MINERAL-COMPOSITION AND FORMATION CONDITIONS OF THE PIAOTANG TIN-TUNGSTEN DEPOSIT, SOUTH CHINA

The formation conditions of giant tungsten deposits were examined on t he example of the largest tungsten deposits of south China (Piaotang a nd Xihuashan). The existence of a homogeneous source of mineral-formin g fluids responsible for the formation of the deposits under study was proved by data on mineral composition of the ore-bearing zones, the c hemical composition of individual minerals (wolframite, triplite, spha lerite, and stannite), and the distribution of rare-earth elements in wolframite, scheelite, and fluorite. As was evidenced by thermometric and cryometric studies of fluid inclusions in the minerals of these de posits, the minerals were formed at 350-115 degrees C in slightly mine ralized H2O-CO2 solutions with minor concentrations of CH4 and N-2 (up to 4.1 mol %). The magmatic origin of ore-forming fluids and their mi xing with meteoric waters late in the fluid evolution were established from data on the oxygen and carbon isotopic compositions in different minerals. The geochronological data available on granites and mineral s of quartz-wolframite veins of the Piaotang and Xihuashan deposits po int to the close age relation between the tungsten ores and granites. The analyses of radiogenic isotopes in granites and fluorites from the ore veins testify that the crustal matter (probably the matter of the ancient crust) was involved in the rock and ore formation.