The origin of greisen fluids of the Foley's zone, Cleveland tin deposit, Tasmania, Australia

The Cleveland deposit, located in northwest Tasmania, Australia, was a majo r tin-producing mine until its closure in 1986. The deposit is contained by the Cambrian Creek Formation, which comprises argillite, quartz, and lithi c wacke, basalt lava flows, pyroclastic deposits, calcareous wacke, arenite s, and unfossiliferous limestone. Three styles of mineralization occur in the mine sequence. These are carbon ate replacement, greisenization of a quartz porphyry dike, and fissure vein s. The area in the mine encompassing the dike and the surrounding vein halo is referred to as Foley's zone. Five major alteration facies are recognize d within the dike with distinct zonation between the types. These include s ericitized feldspar greisen, quartz-muscovite greisen, quartz-muscovite-top az greisen, quartz-topaz greisen and quartz ultragreisen. Oxygen, hydrogen, and sulfur isotope data indicate that the hydrothermal fl uids producing the bulk of the mineralization in the Foley's zone veins sho w narrow ranges in isotopic compositions. Measured delta D (-65 to -85 part s per thousand) and calculated delta(18)O (7.7-10.3 parts per thousand) val ues suggest two possible interpretations. First, the fluids may simply be p rimary magmatic fluids. Secondly, the fluids may have originated from outsi de an igneous intrusion and undergone isotopic exchange with a large volume of igneous rock at magmatic temperatures. Sulfur data (1.7-4.1 parts per t housand) are strongly suggestive of a magmatic origin.