赣南盘古山和淘锡坑黑钨矿化学成分和晶体结构及指示意义

Chemical Composition and Crystal Texture of the Pangushan and Taoxikeng Wolframite in Southern Jiangxi and its Indication Significance

赣南地区是世界著名的钨矿资源产区,黑钨矿是该区钨矿中最重要的钨矿石矿物。本文以赣南盘古山和淘锡坑两个典型钨矿床中的黑钨矿作为研究对象,采用电子探针、X射线衍射等分析技术对黑钨矿的晶体结构、化学成分及其空间分布规律开展研究。结果表明,研究区黑钨矿主要属于锰钨铁矿,黑钨矿中Mn^(2+)和Fe^(2+)为类质同象的关系,因此MnO与FeO之间呈明显的负相关。在空间上x(Fe/(Mn+Fe))值有一定的变化规律,由矿脉深部到浅部,x值先变大再变小,反映出矿液的运移从下而上,随后上部矿液又有向下回流的现象;同一脉体各中段均为中间x(Fe/(Mn+Fe))值大,向两侧比值减小,说明同一中段上矿体中部黑钨矿形成温度较高,两侧黑钨矿形成温度较低。盘古山黑钨矿中Nb和Ta的含量均高于淘锡坑黑钨矿,这说明盘古山黑钨矿体比淘锡坑黑钨矿更靠近岩体。单一矿脉自下而上黑钨矿中Nb、Ta含量先是迅速变小,而后略有增大,这也说明矿液运移的复杂性。两矿区黑钨矿都具有重稀土富集左倾的"躺椅式"球粒陨石标准化配分模式。盘古山矿床黑钨矿稀土总量(ΣREEs)较高,La_N/Yb_N比值较低,轻重稀土分馏较为明显;淘锡坑矿床黑钨矿稀土总量(ΣREEs)较低,La_N/Yb_N比值范围较广,轻重稀土分馏程度有强有弱。它们都具有强烈的δEu负异常和弱的δCe负异常,说明矿床是在封闭的还原条件下形成的。将赣南盘古山、淘锡坑钨矿与广西珊瑚、江西浒坑和湖南瑶岗仙钨矿中黑钨矿的晶胞参数进行对比分析,显示产于花岗岩体内接触带的黑钨矿FeO含量较低,晶胞参数值较大;产于花岗岩体外接触带的黑钨矿FeO含量较高,晶胞参数值较小。因此,利用黑钨矿的化学成分和晶体结构的变化特征,可以指示成矿物质在空间上的运移特征,也可作为判断矿床成因的依据。研究成果对同类矿床的研究具有借鉴和启示意义。

Southern Jiangxi province is famous for its tungsten mineral resources in the world, of which wolframite is the most important tungsten ore in the area. Wolframite from two typical tungsten deposits at Panguushan and Taoxikeng in southern Jiangxi was studied in this paper, the crystal structure and chemical composition of wolframite are analyzed to understand its spatial distribution using electron probe and X-ray diffraction. Results indicate that the wolframite in the research area belongs to manganese tungsten ore, and the Mn2＋ and Fe2＋ in the wolframite is a kind of isomorphic relationship, and MnO and FeO shows an obviously negative correlation. The value of x[Fe / （Mn ＋ Fe）] has certain regularity in the space. From deep to shallow of the vein, cr value first increases and then decreases, which reflects the migration of ore fluid from bottom to top,and backflow may occur in the shallow. The x[Fe / （Mn ＋ Fe）] values in the middle section of the vein are higher than those on both side of the same vein, indicating that the formation temperature of wolframite in the middle section of the vein is higher than that on both sides of the vein. The contents of Nb and Ta of wolframite in Pangushan are higher than those in Taoxikeng, indicating that the Pangushan wolframite is closer to the rock mass than the Taoxikeng wolframite. From bottom to top of a single vein, the contents of Nb and Ta in the wolframite firstly decrease rapidly and then increase slightly, which indicates the complexity of the ore-bearing fluid migration. The ehondrite-standardized REEs distribution diagrams of wolframite from Pangushan tungsten and Taoxikeng ore deposits are characterized by left-leaning pattern with relative enrichment of heavy REEs. Wolframite from the Pangeoushan tungsten ore deposit is characterized by relatively high IREEs, low LaN/YbN, and obvious REEs fractionation. Wolframite from the Taoxikeng tungsten ore deposit is characterized by relatively low content of Y.REEs and a wide range of of LaN/YbN, and variable REEs fractionation. They all have a strong negative Eu anomaly and weak negativeCe anomaly, indicating that the deposits were formed in the closed reduction conditions. The comparison study of cell parameters of wolframite from five typical tungsten deposits, including Pangushan, Taoxikeng, Sanhu, Hukeng, Yaogangxian tungsten ore deposits, shows that wolframite occurring within inner contact zone of granite has a low FeO content and high cell parameters, while wolframite in outer contact zone of granite has a high FeO content and low cell parameters. Therefore, the chemical composition and crystal structure characteristics of wolframite can not only be used to indicate the migration features of ore-forming materials in the space, but also discriminate the genesis of ore deposits. The results of the study have reference and enlightenment significance to the similar deposits.