Estudo mineralógico e textural dos minerais de manganês do depósito de Bandarra, Jacaraci, Bahia

Rómulo Machado, Evaristo Ribeiro Filho

Resumo


This paper discusses the mineralogy and the mineralogical and textural changes of the Bandarra manganese deposit which is located in the southern part of the State of Bahia. This deposit comprises lenses of manganiferous rocks deposited within the iron formation and associated with the Licinio de Almeida metamorphic complex. The iron formation, with discontinuous manganiferous lenses, belongs to a Precambrian sequence with mica-schists and amphibolites in its basal portion and mica-schists and quartzites at its top. The metamorphism of Bandarra is thought to be of almandine-amphibolite fades. The assemblage of metamorphic minerals in the protore (primary minerals) includes quartz, spessartite, tephroite, alleghanyite, amphibole, mangano-dolomite, magano-micas, jacobsite, hausmannite, bixbyite and hematite. The assemblage of secondary minerals, formed by a supergene process, contains aMnO2 , malachite, cuprite, goethite and lepidocrocite. Both the hematite and hausmannite show two different phases of mineralization. Polished section analyses revealed that hematite and bixbyite are exsolved in jacobsite.

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