Greisen

A highly variable, low to high-temperature metasomatic rock characterised by the presence of quartz and white mica, commonly with topaz, fluorite, tourmaline and locally with cassiterite, biotite, zinnwaldite, orthoclase, andalusite and diaspore; some contain various sulphides. Typically greisens may host Be, W, Mo, Sn and Ta mineralization. They are associated with high-level late-orogenic leucogranites or alkali-feldspar granite and form during cooling and exsolution of F-rich fluids as replacements either in the granite body and/or in a wide range of country rocks. Zoning may be present.