Petrography, geochemistry and geochronology of San Jorge porphyry Cu-Au deposit, Mendoza, Argentina. Constraints for the timing of magmatism and associated mineralization.

LAURA E. GRECCO; PAVÓN PIVETTA, CECILIA; MIRTA M. GARRIDO

Acta Geológica Lilloana

Fundación Miguel Lillo

Lugar: Tucumán; Año: 2018 vol. 30 p. 1 - 22

1852-6217

The San Jorge porphyry Cu-Au deposit, Argentina, integrates the Paleozoic toEarly Jurassic metallogenic belt recognized in the Southern Andes. San Jorge is currently theonly deposit considered economically viable due to its supergene enrichment. Previous studieshave reported Middle to Upper Permian ages (257-270 Ma) for the intrusion-mineralizationprocesses. Granite porphyry, two granodiorite porphyries (G1 and G2) and an alkali-feldspargranite dike were recognized. These granites intrude sedimentary rocks (Yalguaráz Formation)that hosts the main mineralization. Two tourmaline alteration events occurred prior to thepotassic episode. They are overprinted by phyllic alteration that has an elongated shape withpotassic mineralized cores. The mineralization is linked to the potassic alteration in the sedimentarysequence and in the granite porphyry that has the highest Cu contents (1% to 3%).The phyllic alteration has pyrrhotite, arsenopyrite and minor chalcopyrite. Digenite, chalcociteand covellite appear in the supergene; malachite and brochantite in the oxide; and goethite,hematite and jarosite in gossan zones.The granitic porphyry, granodiorite porphyries G1 and two potassic alteration biotites areof Early Permian age. This event produces the potassic alteration and mineralization and is15 Ma older than the ages determined by other authors. The granodiorite porphyry G2 andthe alkali feldspar granite dike are Upper Permian in age. The results suggest that the evolution of the western margin of Gondwana began in late Carboniferous and continued during the Permian period. In this Paleozoic to early Jurassic metallogenic belt, La Voluntad Cu-Mo porphyry is the oldest deposit (early Pennsylvanian, Garrido et al. 2008). Mineralized and no mineralized San Jorge granites (Early Permian-Late Permian) integrate the intrusive event of the Choiyoi Group.