| 砂岩型铀矿的“双阶段双模式”成矿作用 |
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| 关键词:sandstone-type uranium deposit two-stage and two-mode uranium mineralization seepage oxidation reworking by hot fluid flow |
| 基金项目:国家自然科学基金项目(编号: U2067202; 41772068; 41562006);国家重点基础研究发展规划973计划“中国北方砂岩型铀矿流体成矿过程研究”(编号: 2015CB453002) |
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| 摘要: |
| Two-stage and Two-mode Uranium Mineralization for Sandstone-type Uranium Deposits |
| Uranium mineralization by low temperature epigenic oxidized fluid flow (EOF) in sandstone type-uranium deposits (SUD) has been emphasized by uranium geologists and explorers for long time, ignored of the complex geologic processes and multi stage mineralization. But SUDs in the basins of north China are difficultly genetically explained by one single mineralization stage and mode of EOF because the basinal geologic evolution of the eastern north China reveals extensional-compressional-extensional tectonic processes. Multi-stage uranium mineralization in the region responses this kind of tectonic setting changes. Taking the large/huge scaled SUDs like Tamusu in Bayingobi Basin, Hadatu in Erlian Basin and Qianjiadian-Baixingtu in south Songliao Basin for example, we generalize and comprehensively analyze the features of uranium orebodies, the interaction between uranium-bearing fluid flow, and the controlling factors like tectonics, depositional facies, uranium sources and reducing agents, especially the subduction ages and modes of the (paleo-) Pacific Plate for mineralization. Based upon the tectonic evolution, the depositional facies and spatial distribution of hosting sandbodies for Tamusu (K1b), Hadatu(K1bs) and Qianjiadian-Baixingtu(K2y) deposits are interpreted as braided delta, braided river for both latter two, respectively, during the initial extensional stage for a basin under the high-angle subduction of the paleo Pacific Plate. During the Late Cretaceous, the basins firstly positively inverse evolution from extension into compression due to the subduction from high angle into low angle of Pacific Plate. Uranium-oxygen-bearing fluid flow (UOF) penetrates hosting sandstone from the basinal margin into basin center. The interaction between UOF and sandstone results in hematitization and limonitization in the oxidized zone and the early uranium mineralization in the redox zone. Since Eocene, the basins secondly negatively inverse evolution from compression into extension due to the subduction from low angle into high angle of Pacific Plate. The normal faults and basic magma activities cause the interaction between hydrothermal fluid flow (HFF) and mineralization hosting sandstones. A large amount of Fe and Mg carbonates, hydrothermal sulfides, chlorite and sericite come into the sandstone. Meanwhile, the uranium mineralization is reworked and uranium orebodies change from “rollfront” into “lenticular”, “cystid” and/or “tabular”, hydrothermal uranium mineral brannerite occurring in deposits. This process is taken as the late uranium mineralization in the study area. The early and late two uranium mineralization is here refined as “Two-stage and two-mode mineralization” for SUDs in north China. Hence, both UOF and HFF mineralization should be paid enough attention in the theoretic study and exploration in north China basins, even in northeast Asia. |
| NIE Feng-jun,YAN Zhao-bin,XIA Fei,HE Jian-feng,ZHANG Cheng-yong,FENG Zhi-bing,ZHANG Xin,YANG Dong-guang,CHEN Meng-ya,TAN Shun-jia,ZHANG Jin,KANG Shi-hu,NING Jun,YANG Jian-xin,SHEN Ke-feng,CAI Jian-fang.2021.Two-stage and Two-mode Uranium Mineralization for Sandstone-type Uranium Deposits[J].Acta Geoscientica Sinica,42(6):823-848. |
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