离子吸附型稀土矿成矿特点及元素赋存形式

离子吸附型稀土矿是世界中重稀土的主要来源，广泛分布于我国南方的江西、广东、福建、湖南、广西、云南等地，而在世界其他地区鲜少见到。离子吸附型稀土矿床的矿体赋存于母岩形成的风化壳中，大多数情况下，风化壳的稀土元素模式由母岩继承而来，母岩特征因此对成矿有着重要的控制作用；此外，外生条件如亚热带气候、低洼缓坡地形、充足的降雨量和地下水等也对成矿性有着重要影响。自风化壳上部向下，随着土壤水pH的增加和氧化还原条件的改变，稀土元素在全风化层下部和半风化层中被黏土矿物固定，此过程中，物质（主要元素）的移除和淋溶-沉积动力学是风化壳中稀土元素富集的主要机制。一般认为离子吸附型矿石中的稀土主要存在于高岭石等黏土矿物中，而稀土元素在单个矿物中的赋存形式不清楚。近年来有同步辐射实验表明，稀土元素在高岭石中既以8或9配位的水合自由离子形式作为外层络合物吸附于高岭石表面，也可以内层络合物形式与黏土矿物表面Al-O、Si-O键结合或与黏土矿物边缘位置结合。对离子吸附型稀土矿成矿特点和稀土元素的赋存形式的研究是指导找矿与进一步高效、环保的资源利用的基础，于世界尖端科技产业发展而言至关重要。

Metallogenic characteristics and occurrence of REE in ion adsorption type rare earth deposits

Ion adsorption rare earth ore is the main source of heavy rare earth in the world. Ion adsorption rare earth deposits are widely distributed in Jiangxi, Guangdong, Fujian, Hunan, Guangxi, Yunnan and other places in south China, but rarely seen in other places of the world. The ore bodies of ion adsorption type rare earth deposits occur in the weathering crust. In most cases, the REE patterns of the weathering crust are inherited from the parent rock, thus the nature of the parent rock significantly controls the features of the ion adsorption type deposits. In addition, exogenous conditions such as subtropical climate, low-lying gentle slope terrain, sufficient rainfall and groundwater also have an important impact on ion adsorption mineralization. From the upper part of weathering crust down, rare earth elements are fixed by clay minerals at the lower part of completely weathered layer and semi weathered layer along the vertical pH and redox gradients in weathering crusts. In this process, mass removal (major elements) and eluviation-illuviation dynamics are the main mechanisms of rare earth enrichment in the weathering crusts. It is generally believed that rare earth elements in ion adsorption ores mainly exist in clay minerals such as kaolinite, while the occurrence forms of rare earth elements in minerals remain unclear. In recent years, synchrotron X-ray absorption spectroscopy studies have shown that rare earth elements in kaolinite were not only adsorbed on the surface of kaolinite in the form of 8- to 9-coordinated outer-sphere hydrated complexes, but also can directly bonds with Al-O and Si-O groups on the aluminol or siloxane surfaces, or edge sites of clay particles in the form of inner complexes. The study on the metallogenic characteristics of ion adsorption rare earth deposits and the occurrences of rare earth elements therein is the basis for guiding ore prospecting and further efficient and environmentally friendly resource utilization, and it is of great importance for the development of world high-tech science and technology industries.