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VIII. — Description of the operations at Dolcoath Mine. — By Me. 

 JosiAH Thomas, the Managing Agent. 



ON the 31st August last tlie members and friends of the Eoyal 

 Institution of CornAvall honoured us with a visit to this 

 mine ; and having accompanied them with much pleasure through 

 the various surface and dressing operations, I have since been 

 asked to write a short description of the mine for the pages of 

 the Journal,- — a request which I gladly accede to in pleasant re- 

 membrance of the day. 



The chief geological features of the district, as well as the 

 general character and composition of the lodes in this mine, having 

 been so clearly and correctly described by Mr. Henwood * in the 



*• The ancient mine of Dolcoath is wrought at the foot of Cam Entral 

 and Camborne-beacon, granitic hills surrounded by slate at the surface, but 

 is probably connected downward with the body of granite which extends from 

 Illogan and Camborne to Constantine, Wendron, and Crowan. 



In the southern and central parts of Dolcoath, the granite, which con- 

 sists of the usual ingredients, and presents the ordinary structure — is 

 generally overlaid by greenish, deep blue, or brownish slate, of thick lamellar 

 structure ; and this is, in one case, interlaid by a thin, but rather extensive, 

 bed or floor of granite. 



Both granite and slate are intersected by broad bands of felspathic and 

 quartzose porphyry (elvan-courses), which aisplay marked changes of char- 

 acter in passing from one rock to the other ; their usual direction is about 

 N.E. — S.W., and, in Dolcoath, at least they dip towards the N. 



The principal lodes bear 10 degs. to 30 degs. N. of E. — S. of W. ; the 

 main lode of Dolcoath, however, takes much the same direction as the elvan- 

 courses, whilst lodes of a second series (the caunter lodes) range from 10 to 

 30 degs. S. of E. — N. of W. In the southern part of the mine the lodes 

 mostly dip (S.) towards — but in the northern part they decline (N.) from- — 

 the granite. In width they vary from a mere parting between opposite 

 (walls) faces of rock to at least 20 feet ; but on an average they are perhaps 

 3 or 4 feet. Their principal ingTedient is quartz ; but slaty or granitic matter, 

 as the neighbouring (country) rock is of slate or granite, also abounds, as 

 well as larger or smaller quantities of other earthy substances. Most of 

 the rarer Cornish Minerals have been, from time to time, found in the lodes 

 of Dolcoath. Near the surface earthy brown iron ore, iron pyrites, and 

 earthy black copper ore were mixed with vitreous copper, copper pyrites, and 

 several of the less plentiful ores of copper, and in such parts crystallized 

 minerals were often obtained ; but in some places, particularly^ in the eastern 

 parts of the mine, much tin-ore was procured. At greater depths, however, 

 the ores of copper were so abundant that Dolcoath was for some time the 

 richest copper mine in Cornwall, and for a far longer period its returns were 



