| 湖南包金山矿区白钨矿的地球化学特征及Sm-Nd同位素年代学 |
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| 引用本文： | 彭建堂,王川,李玉坤,胡阿香,鲁玉龙,陈宪佳.湖南包金山矿区白钨矿的地球化学特征及Sm-Nd同位素年代学[J].岩石学报,2021,37(3):665-682. |
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| 作者姓名： | 彭建堂 王川 李玉坤 胡阿香 鲁玉龙 陈宪佳 |
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| 作者单位： | 中南大学地球科学与信息物理学院, 有色金属成矿预测与地质环境监测教育部重点实验室, 长沙 410083;中国科学院地球化学研究所, 矿床地球化学国家重点实验室, 贵阳 550081;湖南城市学院土木工程学院, 益阳 413000;湖南科技大学资源环境与安全工程学院, 湘潭 410201 |
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| 基金项目： | 本文受国家自然科学基金项目（41972090、41473043）资助. |
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| 摘 要： | 包金山金钨矿床位于湘中白马山-龙山-紫云山金矿带的东段,是近年新发现的一个赋存于前寒武纪浅变质岩中的金矿床。在野外调研和室内镜下研究的基础上,本文利用XRD、EMPA、ICP-MS、ID-MS等多种分析手段,对其进行了元素地球化学和同位素地球化学研究,进而揭示了该区金矿床的形成时代和矿床成因。研究表明,该区白钨矿的化学成分较均一,其WO_3含量大体与理论值一致,但Ca O含量稍低于其理论值,这可能与Sr、REE、Na等微量元素对白钨矿晶格中Ca的类质同象置换有关。除Sr、REE、As以外,该区白钨矿中的微量元素,特别是Mo、Bi、Sn、Be、Nb、Ta等均低于1×10~(-6),明显有别于华南与燕山期花岗岩有关钨矿床中的白钨矿。该区白钨矿的稀土元素含量为484.5×10~(-6)~972.9×10~(-6)(平均721.3×10~(-6)),显著高于湘西、湘中一带其它矿床中的白钨矿;其稀土元素配分模式均表现出向上拱曲的富MREE特征。该区白钨矿的~(147)Sm/~(144)Nd比值为0.2079~0.4070,~(143)Nd/~(144)Nd为0.512126~0.512398,在Sm-Nd同位素图解中构成了一条很好的等时线,其对应的等时线年龄为207.8±1.5Ma(MSWD=1.03),表明该矿形成于晚三叠世。该区白钨矿的~(87)Sr/~(86)Sr值较高(0.73164~0.73974),大体与渣滓溪矿区的白钨矿一致,高于廖家坪和龙山矿区的白钨矿,但明显低于沃溪和西安矿区的白钨矿,这暗示湘中、湘西一带不同时代形成的金钨矿床,其成矿物质来源和成矿机制可能存在差异。Sr-Nd同位素联合示踪显示,包金山矿区白钨矿的Sr-Nd同位素组成,明显不同于新元古界板溪群和紫云山岩体的主体,而是与紫云山补体花岗岩较吻合,暗示该区金钨成矿可能与紫云山晚期岩浆活动有关。结合区域年代学资料,可进一步推断出,晚三叠世金、钨成矿作用在湘中地区广泛存在,这些成矿作用均与印支期花岗质岩浆活动有关。湘中一带前寒武纪浅变质岩中的金矿床,在成因上是属与还原性侵入岩有关的金矿类型(IRGS型)。
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| 关 键 词： | 地球化学特征 SM-ND同位素定年 白钨矿 矿床成因 包金山金钨矿床 |
| 收稿时间： | 2021/1/2 0:00:00 |
| 修稿时间： | 2021/2/20 0:00:00 |
Geochemical characteristics and Sm-Nd geochronology of scheelite in the Baojinshan ore district, central Hunan |
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| PENG JianTang,WANG Chuan,LI YuKun,HU A''Xiang,LU YuLong,CHEN XianJia.Geochemical characteristics and Sm-Nd geochronology of scheelite in the Baojinshan ore district, central Hunan[J].Acta Petrologica Sinica,2021,37(3):665-682. |
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| Authors: | PENG JianTang WANG Chuan LI YuKun HU A'Xiang LU YuLong CHEN XianJia |
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| Institution: | MOE Key Laboratory of Metallogenic Prediction of Nonferrous Metals and Geological Environment Monitoring, School of Geosciences and Info-physics, Central South University, Changsha 410083, China;State Key Laboratory of Ore Deposit Geochemistry;Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;College of Civil Engineering, Hunan City University, Yiyang 413000, China;School of Resource & Environment and Safety Engineering, Hunan University of Science and Technology, Xiangtan 410201, China |
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| Abstract: | The Baojinshan gold-tungsten deposit, located in the eastern segement of the Baimashan-Longshan-Ziyunshan EW-trending gold belt, is a typical gold deposit hosted in the Precambrian metasedimentary rocks, central Hunan Province. Based on the field investigations and indoor observations, different analytical methods including XRD, EMPA, ICP-MS and ID-MS have been adopted in this paper to study the geochemical compositions of the scheelite samples collected from the Baojinshan ore district in order to reveal their elemental and isotopic signatures. Metallogenic time and ore genesis of gold deposits hosted in metasedimentary rocks in central Hunan are further discussed. It is revealed that, the studied scheelite samples are relatively homogenous in chemical compositions: their WO3 concentrations are basically consistent with the theoretical value of scheelite (CaWO4), and their CaO concentrations are slightly less than its theoretical value, which can be ascribed to the substitution of Sr, REE, Na and other trace elements into Ca site in scheelite lattice. Expect for Sr, REE and As, the concentrations of other trace elements are less than the corresponding Clarke values in the continental crust, especially those elements including Mo, Bi, Sn, Be, Nb and Ta, are less than 1×10-6, obviously different from those scheelite occurring in the tungsten deposits related to Late Mesozoic granite in South China. The REE concentrations of scheelite in this study vary in the range of 484.5×10-6~972.9×10-6, with an average of 721.3×10-6, significantly higher than those of scheelite samples from other Au-W deposits or W deposits in central and western Hunan. All scheelite samples in the Baojinshan ore district are characterized by the convex MREE-rich pattern. The 147Sm/144Nd values of scheelite samples in this study vary from 0.2079 to 0.4070, and their 143Nd/144Nd values change from 0.512126 to 0.512398. On the 147Sm/144Nd-143Nd/144Nd diagram, the scheelite samples from the Baojinshan deposit display an excellent linear relationship, which corresponds to an isochron age of 207.8±1.5Ma (MSWD=1.03), thus, the gold-tungsten mineralization at the Baojinshan ore district took place during the Late Triassic. The 87Sr/86Sr values of the studied scheelite samples vary in the range of 0.73164~0.73974, roughly consistent with those of the Zhazixi deposit, higher than those of the Liaojiaping and Longshan deposits, but are obviously less than those of the Woxi and Xi''an deposits, revealing there exists some distinct differences for gold deposits or tungsten deposits formed at different times in central Hunan, on their ore-forming materials and mineralization mechanism. It is revealed that Sr-Nd isotope compositions of the scheelite in this study, obviously different from those of the Banxi Group and the main part of the Ziyunshan pluton, and partly overlap with those of the complement part in the Ziyunshan pluton, which reveals that gold-tungsten mineralization is related to the late magmatic activity. Combined with the regional date data, it is concluded that the Late Triassic Au-W mineralization is widespread throughout central Hunan, and is intimately associated with the Indosinian granitic activities, the gold deposits hosted in metasedimentary rocks in this region, genetically belong to the reduced intrusion-related gold system (IRGS) rather than orogenic deposits. |
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| Keywords: | Geochemical characteristics Sm-Nd isotopic dating Scheelite Ore genesis Baojinshan Au-W deposit |
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