ISSN 1009-6248CN 61-1149/P 双月刊

主管单位:中国地质调查局

主办单位:中国地质调查局西安地质调查中心
中国地质学会

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    新疆西天山阿尔恰勒Pb–Zn–Cu矿床成因来自流体包裹体和同位素的证据

    Genesis of the Arqiale Pb-Zn-Cu Deposit in the Western Tianshan, Xinjiang: Evidence from Fluid Inclusions and Isotopes

    • 摘要: 阿尔恰勒Pb–Zn–Cu矿床位于新疆西天山乌孙山脉西南缘,矿体产于下石炭统阿克沙克组灰岩中,其产状整体与地层基本一致。由于矿体具有层控特征,矿区地表和深部未见侵入岩体,导致该矿床与岩浆作用的关系尚不清楚。成矿过程大致可分为4个阶段:石榴子石–辉石阶段(I)、阳起石–黑柱石阶段(II)、石英–方解石–多金属硫化物阶段(III)和碳酸盐阶段(IV)。阶段Ⅱ阳起石与阶段Ⅲ石英、方解石和闪锌矿主要发育气液两相水包裹体(L–V型)以及少量单相液相水包裹体(L型)。阶段Ⅱ中阳起石L–V型包裹体均一温度和盐度分别为278~425 ℃和2.1~13.0 wt.% NaCl eqv,阶段Ⅲ热液矿物中L–V型包裹体均一温度和盐度分别为162~342 ℃和0.5~9.0 wt.% NaCl eqv。流体包裹体和C–H–O同位素组成特征显示,初始成矿流体主要为岩浆水,后期大气降水逐渐混入,导致成矿温度和盐度的降低以及矿物质的沉淀。矿石中硫化物的δ34S值变化范围较大(−7.57‰~1.30‰),Pb同位素具有壳幔混合特征。综合矿床地质、流体包裹体和同位素特征,推断阿尔恰勒属于远端矽卡岩型Pb–Zn–Cu矿床,其成矿物质具有深部岩浆和地层的混源特征。矿区内矿体由南侧浅部的Pb–Zn矿化逐步过渡到北侧深部的Cu±Zn矿化,暗示矿区北部深部可能存在隐伏的含矿岩体及接触带铜矿体。

       

      Abstract: The Arqiale Pb–Zn–Cu deposit is located in the southwestern margin of the Wusun Mountain in the Western Tianshan, Xinjiang Province. The orebodies occur in the limestone of Lower Carboniferous Akeshake Formation and are generally consistent with the strata in occurrence. Considering that the orebodies are stratabound and no magmatic rocks are identified in the orefield, whether the deposit is related to magmatism remains controversial. Ore–forming process can be divided into four stages, including garnet-pyroxene stage (I), actinolite–ilvaite stage (II), quartz–calcite–polymetallic sulfide stage (III) and carbonate stage (IV). Two types of inclusions have been identified in the actinolite from stage Ⅱ and quartz, calcite and sphalerite from stage Ⅲ, including the two–phase aqueous inclusions (L–V type) and mono-phase liquid aqueous inclusions (L type). The L–V type inclusions in actinolite have homogenization temperatures and salinities ranging from 278℃ to 425 ℃ and 2.1 wt.% NaCl eqv to 13.0 wt.% NaCl eqv, respectively. By contrast, the L–V type inclusions in stage III hydrothermal minerals have homogenization temperatures and salinities ranging from 162℃ to 342 ℃ and 0.5 wt.% NaCl eqv to 9.0 wt.% NaCl eqv, respectively. Fluid inclusions and C–H–O isotopic compositions indicate that the initial ore-forming fluids were mainly source from magmatic water, with increasing input of meteoric water with time, leading to the decrease of temperatures and salinities, as well as the precipitation of ore-forming materials. The δ34S rations of sulfides in the ores have a wide range (−7.57‰~1.30‰), and the Pb isotopic compositions have the characteristics of crust–mantle mixing. Combined evidence from geology, fluid inclusions and S–Pb–C–H–O isotopes indicate that the Arqiale Pb–Zn–Cu deposit belongs to the distal skarn type deposit, with the ore–forming materials sourcing partially from the magmatic rocks at depth and partially from the strata. The orebodies in the ore field gradually transit from Pb–Zn orebodies at shallow in the south to Cu ± Zn orebodies at depth in the north, implying that the concealed causative intrusions and skarn Cu orebodies in the contact zone may occur in the deep part in the north of the mining area.

       

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