沙特阿拉伯Jabal Twalah地区铀/钍矿化特征与成矿机制

目前,沙特阿拉伯西北部Jabal Twalah地区铀钍资源勘查程度较低,对该地区的铀成矿机制研究相对薄弱。本文主要对该地区新发现的伟晶岩型和花岗岩热液型铀矿化带的矿化特征和成矿机制开展研究。区内与铀钍矿化相关的伟晶岩和围岩花岗岩中锆石LA-ICP-MS U-Pb年龄分别为638.6±3.2 Ma和632.5±1.5 Ma,两者时代基本一致。综合岩相学、地球化学以及扫描电镜能谱分析等研究结果,发现矿化伟晶岩强烈富集U、Th、稀土及稀有金属元素,复杂的高温蚀变矿物组合特征暗示可能经历了岩浆期后热液的改造,改造前后矿化伟晶岩中的铀和钍未发生分离,以副矿物形式存在而无独立铀矿物,具岩浆矿物组合的特征,如金红石、锆石、氟碳铈矿、磷钇矿、钍石等。花岗岩热液型单铀矿化带的地表样品中铀矿物主要为硅铅铀矿和硅钙铀矿,脉石矿物主要为赤铁矿、萤石、石英以及少量方解石,铀矿化受控于高铀含量的碱性花岗岩、强烈硅化构造破碎带以及晚期酸性—基性脉岩活动等因素。强烈硅化的构造破碎带及其转折部位或者与脉岩交汇部位是今后重要的找矿方向。

Characteristics and genesis of uranium- thorium mineralization in Jabal Twalah, Kingdom of Saudi Arabia

At present, uranium exploration and related genetic studies have rarely been conducted in Jabal Twalah, Kingdom of Saudi Arabia. A case study is carried out for identifying mineralization characteristics and genesis of newly discovered pegmatite- hosted uranium- thorium mineralization and hydrothermal uranium mineralization in alkaline granite. Zircon U- Pb dating results show that U- Th mineralized pegmatite and wall rock alkaline granite were formed simultaneously at 638. 6±3. 2 Ma and 632. 5±1. 5 Ma, respectively. Combined with a series of analysis methods including petrography, geochemistry, and SEM- EDS, mineralized pegmatites were demonstrated to be strongly enriched in U, Th, rare earth elements, and rare metals, and suffered from post- magmatic hydrothermal alteration. However, U and Th are still hosted together in accessary minerals rather than occurring as independent uranium minerals. Mineral assemblages in mineralized pegmatite are characterized by magmatic minerals, such as rutile, zircon, bastnaesite, xenotime, thorite, etc. For the epithermal granite- hosted uranium mineralization, uranium minerals sampled from the superficial specimens occur as kasolite and uranophane, while gang minerals comprise hematite, fluorite, quartz, and minor calcite. The granite- hosted uranium mineralization is controlled by high uranium- bearing granite, strongly silicified structural zone, as well as late intrusive felsic- mafic dykes. Thus, uranium targeting in the future should focus on strongly silicified fracture zones, and their turning zone or intersection with dykes.