Fluid Inclusion Study And Its Geological Significance On The Xuebaoding W-Sn-Be Deposit, Sichuan

The Xuebaoding W-Sn-Be deposit located at the country of Pingwu, Sichuan province. So far, it is the only-Sn-Be deposit was found in the Songpan-Ganzi orogenic belt and the Qinling orogeny belt. Combining with previous research and the geological features of ore deposit. A systematic study of inclusions in the deposit has been carried by Petrography and microthermometry, Laser Raman Spectra, thermodynamic calculation to discussed the characters and ource of ore-forming fluid and the mineralization.The Middle Triassic Zhagunao Formation (T2Z) is the main ore-bearing stratum of Xuebaoding deposit. A small part of ore body were controlled by the granite body and Zone of Contact. The ore body is made up of quartz vein and druse.The ore mineral are mainly beryl, scheelite, cassiterite and a small number of tourmaline, chalcopyrite, galena, sphalerite, pyrite, etc. The gangue mineral are quartz, Muscovite, potassium feldspar, fluorite, albite, apatite, etc. The ore has banded structure, massive structure, drusy structure and euhedral crystal and pegmatitic structure.The inclusions in the deposit can be can be divided into three categories, melt inclusions, fluid inclusions and fluid-melt inclusions. And the fluid inclusions can also divided into seven categories,, liquid-gas H2O inclusions, gas H2O inclusions, liquid-gas CO2 inclusions, gas CO2 inclusions,CO2-rich CO2-H2O inclusions, H2O-rich CO2-H2O inclusions. Three kinds of inclusions be found in the deposit show the characteristics of the ore-forming fluid came from granitic magma differentiation and the fluid inclusions show that the observed fluid inclusions assembalges are consistent with a model involving CO2-H2O immiscibility. The homogenization temperature, salinities, densities of liquid-gas H2O inclusions ranged from 167℃ to 255℃, from 3.39 to 6.59(wtNacl%), from 0.6781g/cm3 to 0.7618g/cm3. The CO2-rich CO2-H2O inclusions’homogenization temperatures ranged from 234℃ to 267℃, average of 250℃, the pressures from 124 MPa to 171 MPa, average of 153MPa, the densities from 0.6781g/cm3 to 0.7618g/cm3, the mole fraction of CO2 from 0.6349 to 0.7407. The H2O-rich CO2-H2O inclusions’homogenization temperatures ranged from 224℃ to 286℃, average of 251℃, the pressures from122 MPa to 155 MPa, average of 144 MPa, the densities from 0.9342g/cm3 to 0.9655g/cm3, the mole fraction of CO2 from 0.0962 to 0.1123.The ore-forming has the characteristics of rich CO2, middle temperature and low salinity. Two types of the CO2-H2O inclusions have the same the homogenization tempe-ratures and the pressures indicating that CO2 and H2O are immiscible fluid inclusio-ns having been trapped in the same period.The collision event between Yangtze Plate and North China Plate happened at the Triassic, the strong Tectonic Movement and magmatic activity was happened in this area, The ore-forming fluid which is rich CO2, middle temperature, low salinity and came from granitic magma differentiation was rising along joints and fissures,when it into the intrusive contact zones of granite body and the surrounding rock (Zhuwo formation’s slate and marble) where joints and fissures were development, The ore-forming fluid pressure was reduced, lead to the ore-forming fluid CO2 solubility decrease and the CO2-H2O immiscibility.