Open AccessFluorite mineralization related to the dolomitization: an equilibrium study of the Proterozoic stratabound carbonate Macaia-Ijaci Basin, Lavras, Minas Gerais, Brazil
Author(s) -
Fernando Roberto Mendes Pires,
Carmen Lúcia Oliveira Mendes,
Sandra Cecília Miano
Publication year - 2004
Publication title -
anuário do instituto de geociências
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 0.202
H-Index - 12
eISSN - 1982-3908
pISSN - 0101-9759
DOI - 10.11137/2004_0_11-26
Subject(s) - fluorite , calcite , geology , dolomite , dolomitization , carbonate , geochemistry , proterozoic , petrography , metasomatism , carbonate minerals , mineralogy , dolostone , metamorphism , carbonate rock , chemistry , sedimentary rock , geomorphology , paleontology , structural basin , organic chemistry , facies , mantle (geology) , tectonics
Stratabound fluorite occurring as thin films in the concomitantly derived dolomitic portions of the calcitic limestone of the Proterozoic Carandaí Formation in the Macaia-Ijaci Basin was supposedly formed by metasomatic reactions between the carbonate and HF- and Mg2+- rich brines, during metamorphism. Thirteen electron microprobe analyses from the carbonate in a single petrographic thin section, allowed the determination of the temperature of the carbonate formation in the range 180º-230ºC, using the Mg-calcite solvus geothermometer. Five key mineral reactions in the system Mg-Ca-C-H-O-F plotted in diagrams in terms of either, CO2- and HF-fugacities or chemical potentials of CO2 and HF yielding fluorite + dolomite from calcite + Mg2+, are proposed. Apparently the fluorite formation is related with dolomitization. Additional reaction involving fluorite was calculated and inserted in the phase diagram, according to the existence of calcite-fluorite veinlets bordered by dolomite selvages, at the Casa de Pedra quarry.