橄榄玄粗岩铀地球化学与成矿关系研究——以赣南草桃背(6722)铀矿床为例  

Uranium geochemistry of shoshonite and its relationship with uranium metallization: A case study of Caotaobei (6722) uranium deposit in southern Jiangxi Province

作　　者：章邦桐[1] 吴俊奇[1] 凌洪飞[1] 

机构地区：[1]南京大学地球科学与工程学院内生金属矿床成矿机制研究国家重点实验室,江苏南京210093

出　　处：《矿床地质》2015年第2期225-234,共10页Mineral Deposits

基　　金：中国核工业地质局"十二五"高校科研项目(编号:2011-D03);973项目(编号:2012CB416703)联合资助

摘　　要：采用活动性U、Th溶浸实验、235U诱发裂变径迹、Pb同位素组成示踪等方法,对草桃背橄榄玄粗岩铀地球化学进行的研究表明:1草桃背橄榄玄粗岩U含量偏高(众数值3.23×10-6),为世界安山岩平均值的2倍左右;2 U的存在形式以结构铀为主,活动性U含量及其所占全U比例(浸出率)非常低,分别为0.7×10-6和15.9%;3根据Pb同位素组成计算,草桃背橄榄玄粗岩以U带入为特征。对流体作用敏感的元素对比值(U/Th、Pb/Ce、Ba/La、Cs/Rb)研究判明,地幔流体参与了草桃背橄榄玄粗岩的形成。草桃背橄榄玄粗岩地球化学特征表明,源区富集地幔流体的交代作用是形成草桃背橄榄玄粗岩富含U等大离子亲石元素的主要制约因素,但草桃背橄榄玄粗岩不能为6722矿床提供主要的成矿铀源。Using the mobile U leaching experiment, the 235U induced fission-track method, and lead isotope analysis, the authors investigated uranium geochemical features of the Caotaobei shoshonite, and the conclusions reached are as follows. （1） The uranium content of the Caotaobei shoshonite （Mode, 3.23 × 10-6）is as high as about twice that of the world average andesite. （2） The U in the Caotaobei shoshonite is mostly immobile, probably lattice-seated, and the content and the leachable rate of mobile U are very low （0.7 × 10-6 and 15.9% respec- tively）. （3） Calculation based on lead isotopes shows that the Caotaobei shoshonite gained uranium after its for- mation （△U= 0.998 × 10-6--3.92 × 10-6）. Fluid-sensitive trace element ratios, such as U/Th, Pb/Ce, Ba/ La and Cs/Rb, in the Caotaohei shoshonite, were studied in this paper, and the results provide evidence for mantle fluid in the formation of the Caotaobei shoshonite. These features suggest that the enrichment of LILE in the Caotaobei shoshonite was constrained by the mantle-derived fluid metasomatism, and the Caotaobei shoshon- ite could not directly contribute U to uranium mineralization.

关 键 词：地球化学 橄榄玄粗岩 活动性铀溶浸实验 235U诱发裂变径迹 地幔流体 草桃背铀矿床 

分 类 号：P619.14[天文地球—矿床学]