Adivane Terezinha Costa

Análise estratigráfica e distribuição do arsênio em depósitos sedimentares quaternários da porção sudeste do Quadrilátero Ferrífero, bacia do Ribeirão do Carmo, MG

The Quadrilatero Ferrifero region, in the State of Minas Gerais, became internationally known due to the exploitation of gold in the eighteenth century. In this paper, we will present background values for arsenic in alluvial sediments from areas that were heavily affected by the exploitation of gold in the past, in the Carmo River Basin. The analyses of the facies succession of the alluvial profiles were carried out in the sedimentary deposits of flood plains, cutbank and alluvial terraces; this being the foundation for obtaining the arsenic background in the facies of the channel and flood plains. From the knowledge of the background obtained by the statistical method, and based on the construction of cumulative frequency curves on a linear scale, geochemical maps were generated in the SIG system. The acquisition of the background values and the geochemical map for arsenic in the Carmo River Basin, representing areas with anomalous concentrations of this element, are essential for the diagnosis and environmental planning of a mining district potentially contaminated by arsenic.

Evaluation of the mineral exploration influence on sediment composition in the Gualaxo do Norte River Basin (MG-Brazil) based on geochemical and stratigraphic data

The aim of this study was to investigate the influence of mining on the geochemical composition of the alluvial sediments of the Gualaxo do Norte River Basin, located in the eastern-southeastern portion of the Quadrilátero Ferrífero (Minas Gerais State, Brazil). The analysis of the sedimentological succession was carried out using 16 stratigraphic sections (cutbanks and alluvial terraces) and analysis of 111 sediment samples for major- and trace-elements by ICP-OES. The stratigraphic analysis revealed the deposition history of the collected sediments. Anomalous concentrations of certain elements such as As and Pb were found, which are associated with stratigraphic facies with evidences of gold artisanal mining, and Fe anomalies associated with iron ore mining. The classification of the sections was possible by means of principal component analysis. From the sediment characteristics, three groups were identified: (1) those influenced by iron ore mining and gold artisanal mining; (2) those influenced by iron ore mining and (3) those with no influence of human activities.

BACKGROUND VALUES FOR CHEMICAL ELEMENTS IN SEDIMENTS OF THE GUALAXO DO NORTE RIVER BASIN, MG, BRAZIL

The aim of this study was to establish local background values for Fe, As, Pb, Mn, Ba, Zn and Ni using sediments from cutbanks and alluvial terraces of the Gualaxo do Norte River basin, Minas Gerais State, Brazil. A total of 16 stratigraphic sections were surveyed along the basin and 120 samples were analyzed. To establish background values we took into account mineralogical and grain-size analyses, faciologic interpretations, geochemical evaluations (by means of aqua regia partial digestion and ICP-OES readings), and the application of statistical techniques (boxplot representations, iterative 2σ technique, cumulative frequency curve and calculated distribution function). The results reveal relatively high background values for As, Pb, Mn, Ba, Zn and Ni (respectively 64.2; 43.8; 1636.0; 141.4; 65.3 and 39.0 mg.kg-1). The concentrations of these elements are possibly related to the local geology, being the concentrations higher than these values linked to mining activity in the study region, in special gold mining. On the other hand, the background values established for Fe is lower than the values identified in the majority of the sections analyzed. The background value established for Fe corresponds to a concentration of 8.2%. However, concentrations higher than 48% were identified in the study area. There is a strong evidence of Fe enrichment due to mining at the head of the basin. In conclusion, we can say that the proposed values are important parameters for local environmental/territorial management and may help alerting public managers of the necessity of remediation of certain sites, where anomalous toxic element concentrations are identified.

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

O presente estudo objetivou determinar, via extracao sequencial (metodo adaptado a partir do Bureau de Referencia de Romunidade), as diferentes maneiras em que os elementos Fe, As, Pb, Mn, Ba, Zn e Ni sao associados com sedimentos dos terracos aluviais e da bacia do Rio Gualaxo Norte (leste-sudeste da Quadrilatero Ferrifero, Minas Gerais, Brasil). A fim de complementar os dados obtidos por extracao sequencial, foram incluidas descricao sedimentologica e interpretacao de facies, bem como, analise mineralogica e granulometria de amostras coletadas em cada perfil. Os resultados mostram altas concentracoes dos elementos Pb, As, Fe, Mn e Ba em amostras de solo. No entanto, apenas uma pequena percentagem desses recursos sao prontamente biodisponiveis por estar associado com a fracao trocavel. Atencao especial deve ser dada aos elementos Ba e Ni, que podem ser mobilizados em caso de reducao do pH, quando a liberacao de drenagem acida de rejeitos das atividades de mineracao. Sobre os elementos toxicos As e Pb, estes aparecem predominantemente associados com a fracao residual (sugerindo uma origem geogenic), embora a analise dos perfis estratigraficos revelam que grandes concentracoes desses elementos aparecem para ser associadas com atividades antropogenicas, tais como a mineracao de ouro na regiao estudada. Nesses casos, estimula o desenvolvimento ou adaptacao de extrair um protocolo especifico, considerando as caracteristicas de amostras (ricos em ferro, pobre em materia orgânica, com ou sem a presenca de sulfetos).

Evaluation of sediment contamination by trace elements and the zooplankton community analysis in area affected by gold exploration in Southeast (SE) of the Iron Quadrangle, Alto Rio Doce, (MG) Brazil

AIM: The aim was to verify the geochemical composition of sediments samples (riverbed and bank) and the relationship of the following elements: Al, As, Cd. Cr, Cu, Fe, Mn, Ni and Zn with the zooplankton community. METHODS: Bank and riverbed sediments were collected in four sampling points along the studied area, in June/2010 (dry season) and March/2011 (rainy season). Three types of analysis were performed: granulometric, mineralogical (by X-Ray diffractometer) and geochemical (by ICPOES), where for the last two types, only a fraction of silt/clay (<0.062 mm) was used, and the results were compared with the following reference values: Local Reference Value (Costa et al., 2010), Quality Reference Values (Sao Paulo, 2005), PEC and TEC values (MacDonald et al., 2000). For identification of the zooplankton community, riverbed and bank samples were collected in polyethylene bottles, suspended with deionized water (bank sample only), stained with Rose Bengal and preserved in formalin at 4%. RESULTS: As concentrations at Col sampled point were 18 times greater than the Local Reference Value (3.84 mg.kg-1). Cd concentrations were greater than the values established by the QRV (<0.5 mg.kg-1) and PEC (4.98 mg.kg-1) in almost all the sampled points, regarding seasonality. The following zooplanktonic species were identified: Arcella costata (Ehrenberg, 1847), Arcella discoides (Ehrenberg, 1843), Arcella vulgaris (Ehrenberg, 1830), Centropyxis aculeata (Ehrenberg, 1838), Centropyxis ecornis (Ehrenberg, 1841), Difflugia sp., Difflugia acuminata (Ehrenberg, 1838), Euglypha laevis (Perty, 1849), Trynema enchelys (Ehrenberg, 1938), Asplanchna priodonta (Gosse, 1850), and Bedelloida, with, approximately 81% belonging to the Protozoa group. CONCLUSIONS: The studied area, with the exception of the Tripui point, was found to be impacted by historical gold exploration in the region, as well as by the growing urbanization. Within the elements considered to be the most toxic to the biota, As and Cd violated all their reference values. In spite of high concentrations of major and trace elements encountered at downstream points, testacea species were identified, suggesting that this group has the capacity to adapt to adverse situations.