Estudo lito-estrutural das mineralizações auriferas nos arredores de São Gonçalo do Sapucai - Campanha Minas Gerais / A litho-structural study of gold mineralization in the environs of São Gonçalo do Sapucai - Campanha, Minas Gerais

AUTOR(ES)
DATA DE PUBLICAÇÃO

1994

RESUMO

A detailed geological study around São Gonçalo do Sapucaí, Campanha and Monsenhor Paulo in southern Minas Gerais, has shown the area to be underlain by two distinct lithological units; one belonging to the Amparo Group - (X" basement gneisses; and the other to the supracrustals of the Andrelândia Group. The basement gneisses comprise hornblende tonalite gneisses and granitic augen gneisses whereas the supracrustals are paragneisses (biotite gneisses, garnet-biotite gneisses and muscovite-biotite gneisses) with interca1ations of quartzites and subordinated amphibolites, hornblende-biotite gneisses, chlorite-actinolite schists and hornblende schists. Structurally, two main tectonic events have been recognized in the area, each with separated metamorphic and kinematics imprints: 1) the older Dn event was responsible for low angle ductile shear in the amphibolite fades, thus giving rise to the regional Sn foliation; 2) the younger Dn+ 1 event caused transcurrent tectonics at a slightly lower metamorphic grade and was accompanied by a greater fluid flow. The effects of these fluids were more intense along the Três Corações Shear Zone. Disseminated primary gold mineralization, occurs at the prospects Andaime, Xicão, Irmão and Barro Alto, and is hosted by finely banded biotite gneisses and muscovite-biotite gneisses of the supracrustals. The mineralized zones are narrow, discontinuos and contain disseminated pyrite along the Sn foliation. Althougb it was not possible to determine where the gold occurs, due to its fine grain size, it is very likely that it is associated with pyrite either disseminated or in its crystal structure or dispersed in the matrix. Petrofabric analysis of the host rocks indicate that the minera1ized zones are related to the Dn event during which the rocks underwent amphibolite fades metamorphism and local partial fusion. Selected chemical analysis of rocks from mineralized and barren zones at the prospects reveal that chemical elements remained immobile during the process leading to gold concentration. Considering the tectonic and metamorphic effects of the Dn event, it can not be roled out that partial fusion and accompanying higb grade hydrothermal fluids were responsible for gold mineralization. This process was augmented by ductile shear deformation and lack of brittle shear regimes, thus enabling the mineralizing fluids to be located within planar and linear discontinuities with rheological contrasts, such as specific foliation planes or even fold hinges related to the ductile shear

ASSUNTO(S)

geoquimica ouro - minas e mineração - minas gerais sul petrologia - minas gerais sul sul mapeamento geologico - minas gerais

ACESSO AO ARTIGO

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