ÓXIDOS DE FE E TI DO DEPÓSITO DE COBRE DE SURUBIM, VALE DO CURAÇÁ, BA

ROSA MARIA DA SILVEIRA BELLO, JOSE VICENTE VALARELLI, JOHILDO S. FIGUEIREDO BARBOSA, RAINER SCHULTZ GUTTLER

Resumo


The Surubim copper deposit belongs to the Curaca River Valley Copper Province, Bahia, characterized by high-grade precambrian terranes. The mineralization is present as disseminated copper and iron sulfides in granulitic bodies with mafic-ultramafic compositions, enclosed in gneisses of several kinds. Lenses of calc-silicate rocks and iron-formations, besides garnet-rich or graphitic horizons, occur associated with these rocks. The iron-titanium oxides, frequent in mineralized and country rocks, are associated with sulfides and certain silicates. Mineralogical, textural and paragenetic aspects of these minerals, and the application of geothermometry/oxygen barometry methos in coexisting magnetite-ilmenite reflect the complexity of the post- granulitic subsolidus cooling history. The data suggest that these reequilibrations ceased at quite low temperatures, and reached oxygen fugacities close to the HM buffer curve. The T and ƒO2 conditions in the peak of the granulitic metamorphism were obtained from geothermobarometric methods, with the original oxide composition estimated. Depending on the method used to recalculate the original composition of the i1 menites, the following T and ƒO2 ranges were determined: T = 617 to 780°C/logƒO2 = -17,68 to - 13,37 and T = 675 to 780°C/logƒO2 = -15,24 to - 13,37. In a T x logƒO2 diagram these values are located close to or slightly above the QMF buffer curve. These results define the peak of the granulitic metamorphism, with average temperatures similar to those obtained by other geothermometric methods.


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