CHARACTERISTICS OF FLUID INCLUSIONS OF THE DAMOGOU-NAOYANGPING FLUORITE DEPOSIT IN SHAANXI PROVINCE

The Damogou-Naoyangping fluorite deposit of Shaanxi occurs in the secondary fractures of the regional east-westtrending fault F₁. The metallogenesis can be divided into four stages, i.e. Ⅰ) giant calcite crystal stage; Ⅱ) coarse-grained fluorite-calcite fluorite-quartz fluorite stage; Ⅲ) quartz sulfide (sphalerite) stage; and Ⅳ) calcite veinlet-fluorite veinlet stage. The result of petrographic observations indicates that, the inclusions are mainly of gas-liquid two-phase, pure gas phase, pure liquid phase, CO₂-H₂O three-phase and daughter mineral-bearing type. Microthermometry reveals that the homogenization temperatures of fluid inclusions in fluorite of Damogou deposit range from 290 to 340℃, with salinities from 0.5% to 6.16%(NaCl eqv.). The gas-liquid two-phase fluid inclusions in fluorite yield trapping pressures of 22.072-25.089 MPa, corresponding to a depth of 776.3-1268 m. The homogeneous temperatures of fluid inclusions of Naoyangping deposit are between 289 and 329℃, with a high salinities. The variation of salinity can be used to infer the migration direction of fluid. In the process of fluid migration, the abrupt reduce of pressure in the brittle structural fissures may result in hydrothermal boiling.