Mineralogical, micromorphological and geochemical evolution of the facies from the bauxite deposit of Barro Alto, Central Brazil.
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Date
2013
Authors
Oliveira, Fábio Soares de
Varajão, Angélica Fortes Drummond Chicarino
Varajão, César Augusto Chicarino
Boulangé, Bruno
Soares, Caroline Cibele Vieira
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Abstract
The 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.
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Keywords
Bauxite, Mineralogy, Geochemistry, Micromorphology, Alteration facies
Citation
OLIVEIRA, F. S. de et al. Mineralogical, micromorphological and geochemical evolution of the facies from the bauxite deposit of Barro Alto, Central Brazil. Catena, Cremlingen, v. 105, p. 29-39, 2013. Disponível em: <http://www.sciencedirect.com/science/article/pii/S0341816213000167>. Acesso em: 18 set. 2014.