| 桂北沙子江铀矿床沥青铀矿原位微区年代学和元素分析:对铀成矿作用的启示 |
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| 引用本文： | 陈佑纬,胡瑞忠,骆金诚,董少花.桂北沙子江铀矿床沥青铀矿原位微区年代学和元素分析:对铀成矿作用的启示[J].岩石学报,2019,35(9):2679-2694. |
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| 作者姓名： | 陈佑纬 胡瑞忠 骆金诚 董少花 |
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| 作者单位： | 中国科学院地球化学研究所矿床地球化学国家重点实验室, 贵阳 550081,中国科学院地球化学研究所矿床地球化学国家重点实验室, 贵阳 550081;中国科学院大学地球与行星科学学院, 北京 100049,中国科学院地球化学研究所矿床地球化学国家重点实验室, 贵阳 550081,中国科学院地球化学研究所矿床地球化学国家重点实验室, 贵阳 550081 |
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| 基金项目： | 本文受中国科学院先导专项B类（XDB18030200）、国家重点研发计划（2016YFC0600207）和国家自然科学基金项目（41473049）联合资助. |
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| 摘 要： | 微区原位分析是地球科学研究的重要手段,但这些分析技术在华南热液铀矿床中的应用相对较少,限制了对铀矿床成矿机理的深入认识。沙子江铀矿床是华南著名的花岗岩型热液铀矿床。本文利用电子探针(EMPA)、激光电感耦合等离子体质谱(LA-ICPMS)以及二次离子探针(SIMS)等微区原位分析技术,对沙子江铀矿床中的沥青铀矿开展了U-Pb同位素年代学及元素组成研究,确定了沥青铀矿的形成时代及成分特征,并探讨了蚀变作用对沥青铀矿成分及其表面年龄或化学年龄的影响。电子探针分析结果显示,该沥青铀矿以富铀和钙、极低含量的ThO_2和稀土元素为特征,揭示其为低温热液成因,成矿热液富含Ca。LA-ICP-MS分析结果显示,沥青铀矿的稀土元素总量较低,其配分模式呈轻稀土富集型,具有明显的负Eu异常,与赋矿围岩豆乍山花岗岩的稀土元素组成相似,暗示其铀源可能与豆乍山岩体有密切的关系。蚀变和未蚀变沥青铀矿成分的对比研究显示,蚀变作用会导致硅元素大量进入沥青铀矿晶格,造成铀和铅的丢失,从而影响沥青铀矿的表观年龄或化学年龄,但沥青铀矿的稀土元素配分模式不会受到蚀变的影响。未蚀变沥青铀矿的SIMS微区原位分析获得的U-Pb年龄为101. 3±4. 5Ma,表明沙子江铀矿床存在100Ma左右的铀成矿事件。受岩石圈伸展控制形成的富CO流体与富铀花岗岩相互作用浸取出花岗岩中的铀,并在合适的构造部位沉淀形成了沙子江铀矿床。
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| 关 键 词： | 沙子江铀矿床 沥青铀矿 微区分析 矿物化学 年代学 |
| 收稿时间： | 2019/3/10 0:00:00 |
| 修稿时间： | 2019/6/18 0:00:00 |
In-situ mineral chemistry and chronology analyses of the pitchblende in the Shazijiang uranium deposit and their implications for mineralization |
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| CHEN YouWei,HU RuiZhong,LUO JinCheng and DONG ShaoHua.In-situ mineral chemistry and chronology analyses of the pitchblende in the Shazijiang uranium deposit and their implications for mineralization[J].Acta Petrologica Sinica,2019,35(9):2679-2694. |
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| Authors: | CHEN YouWei HU RuiZhong LUO JinCheng and DONG ShaoHua |
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| Institution: | State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China,State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China;College of Earth and Planetary Sciences, University of Chinese Academy of Sciences, Beijing 100049, China,State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China and State Key Laboratory of Ore Deposit Geochemistry, Institute of Geochemistry, Chinese Academy of Sciences, Guiyang 550081, China |
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| Abstract: | In-situ analyses are important techniques in earth science researches. However, these techniques are rarely used in hydrothermal uranium deposits in South China, which restrain the understanding of the metallogenies of hydrothermal uranium deposits. The Shazijiang uranium deposit is a famous granite-type (hydrothermal) uranium deposit in South China, but the mineral chemistry and chronology characteristics of uranium minerals are still obscure. This paper revealed the mineral chemistry and chronology of the pitchblende (uraninite) of the Shazijiang uranium deposit, by using EPMA, LA-ICP-MS and SIMS. The effects of alternation on the chemistry and chemical age of the pitchblende are discussed as well. The results of EMPA show that the pitchblende is characterized by high contents of uranium and calcium, but extremely low contents of ThO2 and rare earth elements, indicating the pitchblende was precipitated from a low-temperature hydrothermal fluid, which was characterized by high Ca ions. A comparative study of unaltered and altered pitchblende shows that alteration can cause a large amount of silicon to enter the pitchblende, replacing the uranium and lead. However, the apparent age or chemical age of the pitchblende is significantly affected by its alteration. The SIMS U-Pb age dating of the pitchblende obtained an age of 101.4±5Ma, indicating that there is an early uranium metallogenic event of about 100Ma in Shazijinag uranium deposit. The results of LA-ICP-MS show that the pitchblende is characterized by low total amount of rare earth elements. But the chondrite-normalized patterns of rare earth elements are rich in light-REE, with obvious negative Eu anomalies. It is indicated that the uranium source rocks may be the Douzhashan wall rock granite. The extension of the lithosphere caused the upwelling of the mantle fluid which interacted with the deep uranium-rich granite, forming a uranium-rich hydrothermal fluid. The Shazijiang uranium deposit formed due to the precipitation of the pitchblende in the structural fracture zone. |
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| Keywords: | Shazijing uranium deposit In-situ microanalyses Pitchblende Mineral chemistry Chronology |
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