The Rosario porphyry Cu-Mo deposit, northern Chile: Hypogene upgrading during gravitational collapse of the Domeyko Cordillera

Abstract

Porphyry style mineralisation at the Rosario deposit in northern Chile formed during the waning stages of the Incaic Orogeny (∼34–32 Ma). Early-formed copper-molybdenum mineralisation formed in association with potassic and intermediate argillic alteration during the emplacement of the Rosario Porphyry. Late-stage high sulfidation state epithermal veins (including the Rosario Vein) formed when NW-trending, SW-dipping normal faults cut the Rosario Porphyry. The massive sulfide veins overprinted earlierformed potassic alteration and related mineralization, producing a high grade core of copper-silver mineralization associated with advanced argillic and phyllic alteration. Pressure-depth estimates from fluid inclusion analyses imply that more than a kilometer of overburden was removed in 1.8 m.y., from the time of porphyry ore formation to the deposition of high sulfidation veins. Gravitational collapse of the Domeyko Cordillera at the end of the Incaic Orogeny promoted rapid exhumation of the porphyry system. This allowed for the formation of an extensional vein array infilled by high sulfidation state mineralization in a terrane undergoing compressional tectonism.