The Biards Sb-Au bearing Variscan shear zone, French Massif Central

摘要

Results from new structural, mineralogical, microthermometric and isotopic data has been obtained on the Biards Sb-Au bearing shear zone, located in the South-Limousin (French Massif Central) close to the St-Yrieix gold district. Geophysical recent data, coeval with fields observations argue for a crustal-scale and sinistral component Sb-Au bearing shear zone, acting at shallow level under brittle regime. Textural and mineralogical evidences indicate that the mineral succession consists of an arsenopyrite-pyrite first stage, followed by a sphalerite-Pb/Sb sulfosalts-native gold and late stibnite deposition. Combined fluid inclusion and isotopic studies reveal that the early mineralising fluids were hot (minimum 236 +- 35°C) mid-saline (from 6-9 NaCl wt. % eq.) with metamorphic isotopic affinity. Fluids associated with late stibnite deposition are characterised by low salinity (3 NaCl wt. % eq.), low-temperature (around 150°C), and an isotopic signature suggesting a significant participation of meteoric fluids. These fluids cannot totally equilibrate with host rocks.