Geological characterization of "El Abuelo" skarn deposit, Alto Rio Senguerr, Chubut

Abstract

"El Abuelo" skarn deposit is located in southwest Chubut province. It was formed in a magmatic arc tectonic environment, developed in continental crust. The skarn is hosted in low cretaceous silicoclastic sands interbedded with limestones, and it is related to small rhyodacitic sub-volcanic bodies. Anomalous contents of metals (Fe, Cu, Pb, Zn, Ag) provide an interesting exploration guide. This paper is devoted to give a geological and a mineralogical characterization of the skarn, in order to establish the deposit type. Paragenetic mineral assemblage identified, allow to distinguish two stages: a metasomatic and an hydrothermal one, both developed upon the sedimentary rocks (exoskarn). The first one is originated by magmatic fluids, which lead to the formation of calc silicate minerals. During the later phase of the skarn formation, water infiltration produced the skarn retrograding, which is represented by hydrous mineral association, followed by the precipitation of hematite, magnetite and sulphides, associated to silica veins. The calc-silicate assemblages identified, together with the chemical composition of pyroxene and garnet, and the mineralization recognized, permit to classify skarn "El Abuelo" as calcic type, with iron as dominant metal.