Carlin-type Gold Deposits In Southwestern Guizhou Forming Fluid Characteristics And Its Significance

Southwestern of Guizhou province is an important Carlin-type gold deposits district, its tectonic position is in the intersection protion between southwest edge of Yangzi paraplatform and Youjiang fold belt belonging to South China fold system. Ore-bearing strata consists of carbonate rocks, silica rocks, tuff, mudstone and clastic rocks occurred in Permian and Triassic; in addition, deposits are significantly affected by the fold stucture. Regional magmatic rocks are developed, wall rock alteration are common. Gold exists in the form of wrapped-gold. pyrite is the main carrier of gold.This papper take fluid inclusions as study objects, through studying petrography, micro-thermometry, hydrogen and oxygen isotopics, thermodynamic calculation, we discussed the character and genesis of ore-forming fluid and the mineralization and precipitation process of the Carlin-type gold deposits in southwestern of Guizhou province.There are three types of fluid inclusions in the Carlin-type gold deposits of Gui-zhou, which includes H2O inclusions, CO2-H2O inclusions and CO2inclusions.Then, H2O inclusions can also divede into two forms:pure liquid H2O inclusions and liquid-rich H2O inclusions:CO2-H2O inclusions can be further classified into H2O-rich CO2-H2O inclusions and CO2-rich CO2-H2O inclusions. The homogenization temperatures, salinities and densities of ore-forming fluid ranged from176.9℃-267℃,0.02%～7.73%.0.870g/cm3-0.986g/cm3, and the average values of homogenization tempera-tures,salinities,pressure and densities were191.87℃,3.65%.162.1MPa,0.937g/cm3respectively, show that the ore-forming fluid was charactered by low temperature, low sality, middle density.and overpressure fluid. The research of hydrogen and oxygen isotope showed that the average values of δ18O and δD were3.81%o and-78.6%o,show that the ore-forming fluid are mainly from meteoric water or basin fluid.When the late Yanshan period, there are strong structural fault activity in this area, the shield layer of water-isolation what composition of graywacke or siltstone and clay rock in mining area were destructed by faulting, which makes the ore-forming pressure of overpressure fluid property suddenly decreased and occurred fluid immis-cibility, with CO2.CH4.SO2and other volatiles escaping.fs2reduction,pH increasing,the ore-forming occurred phase separation and formed two fluids, which one was rich with CO2and the other was rich with H2O, and the solubility of Au in the ore-forming was decreased rapidly, then precipitated in the fault zone, interlayer gliding and other site of pressure release, which is the main cause of the formation of Yata gold deposit.