even though the eastern part of the 80-Fathom Level has given unfavourable results, it still remains possible that a substantial root may underlie the oreshoot. This would be consistent with the thermometric results obtained by F W Smith (1975, and Greenwood and Smith, 1977) indicating a range of temperatures of formation, based on numerous samples throughout the mine from the outer 10 ins (25 cm) of main phase fluorite, from 190°C to below 140°C. Plotting of isotherms (their fig. 3) reveals three 'hot spots' with a considerable vertical element, the most important being associated with the Red Vein intersection; the temperatures fall laterally away from these. The results lend some confirmation to the view expressed in Dunham (1934) that Groverake contained a feeder centre. Away from this centre the temperatures fall off laterally both to the E and W. In the latter direction, the oreshoot continued in the Great Limestone for 1400 ft (427 m) beyond the shafts, but apparently died out after a branch, believed to link NW with Greencleugh Vein, left the footwall.

    After the Steel companies' takover, Groverake Mine produced up to 1985, 695 341 t (684 396 tons) of crude fluorspar averaging perhaps 54 per cent CaF2, and yielding less than 1 per cent recoverable PbS: over the whole life of the mine to date PbS recovery equals 4 per cent. To 1989, this mine has been the leading fluorspar producer of the field.

    Between the western forehead of Redburn Mine (worked by Weardale Lead Co. and SAMUK 1964–1981, now closed) [NY 928 432] and the eastern end of Groverake lies 2410 ft (735 m) of untested ground, but the direction of this part of the Red Vein complex is N70°W and it offers no attraction. The Redburn deposits were the most recent oreshoots to be found. Attention was directed (Dunham 1959, p.142 and fig. 7) to the valuable prospect offered by the untested 8250 ft (2.5 km) of Red Vein between Rookhope Smelt Mill and Groverake and the point was further elaborated by Dunham et al. (1965, p.410 and fig. 6) in connection with the zigzag opening mechanism then proposed for 'quarter point' veins. In 1964 Weardale Lead Co., taking into account a tradition in Rookhope Village that fluorite was to be seen at very low water in the bed of Rookhope Burn where Red Vein crosses it [NY 9310 4299], commenced sinking an inclined drift at Low Redburn [NY 9285 4313] and were rewarded, at the base of the Great Limestone with a vein, mainly fluorite, 12 ft (3.7 m) wide. A short distance SE of the incline foot an intersection with a small ENE vein, considered to be Straightlegs Vein (p.184) was cut and beyond this the E–W strike changed to ESE. This oreshoot proved to be 1017 ft (310 m) long W of the incline, forming a single lens, sigmoidal in plan (Greenwood and Smith, 1977, p.B185) containing a vein of massive fluorite up to 12 ft (3.7 m) wide within a mineralised zone reaching 22 ft (6.7 m) wide. A vertical shaft was sunk to a depth of 320 ft (98 m) at [NY 9278 4312] with levels at 17-, 40- and 50-Fathoms (respectively 1061, 912 and 850 ft, (323, 278 and 259 m) above OD). At depth there appeared three E–W mineralised lenses linked by a narrow WNW shattered vein. In the Great Limestone the hade is to the N, but below this the vein turns over to the S; there is vertical continuity even through the shales between this limestone and the Five Yard Limestone, but the worked length at the lower levels amounted to less than 500 ft (152 m). To the W the oreshoot terminated where the strike of the whole zone changed to WNW, but the 17-Fathom Level was continued, intersecting the ENE Scarsyke and Rispey veins (all poorly mineralised) but finding a second oreshoot on Red Vein 3937 ft (1200 m) from the first. Dr Smith (personal communication) reports that between the two oreshoots, the main Red Vein structure consists of en échelon and looped faults and gash zones that are virtually barren, though with late-stage carbonates, quartz and pyrite. In one E–W stretch, up to 33 ft (10 m) wide, there were vertical cavities up to 2 m across loosely filled with angular limestone fragments; this Smith reasonably regards as a portion of the Red Vein structurally prepared for mineralisation, but never actually reached by the fluids. In much earlier times, the barren stretch between the Redburn oreshoots had been prospected by Mill Level [NY 9242 4302] by way of Rispey Vein (p.184) and by a drift [NY 9258 4323] in the Little Limestone from Red Burn, shown on Weardale Iron Co. plans, but with negative results in both cases.

    The western oreshoot, in which the trend returns to E–W, is nearly 2000 ft (610 m) long; it is remarkable for the complexity of its structure, consisting of interweaving loop and branch veins cutting a gentle N–S anticline. The branching vein system has been illustrated in cross section by Greenwood and Smith (1977, fig. 4). The main productive ground was from the Great to the Little Limestone, vein widths up to 18 ft (5.5 m) occurring with lenses up to 100 ft (30 m) long. Diamond drilling totalling 15 400 ft (4700 m) was necessary for exploration and mine development at Redburn. Wallrocks up to the Low Slate Sill also yielded ore. The 40-Fathom Level was driven up from Redburn to provide a main haulage; this gave access to ground in and above the Nattrass Gill Hazle, and a 50-Fathom Level was developed from an incline. Wolfcleugh ENE Vein was recognised near the western termination of this oreshoot, and the structural relations can be interpreted as indicating a dextral drag of this intersection. Although mineralised near Red Vein, it did not prove worthwhile to follow this vein in either direction away from it. Wolfcleugh New Vein can possibly be recognised and is known to be present both S and N of Red Vein (p.183). The oreshoot terminated to the W when the trend swung round to WNW.

    Although mineralised intersections were found by drilling in the Tynebottom Limestone and, beneath the eastern oreshoot, in the Great Whin Sill, (its top here at 335 ft (102 m) above OD, under the Jew Limestone) the prospects in depth were regarded by SAMUK as insufficient and production ceased early in 1981. The total output of crude fluorspar from Redburn amounted to 328 805 t (323 626 tons), containing 46 per cent recovered CaF2 and close to 1 per cent recoverable PbS.

    From Redburn Mine, Rookhope Burn approximately follows the course of Red Vein ESE through the village to Stotfield Burn, 1 mile (1.6 km) distant. Boltsburn Old West Level, driven from the confluence of Bolts Burn and Rookhope Burn at [NY 9376 4272] was driven obliquely into the vein and followed it WNW at 1053 ft (321 m) above OD starting at the top of the Great Limestone. At 720 ft (219 m) it cut the Boltsburn Vein–Red Vein intersection, continuing to reach a short, nearly E–W stretch where Fulwood Vein cuts Red Vein. Ironstone flats were found adjacent to both intersections, but other minerals were not found in quantity. The level continued to 3300 ft (1006 m) from the portal and ends 15 ft (4.6 m) above the base of the limestone. Some 800 ft (244 m) short of the W forehead, the weak E–W Mary's Vein was cut and followed by branches of the level 1125 ft (343 m) W and 260 ft (79 m) E. A shaft [NY 9297 4298] 500 ft (152 m) W of the intersection was sunk from surface and carried down into the Tuft at 1060 ft (323 m) above OD. Red Vein shifts Mary's Vein a few metres E side S. Evidently Mary's Vein showed some promise but nothing workable appears to have been developed. In 1928–30 Weardale Lead Co. tested this vein by means of a shaft near the smelt mill also without success. Beneath the Old West Level, a drift from Boltsburn Engine Shaft tested Red Vein at 900 ft (274 m) above OD in the Four Fathom Limestone, but here the vein contained gouge only.

    The vertical Rookhope Borehole (University of Durham and DSIR, 1960–61) was sited at [NY 9374 4278] in the angle between Red Vein and Boltsburn Vein, both of which dip towards it. The position of the former was recognised in the borehole from a small fold with dips up to 40° in the Alternating Beds from 509–506 ft (155–154 m) above OD; a similar feature persistently accompanies the vein at Redburn and Stotfield Burn mines. Although there were numerous mineralised intersections, no vein oreshoot was cut by this borehole; however, of some interest was the presence of flat replacement bodies in the Tynebottom, Jew, Lower Little and Lower Smiddy limestones. Though dominated by introduced quartz, sampling of the Jew replacement from 371–363 ft (113.1–110.6 m) above OD showed 31 per cent calcium fluoride, 45 silica, 8.9 zinc, 0.7 lead. The zinc is present as 'schalenblende' with colloform banding, while the fluorite is green. In the Lower Little Limestone from 126–117 ft (38.4–35.7 m) above OD, the comparable figures were respectively 2.4, 57, 7 and 1.7 per cent (Dunham et al., 1965, tables 4, 5). Small veins carrying fluorite continued to be encountered after the granite was entered at 222 ft (67.7 m) below OD, the deepest being at 1079 ft (329 m) below OD; some of these may be flyers from the footwall of Red Vein, but Boltsburn Vein may be represented among them. The discovery of flat replacements led to further drilling, in the first case by COMINCO in association with Weardale Lead Co. (four borings in 1966–68) and later by SAMUK (four additional holes in 1978–9). Six of these holes found the Jew Limestone replacement, and three that in the Lower Little Limestone also and a possible interpretation would be that the former is present in an area at least 1640 x 656 ft (500 x 200 m) aligned along Red Vein including both foot- and hangingwall sides. However, in no cases were values equal to the original discovery in the Rookhope Borehole and mining development was not, therefore, undertaken. Some 1640 ft (500 m) WSW of the area indicated, a borehole drilled from the 66-Fathom Level of Stotfield Burn Mine also encountered green fluorite in the Jew Limestone, but sufficient encouragement to sink to it was not obtained.

    The new evidence as to the position of the Great Whin Sill provided by this small area of borings shows it to be directly beneath the Jew Limestone except in the hole at [NY 9388 4293], ENE of the original borehole, where it occurs beneath the Lower Little Limestone.

    The mineralisation at Stoyield Burn Mine (sometimes spelt Stotsfield) (disused) begins exactly where the direction of Red Vein returns to an E–W course. This mine was developed for lead by the Rookhope Valley Mining Co. in 1863–84, from shafts at [NY 9431 4237] (Low Shaft) and [NY 9457 4233] (High Shaft), an adit level [NY 9435 4238] at 1103 ft (336 m) above OD and from levels at 15-Fathoms (1021 ft, (311 m) above OD), 25-Fathoms (958 ft, (292 m) above OD) and 42-Fathoms (850 ft, (259 m) above OD). These operations are credited in official statistics with only 1808 tons of lead concentrates, but though no section of the stoped ground survived the company, workings above the 25-Fathom Level were found 1700 ft (518 m) E of Low Shaft. Some fluorspar may have been sold from the dumps in the early 20th century, but the next important development was when Weardale Lead Co. reconditioned Low Shaft to the 15-Fathom Level, which in this stretch commands the upper two-thirds of the Great Limestone. For the next nine years fluorspar was obtained by running fill from the old stopes above this level and above the adit, 1700–4000 tons per year being produced. In 1938 the Low Shaft collapsed, and attention was concentrated on the adit, which by 1945 reached 3065 ft (934 m) from the portal and four underground vertical shafts had been sunk to give access to the Great Limestone and underlying ground, in addition to one (Jubilee Shaft) sunk at an earlier stage. The main oreshoot was found to persist 400 ft (122 m) beyond No. 4 Shaft to the E, and a subsidiary orebody on a N branch 120 ft (37 m) farther, making the length of mineralised ground here 3585 ft (1.09 km). As at Groverake, continuity of values was greatest in the Great Limestone, but in the eastern part of the mine a considerable downward extension of the orebody, to the 34-Fathom Level, was the result of a washout channel filled with hard sandstone cutting out the shale between the Tuft and Quarry Hazle, adding 60 ft (18 m) of bearing ground beneath the Great Limestone. In the same area the Low Coal Sill increases to over 30 ft (9 m) thick and rests directly on the limestone; workable ground here extended 50 ft (15 m) above the limestone. At about 700 ft (213 m) W of No. 4 Shaft the side of the Tuft channel is reached, and shale reappears between this sandstone and the Quarry Hazle, limiting the height of the oreshoot severely. From the 34-Fathom Level an incline was carried down to a 50-Fathom Level in the Nattrass Gill Hazle, beneath No. 4 Shaft. A section of the situation at this shaft has been published (Dunham, 1959, fig. 5); it is a classic case of the refraction of a vein which stands nearly vertical in the hard beds, but hades over in the intervening shale. A wide body of mineral was found in the Four Fathom Limestone and underlying sandstone, but it proved to be too siliceous for extensive working.

    The structural conditions where the oreshoot terminates to the E are complex. At about 200 ft (61 m) W of No. 4 Shaft an increase in the dip of the limestone from its normal 1°E to 4–5° set in; this had been anticipated from the position of the limestone in the foremost W workings from Stanhopeburn Mine (described below). At 400 ft (122 m) E of the shaft, the wide oreshoot was abruptly terminated against an oblique shear coming in from the WSW, evidently of postmineralisation date since this was proved by drilling to displace the oreshoot S side W about 50 ft (15 m); however the oreshoot soon became impoverished and did not survive the intersection with the weak ENE Thornybrow Vein (see p.196) encountered 920 ft (280 m) E of the shaft. Meanwhile in the neighbourhood of the shaft a weak S branch (which proved to be only a loop) and a strongly mineralised N branch were found. These terminated 800 ft (244 m) NE of the shaft against a WNW gouge-filled channel dipping steeply NE which must be taken to represent the resumption by Red Vein of its unfavourable direction towards the ESE. The E end of the mine thus ended as it had begun, with an abrupt change in the direction of Red Vein. Many subsidiary fractures, several running N70°E with the North Branch, others only slight oblique to the main vein gave evidence of dextral movements. The E end was investigated by means of horizontal or low-angled diamond borings, which incidentally revealed ankeritisation of the limestone for as much as 75 ft (23 m) from the vein.

    The minerals present in Red Vein and its branches are dominated by purple, green and white fluorite, interbanded with quartz, chalcedony, siderite and with bands, often incomplete, of galena. Other minerals present include minor amounts of sphalerite, marcasite in plates up to 10 cm across and pyrite. Ankerite may occur in the vein and is abundant in the wallrock. There is a late generation of quartz, chalcedony and calcite. Substantial parts of the deposit have, however, been disturbed by postmineralisation shearing, producing horizontally grooved slickensides which may form a false wall in the vein or may migrate into the wallrock. Accompanying these, the vein-filling may be extensively crushed to a coarse powder, several feet wide. It is possible that some of the very great widths of up to 45 ft (14 m) in the Stotfield Burn oreshoot may be due to lateral transport into juxtaposition of two previously separated wide stretches. Widths of 10–12 ft (3–3.7 m) were more normal in the eastern ground. The removal of silica and siderite both presented difficult problems while gravity treatment was the only available process, but recovery of fluorspar improved with the establishment of flotation processing.

    By 1957 the eastern ground around No. 4 Shaft had been worked down to the 34-Fathom Level and this part of the 180 ft (55 m) high oreshoot was approaching exhaustion with 100 000 tons dressed fluorspar and 5700 tons galena to its credit. The decision was then taken to abandon the eastern part of the adit level E of No. 1 Shaft, to permit completion of the stopes below. The 15-Fathom Level, reached by a new incline from surface, now became the main haulage level, and a return was made to the old ground at the western end of the mine. High Shaft was reconditioned from the 15-down to the 42-Fathom Level, a limited quantity of ore being drawn from the old ground. Around High Shaft the Red Vein reached a great width and was structurally more complex than at No. 4 Shaft, being accompanied by a monoclinal fold on the S side, and by a number of subparallel veins. Tests were made on one of these (Gowland's Vein) but without finding more than 3.5 ft (1 m) of width. From a N crosscut at the shaft bottom inclined boreholes were used to establish that strong mineralisation continued down to the Three Yard Limestone, Little Whin Sill above it and Six Fathom Hazle below, and from a sublevel above the 42-Fathom level an incline was carried down to give access to levels at 54-Fathoms (775 ft, 236 m above OD), 60-Fathoms (738 ft, 225 m above OD) and 66-Fathoms (702 ft, 214 m above OD); the first two yielded stoping ground in the Nattrass Gill Hazle and Three Yard Limestone, but the 66-Level was used for boring to a maximum depth of 240 ft (73 m) into the Jew Limestone at 500 ft (152 m) above OD but without revealing sufficient encouragement for deeper development. Near the end of the operations a substantial body of limonite-stained fluorspar, up to 20 ft (6.1 m) wide was found above the old adit, and worked opencast; it may be assumed that washout channelling from the White Hazle and High Coal Sill must have given rise to the locally favourable conditions here, for little or nothing was got above the Low Coal Sill elsewhere in the mine. Greenwood and Smith (1977) give the total crude fluorspar output from Stotfield Burn Mine as 275 392 t plus 55 275 t from the opencut, making a total of 330 667 t ( = 325 460 tons) yielding 203 310 t dressed fluorspar. The production of lead concentrates from 1939 to 1966 was 4257 tons making a grand total of 9957 tons. Operations ceased in 1966.

    A minor NNW cross fault that passed through the Red Vein about 25 ft (7.6 m) W of No. 4 Shaft may be the continuation of the No. 1 cross vein of Boltsburn Mine but neither it nor other similar small fractures farther W brought about the termination of the Stotfield Burn oreshoot, which is clearly the result of the abrupt change in direction of Red Vein. The unproductive stretch leading to the next mine to the E, Stanhopeburn, is altogether almost 5000 ft, (1.52 km) long. All but the westernmost 1300 ft (396 m) has been tested by a continuation of Shield Hurst Adit, finishing at 912 ft (278 m) above OD in a direction aimed at the crosscut leading to the dextrally shifted portion of the main vein at Stotfield Burn. The main fracture which terminated North Branch there evidentlyrepresents a second, more easterly part of the WNW barren zone.

    Stanhopeburn Mine (Weardale Minerals Ltd, inactive), first worked for lead ore, has had a long history of working by ten different companies. The earliest records are of work by the Earl of Carlisle and Company in the eighteenth century. Probably the main Red Vein had not by then been discovered at Stanhope, for after the London Lead Co. acquired the lease in the early nineteenth century they were working flats in the Great Limestone N of Noah's Ark Quarry. In 1820 the vein was discovered, and Shield Hurst Adit was started from the W side of the Burn [NY 9867 4130] at 828 ft (252 m) above OD. The very irregular course of this adit in its early stages was inherited from the flat workings. By the end of the London Lead Co.'s tenure in 1864 the adit had been driven 4200 ft (1.28 km) from the portal, an engine shaft had been sunk [NY 9776 4126] and additional levels had been developed at 750 ft, (229 m) above OD (the Widley Water Level, linked to surface [NY 9825 4036] and a lower level at 640 ft (195 m) above OD. These had exploited an oreshoot 1700 ft (518 m) long, 380 ft (116 m) maximum height, extending from the Little Limestone down to the Three Yard Limestone, and owing its unusual vertical extent to washout channelling in the Coal Sills Group and particularly by the Tuft which, combined with the Quarry Hazle produced sandstone 95 ft (29 m) thick directly beneath the Great Limestone. The western workings on Shield Hurst Level were by 1864 in poor ground. Output of lead concentrates since 1816 had totalled 15 476 tons. The Beaumont Co. took over in 1866 and seem to have worked mainly on Shield Hurst Level, driving it westward until strong mineralisation was again encountered. An agent's report of 1871 describes this ground: The ... workings on the whole extremely poor in ore ... workings in the vein are 12–24 ft (3.7–7.3 m) wide of coarse spar with a sort of bracking rider, probably broken carbonatised limestone or half spar half rider, here and there a little strong brangle scattered crystals or aggregates of galena. But the ore very much scattered and requires a continuous search ... The length S of the above all spar, working 25–30 ft (7.6–9.1 m) wide, the ore very much scattered". The workings to which these notes refer were in the Great Limestone and Coal Sills sandstones and shales. Later spar workings have confirmed the great width of the vein here. It is filled with massive fluorite, white with patches tinted purple and green. Quartz, chalcedony and ferriferous carbonates are present; barium minerals are completely absent. Galena is scattered near the margins of the vein and there are small amounts of sphalerite and iron sulphides, with traces of copper sulphides. In the oxidation zone, extending on the average 250–300 ft (76–91 m) from surface, limonite is present, and at one time pockets of well-crystallised cerussite were found.

    The analyses quoted in (Table 60) are intended to indicate the range of variations in the constituents. In the western part of the oreshoot a northern loop, also mineralised, is known as Swan's Vein. The two branches come together near the top of the Great Limestone; the Beaumont Co. sank a winze to investigate the loop in depth. The oreshoot terminates to the W where the vein splits into two principal branches. The S branch had been tested for 900 ft (274 m), the N branch for over 3500 ft (1.07 km) by an extension of Shield Hurst Level (referred to above) driven by the Weardale Lead Co., with drifts 40–55 ft (12–17 m) above in the Great Limestone, but no additional workable ground was found. After a closure lasting 27 years, the same company reopened it to extract the fluorspar proved by the Beaumonts. Stanhopeburn soon became the leading fluorspar mine in the district, the ground worked lying above Shield Hurst Level, extending in places 160 ft (49 m) above the adit, and at the W end into the Firestone, 280 ft (85 m) above rail. The block worked extended from 4600 ft (1.4 km) to 6200 ft (1.89 km) from the portal. Vein-widths continued as indicatd in the Beaumont report, but with only the simplest of gravity plants, silica-contents prevented the making of a product of the highest quality. For this reason, and because of the long haul to surface, production slowed down after 1923, and came to a halt in 1933; to be revived briefly in 1938 by Beaston and Elliott. To 1940, production from the mine may be summarised as follows: Lead Concentrates, 1816–1864, London Lead Co., 15 476 tons; 1868–1879, Beaumont Co. (including West Pasture Vein), 2053 tons; 1884–1931, Weardale Lead Co., 2550 tons; 1938, Beaston and Elliot, 26 tons; total 20 165 tons. Fluorspar, 1907–1933, Weardale Lead Co., 114 439 tons; 1937–1940, Beaston and Eliot, 9052 tons; total 123 491 tons.

    The rising demand-and price-for metallurgical and acid-grade fluorspar attracted interest to the potential beneath Shield Hurst Level, and in 1940, Fluorspar Ltd was formed to take over the mine (Wynne, 1940). Little now remained above adit level, so their first task, a formidable one, was to drain the deeper workings by reconditioning Widley Water Level, which had collapsed. This was accomplished, and as an examination of the Beaumont sump at the W end of the mine showed both Red and Swan's vein continuing downwards in strength, a shaft was sunk 120 ft (37 m) from the Beaumont winze, eventually reaching 683 ft (208 m) above OD, where a bottom level, Poole Level was driven; a connexion was also made from the Widley Level as development proceeded. Both Red and Swan's Veins were fully stoped down to Poole Level, but here, where the Three Yard Limestone enclosing the Little Whin Sill was cut, there were strong indications that the bottom of the oreshoot had been reached. When Poole Level was joined by a long gentle slope with the London Lead Co.'s bottom level, this appeared still to hold true except for a short stretch near the underground shaft, where some ore was got in the Six Fathom Hazle. The shale between this and the Five Yard Limestone proved to contain beds virtually of clay (this was also the case at Stotfield Burn) and the vein became quite unproductive here. The ground up to the Nattrass Gill Hazle, on the other hand, proved to be the most continuously productive in the mine, and here the stoping bridged the 650 ft (198 m) long gap between the London Lead and Beaumont/Weardale Lead Co. stoping in the upper strata. By 1964 Fluorspar Ltd may be estimated to have mined 146 000 tones of crude fluorspar. A flotation mill was installed at an early stage and if the bulk of the production (approximately 74 893 tons) was of acid-grade, the remaining tailings indicate that the grade of the crude ore must have been of the order of 65–70 per cent CaF2. By-product lead ore recovered was 2526 tons. Fluorspar Ltd obtained the bulk of their ore from mining in virgin ground, and when in 1964 they ceased operations and Laporte Chemicals Ltd took over, the fill in the stopes above the London Lead Co.'s bottom level was still intact. At the time this was not considered worth extracting and the mine and mill were dismantled.

    In 1971 the mine was reopened by Ferguson Wild & Co. Ltd. The Widley Level was again restored and the shaft at the W end of the mine made operational but no significant production was obtained before Swiss Aluminium (UK) took over. An ambitious programme was now carried out. Shield Hurst Level was straightened; the London Lead Co.'s engine shaft was reopened reducing the out-bye haul to 2820 ft (860 m); and the shaft was sunk 120 ft (37 m) to a total depth of 370 ft (113 m), providing for a new bottom level at 520 ft (158 m) above OD, in the lower part of the Scar Limestone. This was driven 2000 ft (610 m) W and 160 ft (49 m) E, but the vein proved to be narrow and unworkable, only one small block of stoping ground in the Slaty Hazle being worked. From 1977 to 1982 the fill was run from the London Lead Co.'s stopes, yielding 75 800 tons crude fluorspar averaging 44 per cent CaF2. Meanwhile from a point 1300 ft (396 m) W of the underground shaft an incline was carried down westward to the Tynebottom Limestone, where more promising ground was discovered. It is clear that the shales of the Five Yard, Scar and perhaps the Tynebottom cyclothems were unfavourable to mineralisation. Exploration has now reached the summit of what could be much more favourable ground, including the Great Whin Sill, but it is likely that this could be developed only with difficulty from the existing workings.

    The Stanhopeburn oreshoot or series of oreshoots covers a maximum length of 4000 ft (1.22 km) and in one place attains a vertical range of 450 ft (137 m). It has yielded 380 000 tons of crude fluorspar with at least 70–75 per cent CaF2, and at least 24 000 tons lead concentrates. Lead was relatively more concentrated in the eastern part of the ground.

    At the eastern end of Stanhopeburn Mine, in the ground worked for flats by the London Lead Co., the main Red Vein splits up or dies out. About 800 ft (244 m) S, on the S side of Reahope Burn, a strong vein appears which may be regarded as its continuation, en echelon. W of Stanhope Burn limonitic ironstone has been worked from flats related to the vein at Noah's Ark Opencut [NY 694 408], where a shift en echelon to the S occurs. In depth Widley Level follows it for about 1000 ft (305 m). E of Stanhope Burn a branch trending N80–85°E is known as West Pasture Vein. This has been followed eastwards for about 1850 ft (564 m) in the Great Limestone from a level at [NY 9879 4089], where it was associated with small flats at the High Flat horizon, which have yielded a small quantity of lead ore. The main vein continues beneath Crawleyside, N of Stanhope. For a distance of 3000 ft (914 m) ESE of Stanhope Burn the vein and flats related to it were worked in the Great Limestone for iron ore. The most important belt of flats lay E of the Stanhope–Blanchland road, where the E–W Lanehead Vein intersects Red Vein. Access to this ground was by means of Red Vein Level (disused) [NY 9884 4073] driven on Red Vein from Stanhope Burn at 800–810 ft (244–247 m) above OD, and by a level following Lanehead Vein. E of these workings the vein opened out and carried a wide fluorspar oreshoot, which was first worked opencast in the thick Low Grit Sill on Crawley Top [NY 996 403], where one of the most spectacular surface workings in the area could be seen until SAMUK removed the last remaining 7800 tons of ore and then backfilled the opencut. The vein was 10–20 ft (3–6 m) wide between nearly vertical walls of coarse sandstone. An attempt was made to work fluorspar here by the Weardale Iron Co. as early as 1854, but the real beginning of the spar trade in Weardale was in 1884. Beneath the opencut, the vein was worked over a length of 1600 ft (488 m) to a depth of 140 ft (43 m) from surface, probably to the base of the Firestone, from a series of inclines and counter-inclines. Deeper developments on Red Vein beneath Crawley Top commenced with the driving of a crosscut adit from the west side of the main road, starting at [NY 9829 4022] and running NE. This was at about the horizon of the Pattinson Sill, but was not a success for lead ore. In 1868–77 the Beaumont Co. drove Hope Level (disused) [NY 9906 3973] now the main entrance to the mine of that name until recently operated by Mr G M Brown; this starts from the E bank of Stanhope Burn, 1250 ft (381 m) N of Stanhopeburn Bridge and runs in the Nattrass Gill Hazle and Four Fathom Limestone 2675 ft (815 m) NE to reach Red Vein, and a loop on the S side of it which rejoins the main vein both E and W of the adit, as well as vertically above it. Rises put up by the Beaumont Co. to the Great Limestone revealed no workable lead ore, though wide spar veins were found. No further work was done until 1914, when the wasteful mining method adopted below Crawley Top led to an exhaustion of those workings. Spar mining was then transferred to Hope Level, both Red Vein and its loop yielding fluorspar, the widths of the veins varying from 2 to 12 ft (0.6 to 3.7 m). The principal stopes were in the Four Fathom Limestone and the Quarry Hazle, separated by barren ground due to the intervening shale. The Quarry Hazle is not so thick as at Stanhopeburn, being only 35 ft (10.7 m) here. The vein also carries wide spar bodies in the Great Limestone, but the fact that flats in the limestone had previously been worked for ironstone introduced mining difficulties here though these were largely overcome. A length of over 1250 ft (381 m) has been worked. The vein contains fluorite and quartz as its main constituents; sulphides of any sort are very rare. The Weardale Steel, Coal and Coke Co. continued operations for fluorspar to 1932; the mine was closed until 1941 when it was reopened by Beeston & Johnson. In the Great Limestone stopes directly above the main rises yielded crude spar containing 80 per cent calcium fluoride, 17 per cent silica. When, however, this ground became unworkable for mining reasons, stopes farther E proved to be more siliceous; with good flotation treatment available at Frosterley this is no longer a problem; indeed the Hope Level ore was regarded as better than average. Between the Hope Level workings and those from Crawley Top there was no known mine-connection, though the excellent ventilation in Hope Level, coupled with an unexplained rush of water into the high stopes, suggest that there may be a natural connection. Some 125 ft (38 m) vertical height of ground remains untested.

    In 1979 SAMUK drilled a deep borehole at [NY 9962 4010] to test the Red Vein at depth beneath Hope Level. According to the log by Dr A A Wilson and petrographical investigation by Dr N G Berridge, (E54533) mineralisation consisting of sphalerite, quartz and calcite, perhaps 3 ft (0.9 m) true width dipping at 40° to the bedding was cut in the Tynebottom Limestone at 210 ft (64 m) above OD with associated silicified limestone here and at 205 ft (62 m) above OD. The top of the Great Whin Sill was found at 179 ft (54.6 m) above OD, but although the sill was penetrated to 100 ft (30.5 m) true thickness, no further vein or evidence of alteration was found. It could, however be argued that since the Crawley-Hope Level oreshoots pitch W this boring was sited far to the E of the pitch axis.

    It should nevertheless be recalled that the Red Vein has yet to be seen against Great Whin Sill wallrock. Production data for the Crawley Mines (including Red Vein Level) are as follows: Lead concentrates: 1818–1846, 3574 tons; in addition, Lanehead and other small veins in Lanehead limestone quarries yielded 384 tons between 1848 and 1866. From 1847–1878 the Crawley Mines contributed to the Weardale Iron Co.'s total of 8571 tons of galena produced as a by-product in their ironstone operations. Fluorspar: 1884–1932, 70 157 tons. Total yield of crude fluorspar to 1985 is estimated at 163 000 tons, product spar about 95 000 tons.

    East of the Crawley Top and Hope Level foreheads some 1300 ft (396 m) of ground remains untested up to the line of a N–S fault, the course of which is indicated by old shafts. This is believed to shift the vein, E side S about 650 ft (198 m) and the supposed continuation E has been worked opencut in Rogerwell Hush, W of Shittlehope Burn [NZ004 399]. Along the hush, which is in the Firestone and Low Grit Sill, coarse purple fluorite and quartz are abundant, and some fluorspar has been obtained by hand-picking here. Some 1200 ft SSE of the E end of the hush, Canada Shaft (disused) [NZ0076 3959] 141 ft (43.1 m) deep has been sunk to the Great Limestone, and a crosscut driven N to Rogerwell Vein. The trial does not appear to have been particularly successful, but iron ore containing 53.2 per cent iron was picked up on the heaps. Apparently the crosscut from Canada Shaft failed to find the vein on the E side of Shittlehope Burn, but the intersection confidently identified as Red Vein in the Derwent–Wear Tunnel (Table 51) lies on line, 3300 ft (1 km)to the ESE. As it has resumed an E–W course it may well be worth prospecting in the drift-covered country farther E.

    In 1948 Red Vein had yielded a recorded production of 50 525 tons of lead concentrates and 240 633 tons of fluorspar; the estimated yield of iron ore was not less than 500 000 tons by 1940. By 1985 the total for crude fluorspar has reached 1 910 000 t, recovered and sold fluorspar over 1 million tonnes, lead concentrates approximately 100 000 t. Lateral exploration and development may be said to be complete except at the western (Frazer's Hush) and eastern (Frosterley) ends; exploration of the second group of bearing beds in depth has hardly begun.

    Sedling = Longsike Vein—Lead ore, fluorspar

    NY84SE; Durham 22 NE, NW. Direction N75–90°W, throw 33 ft (10 m) N near Sedling Burn, decreasing E to 7 ft (2 m) N.

    W of the divide between the Middlehope and Sedling valleys, the vein was worked from Sedling Mine (disused) [NY 860 411] by the Weardale Lead Co., and was the principal fluorspar producer of the district until its closure in 1948. The vein originates from the ground in which Breckonsike, Burtree Pasture and Copt Cleugh veins converge upon the Burtreeford Disturbance. Sedling Vein (Figure 30), p.182) is mineralised through an unusually wide range of beds, extending from the Scar Limestone up to the Grindstone Sill, including over 1000 ft (305 m) of strata, though with gaps against the shaly parts. The disposition of the worked oreshoots, shown in (Figure 30), suggests that there are two main groups on Sedling Vein proper, but lack of information about old stopes in the higher sandstones, which from the abundance of surface shafts are undoubtedly extensive, makes it impossible to form a complete picture. The main drawing shaft [NY 8600 4105] was sunk into the western group of oreshoots to a depth of 425 ft (130 m). The ore-bearing ground here extends 830 ft (253 m) W and about 1200 ft (366 m) E of the shaft, ribbon-like oreshoots having been extracted from the vein in the Great Limestone, Four Fathom Limestone, Nattrass Gill Hazle, Three Yard Limestone, Six Fathom Hazle, Five Yard Limestone and Slaty Hazle. The Scar Limestone was apparently not productive. The main levels are shown on (Figure 30); the uppermost one, at 1230 ft (375 m) above OD, communicates with Burtree Pasture Water Level [NY 8573 4075] which issues near Cowshill Bridge. E of the drawing shaft this drive rises rapidly, to join at 1950 ft (594 m) E of the shaft a level driven from surface [NY 8586 4092]; this, on a S branch of Sedling Vein known as Midge Pits Vein, formed the main entrance to the 1900–48 workings which eventually carried on from an underground shaft 2040 ft (622 m) E of the junction of the levels. These workings were in the eastern oreshoots, which proved to extend from the Little Limestone (possibly from the Firestone) down to the Four Fathom Limestone. This end of the mine was drained by the New Sedling crosscut from Blackdene Level, 3500 ft (1066 m) long, driven by the Beaumont Co. in 1863–73. The crosscut starts in the Six Fathom Hazle, passes through the Three Yard Limestone and reaches Sedling Vein in the shale beneath the Nattrass Gill Hazle. In the Great Limestone the vein varied from 8 to 12 ft (2.4 to 3.7 m) wide, mainly filled with pale massive fluorite, with small bands of sulphides parallel to the walls (Dunham 1934, fig. 3). On the average the width decreases downwards. Quartz is present in the vein as small bands, veinlets and inclusions in the fluorite. Sulphides include galena, which averaged about 4 per cent of the crude ore, with minor amounts of sphalerite, marcasite and chalcopyrite. Between 1900 and 1916 the mine produced 49 732 tons of fluorspar and 2708 tons of galena (Louis, 1917, p.22). A sample of typical crude ore, taken from the mill feed in 1941, assayed as follows: 79.2 per cent calcium fluoride, 13.5 silica, 1.0 calcium carbonate, 5–6 total sulphides. The ore was treated in a specially designed gravity mill of 4 tons hourly feed capacity; the product averaged about 90 per cent calcium fluoride, 6–8 silica. Galena was recovered from jigs and tables in sufficient quantity to meet the whole cost of treatment of the ore. The production of fluorspar amounted to 166 421 tons from 1900 to 1948. From 1818 to 1878 the Beaumont Co. produced 10 411 tons of lead concentrates from the western group of oreshoots; 7044 tons had been obtained by the Weardale Co. from extensions of the western shoots; and from the new ground on the eastern shoots during the period 1889–1948; total, 17 455 tons. The mine was closed in 1948 owing to the exhaustion of the eastern oreshoot, the Nattrass Gill Hazle having proved to be unproductive. Borings between the western and eastern oreshoots failed to find new ore, but no test has yet (1984) been made beneath New Sedling Level into the strata that have been the main producers of Blackdene Mine.

    Above the workings already described, the vein has been worked at High Sedling Mine (disused) for fluorspar. Here Messrs Hinchcliffs, in 1926–30, drove an incline [NY 8658 4087] commencing at 1740 ft (530 m) above OD which dipped down to a level at 1700 ft (518 m) above OD, at the horizon of the Coalcleugh Beds. A stope about 300 ft (91 m) long was taken out, producing 4657 tons. Dumps in the vicinity yielded 1002 tons in 1905–10. At the horizon of the Firestone, High Sedling Level, [NY 8628 4101] at 1460 ft (445 m) above OD was reopened by the Weardale Lead Co. for about 2200 ft (671 m). A small quantity of fluorspar was obtained where Midge Pits and Sedling veins intersect, and it is probable that reserves of spar remain above this level farther E; the work, however, was abandoned. In 1966 an attempt was made to win spar from the western ore zone by opencast methods, but collapsing old workings below inhibited this.

    The eastern oreshoot in the Great Limestone at Sedling Mine terminates 600 ft (183 m) E of the underground shaft, where the vein splits into two branches. It is not known whether the branches reunite. Farther to the E, the vein passes under Race Head and runs thence along the S side of the road at Middlehope Bank, its course marked by many shaft-heaps on which fluorite is abundant. The workings of Middlehope Mine (disused) are very old and although plans, some of the oldest on record for the district, show the main levels, nothing is known as to the extent of stoped ground or the condition of the vein. The main adit [NY 8902 4054] started at about 1450 ft (442 m) above OD above the Firestone, but enters this bed to the W; its length was at least 4200 ft (1.28 km), and it may have been connected by means of a rise with High Sedling Level. Fluorite is present on the dumps. Lower horizons were explored by a branch level from Levelgate Mine (p.187), which reached Sedling Vein by way of Bleaklaws Cross Vein. About 900 ft (274 m) W of the point where this level reaches it Sedling Vein bifurcates; mineralisation appears to have followed the N 'quarter-point' branch, called Longsike Vein in preference to the S branch. E of Middlehope Mine, Longsike Vein was worked from Douks Level (disused) [NY 9022 4026] in the vicinity of its intersections with Lodgefield and Old Fall veins (p.188) in the Great Limestone. In 1971 Swiss Aluminium (UK) Ltd investigated Longsike Vein by drilling nine boreholes from the S side, from six sites spaced along the 5200 ft (1.58 km) length of the vein between the split from Sedling SE, and the apparent termination against Old Fall Vein. Longsike Vein was intersected in strata including the Little Limestone, Coal Sills and Great Limestone but though three holes were drilled to the Four Fathom Limestone and one to the Three Yard, these were beyond the vein in those beds. The results were disappointing; the only wide intersection, 11.8 ft (3.6 m) showed very poor values and the best was 4.3 ft (1.3 m) with reasonable values. No encouragement to proceed with development was obtained. Stratigraphically, Low Grit Sill was found close above the Firestone, suggesting chanelling, and in the westernmost hole the Low Coal Sill reached nearly 60 ft (18 m) thick but had cut out the upper 30–40 ft (9–12 m) of the Great Limestone. No test was made at the levels so productive at the nearby Blackdene Mine (Six Fathom Hazle to Alternating Beds and Whin Sill) though British Steel Corporation considered proposals to drive the Blackdene Main Haulage level, at least 3500 ft (1.07 m) long, to Sedling Vein. In 1968 Weardale Lead Co. drilled a borehole W of the western oreshoot that revealed highly mineralised ground in the Whin Sill and perhaps deep development will eventually be from that end.

    Slitt Vein—Lead ore, iron ore, fluorspar, quartz

    NY83NE, 93NW, NE, NZ03NW, NE; Durham 22 SE, 23 SW, SE, 31 NE, 32 NW, NE. Direction N60–90°W; throw: small N throw at Elmford Mine; 13 ft (4 m) N in Levelgate Mine, E of Old Fall Vein intersection; 17 ft (5.2 m) S in depth at Slitt Mine, but vein branches upward, S branch throws N; 27 ft (8.2 m) N at Park Burn; 29 ft (8.8 in) NE at Cammock Eals Mine; about 15 ft (4.6 m) NE in Ludwell Burn; vein hades N at Harehope Gill Mine.

    Slitt Vein is the longest single vein of the orefield; with a total length of 13.5 miles (21.6 krn) it runs from Wearhead along the N side of Weardale through Elmford, Blackdene, Levelgate, West Slitt, Slitt, Rigg, Park Burn and Cammock Eals mines; crossing the Wear 1 mile (1.6 km) W of Eastgate, and continuing through Billing Hills Mine; across Horsley Burn there is an unproved gap, but to the E the vein is strongly developed along the crest of Catterick, between the Wear and Bollihope valleys, whence it continues through Harehope Gill and Sunniside mines to converge upon and probably unite with the fault representing the eastward prolongation of the Sharnberry Vein at the E end of the great North Teesdale complex.

    The vein has not been proved W of the river at Wearhead, but it converges upon the Burtreeford Disturbance. E of the river and N of the village, there are superficial workings [NY 861 397] in the beds between the Great and the Four Fathom Limestone near the intersection with Wearhead Vein, but no considerable oreshoots have been found.

    Well mineralised ground begins where the vein enters the Great Limestone at Elmford Mine (disused), the workings of which extend E from Elmford Cleugh, N of West Blackdene. Elmford Level [NY 8676 3968] starts at 1231 ft (375 m) above OD in shale beneath the Great Limestone, reaching the base of the limestone 700 ft (213 m) from the portal. At 1700 ft (518 m) a branch known as Rogers Vein (p.185) leaves Slitt Vein on the N side. The level continues in Slitt Vein a further 1500 ft (457 m). There was also a level on top of the limestone [NY 8690 3971]. Although no stope section remains it is known that a substantial oreshoot occurred in the Great Limestone, possibly extending into higher beds in this part of the vein. This was worked for lead ore by the Beaumont Co., yielding 12 387 tons of concentrates in 1833–1878. Flats, of which no plans remain, were found at the High Flat horizon on the S side of the vein. The vein here is wide, filled with fluorite, quartz, small quantities of carbonates and galena. Fluorspar production commenced about 1908 and continued until 1935 under various owners. Details of production up to 1926 are lacking, but the owner of part of the land traversed by the vein, Mr J R Peart, estimated that about 12 500 tons were obtained in this period. After 1926 the spar workings are said to have been extended from the branching of Rogers Vein by Messrs Hinchcliff's into lands owned by the Ecclesiastical Commissioners. The spar was largely got by running fill from the old lead stopes. From 1927 to 1935, 12 593 tons were obtained, but some of this came from Blackdene Vein when the ancient Allercleugh workings tapped the thick coal sill. This was found to be less siliceous than that in Slitt Vein. During spar workings 156 tons of lead concentrates were produced in 1908–1935.

    Some 220 Tt (67 m) below Elmford Level, Slitt Vein has been worked from a drift, under the Three Yard Limestone, which branches from Ridley's Crosscut, Blackdene Mine (disused) (which also gives access to New Sedling Level, p.208). Three rises link the drift with Elmford Level and probably some stoping for lead was done in this ground. In the vicinity of Blackdene Rise, 2350 ft (716 m) E of Elmford Level mouth, an old plan recorded that much of the vein was in place, 4 ft (1.2 in) wide of fluorspar. While it is probable, therefore, that the oreshoot in the Great Limestone is exhausted or in such a condition that further mining would be difficult the existence of reserves between Blackdene and Elmford levels appeared possible when Blackdene Mine was reopened (p.185).

    Silverdikes Level (disused) [NY 8794 3946] in the shale below the Firestone at 1477 ft (450 m) above OD reaches Slitt Vein close tothe intersections with Blackdene and Silverdykes veins. Though the level is closed, the old plan gives valuable information on the geometry of the veins at this high level.

    Levelgate Level (disused) [NY 8817 3890] at 1210 ft (369 in) above OD in the Quarry Hazle, gave access to Slitt Vein in the vicinity of itsintersections with Lodgefield and Old Fall veins, and extended 2600 ft (792 in) ESE of the latter. In 1862 middlings 3.5 ft (1 m) wide were being extracted from old workings in this part of the vein above Levelgate Level, and about this time two sumps were sunk to the Four Fathom Limestone. In the Quarry Hazle the vein consisted of "spar, thinly mixed with ore", but in the Four Fathom Limestone it was 3 ft (0.9 m) wide "white and black stone, without spar or ore; there is some ore at the top of the limestone". From 1100 ft (335 m) E of Old Fall Vein to the E forehead of Levelgate Level, a considerable belt of flats, best developed in relation to in- tersecting NW and E–W strings on the N side of the vein, were worked in the Great Limestone, under Black Laws. These may have been in the Low Flat horizon, but this is not certain; nor is it quite certain whether they were worked for lead ore or iron ore, or both. There is a connexion to them from West Slitt Level (disused) [NY 9015 3923]–an ironstone level driven on the vein from the out- crop of the Great Limestone on the W side of Middlehope at approximately 1200 ft (366 m) above OD. Although detailed plans are lacking, flats are known to have been worked 2000–3000 ft (610–914 m) W of the portal of this level and probably extended considerably nearer to it. From the N side at [NY 9023 3950] another adit, also low in the Great Limestone was driven from Seeing Sike, meeting the vein some 1000 ft (305 in) W of West Slitt Level (marked Middle Slitt on the 6-inch map). Evidence of surface as well as underground workings extends at least 1500 ft (457 in) farther W, in ground underlain by beds at least up to the Firestone. These workings are very ancient, predating both Beaumont and Iron Co.'s plans; purple fluorite is present on the much-overgrown heaps. West Slitt level terminated at 4210 ft (1.28 km) from the portal, the western 1000 ft (305 m) having risen 2° with the increased rise of the Great Limestone; 1700 ft (518 in) short of the forehead the E end of Levelgate Level was directly under it.

    The position when the first edition of this Memoir appeared was, therefore, that Slitt Vein had been tested continuously from Elmford Mine to West Slitt in the Great Limestone, yielding fluorspar in the western part, mainly ironstone in the eastern.

    Beneath this, the deepest test as far E as Blackdene Vein intersection was by Blackdene Level in or near the Three Yard Limestone, while E of this Levelgate Level, gradually losing command of the Quarry Hazle, was the lowest working until Slitt Lead Mine, described below, was reached.

    In 1962 development of the Blackdene Vein at Blackdene Mine (disused) in the beds between the Three Yard Limestone and the top of the Whin Sill had reached an advanced stage and Slitt Vein was within striking distance. Accordingly, Ridley's Crosscut which drains Sedling Mine to Blackdene Level was used to drill low-angle boreholes northward into Slitt Vein at the Six Fathom Hazle horizon, promising widths of fluorite being encountered. A crosscut was thereupon driven from the 95 ft (29 m) level below Blackdene Level, and later a connection was made at the Blackdene 195 ft (59 m) level. An oreshoot with maximum dimensions 1000 ft x 170 ft (304 x 52 m) with widths up to 14 ft (4.2 m) but averaging 5.5 ft (1.7 m) was worked, and by 1972 had largely been extracted. Meanwhile the Main Haulage Level was being driven in the bottom of the Alternating Beds and top of the Whin Sill, but the appearance of the Slitt Vein on the 195 ft (59 in) Level, and in one winze below, which found mainly ankerite, did not justify driving the new level to the Slitt oreshoot W of Blackdene Vein. In British Steel Corporation records this oreshoot is referred to as 'North Slitt' because it was expected, from the primary geological survey, that Slitt Vein would be shifted to the S, E of Blackdene vein; subsequent development showed this not to be the case. To the E, values continued to within 100 ft (30 m) of Ridley's cross vein, but to the W the oreshoot became unworkable 750 ft (229 m) from the intersection of Slitt and Blackdene veins. Two rises above the Three Yard Limestone were opened up to the Elmford Horse Level in the Great Limestone, but little ore was found in the intervening ground, only 5000 tons of spar being run from old stopes. The "North Slitt" workings were eventually connected to the Main Haulage by a 200 ft (61 m) Level driven on vein from the W, which showed that if there was any displacement of Slitt Vein by Blackdene, it was no more than 5 ft (1.5 m) E side S. A small block of workable ground 200 ft (61 m) long was found in the Scar Limestone between the latter vein and the E end of "North Slitt" orebody.

    Meanwhile, from a level 40 ft (12 m) below Blackdene Level, attempts had been made to find Slitt Vein E of Blackdene, and it became evident that the supposed 300 ft (91 m) E side S shift is to a continuation of a weak ENE vein, Dick's Vein, worked at higher levels N of Slitt Vein. A fan of horizontal boreholes drilled northward revealed the main Slitt Vein continuing more or less in line with the workings W of Blackdene Vein. The eastern ground was now tested by Rise H 8 which revealed good ore in the Scar Limestone extending a short distance into overlying baked shale, and at a higher level, the 40 ft (12 m), in the Six Fathom Hazle. Driving eastward in the latter horizon showed that ore continued only for 250 ft (76 m) but then as the sandstone became intercalated with shale, the vein swung away to N 78–80°E. After 380 ft (116 m) of driving a crosscut S was made to the expected Slitt Vein position, but yet another ENE fracture was found and followed for about 200 ft (61 m). A S crosscut from this found the vein restored to its normal direction, and workable ground reappeared in the Six Fathom Hazle. Development of the Scar Limestone and Alternating Beds below showed none of this divergence, but it does appear that while in the hard brittle beds of the Scar Cyclothem the vein runs E–W and stands vertical, for the first 500 ft (152 m) E of Blackdene, it is represented by an echelon of ENE fractures in the shaly beds of the Five Yard Cyclothem. Fully developed, the length of the Scar Limestone oreshoot has proved to be 2270 ft (692 m); its average width along the Scar sublevel, 5.46 ft (1.66 m), (averaging 87 measurements), and on the Main Haulage Level in Alternating Beds invaded by Whin Sill, 4.96 ft (1.51 m), (84 measurements). The upper oreshoot in the Six Fathom Hazle averaged 5.01 ft (1.53 m), (38 measurements), and towards the E end of the run, an intermediate shoot appeared in Five Yard Limestone and Slaty Hazle. The whole run of ore terminated to the E at Rise H 39, where the direction of SEW Vein changes abruptly from E–W to ESE. This change of direction occurred near the intersection area of Lodgefield Vein but tests from the Main Haulage Level in that vein, and on Old Fall Vein 540 ft (165 m) farther ESE showed nothing workable at this level. To complete the detail of Slitt Vein structure, the dip of the vein is steeply N for the first 900 ft (274 m) E of Blackdene Vein; there is then a marked change, as indicated by the relative positions of the Great Limestone and Main Haulage levels, the dip, now to the S, decreasing to 65° between the former level and the top of the intermediate oreshoot, while below this, the vein is virtually vertical, as with Blackdene Vein. A rise (above H 28) through the beds between the Six Fathom Hazle and Tuft failed to find workable ground. The Slitt oreshoot E of Blackdene Vein was proved, by means of an incline starting 240 ft (73 m) E of the intersection to extend down into the Whin Sill, and two levels were driven, respectively 50 and 100 ft (15 and 30 m) below Main Haulage, showing widths of fluorspar which are similar to those above. These were driven (1984) to the E end of the oreshoot before further development in depth was attempted. By 1986 the ore had been extracted and a third level had shown a marked restriction of the oreshoot in depth, apparently owing to the termination of the Whin Sill eastwards as a tongue; operations were therefore suspended.

    From H 39 where the change in direction occurs, the Main Haulage Level was driven 355 ft (108 m) following a barren vein on a course S 55°E; it then followed a branch N of E, turning to resume an ESE trend after 260 ft (79 m). The forehead, reached in 1979 stands 1140 ft (347 m) from H 39. The Scar Limestone sublevel or 200 ft (61 m) Level was advanced with it, and was continued 360 ft (110 m) farther, cutting a zone of cross veining. Though strong shear walls accompanied Slitt Vein, which showed a width which would have been workable had it been fluorite, the mineralisation was siderite and other carbonates, and only one short stretch with recoverable fluorite was found at rises H 50 and H 51. From the junction already mentioned a drive was continued S 75°E, presumably on another branch of the vein, but without result. The forehead of the 200 ft (61 m) Level, at about 880 ft (268 m) above OD, is some 1900 ft (579 m) distant from the W forehead of the Scar Limestone Level from the next deep mine, Slitt Mine, to be described below; owing to the continuing eastward dip, this is about 830 ft (253 m) above OD. The belt of large ironstone flats worked from West Slitt (p.209) begins in this stretch, but the completion of the connexion to Slitt Mine in the Scar Limestone appears to have little attraction Blackdene Mine, including Blackdene Vein as well as the substantial oreshoots on Slitt Vein, have produced 364 406 tons (370 237 t) of crude fluorspar, and about 4500 tons of lead concentrates.

    The main shaft of Slit Mine (disused), by Middlehope Burn 0.75 mile (1.2 km) N of Westgate [NY 9058 3920] begins in shale above the Three Yard Limestone and has been sunk 585 ft (178 m), reaching the base of the Whin Sill (here intruded beneath the Tynebottom Limestone) on the footwall of the vein. A drainage adit, Spring Bank Level [NY 9066 3854], starts 2700 ft (823 m) S of the shaft in the shale below the Six Fathom Hazle at about 950 ft (290 m) above OD. The arrangement of the principal levels is shown on (Figure 33). There is no information as to stopes above Spring Bank Level. Between this level and the 70 Fathom Level there is only sketchy written information; but deeper stopes between the 70 and 100 Fathom levels are recorded with precision. It is, however, clear that there was an extensive oreshoot, developed against beds from the Six Fathom Hazle down to the bottom of the Whin Sill. In the Alternating Beds above the Tynebottom Limestone the vein is recorded as 2–4 ft (0.6–1.2 m) wide, "moderate in ore"; similar widths were noted in the limestone. Beneath the Tynebottom Limestone W of the shaft the vein was 4–5 ft (1.2–15 m) wide. In Kirk's Level in the upper part of the Whin Sill, and in the related stopes W of the shaft, widths up to 41,4 ft (1.4 m) were found, but E of the shaft the vein decreased to 1.5–2 ft (0.5–0.6 m), and was not workable except for a short length. In the middle part of the Whin Sill W of the shaft the width increased to 6 ft (1.8 m) "coarse spar with iron carbonate". The average width on the 100-Fathoms Level was somewhat less, and the vein proved to be variable as to ore-content. There are frequent mentions of coarse spar in the reports. A winze beneath the Whin Sill W of the shaft was carried down 54 ft (16.5 m); in the bottom the vein was 4 ft (1.4 m) wide, "coarse spar and stone with spots of ore". It seems clear, therefore, that the vein width and its fluorite-content is maintained or perhaps increased as the vein is followed downwards through the Whin Sill. In the later years of activity, however, costs became prohibitive; in 1872 the cost of producing lead concentrates here had risen to 160/-per bing (£20 per ton); in 1878 the mine was closed down and dismantled. The recorded production, 1818–1880 amounted to 40 706 tons of galena, but comparing the stopes for this period with the total volume extracted, it is reasonable to conclude that the mine contributed not less than 100 000 tons to the aggregate Beaumont production. The minerals present included fluorite, quartz, siderite, ankerite, galena, marcasite and a little sphalerite. It is, of course, impossible to say what the Slitt Vein carried in the Great Limestone vertically above the Slitt Mine oreshoot as this bed has here been removed by erosion. Immediately to the E, however, it was very extensively mineralised in the limestone, but mainly with iron minerals. The Slitt Pasture [NY 910 392] and West Rigg [NY 911 392] opencuts (disused) (Plate 6), lying respectively west and east of the Westgate–Rookhope road, bear eloquent testimony to the extent of the ironstone flats here related to the vein and to a series of NW flyers from it. Adjacent to the vein more or less the full thickness of the limestone was impregnated with limonite, derived from the oxidation of siderite and ankerite, with small quantities of fluorite and some galena. Away from the vein the lower parts of the limestone became unproductive, but at the High Flat horizon flats extended 150–200 ft (46–61 m). The vein itself carried much quartz, and has been left as an unworked pillar in West Rigg opencut. These quarries were among the Weardale Iron Co.'s principal producers in the second half of the 19th century. In 1884–1885 the average iron-content of the ore obtained varied from 34.3 to 43.4 per cent. The ore was transported by means of a full-gauge railway which, starting from Middlehope, followed the N side of the valley at about 1250 ft (381 m) above OD to Rookhope, where it connected with an incline on which the trucks were hauled up to Bolts Law [NY 950 443] (1650 ft (503 m) above OD), whence the track continued round the head of the Stanhope Burn valley to connect with the Stanhope-Consett line. These railways have now been dismantled.

    From West Rigg opencut which extends 800 ft (244 m) E from the Westgate–Rookhope road there is then an apparently unproductive gap of some 900 ft (274 m) to the Rigg Mine opencuts (disused) [NY 915 390], where ironstone flats were also worked in the Great Limestone. Lower horizons were made accessible from Siders Level [NY 9169 3866], which starts 950 ft (290 m) NNE of Warden Hill, and as a crosscut 1100 ft (335 m) long in the shale below the Quarry Hazle which reaches the vein. This level is blocked at the first shaft [NY 9167 3878], 380 ft (116 m) from the portal. The extent of the workings related to it is not known. Purple fluorite occurs on the dump. North of the Rigg opencut fluorspar was being worked in 1941 by Mr A Dalton from a branch or loop of the main vein reached by a crosscut level 70 ft (21 m) long [NY 9156 3900]. The workings lie beneath this level but above Siders Level; the vein was 4–6 ft (1.2–1.8 m) wide, containing fluorite, quartz and a little galena. A sample across the full width of the vein taken in 1941 gave an assay: 84.33 per cent calcium fluoride, 12.96 silica, 0.42 lead sulphide (assay by Mineral Resources Laboratory, Imperial Institute). To the W the small oreshoot appears to be terminated against a downthrow cross-vein, while to the E the continuation of Heights North Vein may be expected to occur. Production of fluorspar during 1907–1914 amounted to 1284 tons; after 1940 an output of about 50 tons per week was maintained for several years. Immediately to the E some fluorspar has been obtained from Gowland's Shaft (disused) [NY 9166 3899] but still farther E to Park Burn there appears to be a virgin stretch of about 1500 ft (457 m) in the upper measures.

    In 1974, EXSUD Ltd drilled seven inclined boreholes (totalling 3256 ft, 992 m) to prospect the West Rigg- Rigg area of Slitt Vein at depth. Two holes, SH 1 and SH 5 were aimed at the vein from opposite sides, approximately 500 ft (152 m) E of the Westgate–Rookhope road and thus beneath West Rigg opencut. The northern hole, SH 1 [NY 9126 3922] ended in sandstone below the Jew Limestone at 573 ft (175 m) above OD, 771 ft (235 m) below surface, without intersecting a vein or structure. The Whin Sill was not found in this hole and must therefore be below the sandstone under the Jew Limestone; its downward transgression, below the Single Post Limestone (as at Blackdene Mine) to below the Tynebottom Limestone (as at Slitt Mine) is evidently continuing. The southern hole SH 5 [NY 9126 3916] cut fluorite with quartz, ankerite and galena in the Six Fathom Hazle and again in the Slaty Hazle, but samples taken at intervals between 1020 ft (311 m) and 951 ft (290 m) above OD showed no more than 1 per cent calcium fluoride in these intersections, and less lead. The vein is vertical to the upper intersection, and dipping steeply N to the second, but the latter may be a loop. A slight change of dip of the vein towards the S, or what is perhaps more likely, a deviation of hole SH 1 towards the vertical would explain its failure to intersect. A low-angle hole, SH 2, [NY 9138 3913] farther E, explored the lower part of the Great Limestone, here mainly ironstone, but with a channel from 34 to 61 ft (10.4 to 18.6 m) rod length where the samples varied between 6.7 and 14.2 per cent calcium fluoride. Holes SH 3 to 4C were drilled from [NY 9145 3895], S of The Rigg opencut. Hole SH 3 entered Whin dolerite at 513 ft (156 m) OD, under 82.5 ft (25.1 m) of beds, mainly sandstone, underlying the Jew Limestone. It appears that this limestone has thinned or become intercalated with thin sandstone layers, its thickness in SH 1 being 21 ft (6.4 m), while in SH 3 it is 12.4 ft (3.8 m); the correlation of the overlying beds is however satisfactory. Calcite, quartz, pyrite, sphalerite and a little fluorite were found at the Tynebottom Limestone horizon, where the vein was apparently cut. Hole 4A tested the vein in the Six Fathom Hazle and Five Yard Limestone, where the best intersection of the campaign was obtained, an average of 41.6 per cent calcium fluoride over a probable true width of 4.5 ft (1.37 m). Holes 4B and 4C failed to confirm the continuity of values along strike. The results of this investigation do nothing to dispel the impression that an ESE strike is unfavourable for fluorite mineralisation, even though iron carbonates were admitted in quantity, probably at an earlier stage. Taking evidence from Blackdene Mine together with these indications at the Riggs suggests that the sinistral transcurrent movements (Greenwood and Smith, 1977) which opened up those parts of the vein trending near E-W probably postdated the early sideriteankerite metasomatism.

    The trend of Slitt Vein from the E end of the E–W Slitt Lead Mine oreshoot through the Rigg opencasts is S 58°E, but between Rigg and Park Burn the average direction alters to S 75°E and the next 1 IA miles (2 km) to Cammock Eals, where the vein crosses the River Wear carries very strong vein mineralisation, in which quartz is probably the most abundant constituent, though three or perhaps four shoots with workable fluorite where the wallrock is favourable have been distinguished by Mr D Strutt of Weardale Minerals Ltd (personal communication).

    Investigation of this stretch was begun at surface E of Park Burn by the Beaumont Co. in 1861, when the vein was reported as strong but extremely poor in galena. It was nevertheless decided in 1862 to drive a crosscut adit from Park Burn at [NY 9217 3860]; this reached the vein at 806 ft (246 m) near the base of the Nattrass Gill Hazle, where it proved to be 25 ft (7.6 m) wide, coarse fluorite and quartz but without galena. An exploratory drift found that part of the vein on which it was driven closed to the W of Park Burn. Not discouraged, the Beaumont Co. started a Horse Level from Cammock Eals [NY 9846 3831] at 800 ft (244 m) above OD and kept this, and a ventilation drift 60–80 ft (18–24 m) above driving for many years, eventually reaching 6300 ft (1.92 km) WNW of the portal; there was a shaft to surface [NY 9280 3860] at 2425 ft (739 m) from the portal and a rise connexion to Park Burn Level at 4350 ft (1.33 km). Great widths of spar were proved, but no ground payable for lead ore, and the mine was abandoned in 1871.

    Recovery of fluorspar commenced in 1905 at Heights Pasture Mine (disused) by W Hird & Co., at first by opencasting in a cut [NY 9215 3884] 550 ft (168 m) long and later by stoping above Park Burn Level. Vein-widths up to 31 ft (9.4 m) were found, and by 1918 the main orebody had mainly been extracted, but some intermittent working of middlings between 1925 and 1940 continued; the total output of fluorspar at this mine was 41 721 tons.

    The Cammock Eals or Cambokeels Mine (idle) (Weardale Minerals Ltd) first produced fluorspar in 1906–09, when Mr J Coulthard was the leaseholder. Subsequently, W Hird & Co. worked it until 1927, but the first shaft was reached during Mr A Dalton's operations from 1935–1939, and the output from 1909–1939 amounted to 28 086 tons. Metallurgical spar supplied to Consett Iron Co. in 1936–37 contained 77.4 per cent calcium fluoride, 16.3 silica, 3.5 alumina, 0.6 calcium carbonate, 0.66 lead sulphide. In the first edition of this Memoir (Dunham, 1948, pp.255–256) the significance of the Beaumont Co.'s discovery of extensive spar deposits at depth beneath Park Burn was emphasised. In the late 1940s the mine was acquired by Anglo-Austral Mines Ltd, and the Horse Level [NY 9846 3831] was reopened to and beyond the rise to Park Burn Level. It now emerged clearly that Slitt Vein consists of two main fractures about 25–70 ft (7.6–21.3 m) apart and that oreshoots occur intermittently on both the N and S fractures. The geological results of work during Anglo-Austral's tenancy have been described by R J P Lyon and B Scott (1957). Gentle differential folding is illustrated from the position of the Scar Limestone above Cambokeels Level; it is noted that the stratigraphy between the Five Yard and Three Yard limestones differs on the two sides of Slitt Vein, but the conclusion that transcurrent faulting is the most likely explanation is not drawn. The chief variation arises from the fact that the Six Fathom Hazle has thickened in part of the mine area, cutting out a thick shale with a coal near the base found particularly on the N wall. The stopes shown on the longitudinal section (Figure 33) were mainly the work of Anglo-Austral Mines above Cambokeels Level. Output figures for the company, but an estimate of its production to the end of its tenancy, show a production of 26 128 tons acid-grade spar, 1203 tons galena and 51 tons zinc concentrates. The crude ore was lorried over the Killhope Pass to a new flotation plant installed in the Krupp building at Nenthead from which the Non-Ferrous Mineral Control's wartime zinc flotation plant had been sold off only in 1946. Some drilling to test Slitt Vein beneath Cambokeels Level was done, proving strong mineralisation but rich in quartz, some of it containing the iron sulphides marcasite, pyrrohotite and pyrite in platy aggregates characteristic of the Great Sulphur Vein, but enough evidence was not obtained to show whether this was a gradual or rapid change, and development in depth was not undertaken. This started in the early 1970s by Malcolm Brown & Maddison, who drove an incline beneath the Horse Level, some 2400 ft (732 m) WNW of the portal finding good fluoritic ore, and from the foot of this a level 131 ft (40 m) below the adit began to be developed. Aluswisse then acquired the mine for SAMUK and much of the work leading to its establishment as the recent leading fluorspar producer in the field was due to their efforts. An incline to the W was started close to the mouth of the Horse Level (which then became known as the 160 m Level) and the decline was carried down in stages at 12° inclination to reach the 280 m Level 2280 ft (695 m) from the entrance. Levels were developed at 200 m and 240 m as shown on (Figure 33). The 200 m level commands the Tynebottom Limestone and upper part of the Alternating Beds; productivity was not high at this level. The 240 m Level is in dolerite of the Whin Sill at the incline and good orebodies were got on both S and N fractures in this and in metamorphosed Alternating Beds above. The level was continued 600 ft (183 m) E to the boundary at the river; ore was worked in the Alternating Beds, but the top of the Sill drops in this direction. Hot water was found here containing 2500 ppm sodium, 1750 calcium, 401 potassium, about 1700 chlorine, 0.4 iron, 75 magnesium, 0.6 zinc; methane and traces of radon were also found together with a distinct smell of H2S. Followed westward, the top of the Whin Sill plunges down westwards beyond the incline and the Jew Limestone appears above the sill in the 240 m Level; the position of the intrusion is now close to that mentioned in connection with the Rigg borehole. The 280 m Level is entirely in dolerite wallrock; six separated orebodies have been stoped.

    In 1982 the present company, a subsidiary of Minworth Ltd, acquired the mine and the flotation mill at Broadwood, Frosterley from SAMUK, and production was continued at the rate of 1100–1700 t per week until 1987. The principal developments have been the extension of the 280 m Level eastward, and the sinking of a subsidiary incline from which to develop a new main level at 320 m. The incline passed through the base of the Whin Sill, revealing its full thickness as 220 ft (67 m) here. The crosscut to the South Vein is in structurally complex ground including the displaced Jew Limestone and showing strong values in sphalerite and pyrrhotite (Plate 7); the vein itself is continuing in strength as anticipated from preliminary borings from the 280 m Level.

    Mr Stutt's detailed geological observations made during these developments show many points of interest. As to the attitude of the Slits Vein, the North and South veins and the fractures intermediate between them they generally stand steeply, but they may dip either N or S, and in several cases a marked change from S to N has been observed. The main postmineralisation movements, grinding up the fluorite into a dense powder similar to that commonly seen at Stotfield Burn, occurs along the northern fracture. At least one cross-section (200W) where there has been adequate drilling suggests that the vein lies axially within a gentle anticline but it is not known how persistent is this relationship. One of Lyon and Scott's cross-sections (1957, p.279) might be similarly interpreted but another shows a syncline or trough across the structure. Displacement of the beds in either direction may be present, but it is nowhere more than a few metres.

    Fluid inclusion studies by Dr J B BaileyGratitude is expressed to Dr Bailey for his permission to mention these results. from the University of Manchester (see p.94) are of particular interest because here the unstressed oreshoot was sampled right across; the results showed two stages of heating up to 172°C separated by cooling stages before the centre of the vein was reached. No good correlation with the change from green to purple fluorite was found.

    At the river crossing [NY 9375 3829] a further small change in direction to S 57° E occurs as the vein passes into Blue Circle Cement Co. property. The next 0.5 mile (0.8 km) passes under river alluvium and low ground and has not been prospected, so that it is not known whether the Cambokeels oreshoots terminate near the river.

    From 1977 to 1983 the output of crude spar from Cambokeels Mine amounted to 378 126 tons, mined to a cut off of 35–40 per cent calcium fluoride. The aggregate production, not including Heights Pasture, may be estimated at 474 633 tons (482 281 t): recorded and estimated lead concentrates, to 1982, 2866 t. S of the Wear, the vein has been worked at Billing Hills Mine (disused) [NY 946 377] by Billing Ganister Co., on Mr E J W Hildyard's royalty. The vein is exposed in a series of opencuts extending from the Four Fathom Limestone through the Quarry Hazle and Tuft sandstones to the Great Limestone. It has a great width not less than 30 ft (9 m) in the Great Limestone, but much of it consists of massive quartz enclosing fluorite in a series of lenses. There are also levels in the Nattrass Gill Hazle [NY 9446 3767], the Quarry Hazle [NY 9466 3782] and the Great Limestone [NY 9470 3763], lengths stoped from the levels aggregate respectively 370 ft (113 m), 100 ft (30 m) and 520 ft (158 m). The output of fluorspar, 1918–1931, amounted to 12 685 tons. E–W veins known as Plantation and Old Chert cut the Slitt Vein on Billing Hills, and there is evidence of subparallel veins and branches. These contain some fluorite, but the principal mineral in them is quartz.

    In the valley of Horsley Burn no mining has been done on Slitt Vein itself, though there is an opencut on a SE branch at the head of Dry Gill, in the Great Limestone [NY 9526 3721]. On the opposite side of the valley, 1500 ft (457 m) SW of Snape Gate, the vein is partly exposed as a rib of quartz where it crosses an unnamed side stream [NY 9627 3681], in the Great Limestone, which on the S side of the vein is converted into limonite at least 20 ft (6 m) wide. Hereabouts Allergill Vein is believed to intersect Slitt Vein (p.215). Limonite is again seen in shallow excavations [NY 9645 3673] about 600 ft (183 m) E, but it is highly siliceous, a sample containing 17.75 per cent iron, 62 insoluble matter, 0.163 phosphorus pentoxide (assay by Pattinson and Stead 1942). There remains the possibility of extensive iron mineralisation in this little-explored locality. Eastwards a completely unexplored gap of 1 .25. miles (2 km) now follows, the next exposure being at the W end of Catterick, where the supposed continuation of the vein, now trending nearly E–W, makes a series of bold outcrops of coarse quartz and silicified sandstone along the Wear–Bollihope watershed eastward from [NY 9847 3605] at the horizon of the Coalcleugh Beds and the Hipple Sill. In this stretch Yew Tree Vein (p.216) intersects Slitt Vein. Very little fluorite remains in the vein at outcrop; it has not been tested in depth unless it was reached in Yew Tree Mine for which a complete plan is not available. Small quantities of vein quartz have been obtained from this stretch of the vein, the total output, by the Weardale Steel, Coal and Coke Co. being 84 tons.

    The vein was cut by the NWA tunnel (Table 51), where it was mainly quartz (58.6 per cent silica, 7.3 per cent calcium fluoride, 0.003 per cent zinc), associated with sandstone breccia 16.4 ft (5 m) wide.

    In Bishopley Wood [NZ 0223 3550] 2200 ft (671 m) SW of White Kirkley Bridge, the vein crosses Bollihope Burn. Here again it is a wide vein, but the filling, as seen in the Great Limestone, is mainly quartz. There are, however, small narrow stopes in it from both banks of the stream presumably for galena. From Harehope Gill 2000 ft (610 m) E of White Kirkley, the Harehope Gill Mine (disused) got the vein from a crosscut adit [NZ 0329 3598] 2175 ft long (663 m) driven on top of the Great Limestone. From this workings extended 1500 ft (457 m) E and 1050 ft (320 m) W of the level head, winzes giving access to deeper ground: at least one was carried down to the bottom of the Four Fathom Limestone. The spoil heaps show much quartz, some fluorite, marcasite and galena. Production of lead concentrates, 1818–66, 1888–91 amounted to 1165 tons; 192 tons of fluorspar were obtained from the dumps in 1918–20.

    The last surface exposure of the vein is on Harvey Hill, 1 mile (1.6 km) S of Frosterley, where the Grindstone Sill is veined with quartz [NZ 0395 3531].

    Sunnyside Mine (disused) 1.25 miles (2 km) SE of Frosterley, is thought to be the easternmost mine on the Slitt Vein, but, owing to the fact that the two existing plans (Mines Dept Nos. R.316, 2631A) are seriously inconsistent, it is not possible to be certain that the Slitt Vein was reached, for several veins are involved. The main adit [NZ 0547 3609] starts from Hole Beck Gill, 700 ft (213 m) NNE of Sunnyside Farm, in the shale above the Crag Limestone: it runs 820 ft (250 m) SSW, then turns to slightly W of S and continues through South Beck Shaft [NZ 0526 3554] to Bell's Shaft [NZ 0525 3527] 2000 ft (610 m) from the turn. The old plans, show two NNW veins, Whiteheaps and Smith's, near the adit mouth. The primary 6-inch survey, but neither of the old plans, shows an ENE vein, Eddy's Vein, as having been worked west of the adit mouth. The position near Bell's Shaft is equally confusing. It seems certain that an ENE vein, Lonsdale's or Sparry Vein, throwing 15 ft (4.6 m) SE has been wrought, but it is not clear whether Slitt Vein was found, though one plan (definitely incorrect in some respects) shows a level in the right direction. The dumps at Bell's Shaft show quartz and purple fluorite. This shaft (Figure 4), section 13) starts above the (supposed) Lower Felltop Limestone and if the section is accurate, has been sunk almost to the Little Limestone, 290 ft (88 m) in all. The lead ore from this mine appears to have been trammed along the main adit to South Beck Shaft, 925 ft (282 m) N of Bell's Shaft, where it was hoisted and dressed. The tailings consist of purple fluorite, quartz, sandstone and limestone. The only record of production is 92 tons of galena in 1867–76, silver being recorded for one year only (1872) when less than 3 oz silver per ton of lead was recovered. This may be compared with the recovery of 8.6 oz. recorded for Harehope Gill Mine. A small NW vein called Thorn-hope Lode was tried from a level [NZ 0552 3543] E of Bell's Shaft.

    In 1980 SAMUK drilled a borehole inclined at 46–60° NE from [NZ 0519 3500] which found sphalerite, quartz and siderite against the Black Beds of the Great Limestone at 218 m rod length; quartz with a little galena, sphalerite and ankerite lower in the limestone at 237–241 m rod length; silicification and dolomitisation in the Four Fathom Limestone; and brecciated and faulted ground in the Nattrass Gill Hazle with siderite, calcite and quartz at 275 m. These intersections may represent Slitt and Lonsdale veins but this cannot be regarded as certain.

    Half a mile E of Bell's Shaft, Slitt Vein should converge on the Sharnberry Fault; possibly the line of old pits from [NZ 0676 3490] to [NZ 0720 3485], the dumps from which show white baryte, marks its course.

    The total recorded output from Slitt Vein is as follows: lead concentrates, 73 296 tons (including the whole of the Levelgate production of 15 617 tons but not including any production from Blackdene); Fluorspar sales 430 000 tons. The main potentiality of the vein is as a fluorspar producer, as suggested in the 1948 edition of this memoir. The development of Blackdene and Cammock Eals mines has increased output almost tenfold.

    Allergill = Softleyside = Ridley's or Crawleyside Vein—Lead ore, fluorspar

    NY93NE; Durham 24 SW, NW; 23SE. Direction N50°E

    The vein traverses the Great Limestone outcrop SE of Horsley Beck from a point [NY 9627 3682] 1800 ft (549 m) E of Snowhope Close, where it apparently terminates against Slitt Vein, to a point 2000 ft (610 m) NE of Snape Gate, where it was worked from opencuts [NY 9710 3760] and shallow shafts, the workings being drained by a water level driven beneath the Nattrass Gill Hazle from Horsley Burn [NY 9722 3804]. It was also worked opencast in the Four Fathom Limestone [NY 9745 3789]. Coarse purple fluorite, with quartz, chalcedony and limonite occurs on the heaps from these workings, collectively known as Allergill Mine (disused). No plan or section remains. It must be assumed that the workings are ancient, and that they yielded more galena than the 103 tons recorded for 1848–70. Some fluorspar is said to have been obtained from the dumps by hand picking.

    SE of Stanhope the vein apparently splits into two parts; the northern one, known as Softleyside Vein, was worked from levels [NY 9826 3877] and [NY 9852 3889] and shafts between [NY 9820 3860] and [NY 9860 3890] in West Softely Plantation, the horizon of the workings being the Nattrass Gill Hazle. Purple and amber fluorite, pyrite, sphalerite, quartz and galena occur on the dumps. There is no evidence from the dumps that the Little Whin Sill (which occurs within the Three Yard Limestone and is, therefore, only a short distance beneath the workings) was tested.

    The Wear near Newtown House, where the vein would cross the river, runs in alluvium, but the vein appears again between the two parts of Ashes Quarry [NY 998 398] in the Great Limestone, where it is known as Ridley's or Crawleyside Vein. Here a belt of altered limestone containing silica and limonite at least 300 ft (91 m) wide, is associated with it. It has been tried by a level near the top of the limestone for 1600 ft (488 m) but appears to have yielded little ore. Probably the vein terminates against the cross vein which shifts Red Vein E of the Hope Level workings.

    West Newlandside Vein

    NY93NE; Durham 24 SW

    In the western section of Newlandside Limestone Quarry, 0.75 mile (1.2 km) SSW of Stanhope [NY 9851 3826], a NE vein in the Great Limestone, containing a width of up of 30 ft (9 m) of limonite was exposed. A representative sample taken in 1942 assayed: iron, 18.25 per cent; silica, 50.45; sulphur, 0.055; phosphorus pentoxide, 0.117; lead, trace (assay by Messrs Pattinson and Stead, 1942), showing that silica, present in the form of chalcedony, is very high. The occurrence is thus not of economic importance.

    Quarry Hill Veins—Lead ore

    NYO3NW; Durham 24 SW

    Two veins: directions N50°E and N85°E, intersect near the main face of the eastern sections of Newlandside Quarry [NY 9908 3831], 1500 ft (451 m) E of the Stanhope Middleton road. The NE vein has been worked from shafts between [NY 7875 3805] and [NY 9904 3826] starting above the Little Limestone. In the quarry there is a broad belt of alteration, but the veins are very narrow. A little galena occurs in a flat at the High Flat horizon. The altered rock contains, according to analyses by Messrs Dorman Long and Co., 60–80 per cent silica, and 6–15 iron. A production of 14 tons of galena for 1851–53 is recorded. On the W side of the road the southern vein has been left as an unworked pillar in the western section of the quarry [NY 9850 3786]. The vein carries purple fluorite, quartz and a little galena and is associated with limonitic alteration of the adjacent Great Limestone.

    Kilnbank Vein

    NZ03NW; Durham 24 SW

    This small NE vein cuts through the face of Newlandside Quarry [NY 9943 3810] 2800 ft (853 m) ESE of the Stanhope–Middleton road, producing a belt of altered limestone about 100 ft (30 m) wide, in which silicification is again strong. A little fluorite and galena occur in the vein, which has been tried, without success, from a level [NY 9976 3832] beneath the Four Fathom Limestone.

    Coves or Park Vein—Lead ore

    NY93NE, NZ03NW; Durham 24 SW

    Passing beneath Parson Byres Farm, 1 mile (1.6 km) SSE of Stanhope, this vein trends N50°E. A level at the base of the Four Fathom Limestone [NZ 0028 3800], starting 500 ft (152 m) NE of the farm, shows fluorite, quartz and siderite on the dump; no ore appears to have been dressed here. Farther SW the vein runs between Newlandside and Jack Crags Quarries in the Great Limestone; here it has made the limestone unfit for quarrying over a width of 450 ft (137 m) [NY 9995 3765] converting it into limonite rich in silica; the altered belt mainly lies on the NW side of the vein. At Coves Mine (disused) a level and shafts [NY 9959 3732] in Cow Burn, W of the quarry gave access to old workings which were extended from the Coal Sills sandstones down to the Four Fathom Limestone. Galena, in a matrix of coarse purple fluorite with quartz and limonite, was raised, 115 tons being obtained between 1850 and 1864; silver recovery was 6 oz silver per ton of lead. Total production must have been much greater. The dumps yielded 90 tons of fluorspar in 1918. Dr G A L Johnson reports that when Ferguson, Wild and Co. reopened Coves Mine in 1970, large empty scopes were found, but nothing workable was found.

    Yew Tree-Hollywell Vein—Lead ore, fluorspar, iron ore

    NY93SE, NE, NZ03NW; Durham 32 NW, 24 SE Direction N55°E

    The vein has been followed from the S slopes of the Bollihope valley to the N side of Weardale, a total distance of 3.5 miles (5.6 km), though the workings are not continuous. SW of Bollihope Burn the vein has been traced for 3750 ft (1.14 km) in the Harnisha Burn Mine (disused). There is an opencut in the Great Limestone, with levels below the limestone [NY 9892 3510], including a water-level [NY 9901 3514] in the Quarry Hazle. A strong cross vein at 1000 ft (305 m) SW of Harnisha Gill was followed for 1200 ft (366 m) SE at the water level horizon, and was also tried by a level [NY 9866 3454] in the Coal Sills sandstone. On the west side of the Stanhope–Middleton road, 250 ft (76 m) SE of its crossing over Harnisha Burn, a deep shaft (boarded over) has been sunk on Yew Tree Vein, probably communicating with workings beneath the water level. None of the adit levels is now accessible. It is probable that these workings remain from the London Lead Co.'s tenure of the royalty, but no details are extant. On the extensive dumps at Harnisha Burn foot, purple fluorite, chalcedony and quartz are abundant. It is probable in view of the extensive spread of gravel tailings here that a fairly considerable quantity of ore was dressed (analysis, (Table 61). The old plan of the Bollihope Mines, in the North of England Institute of Mining Engineers, Newcastle, shows that the vein terminated SW against an unproductive E–W vein. A further y4 mile (0.4 km) W two parallel cross veins trending about N15°W have been tried by levels [NY 9757 3477] and [NY 9769 3481] near the top of the Great Limestone from the S bank of Bollihope Burn; a little galena, purple and green fluorite and quartz were found, but the levels were not carried far enough to intersect Yew Tree Vein. A higher level [NY 9773 344], in the Firestone, may have cut the continuation of this vein W of the cross veins, but if so it was not mineralised.

    The workings of Yew Tree Mine (disused) lie on the S side of Catterick. A track from them runs across the fell top 1.5 miles (2.4 km) eastward to join the Middleton–Frosterley road at Hill End, a mile from Frosterley. This mine was also worked by the London Lead Co., and, prior to 1854, by the Beaumont Co. The main level [NY 9930 3527] N of Bollihope Burn was driven near the top of the Great Limestone, commencing as a flank level at 980 ft (299 m) above OD. A second level [NY 9942 3545] entered the thin shale above the Firestone. There was a considerable opencut [NY 9950 3550] in the thick overlying grit, where the vein may still be seen. Deep shafts from the fell top probably go down to the Great Limestone level, and from their position suggest a strong SE dip. All along the vein fluorite is abundantly present on the heaps. Almost all the fluorspar production up to 1937 came from dumps. In that year, however, mining operations were commenced in the Low Grit Sill which is 96 ft (29 m) thick here, separated from the underlying Firestone by only a few feet of shale. From a shaft much of the available spar was stoped out to surface over a length of about 300 ft (91 m), and to about 20 ft (6 m) above the upper level mentioned above. The vein was 5–6 ft (1.5–1.8 m) wide, filled with good quality fluorite. At the NE end of this working the spar becomes very siliceous (Table 61), and it is presumed from the evidence of surface shafts that it continues in this condition to the Slitt Vein, 1500 ft (457 m) ahead. The Great Limestone level was reopened in 1941. A prospect of some interest may remain at Yew Tree now that facilities are available nearby for the treatment of siliceous flurospar ore.

    In spite of local tradition it is not certain that the workings of Yew Tree Mine reached the Suitt Vein. NE of that vein there is an unworked stretch of at least 1700 ft (518 m). The vein, now known as Hollywell Vein, was worked from shafts extending from the outcrop of the Great Limestone up to that of the Low Grit Sill on the southern slopes of Weardale [NZ 0088 3658]–[NZ 0042 3626], the lowest workings being adjacent to the SE corner of Dryburn Quarry [NZ 0088 3658] in the Great Limestone. On the heaps, purple fluorite, quartz and galena (including some of the "steel-ore" type) occur. On the N side of Weardale the vein was worked at the old Hollywell Mine (disused 0.5 mile (0.8 km) WNW of Frosterley, close to which the vein, and a N branch from it may be seen in Rogerley Quarry. At the mine the main vein was worked from an adit [NZ 0202 3733] in the Great Limestone for 1740 ft (530 m), the North Vein for 1225 ft (373 m); both are cut by a cross vein trending N50°W. Limonitic iron ore was obtained from both veins by the Weardale Iron Co.

    Yew Tree Mine yielded 2476 tons of lead concentrates under the Beaumont Co. between 1820 and 1854, and probably contributed to the London Lead Co total of 5853 tons for the Bollihope Mines between 1854 and 1867. Hollywell Mine yielded 321 tons of galena between 1848 and 1857. From Harnisha Beck foot, 1134 tons of fluorspar were obtained between 1913 and 1937; Yew Tree Mine and dumps have produced a recorded total of 14 693 tonnes of fluorspar.

    Dryburn Vein—Lead and iron ore

    NZ 03 NW; Durham 32 NW, 24 SE Direction N55°E

    At Dryburn Side, 0.25 mile (0.4 km) N of Hill End, old shafts extend over 2000 ft (610 m) on the vein, and there is a level [NZ 0143 3633] above the Great Limestone. The heaps show purple and green fluorite, chalcedony, quartz and aragonite. No details of the workings are available but it appears that trials from shafts were carried down to the Four Fathom Limestone. The East Dryburn Mine (disused) at Frosterley consisted of a level [NZ 0315 3693] at the base of the Great Limestone driven 1250 ft (381 m) NW from Mill Eal to cut the vein. The workings in the limestone were only 500 ft (152 m) long; ironstone bodies of irregular width were worked to a height of 36 ft (11 m), according to the Weardale Iron Co.'s records. No separate record of production remains. Dryburn Vein was not found in the Bollihope valley, though trials were made for it [NZ 0009 3534] at the base of the Low Grit 2000 ft (610 m) ESE of Yew Tree opencut.

    Birch Vein

    NZ03NW; Durham 32 NW, NE Direction N60°E, probable throw SE

    A line of old shafts from [NZ 0161 3586]–[NZ 0228 3624] marks the vein NE from Hill End, the dumps showing quartz, chalcedony, fluorite and a little malachite. A level [NZ 0272 3559] from Bands Eale, 1200 ft (366 m) S of Frosterley church, driven to the vein on top of the Four Fathom Limestone, and continued in it 900 ft (274 m) SW appears to have been unsuccessful, as was the High Shaft [NZ 0189 3600], 1225 ft (373 m) SW of the junction of the Frosterley–Middleton road with the road to Bishopley, sunk in 1849 to the Great Limestone. No record of production from this vein remains. The vein was not found in the Northumbrian Water Authority tunnel.

    Bollihope Freehold Cross Vein

    NY93SE, NZ03SW; Durham 32 NW, SW Direction N23°W, throw 12 ft (3.7 m) SW

    A level [NY 9984 3484] starting 4000 ft (1.22 km) ESE of the crossing of the Stanhope–Middleton Road over Bollihope Burn runs in the Tuft, reaching the vein at 300 ft (91 m) SW. The London Lead Co. plan shows only a short stretch of workings from this level, but the large dumps of sandstone and limestone with quartz, calcite, fluorite and sphalerite suggest that the level communicates with fairly extensive workings, perhaps joining with those on the Markiel Vein, 1025 ft (312 m) SSE of the level head.

    Markiel Vein–Wager Burn Vein group

    The veins listed above constitute the most important group in the Bollihope valley. They were worked at Whitfield Brow Mine (disused), the main development of which was due to the London Lead Co. The principal orebodies appear to have been found on the NW veins. Markiel Vein W of Howden Burn was worked from a level [NZ 0042 3489] driven close to the junction of that burn with Bollihope Burn in the Great Limestone. There is also an opencut [NZ 0024 3466] on the SE side of the Middleton–Frosterley road, in the Great Limestone. Limonite, quartz, purple fluorite, galena and sphalerite occur on the heaps; some iron ore is understood to have been obtained here by the Weardale Iron Co. Close to the head of the level, Markiel Vein is considered to be shifted NE side SE 150 ft (46 m) by the Copper Vein. In the NWA Tunnel, however, the vein appears to be on its original line, 2250 ft (686 m) ENE of the shift. There are the remains of opencast workings [NZ 0060 3480] in the Great Limestone E of the Copper Vein, from which ironstone was probably mined. The belt of NW veins, of which the Copper Vein forms the western member, varies from about 125 to 250 ft (38 to 76 m) wide, and has been followed for 4000 ft (1.22 km) SSE from Howden Burn, from the right bank of which the Low Level [NZ 0045 3465] starts in the upper part of the Great Limestone at 836 ft (255 m) above OD. It appears likely from the dumps that the main oreshoots were above the horizon of the Great Limestone, in the Grit Sills which here, as at Yew Tree, are exceptionally thick; they were mainly worked from Top Level [NZ 0058 3443], beneath the Firestone, but mineralised ground extended, from the evidence of surface cuts, up to the sandstone beneath the Upper Felltop Limestone. No stope section remains, nor is the relative productivity of the various members of the NW vein-belt known. About 300 ft (91 m) SSE from the point where Top Level reaches the Rain's Vein, Wager Burn Vein, trending ENE was cut, and followed for about 650 ft (198 m). Another NNW vein or fault found here, shifting Wager Burn Vein a few feet NE side NW, for part of its course was followed by the drainage level of the mine [NZ 0083 3491] driven in the Tuft, starting at 769 ft (243 m) above OD. The minerals in the Whitfield Brow veins included quartz, coarse purple fluorite, calcite, limonite and galena, with malachite (probably derived from chalcopyrite) in the Copper Vein.

    Recorded production of lead concentrates from Whitfield Brow Mine from 1868–1882 amounted to 23 395 tons; from 1884–1899, 1,461 tons. In addition, the mine probably contributed to the total for the Bollihope Mines of 5853 tons in 1854–1867, and 779 tons in 1883. The Bollihopeburn Mines (possibly the workings on Markiel and Freehold cross veins) yielded 2960 tons from 1868 to 1882, 1834 tons from 1884 to 1899. In 1906–1911, 6126 tons of fluorspar were got from the heaps at Bollihope Shield.

    Wager Burn Mine (disused) consists of a level [NZ 0129 3490] starting from Wager Burn, 2800 ft (853 m) ENE of Whitfield Brow Bottom Level mouth, some 18 ft (5.5 m) below the top of the Great Limestone, at 799 ft (244 m) above OD, running 1625 ft (495 m) SE. At 800 ft (244 m) Wager Burn Vein is cut by this level from which it has been worked on both sides. The ore consists of galena in limonitised limestone, of replacement origin. A small production was obtained in the 1930s, but the vein has not yet been extensively developed. Under the London Lead Co., 330 tons of galena were produced in 1877–84; the more recent owners obtained 86 tons in 1928–30 from hand dressing of the ore.

    Hawkwood Sike Vein

    NZ03SW; Durham 32 SW

    This vein trends ENE and throws 7 ft (2 m) NW; it crosses Hawkwood Sike about 900 ft SE of its confluence with Howden Burn. Here a level [NZ 0024 3345] has been driven about 1000 ft (274 m) ENE on it. At about 600 ft (183 m) the supposed continuation of Bollihope Freehold Cross Vein was cut; it was found to be shifted by the Hawkwood Sike Vein SE side NE about 50 ft (15 m). Nothing is known as to the content of either vein. The horizon of the trial was the Crag Limestone and underlying thin shale.

    Cornish Hush Vein—Lead ore

    NY93SE, NZ03SW; Durham 32 NW, SW. Direction N30°W, throw at Cornish Hush (Shaftwell Burn) about 20 ft (6.1 m) NE

    The Cornish Hush cross vein provides a link between the Bollihope mineralised area and the great belt of veins lying N of Middleton-in-Teesdale. It appears to have been discovered in the Low Grit at Cornish Hush [NY 9990 3315] an opencut by Shaftwell Burn, one and one-eighth miles (1.8 km) SSW of the confluence of Howden Burn and Bollihope Burn. Cornish Hush Mine (disused) is situated in the valley of Howden Burn about 2000 ft (610 m) NNE of the Hush. From here Low Level [NZ 0015 3380] in the Little Limestone and adjacent strata at 979 ft (298 m) above OD was driven 1950 ft (594 m) to the vein, and continued on it 1275 ft (389 m) NNW, 2450 ft (747 m) SSE of Shaftwell Burn. Near the southern forehead Cornish Hush Air Shaft [NZ 0014 3270] see (Figure 4), section 9 in Dunham, 1948) communicated with the surface. Upper Level [NY 9989 3339] started from Shaftwell Burn, 350 ft (107 m) from the vein in the Low Grit at 1088 ft (332 m) above OD; the N drive on the vein was extended through to Black Burn and there connected to surface; the S drive reached 4200 ft (1.28 km) from Shaftwell Burn and a note on the plan states that here it is 141 ft (43 m) immediately below the Sharnberry High Level (p.00) which is at about 1380 ft (421 m) above OD. This figure can only be correct if it refers to Sharnberry Low Level at 1210 ft (369 m) above OD. Minerals present on the dump from Low Level include quartz, galena, calcite and a little chalcopyrite. A similar suite occurs on the larger Upper Level dumps, and here pyrite, partly oxidised to limonite, is abundant. Underground mining at Cornish Hush is believed to have been wholly the work of the London Lead Co. Unfortunately no section of the mine remains, strata below the Little Limestone possibly down to the Four Fathom Limestone may have been tried from Engine Sump [NY 9995 3303], 600 ft (183 m) SSE of Shaftwell Burn. The only NE vein cut in the whole of the extensive drivages on this vein lay 1600 ft (488 m) SSE of Cornish Hush Air Shaft; possibly it was a flyer from Eggleshope Vein; little work was done on it.

    In 1971–72 Swiss Aluminium (UK) Ltd reopened the Upper Level, which they found to have been extensively understoped. Their objective was to test the Sharnberry veins in depth, and although timbering over the stopes was necessary, their reopening was continued as far as the flyer from Little Eggleshope Vein, about 4300 ft (1.31 km) from the level head. Small pockets of galena were seen in the sandstone, but no fluorite. Sharnberry Veins were not reached.

    The production of lead concentrates from 1868 to 1882, 1884 to 1899 amounted to 6483 tons, from which silver was recovered at the rate of about 7 oz per silver per ton of lead. From the wide stratigraphic range of the stoping on this anomalous NNW oreshoot, a greater output might have been expected.

    Broadwood Vein

    NZ03NW; Durham 32NE

    At the NE end of Harehope Quarry [NZ 038 364] in the Great Limestone, which lies athwart Bollihope Burn between Harehope Gill and the Wear, a belt of strong limonitisation occurs which, acording to the primary 6-inch map, is due to the proximity of a NNE vein. A level [NZ 0392 3645] starting close to Broadwood Mill was driven by the Weardale Iron Co., in or near the vein for 1750 ft (533 m); no other information is available.

    Firestone Vein—Lead ore

    NZ03SE; Durham 32NE, SE

    This ENE vein which was worked at Pikestone Mine (disused) around [NZ 053 336], remotely situated on Wolsingham South Moor , 2.75 miles (4.4 km) SSW of Wolsingham, is believed to lie on the fault linking the Teesdale Mineral Belt (Chapter 11) with the Deerness system (Chapter 13). It consists of shafts into the Third Grit of the "Millstone Grit" series. Mineralisation, which included galena, purple fluorite and baryte, extended over a length of 1600 ft (488 m). The occurrence constitutes one of the stratigraphically highest records of galena in workable quantity. A production of 604 tons in 1820–59 is given in the Beaumont records. Geochemical prospecting has revealed strong zinc anomalies.

    Harthope Vein

    NZ03SE; Durham 33NW

    N of Harthope Beck, 1750 ft (533 m) NE of St John's Hall [NZ 0723 3435], a vein trending about N 20°E through the highest beds of the Namurian has been tried by means of a short level, with possibly a sump, for pieces of limestone, probably the Upper Felltop, are present on the dumps. The vein contained purple and amber fluorite, chalcedony and galena. It is doubtful whether the trial was carried deep enough to reach favourable strata. This vein also lies on or near the Sharnberry–Deerness link or Pikestone Vein.

    North Harthope Vein—Barytes

    NZ03SE; Durham 33NW Direction N85°W

    On the northern slope of the valley of Harthope Beck, 3000 ft (914 m) N of St John's Hall, and 600–1 100 ft (182–335 m) W of the Wolsingham–St John's Hall road, a vein of baryte, on line with Slitt Vein has been worked to a small extent in the Second Grit [NZ 0695 3488]. A sample of the mineral examined in 1940 by Mr F Jeffrey Pratt for Messrs J Dampney and Co. (Newcastle) showed over 99 per cent barium sulphate, but it did not yield a perfect white colour. The width of the vein is not known. An attempt to find it by means of a level [NZ 0712 3480] driven in the shale beneath the Grit was apparently unsuccessful.

    Knitsley Fell Veins—Barytes

    NZ03NE, 13NW; Durham 33NW

    Four small veins have ben worked for barytes on Knitsley Fell, W of the quarries in the ganister mapped as the lowest bed of the Coal Measures on the primary 6-inch maps. Near Crowsfield Farm one of these veins trends N50°E through the First Grit of the Millstone Grit facies. It consists of several strings of pink baryte, individual strings reaching 1 ft (0.3 m) wide. A trial was made in 1939 at the point [NZ 0851 3524] where an E–W string joins the vein from the E, SW of Crowsfield Farm. At 900 ft (274 m) NE of this trial a shaft had been sunk at [NZ 0874 3537] on another branch, of which there are several. The Crowsfield belt of intersecting strings runs for about 1800 ft (549 m) roughly parallel to and within 600 ft (183 m) of the Sharnberry–Deerness fault; they could be regarded as part of the same structure. Although too pockety to be attractive prospects, they might be leaks from a barium oreshoot in the Brigantian strata beneath.

    A second vein running NE across one of the summits of Knitsley Fell, south of triangulation point 928, has been tried by a surface cut [NZ 0937 3499] 3800 ft (1.16 km) ESE of the junction of Howleel Lane with the road to Bedburn. It occupies a fault with a throw exceeding 16 ft (4.9 m) NW, shale on the NW being brought against grit. The deposit of baryte in it varies from 1 to 2 ft (0.3 to 0.6 m) wide over a length of 900 ft (274 m). The next vein to the E also trends NE. The workings start 250 ft (76 m) NE of the road, at a point 4600 ft (1.4 km) SE of the Bedburn road junction, continuing for 600 ft (183 m); they consist of shallow opencuts [NZ 0955 3471] with a shaft [NZ 0966 3489] 30–40 ft (9–12 m) deep in the Third Grit, and have been the most productive on Knitsley Fell. The vein varies up to 5 ft (1.5 m) wide, but it is very subject to swells and pinches. In 1939 it was being worked south-westwards by Mr Robinson of Wolsingham. To the NE it apparently terminates against a NNW vein which has been tried at intervals for 1000 ft (305 m) NNW of the junction, but which carries only a few inches of baryte.

    In Knitsley Fell Ganister Quarry a vein containing a few inches of baryte was found almost underneath and parallel to the aerial ropeway which ran from Doctor's Gate Quarry to Harperley [NZ 0972 3458].

    On the S slopes of Knitsley Fell, two small NE veins have been tried in the upper part of the First Grit group; a level [NZ 0927 3403] entering 1400 ft (427 m) E of Knitsley Cottage Farm, driven by the Weardale Barytes and Mining Co. in 1918–19, was not a success. The aerial ropeway installed at that time has been removed.

    The Knitsley Fell deposits yielded 400 tons of barytes in 1886–87, and 909 tons in 1918–21. The veins of Shull Rigg produced 231 tons in 1919. While other small pockets may well be found, it is impossible to regard these small veins in the "Millstone Grit" as having serious possibilities. The assumed junction of the Slitt Vein system with the Teesdale Mineral Belt and its continuation towards Deerness lends some interest to this area for prospecting at depth.

    Burn Hill Vein—Barytes

    NZ04SE; Durham 18SW

    Another small vein in the "Millstone Grit", trending N30°W, occurs 0.25 miles (6.8 km) N of Wolsingham, on both sides of the Salters Gate-Oxen Law road, 1500 ft (457 m) ESE of Burn Hill Farm. It was worked W of the road [NZ 0735 4389], on Mr Featherstone Fenwick's property, between 1885 and 1888, producing 98 tons of barytes. An unsuccessful effort to reopen this working is said to have been made during the First World War; the spar is recorded as having disappeared at small depth. East of the road [NZ 0740 4382] trials were made in 1940 by Weardale Limestone Co. (Frosterley). Three pits showed the vein 1.5–2 ft (0.45–0.6 m) wide, and indicated continuity for about 230 ft (70 m). One of the pits showed hard sandstone on the W wall, soft grit on the E, so that a fault definitely accompanies the vein. The only minerals found were baryte and a little limonite; an analysis by Messrs Orrs Zinc White Laboratories showed 98.6 per cent barium sulphate, 0.71 silica. The horizon of the trials is the Third Grit and possibly the ganister formerly mapped as marking the base of the Coal Measures. An old level [NZ 0734 4484] 0.75 mile (1.2 km) farther N, with pink baryte on the dump, may have tested a NE branch of the Burn Hill Fault or the Healeyfield Fault in Lower Coal Measures sandstone.

    Drypry Vein—Lead ore

    NYO4SE; Durham 18SW, 25NW

    A small vein trending slightly W of N was being worked about 1880, 0.75 mile (1.2 km) N of Tunstall House, 0.75 mile (0.4 km) W of Salters Gate Cottages [NZ 0676 4327]. A report by T Rumney in the Beaumont records notes that two shafts 180 ft (55 m) apart were sunk, the northern one 65 ft (20 m) deep; the southern one 36–42 ft (11–13 m) deep. A drift N from the bottom of the former shaft showed the vein 2–3.5 ft (0.6–1 m) wide, consisting of broken sandstone, and quartz, thinly mixed with galena; the vein improved when intersected by strings. About 60 tons of galena is said to have been raised from the two shafts. The horizon is the Second Grit.

    Bowlees Farm Vein—Barytes

    NZ03NE; Durham 25SW

    Near Bowlees Farm, 1.5 miles (2.2 km) E of Wolsingham, a small vein, probably trending NNE, has been tried in the First Grit, a coarse feldspathic sandstone at [NZ 0968 3753]. Fragments of veinstone consisting of pink baryte containing epimorphs after quartz may be seen lying about the collapsed opencut.

    Black Hill Top Vein—Barytes

    NZ03SE; Durham 33SW

    Between Black Hill Top and White Hill Top farms, 1 mile (1.6 km) W of Hamsterley, a vein trending NNW through the Third Grit yielded 57 tons of barytes in 1918 [NZ 0980 3116]. The Hett quartz-dolerite dyke, striking at right angles to the vein, crops out a short distance S, but the vein has not been followed to it. During the revision of Sheet 27 (Wolsingham) it was shown that the associated fault can be traced for over a mile (1.6 km).

    Cabin Hill Vein—Barytes

    NZ03SE; Durham 33SW

    A small vein trending N30°W and carrying baryte has been tried on the slopes of Cabin Hill, E of the ganister quarries at Doctor's Gate, 1 mile (1.6 km) W of Hoppyland Hall [NZ 0815 3256]. There are also traces of baryte S of the main quarry. The ganister worked is near or at the top of the Millstone Grit facies of the Namurian.

    References

    CARTER, P, and MILLS, D. 1976. Engineering geology investigations for the Kielder Tunnels. Q. J. Eng. GeoL, Vol. 9, 125–141.

    CARRUTHERS, R G, and STRAHAN, A. 1923. Lead and zinc ores of Durham, Yorkshire and Derbyshire, with notes on the Isle of Man. Spec. Rep. Miner. Resour. G.B., Vol. 26. 114pp.

    CARRUTHERS, R G,, POCOCK, R W, and WRAY, D A. 1922. Fluorspar (3rd edition). Spec. Rep. Miner. Resour. Mem. Geol. Surv. Mem. Geol. Surv. G.B., Vol. 4. 42pp.

    DAVIES, T P, CARTER, P G, MILLS, D A C, and WEST, G. 1983. Kidder aqueduct tunnels-predicted and actual geology. Rep. Transport & Road Res. Lab., No. 676.

    DUNHAM, K C. 1934. The genesis of the North Pennine ore deposits. Q. J. Geol. Soc. London, Vol. 90, 689–720.

    DUNHAM, K C. 1937. The paragenesis and color of fluorite from the English Pennines. Amer. Miner., Vol. 22, 468–478.

    DUNHAM, K C. 1941. Iron ore deposits of the Northern Pennines. Geol. Surv. Wartime Pamph., No. 14.

    DUNHAM, K C. 1944. The production of galena and associated minerals in the Northern Pennines; with comparative statistics for Great Britain. Trans. Inst. Min. Metal., Vol. 53, 181–252.

    DUNHAM, K C. 1952. Fluorspar (4th edition). Spec. Rep. Miner. Resour. Mem. Geol. Surv. G.B. Vol. 4. 141pp.

    DUNHAM, K C. 1959. Non-ferrous mining potentialities of the northern Pennines. 115–147 in Future of non-ferrous mining in Great Britain and Ireland. (London: Institute of Mining and Metallurgy.)

    DUNHAM, K C. DUNHAM, A C, HODGE, B L, and JOHNSON, G A L. 1965. Granite beneath Visean sediments with mineralization at Rookhope, northern Pennines. Q. J. Geol. Soc. London, Vol. 121, 383–417.

    EGGLESTONE, W M. 1882. Stanhope and its neighbourhood. (Stanhope.)

    EGGLESTONE, W M. (Undated). A productive mountain rock: The Great Limestone. (Stanhope.)

    EGGLESTONE, W M. 1908. The occurrence and commercial uses of fluorspar. Trans. North of England Inst. Min. Eng., Vol. 35, 236–268.

    KING, R J. 1982. The Boltsburn Mine, Weardale, County Durham, England. Mineral. Record, Vol. 13, 5–18.

    LOUIS, H. 1917. Lead mines in Weardale, County Durham, worked by the Weardale Lead Company, Limited. Mining Mag., Vol. 16, 15–25.

    LYON, R J P, and SCOTT, B. 1957. Stratigraphgical and structural ore controls on the Slitt Vein, at Heights Mine, Weardale, County Durham. Trans. Inst. Min. Metall., Vol. 66, 273–282.

    SHERLOCK, R L. 1919. 4–11 in Sundry unbedded ores of Durham, east Cumberland, North Wales, Derbyshire, the Isle of Man, Bristol district and Somerset, Devon and Cornwall. Spec. Rep. Miner. Resour. Mem. Geol. Surv. G.B.

    WATSON, S. 1900. Recent mineral deposits and their relation to vein-formation. Trans. Weardale Nat. Field Club, Vol. 1, 57–61.

    WATSON, S. 1904. The Boltsburn Flats–their interest to the student of nature. Trans. Weardale Nat. Field Club, Vol. 1, 146–150.

    WILSON, G V, EASTWOOD, T, POCOCK, R W, WRAY, D A, and ROBERTSON, T. 1922. Barytes and witherite (3rd edition). Spec. Rep. Miner. Resour. Mem. Geol. Surv. G.B.

    WYNNE, I, NORMAN. 1943. The Stanhope Burn fluorite mine. Mining Mag., Vol. 69, 265–273.

    YOUNG, B. 1985. Strontianite from the northern Pennine orefield. Mineral. Mag., Vol. 49, 762.

    Chapter 11 Mineral deposits

    Details, Area 6 The Derwent Valley

    The north-eastern part of the orefield lies among the headwaters of the River Derwent, a major tributary of the Tyne, centred on the villages of Blanchland in Northumberland and Hunstanworth in Durham, but extending eastwards through Edmondbyers and Muggleswick to Healeyfield, on the edge of the Durham Coalfield (Figure 34). The solid formations at surface belong to the Pendleian and later Namurian Stages (mainly the higher beds) including the Millstone Grit facies. The existence of substantial oreshoots at such high stratigraphical horizons is attributable to the presence of sandstone of exceptional thickness, with very little shale, between the Crag and Upper Felltop limestones, probably as a result of the Rogerley and Coalcleugh washouts. The Great Limestone is not exposed at surface; it has been reached by deep shafts in the Hunstanworth and Blanchland districts but it is untested farther E. The Hunstanworth veins, which have proved to be the most important in the area, were probably discovered at outcrop in the Grit Sills. Following the sequestration of the estates of Thomas Forster the mines were acquired by the London Lead Co. about 1725, and worked until the end of the century; unfortunately no record of production has been obtained. In the only surviving mine report book of the Company, Thomas Dodd in 1806 urges that all the mines in the Derwent area should be given up "as there are no encouraging prospects in that country". The London Lead Co. were nevertheless followed by several other concerns, including Easterby, Hall & Co. (1807–1810); Derwent Mining Co. (1810–1883); and in the 1920s–30s Hunstanworth Mines Ltd. Fluorspar replaced lead ore as the main product in the 1920s but Hunstanworth Mines Ltd failed as a result of the low pre-war price. In 1940 Blanchland Fluor Mines Ltd was formed by Colvilles Ltd to supply spar to their Scottish steelworks. A modern mill was installed, and much of the ore from Groverake Mine was also lorried to Hunstanworth for treatment. Upon nationalisation, this company passed to British Steel Corporation. The present operators, Weardale Mining and Processing Ltd took over in 1982 but in 1987 work was suspended when known reserves were exhausted. Lead and fluorspar production in the area has now ceased. A little barytes was mined some years ago.

    The area consists mainly of fell country, lying between 600 and 1600 ft (183 and 488 m) above OD, with fertile strips along the Der-went. It is served by good roads. No railways remain in or near the area. The population is small and is mainly occupied in sheep-farming.

    Steel Crags Vein

    NY95SW; Northumberland 108 NW (Old Series)

    In the drainage area of the Devil's Water, a tributary of the Tyne lying between the River Allen and the Derwent, several isolated mineral occurrences are known. These are included with the Der-went area for descriptive purposes. Some 1500 ft (451 m) ESE of Harwood Shield farm, the Devil's Water changes course from ESE to NE continuing in the latter direction for about 1 mile (1.6 km). Here it is following a small but sharp anticline, in the core of which the Crag Limestone is exposed. A small fault which may be traced along the anticlinal axis from [NY 9111 5109] to [NY 9167 5157] contains both fluorite and quartz. A shaft [NY 9101 5109] sunk NW of the fault appears to have failed to discover workable mineralisation, but nothing is known of the history of this trial. The occurrence is of interest because the fold and fault lie approximately on the line of St Peter's Vein, East Allendale (p.164). The vein may some day repay exploration in the Great Limestone; this should require a sinking of about 250 ft (76 m).

    About 1 mile (1.6 km) ENE, in Black Burn 1250 ft (381 m) above its confluence with Devil's Water, a NE line of shafts between [NY 9265 5178] and [NY 9293 5198] have been sunk on a vein, in which a little fluorite occurred. The vein crosses the stream at [NY 9268 5181].

    Burntshieldhaugh Vein—Lead ore

    NY95SW; Northumberland 103SW, 108NW, SE (Old Series) Durham 16NE, SE. Direction N24°W throw uncertain, probably to NE

    The only workings on this vein lie near the Devil's Water, opposite Hackford Mill, 0.75 mile (1.2 km) N of Burntshield Haugh farm. Here there is a hush on the course of the vein about 1600 ft (488 m) long extending from about 700 up to 925 ft (213 to 282 m) above OD [NY 9261 5389]–[NY 9290 5346], and a level [NY 9255 5400] driven from the side of Embley Beck. A little galena, with quartz, calcite, limonite and traces of siderite remains. The work was probably done by the Beaumont Co. whose Dukesfield Smelt Mill was situated near Steel on Devil's Water [NY 9412 5800]; but no record of production has been discovered.

    The remarkable feature about this cross vein is its apparent persistence. It is said to cross the Derwent 0.5 mile (0.8 km) WSW of Newbiggin Hall [NY 9464 4926], where there are traces of old shafts on the N bank; while in the Derwent Mines, a cross vein on almost exactly the line of Burntshieldhaugh Vein was cut in the Jeffries workings at Jemmy's Shaft [NY 9527 4739]. Still farther SE, two small faults on the same line were cut at Boltsburn Mine (p.191). Both at Jeffries and Boltsburn mines, an increase in the north-eastern dip of the measures accompanied the cross vein. If these widely separated occurrences may be taken to indicate a continuous cross vein, its total length is at least 6'/ miles (10 km).

    Smith's or Pennypie Vein—Barytes

    NY95SW, SE; Northumberland 108NE (Old Series)

    A small vein carrying some baryte has been tried 1500 ft (457 m) N of Pennypie House, 1.5 miles (2.4 km) NW of Blanchland. The principal shaft [NY 9509 5228] is said to have been sunk 139 ft (42.4 m) as a lead prospect; it was reopened to 25 ft (7.6 m) and a drift driven NE for 60 ft (18 m) in 1919, some barytes being obtained, the maximum width being 3.5 ft (1 m). A later attempt to reopen the prospect was unsuccessful. The horizon is mapped as Third Grit.

    Standalone Vein–Andrew's Vein group

    The veins listed above form a NE-trending belt about 0.5 mile (0.8 km) wide, 2.25 miles (3.6 km) long in which they have been worked in three of the Derwent headwater burns, Beldon, Reeding and Shildon. None of these veins appears to have carried particularly substantial oreshoots, and as far as is known, in no case has it proved possible to work a vein through from one valley to the next. Beldon Mine (disused), 2 miles (3.2 km) W of Baybridge, consists of a pair of stone-walled shafts [NY 9285 4955] on a belt of NE strings considered to be formed by the union of Standalone and Fellgrove veins. According to a section preserved at the Durham County Archive, the square (Drawing) shaft is 360 ft (110 m) deep, starting 31 ft (9.4 m) above the base of the Low Grit Sill, and ending beneath the Great Limestone, in the shale below the Tuft. The oval (Engine) shaft is sunk to the same horizon. Crosscuts linked the shafts at 43, 98, 161 and 218 ft (13, 30, 49 and 66 m) below the collar of the Drawing Shaft as well as at the shaft bottoms. Two strong veins and many weak strings were cut, but the extent of the workings from the shafts is not known. It is, however, known that less than 100 ft (30 m) SW of the shafts a strong NNW fault was cut, throwing 40 ft (12 m) NE, beyond which the veins have not been found; the workings presumably extended NE of Beldon Burn. Veinstuff is abundant on the dumps, which provides evidence that in the sandstones, the matrix of the veins was purple fluorite with quartz; while in the Great Limestone siderite and calcite were present in addition. Sphalerite and galena both occur on the heaps. South of Beldon Burn, an adit [NY 9281 4950] driven under the Firestone along the west side of the cross vein mentioned above (which here runs N–S) gave access to the Shildon Vein (on some plans called Castleberry Vein). Purple fluorite is abundant in the vicinity of opencuts on this vein in the Low Grit Sill. At about the point where this vein reaches Beldon Burn, the Linnbank cross vein (described below) intersects it and apparently terminates the mineralised ground, for a level [NY 9315 4956] on the N bank has found no veinstuff. About 1500 ft (457 m) ESE of this level, Old Shildon Vein was formerly exposed in the mouth of a level [NY 9358 4934] in the Low Grit Sill on the N bank of the burn; it was 4.5 ft (1.4 m) wide, consisting of narrow bands of fluorite and quartz cementing broken grit fragments. These minerals, together with chalcedony and sphalerite, occur on the extensive dumps from the level. Surface shafts here suggest that the workings extended for at least 1500 ft (457 m) NE of the burn; mineralised ground to the SW probably continued to but not beyond Linnbank Vein.

    That the workings here are ancient is shown by the presence of heaps of lead-slag from primitive smelting operations. The only recorded production is in 1863–4 and 1872, when 148 tons of lead concentrates were obtained, the silver recovery from which was 18 oz. silver per ton of lead. Surface trials for fluorspar are said to have been made about 1924, when the shaft was reopened to the 43 ft (13 m) level, but nothing appears to have come of this work.

    At Reeding Mine (disused) there were levels and shafts [NY 9433 5051] on Standalone and Fellgrove veins (here about 200 ft (61 m) apart) at about the horizon of the Hipple Sill and Upper Felltop Limestone; quartz and chalcedony are the principal minerals on the heaps. On Shildon Vein, an opencut [NY 9486 5054] and old shafts followed the vein about 700 ft (213 m) SW from Reeding Burn; quartz and purple fluorite occur on the heaps. A level [NY 9506 5042] driven SW on Old Shildon Vein appears to have found little mineralisation.

    The Shildon Mines (disused), extending up the valley NW of Blanchland, were probably the most productive of the three groups, but even here the veins, which generally haded N, are said to have been narrow. An adit [NY 9628 5079] starting 1700 ft (518 m) NNW of Blanchland church on the left bank of the stream, was driven in the shale between the High Grit and Hippie Sills to give access to the vein; it followed a sinuous course beneath the Shildon Burn for over 3000 ft (914 m). The only existing plan shows levels driven from this adit 1600 ft (488 m) SW on Shildon Vein, and 1300 ft (396 m) SW on Fellgrove Vein, but the workings were presumably considerably more extensive; all the veins listed above were accessible from the level except Gin O'The Wood Vein, which lies just S of the adit portal. No other mining information is, however, available, save on Old Shildon Vein. A shaft close to Shildon Farm [NY 9594 5107] was sunk 715 ft (218 m) starting in the shale above the Grindstone Sill and finishing at the top of the Great Limestone. Smith (1923, p.44) gives the depth of the Engine Shaft as 630 ft (192 m), but this was probably the depth below adit level. Wallis (1769) mentions two 'subterranean engines' (no doubt waterwheels) but later a steam engine was installed, the engine house of which may still be seen adjacent to the open shaft. On the dumps chalcedony is probably the most abundant mineral (analysis p.74) but there is also a substantial amount of purple fluorite, a little quartz and sphalerite, with traces of galena. Shildon Mines were last worked by Derwent Mining Co., the ore being carted to Hunstanworth for dressing. No separate statistics of production are available.

    Here, as at Hunstanworth, the Great Limestone was first reached after the installation of Cornish pumping engines in 1807–10. The lack of records makes it impossible to say whether reserves of workable fluorspar remain underground.

    Linnbank Vein

    NY94NW: Durham 16NE Direction N25–35°W

    This cross vein is in two branches, about 75 ft (23 m) apart, tried by levels from Beldon Burn [NY 9314 4953] and [NY 9314 4453] (with what result is not known). Where it crosses Knucton Burn 3200 ft (975 m) SW of its confluence with Beldon Burn, there is an opencut in the coarse pebbly Low Grit Sill [NY 9376 4844] with traces of galena and sphalerite without matrix minerals. A level [NY 9381 4839] has been driven south on the vein from the valley bottom, at the base of the Low Grit Sill, which is here separated by only 2 ft (0.6 m) of shale from the Crag Limestone. The vein cuts the Ramshaw Veins (below) near Palfram Shaft [NY 9459 4709] from which it has been tested by a crosscut from the 70-fathom Level.

    White Vein–Ferneygill Vein group

    The Hunstanworth Mines will be considered in three groups, of which the Whiteheaps–Sikehead group, working the veins listed above, constitute the first. The other two are (i) the Jeffreys–Ramshaw group (ii) the more recently discovered Boltshead group. The White Vein is a typical member of the "Quarter-point" series of veins, of which the other examples are the Red, Sedling and Slitt veins of Weardale. The course of White Vein suggests that it might perhaps be the continuation of the Sipton Vein of East Allendale, but against this view it should be noted that whereas Sipton Vein throws N, White Vein hades S at 40° and most probably throws in this direction; on the other hand, it has now been established that principal movements on Quarter-Point veins were mainly transcurrent. The westernmost trials on White Vein lie on either side of Knucton Burn, where small sharp WNW folds accompanying the vein are exposed 1.5 miles (2.4 km) SW of its outfall into the Derwent. These cut across the course of the small but sharp anticline well exposed at Coal Crag, whose course is followed by Knucton Burn. N of the burn, Park Sike Level [NY 9255 4752] and a number of shafts have explored the vein, finding only quartz. On the S side Smithy Cleugh Level [NY 9281 4757] has been driven 940 ft (287 m) SW, passing through the vein and its branches, and continued 400 ft (122 m) S. These trials are at or near the horizon of the Firestone and Crag Limestone. The primary survey shows White Vein split into three here. Recent surface prospecting showed some fluorspar in place beneath drift deposits and peat. On the main vein, 200 ft (61 m) ESE of the point where Smithy Cleugh Level cuts it, a shaft [NY 9282 4750] was sunk 222 ft (68 m) reaching the Coal Sills sandstones; quartz and purple fluorite, with some galena is present on the dump, but little workable ore was obtained here. A further 0.5 mile (0.8 km) ESE, Johnson's Hole Level [NY 9330 4734] tested the vein in the upper section of the Low Grit Sill, again without success. This level starts 1500 ft (457 m) up Little Knucton Burn. At Baxton Law [NY 939 470], on the Hunstanworth–Rookhope road 1.5 miles (2.4 km) S of Hunstanworth, there is a small outlier of the basal grit of the "Millstone Grit" Series, on the downthrow side of the White Vein. The nearby McDonnel's Shaft [NY 9411 4683] with collar at 1440 ft (439 m) above OD is connected with Ramshaw Low Adit at 1150 ft (351 m) above OD and a lower level on White Vein at 1094 ft (333 m) above OD, but the vein was found to be poor for lead at both horizons, in spite of the proximity of the intersection to the Ramshaw Veins. Surface mapping provides some clue to the poverty of the accessible western stretch of the White Vein; it shows that substantial shale beds are present between the Low and High Grit Sills, and also between the two parts of the Low Grit. Records of the MacDonnel's workings seem nevertheless to leave open the possibility that wide spar bodies were found at depth.

    Whiteheaps Mine (disused) on Bolts Hope, on the other hand, reveals that these shales are absent in the vicinity of the main shafts, but since this area lies within the Rogerley washout channel, the thick sandstones of the Grit Sills are at their maximum development. Bolts Hope has been eroded along the flat crest of a gentle anticline of amplitude about 120 ft (37 m) which here disturbs the general NE dip of the measures, as illustrated by the longitudinal section of the mine, (Figure 35). On the W side of the valley, White and Red veins outcropped in the High Grit Sill. Productivity begins where the White Vein abruptly changes direction from WNW to approximately E–W, some 1500 ft (457 m) W of the stream. Two crosscut adits, Whiteheaps [NY 9491 4679] from the left bank, and Skottowe [NY 9492 4672] from the right, reach the vein-system respectively at 1206 and 1212 ft (367.6 and 369.4 m) above OD. Whiteheaps adit was fully accessible early in the tenancy of Blanchland Fluor Mines Limited in 1941, and detailed underground mapping of the adit level and of six N-directed crosscuts to which it gave access revealed the following situation: White Vein, pursuing a sinuous but generally E–W course, varies from 4 to 18 ft (1.2 to 5.5 m) wide, dipping S and containing quartz and fluorite, with low lead values in the form of narrow and discontinuous bands of galena. Characteristically the White Vein is partly or wholly comminuted by postmineralisation movements. In some places a slickenside face with more or less horizontal grooves is associated with these movements. It is separated by widths up to 25 ft (7.6 m) of sandstone from an almost parallel vein known as Poor Vein so called because the filling is almost entirely quartz; in places this reached 29 ft (8.8 m) wide. Red Vein, 200 ft (61 m) S of White Vein at the W end of the adit development is only 1 ft (0.3 m) wide here, but as it converges upon the other two veins, it widens to 15 ft (4.6 m) mainly fluorite but with narrow ribs of galena near the walls. A sample 8 ft (2.4 m) wide taken in 1940 assayed 91.2 per cent calcium fluoride, 7.8 silica, 1.0 carbonate and 2–3 total sulphides, but it was clear that the bulk of the fluorspar ore in this and other veins was substantially more siliceous. Red Vein, as it approaches White Vein narrows considerably and although the complex junction is not exposed, it is assumed that the latter vein is continuous across it. Red Vein, however, reappears on much its old course on the E side of the valley, where it was worked opencast near Crag Shaft.

    During the 19th century, the White Vein complex was developed from two pairs of deep shafts, Whiteheaps [NY 9467 4661] and Ellen's and Ruth's at Sikehead [NY 9547 4642], 2625 ft (800 m) to the ESE. Collared at 1338 ft (408 m) above OD, the Whiteheaps shafts were sunk to below the (present) 80-Fathom Level at 767 ft (234 m) above OD. The veins, particularly White Vein, were stoped for lead (Figure 35) in the Grit Sills and Firestone, but the deeper levels showed such poor lead values that no extraction took place; the veins were reported to the Derwent Mining Co. in 1855–58, when the deep sinkings were completed, as wide, coarse, strong but poor. They were sufficiently promising to encourage the company to sink the shafts to the base of the Great Limestone, and to undertake some lateral drivage. Near its junction with Red Vein, White Vein resumes its ESE course, but stoping above the 30-fathom Level at 1070 ft, (326 m) above OD in the Grit Sills continued some 900 ft (274 m) farther, to a second intersection with a vein–Company's Vein–pursuing a nearly E–W course. This vein, and perhaps its branch known as Shield's Vein, was stoped W of the intersection, but in the higher levels the combined White and Company's Vein was only workable in limited patches until, about 1000 ft (305 m) ahead, a further change of direction to an easterly course occurred, near the Sikehead shafts. The deepest of these was sunk 800 ft (244 m) to the base of the Great Limestone at 657 ft (200 m) above OD, but stoping was only carried down to the 50-fathom Level 936 ft, (285 m) above OD. The veins form a complex loop at Sikehead, but its long axis is no more than 500 ft (152 m) long, E of which the mineralisation dies out, as demonstrated by the extensions of the old 30- and 40-fathom Levels the directions of which gradually swing round towards ESE.

    Lead values throughout the Whiteheaps mines were low, probably no more than 2 or 3 per cent overall, and the ground was workable only by taking out narrow slits along the galena-bearing bands. Lead production data is combined with that from the adjacent Jeffries–Ramshaw mines on p.226. Fluorspar production was begun by Hunstanworth Mines Ltd in 1921, output up to 1932 being about 15 000 tons. This was obtained mainly from opencuts and subsurface stopes on Red Vein on both sides of Bolts Hope. After Blanchland Fluor Mines Ltd took over in 1938, Red Vein continued to be worked because of its low silica-content, one 12 ft (3.7 m)-wide pillar yielding 5038 tons in 1939–40. Later, treatment plant was installed and up to nationalisation of the steel industry in 1962, fluorspar production seems to have come from the reworking of former stopes around the Whiteheaps shafts. When the British Steel Corporation took over, the mill was rebuilt to include a flotation circuit, and an ambitious development plan was applied to the mine. The Sikeheads shafts had long fallen into disrepair, though the remains of the buildings which contained the Cornish pumps can still be seen. To reach this area, BSC drove an incline from [NY 9491 4660], direction S77°E, 2650 ft (808 m) long, starting at 1282 ft (391 m) and ending at 704 ft (215 m) above OD. A new 80-fathom Level was driven at 747 ft (228 m) above OD, and connections were made en route to the 30-fathom and 50-fathom Levels. The former gave access to the new ground on Red Vein, here a new 30-fathom Level was driven with a flatter gradient than the old one and the vein was stoped back successfully as far as the Whiteheaps shafts.

    Beneath this level and down to the 50-Fathom Level the extent of stoping was considerably more limited and effectively confined to the loop springing from the White Vein in the Sikehead neighbourhood. The 50-Fathom Level was extended following the northern most branch of the loop for a total distance of 2440 ft (744 m) in virgin ground, but unfortunately without disclosing new reserves. This extension was assumed to be on the White Vein though the characteristic comminuted form was not found, instead the vein passed into a channel loosely filled with sandstone debris and with calcite, giving the impression that the mineralising solutions had not been able to reach it. Mr J Sherwen has suggested that the postmineralisation cheek may have been missed at the beginning of the loop and this is mentioned again after the 80-Fathom Level has been described. On the 80-Fathom and above at the point where the direction changes from ESE to E–W at the beginning of the loop there was a pipe-like body of fluorspar at least 30 ft (9 m) wide but followed eastward this split into three veins. The spar in this ground was similar to that in the Red Vein (though it cannot of course be directly connected to that vein) and it has been the practice in the mine to refer to this as "Sikehead Red Vein". The 80-Fathom Level has also been driven through to connect with Whiteheaps shafts, and this has been more successful. A block on the combined Company's/White Vein has been stoped from 200 ft (61 m) WNW of Ruth's Shaft to the point where Company's Vein diverges at 1100 ft (335 m) from the shaft, to a maximum height above the 80-Fathom Level of 105 ft (32 m), in Coal Sills sandstones and the top part of the Great Limestone. There is then a barren gap 440 ft (134 m) to what is believed to be the vicinity of the Red Vein intersection and here there are stopes in the vein over a total length of 540 ft (165 m). Red Vein then apparently pinches, but further ground was worked on Red Vein over a distance of 480 ft (146 m) W of the Whiteheaps shafts, in the Great Limestone which at this end of the mine is commanded by the 80-Fathom Level.

    Comparing the surface and 80-Fathom Level positions of the White Vein/Red Vein junctions it is apparent that this junction plunges towards the SW at a steep angle. Attempts using long-hole drills to locate White Vein north of Red Vein in this part of the mine were not successful but it is possible that it may be worth driving the abandoned face of White Vein further towards the W. E of the junction it might be supposed that additional ground should be available on Red Vein but two long-hole drills from White Vein directed NNW through Great Limestone, though they have found much disseminated fluorite and quartz, did not locate a collected Red Vein. At the E end, on the distant side of the anticline, the limestone has dipped beneath the 80-Fathom Level and a second incline was driven from the E end of the level, WNW for 400 ft (122 m) to reach below the base of the limestone at 656 ft (200 m) above OD.

    The question of the eastern extension of White Vein is of some importance. If the channel followed by the 50-Fathom Level already mentioned is in fact the White Vein that would line up reasonably well, though not perfectly, with the intersections in the Northumbrian Water Authority Derwent–Wear tunnel (Table 51), p.176). On the other hand in the S crosscut from the foot of the main incline at 110 ft (34 m) S of the main turnoff, there is a structure which could be the White Vein. The importance of following this is that although it is diverging considerably to the ESE, in order to join up with the intersection in the NWA tunnel, it would have to turn back to E–W thus resuming the favourable direction.

    The minerals present at Whiteheaps, in addition to coarsely crystalline fluorite, quartz and galena, include sphalerite, pyrite and chalcedony. According to Vaughan and Ixer (1980) a little early pyrrhotite is present, but the earliest sulphide is framboidal pyrite. Marcasite also occurs, and the iron-content of sphalerite varies between 5.14 and 5.94 per cent. It will be noted below that the silver contents of galenas from the Hunstanworth area are substantially higher than the average for the field, and this must have contributed towards making these lean veins workable for lead. Up to the end of 1984, the output of crude fluorspar from Whiteheaps amounted to 252 643 tons. Total production of fluorspar product is as follows: 1924–32 and 1946–82–97 227 t, 1982–85–28 915 t. The total up to 1977 was estimated by Greenwood and Smith (1977) at 125 000 tons; the difference between the two figures is a measure of the output from the oreshoots made accessible by the 80-Fathom Level. These authors cite fluid inclusion homogenisation temperatures, corrected for pressure, of 151 to 178°C for Whiteheaps 30-Fathom Level and 118–152°C for fluorite from Sikehead. They suggest that the intersection of the weak Fernygill and White Veins may be a distributing centre, but more recent development suggests the Company's Vein/White Vein intersection as a more interesting candidate.

    A trial appears to have been made for White Vein in the headwaters of Eudon Burn, 1.25. miles (2 km) ESE of the forehead of the 50-Fathom Level from Whiteheaps. Three old shaft heaps [NY 9796 4579 to 9804 4577] line up with the line joining Whiteheaps with the postulated intersection of White Vein in the Northumbrian Water Authority Derwent–Wear tunnel (Table 51), p.176). A level driven from [NY 9826 4592] towards these heaps lies on or near the projected line of Boltsburn Vein. Mr D Strut, who has examined the level and heaps found a little galena on the heaps, but no fluorite. The stratigraphic level is near the Upper Felltop Limestone.

    Fernygill Vein, reached by a continuation of Whiteheaps Adit Level, has been stoped over a length of 670 ft (204 m) above that level to an average height of 30 ft (9 m) in the Low Grit Sill. There was also a small stope, supposed to be in the Firestone, above the 30-Fathom level. The mineralised ground terminated to the SW against cross-fractures, while it failed to reach White Vein to the NE. The junction was not recognised in the 90-Fathom Level. The NE continuation of the vein is supposed to cut through Jeffreys South Vein 1900 ft (579 m) NE of Jeffreys shafts [NY 9608 4781] and to unite with Jeffreys Middle Vein.

    Ramshaw North Vein–Shilford-Haugh Vein group

    The NE veins listed above constitute the group worked at the Ramshaw and Jeffreys mines (disused); the former mine lying SW of Bolts Burn, the latter NE of the burn. The whole series of veins constitutes a single belt of mineralisation, lying more or less on the projected course of Burtree Pasture Vein. While the simplest interpretation of the relationships of the first six veins is that adopted on the primary Geological Survey maps, that Ramshaw South = Jeffreys North Vein, Ramshaw North = Jeffreys South Vein, and that the Middle Vein is the same in both mines, with intersections in the vicinity of Bolts Burn, the discrepancy in hade raises some doubt as to the correctness of this view.

    In all cases the veins, so far as the records show, are of small throws. The principal oreshoots on the Jeffreys North and South veins, and on the NE part of Middle Vein, were in the thick Grit Sills. Probably the same was true on the Ramshaw veins, but here, owing to the ancient date of the workings, exact information for much of the ground at this horizon is lacking. Only near Westgarth's Shaft [NY 9564 4759] was the next sandstone above the High Grit Sill, the Hipple Sill, mineralised, this occurrence being confined to North Vein. Higher sandstones, up to the First Grit, are barren. The Grit Sills oreshoots extended down to the Firestone, or in places to the Pattinson Sill; beneath this the preponderance of shale produced barren ground down to the Little Limestone, averaging 100 ft (30 m) in height. On Middle Vein in both mines, oreshoots were found between the Little Limestone and the base of the Great Limestone; near Pearse's Shaft, Ramshaw Mine [NY 9479 4712], a small oreshoot continued down to the Four Fathom Limestone. The relations at Jeffrey's Mine are shown in (Figure 35). The depths of the principal shafts have been listed by Smith (1923, p.47). No information remains regarding the widths of the Jeffreys and Ramshaw veins, but detailed estimates of values are given in the Derwent Mining Co.'s records. The information in (Table 62) is extracted from the Tutwork Books for the period 1852–1865.

    Each of the average values stated is based upon a large number of individual estimates. The figures bring out the surprising fact that the lower oreshoot in the Coal Sills and Great Limestone, was decidedly richer than the Grit Sills oreshoots during the period under consideration. The minerals present were purple fluorite, quartz, galena and traces of sphalerite. The Great Limestone adjacent to the lower oreshoot, as shown by abundant blocks on the dumps, was converted into an ankerite-siderite rock rich in silica; an analysis of a typical specimen from Deborah Level dumps [NY 9574 4825] (supplied by Mr Adamson of Hunstanworth) showed 16.6 per cent of iron, 51.7 silica, 0.051 phosphorus pentoxide, 13.5 loss on ignition. The low lead-content of the Hunstanworth veins would probably have made their exploitation impossible but for the fact that the galena is abnormally rich in silver. From the recorded total production of the Derwent Mines for 1845–1883, the bulk of which probably came from Jeffreys Mine, the average silver recovery was 10 oz silver per ton of lead. The output of lead concentrates for the period was 39 409 tons. It is probable that the total output of the Whiteheaps and Jeffreys-Ramshaw mines exceeded 100 000 tons, but data other than the official records have not been obtained. The only mining for fluorspar was on Ramshaw North Vein, W of Jemmy's Shaft [NY 9527 4239] where old stopes, drained as a result of pumping water from Presser Shaft by Consett Water Co., had become accessible. In 1972, Presser Shaft, Jeffreys Mine [NY 9602 4781], formerly pumped for Consett water supply, was reopened by EXSUD Ltd but the narrow vein-stopes were found to be empty. Some years earlier there was some production from the dumps. The best quality fluorspar is said to have been obtained from those near Jemmy's Shaft which was sunk on the Jeffreys veins close to the intersection with Burntshieldhaugh Cross Vein. Total fluorspar production perhaps amounted to 50 000 tons.

    Towards the end of its tenure British Steel Corporation had a plan to redevelop Ramshaw Middle and North veins from an incline from surface with the ultimate objective of reaching the MacDonnel's Shaft area in depth. A reserve of fluorspar may remain.

    To the SW, the Ramshaw veins become unproductive before reaching the White Vein, which cuts across their courses. SW of White Vein, the Yawd Sike Level [NY 9328 4682] was driven from Little Knucton Burn, starting 3150 ft (960 m) S of the confluence with Knucton Burn, in the shale beneath the High Grit Sill. The level was driven 2200 ft (671 m) SSE, crossing ground in which the SW continuations of the Ramshaw Veins would be expected to occur. Although a number of small faults in the right direction were cut, none of them appears to have been mineralised. In view, however, of the considerable thickening of the shale between the Low and High Grit sills in this area, the negative results of this trial cannot be taken to disprove the continuance of mineralisation at lower horizons here.

    The total length of mineralised ground in the Ramshaw–Jeffreys belt of veins amounts to 1.75 miles (2.8 km). At the NE extremities of the Jeffreys workings from the deep Taylor's Shaft [NY 9658 4824], the veins presumably pinch, though it is significant that the lower oreshoot on Middle Vein was stoped to within a few feet of the forehead in the Coal Sills.

    The Shilford-Haugh Vein was cut through by the Deborah Adit [NY 9574 4825] which served as the main entrance to the workings from Reed's and Jeffreys shafts, but there is no record that it was mineralised. Moreover, it appears to have terminated the oreshoot on Jeffreys North Vein to the NE.

    Boltshaw or Boltshead Vein

    NY94NW; Durham 16SE, NE

    This is a small ENE vein said to have been found when the foundations for Bolts Shaws cottage [NY 9499 4634] were excavated. It was tested by the western branch of Skottowe's Adit from Whiteheaps Mine, which reached it 1200 ft (366 m) SSE of the portal. No information regarding its contents is available.

    Florence Vein—Lead ore

    NY94NW; Durham 16SE Direction N60°E

    The operations of Hunstanworth Mines Ltd during 1925–32 included the exploration of ground lying SE of the head of Bolts Burn. The Power House Drift [NY 9447 4615] (disused) in sandy shale between the Hippie Sill and Upper Felltop Limestone, ran 730 ft (223 m) E of S, to cut Florence Vein, which may perhaps be the continuation of one of the Wolfcleugh veins of Rookhope (p.183). Some 60 ft (18 m) above this, Burnhead Level [NY 9436 4607] (disused) was driven in the shale immediately above the Felltop Limestone. Florence Vein was explored in the 400 ft (122 m) stretch separating the two adits; its width varied from 1 ft 10 in to 4 ft (0.56 to 1.2 m), the filling being fluorite, with spots of galena and sphalerite; there was some suggestion of a downward increase in width. Considering the unfavourable horizon at which this exploration was carried out, the results are not without interest. The levels are more readily accessible now than formerly and a drilling programme is under consideration.

    Grindstone Veins

    NY94NW; Durham 16NW, SW

    In Grindstone Cleugh, 2 miles (3.2 km) W of Bolts Burn, two small veins have been located. The Low Grindstone Vein, explored by a short level [NY 9172 4662] starting on the W bank of the stream 1425 ft (434 m) above its confluence with Knucton Burn, proved to run SW, to be about 6 in (15 cm) wide in the upper part of the Low Grit Sill, and to contain fluorite with quartz and traces of galena. At 1600 ft (488 m) higher up the cleugh, High Grindstone Level [NY 9168 4612] was driven 1800 ft (549 m) SE and SSE in shale below the Hipple Sill. At 675 ft (206 m) from the portal, the ENE High Grindstone Vein was cut. A report by T J Bewick dated 1869 states that the vein was followed westwards for 411 ft (125 m). A rise was also put up into the Hippie Sill; both in this and in the level "some nice ore was obtained, yet the prospects were not sufficiently encouraging to follow the trial further". No veinstuff remains on the level dump. Ancient slags which occur at several places in the remote headwaters of the Derwent have been described by Smith (1923, p.51).

    Little Knucton Vein—Barytes

    NY94NW; Durham 16NE

    Small amounts of barytes have been obtained from a NNE vein in the beds above the Felltop Limestone about 1200 ft (366 m) S of the portal of Yawd Sike Level (above). The baryte is massive and rather heavily iron-stained. The workings consist of shallow pits [NY 9332 4647]; a trial level [NY 9302 4614] from Foul Sike to the S in shale appears to have been unsuccessful.

    Sandyford Vein

    NY94NE; Durham 16NE

    A shaft [NY 9693 4704] sunk near the confluence of Sandyford Burn and the headwater stream of Burnhope Burn proved a vein which, according to an old plan at Allenheads Estate Office, trends about N75°E. The shaft is stated to be 140 ft (43 m) deep, it starts about 30 ft (9 m) above the Upper Felltop Limestone, which is exposed at the junction of the burns. At 125 ft (38 m) a level was driven in sandstone, probably the High Grit Sill. The sinking was done during the nineteenth century, but the shaft was reopened by Mr G Beeston about 1926. The vein was found to be about 1.5 ft (0.46 m) wide, filled with amber and purple fluorite, galena and sphalerite, and strings of partly oxidized siderite. A winze to 9 ft (2.7 m) below the level gave indications of a downward increase in width. The indications appear to be sufficient to warrant a trial to greater depth.

    Swandale Head Vein—Barytes

    NY94NE; Durham 10SW

    At the head of Swandale Burn, 1.25 miles (2 km) W of Edmondbyers church a baryte vein has been worked in the Second Grit. The trend is N68°E; the vein appears to lie on the direct line and 2 miles (3.2 km) ahead of Jeffreys South Vein at Jeffreys Mine. The width of the vein varied up to 3 ft (0.9 m), but like the other small veins at this horizon, it was pockety. The opencast workings [NY 9927 4967] are about 500 ft (152 m) long, and nowhere exceed 10 ft (3 m) in depth: mineralisation cut out at the base of the grit, a level [NY 9935 4971] driven in the underlying sandy shale from the NE end being unsuccessful. A total of 138 tons of barytes was produced in 1920–21.

    College Edge Vein—Barytes

    NY94NE; Durham 17NW

    Some 2050 ft (625 m) S of the Swandale Head workings, an ENE vein 4–12 in (0.1–0.3 m) wide of slightly iron-stained baryte occurs in the First Grit [NY 9940 4910]. A level [NY 9938 4904] commenced from the base of the grit feature nearby did not reach the vein.

    Swandale Vein—Lead ore

    NZ04NW; Durham 17NW. Direction approximately N35°W; probably hades NE

    The vein crosses Burnhope Burn about 0.5 mile (0.8 km) W of Edmondbyers to follow the side valley of Harehope Burn, where it appears to have been discovered about 1850. It was worked from three separate mines. Harehope Gill Mine (disused) consistes of a shaft [NZ 0097 4846] 348 ft (106 m) deep, sunk 700 ft (213 m) SE of the point where the Stanhope–Edmondbyers road crosses Harehope Burn. The old plan of the mine (Mines Dept No. 2631) is unsatisfactory and difficult to interpret, but it shows a total length of 1600 ft (488 m) worked from the shaft, the principal workings being in a sandstone supposed to be the Pattinson Sill. Unless the measures have thinned very substantially, this identification is open to suspicion when the depth of the shaft, which starts at the base of the First Grit, is compared with the Hunstanworth section. The plan suggests that the vein may have been worked in several subparallel parts. An adit level [NZ 0090 4847] driven along the W side of the valley seems to have been unsuccessful. Very little veinstuff remains on the dumps.

    A gap of 1000 ft (400 m) separates the Harehope workings from those of Burnhope Mine (disused) [NZ 0061 4884] to the NW. A section of this mine, and the Swandale Mine (disused) [NZ 0040 4912], still farther to the NW, will be found in Smith (1923, pl. 7, opp. p.40). This shows that Burnhope valley is floored by a glacial material at least 70 ft (21 m) deep, beneath which oreshoots were worked in sandstones thereon termed the Grit Sills, Crag Sill and Pattinson Sill. It appears more probable, by comparison with Hunstanworth, that all three sandstones represent the Grit Sills, split by substantial shale beds; these mines thus provide some evidence of the south-eastern edge of the "thick grit" area (Figure 7), p.42). The vein is stated to have varied from a few inches to 5 ft (1.5 m) wide; the principal matrix mineral was massive siderite, blocks of which occur abundantly on the dumps from Burnhope Shaft; calcite, a little sphalerite and traces of galena are also present. Baryte, a heap of which lies near the burn, is stated to have come from the College Edge and Swandale workings (described above); it is not, as far as can be ascertained, present in the Swan-dale Vein. Production figures are as follows: Harehope Gill Mine, 1852–1866, 219 tons; Burnhope Mine, 1880–1887, 1052 tons; Swandale Mine, 1876–1887, 266 tons lead concentrates. Silver recovery varied from 4 to 24 oz silver per ton of lead, the average being about 15 oz. Total production, Swandale Vein ? 1537 tons lead concentrates. It is impossible to be certain that the figure for Harehope Gill Mine does not refer to the mine of the same name in Weardale (p.214), known from the Beaumont records to have been active at the time.

    In the Northumbrian Water Authority's Derwent–Wear Tunnel, a NNW vein intersected in the Low Slate (or Grit) Sill 5.06 miles (8.1 km) N of the Wear Portal containing up to 30 cm galena lies on the line of Swandale Vein 2.33 miles (3.7 km) SSE of Harehope Gill Shaft. (See (Table 51) p.176).

    Harehope Shaft appears to be open and in good condition. One mile (1.6 km) W of the shaft, a prospecting level [NY 9934 4844] has been driven from Burnhope Burn at Pedamsoak, a distance of at least 1300 ft (396 m), possibly (Smith, 1923, p.41), 1800 ft (549 m) NW at about the horizon of the Hippie Sill, but without success. This level may have been the work of the London Lead Co. who occupied the ancient Feldon Smelt Mill [NY 9995 4852], nearby, in 1725.

    Silvertongue Veins—Lead ore

    NZ04NE; Durham 17NE; Northumberland 109SE (Old Series)

    In the remarkable incised meander of the Derwent which lies SE of the village of Muggleswick, a series of small NNW veins cross the narrow promontory enclosed by the river S of Crooked Oak farm. These were worked at Silvertongue Mine (disused), the adit level [NZ 0570 4912] of which starts from the W bank of the river, 1600 ft (488 m) SSE of Crooked Oak, in the beds beneath the Upper Felltop Limestone. This, a short distance from the portal, probably cut the Old Silvertongue Vein with a throw of 9–18 ft (2.7–5.5 m) W. South of the meander, in the narrow strip of ground separating the Derwent from the Hisehope valley, it unites with the Middle Vein, which throws 12 ft (3.7 m) E. Aragonite and quartz, with traces of galena and some limonite, occur on the mine dumps; Smith (1923, p.39) also records baryte. No plan of the workings remains, but the Geological Survey 1-inch map (but not the 6-inch) shows a third vein, W of Middle Vein. The only record of output is 138 tons galena in 1848; the silver content is stated to have been 30 oz per ton of lead (Smith, 1923).

    Healeyfield Vein—Lead ore

    NZ04NE, SE; Durham 18NW, SW; 10SE. Direction N10–15°W average, but sinuous and branching; throw 156 ft (47.5 m) E, North of Healeyfield Mine.

    The Healeyfield deposit occurs within a major fault-zone with a strong eastward downthrow, which at the surface brings Lower Coal Measures on the E against members of the "Millstone Grit Facies" of the Namurian along a considerable part of its course between Wheatley Grange, 3.5 miles (5.6 km) N of Wolsingham and Greymare Hill, 2 miles (3.2 km) SW of Whittonstall. At Greymare Hill it encounters the fault which becomes the "90-fathom Dyke" of the Northumberland coalfield. Healeyfield Mine (disused) is situated in Dene Howl (0.5 mile (0.8 km) W of the crossroads at Castleside from which the main adit level [NZ 0689 4866] at 655 ft (200 m) above OD extends 4500 ft (1.37 km) S. The footwall rock here is the Dene Howl Firestone, considered to be the principal member of the First Grit. The mine-section (Mines Dept Plan No. 2728) shows stoped ground extending above this level for a length of 3200 ft (975 m) to beyond Gill Shaft [NZ 0705 4763], up to 300 ft (91 m) high, but it is hard to believe that stoping on this vein was in fact so extensive; it seems more probable that this area represents a generalisation of smaller "old man's" scopes at the time of the last period of operation of the mine. Nevertheless, if the hangingwall geology is interpreted in the light of Mr D A C Mills (1974) compilation of the 1947–51 6-inch resurvey, it emerges that the greater part of the Healeyfield oreshoot occurs in the ganister-bearing Lower Coal Measures up to the Marshall Green Seam, and the coarse sandstones of the "Millstone Grit" facies. Near Spottiswood Shaft [NZ 0693 4807] a fault shown on the section has been mapped to the ESE; this reveals uppermost "Millstone Grit" near the hangingwall and repeats the raised sequence to the Marshall Green Seam to the S. Extensive mineralisation above the main adit dies out a short distance S of Gill Shaft. In the footwall rocks, which reach 300 ft (91 m) maximum above the main adit, about two-thirds of the Millstone Grit (facies) sequence must be present but without definite markers. Near Healeyfield Farm [NZ 0695 4815] two shafts, S of the farm, pass through Second and First grits. From Dene Howl the main or Whitwell Shaft [NZ 0687 4863] was sunk 350 ft (107 m), with principal levels at 580 ft (177 m) above OD (driven 920 ft (280 m) S), 570 ft (174 m) above OD (600 ft (183 m) N), 485 ft (148 m) above OD (the Derwent Adit Level [NZ 0656 4980], extending 4000 ft (1.22 km) N to adit mouth on the Derwent, and 1370 ft (418 m) S) and 320 ft (98 m) above OD (1940 ft (591 m) S, 250 ft (76 m) N). According to Smith (1923, p.37) the Derwent Adit is at the horizon of the Upper Felltop Limestone; this provides a key to the footwall stratigraphy. Another adit level [NZ 0687 4870] from Dene Howl is driven 800 ft (244 m) N. Northwards the mineralisation ceased about 600 ft (183 m) N of Whitwell Shaft, and the Derwent Adit, though it cut many small strings, found no other workable ground. The dump shows only a few pieces of baryte. South of Whitwell Shaft there were small stopes extending to 200 ft (61 m), then barren ground except on the 580 ft (177 m) above OD level, which is shown as mineralised to the forehead, and on the bottom level, from which a little stoping was done near the S end. In the neighbourhood of Healeyfield Farm a number of branches diverge; some return to the vein near Charlton Howl, where the southernmost shaft [NZ 0711 4702] is situated. The minerals present in the Healeyfield oreshoots included galena, quartz, baryte and probably siderite; limonite is the most abundant mineral on the spoil heaps and traces of pyromorphite are also present. The galena carried the high content of 15 oz silver per ton of lead. The returns for its last period of activity, 1853–1891, amount to 10 490 tons of lead concentrates (1875 missing, 1860 and 1862 stated as Healeyfield and Beldon). The lowest horizon reached at Whitwell Shaft on the footwall of the vein was, according to the mine-section, the Low Slate Sill; it is very probable that this sandstone is the equivalent of either the High or Low Grit Sill of Hunstanworth. A trial to the Great Limestone would involve a further sinking of at least 360 ft (110 m).

    The only other trial of the Healeyfield fault is near where it dies out to the south, 1.5 miles (2.4 km) S of the southernmost shaft of the mine, where a level driven on the N side of Long Burn [NZ 0734 4484] proved the presence of baryte.

    References

    DUNHAM, K C. 1952. Fluorspar (4th edition). Spec. Rep. Miner. Resour. Mem. Geol. Surv., Vol. 4, 141 pp.

    GREENWOOD, D A, and SMITE, F W. 1977. Fluorspar mining in the northern Pennines. Trans. Inst. MM. Metall., Vol. 86, B181–190.

    SMITH, S. 1923. Lead and zinc ores of Northumberland and Alston Moor. Mem. Geol. Surv., Miner. Resour., Vol. 25, 110 pp.

    VAUGHAN, D J, AND IXER, R A. 1980. Studies of the sulphide mineralogy of north Pennine ores and their contribution to genetic models. Trans. Inst. Min. Metall., Vol. 89, B89–100.

    WALLIS, J. 1769. The natural history and antiquities of Northumberland. (London: W and W Strahan.)

    Chapter 12 Mineral deposits

    Details, Area 7 Teesdale

    In Teesdale the principal lead-mining area lay in the northern side-valleys of Hudeshope and Eggleshope, N of Middleton-in-Teesdale (Figure 36). Here the London Lead Co., starting in 1752, worked an extensive complex of veins in the Lower Namurian (Pendleian), the largest oreshoots occurring in sandstones high in the group. The Quaker company's operations continued until 1904. From Middleton-in-Teesdale, north-westwards to the source of the Tees on Cross Fell, and westwards to the head of the Lune, there are, however, many other mineral veins at lower horizons. In the main dale and the Harwood valley, its direct continuation northwestwards from Langdon Beck, the horizon of these is the Brigantian Stage. Near Langdon Beck the Tees follows an incised meander between cliffs of Whin Sill, W of which lies the remote Weel of Tees and the southern tributaries Maize Beck and Trout Beck. Here the Lower Palaeozoic foundation rocks appear at surface, and surrounding them there is a region of Asbian Limestone country in which many veins have been worked, among them the barytes deposits of Cowgreen. The Cowgreen Reservoir now partly covers these.

    Middleton-in-Teesdale was formerly the head of a branch railway from Barnard Castle. Above this small town, the population is scanty and is confined mainly to sheep farmers and smallholders whose whitewashed homesteads on the Raby Estate are a feature of the Teesdale scene. The main road to Alston follows the N side of the Tees up to Langdon Beck, then continues up the Harwood valley to Yad Moss, on the South Tyne watershed. From Langdon Beck a private road gives access to Cowgreen Reservoir. Langdon Beck is connected northward to St John's Chapel by a hill road. Minor roads lead from Westgate-in-Weardale over Pike Law to the hamlet of Newbiggin, and from Stanhope to Middleton by way of Eggleshope. The main road from Brough to Middleton follows Lunedale. Away from these roads, the old mines are generally inaccessible, as illustrated by the fact that the reopening for barytes of the two principal mines recently and at present active, Cowgreen and Closehouse, both entailed the construction of several miles of access road.

    Details of production of lead ore in Teesdale prior to 1816 are lacking. From 1816 to 1851, the London Lead Co.'s mines produced a total of 122 420 tons of lead concentrates. After 1851 figures for individual mines are available and are given below. Most of the mineral royalties are owned by Lord Barnard (on the Durham side) and the Earl of Strathmore (on the side until recently in Yorkshire).

    In addition to the historical sources mentioned in Chapter 1, Beadle (1980) has described mining and smelting operations in Teesdale, referring especially to the evidence remaining in the present century.

    Hardshins Vein and Troutbeck Foot Vein

    These veins were worked at the Teeside Mine (disused). Hardshins Vein crosses the Tees 1300 ft (396 m) WNW of its junction with Trout Beck; its course is marked by a line of old shafts extending 200 m south-westwards from the river at [NY 7570 3393]. Hardshins Level [NY 7579 3388] gave access by means of a crosscut running due west from the portal at 1745 ft (532 m) above OD to the vein in the Tynebottom Limestone which as far as is known was the only productive horizon. The dumps show galena and sphalerite associated with quartz, ankerite and purple fluorite. From Trout Beck, 3600 ft (1.1 km) SW of its confluence with the Tees, the London Lead Co. drove a crosscut adit known as Troutbeck Level, [NY 7305 3323] reaching Hardshins Vein. 1150 ft (351 m) from the portal. This drive was continued south-westwards along Hardshins Vein for 900 ft (274 m), but the vein does not appear to have proved productive. From the end of this drive a crosscut was carried 3300 ft (1.006 km) N47°W, continuing 1550 ft (472 m) farther at N43°W. There were air shafts at 1250 ft (381 m) [NY 7434 3358] from the point of origin of the crosscut on Hardshins Vein, and within 150 ft (46 m) [NY 7359 3434] of the forehead. Troutbeck Level starts in the Tynebottom Limestone, but it may have penetrated higher beds in the long crosscut. No veins were discovered N of Hardshins Vein.

    The subparallel Troutbeck Foot or Providence Vein crosses the Tees close to its confluence with Trout Beck [NY 7605 3377]. The vein seems to have been productive for only about 800 ft (244 m) SW of the river. A shaft near the river [NY 7598 3378] reached the top of the Whin Sill 54 ft (16.5 m) below the collar, and ended at 108 ft (33 m) in dolerite. Some work was done 18 ft (5.5 m) below the top of the sill (Mines Dept Plan No. 2525). NE of the river, the Teesside Shaft [NY 7609 3384] also penetrated the vein in the Whin Sill, the top of which was reached 50 ft (15 m) below the collar. Here the sill is only 42 ft (12.8 m) thick, and the shaft reached sedimentary rocks beneath the sill before ending at 118 ft (36 m). The minerals are similar to those along Hardshins Vein. The Teeside mines, probably including the workings on both Hardshins and Troutbeck Foot veins, produced 1455 tons of lead concentrates between 1816 and 1861.

    Metalband Old Vein and Metalband Sun Vein

    The two veins converge near the Tees; the workings were from Metalband Shaft (disused) [NY 7681 3379] on the N side of the river, 2600 ft (792 m) E by N from Troutbeck Foot. The shaft is 118 ft (36 m) deep, passing through 82 ft (25 m) of shale and sandstone into the Jew Limestone, here 30.5 ft (9.3 m) thick. It is instructive to compare this section with those on Troutbeck Foot Vein (above); evidently from the absence of the Whin Sill beneath the Tyne-bottom Limestone at Metalband and its small thickness at Troutbeck Foot, this is an area of change-of-horizon of the Whin. The minerals at Metalband include quartz, purple fluorite, galena, sphalerite and limonite. The output of lead concentrates, probably the total obtained, was 117 tons.

    Nether Hearth Veins—Lead ore

    Westmorland 6NW

    In the vicinity of Nether Hearth and Moor House a complex of small E–W, NE and NNW veins have been worked from apparently shallow shafts in the Tynebottom Limestone. The northernmost NE vein is possibly the continuation of Metalband Sun Vein. Two of the veins are well exposed in the limestone in small streams W of Moor House [NY 7575 3280]; the maximum width is not over 1.5 ft (0.45 m). The minerals include, besides galena, sphalerite, purple and amber fluorite, quartz and limonite. The southern E–W vein of the complex, Old Sun Vein was reached by a crosscut level [NY 7648 3280] from Great Dodgen Pot Sike, starting 2400 ft (732 m) E of Moor House in shale and sandstone below the Tynebottom Limestone. At the head of the same sike, limonite has been exposed by a short level [NY 7651 3246] on a NE vein 1100 ft (335 m) S of Old Sun level. No records of production exist, but it is unlikely that the output was considerable, and the small veins do not appear to invite trial in depth.

    Dun Fell Vein—Lead ore

    NY 73 SW, SE; Westmorland 6NW Direction E–W; throw uncertain

    The western portion of this strong vein has been described under area 1, pp.110–111: it has been worked at Silverband and Dun Fell mines. Mapping suggests that it crosses Banks Sike, one of the headwaters of Trout Beck, 2.25 miles (3.6 km) SW of Troutbeck Foot, continuing eastward across Moss Burn to Green Burn. Between Ninewells Sike and Moss Burn it has been tested by means of the Overhearth Level (disused) [NY 7402 3243] driven by the London Lead Co. This starts from the S bank of Trout Beck, 1.5 miles (2.4 km) SW of Troutbeck Foot; it runs S by W reaching Dun Fell Vein 2575 ft (785 m) from the portal, and is driven in the Alternating Beds, probably beginning a few feet above the Cockle Shell Limestone. From the level head drifts were extended along the vein 2900 ft (884 m) W, 1400 ft (427 m) E, the former penetrating the Tynebottom Limestone. The workings were ventilated by means of a shorter adit [NY 7383 3190] driven in shale and sandstone beneath the Scar Limestone at about 2040 ft (622 m) above OD. The only stopes shown on the remaining plan and section now, in the collection of the North of England Institute of mining Engineering, appear to indicate the presence of flats in the Single Post Limestone, worked from the upper adit; minerals present on the dumps include siderite and ankerite, with very small quantities of amber fluorite. The relative positons of the levels indicates a northward hade, and the plan gives the throw as 84–90 ft (26–27 m). Surface mapping does not confirm a displacement of this order where the vein crosses Moss Burn, but here the beds dip northwards at 21–27° in the vicinity of the vein. Some limonite, similar to that at Dun Fell, accompanies the vein in the Scar Limestone here. At 150 and 200 ft (46 and 61 m) respectively N of the Dun Fell Vein, the Overhearth and Upper levels encountered a small fault throwing 7 ft (2.1 m) N; possibly the continuation of Henrake Vein. A shaft [NY 7434 3168] sunk to test this on the E bank of Moss burn is full of water; no veinstuff is to be seen on the dump.

    East of Moss Burn there is a gap of 4200 ft (1.28 km) in which the vein has not been tested. The next workings are those from Green Bourne Level (disused) [NY 7675 3150] also driven by the London Lead Co., starting from Green Burn 4000 ft (1.22 km) WSW of its junction with the Tees. The level runs 525 ft (160 m) W along a subsidiary fault, then turns NNW and reaches the main vein by means of a crosscut 280 ft (85 m) long. The workings extend 3000 ft (914 m) along Dun Fell Vein at the horizon of the Lower Little Limestone and underlying sandstone. At 925 ft (282 m) E of the forehead the plan shows a N–S "Whin Dyke". This is in line with a cross vein in the same direction cut in the Nether Hearth workings. It is impossible now to confirm that it contains dolerite. The results of the Green Bourne trial appear to have been very poor, small amounts of baryte, calcite and siderite occur on the dump, but no stoping is known to have been done.

    Greenhurth Vein–Emmerson's Vein group

    The group of veins listed above were worked at the Greenhurth Mine (disused), situated on the western slopes of Herdship Fell, 5 miles (8 km) WNW of Langdon Beck and 12 miles (19.2 km) NW of Middleton-in-Teesdale. The royalty was formerly held by Wrentnall Baryta Co. Ltd.

    An old book in the Raby Estates office records that in 1799 Greenhurth Mine was granted to John Surtees & Co., 1200 ft (366 m) long by 100 ft (30 m) wide, for 21 years, at a royalty of one-fifth. It is also recorded that this company were obliged to give up the mine "by not beginning to work", in fact, up to 1828 no work was done. From 1845 to 1852 the mine was included in a group operated by Sherlock & Co., who held also the Langdon, Grasshill, East Cowgreen, Trough and Willyhole mines (mentioned below). The annual "duty ore" returned from the whole group averaged 108 tons in this period, from which it may be concluded that production was not much over 500 tons per year. After Sherlock & Co. ceased operations, prospecting was carried on, presumably by local men, until a discovery made about 1868 justified the formation of a new company, the Greenhurth Mining Co. Operations under this company continued until the final closing of the mine in 1902, the total output of lead concentrates produced during its life being 18 240 tons, with 21 tons of zinc concentrates and 25 tons of barytes. The silver content of the galena is discussed on p.71.

    The first vein discovered was probably Greenhurth Vein, cut beneath the Tynebottom Limestone by the Middle Level [NY 7797 3287] at 300 ft (91 m) from the portal. This level follows the vein eastwards, and it is possible, though not certain, that some ore was obtained from the Tynebottom Limestone along its course. At 1000 ft (305 m) from the point where Middle Level turns on this vein, a strong cross vein (No. 1) was cut. This proved to carry the principal oreshoot of the mine, a section of which is given in (Figure 37). The vein is nearly vertical; the oreshoot was at its best from the Tynebottom Limestone down to the Smiddy Limestone, but workings were continued through the full thickness of the Whin Sill (240 ft (73 m), revealing small shoots which are said to have been rich. It is said that at the bottom of the deepest workings the vein was 3.5 ft (1 m) wide, filled with solid ore; and that these workings were flooded out, the process happening sufficiently rapidly for the tools to have been lost. The mine thus enjoys a considerable local reputation. On the other hand, certain economic data preserved in the Estate records strongly suggest that in the last ten years of its life the mine had become uneconomic at the current price of lead.

    Greenhurth Vein is apparantly shifted 80 ft (24 m) E side S by No. 1 Cross Vein: when followed eastwards, three more cross veins were encountered, No. 2, Annie's and No. 4. The first two were developed at the Middle Level horizon, and may have yielded some ore from the Tynebottom Limestone; trials at deeper horizons do not seem to have been successful, but exact details are lacking. Development to the south revealed Emmerson's Vein 250 ft (76 m) S of Greenhurth Vein on the east side of No. 1 Cross Vein. It is not certain that this was productive, even in the Tynenbottom Limestone, in Greenhurth Mine, but 900–1200 ft (274–366 m) E of No. 1 Cross Vein it appears to have carried a small oreshoot in this limestone, worked from Bodder Mea Level, [NY 7867 3262] which runs as a crosscut 820 ft (250 m) northwards from the portal beside the Greenhurth–Dubbysike track.

    The following minerals occur on the Greenhurth dumps: coarse ankerite (ω = 1.700); galena, quartz, sphalerite, pyrite, calcite, baryte and witherite. The amount of baryte is very small and it may have been confined to the upper levels. The deposits belong to the intermediate zone between the fluorite and baryte zones. Approximately 35 000 tons of mineralised material is estimated to remain in the dumps, including coarse cuttings, jig tailings and slimes. A weighted average of five samples (assayed by Mineral Department, Imperial Institute) taken from many superficial pits, showed 1.63 per cent lead, 1.73 zinc. Dressing thus appears to have been thorough.

    The principal levels are shown in (Figure 37): Middle Level, the main adit, is at about 1810 ft (552 m) above OD, while the deepest shaft (New Shaft) [NY 7838 3281] reaches 1385 ft (422 m) above OD, though Swan's Shaft [NY 7838 3277] situated beside the old mine road, was the main drawing shaft. No equipment remains now on the surface; the shafts have collapsed but the adit levels are open in part.

    West of the mouth of Middle Level [NY 7757 3296], a deeper adit was started beneath the Jew Limestone. This seems to have cut a number of strings, some of which may represent Greenhurth Vein, but no workable ground was found. The forehead stands near the entrance to Middle Level.

    It appears from a comparison of the tonnage of dumps and the known output that the ore must have been rich, containing as much as 25 per cent lead sulphide. Nevertheless reopening to develop the Melmerby Scar Limestone in depth ought to be regarded as a very speculative undertaking, notwithstanding tales of rich ore and flooded workings.

    Dubbysike, = Force Burn Vein—Barytes

    NY 73 SE, 83 SW; Durham 30 SW, Westmorland 6NE, NW. Direction N65°E, throw at least 30 ft (9 m) SE

    The vein has been worked at Dubbysike Mine (leased by Sanbar Ltd, 1984) on the south-western slope of Herdship Fell, 1.25 miles (2 km) NW of Cowgreen Mine. The mine was developed for lead prior to the middle of the nineteenth century, the old workings including an opencut in the Tynebottom Limestone [NY 7965 3200], a level at the base of this limestone at 1820 ft (169 m) above OD [NY 7960 3193] and a crosscut adit, called Hunter's Level [NY 7934 3160] driven 1060 ft (323 m) northwards from Dubby Sike at the base of the Lower Little Limestone. At still lower horizons Muse's Level [NY 7880 3162] was driven in sandstone on top of the Whin Sill from Bothermere Sike, and a stone-lined oval shaft [NY 7862 3154] on Bother Mere was sunk directly into the Whin Sill. It is unlikely that there was any substantial production of lead, since the filling of the veins consists largely of baryte. The Hedworth Barium Co. worked the mine during the First World War, from a new crosscut adit [NY 7953 3194] driven from the side of the Greenhurth mine-road at 1800 ft (549 m) above OD. This commanded the Tynebottom Limestone on the hangingwall of the vein. Barytes produced by the Hedworth Co. from stapes above this level is included in the general total for this company's output from the Cowgreen Mines group, given below. The mine was reopened in 1940 by the Wrentnall Baryte Co. Ltd who sank a new shaft [NY 7951 3198]. Owing to labour shortage it had not been brought into production by 1948.

    NE of the Greenhurth road the throw of the vein is equal to the thickness of the Tynebottom Limestone (about 30 ft) (9 m). The high level at the base of the Tynebottom Limestone appears to have been driven for part of its course along a parallel fault of small displacement, lying 40–60 ft (12–18 m) SE of the main vein. SW of the road Hunter's Level shows two or possibly three branches of the vein, but critical evidence as to the displacement is lacking. In the measures from the Tynebottom Limestone down to the base of the Lower Little Limestone, the vein is filled with good-quality white baryte, carrying small quantities of galena. Run-of-mine samples showed barium sulphate contents varying from 93 to 97 per cent, with 1.0–3.3 silica. In these beds the width of the vein varies from 5 to 13 ft (1.5 to 4 m) the greatest width being that proved in the new shaft opposite the footwall position of the sandstones and sandy shales below the Jew Limestone. Witherite is common on the dumps from the new shaft and the high level. Beneath the Lower Little Limestone the oreshoot, from evidence provided by the shaft and Hunter's Level, pinches. At still lower horizons, however, there is reason to expect the presence of a second oreshoot, for the oval shaft into the Whin Sill shows coarse baryte on the dumps, while the south-westward continuation of the vein on the Cumbria (southern) side of the Tees, between walls of Whin Sill is well exposed for 500 ft (152 m) [NY 7782 3122] in the bed of Force Burn and shows a width of 4 ft (1.2 m) of fibrous baryte, with a thin band of galena near the walls. No mining has been done at Force Burn, though trial shafts have been sunk SW of the exposed part of the vein.

    The 1941 Dubbysike Shaft [NY 7954 3198] commences at 1840 ft (561 m) above OD and has been sunk 144 ft (44 m), meeting the Hedworth adit level at 44 ft (13 m). The vein is more-or-less vertical to a depth of 75 ft (23 m) from the shaft-collar, below which it hades 10°SE. The total length of ground developed on the Hedworth Level amounts to 600 ft (183 m). Levels from the shaft had not been developed when mining was suspended because difficulty was experienced with the soft hangingwall of the vein.

    Winterhush Vein–Angle = Rods Cross Vein group

    The veins listed above are those formerly worked at Cowgreen Mines (disused). Construction of the Cowgreen Reservoir in the 1960s flooded most of the workings (Figure 38) and (Figure 39). All the veins listed had yielded barytes from superficial workings under the Hedworth Barium Co. but the last operations, which were commenced in 1935 by the Anglo-Austral Mining Co. Ltd. were mainly confined to the Winterhush and Greenhush veins though some other veins were tested as operations proceeded. The group as a whole lies near the crest of the Teesdale dome, in beds belonging to the Asbian and the lowest part of the Brigantian Stage. The Whin Sill, 240 ft (73 m) thick, is intruded 90 ft (27 m) below the top of the Melmerby Scar Limestone; it is thus at a lower horizon here than at Greenhurth and Dubbysike mines, where it underlies the Smiddy Limestone. Locally in the Cowgreen area whin appears to reach higher levels; for example, at 2000 ft (610 m) SSE of Wrentnall Shaft it could be seen in the upper part of the Melmerby Scar Limestone, while the most recent explorations along Greenhush Vein suggested that here, too, there may be an upward transgression. The Whin Sill and Melmerby Scar Limestone together form a competent formation of unusual thickness for the Pennine field. The principal oreshoot on Winterhush Vein occurs in these beds, but development did not reach the Whin Sill on most of the other veins. Beneath the Whin Sill, the exposures at Falcon Clints [NY 825 281] S of Cowgreen, show a small thickness of metamorphosed limestone, followed by shales, sandstones and thin limestones, underlain by conglomerates which rest on Lower Palaeozoic rocks. Above the Melmerby Scar Limestone, a series of thin limestones, interbedded with sandstone and shales, begins the rhythmic sequence characteristic of the Brigantian Stage section, (Figure 2) and (Figure 3). The metamorphic effect of the Whin Sill, converting the whole of the Melmerby Scar Limestone into coarse marble (known as the Saccharoidal or "sugar Limestone", from its crumbly weathering) extends to the top of the Robinson Limestone. The sandy shale or "whetstone" immediately adjacent to the top of the sill is albitised, and lime-silicates, including grossularite, diopside and vesuvianite, have been developed in impure parts of the limestone.

    The dominant mineral in all the veins is baryte. Galena, though rarely completely absent, makes only an insignificant fraction of their contents, probably not exceeding 0.5 per cent. Sphalerite is occasionally found. In the Melmerby Scar Limestone, the important impurities are the carbonates of magnesium calcium and iron, including an ankerite near dolomite (with ω = 1.685) and smaller amounts of a more ferruginous ankerite (ω = 1.710). Some siderite is also present. Silica occurs in sugary aggregates which probably owe their origin to replacement of marble. In certain types of barytes veinstuff from Winterhush Vein, Dr Phemister noted inclusions of quartz varying from.0.05 mm to 1 mm diameter. Witherite has so far been found only on Winterhush Vein near the footwall position of the base of the Whin Sill. The ankerite occurs in flesh-coloured masses which at first sight resemble baryte. A little colourless to pale yellow fluorite may be seen on the walls of Greenhush Vein in the Smiddy Limestone, immediately W of the intersection with Winterhush Vein [NY 8099 2106]. The fluorite is clearly earlier than the baryte which overgrows it (B. Young, personal communication).

    The most important oreshoot developed was that on Winterhush Vein. Its total length is 2340 ft (713 m) and the maximum height worked, 275 ft (84 m). In the Melmerby Scar Limestone the width of the vein probably averages 8–10 ft (2.4–3 m) but owing to admixture of carbonates and quartz, only part of the width is baryte.

    In the Whin Sill, the width is probably not more than 4–5 ft (1.2–1.5 m) on the average, but the filling is mainly platy baryte. In the older Hedworth workings, in the limestones between the Smiddy and Robinson, widths up to 7 ft (2.1 m) appear to have been stoped. The throw of Winterhush Vein, owing to gentle differential folding of the beds forming its walls, varies considerably. At the main shaft it is 60 ft (18 m) E; at 710 ft (216 m) N, it has increased to 80 ft (24 m); at 1245 ft (379 m) N it is 75 ft (23 m), while as the intersection with Greenhush Vein is approached, the throw decreases to zero and may even be reversed. The oreshoot pinches in the vicinity of this intersection (or perhaps it may be regarded as continuing along Greenhush Vein). N of Greenhush Vein, the Winterhush Vein splits and there is evidence in the Winter Hush that a step-faulted structure is present which has caused large shale masses to be dropped down between limestone or sandstone walls, with an adverse effect upon the mineralisation. At the northern end an added adverse factor is the thickening, from 4 ft (1.2 m) near the main shaft to 20 ft (6 m), of a soft sandstone at the top of the Melmerby Scar Limestone, which causes an upward nip in the oreshoot. At the S end of the workings, the oreshoot had pinched but the fracture continues.

    The Wrentnall Shaft [NY 8105 3053] was started by the Hedworth Company, who sank it from 1575 ft (480 m) above OD to the 56 ft (17 m) Level on Winterhush Vein. The workings on this vein by the Hedworth Co. consisted of an adit level [NY 8106 3058] starting 160 ft (49 m) N of the shaft, 1640 ft (500 m) long and shorter levels from the shaft at 30, 40 and 56 ft (9, 12 and 17 m) depth. The Wrentnall (Anglo-Austral) company deepened the shaft to the 191 ft (58 m) Level, and made their principal levels at 106 ft (32 m) and 191 ft (58 m). The former runs 2200 ft (671 m) N and 846 ft (258 m) S; the latter 1500 ft (457 m) N and 720 ft (219 m) S. The 106 ft (32 m) Level commanded the Melmerby Scar Limestone on both walls of the vein, while at the 191 ft (58 m) Level the vein is between Whin Sill walls. Inclined diamond boreholes were used to test the vein beneath the lowest level both N and S of the shaft; the limited evidence from them suggested that the oreshoot pinches in depth. This was borne out when, towards the end of the life of the mine, Wrentnall Shaft was deepened to 340 ft (104 m), entering Skiddaw Slates on the footwall side of the vein at 328 ft (100 m). The 340 Level was driven 170 ft (52 m) N, and a rise put up 105 ft (32 m) on the vein without finding any improvement. The southern foreheads of the main levels showed the vein split, but still, mineralised. Mining from the 106 ft (32 m) Level in this direction could not be carried much farther, because the backs have been very much reduced owing to the presence of glacial or alluvial deposits, associated with the channel of the River Tees, which reach a thickness of at least 45 ft (14 m). Winterhush Vein provided the bulk of the Wrentnall Co.'s production from Cowgreen. The mining system followed was cut-and-fill, the fill material being derived from surface quarries or mill tailings; it was passed down rises made specially for the purpose.

    Greenhush Vein carried a series of wide pockets in the Jew and Lower Little limestones, which were extracted by the Hedworth Co. from a level at about 1695 ft (517 m) above OD [NY 8106 3104]. This was reopened by the Anglo-Austral Company who developed the vein in the Smiddy and Melmerby Scar limestones. A branch from the 106 ft (32 m) Level on Winterhush Vein starts at 1740 ft (530 m) N of the main shaft to follow Greenhush Vein. The old adit or Horse level on Winterhush Vein was reclaimed, and extended along Greenhush Vein. Above Horse Level, bearing ground with 4 ft (1.2 m) of barytes was exposed, while similar widths were developed in lower limestones beneath this level. In the Melmerby Scar Limestone, however, the continuity of the vein is disturbed by ramifying postmineralisation caverns. On the 106 ft (32 m) Level, an upward transgression by the top of the Whin Sill was encountered 300 ft (91 m) from the junction with Winterhush Vein, the vertical jump taking the sill to the base of the Robinson Limestone. The level was driven to the Teesdale Vein, but without finding workable ground (Figure 38)

    There is some evidence of a small vein running N of Greenhush Vein and intersecting it about 1250 ft (381 m) NE of Winterhush Vein. The workings appear to have been in the Jew Limestone, but there is no information as to oreshoots.

    Isabella Vein, still farther N yielded good quality barytes to the Hedworth Co. in Isabella Level, [NY 8162 3179] from the E side of Herdship Fell in the Jew Limestone at about 1700 ft (518 m) above OD. A trial of this vein in the Tynebottom Limestone midway between the Isabella Level portal and the intersection of the vein with Winterhush Vein was unsuccessful. A small vein, possibly the continuation of Isabella, was cut on the Horse Level on Winterhush Vein at 2800 ft (853 m) N of Wrentnall Shaft. Seen at the horizon of the Peghorn Limestone, it has a throw of a few feet only, but it shifts Winterhush Vein N side E. Up to 2.5 ft (0.76 m) of baryte is seen in the vein here.

    Isabella Level passed through a series of fractures representing the Teesdale or East Cowgreen veins, but the principal workings on these twin fractures were in the vicinity of East Cowgreen, 0.5 mile (0.8 km) S of Isabella. On the eastern fissure, old shafts indicate that mineralisation extended over a length of about 850 ft (259 m); it is not, however, known whether baryte was present in quantity. On the western fissure workings appear to have been less extensive. It is doubtful whether either has as yet been tested beneath the Peghorn Limestone; the horizon of the workings at East Cowgreen being the Smiddy Limestone and underlying beds down to the Peghorn Limestone. The East Cowgreen workings are said to have been drained down to about 1590 ft (485 m) above OD by means of a level driven along Holmes Vein [NY 8229 3016]. South of the East Cowgreen shafts, dumps indicate that an old shaft in Sand Sike , [NY 8199 3055] possibly near the intersection of Rods Vein with the Teesdale veins, proved baryte in quantity. To the N, the East Cowgreen fracture was tested at the forehead of Martha Level [NY 8123 3290], which was driven 1375 ft (419 m) S and SW. White baryte is present on the dump but this might also have come from a vein 740 ft (226 m) S of the entrance on the line of Dubbysike Vein, though with a more easterly trend. The horizon is in and below the Lower Little Limestone. East Cowgreen Vein may also have been reached by a trial level on a weak ENE vein from [NY 8162 3280].

    Hopkins Vein was worked by the Hedworth Co. from a crosscut adit [NY 8212 3120] at about 1625 ft (495 m) above OD in the sandstone beneath the Smiddy Limestone; the oreshoot, 750 ft (229 m) long, was probably mainly in the Smiddy Limestone. Mr Philip Beadle states that the W forehead of this level, approximately 500 ft (152 m) ENE of the East Cowgreen eastern vein, showed the vein to be split, with 9–12 in (0.23–0.3 m) of baryte on either side of a horse of stone 6 ft (1.8 m) wide. A lower level [NY 8236 3130] was driven on Hopkins Vein at about 1590 ft (485 m) above OD, but no information as to its length or contents is available.

    Middle Vein, worked in shallow opencuts in the Smiddy [NY 8185 3101] and Peghorn limestones, [NY 8215 3113] is assumed to have been a narrow baryte vein, but it is nowhere visible.

    Holmes Vein was also worked in opencuts in the Peghorn Limestone, [NY 8216 3110] where the width between the limestone walls is 4–6 ft (1.2–1.8 m). Its condition in the level at 1590 ft (485 m) above OD mentioned above is not known.

    Rods Vein and a narrow subparallel vein to the S were worked opencast in the Melmerby Scar Limestone where the main vein appears to have been 3.5–6 ft (1.1–1.8 m) wide. The oreshoot probably terminates westward against Rods Cross Vein, and it is unlikely that it was reached by an old level which started at or near the top of the Whin Sill 400 ft (122 m) W of this intersection. It remains, therefore, to be proved in the Whin Sill. Between Rods Vein and East Cowgreen there are numerous narrow ENE veins, some of which carried baryte in the sandstone between the Melmerby Scar and Robinson limestones; all appear to have been small and pockety.

    Rods Cross, or Angle Vein, contains up to 4 ft (1.2 m) of baryte in the Peghorn Limestone where tried at surface [NY 8115 3068], but was proved unpayable at the 106 ft (32 m) Level, from a crosscut in the Melmerby Scar Limestone starting 410 ft (125 m) N of Wrentnall Shaft.

    The general position as to oreshoots at Cowgreen may be summarised as follows (i) the Jew and Lower Little limestones carry oreshoots of restricted height, but none has so far been found in the shaly measures between the Lower Little and Smiddy limestones (ii) the strata from the Smiddy Limestone down to the base of the Whin Sill consists mainly of hard beds, and is therefore potentially favourable to mineralisation; in this belt the Melmerby Scar Limestone carries the widest oreshoot yet proved, but this is more contaminated with ankerite and silica than oreshoots at lower and higher horizons. In 1949 a shaft was sunk on Rods Vein which showed a maximum width of 3.5 ft (1 m) of baryte in saccharoidal limestone; when the vein entered Whin sill at 67 ft (20 m) depth it became narrower. A winze 50 ft (15 m) deep on Winterhush Vein beneath the 191 ft (58 m) level in 1951 prepared the way for the sinking of Wrentnall Shaft to the 341 ft (104 m) level at 1230 ft (114 m) above OD, entering Skiddaw Slate at 1275 ft (389 m) above OD on the footwall of the vein. A N drive of 141 ft (43 m), and a rise of 100 ft (30 m) failed to disclose workable vein widths and in 1952 the mine was abandoned as exhausted.

    During 1940–41 average run-of-mine ore from Winterhush Vein was estimated to contain 65–70 per cent barium sulphate but later on it proved possible to treat economically ore with less than 40 per cent barium sulphate. An example of the composition of the finished product, all of which was used for the production of lithopone, is given below:

    BaSO4 93.1
    SiO 2.8
    Fe2O3,A12O3 1.5
    CaO 0.8
    Pb tr.
    Ignition loss 1.2
    99.4

    Analysis by Orr's Zinc White Ltd, 1945

    Although a number of promising baryte-bearing veins on the Cowgreen property remain untested in the Melmerby Scar Limestone and Whin Sill, the information given above is of historical and academic interest only since these beds, as well as the collar of Wrentnall Shaft lie beneath the water of Cowgreen Reservoir with its level at about 1700 ft, (518 m) above OD.

    Production records for the Cowgreen Mines are as follows: lead concentrates–East Cowgreen, 1855–1871, yielded 128 tons; Teesdale Vein, 1876–1881, yielded 319 tons; Cowgreen mines under the Hedworth Co. 1902–1919, produced 254 tons as a byproduct in barytes mining. Silver recovery amounted to 4.4 oz per ton of lead. Barytes–Messrs Robinsons, 1886–1895, 1293 tons; Hedworth Barium Co. 1898–1920 (including Dubbysike Mine), 57 830 tons; the last owners, starting in 1935, had up to the closing of the mine in 1952 produced some 240 000 tons. The Cowgreen group has thus produced 1600 tons of lead concentrates and nearly 300 000 tons of barytes.

    A sample of product barytes, representative of the Wrentnall Company's years, assayed as follows: BaSO4 93.1; SiO2 2.8; Fe2O3+ A12O3 1.5; CaO 0.8; Pb trace; ignition loss 1.2; total 99.4.

    Lodgegill Sike Vein

    NY 73 SE; Westmorland 6 NE

    In Lodgegill Sike, 1.5 miles (2.4 km) W of Cowgreen Mine, two short levels have been driven to test an E -W vein in and below the Whin Sill [NY 7871 3028] and [NY 7900 3033]. Baryte is present on the dump from the upper level, [NY 7871 3028] associated with limonite and traces of galena.

    Birkdale Farm Veins

    NY 72 NE, 82 NW; Westmorland 6 SE

    Three narrow NE-trending veins cross Cocklake Sike, NW of Birkdale Farm, 1.5 miles (2.4 km) SSW of Cowgreen Mine. Shallow workings in the Robinson Limestone and associated beds [NY 803 280] have shown that white platy baryte, accompanied by traces of galena, fills the veins. Alongside Grain Beck, 0.25 mile (0.4 km) W a vein striking NNW has been tested by means of a hush [NY 7987 2787] and shafts; [NY 7976 2800] and [NY 7978 2797]; baryte, associated with limonite and traces of galena, is present on the dumps. At the head of Grain Beck, 0.75 mile (1.2 km) WNW of Birkdale Farm, a short adit [NY 7917 2804] to a NNW vein in the Lower Little Limestone reveals the presence of galena in an ankerite matrix. At Moss Shop, 0.5 mile (0.8 km) WSW of the farm, a level [NY 7958 2731] driven in sandstone and shale immediately above the Whin Sill, possibly to test the Maizebeck Cross veins (below) has proved baryte in small quantity. On the slopes of Rasp Hill baryte occurs in a small vein proved by shafts into the Tyne-bottom Limestone at the head of Stoneymea Sike.

    Ashgillhead Vein and Ashgillhead North Vein

    Along the watershed between Burnhope (one of the main tributaries of the Wear) and the Harwood valley runs a strong E–W vein; the eastern workings have already been described (North Langtae Head Vein, p. 180). On the Teesdale side of the divide, the western stretch of the vein is known as Ashgillhead Vein, worked from the Ashgillhead Mine (disused), 1.5 miles (2.4 km) NNW of Harwood church. The earliest workings were probably whimsey shafts into the Firestone Sill, where the vein appears to have been well mineralised with purple and amber fluorite, quartz and galena. The main entrance to the underground workings was Ashgillhead Level, [NY 8083 3550], a straight crosscut adit at about 1800 ft (549 m) above OD, driven N12°W beneath the Three Yard Limestone. This reached the vein at 3400 ft (1.04 km) from the portal. The main oreshoot on the vein, 4200 ft (1.28 km) long, was at the horizon of the Great Limestone and Coal Sills; two small oreshoots, respectively 400 and 300 ft (122 and 91 m) long were found in the Four Fathom Limestone. Beneath this horizon there is no evidence that workable ground was found. At 3650 ft (1.11 km) W of the level head, Ashgillhead Vein is joined by North Vein (the Lodgegill Vein of Weardale, see p.180); and the western part of the Great Limestone oreshoot, 600 ft (183 m) long, may be regarded as being on this vein. From the western end of the workings, a crosscut, said to be in the shale above the Four Fathom Limestone, was driven 1900 ft (579 m) WNW, with the hope of finding the Scraith Head Vein of Weardale. A number of small veins were encountered, but there is no evidence that any of them were productive. At 2000 ft (610 m) W of the level head, a small ENE branch was explored on the north side of the Ashgillhead Vein; the name Fenwick's Blue Vein was given to this, indicating that it was filled either with shale gouge or fluorite. Ashgillhead Mine belonged to the London Lead Co. who operated it until 1885. The recorded output of lead concentrates, 1852–1883, of 4622 tons (containing 3 oz silver per ton of lead) probably hardly does justice to the substantial oreshoot worked here. The tailings dumps near the mouth of Ashgillhead Level consist mainly of fluorite and quartz, but contained 3.2 per cent lead and 0.81 zinc (assay by Mineral Resources Laboratory, Imperial Institute, 1941).

    The growing recognition of the importance of Quarter-Point veins as carriers of major fluorspar-producing oreshoots led to attempts to reopen Ashgillhead Mine, one in 1950 by Anglo-Austral Mines Ltd another in the 1970s by EXSUD Ltd. The second reopening is said to have given access to the full extent of the main level but neither was successful. The dumps have largely been removed for fluorspar.

    South Langtae Head Vein—Lead ore

    NY 73 SE, NE, 83 NW; Durham 30 NW

    The workings on the Weardale side of the watershed along this vein have already been described (p.180). It continues south-westward down South Langtae Sike, where ancient shafts between [NY 8108 3585] and [NY 8143 3615] gave access to the vein and to a branch on its NW side in the Great Limestone, Purple fluorite, galena, quartz and aragonite were present. Ashgillhead Level must have passed through the vein, probably in the Six Fathom Hazle, but there is no record of any development on it. Farther to the SW, Cadger Well Level [NY 7970 3482] at the head of Harwood Beck, proved at 600 ft (183 m) NNW of the portal a weak vein supposed to be South Langtae Head Vein. This level, driven by the London Lead Co., is said to have been started about 1890 because a lump of float galena, carrying exceptionally high silver-values, was found in the headwaters of the beck. A westward branch from Cadger Well Level is said to have been carried through the Teesdale Fault (the course of which is followed by Harwood Beck) into dolerite. No mineralised veins appear to have been found in the trial though small quantities of altered limestone present on the dumps, contain magnetite, chlorite and lime silicates such as ugrandite garnets and hydrogrossular (Young et al, 1985). These magnetite-bearing rocks are similar to those described from Lady's Rake Mine (below).

    Grasshill North Vein, Middle Streak Vein and Black Leader Vein

    The workings on these veins lay to the NE of Grasshill House. Highfield Hushes [NY 817 355] are opencuts in the Great Limestone, and provide evidence that mineralisation was not confined to the veins, but included some replacement of the limestone. Higher up the fell [NY 821 358] there is a great spread of tailings from old shafts and it is possible that sandstones above the Great Limestone were also productive. The minerals present include baryte, subordinate amounts of amber fluorite, traces of galena, and pyromorphite. Beneath the Great Limestone, Blackway Level [NY 8226 3536] starting 2150 ft (655 m) E of Grasshill House, is a crosscut adit reaching the vein, probably in the Quarry Hazle, 1300 ft (396 m) from the portal; baryte and amber fluorite are equally abundant on the dump. The Baking and Cowby levels ([NY 8146 3526] and [NY 8153 3519] respectively) driven into Black Leader Vein from Mill Sike and Cowby Pasture respectively, both in the Nattrass Gill Hazle, appear to have been unsuccessful. No plans or section of these mines remain extant, nor is there any record of production, so that it is likely that they were considered to be exhausted before the early part of the nineteenth century. A small quantity of barytes has been taken from the dumps from time to time, but there is no evidence that substantial amounts remain underground.

    Coldberry Hill Vein and Coldberry Sun Vein

    The workings on these veins lie near the summit of the track from Grasshill to Weardale. The Coldberry Hill Vein has been worked opencast in the Great Limestone, [NY 828 358] where it carries white baryte, with subordinate quantities of amber fluorite and galena, up to 6 ft (1.8 m) wide. Small flats are said to occur. A few cartloads of barytes were obtained here during the Second World war. Assays (supplied by Wrentnall Baryta Co.) show 94–97 per cent barium sulphate, 2.0–2.7 silica, 0.3–0.9 ferric oxide + alumina. On the Sun Vein, which outcrops below the base of the Great Limestone, ore-bearing ground 1650 ft (503 m) long was worked from Coldberry Low Level, [NY 8261 3503] a crosscut adit starting 0.7 mile (1.2 km) ESE of Grasshill House at the base of the Three Yard Limestone. The level followed the northward course of an ancient cross-measure hush and must be over 1800 ft (549 m) long. Massive purple fluorite and some amber fluorite occur on the dump. The superficial workings on Sun Vein show the presence of witherite, largely converted to secondary baryte, associated with some amber fluorite. The level, however, which gave access to oreshoots in the Quarry Hazle, Four Fathom Limestone and Nattrass Gill Hazle, proved only fluorite in the vein; barium minerals are absent. An attempt was made to find both the Coldberry veins on the Weardale side of the watershed, by means of Weardale Coldberry Level, [NY 8344 3605] driven by the London Lead Co. from the head of Cutthroat Sike near the top of the Six Fathom Hazle. Several strings were cut, but none appears to have been workable. Some disseminated galena and sphalerite in limestone (probably the Three Yard) occurs on the dump.

    Lady's Rake–Hawksike Vein—Lead ore

    NY 83 NW, SW; Durham 30 NW. Direction N50–85°E, displacement in Hawksike Hush, 10 ft (3 m) S

    Hawksike Hush is crossed by the Alston–Middleton main road 0.25 mile (0.4 km) S of Grasshill House [NY 8144 3495]; the principal workings on Hawksike Vein lie to the E of the road, and consist of a series of whimsey shafts, probably of early date. The dumps show amber fluorite, siderite, ankerite and galena; the principal horizon worked was probably the High Brig or Six Fathom Hazle. At 300 ft (91 m) W of Hawk Sike Shop [NY 8182 3504] the vein is apparently shifted W side N 100 ft (30 m) by a cross vein which has also been encountered in the workings of the Grasshill veins. In the hush, the vein splits up into a number of SW branches. In the centre of the hush, the London Lead Co. sank their Grasshill Shaft (disused) [NY 8123 3484] 225 ft (69 m) deep, starting in the shale above the Scar Limestone and ending beneath the Tynebottom Limestone. Drifts of 225 ft (69 m) NE and 250 ft (76 m) SE were made along the vein, and a cross vein throwing 12 ft (3.7 m) SW was explored at the south-western end of the workings. Part of, or all of, the 738 tons of lead concentrates containing 4 oz silver per ton of lead recorded for the Grasshill mines between 1852 and 1896 may have come from these workings.

    Further SW the main vein or a branch from it was discovered beside the Harwood Beck at Lady's Rake Mine (disused), one of the last of the London Lead Co.'s operating mines. Here an adit level, Wigrams Level [NY 806 3424] gave access to an oreshoot 1400 ft (427 m) long in the Tynebottom Limestone; the plan shows many strings diverging from the vein. The level was continued 600 ft (183 m) NE beyond the end of the oreshoot without finding payable ground. On the eastern bank of the beck, Jensen's Shaft [NY 8059 3423] was sunk 103 ft (31.4 m) starting near the base of the Tynebottom Limestone, and ending beneath the Jew Limestone. The hade of the vein here appears to be NW. In the Jew Limestone stopes 300 ft (91 m) long were worked and the Jew Limestone Level was continued 400 ft (122 m) SW of Harwood Beck, passing through the Teesdale Fault close to the point where the supposed continuation of the Teesdale and Winterhush veins of Cowgreen converge, as a single fracture, upon this fault. On the Teesdale–Winterhush vein an oreshoot 440 ft (134 m) long was worked to 80 ft (24 m) above and 100 ft (30 m) below the level. A drift 900 ft (274 m) long was also driven on the supposed continuation of this vein E of the Teesdale Fault, but without success. At 1000 ft (305 m) SSE of the forehead of the workings in the Teesdale–Winterhush oreshoot, Nerr Shaft [NY 8062 3380], sunk from the north bank of Reddycomb Sike, cut the vein, which carried siderite, limonite and baryte, but no mine was developed here.

    The Teesdale Fault is recorded on the plan as taking the form of a "Whin Dyke", 40 ft (12 m) wide. As noted above dolerite is also supposed to have been cut at Cadger Well Level. Although the presence of dolerite cannot be confirmed with certainty at Lady's Rake the recent discovery (Young et al., 1985) of rock containing abundant magnetite, talc and calcite on the dumps suggests possible alteration of limestones by the Whin Sill, perhaps along the Teesdale Fault. In addition this magnetite-rich rock contains galena, sphalerite, and locally abundant niccolite with minor  amounts of pyrrhotite, chalcopyrite, ullmannite and gersdorffite. Introduction of metal-bearing brines into the Whin Sill and its contact rocks whilst the latter were still hot has been proposed to explain this remarkable assemblage which was probably restricted to the workings in the Teesdale Fault. Other minerals present at Lady's Rake include baryte, ankerite, siderite and quartz. Galena values are said to have been poor. The output under the London Lead Co. 1882–1902, was 7106 tons of lead concentrates, yielding 5.5 oz silver per ton of lead. After this company surrendered its leases, work was continued by a local syndicate from 1904 to 1908, the production being 380 tons of lead concentrates. In an historical account of the mine Beadle (1980) includes photographs from this period.

    On the W bank of the beck, 1400 ft (427 m) NW of Lady's Rake shaft, a shaft [NY 8028 3446] said in 1931 to be 72 ft (22 m) deep had recently been sunk, and a crosscut driven W, cutting a vein which may be the continuation of the supposed Teesdale–Winterhush vein. Coarse galena accompanied by magnetite occurs on the dumps. An assay of a picked lump by Dr Smythe showed 75 per cent lead, with 8.8 oz silver per ton of lead. The occurrence appears to merit further investigation.

    Rough Rigg Vein, Trough Vein and Scar Head Vein

    About Rough Rigg and Rigg End there is a complex of small veins of which the three principal members are listed above. The beds exposed at surface range downwards from the Scar to the Jew Limestone. Although a great deal of shallow exploration has been done, it appears unlikely that any great quantity of lead ore has been found. One of the principal levels starts from Dry Gill [NY 8196 3393] 1250 ft (381 m) S of Rough Rigg, following a NNW cross-course 1300 ft (396 m) to cut Trough Vein. Amber fluorite and galena are present on the dump. Workings from this level are known to have extended 800 ft (244 m) SW and 1450 ft (442 m) NE of the level head, in beds between the Tynebottom and Jew limestones. Another level, at about 1670 ft [NY 8224 3420] above OD, runs north-eastward from Tongue Sike to Trough Vein. This vein is exposed in the Scar Limestone, where it carries purple fluorite and limonite.

    Scar Head Vein was followed east of the Alston–Middleton road into higher beds. Coarse platy baryte was present in the High and Low Brig Hazles. A pocket of baryte in the Scar Limestone is also exposed in an old hush [NY 8267 3420] on the vein; nearby a small heap of barytes has been collected at some time. No plans of the workings on this vein remain. A total of 667 tons of lead concentrates, yielding 6.6 oz silver per ton of lead, was obtained from Trough and Scar Head veins in 1852–1874.

    Reddycomb Vein and Willyhole Vein

    The two veins occur on the eastern slope of Herdship Fell, west of Harwood church; Reddycomb Vein lies S of the sike of the same name, while Willyhole Vein approximately follows the course of Willyhole Sike. Reddycomb Mine (disused) consisted of a level [NY 8020 3355] beneath the Tynebottom Limestone, which exposed Reddy-comb Vein for 1500 ft (457 m) and a crosscut running 900 ft (274 m) S from this vein to Willyhole Vein. Smithsonite, baryte, galena and some sphalerite occur on the dump. Coatings of yellow earthy greenockite are common here on partly oxidised sphalerite (Young et al., 1987). A little baryte showing characteristic secondary morphology is also present suggesting the former presence of a barium carbonate though none has been found (Young, personal communication). Reddycomb Vein was also reached by adit levels in the shale beneath the Jew Limestone [NY 8049 3360], and in shale beneath the Lower Little Limestone [NY 8060 3364]. The dumps from the lower levels show sphalerite, quartz, baryte and galena. On Willyhole Vein there was an adit level [NY 8076 3327] commanding the Jew Limestone; here baryte, with sphalerite, was present. The mines were active as lead producers from 1852 to 1889, raising 758 tons of lead concentrates with 3.1 oz silver per ton of lead. In 1896, under the name of Willyhole Mine, production of zinc ore was commenced. A dressing plant was erected, but it is understood that difficulty was experienced in separating the sphalerite and baryte using gravity methods (Beadle, 1980). A total of 716 tons of zinc ore had been produced up to 1912, when operations ceased. It is recorded of Reddycomb that the vein averaged 2–3 ft (0.6–0.9 m) wide, increasing in places to 10 ft (3 m); and that one mass of sphalerite 2 ft (0.6 m) across was found when the bottom level was reopened during the 1914–18 war by Hedworth Barium Co. (Carruthers, 1923, pp.24, 25). Presumably, therefore, some zinc ore remains in these veins.

    Winterhush and East Cowgreen veins are believed to cross Willyhole Sike respectively 2000 and 1900 ft (610 and 579 m) WSW of its confluence with Harwood Beck [NY 8080 3328] and [NY 8083 3329] and to unite a short distance N of the sike. A level [NY 8082 3327] driven southwards on the former vein from the sike shows white baryte on the dump. At the foot of Willyhole Sike, a level [NY 8123 3347] driven on a weak vein which may represent the continuation of Willyhole Vein E of the Teesdale Vein shows some amber fluorite, in metamorphosed limestone and baked shale which indicate the proximity of the Whin Sill.

    Bands Vein—Barytes, iron ore

    NY 83 SW; Durham 30 SE

    Bands Mine (disused) lies on the east side of the Alston- Middleton road, 2 miles (3.2 km) NW of Langdon Beck Hotel. Two NE veins, 50 ft (15 m) apart, cross the outcrop of the Jew and Tynebottom limestones, and form a fault trough with throws of 6 ft (1.8 m). E of the outcrop of the Single Post Limestone, the southern vein changes course to N80°E. Iron ore has been obtained from the Jew and Tynebottom limestones, each about 30 ft (9 m) thick. The level to the Jew Limestone workings [NY 8294 3315] showed a face 12 ft (3.7 m) wide and 6 ft (1.8 m) high with what appeared to be good limonitic ore. An analysis (quoted below) of a channel sample shows, however, that it is exceptionally high in silica, which exists in chalcedonic form. A small dump [NY 8300 3320] of ore from the Tynebottom Limestone is of somewhat better quality, but neither sample appears to be of workable grade. Ore of better quality was formerly obtained here, if two analyses of Bands ore contained in notes in Geological Survey records by the late Mr C T Clough are representative, for they show 43.3 per cent ferric oxide, 14.2 Insolubles (Table 63).

    In the Single Post Limestone, flats have been worked for barytes [NY 8315 3329], producing, between 1915 and 1920, 1324 tons of this mineral. The width of the flats is said to have been at least 20 ft (6 m); the limestone, the full thickness of which appears to have been replaced since it is recorded that the deposits were worked between a shale roof and a sandstone floor (Wilson, Eastwood et al., 1922, p.21) is 4–6 ft (1.2–1.8 m) thick. It is not known how far the flats were followed along the strike of the veins, though the small output suggests that the workings were not extensive. Nor is it known whether the deposits had been exhausted before the mine was abandoned. Limonite and traces of fluorite are associated with the baryte.

    An opencut [NY 8332 3334] on the southern vein in the Scar Limestone shows 2–3 ft (0.6–0.9 m) of baryte.

    Castenhole Vein

    NY 83 SW; Durham 30 SE. Direction N70°E, displacement 24 ft (7.3 m) SE

    A small group of small veins have been worked on the E side of the Alston-Middleton road, 0.5 mile (0.8 km) S of Bands Mine. The Main Castenhole Vein is accompanied by a small parallel vein 70 ft (21 m) to the S, while on the N another small vein trending N65°E and throwing 5 ft (1.5 m) SE cuts through the Single Post Limestone. The main vein has been tried from levels beneath the Jew Limestone on the downthrow side [NY 8337 3264] and above the Tynebottom Limestone [NY 8373 3274]; Several shafts one of them at least 60 ft (18 m) deep, have been sunk into the Tynebottom Limestone around [NY 8365 3275]. Amber fluorite, baryte and small quanitites of galena are present on the dumps from all three horizons tried, associated with limonitised limestone. W of the road a crosscut adit appears to have been driven N from Slack Sike [NY 8308 3246] to test the vein in the sandstone under the Smiddy Limestone, but no mineralisation appears to have been found. There is no record of any production.

    Burtreeford Disturbance

    NY 83 SW; Durham 30 SE

    At the head of Drygill Sike, 3600 ft (1.1 km) NW of the Langdon Beck Hotel, a limestone, believed to be the Tynebottom, within the Burtreeford Disturbance, is replaced by limonite with nests of piro: baryte [NY 8459 3208]. The bed dips 65°ENE.

    Langdon Head Vein, Arthur Lee's Vein and Botany Bay Vein

    The three veins listed are the strongest members of a complex of E–W and ENE veins worked at the Langdon Head Mines (disused), 2.5 miles (4 km) N of Langdon Beck Hotel. The workings range in horizon from the Firestone down to the Great Limestone. They are situated immediately E of the Burtreeford Disturbance, and there is a sharp westward rise in the beds towards this fold. N of Langdon Head Vein, three small unnamed veins have been reached from adits [NY 8463 3485] and [NY 8464 3487] running northwards from the stream, probably in the Coal Sills. Amber fluorite, limonite and galena occur on the dumps; an analysis of the limonite is quoted below. Langdon Head Vein also carried amber fluorite and limonite. The western stretch of Botany Bay Vein appears to have been mineralised in the Great Limestone with white baryte, but east of the beck siderite becomes abundant both on this and the Arthur Lee's Vein. The general character of the material on many of the dumps recalls the partly oxidised iron ores of the Carricks Mine (p.193), which lies 1.5 miles (2.4 km) to the N and it is likely that ironstone bodies of similar origin exist here. The deposits are, however remotely situated, the nearest road being 0.75 mile (1.2 km) distant; conditions cannot therefore be regarded as favourable for ironstone working. The Langdon Head mines were drained by a level beneath the Great Limestone 3200 ft (975 m) long, running southwards from Langdon Head Vein to the vicinity of West Beck at about 1520 ft (463 m) above OD. This appears to have been driven from the shafts which mark its course; there is no dump at the level mouth which cannot be located precisely.

    West End Vein–Moss Vein group

    The Langdon Mines (disused), 1.5 miles (2.4 km) N of Langdon Beck Hotel, worked the group of veins listed above, together with numerous smaller veins. West End Vein, the northernmost strong vein of the complex, appears to have carried baryte as its chief constituent; small quantities of this mineral are said to have been worked from opencuts and short levels [NY 8501 3399] in the Great Limestone. North Slit, Coulthard's and Moss veins were worked from Langdon Shop Level [NY 8504 3355], driven in shale and sandstone between the Great and Four Fathom limestones to Coulthard's Vein, and connected by a crosscut to the point where West End and North Slit veins intersect. Coulthard's Vein joins Moss Vein to the E. North Slit, Moss and Coulthard's veins carried galena in a matrix of purple and amber fluorite. Iron carbonates probably replaced the wall rocks where these were limestone, since the outcrop of Moss Vein in the Great Limestone is accompanied by a development of limonite (analysis (Table 64). Moss Vein gives off a number of E-W branches; named from NE to SW: Roddam's, Jacob's, Craig's, Teward's Lead, Race's Lead and Sun Moss veins. Mineralisation appears to have been principally in the Great Limestone and Coal Sills, perhaps reaching up to the Firestone in places. No sections of the workings remain. An adit level [NY 8506 3327] shown on the 6-inch plan preserved in the Roby Estate records starts beneath the Four Fathom Limestone and runs to a shaft on Coulthard's Vein [NY 8559 3382] 1950 ft (594 m) ENE of Langdon Shop. The portal of this adit cannot be located on the ground, and if it were in fact driven, it is unlikely that it proved ore-bearing ground. S of Moss Vein, baryte again makes its appearance on Sun Moss Vein and on two weak NE veins still farther S.

    Some of the Langdon veins presumably represent the continuation of those of the Greenlaws Mine of Weardale; the appearance of the Langdon complex suggests the splitting-up and fingering-out along strike of a powerful vein. About 1.25 miles (2 km) of unexplored virgin ground lie between the foreheads of the Langdon and Greenlaws workings.

    The Langdon Mines produced 242 tons of lead concentrates between 1853 and 1875, yielding 5.5 oz silver per ton of lead. In 1949–50 Anglo-Austral Mines Ltd investigated West Beck by trenching, and examined Langdon Shop Level, but did not proceed to reopen the mine.

    Harthopeburn Vein

    NY 83 SE; Durham 30 SE

    The vein trends N55°E, along the north-west side of Harthope Burn. Levels driven northwards from the burn beneath [NY 8591 3262] and above the Great Limestone [NY 8615 3278] have tested the vein, which throws 8 ft (2.4 m) NW, but the only veinstuff to be seen on the heaps is a mixture of quartz and marcasite.

    Red Gill Sike Vein

    NY 83 SE; Durham 30 SE

    Levels in the Tuft [NY 8612 3692] and at the top of the Great Limestone [NY 8626 3203] have proved a vein at the head of the stream named Red Gill Sike on the six-inch County Sheet, 0.5 mile (0.8 km) NE of the Langdon Beck Hotel, trending N45°E and downthrowing 10 ft (3 m) NW. Coarse iron-stained baryte occurs on the dumps. This stream is unnamed on the modern National Grid sheet: the name Red Gill Sike is applied to a separate stream a little way to the north.

    High Hurth Vein—Barytes

    NY 83 SE; Durham 30 SE, 31 SW Direction N60°E

    Trials at High Hurth Edge, 0.75–1 mile (1.2–1.6 km) E of the Lang-don Beck Hotel exposed the vein in an opencast in the bottom part of the Great Limestone [NY 8645 3132], where it was 9 ft (2.7 m) wide, consisting mainly of limestone with strings of baryte passing through it. On the dump of an adit [NY 8647 3128] driven at the base of the limestone, colourless baryte is present. Replacement deposits, said to have been explored during the 1914–18 war (Wilson, Eastwood et al., 1922, p.22) were possibly reached by this level. A trial [NY 8623 3116] in or below the Nattrass Gill Hazle was unsuccessful. Above the Great limestone three flank levels [NY 8676 3146], [NY 8699 3140] and [NY 8706 3153] reached the vein below the Little Limestone; only traces of baryte occur on the dumps. Shafts sunk through shaly measures into the Great Limestone proved baryte, with some limonite and galena.

    It is possible that a level [NY 8823 3247] driven from High Flood Beck, one of the headwaters of Ettersgill, starting high up in the Pendleian a mile (1.6 km) N of High Beck Head Farm, and running 1350 ft (411 m) N15°W, was designed to test the north-eastward continuation of High Hurth Vein. The plan records a northward dip of the measures at 2°. A number of strings were cut, but all were filled with shale gouge.

    West Binks Edge Vein—Barytes

    NY 83 SE; Durham 31 SW

    At West Binks Edge, 1.25 miles (2 km) NNW of Dirt Pit Farm, east of the Ettersgill valley, an adit [NY 8873 3090], driven NNE in the lower part of the Great Limestone has revealed small replacement deposits containing colourless baryte, associated with a fault (here called West Binks Edge Vein) trending NW and downthrowing a few feet SW. No work has been done here since the First World War. To the west the vein strikes a fault, which appears to have determined the course of the Ettersgill Beck for 1200 ft (366 m) NE from High Beck Head Farm against which the Great Limestone and Tuft dip 35° SE. A level driven along the fault from Gill Shop [NY 8845 3120] revealed a little galena, purple fluorite and baryte.

    Westerhead Vein–Flask Vein group

    The outcrop of the beds between the base of the Great Limestone and the Firestone on Pike Law, between Wester Beck and Flushiemere Beck, is traversed by a remarkable complex of veins, among which the strongest are those listed above. The veins are accompanied by minor folding both parallel and oblique to their courses, inducing dips up to 30° in the beds. Throughout the complex, which covers approximately three-quarters of a square mile of ground, the dominant minerals are purple fluorite, galena, quartz and aragonite. Baryte has been noted only in the highest workings on Westerhead Vein, probably at the horizon of the Firestone. Pike Law Old Vein, Leonard's and the Flask veins were wrought in large opencuts in the Great Limestone around [NY 903 314] the workings extending in places into the overlying Coal Sills. Few plans remain of the underground workings, but numerous shafts and levels suggest that they were probably extensive. Small veins lying north of Westerhead Vein were reached by means of levels driven on top of the Great Limestone from Wester Beck [NY 8957 3177] and [NY 8961 3179]. From the E bank of this beck an adit [NY 8970 3157] ran 1250 ft (381 m) NE in the Tuft to Tarn Streak Vein. Farther south New Streak Vein was drained by an adit [NY 8978 3139] at the same horizon. The main working level on the Broadly Hill veins started from Leonard's Hush [NY 9062 3162] on the E side of Pike Law, and reached the North Vein at 400 ft (122 m) from the portal. The workings are no longer accessible. The evidence points strongly to the fact that all the oreshoots pinched at the base of the Great Limestone. A start was made with a level from Wester Beck [NY 9029 3078] in the Four Fathom Limestone to drain the complex to this horizon, but is not known to have reached the veins, and unaltered limestone makes up the whole of the dump. The oreshoots had evidently been almost completely exhausted before the middle of last century, for the production of lead concentrates from 1852 to 1891, when all work ceased, was only 1725 tons, yielding 6 oz silver per ton of lead. It is likely that since so many of the oreshoots came to outcrop, work here commenced in ancient times. Some thousands of tons of fluorspar of good quality lie scattered about, but mainly in small heaps. Tailings near the mouth of Broadley Hill Level contain 44.8 per cent calcium fluoride, 23.2 silica, 2 lead. The veins appear to have died out to the W of Wester Beck; to the E most of them terminate against the Flushiemere Great Vein, described below.

    The exploration in depth of this complex of veins concentrated into a restricted area appears to offer some attractions, which would be enhanced if the position of the feeder, through which the mineralising solutions gained access to the Great Limestone, were known.

    Flushiemere Great Vein–Ryland No. 2 Vein group

    The Flushiemere Great Vein represents the southward continuation of the Swinhope fault-belt of Weardale, already mentioned in connection with Carricks, Greenlaws and Swinhopehead mines (pp.193, 196 and 198). When last seen in Weardale it is mineralised with fluorite and galena. On the NE side of the Pike Law complex, it carries baryte and limonite, in striking contrast to the contents of nearly all the Pike Law veins. Starting W of Flushiemere Beck, the Broadley Hill Low Level [NY 9088 3168] follows the eastern side of the fault-belt north-westwards; in 1941 the level was accessible for 1100 ft (335 m) exposing limonitised Great Limestone along the hangingwall side of the fault. No other mineral is present here. SE east of the beck, a line of old shafts marks the course of the same fault across the fell. The presence of limestone, replaced by baryte and limonite on the dumps from these shafts indicates that they reached the Great Limestone. Barytes of good quality has been collected from the heaps from time to time, and sold. One of these shafts was being reopened in 1945–46. Still farther S the fault-belt is penetrated by the workings of Flushiemere Mine (disused). The main level here was driven by the London Lead Co. early in the nineteenth century. Its purpose was to explore the ground east of the Great Vein, presumably with the hope that this would reveal continuations of the Pike Law lead veins, but only 14 tons of lead concentrates were obtained between 1853 and 1870. The portal of the level is at Flushiemere House [NY 9095 3104], 2.25 miles (3.6 km) N of Newbiggin. The level runs straight for 1475 ft (450 m) N62°E and is arched through superficial deposits and shale for the first 200 ft (61 m). At the end of the arching the top of the Four Fathom Limestone is seen rising from the level sole, and reaches the level roof at 460 ft (140 m) from the portal. The base of this limestone goes into the roof at 525 ft (160 m) from the portal. After passing through not more than 20 ft (6.1 m) of Nattrass Gill Hazle, the level continues in argillaceous beds until it enters, at about 1150 ft (351 m) from the portal, the fault zone of the Great Vein. Much of this is concealed behind arching, but it is clear that the faulting is accompanied by an anticline of not less than 50 ft (15 m) amplitude. At 1350 ft (411 m) from the portal, the hangingwall fracture (called by the London Lead Co. "A" Vein) is cut and the level enters the Great Limestone. At 125 ft (38 m) farther in, where a subsidiary fold carries the base of the limestone above the level roof, the level branches. One branch runs S60°E, meeting at 100 ft (30 m) from the turn, "B" Vein. At this point Flushiemere No. 2 Shaft [NY 9138 3126] communicates with the level; it is 252 ft (77 m) deep, starting above the Firestone, and ending near or at the base of the Great Limestone. A section of this shaft is given in Borings and Sinkings (North of England Institute of Mining Engineers,) Supplementary Volume, 1910, No. 2843, p.365. The S branch and the "B" Vein workings are inaccessible, and nothing is known of the contents of this vein. The plan preserved at the North of England Mining Engineers, Newcastle, shows that the S branch continues a further 900 ft (274 m) SE, then turns and runs south-westwards, presumably again reaching the Great Vein. A note records the presence of a flat of ore south of "B" Vein. The N branch of the Flushiemere Level was reopened completely by the late owner, Mr F J Ryland. It runs N34°W for 840 ft (256 m) then continues at N27°W for 2925 ft (892 m). At 50 ft (15 m) N of the turn, Fullock's Rise was reopened; this revealed the base of the Great Limestone 15.5 ft (4.7 m) above the main level sole. At 39 ft (11.8 m) above the sole a drift has been driven through limonitised, ankeritised and dolomitised limestone for 185 ft (56.4 m) WSW. In the vicinity of the rise, old workings reveal limonitic ironstone at least 40 ft (12 m) wide. An analysis of a representative sample is quoted in (Table 65).

    At 132 ft (40 m) WSW of the rise, the new drift cut a fissure hading W, containing clay, altered limestone and small quantities of galena and calcite. The highly altered limestone appeared to dip W at angles up to 65°. The drift does not, however, appear to have reached the main fault of the Great Vein.

    At 450 ft (137 m) NNW of the turn, the N branch of the Flushiemere Level cuts "C" Vein in the shale beneath the Tuft. A branch follows the vein eastwards for 1675 ft (511 m); rises communicate with workings in the Great Limestone where the deposits consist of replacements up to about 20 ft (6.1 m) wide, containing coarse white baryte in a matrix of slightly limonitised limestone. Traces of galena and amber fluorite are present. Between 1889 and 1920 these deposits were worked by Mr Lee, the associated limestone being removed by hand jigging; a total of 2400 tons of barytes was produced. Shortly before the Second World War the mine was reopened with the assistance of the North-East Development Board (Poole, 1937 p.3) and work was again started on "C" Vein. Reserves of barytes remain here, but there are mining obstacles to removing them-the dangerous condition of the ground being the chief.

    An attempt was made in 1941 to reach the Great Vein from a rise on "C" Vein communicating directly with the main level, by means of a westward drive. The ground proved very heavy, consisting of altered limestone masses and clay, and the attempt was abandoned.

    At 300 ft (91 m) and 1150 ft (351 m) NNW of the "C" Vein branch level the top and base of the Quarry Hazle appear in the level sole. Thence to the NNW forehead, the level is in the shale between the Quarry Hazle and the Four Fathom Limestone, with 2300 ft (701 m) NNW of "C" Vein, a NE string with a few inches of calcite. A rise was started on this, but appears to have been stopped before reaching the Great Limestone. At 150 ft (46 m) NNW of this rise, another string was cut. This one was followed up to the Great Limestone, where it proved to be accompanied by a belt of flats with baryte, similar to those along "C"Vein. This belt is now called Ryland No. 1 Vein; it may be regarded as the continuation of the Broadly Hill North Vein of Pike Law. The deposits occupy the middle 20–25 ft (6.1–7.6 m) of the Great Limestone; their maximum width is 20 ft (6.1 m). The total length developed amounted to about 400 ft (122 m). Access from the surface is obtained by means of the old Bropery Gill Level [NY 9088 3200], which runs north-eastwards along the same string or vein in the shale above the Great Limestone. At about 300 ft (91 m) ENE of the rise from Flushiemere Level, a branch from Ryland No. 1 Vein, known as Ryland No. 2 Vein, with similar deposits, runs westward; ore yielding on average 30–40 per cent barium sulphate has been obtained from these deposits. Good-quality barytes was produced from the dressing of the ore in a gravity mill situated at the mouth of Flushiemere Level; the total output from the operations is said to have been of the order of 3000 tons of finished product. Ryland No. 2 Vein is represented in the shale in the main level by numerous small strings of calcite. Similar strings occur farther N, but a crosscut near the base of the Great Limestone from Ryland No. 2 Vein, which is only partly accessible, does not appear to have revealed other deposits at this horizon. Small quantities of witherite have been noted in the Great Limestone near the junction of Nos. 1 and 2 veins. The mine closed in 1946.

    From Blea Gill, 3000 ft (914 m) SE of the mouth of Flushiemere Level, the London Lead Co. drove an exploratory level [NY 9157 3036] 1400 ft (427 m) N5°E in the Tuft and Great Limestone, to reach the Great Vein in the vicinity of its intersection with a small vein supposed to have been worked in Bales Hush [NY 913 306]. At 1260 ft (384 m) from the portal small flats trending NNW were cut in the Great Limestone; these carried purple fluorite with small amounts of galena, but very little work was done on them. A SE branch from this level reached a point 1400 ft (427 m) SE of the portal, but failed to fmd anything of value in the continuation of a feeble vein formerly worked at Bleak Ley Green Hush [NY 917 301].

    Ettersgill deposits—Zinc, iron ore

    NY 82 NE° ; Durham 39 NW

    From 300 to 460 ft (91 to 140 m) NNW of the road bridge at Dirt Pit Farm [NY 8912 2902] 1 mile (1.6 km) WNW of Bow Lees, the bed of Ettersgill Beck exposes a deposit the main constituents of which are siderite and sphalerite. Between this exposure and the farm, mapping reveals the presence of an E–W fault, downthrowing 23 ft (7 m) S. This fault is considered to be the westward continuation of the Lodgesike- Manorgill Vein of the Coldberry mines, described below. Trials by boring at Ettersgill have failed to reveal any mineralisation in the fault itself. The zinc-iron deposit appears to be related to a minor fault trending N55°E and down NW exposed on the east bank of the beck, 330 ft (101 m) NNW of the bridge [NY 8904 2909]. About 1906 a level [NY 8905 2910] was driven north-eastwards along the fault for a distance of 130 ft (40 m) revealing on the foot-wall side material similar to that exposed in the stream. The deposit is a replacement of the Single Post Limestone. Boring has shown that when unreplaced, the limestone is 4–6 ft (1.2–1.8 m) thick. Replacement has led to a reduction in thickness, causing brecciation of the metamorphosed sandy shale which overlies the limestone to a distance of up to 5 ft (1.5 m) above the top of the limestone, a feature in which these deposits are almost unique in the field. Starting at 110 ft (33.5 m) from the level mouth, a crosscut N of 400 ft (122 m) passes through a number of small strings in beds which range from the Cockle Shell Limestone adjacent to the fault to the Single Post Limestone, brought into the crosscut by the gentle northward rise of the beds. This exploration is said to have been carried out by the Vieille Montagne Zinc Co. but samples of the ore tested at their Nenthead plant showed that it was impossible by gravity methods to effect a satisfactory separation of the sphalerite and siderite. In (Table 66) below an analysis of a sample representing the dumps from the 1906 exploration is given.

    The deposit was considered sufficiently promising to merit short-term exploration as a wartime emergency measure. This was undertaken in 1941–42 under the Non-ferrous Minerals Development Control (Ministry of Supply) by Non-ferrous Minerals Development Ltd. A programme of 20 diamond borings carried out by units of the Royal Canadian Engineers showed that zinc mineralisation persists for at least 1050 ft (320 m) in the Single Post Limestone along the general direction of the fault north-eastwards from Ettersgill Beck. Mineralisation proved to be present at maximum distances of 70 ft (21 m) NW and 170 ft (52 m) SE of the fault in this area, to a thickness of from 1.5 to 5 ft (0.45 to 1.5 m) averaging 2.9 ft (0.88 m). Zinc-contents varied from 4.7 to 29.0 per cent.

    Underground exploration was carried out by means of an incline, starting close to Dirt Pit Level, driven so as to reach the Single Post horizon on the NW (downthrow) side of the fault. The deposit was systematically explored by crosscuts at 100 ft (30 m) intervals from a main drift a the foot of the incline, which together reached a total length of 760 ft (232 m) when work was suspended; the forehead stands beneath the E bank of Smithy Sike. Underground work confirmed the accuracy of the information obtained from boring; the overall zinc-content of the deposit was proved by sampling (mainly carried out by Mr J D Willson) to be 10 per cent. It was found, however, that the area was less than would have been anticipated from the boring results had the deposit been uniform; it may be noted that the poor areas coincided with ground in which the Single Post Limestone is directly overlain by sandstone. The breccia of shale overlying the mineralised limestone was found to vary between 1 and 5 ft (0 and 1.5 m) thick, in a single instance reaching 7.5 ft (2.3 m). Patchy zinc values occurred in the breccia. Gentle folding of the beds was proved on both sides of the fault.

    W of Ettersgill Beck a programme of 16 borings showed that both the thickness of the deposit and its zinc-content were less than to the E and this area was not considered worth exploring underground. Borings here were undertaken as far W as the farm-road from Dirt Pit to New House; the farthest boring, 1150 ft (351 m) W of Dirt Pit level mouth [NY 8872 2912], proved boulder clay resting on beds below the Single Post Limestone.

    Ettersgill Beck is crossed by a fault, believed to trend NW at a point 450 ft (137 m) NE of New House, [NY 8866 2940] bringing Whin Sill on the W side against the Single Post Limestone. Sideritesphalerite mineralisation is present here. Between this point and Dirt Pit Level at least three small ENE or E–W fractures cut through the Cockle Shell Limestone and associated beds, but borings showed low zinc-values in the Single Post Limestone only.

    Near the exposure of the Lodgesike Fault in Smithy Sike [NY 8927 2905] a boring passed through the Whin Sill into the Tynebottom Limestone, which proved to be unmineralised (for log see p.49). On the other hand, beds above the Single Post Limestone in Smithy Sike, particularly the Scar Limestone, show indications of mineralisation, near the course of the main fault of the zinc area. Limonitic iron ore has been worked here in the past from levels on both sides of the stream, [NY 8924 2914] and [NY 8925 2922] 2126 tons being obtained in 1882–1884. Blocks of ironstone remaining show traces of sphalerite.

    Summing up the results of wartime exploration at Ettersgill, it may be stated that between Ettersgill Beck and Smithy Sike an oreshoot containing 10 per cent zinc was brought to a stage where exploitation would have been possible; the supply situation did not, however, make it necessary to mine the deposit, and it remains in place. Experiments undertaken in connection with the work by Minerals Separation Ltd, and by Mr L A Wood, showed that a high-grade zinc concentrate can be obtained readily from the ore by means of flotation.

    Geologically the deposit is remarkable for the absence of galena, fluorite and barium minerals. Siderite, with a little calcite, pyrite and quartz were the sole matrix minerals. The stratigraphical results of the borings are summed up in section 15, (Figure 3), p.15.

    Most of them were carried down to the top of the Whin Sill, revealing that this intrusion varies in position in the small area explored from 10–49 ft (3–15 m) below the Single Post Limestone. The metamorphic effect of the Whin Sill is apparent up to the Cockle Shell Limestone, but this is seldom completely marmorised, as is the case with the Single Post Limestone throughout the area.

    Wynch Bridge deposits—Zinc ore, iron ore

    NY 92 NW; Durham 39 NW, Yorkshire 2 SW

    The Single Post Limestone is exposed along the banks of the Tees between Wynch Bridge [NY 9040 2791] and Scoberry Bridge [NY 9104 2736] 1–1.5 miles (1.6–2.4 km) SE of Dirt Pit Farm. Here small siderite-sphalerite deposits closely resembling those of Ettersgill are found, suggesting that this may represent a type with more examples in this part of Teesdale than have been revealed by erosion. The feeding fissures are exposed in the Whin Sill as they cross the bed of the river; the alteration of the dolerite adjacent to them here has been studied by Wager (1929). The westernmost deposit has been tested by an adit [NY 9053 2767] on the southern side of the river, 900 ft (274 m) SE of Wynch Bridge. The feeding fissure runs nearly E–W; the deposit varies from 2 to 4 ft thick (0.6 to 1.2 m) thick. The composition of the dump from early explorations on this deposit is given above (Table 66). The beds rise south-westwards, and at about 400 ft (122 m) SW of the adit mouth, boring proved that the mineralised Single Post Limestone crops out under boulder clay. In spite of the good zinc-values in this oreshoot, it seems clear that it is too limited in size to be of any economic interest in view of its not too accessible situation. Eight more fissures lie between this deposit and Scoberry Bridge, each of them accompanied by replacements in the Single Post Limestone. The best exposed lies 350 ft (107 m) W of Scoberry Bridge, [NY 9094 2739] where the width of siderite-sphalerite ore is 17 ft (5.2 m). Four of the deposits have been tried by means of levels [NY 9072 2754], [NY 9075 2750], [NY 9081 2745] and [NY 9085 2742] on the S bank, and one by means of an opencut and level [NY 9084 2754] on the N bank of the Tees, but in view of the limited extent of the ground to the S of the river, the small width of the replacements, and the uncertainty of the position beneath the alluvium of Bow Lee Beck to the N, this area offers little inducement for further work.

    Hell Cleugh Veins

    NY 92 NW; Durham 39 NW

    At the N end of Hell Cleugh, 1000 ft (305 m) W of Moor House, two veins running respectively E–W and ENE have been tried by short levels [NY 9100 2973] and [NY 9100 2965] in the High Brig or Six Fathom Hazle. Each contain 1–2 ft (0.3–0.6 m) of limonite in the sandstone.

    Lodgesike–Manorgill Vein–Manorgill North Vein

    The Lodgesike–Manorgill Vein is the main vein of the important complex lying N of Middleton-in-Teesdale, from which the bulk of lead production of the dale has been derived (Figure 40). As noted above, the vein is considered to be represented in Ettersgill Beck by the E–W fault throwing 23 ft (7 m) S, exposed in Smithy Sike immediately north of Dirt Pit Farm. In Bow Lee Beck, 1 mile (1.6 km)

    The silica in this sample is due in part to inclusions of sandstone in the ore. The effect of the fault is to bring the top of the Scar Limestone on the footwall 4 ft (1.2 m) above the top of the Low Brig or Slaty Hazle on the hangingwall, indicating a displacement of 46 ft (14 m) S. The beds dip N on the N side of the fault.

    E of Bow Lee Beck the fault is concealed under boulder clay for 0.75 mile (1.2 km). At Red Grooves Mine (disused) it reappears, accompanied by structural conditions of greater complexity. The direct line of the fault would bring it into Red Groves Hush [NY 927 289] at the head of Laddie Gill, which exposes an E–W anticline in the Great Limestone; in a level [NY 9239 2911] driven north-eastwards to Hope Slit Vein, a small string worked in Hunt's Hush, [NY 924 292] the beds dip northwards; in the main Red Grooves Level at 1347 ft (411 m) above OD [NY 9237 2905] driven south-eastwards, the beds dip S. The main vein, which may be regarded as the en-échelon rather than the direct continuation of the fault exposed in Bow Lee Beck, here lies on the S side of the anticline. It has been worked opencast in Coldberry Gutter [NY 9285 2895] to  [NY 9355 2900] which, cutting through the summit of the divide between the Bow Lee and Hudeshope valleys, is one of the most spectacular of the Pennine hushes. On the north side of the vein, beds from the Firestone up to the Low Grit Sill are exposed, while the S side reveals beds up to the supposed equivalent of the Grindstone Sill including a thin limestone which may represent the Upper Felltop. The Gutter also reveals the continuation of the Cleveland dyke adjacent to the vein (see p.52). It is not known whether a substantial quantity of lead ore was obtained from the opencut, but its great size suggests that there must have been some return for the work. Red Grooves Level, [NY 9237 2905], starting at the head of Laddie Gill, reaches the main vein 750 ft (229 m) SE of the portal, in shale above the Great Limestone. The workings from this level continue 2750 ft (838 m) E beneath the gutter; they include a sump sunk to 1220 ft (372 m) above OD on the downthrow (south) side of the main vein; exploration of the limestone was carried out, apparently without much success. The principal workings appear to have been above the level, in the Firestone and Low Grit Sill. Purple fluorite, siderite, ankerite and quartz occur on the dumps. The mine formed part of the London Lead Co.'s Coldberry group of mines; from 1852 to 1886 it yielded 10 110 tons of lead concentrates. The whole group was explored by English Lead Mines Exploration Ltd in 1938–1939Acknowledgement is made of the valuable help received from Mr J D Willson and the late Dr G A Schnellrnann, geologists to this company, whose structural study and reports were placed at our disposal..

    At Coldberry Mine (disused), situated at the E end of the Gutter, Coldberry North Level [NY 9399 2913] at 1295 ft (395 m) above OD has explored the Lodgesike-Manorgill Vein in the Great Limestone, but with little success. It is represented by a broad shatter-belt, not mineralised but containing clay. A crosscut which runs southwards, starting 275 ft (84 m) from the portal of this level shows that the crest of the anticline lies about 100 ft (30 m) S of the vein here; it appears therefore that between Red Grooves and Coldberry North the vein cuts obliquely across the axis of the fold. A lower level [NY 9425 2921] starting 900 ft (274 m) E by N of the portal of North Level was driven south-westwards through the fold and vein in shale and sandstone below the Great Limestone, without revealing mineralisation. The fault is exposed in Longmire's Gutter [NY 9500 2932], 1500 ft (457 m) NNE of the point where this joins Hudeshope Beck; here it brings Great Limestone on the footwall into contact with shale and sandstone, possibly near the horizon of the Little Limestone; again there is no mineralisation. The great oreshoot for which this vein is famous begins 1750 ft (533 m) ENE of this point, and extends a further 3200 ft (975 m) ENE; its maximum continuous vertical extent is 325 ft (99 m) the average over 200 ft (61 m). The stratigraphical range of the beds on the footwall of the oreshoot is from the Low Grit Sill up to the Grindstone; complete stratigraphical data are lacking but it is suggested that the shoot owes its considerable vertical extent to the incoming of the thick-sandstones in the Grit Sills (p.37). From Lodgesike Mine (disused), on the E side of Hudeshope opposite Coldberry, the principal working levels were Lodgsike Low Level [NY 9529 293 ] at 1381 ft (421 m) above OD and Lodgesike High Level [NY 9550 2947] at 1520 ft (463 m) above OD. At 660 ft (201 m) from the portal of the former the Knuckton Shell Bed is seen on the footwall opposite one of the sandstones of the Grit Sills on the hangingwall. The base of the Low Grit Sill, and the bottom of the oreshoot, reaches this level about 1800 ft (167 m) ENE of the portal; the level continues to the Great Eggleshope valley, where it comes to surface as the Manorgill Middle Level [NY 9673 3015] at 1400 ft (427 m) above OD. High Level is also driven through to Manorgill Mine. From Great Eggleshope, Manorgill Low Level, [NY 9754 3011] at 1200–1230 ft (366–379 m) above OD, gives access to the vein at horizons varying from the Firestone at the E end to the Coal Sills farther W. It is probable that the Firestone, present as a coarse grit in Great Eggleshope, dies out westwards; the Low Level found no ore at this horizon beneath the large oreshoot, nor were any of the lower beds productive. From Hudeshope, a crosscut from Marlbeck Mine (described below) gave access to a level 1200 ft (366 m) long at 1067 ft (325 m) above OD with the Great Limestone on the hangingwall of the vein. A rise at the E end of this level connected it with Manorgill Low Level, exposing the Great Limestone on the footwall; the throw of the vein is recorded on the plan preserved at Raby Castle, Staindrop as 105 ft (32 m) S. No mineralisation was found in these workings and this is not surprising since the effect of the faulting is to bring shale into contact with the Great Limestone on both foot-and hangingwalls. A sump to 240 ft (73 m) beneath Manorgill Low Level near the eastern end of the oreshoot is believed to have reached the Great Limestone on the footwall of the vein; here, too the vein was unproductive.

    About 1200 ft (366 m) ENE of the end of the LodgesikeManorgill oreshoot a branch known as Manorgill North Vein leaves the fault in a westward direction. Ore-bearing ground, commencing 400 ft (122 m) W of the split, extended along this vein in the Grit Sills for 2600 ft (792 m) but it was more patchy than on the main vein. A small oreshoot was worked in the Firestone, but trials of lower beds down to and including the Great Limestone from two sumps met with no success. W of the forehead a stretch of 2500 ft (762 m) along this vein is believed to be virgin. From Hudeshope the vein was reached by the Pikestone Brow crosscut adit, [NY 9481 2948] starting 450 ft (137 m) NE of Pikestone Brow Farm, driven in the Coal Sills at 1296 ft (395 m) above OD, and by Hudeshope Level [NY 9421 2978] starting 2100 ft (640 m) NW of the farm, driven in shale beneath the Great Limestone at 1188 ft (362 m) above OD. These workings gave access to an oreshoot in the Great Limestone 1060 ft (323 m) long by 60 ft (18 m) high, commencing 1160 ft (354 m) E of Hudeshope. Above this, oreshoots in the Coal Sills 1200 ft (366 m) long by 30–40 ft (9–12 m) high, and in the "Pattinson Sill", 450 ft (137 m) by 20 ft (6 m) were worked. Levels at all three horizons were extended eastward beyond the ends of the oreshoots without success.

    The tailings-heaps from all the levels mentioned show similar minerals; the matrix of the veins consisted of quartz and purple fluorite; sphalerite and pyrite were present in very minor amounts. The Hudeshope Level dumps show some ankerite, presumably from the Great Limestone. The Lodgesike-Manorgill and Manorgill North oreshoots were largely exhausted before 1850, but it may be assumed that they contributed the bulk of the London Lead Co.'s production of 122 420 tons of concentrates between 1816 and 1851. The combined production, 1852–1902, was only 2650 tons. It is considered that all reasonable possibilities of development at the Lodgsike and Manorgill mines have been exhausted, with the possible exception of the virgin stretch on Manorgill North Vein.

    Beadles Vein–Ravelin–Hunt's Coldberry Vein group

    Between Red Grooves Mine and Stable Edge, the outcrop of the Great Limestone E of Newbiggin Beck is traversed by several weak E–W or NE veins, including (from N to S) Hungry, Harrison's, Wearmouth's, Mill House and Stable Green veins. These contain small quantities of fluorite, baryte and calcite, but only traces of galena. The courses of most of them are crossed by the southward continuation of Red Grooves Level, but there is no record that any of them were found there. High Stable Edge Vein, tried by levels above and below the Great Limestone at High Ravelin House [NY 9227 2788] and Mount Pleasant [NY 9203 2773] respectively, was also a feeble vein, and nothing workable was found where Red Grooves Level ended against it. Farther NE, however, it continues as the productive Hardberry Hill Vein. Beadle's Vein may be regarded as a northern branch of it, while Hardberry Hill Vein possibly continues to the E as Richardson's Vein.

    This group of veins was worked at Coldberry Mine (abandoned 1960) the levels to which lie SE of Coldberry Gutter, on the W side of Hudeshope. Coldberry North Level [NY 9399 2913] at 1295 ft (395 m) above OD, gives access to Hardberry Hill Vein by way of a crosscut running S by W, starting 1250 ft (381 m) W of the portal and connected with a level commanding horizons varying from the Coal Sills to the Firestone on the vein. The Slate Sill Level [NY 9375 2891] at 1510 ft (460 m) above OD, also enters Hardberry Hill Vein, revealing at about 1275 ft (389 m) from the portal, a NW crosscourse which throws 40 ft (12 m) SW. The oreshoot on Hard-berry Hill Vein commences at the crosscourse, and extends 1700 ft (518 m) SW; its maximum height above Coldberry North Level is 310 ft (94 m). The wall rocks range from the Grit Sills down to the Little Limestone. The extraction of the oreshoot down to Coldberry North Level was completed by the London Lead Co. After the company surrendered its leases, Mr R W Raine commenced the sinking of a shaft at [NY 9317 2868] 850 ft (259 m) SW of the crosscourse mentioned above, with the object of exploring the vein below the North Level. Under English Lead Mines Exploration Ltd, the shaft was completed to 143 ft (43.6 m) and levels were driven at 43 ft (13 m), in the Little Limestone and associated beds, and from the bottom, in the upper part of the Great Limestone. An orebody 510 ft (155 m) long at the North Level horizon, and 300 ft (91 m) long at the 143 ft (43.6 m) Level was developed, and the 43 and 143 ft (13 and 43.6 m) levels were linked by an additional rise. The orebody, which was still in place in 1940, averaged 10 per cent lead. In the Great Limestone the vein consisted of parallel bands or strings of galena replacing the limestone over a width of 10 ft (3 m). The associated minerals were fluorite, quartz, calcite and ankerite. Ventilation difficulties were experienced during the operations at Raine's Shaft, but these were overcome by the company, Coldberry Mines Ltd, formed after World War II to extract the oreshoot. A possible solution was to drive up Skears Low Level (portal at [NY 9469 2759] at 680 ft (207 m) (described below) a distance of 1800 ft (549 m) from Skears Great Rise. A start was made with the rehabilitation of the Low Level but it was not proceeded with and in the 1950s the ore was got out through North Level. Coldberry Mines Ltd erected a mill and produced approximately 5000 tons of lead concentrates, but with little development.

    Richardson's Vein was worked from Richardson's Level (9404 2902] at 1334 ft (407 m) above OD, the North Level, and a level [NY 9425 2921] commanding the Great Limestone at about 1155 ft (352 m) above OD. Ore-bearing ground was wrought in the Firestone, 600 ft (183 m) long, in the Coal Sills 1050 ft (320 m) long, and in the upper part of the Great Limestone, 400 ft (122 m) long, but the London Lead Co.'s sections indicate only medium and low values. The beds dip westward along this vein, the oreshoots following the hard beds. The principal workings on Lowe's Vein and South Lead were above the North Level, probably in the Coal Sills and Firestone; a winze sunk to the Great Limestone 950 ft (290 m) ENE of Raine's Shaft was unsuccessful.

    S of the group of veins so far described runs the other principal vein of Coldberry Mine, Hunt's Coldberry Vein. This was worked from Ravelin Shop by means of a level [NY 9249 2744] 2075 ft (632 m) long in the Coal Sills; trials here in the Great Limestone were not successful. The Ravelin workings yielded only small quantities of galena, in a matrix of baryte and amber fluorite. The principal oreshoots on the vein commenced 2650 ft (808 m) NE of Ravelin Shop, and continued to Coldberry, a distance of nearly 5000 ft (1.52 km). The principal horizons mineralised were the Firestone and Coal Sills, better values being obtained in the former than the latter. The Great Limestone was productive only near Hudeshope, and even here it was poor as compared with the Firestone. The principal levels, were Hunt's Level [NY 9418 2899] at 1325 ft (404 m) above OD, commencing near the mine-office at Coldberry; the Low Level [NY 9420 2903] at 1275 ft (389 m) above OD, near the old dressing floors, and the Great Limestone Level [NY 9425 2921] at 1155 ft (352 m) above OD, which has already been mentioned as giving access to Richardson's Vein. Hunt's Level starts in the White Sill. At 1400 ft (427 m) from the portal, a crosscourse throwing 60 ft (18 m) SW passes through the vein, and for the rest of its course this level is near the top of the Firestone. At 2000 ft (610 m) SW of the crosscourse, the Firestone Level of Skears Mine (portal at [NY 9424 2787]) gave access to the vein at 1250 ft (381 m) above OD; probably much of the Firestone ore SW of the crosscourse was extracted through this level. The Low Level from Skears Mine (portal at [NY 9469 2759] (described below) at present ends at Hunt's Cold-berry Vein in the Four Fathom Limestone on the hangingwall of the vein at about 955 ft (291 m) above OD. The vein proved to be unworkable here. Skears Great Rise [NY 9378 2859], following Hunt's Vein up to surface, 545 ft (166 m) above, found nothing of value beneath the Coal Sills, though 1320 ft (402 m) of drifts were driven to test the Great Limestone.

    The Ravelin Old Veins carried a little fluorite, baryte and galena at Ravelin; as Lead "C" they intersect Hunt's Coldberry Vein near Skears Great Rise. Lead "C" was tested from the Firestone Level, as well as at Hunt's Level, but was not workable. Lead "B",an eastward branch from the S side of Hunt's Vein cut 1200 ft (366 m) SW of Hunt's Level mouth, was worked in the Firestone.

    The extensive tailings heaps of Coldberry Mine contain purple fluorite and quartz, with abundant sandstone fragments. Attempts had been made to obtain saleable fluorspar from them, but dressing to remove silica only became possible with the erection of the Broad-wood flotation mill at Frosterley. In 1984 the dumps were estimated at a rough figure of 50 000 tons carrying 24 per cent CaF2, including Lodgesyke. Under the London Lead Co., Coldberry Mine produced 45 059 tons of lead concentrates, yielding 3 oz silver per ton of lead, between 1852 and 1902; Mr Raine produced 59 tons between 1907 and 1912. Wartime activity included hand jigging by Mr Allison of ore brought out during English Lead Mines Exploration Ltd work at Raine's Shaft; it is understood that the postwar extraction of the ore remaining at Hardberry Hill brought the lead concentrates total to 50 200 tons.

    Skears Veins—Lead ore

    NY 92 NW; Durham 39 NE

    South of Coldberry Mine, Low Skears Mine (disused) worked a complex of small veins in beds ranging down from the Firestone to the Great Limestone. There were two adit levels, both running WNW, cutting across the bearing veins. Firestone Level, [NY 9424 2787] starting 900 ft (274 m) ESE of Hardberry House at 1232 ft (376 m) above OD was driven straight for 2900 ft (884 m) to Hunt's Cold-berry Vein. Skears Low Level [NY 9469 2759] (Figure 40), starting 2600 ft (792 m) ESE of Hardberry House is 4625 ft (1.4 km) long, also ending at Hunt's Vein; for the first 625 ft (191 m) it follows the course of a NW fault known as Hall's Vein, which downthrows NE about 60 ft (18 m) though at 270 ft (82 m) from the portal it passed from the Great Limestone on the footwall side of this fault into boulder clay, which continued to 720 ft (219 m), when the level reenters solid rock, turning away northward from Hall's Vein. At 1900 ft (579 m) from the portal it cuts Skears "C" Vein (ENE, downthrow 15 ft (4.6 m) SE) in the shale below the Quarry Hazle. In the Great Limestone this vein carried an oreshoot 350 ft (107 m) long which terminated to the W against Hall's Vein. At 2150 and 2225 ft (655 and 678 m) from the portal, faults throwing respectively 3 ft (0.9 m) and 2 ft (0.6 m) NW were cut, and at 2400 ft (732 m) Skears "D" Vein (direction NE, displacement 15 ft (4.6 m) NW). Small irregular oreshoots in the Great Limestone were worked from rises on "D" Vein for 1650 ft (503 m) NE and 1370 ft (418 m) SW of the Low Level; it was the first vein cut in the Firestone Level, 800 ft (244 m) from the portal, but it was apparently not mineralised in the Firestone Sill. At 2800 ft (853 m) from the portal the Low Level cut Skears "E" Vein (direction NE displacement 7 ft (2.1 m) NW) in the shale between the Quarry Hazle and the Four Fathom Limestone. This also carried a series of patchy oreshoots in the Great Limestone, extending 850 ft (259 m) NE and 1260 ft (384 m) SW of the level. An oreshoot 400 ft (122 m) long was also worked in the Coal Sills, while the Firestone Level gave access to two small oreshoots near the top of the Firestone. An air-shaft (Anon, 1910a) on "E" Vein, 1100 ft (335 m) NE of the Low Level ventilated its north-eastern workings. From its south-western end, a branch known as Skears "D" Vein is given off. Ore-bearing ground in the Great Limestone 650 ft (198 m) long, and in the Coal Sills 1150 ft (351 m) long was worked, together with three small oreshoots in the Firestone; an air-shaft (Anon, 1910b) to these workings communicated with the Firestone Level 1120 ft (341 m) from its portal. The next important vein, Skears "F" (direction NE, displacement 17 ft (5.2 m) SW) was cut by the Low Level at 3050 ft (930 m) from its portal, and Firestone Level at 1725 ft (526 m) from that portal. W of the Low Level, this vein split; its branches include Raines's Vein (displacement 12 ft (3.7 m) SW) and the Quarter-Point Vein. Though tried in the Great Limestone, little ore was obtained from this group. Vein "F" brings the Four Fathom Limestone into the Low Level on its footwall. Two more weak NE veins were cut in the Low Level NW of "F" Vein, Skears "G" Vein at 350 ft (107 m) (displacement 4 ft (1.2 m) NW) and "H" Vein at 550 ft (168 m) (displacement 6 ft (1.8 m) NW). Neither proved productive either in the Four Fathom or Great Limestone. The continuation of Hall's Vein, here known as Skears East Cross Vein, was, however, productive in the Great Limestone from a point 330 ft (101 m) NW of its intersection with "H" Vein south-eastwards to "E" Vein, a total distance of 1350 ft (411 m). It is also worth noting that two other groups of cross-veins were explored to some extent. The north-eastern workings on "D" and "E" veins encountered the continuation of the crosscourse mentioned as throwing 60 ft (18 m) SW in the Coldberry Mine (p.249); here it is in two parts 250–275 ft (76–84 m) apart, dividing the throw, somewhat reduced, between them. In the south-western workings on "E" and "F" veins cross-veins linking the two NE veins were followed in the Great Limestone without success.

    The ore from Skears Mine was probably dressed at Coldberry mill; the veins appear to have contained purple and amber fluorite, quartz, siderite and limonite. The production of lead concentrates from 1852 to 1885 amounted to 7571 tons, containing 5.0 oz silver per ton of lead.

    The complete absence of any workable ground in the extensive trials below the Great Limestone is noteworthy; probably this is because shale greatly predominates over sandstone in the section exposed below the limestone in the Low Level, both Quarry Hazle and Nattrass Gill Hazle being abnormally thin. Little hope can, therefore, be entertained on stratigraphical grounds for oreshoots below the Great Limestone under Coldberry, unless a second series occurs in the lowest Brigantian and Asbian, and no lead-in to this is known.

    Marlbeck Veins—Lead ore

    NY 92 NE; Durham 39 NE

    On the E side of Hudeshope, S of Lodgesike Mine, a group of E–W and WNW veins have been exposed by hushes at Marlbeck Mine (disused), Marlbeck Level [NY 9499 2873] at 1069 ft (326 m) above OD, driven in shale below the Great Limestone, is accessible; it shows stoped ground in the limestone on Marlbeck "B" Vein (direction E–W, displacement 24 ft (7.3 m S), with which some replacement deposits appeared to have been associated. A rise near the junction of Marlbeck Level with "B" vein shows the top of the limestone 85 ft (26 m) above the level sole on the N side of the vein . From "B" vein a crosscut runs N to Lodgesike Mine (p.248), meeting at 850 ft (259 m) a fault which brings the Great Limestone into the level. The beds rise northwards towards Lodgesike Vein, the workings on which have already been described. Some 1600 ft (488 m) E of Marlbeck Level mouth, Cat Level [NY 9546 2878] at 1377 ft (420 m) above OD has been driven north-eastwards in shale beneath the Low Grit Sill. Vein "D" does not appear to have been productive at this high horizon; but a continuation E of the level revealed a WNW fault, throwing 13 ft (4 m) NE. This fault was also reached by a crosscut southwards from Lodgesike High Level (1520 ft (463 m) above OD) 2800 ft (853 m) long, communicating with an air-shaft sunk from Low Monks [NY 9591 2877]. Although many strings and small faults were met in the crosscut, presumably in the Grit Sills, no workable vein seems to have been found. Tailings from Marlbeck Level show quartz, limonite and subordinate amounts of purple fluorite. No records of production remain.

    High Skears Veins—Lead ore

    NY 92 NE; Durham 39 NW

    At High Skears Mine (disused), on the E side of Hudeshope 0.75 mile (1.2 km) S of Lodgesike Mine, Grahams Vein (direction NE), Walton's Vein (ENE) and Skears Old Vein (E–W) were worked. A note on the plan states that ore was raised from the Great Limestone only; none was met in the Upper Sills. The main level [NY 9502 2825] was a crosscut adit driven south-eastwards beneath the Great Limestone; on the dumps limonitised limestone, amber fluorite and quartz occur. If this is the mine referred to as High Skears in the Estate records, it was worked by Backhouse & Co. from 1845–1862, yielding 3890 tons of lead concentrates. London Lead Co. operations from 1863–1881 yielded only 10 tons.

    Aukside Vein

    NY 92 NE, NW; Durham 39 SE, NE

    Shale gouge associated with a NE fault throwing NW is exposed in How Gill, [NY 9472 2703] 1 mile (1.6 km) N of Middleton-in-Teesdale. A level [NY 9464 2705] driven to test the fault in the Great Limestone in How Gill showed only limonite; levels on the E side of Hudeshope at the base of the Low Grit Sill [NY 9530 2731] and from Snaisgill near the Felltop Limestone [NY 9586 2751] were equally unsuccessful.

    Snaisgill Veins—Lead ore, barytes

    NY 92 NW, NE

    Holm Head Vein (direction N50°E, displacement 10 ft (3 m) SE), High Dike Vein (direction NNW, displacement 7 ft (2.1 m NE) and an unnamed E–W vein S of Hunter's Well House werre worked at Snaisgill Mine (disused). An adit [NY 9500 2680] driven SSE from Snaisgill in the shale beneath the Tuft cut Holm Head Vein 1050 ft (320 m) from the portal and continued south-eastwards to reach High Dike Vein. Flats associated with the latter vein are shown on the plan; they contained white baryte, associated with a little amber fluorite and galena. In the later years of the nineteenth century, the London Lead Co. drove an adit [NY 9472 2607] called Deputation Level, starting from Hudeshope beneath Holm Head Bridge in the shale above the Three Yard Limestone. This runs 950 ft (290 m) NNE to reach Holm Head Vein, then turns due E, continuing as a crosscut for 1800 ft (549 m) to reach High Dike Vein, along which a level was driven 1250 ft (381 m). There is no evidence that any of the veins were productive at the horizon of Deputation Level; it is difficult to understand what inducement there was to explore the feeble veins of this mine at depth.

    N of the mine workings, High Dike Vein, split into two branches, is exposed where it crosses the Great Limestone in Snaisgill [NY 9511 2675]. Here a body of limonitised limestone 30 ft (9 m) wide is associated with it. A sample representing the full width proved to be highly siliceous, as the following partial analysis shows: ferric oxide, 17.5 per cent; silica, 64.7; manganous oxide, 2.8; phosphorus pentoxide, 0.14, water, 1.1 (analyst; G A Sergeant, Geological Survey and Museum Lab. No. 1182, 1941).

    Snaisgill Mine produced 53 tons of lead concentrates between 1877 and 1894. From 1886 to 1893 it was worked for barytes, yielding 1808 tons. Ironstone was produced in 1882–83, 1639 tons being shipped.

    Hudeshope Head Vein

    NY 93 SW, 92 NW; Durham 31 SE. Direction E–W, displacement S, exact throw not known

    At Hudeshope Grains, 2 miles (3.2 km) N of Coldberry Mine, a fault trending E–W is exposed at horizons between the Upper Felltop Limestone and the First Grit. Two levels have been driven to prospect this fault, and to search for the continuation of the Westernhope Vein of Weardale, which may be expected to cross the head of Hudeshope. The Upper Level [NY 9368 3209] at 1856 ft (568 m) above OD, is 30 ft (9 m) above the Felltop Limestone; it cut the fault at 330 ft (101 m) from the mouth, and was continued 500 ft (152 m) NNW, but without finding ore. At 1600 ft (488 m) above OD the lower level [NY 9379 3165] was driven at the base of the Low Grit, to a total length of 1610 ft (491 m). This appears to have stopped short of the fault.

    Racketgill Vein

    NY 93 SW, 92 NW; Durham 31 SE, 39 NE

    A mile (1.6 km) N of Coldberry Mine, and 800 ft (244 m) N of Manorgill North Vein, an E–W vein was discovered by hushing in the Great Limestone [NY 937 303] and [NY 941 303]. W of Hudsehope this was tested by levels beneath the Great Limestone [NY 9377 3039] and in the Coal Sills [NY 9366 3032] at Parkin Hush, while E of the beck Hudeshope Level [NY 9421 2978] was continued beyond Manorgill North Vein for 800 ft (244 m) to try the vein in the Great Limestone. All of these trials were unsuccessful.

    Little Eggleshope Vein–Potts Vein group

    Wiregill Mine (disused), in Great Eggleshope 1 mile (1.6 km) NNE of the bridge on the Middleton–Stanhope road, was the centre of lead mining activity in that valley. Close to the old dressing floors, Manorgill Low Level [NY 9754 3011], to which reference has already been made, gave access to the Lodgesike–Manorgill and Manorgill North veins. Both become impoverished before reaching the W side of the valley. Wiregill Low Level [NY 9734 3031] at 1234 ft (376 m) above OD on the E side of the valley proved a weak vein known as Wiregill Old Vein, 460 ft (140 m) from the portal; this vein may be regarded as the continuation of the Lodgesike–Manorgill Vein. The main channel of mineralisation proved, however, to lie farther N, along the Little Eggleshope Vein. In Great Eggleshope, this vein is represented by three or four minor faults, exposed at the horizon of the Knucton Shell Beds. Short levels [NY 9610 3113], [NY 9613 3114] and [NY 9657 3089] have tested these on the W bank without success. On the E side a level [NY 9661 3093] at 1354 ft (413 m) OD, starting 0.5 mile (0.8 km) N of Wiregill Mine at the base of the Low Grit Sill proved that -these small faults link up to form a powerful vein about 800 ft (244 m) E of the beck. From this point one of the largest oreshoots in the Pennine fields was worked for a distance of 8000 ft (2.44 km) to the ENE (Figure 40). The western half is continuously mineralised, reaching a maximum height of 300 ft (91 m), and maintaining an average of over 200 ft (61 m). The horizon of the oreshoot is again the Grit Sills. Approximately 80 per cent of the stoped area in this part of the oreshoot is shown on the London Lead Co.'s longitudinal section as high-grade ore (coloured blue). In a stretch 1600 ft (488 m) long to the E, values were more patchy and stoping was intermittent; but the succeeding 2100 ft (640 m) worked from Little Eggleshope, was again rich, and was stoped consistently to a height of 300 ft (91 m). The western section of the oreshoot did not reach outcrop; apparently it pinched in the shaly measures above the Upper Felltop Limestone. In the eastern stretch, however, the oreshoot cropped out beneath thin drift and peat.

    Geological information, particularly wall-rock stratigraphy, was not recorded with the London Lead Co.'s usual care along this vein, perhaps because the measures seen were largely sandstone. For this reason the exact horizon of the deepest workings cannot be fixed with certainty, but there is sufficient evidence to give a close approximation.

    From Wiregill Mine, the Low Level [NY 9736 3031] 1234 ft above OD (376 m) was continued 2000 ft (610 m) N from Wiregill Old Vein to reach Little Eggleshope Vein, and was observed by Mr J D Willson and Dr G A Schnellmann during the reopening by English Lead Mines Exploration Ltd to pass through a gentle syncline and anticline in the shale beneath the Low Grit Sill. At 300 ft (91 m) S of Little Eggleshope Vein a small vein known as Wiregill South Vein was worked for a distance of 870 ft (265 m) westwards to its intersection with the main vein, and for 1380 ft (421 m) E of the level. The maximum height of the oreshoot was 120 ft (37 m); probably it was confined to the Grit Sills. After passing through the main vein, the Low Level was continued 625 ft (191 m) N to give access to a second branch, the Wiregill North Vein. A limestone considered to be the Crag Limestone appears in the level N of the main vein. On the North Vein, an oreshoot 2100 ft (640 m) long by 100 ft (30 m) high was worked in the Grit Sills north-eastwards from the intersection of the vein with Little Eggleshope Vein. An underground shaft 148 ft (45 m) deep near the Low Level head gave access to a level at about 1100 ft (335 m) above OD on the North Vein, above which oreshoots in the Coal Sills and Firestone were worked over a length similar to that worked in the Grit Sills. At least two winzes were sunk into the Great Limestone beneath this level, but are believed to have proved unproductive. From the level at 1100 ft (335 m) above OD a crosscut was driven S to Little Eggleshope Vein, which must have been reached between a Coal Sills footwall and the shale beneath the Firestone on the hangingwall. The level was driven 850 ft (259 m) along Little Eggleshope Vein, which was tried from rises, but apart from one small patch of ore, it was barren. The evidence that Little Eggleshope Vein has not been tested in the Great Limestone seems clear. The large oreshoot on it has not been worked beneath the Wiregill Low Level. The stopes above this level terminate 2450 ft (747 m) ENE of the adit crosscut, but the level continues 400 ft (122 m) farther. Wiregill Middle Level [NY 9768 3072] at 1349 ft (411 m) above OD, driven from Wire Gill, communicates with the level from Great Eggleshope mentioned above; it is the longest level in the mine, running altogether 8350 ft (2.55 km) from Great Eggleshope, and serving as a water level for the Little Eggleshope workings. There was also a shorter High Level [NY 9774 3099] at 1490 ft (454 m) above OD from Wire Gill.

    In Little Eggleshope the main entrance to California Mine (disused) is an adit level [NY 9874 3130] at 1500 ft (457 m) above OD, at the head of the valley, driven N by W in the shale above the Upper Felltop Limestone which crops out farther S. The beds dip steeply N close to the vein, i.e. in the opposite direction to that expected from the downthrow of the fault. Little Eggleshope Vein is cut at 600 ft (183 m) from the portal. Here the adit meets the main engine shaft, [NY 9869 3147] sunk from surface 100 ft (30 m) above the adit, through Wiregill Middle Level, 120 ft (37 m) below the adit, to a total depth of 330 ft (101 m). The bottom level runs 1700 ft (518 m) E and 410 ft (125 m) W of the shaft. Its probable horizon is about the middle of the Low Grit Sill on the hangingwall, and near the top of the Firestone on the footwall of the vein. The longitudinal section suggests that ore was left in the sole of this level over a length of 1780 ft (543 m) but the stopes immediately above the level were all of medium or low grade. At the E end of the main oreshoot, subsidiary oreshoots 300 ft (91 m) long followed a south branch before dying out. The adit level was continued 1900 ft (579 m) E of the main oreshoot, and a level from surface at 1600 ft (488 m) above OD [NY 990 3153] followed the vein for 1300 ft (396 m) in this ground, both without success. At 2630 ft (802 m) ENE of California Shaft this level found and followed for a short distance an ESE-trending branch from the vein which probably joins up with a S-throwing fault mapped during the 1973 revision of 6-inch NZ03SW by D A C Mills. If this is the case, the fault loops back into Little Eggleshope Vein, reaching it 3700 ft (1.13 km) from the point where it was first observed in the 1600 ft (488 m) adit.

    In 1971–72 Swiss Aluminium Mining (UK) Ltd drilled three inclined boreholes from the hangingwall (S) side of Little Eggleshope Vein to test its continuity in depth and on strike. Hole LI [NY 9894 3148], (direction N 22°W, inclination 72°) found the thin Grindstone Limestone at 1385 ft (422 m) above OD, underlain by 40 ft (12 m) of sandstone; the base of the Upper Felltop Limestone at 1289 ft (393 m) above OD and it entered the vein at 1188 ft (362 m) above OD, near the top of the High Grit Sill. The vein, estimated true width 22 ft (6.7 m), consisted of a breccia cemented by quartz and calcite with traces of galena, in part cavernous on the hangingwall side, but with bands totalling 9 ft (2.7 m) wide with 50 per cent CaF2 against the footwall. The wallrock on the (N side was sandstone, probably also of the Grit Sills. Hole L2 [NY 9904 3152], N 21°W, dip 75°), proved Upper Felltop Limestone base at 1322 ft (403 m) above OD, found blebs of galena and a stringer of quartz and galena in the Hippie Sill, and reached the vein at 1230 ft (375 m) above OD and passed through the footwall at 1179 ft (359 m) above OD. The full width of the vein, about 12 ft (3.7 m) included 2.2 ft (0.7 m) with over 10 per cent Pb and 9 per cent CaF2. These two borehole intersections were respectively about 66 and 42 ft (20 and 12.8 m) below California Bottom Level. The geological implications are significant, since there is now accurate information for the E end of the oreshoot (Figure 40). While in Wiregill the ore was principally against Grit Sills wallrocks, beneath the interfluve the horizon of the orebody rises as the beds dip eastward, so that in Little Eggleshope the wallrocks include, in upward succession, the Hipple Sill, the Grindstone and, on the hangingwall side, the 1st Millstone Grit. Here the Grit Sills are largely virgin. Borehole L3 [NY 9983 3165], (direction N 32°W, dip 60° (probably increasing downwards), was the deepest hole of the series, collared at 1710 ft (521 m) above OD, it was drilled open hole through the 1st Millstone Grit at 1457 ft (444 m) above OD; the Upper Felltop Limestone was cut at 1345 ft (410 m) above OD and the Coalcleugh Coal at 1263 ft (385 m) above OD. The hole passed through the vein from 1119 to 1079 ft (341–329 m) above OD in the Low Grit Sill and at 1053 ft (321 m) above OD, ended in a fossil band tentatively identified by I C Burgess as the Knucton Shell bed, in the footwall of the vein. This intersection showed three mineralised bands separated by rock, the best carrying 42 per cent CaF2. The footwall identification would indicate that the vein has little or no throw, and it is likely that the structure is not continuous with the California Vein of Sharnberry Mine (below) since nothing was cut on this line in the Northumbrian Water Authority Aqueduct Tunnel which passes through it at 601 ft (183 m) above OD in the Four Fathom Limestone between the two mines.

    The logs of Borehole L3 by Mr Burgess, and of the nearest borehole on the NWA Aqueduct (the pilot bore for Sharnberry Air Shaft, [NZ 0072 3073]) by Messrs I Smith and D A C Mills show that the Grindstone and Hipple sills where unweathered are light to dark grey medium-grained sandstone, while in part the Grit Sills sandstones are coarser. Siltstone and mudstone bands are present, but their thicknesses are generally small compared with those of the sandstones. Probably this is why the mineralisation has been able to penetrate through these beds to reach the 1st Millstone Grit at Little Eggleshope and at Sharnberry.

    S of the Little Eggleshope Vein, E of California Shop, the London Lead Co. worked a small oreshoot on Pott's Vein in the 1st Millstone Grit. Swiss Aluminium (UK) Ltd in the 1970s tested this by means of an incline and five inclined boreholes but failed to find the vein in depth, though each hole was drilled to the High Grit Sill.

    Throughout the Wiregill and California mines, the matrix of the oreshoots was purple and amber fluorite and quartz. Baryte is present only in the highest workings at Carlfornia; a little can be found on the dump from the level at 1600 ft (488 m) above OD [NY 9900 3153]. Some of this shows the crystal morphology characteristic of secondary baryte after a barium carbonate (B Young, personal communication).

    The tailings at both mines contain much sandstone in addition to fluorite and quartz; representative assays for Wiregill, supplied by the late Mr F J Ryland showed ranges of 27–56 per cent CaF2, 30–55 per cent SiO2 with about 2 per cent CaCO3. He was to produce, by selection, some shipments with 65 per cent CaF2, 16 per cent SiO2. Recent estimates of tonnages by SAMUK indicate 20 700 t at Manorgill-Wiregill and 20 000 t at California (the latter including coarse rock as well as gravel), carrying respectively 19 and 20 per cent CaF2.

    The whole of the production shown in (Table 67) was from London Lead Co. operations. After this company ceased work, the Wiregill Deep Mining Co. continued operations from 1902 to 1913, producing 1690 tons; the total for the whole group 1852 to 1913 thus amounts to 125 197 tons. Taking Coldberry, Lodgesike–Manorgill and Wiregill together, at least 300 000 tons of lead concentrates were produced after the beginning of the 19th century. Yet hardly 100 000 tons of tailings remain. It cannot be supposed that the veins carried 75 per cent galena; loss of tailings into the drainage and perhaps back filling must account for this discrepancy, which is also evident elsewhere in the orefield.

    Dusty Gill–Flake Brig Vein and East Rake = Sharnberry Vein

    East Rake Mine (disused) worked both Dusty Gill and East Rake veins in Great Eggleshope. It consisted of an adit level [NY 9828 2927] at 1135 ft (346 m) above OD starting from the beck 1700 ft (518 m) N of the bridge on the Middleton–Stanhope road, driven 3425 ft (1.04 km) N by W in shale beneath the High Grit Sill. At 1140 ft (347 m) from the portal it cut East Rake, along which a branch level was driven for 1840 ft (561 m) NE. No stopes are shown on the longitudinal section. At 1200 ft (366 m) N of East Rake, the adit cut a fault believed to represent the continuation of Manorgill North Vein; a rise into the sandstone failed to prove mineralisation. The adit ends in Dusty Gill Vein, which may be regarded as a NE branch from Manorgill North Vein; a level turned 600 ft (183 m) ENE along the vein failed to find workable ground. Another level [NY 9790 3008] in this vein was driven from surface at 1260 ft (384 m) above OD, starting opposite Wiregill Mine; little or no ore appears to have been obtained. East Rake was also tried by hushing on both sides of the beck, but the results were evidently poor. The high stratigraphical horizon of all these trials may perhaps be regarded as an unfavourable factor.

    In Little Eggleshope, dumps of old shafts, around [NY 990 308], sunk to a footwall branch of Flake Brig Vein at or near the horizon of the Upper Felltop Limestone show purple and amber fluorite with galena in veins in sandstone and grit. An adit starting W of the beck [NY 9938 3034] 1400 ft (427 m) S of the vein drained these workings. E of the beck the veins pass into Mr Hutchinson's Estate. Hutchinson's Level [NY 9936 3015], the principal entrance to Flake Brig Mine (disused) starts from the E bank of Little Eggleshope Beck, 2200 ft (671 m) from Flake Bridge, near the horizon of the Upper Felltop Limestone on the S side of the vein, and reaches the vein 800 ft (244 m) E of the point where the vein crosses the beck. Of a total of 1400 ft (427 m) of drivage in the vein from this level, 300 ft (91 m) proved to be workable ground. Purple fluorite is abundant on the dumps. About 1000 ft (350 m) E of the level head. Flake Brig Vein unites with East Rake to form the Sharnberry Vein, worked from Sharnberry Mine (disused), situated in Sharnberry Gill a mile (1.6 km) E of Flake Bridge on the Stanhope–Middleton road. The principal entrance was Sharnberry Low Level [NZ 0120 30801 at 1210 ft (369 m) above OD, driven as a crosscut 2900 ft (884 m) NW to meet the vein at Sharnberry "A" Shaft [NZ 0053 3143] (Anon, 1910c). The SW branch of this level followed the vein to its junction with Flake Brig Vein along which it continued to the boundary of the Hutchison royalty. At 2100 ft (640 m) SW of the level head Sharnberry "B" shaft [NZ 0005 3099] communicated with surface. A cross section at this shaft has already been published (Carruthers and Strahan, 1923, fig. 4, p.17) (It should be noted that the scale of this section is not as stated 44 fms to 1 inch, but approximately 150 ft to 1 inch. Sharnberry Low Level runs at the point marked 'G' on the section). The productive part of the vein here was opposite the footwall position of a sandstone identified by the London Lead Co. engineers as the Upper Slate Sill though there is evidence that this is the same as one mapped during the present work as the High Grit Sill . The oreshoot extended 720 ft (219 m) SW and 510 ft (155 m) NE of the shaft; its maximum height was 130 ft (39.6 m) the average about 70 ft (21 m). The old High Level [NY 9997 3074] at 1380 ft (421 m) above OD, proved that west of the shaft the vein is barren or unpayable, apart from one small shoot 140 ft (42.7 m) long, at higher horizons. A winze sunk 110 ft (33.5 m) near the shaft proved that the ore dies out 35 ft (10.6 m) below Sharnberry Low Level.

    This western oreshoot on Sharnberry Vein is succeeded by barren ground which extends 1870 ft (570 m) NE. In the vicinity of Sharnberry "A" Shaft, the vein splits into two branches, both of which become productive. The northern branch carried an oreshoot 1670 ft (509 m) long, averaging about 60 ft (18 m) high. The bottom of this oreshoot corresponded with Sharnberry High Level, [NZ 0107 3136] which starts as a crosscut adit with its portal 1950 ft (594 m) NNW of the Low Level mouth, at 1388 ft (423 m) above OD. The North Branch oreshoot had the Grindstone Sill, the thick sandstone above the Upper Felltop Limestone, as its footwall. Only small patches were payable below the High Level. On the South Branch the total length of ground worked was 2100 ft (640 m) by 100 ft (30 m) average height. Since the South Branch apparently carried the main throw of the fault, the hangingwall here must have been the First Grit of the Millstone Grit. On the North Branch 2100 ft (640 m) NE of "A" Shaft, a strong E–W fault, in line with Little Eggleshope Vein, was encountered.

    This was workable for 380 ft (116 m) W of the intersection, but the mineralisation apparently died out before reaching the South Branch. Both branches were traversed at about 1150 ft (351 m) NE of "A" Shaft by a NNW crosscourse, the probable continuation of Cornish Hush Vein of Bollihope (p.218). A drive 1600 ft (488 m) long followed this crosscourse north of the North Branch at Sham- berry High Level horizon, ending near the SE forehead of Cornish Hush High Level. A note on the plan states that the Sharnberry Level was 141 ft (43 m) above that from Cornish Hush; but if this is correct the level from Bollihope must have risen 150 ft (46 m) in a mile (1.6 km).

    The Sharnberry oreshoots carried fluorite and quartz as matrix, with only traces of baryte. Representative analyses of tailings are given in (Table 68). The production of lead concentrates from Flake Brig Mine, 1853–1882, was 8816 tons; from Sharnberry, from 1833–1881, it amounted to 13 305 tons, making a total of 22 121 tons for this group of veins. Production of gravel fluorspar from the dumps was in progress during World War II.

    In the 1950s the Low Level was reopened by Mr Ward and a mill was constructed but sufficient ore to keep it going was not found during north-eastward development. In 1971–72 Swiss Aluminium Mining (UK) commenced the reopening of Cornish Hush Mine with the intention of driving on to test the Sharnberry Veins in depth (p.218) but this project was suspended when the NWA aqueduct tunnel was begun. The tunnel proved a wide mineralized zone in Great Limestone (Table 51), p.176) beneath the Sharnberry oreshoots but with quartz and traces of pyrite only.

    E of the Sharnberry workings, the South Branch was revealed by a hush at the head of South Grain Beck [NZ 0175 3230]. Crosscut adits at 1270 and 1220 ft (387 and 372 m) above OD proved the vein [NZ 0192 3226] and [NZ 0212 3223]. Galena, cerussite, purple fluorite and quartz occur on the dumps, in part as a replacement of a limestone, presumably the Upper Felltop. The fault then appears to turn eastwards for about 1 mile (1.6 km) and then is known to continue, from evidence provided by geological mapping, for at least 3 miles (4.8 km) NE to the vicinity of Sunnyside Mine, Weardale (p.214); it is now considered to cross Weardale to link up with the Deerness Valey fault system of the Durham Coalfield (pp.278–281). There appear to be opportunities for further exploration along the course of this major channel of mineralisation. The possibility that other oreshoots occur at intermediate depth at Sharnberry, or between there and Weardale remains open.

    Stakebeck Vein

    NY 72 SE; Westmorland 6 SW

    Remotely situated in the headwaters of Stake Beck, a northern tributary of the Maize Beck, 4 miles (6.4 km) ENE of Dufton, the position of this vein is marked by a 1100 ft (335 m) line of shafts running E–W between [NY 7439 2959] and [NY 7472 2959]. The workings appear to have been mainly in the sandstone beneath the Three Yard Limestone. Witherite and barytocalcite are the principal minerals on the small dumps, associated with a little galena and secondary baryte. Blocks of limestone, partly veined and replaced by barytocalcite, suggest that the workings may have reached the Five Yard Limestone locally (Young, 1985).

    Maizebeck Cross Veins

    NY 72 NE, 82 NW; Yorkshire 1 SW

    Three quarters of a mile (1.2 km) SW of Birkdale Farm the London Lead Co. drove a level [NY 7986 2687] 1200 ft (366 m) SE from the side of the Maize Beck following a NNW vein in the Smiddy Limestone. At 350 ft (107 m) from the portal the vein split and the level was continued obliquely through three branches trending about N20°W, the eastermost branch throws 4 ft (1.2 m) NE. Baryte, associated with sugary vein-stuff similar to that found in Winterhush Vein (p.236), occurs on the dump, together with galena and oxidised copper minerals.

    Green Mines Vein and Green Mines East Cross Vein

    The Green Lead Mines (disused), 2.25 miles (3.6 km) S of Cowgreen Mine, worked Green Mines Vein opencast in the Tynebottom Limestone between [NY 8077 2631] and [NY 8097 2643] and shallow shafts indicate its continuation SW to [NY 7996 2580]. The workings terminate to the E against the East Cross Vein at [NY 8115 2658] the position and direction of which strongly suggest that it is the southward continuation of Winterhush Vein (p.235). Baryte, with a little galena, is present in both veins, as well as in a series of subsidiary strings branching NW and N from the main vein.

    Birkdale Hush Vein—Lead ore

    NY 82 NW; Yorkshire 1 SW Direction N20–30°W

    This vein, which may be regarded as a branch of the Winterhush vein-system, has been worked opencast for 1500 ft (457 m) 0.75 mile (1.2 km) from [NY 8167 2745] ESE of Birkdale Farm. Four levels have been driven into it, the lowest [NY 8179 2769] at 1500 ft (451 m) above OD, being a crosscut reaching the vein 900 ft (274 m) SSW from the portal. For part of its course, exposed in the hush, the vein appears to coincide with a transgressive change in horizon of the Whin Sill, reaching the Smiddy Limestone, which appears in the upper part of the opencut. Baryte is present on the dumps, associated with galena. At the lowest level (probably in the Robinson Limestone) siliceous veinstuff is associated with the baryte. The three higher levels are at [NY 8168 2740], [NY 8174 2731] and [NY 8179 2723]. The workings terminate to the S at [NY 8185 2707].

    Merrygill Beck Veins

    NY 82 NW; Yorkshire 1 SW, SE

    Half a mile (0.8 km) S of its confluence with the Tees, Merrygill Beck receives a tributary from the SE whose course has been substantially modified by hushing operations around [NY 827 270]. Exposures range from the Smiddy Limestone down to the Whin Sill, here intruded beneath the Robinson but above the Melmerby Scar Limestone. The hushes expose a belt of four NW faults with which a little baryte is associated. A level driven in the Smiddy Limestone along a N–S a fault which downthrows W to the E of the hushes, has also encountered baryte. There may also be three minor E–W veins.

    Silverband Vein and Old Band Vein

    Silverband Vein, with a number of branches, was worked at Yorkshire Silverband Mine (disused), which should not be confused with Westmorland, Silverband Mine, Cumbria. The mine lies on Cronkley Fell, E of Merrygill, and 2 miles (3.2 km) E of Birkdale Farm. As a lead mine it was active during the early part of the nineteenth century; a plan and section were published at this time by T Sopwith (1829). Silverband Vein has been "hushed" in the headwaters of Crookus Gill, around [NY 8365 2720] exposing beds on the walls from the Whin Sill (here beneath the Robinson Limestone) up to the Smiddy Limestone. The principal level [NY 8345 2736] starts from the hush at 1760 ft (536 m) above OD and runs 900 ft (274 m) SE on this vein. Small lead oreshoots were worked in a limestone above the level, believed to be the Peghorn and the "Whin Top" (probably Robinson) Limestone, reached by winzes beneath the level. At least one winze was carried into the Sill, but apparently without success. At 250 ft (76 m) from the portal of this level, Old Band Vein intersects the main vein, and has been followed 450 ft (137 m) to the E. Good white baryte is present on surface dumps along this vein. Nearer the head of the hush, two branches running S are given off from Silverband Vein and are known as West and Second West veins. At 200 ft (61 m) SE of Silverband Shop, a second E–W vein has been proved on the E side of the main vein, carrying baryte in the Smiddy Limestone. The recorded production of lead concentrates amounted to 48 tons in 1852–1853, and 13 tons in 1899–1900. An attempt to work barytes may have been made at the latter period. The southernmost shaft is at [NY 8666 2690].

    Black Ark Vein

    NY 82 NW, SE; Yorkshire 1 SE

    In the headwaters of Black Ark, the stream which runs from Cronkley Fell over White Force 2.25 miles (3.6 km) S of the Langdon Beck Hotel, a line of shafts at about 1700 ft (518 m) above OD between [NY 8444 2778] and [NY 8454 2777] proves the presence of a vein running N80°W through metamorphosed limestone, considered to represent part of the Melmerby Scar Limestone, here above the Whin Sill. The vein filling was baryte with subsidiary galena. From the foot of White Force the London Lead Co. drove an exploratory level at about 1410 ft (430 m) above OD [NY 8521 2801] running 800 ft (244 m) S14°W then following a fissure for 250 ft (76 m) S44°E, and finally turning to S7°E for 850 ft (260 m). The level is driven in mentamorphosed limestone, the lower part of the Melmerby Scar Limestone, beneath the Whin Sill. Although the level crosses the line of Black Ark Vein there is no indication on the plan that this vein was discovered in the level; small amounts of baryte present on the dumps probably came from the SE fissure.

    Thistle Green Veins

    NY 82 NW;Yorkshire 1 NE

    On the flat top of Cronkley Fell, 1 mile (1.6 km) SSE of Widdybank Farm, and 2 miles (3.2 km) S of the Langdon Beck Hotel, an E–W vein throwing 20 ft (6 m) S cuts through metamorphosed limestone and sandstone capping the Whin Sill exposures. At least one shaft [NY 8420 2818] on this vein appears to have reached the fine-grained dolerite at the top of the sill. Baryte with some galena is present on the dumps, as well as on those from trials on a small NNE vein farther N where there are also traces of fluorite [NY 8425 2832]. Neither vein appears to reach the Whin Sill scarps surrounding Cronkley Fell.

    Maize Beck Mines (disused) is a term which may usefully be applied to the mines and trials from Birkdale Farm to Cronkley Fell, described above. Their chief interest is as possible sources of barytes. Were it not for the inaccessibility of the area, there is little doubt that they would already have been explored for this mineral. Although no evidence of the existence of large oreshoots containing it has yet come to light, the conditions both of structure and stratigraphy closely resemble those obtaining at the Cowgreen mines and it may be suggested that, provided the transport and environmental problems are not regarded as insoluble, the mines are worthy of systematic prospecting for barytes.

    Orepit Holes Vein—Iron ore

    NY 82 NE; Yorkshire 2SW

    Ore Pit Holes opencast, 1.5 miles (2.4 km) W of Holwick village on the fell side S of the Tees, is 2500 ft (762 m) long from [NY 8756 2725] to [NY 8737 2728] following an E–W vein in the Scar Limestone. From the presence of limonite in the vein, and the existence of scattered heaps of iron-slag, it is believed that iron ore was mined and smelted here in ancient times.

    Holwick Scars Veins

    NY 92 NW; Yorkshire 2SW

    The Whin Sill escarpment SW of Holwick is cut by remarkable ENE gullies, including Hind Gate [NY 9025 2695], Water Gate [NY 9035 2685], Strands Gill [NY 9040 2680], Rake Gill [NY 9050 2670] and Bedale Gill [NY 9080 2660]. On an old plan of the London Lead Co.'s Yorkshire mines these are marked as indicating the courses of veins, but this only appears to be justified in the cases of the first two mentioned both of which follow narrow veins and strings of baryte.

    Park End Deposits—Iron ore

    NY 92 NW; Yorkshire 2 SE, SW

    W of West Crossthwaite Farm 1 mile (1.6 km) W of Middleton-inTeesdale, a little iron ore was got, according to notes by C T Clough, from a vein at [NY 9280 2548] related to one of the strong NW faults which run along the Yorkshire side of the Tees. The deposit was in the Tynebottom Limestone; the site is now covered with dumps from Crossthwaite Whinstone Quarry. Similar deposits may perhaps occur farther north-west related to the same fault, which is exposed near Hungry Farm [NY 9110 2655] VS mile (0.8 km) SE of Holwick.

    Hargill Beck Veins

    NY 82 SE; Yorkshire 3NE

    In Hargill Beck, 2 miles (3.2 km) NNW of the bridge on the Middleton–Brough road, small folds, accompanied by faulting in NW and NE directions are exposed in the neighbourhood of [NY 8638 2397]. Probably the structures are part of the Burtreeford Disturbance, here dying out as it approaches the Lunedale Fault. Baryte occurs in the stream, and W Gunn recorded that a boulder of galena weighing 14 stones was found here, indicating the nearby presence of mineral deposits. No development has been done here.

    Closehouse North Vein–East Hush and Standards Hush Faults group

    A complex of intertwining, mainly steep faults, the overall effect of which is a substantial S downthrow.

    The structures listed above all form part of the Lunedale Fault-system to which reference has already been made on p.54. The system is regarded as the southern boundary of the Alston Block, separating it from the Stainmore Trough and Cotherstone Syncline to the south. In 1948 there was already evidence of an abrupt increase in thickness across the Swindale Beck Fault. It was described as a hinge at that time, but the term growth-fault now almost certainly applies, indicating differential movement on it during Carboniferous sedimentation. At the E end of Standards Hush, near [NY 863 230] the Lunedale Fault is joined by the southern continuation of the Burtreeford Disturbance, which swings round into the Standards Fault, but the Lunedale faults continue E of this until, E of Middleton in Teesdale, they merge with the Butterknowle–Wigglesworth System. Mineralisation is confined, as at present known, to the western stretch of the Lunedale Faults.

    Here it was exposed, in ancient times, by a series of very large hushes, cutting through the spurs of the hills on the N side of the dale. From W to E these are: Closehouse Hush [NY 839 225], West Hush [NY 847 227], South Hush [NY 849 226], East Hush [NY 856 229] and Standards Hush [NY 861 229].

    Probably the opencasting which must have shifted over 2 million tons of rock was completed before the London Lead Co. acquired the lease in 1770 but it may be doubted whether more than small tonnages of lead had been won, though there must have been some return for so much labour. The Company held Lunedale with the Maizebank Royalty until 1880. Their main contributions were the driving of Deerfold Level [NY 8416 2242] beneath Closehouse Hush and a stone-arched adit from West Hush [NY 8485 2271]; these are discussed below. Any production of lead obtained was presumably included with the modest lead output from Lunehead (p.260). The search for lead at both mines had revealed that baryte is far more abundant than galena in the deposits. The Closehouse Lease, with Lunehead, was acquired by Athole G Allen (Stockton) Ltd in 1939. The first objective was massive baryte exposed in the stone-arched adit [NY 8485 2271]. Trenching across the structure nearby showed a width of at least 70 ft (21 m) of baryte, of which the N part was water clear, forming a flat in a limestone identified from the presence of Girvanella nodules as the Smiddy; but the greater part of the ground appeared to be a massive vein. While driving and trenching went on an access road, 1.75 miles (2.8 km) long was constructed from the Middleton-in-Teesdale–Brough road. The mine was brought into production in 1945 and had produced 120 000 tons of dressed barytes by the time the first detailed description of the underground geology was published (Hill and Dunham, 1968). Much of the output so far had come from room-and-pillar workings in the wider part of the vein, and conventional stoping in narrower stretches, but by now an opencast operation was starting in the Arngill Valley. During the ensuing years, up to 1981 when the company went into liquidation, a further 160 000 tons of dressed product had been added, dominantly from opencut, but also from block-caving workings underground in the course of which a level at 5 fathoms (9 m) below the adit had been driven over 0.25 mile (0.8 km) westward, linking with old workings beneath Closehouse Hush. In 1981 the mine was taken over by Fordamin Ltd, a subsidiary of English China Clays plc, who, up to 1985, added over 30 000 tons from opencasting. Galena recovery during the operations from 1945 onward amounted to roughly 0.5 per cent, indicating a production of 15 000 tons. The mine was taken over in 1989 by Closehouse Minerals Ltd.

    The primary 6-inch geological survey of Yorkshire Sheet 3, carried out between 1870 and 1882 was by W Gunn and published uncoloured. A revision was undertaken in 1958–1967 and 1:50 000 sheet 31 (Brough under Stainmore) was published in 1974, accompanied by a descriptive memoir (Burgess and Holliday, 1979), containing accounts of the regional structure (especially fig. 45) and the mineral deposits (chapter 12). The Closehouse area has also been the subject of an IGS Mineral Reconnaisance Study, including airborne magnetics, EM and radiometry (Cornwell and Wadge, 1980). In addition to the surface and underground geological mapping published by Hill and Dunham (1968) an unpublished PhD thesis by C J Carlon (1975) contains 1:480 mapping of the two principal levels and a series of isometrtic drawings tracing the changing shape of the deposit.

    The Lunedale Fault, linking W with the Swindale Beck Fault, is believed to follow a curving SW course W of Closehouse Hush, crossing the heavily drift-covered area of Lunehead Moss. The southernmost outcrop of the Great Whin Sill, here intruded between the Smiddy and Lower Little limestones terminates against the fault, as can be seen in Closehouse Hush, where Single Post and

    Scar limestones, and Slaty Hazle on the hangingwall are faulted against dolerite and overlying sandstone (the quartzitic bed above the Smiddy Limestone) on the footwall. Baryte is present in what may now be called the Closehouse North Vein, indeed exploration from the head of the hush, incomplete in 1981, suggests it may be present in quantity. The dolerite shows a sill edge magnetic feature (Cornwell and Wadge, 1980, fig. 5), but the North Vein Fault has been intruded by a dyke (of the Whin Sill Suite since it shows no signs of the phenocrysts so conspicuous in the Cleveland suite) along much of its course. Deerfold Level, driven from [NY 8416 2242] at 1623 ft (495 m) above OD and running 738 ft (225 m) N 30°W gives a useful section across the Lunedale Fault structure. At 640–605 ft (195–184.4 m) a fairly fresh quartz dolerite dyke, inclined 55° S, has shaly gouge on the S side of it; it is not yet certain whether the dyke lies N or S of the North Fault, but the latter appears more probable from the position of the 5-Fathom Level, discussed below. No strong mineralisation was found at this end of the level. The beds, probably belonging to the Alternating Beds beneath the Scar Limestone, dip steeply N and their apparent thickness is increased by S-opposing low-angle faults at 460 ft (140 m) along which a crosscut has been driven WNW, and at 365 ft (111 m) from the portal; here there is an inclined rise up 30 ft (9 m) but very little mineralisation was found. At 260 ft (79 m) a steep fault, hading 10°N was passed through, and was followed by, a drift to the E; this is (according to Gunn) Closehouse Vein and shafts along it farther E show some quantity of barytes; this was referred to erroneously in the 1st edition of this Memoir as the Closehouse–Standards Fault; it is now considered to merge with the North Vein at the No. 3 or 'Shale' deposit, described below. Finally, Deerfold Level cuts through another dolerite dyke dipping 80° N, from 152 to 185 ft (46.3 to 56.4m); this has been intruded into the South Fault, but here there seems to have been little if any postdyke movement and the dolerite is little altered. S of the dyke the beds cross an anticlinal crest to dip 10–15°S into the Cotherstone syncline. Thus the S margin of the Lunedale fault-belt is followed by a well-defined assymetric antincline, with the South Fault and Dyke at or near its crest. This structure is well displayed in the West and South hushes at Arngill and the crosscuts from Closehouse Mine. The dyke gives off a small sill to the S, about 1000 ft (305 m) long forming the crest of the hill above Closehouse Crags, which expose the Slaty Hazle; southward there is a gentler dip slope on Scar Limestone, with Cockleshell and Tynebottom limestones under drift in the Arngill Valley. Steep dips to the N on the Tynebottom Limestone on the E side of the valley show that it has become involved at surface in the steep limb of the anticline (see Cornwell and Wadge, 1980, fig. 3, section). Above South Hush, however, fault and dyke coincide with the crest of the fold.

    Closehouse Mine (Closehouse Minerals Ltd) works barytes from the Closehouse North Vein (Plate 8). The fault dips at 45–52° S and was intruded, prior to mineralisation, by a quartz dolerite dyke up to 100 ft (30 m) wide, though probably averaging somewhat less than this; it is likely that it was a feeder for the Great Whin Sill which, in Arngill as well as W of Closehouse Hush, was intruded at the horizon of the sandstone between the Lower Little and Smiddy limestones; the dyke may well not have extended above this level. Compression probably preceded the intrusions, producing the asymetric anticline and complementary sharp syncline N of it (see Hill and Dunham, 1948, figs. 1 and 2) or this folding may represent subsidence into the Stainmore Trough, already containing more than 2 km thickness of Carboniferous sediment, down the growth fault. Tensional conditions must however have prevailed when the dykes were emplaced, and No. 1 crosscut the 5-Fathom Level gives evidence that the South dyke was fed from the North by way of an inclined channel beneath the Smiddy Limestone. Further tension and perhaps some transcurrent movement after the consolidation of the dykes produced many closely spaced, near-vertical fractures in the North dyke, meanwhile converting it into 'white whin' composed essentially of carbonates, clay minerals and subsidiary anatase; and the flow of mineralising brines, bringing BaSO4 in large quantities, with minor zinc, lead, iron, arsenic and antimony sulphides (Vaughan and her, 1979) followed. For the most part the baryte crystals are coarse, commonly 4 inches (10 cm) or more long, suggesting quiet conditions during crystallisation (Plate 9). The ore from No. 1 orebody, the largest and most important, largely consists of a mixture of these with white whin, but masses of nearly pure baryte up to 8 ft (2.4 m) across were not uncommon and so long as a room and pillar mining method was used, these could be mined selectively. The working levels were the 5-Fathom at 1587 ft, (484 m) above OD and the 17-Fathom at 1512 ft, (461 m) above OD). An attempt to establish a level at 23-Fathoms failed because the inflow of water was too heavy. The No. I orebody extended westward to grid ordinate 8470 E; the mineralisation then fingered out on both levels into 'white whin', and the width of the dyke diminished. The 17-Fathom Level was driven on and after 300 ft (91 m) a lenticular baryte vein, widening to 6 ft (1.8 m), appeared against the footwall. In passing it may be noted that the footwall of the North Vein throughout shows flat-lying sediments typical of the Alston Block (see Hill and Dunham, 1948, p1.12) ranging from the Smiddy Limestone down to the Melmerby Scar Limestone; the 17-Fathom Level was remarkable in remaining for virtually its whole length, against a wall of Robinson Limestone. Hangingwall conditions vary considerably, owing to the differing impact of the strata in the syncline. At grid co-ordinate 8470 E a fracture which diverged from the footwall trending S 78°W brought in a remarkable belt of black ore, consisting of coarse baryte crystals with carbonaceous and argillaceous material between them, associated with black clay and gouge. It is suggested that the area where this, the so-called 'Shale' orebody, occurs coincides with the merging of Closehouse Vein (p.256) with North Vein. The dyke virtually disappears for over 100 ft (30 m) here and may have been prevented from being intruded by a wall of strong gouge; but if this was so, the gouge must later have become largely liquified in the presence of the mineralising brines, acting as dispersing agents. The 'Shale' orebody continues along the footwall for about 550 ft (168 m) and averages about 40 ft (12 m) wide. White whin then reappears at a WSW junction which is, however, less well defined than the eastern one since here, fragments of dyke occur in the gouge. This orebody was developed considerably above the 5-Fathom Level, and an incline was sunk successfully to 100 ft (30 m) below the 17-Fathom Level. This orebody, No. 3, was extracted by block caving methods until 1981 when the underground mine was closed. Further development of the 5-Fathom Level to grid co-ordinate 8415 E brought to light additional lenticular masses of baryte, but the last 200 ft (61 m) showed only a tight limestonedolerite contact. Impoverishment in the 17-Fathom level had set in earlier.

    Reverting now to No. 1 orebody, it was decided in 1962 to try civil engineering methods of recovery. Pumping tests using two borehole pumps and one air pump, with total capacity about 700 gpm failed to lower the water below 1460 ft (445 m) above OD, but Arngill Beck was diverted to the E side of the valley, the Fish Lake was drained, and opencast operations began following the drilling of a line of four boreholes across the valley of which the western three, though not well recovered, indicated a probable extension down the dip on North Vein for as much as 180 ft (55 m) below valley level, under drift and alluvium about 60 ft (18 m) thick (Plate 10). Once established for the pit, the pumping rate required proved to be about 400 gpm, according to information supplied by Mr Alan Orr, and the ore, against a footwall of Melmerby Scar Limestone, was extracted down to approximately 1444 ft (440 m) above OD when the operation ceased in 1981. The new owners have backfilled this part of the pit, in order to gain access to the block around the former underground incline to the W, and shortly the whole of No. 1 orebody will have been removed in this direction. Additional boreholes have confirmed the downard extension of the oreshoot beneath 1444 ft (440 m) above OD, sufficient for further opencast operations. Already with 310 000 tons of dressed barytes production, sufficient probably remains, according to Mr C M Bristow, to place Closehouse in a leading positon among epigenetic barytes deposits in Britain. He considers that No. 1 orebody terminates to the E against a fracture indicated by a photolinear running NNW on the E side of the access road. An early magnetic survey by P Fenning of IGS (unpublished) suggests a shift of the South Dyke by the same fracture. The total dimensions of the mineralised dyke constituting No. 1 orebody as at present known are: length, 1400 ft (427 m), height (base of Melmerby Scar Limestone to top of Smiddy Limestone on footwall) 250 ft (76 m), width 60–100 ft (18–30 m), yielding mill feed with 60–70 per cent BaSO4. Part of this orebody was of course eroded in late Pleistocene times, leaving very large baryte boulders near the bottom of the superficial deposits (see discussion by Hill in Hill and Dunham, p.369). At least one-third of the original orebody must have been so removed. In addition to the substantial solid resource remaining in No. 1 deposit beneath the valley, it may be noted that Mr Alan Orr (personal communication) estimated reserves remaining in 1981 in and W of No. 3 orebody as at least 50 000 tons, without including the extension of No. 3 beneath the 17-Fathom Level or prospective ore at the head of Closehouse Hush.

    A cluster of large baryte boulders was also found on the E side of the Arngill Valley, about 500 ft (150 m) N of the main structure, in a position corresponding with an ENE fault mapped by W Gunn as branching from North Vein. Magnetic measurements by Hallimond and Butler (1949) gave support to the existence of the fracture, but later attempts to prove it by boring were unsuccessful. A number of borings were made on the N side of East Hush following the discovery of other baryte boulder trains, but no orebody was found. Mr Bristow (in litt.) suggested that those low down in Arngill may be related to the NW fracture already mentioned. This view has now been justified by the discovery of a new replacement orebody on the line of this fracture, E of the stream.

    The continuation of the Lunedale Fault-system E of Arngill reveals further complexity. According to the revised geological mapping for Sheet 31, the North and South fractures cross near the low end of East Hush. Faults are certainly required on either side of this excavation, which exposes a tight anticline with axial plunge about 30° W, bringing limestones identified as the Jew, Lower Little and Smiddy to surface at successively higher elevations. There appears to be little mineralisation, and the bounding faults have not been drilled or exposed underground. According to Cornwell and Wadge, dolerite may be present at depth, producing anomaly 6 on their 1980, fig. 9. S of East Hush the dips indicate that the steep limb of the anticline is probably S of the bounding fault, and indeed the steep structure already mentioned as exposed by the hush may be regarded as a segment of this anticline swung round between the faults. Farther S a small patch of Whin Sill appears between the Tynebottom and Scar limestones, and interpretation of the airborne magnetics suggests a NNW fracture nearby; this and several other faults cross the col between East and Standards hushes. The latter reveals, in its deep cutting, simpler conditions, with Whin Sill on the N side faulted against structureless sandstone on the S. Near the head of the hush, digging in 1976 revealed massive baryte up to 10 ft (3 m) wide, and Mr Orr (personal communication) described the finding of many large blocks during bulldozing of the loose fill in the cut. Lenses up to 3 ft (1 m) wide can also be seen in the steep face of the dolerite, but so far, no large deposit has been located. An access road to the col was however completed by A G Allen Ltd, and the area is ripe for prospecting.

    Wensley Vein–Hunter's Vein group

    The veins listed above were worked at Lunehead Mine (disused) situated on the south side of the Middleton-in-Teesdale to Brough road, 6 miles (9.6 km) E of Brough. The mine is an old lead mine, probably dating back at least as far as the eighteenth century. It was worked by the London Lead Co. between 1770 and 1880, probably contributing the major part of the 2369 tons of lead concentrates obtained by this company from its Yorkshire mines between 1843 and 1879. Barytes production commenced in 1884 and continued, mainly under the Reynoldson family of Brough, until 1937. The recorded output from 1884 to 1913 was 35 707 tons, and it is likely that this mine contributed the greater part of the Yorkshire output of 41 538 for 1914–1937. The total yield is thus estimated to have been not less than 70 000 tons. Some additional production was obtained from Nacky Vein by Athole G Allen Ltd who held the lease from 1939 to 1981, and who undertook exploratory work both for barytes and witherite.

    The main adit level [NY 8460 2051] runs slightly E of S from the bank of Cleve Beck, one of the Lune headwaters, starting in the shale below the Quarry Hazle, at about 1350 ft (411 m) above OD.

    It cuts successively the veins listed above, in the order stated. At 925 ft (282 m) from the portal the base of the Quarry Hazle appears in the level roof, dipping S. Nacky Vein brings the Tuft into the level, while S of White Vein it is in the Great Limestone, continuing at this horizon to No. 1 Vein. The oreshoots on the veins were prin- cipally in the Great Limestone. The broad structure appears to be a gentle half-dome, for on the E side of the mine, the beds dip eastwards, on the S side there is a gentle S dip, while to the west the dip swings westward. The inclination of the beds nowhere exceeds 10°. The London Lead Co. section showed the Great Limestone reaching the abnormal thickness of 102 ft (311 m) but more recent examination of mine and adjacent boreholes has failed to confirm this thickness. It is overlain by shales with thin sandstones and limestones up to the Crag or Crow Limestone. Underlying the Great Limestone, the Tuft consists of 18 ft (5.5 m) of fairly hard sandstone. The height of potential productive ground thus amounts to 80–90 ft (624–27 m).

    The veins are all mineralised, baryte being the principal constituent, associated with small quantities of galena and aragonite, with, rarely, a little witherite and barytocalcite. In addition to the vein oreshoots, flats carrying baryte in a matrix of slightly limonitised limestone and clay occur between the Cavern and No. 1 veins, apparently related to a series of minor strings. Cutting through Nacky and Cavern veins, and traversing the replacement ground there is a belt of postmineralisation caverns having a general WNW trend. These are clearly later than the veins and flats, which are exposed on their water-worn walls. Residual galena was at one time obtained from the clay covering the floors of these caverns. Wensley Vein, 375 ft (114 m) from the portal of the adit level, has only been worked from shallow opencuts. Trials for barytes have revealed widths up to 4 ft (1.2 m) but no workable continuous oreshoot has yet been found on this vein. It may, however, merit further investigation.

    A string cut 1050 ft (320 m) from the adit mouth has been worked to a small extent from a shaft 30 ft (9 m) deep, 500 ft (152 m) S of BM1460.7 on the main road, in the Great Limestone [NY 8449 2013], but it has not been worked from the adit.

    Read Vein (1175 ft (358 m) from adit mouth) has been extensively worked from a branch of the main level known as Black Level; the workings are said to extend 1700 ft (518 m) SW of the adit, nearly to the intersection with Wensley Vein. They are said to contain some reserves. NE of the main level, ground which may not have been worked over for barytes may remain; Read Vein has been proved to extend 1000 ft (305 m) in this direction, and baryte is scattered round old surface shafts.

    Nacky Vein (1500 ft (457 m) from adit mouth) has been worked underground only to the NE of the main level. It is said to be ex- hausted to the first rise, 500 ft (152 m) from the adit, and to have been partially worked out to Nacky Shaft, 910 ft (277 m) farther ahead [NY 8498 2021]. Nacky Shaft is 76 ft (23 m) deep, reaching the Tuft on the footwall side of the vein. In the succeeding 1150 ft (351 m) there are shallow superficial workings only, and the vein is assumed to be intact in depth apart from a level 55 ft (17 m) below the collar of Nacky Shaft. There is a shaft 60 ft (18 m) deep [NY 8535 2035] 1160 ft (354 m) farther NE, where the vein begins to change course to ENE. The vein had been opencut 15 ft (4.6 m) deep and up to 14 ft (4.3 m) wide nearby and at [NY 8541 2036] Athole G Allen Ltd sank an incline dipping WSW to produce barytes while Closehouse Mine was being developed; little now remains in the vein which narrows as it continues about 1150 ft (351 m) farther to the ENE.

    White Vein (1550 ft (472 m) from adit mouth), tried on both sides of the level, carries 1–1.5 ft (0.3–0.45 m) of baryte with specks of galena. This vein was also tried from the Nacky workings 250 ft (76 m) NE of the adit, where it is said to have been wider.

    Little White Vein (1950 ft (594 m) from adit mouth), carrying baryte 1.5 ft (0.45 m) wide, has been worked for a length of little more than 20 ft (6.1 m) NE of the main level, to a height of 50 ft (15 m).

    Cavern Vein, split into two subparallel branches where the main level reaches it at 2150 ft (655 m) from the portal, is too narrow, poor, and disturbed by postmineralisation erosion to be workable. To the SW, where the branches unite, the vein has been extensively wrought, the average stoping width being 4 ft (1.2 m). Near the forehead, 1900 ft (579 m) SW of the adit crosscut, the mineralisation changes to witherite. The replacement deposits lying S of Cavern Vein appear to offer little prospect of successful barytes working, owing to their low grade.

    Lunehead No. 1 Vein (2800 ft (853 m) from adit mouth) was reached by three branch levels from the main adit; the central one was extended a short distance beyond the vein to [NY 8472 1960] which represents the southermost penetration of lead exploration into the Stainmore Trough from the N. There would be little incentive to continue this drive since it would lose control of the Great Limestone. No. 1 Vein has been worked for barytes from the central branch only, the workings lying W of this branch. Galena increased in amount as the vein was followed westward. The vein also yielded galena eastward from the middle branch level for 1400 ft (427 m) to the point where Hunter's Vein branches off. Here the old lead stopes are stated to have been filled with barytes, but the ground is in a partly collapsed condition.

    Hunter's Vein has been explored from Rennygill Level [NY 8638 2058] starting 5800 ft (1.77 km) E of the main adit portal, beneath Rennygill Bridge at 1254 ft (382 m) above OD. The level runs 2250 ft (686 m) S55°W, then turns NW into Hunter's Vein. It starts near the base of the Great Limestone, but owing to the westward rise of the beds, ends in the Quarry Hazle; it is no longer accessible. Hunter's Vein crops out at Foster's Hush [NY 8594 2044], close to the main road; here its principal constituents are witherite and barytocalcite (Young, 1985). These minerals are also present on shaft dumps around [NY 8570 2020] near the workings from Rennygill Level, 1250 ft (381 m) SW of the hush. Samples from Foster's Hush, taken when Athole G Allen Ltd opened it up, averaged as follows: BaCO3, 87.0 per cent; Insol. (SiO2), 7.52; Fe2O3 + A12O3, 0.14; CaCO3, 6.18. Five borings were drilled into the vein between the hush and the intersection by Hunter's Level. A drift 486 ft (148 m) was driven SW from the hush, and an old shaft 675 ft (206 m) SW of the forehead of the drift was reopened. For the most part, the vein proved to contain only a few inches of witherite, in places associated with weak flats in the Great Limestone. The extensive explorations here by Athole G Allen Ltd in 1959–62 thus failed to disclose a workable witherite deposit. Hunter's Vein is the easternmost of the Lunehead veins.

    A thorough underground examination of Lunehead Mine by J R Foster-Smith, A R D Orr and A C Dunham for Messrs Allen's suggested that the mine was effectively exhausted when J G Reynoldson ceased operations in 1936, save possibly that flats related to the Cavern veins might have been workable had the main adit been in good condition; the adit has now been closed.

    Between 1963 and 1967 Messrs Allens investigated the area west of the mine workings adjacent to Rowton Syke, around [NY 842 199], where Wensley, Read and Nacky veins converge. A total of eight boreholes were drilled along a line extending from [NY 8394 2003] to [NY 8403 1986]; of the six on NY 81NW, three were inclined NW, the remainder inclined SE. These showed that the beds are downfaulted to the SE in a series of steps, accomplishing a total displacement of 120 ft (36.6 m), with a NW upthrow of only 11 ft (3.4 m) on the southern fracture, perhaps a flyer off Nacky Vein. Baryte was widespread in the boreholes, but in small widths, and when a shaft [NY 8397 1986] was sunk to 60 ft (18 m) and crosscutting was carried out, only one lens reached 3 ft (0.9 m) wide and most intersections in the Great Limestone and Coal Sills Group were no more than 1 ft (0.3 m) wide, including some replacement in the limestone. The indications were not regarded as sufficiently favourable to justify sinking to the lower intersections and though a substantial mineralised body may exist as a result of replacement of limestone between the several fractures, the grade appeared likely to be too low for mining. The group of boreholes gives evidence of a reduction in thickness of the Great Limestone, to about 72 ft (22 m), with the inclusion of Cherty shale ('lime plate') in its upper part; these changes might also be regarded as unfavourable. A series of surface trenches between Rowton Sike and Boundary Shaft [NY 8347 1959] on the former Yorkshire/Westmorland, (now Durham/Cumbria) border reached solid rock under as much as 16 ft (4.9 m) of drift, and showed podiform baryte continuing against limestone, sandstone and shale wallrocks. The mineral is present on the dump from Boundary Shaft. This shaft was drained by a level [NY 8342 1980], driven from Dirty Pool, in the shale above the Great Limestone. The fault can be traced 1 mile (1.6 km) SW into Cumbria, and though no baryte was found in an old level above the Great Limestone at Deadmangill Bridge [NY 8234 1890], it is present in the limestone W of the road to Brough.

    Silver Keld Vein—Lead ore (barytes)

    NY 81 NW, 82 SW; Westmorland 17 NW; Yorkshire 3SE Direction N40–55°E, displacement on S fracture up to 43 ft (13 m) SE

    A complex of small faults crossing the Durham/Cumbria border adjacent to the Middleton-in-Teesdale to Brough road has been tested at intervals over a distance of 0.5 mile (0.8 km) SW of the boundary, and a similar distance to the NE between [NY 825 197] and [NY 838 203]. The southern fracture has also been called Green Hill Vein. Athole G Allen (Stockton) Ltd carried out a trenching programme on both sides of the county boundary in the 1960s, and five borings were put down into the northern fracture on the Durham side, but without disclosing ground workable for barytes. There may have been a small production of lead ore from here in the remote past.

    Thornwaite Fault

    NY 81 NW; Westmorland 17 NW. Direction N5–25°E, displacement up to 175 ft (53 m) E

    The three faults of the Closehouse mining area (p.255) unite to the SW of Closehouse Hush, and the direction gradually changes from near E–W to N–S before its junction, at [NY 8189 2062] with the Swindale Beck Fault, which carries the greater part of the displacement towards the SW. The Thornwaite Fault continues the southerly trend S of the junction. Veinlets with baryte were noted during the resurvey in Great Limestone adjacent to Coal Sills Sandstone at [NY 8095 2005] and a width of 5 ft (1.5 m) of the mineral was formerly exposed in the fault at [NY 8143 1893]; bulldozing at the latter site indicated that the lens is not large enough to be workable.

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    POOLE, G. 1937. The barytes, fluorspar and lead resources in Upper Teesdale and Weardale. Report of the Technical Advisory. Committee., North-East Development Board, Newcastle.

    SHAYLER, A E, ALMOND, J K, and BEADLE, H L. 1979. A guide to the past lead industry in Swaledale and Weardale. Cleveland Ind. Archaeol. Soc. Res. Rep., No. 2. 48pp.

    WAGER, L R. 1929. Metasomatism in the Whin Sill of the North of England. Part II. Metasomatism by lead-vein solutions. Geol. Mag., Vol. 66, 97–110.

    WILSON, G V, EASTWOOD, T, POCOCK, R W, WRAY, D, and ROBERTSON, T. 1922. Barytes and witherite (3rd edition). Spec. Rep. Min. Resour. Mem. Geol. Surv. G.B., Vol. 2. 119pp.

    YOUNG, B. 1985. The distribution of barytocalcite and alstonite in the Northern Pennine Orefield. Proc. Yorkshire Geol. Soc., Vol. 45, 199–206.

    YOUNG, B. BRIDGES, T F, and INESON, P R. 1987. Supergene cadmium mineralisation in the Northern Pennine Orefield. Proc. Yorkshire Geol. Soc., Vol. 46, 275–278.

    YOUNG, B. STYLES, M T, and BERRIDGE, N G. 1985. Niccolite magnetite mineralization from Upper Teesdale, North Pennines. Mineral. Mag., Vol. 49, 555–559.

    Chapter 13 Mineral deposits

    Details, Area 8 Haydon Bridge

    The small mining field lying in the Tyne Valley near the towns of Haydon Bridge and Hexham is separated by at least 7 miles (11.3 km) of country devoid of known mineral deposits from the northernmost veins of the main mining field. The deposits, however, both in their form and mineral contents, quite evidently belong to the same mineralisation province, and the only important geological difference between the fields lies in the greater thickness of the argillaceous and arenaceous beds in the Carboniferous Limestone Series at Haydon Bridge, a subject which has already been discussed in Chapter 2.

    W and N of Haydon Bridge, a NE-trending belt of mineral veins, 5.25 miles (8.4 km) long extending from Morralee, south of the Tyne, through Waterhouse, Langley Barony and Settlingstones mines to the Stonecroft-Greyside group has yielded important quantities of lead ore, and has produced (at Settlingstones) half the world's supply of witherite. The only other mine of major stature in the field is at Fallowfield, 2 miles (3.2 km) N of Hexham. Among all these deposits, the fluorite zone is unrepresented and there are only the two outer zones–galena-barium minerals, with subsidiary sphalerite, and barium minerals with subsidiary sulphides.

    Owing to the presence of the Carlisle–Newcastle main railway in the Tyne Valley, and the good road communications, the mines of the Haydon Bridge area are more favourably placed than many in the Northern Pennines. Mineral royalties are owned by the Catholic Trust, the Duke of Northumberland, and other private landlords.

    Morralee Vein—Lead ore

    NY86SW; Northumberland 90SW (New Series). Direction N60–70°E, displacement 28 ft (8.5 m) SE

    In Morralee Wood, on the east bank of the River Allen, 1 mile (1.6 km) S of its confluence with the South Tyne, four ENE faults are exposed traversing thin limestones, sandstones and shales in the upper part of the Namurian. None of them is mineralised at outcrop, but the southernmost one was proved to carry ore by a crosscut adit [NY 8042 6350] driven S from the N side of Morralee Wood, starting 1000 ft (305 m) E of the Allen. The Haydon Bridge whin dyke crosses the Allen 900 ft (274 m) N of the southernmost fault. An adit [NY 8042 6368] starting 1100 ft (335 m) ENE of the Morralee Wood adit has, according to the primary geological map, been driven through the dyke to the vein, which here lies 400 ft (122 m) to the S. A shaft 200 ft (61 m) E of the line of this adit has been sunk near the south wall of the dyke in shale and sandstone. It appears, therefore, that some exploration has been done along the dyke, but no plan is available to confirm this.

    The minerals on the small dumps are calcite, baryte and limonite; the workings appear to have been in sandstone and limestone. The mine was active from 1856 to 1864, and again in 1880–81, producing a total of 119 tons of lead concentrates containing 7 oz silver per ton of lead.

    Bewick Vein–Dixon-Brown Vein group

    On the north bank of the South Tyne, 1500 ft (457 m) WNW of Lipwood House, the Waterhouse Mine (disused) has worked a vein, believed to be the Bewick Vein of Langley Barony Mine farther north. A level starts on the S side of the Haydon Bridge–Bardon Mill road [NY 8102 6471], running N as a crosscut to reach the vein 150 ft (46 m) from the portal. Workings extend 950 ft (290 m) NE along the vein, probably in sandstone and shale above the Four Fathom Limestone and cut at least three cross veins. Minerals on the dump include pink massive baryte, with subordinate amounts of witherite, ankerite and galena. The total output of lead concentrates for the years 1861–65, 1880–81 amounted to 572 tons, carrying 7 oz silver per ton of lead; this figure, however, includes a small tonnage from Morralee and Howdenside mines in 1865 (Smith, 1923, p.34).

    The same vein was tested at Whinnetley Mine (disused) by an adit level [NY 8153 6478] starting from Honeycrook Burn 1000 ft (305 m) NNE of Lipwood House. The level pursues a sinuous NNW course, reaching the vein about 1200 ft (366 m) from the portal. It begins in the Four Fathom Limestone, but owing to the northward dip of the beds, the top of this limestone goes into the level sole 350 ft (107 m) from the portal, and the section shows that the vein is cut in grey beds 60 ft (18 m) above the Four Fathom Limestone. The workings from the level were not extensive. On the dump from an old dressing-place near Lipwood House pink baryte is present. The recorded output of lead concentrates, 1858–1860, was 136 tons. A 0.5 mile (0.8 km) untried stretch of the vein lies to the NE of Whinnetley Mine.

    Langley Barony Mine (disused), on the N side of Honeycrook Burn, 2 miles (3.2 km) N of Haydon Bridge railway station is the first of the important producers in the Haydon Bridge mineral belt. The bulk of the output of lead concentrates obtained during the short life of the mine from 1873–1893, a total of 40 761 tons, containing 75 per cent lead and 2.3 oz silver per ton of lead, came from the Bewick Vein. The oreshoot on this vein was probably discovered by the driving of an adit [NY 8254 6587], following a NW fault which crosses Honeycrook Burn throwing 24 ft (7.3 m) NE; this reached the Bewick Vein 450 ft (137 m) NW of the portal. The mine was developed from a new adit [NY 8263 6592], starting 300 ft (91 m) ENE of the old one, following a second NW fault which throws 9 ft (2.7 m) NE; and from two main shafts, Leadbitter Shaft [NY 8260 6612], 650 ft (198 m) N of the new adit portal, and Joicey Shaft [NY 8314 6659], 2200 ft (671 m) to the NE of Leadbitter Shaft, both sunk on or to Bewick Vein. Leadbitter Shaft is 520 ft (158 m) deep, starting 60 ft (18 m) N of the outcrop of the vein (here under 94 ft (29 m) of boulder clay) in grey beds 61.5 ft (18.75 m) above the top of the Four Fathom Limestone, and ending in shale 140 ft (42.7 m) below the base of the Three Yard Limestone, 40 ft (12.2 m) S of the vein, which has a very small hade. Joicey Shaft (a section of which has been published by Smith, 1925Note, however that the limestone identified by him as the Five Yard 57 ft (17.4 m) below the Three Yard, would now be regarded as the Upper Redhouse Burn Limestone; see (Figure 6), p.40 pp. 31–32) is 530 ft (161.5 m) deep; between the 27- and 41-fathom levels the vein passes through this shaft. The important features of the stratigraphy have been incorporated into (Figure 6), p.40.

    The principal oreshoot was on Bewick Vein, with a length of 4400 ft (1.341(m), and an average height of about 175 ft (53 m), following the beds from the Four Fathom down to the Three Yard Limestone. The beds beneath the Three Yard Limestone carried two smaller oreshoots, each about 400 ft (122 m) by 100 ft (30 m), separated from one another and from the main oreshoot above by barren ground. The bottom level was below the limit of the two smaller oreshoots except for two very short stretches: in these, winzes failed to find any extension of workable ground. The principal levels on Bewick Vein were the adit, at 450 ft (137 m) above OD; and levels from the shafts at about 400, 220 and 120 ft (122, 67 and 37 m) above OD.

    A crosscut was driven 950 ft (290 m) NW beyond Bewick Vein from the 400 ft (122 m) above OD level, to reach St Andrew Vein, and its NE branch, New Vein. Small oreshoots were found in the Great and Four Fathom limestones, but these veins were of slight importance compared with Bewick Vein. The crosscut was continued 1100 ft (335 m) NW beyond St Andrew Vein, reaching a point beneath the workings of Whinnetley Colliery in the Little Limestone Coal (formerly worked, with Langley Barony lead mine, by Bewick and Partners), but without discovering any additional veins. The forehead of the crosscut, at 400 ft (122 m) above OD, is approximately 235 ft (71.6 m) below the Little Limestone Coal. St Andrew and Bewick veins were also linked by a crosscut at 225 ft (69 m) above OD, which revealed a small vein called Dixon-Brown Vein 650 ft (198 m) NW of the latter. This vein did not prove workable either here or where found by two crosscuts in the northeastern part of the mine.

    Baryte dominates the mineral assemblage at Langley Barony. The average galena-content of the ore is said to have been 2 tons per cubic fathom (Smith, 1923, p.33) equivalent, at 10 cu. ft per ton, to 9.2 per cent. Sphalerite is present, but was not recovered during the initial operations, no doubt owing to the difficulty of separating it from the baryte by gravity methods. Witherite, ankerite and pyrite are present in subordinate quantities. The tailings dumps remaining are extensive; their total tonnage was estimated by Mr J H Hohnen for Non-ferrous Minerals Development Control at 92 000. Preliminary samples taken during the Geological Survey investigation from numerous superficial pits gave the results shown in (Table 69).

    Sampling by boring, carried out by Mr Hohnen, gave a figure of 5.2 per cent zinc, 0.8 lead (in sulphide form) for the Langley Barony dumps. A complete estimate of barium-content is not available, but the preliminary estimate suggests that nearly half the dumps consist of barium minerals. During the 1950s these dumps were treated in the portable flotation plant of Minerals Treatment Ltd, recovering about 4000 tons of zinc concentrates. The remaining tailings which should contain about 40 000 tons of baryte, await flotation treatment. Underground there is no evidence of any substantial tonnage of barium minerals left in the workings. The next likely horizon for major oreshoots would be, on the evidence of Settlingstones and Stonecroft mines farther N, the Whin Sill. Stratigraphical considerations (see pp.36, 37) indicate that if this is at the same horizon as at Settlingstones, a sinking of 550 ft (168 m) at Leadbitter Shaft, or 500 ft (152 m) at Joicey Shaft, would be required to reach the top of it. However the section accompanying Geological Survey Sheet 13 (Bellingham) shows that the sill tends to change its stratigraphical horizon upwards towards the SE, so that these figures could probably be regarded as maxima.

    Settlingstones Vein—Witherite, lead ore

    NY86NW, NE; Northumberland 90NE, 81SE (New Series) Average direction N50°E, displacement: near Grindonhill Mine, 55 ft (16.8 m) SE; at Frederick Shaft 86 ft (26.2 m) SE; NE of Winter's Shaft, 12 ft (3.7 m) SE.

    Some 2430 ft (740 m) of virgin ground lie between the Langley Barony NE foreheads and the workings of the next mine to the N, Settlingstones Mine (disused). The vein formerly worked here lies at least 1000 ft (305 m) NW of the course of Bewick Vein, and if it is equivalent to any of the veins at Langley Barony, New Vein appears the most likely. Settlingstones Vein was probably discovered at outcrop in Settlingstones Burn, which it crosses at [NY 8512 6903] 1 mile (1.6 km) WNW of Newbrough Lodge; here the uppermost fine-grained part of the Whin Sill is exposed on the footwall of the vein while "whetstone" (metamorphosed sandstone and shale) and the limestone identified during the primary geological survey as the Scar (but on the revised sheet is regarded as the Colwell) appear on the hangingwall. The lead oreshoot here was known by the later years of the seventeenth century (Smith 1923, p. 29; Trestrail 1931); lead ore was produced until 1873. It extends 450 ft (137 m) NE and 1900 ft (579 m) SW of Settlingstones Burn; the bearing horizon throughout is the Whin Sill, 128.5 ft (39 m) thick at Old Engine Shaft, 450 ft (137 m) SE of the beck. The deepest productive level in this stretch of the vein was the 80-Fathom, at 134 ft (41 m) above OD. Continued exploitation to the SW revealed a cross-course striking N75°W, which imparted a shift of 150 ft (46 m) S side W to the main vein. Here a remarkable change in mineral-content took place. The gangue of the lead oreshoot was a mixture of baryte and ankerite. SW of the crosscourse, after a barren interval 400 ft (122 m) long, the mineralisation changed to witherite, with only very small amounts of sulphides, and a little baryte, strontianite, harmotome and traces of barytocalcite. From 1873 to 1968 the mine was a steady producer of witherite and, indeed, for long periods was the only producer of this mineral in the world.

    The length of the witherite oreshoot was 4300 ft (1.31 km). To the SW it appears to terminate against a second major crosscourse in the neighbourhood of Grindon Hill Shaft [NY 8346 6767]. The bearing bed is again the Whin Sill dipping gently to the SW in the plane of the vein (Figure 41) but 155 ft (47 m) of beds beneath the sill also carried where the vein cut a quartzite-filled washout (see p.37). The average width of the oreshoot has been stated to be 8 ft (2.4 m) (Trestrail 1931); but in places it reached 30 ft (9.1 m). The average composition of the ore, based on many estimations made by Mr G F W Trestrail, when manager, is given in the table below. Many of the impurities were due to dilution with material from the walls. The baryte, however, appears to be due to late-stage alteration of the carbonate to sulphate. This effect, well seen in numerous cavities in the vein, is probably not due to changes in the oxidation-zone, as it extended far below the groundwater level and produced baryte crystals with well-developed characteristic morphology. Whereas the orebody was at its best with the Whin Sill on both walls, it also carried well with the Whin Sill on one wall only. The vein nips, however, above the top of the sill on the footwall, and the whole witherite oreshoot is "blind" upwards, as (Figure 41) shows. It has been worked to 110 ft (34 m) beneath the sill on the hangingwall and its economic limit was reached on the 145-Fathom level in the softer beds beneath the sill. The maximum vertical extent of the oreshoot proved to be about 500 ft (152 m). Minor constituents found in the vein near the 70-Fathom Level included niccolite and ullmanite, (Russell 1927) and gersdorffite (Young et al., 1985). Sir Arthur Russell has also identified harmotome in the vein (Young and Bridges, 1984).

    The vein is subject to the development of "loops" both on the small and the grand scale, and two such loops, the N and S branches, were respectively 600 and 1600 ft (183 and 488 m) long, both rejoining the main vein and both carrying workable witherite. A number of minor cross-veins, trending a little W of N and throwing a few feet E traverse the vein.

    The main working shaft, Frederick [NY 8423 6825] situated on the N side of the Fourstones–Grindon Hill road (Stanegate), 2 miles (3.2 km) W of Fourstones, is 700 ft (213 m) deep. The active levels prior to 1946 were the 80-Fathom (134 ft (41 m) above OD), the 90-Fathom (82 ft (25 m) above OD), the 100-Fathom (20 ft (6.1 m) above OD) and the 110-Fathom (35 ft (10.7 m) below OD). All the working ground was SW of Frederick Shaft, but north-east of it the 80-Fathom level was maintained as a water level, to the Ellen pumping shaft [NY 8500 6878] 3025 ft (922 m) NE of Frederick Shaft, close to which the treatment plant was situated. Pumps were installed at the 100-Fathom Level at Frederick Shaft to raise the water to the 80-Fathom Level; the total water pumped from the mine amounted to about 500 g.p.m. Winter's Shaft [NY 8460 6855] near the crosscourse which terminated the lead oreshoot, is 1500 ft (457 m) NE of Frederick Shaft; it has been filled in. Grindon Hill, or Dodsworth Shaft [NY 8346 6767], 3175 ft (968 m) SW of Frederick Shaft is an old trial shaft approximately 300 ft (91 m) deep, with levels at 20-Fathoms (560 ft (171 m) above OD) and 42-Fathoms (430 ft (131 m) above OD). These workings proved the Settlingstones Vein and the south-western crosscourse, but being some 300 ft (91 m) above the Whin Sill on the footwall of the former, very little mineralisation was found. No connection has been made from the Frederick Shaft workings to Grindon Hill Shaft, in which water stands to within 60 ft (18 m) of the collar.

    Additional details of the mine as it was up to World War II will be found in papers by G F W Trestrail (1931, 1938). The state of development in 1946 is shown on (Figure 30) of Dunham (1948). The lowest level, the 110-Fathom, gave adequate access to the main oreshoot which was following the 2–3° SW dip of the Whin Sill. However, at 1480 ft (451 m) SW of Frederick Shaft, the dip of the measures and the nearly concordant sill increased to 10° on the hangingwall side, and there proved to be a corresponding increase on the footwall side, offset some 425 ft (130 m) SW. In effect, the increased dip constitutes a monocline of amplitude 65 ft (20 m) facing SW. The effect upon the orebody was important since it followed the small fold downward; but this was reinforced by a significant change of lithology. At Frederick Shaft, the metamorphosed shale ('whetstone') under the Whin Sill is underlain by about 40 ft (12 m) of sandstone with some shale partings resting on black shale 12 ft (3.7 m) thick in turn resting on a limestone. In a south-westward direction the sandstone passes into, or gives place to white, medium-grained silica-cemented quartzite, known in the mine as the 'Carstairs Quartzite', the thickness of which, adjacent to the monocline, reached 120 ft (36.6 m). The quartzite may occupy a washout channel (as suggested on p.35) in which case the limestone already mentioned would be transgressed by it, but unfortunately the critical evidence was not exposed in the mine. Alternatively, the whole section may have thickened, for near the monocline 50 ft (15.2 m) of underlying black shale are succeeded by a 4–5 ft (1.2–1.5 m) limestone which seems to rise parallel to the base of the quartzite through the workings to the NE, and which might be the same one cut in Frederick shaft.

    The economic importance of these geological changes was that the witherite oreshoot went to much greater depths than previously expected. From inclines, levels were driven at 120-Fathoms (60 ft (18 m) below OD), 130-Fathoms (126 ft (38 m) below OD), 140-Fathoms (176 ft (54 m) below OD) and 145-Fathoms (206 ft (68 m) below OD). On the two lowest levels the lengths of productive ground were 400 ft (122 m) and 140 ft (43 m) respectively; the quartzite on the hangingwall was continuing to dip down, but the continuation of good ore values was limited to the SW by a minor crosscourse.

    From the 130-Fathom Level, a vertical borehole, starting 156 ft (47.5 m) below the base of the Whin Sill on the footwall, was put down to obtain stratigraphical data; a summary of the log is included in (Figure 6) (p.40). No further substantial hard beds comparable with the Carstairs Quartzite (which was to a large extent responsible for the postwar success of the mine) were discovered; moreover, at 170 ft (51.8 m), artesian water was cut in the porous sandstone underlying the limestone identified as the Oxford, this correlation depending on the second hypothesis outlined above, namely that the limestone at 40 ft (12 m) in the borehole is the same as that beneath the sandstone in Frederick Shaft, and which can be correlated with the Dalla Bank Limestone of Sheet 13 (Bellingham). This correlation is further discussed in connection with BGS boreholes at Newbrough (p.269).

    The south-western termination of the Settlingstones witherite oreshoot was supposedly reached when the 90-Fathom Level was driven into and along the Western or Grindon cross vein, finding among several others, an ENE vein with up to 6 ft (1.8 m) of mixed baryte and witherite, apparently offset NE from the North Branch of Settlingstones Vein that the 90-Level had been following. Examination of the wallrock showed, however, that this could not be the North Branch since the SE downthrow, about 50 ft (15 m), of that vein was not present. Near-horizontal slickensides on the cross vein suggested, from the roughness test, a S-side-E sense of movement, and the true continuation of the North Branch was located by driving on the 100-Level, revealing an offset in this direction of 80 ft (24 m), with a similar SW-side-SE offset of the South Branch. At least part of the movement on Grindon Cross Vein postdates the mineralisation, which is dragged in it and slickensided. For up to 20 ft (6 m) beyond the crosscourse, witherite is still present. In this area the fact that the witherite has replaced baryte can be established with certainty: the witherite, when thin-sectioned, shows interlocking platy pseudomorphs after baryte, and what is more striking bands of galena and sphalerite seen as part of the crustified structure when the vein is dominantly baryte can be seen to continue through cavities in the later witherite, or to hang into them. The view expressed by Hancox (1934) for witherite at Nentsberry is equally justified here. Beyond about 30 ft (9 m) from the cross vein, both branches are baryte veins showing narrow bands of sulphides alternating with the baryte near the walls, and colour-banding of the baryte, presumably related to iron-content, towards the centre. The South Branch reaches widths of 6 ft (1.8 m) or more, and shows more sulphide than the North Branch. It was developed for 330 ft (101 m) SW of the cross vein, and also explored for a short distance from the 110-Level, where its composition is similar. On the North Branch a drivage at the 100-Level revealed a baryte oreshoot about 4 ft (1.2 m) wide starting 130 ft (40 m) from the cross vein, and some stoping was done here revealing, however, that with existing transport arrangements at the mine, barytes production from mining could not be made to pay in 1954. The drive was nevertheless carried on 350 ft (107 m) farther, passing through crosscourses both imparting postmineralisation shifts SW side SE at 182 ft (55 m) (7 ft (2.4 m) and 332 ft (101 m) (4 ft (1.2 m) while at the end of the drive a stronger crosscourse was followed SW for 50 ft (15 m) without discovering the shifted vein. Some detail has been given here because this block of potential barytes-sulphide is the only reserve remaining in the mine; even on the existing limited evidence, this could amount to a possible 90 000 tons, with a long virgin stretch ahead; on the other hand a new shaft at least 750 ft (229 m) deep would be needed if redevelopment is ever contemplated.

    Two attempts have been made to find a northward continuation of the Langley Barony veins near Settlingstones. From the 120-Level a crosscut was driven S 38°E starting near the base of the Whin Sill at [NY 8370 6385]. The beds rose gently towards the SE, the base of the sill going into the roof at 625 ft (191 m) and at 700 ft (213 m) an ENE vein throwing 4 ft (1.2 m) N was cut. Upon development to the SE, witherite up to 2.5 ft (0.76 m) was found and limited stoping was done; a boring from surface gave no better encouragement. It was interesting however that the mineral was found in this ground between the prolongations of the Winter's Shaft and Grindon cross veins. The crosscut was continued to 770 ft (235 m) and a borehole rising at 14°S completed the exploration to 1150 ft (351 m) SE of the point of origin without discovering any other vein.

    In 1978–80, inspired by a magnetic survey by Lea Cross Geophysics Ltd that suggested that a NE-throwing fracture could exist farther to the SE, Selection Trust Ltd drilled a line of cored boreholes from [NY 8396 6788] to [NY 8430 6756] passing through the Eelwell Limestone and ending in the limestones above the Whin Sill or in the top of the sill. Six percussion and two cored holes proved to be sufficiently capable of correlation to disprove the presence of a fault of the magnitude suggested by the magnetic survey, but some witherite was found in the southernmost holes, and several holes showed dolomitisation of the Eelwell Limestone accompanied by minor zinc and lead values. A fracture or fractures of small displacement, to which this mineralisation could be related, may thus pass through the area. In a second phase, following seismic surveys, a second line of percussion holes (between  [NY 8420 6803) to  [NY 8446 6779]), aimed at the top of the Eelwell Limestone, was drilled, N of but converging upon the earlier line of holes. Although the top surface of the limestone was not found to be regular, no fault of the magnitude of Bewick Vein (42 ft (12.8 m) NW throw) passed through it, but the best interpretation of the data suggested, according to Dr F W Smith, two smaller faults that could represent the continuation of Bewick and Dixon Brown veins. Dolomitisation and other mineralisation was again found in the upper part of the limestone. No sufficient target for deep drilling was, however, considered to have been located. At the end of the life of Langley Barony Mine in 1892, T J Bewick had evidently recognised that the next main target (below the Redhouse Burn Limestone, in which the oreshoots then known are considered to have bottomed) was the Whin Sill but unfortunately he was not able to raise the funds to sink Joicey Shaft to this horizon. This, and the extension of the SW foreheads from Settlingstones beneath the St Andrews Vein workings remain the best prospects in the Haydon Bridge western area.

    N and NW of Settlingstones Vein a fault running nearer NNE and downthrowing NW has been mapped on the Bellingham Sheet, where it has been named the Grindon Hill Fault (not to be confused with the crosscourse of that name). It apparently produces a marked displacement of the Whin Sill outcrop, but it is not known to be mineralised unless the prospects at Tepper Moor (Wilson et al., 1922 p.8) or at Bath House are related to it; baryte is present at both. Recent geophysical exploration has been unable to detect any displacement in the Whin Sill by this fault. In the mid-1950s, a cross vein found on the footwall side of Settlingstones Vein from the North Branch, running almost due N was developed from the 70-and 80-Fathom levels in the upper part of the Whin Sill, yielding good stoping ground for witherite; values did not persist down to the 90-fathom level. At 300 ft (91 m) from the main vein a weak ENE vein was found on the NE side of the drive and followed for 80 ft (24 m), but though witherite was present it did not exceed 2 ft (0.6 m) wide and was unpayable. N of this junction, the crosscourse also deteriorated, and though it was pursued to 450 ft (137 m), it could not meet costs, and the untested fault mentioned above still lay about 4000 ft (1.2 km) ahead. This was the sole attempt to prospect northwards from Settlingstones, apart from a limited drive NW along Grindon Cross Vein until the narrow filling in it changed to baryte.

    The north-eastward continuation of Settlingstones Vein, beyond Winter's Shaft, was worked for lead over a length of 2190 ft (668 m), to beyond Settlingstones Burn. The height of the oreshoot here was less than in the witherite-bearing stretch, by reason of the sudden reduction in thickness of the Whin Sill N of Ellen's Shaft from 150 ft (46 m) to about 100 ft (30 m) and probably due to diminution of throw.

    In (Table 70), the quality of the product witherite is compared with typical run of mine ore during the 1940s. The dumps remaining from witherite treatment contain, in addition to rejected witherite, baryte, calcite, rock fragments and small amounts of sulphides, principally sphalerite. Presumably these dumps rest on older dumps richer in baryte, for this mineral was never recovered in the lead-mining period owing to the presence of sphalerite. No estimates of tonnage or composition are available. The dumps have now been landscaped. A recent proposal to rework the dumps for witherite failed to obtain planning approval.

    The output of product witherite from Settlingstones, 1873–1970 amounted in round figures to 630 000 tons; it was not only the leading producer of natural barium carbonate in the world but, so far, the leading producer of barium minerals in the United Kingdom. The output of lead concentrates, 1849–1873, was 16 902 tons, containing 70 per cent lead and 2.65 oz of silver per ton lead. No galena was produced from the witherite oreshoot.

    The north-eastern extension of Settlingstones Vein has been tested at Douglas Shaft [NY 8544 6912], which was sunk through 66 ft (20.1 m) of boulder clay, 14 ft (4.3 m) into the Whin Sill. The vein, proved by means of a NNW crosscut, carried only traces of galena, and it is presumed that it dies out in this direction. A branch, possibly diverging from the structurally complex ground in the vicinity of Ellen's shafts, may link up with the Stonecroft Vein described below, but strangely, this gap was apparently left untested.

    Stonecroft-Greyside Vein, Stonecroft Sun Vein and Greyside Cross Vein

    On the N side of Settlingstones Burn, the Stonecrofi-Greyside Mines (disused) worked the group of veins listed above. Stonecroft shafts [NY 8545 6892] in Mr Laidlaw's royalty lie 1400 ft (427 m) ENE of the site of Settlingstones Mill. Greyside Shaft on the main vein, in the Duke of Northumberland's royalty, is 1730 ft (527 m) ENE of Stonecroft shafts; Greyside Ail- Shaft [NY 8597 6889] on the Sun Vein, is 2225 ft (678 m) E of Stonecroft shafts. A general plan of the veins, and those at Settlingstones has previously been published (Smith, 1923, pl. 6). The horizon of the oreshoots is the Whin Sill, here 153 ft (47 m) thick. The full section of beds encountered in the workings includes 200 ft (61 m) of alternating thin sandstones, shales and limestones above the sill, the details of these beds being similar to those at Settlingstones (Figure 6), p.40); and about 150 ft (46 m) of similar beds beneath the sill. On the Stonecroft-Greyside Vein the total length of ground worked amounts to 3050 ft (930 m). The oreshoot reaches a maximum height of 250 ft (76 m) near Greyside Shaft, where it appears to have extended from the top of the Whin Sill on the footwall to the bottom of the sill on the hangingwall. The average height of the shoots does not, however, exceed 150 ft (46 m). At 1080 ft (329 m) ENE of Stonecroft Winding Shaft the Cross Vein was cut on the N wall of the main vein. This carried a "wing" type oreshoot which was worked for 900 ft (274 m) from the main vein, the height progressively decreasing from 160 ft (49 m) adjacent to this vein to less than 50 ft (15 m) at the NW limit of working. On the Sun Vein the total length of the oreshoot was 2500 ft (762 m), the greatest height being 270 ft (82 m) in a stretch lying E of the Greyside Air Shaft. The Cross Vein was.unproductive SE of the main vein.

    Baryte is the principal gangue mineral, but it has never been recovered because it is intimately mixed with sphalerite, from which it cannot be separated by gravity methods. Ankerite with refractive index ù = 1.711 (analysis No. 3, (Table 22), p.75) is also an important constituent of the veins. The specific gravity of this mineral, determined by Dr Smythe, is 2.95. Small amounts of witherite and quartz are also present, together with oxidised lead and zinc minerals. Sir Arthur Russell has found good specimens of harmotome on the dumps (Young and Bridges, 1984). An indication of the composition of the veins may be obtained from the analyses of samples taken during the Geological Survey investigation from numerous superficial pits in the tailings heaps near the Stonecroft shafts shown in (Table 71).

    The ankerite-content of samples Nos. 1 and 2, recalculated from the magnesia content using as a basis Dr Smythe's analysis referred to above, amounts to 30 and 16 per, cent respectively. The high content of these carbonates in the veins is due to the intense alteration of the dolerite to 'white whin', a conspicuous feature both here and at Settlingstones. The movements of trace elements during the alteration process at Settlingstones have been described by Ineson (1972).

    According to a detailed estimate by Mr J H Hohnen, made for the Non-Ferrous Minerals Development Control, the total tonnage of the Stonecroft dumps amounted, in 1944, to 103 000 tons containing 4.3 per cent zinc and 0.96 per cent lead; barium was not determined during this sampling campaign. In the early 1950s these dumps were put through the portable flotation plant of Minerals Treatment Ltd, recovering approximately 5000 tons of zinc concentrates, or about 5/8 of the available zinc content. According to grab samples taken by Mr A R D Orr of the tailings remaining after this treatment, the content of barium sulphate is only about 21 per cent. Such material is of little interest for barytes recovery.

    The Stonecroft deposits were discovered about 1853; the yield of lead concentrates to the end of operations in 1896 amounted to 74 264 tons containing 75 per cent lead and 2.45 oz silver per ton of lead. Comparing the output with the tonnage of dumps remaining would suggest of the order of 30 per cent lead sulphide in the crude ore, surely too high a figure to be credible. Here, as elsewhere in the orefield, the question arises of where the waste that ought to be present has gone.

    Stonecroft Winding Shaft is 360 ft (110 m) deep; the Pumping Shaft, 150 ft (46 m) to the NNW is 380 ft (116 m) deep. The principal levels from these shafts were the Adit (about 400 ft (122 m) above OD, 15-Fathom, 30-Fathom, 45-Fathom and 50-Fathom, the last-mentioned being at approximately 135 ft (41 m) above OD. Greyside Shaft is 410 ft (125 m) deep, and Greyside Air Shaft 450 ft (137 m) deep, the bottom being at about sea level. Here there were levels at 60- and 70-Fathom, respectively 70 and 115 ft (21.3 and 35 m) below the 50-Fathom. The bottom levels clearly lie below the bottoms of the oreshoots throughout the mines. It is not known whether unworked baryte-rich ground was left, but there is little inducement to reopen these mines. Water is said to have averaged between 700 and 800 g.p.m., high figures for the orefield.

    In connection with the Department of Industry Mineral Reconnaissance Programme, the IGS commissioned an airborne survey of that part of the Northumberland Basin underlain by the Whin Sill at 213 ft (65 m) ground clearance (Evans and Cornwell, 1981). Good correlation between a magnetic low 4 km long and the Settlingstones–Stonecroft–Greyside vein system was demonstrated and two areas, one E of the foreheads of Stonecroft Sun Vein, and the other at Brown Moor, N of Settlingstones were selected for ground investigation. Soil sampling, with determination of lead, zinc and barium gave inconclusive results (Bateson, Johnson and Evans, 1983), but there was a possible correlation between a magnetic anomaly in the Brown Moor area and radon in the soil. Airborne and ground magnetic measurements made it possible to follow Stonecroft Sun Vein for over 1 km ESE and E of the existing end of the workings (Bateson, Evans and Johnson, 1984). Two boreholes were drilled from each of two sites, respectively [NY 8694 6852] and [NY 8689 6858]; the interpretation of the results of these suggests that there are two vein-fractures dipping steeply S, but each downthrowing about 11.5 ft (3.5 m) to the N; the fractures may unite in depth. Extensive alteration accompanies them in the Whin Sill and some mineralisation is present. A dome swelling out of the sill S of the fractures is indicated, accompanied by banding in the quartz dolerite (Bateson and Johnson, 1984). The deepest borehole penetrated to 93.5 ft (28.5 m) below the Oxford Limestone; the first limestone penetrated hereabouts, beneath thick boulder clay, is the Shotto Wood Limestone (Figure 6), p.40).

    The correlation of the strata in the Selection Trust (BP Minerals Ltd) boreholes with those in the BGS boreholes at Newbrough, referred to above, and with the section exposed in the North Tyne river has been discussed by D V Frost (1984, p.45). The beds range downward from the Eelwell Limestone through thin sandstones, shales and thin coals, with three thin limestones, identified respectively as the Shotto Wood, Bath House Wood and Cockleshell horizons, to a limestone identified as the Colwell, 19–26 ft (6–9 m) thick including a shale parting near the top. The top lies on average 277 ft (84 m) beneath the base of the Eelwell Limestone. In Settlingstones Mine, the North Branch Vein workings exposed a limestone 12–14 ft (3.7–4.3 m) thick, the top of which, on the foot-wall of the vein, is 280 ft (85 m) below the bottom of the limestone in Grindon Hill Shaft accepted by Frost and Holliday, (1980, p.38) as the Eelwell. The limestone exposed in the deep workings directly overlies the Whin Sill, or is separated from it by a thin baked shale ('whetstone'). The continuity of the workings between Grindon Hill and Settlingstones Burn suggest that the limestone is the same as that exposed above the Sill in the burn. This was traditionally regarded as the Scar, but it now seems that it should be identified as the Colwell. However, in the boreholes, the top of the Whin Sill was found 39–47 ft (12–14.3 m) below the top of the Colwell Limestone, beneath a thin limestone identified by Frost (Frost and Holliday, 1980) as the Dalla Bank. This may be the thin limestone found underneath the sill in an inclined borehole (120/1) into the hangingwall of the vein from Bewick Crosscut, and also noted midway in the whetstone beneath the sill during underground mapping. If this is the case, there is a downward transgression of perhaps 30 ft (9 m) by the Whin Sill between the vein and borehole ST/2b. In detail, the contacts of the sill are seldom perfectly concordant (p.48). Whether this feature is sufficient to explain the magnetic anomaly that led to the drilling of the Selection Trust series of holes is not clear. It should be added that underground mapping enabled the upper of the two limestones shown on Trestrail's (1931) section to be followed throughout the deep workings of the mine; this may be correlated with the Barrasford Limestone of Frost and Holliday (1980) and was well exposed opposite the shaft eye at the 100-Fathom Level. Trestrail's lower limestone was not found. Perhaps it is represented by limey shale in the 116-Fathom Level. As already mentioned (p.265) from the 130-Fathom Level, close to the top of the main incline (Figure 41) a vertical borehole was drilled in the footwall in 1958 in the hope of finding competent strata to carry the mineralisation still further in depth. The section is included in (Figure 6), from which it will be seen that the lowest limestone intersected is now identified as the Greengate Well ( = Lower Little of Alston); it may be noted that the recent drilling programmes from surface, and other considerations, have made it necessary to abandon the interpretation of this borehole given by Frost and Holliday (1980, fig. 18). No thick competent strata were found, but artesian water was cut in the sandstone beneath the thin Oxford Limestone. The Settlingstones oreshoot became uneconomic opposite the footwall position of the sandstone underlying the Barrasford Limestone, and the question of how this great oreshoot, one of the largest in the orefield, was fed remains unsolved.

    Haydon Fell Vein

    NY86NE, NW; Northumberland 90NE (New Series)

    At the head of Caponscleugh Burn, 0.75 mile (1.2 km) NNW of East Brokenheugh, a level [NY 8543 6709] has been driven eastwards in shale and sandstone below the Four Fathom Limestone to reach a vein trending N65°E, downthrowing about 20 ft (6 m) SE. Limestone with veinlets of pink baryte occurs on the dump. About 0.5 mile (0.8 km) WSW, at Carrstones Quarry [NY 8485 6655], the Great Limestone is exposed, gently folded on NE axes. Baryte skins occur on joints running N45–50°E.

    Sillyburn Vein

    NY86NE, NW; Northumberland 90NE (New Series)

    About 0.25 mile (0.4 km) S of Carrstone Quarry, the dip slope of the Great Limestone is traversed by a weak vein running parallel to the Haydon Fell Vein, which has been tried by two levels [NY 8500 6604] from the field NW of Plunder Heath. Baryte and ankerite occur on the dump of the upper level. Small flats are said to have been found in the limestone here (Smith, 1923, p.34).

    Fallowfield Vein—Witherite, lead ore

    NY96NW; Northumberland 91NE (New Series). Direction N77–50°E, displacement 183 ft (55.8 m) SE at New Engine Shaft; 275 ft (83.8 m) SE at Windy Hill Shaft (4000 ft (1.2 km) to the NE).

    The workings of Fallowfield Mine (disused) extend 1.5 miles (2.4 km) NE from New Engine Shaft [NY 9309 6725], situated on the east side of the Acomb–Fallowfield road, 0.5 mile (0.8 km) NNW of Acomb Cross, 2.5 miles (4 km) from Hexham station. The Fallowfield Vein trends N77°E for 2250 ft (686 m) from the shaft. A major split then occurs, the oreshoot following a branch trending N50°E for the next 2500 ft (762 m). Another split then occurs, and it is not certain that values continued beyond this split. The vein is a strong fault with a greater hade than normal reaching nearly 20° near New Engine Shaft but decreasing to the NE. Probably because of the considerable throw of the fault, the hade is not much affected by the wall-rocks.

    A detailed section of the beds exposed in the workings is given by Smith (1923, p.22). (Figure 6), p.40 gives a summary of the significant features of the available shaft sections. The lowest beds reached on the footwall of the vein were the sandstones and shales beneath the Four Fathom Limestone. If the Whin Sill is here at the same horizon as at Settlingstones, its top may be expected to be about 700 ft (213 m) below the lowest workings at Fallowfield.

    The length of the oreshoot, as indicated by a plan and section formerly preserved at Allenheads Estate Office, was 4750 ft (1.45 km), extending from New Engine Shaft to a point 750 ft (229 m) NE of Windy Hill Shaft [NY 9412 6792] (Figure 42). The maximum range of worked ground was of the order of 450 ft (137 m) near Old Engine Shaft, but the overall average is probably not more than 200 ft (61 m). The width is said to have been at least 20 ft (6.1 m) in places, for example in a stretch some hundreds of feet long near Lonage Shaft [NY 9334 6740], 40 ft (12.2 m) was reached, the great width here being due in part at least to replacement of the Great Limestone on the footwall and in masses included within the vein. The minerals present were, beside witherite and galena, for which the oreshoot was worked, calcite and alstonite: barytocalcite is also said to have been present. The production record suggests that the ratio of witherite to galena was about 10:1, but the grade of run-of-mine ore is not known. Towards the south-western end of the oreshoot, calcite became plentiful, reaching 10 per cent of the orebody, as compared with an average for the whole oreshoot of about 2.5 per cent (Wray in Wilson, Eastwood et al., 1922, p.9). Individual ribs of witherite reached as much as 6 ft (1.8 m) wide, containing up to 70 per cent barium carbonate. The vein is recorded as having consisted of two ribs of spar, with a "rider" of country rock mixed with spar between them. Soft gouge was present against the footwall. The galena occurred near the vein walls, though in places it was mixed with the witherite.

    New or Low Engine Shaft [NY 9309 6725] (collar 326 ft (99.4 m) above OD), the pumping shaft, was 328 ft (100 m) deep, the main 69-Fathom Level being approximately at sea level. This shaft was sunk on the hangingwall side of the vein and communicated with an adit from Acomb Burn at 206 ft (63 m) above OD. Lonage Shaft [NY 9334 6740], 925 ft (282 m) NE of New Engine, on the footwall side was actually a series of rises totalling 400 ft (122 m) above the 69-Fathom Level. Old Engine Shaft [NY 9354 6751], 1775 ft (541 m) NE of New Engine, was the deepest shaft, starting at 420 ft (128 m) above OD, sunk 510 ft (155 m) to 90 ft (27 m) below OD. Thorntree Shaft [NY 9393 6775], 3175 ft (968 m) NE of New Engine, collar at 470 ft (143 m) above OD, is sunk 340 ft (104 m). Windy Hill Shaft [NY 9412 6792], 4020 ft (1.23 km) NE of New Engine is down 360 ft (110 m) from the collar at 540 ft (165 m) above OD. There is an old shaft with a fairly large dump on the line of the South Branch in Codlawdean [NY 9451 6820] 1550 ft (472 m) NE of Windy Hill Shaft, but hitherto no plans of the worksings from it have been obtained. Exploration from Codlawdean was continued by means of a level [NY 9440 6823] at 600 ft (183 m) above OD, probably driven by the Beaumont Co., extending to Codlaw Hill Shaft [NY 9498 6844] 1700 ft (518 m) NE of Codlawdean Shaft; this shaft, 166 ft (51 m) deep, passes the level at 106 ft (32 m). There is no evidence either from the dumps or from plans and sections that the Codlawdean exploration met with any success.

    Fallowfield Mine was worked for lead ore alone up to 1846; it is known to have been working as early as 1611 (Smith, 1923, p.21). The section formerly at Allenheads Estate Office shows the situation wheri mining for lead ore alone ceased. The main development levels were then the 45-Fathom (180 ft (55 m) above OD), running from Old Engine Shaft to 750 ft (229 m) beyond Windy Hill Shaft i.e. the full length of the oreshoot; and the 69-Fathom (0–10 ft (0–3 m) above OD) running from New Engine to a point 910 ft (277 m) beyond Old Engine. There were substantial stopes for lead ore above both these levels, and near Old Engine Shaft the ore had been followed down to 90 ft (27 m) below OD at which level ore was in the sole over a length of 200 ft (61 m) out of a total length of 280 ft (85 m). A winze 25 ft (7.6 m) deep gave access to a small stope below this level, but the section suggests that this part of the mine was never exhausted. The same section shows new levels driven for the reworking of the mine for witherite (Figure 42). These were at 300, 230, 175, 120 and 80 ft (91, 70, 53, 37 and 24 m) above OD at Old Engine Shaft, extending to varying distances between Old Engine and Thorntree shafts. Reworking for witherite commenced when the mine came into the possession of Messrs Walton and Cooper in 1846, and continued until 1912. The output for the recorded period 1855–1912, was 98 986 tons of witherite. Allowing for the early gaps in the record, the total is probably of the order of 105 000 tons. For much the same period, 1848–1907, and 1911, the mine raised 11 196 tons of lead concentrates containing 73 per cent lead with 4 oz silver per ton of lead.

    The reason for the closing of the mine is not fully known; competition from Settlingstones for a limited market may explain it, but it was important in considering its possible future to note that even in the deepest workings, the Great Limestone was barely reached on the hangingwall. This fact, together with the record that witherite was continuing abundantly in the sole of the 69-Fathom Level (the lowest reworked for that mineral) suggested that workable ground might remain in this mine. Accordingly, in 1958–59 the owners of Settlingstones Mine Ltd carried out a programme of underground exploration. The old Thorntree Shaft [NY 9393 6775] was reopened to a level in the Little Limestone Coal 260 ft (79.3 m) below the collar (210 ft (64 m) above OD); the shaft is sunk on the hangingwall side of the vein and cut the base of the Firestone at 108 ft (33 m) below the collar, the Pattinson sandstone from 150 to 173 ft (45.7–52.7 m) and the top of the Little Limestone at 238 ft (72.5 m). Twelve inclined boreholes were drilled totalling 2817 ft (859 m) at angles of dip varying from 20 to 68°, through the hangingwall into the vein from three stations: (i) 80 ft (24 m) SW of the shaft (ii) 600 ft (183 m) ENE (iii) 820 ft (250 m) NE. According to the records, witherite had been worked NE of Thorntree Shaft, up to Windy Hill Shaft, to the 51-Fathom Level but not below. The first group of holes showed witherite 4 ft (1.2 m) true width at 50 ft (15 m) below this level while the deepest hole intersected 11 ft (3.35 m) true width of vein 180 ft (55 m) below the level, but recovered only 4 ft (1.2 m) of mixed witherite and shale core. From site (iii) the best intersection of witherite, at about the 51-Fathom Level was barely 3 ft (0.9 m), while the two deep holes were barren. At site (ii), the shallow intersections showed witherite, but in depth, at about 210 ft (64 m) below the Little Limestone Coal, nearly 25 ft (7.6 m) vein-width of massive baryte was encountered. The six deepest holes in this programme reached the Great Limestone on the hangingwall side of the vein, faulted against sandstone and shale beneath the Four Fathom Limestone on the footwall. The section of beds beneath the Little Limestone Coal on the hangingwall may be summarised as follows:

    ft m
    Shale 19 5.8
    Snope Burn Marine Beds 13 4.0
    Coal Sill Sandstone 86 26.2
    Shale 76 23.0
    Great Limestone 32+ 9.8 +

    On the footwall side, the Three Yard Limestone was proved 140–153 ft (42.6–46.6 m) below the supposed base of the Four Fathom Limestone.

    The results of this programme were not regarded as sufficiently encouraging to proceed to redevelopment of the mine. Some witherite undoubtedly remains, and the massive baryte may merely be a lens that escaped the carbonating fluids, or it might be symptomatic of a more substantial deposit. Any future examination of this mine must also take into account the presence of extensive flooded workings in the Little Limestone Coal, particularly to the downthrow side of the vein. In 1959 Acomb Colliery (NCB, formerly Mickley Coal Co. Ltd) was operating and pumping down to 247 ft (75 m) below OD at its main shaft, and it is assumed that this enabled the reopening of Thorntree Shaft to be undertaken with only local pumping, though water was standing above the 51-Fathom Level. The colliery has subsequently closed and is abandoned. (Figure 42) shows the trace of the coal on the foot- and hanging-walls of the vein. At the time when Fallowfield Mine was operating as a lead mine, coal was also raised at New Engine and Windy Hill shafts, the main coal working lying NW of the vein, about Halfway House. A pair of parallel exploratory headings, starting at about sea level and rising to 30 ft (9 m) above OD were driven in the coal on the hangingwall side from the 69-Fathom Level some 1400 ft (427 m) SSE cutting a NW fault at the southern end. The rise district of Acomb Colliery encountered these headings and drained off the water from them before continuing coal extraction farther east. Before leaving the district, these headings were again dammed-up. Unfortunately the workings in the bottom level of the vein were not examined at the time. Some 700 ft (213 m) SW of the New Engine Shaft, a main road in the colliery at 125 ft (38 m) above OD was carried to within a short distance of the vein, but the vein was not opened up for investigation. However, the vein was cut through in a stone drift at a point 2825 ft (861 m) SW of New Engine Shaft, the drift rising from the Acomb Coal at 254 ft (77 m) below OD on the downthrow side of the vein to reach the same coal at 74 ft (22.6 m) below OD on the upthrow side. No mineralization was noticed here; the nearest ground known to be orebearing beneath the 69-Fathom Level would have required a drive in the vein of 3500 ft (1.07 km) to unwater it from this drift. The same stretch of the vein as that cut by the stone drift was explored from surface by the North Tyne Level, starting from the E bank of the Tyne, at Warden Mill [NY 9184 6704] opposite Nether Warden. This runs 1750 ft (533 m) eastwards, with S crosscuts driven through the fault at 600 ft (183 m) from the portal, and at the end. This exploration was also unsuccessful. Still farther SW, on the S side of the Tyne Valley, an attempt was made to find the vein by shafts in Windyhurst Plantation [NY 8914 6627], 3.25 miles (5.2 km) W of Hexham, and a level in Glen Dhu Wood [NY 8867 6614], without success. A level [NY 8622 6532] driven SSE from the foot of Carrs Burn, 5.25 miles (8.4 km) W of Hexham, was possibly driven for the same purpose.

    North-east of Codlaw Hill Shaft, attempts have been made to follow the vein, the principal being at the Grottington or Pont Head Mine (disused) 0.33 mile (0.5 km) W of Grottington, 0.5 mile (0.8 km) N of the Military Road. Reports by G C Greenwell, Adam Murray and J C NairTo which we had access by the courtesy of the Basinghall Mining Syndicate at Greenside Mine, and later through Mr Arthur Roberts of the Beamish Museum. indicate that operations here were in progress from 1852 to 1856. Three shafts [NY 9705 6991], [NY 9713 6991] and [NY 9707 6987] were sunk, one of which was 120 ft (37 m) deep, with levels at 60 ft (18 m), 90 ft (27 m) and possibly at the bottom. This should have reached the Great Limestone. Three divergent veins were found; if these represent Fallowfield Vein it is evidently splitting up here. Some 40 tons of lead concentrates were obtained from the upper level. Little remains today to mark the site of the operations.

    Birkey Burn Deposit—Witherite

    NY96NW; Northumberland 91NE (New Series)

    Smith (1923, p.25) records that the workings of Acomb Colliery (disused) encountered a fault south of Acomb in the vicinity of Birkey Burn, carrying witherite. A winze sunk 90 ft (27 m) found the vein widened to 15 ft (4.6 m), but the work was abandoned owing to an explosion, which took place in 1872.

    This deposit must have been in the old Acomb Colliery, long since abandoned, the workings of which lie S of the recent colliery workings, from which they are separated by a fault throwing 240 ft (73 m) N.

    References

    BATESON, J H, JOHNSON, C C, and EVANS, A D. 1983. Mineral reconnaissance in the Northumberland Trough. Miner. Reconnaissance Rep. Inst. Geol. Sci., No. 62.

    BATESON, J H, and JOHNSON, C C. 1984. Whin Sill in exploratory boreholes from Newbrough, Northumberland. Proc. Yorkshire Geol. Soc., Vol. 45, 1–10.

    EVANS, A D, and CORNWELL, J D. 1981. An airborne geophysical survey of the Whin Sill between Haltwhistle and Scots Gap, south Northumberland. Miner. Reconnaissance Rep. Inst. Geol. Sci.,.No. 47.

    DUNHAM, K C. 1959. Non-ferrous mining potentialities of the northern Pennines. 115–147 in Future of non-ferrous Mining in Great Britain and Ireland. (London: Institution of Mining and Metallurgy.)

    DUNHAM, K C. and DINES, H G. 1945. Barium minerals in England and Wales. Geol. Surv. Wartime Pamph., No. 46.

    FROST, D V. 1984. New information on the Dinantian stratigraphy and structure of Tynedale, Northumberland. Proc. Yorkshire Geol. Soc., Vol. 45, 45–49.

    HANCOX, E G. 1934. Witherite and barytes. Mineral. Mag., Vol. 51, 76–79.

    INESON, P R. 1972. Alteration of the Whin Sill adjacent to barytes-witherite mineralisation, Settlingstones Mine, Northumberland. Trans. Inst. Min. Metall., London, Vol. 81, B67–72.

    RUSSELL, A. 1927. Notice of an occurrence of niccolite and ullmannite at Settlingstones Mine, Fourstones, Northumberland. Mineral. Mag., Vol. 21, 383–387.

    SMITH, S. 1923. Lead and zinc ores of Northumberland and Alston Moor. Spec. Rep. Miner. Resour. Mem. Geol. Surv. G. B. , Vol. 25. 110pp.

    TRESTRAIL, G F W. 1931. The witherite deposit of the Settlingstones Mine, Northumberland. Trans. Inst. Min. Metall., London, Vol. 40, 55–65.

    TRESTRAIL, G F W. 1938. Witherite in Northumberland. Mine & Quarry Eng., Vol. 3, 247–251.

    WILSON, G V, EASTWOOD, T, POCOCK, R W, WRAY, D A, and ROBERTSON, T. 1922. Barytes and witherite (3rd edition). Spec. Rep. Miner. Resour. Mem. Geol. Sun,. G. B. Vol. 2. 119pp.

    YOUNG, B, and BRIDGES, T F. 1984. Harmotome from Northumberland. Trans. Nat. Hist. Soc. Northumbria, Vol. 52, 24–26.

    YOUNG, B, STYLES, M T, and BERRIDGE, N G. 1985. Niccolitemagnetite mineralization from Upper Teesdale, North Pennines. Mineral. Mag., Vol. 49, 555–559.

    Chapter 14 Mineral deposits

    Details, Area 9 Durham Coalfield

    The coalfield of E Durham, lying NE of the main mineral field, may be regarded at least in part as the eastern continuation of the fault-block structure. The principal workable coal seams occur in the Lower Coal Measures, the base of which is taken at a marine band lying between the second and third grits of the Millstone Grit facies (Mills and Hull, 1968) as nearest to the internationally recognised base of the Westphalian; as well as in the Middle Coal Measures, lying above the Harvey Marine Band (Smith and Francis, 1967). For the whole Westphalian, the total thickness of strata is approximately 2000 ft (610 m) but nearly all the worked seams are found in the lower part, covering a range of about 1200 ft (366 m). The Lower Coal Measures, 600 ft (183 m) thick, contain at least eight coals which have been worked. Comparative sections of the measures at collieries where mineral deposits have been found are given in (Figure 7), p.42. It should be noted that on official geological maps published prior to 1960, as well as in the first edition of this Memoir, the base of the Lower Coal Measures was taken at the top of the Third Millstone Grit, and the base of the Middle Coal Measures at the Brockwell seam.

    The exploitation of the Durham coalfield has, from time to time, revealed the presence of mineral deposits filling fault fissures. Most of them have been found on faults trending E–W or ENE (corresponding in direction with the productive veins of the main orefield), and it is reasonable to regard them, as Spencer (1910) has suggested, as the upward continuation of veins which intersect the Lower Carboniferous rocks. Two of the principal channels of mineralisation in the Coal Measures, the Great Spar Dyke and the Deerness Fault-system can, moreover, be traced through from the orefield, the former springing from the Healeyfield Vein (p.228), the latter from the great Lodgesike-Manorgill-Sharnberry complex of Teesdale (pp.246–254). All the oreshoots so far worked in the Coal Measures belong to the outer zone of the Pennine mineralisation; their commercial importance has been for their witherite or baryte content. The presence of small quantities of galena of sphalerite, and traces of fluorite indicate their community of origin with this suite. The need for reconciling this view with the existence in depth beneath NE Durham and the extreme south-eastern part of Northumberland of saline waters carrying between 750 and 2700 parts per million barium chloride (Anderson, 1945), known to be capable of depositing barium sulphate at the rate of 100 tons per week at a single mine by reaction with sulphate-bearing meteoric waters, may be noted in passing (see also Chapter 5, p.95). Commercial production of precipitated barium sulphate was carried on at Backworth Colliery, Northumberland [NZ 304 719] until its closure prior to 1947, and such production has been contemplated at other collieries in County Durham.

    The deposits described in detail below are all of past or potential commercial value. In addition, the following occurrences of introduced minerals may be mentioned. A mass of baryte was discovered at Felling Colliery, near Gateshead [NZ 280 628] (Clapham and Daglish, 1864). At Wearmouth Colliery, Sunderland [NZ 393 580], a mineral vein carrying up to 5 in (13 cm) of galena was discovered in shale and sandstone forming the roof of the Maudlin Seam (Louis, 1903); the associated minerals were pyrite and mixed carbonates. The vein continued through the coal as a mineralised breccia free from galena, but containing sphalerite associated with carbonates, the ascertained composition of which suggests the presence of ankerite similar to that commonly found in the orefield. Dr J A Smythe (1923, p.89) has recorded the presence of galena at Ryhope Colliery [NZ 398 535], 3 miles (4.8 km) S of Sunderland, at a depth of 2190 ft (668 m) beneath Warden Law; as well as at Bothal [NZ 231 877], Blythe [NZ 305 822] and Newbiggin collieries [NZ 310 886] in Northumberland, the Hilda Pit, South Shields [NZ 362 668], and at Jarrow [NZ 331 654] and Boldon collieries [NZ 347 623] (in litt., 1942) in Tyne and Wear. Dr Smythe finds that the silver-content of the galena in all these occurrences is very much lower than that of the average galena of the main orefield; he has supplied the following silver assays in ozs. per ton lead metal: Newbiggin, 0.25; Ashington, 0.4; Blythe, 1.75; Jarrow, 1.3; Boldon, 1.6; Monkwearmouth, 1.6 (Louis, 1903). On the other hand, galena associated with witherite at South Moor colliery (p.274) carries abnormally high silver values. Occurrences of baryte other than those described below include one at Croxdale Colliery [NZ 267 370], 3 miles (4.8 km) S of Durham (Wilson, Eastwood and others, 1922, p.14), at Ryhope [NZ 398 535] (Smythe, 1922, p. 91) and more recently at Houghton Colliery [NZ 338 503], (Mr W Carroll, personal communication). It is less certain, in the present state of knowledge, that ankerite, in its widespread occurrences as veinlets in the Coal Measures should be regarded as connected with the Pennine mineralisation (Hawkes and Smythe, 1935; Smythe and Dunham, 1947).

    At Raisby Hill dolomite quarry [NZ 342 352], irregular fissures contain chalcopyrite, malachite and limonite in the Lower Magnesian Limestone (Permian), overlying the Coal Measures (Smythe, 1924, p.7). Native copper is said to have been found here. Near Blackhall Rocks galena has been found in the Upper Magnesian Limestone, and an adit [NZ 4708 3917] is said to have been driven into the cliffs in search of lead ore. Dr C T Trechmann, who found this occurrence and personally communicated the information, also stated that he found fluorite in the concretionary limestone at Hartlepool. Black to dark purple hydrocarbon-rich fluorite is present in siliceous nodules in the Upper Magnesian Limestone at Marsden Bay [NZ 398 651] (B Young, personal communication). At Marden Old Quarry, near Cullercoats [NZ 355 715], now filled up, a band of baryte about 2 ft (0.6 m) thick was noted by Dr Smythe (in litt. to Mr Tonks, 1939; and 1922, p.93), dipping gently N with the bedding. The occurrence of fluorite, baryte, galena, sphalerite and pyrite replacing the Lower Magnesian Limestone in boreholes W and N of Sedgefield has been described (Fowler, 1943).

    Fine examples of amber fluorite with white baryte, and in places galena and sphalerite, can be seen at Chilton Quarry, Ferryhill Station [NZ 3008 3137]. Mineralisation of this kind is, in fact, widespread in a belt following the Butterknowle Fault, which forms the eastern extension of the Lunedale Fault of the main orefield, and in structures folded both in pre- and post-Hercynian times associated with it. Boreholes S of Fishburn, through the limestone into Westphalian beds show the widespread nature of the effect (see Smith, 1981, fig. 2). A full account has been given by Hirst and Smith, (1974) and the wider question of metals in the Permian Limestone has been investigated by Jones and Hirst (1972). Although the Lower Magnesian Limestone has nowhere proved workable for spars or metals, the possibility that a concealed concentration may exist cannot wholly be discounted. At present these mineral occurrences in the Permian have no commercial importance other than that of their possible deleterious effect on the enclosing rock as a source of dolomite.

    Smith and Francis (1967) list introduced mineral occurrences relative to stratigraphy, while Hirst and Dunham (1963) have discussed the possibly syngenetic occurrence of galena in the Marl Slate.

    Great Spar "Dyke"—Barytes

    NZ04NE, 14NW, NE; Durham 18NW, NE, 19NW

    Branching from the Healeyfield Vein near Healeyfield Farm, the so-called Great Spar "Dyke" is a major fault which pursues a curving but generally eastward course for at least 8 miles (12.8 km) to the Burnhope royalty. Its total displacement, generally in a series of steps on subparallel branches, varies up to 126 ft (38.4 m) N of Burnhope. In Lowedge Plantation, 3.5 miles (5.6 km) W of Lanchester, 4500 ft (1.37 km) E of Woodlands Hall, shallow pits [NZ 1102 4730] have revealed the presence of pink baryte, superficially stained with limonite, in the fault. In Sheep Walks, 2000 ft (610 m) SW of this occurrence, a baryte vein trending N45°E through sandstone and shale mapped as Lower Coal Measures has been worked opencast for a length of 400 ft (122 m) SW of [NZ 1061 4690], intermittently up to 1956 (Smith, 1981). The main fault farther E probably passes beneath the village of Lanchester. At about 2250 ft (686 m) ENE of St Mary's Church it gives off an ENE branch which becomes the South Moor Witherite Vein (below), according to plans of the Malton royalty. The main Great Spar "Dyke" lies approximately beneath the Lanchester–Burnhope road here. At Peth Lane Head, near B.M. 801.0, 450 ft (137 m) W of the crossroads, baryte has been found at surface [NZ 1827 4773], but not investigated underground. An interpretation of the structure, based on seam levels from the Malton and South Moor colliery plans, is given in (Figure 43).

    South Moor Witherite Vein—Witherite

    NZ14NE, 15SE; Durham 19NW. Direction N60°E; displacement 53 ft (16 m) N at the Witherite Shaft; decreasing eastwards to zero in a distance of 900 ft (274 m).

    The South Moor witherite deposit was discovered in the workings of Morrison Pit (disused) [NZ 1734 5109] in 1931, when a drift was made from the Hutton Seam Engine Plane to prospect a faulted area of coal in the extreme SW part of the company's royalty. The Hutton Engine Plane reaches the vein 2 miles (3.2 km) S of Morrison North Pit, 1200 ft (366 m) N of the crossroads on the Maiden Law–Witton Gilbert and Lanchester–Burnhope roads. The vein was developed over a total length of 2430 ft (741 m), and exploration reached a maximum depth of 820 ft (250 m) below surface. A remarkable feature of the vein in the vicinity of the main shaft [NZ 1799 4794] is that its throw appears to decrease as it is followed downwards. The displacement at the Hutton Seam is 53 ft (16 m) N; at the Brockwell it is only 39 ft (11.9 m). The explanation of this is that flyers are given off on the footwall side of the vein, with a less hade than the vein, carrying part of the throw. One such flyer was exposed in the pump chamber at the Brockwell horizon, throwing 8 ft (2.4 m) N.

    Three major oreshoots, one above the other, were developed; their dimensions are shown on the longitudinal section, (Figure 44). An examination of the wall rocks formerly exposed in the shaft, rises and winzes show clearly that the oreshoots were controlled by the hardness of the enclosing rocks, like those in the Lower Carboniferous rocks. The upper oreshoot which extended from the Main Coal near surface to the footwall position of a sandstone 80 ft (24.4 m) above the Townley Coal, was in a part of the sequence in which thick sandstones predominate, interbedded with measures which in the Pennines would be called hard grey beds. The barren interval beneath this oreshoot corresponds with the footwall position of a shale 44 ft (13.4 m) thick, the thickest individual shale in the sequence. Beneath it, the second oreshoot followed the footwall position of a sandstone 46 ft (14 m) thick which overlies the Townley Seam. The underlying barren stretch is due, it is suggested, to a high proportion of shale in the measures extending down to a sandstone 22 ft (6.7 m) above the Top Busty Coal. The third and largest oreshoot extended from the footwall position ofthis sandstone down to the Brockwell Coal, again opposite wall-rocks dominated by sandstone. Two winzes were carried beneath the Brockwell Seam from No. 5a Level. In the shaly sandstones between the Brockwell and Marshall Green seams on the footwall, the vein was generally poor, though a patch of ore averaging 2.5 ft (0.76 m) wide was found in the western winze. The deepest point reached was 85 ft (25.9 m) below the footwall position of the Marshall Green Seam. Witherite ore 1–1.5 ft (0.3–0.46 m) wide was found 20–50 ft (6.1–15.2 m) beneath the Marshall Green Seam. It may be anticipated that the Great Limestone lies about 1150 ft (351 m) below the Brockwell Seam here and it is to be regretted that the manager in the 1930s, Mr W Scott's, intention to sink to this horizon was never carried out. The oreshoots and the barren intervals between them dip gently to the east, following the bedding. The width of mineralisation in the oreshoots varied up to 16 ft (4.9 m) with considerable stretches 4–5 ft (1.2–1.5 m) wide. The exceptional width of nearly 60 ft (18.3 m) was reached 1550 ft (472 m) WSW of the Witherite Shaft on No. 4 Level, where a S branch apparently left the vein. The branch, probably part of the "Great Spar Dyke" is well mineralised, and was developed for a length of 600 ft (183 m) to a maximum height of 100 ft (30 m) above No. 4a Level.

    The vein is remarkable in containing nearly pure witherite with only insignificant amounts of other minerals. Many of the samples which were cut systematically during development show over 92 per cent barium carbonate. A little baryte, calcite, galena, sphalerite and pyrite complete the assemblage; silica in the run-of-mine samples probably represents sandstone fragments rather than vein-quartz. Dr Smythe (in litt. 1941) has investigated a concentrate of heavy minerals which was formerly obtained in very small quantities from the tables in the dressing plant. This contained 14.7 per cent lead sulphide, 3.8 lead carbonate, and 13.0 iron disulphide; zircon detected in this concentrate probably came from the sandstone wall-rocks. The galena carried 28.4 oz silver per ton of lead. Above the upper oreshoot, from "C" Level up to the surface, the vein carries an oxidised capping in which the witherite has been partially or wholly converted into fine-grained, limonite-stained baryte. The depth of the capping varies up to 150 ft (46 m) from surface.

    The ore was hoisted at the Witherite Shaft [NZ 1799 4794], the site of which is now obscured by restored opencasts on the N side of Peth Lane. The shaft (Figure 44) was sunk directly on the vein, which hades at nearly 5°N, down to 437 ft (133 m) below the Hutton Coal workings. Here the hade of the vein changes to 12°N, but the shaft continues on its original inclination down to No. 4a Level at about 225 ft (69 m) above OD. The mill was situated close to Morrison North Pit, nearly 2 miles (3.2 km) from Witherite Shaft. Until the completion of the shaft, the ore was transported underground by way of the Hutton Engine Plane to North Pit. The mill had a normal gravity flow sheet. For additional details of the deposits, and the mining and milling equipment, reference should be made to an article by E W Muddiman (1942). The composition of the ore is compared with that of three types of dressed witherite in (Table 72).

    A total of 55 876 tons of witherite had been produced from the commencement of operations in 1932 up to the end of 1944; the total output to 1958, when mining ceased, amounted to 237 000 tons (Ashburn, 1963).

    Craghead Deposits—Witherite

    NZ14NW; Durham 12SW, SE, 19NW

    Two small witherite deposits have been worked at Craghead Colliery (disused) [NZ 212 505]. The West Busty deposit, discovered in 1934, lies approximately one mile (1.6 km) SW of the shafts 3000 ft (914 m) due west of Holmside Hall, on an E–W fault throwing 13.5 ft (4.1 m) S. It was cut in the workings of the Busty seams at 14 ft (4.3 m) below OD and consisted of two oreshoots separated by a barren interval. The upper shoot was 690 ft (210 m) long by 30 ft (9 m) high, bottoming at the footwall position of the Busty seams (the Top and Bottom Busty seams are close together in the Craghead workings and were worked together). The lower shoot, its top 13 ft (4 m) below the Busty seams, was 425 ft (130 m) long by 25 ft (7.6 m) high. A winze was carried down to the Brockwell seam on the footwall, and a rise was tried to 40 ft (12 m) above the Busty but without success. This deposit, which was 2–3.5 ft (0.6–1 m) wide, is regarded as worked out.

    About 0.5 mile (0.8 km) SW of this deposit, witherite 4 in (10 cm) wide was noticed on an E–W fault throwing 30 ft (9.1 m) N at the horizon of the Low Main Seam.

    A wider deposit was also discovered in the E district of Craghead Colliery, 0.5 mile (0.8 km) ESE of the shafts. This also lies on an E–W fault, throwing 15 ft (4.6 m) S. The deposit was proved for a length of about 350 ft (107m) and a height of 18 ft (5.5 m) from the Busty workings, beneath which it nips. The width varies up to 3.75 ft (1.1 m) and the witherite is of excellent quality without, so far as could be seen, any other mineral except a little baryte.

    Tanfield Moor Deposit

    NZ15SE; Durham 12NW

    At the Tanfield Moor Colliery (disused) witherite, contaminated with calcite, up to 6 ft (1.8 m) wide has been found. Samples showed the compositions quoted in (Table 73).

    The deposit occurs in a NNW fault throwing 32 ft (9.8 m) E and was discovered where a drift passed through the fault, 1300 ft (396 m) N10°W of Willey Pit [NZ 1699 5438]. The fault is adjacent to the great NW fault throwing 240 ft (73 m) S which passes beneath Tantoby.

    Lumley Sixth Pit Deposits—Barytes

    NZ24SE; Durham 13SW. Direction N70°W, displacement 80 ft (24.4 m) NE

    In 1941 a pair of rising drifts were being driven south-westwards from the Brass Thill Seam workings of Lumley Sixth Pit (disused) [NZ 3100 50580] starting 1000 ft (305 m) W of the shafts to reach a faulted portion of the Low Main Seam in the neighbourhood of Lumley Thicks. These passed through a strong fault which proved to be mineralised with baryte. The section through the fault, as exposed in 1941 in the foredrift, showed the main fault-plane to be vertical, filled with 2–3 ft (0.6–0.9 m) of shale gouge on the S side of which baryte, 4–5 ft (1.2–1.5 m) wide, massive and white, but containing some inclusions of rock, occurs. The S wall of the deposit has an apparent hade to the S, but this is probably due to a bulge in the vein. Farther S, 24 ft (7.3 m) from the wall of this deposit, a second vein, hading 25°N, carried up to 1.5 ft (0.46 m) of baryte. In the backdrift which cuts the fault approximately 100 ft (30 m) SE of, and at a horizon 40 ft (12 m) below the foredrift, the main deposit is 6 ft (1.8 m) wide, containing excellent quality barytes.

    The only mineral apart from baryte, which could be detected with the unaided eye is pyrite, which occurs in a few tiny veinlets. The analyses ((Table 74) show, however, a small quantity of witherite. This promising deposit, like the others in the western or central part of the Durham Coalfield, has been rendered inaccessible by the closing of the collieries.Another deposit of baryte was noticed at this colliery (Louis, in discussion on Peel, 1900). This is said to have been in the western continuation, or a branch of the same fault as that described above, about /2 mile (0.8 km) away from the new locality, where the fault was cut by the Maudlin Seam Engine Plane.

    Deerness Valley Deposits—Barytes, witherite

    NZ03NE, 13NW ,NE, 14NE, 24NW; Durham 25SE, 26SW, NW, NE

    The valley of the River Deerness, a tributary of the Wear running westward from Durham towards Tow Law, follows a belt of strong faults having a general ENE trend. From east to west, the faults have been encountered in the workings of Bearpark, New Brancepeth. Ushaw Moor, Esh Winning, Waterhouse, Wooley, Stanley and Thornley collieries, reaching the Coal Measures escarpment overlooking the Wear valley west of the last-mentioned. The main fault has been mapped westward to Bradley Hall [NZ 1055 3626] through Namurian rocks. The recent resurvey of Sheet 26 (Wolsingham) has confirmed that it joins up via Firestone Vein (p.218) with the Sharnberry Fault on the south side of Weardale, the eastern continuation of the Coldberry–Eggleshope complex of Teesdale. If this is the case, the whole mineralised belt is 24 miles (38.4 km) long, with oreshoots at intervals along it. In the Coal Measures the oreshoots carry barium minerals; they are described below from E to W (Figure 45).

    At New Brancepeth Colliery (disused), the fault-belt passes NE of the shafts [NZ 2228 4200], which are situated S of the River Deerness. The main fault enters the north-eastern corner of the royalty near Auton Field, running S85°E, changing to E–W, north of Broom Hall, and farther W to S60°W, before the fault passes north of the cross-roads at Ushaw Moor village into the Ushaw Moor royalty. The discovery of workable barytes oreshoots on the fault here has been described by Peel (1900). The first stone drift through the fault, driven from the Busty Seam workings 400 ft (122 m) SW of the boundary near Auton Field proved that the fault hades 24°SE bringing the Brockwell Seam on the footwall 40 ft (12 m) above the position of the Busty Seam on the hangingwall. A section formerly at the colliery office showed that as the hangingwall of the fault was approached from the SW, the Busty Seam dipped gently towards it at about 5°, immediately against the fault, however, the seam turned up, dipping at 70° SW, according to Peel's account (1900); the vertical displacement here amounted to 120 ft (36.6 m) SW. At 1000 ft (305 m) further W, the Harvey Engine Plane was driven through the fault, reaching the Busty Seam on the footwall; the throw here is estimated to be 126 ft (38.4 m) SE. At 500 ft (152 m) NE of the Ushaw Moor crossroads, the evidence at an underground shaft suggested a throw of 107 ft (32.6 m) SE. Here a crosscut at the horizon of the Brockwell Seam on the footwall showed the seam rising towards the fault at angles of up to 45°, then sharply folded and cut by subsidiary faults before reaching the main fault. The evidence, both from the Busty stone drift and the underground shaft thus indicates that the major tension-fault coincides approximately with a line of minor compressional folding, a feature also noted along Winterhush Vein at Cowgreen Mine. At the underground shaft the hade of the fault varies between 10° and 27°, possibly responding to the hardness of the wall-rocks; the average hade is 20°SE.

    The highest workings for barytes were opposite the hangingwall position of the Harvey Seam, varying from 62 ft (18.9 m) above OD in the western to 14 ft (4.3 m) above OD in the eastern part of the royalty. The vein was not worked above the Harvey Seam because of the possibility of encountering the glacial washout which follows the Deerness valley, but also, as shown below because the oreshoots become blind upwards. The lowest seam reached in the workings was the Victoria (Figure 7), p.42). The section contains sandstones, sandy shales, shales and fireclays; it appears probable that the sandstone, 60 ft (18 m) thick, which lies between the Top Busty and Three Quarter seams may have had some influence on the width of the oreshoots, since these appeared to be at their best between the top of this bed on the footwall and its base on the hangingwall. Control of mineralisation by wall rock stratigraphy was nevertheless not as well displayed in these deposits as in many others.

    Two workable oreshoots were found at New Brancepeth. The eastern one, extending from the Busty stone drift mentioned above, eastwards for upwards of 1000 ft (305 m), was worked during the first period of barytes operations here (1904–1921), from the Harvey and Brockwell engine planes. It was believed to have been worked for about 40 ft (12 m) below the hangingwall position of the Harvey and about 40 ft (12 m) above the hangingwall position of the Brockwell Seam. Unworked ground thus remained between these workings. Below the Brockwell it was followed down by means of a staple to the hangingwall position of the Victoria Seam. The 1940's reopening of this oreshoot included sinking of a new 75 ft (23 m) shaft, from the Harvey-Busty drift which gave access to further stoping ground; the vertical range of this oreshoot, though patchy, was about 240 ft (73 m). The condition of the vein in the deepest workings is not known and the reopening here gave less satisfactory results. The filling consisted of baryte varying from a few feet up to 16 ft (4.9 m) wide, averaging over 5 ft (1.5 m) with witherite along the walls and (in places) in the centre of the vein, reaching a total maximum width of 3 ft (0.9 m). Very minor amounts of galena, sphalerite, chalcopyrite, pyrite, ullmannite and alstonite have been detected in this oreshoot by Spencer (1910).

    West of this oreshoot, the solid baryte filling gave place to a breccia of rock inclusions cemented by barium minerals. From the Harvey Engine Plane, however, a second oreshoot was discovered in the NE of the royalty, NE of the cross roads at Ushaw Moor. This proved to have a maximum length of 1030 ft (314 m). It had been worked to a small extent from the Harvey Engine Plane, but when the mine was reopened for barytes in 1938 the workings were extended to a maximum depth of 175 ft (53 m) below this horizon. The bulk of the production since 1938 came from this oreshoot; its maximum width was 18–20 ft (5.5–6 m), but the average width did not exceed 10 ft (3 m). There was some indication of a tendency for the oreshoot to decrease in width with increasing depth. The filling consisted of white platy baryte, with the crystals mainly grown perpendicular to the vein walls. Witherite occured adjacent to the walls, but only comprised a few per cent of the total contents. Very small amounts of sphalerite occured in tiny veinlets; traces of arsenopyrite were also found. The composition of the run-of-mine ore, extracted from this oreshoot, is indicated by the analysis quoted below. Both to the W and E the foreheads showed an increase of rock inclusions, but there can be little doubt that were the mine still open and equipped with dressing plant, these could still be workable.

    Between the two oreshoots approximately 1500 ft (457 m) of ground on the fault remained untested when, in 1955, the colliery was closed as exhausted, bringing barytes production to an end.

    The barytes workings were concentrated on the Harvey Engine Plane, which ran NE from the shafts. At 2900 ft (884 m) a WNW branch led to the underground shaft on the western oreshoot at [NZ 2300 4270] while another led to the shaft on the eastern oreshoot at [NZ 2375 4292], close to the original point of discovery. The whole output from this second phase of barytes mining was shipped, without treatment, to the grinding plant of Athole G Allen at Stockton. (Table 75) illustrates the grade obtained. It is clear that a grade such as this could only be maintained by selective mining; resources of lower grade ore, together with unworked high-grade, remained when mining ceased; the tonnage could be considerable, but data are inadequate to place a figure on this.

    After mining ceased, pumping was continued at New Brancepath Harvey Shaft, keeping the water level at a little below sea level. Athole G Allen (Stockton) Ltd accordingly considered the possibility of reaching the eastern oreshoot by means of an incline from surface at Auton Stile, but it was considered that this could only be justified if substantial resources could be shown to exist above the hangingwall level of the Harvey. The only evidence of this was a single rising drift on the western oreshoot, reaching about 20 ft (6 m) above the seam; the evidence otherwise suggested that both oreshoots pinched at about this level, but there was adequate space for a second run of orebodies nearer the surface if stratigraphical conditions permitted. Accordingly, six inclined boreholes were drilled from surface, irregularly spread along a line between [NZ 2336 4293] and [NZ 2375 4292] at inclinations varying from 45 to 60°N. Two borings intersected the vein between the hangingwall and footwall positions of the Harvey Coal and two intersected at higher levels with the Low Main Post sandstone on the hangingwall; the two others cut the vein in the thick shale above the foot-wall Harvey. Small amounts of witherite were found in only two intersections and all six were effectively barren. A length of 1530 ft (466 m) above the eastern oreshoot had been tested, and it must be concluded that this orebody is blind upwards, blanketed by the shale above the Harvey Coal see (Figure 7), p.42, where the very consistent stratigraphic results of these borings between the Low Main and Harvey coals have been incorporated in the New Brancepeth section). The reopening project was abandoned, and all the workings are now flooded.

    The output of barytes from New Brancepeth from 1904 to 1921 amounted to 117 659 tons; the inclusive yield to 1958 was 221 659 tons.

    At Ushaw Moor Colliery (disused), the shafts [NZ 2204 4275] of which were situated south of the Vshaw Moor–Esh Winning road, 0.5 mile (0.8 km) W of Ushaw Moor, the mineralised ground continues from the New Brancepeth royalty to the E. Two oreshoots were worked; the eastern one, situated 1400–2500 ft (427–762 m) E of the shafts, was known as the South Busty Vein. The eastern part of this oreshoot, trending nearly E–W, carried mainly baryte, and was worked up to the royalty boundary. At 1800 ft (549 m) E of the shafts the direction of the fault changes to SW, and here the filling is said to have been witherite, 4–16 ft (1.2–4.9 m) wide. According to Wray (in Wilson, Eastwood et al., 1922, pp.13, 14) the workings extended up to 132 ft (40 m) above the Brockwell Seam, or 36 ft (11 m) above the Busty Seam. These statements presumably refer to the footwall positions of these seams; the fault here brings the Brockwell Seam on the footwall (N) against the Busty Seam on the hangingwall. The length worked is stated to have been 396 ft (121 m). The ore was transported to the shafts by way of the Brockwell Engine Plane at 40 ft (12 m) below OD.

    The second oreshoot, known as the Tow Law Vein, lies 3000 ft (914 m) SW of the shafts, and was worked from the Busty Engine Plane, over a length of only 200 ft (61 m); as exposed in 1931 the vein was 4–6 ft (1.2–1.8 m) wide, filled with good witherite. Between the two oreshoots a stone drift linking the Busty workings of Ushaw Moor Colliery with No. 2 Shaft of New Brancepeth Colliery must have passed through the fault 700 ft (213 m) NNW of Sleet-burn House, but there is no record that barium minerals were found. The western oreshoot, and possibly the eastern one, contain reserves but neither are now accessible, since the colliery is now abandoned and the engine planes have collapsed. The production amounted to approximately 22 000 tons of barium minerals, largely witherite, between 1921 and 1931, under Messrs Pease & Partners Ltd.

    W of the Tow Law Vein workings of Ushaw Moor Colliery, the main Deerness fault was cut in two southern branches of the Main (or Brockwell) Engine Plane at Esh Colliery (disused). The colliery shafts [NZ 1955 4234] were situated on the N side of Priest Burn, 36 mile (1 km) WSW of Flass Hall. The Brockwell Engine Plane, starting from the shafts at 270 ft (82 m) above OD reaches 172 ft (52 m) above OD before cutting the fault on its eastern branch. Here it communicated with a dipping drift (172–72 ft (52.4–22 m) above OD) which passed through the fault and through subparallel subsidiary faults lying to the S of it. The main fault here brings the Yard Seam into the drift, indicating a throw of 182 ft (55.5 m) SE and where cut in the drift, it carried a width of 1.5 ft (0.46 m) of barium spars. The next branch of the Engine Plane to the W also communicating with a dipping drift through the faulted belt, showed baryte on both the subsidiary faults, the throws of which are respectively 45 ft (13.7 m) SE and 96 ft (29 m) NW. Workings in the Brockwell Seam to the W, beneath Holburn Beck, 2100 ft (640 m) S of its confluence with the Deerness, showed traces of baryte, with witherite and pyrite, in an ENE fault throwing 15 ft (4.6 m) NW. None of these occurrences has been exploited. In 1951, when an area of Brockwell coal on the downthrow (S) side of the Deerness faults was being worked, a crosscut near [NZ 2000 4110] was driven NW to explore the fault from the downthrow side. Shale gouge against the hangingwall contained pyrite veinlets and pockets with tabular baryte crystals but not in workable quantity; this was succeeded to the NW by anticlinally folded sandstone overlain by shale leading at 21 ft (6.4 m) to a second belt of shale gouge; the footwall was not reached. This was the first of a series of investigations carried on by the National Coal Board on behalf of Athole G Allen (Stockton) Ltd, in the hope of replacing the barytes production lost by the closure of New Brancepeth Colliery. In the same area about 1 ft (0.3 m) of baryte was seen in a fault, probably part of the Deerness system, cut in a rising drift from the main engine plane to the Busty Seam. In spite of these indications, and the presence of a few pockets of witherite found in the Standalone Brockwell area, no substantial body of spar was found in the Esh Winning workings.

    Waterhouses Colliery (disused), the next mine to the W, included shaft workings [NZ 1856 4107] and a pumping installation in the Brockwell Coal, and a series of drifts from the hillside to the S, giving access to other seams. Lymington Drift (entrance: [NZ 1940 4123]) driven SE in the Yard ( = Tilley) Coal approached the foot-wall of the Deerness Fault at about 1100 ft (335 m), giving access to coal workings to the SW. One of these, close to [NZ 1958 1066] touched the footwall and revealed spar; two borings showed 15 cm of witherite against the wall, followed by up to 4.5 ft (1.4 m) of clean baryte. Bunney's Drift, inclined downwards from [NZ 1899 4095] gave access to the 'B' or Three-Quarter Seam, about 105 ft (32 m) below the Yard Coal, and also to the Victoria Seam, 145 ft (44 m) lower still. In the former, an excavation was made into the fault at [NZ 1947 4054]; here a rib of witherite at least 1 ft (0.3 m) thick was exposed across the full 6 ft (1.8 m) face of the drift in 1955. The Victoria Seam workings in 1963 enabled a crosscut to be driven into the fault at [NZ 1961 4074] revealing, against a sharply defined footwall of sandstone overlying 1.5 ft (0.46 m) of coal, clean witherite 2.5 ft (0.76 m) wide, followed by sandstone dipping gently N; then a second rib of witherite tapering down from 2 ft (0.6 m) in the roof to zero in the floor; then 2 ft (0.6 m) of sandstone followed by a witherite vein less than 1 ft (0.3 m) wide before the hangingwall of grey beds and sandstone was reached. Headings driven 17 ft (5.2 m) NE and 18 ft (5.5 m) SW showed similar ground with ribs of witherite alternating with rock, the yield probably being not much over 50 per cent BaCO3. The elevations of the three Waterhouses intersections were: Lymington 480 ft (146 m) above OD; footwall 'B' seam, 356 ft (111 m) above OD and Victoria, 224 ft (68 m) above OD; the vertical range is thus similar to that on the eastern oreshoot at New Brancepeth. The lateral distance range is about 900 ft (274 m); but though showing some promise, it must be added that the existence of a workable orebody was not established; it might have been had it been possible to negotiate the necessary arrangements for rising and driving. At 1500 ft (457 m) SSW of the Victoria intersection, Crowgill Drift [NZ 1898 4059] in the Yard Seam may have cut the fault, but the result is not known.

    The sole surface exposure of mineralisation on the Deerness Faults was formerly to be seen on Baal Hill at [NZ 1902 3489], 2100 ft (640 m) ENE of the farm of that name, where a small quantity of pink baryte had been dug from surface excavations. The mineral is pink, showing two colour generations, and containing microbands with tiny chalcopyrite crystals. From 1950 Athole G Allen (Stockton) Ltd carried on a programme of trenching and sank a NE-dipping incline 130 ft (40 m) long which reached 46 ft (14 m) below surface. Up to 16 ft (4.9 m) width of baryte was exposed, but the width was partly due to hill creep; lesser widths, down to 2 ft (0.6 m) were commoner, but these were accompanied by sticky clay, perhaps weathered gouge, containing included lumps of baryte. The footwall rock is the Low Main Post forming the hill feature, and according to G Armstrong's revision for Sheet 26 (Wolsingham) this lies between two branches of the fault. A crosscut driven out from the incline to the base of the hill feature to unwater the workings showed partly broken sandstone with a band of barytic gouge. About 2000 tons of the mineral were estimated to have been exposed but as the ground had to be made good, this was not mined. The workings have subsequently been obscured by the Standalone opencast coal site. The branch explored probably had a displacement of 60 ft (18 m) SE. Between the Standalone prospect and Baal Hill Farm, the Busty Drift from Waterhouses colliery which cut the fault at about [NZ 1869 3954] is said to have found baryte; however a drive running NNW from Wooley Colliery (disused) [NZ 1790 3846] in the Harvey Seam, which passed through the fault near Stanley Cottages at [NZ 1738 3904] into the Brockwell Seam on the footwall is said not to have found mineralisation. The indicated displacement here amounts to 210 ft (64 m).

    Still farther W, a rising drift forming part of White Lea Drift, Roddymoor Colliery (disused) [NZ 1579 3719], cut the main fault opposite the hangingwall position of the Five Quarter Seam. Gouge with spar was noticed and when a drive was made from the Ballarat (Upper Busty) Seam to reach the Victoria coal in 1946, witherite 4 ft (1.2 m) was discovered near [NZ 1560 3806]. According to information supplied by Wm Armstrong Ltd to Dr F W Smith, Pease & Partners worked this, recovering 1701 tons. Extraction was not resumed after nationalisation. Proceeding westward, this is the last recorded discovery of a barium mineral in the Deerness Fault system, but its course can be followed through the workings of Thornley Colliery (disused) [NZ 1350 3864] and is shown in detail on G Armstrong's six-inch revised maps. A sudden change of direction from near W to SSW takes place here; the continuation appears to have been seen in opencast coal sites around [NZ 134 372] and [NZ 129 370], but no spar is known to have been found. The fault then crosses untested drift-covered Millstone Grit country to near Bradley Hall, where its position is marked by dips up to 27° and by a spring known as Bradley Spa [NZ 1063 3662]. The Crowsfield baryte deposits lie near the same line on the south side of the River Wear.

    Brandon Deposit–Witherite

    NZ23NW; Durham 26 SE

    At Brandon Colliery (disused) the Busty Engine Plane from 'B' Pit [NZ 2442 3965], driven in the Bottom Busty ( = Five Quarter) Seam, cut obliquely through the Ludworth dyke of the Whin suite beneath Scripton Gill [NZ 2284 3900]. On the S wall of the dyke a vein of witherite 2–3 ft (0.6–0.9 m) wide was discovered, but it was not exploited. An analysis of the spar supplied by Strakers & Love Ltd, former owners of the colliery, showed 96.03 per cent barium carbonate, 1.87 barium sulphate, 0.51 ferric oxide and alumina, 1.25 silica, 0.30 water.

    References

    ANDERSON, W. 1945. On the chloride waters of Great Britain. Geol. Mag. , Vol. 62, 267–273.

    ASHBURN, J. 1963. Mining witherite in N.W. Durham. Colliery Guardian, Vol. 207, 269–276.

    CLAPHAM, R C, and DAGLISH, J. 1884. On minerals and salts found in coal pits. Trans. North England Inst. Min. Eng., Vol. 13, 219–226.

    DUNHAM, K C. 1959. Non-ferrous mining potentialities of the Northern Pennines. 136–139 in Future of non-ferrous mining in Great Britain and Ireland. (London: Institute of Mining and Metallurgy.)

    DUNHAM, K C. and DINES, H G. 1946. Barium minerals in England and Wales. Geol. Surv. Wartime Pamph., No. 46.

    EDMUNDS, W. 1975. Geochemistry of brines in the Coal Measures of north-east England. Trans. Inst. Min. Metall., London, Vol. 84, B39–52.

    FOWLER, A. 1956. Minerals in the Permian and Trias of north east England. Proc. Geol. Assoc., Vol. 67, 251–265.

    HAWKES, L, and SMYTHE, J A. 1935. Ankerites of the Northumberland Coalfield. Mineral. Mag., Vol. 24, 65–75.

    HIRST, D M, and DUNHAM, K C. 1963. Chemistry and petrography of the Marl Slate of S.E. Durham, England. Econ. Geol. , Vol. 58, 912–940.

    HIRST, D M, and SMITH, F W. 1974. Controls of barite mineralization in the Lower Magnesian Limestone of the Ferryhill area, Co. Durham. Trans. Inst. Min. Metall., Vol. 83, B49–55.

    JONES, K, and HIRST, D M. 1969. The distribution of barium, lead and zinc in the Lower and Middle Magnesian limestones of Co. Durham. Chem. Geol. , Vol. 10, 223–236.

    MUDDIMAN, E W. 1940. Witherite (natural barium carbonate) and its industrial uses. Handbook issued jointly by Holmside and South Moor Collieries Ltd and the Owners of Settlingstones Mines Ltd, Newcastle.

    MUDDIMAN, E W. 1942. Witherite. J. Oil & Colour Chem. Assoc., Vol. 25, 127–142.

    PEEL, R. 1900. Notes upon the occurrence of barytes in a twenty-fathom fault at New Brancepeth Colliery. The Colliery Manager J. Colliery Eng., Vol. 16, 56–58.

    SMITH, D B, and FRANCIS, E A. 1967. Geology of the country between Durham and West Hartlepool. Mem. Geol. Surv. G.B. 354pp.

    SMITH, F W. 1981. Some environmental aspects of geology and mining in Coal Measures and younger rocks in north-east England. 19–28 in Heavy metals in northern England: environmental and biological aspects.

    SAY, P J, and WHITTON, B A, (editors). (University of Durham, Department of Botany.)

    SMYTHE, J A. 1922. Minerals of the North Country: barium minerals. Vasculum, Vol. 8, 90–93, 113–116.

    SMYTHE, J A. 1924. Minerals of the North Country: sulphides other than galena. Vasculum, Vol. 11, 7–14.

    SMYTHE, J A. and DUNHAM, K C. 1947. Ankerites and chalybites from the northern Pennine Orefield and the north-east coalfield. Mineral. Mag., Vol. 28, 53–74.

    SPENCER, L J. 1910. On the occurrence of alstonite and ullmannite (a species new to Britain) in a barytes-witherite vein at the New Brancepeth Colliery, near Durham. Mineral. Mag., Vol. 15, 302–311.

    WILSON, G V, EASTWOOD, T, POCOCK, R W, WRAY, D A, and ROBERTSON, T. 1922. Barytes and witherite (3rd edition). Spec. Rep. Miner. Resour. Mem. Geol. Surv. G.B.,, Vol. 2. 119pp.

    Chapter 15 Future prospects

    The northern half of the Northern Pennine Orefield, with a past record of output of nearly 3 million tonnes of lead concentrates, and having regard to the gaps in the earlier records, an estimated total yield of the order of 4 mt, has been the most productive source of lead in Britain. The district has not been in the front rank of producers of zinc ore, but it has provided almost the whole world's supply of witherite (natural barium carbonate) with over a million tonnes to its credit. In 1986 the field remains a major source of fluorspar, output of all grades having risen from a total of 0.66 million tonnes 1884–1938 to 0.94 mt by 1956, now reaches over 2.1 mt. Production of barytes now approaches 1.5 mt. At current prices, the value of the output so far achieved would exceed £1 billion (109). On the basis of the geological and mining history, summarised in this memoir, orebody by orebody, mine by mine it is now proposed to address the question of what resources may remain for future exploitation.

    Lead ore

    The surrender of their Alston Moor and Weardale leases after two centuries of activity by the two principal firms in the orefield, respectively the London Lead Co. and the W Beaumont Co. in 1882–84 seems to have been based upon the view that the state of the lead market no longer justified the hope of profitable mining in the Pennines. The known Alston Moor deposits were almost exhausted for lead ore at that time; Wallace, writing in 1890 (p.188) remarks:

    "My examination of the district, repeatedly made at intervals during a number of years, always resulted in an opinion unfavourable to the existence of undiscovered lead deposits, even in the upper strata." Presumably he was referring here to the Great Limestone and overlying beds, but later he adds the view that "no extensively productive mines in the lower strata remain to be discovered". Only one new discovery, the Tynebottom Limestone flats at Rotherhope Fell Mine, has been made in the Alston area since then. In Weardale the same degree of exhaustion had not been reached by 1884, its highest annual production having been achieved only a few years before. Nevertheless, Burtree Pasture Mine, the principal producer, did not long survive the Beaumont regime. The discovery of the rich Boltsburn flats by the Weardale Lead Co. at the close of the century, kept alive the industry, which again became profitable, until 1931. In West Allendale the extension of workings on High Raise Vein from Alston Moor after the Great War led to the finding of several new and profitable oreshoots in Nentsberry Mine but these, too, were exhausted as lead ore producers by 1931. In East Allendale, three veins cut during the driving of the Blackett Level were successfully developed, but had been worked out by 1946. It is perhaps important to note that these deposits were richer than average for the orefield, in the case of Boltsburn, with 0.52 million tonnes of ore averaging 17.4 per cent recovered PbS, considerably richer. In Teesdale, the London Lead Co. ceased operations in 1905, but before 1939 a downward extension of the orebody on Hardberry Hill Vein in the Great Limestone had been located by a local operator and this was extracted by Cold-berry Mines Ltd between 1952 and 1958, yielding 0.076 mt of ore with 7 per cent PbS. This was the last mine worked for lead ore alone, though up to 1960 it was the practice at Stotfield Burn fluorspar mine to send outby bouse (galena-rich ore) separately from the run-of-mine crude fluorspar. Lead ore produced since 1958 has come entirely as a byproduct of the mining of industrial minerals, principally of fluorspar.

    However, three important efforts to locate workable lead orebodies have been made during the past thirty years: (1) from the Old Swinhope Mine (p.166) the substantial area of virgin Great Limestone between the Nenthead and Allenheads vein-complexes was tested, in the manner traditional to the district, by driving a tunnel holding the base of the limestone, in a SE direction, perpendicular to the principal direction of the veins; new deposits were found, but the values were too low to justify development; (2) a borehole was drilled from surface to prove the Boltsburn East deposit near the 1931 forehead (p.191); this was successful, but two subsequent boreholes farther NE failed to intersect the target (at best a difficult one); had ore been proved, a sinking of the order of 800 ft (245 m) would have been required to reach it; (3) three boreholes were drilled to prospect the Wiregill–Eggleshope Vein (p.252) where the large worked oreshoot had not been tested in the thick Low Grit Sill; good intersections were obtained, but the evidence was regarded as insufficient to justify reopening of the mine; subsequently the Wear–Tees aqueduct tunnel proved the vein in the Great Limestone beneath Sharnberry ((Table 51), p.176) to be mineralised, but only with quartz.

    With the exceptions of the E–W vein at Old Slitt Mine, all the major lead-producing mines with yields over 40 000 t PbS have worked ENE-trending veins or flats associated with such veins; though among flats the E–W belt at Allenheads and the NNW Smallcleugh zone at Nenthead are also exceptional. While it is not possible to arrive at an accurate mean width, it is difficult to avoid the impression that on the ENE veins, widths only rarely exceeded 6.5 ft (2 m). From this it follows that the mining of the lead oreshoots is expensive in present day terms because cheap methods like block-caving or long-hole stoping cannot be adopted without excessive dilution. Lead oreshoots have been worked in virtually every hard, brittle wallrock in the Carboniferous from Basement Group conglomerate and thick Asbian limestone at Scordale up to low Westphalian A at Healeyfield. The vertical dimension of individual oreshoots is, nevertheless, small being controlled normally by the thickness of the favourable wallrock member minus the displacement of the vein. Vertical dimensions are thus at their maximum in the Rogerley Channel belt of thick Grit Sills (pp.41 and 67). Next to these sandstones should come the Whin Sills, which reach 180 ft (55 m), probably over wide areas of the orefield, and may reach as much as 300 ft (90 m). However, only five mines, Stonecroft-Greyside, Burtree Pasture, Slitt, Rotherhope and Greenhurth have successfully worked for lead ore in these, while at three others, Greenlaws, Barbary and Blackdene, negative results have been given by trials on ENE veins in Whin. The fact nevertheless remains that the sills are untested beneath such lead-rich areas as Nenthead and the Allendales, even though there is now ample evidence that the status of the Whin dolerite is quite different from that of the Toadstones in Derbyshire; P R Meson's suggestion (1976, p.121) that the Whin Sill might act as a cap rock, ponding back deeper oreshoots, is considered unlikely, having regard to the brittle nature of the quartz dolerite. It is clear that among the bearing beds, the Great Limestone has been far more important than any other (pp.66–68) as a host rock for lead ore, but this has led to its having been prospected almost everywhere in the orefield and if there is to be future exploitation more attention should be paid to the Whin Sills and the adjacent hard strata from the Jew to the Melmerby Scar Limestone, where hard sandstones also occur. Further consideration also needs to be given to what have been described as watershed areas (Dunham, 1959) where blind oreshoots may be expected to occur beneath a cover of high Namurian. Those inviting attention include untested stretches between aligned portions of presumed continuations of the same vein; for example, St Peter's Vein NE forehead to the supposed continuation in the Devil's Water (p.222) 3.75 miles (6 km); Henry's Vein forehead at Allenheads to Beldon, 4 miles (6.4 km); Burtree Pasture Vein, cut at Groverake (p.199) to Ramshaw Vein SW of White Vein, 2.8 miles (4.5 km). The 5 mile (8 km) stretch continuing the Teesdale Mineral Belt NE of Sharnberry falls into the same category. All these virgin stretches cross inaccessible fell country in which problems of prospecting are not underrated. Geologically, lead oreshoots may be expected to occur where a position in mineral zones II–IV (p.81) combines with favourable structure and thus stratigraphy. There is no reason to suppose that all such positions have been tested, and from this point of view, the orefield cannot be said to be exhausted. The doubt that must exist however is whether the search can be justified economically at the metal prices of the time. After nine centuries or more of mining activity, all the easily found deposits have been located and many others have come from the policy of pursuing long crosscuts, but interesting prospects still remain.

    Zinc ore

    Towards the end of the London Lead Co.'s operations at Nenthead some zinc ore was produced and a smelter was erected in Tynedale; the bulk of the output however came from their successors the Nenthead & Tynedale Zinc Co. and particularly from the Vieille Montagne Zinc Co. of Liege, who acquired the Greenwich Hospital leases in 1896. The London Lead Co., in the numerous veins at the head of the Nent Valley had extracted for the most part only ore with reasonable galena contents, leaving behind as unworked ground and as stope fill, veinstuff with sphalerite, siderite and ankerite. The specific gravities of these minerals are sufficiently close to make gravity separation less than easy, and an elaborate mill, the largest ever seen in the district was engineered by Krupps and built in Nenthead, the circuit providing for repeated jig treatment. Output from Nenthead and West Allendale was near 0.25 mt zinc concentrates from 1896 to 1921, when operations ceased; the key veins, Gudamgill, Scaleburn, Rampgill-Barneycraig, the Middlecleugh and Capleclough groups must be reckoned as exhausted down to the Four Fathom or Three Yard Limestone. A single trial in depth reached the Jew Limestone (Smith, 1923) but found no ore on Rampgill Vein below the Scar Limestone. No deep test has been made in West Allendale. Recovery in the Krupp Mill was not good, and when sampled early in World War II, the 0.63 mt of gravel tailings were found to carry 3.5 per cent Zn, 0.4 per cent Pb. A 1000/t per day flotation plant recovered most of this metal for wartime purposes and the residues were exhausted by a private operator after the War. However, the Vieille Montagne Co.'s mining operations had brought to light two oreshoots which, because they were dominated by mixtures of sphalerite with witherite, could not be treated by gravity, and neither was milled in the flotation plant subsequently erected for fluorspar at Nenthead. These deposits are on First Sun Vein at Nentsberry Mine (pp.154–156) where (small tonnages of other veins being included) some 54 000 t with 8.7 per cent Zn (say 15.5 ZnS) and 1.6 PbS are believed to be in place and appear capable of substantial extension, both SW into Cumbria and NE towards Carrshield in West Allendale. An adit from the latter locality would drain the whole mine, at present blocked by serious falls, and could probably be driven in part on live vein. A second sphalerite–witherite deposit occurs on Scraithole Vein, the next ENE vein to the SE which since its reopening a few years ago is said to have 34 000 t possible ore with 17 per cent Zn (30 per cent ZnS) in a part witherite matrix. Also, the reopening of Swinhope Mine (East Allendale) referred to above showed not only the North Vein well mineralised with sphalerite, but also widths of 20 ft (6 m) or more alongside Williams Vein with low-grade disseminated sphalerite. Large tonnages of low-grade zinc ore may exist but a more conservative estimate by Mr D W Strutt of Weardale Minerals Ltd (personal communication) indicates 53 000 t possible, with 5.6 per cent Pb, 6.8 per cent Zn. In three different mines (unfortunately not one) there are modest reserves of zinc ore that could be developed. These may become of some interest while a custom flotation mill is available at Blackdene (Weardale Mining & Processing Ltd).

    The deepest workings at Allenheads, on Henry's Vein in the Three Yard Limestone, showed some passage into zinc ore (and some has been recovered from the wastes) but this particular zonal change, common in lead deposits elsewhere, is rarely seen in the Northern Pennines. Sphalerite was very clearly deposited in the intermediate zone (III) and nearby, with only traces in lower zones; also it occurs chiefly W of the Burtreeford Disturbance. Small deposits that have provided some zinc production occupy a comparable position to those of the Allendales in the Harwood headwaters of Teesdale at Willyhole; the occurrence of greenockite here and elsewhere in the field (Young et al., 1987) and at Ashgillhead (p.90) suggests high Cd values. Finally, E of the Disturbance there are persistent replacements of the Single Post Limestone by sphalerite, siderite, ankerite and pyrite at Ettersgill (p.245) and Wynch Bridge (p.246). Only the former offers sufficient tonnage to be of any interest, and its position at the western end of the Teesdale Mineral Belt could suggest much more extensive flat deposits similarly controlled.

    Summarising, Areas 2, 3 and 7 offer scope for limited production of custom zinc ore, from part of which witherite could be obtained as a byproduct.

    Fluorspar

    Much has been learned about the geology and mineralogy of fluorspar in the course of the 100 years in which it has become established as the principal product of the northern half of the Northern Pennine Orefield; there is much to add to the 4th edition of the Fluorspar Special Report (1952). In particular, it has now become clear that all but two of the significant fluorspar orebodies occur on 'Quarter-Point' veins, which tend to follow courses abruptly alternating between E–W and ESE–WNW. The fundamental reason for this presumably relates to basement tectonics but at the present level of erosion it merely emerges as an empirical fact. Moreover, the oreshoots occur (except at Cambokeels) only where the direction is near E–W, and the ESE stretches are barren. The mechanism is easily understood in terms of a sinistral transcurent shift on the N wall of the vein relative to the S, creating wide open spaces for the ingress of mineralising fluids. At Blackdene/South Slitt, Greenwood and Smith (1977, (Figure 5) have demonstrated the extent of the sideways movement as 88.5 ft (27 m) and the condition of the vein filling here indicates that the movement preceded the crystallisation of the contents; elsewhere on veins in this category, strong postmineralisation movements have been superimposed, comminuting the contents considerably. Vein-widths up to 25–30 ft (7.6–9 m) are not uncommon and the filling is dominated by fluorite, with quartz in second place, east of the Burtreeford Disturbance; while to the W, the chief example of a vein of the 'Quarter-Point' suite is the Great Sulphur Vein, filled with quartz of zone GSV2, and at the E end underlain by sulphides of GSV1. It must now be conceded that zone GSV2 underlies Weardale between Stanhope and Harehope Gill, E of Frosterley; it outcrops on Catterick Moss and in Bollihope; the Slitt Vein where cut by the aqueduct tunnel carried massive quartz with no more than 6 per cent CaF2; as already mentioned, the condition of the Teesdale Mineral Belt at depth near Sharnberry was similar. In the special case of Cambokeels, massive early quartz has been invaded by oreshoots of fluorite, which in turn have been subjected to quartz veining. At Groverake and Stotfield Burn mines on Red Veins, there is an early phase of quartz with chalcopyrite and marcasite. These facts suggest the possibility of increasing silica and decreasing fluorite as the large fluorspar orebodies are worked downwards; indeed this was well illustrated by the eastern workings in the Three Yard Limestone and adjacent strata at Stotfield Burn.

    The most fully developed vein system is the Red Vein, which has so far yielded 1.81 mt crude fluorspar, the largest single orebody being Groverake with 0.71 mt, and a stratigraphic range from the Lower Felltop Limestone down to the Three Yard Limestone. It is probably a coincidence, but all six orebodies on the Red Vein terminate downwards at this horizon in the present state of development, save that at Stanhopeburn fluorspar has reappeared beneath the barren measures, in the Tynebottom Limestone. The position of the Whin Sill is known to be directly under this limestone at Groverake, but as borings at Redburn East and the Rookhope borehole (Dunham et al., 1965) show in middle Rookhope it has descended to below the Jew Limestone. What may be a flat developed in sheared Jew Limestone near the Red Vein at Rookhope proved disappointing on investigation by boreholes additional to the Rookhope bore, but the only test of the Sill so far was at Crawleyside, which was negative, but may have missed the oreshoot on plunge. If the Whin Sill carries beneath one or more of the Red Vein orebodies, that will generate important new reserves. It is particularly hoped to reach it at Groverake (where Greenwood and Smith (1977) have shown a strong vertical gradient in temperatures and yttrium-contents around the intersection of the Red and Groverake veins) and at Stanhopeburn. At the two extremities of Red Vein, Frazer's Hush at the W end, and Stanhopeburn at the E end, extensive ironstone flats worked during last century signal the proximity of a strong vein. The Greencleugh Vein has been tested by boring over a length of 1650 ft (503 m) and shown to carry fluorspar down to the Nattrass Gill Hazle, 600 ft (183 m) below surface. An incline has been sunk to it. Frazer's Hush Mine has now (1989) been successfully brought into production by means of an incline from surface, and also a connection from the 60 fathom level of Groverake Mine; the deepest workings at present are in the Great Limestone.At the other extremity, although Red Vein E of the Hope-Crawley workings gave negative results to boring at Rogerwell Hush, where it was cut in the Great Limestone by the aqueduct tunnel it carried fluorite, quartz and sphalerite and was swinging into the E–W direction. In the ground heavily concealed by drift to the E there is, therefore, an interesting prospect.

    The proved length of the Rookhope Red Vein system from Frazer's Hush to the tunnel amounts to nearly 10 miles (16 km) and the aggregate length of oreshoots (including Frazer's) is roughly 4 miles (6.4 km). All the oreshoots on it are assigned to Zone I (fluorite with sparse galena) but both Groverake and the eastern part of Stanhopeburn were originally worked as reasonably productive lead mines, and may thus be transitional to Zone II. At Groverake the lead miners had taken the galena from narrow slits in the wide vein, leaving the spar, and the extraction of more than 0.5 mt of fluorspar has changed very little the appearance of the longitudinal section. At Stanhopeburn the fluorspar was robbed from the stope fill in the old lead workings successfully.

    Sedling Vein is short in comparison with other veins of its class, but it carried a western lead orebody and an eastern fluorspar oreshoot of exceptional quality, at times yielding over 80 per cent CaF2. Its apparent E continuation, Longsyke Vein has been thoroughly drilled but found too narrow for profitable extraction. Sedling will someday repay investigation in depth.

    Slitt Vein, the other mainstay of the industry, is known over a total length of 13.6 miles (21.9 km) but E of the Blue Circle Cement works there is an untested stretch to Catterick Moss where it enters the GSV2 quartz zone. At Harehope Gill some fluorite reappears but a borehole at the Old Sunnyside Mine found no orebody; still futher E the vein enters the Barium Zone before impinging on the Teesdale–Deerness fault-system. On Slitt Vein in 1985, two mines were producing fluorspar. Blackdene, where two major oreshoots on Slitt Vein were opened up, one on either side of the intersection with the formerly very productive ENE Blackdene Vein. Beds from the Three Yard Limestone down to the Alternating Beds have proved unusually favourable owing to the high proportion of hard sandstones in the sequence, and the indurated nature of the beds associated with the Cockle Shell and Single Post Limestones. The eastern orebody (formerly known as 'South Slitt') was mined from Whin Sill wallrocks but cut out in depth. In this western part of Slitt Vein, structural controls similar to those on Red Vein apply, and the eastern oreshoot terminates where the direction changes from E–W to ESE. However, as (Figure 46) shows, after a barren interval, the E–W direction is resumed and here the W B Company in much earlier times worked lead oreshoots that extended down from the Great Limestone to the Whin Sill, here beneath the Tynebottom Limestone. These deposits must be assigned to Zone II, but they may prove to offer a resource of backfilled fluorspar. The second recently operating mine, Cambokeels (Cammock Eals) may still offer potential for extension laterally and in depth (Dunham, 1988). The stratigraphical range here is from the Nattrass Gill Hazle at Heights Pasture opencut down to beds below the Jew Limestone, and within the workings the Whin dolerite changes horizon from beneath the Tynebotton to under the Jew Limestone. Structural and mineralogical conditions are complex and although three main oreshoots, plunging steeply E can be made out, these are interrupted where unfavourable wallrocks such as soft shale impinge on them. The mineralisation continued strongly into the sole of the 320 m Level. Beyond the W foreheads lie the two ironstone flats of Rigg and West Rigg and small quantities of fluorspar were formerly raised near these; but a deep drilling programme (p.212) gave negative results in this stretch. Mr D W Strutt (personal communication) has shown that plunging oreshoots on the Cambokeels model could be fitted between the intersections, and a drivage through this ground, ultimately having the Old Slitt workings as the main objective, is under consideration. To 1985 the contribution from Slitt Vein totalled 0.80 mt crude fluorspar and 9520 t PbS as byproduct, not including the lead production from the Old Slitt Mine.

    The two ENE veins mentioned as exceptional in carrying Zone I fluorspar mineralisation are Blackdene and Barbary (Ireshopeburn) veins. Both are regarded, on good grounds, as exhausted; neither carried ore in the Whin Sill. Some fluorspar was obtained from the Whin Sill and overlying formations up to the Scar Limestone at Rotherhope Fell Mine, but here the dumps have now been exhausted and the mine entrance has been blasted in, notwithstanding the possibilities that this mine holds for further development beneath Smittergill (pp.125–126). Also in Alston Moor, the extensive East Cross Fell Mines found high quality fluorspar, but their inaccessibility has so far made it impossible for more than a few tons to be removed.

    There remains what may yet prove to be the major future development for fluorspar in the orefield. (Figure 46) shows, in the Derwent and East Allen drainage, another 'QuaterPoint' structure, complementing the Red, Sedling and Slitt veins, and if it is correctly interpreted, of greater length (15.6 miles, (25 km) than these. At the western end, the ESE Sipton Vein is accompanied by a N-facing monoclinal fold in the Great Limestone, with many veinlets of fluorite in it, but too poor to work. Its ESE continuation has been mapped as a fault for 5.6 miles (9 km) on indifferent surface evidence, but it is not too far-fetched to suppose that this same line connects with the western foreheads on White Vein at Hunstanworth. At Whiteheaps Mine (production of crude fluorspar up to 1985, 295 000 t) the best ore has come from the Whiteheaps and Sikehead Red veins, two different veins both nearer to E–W than the White Vein; but the latter has yielded useful tonnages, particularly above the 80-Fathom Level (Figure 35). East of Sikehead, a fracture supposed to be the continuation of White Vein has been tested by drivage at the 30-Fathom Level for 0.475 miles (0.76 km) but this was entirely barren, the fissure when seen containing dry, unmineralised breccia similar to that found between the two orebodies at Redburn. Four miles (6.4 km) farther ESE, White Vein was cut in the aqueduct tunnel strongly though probably not payably mineralised with fluorite and quartz. This fracture must link with the fault mapped on surface evidence during the. resurvey of Sheet 26 from [NZ 037 442] near Waskerley to [NZ 106 404] near High House. It might be objected that this Sipton–White–Waskerley–High House fault system shows too few changes of direction to be analogous with Red Vein; but it should be recalled that before mining revealed the numerous changes of strike, Red Vein too was generalised as a smooth curve see (Figure 16), where owing to the scale the generalisation is retained). The presence of another major series of oreshoots, concealed by high Namurian and Low Westphalian strata, the significance of which is seen only where erosion has cut down into the main bearing beds at Whiteheaps, is worth considering. Nevertheless, the additional difficulties inherent in prospecting this belt are not to be under-rated, and it is to be regretted that a case was not made for geophysical work on it before the Department of Industry/IGS Mineral Reconnaisance Programme was brought to an end. In 1986 a modest start on investigating it was made by means of underground borings in the Great Limestone at the W end of Whiteheaps Mine and by surface work at MacDonnel's Shaft and Smithy Sike; a record of an examination of the old shaft by Banchland Fluor Mines Ltd states that the White Vein here is 20 ft (6 m) wide, 50 per cent CaF2 . Even if this prospect succeeds, much more vigorous action will be required to establish a belt that could secure the fluorspar industry for a long time to come.

    The erection of two modern flotation plants in Weardale with a combined feed capacity of 7500 t/week makes demands on the mines far in excess of anything achieved before 1978. These have been partly met from the residues of former lead and fluorspar mining in this and adjacent areas. Less than 15 000 t of dumps worth treating now appear to remain, save in slimes below flotation size. In the late 1960s a suggestion was considered that Burtree Pasture Mine, where the Beaumont and Weardale Lead Co. sections indicated extensive 'quoting' (backfill) of lead ore stopes, might contain as much as 1 mt recoverable crude fluorspar. The attempt to reopen the deep underground shaft (Figure 13) and (Figure 30) unfortunately failed because much timber from the former headworks and water wheels had been thrown down it, and only Garget's Level was reached. Some spar was raised here, but it was unpayble; however, subsequently an incline was driven to give access to the vein at the base of the Great Limestone, and here acceptable spar averaging 43 per cent CaF2 was extracted until a range of empty stopes, with the limestone dipping below, could be seen ahead; the operation was then abandoned. The decision may have been influenced by the failure to find fill that could safely be recovered in the northern stopes on Henry's Vein at the Beaumont Mine, Allenheads. The question of Burtree Pasture, where only a minor effort at fill recovery has so far been made, will arise again in the future, particularly with respect to the extensively but not completely worked ground between Garget's Level and the base of Whin Sill. The northern stopes in the beds above the Great Limestone may be regarded as less attractive, but even these, and Henry's Vein southern stopes, may some day be examined. Backfill at Old Slitt Mine has already been mentioned; the only other large orebodies worth considering are Lodgesike–Manorgill–Wire-gill–Calfornia on the Teesdale Mineral Belt; Sharnberry has already been examined and found unfilled, and this may also apply to the others since the veins were relatively narrow, but we are not aware of any definite information on this point. At Hunstanworth, the Jeffreys veins were thoroughly examined when Presser Shaft was reopened about 1972, and the stopes were empty; only Ramshaw North Vein above adit appears to offer interest.

    Summarising the future resource position for fluorspar; (1) a partly explored orebody at Frazer's Hush is being extracted and another might be found beneath the glacial drift E of the NWA Aqueduct tunnel on Red Vein; (2) downward extensions of major orebodies into the Whin Sill are hoped for at Groverake and Stanhopeburn and such extensions, already extracted at Cambokeels and Blackdene may go deeper still (Dunham, 1988); Rotherhope Fell could extend SW in the Sill; (3) the principal hope for new major discoveries is in the Sipton–Whiteheaps–High House fault-zone where, unfortunately, prospecting offers more serious problems than in the other two main 'Quarter Points' ; (4) surface residues are becoming depleted, but it may be possible to supplement these from backfill.

    Witherite

    Settlingstones, the world's leading producer closed, exhausted, in 1968 after mining about 0.8 mt to produce 0.63 mt high-grade (92 per cent) BaCO3 . Attempts to discover new orebodies, for example on Bewick Vein between Grindon and Winter's cross veins, where carbonation of baryte had been virtually complete in the Settlingstones complex, failed. South Moor, the other chief producer, closed in 1958. The management's, plan to sink from Westphalian B to the Great Limestone was unfortunately not carried out, though the shaft and sump almost reached Namurian strata. The old Fallowfield Mine was drilled underground from Thorntree Shaft but sufficiently encouraging results were not obtained to justify reopening, even while the adjacent Acomb Colliery was still pumping the water. An attempt to find the source of the good-grade witherite seen on dumps at Longcleugh (p.152) showed that this came from a minor vein N of the mine, and a test of the Whin Sill proved negative. If the zinc-bearing veins at Scraithole and Nentsberry are extracted, witherite may be produced as a byproduct and there would be some inducement to float the roughly 11 000 t of residues from Settlingstones; but it is difficult to identify any very attractive prospect for a new discovery of this unusual mineral in quantity, save perhaps from White Lea, in the Coalfield (p.281). No doubt other bodies like South Moor and Ushaw Moor exist in the major faults crossing the coalfield, but now that so much of this once-great coal mining area has been exhausted and flooded, with a minimum number of penetrations of the faults, the task of prospecting for spar bodies becomes almost impossible.

    Barytes

    During the years since 1949 the Silverband and Closehouse barytes mines (Dunham, 1959, Hill and Dunham, 1968) have been brought into full production; their combined production record probably now exceeds 0.6 mt. Both have changed hands and now rely solely on opencast mining, but there are underground reserves at both mines that may come under consideration. New Brancepeth Colliery closed in the 1950s without exhausting the two substantial baryte bodies in the Deerness Fault. They were proved by boring to be blind above the Harvey Seam but with a resource very likely to remain between the two; the current economics of barytes mining could hardly encourage reopening to extract this. Surface operations at Weather Hill proved disappointing, but intersections of witherite and baryte in the drift workings at Waterhouses may yet prove of interest. The Cowgreen barytes mine, considered exhausted, has been inundated by the reservoir constructed on the Wheel of the Tees, but Dubbysike Mine between here and Harwood still has unworked reserves. The newest barytes mining venture is at the old London Lead Co.'s Dufton Fell Mine, where surface residues have yielded well, and where three different stratigraphic horizons of mineralised flats may yield further baryte if underground operations are undertaken. The Great Spar 'dyke' (p.274) may deserve further prospecting for baryte near surface, or perhaps for witherite below and the unique Healeyfield Mine (p.228), with which it connects may someday deserve a deep test for new oreshoots since it overlies a separate cupola of the Weardale Granite (see Bott and Masson Smith, 1957, pl. 10). At Settlingstones, a possible reserve of 100 000 t good-grade baryte with lead and zinc values exists SW of Grindon cross vein, but it proved unpayable to extract this even when the witherite mine was fully operational, and since it would now involve reopening Grindon Hill Shaft and sinking it at least 600 ft (182 m) to take account of the SW dip of the controlling Whin Sill wallrock, this project is not immediately attractive. The nearby residues from flotation treatment of the Langley Barony dumps for recovery of sphalerite may be worth retreatment for barytes, but those at Stonecroft are too much contaminated with ankerite to be of interest.

    Summarising, further output of barytes may be expected from Closehouse and from at least two properties in Area 1, and the orefield offers other possibilities for this mineral, though of varying degrees of interest. The closing of all but the coastal collieries in the North East Coalfield makes it unlikely that further deposits, like that at Lumley Sixth Pit, or the clean baryte seen at Houghton shortly before that mine closed, will be found unless this style of mineralisation continues under the North Sea. The utilisation of barium chloride brines ceased with the closing of Backworth Colliery prior to 1947

    Iron ore

    The Bilbao-type iron orebodies of the Northern Pennines, mainly taking the form of more or less completely oxidised flats derived from siderite–ankerite protores in limestone, are probably not exhausted, but their scale is too small for modern interest. They enjoyed a good reputation during the 19th century, when a special railway across the high fells, with inclines to the valley bottoms at Rookhope and Stanhope, was built to transport them. The most recent working was at Carricks Mine (p.193) during World War II. The deposits may be regarded as gossanlike indicators of feeding veins no great distance away, and some such veins have proved to be important lead and fluorspar producers. This is true at Groverake, while across the valley the ironstone extends well beyond the ground stoped for lead at Burtree Pasture. The extensive limonite flat at Frazer's Hush similarly indicates the proximity of a major vein of fluorspar and the same may be true of the well-exposed flats at West Rigg and Rigg. The North Slitt ironstone mine lies, as far as is known at present, in flats in a westward extension of the Old Slitt lead ore mineralisation.

    References

    ALMOND, J K. 1977. The Nenthead and Tynedale Lead and Zinc Company Ltd, 1882–1896. Northern Mine Res Soc., Br. Min. , No. 5, 26–40.

    BOTT, M H P, and MASSON SMITH, D. 1957. The geological interpretations of a gravity survey of the Alston Block and the Durham Coalfield. Q. J. Geol Soc. London, Vol 113, 93–113

    DUNHAM, K C. 1944. The production of galena and associated minerals in the northern Pennines, with comparative statistics for Great Britain. Trans Inst. Min. Metall., London, Vol 53, 181–252.

    DUNHAM, K C. 1949. Geology of the Northern Penine Orefield Vol 1–Tyne to Stainmore (1st edition). Mem. Geol. Surv. G. B. 357pp.

    DUNHAM, K C. 1952. Fluorspar (4th edition). Spec. Rep. Miner. Resour. Mem. Geol. Surv. G.B., Vol. 4. 141pp.

    DUNHAM, K C. 1959. Non-ferrous mining potentialities of the northern Pennines. 115–147 in The future of non-ferrous mining in Great Britain and Ireland. (London: Institute of Mining and Metallurgy.)

    DUNHAM, K C. 1988. Pennine mineralisation in depth. Proc. Yorkshire Geol. Soc. Vol. 47, 1–12.

    DUNHAM, K C. DUNHAM, A C, HODGE, B L, and JOHNSON, G A L. 1965. Granite beneath Visean sediments with mineralization at Rookhope, northern Pennines. Q. J. Geol. Soc. London, Vol. 121, 383–412.

    GREENWOOD, D, and SMITH, F W. 1977. Fluorspar mining in the northern Pennines. Trans. Inst. Min. Metall., London, Vol. 86, B181–190.

    HILL, J A, and DUNHAM, K C. 1968. The barytes deposit at Closehouse, Lunedale, Yorkshire. Proc. Yorkshire Geol. Soc., Vol. 36, 351–372.

    INESON, P R. 1976. A review of mining potentialities in the Alston Block of the northern Pennine Orefield. Bull. Peak District Mines Hist. Soc., Vol. 6, 171–26.

    SMITH, S. 1923. Lead and zinc ores of Northumberland and Alston Moor. Spec. Rep. Miner. Resour. Mem. Geol. Surv. G.B. , Vol. 25. 110pp.

    WALLACE, W. 1890. Alston Moor, its pastoral people: its mines and miners. (Newcastle: Swan and Morgan.)

    YOUNG, B, BRIDGES, T F, and INESON, P R. 1987. Supergene cadmium mineralisation in the Northern Pennine Orefield. Proc. Yorkshire Geol. Soc. Vol. 46, 275–278.

    Figures, plates and tables

    Figures

    (Figure 1) Sketch-map to show the main formations and subdivisions of the Northern Pennine Orefield (Tyne to Stainmore) with 1-inch and 1:50000 sheet boundaries

    (Figure 2) Comparative section of the Basement Group and Asbian strata

    (Figure 3) Comparative sections of Brigantian strata

    (Figure 4) Comparative sections of Namurian strata

    (Figure 5) Isopach maps showing thicknesses of Pendleian and Brigantian strata. (Channels in Great Cyclothem after B L Hodge, 1965)

    (Figure 6) Comparative sections at the Haydon Bridge and Alston mines

    (Figure 7) Comparative sections of Upper Namurian and Westphalian strata

    (Figure 8) Sketch-map to show the horizon and thickness of the Whin Sill

    (Figure 9) Structure-contour map of the Northern Pennine Orefield (Tyne to Stainmore)

    (Figure 10) Diagram illustrating the statistical analysis of structural trends

    (Figure 11) Idealised cross-section of a fissure vein influenced by regional domal folding

    (Figure 12) Cross-section of Killhopehead Vein (Weardale Lead Co.)

    (Figure 13) Cross-section of Burtree Pasture Vein (Weardale Lead Co.)

    (Figure 14) Plan of the North Central Flats, Rotherhope Fell Mine (Vieille Montagne Zinc Co.)

    (Figure 15) Plan of the East End Flats, Allenheads Mine (W. Beaumont Co.)

    (Figure 16) Map to illustrate the distribution of primary minerals

    (Figure 17) Sketch-map of Silverband Mine

    (Figure 18) Key map, area 1, The Escarpment. Key to numbered mines 1 Hartside; 2 Knapside; 3 Ardale Head; 4 Silverband; 5 Hunter's Vein; 6 Swathbeck; 7 Loppysike; 8 Dun Fell; 9 Threlkeld Sike; 10 Dufton; 11 White; 12 Murton; 13 Hilton; 14 Amber Hill; 15 Long Fell; 16 Augill; 17 Cabbish.

    (Figure 19) Sketch-map of Scordale Mines

    (Figure 20) Key map, area 2, Alston Moor Key to numbered mines 1 Park; 2 Woodlands Level ; 3 Manor House; 4 B1agill; 5 Nest; 6 Bayle Hill; 7 Holyfield; 8 Nattrass; 9 Flow Edge; 10 Rotherhope Fell; 11 Crag Green; 12 Whitesike; 13 Ashgill Field; 14 Sear Ends Level; 15 Leehouse Well; 16 Stow Crag; 17 Sir John's; 18 Clargillhead; 19 Hiddenhole; 20 Smittergill Head; 21 Slatesike; 22 Cashwell; 23 Doukburn; 24 Calvert; 25 Hudgill Burn; 26 Galligill Sike; 27 Nentsberry; 28 Grassfield; 29 Brownley Hill ; 30 Bentyfield; 31 Greengill; 32 Dowgang; 33 Scaleburn; 34 Rampgill; 35 Tynebottom; 36 Whitesike; 37 Smallcleugh; 38 Capleclough.

    (Figure 21) Section of the Great Sulphur Vein, Sir John's Level.

    (Figure 22) Structure-contour map of the Nenthead–Coalcleugh–Killhope area

    (Figure 23) Longitudinal section, Gudhamgill and Rampgill veins (London Lead Co. and Vieille Montagne Zinc Co.)

    (Figure 24) Longitudinal section, Browngill-Capleclough, Middlecleugh and Longcleugh veins (Vieille Montagne Zinc Co.)

    (Figure 25) Key map, area 3, West Allendale. Key to numbered mines 1 Longcleugh; 2 Mohopehead; 3 Heartycleugh; 4 Wellhope; 5 Wellhopehead; Scraithole.

    (Figure 26) Key map, area 4, East Allendale Key to numbered mines 1 St Peter's; 2 Swinhope; 3 Allenheads.

    (Figure 27) Contour plan of the western part of St Peter's Mine

    (Figure 28) Plan and sections of Allenheads Mine (W. Beaumont Co.)

    (Figure 29) Key map, area 5, Weardale. Key to numbered mines 1 Killhope; 2 Cowhouse; 3 Guinea Grove; 4 Scraith Head; 5 Loddegill; 6 Langtae Head; 7 Queensberry; 8 Breckonsike; 9 Burtree-pasture; 10 West Groverake Opencast; 11 Wolfcleugh; 12 Rispey; 13 Elmford; 14b Ireshopeburn (or Barbary); 15 Blackdene; 16 Allercleugh 17 Lodgefield; 18 Old Fall Level; 19 Levelgate level; 20 Douks; 21 Middlehope; 22 Low Fulwood; 23 Sunnyside opencut; 24 Boltsburn; 25 Lodge Sike; 26 Gravelheads Green opencut; 27 Broadsike; 28 Glints level; 29 Carricks; 30 Rowantree; 31 Middlehope Shield; 32 Greenlaws; 33 Heights; 34 Hanging Wells; 35 Brandon Walls; 36 Swinhopehead; 37 Westernhope Old; 38 Westernhope News; 39 North Grain ironstone opencut;Frazer's Hushes; 41 Rookhopehead; 42 Groverake; 43 Redburn; 44 Stotfield Burn; 45 Stanhopeburn; i Noah's Ark opencut; 47 Sedling; 48 High Sedling; 49 Middlehope (old); 50 Slitt; 51 Slitt Pasture; ! West Rigg; 53 Heights Pasture; 55 Cambokeels (Cammock Eals); 56 Billing Hills; 57 Harehope Gill; 3 Sunnyside; 59 Allergill; 60 Harnsisha Burn; 61 Yew Tree; 62 Hollywell; 63 Whitfield Brow; 64 Wagerarn; 65 Cornish Hush; 66 Pikestone.

    (Figure 30) Longitudinal sections, Burtree Pasture, Sedling and Greenlaws veins (Weardale Lead Co.)

    (Figure 31) Plan and section of Boltsburn East Mine (Weardale Lead Co.)

    (Figure 32) Plan of Carricks Ironstone Mine (Weardale Steel, Coal and Coke Co.).

    ((Figure 33) Plans and longitudinal sections of mines on the Red Vein of Rookhope and the Slitt Vein (Weardale Minerals and Weardale Mining and Processing Cos. up to date 1985)

    (Figure 34) Key map, area 6, Derwent. Key to numbered mines 1 Burntshieldhaugh; 2 Beldon; 3 Reeding; 4 Shildon; 5 Whiteheaps; 6 Sikehead; 7 Ramshaw; 8 Jeffrey's; 9 Swandale; 10 Burnhope; 11 Harehope Gill; 12 Silvertongue; 13 Healeyfield

    (Figure 35) Longitudinal sections, Jeffreys and Whiteheaps mines (Hunstanworth Mines Ltd and Weardale Mining and Processing Ltd)

    (Figure 36) Key map, area 7, Teesdale Key to numbered mines 1 Hardshins; 2 Overhearth; 3 Green Bourne; 4 Greenhurth; 5 Cadger Well; 6 Dubbysike; 7 Cowgreen; 8 East Cowgreen; 9 Ashgill Head; 10 Grasshill; 11 Lady's Rake; 12 Willyholc; 13 Bands; 14 Langdon Head; 15 Langdon; 16 Pike Law; 17 Flushiemere; 18 Ettersgill; 19 Wynch Bridge;20 Red Grooves; 21 Coldberry; 22 Lodgesike; 23 Low Skears; 24 Marlsbeck; 25 High Skears; 26 Snaisgill; 27 Wiregill; 28 Manorgill; 29 California; 30 East Rake; 31 Flake Brigg; 32 Skarnberry; 33 Green Lead; 34 Silverband; 35 Closehouse; 36 Lunehead.

    (Figure 37) Longitudinal section, Greenhurth Mine.

    (Figure 38) Sketch-map to show the geology of the Cowgreen area (based on 1:2500 geological survey, 1940)

    (Figure 39) Longitudinal section, Winterhush Vein (Wrentnall Baryta Ltd)

    (Figure 40) Longitudinal sections of Lodgesike -Manorgill and Eggleshope veins in the Teesdale Mineral Belt, and of Skears Low Level (London Lead Co. with additions from English Lead Mines Exploration Ltd and Swiss Aluminium Mining (UK) Ltd) to the E, 3000 ft (914 m) N of Bow Lee old bridge, an E – W fault is exposed on the same line, accompanied by limonite mineralisation 40 ft (12 m) wide [NY 9088 2908] which may be followed up the steep eastern side of the gorge. The mineralisation is in part a replacement of the Five Yard Limestone on the footwall side of the fault. A short level has been driven eastwards in the deposit. The analysis (No. 2 on Table 33, p.91) represents a channel sample across the full width.

    (Figure 41) Plan and longitudinal sections of Langley Barony, Settlingstones and Stonecroft -Greyside veins (owners of Settlingstones Mine Ltd)

    (Figure 42) Longitudinal section, Fallowfield Mine

    (Figure 43) Cross-section of the Great Spar 'Dyke' and South Moor veins

    (Figure 44) Longitudinal section, South Moor Witherite Vein (Holmside and South Moor Colliery Co. and National Coal Board)

    (Figure 45) Sketch-map of the Deerness fault-system

    (Figure 46) illustrates the distribution of fluorspar orebodies E of the Burtreeford Disturbance, giving extra emphasis to the worked oreshoots and indicating the output to 1985 of crude fluorspar from each.

    (Figure 46) Map of the Eastern Fluorine Zone showing location of major oreshoots and tonnages of crude fluorspar extracted to 1985 (tonnes)

    Plates

    (Plate 1) Purple fluorite crystals from a cavity in the Great Limestone flats, Boltsburn Mine. Collected by Sir Arthur Russell and now in the British Museum (Natural History) (Registration number BM 1964 R 1444). Photograph by courtesy of the British Museum (Natural History). Specimen approximately 20 cms across.

    (Plate 2) Sections of Weardale Granite from the Rookhope Borehole. a Thin section of granite from 1402.7 feet (427.5 m) showing alignment of micas. Large grains of rather turbid microcline occupy much of the upper field of view; clear quartz fills much of the lower field. Crossed polarisers. University of Durham thin-section number 25 862 (Photo: C H Emeleus) b Vertical section of core from 1407 feet (429 m) showing conspicuous foliation marked by muscovite and biotite. (Photo: C J Jeffrey, BGS)

    (Plate 3) Handsome Mea Flats, Smallcleugh Mine, Nenthead. Metasomatised Great Limestone, replaced mainly by ankerite and silica, contains conspicuous roughly horizontal bands of vugs lined with crystals of ankerite, galena and sphalerite. Above the hammer a limestone bed with numerous shaly partings has escaped intense alteration. (Photo. T F Bridges)

    (Plate 4) Scraithole Vein, Scraithole Mine, West Allendale. The vein, here in the Great Limestone, consists predominantly of witherite with smakquantities of sphalerite and numerous clasts of limestone wallrock. (Photo. T F Bridges)

    (Plate 5) Groverake Mine, Rookhope. The Old Whimsey Shaft (right), sunk to the Three Yard Limestone, provides the main access to the mine. Behind the Old Drawing Shaft headframe (left) may be seen the heapstead buildings of the Firestone Incline. The outcrop of Groverake Vein runs between the two shafts. (L2937/25/14)

    (Plate 6) Slitt Vein in the Great Limestone, West Rigg Quarry, Westgate, Weardale.; Large metasomatic ironstone flats in the Great Limestone adjacent to Slitt Vein have been removed leaving the vein, here composed mainly of quartz and a little fluorite, as a conspicuous rib across the centre of the quarry. Old lead workings in the centre of the vein may be seen to the left of the figure. (Photo. B Young)

    (Plate 7) Mineralised Jew Limestone, Cambokeels Mine, Eastgate, Weardale. The Jew Limestone, here immediately beneath the Whin Sill, has been veined and partly replaced by quartz, fluorite, pyrrhotite and some sphalerite. Silicified limestone clasts are rimmed by concentric bands of quartz and fluorite. (Photo. T F Bridges)

    (Plate 8) Closehouse Mine, Lunedale A view of the workings from the East Hush in 1964, looking west. North of the opencut on Closehouse North Vein flat-lying Whin Sill dolerite, intruded above the Smiddy Limestone forms the side of the valley. South of the mineralised structure Middle Brigantian sediments form the dip slope inclined south to the Stainmore Syncline. (Photo. K C Dunham)

    (Plate 9) Closehouse North Vein, Closehouse Mine, Lunedale. Exposure of Closehouse North Vein in the 170 Fathom Level in 1960. Coarse baryte interdigitating with and partially replacing carbonatised White Whin dolerite. Exposure about 6 ft (2 m) wide. (Photo. The late J A Hill)

    (Plate 10) Closehouse North Vein, Closehouse Mine, Lunedale. Modern opencast workings expose the wide barytes orebody in which old levels from previous underground operations may be seen. Almost horizontal limestones and shales on the footwall are exposed on the right of the picture. Steeply folded sandstones and limestones on the hangingwall can be seen on the left. (Photo. B Young)

    Tables

    (Table 1) Total recorded production of lead and zinc concentrates 1666 –1985 Copper ore was mined only in Area 2, where 1608 t were produced prior to 1938. Iron ore of 'Bilbao' type was mined in Area 5 (1 504 207 t to 1938, with one mine reopened during World War II producing up to 1000 t per week); Area 2 (52 853 t) and Area 7 (4045 t); total output approximately 1.7 mt.

    (Table 2) Total recorded production of nonmetallic minerals 1850–1984

    (Table 3) Analyses of the Weardale Granite

    (Table 4) The Scar Cyclothem. (UG = Underground; BH = Borehole)

    (Table 5) The Five Yard Cyclothem

    (Table 6) The Three Yard Cyclothem

    (Table 7) The Four Fathom Cyclothem

    (Table 8) The Iron Post Cyclothem

    (Table 9) Comparison of two rises at Skears Mine

    (Table 10) The Great Cyclothem

    (Table 11) Little Limestone to Firestone Sill

    (Table 12) Section at North Grain opencast: [NY 883 448]

    (Table 13) Crag Limestone to Grindstone Sill

    (Table 14) Ettersgill Borehole ET/16 [NY 8904 2941]

    (Table 15) Summary of tectonic history

    (Table 16) Statistical analysis of horizon of vein oreshoots

    (Table 17) Statistical analysis of horizon of flat oreshoots

    (Table 18) Analyses of galena concentrates

    (Table 19) Silver recovered from galena concentrates

    (Table 20) Assays of galena for silver

    (Table 21) Analyses of sphalerite concentrates

    (Table 22) Analyses of Northern Pennine ankerites

    (Table 23) Refractive indices of ankerites *

    (Table 24) Analyses of siderite

    (Table 25) Analyses of baryte

    (Table 26) Analyses of witherite and barytocalcite

    (Table 27) Summary of mineral zones

    (Table 28) Approximate bulk composition of oreshoots

    (Table 29) Analyses of metasomatised limestone

    (Table 30) Analyses of fresh and altered quartz-dolerite

    (Table 31) Comparison of unaltered and altered dolerite assuming constancy of alumina

    (Table 32) Oxidation of primary minerals and related processes. (Minerals shown in brackets are soluble in water and therefore seldom remain in normal deposits in the oxidation zone)

    (Table 33) Analyses of oxidised ores

    (Table 34) Hydration of limonites

    (Table 35) Analyses of iron ores, Ardale Head

    (Table 36) Analyses of barytes ores and dressed product, Silverband

    (Table 37) Analyses of iron ores, Dun Fell

    (Table 38) Analyses of iron ore and umber, Horse Edge

    (Table 39) Analyses of iron ores, Park Fell

    (Table 40)  Analyses of iron and barium ores, Blagill Upper Level are given in (Table 40).

    (Table 41) Analyses of iron ore, Brownside and Nest

    (Table 42) Analyses of tailings, Rotherhope Fell

    (Table 43) Analyses of sulphur ores and concentrate, Great Sulphur Vein

    (Table 44) Shafts between Nentforce Level Portal and Nentsberry

    (Table 45) Principal horse levels near Nenthead

    (Table 46) Lead and zinc concentrates obtained from Nenthead sub-area

    (Table 47) Partial analyses of barium spars, West Allen Mines1 Dump near Longcleugh Level 0.75 mile (1.2 km) SE of Ouston [NY 7725 5204]

    (Table 48) Analyses of witherite and zinc-witherite products, Nentsberry

    (Table 49) Production from the Coalcleugh and Barneycraig veins

    (Table 50) Succession in the first 3000 ft (914 m) of the Blackett Level

    (Table 51) Mineralisation in the Tyne-Tees Tunnels of the Northumbrian Water Authority

    (Table 52) Analyses of iron ore, Killhope and Snodberry

    (Table 53) Burtree Pasture Vein

    (Table 54) Analyses of iron ores, Sunnyside and Boltsburn West

    (Table 55) Section in the Great Limestone, Boltsburn Flats

    (Table 56) Production from Boltsburn mines, 1818 - 1940

    (Table 57) Assays in North Side Flat, Boltsburn East, Acmin No. 2 Borehole. Weighted averages of samples

    (Table 58) Analyses of iron ores, Broadsike and Clints

    (Table 59) Analyses of iron ores, Carricks

    (Table 60) Analyses of fluorspar, Stanhopeburn

    (Table 61) Analyses of fluorspar, Harnisha Burn and Yew Tree

    (Table 62) Estimates of lead values in Jeffries Veins

    (Table 63) Analyses of iron ores, bands

    (Table 64) Analyses of iron ores, Langdon Beck Mines

    (Table 65) Analyses of limonitic iron ore, Flushiemere

    (Table 66) Analyses of zinc ore, Ettersgill and Wynch Bridge

    (Table 67) Production of lead concentrates from the Little Eggleshope and Wiregill ore shoots

    (Table 68) Analyses of tailings, Sharnberry

    (Table 69) Analyses of tailings, Langley Barony

    (Table 70) Analyses of ore and product witherite, Settlingstones

    (Table 71) Analyses of tailings, Stonecroft

    (Table 72) Analyses of ore and product witherite, South Moor

    (Table 73) Analyses of witherite, Tanfield Moor

    (Table 74) Analyses of barytes, Lumley Sixth Pit

    (Table 75) Average analysis of run-of-mine barytes, New Brancepeth

    Geology of the Northern Pennine Orefield Volume I–Tyne to Stainmore–Tables

    (Table 1) Total recorded production of lead and zinc concentrates 1666–1985

    Copper ore was mined only in Area 2, where 1608 t were produced prior to 1938. Iron ore of 'Bilbao' type was mined in Area 5 (1 504 207 t to 1938, with one mine reopened during World War II producing up to 1000 t per week); Area 2 (52 853 t) and Area 7 (4045 t); total output approximately 1.7 mt.

    Lead concentrates (tones)

    Zinc concentrates (tones)
    To 1938 1939–1984 Total To 1938 1939–1964 Total
    1 Escarpment 26245 100 26345 – – –
    2 Alston Moor 830211 6167 636378 193809 20802 214611
    3 West Allendale 245646 64 245700 57466 913 58380
    4 East Allendale 310484 3193 313677 91 2009 2100
    5 Weardale 934858 25203 960061 – 182 182
    6 Derwent 52252 1555 53807 – – –
    7 Teesdale 383264 4974 388238 749 – 749
    8 Haydon Bridge 146294 725 147019 10224 10224
    2929254 41981   2771225 252115 34130 286246

    (Table 2) Total recorded production of nonmetallic minerals 1850–1984

    Area

    Fluorspar (tonnes)

    Witherite (tonnes)

    Barytes (tones)
    To 1938 1939–1984 Total To 1938 1939–1970 Total To 1938 1939–1984 Total
    1 – – – 90 – 90 74 717 375 920 450637
    2 902 14 198 15100 1 626 – 1626 1 060 – 1060
    3 – 200 200 3 582 – 3582 – – –
    4 – 2 600 2600 – – – – –
    5 651 417 1 287 872 1 939289 – – – 1 867 – 1867
    6 15 513 110 629 126142 – – 240 – 240
    7 – 22 000 22000 – – – 196 619 528 321 724920
    8 – – – 455 044 285 605 740649 400 500 900
    9 Durham Coalfield – – 47 811 246 704 264515 118 932 105 364 234246
    667 832 1 437 499 2 105331 508 153 532 309 1 010468 393 835 1 010 105 1 413870

    (Table 3) Analyses of the Weardale Granite

    Main constituents, per cent
    SiO2 72.18 73.90 72.16 72.17 72.17
    TiO2 0.16 0.25 0.21 0.16 0.18
    A12O3 15.57 15.30 15.52 15.39 15.45
    Fe2O3 0.27 0.13

    1.66**

    1.54   *

    1.59*
    FeO 0.78 0.55
    MgO 0.50 0.07 0.34 0.22 0.27
    CaO 0.86 0.30 0.83 1.01 0.93
    Na2O 2.93 4.05 3.75 4.56 4.20
    K2O 5.96 4.52 5.49 4.89 5.16
    H20+ 0.69 0.50
    H2O- 0.22 0.02
    P2O5 0.17 0.17
    MnO 0.07 0.05 0.059 0.062 0.061
    F n.d. 0.04
    Total 100.98 99.85 100.02 100.00 100.01
    Trace elements, parts per million
    Zr 52 57 100 85 92
    Sr 103 93 117 98 106
    Rb 170 330 419 426 423
    Ba 404 338 367
    Li 136 142 139
    Cu 11 9 10
    Ni 16 15 16
    Zn 42 47 45
    Pb 33 40 37

    (Table 4) The Scar Cyclothem. (UG = Underground; BH = Borehole)

    Area Mine or section Grid reference

    Scar Limestone

    Slaty Hazle

    Scar Cyclothem
    ft m ft m ft m
    1 Middle Tongue Beck [NY 704 324] 40 12.2 - 70 21.3
    2 East Cross Fell Mines [NY 717 367] 36 11.0 23 7.0 94 28.7
    Rotherhope Fell Mine [NY 700 427] 35 10.7 18 5.5 67 20.4
    Hudgill Burn Mine [NY 750 456] 36 11.0 13 4.0 62 18.9
    High Nent Force Shaft [NY 7333 4685] 55 16.7 24 7.3 87 26.5
    Foreshield Shaft [NY 7477 4677] 55 16.7 27 8.2 93 28.3
    Lovelady Shield Shaft [NY 7568 4621] 64 16.5 30 9.1 97 29.6
    Nentsherry Haggs Mine [NY 766 450] 30 9.1 12 3.7 60 18.3
    Rampgill UG Shaft [NY 7975 4417] 43 13.1 34 10.4 98 29.9
    3 Longcleugh BH [NY 7686 5180] 55 16.8 20 6.1 92 28.0
    4 Allenheads No. 1 BH [NY 8604 4539] 35 10.3 30 9.1 80 24.4
    5 Burtree Pasture UG Shaft [NY 8603 4180] 35 10.7 15 4.6 92 28.0
    Sedling Mine East [NY 860 411] 35 10.7 35 10.7 98 29.9
    Blackdene Mine [NY 868 390] 30 9.1 52 15.8 91 27.7
    Old Fall Shaft [NY 8733 3871] 32 9.8 23 7.0 92 28.0
    Greenlaws Mine [NY 889 370] 23 7.0 38 11.6 83 25.3
    Slitt Shaft [NY 9058 3920] 29 8.8 23 7.0 95 29.0
    Rigg BH [NY 9145 3895] 30 9.1 50 15.2 100 30.5
    Cammock Eals Mine [NY 935 383] 35 10.7 42 12.8 110 33.5
    Rookhope BH [NY 9334 4278] 30 9.1 24 7.3 108 32.9
    Crawleyside BH [NY 9962 4010] 32 9.8 15 4.6 86 26.2
    7 Grasshill Shaft [NY 8123 3484] 30 9.1 14 4.3 77 23.5
    Ettersgill BHs [NY 890 290] 22 6.7 30 9.1 79 24.1
    9 Roddymoor BH [NZ 1513 3635] 30 9.1 3 0.9 51 15.5

    (Table 5) The Five Yard Cyclothem

    Five Yard Limestone

    Six Fathom Hazle

    Five Yard Cyclothem
    Area Mine or section Grid reference ft m ft m ft m
    1 Middle Tongue Beck [NY 704 324] 10 3.0 50 18.2 80 24.4
    2 East Cross Fell Mines [NY 717 367] 20 6.1 35 10.7 83 25.3
    Crag Green Mines [NY 730 430] 16 4.9 33 10.1 58 17.7
    Hudgill Burn Mine [NY 750 456] 7 2.1 48 14.6 57 17.4
    Foreshield Shaft [NY 7477 4677] 13 4.0 29 8.8 47 14.3
    Lovelady Shield Shaft [NY 7568 4621] 13 4.0 30 9.1 48 14.6
    Nentsberry Haggs Mine [NY 766 450] 15 4.6 36 11.0 61 18.6
    Bentyfield Mine [NY 756 425] 16 4.9 24 7.3 58 17.7
    Guddamgill UG Shaft [NY 7876 4508] 14 4.3 36 11.0 66 20.1
    Rampgill UG Shaft [NY 7975 4417] 11 3.4 21 6.4 56 17.1
    3 Longcleugh BH [NY 7686 5180] 18 5.5 - 55 16.8
    4 Sipton Shaft [NY 8468 4987] n.p. 15 4.6
    Allenheads No. 1 BH [NY 8604 4539] 15 4.6 25 7.6 49 14.9
    5 Burtree Pasture UG Shaft [NY 8603 4180] 16 4.9 28 8.5 64 19.5
    Sedling Mine East [NY 860 411] 15 4.6 10 12.2 60 18.3
    Blackdene Mine [NY 868 390] 8 2.4 20 6.1 32 9.8
    Old Fall Shaft [NY 8733 3871] 20 6.1 43 13.1 72 22.0
    Greenlaws Mine [NY 889 370] 23 7.0 37 11.3 77 23.5
    Slitt Shaft [NY 9058 3920] 13 4.0 33 10.1 66 20.1
    Rigg BH [NY 9145 3895] 9 2.7 6 1.8 44 13.4
    Cammock Eals Mine [NY 935 383] 20 6.1 0–30 0–9.1 50 15.2
    Rookhope BH [NY 9374 4278] 15 4.6 20 6.1 61 18.6
    Crawleyside BH [NY 9962 4010] 17 5.2 12 3.7 44 13.4
    Stanhopeburn Mine [NY 986 413] n.p. 32 9.8 -
    7 Grasshill Mines [NY 815 350] 16 4.9 36 11.0 72 21.9
    Ettersgill Beck [NY 890 290] 14 4.3 40 12.2 60 18.3
    9 Roddymoor BH [NZ 1513 3635] 28 8.5 - 71 21.6

    (Table 6) The Three Yard Cyclothem

    Three Yard Limestone

    Nattrass Gill Hazle

    Three Yard Cyclothem
    Area Mine or section Grid reference ft m ft m ft m
    Middle Tongue Beck [NY 704 324] 9 2.7 35 10.7 90 27.4
    2 East Cross Fell Mines [NY 717 367] 9 2.7 38 11.6 82 25.0
    Crag Green Mines [NY 730 428] 15 4.6 15 4.6 99 30.2
    Hudgill Burn Mine [NY 750 456] 14 4.3 14 4.3 90 27.4
    Blagill Mines [NY 740 474] n.p. 24 7.3 - -
    Nentsberry Haggs Mine [NY 766 450] 9 2.7 16 4.9 93 28.3
    Bentyfield Mine [NY 756 425] 14 4.3 33 10.0 119 36.3
    Guddamgill U.G. Shaft [NY 7876 4508] 13 4.0 16 4.9 96 29.3
    Rampgill U.G. Shaft [NY 7975 4417] 8 2.4 21 6.4 95 29.0
    3 Longcleugh BH [NY 7686 5180] 9 2.7 44 13.4 65 19.8
    4 Sipton Shaft [NY 8468 4987] 10 3.0 25 7.6 99 30.2
    St Peter's Shaft [NY 8515 4876] 10 3.0 24 7.3 93 28.3
    Breckon Hill [NY 8503 4761] 10 3.0 31 9.4 95 29.0
    (Brackenhill) Shaft Allenheads High U.G.Shaft [NY 8244 4449] 10 3.0 51 15.5 100 30.5
    Allenheads No. 1 BH [NY 8604 4539] 9 2.7 65 19.8 90 27.4
    5 Killhope Mines [NY 816 433] n.p. 12–34 3.7–10.4 -
    Burtree Pasture U.G.Shaft [NY 8603 4180] 10 3.0 36 11.0 99 30.2
    Sedling Mine West [NY 860 411] 10 3.0 64 19.5 105 32.0
    Blackdene Mine [NY 868 390] 8 2.4 24 7.3 91 27.7
    Greenlaws Mine [NY 889 370] 11 3.4 32 9.8 102 31.3
    Slitt Shaft [NY 9058 3920] 9 2.7 38 11.6 80 24.4
    Rigg BH [NY 9145 3895] 9 2.7 35 10.7 110 33.5
    Cammock Eals Mine [NY 935 383] 10 3.0 35 10.7 85 25.9
    Rookhope BH [NY 9374 4278] 6 1.8 28 8.5 101 30.8
    Stanhopeburn Mine [NY 986 413] 10 3.0 18 5.5 78 23.8
    Crawleyside BH [NY 9962 4010] 9 2.7 30 9.0 80 24.4
    Groverake Mine [NY 896 441] n.p. 27 8.2 - -
    Wolfcleugh Mine [NY 902 432] n.p. 35 10.7
    7 Ashgillhead Mine [NY 805 355] 9 2.7 12 3.7 92
    Meldon Fell [NY 776 292] 10 3.0 15 4.6 77
    Langdon Beck [NY 858 317] 9 2.7 13 4.0 81 28.0
    9 Roddymoor BH [NZ 1513 3635] 11 3.4 85 26.0 137 41.8

    (Table 7) The Four Fathom Cyclothem

    Four Fathom Limestone

    Hazle Quarry

    Four Fathom Cyclothem
    Area Mine or section Grid reference ft m ft m ft m
    1 Middle Tongue Beck and Silverband Mine [NY704 324] and [NY 703 317] 22 6.7 11 3.4 68 20.7
    2 East Cross Fell Mines [NY 717 367] 25 7.6 15 4.6 71 21.6
    Holyfield Mine [NY 732 491] 23 7.0 16 4.9 80 24.4
    Thorngill Mine [NY 740 472] 24 7.3 15 4.6 82 25.0
    Galligill Sike Mine [NY 758 445] 24 7.3 20 6.1 73 22.3
    Hudgill Burn Mine [NY 750 456] 24 7.3 18 5.5 76 23.2
    Nentsberry Haggs Mine [NY 766 450] 24 7.3 30 9.1 94 28.7
    Brownley Hill Mine [NY 776 446]] 24 7.3 30 9.1 91 27.7
    Dowgang Mine [NY 775 430]] 24 7.3 30 9.1 94 28.7
    Rampgill UG Shaft [NY 7975 4417] 18 5.5 29 8.8 86 26.2
    3 Barneycraig Mine [NY 804 466] 23 7.0 22 6.7 100 30.5
    4 Esp's Rises, Sipton Mine [NY 8450 5079] 24 7.3 24 7.3 80 24.4
    Sipton Shaft [NY 8468 4987] 22 6.7 31 9.4 89 27.1
    St Peter's Mine [NY 8515 4876] 22 6.7 24 7.3 109 33.2
    Breckon Hill(Brackenhill) Shaft [NY 8503 4761] 22 6.7 75 22.9 106 32.3
    Allenheads Low UG Shaft [NY 8682 4529] 19 5.8 33 10.1 92 28.0
    Allenheads High UG Shaft [NY 8244 4449] 18 5.5 32 9.8 98 29.9
    5 Groverake Mine [NY 896 441] 20 6.1 34 10.4 90 27.4
    Wolfcleugh Shaft [NY 9019 4324] 19 5.8 20 6.1 80 24.4
    Boltsburn Engine Shaft [NY 9368 4279] 18 5.5 13 4.0 81 24.7
    Boltsburn No. 1 UG Shaft [NY 9542 4407] 38 11.6 21 6.4 75 22.9
    Rookhope BH [NY 9374 4278] 18 5.5 24 7.3 84 25.6
    Killhopehead UG Shaft [NY 8156 4331] 20 6.1 32 9.8 90 27.4
    Burtree Pasture UG Shaft [NY 8603 4180] 19 5.8 17 5.2 80 24.4
    Sedling Mine West [NY 860 411] 20 6.1 22 6.7 80 24.4
    Blackdene Mine [NY 868 380] 19 5.8 35 10.7 79 24.1
    Greenlaws Mine [NY 889 370] 19 5.8 13 4.0 62 18.9
    Scarsike Mine [NY 904 401] 20 6.1 48 14.6 95 29.0
    Harehope Gill Sump [NZ 033 360] 33 10.1 6 1.8 73 22.3
    7 Ashgillhead Mine [NY 805 355] 22 6.7 12 3.6 76 23.2
    Skears Level [NY 9469 2759] 24 7.3 32 9.8 73 22.3
    Roddymoor BH [NZ 1513 3635] 17 5.2 19 5.8 87 26.5

    (Table 8) The Iron Post Cyclothem

    Iron Post Limestone

    Tuft

    Iron Post Cyclothem
    Area Mine or section Grid reference ft m ft m ft m
    1 Dun Fell and Silverband [NY 712 320] 1 0.3 11 3.4 32 9.8
    2 East Cross Fell Mines [NY 717 367] -- 15 4.6 27 8.2
    Holyfield Mine [NY 732 491] 2 0.6 9 2.7 28 8.5
    Blagill Mine [NY 740 474] 3 0.9 6 1.8 22 6.7
    Hudgill Burn Mine [NY 750 456] 2 0.6 13 4.0 33 10.1
    Nentsberry Haggs Mine [NY 776 446] 2 0.6 9 2.7 32 9.8
    Brownley Hill Mine [NY 778 456] 1 0.3 16 4.9 26 7.9
    Guddamgill Mine [NY 785 447] 3 0.9 10 3.0 29 8.8
    Dowgang Mine [NY 775 430] 2 0.3 9 2.7 32 9.8
    Rampgill UG Shaft [NY 7975 4417] - 9 2.7 26 7.9
    3 Scraithole Mine [NY 803 469] 2 0.6 5 1.5 17 5.2
    Mohopehead Mine [NY 770 490] 2 0.6 5 1.8 21 6.4
    4 Whintings Rise [NY 8430 5191] - - 4 1.2 14 4.3
    St Peter's Mine [NY 8515 4876] 7 2.1 23 7.0
    Breckon Hill(Brackenhill) Shaft [NY 8503 4761] 3 0.9 20 6.1
    Allenheads High UG Shaft [NY 8682 4529] 2 0.6 4 1.2 22 6.7
    5 Wolfcleugh Shaft [NY 9019 4324] - 9 2.7 36 11.0
    Rispey Mine [NY 9109 4280] 3 0.9 8 2.4 31 9.4
    Boltsburn Mine East [NY 938 4293] 2–3 0.6–0.9 19 5.8 29 8.8
    Killhope Mine [NY 816 432] - - 8 2.4 23 7.0
    Burtree Pasture Mine [NY 830 418] 9 2.7 22 6.7
    Sedling Mine [NY 860 411] 6 1.8 27 8.2
    Elmford Mine [NY 880 395] 11 3.4 25 7.6
    Blackdene Mine [NY 868 390] 11 3.3 23 7.0
    Levelgate Mine [NY 8817 3890] - 6 1.8 24 7.3
    Greenlaws Mine [NY 889370 2 0.6 29 8.8 41 12.5
    Rookhope BH [NY 9374 4278] 2 0.6 27 8.2 41 12.5
    Scarsike Mine [NY 916 427] 3 0.9 6 1.8 27 8.2
    Harehope Gill Mine [NZ 033 360] 2 0.3 6 1.8 25 7.6
    6 Jeffries Shaft [NY 9602 4781] 6 1.8 11 3.4 29 8.8
    7 Ashgillhead Mine [NY 805 355] - - 16 4.9 29 8.8
    Skears Vein D2 [NY 9431 2814] 3 0.9 6 1.8 9 2.7
    Skears Vein F [NY 9570 2308] 4 1.2 7 2.1 26 7.9
    Manorgill North [NY 963 301] 2 0.6 9 2.7 29 8.8
    9 Roddymoor BH [NZ 1513 3635] 2 0.6 3 0.9 25 7.6

    (Table 9) Comparison of two rises at Skears Mine

    Vein [NY 9570 2308]

    Great Rise [NY 9580 2381]
    ft in m ft in m
    Little Limestone
    White Hazle 14 6 4.4 2 0 0.6
    Shale ?parting 8 0 2.4
    High Coal Sill 31 0 9.4 10 0 3.0
    Shale ?parting 18 0 5.5
    Low Coal Sill 27 6 8.4 20 0 6.1
    Shale 6 0 1.8
    Great Limestone

    (Table 10) The Great Cyclothem

    Great Limestone Strata between Great and Little Sandstone Shale
    Area Mine or section Grid reference ft m ft m ft m ft m
    1 Silverband Mine [NY 703 317] 60 18.3 88 26.8 42 12.8 46 14.0
    2 East Cross Fell Mines [NY 717 367] 66 20.1 83 25.3 57 17.4 26 7.9
    Holyfield Mine [NY 732 491] 59 18.0 61 18.6 12 3.7 49 14.9
    Blagill Mines [NY 734 474] 53–64 16.2–19.5 69 21 28 8.5 41 12.5
    Galligill Sike Mine [NY 758 445] 63 19.2 70 21.3 21 6.4 49 14.9
    Hudgill Burn Mine [NY 750 456] 57 17.4 58 17.7 12 3.7 46 14.0
    Nentsberry Mine West [NY 766 450] 63 19.2 61 18.6 22 6.7 39 11.9
    Brownley Hill Mine [NY 776 446] 67 20.4 72 21.9 39 11.9 33 10.1
    Guddamgill Mine [NY 785 447] 65 19.8 69 21 29 8.8 40 12.2
    Bentyfield Mine [NY 756 425] 63 19.2 61 18.6 28 8.5 33 10.1
    Dowgang Mine [NY 775 430] 63 19.2 61 18.6 28 8.5 33 10.1
    Rampgill Mine [NY 782 435] 62 18.9 61 18.6 21 6.4 40 12.2
    3 Coalcleugh [NY 801 451] 63 19.2 70 21.3 25 7.6 45 13.7
    Barneycraig East [NY 804 466] 59 18.0 60 18.3 20 6.1 40 12.2
    Scraithole Mine [NY 803 469] 63 19.2 60 18.3 20 6.1 40 12.2
    Wellhope Shaft [NY 7790 4661] 63 19.2 61 18.6 23 7.0 38 11.6
    Mohopehead Mine [NY 770 500] 60 18.3 56 17.1 13 4.0 43 13.1
    Longcleugh Mine [NY 772 520] 63 19.2 62 18.9 26 7.9 36 11.0
    4 Holmes Linn Shaft [NY 8419 5240] 73 22.3 78 23.8 36 11.0 42 12.8
    Esp's Plantation Shaft [NY 8439 5067] 65 19.8 84 25.6 38 11.6 46 14.0
    St Peter's Mine [NY 8515 4876] 60 18.3 71 21.6 21 6.4 50 15.2
    Swinhopehead Shaft [NY 8249 4751] 66 20.1 74 22.6 20 6.1 54 16.5
    Allenhead's Gin Hill Shaft [NY 8602 4534] - - 66 20.1 25 7.6 41 12.5
    Plantation Shaft [NY 8580 4456] 66 20.1 88 26.8 23 7.0 65 19.8
    Low UG Shaft [NY 8682 4529] 66 20.1 53 16.2 21 6.4 32 9.8
    High UG Shaft [NY 8244 4449] 64 19.5 52 15.8 17 5.2 35 10.7
    5 Killhopehead Mine [NY 8156 4331] 60 18.3 60 18.3 29 8.8 31 9.4
    Burtree Pasture Mine [NY 830 418] 63 19.2 56 17.1 16 4.9 40 12.2
    Sedling Mine West [NY 860 411] 59 18.0 57 17.4 18 5.5 39 11.9
    Levelgate Mine [NY 8817 3890] 60 18.3 95 30 73 22.3 22 6.7
    Middlehope Mines [NY 890 405] 58 17.7 104 31.7 77 23.5 27 8.2
    Groverake Mine [NY 896 441] 67 20.4 57 17.4 21 6.4 36 11.0
    Boltsburn Mine West:
    West Rise [NY 9218 4175] 64 19.5 33 10.1 31 9.4
    Stony Hill Shaft [NY 9275 4217] 74 22.6 38 11.6 41 12.5
    Boltsburn Mine East:
    Redway Rise [NY 9468 4348] 65 19.8 89 27.1 75 22.9 14 4.3
    Hopeburn Shaft [NY 9564 4423] 68 20.7 77 23.5 55 16.8 22 6.7
    Foremost Rise [NY 9634 4458] - - 44 13.4 9 2.7 35 10.7
    Fulwood Mine [NY 934 429] - 57 17.4 19 5.8 38 11.6
    Carrick's Mine, Carr's Shaft [NY 8610 3712] 60 18.3 58 17.7 28 8.5 30 9.1
    Dawson's Shaft [NY 8620 3680] 59 18.0 53 16.2 20 6.1 33 10.0
    Greenlaws Mine [NY 888 379] 58 17.7 67 20.4 28 8.5 37 11.3
    Bollihope [NZ 004 349] 60 18.3 82 25 62 18.9 20 6.1
    Harehope Gill [NZ 032 353] 67 20.4 75 22.9 59 18.0 14 4.3
    6 Whiteheaps Engine Shaft [NY 9467 4661] - - 105 32 91 27.7 14 4.3
    Ramshaw Shaft [NY 9500 4722] 54 16.5 108 32.9 87 26.5 21 6.4
    Jemmy's Shaft [NY 9527 4239] - - 81 24.7 67 20.4 14 4.3
    Jeffries Shaft [NY 9602 4781] 72 21.9 - - 51 15.5 13 4.0
    Taylor's Shaft [NY 9658 4824] - - 43 13.1 24 7.3 19 5.8
    Shildon Mine [NY 963 509] - 62 18.9 36 11.0 26 7.9
    Beldon Mine [NY 928 495] 56 17.1 79 24.1 42 12.8 37 11.3
    7 Ashgillhead Mine [NY 805 355] 57 17.4 68 20.7 42 12.8 26 7.9
    Flushiemere (No. 2) Shaft [NY 9138 3126] 63 19.2 67 20.4 43 13.1 24 7.3
    Skears D2 Vein [NY 938 279] 66 20.1 81 24.7 72 21.9 9 2.7
    Skears F Vein [NY 939 281] 66 20.1 81 24.7 75 22.9 6 1.8
    Manorgill North Sump [NY 963 301] 73 22.3 78 23.8 66 20.1 12 3.7
    Pikestone Brow Mine [NY 948 294] 60 18.3 78 23.8 66 20.1 12 3.7
    Parkin Hush Mine [NY 937 303] - - 65 19.8 36 11.0 29 8.8
    9 Roddymoor BH [NZ 1513 3635] 61 18.6 74 22.6 44 13.4 30 9.1
    Chopwell BH [NZ 1438 5743] 68 20.7 67 20.4 27 8.2 40 12.2

    (Table 11) Little Limestone to Firestone Sill

    Little Limestone

    Pattinson Sill

    White Sill Sandstone

    Firestone

    Whole Subgroup
    Area Mine or section Grid reference ft m ft m ft m ft m ft m
    1 Dun Fell Hush [NY 726 320] 4 1.2 - - - - 20 6.1 125 38.1
    2 East Cross Fell Mines [NY 717 367] 11 3.4 6 1.8 - - 38 11.6 121 36.9
    Blagill Mines [NY 740 474] 7 2.1 17 5.2 2 0.6 28 8.5 139 42.4
    Galligill Sike Mine [NY 758 445] 8 2.4 7 2.1 14 4.3 32 9.8 124 37.8
    Nentsberry Mine West [NY 766 450] 10 3.0 12 3.7 11 3.4 33 10.1 149 45.4
    Gudhamgill Mine [NY 785 447] 6 1.8 12 3.7 14 4.3 44 13.4 174 53.0
    Bentyfield Mine [NY 756 425] 6 1.8 6 1.8 4 1.2 6 1.8 113 34.4
    Dowgang Mine [NY 775 430] 12 3.7 2 0.6 - - 12 3.7 125 38.1
    Middlecleugh Mines [NY 789 425] 5 1.5 15 4.6 - - 20–50 6.1–15.2 154 46.9
    Rampgill Mine [NY 782 435] 18 5.5 12–15 3.7–4.6 12 3.7 38 11.6 160 48.8
    3 Coalcleugh [NY 801 451] 8 2.4 18 5.5 6 1.8 20 6.1 111 33.8
    Scraithole Mine [NY 803 469] 9 2.7 14 4.3 9 2.7 15 4.6 127 38.7
    Mohopehead Mine [NY 770 500] 5 1.5 20 6.1 5 1.5 20 6.1 144 43.9
    4 Allenheads Gin Hill Shaft [NY 8602 4534] 12 3.6 11 3.4 15 4.5 33 10.1 142 43.3
    Plantation Shaft [NY 8580 4456] 10 3.0 14 4.3 30 9.1 33 10.0 127 38.7
    Craigshield Shaft [NY 8569 4532] 14 4.3 9 2.7 21 6.4 39 11.9 168 51.2
    Low UG Shaft [NY 8682 4529] 10 3.0 18 5.5 31 9.4 31 9.4 151 46.0
    High UG Shaft [NY 8244 4449] 8 2.4 24 7.3 22 6.7 35 10.7 148 45.1
    5 Killhopehead Air Shaft [NY 8098 4321] 8 2.4 4 1.2 6 1.8 38 11.6 154 46.9
    Burtree Pasture Mine [NY 830 418] 10 3.0 7 2.1 - - 32 9.8 97 29.6
    Groverake Mine [NY 896 441] 10 3.0 12 3.7 3 0.9 40 12.2 130 39.6
    Boltsburn Mine West [NY 9218 4175] 8 2.4 8 2.4 4 1.2 45 13.7 135 41.1
    Redway [NY 9468 4348] 10 3.0 12 3.7 5 1.5 39 11.9 133 40.5
    Hopeburn [NY 9564 4423] 10 3.0 10 3.0 3 0.9 49 14.9 148 45.1
    Fulwood Shaft [NY 934 429] 14 4.3 22 6.7 - - 34 10.3 133 40.5
    Cornish Hush Air Shaft [NZ 0014 3270] 5 1.5 - - - 34 7.3 93 28.3
    Greenlaws Mine [NY 888 379] 7 2.1 10 3.0 - - 28 8.5 125 38.1
    Harehope Gill Mine [NZ 032 352] 21 6.4 28 8.5 - - 17 5.2 97 29.6
    6 Whiteheaps Engine Shaft [NY 9467 4661] 12 3.7 3 0.9 23 7.0 36 10.9 166 50.6
    Ramshaw Shaft [NY 9500 4722] 8 2.4 - 18 5.4 36 11.0 155 47.2
    Jemmy's Shaft [NY 9527 4239] 11 3.4 - - 22 6.7 30 9.1 149 45.4
    Jeffries Shaft [NY 9602 4781] 12 3.7 9 2.7 30 9.1 48 14.6 174 53.0
    Taylor's Shaft [NY 9658 4824] 13 4.0 11 3.4 14 4.3 37 11.3 167 50.9
    Shildon Mine [NY 963 509] 13 4.0 81 24.7 - - 26 7.9 224 68.3
    Beldon Mine [NY 928 495] 9 2.7 27 8.2 16 4.9 26 7.9 138 42.1
    7 Ashgillhead Mine [NY 805 355] 4 1.2 3 0.9 - 38 11.6 88 26.8
    Skears D2 Vein [NY 938 279] 7 2.1 - - - - 62 18.9 105 32.0
    Manorgill North Sump [NY 963 301] 3 0.9 10 3.0 24 7.3 16 4.9 142 43.3
    9 Roddymoor BH [NZ 1513 3635] 2 0.6 - 7 2.1 23 7.0 97 29.6
    Chopwell BH [NZ 1438 5743] 12 3.7 10 3.0 72 21.9 14 4.3 167 50.9
    Woodland BH [NZ 0908 2770] 4.5 1.4 - - - - ?11 3.4 71 21.6

    (Table 12) Section at North Grain opencast: [NY 883 448]

    ft in in
    Coalcleugh Transgression Beds Black micaceous shale 20 0 6.1
    Shale with ironstone nodules 14 0 4.3
    Shale with marine fossils 2 0 0.6
    Coalcleugh Coal 0 3 0.07
    Ganister 1 0 0.3
    Soft sandstone with roots 2 6 0.76
    Fissile sandstone and shale 4 0 1.2
    Poor ganister 8 0 2.4
    Lower Felltop Limestone(worked out for iron ore)

    (Table 13) Crag Limestone to Grindstone Sill

    Crag to Lower Felltop Limestone

    Crag to Upper Felltop Limestone

    Upper Felltop Limestone to top of Grindstone Sill
    Area Mine or section Grid reference ft m ft m ft m
    2 Middle Fell, Alston [NY 750 440] 220 67
    Dowgang Hush and Mine [NY 775 430] 240 73
    Rampgill Mine [NY 782 435] 220 67
    3 Coalcleugh [NY 801 451] 225 69 325 99 150 46
    Scraithole Mine [NY 803 469] 260 79
    4 Collier Shaft [NY 8690 4530] 220 67
    5 Rookhopehead [NY 886 456] 220 67 320 98
    Burtree Pasture Mine [NY 830 418] 235 72 335 102 145 44
    Groverake Mine [NY 896 441] 220 67 315 96
    Greenlaws Mine [NY 888 379] 300 91
    Cornish Hush Mine [NZ 001 327] 350 107 77 + 23 +
    Boltsburn Mine East [NY 956 442] 305 93
    Dead Friars Borings [NY 9682 4480] 351 107 90 27
    Sunnyside Mine [NZ 055 361] 230 70 335 102
    6 Ruth's Shaft [NY 9547 4642] 290 88
    Taylor's Shaft [NY 9658 4824] 320 98 80 24
    7 Sharnberry 'A' Shaft [NZ 0053 3143]
    Hudeshope [NY 942 298] 290 88
    Coldberry Gutter [NY 932 290] ?175 53
    9 Roddymoor Bh [NZ 1513 3635] 135 41 250 76 107 33
    Chopwell Bh [NZ 1438 5743] 340 104
    Woodland Bh [NZ 0908 2770] 175 53 292 89 66 20

    (Table 14) Ettersgill Borehole ET/16 [NY 8904 2941]

    Thickness

    Depth
    ft in m ft in m
    Alluvium 5 6 1.7 5 6 1.7
    Sandstone and shale 9 6 2.9 15 0 4.6
    Metamorphosed shale 3 6 1.1 18 6 5.0
    Cockle Shell Limestone, unaltered 4 3 1.3 22 9 6.9
    Metamorphosed shale and sandstone 13 9 4.2 36 6 11.1
    Single Post Limestone, marmorised 4 0 1.2 40 6 12.3
    Metamorphosed shale and sandstone 18 6 5.6 59 0 18.0
    Whin Sill, Type 1 0 9 0.2 59 9 18.2
    Whin Sill, Type 2 30 3 9.2 90 0 27.4
    Whin Sill, Type 3 29 6 9.0 119 6 36.4
    Whin Sill, Type 4 0 1 0.03 119 7 36.4
    Whin Sill, Type 3 (coarser than above) 7 11 2.4 127 6 38.9
    Whin Sill, Type 4 0 6 0.15 128 0 39.1
    Whin Sill, Type 3 6 5 2.0 134 5 41.1
    Whin Sill, Type 4 1 11 0.6 136 4 41.7
    Whin Sill, Type 3 (coarser) 5 11 1.8 142 3 43.5
    Whin Sill, Type 4 3 5 1.0 145 8 44.5
    Whin Sill, Type 3 29 4 9.0 175 0 53.4
    Whin Sill, Type 3 (finer) 63 0 19.2 238 0 72.6
    Whin Sill, Type 2 41 6 12.6 279 6 85.2
    Whin Sill, Type 1 1 0 0.3 280 6 85.5
    Metamorphosed shale and sandstone 42 6 13.0 323 0 98.4
    Unaltered shale and sandstone 22 0 6.7 345 0 105.2
    Tynebottom Limestone, unaltered, into shale 25 6 7.8 370 6 112.9

    (Table 15) Summary of tectonic history

    PERIOD Strain effect in the orefield Inferred regional or local stress and possible cause
    Stage
    Orogeny
    LOWER PALAEOZOIC
    Llanvirn/Llandeilo 1     Precursor folding of Skiddaw Group on ENE axes Compression connected with SE-dipping subduction zone
    Caradoc Borrowdale volcanic areas to W. Compression connected with SE-dipping subduction zone
    Late Caradoc Folding of volcanics and slates Compression connected with SE-dipping subduction zone
    Caledonian (?Ludlow/ Llanvirn) 2     Major folding of Ordovician and Silurian on ENE axes with axial plane and other cleavage Closing of Iapetus (proto-Atlantic) Ocean
    (410–400 Ma) 3      Intrusion of Weardale and Lake District granites Post-tectonic stoping
    ?DEVONIAN
    (Stage unknown) 4     Initiation of down-west Pennine fault line Granite First movements on Swindale Beck–Lunedale line Tension, separating Alston and Lake District blocks but separate identity not maintained
    CARBONIFEROUS
    Courceyan (or earlier) 5     Downwarping of Stainmore–Ravenstonedale Trough, Lunedale hinge active until end of Brigantian Crustal tension N–S
    Holkerian (or earlier) Initiation of Stublick hinge and Northumberland basin
    Holkerian to Westphalian C 6     Vertical up and down movements controlling shelf and cyclic deltaic/paralic sedimentation Intermittent withdrawal of deep magma (regional) or sea-level changes under eustatic control (global)
    Hercynian (post- Stephanian, pre-Upper Permian) 7     Master joints NNW, subsidiary ENE joints. Possible N–S compression transmitted from distant E–W, orogenic belt
    Broad folds on E–W axes e.g. Cotherstone
    8     NNW thrusts and E-facing monoclines, later relaxation faults, depressing Alston Block. E–W to ENE direct pressure from Lake District Block, now separated
    (295 Ma) Intrusion of Whin Sill. Dykes along ENE tension fractures. Jointing of sills
    9          Gentle doming of Alston Block, with formation of conjugate vein-fractures, ENE, WNW/EW, NNW Related to presence of low-density granite
    (280 Ma) Mineralising fluids aid propagation? Downwarping of Vale of Eden
    UPPER PERMIAN 10 Normal down-west faulting on Pennine Line
    TRIASSIC TO CRETACEOUS Burial under 1–2 km of sediments
    Cimmerian
    (Kimmeridgian/ Portlandian) No critical evidence of strain
    TERTIARY
    Paleocene (58 Ma) 11   Intrusion of E–W dykes in linear echelon trending WNW Deep sinistral wrench movement
    Fault block uplift in Pennines, doming of Lake District Block
    Alpine (Miocene) 12 Major NNW and E–W faults along margins of block, elevating it and tilting to E
    Pleistocene and earlier 13   Postmineralisation slickensides in veins Small wrench adjustments perhaps in part during isostatic, depression under ice and recovery

    (Table 16) Statistical analysis of horizon of vein oreshoots

    Horizon

    Number of oreshoots by area
    1 2 3 4 5 6 7 8 9 Total
    Westphalian
    Above Brockwell (A & B) — — — — — — — — 9 9
    Brockwell to Marshall
    Green (A) — — — — — — — — 2 2
    'Third Grit' — — — — 3 1 — — — 4
    Namurian
    'Second Grit' — — — — 2 1 — — — 3
    'First Grit' — — — — 3 1 2 — — 6
    Grindstone — — — — — 3 4 — — 7
    Grit Sills — 3 2 1 10 15 12 — — 43
    Firestone — 10 3 2 11 11 15 — — 52
    Little Lst 1 11 2 2 14 4 7 1 — 42
    Coal Sills 2 9 3 1 19 2 15 1 — 52
    Great Lst 15 55 18 16 53 2 49 1 — 209
    Visean (Brigantian)
    Quarry Hazle — 7 1 2 12 — 1 1 — 24
    Four Fathom Lst 3 5 1 2 16 — 1 2 — 30
    Nattrass Gill Hazle 3 2 — 1 13 — — 1 — 20
    Three Yard Lst 1 — — 1 14 — 1 1 — 18
    Six Fathom Hazle — 2 — — 14 — 3 1 — 20
    Five Yard Lst — 3 — — 11 — 1 1 — 16
    Slaty Hazle — 5 — — 10 — 2 — — 17
    Scar Lst — 9 — — 9 — 3 1 — 24
    Alternating Beds — 7 — — 11 — 1 1 — 20
    Tynebottom Lst 5 7 — — 4 — 19 1 — 36
    Sandstone — — — — 3 — 5 — — 8
    Jew Lst 2 1 — — 4 — 7 — — 14
    Sandstone 4
    Lower Little Lst 1 — — — — — 3 — — 6
    Stniddy Lst 2 — — — — — 7 — — 9
    Peghorn Lst — — — — — — 4 — — 4
    Visean (Asbian)
    Robinson Lst — — — — — — — — — 6
    N1elmerby Scar Lst 10 — — — — — 6 — — 16
    Whin Sill 1 2 — — 2 — 6 7 — 18

    (Table 17) Statistical analysis of horizon of flat oreshoots

    Limestone

    Number of oreshoots by areas
    1 2 3 4 5 7 Total
    Lower Felltop 2 – – 5 – 7
    Little 1 1 – – – – 2
    Great 10 14 9 15 35 4 87
    Four Fathom – – 1 1 – 2
    Scar – 7 – – 1 – 8
    Single Post – – – – – 4 4
    Tynebottom 4 5 – – – – 9
    Jew 2 – – – – – 2
    Melmerby Scar 5 – – – – – 5

    (Table 18) Analyses of galena concentrates

    1 2 3 4 5
    Pb 81.0 78.6 81.0 80.5 86.6
    S 13.5 13.9 13.0 12.6 13.4
    Ag 0.008 0.021 0.009 0.015 –
    Sb 0.1 n.d. 0.0035 0.1 –
    Bi 0.001 n.d. 0.0005 0.0005 –
    Cu 0.02 0.75 0.0025 0.1 –
    Zn 1.2 1.0 1.2 0.5 –
    Fe 1.08 1.6 1.08 1.54 –
    SiO2 1.1 0.7 0.4 0.8 –
    A12O3 0.5 0.35 0.22 0.4 –
    CaO tr 0.42 2.1 3.1 –
    98.50 97.34 99.01 99.66 100.00

    (Table 19) Silver recovered from galena concentrates

    Area Mine* Years Ounces silver per ton of lead metal Ag ppm
    1 Silverband (Cumbria) 1863–1876 6.9 193
    Dufton Fell 1863–1873 6.9 193
    Hardshins 1861–1870 6.2 173
    Hilton and Murton 1861–1870 5.9 165
    2 Blagill 1848–1881 6.0 167
    Rotherhope Fell 1854–1902 6.8 190
    Holyfield 1854–1873 10.5 293
    Nattrass 1854–1867 10.7 299
    Guttergill 1860–1878 8.6 240
    Stow Crag 1855–1871 38.5 1074
    St John's 1850–1859 40.0 1116
    Clargillhead 1856–1867 43.0 1200
    Long Katelock 1856–1865 7.3 204
    Slatesike 1856–1865 9.0 251
    Cashwell-Doukburn 1856–1865 6.4 179
    Calvert 1854–1870 7.7 215
    Hudgill Burn 1854–1870 13.0 363
    Galligill Sike 1854–1870 11.7 326
    Nentsberry 1854–1904 6.5 181
    Grassfield 1854–1864 17.8 497
    Brownley Hill 1854–1884 5.0 140
    Bentyfield 1854–1875 7.6 212
    Gudhamgill 1854–1882 7.0 195
    Nenthead mines 1854–1882 7.0 195
    3 Carrshield mines 1899–1918 8.0 223
    4 Sipton 1913–1918 5.0 140
    Allenheads 1882–1896 5.0 140
    4–5 Beaumont Allendale and Weardale mines 1854–1881 5.8 162
    5 Brandon Walls 1854–1886 6.0 167
    Captain's Cleugh 1854–1858 5.3 148
    Coves 1854–1864 6.0 167
    Cornish Hush 1884–1899 7.0 195
    6 Derwent mines 1854–1883 10.0 279
    Harehope Gill 1854–1866 8.0 251
    Burnhope 1887 15.0 419
    Healeyfield 1854–1890 15.0 419
    7 Greenhurth 1861–1871 5.9 167
    Greenhurth 1872–1881 5.3 149
    Greenhurth 1882–1892 10.3 287
    Greenhurth 1893–1902 12.1 338
    Cowgreen 1869–1906 4.6 128
    Willyhole 1862–1883 3.1 96
    Lady's Rake 1904–1910 5.5 153
    Grasshill 1862–1883 4.0 112
    Trough and Scar Head 1862–1874 6.6 184
    Langdon Beck 1862–1874 5.5 153
    Pike Law 1862–1883 6.0 167
    London Lead Cos. Teesdale mines (incl. Bollihope) 1861–1875 3.0 94
    5–7 London Lead Cos. Teesdale mines 1876–1883 5.0 140
    7 London Lead Cos. mines (incl. Bollihope) 1891–1902 10.6 296
    Wiregill 1903–1910 6.7 187
    Coldberry 1908–1910 9.5 265
    8 Langley Barony 1873–1886 2.3 64
    Settlingstones 1854–1873 2.6 73
    Stonecroft-Greyside 1854–1882 2.5 70
    Fallowfield 1854–1902 4.0 112

    (Table 20) Assays of galena for silver

    Area Mine or locality Ounces silver per ton of lead metal Ag ppm Assayer
    1 Melrnerby Fell 4.4 123 JAS
    2 Horse Edge 9.3 259 JAS
    Chesters, Tynehead 75.5 2107 JAS
    Sipton, typical ore 4.9 137 WLC
    Esp's, boulder in washout 6.9 193 WLC
    Esp's, granular ore 3.4 95 JAS
    Esp's, 'Steel ore' 7.3 204 JAS
    5 Groverake 6.9 193 WLC
    Mary's Vein 7.6 212 WLC
    Boltsburn West Level 5.3 148 WLC
    Boltsburn East, western flats 8.2 229 WLC
    Boltsburn East, eastern flats 5.6 156 WLC
    Barbary 5.8 162 WLC
    Sedling 4.5 126 WLC
    Lodgefield 5.7 159 WLC
    Billing 8.7–12.5 243–349 WLC
    Stanhopeburn 6.1 170 WLC
    Pencilcleugh 3.2 99 JAS
    7 Hazel Sike, Harwood 8.8 246 JAS
    Ettersgillhead 3.5 98 JAS
    Flushiernere 4.2 117 JAS
    Closehouse 4.4 123 JAS
    8 Settlingstones 1.1–1.8 31–50 WLC
    Fallowfield 1.3 36 JAS
    9 South Moor 28.4 792 JAS
    Graghead 6.6 184 JAS

    (Table 21) Analyses of sphalerite concentrates

    Analyses

    Approximate mineral composition
    1 2 1 2
    Insol. 1.42 tr. ZnS 89.2 97.7
    Zn 59.9 65.5 PbS 2.3 -
    Pb 2.02 n.d. FeS 3.0 0.5
    Mn 0.02 n.d. FeS2 2.0 1.3
    Fe 3.2 0.94 CdS 0.3 0.3
    S 31.9 32.12 CuFeS2 0.3 0.06
    Cd* 0.26 0.25 Ag2S3 0.01? 0.01?
    Cu* 0.1 0.02 Sb2S3 0.07?
    Ag* tr. - 0.01 tr. - 0.01 MoS2 0.06
    Sb* tr. - 0.05 nt. fd Ankerite 1.5
    Mg* 0.1 n.d. SiO2 0.9
    Si* 0.4 n.d.
    Ca* 0.2–0.3 n.d.
    Mo* 0.02–0.05 n.d.
    Sn* slight trace n.d.
    99.64 99.87
    <

    (Table 22) Analyses of Northern Pennine ankerites

    1 2 3 4 5 6
    Insol. in HCL 0.25 0.30 9.48 2.15 0.35 0.83
    A12O3 0.63 3.01 0.69 0.73 0.66 1.96
    Fe2O3 FeO 3.30 5.20 13.90 14.92 20.20 0.57

    22.61
    MnO 1.18 1.39 0.42 2.53 2.38 2.24
    MgO 18.71 14.60 8.52 8.01 6.24 3.01
    CaO 29.85 31.20 27.20 29.25 27.80 28.30

    CO2

    		 45.72 44.23 39.45 42.22 42.07 40.91
    99.64 99.93 99.66 99.81 99.70 100.43
    Total carbonate: 98.76 96.6 89.5 97.1 98.7 96.9
    Composition of carbonate
    FeCO3 5.3 8.7 25.0 24.8 32.9 37.6
    MnCO3 1.9 2.3 0.8 4.2 3.9 3.7
    MgCO3 38.3 31.5 19.9 17.2 13.2 6.5
    CaCO3 53.5 57.5 54.3 53.8 50.0 52.2
    100.0 100.0 100.0 100.0 100.0 100.0
    Specific Gravity* 2.86 2.91 2.95 3.032 3.086 3.115
    Refractive Index ù 1.685–1.689 1.690–1.695 1.709–1.711 1.716–1.722 1.720–1.729 1.727–1.734
    ϵ 1.507 n.d. 1.523 1.529 n.d. 1.536

    (Table 23) Refractive indices of ankerites *

    Area Locality Refractive index

    Approximate indicated cornposition*†
    % Ferromangan- dolomite % Fe + Mn
    2 Rotherhope Fell Mines 1.690 14 3
    Rotherhope Fell Mines 1.730 68 17
    Sir John's Vein, Crossgill 1.709–1.725 40–60 10–15
    Sir John's Vein, Pettergill 1.708 40 10
    Loveladyshield Level 1.708 40 10
    Smallcleugh flats 1.682–1.728 0–66 0–16
    Brownley Hill Mine 1.730 68 17
    3 Nentsberry Mine 1.703–1.722 35–55 7–14
    4 St Peter's Mine 1.720–1.730 53–68 13–17
    5 Sedling Mine 1.730 68 17
    Lodgefield Shaft 1.720–1.730 53–68 13–17
    Middlehope 1.730 68 17
    Boltsburn Mine 1.721–1.730 54–68 14–17
    Boltsburn Mine 1.680 nil nil
    Carricks Mines, flats 1.722–1.734 55–72 14–18
    Carricks Mines, cross vein 1.690–1.695 20 5
    7 Greenhurth Mine 1.700 27 7
    Cowgreen Mine 1.708–1.713 40–45 10–11
    Cowgreen Mine 1.685–1.689 14 3
    Flushiemere Mine 1.715 48 12
    Wynch Bridge 1.724–1.731 58–70 15–17

    (Table 24) Analyses of siderite

    Insol. in HCI 2.65 tr -
    SiO2 - - 2.7
    A12O3 0.55

    0.40

    		 -
    Fe2O3 0.94 1.6
    FeO 47.20 51.87 47.1
    MnO 3.45 3.17 n.d.
    MgO 2.86 2.50 n.d.
    CaO 4.80 3.60 n.d.
    CO2 37.74 38.28 n.d.
    100.19 99.82
    Total carbonate 96.2 99.4
    Composition of carbonate
    FeCO3 79.1 83.3
    MnCO3 5.8 5.1
    MgCO3 6.2 5.2
    CaCO3 8.9 6.4
    100.0 100.0
    Specific gravity 3.576 3.766
    Refractive Index ω 1.838 1.841 1.843
    å n.d. 1.611 n.d.

    (Table 25) Analyses of baryte

    1 2 3 4 5 6
    BaSO4 95.5 89.8 91.2 97.3 94.8 n.d.
    SrSO4 1.2 0.63 3.6 2.1 0.49 0.29
    CaSO4 0.1 1.00 n.d. n.d. 0.14 0.07

    (Table 26) Analyses of witherite and barytocalcite

    1 2 3
    SiO2 0.7 0.7
    BaO 74 50
    CaO 1 19
    Total S 0.4 0.3
    Sr* 1.0 0.3
    Pb 0.1 0.1
    Zn* 0.04 0.0
    Proximate mineral composition
    BaCO3 92.8 61.3 66.3
    SrCO3 1.7 0.6
    BaSO4 2.9 2.2
    CaCO3 2.5 35.0 33.7
    PbS 0.12 0.12
    ZnS 0.08 0.0
    SiO2 0.7 0.7

    (Table 27) Summary of mineral zones

    Zone West of Burtreeford Disturbance East of Burtreeford Disturbance
    V BARYTE BARYTE
    Aragonite WITHERITE
    Barytocalcite
    IV WITHERITE
    BARYTE BARYTE
    Galena Galena
    Sphalerite
    III GALENA GALENA
    SPHALERITE Quartz
    Quartz Siderite
    II GALENA GALENA
    Sphalerite Fluorite
    Fluorite Quartz
    Quartz Siderite
    I Galena Galena
    FLUORITE FLUORITE
    Chalcopyrite Chalcopyrite
    Quartz Quartz
    Marcasite
    Pyrrhotite
    GSV2 QUARTZ
    GSV1 Quartz
    Pyrrhotite
    Pyrite
    Marcasite

    (Capitals indicate workable minerals; zones GSV1 and 2 refer only to the Great Sulphur Vein).

    (Table 28) Approximate bulk composition of oreshoots

    1 2 3 4 5 6
    CaF2 84.50 46.52 20.8 tr. 0.6 n.d.
    SiO2 13.0 30.9 13.4 2.6 0.9 6.7
    BaSO4 0.0 n.d. tr. tr. 93.8 4.5
    BaCO3 n.d. n.d. n.d. n.d. 0.0 77.7
    PbS 0.6 8.0 18.7 tr. 1.3 tr.
    ZnS n.d. n.d. 0.4 18.2 0.2 0.6
    A12O3

    (Fe, Mn)2O3

    		 -  0.7 n.d. n.d.

    4.2

    		 1.3

    6.7

    		 0.4

    1.6

    		 1.6

    0.8
    FeCO3 n.d. n.d. 23.1 48.8 n.d. n.d.
    MnCO3 n.d. n.d. tr. 7.3 n.d. n.d.
    MgCO3 0.1 n.d. 4.1 3.5 n.d. 0.8
    CaCO3 0.5 4.7 12.4 11.1 0.1 5.6
    Totals 99.4 90.1 97.1 99.5 98.9 98.3

    (Table 29) Analyses of metasomatised limestone

    1 2 3 4 5 6
    SiO2 66.24 2.9 16.5 5.25 20.60 13.4
    A12O3 4.00 1.3 n.d. n.d. n.d. tr.
    Fe2O3

    5.07

    		 n.d. 4.8 0.0 0.0 n.d.
    FeO n.d. 17.6 44.10 18.40 n.d.
    Total Fe 24.6**
    Mn 0.39 3.2 n.d. 3.17 2.05 0.2
    MgO 1.05 1.7 2.4 2.38 4.43 0.2
    CaF2 2.87 tr. 24.0 n.d. n.d. 5.8
    CaO 9.60 5.5 13.5 5.60 18.40 5.5
    CO2 6.90 21.1 32.79 28.80 3.6
    Ignition loss 18.8
    BaO n.d. tr. n.d. n.d. n.d. 45.2
    Pb n.d. tr. 1.1 n.d. n.d. n.d.
    Zn n.d. 19.4 0.4 n.d. n.d. n.d.
    Total S 1.08 9.6 n.d. 1.04 0.18 9.5
    97.20 89.3 99.1 94.33 92.86 84.6

    (Table 30) Analyses of fresh and altered quartz-dolerite

    1 2 3 4 5 6 7 8
    SiO2 50.32 50.23 40.50 36.78 35.10 48.90 62.29 38.20
    A12O3 15.41 15.40 14.98 16.24 18.09 17.04 12.27 20.95
    Fe2O3 3.09 3.74 0.14t 0.07 tr. 0.53 1.29 18.93
    FeO 8.92 9.32 2.42t 2.71 3.74 5.35 8.65 1.59
    MgO 4.89 3.47 5.43 0.39 5.79 1.43 2.45 tr.
    CaO 8.86 8.87 10.54 17.08 11.89 9.45 3.29 0.15
    Na20 2.03 2.39 1.13 0.71 1.03 2.34 0.23 0.16
    K2O 1.06 1.35 2.17 1.81 1.60 1.82 2.66 0.81
    TiO2 2.48 2.40 2.67 2.87 2.31 2.60 1.13 3.08
    P2O5 0.22 0.23 0.29 0.32 p.n.d. 0.29 0.32 0.27
    MnO 0.18 0.18 0.36 0.28 p.n.d. n.d. 0.27 n.d.
    CO2 0.46 0.18 14.72 14.75 16.12 7.30 4.34 0.05
    S 0.15 0.09 0.25 - - 1.21 n.d. nil
    SO3 n.d. n.d. tr. 0.06 n.d. 0.05 n.d. tr.
    Cl n.d. n.d. tr. tr. n.d. n.d. n.d. n.d.
    FeS2 n.d. n.d. n.d. 0.63 nt.fd. - n.d. nil
    Fe7O8 n.d. n.d. n.d. tr. - - n.d. nil
    Cr2O3 n.d. n.d. 0.01 0.01 0.01 n.d. n.d. n.d.
    BaO 0.03 n.d. 0.06 0.18 n.d. 0.03 n.d. n.d.
    SrO n.d. n.d. 0.02* 0.05* n.d. n.d. n.d. n.d.
    PbO n.d. n.d. 0.02* n.d. n.d. 0.006 n.d. n.d.
    ZnO n.d. n.d. 0.2* n.d. n.d. tr. n.d. n.d.
    Li2O n.d. n.d. tr. tr. n.d. n.d. n.d. n.d.
    100.15 99.95 100.67 100.32 99.85 100.916 100.84 100.39
    Less O for S 0.05 0.03 0.13 0.40
    100.10 99.92 100.54 100.516

    (Table 31) Comparison of unaltered and altered dolerite assuming constancy of alumina

    1 2 3 4 5 6 7
    SiO2 50.3 41.7 34.9 29.9 44.4 78.2 48.8
    Total Fe 9.1 1.8 2.1 2.5 4.1 79.6 3.0
    Mn 0.1 0.3 0.2 n.d. n.d. 0.3 n.d.
    MgO 4.9 5.6 0.4 4.9 1.3 3.1 1.1
    CaO 8.9 10.8 16.9 10.1 8.6 4.1 8.4
    Na2O 2.0 1.2 0.7 0.9 2.2 0.3 0.6
    K2O 1.1 2.2 1.7 1.4 1.6 3.3 3.3
    1.3 4.0 4.6 n.d. 1.9 n.d. 3.3
    CO2 0.5 15.1 14.0 13.7 6.6 5.5 8.7
    BaO 0.03 0.06 0.17 n.d. 0.03 n.d. 0.3
    A12O3 15.4 15.4 15.4 15.4 15.4 15.4 15.4
    GAINS AND LOSSES
    SiO2 - 8.6 - 5.4 - 20.4 - 5.9 + 27.9 - 1.5
    Total Fe - - 7.3 - 7.0 - 6.6 - 5.0 - 0.5 - 6.1
    MgO - + 0.7 - 4.5 0 - 3.6 - 1.8 - 3.8
    CaO - + 1.9 + 8.0 + 1.2 - 0.3 - 4.8 - 0.5
    Na2O - - 0.8 - 1.3 - 1.1 + 0.2 - 1.7 - 1.4
    K2O + 1.1 + 0.6 + 0.3 + 0.5 + 2.2 + 2.2
    + 2.7 + 3.3 - + 0.6 - + 2.0
    CO2 - + 14.6 + 13.5 + 13.2 +6.1 -5.0 +8.2
    ZONE V V III V II V

    (Table 32) Oxidation of primary minerals and related processes

    Primary mineral

    Alteration by waters carrying:
    (i) Oxygen (ii) Carbon dioxide (iii) Sulphates (iv) Phosphate (v) Silica
    Galena Anglesite Cerussite Linarite ( + Cu) Pyromorphite
    Sphalerite,
    Chalcopyrite Rosasite and Aurichalcite
    Sphalerite (Goslarite) Smithsonite Hemimorphite
    Hydrozincite —
    Chalcopyrite Malachite and Azurite Chalcanthite — —
    Brochanthite
    Pyrrhotite Limonite — — — —
    Pyrite Limonite — Ferricopiapite

    Melanterite)

    		 — —
    (
    Marscasite Limonite — — Vivianite -
    Sulphur
    Minor Co-Ni-As-Sb Erythrite — — — —
    Sulphides and sulphosalts Annabergite
    Fluorite — ?Etched Etched — -
    Quartz, Chalcedony — — — — —
    Ankerite Limonite — (Epsomite) —
    Siderite Limonite — -
    Calcite — Dissolved (Gypsum) — -
    Baryte — — — — -
    Witherite — — Baryte — —
    Barytocalcite — — Baryte — —

    (Table 33) Analyses of oxidised ores

    Calculated mineral compositions 1 2 3
    SiO2 14.6 23.50 15.65
    A12O3 n.d. 0.30 n.d.
    Fe2O3 n.d. 47.42 61.61
    FeO n.d. 2.57 0.00
    Fe (total) 29.3
    Mn 2.3 3.03 4.15
    MgO 1.5 1.45 0.20
    CaO 10.6 2.00 0.88
    CO2 15.7 n.d. n.d.
    n.d. n.d. n.d.
    H2O n.d. n.d. 2.2
    Ignition loss 14.58 16.62
    P2O5 tr. 0.073 0.039
    S 1.4 0.78 n.d.
    Zn 3.2 0.78 n.d.
    Pb 1.2 0.00 n.d.
    F 3.3 n.d. n.d.
    Quartz, Chalcedony 14.6 23.5 15.6
    Limonite, (Fe, Mn)2O3.xH2O 34.8 62.0 79.1
    Carbonates: FeCO3 19.3 4.1 0.0
    Carbonates: MnCO3 1.8 0.0 0.0
    Carbonates: MgCO3 3.1 2.9 0.4
    Carbonates: CaCO3 10.0 3.9 1.7
    Fluorite 6.8 n.d. n.d.
    Sphalerite 3.8 1.2 n.d.
    Smithsonite 1.2 - n.d.
    Galena 1.4 0.0 n.d.
    Totals 96.8 97.6 96.8

    (Table 34) Hydration of limonites

    (Fe, Mn)2O3 H2O* Molecular ratio X in (Fe, Mn)2O3.x H2O
    Ardale Head No. 1 70.1 9.6 1.2
    Ardale Head No. 2 66.2 10.4 1.4
    Ardale Head No. 3 72.8 9.7 1.2
    Dun Fell No. 2 62.7 11.6 1.5
    Horse Edge, Umber 36.0 5.0 1.2
    Horse Edge, Ironstone 64.6 8.4 1.1
    Boltsburn West No. 1 37.4* 4.8 1.2
    Boltsburn West No. 2 15.8* 2.1 1.2
    Broadsyke 54.6 9.7 1.6
    Carricks, Opencast 60.4 10.4 1.5
    Carricks, Mine 67.6 11.6 1.5
    Langdon, Moss Vein 69.7 11.5 1.5

    * Mn not determined in these analyses

    (Table 35) Analyses of iron ores, Ardale Head

    1 2 3
    Fe2O3 65.7 65.7 62.9
    FeO tr. tr. tr.
    SiO2 11.3 13.1 3.2
    MnO2 (approx) 4 0.5 9
    P2O5 1.1 0.9 0.4
    H2O + 105° 9.6 10.4 9.7
    H2O - 105° 1.5 1.4 0.8
    Fe (Wet) 45.9 45.9 43.5

    (Table 36) Analyses of barytes ores and dressed product, Silverband

    1 2 3 4 5
    BaSO4 94.5 93.9 83.8 68.7 92.7
    SrSO4 n.d. n.d. 0.4* 0.5* 0.9
    SiO2 1.25 0.82 7.6 13.4 0.72
    Fe2O3 2.30 0.80 3.9 1 . 7 1.33
    A12O3 0.0 0.0 0.1 tr. 0.98
    CaO 0.0 0.74 0.4 8.5 0.28
    MgO 0.0 0.0 0.1 0.2 0.01
    CO2 0.03 0.05 0.3 3.6 0.21
    F 0.08 0.52 tr. 2.8 0.14
    Mn 0.08 0.25 0.5 0.2 0.20
    PbS 0.08 2.48 n.d. n.d. 1.81
    Zn tr. 0.0 0.4* n.d. 0.8
    Cu n.d. n.d. n.d. n.d. 0.009
    Na2O n.d. n.d. n.d. n.d. 0.05

    (Table 37) Analyses of iron ores, Dun Fell

    1 2 3 4 5 6 7
    Fe 29.51 39.16 34.80 40.70 42.60 43.30 23.77
    Mn

    _

    		 4.04 4.77 4.39 1.15 0.91 1.04 3.39
    SiO2

    36.09

    		 12.75 23.90 16.60 17.02 13.50 43.45
    Al2O3 7.34 5.39 3.10 8.04 5.76 5.61
    P2O5 0.706 0.094 0.221 0.315 0.94 0.82 0.186
    Ignition loss 10.62 11.57 10.26 11.25 11.38 10.50 7.07
    H2O - 6.00 - 6.00 - 6.00 -

    (Table 38) Analyses of iron ore and umber, Horse Edge

    1 2 3 4 5 6
    Fe2O3 28.73 34.33 49.97 63.04 66.22 65.57
    FeO n.d. n.d. n.d. n.d. 0.00 0.19
    MnO2 3.97 1.17 5.29 1.25 n.d. n.d.
    MnO 0.66 0.48 1.10 0.35 3.19 0.10
    SiO2 29.50 52.60 27.70 17.10 16.74 20.10
    TiO2 0.08 0.06 0.10 0.16 n.d. 0.06
    A12O3 1.81 2.00 3.27 4.87 n.d. 0.75
    MgO 0.27 0.36 0.24 0.32 n.d. 0.15
    CaO 4.90 1.85 1.20 1.55 n.d. 0.43
    BaO 13.66 0.12 0.36 0.30 0.00 0.82
    Na2O 0.03 0.05 0.09 0.77 n.d. 0.21
    K2O 0.05 0.02 0.09 0.22 n.d. 0.05
    Cu 0.008 0.128 0.007 0.012 n.d. 0.010
    Zn 0.240 0.272 0.240 0.056 0.50* 0.00
    Pb 0.136 0.022 1.392 0.265 0.50* 0.023
    Ni 0.01 0.02 0.01 0.01 n.d. 0.00
    As 0.00 0.075 0.008 tr. n.d. tr.
    P2O5 0.105 0.266 0.092 0.096 0.44 0.089
    S 2.99 0.229 0.216 0.137 n.d. 0.20
    C 0.45 0.90 0.55 1.00 n.d. 0.90
    CO2 2.80 tr. 0.35 tr. n.d. 0.14
    H2O 5.39 5.01 7.61 8.41 n.d. 9.86

    (Table 39) Analyses of iron ores, Park Fell

    1 2
    Fe2O3 47.54 56.4
    FeO 0.00 tr.
    SiO2 34.30 24.6
    MnO 2.00 0.9
    BaO 0.00 n.d.
    Pb (approx) 0.50 n.d.
    Zn tr. n.d.
    0.10 0.2
    P2O5 0.11 0.1
    H2O 5.60 1.4

    (Table 40) Analyses of iron and barium ores, Blagill Upper Level are given in (Table 40).

    (Table 40) - Analyses of iron and barium ores

    1 2
    Fe2O3 37.94 n.d.
    FeO 8.78 n.d.
    MnO 2.23 n.d.
    SiO2 8.21 0.7
    CaO n.d. 19
    BaO nt.fd 50
    Zn 3.00* 0.00
    Pb 0.50 0.1
    Sr n.d. 0.3*
    P2O5 0.06 n.d.
    S 1.07 0.3
    H2O 4.30 0.0

    (Table 41)Analyses of iron ore, Brownside and Nest

    1 2
    Fe2O3 47.5 69.77
    FeO tr. nt.fd.
    MnO 3.7 3.98
    SiO2 32.6 8.44
    CaO 0.9 n.d.
    P2O5 tr. 0.06
    S tr. 0.03
    H2O 1.9 5.30

    (Table 42) Analyses of tailings, Rotherhope Fell

    1 2 3 4 5
    SiO2 33.57 58.49 38.37 11.81 14.84
    CaF2 50.57 27.54 40.16 81.34 74.61
    CaCO3 5.11 6.43 n.d. 3.02 3.12
    Zn n.d. n.d. 0.48 n. d. n.d.
    Pb n.d. n.d. 0.93 n.d. n.d.

    (Table 43) Analyses of sulphur ores and concentrate, Great Sulphur Vein

    1 2 3 4
    SiO2 46.90 46.98 42.35 7.97
    A12O3 2.02 1.02 1.67 0.30
    Fe 24.92 24.80 25.89 42.07
    S 24.70 23.30 27.32 42.90
    CaO 0.48 0.19 0.10 tr.
    MgO n.d. 0.04 0.08 n.d.
    C n.d. 0.61 0.30 n.d.
    Sn 0.01 n.d. n.d. n.d.
    Cu n.d. n.d. n.d. 0.15
    Zn n.d. n.d. n.d. 0.27
    Pb 0.05* n.d. n.d. 0.05
    As 0.05* 0.010 0.018 0.02
    Co 0.02* n.d. n.d. n.d.
    Ni tr. tr. tr. n.d.
    F n.d. n.d. n.d. 0.00
    Ba, Sr tr. n.d. n.d. n.d.
    Au, Ag n.d. n.d. n.d. nt. fd.

    (Table 44) Shafts between Nentforce Level Portal and Nentsberry

    Shafts Gossip Gate

    [NY 7253 4681]

    		 High Nent Force

    [NY 7333 4685]

    		 Water Greens

    [NY 7408 4688]

    		 Foreshield

    [NY 7477 4677]

    		 Lovelady Shield

    [NY 7568 4621]

    		 Nentsberry Haggs

    [NY 7557 4804]
    From portal ft 1875 4520 7020 9325 12 825 17 700
    From portal km 0.57 1.38 2.14 2.84 3.91 5.40
    Surface, above OD, ft 952 1037 1065 1105 1131 1250
    Surface, above OD, km 290 316 325 337 345 381
    Superficial & stage 19(6) 7(2) 10(3) 30(9)
    Shale, grey beds 17(5) 50(15)
    Three Yard Limestone 20(6) 16(5) 17(5)
    Shale 5(2) 5(2) 4(1)
    Six Fathom Hazle 35(11) 30(9) 29(9) 30(9) 57(17)
    Five Yard Limestone 12(4) 12(4) 13(4) 13(4) 13(4)
    Slaty Hazle 24(7) 24(7) 27(8) 30(9) 27(8)
    Shale 9(3) 8(2) 10(3) 13(4) 12(4)
    Scar Limestone 51(16) 55(17) 55(17) 55(17) 54(16) 52(16)
    Shale, sandstone 11(3) 20(6) 27(8) 32(10) 35(11) 31(10)
    Cockleshell Limestone 2(1) 2(1)
    Shale 30(9) 27(8)
    Sandstone 5(2) 18(5)
    Single Post Limestone 5(2)
    Shale 7(2)

    890 ft (271 m) above OD

    (Table 45) Principal horse levels near Nenthead

    Name of horse level Location of portal[NGR] OD at portal feet (m) Veins worked Approximate length feet (km)
    Hudgill Burn 0.5 mile (0.8 km) WSW Nenthall [NY 7506 4541] 1346(410 m) Hudgill Burn Veins 13 350(4.069 km)
    Nentsberry Haggs 0.75 mile (1.2 km) SE of Nenthall [NY 7661 4503] 1250(381 m) Nentsberry Haggs Wellgill

    High Raise

    Treloar

    Dupont, Cox,

    Liverick, 1st & 2nd Sun

    		 11 440(3.486 km) (in Cumbria) 9350(2.850 km)

    (in Northumberland)
    Bloomsberry or Brownley Hill 0.75 mile (1.2 km) WNW of Nenthead House [NY 7762 4465] 1330(405 m) Brownley Hill Veins

    Wellgill

    Guddamgill

    Scaleburn

    		 21 120(6.437 km) (in Cumbria)

    1400(0.427 km) (in Northumberland)
    Rampgill 300 ft (91 m) SW of Nenthead House [NY 7818 4350] 1432(436 m) Scaleburn

    Rampgill

    Rampgill Cross

    Smallcleugh

    Middlecleugh

    		 18 480(5.633 km)
    Smallcleugh 2000 ft (610 m) SE of Nenthead House [NY 7877 4290] 1580(482 m) Smallcleugh

    Handsome Mea

    Middlecleugh Veins

    Longcleugh

    		 22 430(6.837 km)
    Capelclough 500 ft (152.4 m) SW of Nenthead House [NY 7811 4349] 1430 (436 m) Brigal Burn, Caplecleugh

    Middle Cleugh Veins

    Black Ashgill

    		 20 950 (6.386 km)

    (Table 56) Lead and zinc concentrates obtained from Nenthead sub-area

    Company Years Lead concentrates tons Years Zinc sulphide concentrates tons
    London Lead Co. 1797–1805

    209 967*

    1854–1913

    32 901
    London Lead Co. 1816–1882
    Other Companies 1803–1912

    93 188*
    Other Companies incomplete
    Nenthead & Tynedale Zinc Co. 1883–1895 14 213 1883–1895 50 953
    Vieille Montagne Zinc Co. 1896–1920 10 684 1896–1921 90 750
    328 052 174 604

    (Table 47) Partial analyses of barium spars, West Allen Mines

    1 2 3 4 5 6 7
    BaO 65 60 64 66 49 61 65
    Total S 3.3 13.4 13.6 3.7 2.9 1.5 2.1
    Pb n.d. 1.1 n.d. n.d. 0.6 0.5 n.d.
    H2O -150° 0.1 0.1 tr. 0.1 tr. 0.1 0.1

    Approximate figures obtained spectrographically:
    Ca 5 0.3 0.1 5 10 5 5
    Sr 0.7 1.7 1.0 0.6 0.2 0.5 0.5
    Si 0.6 0.4 0.4 0.4 0.7 5 0.5
    Zn 0. 0.05 0.1 nt.fd. nt.fd. 0.3 nt.fd.

    Approximate mineral compositions:
    BaSO4 24 91 97 27 20 11 15
    SrSO4 - 3 2 - - - -
    BaCO3 63 - - 64 46 69 71
    SrCO3 1 - - 1 - 1 1
    CaCO3 12 - - 9 25 9 12
    SiO2 1 1 1 1 2 10 1
    PbS - 1 - - - - -

    (Table 48) Analyses of witherite and zinc-witherite products, Nentsberry

    1 2 3 4
    SiO2 0.7 1 . 5 0.78 4.9
    A12O3 n.d. 0.1 2.28 0.8
    Fe2O3 n.d. 3.0 1.7
    MnO n . d. 0.6 1.37 0.5
    CaCO3 1.8 1.8 3.39 1.6
    BaCO3 92.6 86.8 62.23 3.6
    BaSO4 2.7 1.6 5.26 6.3
    SrCO3 1.7* 0.0 n.d. n.d.
    ZnS 0.06* 3.1 23.16 64.2
    PbS 0.11 tr. tr. 6.8
    FeS2 n.d. n.d. n.d. 9.3
    Cd n.d. n.d. n . d. tr.

    (Table 49) Production from the Coalcleugh and Barneycraig veins

    Mine or vein Years

    Tons of lead concentrates

    		 Tons of lead concentrates
    Coalcleugh Mines (undifferentiated) 1729–1753

    10 830
    Coalcleugh Mines (undifferentiated) 1808–1836

    29 920
    Coalcleugh Mines (undifferentiated) 1854–1860

    11 105

    		 51 855
    Low Coalcleugh 1754–1808

    9384
    Low Coalcleugh 1837–1853

    9442
    Low Coalcleugh 1861–1878

    879

    		 19 705
    High Coalcleugh 1754–1808

    62 253
    Barneycraig 1823–1836

    22 710
    Barneycraig 1837–1853

    12 229
    Barneycraig 1861–1878

    4689

    		 101 881
    Whitewood 1837–1853

    4090
    Whitewood 1861–1878

    1512

    		 5602
    Engine String 1837–1853

    1426
    Engine String 1861–1878

    1534

    		 2960
    Sun Vein 1837–1853

    3696
    Sun Vein 1861–1878

    461

    		 4157
    Recovered from slimes 1837–1853

    1468
    Recovered from slimes 1861–1864

    296

    		 1764
    Recovered from slimes 1865–1878

    included with Allenheads
    Beaumont, Total 1729–1878 187 924
    Vieille Montagne, Total 1899–1920 6687
    Total Coalcleugh mines 1729–1920 194 611

    (Table 50) Succession in the first 3000 ft (914 m) of the Blackett Level

    Blackett Level ft (m) Studdon Shaft ft (m)
    Shale
    Sandstone 11 (3.4)
    Shale 10 (3.0)
    Sandstone ?40 ?(12.2) Sandstone 30+ (9.1 + )
    Shale 21 (6.4) Shale 27 (8.2)
    Sandstone 16 (4.9) 0 0
    Limy Sandstone 5 (1.5) Limestone 6 (1.8)
    Shale 9 (2.7) Shale 3 (0.9)
    Sandstone 45+ (13.8 +) Sandstone 45 (13.7)

    (Table 51) Mineralisation in the Tyne-Tees Tunnels of the Northumbrian Water Authority

    Distance from West Portal miles (km) Horizon Direction throw (m) Mineralisation width (m) Identification
    North
    5.830–5.744(9.380–9.242) Shale below High Slate Sill various Siderite in joints
    5.366 (8.634) Low Slate Sill Siderite, traces bornite, chalcopyrite 0.1
    5.103 (8.211) Low Slate Sill N40°W Calcite, quartz pockets of galena 0.25–0.5
    5.064 (8.148) Low Slate Sill N37°W Galena up to 0.3, siderite, calcite traces chalcopyrite Swandale Vein of Edmondbyers
    4.394 (7.070) Shale and underlying Crag Limestone N56°E dips SE Green fluorite, quartz and galena in fracture zone 3.0 New Vein
    4.048 (6.513) Firestone N70°W Silicified with pockets of fluorite 1–2 White Vein of Hunstanworth
    2.668 (4.293) Little Limestone and sandstone N75°E small NW Green fluorite, flat in limestone to 4.328 km. Siderite, calcite West Pasture Vein
    2.356 (3.792) Coal Sills sandstone N80°E Calcite 0.06 ?West Pasture South Vein
    1.588 (2.555) Great Limestone E–W Quartz, siderite, pyrite 0.2
    1.198 (1.928) Great Limestone E-W Green fluorite 18–32%; siderite, sphalerite 0.9 max. Also strings at 1.919 and 1.912 km Red Vein of Rookhope
    1.159 (1.865) Great Limestone N50°E Siderite, calcite, quartz0.6–1.0. Also strings at 1.879 and 1.830 km
    1.084–1.107(1.744–1.781) Great Limestone N40°W Brecciation, calcite, siderite pyrite
    N50°E Little fluorite at 1.77 km
    0.876 (1.410) Great Limestone N75°E Gouge with carbonates ?Coves Vein
    South
    0.242 (0.389) Shale under Nattrass Gill Hazle N50°E Galena 0.001 Honeywell Vein
    0.889 (1.430) Shale under Nattrass Gill Hazle E-W ?4S Quartz with 7.5% fluorite 1.5–3 Slitt Vein
    Main fault Brecciated sandstone, much quartz, little fluorite; iron carbonates, traces Pb, Zn only Slitt Vein
    1.215 (1.955) Shale under Nattress Gill Hazle N60°E c.6 SE Quartz, fluorite, calcite 0.3 ?Merkiel or Tomkin Vein
    1.625 (2.615) Shale under Nattrass Gill Hazle ENE Calcite, minor fluorite 0.2 Harnisha Burn Vein
    1.923 (3.094) Nattrass Gill Hazle N30°W SW hade Unmineralised ?Woodhall's or Wallace Vein
    3.461 (5.569) Four Fathom against Great Limestone N40°E Footwall fault, little mineralised limestone to S Sharnberry Vein
    3.462–3.474 (5.570–5.590) Four Fathom Lsst. dips steeply N heavily silicified, quartz, calcite, trace pyrite
    3.484 (5.606) Great Limestone NE
    3.495 (5.623) Great Limestone NE minor fault
    6.440 (10.623) Dolerite dyke (N Wall) N70°E Unmineralised 10 Hett Dyke of Whin Suite
    7.251 (11.667) Dolerite (N Wall) E–W Unmineralised 30 Cleveland Dyke
    8.123–8.158(13.070–13.128) Great Limestone and shale N65°E Fault zone 55 Quartz and calcite veins 20–30% Egglestone Fault
    8.357 (13.446) Shale below Nattrass Gill Hazle E-W Sandstone and mudstone in fault breccia Lunedale Fault
    8.880 (14.288) Shale over Grit Sill ?NNW Witherite 0.2

    (Table 52) Analyses of iron ore, Killhope and Snodberry

    1 2 3 4
    Fe2O3 n.d. n.d. 58.3 50.86
    FeO n.d. n.d. tr. 5.01
    MnO2 n.d. n.d. n.d. 0.31
    MnO n.d. n.d. 3.5 5.41
    SiO2 14.6 19.55 19.9 15.92
    A12O3 n.d. n.d. n.d. 0.21
    MgO 1.5 n.d. n.d. 0.76
    CaO 10.6 8.22 n. d. 1.80
    CaF2 6.8 3.03 n.d. n.d.
    BaO n.d. n.d. n.d. 0.098
    Na2O, K2O n.d. n.d. n.d. 0.29
    Zn 3.2 2.31 n.d. 0.43
    Pb 1.2 0.15 n.d. nt.fd.
    P2O5 tr. 0.039 tr. 0.069
    S 1.4 0.98 tr. 0.144
    CO2

    H2O + 105°

    		 15.7 n.d. 18.60 n.d. n.d. 11.30

    6.91
    H2O - 105° 0.0 0.0 1.5 0.00
    Fe 29.3 27.88 40.7 39.50
    Mn 2.3 2.28 4.39

    (Table 53) Burtree Pasture Vein

    Width of oreshoot
    Horizon of oreshoot Number of measures Maximum

    ft

    		 Maximum

    m

    		 Minimum ft Minimum m Statistical average ft Statistical average m
    Low Slate Sill to Coalcleugh Beds 73 4.5 1.4 0.5 0.2 3.3 1.0
    Firestone Sill 25 4.0 1.2 0.5 1.2 2.0 0.6
    Low Coal Sill to Pattinson Sill 21 5.0 1.5 2.0 0.6 2.8 0.9
    Great Limestone 21 3.0 0.9 0.75 0.2 1.5 0.5
    Four Fathom Limestone 83 8.0 2.4 1.5 0.5 4.0 1.2
    Nattrass Gill Hazle 145 7.0 2.1 0.75 0.2 3.0 0.9
    Three Yard Limestone 64 7.0 2.1 0.5 0.2 2.8 0.9
    Six Fathom Hazle 71 7.5 2.3 1.0 0.3 3.5 1.1
    Five Yard Limestone 42 10.0 3.0 2.0 0.6 4.0 1.2
    Slaty Hazle 50 8.0 2.4 0.5 0.2 3.0 0.9
    Scar Limestone 138 12.0 3.7 2.0 0.6 6.1 1.9
    Alternating Beds 104 12.0 3.7 1.0 0.3 5.0 1.5
    Single Post Limestone 47 9.0 2.7 1.0 0.3 3.6 1.1
    Whetstone Bed 43 9.0 2.7 1.0 0.3 4.0 1.2
    Whin Sill 59 6.0 1.8 1.5 0.5 3.6 1.1

    The width stated for the Great Limestone applies to the north-east workings

    (Table 54) Analyses of iron ores, Sunnyside and Boltsburn West

    1 2 3 4
    Fe2O3 n.d. 1.6 15.8 37.4
    FeO n d . 47.1 25.8 3.7
    SiO2 13.3 2.7 8.0 14.4
    CaO 0.4 n.d. n.d. n.d.
    MgO 3.1 n.d. n.d. n.d.
    P2O5 0.027 tr. tr. 0.1
    S 0.028 n.d. n.d. n.d.
    H2O + 105° n.d. 0.2 2.1 4.8
    H2O - 105° 0.0 0.1 0.6 1.6
    Total Fe 44.3 37.7 31.1 29.0

    (Table 55) Section in the Great Limestone, Boltsburn Flats

    ft m
    Limestone with thin shale beds ("Tumblers") 9 2.7
    Yard Post, limestone 3 0.9
    High Flat, Limestone, coral bed at base 10 3.0
    Barren limestone 11 3.4
    Middle Flat, limestone 7 2.1
    Barren limestone 11.5 3.5
    Low Flat, limestone 5 1.5
    Limestone 15 4.6

    (Table 56) Production from Boltsburn mines, 1818–1940

    Years Company Oreshoots Tons lead

    concentrates

    		 Tons fluorspar
    1818–1880 Beaumont Vein 23 896
    1884–1900 Weardale Vein (mainly) 11 831
    1901–1931 Weardale Flats 89 320
    Vein 7299
    1932–1940 Weardale Vein* 2738
    Totals 127 785 7299

    * Mainly from Boltsburn West Level

    (Table 57) Assays in North Side Flat, Boltsburn East, Acmin No. 2 Borehole. Weighted averages of samples

    Rod length ft Rod length m PbS ZnS CaF2
    840.5–852 256.2–259. 7256.2–259.7 4.59 0.015 2.7
    852.5–860 259.8–262.1 2.497.6 0.19 2.58
    869.5–878.25 265–267.7 2 0.28 3.9
    833–878.25 253.9–267.7 3.1 0.19 2.2

    (Table 58) Analyses of iron ores, Broadsike and Clints

    1 2
    Fe2O3 50.34 16.02
    FeO 0.87 33.75
    SiO2 4.98 4.77
    Mn 3.00 3.11
    CaO 12.68 5.55
    MgO 1.26 2.12
    P2O5 0.023 0.007
    Calcination loss 20.71 27.13
    H2O - 150° 3.20 1.70
    Total Fe (wet) 35.91 37.45

    (Table 59) Analyses of iron ores, Carricks

    1 2 3 4
    Fe2O3 60.36 46.40 n.d. 52.91
    FeO 0.00 0.00 n.d. 0.00
    Mn 2.97 13.59 2.52 2.09
    SiO2 12.47 16.63 20.38 21.50
    CaO 0.18 0.60 0.07 4.90
    MgO 0.16 0.22 0.40 0.97
    S n.d. n.d. 0.022 0.06
    P2O5 0.108 0.202 0.112 0.017
    CO2

    H2O + 105°

    10.76

    n.d.

    n.d.

    		 5.40

    8.90
    H2O + 105° 8.90
    H2O - 105° 10.30 14.38
    0.00
    Fe, total 42.25 32.30 34.40 36.93
    5 6 7 8
    Fe2O3 41.61 33.46 52.34 43.70
    FeO 6.43 15.43 0.00 2.32
    Mn 2.81 3.10 3.31 2.98
    SiO2 6.35 6.15 11.30 6.72
    CaO 12.00 8.20 6.20 16.04
    MgO 3.17 2.38 0.58 1.16
    S 0.121 0.373 0.321 n.d.
    P2O5 0.016 0.015 0.026 0.062
    CO2 16.60 14.60 3.40 n.d.
    H2O + 105° 8.15 10.40 12.00 n.d.
    H2O - 105° 0.00 0.00 0.00 0.00
    Fe, total 34.62 35.33 36.53 32.01

    (Table 60) Analyses of fluorspar, Stanhopeburn

    1 2 3 4 5 6
    CaF2 96.06 84.50 93.85 87.61 80.96 76.70
    SiO2 3.24 13.03 5.17 3.10 7.90 19.70
    A12O3 + Fe2O3 0.60 0.66 0.04 8.10 10.95 n.d.
    CaCO3 n.d. 0.53 0.57 0.99 1.04 1.0
    MgCO3 tr. 0.14 n.d. tr. n.d. n.d.
    BaSO4 n.d. n.d. 0.00 0.00 0.00 n.d.
    PbS 0.09 0.58 0.24 tr. tr. 2–3*
    ZnS 0.13 n.d. 0.00 n.d. n.d.

    (Table 61) Analyses of fluorspar, Harnisha Burn and Yew Tree

    1 2 3 4
    CaF2 92.87 86.54 72.79 55.90
    SiO2 2.83 3.0 23.41 24.44
    Pb 1.21 2.3 0.18 tr.
    CaCO3 – 7.2 – –

    (Table 62) Estimates of lead values in Jeffries Veins

    Vein Jeffreys Level

    Fathoms

    		 Horizon Average estimated values tons/fathom lead concentrates Approx. percentage PbS assuming 6 X 6 X 4 ft* Ore calculated at 12 cu ft/ton
    North Above 20 High Grit Sill 0.38 3.2
    20–40 Lowe Grit Sill 0.51 4.2
    40–50 Firestone, Pattinson 0.42 3.5
    Middle Above 25 High Grit Sill 0.43 3.6
    30–50 Low Grit, Firestone 0.59 5.0
    50–60 Firestone, Pattinson 0.98 8.1
    60–70 Shale below Pattinson 0.00 0.0
    70–80 Little Limestone to top of Great Limestone 1.64 13.2
    80–95 Great Limestone 1.34 11.1
    South Above 50 Grit Sills 0.37 3.1
    95 Great Limestone 0.00 0.0

    (Table 63) Analyses of iron ores, bands

    Fe 21.80 33.00
    SiO2 36.93 18.73
    S 0.045 0.059
    P2O 0.055 0.055
    Mn 3.71 4.86
    CaO 5.58 2.90
    MgO 0.0 0.0
    H2O 8.46 6.80
    Insoluble 37.40 19.10

    (Table 64) - Analyses of iron ores, Langdon Beck Mines

    F e2O3 20.55 57.90 62.91
    FeO 25.62 4.59 0.0
    Mn 3.57 4.10 4.71
    SiO2 12.73 7.77 12.36
    CaO 4.86 2.32 tr.
    MgO 1.44 0.59 tr.
    P2O5 0.023 0.009 0.07
    Calcination loss 21.77 15.44 11.54
    H2O 2.80 3.50 3.80

    (Table 65) Analyses of limonitic iron ore, Flushiemere

    Fe2O3 63.500
    Mn2O3 5.412
    MnO 1.395
    A12O3 1.293
    CaO 2.950
    MgO 0.292
    SiO2 8.850
    BaO 0.348
    S 0.033
    P2O5 0.101
    TiO2 0.020
    K2O 0.213
    Na2O 0.265
    Cu 0.018
    Zn 0.640
    Pb 0.130
    Ni, Co, As 0.000
    Carbonaceous matter 0.500
    CO2 3.200
    H2O + 10.650
    Total 99.810

    Analysts: Pattinson & Stead, Middleborough (1944); analysis supplied by Home Ore Department, Iron and Steel Control, Ministry of Supply

    (Table 66) Analyses of zinc ore, Ettersgill and Wynch Bridge

    1 2
    Zn 11.3 19.4
    Fe 28.2 24.6
    Mn 4.1 3.2
    S 6.0 9.6
    CO2 28.4 21.1
    Pb tr. tr.
    Cu 0.0 0.0
    Cd tr. tr.
    SiO2 2.6 2.9
    A12O3 1.3 1.3
    MgO 1.7 1.7
    CaO 6.2 5.5
    TiO2 tr. tr.
    F tr. tr.
    BaO tr. tr.

    Approximate mineral composition:

    SiO2 + A12O3 3.9 4.2
    ZnS 18.2 29.2
    Fe2O3 6.7 12.6
    FeCO3 48.8 32.9
    MnCO3 7.3 6.6
    MgCO3 3.5 3.5
    CaCO3 11.1 9.8
    Totals 99.5 98.8

    (Table 67) Production of lead concentrates from the Little Eggleshope and Wiregill ore shoots

    Wiregill Mine 1852–1885 56 935
    Wiregill North Vein 1886–1902 11 789
    Wiregill North Vein sump workings 1889–1902 6593
    Wiregill South Vein 1886–1888 2121
    California Mine 1852–1902 46 071

    (Table 68) - Analyses of tailings, Sharnberry

    1 2 3 4
    CaF2 44.9 65.9 66.8 65.2
    CaCO3 n.d. n.d. 8.8 8.6
    SiO2 38.7 21.5 16.6 20.8
    Fe2O3+ A12O3 n.d. n.d. 4.0 3.6
    Pb 2.5 1.7 2.8 1.0
    Zn 0.34 0.33 n.d. n.d.
    BaSO4 n.d. n.d. 0.0 0.0

    (Table 69) Analyses of tailings, Langley Barony

    1 2 3 4
    BaSO4 51.9 40.6 39.0 40.5
    BaCO3 2.8 1.5 9.7 9.1
    Zn in sulphide form 5.7 2.2 6.4 4.4
    Zn in oxidised form 0.3 1.0 0.7 0.9
    Pb in sulphide form 0.4 0.5 0.8 0.9
    Pb in oxidised form 0.7 1.8 1.5 2.1
    Screen test, plus 3/16 in B.S.S. square hole mesh, per cent 9.7 0.6 6.1 9.2

    (Table 70) Analyses of ore and product witherite, Settlingstones

    1 2 3
    BaCO3 77.74 94.68 91.23
    BaSO4 4.51 1.82 3.48
    CaCO3 5.58 0.89 1.07
    MgCO3 0.79 0.35 0.38
    SiO2 6.72 1.67 2.26
    Fe2O3 0.77 0.08 0.65
    A12O3 1.56 0.35 0.40
    FeS2 0.19 n.d. n.d.
    ZnS 0.56 0.12 0.47
    PbS 0.01 n.d. n.d.
    98.43 99.96 99.94

    (Table 71) Analyses of tailings, Stonecroft

    1 2 3
    BaSO4 31.1 42.4 31.7
    BaCO3 2.4 4.5 4.4
    MgO 1.7 0.9 -
    Zn in sulphide form 8.0 8.8 6.1
    Zn in oxidised form 0.6 0.6 1.1
    Pb in sulphide form 0.6 1.0 0.9
    Pb in oxidised form 0.6 1.5 1.6
    Screen test, plus 3/16 in, B.S.S. square hole mesh, per cent 20.2 0.0 9.7

    (Table 72) Analyses of ore and product witherite, South Moor

    1 2 3 4
    BaCO3 85  -90 9394 92–92.5 90–91
    BaSO4 6–7 4 Up to 6 Up to 8
    SiO2 0.1–2.0 0.1–0.5 – –
    CaCO3 0.2 – – –

    (Table 73) Analyses of witherite, Tanfield Moor

    1 2 3
    BaCO3 55.7 38.9 51.1
    CaCO3 23.4 31.3 28.2
    Fe203 + A12O3 (as Fe2O3) 0.9 2.5 1.3
    Insol. (BaSO4 etc.) 19.8 25.3 16.7

    Analyst: E W Muddiman (1937); analyses supplied by Lambton, Hetton and Joicey Coal Co Ltd.

    (Table 74) Analyses of barytes, Lumley Sixth Pit

    1 2
    BaSO4 97.28 95.10
    BaCO3 1.30 2.38
    CaCO3 0.23 0.29
    CaF2 0.00 0.02
    FeS 0.40 0.77
    FeS2 0.00 0.09
    Moisture 0.33 0.21
    Ignition loss 0.41 1.12
    99.95 99.98

    Analyst: E W Muddiman (1941); analyses supplied by Lambton, Hetton and Joicey Coal Co Ltd

    (Table 75) Average analysis of run-of-mine barytes, New Brancepeth

    BaSO4 90.28
    BaCO3 2.36
    SiO2 3.64
    Fe2O3 + A12O3 1.50
    Mn3O4 0.18
    CaSO4 0.20
    Cu 0.013
    ZnS 0.31
    PbS 0.71
    Ignition loss 0.86
    100.05

    Average of monthly analyses covering the 12 months ending March 1945, supplied by Athole G Allen (Stockton) Ltd