Origin of Pb-Zn mineralising fluids in the Variscides of Belgium

Microthermometric and crush-leach analyses of high-salinity H2O-NaCl-CaCl2 fluid inclusions in calcite veins related to the Bleiberg Pb-Zn deposit in eastern Belgium indicate an evaporative origin of the mineralising fluid. The Pb-Zn mineralisations mainly occur in Lower Carboniferous carbonates. Evaporation of seawater occurred during several periods within the Devonian-Carboniferous and we suggest that this high salinity fluid migrated downward into the basement along extensional faults, due to its density, during the Palaeozoic. The composition of the fluid evolved through interaction with Palaeozoic and basement rocks. At depth, the high salinity fluid mixed with gravity-driven meteoric water, which migrated in the subsurface after the Variscan deformation. During the Mesozoic, probably the Jurassic, the mineralising fluids were released along faults, causing the widespread Pb-Zn mineralisation found at the Variscan front zone in Belgium.