Abstract
A review on primary and supergene copper minerals was made for principal Chilean porphyry copper deposits in Cretaceous to Pliocene ages, with the objective to estimate their formational enrvironments. The primary copper mineralization is characterized by disseminated sulfide minerals, such as chalcopyrite, bornite, digenite, enargite, and tetrahedrite-tennantite, locally with primary covellite and nukundamite. This association indicates "high sulfidation" conditions at temperatures below 500°C. The supergene enrichment zone developed extensively in upper parts of the deposits, which is attributed principally to the Miocene Andean orogeny and to the associated climate change, is divided into the oxidized subzone of chrysocolla, atacamite, antlerite, brochantite and tenorite with lesser amounts of malachite and azurite, and the sulfurized subzone of chalcocite, covellite, native copper and cuprite. The sulfurized subzone is inferred to have been generated under reduced conditions below underground water level, in contrast to the oxidized subzone formed under moderately acidic to neutral oxidized conditions.
