Evolution of two similar stratabound fluorite ore deposits in the Ribeira Valley, southern Brazil

Mate Dentro and Sete Barras are two stratabound fluorite ore deposits that show contrasting ore types: a microcrystalline facies predominates at Mate Dentro, while macrocrystalline ore is the most common type at Sete Barras. The Mate Dentro ore results from replacement of marble and collapse breccias, whereas the Sete Barras ore represents recrystallization and/or remobilization of pre-existing ore. Sr and Nd isotopic data suggest a crustal source for the fluorite ore. Fluid inclusion results indicate that the mineralizing fluid at Mate Dentro differed significantly from that at Sete Barras. At each deposit, however, ore types with different textures (macro- and microcrystalline) have similar REE patterns and contain the same type of fluid inclusions, probably due to complete recrystallization and/or remobilization of fluorite by one main fluid type (at each deposit). A complex hydrothermal history from late Proterozoic to Mesozoic is recorded by these two fluorite deposits. Initial fluorite deposition in the Ribeira district occurred in the late Proterozoic, in response to fluid circulation related to granitoids of the Brasiliano cycle (450 Ma to 750 Ma). Copyright (C) 1996 Canadian Institute of Mining, Metallurgy and Petroleum.