桂北广子田铀钨矿床成因——沥青铀矿原位U-Pb定年、矿物地球化学证据  

Genesis of the Guangzitian uranium—tungsten deposit in northern Guangxi——Geochemical evidences from in-situ U-Pb dating of pitchblende and mineral geochemistry

作　　者：肖为[1] 范洪海 陈东欢[1] 庞雅庆[1] 郑可志 罗桥花 XIAO Wei;FAN Honghai;CHEN Donghuan;PANG Yaqing;ZHENG Kezhi;LUO Qiaohua(CNNC Beijing Research Institute of Uranium Geology,Beijing,100029;No.310 Geology Party of Nuclear Industry,Guangxi Zhuang Autonomous Region,Guilin,Guangxi,541000)

机构地区：[1]核工业北京地质研究院,北京100049 [2]广西壮族自治区三一〇核地质大队,广西桂林541213

出　　处：《地质论评》2022年第3期831-844,共14页Geological Review

基　　金：中国核工业地质局“华南富大铀矿空间定位条件与远景预测研究”(编号:202138-10)的成果。

摘　　要：广子田矿床是桂北地区典型的碳硅泥岩型铀矿床,同时具有铀钨共伴生的独特属性,前人对该矿床研究程度较低,对该矿床成矿时代和矿床成因缺乏必要的约束。本文在精细矿物学研究的基础上,利用电子探针(EPMA)开展了白钨矿和沥青铀矿元素成分分析,利用LA-ICP-MS方法开展了沥青铀矿U-Pb同位素及稀土元素含量分析。LA-ICP-MS U-Pb同位素结果表明,沥青铀矿中含有较高的的普通铅,利用Tera—Wasserburg图解计算其下交点年龄为30.8±4.2 Ma(MSWD=0.13),其普通铅初始[n(^(207)Pb)/n(^(206)Pb)]_(0)为0.22,为异常铅,表明其来源于积累了部分放射性成因铅的富铀源区。电子探针和LA-ICP-MS元素分析结果表明,沥青铀矿以较高的UO_(2)、CaO和WO_(3)含量和较低的SiO_(2)、ThO_(2)含量为特征,同时具有较高的LREE/HREE值、中等程度的负δCe异常和负δEu异常,白钨矿则具有较高的MoO_(3)含量,结合(LREE/HREE)_(N)—∑REE图解,认为晚期铀成矿流体为富U、W的中低温、中低盐度氧化性成矿流体。广子田矿床沥青铀矿中具有较高的W含量,其LREE/HREE值及初始[n(^(207)Pb)/n(^(206)Pb)]_(0)与前人对其北部独石岭钨矿中白钨矿LREE/HREE和热液榍石初始[n(^(207)Pb)/n(^(206)Pb)]_(0)的研究结果相近,表明早期形成的钨矿体(床)可能提供了部分成矿物质。Objectives:The Guangzitian deposit is a typical Carbon—Silicon-Shale type uranium deposit in northern Guangxi,with the unique attribute of uranium—tungsten symbiosis,but the previous studies on the deposit are relatively low,and there is a lack of necessary constraints on the mineralization and metallogenic age of the deposit.Methods:In this paper,the electron probe method analysis(EPMA)was carried out to analyze the composition of scheelite and pitchblende,and the LA-ICP-MS method was used to analyze the U-Pb isotope and rare earth element content of pitchblende.Results:The results of electron probe and LA-ICP-MS elemental analysis show that pitchblende is characterized by higher UO_(2),CaO and WO_(3) contents and lower SiO_(2) and ThO_(2) contents,as well as higher LREE/HREE ratio,moderate negativeδCe anomaly andδEu anomaly,while scheelite has higher MoO_(3) content.In-situ LA-ICP-MS U-Pb dating of pitchblende yielded a lower intercept age of 30.8±4.2 Ma(MSWD=0.13),and the initial common lead[n(^(207)Pb)/n(^(206)Pb)]_(0) of pitchblende is 0.22,which is belongs to abnormal lead.Conclusions:The metallogenic age of Guangzitian deposit is 30.8±4.2 Ma,corresponding to the late regional metallogenic event of about 25 Ma in South China.The ore-forming fluid is medium—low temperature and medium—low salinity oxidizing fluid rich in U and W elements,and the tungsten deposit formed in the early stage may provide some ore-forming materials for the formation of Guangzitian deposit.

关 键 词：桂北 铀钨矿床 沥青铀矿 LA-ICP-MS U-Pb定年 

分 类 号：P619.14[天文地球—矿床学] P618.67[天文地球—地质学]