DEGEO - Departamento de Geologia
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/8
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Item Iron Quadrangle stream sediments, Brazil : geochemical maps and reference values.(2015) Vicq, Raphael de; Matschullat, Jörg; Leite, Mariangela Garcia Praça; Nalini Júnior, Hermínio Arias; Mendonça, Fellipe Pinheiro ChagasGeochemical mapping and the determination of reference values receive increasing attention. The need to know regional geochemical background data as well as the spatial allocation of areas with anomalous geochemical concentrations and chances to identify their major sources motivate the interest. Here, results from a high-density geochemical mapping exercise and derived related reference values are presented; 541 stream sediment samples have been collected across the Iron Quadrangle (IQ), Brazil, with a density of one sample per 13 km2. Geochemical maps were compiled using the inverse distance weighted interpolation method. ‘‘Normal’’ concentrations were distinguished from anomalies with the separation-byconcentration- range technique, where positive anomalies are defined by the ‘‘boxplot’’ Upper Inner Fence (UIF) rule. More than 70 % of the IQ show exclusively geogenic concentration ranges for the elements studied. About 20 % represent positive anomalies, likely related to both near surface rock types and to human interference. Distinct anthropogenic anomalies, notably from mining activities explain 5–10 % of all samples. This first high-density sampling in the IQ allows delineating the role of lithology on the elemental composition of stream sediments, and to establish reference values for the main river basins—thus pinpointing localities, cities and fluvial basins that are exposed to environmental risks and need to be protected.Item Iron ore mining promotes iron enrichment in sediments of the Gualaxo do Norte River basin, Minas Gerais State, Brazil.(2014) Rodrigues, Aline Sueli de Lima; Malafaia, Guilherme; Costa, Adivane Terezinha; Nalini Júnior, Hermínio AriasThe objective of the present study is to assess the influence of iron ore mining on Fe concentrations in fluvial sediments of the Gualaxo do Norte River basin (Minas Gerais State, Brazil). Initially background values were determined for Fe by means of the boxplot representation, the iterative 2r technique and the calculated distribution function, using geochemical data obtained for alluvial terraces. Geochronologic analyses in carbonaceous materials attested for the proposed background values. After that, chemical analyses of active drainage sediments collected along the entire basin were carried out and a geochemical map of the study area was prepared. The mean background value for Fe is relatively high (8.2 wt %), when compared to the Fe concentration in the Earth’s crust (5.6 wt %). Such background value is strongly associated with the geological characteristics of the region. It was observed that most of the high Fe concentrations were detected in active sediments collected in the main river of the basin and not in its tributaries. This suggests that Fe enrichment is not only linked to the local geology but also to possible increase resulting from accidental leakage of iron ore mining tailings from containment dams and lakes upstream. It is suggested that measures that help stop or minimize such impact be adopted. The large capacity of Fe to adsorb and form complexes with toxic metals implicates in environmental hazards that may not be restricted only to the Gualaxo do Norte river basin, but may affect the other basins downstream.