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赵慧博,刘亚非,阳珊,叶美芳,王志海,王博,常娜.电子探针测年方法应用于晶质铀矿的成因类型探讨[J].岩矿测试,2014,33(1):102-109
ZHAO Hui-bo,LIU Ya-fei,YANG Shan,YE Mei-fang,WANG Zhi-hai,WANG Bo,CHANG Na.The Application of Electron Microprobe Dating Method on a Genetic Type of Uraninite[J].Rock and Mineral Analysis,2014,33(1):102-109.DOI:
电子探针测年方法应用于晶质铀矿的成因类型探讨
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The Application of Electron Microprobe Dating Method on a Genetic Type of Uraninite
投稿时间:2013-07-11  修订日期:2013-08-11
DOI:
中文关键词: 晶质铀矿  电子探针  定年  环带年龄  成矿期次
英文关键词: uraninite  Electron Probe Microanalysis  age  zone age  mineralized periods
基金项目:中国地质调查局地质调查工作项目(12120113014500)
作者单位E-mail
赵慧博 中国地质调查局西安地质调查中心, 陕西 西安 710054  
刘亚非 中国地质调查局西安地质调查中心, 陕西 西安 710054 dogwuwu@163.com 
阳珊 安徽省地质实验研究所, 安徽 合肥 230001  
叶美芳 中国地质调查局西安地质调查中心, 陕西 西安 710054  
王志海 中国地质调查局西安地质调查中心, 陕西 西安 710054  
王博 中国地质调查局西安地质调查中心, 陕西 西安 710054  
常娜 中国地质调查局西安地质调查中心, 陕西 西安 710054  
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中文摘要:
      电子探针Th-U-Pb测年因其高分辨率与高精度的优势,在独居石、锆石等定年矿物中得到了推广,但在Th、U、Pb含量高的晶质铀矿、沥青铀矿等矿物中则应用较少。本文在铁矿床变质岩绿泥石、阳起石黑云母蚀变岩首次发现U含量高的晶质铀矿,基于此,结合该铁矿床地区的地质背景,利用偏光显微镜与电子探针等分析测试手段,将镜下蚀变现象、年龄计算与其他相关元素分析相结合,重点对晶质铀矿的成矿年龄及成矿规律进行探讨。研究发现:通过镜下观察判断,晶质铀矿的成因类型与澳大利亚著名的变质型铀矿相似,均为古老的变质型,且周围的脉石矿物均为绿泥石,绿泥石皆由黑云母退变质而成,铀矿的赋存位置显示其与黑云母、绿泥石之间有紧密联系,其成矿年龄与黑云母、绿泥石形成年龄息息相关。继而根据电子探针数据计算成矿年龄,判断成矿期次,得出主要成矿期在(1654±17) Ma~(1805±17) Ma,为中元古代中期,且主要成矿期与热液蚀变作用黑云母化有关,后期活化富集时期在(657±17) Ma~(807±17) Ma,为新元古代南华纪时期,此阶段是热液侵入、绿泥石化广泛发育的时期;选取较大颗粒对晶质铀矿的环带年龄进行计算,从年龄分布上证实后期有强烈的流体活动的发生,且主要与绿泥石化相关。另外,对比变质型与沉积型铀矿中Y2O3与UO2含量发现,两者之间存在负相关关系,此关系对判断铀矿成因即是否为变质型或沉积型可能有指示意义,但缺乏大量的数据佐证,需进一步研究。
英文摘要:
      Based on the advantages of high resolution and accuracy, Electron Probe Microanalysis (EPMA) method for Th-U-Pb is conducted to date monazite and zircon, is not typically applied in uraninite, pitchblende and other minerals which contain high contents of Th, U and Pb. Uraninite with a high content of U was first found in the iron deposit, whose rock type was chlorite and actinolite biotite altered rock. Based on the region's geological background, the microscopic alteration, age calculation and other related elements analysis, the uraninite mineralization age and metallogenic regularity have been studied intensely by Microscope and EPMA. The research results indicate that the genetic type of uraninite is similar to the famous metamorphic uraninite in Australia, belonging to the old metamorphic type. The gangue minerals are all chlorite altered by biotite. Occurrence characteristics of the uraninite reveal the close relationship between uraninote and biotite-chlorite. The mineralization age is also intimately related to the formation age of biotite and chlorite. According to the oxide content data of elements (U, Th and Pb) by EPMA, mineralized periods were obtained as the main mineralization stage is (1654±17) Ma-(1805±17) Ma, which is the mid Proterozoic and relate to the hydrothermal alteration of biotite. The later activation and enrichment period is (657±17) Ma-(807±17) Ma, which is the Neoproterozoic Nanhua period when hydrotherm invaded and chloritization was widely developed. Large-sized uraninite grains were selected to calculate their zoning ages. The age distribution shows that the strong fluid activity occurs at the late stage, and is mainly related to the chloritization. In addition, comparing the elements' content (Y2O3 and UO2) between metamorphic uranium and sedimentary uranium, a negative correlation relationship was found between the two types. This relationship may have significance in determining whether it is metamorphic or sedimentary type, but this conclusion needs further study due to the lack of convincing evidence.
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