Stratigraphy and tectonic setting for the Ordovician VMS deposit in La Colorada mine (Argentinian Puna)

摘要

Understanding seafloor massive sulfide mineralizations that have been modified by deformation and meta-morphism requires knowledge of their volcanic substrate, their base and precious metals contents and their geological setting. The massive sulfide ores of La Colorada mine (La Colorada-Limeca District, Salta province, NW Argentina) are hosted by a volcano-sedimentary sequence of Ordovician age with a complex history of superposing magmatism, hydrothermal alteration and metamorphism. La Colorada Mine is located 68 km N of San Antonio de Los Cobres, in the town of Cobres (La Poma department), at an average altitude of 3900 m a.s.l. Previous works described the La Colorada massive sulfides either as Sedex or as VMS-type. In this study, based on the cores from three drill holes in the mine area, we present petrographic and geochemical data of the host rocks and the sulfide ores and discuss them in the context of the lithostratigraphic sequence of the site. The studied ore levels consist of massive sulfides, with the metal association Fe-Cu-Pb-Zn. The sulfide mineral assemblage is dominated by pyrrhotite and pyrite, accompanied by sphalerite, galena, chalcopyrite, and minor amounts of arsenopyrite associated with Au/Ag-sulfosalts. The geochemical information about the ore lenses suggests classifying the deposit into the Au-rich volcanic massive sulfide (VMS) typology, with a Zn-rich lens, in a pelite-mafic subtype, while the geochemical data on interlayered volcanic rocks point towards a back-arc setting, in agreement with the regional geotectonic reconstructions of the Easter basin of Northern Puna.