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新疆且末碧玉矿的成因研究
Petrogenesis of the serpentinite-related nephrite deposit in Qiemo County, Xinjiang
投稿时间:2017-01-20  
中文关键词:碧玉  蛇绿岩  和田玉  且末  新疆
英文关键词:serpentinite-related nephrite  ophiolite  nephrite  Qiemo  Xinjiang
基金项目:中国地质调查局矿产地质志项目(DD20160346);中国地质科学院基本科研业务费项目(YWF201601);中国地质调查局地质调查项目(1212011020151511-03)
作者单位E-mail
贾玉衡 桂林理工大学 地球科学学院, 广西 桂林 541004  
刘喜锋 华南理工大学广州学院, 广东 广州 510800 liuxf@gcu.edu.cn 
刘琰 中国地质科学院 地质研究所, 北京 100037  
张其超 中国地质科学院, 北京 100037  
张勇 自然资源部珠宝玉石首饰管理中心, 北京 100013  
李自静 中国地质科学院, 北京 100037  
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中文摘要:
      以往勘察和研究显示,在新疆和田及其附近地区主要出现与大理岩相关的软玉(和田玉)矿床,而与蛇纹岩有关的软玉(碧玉)矿床尚未有明确报道。笔者通过两年多的野外勘察和室内实验分析,新近在且末县阿尔金断裂附近发现一定规模可开采的碧玉矿床,对其中碧玉样品进行了主量元素、微量元素、电子探针、氧同位素和成矿年龄等方面的研究。岩相学研究显示其主要组成矿物是阳起石和透闪石,全岩的Mg/(Mg+Fe2+)=0.83~0.89,Cr2O3=0.08%~1.65%,NiO=0.14%~0.22%,δ18O=15.2‰~15.4‰,经与世界上已发现的碧玉矿床进行对比并结合野外观察,确定该矿床是一种与蛇纹岩有关的碧玉矿床。蚀变闪长岩(δ18O=14.3‰~14.7‰)、大理岩围岩(δ18O=15.2‰~15.9‰)和透闪石(δ18O=15.3‰)具有相似的氧同位素组成,表明它们很可能经历了同样的流体蚀变作用。根据蚀变闪长岩(Cr=107×10-6~155×10-6,Ni=53.5×10-6~85.8×10-6)和大理岩(Cr=2 036×10-6~2 415×10-6,Ni=1 403×10-6~1 933×10-6)中的Cr、Ni元素含量判断,碧玉中大量的Cr(867×10-6~2 418×10-6)和Ni(960×10-6~1 662×10-6)很可能来自于蛇纹岩中的流体。对碧玉的主要围岩蚀变闪长岩进行的锆石SHRIMP U-Pb年龄测试结果分别为267±14 Ma(n=5)和272±14 Ma(n=6),与碧玉密切共生的黑云母的Ar-Ar坪年龄为260.6±1.5 Ma。鉴于蚀变闪长岩的形成时代与黑云母年龄数值在误差范围内一致,花岗岩、大理岩和碧玉的氧同位素值接近,同时碧玉的Cr、Ni元素含量较高,因此推断碧玉的物质来源很可能是蚀变闪长岩和大理岩,而成矿流体是由蚀变闪长岩中的岩浆水、蛇纹岩中活化的流体和大气降水组成。
英文摘要:
      According to the modes of occurrence, nephrite can be divided into dolomite-related nephrite and serpentinite-related nephrite. In previous studies and exploration, serpentinite-related nephrite was hardly found in Hetian dolomite-related nephrite belt in Western Kunlun Mountains. During 2014~2015, lots of geological examination and collection of information concerning the location of serpentinite-related nephrite were carried out, and then some information about the occurrence of serpentinite-related nephrite orebody near the Altun fault zone was found in Qiemo County. Based on EMPA (electron microprobe analysis), XRF (X-ray fluorescence), ICP-MS (inductively coupled plasma mass spectrometry) and oxygen isotopic analysis, δ18O (15.2‰~15.4‰), Mg/(Mg+Fe2+)=0.83~0.89, Cr2O3=0.08%~1.65%, NiO=0.14%~0.22% and other geochemical data were acquired, which suggest a serpentinite-related nephrite origin. Wall rock of diorite also indicates that they formed at 267±14 Ma and 272±14 Ma, as shown by the SHRIMP U-Pb dating on zircons, which suggests the upper limit of the formation time of the serpentinite-related nephrite. Inverse isochronal age of Ar-Ar dating on biotite associated with serpentinite-related nephrite is 260.6±1.5 Ma. Both ages imply that they have relationship in genesis. Possibly due to the similar hydrothermal alteration of diorite, dolomite marble and tremolite, they have the close oxygen isotopic values (δ18O=14.3‰~14.7‰, δ18O=15.2‰~15.9‰ and δ18O=15.3‰). According to the chemical composition from bulk analysis of diorite (Cr=107×10-6~155×10-6, Ni=53.5×10-6~85.8×10-6), marble (Cr=2 036×10-6~2 415×10-6, Ni=1 403×10-6~1 933×10-6) and nephrite (Cr=867×10-6~2 418×10-6, Ni=960×10-6~1 662×10-6), together with the occurrence of chromite in nephrite, it is concluded that granodiorite and marble provided the ore materials for the formation of nephrite, and hydrothermal fluids were probably derived from both magmatic water and meteoric water in serpentine rock.
贾玉衡,刘喜锋,刘琰,张其超,张勇,李自静,2018,新疆且末碧玉矿的成因研究[J].岩石矿物学杂志,(5):824~838.
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