P-T-X conditions on the genesis of orogenic Au (As, Bi, Ag) deposit in metasedimentary rocks of the Buracao Area, Arai Group, Brasilia Fold Belt, Brazil

摘要

The orogenic Au (As, Bi, Ag) mineralization (up to 31 g/t) of the Buracao area is hosted in the metasedimentary Paleo-Mesoproterozoic Trairas Formation, Aral Group, Brasilia Fold Belt, Brazil. In order to discuss the P-T-X conditions that generated this mineralization, we present mineralogical, geochemical and fluid inclusion data of veins, gold and wall rocks. Coupled with previous structural data these additional data allow us to link metamorphism and deformation with fluid migration and ore genesis. The integration of fluid inclusion micro thermometry with mineral geothermobarometers and structures show that rocks of the study area evolved from: (i) syn-D-1a metamorphic peak (400-560 degrees C, 6 kbar), through to the (ii) development of syn-D-1b type I barren veins from low salinity H2O-NaCl fluids during syn- to late-metamorphic peak; and to the (iii) development of syn-D-2a type II veins with the pyritic ore precipitation from low to high salinity H2O-CO2-CH4-NaCl +/- HCO3 fluids during post-metamorphic peak (345-285 degrees C, 2.7-1.6 kbar).