CORREÇÃO DE TEMPERATURAS OBTIDAS PELO MÉTODO DE WOOD & BANNO PARA PARES DE PIROXÊNIOS RICOS EM AI2O3 DE SURUBIM, BA

ROSA MARIA DA SILVEIRA BELLO, JOSE VICENTE VALARELLI, RAINER SCHULTZ-GÜTTLER

Resumo


The copper deposit of Surubim, Curucá Valley, Bahia State, is constituted by Pre-Cambrian rocks of high metamorphic grade. The mineralization occurs as Cu and Fe sulphides lodged in granulites of mafic-ultramafic composition, intercalated in gneisses of several natures. The application of classical geothermometers, with utilize coexisting orto-clinopyroxene pairs in samples from the region, provided temperatures between 809°C and 940°C (Wood & Banno's method) and between 800°C and 1,125°C (Wells' method), which are abnormally high, even for rocks of high metamorphic grade. In the case of Wood & Banno's method, the highest temperatures were those referent to opx-cpx pairs with higher aluminium content an elementx not considered in geothermometer calibration. Considering that the AI203 contents of the pyroxenes from Surubim reflect the composition of the host rocks, and that the samples come from geographically close places, the high values of temperature are possibly due to imprecisions in the method for aluminium-rich systems (for which the method needs correction) and do not implicate in differences in metamorphic conditions. The proposed correction provided temperatures between 700°C and 750°C, with KD close to 2.0 - consistent values to the ones obtained by other geothermometric methods.


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