粤北棉花坑铀矿床矿物共生组合特征及其意义

基于棉花坑矿床不同类型铀矿石中矿物共生组合关系研究,讨论了棉花坑矿床成矿作用过程中铀的沉淀富集机制。研究结果显示,棉花坑矿床铀矿体主要呈脉状充填或细脉浸染状产出;铀矿石类型包括萤石型、碳酸盐型、硅质脉型和红化型。虽然不同矿石类型中成矿期形成的脉石矿物种类存在差异,但均表现出以下共性特点:铀矿物赋存于脉状充填矿石的中心部位或两壁,或与成矿期脉石矿物相间排列;或呈细脉状、浸染状赋存于碎裂蚀变花岗岩内;与成矿期脉石矿物(主要包括方解石、萤石、微晶石英)镶嵌生长;铀矿物与黄铁矿以集合态或相对独立态密切共生,两者之间及其与成矿期脉石矿物晶体之间界线平直,晶形完好,镶嵌生长。认为棉花坑矿床铀矿石中黄铁矿与铀矿物之间不存在先后的成生关系,均为成矿流体共结晶产物;铀沉淀成矿与氧化还原作用无关,减压、温度下降以及成矿流体p H值、溶解度(饱和度)变化,是制约铀矿物以及相关脉石矿物结晶沉淀的主要因素。

Mineral assemblage characteristics of the Mianhuakeng uranium deposit in northern Guangdong Province and its significance

Based on the relationship between uranium minerals and pyrite from different types of uranium ores in the Mianhuakeng deposit, the authors investigated the mechanism for the deposition and enrichment of uranium during the ore-forming process. The research shows that uranium orebodies in the Mianhuakeng deposit generally occur in vein-filling or vein-disseminated form. Uranium ore types include fluorite type, carbonate type, siliceous vein type and reddening type. Although different ore types have different gangue minerals formed in the mineralization period, they show common characteristics as follows: Uranium minerals in the central part or along the vein walls are alternatively arranged with gangue minerals or occur in veinlike or disseminated form in cataclastic altered granite and are inlaid with gangue minerals such as calcite, fluorite and microcrystalline quartz. Uranium minerals and pyrite are closely associated with each other in aggregate or relatively independent states, and the boundaries between them and gangue minerals in the mineralization period are straight, with good crystal type and in inlaid growth form. The aforementioned evidence indicates that there is no sequential generative relationship between pyrite and uranium minerals, and that they are all co-crystalline products of ore-forming fluid. Uranium precipitation had nothing to do with redox reaction. In contrast, decrease of pressure and temperature and the change of pH and solubility were the main factors that triggered the precipitation of uranium and gangue minerals.