Caracterização metalogenetica do deposito cromotiferos de Pedras Pretas, Santa Luz - BA

AUTOR(ES)
DATA DE PUBLICAÇÃO

1998

RESUMO

The chromitiferous mineralization of Pedras Pretas Intrusive Suite, Bahia, Brazil, is host in serpentinites intrusive into meta-sedimentary and meta-igneous rocks comparable to the 2.2-2.0 Ga old Itapicuru River Greenstone Belt. Field relationships and petrographic data indicate that the study area has undergone four major deformation phases with metamorphic grade reaching upper amphibolite facies conditions during the second to the third ductile deformation episodes. The fourth deformation phase was mostly brittle with mineral assemblages typical of greenschist facies metamorphic grade. Petrographic observations combined with mineral chemical data show that the Pedras Pretas chromites can be grouped into two types, viz. disseminated and massive chromites. Whereas the first one had its primary chemistry modified by sub-solidus metamorphic and/or hydrothermal processes, the second has preserved most of its magmatic characteristics, thus rendering comparisons with its Phanerozoic counterparts for which the tectonic settings are relatively well known. As such, the massive-type chromites are Ti-poor, Cr-rich, show Cr/(Cr+AI) >0.6 and fall in the ophiolite field on Cr-AI-Fe and Cr/(Cr+AI)-Mg/(Mg+Fe) tectonic settings discriminating diagrams. Since the Pedras Pretas Intrusive Suite is host in rocks comparable to the Itapicuru River greenstone belt, which contains juvenile back-arc basalts, it is suggested that its origin may be linked to a geologic scenario similar to present-day island arc

ASSUNTO(S)

metalogenia rochas ultrabasicas cromita

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