GEOLOGIA E GÊNESE DOS DEPÓSITOS DE CAULIM FLORESTA E CAMBUÍ (FORMAÇÃO CAMPO ALEGRE - SC) - 1. FACIOLOGIA E MINERALOGIA DAS ROCHAS E MINÉRIOS

Abstract

ABSTRACT GEOLOGY AND GÉNESIS OF THE FLORESTA AND CAMBUÍ KAOLIN DEPOSITS (CAMPO ALEGRE FORMATION - SC) - 2. PETROCHEMISTRYAND GENETIC MODEL The wide compositional band overlap of the Cambuí and Floresta mines argillaceous fácies preveni the use of chemical composition as indicator of their origins. Despite this fact, the main ore types have chemical peculiarities, and the disseminated green ore is andesitic in composition, the disseminated white ore from the Cambuí mine is rhyolitic and the disseminated white ore from Floresta Mine is dacitic. Rock chemical composition also show that besides the low depth ore evolution line represented by the argillaceous fácies related to fractures, stockworks veins and supergenic zones, displayed by mineralogy, with strong K2O content variations, another evolution line exists, developed at higher depths, with constant or very small K2O variations. This high depth hydrothermal alteration changes the rhyolite composition, strongly leaching SiO2 and moderately leaching toO, Na2O, Fe2O3, CaO and MgO. These chemical changes transform rhyolites in argilised rocks with kaolin and mica. The hydrothermalism developed according to these two lines have changed rocks making easy the later action of supergenic alteration and weathering, responsible for chemical changes that develop up today. It is proposed a genetic model in which hydrothermal alteration has developed in a proximal volcanogenic environment. If hydrothermalism attained the surface, supergenic alterations occurred simultaneously with the hydrothermal alterations. On the contrary, weathering started and continues until today, only after the exhumation of the hydrothermalized rocks. At least three other models could explain the génesis of Cambuí and Floresta kaolin deposits: the volcanic porphyry copper model, the volcanogenic high sulfidation model and the "autometassomatic" model.