Formation process of a newly explored ion-adsorption type REE deposit in Pingtian, Guangdong, South China: A detailed profile analysis

Abstract

Recently, ion-adsorption-type rare earth element (REE) deposits have been explored in Nanxiong Basin (South China), with an estimated total reserve of >100 million tons. The formation of ion-adsorption-type deposits is closely linked to the weathered crust of their parent granitic rocks. To better understand how the weathered crust influences the formation of ion-adsorption type REE deposits, this study presents detailed research on the relationship between the characteristics of the weathered crust and parent rock in Pingtian Town, Nanxiong Basin, Guangdong Province, through a detailed profile analysis. The UPb dating of zircon and apatite indicates that the parent rock (biotite monzogranite) was formed at ca. 220 Ma, which provides favorable metallogenic conditions for the formation of the weathered crust. Minerals such as monazite, zircon, apatite, and plagioclase play critical roles in the formation of the weathered crust. Monazite and plagioclase are the main controlling minerals for REE enrichment in the weathered crust. Monazite, influenced by apatite, determines the REE distribution pattern in the crust, with a particular emphasis on light rare earth elements (LREE). Zircon, being resistant to weathering, leads to the preferential enrichment of LREE in the weathered crust and limits the accumulation of heavy rare earth elements (HREE). Plagioclase, through weathering into kaolinite, provides an adsorption medium for ionized REE. In addition, trace element analysis of zircon and apatite, as well as geochemical studies on the parent rock, indicate that the parent rock belongs to a moderately differentiated granite. The degree of granite differentiation impacts REE enrichment in the weathered crust. The higher the degree of differentiation, the more ionized REE elements and adsorption media are provided, facilitating the formation of ion-adsorption type REE deposits. This highlights the importance of detailed profile geochemical analysis in revealing the genesis of ion-adsorption-type REE deposits.