Ore mineralogy, fluid inclusion, and stable isotopic characteristics of stratiform copper deposits in the coastal Cordillera of northern Chile
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Late-Jurassic stratiform copper deposits in the coastal range of northern Chile (Susana-Lince and Buena Vista of the Carolina de Michilla district, and Mantos de La Luna) are hosted in an andesite-dominant volcanic pile of the Jurassic La Negra Formation which is extensively intruded by gabbroic to granodioritic plutons and dikes. Primary copper mineralization is characterized by chalcocite (~Cu1.90S) + digenite + bornite ± chalcopyrite + hematite. Supergene alteration of these minerals has produced chalcocite (djurleite), covellite, atacamite, chrysocolla and copper oxides (copper wad). Fluid-inclusion data indicate a variable temperature of formation (200 to 380 °C) and a wide range of fluid salinities (7 to 34 wt% NaCl). Carbon and oxygen isotopic compositions of calcite from the Susana-Lince deposit (δ13C=–2.6 to –3.6‰, δ18O=13.7 to 18.7‰) combined with the thermometric data suggest that the fluid responsible for the calcite mineralization derives from mixing of high-temperature meteoric water with cooler basinal brines. These data imply that the stratiform copper deposits of the coastal Cordillera are epigenetic and formed from non-magmatic, moderately oxidized hydrothermal solutions.
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