FRACTIONATION OF CHEMICAL ELEMENTS FROM THE ALLUVIAL TERRACES AND CUTBANKS OF THE GUALAXO DO NORTE BASIN, EASTERN-SOUTHEASTERN OF THE QUADRILÁTERO FERRÍFERO, MG, BRAZIL

Resumo

The present study aimed to determine, via sequential extraction (method adapted from the Community Bureau of Reference), the different ways in which the elements Fe, As, Pb, Mn, Ba, Zn and Ni are associated with sediments of the alluvial terraces and cutbank from river Gualaxo do Norte Basin (east-southeast of the Quadrilátero Ferrífero, Minas Gerais, Brazil). In order to complement data obtained by sequential extraction, were included sedimentological description and interpretation of facies, as well as mineralogical and grain-size analysis of samples collected in each profile. The results show high concentrations of the elements Pb, As, Fe, Mn and Ba in soil samples. However, only a small percentage of these features are readily bioavailable by being associated with the exchangeable fraction. Special attention should be given to the elements Ba and Ni, which can be mobilized in case of reduction of pH, when the release of acid drainage from tailings from mining activities. Regarding the toxic elements As and Pb, these show up predominantly associated with the residual fraction (suggesting a geogenic source), although the analysis of stratigraphic profiles reveal that large concentrations of these elements appear to be associated with anthropogenic activities such as gold mining in the region studied. In these cases, stimulates the development or adaptation of extracting a specific protocol, considering the characteristics of samples (rich in iron, poor in organic matter, with or without the presence of sulfides).