粤北竹筒尖矿床碱交代花岗岩地球化学特征及地质意义

Geochemical characteristics and geological significance of alkali metasomatic granites in the Zhutongjian ore deposit in the north Guangdong province

竹筒尖矿床位于粤北下庄矿田西北部,区内碱交代作用较发育,碱交代花岗岩主要呈面状展布,与铀矿化关系密切。为研究区内碱交代过程元素变化特征及其与铀成矿的关系,文章系统采集了5件碱交代花岗岩样品,分析了其主量及微量元素组成。结果表明,与新鲜花岗岩相比,碱交代花岗岩中SiO2、Na2O含量明显降低,而K2O含量显著偏高,表明区内碱交代以钾质交代为主;碱交代花岗岩中相对富集Rb、Th及U元素,亏损Ba、Sr、Ti等元素,w(LREE)/w(HREE)值相对降低,δEu值与新鲜花岗岩一致。上述特征表明,区内碱交代花岗岩与新鲜花岗岩可能具有相同的形成环境及物质来源,同时暗示流体中的U可能来自花岗岩;碱交代作用的发育有利于富铀花岗岩中铀的活化转移,为成矿流体中铀的富集创造了有利条件。

The Zhutongjian deposit is located in the northwest Xiazhuang ore field in north Guangdong province.The alkali metasomatism is developed in the area,and the areally-distributed alkali metasomatic granite is closely related to uranium mineralization.In order to study the change characteristics of elements in the alkali metasomatism and its relationship with uranium mineralization,five samples of alkali metasomatic granite were collected and the mjor and trace elements were analyzed.The results show that compared with fresh granite,the content of SiO2 and Na2O in alkali lmetasomatic granite is significantly lower,while the content of K2O is significantly higher.This is the indication of dominance of potasium metasomatism.The alkali metasomatic granite is relatively enriched in Rb,Th and U elements,depleted in Ba,Sr,Ti etc.,relative lower in w(LREE)/w(HREE),and itsδEu value consistent with fresh granite.The above characteristics suggest that the alkali metasomatic granite and fresh granite may be the same of formation environment and material source and imply that U in the fluid may come from granite.Development of alkali metasomatism is beneficial to the activation and transportation of uranium from uranium-rich granite so as to creates favorable conditions for the U enrichment to ore.