FLUIDS OF THE HEMMERLEIN SKARN-GREISEN TI N DEPOSIT, ERZGEBIRGE, GERMANY

New data on fluid composition derived from a study of fluid inclusions in minerals coupled with an analysis of available data on geologic st ructure, mineralogy, and geochemistry of the large Hemmerlein skam-gre isen tin deposit suggest an evolution scheme of the ore-forming proces s. A large carbon dioxide amount was released during the transformatio n of a carbonate horizon to pyroxene-garnet skarn. CO2 under high pres sure filled capillary pores and microcracks of ambient rocks and was e ntrapped in fluid inclusions in minerals of the deposit and country ro cks. A large aureole with highest CO2 contents of 4.0-4.5 mol/kg H2O w as produced, which was of importance for subsequent fracturing. The CO 2 concentrations of 1.5 mol/kg H2O that occur within the deposit decre ase successively to early quartz veins (0.57 mol/kg H2O) and than to o re-bearing veins and veinlets (0.08-0.14 mol/kg H2O). The fluid compos itions evolved from being rich in carbon dioxide to being moderately r ich in chloride and later to being low-salinity chloride-carbon dioxid e (during the deposition of cassiterite). The solutions entrapped in c assiterite have high contents of major fluid components (CO2, Cl, and F), which could be accounted for by the enrichment in these components and tin due to water incorporation in minerals during the extensive a mphibole chloritization in the skarns and mica crystallization in the schists. The SnO2 deposition associated with a pH increase in solution s. Each subsequent replenishment of solutions decreased pH to neutral or slightly acidic level and caused quartz crystallization. These alte rnate regimes caused rhythmic precipitation of SnO2 and SiO2, which is typical of the Hemmerlein deposit.