Tipologia das mineralizações e química mineral do depósito de Pb-(Zn) Ranchão, zona interna da Faixa Paraguai, Mato Grosso, Brasil

Abstract

Located about 50 km towards the southeast from Cuiabá city, the Pb-(Zn) Ranchão deposit is hosted by Neoproterozoic meta-diamictites of Cuiabá Group (Coxipó Formation, Mata Mata Member), inner zone of Paraguay Belt. The deeply deformed host rocks underwent greenschist regional metamorphism, as well as contact metamorphism as a result of the intrusion of São Vicente Granite. This work presents the geologic, petrographic, and mineral chemistry characterization of Ranchão deposit lead-zinc ore. The mineralizations are mainly composed of galena, pyrite, and sphalerite, and occur as breccia, veins, and dissemination. The sulfides are associated with silicification in host rocks, which register a pre-ore alteration phases (with quartz sericite and calcite) and a latter post-ore phase (with calcite and chlorite). The more significant concentrations of ore minerals are structured through N60-70W and N80 85W faults, in which the ore, as breccia, is found. Chlorite geothermometry point to temperatures from 120 to 190°C for late hydrothermal fluids. The features indicate a meso to epithermal system, that superimposed hornfels after meta-diamictites. These results represent a perspective for exploration of similar mineralizations in Cuiabá region and other meta-sedimentary folded belts.