Geologia e paragênese mineral das mineralizações no granito Santo Ferreira, Sudeste de Caçapava do Sul – RS

Abstract

The cooper province of Caçapava do Sul is located in the central portion of the Rio Grande Sul. It comprises deposits, prospects and monoelemental or polymetallic occurrences of Cu, Pb and Zn hosted by cryogrenic rocks of the metamorphic basement and by volcanosedimentary rocks ediacaranas of the Camaquã Basin. The study area is located in the central portion of this province, 20 km southeast of the urban area of Caçapava do Sul. At the site, Fe and Cu occurrences were briefly described in the literature being linked to the Santo Ferreira Granite, a spatial and geologically intrusion associated to the Caçapava Granite. Aiming to provide new data in the bibliography and discuss the geological nature of these regions, we employed geological and structural mapping in a scale 1:25,000 focused on outcrops of rocks bearing mineralization, petrography studies using optical microscopy and mineral chemistry using scanning electron microscopy. As results of the geological mapping was identified the following units: i) Passo Feio Formation; ii) Passo Feio Carbonatite; iii) Santo Ferreira Granite; iv) Camaquã Basin, which are represented by the Estancia Santa Fé formations, the Santa Bárbara Group and Guarda Velha, the Guaritas Group and, v) two basic dikes and an intermediate dyke, linked respectively to the Serra Geral and Rodeio Velho magmatism. 13 mineralized outcrops were identified. Of this total, 7 were more interested for this study. No primary copper sulphide was identified. The gangue mineral assembly is composed of hematite, pyrite, quartz and sometimes malachite. Caulinite and ilite are the clay minerals that accompany the hydrothermal alteration. The mineralization presents a strong structural and geological control, occurring predominantly in the brittle structures of the Santo Ferreira Granite, whose directions varies between N20°-70°W, plunging on average 65° to NE. The data obtained in this work, mainly the identification of conglomerates based on the Guaritas Group showing the contribution of fragments from the studied ore and its host rocks, the Santo Ferreira Granite, allied with the data from the bibliography on the regional metalogenesis of the cooper province of Caçapava do Sul, suggest that the hydrothermal event recorded in the study area occured at the Ediacaran age and is related to the intrusions of the Caçapava and Santo Ferreira granites.