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. 1913 Excerpt: ...with precious metals from the upper parts of the veins. It should not be overlooked that ore-shoots of primary origin are common enough. Take, for instance, the Cripple Creek gold ores, in which evidence of enrichment is conspicuously lacking; these primary shoots are usually of a markedly irregular form; many of the ...
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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. 1913 Excerpt: ...with precious metals from the upper parts of the veins. It should not be overlooked that ore-shoots of primary origin are common enough. Take, for instance, the Cripple Creek gold ores, in which evidence of enrichment is conspicuously lacking; these primary shoots are usually of a markedly irregular form; many of the smaller ore-bodies are likely to follow intersections of fissures. In depth the rich shoots show a tendency to contract, to feather out, or simply to become impoverished. In many cases zinc blende in a quartz gangue appears in depth. On the other hand sulphide enrichment is conspicuously marked, especially in silver veins. In gold-bearing veins the enrichment in gold is likely to be localized just below the zone of oxidation. The secondary silver minerals are native silver, argentite, ruby silver, stcphanite, and polybasite--that is, the same minerals (except the native silver) as occur in primary ore. As a consequence it is often exceedingly difficult to distinguish primary ore and enriched ore, and when in addition to this we recognize that the later effects of primary mineralization may sometimes closely simulate the products of descending surface waters, the difficulties of correct interpretation will be fully realized. The distinction is made easier when the secondary sulphides form a distinct zone immediately below the oxidized part of the lode. The conditions for the deposition of gold and silver are apparently much more favorable near the surface than at greater depths; on the other hand, deposition took place rapidly and the gold and silver contents of the solutions were doubtless exhausted before they reached the actual surface. Types of Deposits.--The merging of the various types makes it difficult to establish a rigid classification...
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