The Vil Achay tin deposit of Catamarca, Argentina

Abstract

The Vil Achay tin deposit is located on the south-eastern flank of Sierra de Fiambalá in the province of Catamarca. The oldest exposed rocks are amphibolites of the Fiambalá Gabbro (Ordovician), intruded by the El Salto Granite of possible Carboniferous age. Within the amphibolites, near the contact between the two units, is a mineralized granitic dyke, exhibiting hydrothermal alteration (albitization and greisenization). Cassiterite is disseminated in the dyke. Near the western contact of the dyke are zones with cassiterite concentration controlled by subvertical fractures. The following mineral sequence has been identified: cassiterite, magnetite, wolframite (scarce), chalcopyrite, pyrite, covellite, chalcosine, hematite, limonite, malachite and azurite. El Salto Granite is of post-orogenic, meta- to peraluminous type, enriched in Rb, Nb, Y and Sn. Rare earth element distributions in whole-rock exhibit strong fractionation of HREE relative to LREE. Such fractionation is indicative of the activity of F-anions in the mineralizing fluids. High activity of F in the fluids is responsible for Sn greisen mineralization. It is suggested ed that the deposit is part of a F-rich open greisen system, formed during the late magmatic hydrothermal stage genetically linked to El Salto Granite.