| 纳米比亚湖山铀矿床中黑云母伟晶岩型矿石特征及铀矿化机制 |
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| 引用本文： | 黄冉笑,袁国礼,王果胜,邱坤峰,邵华胜,龚能.纳米比亚湖山铀矿床中黑云母伟晶岩型矿石特征及铀矿化机制[J].岩石学报,2021,37(5):1587-1610. |
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| 作者姓名： | 黄冉笑 袁国礼 王果胜 邱坤峰 邵华胜 龚能 |
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| 作者单位： | 中国地质大学(北京)地球科学与资源学院, 北京 100083 |
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| 基金项目： | 本文受国家自然科学基金项目（41872100）、中非高校20+20合作计划（2019）和科技部重大研发项目（2018YFC0604106）联合资助. |
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| 摘 要： | 湖山铀矿床位于纳米比亚达马拉造山带的南部中央带,属于伟晶岩型铀矿,是世界上最大的铀矿床之一。目前关于不同矿石中铀元素的富集与沉淀机制还存在一定争议。为了厘清岩浆演化过程与铀成矿作用的关系,本文对湖山铀矿床内E型伟晶岩型矿石开展了岩石学、矿物学和地球化学研究。野外调查及镜下鉴定结果表明,产铀的E型伟晶岩可以分为"简单类型"矿体和"复杂类型"矿体:前者具有花岗伟晶结构,工业铀矿物为晶质铀矿(含少量铀钍石),呈浸染状分布于石英、长石和黑云母之间,矿化程度低到中等;而后者表现出非均匀的结构特征,晶质铀矿在成因上与大量黑云母团块有空间联系,矿化程度极高。地球化学研究表明,在"简单类型"伟晶岩中,铀元素的富集受控于分离结晶作用,而在"复杂类型"伟晶岩中,铀矿化与同化混染作用密切相关。矿石的矿物-熔体相平衡模拟结果显示,外来基性组分(FeO、MgO、TiO_2)的混入导致"复杂类型"伟晶岩熔体中矿物的结晶顺序发生了改变,相比于"简单类型"伟晶岩熔体,黑云母初始结晶温度的升高和钾长石初始结晶温度的降低为黑云母提供了更充足的结晶时间和生长空间,促使黑云母以团块状聚集的形式产出。该过程会大量消耗岩浆中的F离子,引发UFm4-m络合物的水解,促使晶质铀矿在团块黑云母的附近沉淀,形成高品位的铀矿化。因此,本文有关"简单类型"和"复杂类型"伟晶岩矿石的研究,有效地揭示了矿化过程,丰富了伟晶岩型铀矿床理论,为推动铀矿勘查与开发提供了科学依据。
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| 关 键 词： | 伟晶岩型铀矿床 同化混染与分离结晶(AFC)作用 矿化过程 纳米比亚 |
| 收稿时间： | 2020/7/12 0:00:00 |
| 修稿时间： | 2021/12/9 0:00:00 |
Characteristics of biotite-pegmatitic ore and metallogenic mechanism of uranium in the Husab uranium deposit, Namibia |
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| HUANG RanXiao,YUAN GuoLi,WANG GuoSheng,QIU KunFeng,SHAO HuaSheng,GONG Neng.Characteristics of biotite-pegmatitic ore and metallogenic mechanism of uranium in the Husab uranium deposit, Namibia[J].Acta Petrologica Sinica,2021,37(5):1587-1610. |
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| Authors: | HUANG RanXiao YUAN GuoLi WANG GuoSheng QIU KunFeng SHAO HuaSheng GONG Neng |
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| Institution: | School of Earth Sciences and Resources, China University of Geosciences(Beijing), Beijing 100083, China |
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| Abstract: | The Husab uranium deposit is a typical pegmatite-hosted ore deposit located in the southern Central Zone of the Damara orogenic belt, Namibia, which is one of the largest uranium deposits in the world. The enriching and precipitating mechanism of uranium in different ores is still in debate. In order to reveal the relationship between magma evolution and uranium mineralization, petrology, mineralogy, as well as geochemistry of E-type pegmatite ores are studied. The results of field and microscopic identification show that the uraniferous E-type pegmatites can be divided into two categories, including "simple-type" and "complex-type" ore bodies. The former has granitic-pegmatitic texture, and its main industrial uranium minerals are uraninites (with few thorites), which are disseminated distributed among quartzs, feldspars and biotites with low to medium mineralization degree. The latter is characterized by heterogeneous texture with extremely high mineralization, in which uraninites and a large number of biotite agglomerates are spatially related in genesis. Geochemical analysis results show that in the "simple-type" pegmatite, the enrichment of uranium is controlled by fractional crystallization process, while in the "complex-type" pegmatite, uranium mineralization is closely related to assimilation process. The mineral-melt phase equilibrium simulation of pegmatite ores concludes that the mixing of external source of mafic components (FeO, MgO, TiO2) led the change of mineral crystallization sequence in "complex-type" melts. Compared with "simple-type" melts, the initial crystallization temperature of biotite increased and that of potassium feldspar decreased, which provided more adequate crystallizing time and growing space for biotite, promoting it to be produced in the form of massive aggregation. This process would consume lots of F ions in magma and induced the hydrolysis of UFm4-m complex, resulting in precipitation of uraninites near the biotite agglomerates and the formation of high-grade uranium mineralization. Therefore, the study of "simple-type" and "complex-type" pegmatite ores in this case effectively reveals the uranium mineralization process, enriches the knowledge about the pegmatite-type uranium deposit, and also provides a scientific basis for the exploration and development of uranium resources. |
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| Keywords: | Pegmatite-type uranium deposit Assimilation-Fractional Crystallization (AFC) process Mineralization process Namibia |
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