DEPÓSITO DE CAULIM DE TIJUCAS DO SUL (MINA FAZENDINHA, TIJUCAS DO SUL - PR)

Abstract

The Tijucas do Sul sedimentary basin, about 45Km south of Curitiba (PR), is the largest deposit of kaolinitic clay from southern Brazil, containing estimated ore resources of 200 Mt. The basin developed on a gneissic and migmatitic basement and is being filled by sediments provided by the weathering and erosion of granites, volcano-sedimentary rocks and basalts. It contains quaternary agglomerates, sands, clays and clayish silts, deposited on fluvial flood plain and, subordinately, lacustrine environments. The intense lixiviation of superficial and shallow sediments by meteoric water acidified by organic matter rich sediments is generating kaolinite and gibbsite, by feldspar desilicification, and gibbsite by kaolinite desilicification. The advanced aluminization of shallow and superficial sediments generated large quantity of gibbsite + kaolinite nodules. Chemical data suggests that this process occurred at least three other times, on periods when the paleo-surface of the sedimentary pile was exposed to weathering for long periods, which caused desilicification and kaolinization also of clay layers presentely buried. Black clays (AP facies) are the only with distinct chemical characteristics, outstanding by their high organic matter and Y contents and their ceramic properties, similar to ball clays. The < 0.04 mm granulometric fraction of sediments contains 45 to 75% kaolinite, 2 to 41% quartz, 1 to 8% gibbsite and 1 to 10% titanium oxides (ilmenite + anatase + "other oxides"). Ti and Fe are incorporated by clay minerals, due to their high grade of crystalline structural disorder, or occur as micro-fragments of minerals brought in from basalt dikes. Kaolinite crystallinity is low to very low and crystals with b axis disordered are the most frequent. These structural characteristics related to the low degree of diagenesis and to the desilicification of kaolinites. MEV-EDS analysis indicated the absence of halloysite and the predominance of detritic, < 0.5 mm, kaolinites over the "book-like" autigenic ones. Octahedrally shaped, high Ti micro crystals, probably anatase, occur mixed with clay minerals.