离子吸附型稀土矿中铁氧化物对Ce迁移与富集的制约

Ion-adsorption type REE deposit is an important type of REE deposits characterized by hosting the heavy REE. It was thought that clay minerals hosting most adsorbed rare earth ions play a significant role on the migration, enrichment and diffraction of REE during weathering . Recent studies have found that iron oxides in the weathered crust are enriched in Ce and have a spatial distribution relationship with Ce. The coupling relationship between iron oxides and Ce migration and enrichment has yet to be determined. Therefore, this project selected Renju ion-adsorption type REE deposit in north Guangdong province, and creatively combined fine mineralogy characterization and simulation experiment. Firstly, conduct detailed investigation into mineralogical characteristics of iron oxides and Ce micro-occurrence status at different depths in the weathered crust to reveal the evolution process of iron oxides during weathering of parent rocks. Then, the Fe-Ce co-precipitation experiment was carried out to synthesize nano-mineral aggregates, followed by investigating the process and primary factors that lead to Ce migrating and crystallizing from nano iron oxides under different physical and chemical conditions. Lastly, discuss the process and controlling factors of Ce migration and enrichment. It will provide a reference for the secondary enrichment mechanism of ion-adsoption type REE deposit. The research makes full use of the remarkable advantages of transmission electron microscopy (TEM) in the analysis of the composition and structure of nano-minerals, and carrys out research on the secondary migration of ore-forming elements from the perspective of nano-mineral crystallization, growth, and transformation.

离子吸附型稀土矿是一类以富集重稀土元素为特征的重要矿床类型。传统观点认为风化壳中黏土矿物作为离子相稀土的主要载体矿物，制约了稀土元素的次生迁移、富集和分异。最近研究发现风化壳中铁氧化物富集Ce且二者存在空间分布上的联系，铁氧化物和Ce迁移、富集的耦合关系仍有待查明。因此项目选取粤北仁居离子吸附型稀土矿床，创新地结合精细矿物学表征与模拟实验，开展铁氧化物在风化壳不同层位精细矿物学和表面Ce显微赋存状态研究，揭示母岩风化时铁氧化物演化特征；然后通过Fe离子和Ce离子共沉淀形成纳米矿物聚集体，查明不同物理化学条件下Ce从纳米铁氧化物中迁移、结晶过程和控制因素，进而揭示风化时Ce迁移、富集过程和制约机制，为离子吸附型稀土矿次生富集机制提供参考。研究充分利用透射电子显微镜（TEM）在纳米矿物成分和结构分析上的显著优势，从纳米矿物结晶、生长、转化角度开展成矿元素次生迁移研究。

华南离子吸附型稀土矿床是全球稀土资源的重要产地。在一系列地球化学性质相近的稀土元素中，Ce由于其易被氧化的性质明显区别于其它稀土元素；此外，Ce异常被认为能够用于指示离子吸附型稀土矿床。为了探究风化成矿过程中Ce的迁移和赋存规律，选择黄畲约90m深风化壳剖面进行精细矿物学研究。我们主要利用透射电镜和选择性提取技术开展Ce赋存状态和矿物学特征的研究。. 黄畲花岗岩经历多期次含氟和碳酸根的热液蚀变活动形成含Ce热液矿物，例如氟碳铈矿、氟碳钙铈矿、独居石和水磷铈矿等，这些热液矿物与岩浆副矿物褐帘石和榍石等为风化壳中Ce提供了初始来源。风化作用导致Ce、Fe和Mn从矿物中释放出来，Fe离子发生氧化和水解形成水铁矿纳米矿物。水铁矿强烈吸附体系中溶解出的Ce和Mn离子，形成Fe-Mn-Ce共存体系，其中，Mn氧化物对于Ce吸附氧化作用强。随着风化作用的进行，无定形水铁矿通过溶解再沉淀及定向生长方式向弱结晶针铁矿转化，与此同时，不断累积的Ce导致次生Ce磷酸盐和吸附Ce黏土矿物的形成。进一步风化形成了赤铁矿，并伴随水铁矿和针铁矿的消失，赤铁矿与方铈矿不断结晶生长，最终形成各自纳米矿物聚集体。. 潜水面以上强烈的淋滤作用和氧化环境是造成Ce氧化富集的重要原因，类似于铁帽对于斑岩铜矿的指示，表层Ce富集可用于指示原地风化且成熟的离子吸附型稀土矿床。潜水面以下还原环境有利于除Ce之外稀土元素的富集，因此存在REE富集带与Ce负异常之间的耦合关系。