40Ar/39Ar AGES OF HYDROTHERMAL FLUIDS OF CABAÇAL Au-Zn-Cu DEPOSIT: IMPLICATIONS OF THE CACHOEIRINHA OROGENY ON MINERALIZATION EVENT IN SW AMAZONIAN CRATON

Idades 40Ar/39Ar de fluídos hidrotermais do depósito de Au-Zn-Cu Cabaçal: implicações da Orogenia Cachoeirinha no evento de mineralização no sudoeste do Cráton Amazônico

Abstract

The Cabaçal deposit is located in SW Amazonian Craton, Mato Grosso State, Brazil, with important Au-Zn-Cu mineralization. The ore is hosted by the Alto Jauru orogenic rocks (1.79-1.74 Ga) comprised of felsic volcanic and volcanoclastic rocks and mineralizations occur as bands concordant with the mylonitic foliation, breccias, quartz-carbonate veins and rock-disseminated, and the polymetallic ore comprises chalcopyrite, pyrite, marcasite, pyrrhotite, sphalerite and galena. The mineralization is related to hydrothermal alteration and includes quartz, chlorite, carbonate, sericite and biotite. Six sericite grains from the hydrothermal zones yielded ⁴⁰Ar/³⁹Ar ages from 1521.3 ±  1.3 Ma to 1510.4 ±  1.2 Ga.  These ages are evidence that hydrothermal solutions originated related to the Cachoeirinha orogen (1.58-1.52 Ga) cutting the Alto Jauru orogen (1.79-1.74 Ga) host rocks. Detailed geology and petrography indicate banded iron formation played an important role in the metal deposition as a chemical barrier for the mineralizing fluids.