越城岭东侧泥盆系地层中白钨矿成因分析

Analysis of the genesis of scheelite deposits in the Devonian strata on the east side of Yuechengling Mountains

桂北越城岭东侧泥盆系白钨矿床产于越城岭加里东期花岗岩体外接触带,矿体呈层状、似层状或透镜状赋存于泥盆系唐家湾组白云岩中,矿床类型为比较少见的一种中低温热液的碳酸盐岩型矿床,矿石以交代结构和细脉浸染状构造为主,矿石矿物主要为白钨矿、黄铁矿等。矿石矿物主要形成阶段为热变质和碳酸盐阶段。电子探针分析表明:白钨矿呈粒状主要发育于方解石脉脉壁,部分被包含于方解石脉中,小部分被包含于白云石脉中。表明含钙、钨的热液沿裂隙运移,在一定的温度压力环境下停留,白钨矿先结晶析出,剩余富含钙质热液在温度缓慢降低过程中结晶形成晶型良好,颗粒较大的方解石。后期再次受力发生破碎,被白云石脉填充胶结。研究认为,本矿床白钨矿成矿与方解石脉、白云石脉发育关系密切,成矿物质可能来源于越城岭花岗岩体或寒武系等较老地层,矿石中未见石英等硅酸盐矿物分布,围岩蚀变主要以碳酸盐化等中低温热液蚀变为主,为比较少见的一类中低温钨矿床。下文结合实践,主要就该矿地质特征及矿床成因进行分析探讨,以期能对该区同类型矿床的找矿工作提供一些参考作用。

The Devonian scheelite deposit on the eastern side of the Yuechengling Mountains in northern Guangxi is located in the contact zone of the Caledonian granite outside the Yuechengling Mountains.The ore body is layered,layered,or lens shaped and exists in the dolomite of the Tangjiawan Formation in the Devonian.The deposit type is a relatively rare carbonate rock type deposit with medium to low temperature hydrothermal fluids.The ore is mainly composed of metasomatic structures and fine vein disseminated structures,and the ore minerals are mainly scheelite,pyrite,etc.The main formation stages of ore minerals are thermal metamorphism and carbonate stage.Electron probe analysis shows that scheelite is mainly developed in granular form on the walls of calcite veins,with some contained in calcite veins and a small portion contained in dolomite veins.It indicates that hydrothermal fluids containing calcium and tungsten migrate along cracks and remain in a certain temperature and pressure environment.Scheelite first crystallizes and precipitates,while the remaining calcium rich hydrothermal fluids crystallize and form calcite with good crystal structure and larger particles during the slow temperature reduction process.In the later stage,it was subjected to force again and fractured,filled and cemented by dolomite veins.Research suggests that the mineralization of scheelite in this deposit is closely related to the development of calcite and dolomite veins.The ore-forming materials may have originated from older strata such as the Yuechengling granite body or the Cambrian system.Silicate minerals such as quartz are not found in the ore,and the alteration of the surrounding rock is mainly caused by medium to low temperature hydrothermal alteration such as carbonation,making it a relatively rare type of medium to low temperature tungsten deposit.The following text,combined with practice,mainly analyzes and discusses the geological characteristics and genesis of the deposit,in order to provide some reference for the exploration of similar deposits in the area.