Sulfur Isotopes in Komatiite-Hosted Ni-Cu Sulfide Deposits from the Morro do Ferro Greenstone Belt, Southeastern Brazil

Abstract

In the Morro do Ferro greenstone belt in southeastern Brazil, Ni-Cu massive sulfides hosted by komatiites occur in the vicinity of the town of Fortaleza de Minas. Sulfur-isotope abundances were analyzed in sulfides from the main orebody in order to determine the source of the sulfur. The main sulfide minerals in the ore are pyrrhotite (65%), pentlandite (30%), and chalcopyrite (5%). The δ 34 S values of the ores fall within a relatively narrow range, but are slightly higher than values for similar occurrences in other greenstone belts. As there does not seem to be evidence of thermal erosion of country rocks and sulfur assimilation, the heavier sulfur possibly is the result of crustal contamination of the ascending komatiite magma and separation of an immiscible sulfide liquid already at this stage.