GEOLOGIA DA RAIZ DE UM GREENSTONE BELT NA REGIÃO DE FORTALEZA DE MINAS. MINAS GERAIS

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Abstract
The aim of this study is to define the volcano-sedimentary sequence of Morro do Ferro, located in Fortaleza de Minas, as a part of a larger greenstone belt. The volcano-sedimentary sequence, in contact with orthogneisses, migmatites, cataclastic rocks of the sialic "basement" is unconformably overlied by the phíllytes and marbles of the Araxa Group. The basal unit of the sequence, Morro do Níquel Unit, is composed of ultramafic flows with spinifex texture intercalated with chemical sediments and aluminous tuffs. Over it is the middle unit called Corrego Salvador, composed of basaltic rocks associated with acid tuffs and chemical sediments. The upper unit, Morro do Ferro, is exclusively constituted of sedimentary rocks, phillytes, marbles, iron formation, and muscovite-chlorite schist and quartz-chlorite schist which may represent reworked volcanic rocks. The volcano-sedimentary belt is intensively tectonized having tight vertical isoclinal N-W folds. There are indications of three fases of deformation. The regional metamorphism is of greenschist facies with choritoid and chlorite-albite-epidote-tremolite parageneses in basic rocks. Potentially the ultramafic flows are the most favorable rocks to have mineralization, Ni-Cu massive sulfides. The aim of this study is to define the volcano-sedimentary sequence of Morro do Ferro, located in Fortaleza de Minas, as a part of a larger greenstone belt. The volcano-sedimentary sequence, in contact with orthogneisses, migmatites, cataclastic rocks of the sialic "basement" is unconformably overlied by the phíllytes and marbles of the Araxa Group. The basal unit of the sequence, Morro do Níquel Unit, is composed of ultramafic flows with spinifex texture intercalated with chemical sediments and aluminous tuffs. Over it is the middle unit called Corrego Salvador, composed of basaltic rocks associated with acid tuffs and chemical sediments. The upper unit, Morro do Ferro, is exclusively constituted of sedimentary rocks, phillytes, marbles, iron formation, and muscovite-chlorite schist and quartz-chlorite schist which may represent reworked volcanic rocks. The volcano-sedimentary belt is intensively tectonized having tight vertical isoclinal N-W folds. There are indications of three fases of deformation. The regional metamorphism is of greenschist facies with choritoid and chlorite-albite-epidote-tremolite parageneses in basic rocks. Potentially the ultramafic flows are the most favorable rocks to have mineralization, Ni-Cu massive sulfides.

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