Polymetallic deposits in the Famatinian orogen of the Sierras Pampeanas of San Luis and Córdoba: fluids, sources and emplacement model.

Abstract

The famatinian cycle determined a mineralising episode between ~ 385 and ~ 292 Ma into the Sierras Pampeanas of San Luis and Córdoba. This episode, related to N - S first order shear zones and granitoids, formed polymetallic linear domains with W, Ag, Pb, Zn, Au and associated metals, within metamorphites and subordinated granitoids. d18O_fluid(H2O) and dD_fluid(H2O) values obtained in representative deposits of San Luis and Córdoba suggest a magmatic and evolved meteoric water origin for the mineralising fluid. Likewise, d34S_{fluido (H2S)} determinations in sulphides suggest that the sulphur was incorporated by thermoreduction from the crustal metasedimentites. 208Pb/204Pb - 207Pb/204Pb - 206Pb/204Pb relations point to a lead source from the homogenised phanerozoic continental crust, although a mantle component has been proved in La Fortuna (Las Aguadas district), La Aspereza (San Martín district) and Fischer (Cerro Áspero district). Tensional mineralised structures between 250º and 319º major direction, and en echelón and stepped internal geometry, respond to the Riedel model in simple shear zones. These secondary structures had been developed in a brittle - ductile and brittle transpressive regimen in an extensional environment, during a maximum principal NW-SE s₁ stress and the regional uplift. Investigated features highlight that the sinorogenic to posorogenic magmatism caused thermal anomalies that implicated hydrothermal convective systems. These systems channeled the aqueous flow through the Tres Árboles 1st order structure and secondary lineaments. No proof was found that the granitic magmatism would have contributed significantly with the sulphur and metallic elements, at least for this kind of ore deposits with stressed structural control.