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利用X射线粉晶衍射和电感耦合等离子体质谱法研究江西西华山钨矿床中黑钨矿的矿物学特征及指示意义

Application of X-ray Powder Diffraction and Inductively Coupled Plasma-Mass Spectrometry in Study on Mineralogical Characteristics and Significance of Wolframite from Xihuashan Tungsten Deposit, Jiangxi Province

  • 摘要: 目前针对江西大型黑钨矿石英脉型钨矿床西华山的黑钨矿矿物学特征及指示意义研究较少.本文利用X射线粉晶衍射分析和电感耦合等离子体质谱分析技术对黑钨矿晶体结构、化学成分特征及空间变化规律开展研究.获得黑钨矿晶胞参数为a0=0.477 nm, b0=0.573 nm, c0=0.498 nm, β=90°21', 属于锰钨铁矿, 与前人得出的黑钨矿晶胞参数略有不同, 代表不同元素对铁锰的类质同象替代.主要化学成分WO3、FeO、MnO的含量在空间上具有一定的变化规律, 反映了成矿物质的运移特征.微量元素Sc、Y、Nb、Ta在垂向含量变化大, 说明矿液运移具有复杂性.稀土总量ΣREEs较高(397.16×10-6~1071.11×10-6), 具有强烈的Eu负异常, 具重稀土富集左倾的"躺椅式"球粒陨石标准化配分模式.将西华山、盘古山、淘锡坑、大吉山4个典型矿床的黑钨矿稀土元素特征进行对比, 反映产在花岗岩内接触带的黑钨矿的稀土总量(ΣREEs)相对最高, 分馏最明显; 产在花岗岩内及其外接触带的黑钨矿的稀土总量(ΣREEs)相对较低, 分馏程度最不明显; 而产在花岗岩外接触带的黑钨矿的稀土总量(ΣREEs)有高有低, 分馏程度有强有弱.因此, 黑钨矿的化学成分变化特征, 可以有效地指示成矿物质空间运移特征、物质来源和矿床成因.

     

    Abstract: The Xihuashan tungsten deposit is a typical large quartz-vein type tungsten deposit with systematical study, but researches on chemical composition and spatial distribution regulation of wolframite are relatively less. Based on microscopic mineralogy, the crystal structure, chemical composition, REEs and trace elements, geochemical characteristics of wolframite selected from different levels of Xihuashan tungsten deposit were studied using X-ray Powder Diffraction and Inductively Coupled Plasma-Mass Spectrometry. The obtained lattice parameters of a0(0.477nm), b0(0.573 nm), c0(0.498 nm), β (90°21') showed that the wolframite belongs to manganese tungsten ore. It is lightly different from lattice parameters of previous studies, which is caused primarily by isomorphous substituting on Fe and Mn. The chemical components of wolframite contain mainly WO3, FeO and MnO, showing some regularity in space, indicating migration features of ore-forming material. The wolframite also contains multiple kinds of trace elements. Sc, Y, Nb and Ta show dynamic changes of content in the vertical direction, which reflect complexity of ore fluid migration. The chondrite-standardized REEs distribution patterns are characterized by left-leaning shapes with high ΣREEs (397.16×10-6-1071.11×10-6), relatively heavy REEs enrichment and strong Eu negative anomaly. By comparing the REEs characteristics of wolframite from four typical tungsten deposits including Xihuashan, Pangushan, Taoxikeng and Dajishan, the results show that the wolframite in the inner contact zone of the granite body is characterized by relatively high ΣREEs with obvious REEs fractionation. Wolframite in the inner granite body and outer contact zone is characterized by relatively low ΣREEs with unobvious REEs fractionation. Wolframite in the outer contact zone of the granite body is characterized by large changes of ΣREEs and REEs contents and fractionation. Wolframite composition characteristics can not only be used to indicate migration features of ore-forming material in space, but also to discriminate ore-forming material sources and ore genesis.

     

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