Fluid inclusion record of the hypozonal orogenic Renco gold deposit (Zimbabwe) during the retrograde P-T evolution
The hypozonal Renco gold deposit in Zimbabwe is hosted by a shear zone system cutting granulite-facies enderbites. The geologic history of the region testifies to a polyphase tectonometamorphic evolution. Along the exhumation path, three major events are notable during which fluid inclusions could have been formed. Detailed petrographic work and comparison of calculated isochores with the P-T evolution, allows correlation of inclusion formation with the tectonometamorphic evolution. Fluid inclusions in the mineralized lithologies of the Renco gold mine are dominated by carbonic inclusions of highly variable densities. The high density carbonic inclusions are related to the peak of metamorphism. Their lower density counterparts show a bimodal occurrence. Some are re-equilibrated equivalents of the inclusions trapped at peak metamorphic conditions whereas others clearly post-date this event and are related to gold mineralization. The latter type of carbonic inclusions occurs in distinct microstructural domains of quartz crystals (i.e. subgrain-, grain boundaries). Therefore, these inclusions are interpreted to have formed because of selective trapping of CO2 from a mixed H2O-CO2 low salinity ore fluid. All the aqueous inclusions observed at Renco can be attributed to a late, retrograde greenschist-facies overprint.