COMPOSIÇÃO QUÍMICA DE BERILOS PEGMATÍTICOS DO BRASIL E SEU SIGNIFICADO PETROLÓGICO E METALOGENÉTICO

J. M. CORREIA NEVES, R. L. B. B. MONTEIRO, C. V. DUTRA

Resumo


This paper deals with the chemical composition of 14 pegmatitic Brazilian beryls and its petrologic and metallogenetic significance. The studied beryls, all collected in pegmatites belonging to the Brazilian Eastern Pegmatíte Province, have been fully analysed, not only for the main elements, but also for Fe, Mg, Ti, Li, K, Na, Cs, Ca, P, Rb, Ba, Zr, Sr, Sc and Zn. Chemical analyses were interpreted using cell parameters and specific gravity values, obtained on the studied samples themselves. Infrared diagrams revealed H20, C02 and CH4 occluded in channels of the beryl structure and/or present in fluíd inclusions of the same mineral. The petrologic and metallogenetic implications of the chemical composition, mainly the variation in the alkali contents, of the studied beryls are discussed and interpreted. Above critical levels, the alkali contents can be used to disclose the potentiality of the pegmatites to become ore bodíes for Li, Cs and Ta. Although the most of the studied beryls reveal little differentiated pegmatites, the regional understanding of the actual metallogenetic potentialities of the pegmatites in the state of Minas Gerais, requires a more detailed and geological oriented sampling, not only of their beryls but also of their other minera1s such as feldspars and micas.

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