Genesis of Clay Rock-Type Rare Earth in the Southwest of the Yangtze Block

Abstract

In the weathering crust of the Emeishan basalt in northwestern Guizhou, significant amounts of rare earth elements (REEs) are present. However, there has been limited research on kaolinite clay rocks formed by the transport and deposition of kaolinite derived from basalt weathering to coastal areas. This study focuses on the weathering crust of the basalt in the Nayong area of Guizhou, conducting mineralogical and geochemical investigations. The results reveal that the weathering crust in the Nayong area is rich in chlorite, quartz, anatase, and kaolinite. Geochemical analysis indicates that the weathering crust contains high concentrations of rare earth elements (108.75–903.03 × 10^–6), primarily originating from the Emeishan basalt. These REEs were released through weathering and transported by rivers to coastal areas for deposition. The Th/Sc vs Zr/Sc and La/Yb vs ΣREE diagrams, along with the significant variations in δEu (0.58–1.69) and δCe (0.87–1.18), suggest that the enrichment of REEs was accompanied by the incorporation of alkaline volcanic ash and may have been influenced by hydrothermal alteration in later stages. According to this study’s research results, it is proposed that the lower part of the weathering crust is in the element accumulation stage, the middle part is in the element leaching stage, and the upper part is in the element accumulation stage.