CHEMICAL DEPOSITS ASSOCIATED TO METAVOLCANOSEDIMENTARY SEQUENCES OF THE CENTRAL PORTION OF THE SÃO FRANCISCO CRATON IN THE STATE OF BAHIA, BRAZIL: A REVIEW

Abstract

Supracrustal suites of metavolcanosedimentary rocks (SC) occur in the central portion of the São Francisco Craton in the State of Bahia. They were primarily formed by calc-alkaline to perialkaline volcanic flows and tuffs, clastic and chemical sediments. The latter are referred to the banded iron (BIF), iron-manganese (BIMF) and manganese (BMF) formations, iron-poor magnesian-rich carbonate formation (IPMRCF), and minor metacherts. BIF and IPMRCF are present in all the reported SC. BIF is typified by the presence of the oxide, carbonate and silicate facies. Occurrences of the sulfide facies are reported for the Sobradinho-Salitre and the Boquira SC. The burial metamorphism and thermal effects pronounced by the Transamazonian migmatization and granitization are accountable for the generation of amphibolites, epidosites, steatite and talc schists, phyllites, sandstones, quartzites, itabirites, metamorphic limestones to include banded carbonates, marbles and calc-silicate rocks. It is suggested that the deposition was similarly processed throughout an extensive crustal segment and that it was part of the cratonic evolution occurred during the end of the Archean to the beginning of the Proterozoic.