Geochronology of cassiterite and trace element compositions of wolframite: Constraints to the ore genesis of Jiguanshi tungsten deposit, eastern Hunan Province

Abstract

钨是我国传统的优势金属矿产，同时也是国家高新技术领域不可或缺的战略性关键矿产之一。鸡冠石矿床是近年湘东邓阜仙地区新发现的一处钨矿床，具有良好的钨锡多金属资源前景，但其成矿时代和成因尚不清楚。本文在详细的矿床地质特征观察基础上，选取鸡冠石钨矿床中黑钨矿和锡石开展原位LA-ICP-MS 微量元素分析和U-Pb定年研究，并将该矿床与相邻矿床进行对比研究。结果显示：1）与黑钨矿密切共生的锡石U-Pb Tera-Wasserburg反等时线年龄为153.2±1.8Ma（MSWD=1.15），与湘东钨矿床晚侏罗世钨锡成矿时代吻合；2）鸡冠石钨矿床紧邻湘东钨矿床北组脉，且矿脉产状和形态等特征也类似；3）鸡冠石矿床中黑钨矿也与湘东钨矿床北组脉典型特征类似，黑钨矿HREE总量和标准化后的REE配分曲线与湘东钨矿床第一期黑钨矿的特征相似。黑钨矿稀土总量对比研究指示成矿流体可能是从湘东钨矿流向鸡冠石钨矿。综合鸡冠石钨矿床与湘东钨矿床紧密的时空关系以及相似的矿床特征，本文认为鸡冠石矿床为一个与晚侏罗世花岗岩有关的岩浆期后热液矿床，同时黑钨矿微量元素特征指示该矿床可能形成于一个富挥发分、低pH和高Eh的流体环境中。;Tungsten is a traditionally dominant mineral resource of China, and it is also one of the indispensable strategic and critical materials for national high-technology. The Jiguanshi tungsten deposit is a newly discovered one in the eastern Hunan Province, which is considered to be a promising tungsten reserve. Whereas, the age and ore genesis of the deposit are remained unclear. Based on detailed geological observations, we present new cassiterite U-Pb ages and wolframite trace element compositions of the Jiguanshi deposit, and compare the ore veins and mineral assemblage features between the Jiguanshi and adjacent deposits to constrain its ore genesis. The result shows that: (1) the cassiterite Tera-Wasserburg U-Pb age is 153.2±1.8Ma (MSWD=1.15) and is consistent with the Late Jurassic mineralization age of the Xiangdong tungsten deposit; (2) the ore veins features of the Jiguanshi deposit is similar to the north vein group in the Xiangdong deposit; (3) the features of the wolframite in the Jiguanshi is similar to those of the north vein group in the Xiangdong deposit, and the HREE contents and chondrite-normalized REE patterns of the wolframite from the two deposits are also similar. The comparative study of wolframite trace elements between the Xiangdong and the Jiguanshi deposits indicates the ore-forming fluid might flow from Xiangdong to Jiguanshi. Combining the timing of the mineralization of the Jiguanshi deposit and the close spatio-temporal relationship between the Jiguanshi deposit and the north vein group of the Xiangdong deposit, we suggest that the Jiguanshi is a magmatic-hydrothermal deposit related to the Late Jurassic granites. The trace element compositions of the wolframite at Jiguanshi indicate that the deposit might be formed in a volatiles-rich, low-pH and high-Eh environment.