CONICET | Buscador de Institutos y Recursos Humanos

San Roque (40°45´54"S; 65°48´07"W) is a mining project located in the eastern sector of Northpatagonian Massif, Río Negro province, Patagonia, Argentina. In this project the polymetallic mineralization has epithermal characteristics and is hosted in the jurassic volcanites, volcanoclastites and sedimentary rocks of the Marifil Volcanic Complex. It was defined as a low to intermediate sulfidation epithermal system in which the ore mineral association mainly consists of native gold, low Fe In-bearing sphalerite, chalcopyrite and galena. This contribution documents the geochemical data and the mineralogical studies carried out in representative samples of two drillholes that intercepted Del Indio Structure in the supergene oxidation zone. This structure represents one of the most explored epithermal manifestations of the project. According to the observations with a scanning electron microscope and semi-quantitative analyses, the main supergene minerals that concentrate In, Cu, Zn, Pb, Ga, Mn, P, As and Cl are attributed to hematite, plumbojarosite, coronadite and mottramite, which are hosted by coarse-grained epiclastic subfacies from the Marifil Volcanic Complex, described in this contribution as polymictic orthobreccia. It is also documented, for the first time, a supergene mineral-association together with base and precious metals, by oxidation of the polymetallic epithermal mineralization in the San Roque project. The veinlets, stockwork and, in a lesser extent, disseminated mineralization style of the hypogene ore, with In-bearing sphalerite and pyrite as the predominant sulfides, combined with the porosity and limited acid-buffering capacity of the host rock, favored the penetration of acidic, and oxidizing relatively V-rich meteoric waters, giving rise the and subsequent oxidation process.

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