Gold deposits and occurrences of the Crixas Goldfield, central Brazil

The Crixas Goldfield is a part of the Tocantins province and consists of a similar to2.9 Ga Archean granite-greenstone terrane. The gold field contain s one large deposit (Mina III, 65 tons Au) and several smaller occurrences, which are structurally controlled by regional shear zones that are either thrust or strike-slip faults. The deposits can be classified as auriferous massive sulfide (pyrrhotite + arsenopyrite) hosted ores within sulfidized b anded iron formations, auriferous quartz veins, and disseminated gold ores in carbonaceous schists. On a more local scale, the ore bodies coincide wit h dilation zones surrounded by hydrothermal alteration haloes of various wi dths within carbonaceous schists, iron formations, and metabasalts. Hydroth ermal alteration related to deposits within thrust faults consists of sulfi dization and carbonatization, whereas, within strike-slip faults, propyliti c, potassic, and sericitic alteration zones occur in concentric haloes. In both cases, quartz veins and veinlets may be abundant. Absolute ages of min eralization are uncertain, but structural data suggest multiple events prob ably occurred during Archean,Paleoproterozoic and Neoproterozoic tectonic e vents.