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Bulletin - United States Geological Survey Volume 246 Geological Survey

Bulletin - United States Geological Survey Volume 246

Geological Survey

Published September 12th 2013
ISBN : 9781230258881
Paperback
22 pages
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This historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1905 edition. Excerpt: ...succession at variousMoreThis historic book may have numerous typos and missing text. Purchasers can usually download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1905 edition. Excerpt: ...succession at various openings, from the wall to the druse, is (1) marcasite- (2) ferriferous sphalerite: (3) galena in cubic crystals- (4) ferriferous sphalerite, subordinate in quantity- (5) marcasite- (6) galena in octahedral crystals, very subordinate in quantity. Some of the elements of this succession are lacking at various veins. A very common order is (1) sphalerite, (2) galena, and (3) marcasite. So far as present observations go the most common order is (1) marcasite, (2) blende, and (3) galena or marcasite, or both. The marcasite first deposited forms a thin sheet, not usually more than 1 millimeter in thickness, lining the solution cavities in the dolomite. It is rarely absent. The blende formed over it varies in thickness from a few millimeters to 3 or 4 inches. On the blende are scattered crystals of galena and marcasite. Grant calls attention to the fact that in the deeper mines the order very frequently is (1) marcasite, (2) galena and blende, and (3) blende. Probably the more significant, however, is a grouping corresponding to the vertical order of succession of the dominant ore minerals. According to this grouping the ores may be classed as (1) galena or lead ores, (2) smithsonite or zinc-carbonate ores, (3) blende or zincsulphide ores. Galena or lead ores.--These are the characteristic ores of the upper horizons and are the ores which attracted attention in the early history of the region. In them galena is the dominant mineral and all other minerals are very subordinate. These ores range in general from the surface down to the level of underground water, and much the largest quantity of mineral so far obtained has been found as loose masses in dolomite sand, which is residual from the decomposition of the country...