Alteração Hidrotermal das Rochas Ultramáficas e Máficas do Greenstone Belt de Goias Velho (GO).

Resumen

Serpentinitos, talc-schists, carbonate and chlorite-tremolite schists of the Goias Velho ``greenstone belt" basal unit, attributed by various authors to ocean-floor hydrothermal alteration, were until now only indirectly observed for gold regional exploration. The research of hydrothermal alteration in ultramafic basal unit rocks showa differentiation trend in komatiites, expressed by its high content of Mg in the base (peridotitic komatíites), evolving to terms of more Aland Ca in the middle and to komatíitic basalts in the upper middle part. Petrographic evidences show abundanı carbonatization during static metamorphism with formation of dolomite in metabasalts and magnesite in metakomatiites. Both were chloritized afterwards during dynamic metamorphism. In the Limeira fault domain, the hydrothermal alteration of metavolcanic middle unit formed abundant aluminosilicates (kyanitites, chloritoidites, kyanite-sericite schists and tourmaline-sericite schists), showing intense metasomatic processes coeval with deformation unknwon till now. Intense carbonated metaultramafic basal unit rocks and hydrothermal middle unit rocks within the Limeira fault, show little anomalies of gold (0.5 and 0.39 ppm, respectively), so both metasomatic processes are expected to develop small gold concentrations.