| 广西苗儿山铀矿田张家铀矿床成矿时代:沥青铀矿微区原位测定 |
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| 引用本文： | 郭春影,秦明宽,徐浩,任忠宝,邹明亮,白芸,赵宇霆.广西苗儿山铀矿田张家铀矿床成矿时代:沥青铀矿微区原位测定[J].地球科学,2020,45(1):72-89. |
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| 作者姓名： | 郭春影 秦明宽 徐浩 任忠宝 邹明亮 白芸 赵宇霆 |
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| 作者单位： | 1.中核集团核工业北京地质研究院, 北京 100029 |
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| 基金项目： | “十三五”国防预先研究项目3210402国家自然科学基金项目41502097国家自然科学基金项目41702102 |
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| 摘 要： | 张家铀矿床是苗儿山铀矿田北部的代表性铀矿床之一，对其开展详细的成矿年代学研究不仅对认识区域铀成矿规律十分重要，也对探讨华南花岗岩型热液铀矿床的成矿大地构造背景及动力学机制具有重要意义.在详细的镜下观察基础上，采用电子探针U-Th-Pb化学法、LA-ICP-MS U-Pb同位素方法对脉状沥青铀矿进行了年代学研究.20个点的U-Th-Pb化学年龄为55.3~81.1 Ma，其中19个点的加权平均年龄为71.4±1.9 Ma.根据稀土元素特征的不同，将34个点的LA-ICP-MS U-Pb同位素年龄分为2组，第一组共15个点，其中13个点的206Pb/238U加权平均年龄为69.4±4.9 Ma；第二组共19个，其中16个点的206Pb/238U加权平均年龄为94.1±3.0 Ma.电子探针U-Th-Pb化学法加权平均年龄（71.4±1.9 Ma）与LA-ICP-MS U-Pb同位素法较年轻的一组206Pb/238U加权平均年龄（69.4±4.9 Ma）一致，代表张家铀矿床的成矿时代，LA-ICP-MS U-Pb同位素法较老的一组206Pb/238U加权平均年龄（94.1±3.0 Ma）可能是沥青铀矿受后期改造和/或样品剥蚀过程杂质矿物影响而地质意义不明确.晚中生代期间，古太平洋板块向欧亚大陆俯冲可能是控制华南大规模花岗岩型铀矿床形成的动力学机制，包括张家铀矿床在内的华南花岗岩型铀矿床大规模成矿作用可能受80~50 Ma古太平洋板块对亚洲东部的斜向俯冲动力体制的控制.
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| 关 键 词： | 华南 热液铀矿床 EPMA U-Th-Pb化学年龄 LA-ICP-MS U-Pb定年 动力学环境 地质年代学 |
| 收稿时间： | 2018-06-29 |
Age of Zhangjia Uranium Deposit in the Miaoershan Ore Field,Guangxi Autonomous Region,China: In Situ Micro-Determination on Pitchblende |
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| Abstract: | The Zhangjia uranium deposit is one of the representative uranium deposits in the northern Miaoershan uranium orefield. The detailed study of metallogenic ages of the Zhangjia uranium deposit is very important not only to understanding the regularity of uranium mineralization at regional scale of the Miaoershan uranium orefield but also to systematically investigating the tectonic setting and geodynamics of hydrothermal uranium deposits in granitoids in Southern China. Based on detailed microscopic observation,the vein pitchblende was studied by in-situ electron microprobe U-Th-Pb and LA-ICP-MS U-Pb isotopic and rare earth element analysis. Twenty spots electron probe micro-analysis (EPMA) show calculated U-Th-Pb chemical ages ranging from 55.3 Ma to 81.1 Ma. 19 of the 20 ages give a weighted average age at 71.4±1.9 Ma. Based on rare earth elements differences,34 spots LA-ICP-MS U-Pb isotopic ages can be classified into two groups. The 13 U-Pb isotopic data of the first group 15 data give a weighted 206Pb/238U average age at 69.4±4.9 Ma. The second group includes 19 data spots,16 of which give a weighted 206Pb/238U average age at 94.1±3.0 Ma. The weighted EPMA U-Th-Pb chemical age 71.4±1.9 Ma is identical to the weighted 206Pb/238U average age 69.4±4.9 Ma of first group 13 data spots calculated by LA-ICP-MS U-Pb isotopic method. Thus we believe that the Zhangjia uranium deposit was formed at some 70 Ma. The weighted 206Pb/238U average age 94.1±3.0 Ma of the second group of the LA-ICP-MS U-Pb isotopic data is believed to have no geological significance and was possibly affected by post-formation alteration and/or impurities minerals in the laser ablation process. In late Mesozoic era,the paleo-Pacific plate was subducted to the eastern Eurasia continent,which affected the tectonics,magmatism and metallogenisis of the South China block. The hydrothermal uranium deposits in grantoids of South China,including the Zhangjia uranium deposit,were mostly formed in 50 Ma to 80 Ma which corresponds to the oblique subduction of the paleo-Pacific Plate to the eastern Eurasia Continent. |
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