Geoquímica das Águas e dos Sedimentos da Bacia do Rio Gualaxo do Norte, Leste-Sudeste do Quadrilátero Ferrífero (MG): Estudo de uma Área Afetada por Atividades de Extração Mineral

AUTOR(ES)
DATA DE PUBLICAÇÃO

2001

RESUMO

The aim of the present geochemical study was to understand the physical-chemical behavior of water and sediments affected by anthropogenic interferences during almost three centuries of mining. Several analytical techniques were used which, together with geological and socio-economic information of the area, permitted to obtain a picture of the environmental geochemistry of the investigation site. The Gualaxo do Norte River, localizeted en the east-southeast of the Quadrilátero Ferrífero, receives the effluents of Timbopeba, Capanema, Samarco and Samitri iron mines and of predatory gold exploration activities (garimpo). Several samples were analyzed: water and sediments inside the Timbopaba mine; effluents of the iron mines and; water and sediments in the main course of Gualaxo do Norte river, from the springs to the low course. The Gualaxo river drains geological sequences which are associated with the occurrence of metallic minerals. Geochemical characterization of the Gualaxo river basin was done by the results obtained for water quality parameters ( T, pH, Eh, electric conductivity, turbidity, total dissolved solids, salinity), for cations ( Ca2+, Mg2+, K+, Na+) and main anions ( HCO3-, Cl-, SO42- ) and by the determination of Fe, Mn, Al and trace metal in bottom sediments and water. The Gualaxo do Norte river was classified as sodium-bicarbonate water. The effluents of the iron mining are the main sources of the HCO3-, SO42- and Na+ anomalies derived from the ore processing. These ions were responsible for anomalous values of electric conductivity, total dissolved solids and salinity of the water. The decreases in the parameter values and in the element concentrations from the mine to the low course of the Galax river is in accordance with this assumption. Seasonal variations of the measured values were only observed for the effluents of the Timbopeba complex. The background values of Fe, Mn and Al are above the limits established by the Brazilian legislation. Elevated concentration of Fe and Mn in the water and sediments derived from the lithogenic sources, garimpo activities and secondary process enrichment (laterites). With the means of x ray diffraction analyses quartz, goethite, hematite, kaolinite and muscovite were indentified as the main mineralogical constituents of the sediments. Correlation diagrams of the elements analyzed indicated that the Antonio Pereira garimpo, which explore gold in sediments and rocks near the spring of the gualaxo do Norte river, is the main anthropogenic source of toxics elements ( As, Sib, Ba and Hg) in the sediments of the river. These elements were associated with Ca and Mg and were liberated and mobilized to the aquatic system by the garimpo activity. The concentration of these metals exceeded the limits established by the legislation and also the local background. Cr, Ni and Mo anomalies were found in the sediments of a gualaxo river tributary (Natividade river). They seem to be related to the rocks composition. Cr concentration was 149 times above the legislation limit. Anomalies of Cu, Pb and Zn, identified in the district of Bento Rodrigues, were probably attributed to the Archean auriferous deposits of the region. The association of Mn with trace metals (As, Ba, Sb, Hg, Ni, Pb, Cu and Co) in sediments indicated a common lithogenic source and the probable presence a scavenging process associated with Mn oxides. The bioavailability and the toxical potential of Fe, Mn and other trace metal depend on their chemical speciation. pH-Eh diagrams permitted to characterize the main chemical species of Fe, Mn, As, Cd and Cr which were presents en the water and sediments of the Gualaxo do Norte river.

ASSUNTO(S)

geoquímica das Águas quadrilátero ferrífero extração mineral engenharias bacia do rio gualaxo do norte

ACESSO AO ARTIGO

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