内蒙古巴尔哲地区碱性花岗岩中铀钍赋存特征及形成机制研究

Baerzhe deposit is not only a super-large Nb-REE-Zr-Be deposit, but also a large to super-large U-Th deposit. The ore body is hosted in the Yenshanian alkali granite. Currently the study of ore-forming mechanism is mainly started from ore-forming elements, such as Nb, REE, Zr and Be. However, the research on uranium and thorium mineralization is almost blank, especially for the occurrence of U-Th, the relationship between U-Th and Nb-REE-Zr-Be, and metallogenic model are still lack of deep understanding. Therefore, this project intends to do detailed study on uranium and thorium mineralization and then reveal the ore-forming process of Baerzhe deposit . Based on the micro-situ geochemical compositions of single mineral, we can find out the occurrence of uranium and thorium. Though the geochemical characteristics of ore-forming fluid and isotopic tracing, we can reveal the origin and time-space evolution of ore-forming fluid, analysis on the source, migration form and discharge mechanism of uranium and thorium, thus discuss the enrichment mechanism, their relationship and interaction of metallogenic elements. Combined with the accurate age of U-Th mineralization, to clarify the relationship between U-Th mineralization and magmatic evolution, then establish the metallogenic model.

内蒙古巴尔哲矿床不仅是超大型Nb-REE-Zr-Be矿床，同时也是（超）大型铀钍矿床，矿体产于燕山期碱性花岗岩体中。目前对其成矿机理的研究，主要从稀土-铌-铍-锆成矿元素入手，而对铀钍成矿作用的研究基本处于空白，尤其是对铀钍赋存状态、铀钍矿化与稀有稀土金属矿化的关系及成矿模式还缺乏深入了解。因此本项目拟通过对铀钍成矿作用的详细研究进而揭示该矿床的成矿过程。利用系统的单矿物原位微区地球化学成分分析，查明铀、钍的赋存状态。通过成矿流体地球化学特征和同位素示踪，揭示成矿流体来源、时空演化，分析铀钍的来源、运移形式和卸载机制，探讨各成矿元素富集的时序关系和相互影响。结合精确的铀钍成矿年龄，阐明岩浆演化与铀钍成矿作用的关系，构建成矿模式。

内蒙古巴尔哲矿床是我国超大型Nb-REE-Zr-Be-U-Th多金属矿床，矿体产于燕山期碱性花岗岩体中。其铀钍矿化成因及成矿机理具有重要的理论研究意义。本项目紧扣铀钍矿化成因和成矿机理这一根本问题，通过开展系统的野外地质调查、岩/矿相学研究，厘定了铀钍赋存形式、蚀变分带及蚀变类型与铀钍矿化的关系，其中铀钍矿化主要赋存在强蚀变钠闪石花岗岩中，铀主要以类质同像赋存于锆石、独居石、烧绿石等，钍主要以钍石、铁钍石、铀钍石等独立矿物产出，少数以类质同像赋存于锆石、独居石中；通过成矿元素地球化学特征及相关性分析，确定了铀钍矿化与稀有稀土元素矿化基本是同期形成的，关系十分密切；本项目初次获得并报道了钠长石的Ar-Ar年龄为122.15±0.65Ma，为本矿床的成岩年代学，钍石的电子探针U-Th-Pb化学年龄为122.8Ma，说明成岩与成矿基本是同时形成的，不存在矿岩时差；通过岩体的Sr-Nd同位素和矿石中石英包裹体的Hr-Ar同位素示踪，确定了本矿床的成矿物质来源于富集地幔，同时受到地壳物质的混染，最终构建了本矿床的成矿模式。本项目获得的新成果及时应用于地质勘探中，取得了找矿资源新突破。此外，对铀钍赋存形式的系统厘定，也为本矿山的综合开发利用提供了矿物学的依据。