Abstract

The principal host rock of the Braden porphyry copper deposit (El Teniente) is altered extrusive andesite of the lower member of the early Tertiary? Farellones formation, peripheral to a breccia-filled pipelike structure inferred to have been formed, following mineralization, on the site of an older dacite porphyry stock which may have been emplaced as a cupola of the Andean batholith. Deposition of chalcopyrite, the predominant primary sulfide, occurred mainly during the second of five stages of mineralization, principally as fillings of stockwork fractures, and was accompanied by deposition of bornite, chalcocite, pyrite, and molybdenite. The depth of the zone of oxidation and supergene enrichment is variable, and is controlled by structure and to a lesser extent by rock type and topography.

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