湖南杏枫山钨矿床热液榍石的地球化学特征、U-Pb定年及其地质意义

杏枫山钨矿床是湘中地区近年新发现的、产出于浅变质岩系中的矽卡岩型钨矿。本文通过电子探针与LA-ICP-MS等技术手段，对杏枫山矿区矽卡岩中的热液榍石进行了主、微量元素组成以及U-Pb年代学研究。研究表明，榍石具有以下特征：(1)较低的∑REE、TiO₂含量，极低的Th/U，以及较高的Al₂O₃和F含量，这些均为典型热液榍石的地球化学特征；(2)富W而亏损Mo，表明其形成的热液流体具有富W贫Mo的特征；(3)稀土配分模式为左倾的、轻稀土显著亏损的重稀土富集型，正Ce、Eu异常表明其形成环境较为还原。此外，榍石原位U-Pb定年结果显示该矿形成于215.2±2.7Ma，与邻近白马山钛铁矿花岗岩形成的时间一致，基于地质及年代学证据，我们认为该矿的形成与白马山印支期的岩浆热液活动有关。结合前人的研究结果，我们发现湘中地区钨成矿与印支期还原性花岗质岩浆岩密切相关，为湘中印支晚期区域性成矿作用的产物。

Geochemical characteristics, U-Pb dating of hydrothermal titanite from the Xingfengshan tungsten deposit in Hunan Province and their geological significance

The Xingfengshan skarn-type tungsten deposit,hosted in low grade metamorphic rocks,was discovered in Xiangzhong region recently.In this paper,major and trace element compositions,U-Pb dating of the hydrothermal titanite from the Xingfengshan skarn were analyzed by EPMA and LA-ICP-MS.The results show that the titanite possesses relatively low∑REE,Ti O2 contents and Th/U ratio,and high Al2O3 and F contents,i.e.,it belongs to typical hydrothermal titanite.The enrichment of W and depletion of Mo in the titanite suggest the hydrothermal fluid was rich in W and poor in Mo.The chondrite-normalized REE pattern of the titanite displays HREE enriched with obvious Ce and Eu positive anomalies,suggesting it formed under reduced environment.In-situ U-Pb dating of the titanite yields the intercept age of 215.2±2.7 Ma,indicating the skarn tungsten deposit formed synchronously with the adjacent Baimashan ilmenite-type granitoid.Based on geological and geochronological evidences,we conclude that the deposit was genetically related to Baimashan magmatic-hydrothermal event in Indosinian.Combined with previous research,it is revealed that tungsten mineralization in Xiangzhong region is closely associated with Indosinian reduced granitoid and is a part of Late Indosinian regional mineralization event that took placed in the study region.