新疆西南天山阿万达金矿床成矿流体演化

阿万达金矿位于新疆阿克苏市拜城县, 属西南天山造山带, 是一新发现的中型金矿床。在简要总结矿床地质特征的基础上, 通过流体包裹体显微测温和毒砂地温计研究, 详尽地探讨了阿万达金矿成矿流体的演化。研究表明:矿化石英中存在含CO₂的三相和气液两相两类包裹体, 且以后者居多;气液两相包裹体均一温度为188~380℃, 呈双峰式分布, 盐度(w(NaCl))为6.9%~20.7%;含CO₂包裹体的最终均一温度为238~347℃, 盐度为2.8%~7.0%。综合分析认为, 阿万达金矿成矿流体经历了由高温向中低温两个成矿阶段的演化过程。高温阶段, 成矿流体均一温度为270~380℃, 捕获温度为345~420℃, 估算的捕获压力为74~142 MPa(按静岩压力估算成矿深度为2.8~5.4 km), 以中低盐度H₂O-CO₂-NaCl体系为主, 形成高温毒砂及其他硫化物;中低温阶段, 均一温度为188~270℃, 捕获温度为270~304℃, 捕获压力为52~104 MPa, 成矿流体成分向中低盐度H₂O-NaCl体系转变, 沉淀出低温毒砂及其他硫化物。综合阿万达金矿的矿床地质特征以及流体演化特点, 认为其成因类型属中浅成造山型金矿。

Evolution of the Ore-Forming Fluid of the Awanda Gold Deposit in Southwestern Tianshan Orogenic Belt,Xinjiang

The Awanda gold deposit,a recently defined medium-size gold deposit in Baicheng County,Xinjiang,is located in the southwestern Tianshan orogenic belt.The gold mineralization occurs primarily within subsidiary faults in ore-hosting schist rocks. The sulfide mineral assemblage is dominated by arsenopyrite,pyrrhotite,loellingite,with minor pyrite and gudmundite;and the sulfide mineral contents in the gold ore are less than 15%.The wall-rock alteration in the deposit includes silicification,sericitization and minor carbonatization.Combining microthermometric analyses of fluid inclusions and the arsenopyrite geothermometer,authors discuss the evolution of the ore-forming fluids of this deposit.It was shown that fluid inclusions in quartz grains from the ore consist of major two-phase aqueous inclusions and minor three-phase CO2-bearing ones.The two-phase aqueous inclusions have a bimodal-distributed homogenization temperatures of 188 380℃ and salinities of 6.9% 20.7%NaCl,while the CO2-bearing inclusions have the homogenization temperatures of 238 347℃ and salinities of 2.8% 7.0%NaCl.The arsenopyrite geothermometer shows that the sulfide assemblage of arsenopyrite+ pyrrhotite + loellingite in Awanda gold deposit formed in a high-temperature condition ranging from 345℃ to 420℃,and there are some low-temperature arsenopyrites that can not to be applied by the arsenopyrite geothermometer.It can be synthesized that the ore-forming fluid experienced from the high-temperature epoch to the low-intermediate-temperature one.In the high-temperature epoch,the ore-forming fluid are characterized by the high homogenization temperatures of 270 380℃, the trapping temperatures of 345 420℃ from arsenopyrite geothermometer and the calculated trapping pressures of 74 142 MPa (the metallogenic depths of 2.8 5.4 km evaluated by lithostatic pressure system),and the ore-forming fluid belonged to a low-intermediate-salinity H 2 O CO2 NaCl system and depositing high-temperature arsenopyrites and other sulfides. In the low-intermediate-temperature epoch,the ore-forming fluid are characterized by the low-intermediate homogenization temperatures of 188 270℃,the trapping temperatures less than 304℃ but larger than 270℃,and the calculated trapping pressures lower than 104 MPa but higher than 52 MPa,and the ore-forming fluid belonged to a low-intermediate-salinity H 2 O NaCl system and forming low-temperature arsenopyrites and other sulfides.According to the geological characteristics and the evolution of the ore-forming fluid of the Awanda gold deposit,it can be conclued that the deposit belongs to the epizonal-mesozonal orogenic gold deposit.