Economic Geology Volume 5

Economic Geology Volume 5

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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. 1910 edition. Excerpt: ... the other hand, at Herrerias and Cabezas del Pasto, where the lodes taper towards the surface and have a shallow gossan, the zone of 3 per cent, ore does not extend below about 40 meters from the surface. This relation is in accordance with the known facts of enrichment by descending waters and emphasizes still further the importance of prolonged erosion in influencing the economics of this field. 1R. H. Solly, Min. Mag., VII., 1887, p. 61. A. La Croix, Ann. d. Mines, ser. 8, XVI., 1889, p. 474, note. 'Zeits. fur prakt. geol., XIV., 1906, p. 180. Zone of Primary and Lean Sulphides.--With increasing depth the copper content, first of the enriched ore and later of the primary ore, progressively decreases, a fact first emphasized by J. H. Vogt. The bulk of primary ores vary between.8 and 2 per cent, of copper, while some, such as those of El Perrunal and La Zarza, assay.5 per cent, or less. The rate of decrease in depth varies greatly. In the low-grade masses, there may be comparatively little change to considerable depths. The Tharsis lodes, on the other hand, were characterized by rapid impoverishment, while the reverse is true of San Dionisio. At Santo Domingo the rate of decrease, over both secondary and primary ore, is about.5 per cent, in 40 meters vertical. At Herrerias the ore at a depth of 60 meters assays only 1.5 to 1.8 per cent, while at the neighboring mine of Cabezas, the ore averages 2 per cent, at 80 meters depth. While the general law of decrease in depth holds good, there are local exceptions. In several mines there have been found patches of rich primary ore (chalcopyrite) at or near the lower terminations of the lodes. This was the case in certain parts of Santa Rosa (Fig. 44, p. 428), Sotiel, La Zarza and other more

Product details

  • Paperback | 272 pages
  • 189 x 246 x 14mm | 490g
  • United States
  • English
  • black & white illustrations
  • 1236916859
  • 9781236916853