Geochemistry of gold in Archean granulite facies terrains

Abstract

Gold distribution in Archean--Precambrian granulite facies terrains from Bahia state, Brazil, is investigated by means of flameless A.A. spectroscopy. The average Au content for 105 samples is 1.51 ppb, which is appreciably lower than normal values for intermediate- mafic igneous and sedimentary rocks. Gold distribution is discussed in terms of the possible effects of high-grade metamorphism and the composition of the initial material. Compositional patterns suggest that metamorphism had little influence on primary Au distribution. Alternatively, if Au was mobilized in the fluids generated by dehydration reactions, most of it would have been reprecipitated not far from the starting point. Acidintermediate igneous and non-mature sediments predominate within the initial material of the Archean granulites.