湘西合仁坪钠长石-石英脉型金矿床的成矿流体研究

Characteristics of Ore-forming Fluid in Herenping Albite-quartz Lode Gold Deposit,Western Hunan Province,China

合仁坪金矿床位于湘西柳林汊金矿带,是典型的钠长石-石英脉型金矿床,本文对其进行了较系统的成矿流体地球化学研究。结果表明,与成矿有关的石英和方解石中的流体包裹体主要为气液两相包裹体。石英中包裹体的均一温度范围为111~375℃,盐度为0.18%~7.86%的NaCl;方解石中包裹体的均一温度范围为196~271℃,盐度为4.18%~6.74%的NaCl;成矿溶液的密度为0.633~0.997g/cm^3,表明该矿床的成矿流体均属于中低温、低盐度和低密度的流体;成矿压力为4~209MPa,成矿深度约为1.2~6.8km,该矿床是在中低压力、中浅成条件下形成的。激光拉曼探针分析表明,包裹体中的气相成分有CO_2、CO、CH_4和N_2,液相成分为H_2O和CO_3^(2-),指示含有机质的沉积物变质脱水可能是成矿流体来源的方式。对石英和钠长石氢氧同位素研究表明,该矿成矿流体的δ^(18)O_(H_2O)值为7.1‰~10.8‰,δD_(H_2O)值介于-69‰^-55‰,合仁坪金矿的成矿流体主要来源于变质水。

Herenping gold deposit, a typical albite-quartz lode gold deposit, is located in the Liulincha gold ore belt, western Hunan Province, China. The ore-forming fluid geochemistry was systematically studied in this paper. It is shown that the fluid inclusions in quartz and calcite related to gold mineralization are predominated by two-phase （liquid-rich） inclusion. The homogenization temperatures and salinities of fluid inclusion in quartz range from 111 ℃ to 375 ℃ and from 0. 18 wt%NaCl to 7. 86 wt%NaCl, respectively. The homogenization temperatures and salinities of fluid inclusion in calcite vary from 196℃ to 271℃ and from 4. 18 wt%NaC1 to 6.74 wt%NaC1, respectively. The densities of the ore-forming fluid are estimated at 0.633- 0.997 g/cm^3. Therefore the ore-forming fluid responsible for gold mineralization in Herenping deposit is characterized by low-to-moderate temperature, low salinity and low density. The pressures of ore-forming fluid are calculated as 4-209 MPa, indicating that the gold deposit formed at the depth of 1.2 -6. 8 km. Based on the laser Raman analysis of fluid inclusion, it is concluded that the gas composition mainly consists of H2O, CO2, CO, CH4 and N2, and liquid phase composition is mainly H20 and C03^2-, which reveals that the ore-forming fluid is caused by the metamorphic dehydration of organic matter-bearing sediments. Hydrogen and oxygen isotope compositions also reveal, that the δDH2O is 7.1‰- 10. 8‰ and the δ 18OH2O is -69‰- -55‰, indicating that the ore-forming fluid in this gold deposit is mainly derived from metamorphic water.