Mineralization of La Salvadora deposit, Province of Mendoza, Argentina

Abstract

La Salvadora ore deposit (35°21′16″S; 68°23′22″W), located in the Province of Mendoza, Argentina, is part of a group of polymetallic veins linked to a porphyry copper that shows a crude temperature zonation away from the potassic centre. This porphyry deposit is genetically related to Lower Permian volcanic rocks from a subduction tectonic setting. La Salvadora is a quartz and carbonate vein deposit hosted by a sericitized, silicified and carbonatized rhyolite. The ore paragenesis is composed of galena, chalcocite, native silver, chalcopyrite, and bornite, along with minor stromeyerite, tetrahedrite, sphalerite and hematite. Myrmekitic intergrowths of galena - rhombic chalcocite, with irregular stromeyerite inclusions in the rhombic chalcocite, are present. Ore mineral analyses show: (i) that the galena is free of silver and copper; (ii) the heterogeneities observed in Pb-free chalcocite are produced by variable contents of silver; (iii) stromeyerite has a very homogeneous composition despite its differences in origins; and, (iv) little copper is observed either in the native silver or in sphalerite. The myrmekitic intergrowths and the stromeyerite inclusions in the chalcocite suggest that they precipitated from fluids at temperatures between 150° and 67°C, which is supported by the morphology of the fluid inclusions which suggest temperatures of formation below 120°C, typical of epithermal systems.