EM - Escola de Minas
URI permanente desta comunidadehttp://www.hml.repositorio.ufop.br/handle/123456789/6
Notícias
A Escola de Minas de Ouro Preto foi fundada pelo cientista Claude Henri Gorceix e inaugurada em 12 de outubro de 1876.
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3 resultados
Resultados da Pesquisa
Item The role of biological agents in the microstructural and mineralogical transformations in aluminium lateritic deposit in Central Brazil.(2014) Oliveira, Fábio Soares de; Varajão, Angélica Fortes Drummond Chicarino; Varajão, César Augusto Chicarino; Schaefer, Carlos Ernesto Gonçalves Reynaud; Boulangé, BrunoPetrological studies using X-ray diffraction (XRD) and micromorphological analyses (Optical Microscopy and SEM), were done to understand the role of biological activity in the evolution of Barro Alto bauxite. The results indicated that this influence came through structural (or microstructural) and mineralogical transformations, namely: I — the bioturbation caused by termites and II — themechanical degradation and geochemical transformation promoted by roots. In the bioturbation caused by termiteswere formed: I — a intergrainmicro-aggregate structure, characterised by gibbsite crystals from isalteritic bauxite fragmentation on the bottom of the profile and II — a granular structure characterised by a termitic microaggregates with fragments of gibbsite immersed in a kaolinite–gibbsite–goethite–boehmite micromass, formed by bioturbation of the degradation clay with nodules of gibbsite,whose origin is the geochemistry degradation of isalteritic bauxite. The processes associatedwith geochemical andmechanical degradation caused by roots were responsible for the genesis of: I—a porphyric texture with bauxite fragments surrounded by nonaggregate material and II — fine monic structure where the gibbsite neoformation has the mould cavities left by old roots, generating riziform features.Item Mineralogical, micromorphological and geochemical evolution of the facies from the bauxite deposit of Barro Alto, Central Brazil.(2013) Oliveira, Fábio Soares de; Varajão, Angélica Fortes Drummond Chicarino; Varajão, César Augusto Chicarino; Boulangé, Bruno; Soares, Caroline Cibele VieiraThe hydrolytic alteration of anorthosite fromthe Barro Alto StratiformMafic–Ultramafic Complex (Central Brazil) caused the formation of an isalteritic bauxite. Petrological studies using X-ray diffraction (XRD),X-ray fluorescence (XRF), mass balance calculation and micromorphological description via optical microscopy were undertaken to understand the evolution of the bauxitic massif. The results suggest the transformation of the isalteritic bauxite (F1) into varied alteration facies and their filiations as follows: the formation of semi-compact massive bauxite (F2) and compact massive bauxite (F3) by the recrystallisation of gibbsite filing voids, resulting in enriched absolute aluminium (9 and 25%, respectively); the formation of laminar bauxite (F4) and fragmentary bauxite (F5), which is associated with different types of fragmented massive duricrust, such as those formed by mechanical (root activity, tectonics, etc.) and geochemical (dissolution of gibbsite, kaolinite neoformation, etc.) processes; the formation of palaeopediment bauxite (F6); the formation of degraded clay with gibbsitic nodules (F7), which is associated with the resilicification process by the oscillation of the water table caused by changes in the shapes of slopes and the cycling of silica by vegetation. Isalteritic clay (F8) facies directly derived fromthe anorthosite are also found. The relationship between the facies reflects the polygenetic evolution of the bauxitic massif.Item Bauxitisation of anorthosites from Central Brazil.(2011) Oliveira, Fábio Soares de; Varajão, Angélica Fortes Drummond Chicarino; Varajão, César Augusto Chicarino; Boulangé, Bruno; Gomes, Newton SouzaPetrological studies using X-ray diffraction (XRD), X-ray fluorescence (XRF), optical microscopy, scanning electron microscopy (SEM-EDS) and electron microprobe analyzer (WDS) showed the mineralogical, micromorphological and geochemical transformations due to the bauxitisation of anorthosite from the Barro Alto Stratiform Mafic–Ultramafic Complex (Central Brazil). The hydrolytic alteration of the anorthosite occurred in two different stages in accordance with the order of stability of the minerals to the weathering: firstly the bytownite and secondly the ferromagnesian minerals. The weathering solutions, benefited from the existing network of fractures, percolated the weakness zones of the minerals characterising the microsystem of contact in which cores of plagioclase and ferromagnesian minerals were formed. In the first stage, the plagioclases are altered directly to gibbsite, and at an early stage, during the change process, the gibbsite crystals surround the primary ferromagnesian minerals that are totally or partially preserved. The transformation is isalteritic and is responsible for formation of porous alteromorphs consisting of septa of coarse gibbsite and fine gibbsite. As the weathering process advances, the ferromagnesian minerals directly enter to goethite. The boxworks of gibbsite and goethite characterise a primary plasmic microsystem.