砂岩型铀矿床成矿年代学研究  

Study of metallogenic chronology of sandstone type uranium deposits

作　　者：林效宾[1] 刘红旭[1] 李西得[1] 郝伟林[1] 王志明 LIN Xiaobin;LIU Hongxu;LI Xide;HAO Weilin;WANG Zhiming(CNNC Key Laboratory of Uranium Resource Exploration and Evaluation Technology,Beijing Research Institute of Uranium Geology,Beijing,100029)

机构地区：[1]核工业北京地质研究院,中核集团铀资源勘查与评价技术重点实验室,北京100029

出　　处：《地质学报》2020年第12期3712-3725,共14页Acta Geologica Sinica

基　　金：中核集团龙灿工程(第二阶段)下设专题一“二连基地砂岩型铀成矿环境和条件调查评价研究”(编号LCEQ01)及专题三“二连基地砂岩型铀矿地质数字平台和大数据找矿预测”(编号LCEQ03);国家科技部973计划项目(编号2015CB453004)联合资助成果。

摘　　要：现阶段砂岩型铀矿床成矿年龄测定主要有铀矿物U-Th-Pb表观年龄、全岩(铀矿物)样品等时线年龄、铀矿物微区原位U-Pb年龄等方法。综合各方法的原理及优缺点,认为砂岩型铀矿床的铀矿物通常颗粒细小且缺少可供扣除初始铅的伴生矿物存在,除等时线年龄方法外,铀矿物的选取及初始铅同位素的扣除均存在极大的不确定性;U-Pb等时线年龄方法的优点是可利用全岩样品分析数据及忽略初始铅的影响,但由于砂岩型铀矿床阶段性成矿的特点,时常会导致所得到的铀铅同位素数据在等时线图解中散乱分布无法成线或所得到的等时线年龄无实际地质意义等问题。本文主要是结合砂岩型铀矿床"幕式"成矿的特点,从改进砂岩型铀矿床等时线年龄拟合的理论基础入手,提出了利用"平行"等时线方法计算矿石最后一次富集成矿年龄的方法,并提出了利用238U-206Pb等时线年龄、235U-207Pb等时线年龄、206Pb/204Pb-207Pb/204Pb图解及初始铅同位素组成等指标对成矿年龄地质意义进行综合判定的方法。以哈达图、蒙其古尔和扎吉斯坦三个铀矿床全岩样品数据进行了实例计算,等时线年龄计算结果表明上述理论方法可行,能够准确计算砂岩型铀矿床的成矿年龄。"平行"等时线方法无需考虑铀矿石矿化次数及最后一次成矿时铅同位素含量及组成,在理论上可应用于其它类型铀矿床成矿年龄计算。At present, the ore-forming age of sandstone type uranium deposits is mainly determined by U-Th-Pb apparent age of uranium minerals, isochron age of whole rock or uranium minerals samples, and in-situ U-Pb age of uranium minerals. According to the principles, advantages and disadvantages of each method, it is considered that uranium minerals in sandstone type uranium deposits are usually small in size and lack associated minerals to deduct the initial lead.In addition to the isochronal age method, there are great uncertainties in the selection of uranium minerals and the deduction of initial lead isotopes. The advantage of the U-Pb isochron age method is that the whole rock sample analysis data can be used and the influence of the initial lead can be ignored. However, due to the characteristics of the stage mineralization of sandstone type uranium deposits, the scattered distribution of the obtained U-Pb isotopic data in the isochron diagram is often either unable to form a line or the obtained isochron age has no practical geological significance.Combined with the characteristics of episodic mineralization of sandstone type uranium deposits, this paper mainly begins with improving the theoretical basis of isochron age fitting of sandstone type uranium deposits, proposes a method for calculating the last ore enrichment age by using "parallel" isochron method, and further puts forward a comprehensive method to determine the geological significance of ore-forming age by using 238U-206Pb isochron age, 235U-207Pb isochron age, 206Pb/204Pb-207Pb/204Pb diagram and initial lead isotopic composition.Based on the data of the whole rock samples of Hadatu, Mengqiguer and Zhajistan uranium deposits, the isochron age calculation results show that the above theoretical method is feasible and can accurately calculate the metallogenic age of sandstone type uranium deposits.The "parallel" isochron method does not need to consider the number of mineralization of uranium ore and the lead isotope content and composition in the last

关 键 词：砂岩型铀矿床 成矿年代学 U-PB同位素 成矿年龄 “平行”等时线 

分 类 号：P619.14[天文地球—矿床学]