Caracterização Petrográfica e Geológica das Ocorrências de Cu-Au Bom Retiro, São Gabriel - RS

Abstract

The region of Palma, São Gabriel - RS, is marked by a wide history of research in mineral exploration since the middle of the eighteenth century, more specifically in the Bom Retiro mine that is currently deactivated, in which occurrences of Cu-Au. However, until the present work, it had not been described in the literature with metalogenetic bias, being, therefore, it became important to characterize it petrographically. With the accomplishment of detailed geological mapping together with a detailed petrographic description, in which garnet and pyroxene minerals and texture characteristic of escarnites were identified, it was possible to define it as a calcium escarnitic, mineralized in a retrograde hydrothermal process, and still having the possibility of being an overprint for a lower temperature mineralogy of a potassium alteration (common in Cu-porphyry systems). It was possible not only to identify it, but also to establish a relationship between the occurrence and a sketch mapped to the southwest. As Bom Retiro is a skarn rich in andradite with an abundance of pyroxenes and Skarn in the southwest rich in glossularia with absence of pyroxenes, it marks not only a compositional mineralogical zonation, but also, differences as to the position of the geothermal source that generated them, being possible to draw a vector of geothermal gradient that increases towards Skarn to the southwest, suggesting that it is closer to the intrusive body. The zonation observed in the present study, along with the characteristics of the mineralization is similar to that of the mining district of Cadia (AUS), in which there is an alkaline Cu-porphyry deposit with a series of Skarns in its surroundings, showing that the occurrence Bom Retiro has great potency for alkaline porphyry.