黔西南紫木凼金矿床流体包裹体特征及对成矿的指示意义

Fluid Inclusion Characteristics and Implications to Mineralization in the Zimudang Gold Deposit in Southwest Guizhou Province,China

紫木凼金矿床是黔西南微细浸染型(卡林型)金矿带上的一个代表性金矿床。本文对该矿床主成矿阶段(Ⅱ)石英和方解石以及晚成矿阶段(Ⅲ)方解石中的流体包裹体进行了岩相学和显微测温研究,结果表明,各成矿阶段包裹体类型有H2O包裹体、CO2包裹体、CO2-H2O包裹体、气相CH4包裹体和CH4-H2O包裹体5类,其中CO2包裹体和CO2-H2O包裹体只在主成矿阶段(Ⅱ)的石英中发育。主成矿阶段和晚阶段流体包裹体均一温度范围分别为180～220℃和100～180℃,盐度分别为0.35%～7.45% NaCl和0.18%～5.71% NaCl,密度分别变化于0.745～0.969 g/cm3和0.868～0.993 g/cm3,总体属于中低温、低盐度、中等密度的H2O-NaCl-CO2流体体系。矿床成矿过程是一个温度退缩、盐度降低、密度增大的过程。主成矿阶段H2O-NaCl-CO2流体发生不混溶作用,是导致矿质沉淀成矿的主要原因。CO2流体、CH4流体在金的成矿过程中起重要作用。

The Zimudang gold deposit is a typical example of micro-disseminated （Carlin-type） gold deposits in Southwest Guizhou Province, China. The petrographic observation and microthermometric study were carried out on the fluid inclusions from main stage （Ⅱ ） quartz and calcite as well as late stage （ Ⅲ ） calcite from the deposit. Ma- jor types of fluid inclusions include aqueous inclusions, pure CO2 inclusions, CO2-H2O inclusions, CH4 inclusions, and CH4-H2O inclusions. The pure CO2 inclusions and CO2-H2O inclusions were only recognized in the main stage （Ⅱ ） quartz. The homogenization temperatures, salinities and densities of the main stage （ Ⅱ） range 180 - 220 22 , 0.35% - 7.45% of SAC1, and 0. 745 - 0. 969 g/cm^3, respectively, while those of the late stage （ Ⅲ） vary in the ranges of 100 - 18022 , 0. 18% - 5.71% NaC1, and 0. 868 - 0. 993 g/cm^3, respectively. The ore-forming fluids were characterized by a H2O-NaC1-CO2 system with medium to low temperature, low salinity, and medium density. The fluid inclusiondata indicate that the gold mineralization was a process of decrease in temperature and salinity and slight increase in density of the ore-forming fluids. Immiscibility of the H2O-NaCl-CO2 fluid system occurred during the main mineralization stage （ Ⅱ）, resulting precipitation of Au and formation of the ore deposit. The CO2- and CH4-bearing fluid played an important role in the formation of the deposit.