Copper and nickel ores of Scotland. Area IV. Caithness, Orkney, Shetland and Fair Isle
|From: Wilson, G.V. with contibutions by J.S. Flett. The lead, zinc, copper and nickel ores of Scotland. Special Reports on the Mineral Resources of Great Britain Vol. XVII: Edinburgh : HMSO, 1921.|
Details of the mines and veins
Copper ore has never been mined in Caithness on an extensive scale, though there are a few records of the occurrence of copper pyrites in the county (at Toftingall, Staxigoe, and Broadhaven). About 1760 an attempt was made to open a copper mine on the east coast, to the south of the Castle of Old Wick. " It was wrought by a company of miners, who carried off several ship-loads of ore; but, having found a better vein in Shetland, it was abandoned."
Chalcopyrite and other cupreous minerals sometimes are found accompanying galena in the lead veins which are not infrequent in the blue-grey flagstones of the Orkneys; but the only vein on which trials have been made for copper ore occurs in reddish sandstones belonging to the John o' Groats, or uppermost, division of the Middle Old Red Sandstone of the archipelago.
This vein is situated at the south-west corner of the island of Burray. It is well exposed in the shore, and seems to have attracted attention at an early date. George Low visited Burray in 1774, and apparently he examined the workings which had been made in this vein some years before his visit. He gives the following particulars. "At the west end of the island are plain indications of copper, and this so easily procured as encouraged Sir Laurence Dundas to send down a set of miners to work it; however, it proved but a poor ore, and was given over. I saw some of the ore; it was but light, sprinkled over with a green matter like verdigris, and on some of the pieces fine blue crystals of copper or vitriol. Mr. Sangster showed me some of the finer ore, which was heavy and good, as also a piece of the smelted metal, which is very good and well coloured. He told me that in breaking through a crumbling sort of rock in working it, they found the pure virgin copper in the appearance of leaves and sprigs of trees, according as it had wrought itself through the fissures of the stone. Where the miners dug it has all the appearance of a large vein, confined on each side by a pretty thick partition of a sort of fuller's earth, which entirely separates it from the rocks on each side.
The vein is on the estate of the Marquess of Zetland, and further trials have been made on it during recent years, but it has not proved possible to trace the vein inland, and no further mining operations have been carried out.
The course of the vein is north-east, and it can be followed for about thirty yards in the rocky beach at Wha Taing. The country-rock is reddish sandstone and shale, and the vein consists of a breccia of these materials. Copper pyrites is the essential ore, with apparently some chalcocite and secondary products, such as azurite and malachite. From the appearances presented by the outcrop it cannot be inferred that the vein is rich, but probably all the best samples have been removed and what is left is of low grade. The vein is 6 to 9 ft. wide, and is obviously a fault or line of crush in the sandstones. The copper ores seem to have occurred in strings scattered through this belt of breccia.
On the east side of the Mainland of Shetland there is an area of Old Red Sandstone, stretching from Rovey Head, a mile or two north of Lerwick, to Sumburgh Head, at the south end of the island. The rocks of this area are principally conglomerates, red sandstones and shales, with occasionally thin-bedded grey flagstones like those of Orkney. Veins of pyrites and copper pyrites occur in these Old Red Sandstone rocks, and at Sandlodge have been the seat of mining operations at several periods during the last century.
Proprietor: Robert R. Bruce of Sumburgh, Shetland.
Maps: One-inch Ordnance, Sheet 126; six-inch, Shetland 62.
Sandlodge is on the east coast of Shetland, about 14 miles south of Lerwick, with which it is connected by a good road. There is a small pier quite near the mine.
The vein trends about N. 10° E., and its course is indicated on the six-inch Ordnance Sheet by the position of three old shafts to the east of Sandlodge House. The country-rock is reddish sandstone, and the weathered back of the vein can be seen in some old pits beside the house. The old shafts are full of water; mining operations ceased in 1881, and though the mine buildings are standing, the engines, head-gear and dressing plant have mostly been removed. In 1920, however, preparations were being made for pumping the old workings dry and machinery was being brought to Sandlodge for this purpose.
The mine was opened about the end of the eighteenth century, when a party of Welsh miners was brought to Shetland. They sunk shafts and raised about £2000 worth of copper ore; difficulties arose, however, owing to the death of the lessee, resulting in the temporary abandonment of the mine. Professor Jameson visited Sandlodge in 1799 and found the mine closed down, but before 1800 it was again at work. From Jameson's descriptions there seem to have been two veins, known as the east and west veins, which possibly came together in depth, and both of these veins had been worked.
The principal vein, as exposed on the east side of the house, is of large size, at least 9 or 10 ft. in width, and dips to the east at 50° to 60°. Patrick Neill was at Sandlodge in 1803, and found that the miners had sunk to a depth of 22 fms. on this vein. The company had spent about £10,000 on the mine, and had shipped one or two cargoes of ore, the best of which, when dressed, was worth £70 a ton. At that time comparatively little was being done, and it was rumoured that the mine was to be shut down. In June 1808 Professor Fleming found the mine abandoned and full of water.
Any further working was on a small scale till 1872, when John Walker obtained a lease, installed machinery and furnaces, and carried on active mining for eight years. It is estimated that he raised about 10,000 tons of iron and copper ore. In 1880 the Sandlodge mine produced 1995 tons of copper ore, worth £5814, and 396 tons of gossan, or iron ore, worth £344, 15s.; the figures for 1878 are: copper ore, 708 tons, worth £1770, and hmatite, 1241 tons, worth £1550. (Mineral Statistics of the United Kingdom, Mem. Geol. Surv. for 1878 and 1880.)
Mr. Walker sold his lease in 1880 to the Sumburgh Mining Company, which had a nominal capital of £60,000 and went into liquidation in 1881. Since that time, although the mine has been repeatedy examined, no further working has been carried on. Arrangements have now been made by a syndicate to have the old workings unwatered' and the mine thoroughly examined.
So far as we have been able to ascertain no accurate plan of the workings is in existence, but a good deal of information as to the state of the mine at the time when Mr. Walker left can be gathered from reports of various mining engineers who have visited it. Mr. R. W. Dron visited the mine in 1907, and has published an account of it (" Iron and Copper Mining in Shetland, Trans. Geol. Soc., Glasgow, vol. xiii., 1908, p. 165). He states that the lode was reported to be 9 or 10 ft. wide. The west shaft was sunk on the incline of the vein to a depth of 180 ft. For the first 100 ft. the vein consisted of hematite (brown hematite or limonite), with rich pockets of copper pyrites. Several thousand tons of this ore were shipped, and it is recorded that it contained 64 per cent. of iron. (It is believed that most of this rusty iron ore was used for desulphurising coal gas.) Below the 100-ft. level the ore assumed the form of light brown spathic iron ore. The material shipped seems to have contained 35 per cent. of iron, with 15 per cent. of lime and magnesia, and it was also accompanied by copper pyrites. The ore above the 100-ft. level was stoped out, and a vertical shaft was next sunk, so as to cut the lode at a depth of 240 ft. From the bottom of this shaft workings were extended downwards in the lode a further depth of 60 ft., and levels were driven northwards for a distance of 220 ft., and southward for a distance of 190 ft. The ore body exposed in these lower workings appears to have consisted of white chalybite (siderite) with chalcopyrites."
From a study of the available evidence it seems clear that the vein is of considerable size, ranging from 9 ft. to more than 16 ft. in width. Most of the material above the 100-ft. level was highly oxidised, rich in iron, and with pockets of good copper ore, but has been to a large extent removed. Below that level there are still large reserves. In depth the vein consists of a white veinstone, mainly carbonates of lime, magnesia and iron, with copper pyrites and iron pyrites in strings and nests. The composition of this unaltered veinstone below the oxidised zone is by no means clear.; it is probably rather variable. Some reports state that it may contain 35 per cent. of iron and 5 or 6 per cent. of copper. Analyses of the white veinstone from the old dumps of the mine show that much of it is by no means so rich as this. But this is not a fair test, and without proper sampling and assays it is impossible to reach any conclusion regarding the value of the ore. It seems quite possible that with modern methods of mining and dressing there is still a future for the Sandlodge mine.
At Setter, on the coast, half a mile north of Sandlodge, a vein of copper ore has been known for many years. And an attempt was made to work it in 1890. Dron (loc. cit.) gives the following particulars, obtained from a member of the syndicate who worked the mine. " Two shafts were sunk. The first one was near the coast-line, and went to a depth of 90 ft., following the vein. At the surface the vein was only a few inches wide, but when the shaft was abandoned it was from 15 to 20 in. wide. This vein, so far as exposed, was lenticular in form, with a strike N.E. and S.W., and dipping to the N.W. at an angle of 60°. The ore was pure copper pyrites, and was shipped direct to the smelter as it came from the mine. There was difficulty about continuing the work in this shaft, owing to the proximity of the sea, and a second shaft was started about 50 yds. inland on the higher ground. The second shaft was sunk to a depth of 83 ft., and a cross-cut started to reach the vein, but at that stage the workings were abandoned." Since then no attempts have been made to reopen the mine.
To the south of Sandlodge also, on what is probably the continuation of the Sandlodge Vein, chalcopyrite is found in the cliffs at Sandwick and No Ness. A few miles farther south, at Levenwick and Hoswick, trials have been made, and old adits are still visible, but it is not known what mineral was sought for. At Garthness and Quendal trials have been made for copper ore, and Professor Jameson and Professor Traill report the existence of a vein of iron pyrites 7 ft. thick at Garthness.
This island, which lies between Shetland and Orkney, is part of the Sumburgh estate. It consists principally of reddish argillaceous sandstone. For over a hundred years copper pyrites has been known to occur in a vein which is exposed on the high cliffs at the west side of the island to the north of Naversdale. A description of this vein has been given by John Fleming, who was let down by a rope from the top of the precipice, but was not able to make a very satisfactory examination of it. A few years ago it was carefully prospected by a party 'of mining engineers, who investigated the whole outcrop, but apparently the results were not such as to lead to the inception of mining operations, as nothing has been done to work the vein.
- New Statistical Account of Scotland, vol. xv., 1845, Caithness, p. 126.
- George Low, A Tour through Orkney and Shetland, 1879, p.' '41.
- The mine was re-opened on Nov. 20, 1920; see " The Shetland News " (Lerwick) of Nov. 25, 1920.
- Robert Jameson, Mineralogy of the Scottish Islands;" vol. ii., 1800, p. 198.
- Patrick Neill, Tour through some of the Islands of Orkney and Shetland, 1806, pp. 169-171.
- John Shirreff, General View of the Shetland Islands, 1817, p. 129.
- Robert Jameson, Mineralogy of the Scottish Isles, vol. ii., 1800, p. 200.
- Dr. T.S. Traill in Patrick Neill, Tour through some of the Islands of Orkney and Shetland, 1806, p.171.
- John Shirreff, General View of the Shetland Islands, 1817, p. 128.