黔东南龙湾大型铀多金属矿床成矿机制研究

The Longwan uranium deposit located in the northwestern Huanan carbonaceous-siliceous-pelitic type uranium metallogenic prospect zone, it is a carbonaceous-siliceous-pelitic type uranium ploymetallic deposit with large metallogenic prospect in Guizhou province. There have some new recognitions about ore deposit genetic with improve the research and exploration degree of carbonaceous-siliceous-pelitic type uranium deposit. More and more geological researchers attention to depth geofluid participation in mineralization process. Preliminary study show that the metallogenic mechanism of deposit is the tectono-magmatism-geofluid coupled mineralization, and it is belong to hydrothermal sedimetary metallogenesis. In order to indicate the metallogenic mechanism of Longwan uranium deposit, On the base of detailed field investigation we have made a systematic study on the character of mineralizing fluid, the activity rule of element during mineralizing, the sources and evolution of ore-forming fluids, the enrichment and ore-forming with the method of mineralogy, element geochemistry, isotopic geochemistry, fluid inclusion geochemistry, geochronology. Then, we will primarily discuss the restraining mechanism of tectono-magmatism-geofluid coupled mineralization effect to uranium minelization and propose a possible genetic modle of the Longwan uranium ploymetallic deposit. The research will has a new understanding about traditional uranium mineralization in South China, of course, the research results will enrich metallogenic theory of the black shale series type uranium ploymetallic deposit. In addition, this study also has important heoretical and practical significance to prospecting and exploration of the same type uranium deposit.

黔东南龙湾铀矿床位于黔中－湘西北碳硅泥岩型铀矿成矿远景带西段，是贵州省近年新发现的具大型远景的碳硅泥岩型铀多金属矿床。近年来随着碳硅泥岩型铀矿的研究与勘查程度不断提高，矿床成因有了新认识，深源流体参与成矿日益受到重视。初步研究表明龙湾矿床与热水沉积成矿有关，构造—岩浆—深部流体活动可能是铀矿的成矿机制。为了查明矿床的成矿机制，项目拟在扎实的野外地质工作基础上，运用矿物学、元素地球化学、同位素地球化学、流体包裹体地球化学、年代学等手段，对龙湾铀矿床成矿物质与成矿流体性质、成矿过程中元素的迁移规律、成矿物质与流体来源与演化及其集聚成矿机制等方面进行系统研究，进而初步探讨构造—深源流体—岩浆活动与铀矿床形成的耦合关系，并建立成矿模式。项目的开展对于突破华南碳硅泥岩型铀矿成矿传统认识，丰富华南地区黑色岩系型铀多金属矿床热水成矿理论，指导该类型铀矿的找矿和勘查均具有重要的理论和现实意义。

本项目开展了龙湾铀多金属矿床地质特征、矿物学工作、元素地球化学（主、微量、稀土）工作以及矿床成矿机制等方面的研究工作，取得了以下进展和成果。.1.矿床地质研究。矿床主要产于震旦-寒武系老堡组中硅质岩所夹碳质页岩中，矿化体产状与围岩产状基本一致，呈层状、似层状产出，较稳定的有3层，自下而上为Ⅰ、Ⅱ、Ⅲ号矿层，其中以Ⅱ矿层较好。老堡组中碳质页岩铀矿体前人关注少，这是一个新的铀矿勘查方向。.2.铀矿物组成及赋存状态的研究。龙湾矿床中原生铀矿物主要为沥青铀矿，表生条件下次生氧化形成的铀矿物较发育，主要有硅钙铀矿、硒铅矿、钛铀矿及铀酰磷酸盐矿物等，它们主要以纳米-微米级粒状、细脉状或隐晶质形式赋存于有机质、粘土矿物等聚铀矿物中。.3.地球化学研究。矿床矿石、围岩微量元素普遍富集As、Mo、Sb、Ba、U等元素，龙湾矿区微量元素含量具有明显富集热水或热水沉积物所特有的微量元素特征。矿石、硅质岩PAAS标准化稀土配分模式为左倾的重稀土富集模式，发育较明显的Ce负异常和较强的Eu正异常。龙湾矿床中矿石沉淀时相对高温的热水流体和较低温的外生水体在成矿界面附近发生了热水喷流沉积成矿作用。.4、成矿机制研究。我们初步认为龙湾铀多金属矿化是深循环热水沿区内深大断裂上升，淋滤交代下伏震旦系富铀磷矿层后在生物吸附作用下和深成流体在海底附近发生多幕次的减压喷流成矿作用形成，矿床形成是多种地质—生物耦合作用的结果，但以热水喷流成矿作用为主。