新疆萨热阔布金矿床流体包裹体研究及矿床成因

摘要

新疆萨热阔布金矿床位于阿尔泰造山带南缘克兰火山-沉积盆地内,矿体呈脉状产于康布铁堡组上亚组地层中(D1k2).不同成矿阶段石英脉中广泛发育流体包裹体,可划分为H2O-CO2包裹体(C型)、纯CO2包裹体(PC型)、水溶液包裹体(W型)及含子矿物多相包裹体(S型)四类.测温结果显示,成矿早阶段主要发育C型和PC型包裹体,均一温度范围为271～446℃,流体盐度介于5.9％ ～ 8.4％ NaCleqv之间；中阶段主要发育C、PC、W和S型包裹体,均一温度低于早阶段,为236～374℃,流体盐度介于4.8％～15.0％ NaCleqv之间；晚阶段主要发育W型包裹体,均一温度范围为139～264℃,流体盐度介于1.1％ ～6.9％ NaCleqv之间.对成矿压力和深度的估算表明,成矿压力为90～330 MPa,成矿深度为9～12 km.综上所述,萨热阔布金矿成矿流体具有富CO2、中低盐度的变质流体特征,流体沸腾导致了成矿物质的沉淀.结合矿床地质特征,萨热阔布金矿床属于造山型金矿床.%The Sarekuobu Au deposit is located in a Devonian volcanic-sedimentary basin of the Altay orogenic belt.Volcanic rocks and sedimentary strata exposed in the area experienced greenschist-facies metamorphism.According to the interrelation of quartz veins,the hydrothermal ore-forming processes of the deposit can be divided into early,middle and late stages,represented by pyrite-quartz,polymetallic sulfide-quartz and carbonate-quartz veinlets,respectively.The early-stage veins or minerals were structurally deformed and brecciated,indicating a compressional or trans-compressional setting.The middle-stage veinlets intruded and filled the fissures of the early-stage assemblages without deformation,suggesting a tensional shear setting.The late-stage veinlets mostly filled open-space of fissures that crosscut and altered the earlier stage veins.Four types of fluid inclusions( FIs) are distinguished,including aqueous (W-type) ,carbonic-aqueous (C-type) ,purely carbonic (PC-type) and solid-bearing (S-type).The early-stage quartz contain the C- and PC-type primary FIs,and the homogenization temperatures of the primary C-type fluid inclusions in the early stage quartz range from 271℃ to 446℃ with salinities ranging from 5.9% to 8.4% NaCleqr The middle-stage quartz trapped C-,PC-,W- and S-type fluids inclusions with the lower temperatures ranging from 236°C to 374°C and higher salinities ranging from 4.8% to 15.0% NaCleqr,.Laser Raman analysis indicate that the gases in fluid inclusions are CO2,CH4and N2.The late-stage quartz veins contain only aqueous fluid inclusions with homogenization temperatures ranging from 139℃ to 264℃,and salinities ranging from 1.1% to 6.9% NaCleqr,.The low salinity and high CO2 content indicate that the ore-forming fluid may be met-amorphic fluid.In the middle stage,coexistence and similar homogenization temperature of C-,W- and S-types indicate that metal precipitation may result from fluid boiling and CO2-escaping.The estimated trapping pressures of boiling FIs assemblage range from 90 to 330 MPa,suggesting an alternating lithostatic-hydrostatic fluid-system,controlled by the fault-valve at the depth of 9 -12 km.In the middle stage,fluid boiling caused CO2 escape and metals precipitation,which resulted in the formation of most of the reserves,and meteoric water added to the ore-forming system in the late stage also caused the precipitation of metals.In conclusion,our results show that the Sarekuobu Au deposit in Xinjiang is an orogenic gold deposit.