Gold mineralization in the Greywacke Zone, Eastern Alps: T-X conditions constrained by IR microthermometry on tetrahedrite

Infrared (IR) microthermometry allows the study of microtextures and fluid inclusions in As-poor (< 2.5 wt% As) tetrahedrite, which is opaque in the visible spectral range. The data allow constraining T-X conditions of tetrahedrite-hosted gold mineralization in the Greywacke Zone, Eastern Alps. Fluid inclusions in tetrahedrite are coeval with small solid inclusions of chalcopyrite, Au-oxysulphides, minor arsenopyrite and gold. They are of low salinity (T(m) -3 to -14 degrees C) and homogenization temperatures range between similar to 85 and similar to 200 degrees C. Gold was transported by these low salinity aqueous fluids and not by synorogenic higher saline fluids found in gangue quartz. Gold-oxysulphides occur in the hydrothermal as well as in the supergene assemblages together with native gold of different chemical composition and microtexture. They indicate that sulphoxyanion species such as thiosulphate complexes played a major role in the mobilisation and transport of gold and its (re-) precipitation in low temperature geological environments.