COMPOSIÇÃO QUÍMICA DE CROMITAS EM CORPOS METAMÁFICO/ ULTRAMÁFICOS DA BORDA LESTE DO ESPINHAÇO MERIDIONAL, MINAS GERAIS

Abstract

The study of variation in chemical composition of chromites associated with mafic/ultramafic sequenceshas a growing in importance because presents a close relation to gold and platinum group elementsconcentration. The researched areas : Serro, Alvorada de Minas and Morro do Pilar present chromites(massive, disseminated and accessory), which show a strong zoning due to hydrotermal/metamorphicprocess. These zones reflect changes in chemical composition of crystals, which are related to neoformationof mineral paragenesis based mainly on leaving of the elements in chromites ( for example the origin ofkammererites).In chromitites from Serro and Alvorada de Minas, as well as in accessory chromites from Morro doPilar, the zoning of the grains was observed. They have a core composed by chromites (aluminous chromites)and a broad margin with ferriferous composition (chromium magnetites to magnetites). In same cases thechromite crystals have a core with primary chemical composition preserved. In the Rio Mata Cavalovolcano-sedimentary sequence a Ir-Pt alloy was found as inclusion in chromium-magnetite. In othersmafic/ultramafic complex of Minas Gerais and Ceará States, high relations of PGE and Au has beenrecorded, and they are associated with chromitites submitted to this alteration process.