The Yalguaraz prospect: a porphyry copper-type deposit related to the gondwanic magmatism in the Andes of Argentina

Abstract

The Yalguaraz gondwanic porphyry-type deposit is located at the eastern margin of the Frontal Cordillera in the Andes of Argentina. In this deposit, two alteration-mineralization stages (early and late) were recognized. The early stage is linked to the intrusion of a dacitic porphyry that produced pervasive potassic alteration (biotite - K–feldspar - quartz - andalusite) along with EB, A, and B veins. Mineralization occurs mainly disseminated in the dacitic porphyry and minor in A and B veins and consists of pyrrhotite, chalcopyrite, pyrite, and minor molybdenite. The late stage led to pervasive phyllic alteration (sericite + quartz + pyrite ± chlorite ± rutile ± chalcopyrite) along D-type veinlets and subsequent tourmalinization. The presence of hypogenic pyrrhotite and the scarce magnetite could indicate that it would be genetically associated with reducing magmas although the lack of ilmenite series oxides in the precursor magmatic rocks suggest that the reducing character of the mineralizing magmas was acquired during the magma evolution. δ18O and the Pb isotopic composition of the mineralizing magma confirm continental crust assimilation processes in its genesis whereas whole rock geochemistry suggests the involvement of marine sediment which would support the change in the redox conditionsof the magma precursor of the porphyry-type mineralization.