The geology and ore deposits of Ely, Nevada

by Arthur Coe Spencer

This historic book may have numerous typos and missing text. Purchasers can download a free scanned copy of the original book (without typos) from the publisher. Not indexed. Not illustrated. 1917 ... of mineralized monzonite porphyry. They lie directly beneath surficial products of complete weathering and grade downward into material of similar appearance to the ore but which is too low in copper to be mined under present conditions. The ore masses are of blanket form, as their horizontal extent is great in comparison with their thickness. This form is dependent on topography and weathering and has not been determined by stratification or by such layering as is found in crystalline schists or gneisses. Masses of porphyry almost uniformly charged with grains of pyrite and chalcopyrite (primary mineralization) became subject to erosion. As the rock was gradually worn away, successively lower and lower portions of the mass were exposed to weathering. Oxidizing waters of atmospheric origin penetrated the surficial portions of the mineralized rock, attacking the metallic sulphides and converting them in part into soluble sulphates, in part into insoluble oxides and basic sulphates, in the case of iron, or into carbonate and other oxidic compounds, in the case of copper, leaving a ferruginous or gossanlike capping of decomposed porphyry. These waters, which were charged with copper derived from the weathering mass, percolated downward through the mineralized porphyry, and by chemical reaction with pyrite or with chalcopyrite deposited their copper, thus converting the previously subgrade material into ore (cementation enrichment). The most marked features of igneous metamorphism and mineralization along the mineralbearing zone, aside from the alteration of porphyry masses, are crystallization of limestone, bleaching of limestones and shales, formation of lime-bearing silicates and of jasperoid, and very general impregnation with pyrite. The total amount of i...

130 pages, Paperback

Published January 1, 2012