Abstract
Cambuí and Floresta kaolin deposits occur within the rocks of Campo Alegre Formation, a tardi-orogenic basin filled with volcanic acidic rocks, dated as 536±65 Ma, and volcano-sedimentary rocks. All mapped rocks in deposits are argillised, but mapping allowed to identify original volcanic rocks and to distinguish several argillaceous facies. The common features observed in both mapped deposits were: (a) Acidic intrusions are always present; (b) Intrusive rocks are hosted by tuffs and volcanic breccias; (c) Veins and fractures are inside and next to intrusions, forming stockworks filled with white argillaceous materials; (d) Locally argillaceous ores are overburden by massive beds of argillite, greywakes and conglomerates. These sedimentary beds contain buried vegetal organic debris at their basal portions, (e) All rocks of both deposits are covered by beige and black massive soils. The identified argillaceous facies were: (a) white or white-reddish ore (argillised laminated rhyolites and/or dacites); (b) green ore (argillised andesitic tuffs and breccias); (c) white massive sedimentary ore; (d) beige massive soil with vegetal organic residues; (e) micaceous, green fractures related rocks, inside the white ore; (f) white argillaceous material that fills veins in stockworks; and (g) black soils. Cambuí and Floresta kaolin deposits were originated in volcanogenic proximal environments, and they have typical conduct and volcanic cone lithofacies. The mineralogy of the argillised rocks allowed to recognize an evolutionary sequence that starts with the fracture, micaceous, hydrothermal high temperature facies (300°C to 500°C) changing upward and laterally to the stockwork-vein, kaolinic, facies, probably formed at low temperature (10CTC to 300°C). The stockwork facies grades, without apparent discontinuity, to the supergenic, low temperatures (20°C to 50°C) altered rocks. If supergenesis started only after hidrothermal rocks have been exhumed, a compositional but not a temporal gradding exists.
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