Mineralização de Au-Cu-(Etr-U) Associada às Brechas Hidrotermais do Depósito de Igarapé Bahia, Província Mineral de Carajás, PA

AUTOR(ES)
DATA DE PUBLICAÇÃO

1999

RESUMO

The Au-Cu Igarapé Bahia deposit, located in the Carajas Mineral Province (Northern Brazil), can be defined as a sequence of metamorphosed volcanosedimentary rocks, with metabasics at the base and metapyroclastics/metasedimentaries at the top of the sequence. The main mineralization occurs between volcanic and metavolcaniclatic rocks, and it is characterized by the presence of magnetitic and sideritic heterolithic breccias. The volcanic sequence underwent an intense hydrothermal alteration which resulted in chloritization throughout the whole sequence, associated with sulphidation, silicification, carbonatization, Fe-metasomatism, tourmalinization and biotitization. Chemical and mineralogical data show an REE, Mo, U, F, Cl and P enrichment of these rocks, specially in the mineralizations neighbourhood. Saline and F-rich fluids at high T may have been responsible for the REE transportation. C and O isotopic data from hydrothermal carbonates suggest the presence of two fluids which promoted alteration and consequent mineralization. A magmatic fluid is characterized by negative values of δ13C (-9,3 to -5,8); moreover, the large variation of δ12O (0,7 to 9,4) suggests a mixture between magmatic fluids of high T (higher isotopic values) and meteoric fluids (lower values). Based on chemical and mineralogical composition, and isotopic data, a genetic model similar to that of Cu-Au-U- REE Olympic Dam deposit (Southern Australia) is suggested to Igarape Bahia deposit. However, some features are quite different for the two deposits such as the age of mineralization. All Fe-oxide(Cu-Au-U- REE) known deposits are of Proterozoic age, while the Igarapé Bahia could be the first described of Archaean age. Moreover, besides the chemical and mineralogical composition of the mineralization are suggestive of granitic sources ivolvement, direct sources were not observed in the deposit region, so that Igarape-Bahia deposit may be related to other granitic intrusions present in that region. In Olympic Dam deposit the mineralization and granitic intrusions are contemporaneous.

ASSUNTO(S)

engenharias mineralização carajás brechas hidrotermais igarapé

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