Synopsis
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. 1916 Excerpt: ...serpentinized eruptive rocks. It however probably no longer exists in its original condition, the ore-bodies now found being the results of concentration which took place during the complete chemical alteration of the original olivine rock.' PRIMARY AND Snconnanv DEPTH--ZONES IN COPPER Dnrosrrs As previously mentioned, secondary alterations of sulphide copper deposits of every genesis take various form in different districts." In some districts, as for instance Butte in Montana and Huelva in Spain, the copper content at the outcrop has been practically completely removed.' In other districts such as Burra-Burra, Moonta, and Wallaroo, in South Australia; Bisbee and Clifton-Morenci in Arizona; at many places in Chili, at Mednorudiansk in the Urals, and at Katanga in the Congo district, on the other hand, particularly large quantities of secondary copper ores are found at the outcrop, close to the surface. At Burra-Burrs, for instance, astonishingly rich carbonate and oxide ores were found near the surface, though in depth no payable sulphide ores existed. The complete removal of the copper from the oxidation zone is connected on the one hand undoubtedly with the occurrence of much pyrite, which upon weathering yields the necessary acid, and on the other with the absence of carbonates to neutralize this acid. Sulphuric acid becomes formed as the final product of the oxidation of FeS2, the reactions being as follows: FeS2 + H20 + O, = FeSO4 + HZSO4, 2FeS2 + H20 + O15 = Fe2(SO,,)a + HQSO4. Chalcopyrite, bornite, and chalcocite, by oxidation are in part altered directly to sulphates, and in part dissolved by the ferric sulphate formed at the decomposition of the pyrite, thus: In the process of this oxidation ferric oxide or hydrate are formed ei...
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