Elements of geology : a text-book for colleges and for the general reader

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Framed Print of Elements of geology : a text-book for colleges and for the general reader

Elements of geology : a text-book for colleges and for the general reader. Geology. MINERAL VEINS. 239 according to the metallic contents, but also according to the nature of the vein-stuffs, and therefore must be learned by observation in each country. We will give three of the most constant as illustrations. Cupriferous Veins.—The original form in which copper seems to exist in veins is copper pyrites, a double sulphide of copper and iron (CuFeS2). Now, along the bach or outcrop of copper-veins, to a depth of thirty to sixty feet, the vein usually contains no copper at all, but consists of. Elements of geology : a text-book for colleges and for the general reader. Geology. MINERAL VEINS. 239 according to the metallic contents, but also according to the nature of the vein-stuffs, and therefore must be learned by observation in each country. We will give three of the most constant as illustrations. Cupriferous Veins.—The original form in which copper seems to exist in veins is copper pyrites, a double sulphide of copper and iron (CuFeS2). Now, along the bach or outcrop of copper-veins, to a depth of thirty to sixty feet, the vein usually contains no copper at all, but consists of vein-stuff (more or less changed, according to its nature), among which are scattered masses of a dark reddish or brownish hydrated peroxide of iron, in a light, spongy condition. This peculiar form of peroxide of iron, so characteristic of the outcrop of copper- veins, is called by the Cornish miners gossan, and by the German and French miners iron hat (eiserner hut; chapeau defer'). Below the in- fluence of atmospheric agencies the vein is in its original condition, i. e. consists of vein-stone containing disseminated masses of copper pyrites. Just at the junction of the changed with the unchanged vein—i. e. running along the back of the vein at a depth varying from thirty to sixty feet—occur rich accumulations of copper, as native copper, red and black oxides of copper, green and blue carbouates of copper, etc. These facts are illustrated by Fig. 216, which is a section of the Duck, town mines of Tennessee. The irregular line,s s, is the out- line of a hill, along the crest of which the vein outcrops; the part b consists almost wholly of gossan, with only small masses of quartz-vein stuff; a i» the rich accumulation of copper ore, here about two or three feet thick ; and c is the unchanged vein, consisting of vein-stuff, inclosing arsenical pyrites, and copper pyrites in very large quantities. These phenomena may be explained as follows: There can be no doubt that. © Paul Fearn

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