DEGEO - Departamento de Geologia
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/8
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Item Depósitos de alexandrita de Malacacheta, Minas Gerais.(2000) Basílio, Márcio Silva; Soares, Antônio Carlos Pedrosa; Evangelista, Hanna JordtSince 1975, alexandrite [Be(Al2-xCrx)2O4], the chromium-bearing crysoberyl variety, has been exploited from alluvial and paleo-alluvial deposits in the Malacacheta region. The alluvial deposits consist of resedimented gravel along the present drainage streams. The paleo-alluvial deposits are richer in alexandrite, and show well-developed soil horizons covering the alexandrite-bearing gravel layer. Alexandrite grains show angular shapes with very sharp edges, suggesting transport for short distances. The country rocks are quartz-mica schist and peraluminous mica schist (Salinas Formation), covered by alternating mica schist and quartzite layers (Capelinha Formation). Both formations are of Neoproterozoic age. They host tectonic slabs of metaultramafic rocks, and are cut by intrusive granites of Cambrian age. No alexandrite-bearing rock has been found in the area, probably due to the intense tropical weathering. However, some of the mapped rocks are sources for Be (granites), Cr (metaultramafics) and Al (peraluminous schists), the essential elements for alexandrite crystallization. We suggest a metasomatic system of Cambrian age for alexandrite genesis in the area, involving the interaction of granite-related Be-rich fluids with metaultramafic rocks and peraluminous schists.Item Adsorção competitiva de As, Cu, Pb e Cr na avaliação da capacidade de fixação de metais por efluentes de mineradoras de ferro.(2005) Basílio, Márcio Silva; Friese, Kurt; Lena, Jorge Carvalho de; Nalini Júnior, Hermínio Arias; Roeser, Hubert Mathias PeterTwo samples of residues from iron mining plants have been investigated for their retention capacity of As, Cu, Cr, and Pb. The sample with the higher content of iron oxides showed the highest capacity to retain metals. The adsorption affinity series changes from Pb>Cu>Cr≈As to As>Pb>Cu>Cr or As>Cu>Cr>Pb, depending on the material and the concentration of the initial solution. In the competitive environment, the Pb adsorption decreases and the As, Cu and Cr adsorption increases. Sequential extraction procedures, carried out after adsorption batch experiments, showed that the most important adsorption process occurs in the oxide fraction and that the major part of the absorbed metal is remobilized from exchangeable and oxide fractions.