藏南拉木由塔锑(金)矿床成矿流体特征及成矿机制初探

The Characteristics of Ore-forming Fluids and Primary Metallogenic Mechanism of the Lamuyouta Sb (Au) Deposit,South Tibet

西藏拉木由塔锑(金)矿床位于藏南Sb-Au成矿带东段,矿(化)体主要赋存于中侏罗统遮拉组地层与辉绿(玢)岩脉接触带上。研究表明:石英中的流体包裹体普遍较小,主要为富液相的气液两相包裹体,形态复杂多样,主要呈长条状、浑圆状、椭圆状及不规则状。方解石中的包裹体普遍较大,也都为富液相的气液两相包裹体,形态简单,以负晶形及不规则状为主。包裹体显微测温结果显示,均一温度范围为150～344℃,盐度(NaCl)介于0.53%～9.61%,密度介于0.55～0.93 g/cm3,成矿压力变化于39～83 MPa,表明成矿过程主要在中低温条件下进行,成矿流体为低盐度、低密度流体。从成矿早期到晚期,流体包裹体的均一温度、盐度、压力不断降低。氢-氧同位素地球化学研究表明,含矿石英脉δDV-SMOW变化范围为-137‰～-163‰,δ18OH2O变化于9.42‰～14.58‰,含矿方解石δDV-SMOW变化范围为-148‰～-151‰,δ18OH2O变化于-9.83‰～-17.02‰,成矿流体中的水主要来自大气降水。该矿床成矿物质的沉淀主要是由水岩反应和混合作用引起的。

Lamuyouta Sb （Au） deposit is located in the eastern section of Sb-Au metallogenic belt, south Tibet. The ore body mainly distributes at the contact between the strata of the Middle Jurassic Zhala Formation and diabase （allgovite） veins. The results show that the dominant fluid inclusion types in quartz are the gasliquid two-phase inclusions with rich liquid. Those fluid inclusions are generally smaller. All of them are texturally complex, display elongated, rounded, oval-shaped and irregular-shaped inclusions. The fluid inclusions in calcite are contrarily bigger. Similarly, all of them are also the gas-liquid two-phase inclusions with rich liquid. However, the texture is rather simple where the negative crystal and irregular shape dominate. The inclusion miero-thermometry results reveal that the homogenization temperatures vary from 150 to 344 ℃while the salinities and the densities change from 0.53% to 9.61% and 0.55 to 0.93 g/cm3 , respectively. The metallogenic pres- sure is deemed from 39 to 83 MPa, which reflect that the metallogenic process was under mid-low temperature conditions and the ore-forming fluid is of low salinity and low density. The homogeneous temperature and salini- ty of the fluid inclusions decreased as the ore deposits formed gradually from early to late phases. H-O isotopic studies shows the δDv_sMOW of ore bearing quartz veins is from - 137 %0 to - 163 %o while 6JSOH2o changes from 9.42%0 to 14. 58%0; the 6Dv_sMow of ore bearing calcite veins is from - 148 %o to - 151%o while 618OH2o changes from -9.83%0 to - 17.02%0 and the ore-forming fluids are considered to be sourced from the precipitation. The ore-forming material derives from water-roek interaction and mixing of fluids.