Ocorrência de Pb-Zn-Cd (Ag) em Cabeceiras do Lajeado, Rio Grande do Sul - Brasil

Abstract

A new Pb-Zn-Cd (Ag) occurrence, named Cabeceiras do Lajeado, was recently discovered by CPRM-Geological Survey of Brazil in the juvenile São Gabriel terrane, Sul-Rio-Grandense Shield, following airborne magnetic and radiometric anomalies. The mineralization is composed of sphalerite, galena and pyrite as the main sulfide phases and is hosted by hornblende gneiss with medium- to fine-grained hornblende needles, with grain size less than 5 mm. The hornblende gneiss shows mineralogical banding composed of quartz, amphibole and sulfides, and of amphibole, quartz, feldspars and/or very fine-grained cordierite. Euhedral to globular pink garnet and chloritized biotite are also present. Pb and Zn (>10,000 ppm), Se (>100 ppm) and Cd (>2,000 ppm) contents exceeded the detection limits of the ICP-MS technique, whereas Ag grades 60.5 ppm.