Discovery and geological significance of new mineral tantalaeschynite-(Ce)

Rare earth elements and rare metals are widely used in the emerging industries and national defense science and technology areas. And they are also regarded as the important key metals for the country and their prospecting is imminent. Recently, new mineral tantalaechynite-(Ce) has been discovered in Huangshan granite pegmatite around Lingshan complex massif in Shangrao of Jiangxi Province, and it has been approved by International Mineralogical Association (IMA), which not only enriches the aeschynite group minerals, but also provides a new direction for rare metal prospecting. Tantalaeschynite-(Ce) occurs in Huangshan tantalumrich pegmatite in the form of acicular or bundle aggregates, and intergrows with feldspar, quartz, fluorites. The composition is extremely enriched in tantalum, titanium and cerium, and the ideal formula is Ce(TiTa)O₆. The structure belongs to the orthorhombic system, and it is composed of cerium oxygen polyhedron and titanium/tantalum oxygen coctahedron. The tantalaeschynite-(Ce) is formed in highly evolved granite pegmatite, indicating that the ore-forming environment is extremely rich in tantalum. Compared with the surrounding columbites, the sudden increase of tantalum content in tantalaeschynite-(Ce) cannot be simply explained by magmatic crystallization differentiation. The existence of boundary layer in pegmatite was put forward in the pegmatite zone-refining model, and this layer is enriched in sodium, fluorine, chlorine and other volatile components (also called fluxes). The boundary layer crystallization results in abrupt change of mineral composition, and incompatible elements are enrich in large quantities, after the exhaustion of melt component, and a large number of incompatible components are continuously accumulated and abundant. The boundary layer of highly differentiated granite pegmatite is characterized by the enrichment of volatile minerals such as albitite and fluorite, which is a vital indication for rare metal prospecting. Lingshan complex massif in Shangrao of Jiangxi Province has good potential of rare metal resources and this reasearch is of great significance for regional rare metal prospecting.