粤北竹筒尖铀矿床特富矿赋矿花岗岩锆石U- Pb年代学、地球化学、Hf同位素及成因研究
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本文为国家自然科学基金项目(编号 41772066)和中国核工业地质局地勘项目(编号 201640)联合资助成果。


Zircon U- Pb geochronology, geochemistry, Hf isotope and genesis of the ore- rich granite in the Zhutongjian uranium deposit, northern Guangdong
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    摘要:

    竹筒尖铀矿床位于下庄矿田西北部,早年的找矿工作陷入瓶颈,近年来由笔者主持的普查项目在该地区有了新的突破,尤其是富含晶质铀矿的特富矿体的首次发现,为下一步的找矿工作提供了新的方向。竹筒尖铀矿床特富矿体的赋矿围岩为粗粒黑云母花岗岩和细粒黑云母花岗岩。本文对该围岩进行锆石U- Pb年龄、Hf同位素及地球化学组成的测定,结果显示:粗粒黑云母花岗岩和细粒黑云母花岗岩成岩年龄分别为241. 1±1. 6Ma和233. 6±1. 4Ma,均属于印支期。化学组成上两者均具有富硅、K>Na、强过铝质和低CaO/Na2O比值等特征。微量元素两者均富集大离子亲石元素Rb和高场强元素Th、U、Ta、Hf,明显亏损Ba、Nb、Sr、Ti等元素,但粗粒黑云母花岗岩具有更加分散的微量元素配分曲线,表明其可能受到交代蚀变的影响。两者均具有较高的稀土总量,轻重稀土分馏明显,稀土配分曲线呈“右倾型”,以及明显的Eu负异常(粗粒黑云母花岗岩:δEu=0. 212~0. 269;细粒黑云母花岗岩:δEu=0. 155~0. 258)。Hf同位素组成上均具有较低的εHf(t)值(粗粒黑云母花岗岩:-10. 9~-9;细粒黑云母花岗岩:-12. 3~-8. 7)和古元古代的模式年龄(粗粒黑云母花岗岩:1951~1834Ma;细粒黑云母花岗岩:2030~1810Ma)。地球化学和同位素特征表明两者均为强过铝质的S型花岗岩,较高的Rb/Sr比值和较低的CaO/Na2O比值表明两者均主要是由富黏土的泥质沉积岩部分熔融而成。粗粒黑云母花岗岩形成于印支期主碰撞期局部的拉张环境,细粒黑云母花岗岩形成于碰撞挤压环境向后碰撞拉张环境的转换时期。

    Abstract:

    The Zhutongjian uranium deposit, located in the northwestern part of the Xiazhuang ore field, is a breakthrough made during prospecting for uranium deposit in South China. Therefore, the discovery of uraninite- rich orebodies provides a new prospecting direction for uranium deposits in this area. The host rocks of the Zhutongjian uranium deposit are comprised of coarse- grained biotite granite and fine- grained biotite granite. In this paper, zircon LA- ICP- MS U- Pb dating, whole- rock geochemistry and Hf isotopes of the coarse- and fine- grained biotite granite were carried out to determine geochronology and petrogenesis of this deposit. Zircon LA- ICP- MS dating yields the diagenetic ages of 241.1±1.6 Ma and 233.6±1.4 Ma for coarse- and fine- grained biotite granite, respectively, indicating that the two plutons were formed in the Indasinian period. Two plutons are geochemically characterized by silica enrichment, K>Na, strong aluminous, and low CaO/Na2O ratio. Trace elements analyses show that two plutons are enriched in LILEs (such as Rb) and HFSEs (such as Th, U, Ta, Hf), depletion in Ba, Nb, Sr, Ti, with slight positive Eu anomalies (δEu=0.212~0.269; δEu=0.155~0.258), revealing the S- type grantie. But the coarse- grained biotitic granite is of the disperser trace element patterns, indicating that it might have been affected by metasomatic alteration. In the primitive mantle normalized trace element pattern and chondrite- normalized REE diagrams, two plutons have high total REE content, distinct fractionation between LREE and HREE, right- dipping pattern, and distinct negative Eu anomalies. The Hf isotope compositions show the lower εHf(t) values of the coarse- grained biotite granite (from -10.9 to -9, with tDM2 age between 1951 Ma and 1834 Ma) and the fine- grained biotite granite (from -12.3 to -8.7, with tDM2 age between 2030 Ma and 1810 Ma), and the model ages of Paleoproterozic for the coarse- grained biotite granite (1951~1834Ma). Geochemistry and isotopic features indicate that the two plutons are strong aluminous S- type granite, and high Rb/Sr and low CaO/Na2O indicate that two plutons might be generated by partial melting of clay- rich argillaceous sedimentary rocks. Combined with the tectonic evolution of the South China, it can be concluded that the coarse- grained biotite granite formed in an extension setting during the main collision period of the Indosinian, while the fine- grained biotite granite probably formed in the transition stage of tectonic regimes from compression to extension.

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刘文泉,江卫兵,李海东,李俊,梁园园.2019.粤北竹筒尖铀矿床特富矿赋矿花岗岩锆石U- Pb年代学、地球化学、Hf同位素及成因研究[J].地质学报,93(7):1720-1737.
LIU Wenquan, JIANG Weibing, LI Haidong, LI Jun, LIANG Yuanyuan.2019. Zircon U- Pb geochronology, geochemistry, Hf isotope and genesis of the ore- rich granite in the Zhutongjian uranium deposit, northern Guangdong[J]. Acta Geologica Sinica,93(7):1720-1737.

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  • 收稿日期:2018-08-30
  • 最后修改日期:2018-11-01
  • 录用日期:2018-11-02
  • 在线发布日期: 2018-11-26
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