不同世代单矿物微量元素组成对山东微山稀土矿床成因的约束  

Genesis of Weishan REE Deposit in the Western Shandong, China:Constraints from Trace Elements of Single Mineral

作　　者：樊凯 张海东[1] 王辰[1] 李振[1] 刘建朝[1] 邓聚庭 张婧雯 FAN Kai;ZHANG Hai-dong;WANG Chen;LI Zhen;LIU Jian-chao;DENG Ju-ting;ZHANG Jing-wen(School of Earth Science and Resources,Chang an University,Xi'an 710054,Shaanxi,China)

机构地区：[1]长安大学地球科学与资源学院,陕西西安710054

出　　处：《地球科学与环境学报》2022年第2期257-274,共18页Journal of Earth Sciences and Environment

基　　金：国家自然科学基金项目(42172090);山东省地质勘查基金项目(203027160439)。

摘　　要：微山稀土矿床位于华北克拉通郯庐断裂西侧,为中国第三大碳酸岩型稀土矿床。微山稀土矿床碳酸岩脉具有明显的分带性,共识别出4类不同岩性的碳酸岩脉,并划分了4个岩性带。基于详细的岩相学研究,在含矿碳酸岩脉中识别出4个世代方解石、4个世代氟碳铈矿和3个世代萤石。单矿物原位微区分析结果显示,第一世代方解石(Cal-1)和磷灰石为岩浆成因,而第三世代方解石(Cal-3)为热液成因。矿物地球化学数据显示,萤石可分为岩浆成因(Tb/La值为0.005~0.043)及热液成因(Tb/La值为0.17~0.28)两类。磷灰石富F(含量(质量分数,下同)为3.86%~5.82%)、贫Cl(<0.03%)的地球化学特征表明其为碳酸盐-硅酸盐系列岩浆结晶作用的产物。磷灰石具有较高的Sr/Y、Th/U值,和极高的Sr含量((8615~19985)×10^(-6))、Ba含量((47~107)×10^(-6)),表明微山稀土矿床岩浆源区可能为富集岩石圈地幔,并受到了富稀土元素流体的改造。萤石地球化学特征指示该稀土矿床中的成矿热液源自碳酸岩熔体,且随着成矿流体的演化,成矿环境由还原环境逐步过渡为氧化环境。成矿流体富含F^(-)、SO_(4)^(2-),表明F^(-)、SO_(4)^(2-)是稀土元素高效迁移的主要载体。Weishan REE deposit,which is located in the western Tanlu fault of North China Craton,is the third largest carbonatite-related REE deposit in China.The orebodies exhibit an obvious zonation,four types of ore veins are identified in Weishan REE Deposit.Among these ore veins,four lithologic zones are divided in the carbonatite dikes.Based on the detailed petrographic research,four generations of calcites,four generations of bastnaesites and three generations of fluorites are identified in the carbonatite dikes.The in-situ microanalysis results of single mineral show that the first generation calcite(Cal-1)and apatite are derived from magmatic system,while the third generation calcite(Cal-3)is derived from hydrothermal system.Origin of fluorite from Weishan REE deposit can be divided into magmatic origin(Tb/La is 0.005-0.043)and hydrothermal origin(Tb/La is 0.17-0.28).Apatite is characterized by high F content(3.86%-5.82%)and low Cl content(<0.03%),which suggests that the apatite is crystallized from carbonate-silicate magma.Apatite exhibits high Sr/Y and Th/U,and extremely high Sr content((8615-19985)×10^(-6))and Ba content((47-107)×10^(-6)),indicating that the source of magma for Weishan REE deposit may derive from the enriched lithospheric mantle,and experience REE-rich fluid metasomatism.The geochemical characteristics of fluorite indicate that the hydrothermal fluids in Weishan REE deposit originate from carbonatite magma,and gradually change from reducing environment to oxidizing environment.The high concentrations of F^(-) and SO_(4)^(2-)of the ore-forming fluid in Weishan REE deposit indicate that F^(-) and SO_(4)^(2-) are major carriers of REE transport.

关 键 词：稀土矿床 碳酸岩 单矿物原位微区分析 方解石 萤石 磷灰石 郯庐断裂 山东 

分 类 号：P618.7[天文地球—矿床学]