地学前缘 ›› 2019, Vol. 26 ›› Issue (5): 270-289.DOI: 10.13745/j.esf.sf.2019.5.14

• 岩浆过程与成矿 • 上一篇    下一篇

陕西商丹陈家庄铀矿区花岗岩体和伟晶岩脉的U-Pb年龄、地球化学特征与铀成矿作用

张帅，刘家军，袁峰，刘刚，王功文，张宏远，张红雨   

  1. 1. 中国地质大学(北京) 地质过程与矿产资源国家重点实验室, 北京 100083
    2. 中国地质大学(北京) 地球科学与资源学院, 北京 100083
  • 收稿日期:2018-07-28 修回日期:2018-12-02 出版日期:2019-09-28 发布日期:2019-09-28
  • 通讯作者: 刘家军(1963—)，男，教授，博士生导师，从事矿床学研究与教学工作。
  • 作者简介:张帅(1982—)，男，博士研究生，矿物学、岩石学、矿床学专业。E-mail：zhangshuai@cugb.edu.cn
  • 基金资助:
    国家重点基础研究发展计划“973”项目(2014CB440903)；中国地质调查局地质调查工作项目(12120114014401)

Zircon U-Pb geochronology and geochemistry of granites and pegmatites, and metallogenesis of related uranium from the Chenjiazhuang deposit, Shaanxi Province

ZHANG Shuai,LIU Jiajun,YUAN Feng,LIU Gang,WANG Gongwen, ZHANG Hongyuan,ZHANG Hongyu   

  1. 1. State Key Laboratory of Geological Processes and Mineral Resources, China University of Geosciences(Beijing), Beijing 100083, China
    2. School of Earth Sciences and Resources, China University of Geosciences(Beijing), Beijing 100083, China
  • Received:2018-07-28 Revised:2018-12-02 Online:2019-09-28 Published:2019-09-28
  • Supported by:
     

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摘要： 陕西陈家庄铀矿床是我国北秦岭商州—丹凤伟晶岩型铀矿集区中一个重要的矿床，铀矿体均产于加里东期花岗岩体周边花岗伟晶岩脉与围岩(秦岭群变质杂岩)的接触部位。本文对矿区花岗岩体、花岗伟晶岩脉开展了详细的岩石学、岩石地球化学、锆石U-Pb年代学研究，进而对其成因、成岩构造环境和铀矿化机理进行了探讨。LA-ICP-MS锆石U-Pb年代学研究表明，黄龙庙黑云母花岗岩体，陈家庄二长花岗岩体和非矿、贫矿、富矿花岗伟晶岩脉的成岩年龄分别为(446±3) Ma、(419±2) Ma、(417±3) Ma、(414±4) Ma和(416±3) Ma。地球化学分析显示：黄龙庙黑云母花岗岩体具有Ⅰ型花岗岩、埃达克质岩特征，源自加厚下地壳的部分熔融，形成于块体碰撞构造环境；陈家庄二长花岗岩体也具有I型花岗岩特征，但源区深度略浅，形成于碰撞后的减压环境。花岗伟晶岩脉与陈家庄二长花岗岩体近于同时形成，且具有亲缘性。铀矿物及富铀黑云母均产于花岗伟晶岩脉中。对比研究揭示，非矿、贫矿、富矿花岗伟晶岩脉地球化学特征和铀赋存状况的差异由同化混染作用程度高低所致。在花岗伟晶岩脉与秦岭群变质杂岩的接触部位，同化混染作用较弱的部位形成的二云母花岗伟晶岩脉仅具有弱的铀富集，同化混染作用较强的部位所形成的富石英、黑云母花岗伟晶岩脉则高度富集铀且构成铀矿体。综合研究表明，花岗伟晶岩脉成岩期后的同化混染作用是铀富集成矿的主导因素。

 

关键词: 秦岭造山带, 伟晶岩型铀矿床, 岩石地球化学, 锆石U-Pb定年, 加里东期

Abstract: The Chenjiazhuang uranium deposit is a typical pegmatite-hosted ore deposit located in the middle part of the Danfeng triangular domain of the northern Qinling Orogen, China. The U-bearing ore bodies mostly occur in the contact zones between the biotite granitic pegmatite in the vicinity of the Caledonian granite and the Qinling Group biotite-plagioclase gneiss. To constrain the petrogenesis, tectonic setting and pegmatite-hosted uranium ore formation, we presented in this paper a detailed geochronological and geochemical study of granites and granitic pegmatites in the ore district. Zircon LA-ICP-MS U-Pb dating results yielded the crystallization ages of 446±3 Ma for the Huanglongmiao biotite granite, 419±2 Ma for the Chenjiazhuang biotite monzonite granite, 417±3 Ma for non-mineralized granitic pegmatite, 414±4 Ma for lean-ore granitic pegmatite and 416±3 Ma for mineralizing granitic pegmatite. The Huanglongmiao biotite granodiorite exhibited the affinity and adakitic characteristics of an I-type formed by partial melting of lower basaltic crust in a collisional setting. The Chenjiazhuang biotite monzonite granite also possessed the I-type properties but formed in a relatively shallow source zone in a post-collisional decompression setting. The age data revealed that granitic pegmatite formed in concurrence with the host Chenjiazhuang biotite monzonite granite and therefore they should have closely related origins. Uranium minerals and U-rich biotite all occur in granitic pegmatite dikes. The differences in petrological and geochemical characteristics among the non-mineralized, U-bearing and U-rich granitic pegmatites were attributed to various degrees of greisenization. The U-poor granitic pegmatites occur within the biotite monzonite, while the U-rich granitic pegmatite dikes always maintain contact with the Qinling metamorphic complex. This suggests that uranium enrichment in ore deposit is strongly associated with uranium extraction from the Qinling metamorphic complex by late stage fluids, and this association resulted in high degree of uranium concentration in the process of quartz and biotite rich greisenization. Therefore, the late stage metamorphic alteration of the Qinling complex is critical for uranium mineralization in the Chenjiazhuang uranium deposit.

Key words: Qinling Orogen, pegmatite-hosted type uranium deposit, petrogeochemistry, zircon U-Pb dating, Caledonian period

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