Weathering of carbonatite at Juquiá, State of São Paulo, Brasil

Abstract

Weathering of rocks of the alkaline carbonatitic complex of Juquiá (State of São Paulo, Brasil) resulted in a phosphatic residual ore with average 16% P2O5 The primary rock cantains iron and manganese -rich dolomite and apatite (fluorhydroxiapatite). Magnetite, baryte and ph1ogopite appear as accessories. Up to 50% ofthe carbonatite may be occupied by apatite, which is the main reason for the preservation of primary structures in the weathering mantle and for the high content in P2O5 . The weathering facies are consequent to dissolution of carbonates followed by recycling of primary apatite, with formation of secondary apatite. The mineralogical and chemical compositions of the material, and their morphological relations indicate the following dinamic behavior for the maio chemical elements: - strong depletion of CO3(2-), Mg2+, H4SiO4, SO4(2-) and K+; - recycling on the profile of PO4(3-), Ca2+, Ba2+ and, subordinately, CO3(2-); - retention of Fe3+, Ti4+, Al3+ and Mn4+.