| 下庄铀成矿古水热系统排泄区（减压区）铀成矿作用研究 |
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| 引用本文：.2001.A Study on Uranium Mineralization in the Discharge Area (Depressuring Area) of the Xiazhuang Uranium Ore forming Fossil Hydrothermal System[J].Mineral Deposits,20(3):259~264 |
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| 基金项目:核工业地质局核科学基金（编号：Y11218910901) |
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| 中文摘要:形成于占水热系统排泄区（减压区）的下庄花岗岩型铀矿床是地下热水与岩石相互作用的产物。矿物流体包裹体水文地球化学分析表明，成矿期铀成矿占热水溶液气体成分主要为CO2，水化学类型为HCO3-Ca-Na型、F-Ca型和HCO3-F-K型。地球化学模式和热力学计算证明，热水溶液巾铀的存在形式为UO2( CO3)2-，UO2 F3-和UO2F4-。热水溶液深循环过程中CO2的加入可使溶液铀沉淀临界电位值(EhC,U)明显降低，从而保持水-铀比电位值(△EhW，U)为正值(△Ehw,u= Ehw- EhC,U)，使铀在深部相对还原的条件下仍能稳定迁移。当富铀成矿热液进入减压排泄区时，由于溶液物理-化学条件的改变，发生CO2脱气作用和中和还原作用，导致△Ehw,u小于零，使铀沉淀、富集．最终形成花岗岩型铀矿床。 |
| 中文关键词:古水热系统 排泄区水 铀比电位值 CO2脱气 铀矿床 |
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| A Study on Uranium Mineralization in the Discharge Area (Depressuring Area) of the Xiazhuang Uranium Ore forming Fossil Hydrothermal System |
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| Abstract:The granite type uranium deposit in Xiazhuang, formed in the discharge area of fossil hydrothermal system, is a product of thermal water-rock interaction. Hydrogeochemical analysis of mineral inclusions indicates that gases in the solution are dominated by CO2, and hydrothermal solutions are of HCO3-Ca-Na, F-Ca and HC03-F-K types in the Xiazhuang uranium ore-forming fossil hydrothermal system. Geochemical model and thermodynamic calculations prove that modes of uranium occurrence in hydrothermal solutions are UO2(CO3)2-, UO2F3- and UO2F42-. In the course of deep circulation of water solution, the precipitation critical potential values of uranium (EhC,U) in the solution evidently decrease when CO2 enters the solution, so that water uranium specific potentials (△EhW,U) are usually of positive values (△EhW,U = EhW - EhC,U). Therefore, uranium could easily migrate under the deep relative reduction condition. When uranium- rich hydrothermal ore solution entered the depressuring discharge area, carbon dioxide would experience degasification, and neutral reducing mineralization would occur due to alteration of physical-chemical conditions in solution, resulting in △EhW,U < 0. In consequence, uranium would be precipitated and concentrated, and large-size granite type uranium deposit would be formed. |
| keywords:fossil hydrothermal system, discharge area, water- uranium specific potential value, CO2 degasification, uranium deposit |
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