Research advances on mineralization and types of the alkaline granite-related rare metal and rare earth element deposits

Abstract

Significance Alkaline granites are one of the most important intrusions associated with rare metal and rare earth element mineralization. Progress Recently, alkaline granite-related rare metal and rare earth element deposits have achieved a number of important advances in classification, sources of ore-forming fluids and materials, and enrichment mechanisms. Alkaline granites are usually enriched in high field strength elements (HFSEs) and rare earth elements (REEs). These deposits can be divided into three types based on the relationships between mafic and oreminerals, i.e., arfvedsonite alkaline granite-related Nb-REE deposits, biotite alkaline granite-related Nb-Sn-rich deposits, and nepheline/aegirine syenite-related Nb-U-REE-rich deposits. Mineralization ages of these deposits are concentrated in the Paleozoic-Cenozoic. The deposits are formed in an extensional setting associated with break-up and convergence of continents and supercontinents. Two stages of ore-forming fluids, early-stage magmatic differentiation and late-stage hydrothermal metasomatism, are recognized for the formation of these deposits. Previous studies indicate that ore-forming fluids exsolved from alkaline magmas are characterized by low temperatures, high salinities and rich fluorine, which can lead to the super high enrichment of HFSEs and REEs in alkaline granites. Incompatible elements in parental magmas can be enriched in exsolved fluids and can lead to the formation of rare metal and rare earth element ores due to F-rich fluid fractional crystallization or hydrothermal alteration in the late magmatic stage. The ore-forming materials were dominantly originated from mantle-derived magmas, crust- and mantle-derived magma mixing, or subducted oceanic crust. Conclusions and Prospects Hydrothermal metasomatism and magmatic fractional crystallization are two enrichment mechanisms commonly used to interpret the formation of these deposits. However, most of these deposits are formed by a combination of the two mechanisms.

Keywords

• alkaline granite
• rare metal and rare earth element deposit
• ore-forming fluid
• ore-forming material
• mineralization mechanism