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。
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
作者
张帅
刘家军
袁峰
刘刚
王功文
张宏远
张红雨
ZHANG Shuai;LIUJiajun;YUAN Feng;LIU Gang;WANG Gongwen;ZHANG Hongyuan;ZHANG Hongyu(State Key Laboratory of Geological Processes and Mineral Resources,China University of Geosciences(Beijing),Beijing 100083,China;School of Earth Sciences and Resources,China University of Geosciences(Beijing),Beijing 100083,China)
出处
《地学前缘》
EI
CAS
CSCD
北大核心
2019年第5期270-289,共20页
Earth Science Frontiers
基金
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）
