Geology and hydrothermal alteration in the Organullo district (Au–Cu–Bi): Evidence of overlapping hydrothermal systems, Argentinian Puna

Abstract

The Organullo District is located in the NE of the Argentinian Puna, Salta province. The mineralization is associated with Miocene andesitic to dacitic subvolcanic domes. In this work, we described the geology of the area, characterizing the host rocks of the hydrothermal alteration and the mineralization of the District. We defined that the mineralized system corresponds to veins and stockworks of quartz veinlets with sulphides hosted in the Puncoviscana, Parcha/Agua de Castilla, Organullo Ignimbrite, and Rumibola formations. Based on illite ages, the oldest event (109.5 ± 2.2 Ma and 137.2 ± 2.7 Ma) correspond to a thermic episode, occurred during the cretaceous rifting. We also defined two Neogene hydrothermal events. The first illite age (middle Miocene, 14.6 ± 0.2 Ma) corresponds to an incipient porphyry system characterized by phyllic alteration with three types of veinlets composed of: quartz-pyrite-chalcopyrite, molybdenite (type B); quartz-pyrite-chalcopyrite, with or without bornite (type D) and green sericite-chlorite-pyrite-bornite (type C). The second and youngest age (early Miocene/Pliocene, 5.33 ± 0.3 Ma) corresponds to a high sulphidation epithermal system characterized by advanced argillic alteration with enargite-famatinite-gold. These two overlapping mineralized systems, enhance the prospective importance in the region.