New Cu-Pb occurrence in gossan and hydrothermal breccias in the Nova Brasilândia Group, Rondônia State, Brazil: preliminary results, perspectives and interpretations

Abstract

Copper- and lead-bearing breccia and gossan were found at the outskirts of Rolim de Moura town, southeastern Rondonia State, Brazil, during geological mapping. Gossans and hydrothermal breccias are hosted by the paragneisses of Nova Brasilândia Group, which, at the studied area, is composed of banded iron formation, sillimanite-biotite-muscovite gneiss, metagabbro and metatonalite, deformed and metamorphosed during the Sunsás orogeny. The hydrothermal system consists of strongly oxidized massif sulfide zones (gossans), iron oxide veinlets and stockworks, silicate breccia and quartz veins. Hydrothermal alteration was mapped continuously along a 2.5 km ESE-WNW trend. ICP OES/ICP MS chemical analyses returned values up to 1668 ppm Cu and 46.9 ppm Pb in whole-rock gossan powders. Portable XRF results yielded copper, lead and zinc grades up to 800 ppm Cu, 720 ppm Pb and 150 ppm Zn in whole-rock gossan powders. Programmed petrographic, SEM, XRD and whole- -rock geochemistry studies will help to better characterize the mineralization.