Professional Paper Volume 95-97

Professional Paper Volume 95-97

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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. 1916 edition. Excerpt: ...per cent. At several places holes have been drilled through the porphyry ore and well into the underlying rock, and assays of the drill cuttings show the presence of copper, usually in proportions greater than 0.2 per cent and less than 0.7. The average amount of copper in material from 20 holes which represent a section aggregating 2,060 feet was found to be 0.43 per cent. ORE PORPHYRY. The ore porphyry of the Ely district consists of pyritized porphyry which has been enriched through the secondary deposition of copper from downward-moving solutions. The enriched material contains secondary chalcocite in addition to primary pyrite and chalcopyrite and minor amounts of molybdenite. The processes of chalcocite enrichment are discussed elsewhere in this paper. (See p. 76.) As exposed in the mine pits, the porphyry ore presents a very uniform light-gray color. When closely viewed it shows innumerable black specks distributed through a white matrix. The black specks are grains either of chalcocite or of chalcopyrite or pyrite, coated with chalcocite. The white groundmass is found under the microscope to be made up of quartz, orthoclase, and sericite. In much of the material noteworthy amounts of fresh yellow pyrite are visible. Although the sulphide grains that are coated with chalcocite differ greatly in size, most of them have diameters of less than half a millimeter. Pyrite that carries no chalcocite occurs mainly in larger grains and in the form of bunches and seams. The chemical composition of the porphyry ores is indicated by two complete analyses of specimens (samples 153 and 154) collected from the Copper Flat pit and by a partial analysis which represents a composite sample of all the ore mined from this pit prior to September, 1910....
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Product details

  • Paperback | 276 pages
  • 189 x 246 x 15mm | 499g
  • United States
  • English
  • black & white illustrations
  • 1236839307
  • 9781236839305