桂北牛塘界加里东期钨矿床年代学、成矿流体性质及其演化

牛塘界钨矿床是桂北地区苗儿山—越城岭岩体南部的一个大型钨矿床，与矿化密切相关的花岗岩为已绿泥石化的中细粒白云母花岗岩。对花岗岩进行了岩石地球化学研究，认为该岩体为高分异、高演化铝过饱和富钨花岗岩；对岩体中锆石进行了U- Pb定年分析，获得成岩年龄为410±4.9Ma；对与白钨矿共生的磷灰石进行了原位U- Pb定年，测得成矿年龄为418±37Ma，两组年龄数据表明，牛塘界钨矿床的成矿花岗岩及成矿作用都属加里东期。 本文还对牛塘界钨矿床的矿石进行了系统的研究，首先，根据蚀变类型划分出三种不同类型的矿石：矽卡岩化矿石、绿泥石化矿石及石英脉(块)型矿石；其次，根据三种矿石的特征划分出三个不同的成矿阶段，即三种矿石的形成与不同的成矿阶段相对应：矽卡岩化阶段、石英-硫化物阶段及晚期硅化-碳酸盐化阶段；第三，对各成矿阶段形成的白钨矿进行了原位微量元素分析，根据白钨矿中Mo含量的变化及白钨矿REE配分曲线中Eu的异常，阐释了成矿环境氧逸度的变化；根据白钨矿中微量元素Na和Nb含量的变化，结合白钨矿REE配分曲线特征，揭示了REE置换进入白钨矿的机理及成矿流体性质的演化趋势；第四，根据白钨矿氧同位素的分析结果，得出成矿流体为岩浆水混入部分经地层循环的大气水；第五，对成矿母岩中成矿元素W的分析结果表明，牛塘界钨矿成矿物质来源于成矿母岩。因此牛塘界钨矿床其成矿物质来源于矿区内高度分异演化的花岗岩，属加里东期晚期的产物。

Chronology, Metallogenic Fluid Properties and Evolution of the Niutangjie Tungsten Deposit, Northern Guangxi, China

Niutangjie large tungsten deposit locates in the south of the Miaoershan- Yuchengling batholith in Northern Guangxi. The ore bodies are closely associated with a slightly chloritized fine- to medium- grained granite. The whole- rock geochemical characteristics of this granite indicate that it is a peraluminous, highly fractionated and evolved, W- rich granite. Zircon in situ U- Pb dating of this granite yielded a diagenetic age of 410±4.9 Ma. The in situ U- Pb dating of apatite co- existed with scheelite in ores gave a metallogenic age of 418±37 Ma. The two ages indicate that both diagenesis and mineralization of the Niutangjie tungsten deposit occurred in the Caledonian period. This paper also carried out a systematic study on the ores of Niutangjie tungsten deposit. Firstly, according to the alteration types, three different types of ores were divided: skarn type ore, chloritized ore and quartz vein (lump)- type ore. Secondly, by the characteristics of these ores, three metallogenic stages were divided: skarnization stage, quartz sulfide stage and the late silication- carbonation stage. These three metallogenic stages are corresponding to the three different types of ores. Thirdly, thein situ trace element compositions of scheelite in each metallogenic stage were analyzed. According to the Mo contents and Eu anomalies in REE patterns of scheelite, the variation trend of the oxygen fugacity was constrained. By the changes of Na and Nb contents and the REE patterns of scheelite, the mechanisms of REE substituted into scheelite and the evolution of metallogenic fluid were revealed. Fourthly, the oxygen isotopic datum of scheelite reveal that the metallogenic fluid is magmatic water mixed with meteoric water. Fifthly, the W compositions of the parental granites indicate that the metallogenic materials of the Niutangjie tungsten deposit originates from the ore- forming parental rock. Thus, the Caledonian highly fractionated and evolved granites in this tungsten deposit are important sources of metallogenic materials.