FLUID EVOLUTION AND ORE DEPOSITION IN THE HARZ MOUNTAINS (GERMANY)

Quartz-stibnite, Pb-Zn, Ba-, and F-vein mineralization developed in the Harz Mts. over a long span of time from the Late Carboniferous to the Late Cretaceous. The economically most important quartz-sulphide and subsequent carbonate-sulphide ore deposits were deposited during the Jurassic. The homogenization temperatures of primary two-phase fluid inclusions in vein quartz lie between 120 and 180-degrees-C on average. Secondary two-phase inclusions in calcite and fluorite show approximately the same range, whereas only few primary fluid inclusions have homogenization temperatures between 210 and 300-degrees-C. Since boiling and effervescence can be excluded, precipitation of calcite may have been achieved from fluids when cooling from 300-200-degrees-C as indicated by the positive delta C-13 vs. delta O-18 relationships in calcite. The evolution of chlorinity in the fluid inclusions reveals that, at different times, fluids from different sources were drained and mixed. Sulphides in the quartz-sulphide and carbonate-sulphide mineralizations were deposited by mixing of an ascending metal- and carbonate-bearing H2S-free metamorphic fluid with a H2S-bearing formation water. By contrast, the gangue minerals precipitated by simple cooling of the ascending fluid. Subsequently, barite was deposited by the mixing of a probably similar metamorphic fluid with descending SO42--bearing fluids from residual evaporites of the Mesozoic cover. Finally, fluorite locally precipitated from ascending brines originating from deeper sources than the carbonate-rich metamorphic fluid.