马扎拉是藏南金锑成矿带内最具有代表性的金-锑矿床.为了更直接地了解该矿床的流体物理化学特征,探讨成矿流体来源、成矿机制及其矿床类型,本文对该矿床中主要载金矿物辉锑矿及石英中的流体包裹体进行了显微测温研究.流体包裹体岩相学观察表明,辉锑矿及石英具有近乎相同的4类流体包裹体类型:富液两相水溶液包裹体、三相CO2-H2O包裹体、纯CO2包裹体和纯H2O包裹体.红外显微测温结果显示,辉锑矿中流体包裹体均一温度(Th)峰值为180 ～ 210℃,盐度峰值介于2.5％～3.4％ NaCleqv,密度峰值在0.895～0.915g/cm3之间.石英中流体包裹体Th、盐度及密度均具有三个明显峰值,Th为270～300℃、225～255℃和180～ 210℃,盐度为4.3％～4.9％ NaCleqv,3.4％ ～4.0％NaCleqv和2.8％ ～ 3.4％NaCleqv,密度为0.895 ～0.915g/cm3、0.835～0.855g/cm3和0.775～0.795g/cm3.对比辉锑矿和石英中流体包裹体测温结果可见,辉锑矿中流体包裹体Th和盐度比石英偏低,而密度较石英偏高,表明含金石英可能先于辉锑矿从成矿流体中沉淀,且辉锑矿大量沉淀成矿时可能不断有较低温、低盐度和较高密度流体混入.辉锑矿及石英中流体包裹体水的δDH2o为-68.1‰～-108‰,δ18OH2o为-2.2‰ ～ 12.2‰,在δD-δ18O投影图上主要位于变质水附近,个别样品靠近大气降水,表明成矿流体为变质水与大气降水的混合.石英中流体包裹体的δ13C为-2.9‰～-3.5‰,平均值为-3.1‰,落入幔源碳同位素组成范围(δ13C=-5‰～-2‰)之内,说明CO2可能主要为幔源,而辉锑矿中流体包裹体的δ13C为-12.6‰,明显小于幔源碳同位素组成,说明在辉锑矿成矿过程中可能有少量地层有机碳加入.马扎拉金锑矿床成矿流体具有富含CO2、低盐度、低密度和中低温度的特征,与造山型金矿成矿流体相似.地质和地球化学特征显示马扎拉金锑矿床为喜马拉雅期陆陆碰撞造山型金锑矿.%The Mazhala Deposit is the most representative gold-antimony deposit in the gold-antimony ore-forming belt in southern Tibet, China. Microscopic observation and microthermometric study were performed on fluid inclusions hosted in gold-bearing mineral ( stibnite and quartz) , in order to directly characterize the physicochemical conditions of ore-forming fluid and investigate the genetic type of the deposit, source of ore-forming fluids and metallogenic mechanism of Mazhala antimony-gold Deposit. The results of microscopic observation show that the fluid inclusions hosted in stibnite and quartz are nearly the same and can be divided into four types; i.e. two-phase aqueous, three-phase CO2-H2O, pure CO2 and pure H2O inclusions, respectively. Infrared microthermometric study show that the homogenization temperature ( Th) values of the fluid inclusions hosted in stibnite peak at 180 ~210℃ , the salinity values peak at 2. 5 ~ 3. 4% NaCleqv, and density values peak at 0. 895 ~0. 915g/cm , and that the Th, salinity and density of the fluid inclusions hosted in quartz show triple peaks at 270~300℃ , 225~255℃ and 180 ~210℃ , 4. 3% ~4. 9% NaCleqv, 3. 4% ~4. 0% NaCleqv and 2. 8% ~ 3. 4% NaCleqv, and the 0. 895 ~ 0. 915g/cm3, 0. 835 ~ 0. 855g/cm3 and 0. 775 - 0. 795g/cm3, respectively. Comparison of the microthermometric measurements shows that the Th, salinity and density of the fluid inclusions hosted in stibnite match with the lower Th and salinity and higher density values of inclusion hosted in the late stage of quartz, indicating that quartz was deposited from the ore-forming fluid before stibnite, also suggesting the input of low temperature and low salinity while high density fluids during stibnite precipitation. The δDH2O of the fluid inclusions hosted in stibnite and quartz is —68.1‰ ~ — 108‰, and their δ18OH2O is -2. 2‰ ~ 12. 2‰, projected near metamorphic fields in the δD-518O diagram, occasionally near meteoric line, indicating that ore-forming fluid is the mixture of metamorphic and meteoric waters. The δ13C of fluid inclusion hosted in quartz is - 2. 9‰~ -3. 5‰, with an average of -3.1‰, which falls within the range of mantle-derived carbon(δ13C = -5‰ ~ -2‰) , indicating CO2 is probably mantle-derived. Moreover, the δ13C of fluid inclusion hosted in stibnite is - 12. 6‰, which is significantly smaller than the mantle-derived carbon, suggesting a considerable amount of organic carbon was involved in ore-forming fluid during stibnite deposited. The ore-forming fluids of the Mazhala gold deposit is characteristics by high content of CO2, low salinity, low to moderate Th and low density, which are similar to those of typical orogenic gold deposits. Geologic and geochemical features show that the Mazhala gold-antimony deposit may be a Cenozoic orogenic gold-antimony deposit formed under continental collisional background.
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