贵州从江污牙钨矿床地球化学特征及其成因探讨

Geochemical Characteristics and Genesis of the Wuya Tungsten deposit in Congjiang Area,Guizhou Province

本文对污牙钨矿区矿石、蚀变围岩、地层围岩及花岗岩进行了微量元素分析,分析结果显示,污牙钨矿床大多数矿石和蚀变围岩样品的Hf/Sm与Th/La值小于1,少部分蚀变围岩的Hf/Sm与Th/La值大于1,表明成矿流体以富Cl热液体系为主,部分显示富F特征,成矿流体具有多源性。云英岩化围岩及矿石与地层围岩样品的微量元素特征相似,主要显示变质成因;其它类型矿石及蚀变围岩样品微量元素特征与地层围岩样品差别较大,可能非单一变质热液作用的产物。类矽卡岩矿石中典型接触交代矿物符山石的大量存在,暗示岩浆热液参与成矿。在微量元素蛛网图上,蚀变围岩和电云英岩型矿石样品皆不显示Zr-Hf亏损,少数样品Ta-Nb也无异常,特征与地层围岩不同,与花岗岩样品相似,支持了岩浆热液作用的存在,污牙钨矿床很可能为变质热液与岩浆热液复合叠加成因。污牙矿区花岗岩和赋矿围岩,W元素均显示富集特点。

In this paper,trace elements of ores,altered wall-rocks,unaltered wall-rocks and granites are analyzed. Results show that values of Hf / Sm and Th / La of most ores and altered wall-rocks are more than 1indicating a solution system enriched in Cl,but that of some altered wall-rocks are less than 1 indicating a solution system enriched in F. Thus,the ore-froming fluid system originated from multiple sources. The trace elements features of wall-rocks and ores of greisenization are simlar to that of unaltered wall-rocks,which mainly suggest a metamorphic origin. However,other types of ores and altered wall-rocks have different trace elements features with that of unaltered wall-rocks,and thus only metamorphic genesis cannot form it. The idocrase,typical contact metasomatic mineral,abound in the skarnlike ores implying the participation of magma hydrothermal fluids. In addition,on the spider diagram of trace elements,altered wall-rocks and tourmalite greisenization-type ores show no Zr-Hf negative anomalies,and some show no Ta-Nb negative anomalies too. That features similar to that of granite samples rather than wall-rocks,which also support the existence of magma hydrothermal mineralization. The deposit was produced by superimposition of metamorphic and magma hydrothe-rmal fluids. Both ganite and wall-rocks are enriched in element W.