Precious and base metals in Las Águilas, Sierra de San Luis: Mineralogy, genesis and evolution.

Abstract

Las Águilas mafic-ultramafic body is located in the Sierras of San Luis and carries a sulfide mineralization of pyrrhotite, pentlandite and chalcopyrite with accessory platinum group minerals (PGM). The results presented in this contribution were obtained from drill core samples made by the Dirección General de Fabricaciones Militares in the 70's and 80's. The mineralization occurs in the ultramafic rocks, associated to spinels levels and shows the following textures: interstitial or net, disseminated and veins. These textures depend on the relationship between sulfides and silicate minerals. The mineralization in Las Águilas deposit was formed at 600-700° C from the crystallization of a monosulfide solid solution responsible for the primary magmatic mineralization (Po1+Ccp1+Pn ±MGP±Cub) which was later affected by a remobilization event (Po2+Ccp2+Pn±MGP±Py±Mck). There is no chemical differences between primary and remobilized sulfides but the distinction of each mineralization type was made based on textural features, with the PGMs mainly associated to remobilized base metal sulfides and the fact that most of the PGMs are located at the rim of sulfides crystals, alteration rims of spinels and associated to serpentine group minerals.