广东仁化棉花坑铀矿床萤石矿物学、地球化学特征及其地质意义

Mineralogical and Geochemical Characteristics of Fluorite and Its Geological Significance in the Mianhuakeng Uranium Deposit,Renhua,Guangdong Province

棉花坑铀矿床产有三类萤石,分别为形成于铀成矿期主成矿阶断的紫黑色萤石、形成于铀成矿期成矿晚阶段的紫色萤石以及形成于铀成矿后期的浅绿色萤石,这三类萤石均属于热液成因。紫黑色萤石和紫色萤石相似的稀土元素配分模式暗示了两者具有相同的物质来源,而浅绿色萤石的物质来源可能与紫黑色萤石、紫色萤石的物质来源不同。从铀成矿期至铀成矿期后,萤石弱的负Ce异常、明显的负Eu异常和U的含量以及这些参数的变化特征都指示了成矿环境由还原向氧化转化,成矿流体性质由还原向氧化演化。在研究棉花坑铀矿床萤石微量元素和稀土元素的基础上,结合长江铀矿区的成矿地质背景和类比邻近相似铀矿区成矿流体的研究成果,认为棉花坑铀矿床成矿流体存在多源性,该成矿流体是一种经历了深部循环的外来流体,并不源于富含Ba、U等元素的前寒武纪结晶基底,也并未与其发生较为充分的水-岩反应。

There are three types of fluorite in Mianhuakeng uranium deposit,which are the violet-black fluorite formed in the main stage of uranium mineralization period,the violet fluorite formed in the late stage of uranium mineralization period and the light green fluorite formed in the post-stage of uranium mineralization.All three types of fluorite belong to hydrothermal genesis.The similar REE distribution patterns of violet-black fluorite and violet fluorite indicate that they have the same material source,while the material source of light green fluorite may be different from that of violet-black fluorite and violet fluorite.From the main stage of uranium mineralization to the post-stage of uranium mineralization,the weak negative Ce anomaly,the obvious negative Eu anomaly of fluorite,the U content in fluorite,and the variation characteristics of these parameters all indicate that the metallogenic environment and ore-forming fluid properties evolved from reduction to oxidation.Based on the study of trace elements and rare earth elements of fluorite in Mianhuakeng uranium deposit,combined with the analysis of metallogenic geological background of the Changjiang uranium mining area and the research results of the ore-forming fluids in the nearby similar uranium mining areas,it is considered that the ore-forming fluids of Mianhuakeng uranium deposit were less likely derived from the Precambrian basement rocks which were rich in U,Ba,etc or to have adequate water-rock interaction with them.There was the possibility of multi-source(mantle fluid and meteoric water)of ore-forming fluid,and relative to Precambrian basement rocks,it was a foreign fluid that experienced deep circulation.