桂北摩天岭地区新村铀矿床沥青铀矿微区年代学和地球化学特征研究  

In-Situ Geochronology and Geochemistry of Pitchblende from Xincun Uranium Deposit in Motianling Area,North Guangxi

作　　者：王勇剑[1] 庞雅庆[1] 范洪海 章健[2] 麻乾坤 Wang Yongjian;Pang Yaqing;Fan Honghai;Zhang Jian;Ma Qiankun(Beijing Research Institute of Uranium Geology,China National Nuclear Corporation,Beijing 100029,China;Research Institute No.203,China National Nuclear Corporation,Changsha 410007,China)

机构地区：[1]核工业北京地质研究院,北京100029 [2]核工业二三〇研究所,湖南长沙410007

出　　处：《地球科学》2024年第4期1307-1323,共17页Earth Science

基　　金：中国铀业有限公司地勘项目(No.地D2210);核工业北京地质研究院院长青年基金项目(No.地QJ2101);广西铀矿成矿规律研究项目(No.地技2201).

摘　　要：为深入探究桂北摩天岭花岗岩体中新村铀矿床的精确成矿时代及矿床成因,利用微区原位分析技术(SEM、EPMA和LA-ICP-MS)对主成矿期(铀-硅化型)沥青铀矿开展了详细的矿相学观察、原位U-Pb定年和化学成分分析.沥青铀矿电子探针化学定年计算得到的年龄值变化范围极大,不能准确地反映矿床的大致形成时间.LA-ICP-MS U-Pb同位素分析结果表明,新村矿床沥青铀矿含有一定量的普通铅,采用Tera-Wasserburg图解法得到一个下交点年龄为57.61±0.34 Ma(MSWD=0.97),可以代表主成矿期的矿化年龄.新村矿床沥青铀矿具有较高的WO_(3)、CaO和极低的ThO含量,暗示成矿流体可能为富U、W的中低温成因流体;沥青铀矿稀土元素配分模式为轻稀土微富集型,整体上与赋矿花岗岩稀土配分型式相似,指示成矿物质可能来自花岗岩体本身.新获得的铀成矿年龄与桂北地区热液型铀矿的主成矿期(70~50 Ma)基本一致,表明新村矿床同华南地区绝大多数中新生代热液铀矿床一样,都是白垩纪-古近纪岩石圈伸展减薄背景之下的产物.To better determine the precise mineralization age and examine the genesis of the Xincun uranium deposit in Motianling granite,North Guangxi,it carried out detailed mineralogical observation,in-situ U-Pb isotope and chemical composition analysis on the pitchblende of U-silicified type mineralization from the Xincun deposit using scanning electron microscopy(SEM),electron probe(EPMA)and laser ablation inductively coupled plasma mass spectrometry(LA-ICP-MS).The chemical age of pitchblende obtained by the electron probe gives a very wide range and thus cannot represent the true formation age of the Xincun uranium mineralization.The results of LA-ICP-MS U-Pb isotope indicate that the pitchblende of the Xincun deposit contains a certain amount of common Pb,and the Tera-Wasserburg diagram yields a lower intercept age of 57.61±0.34 Ma(MSWD=0.97),which can represent the exact timing of Xincun deposit.The major and trace element results show that the pitchblende of the Xincun deposit has high WO_(3) and CaO contents but extremely low ThO content,indicating that the ore fluid may be enriched in U and W and has medium-low temperature.The chondrite-normalized patterns of rare earth elements in pitchblende are slightly rich in light-REE,and similar to the rare earth partition of the ore-hosting granite.It is thus speculated that the uranium is probably derived from the granitoid itself.The newly obtained mineralization age is consistent with the main metallogenic period(70-50 Ma)of the hydrothermal uranium deposits in northern Guangxi.Similar to most of the Mesozoic and Cenozoic hydrothermal uranium deposits in South China,the Xincun deposit was formed due to the extension and thinning of the Cretaceous-Paleogene lithosphere in South China.

关 键 词：微区分析 U-PB定年 沥青铀矿 新村矿床 摩天岭地区 广西 矿床学 

分 类 号：P597[天文地球—地球化学] P611[天文地球—地质学]