This study intends to investigate the occurrence states of rare earth elements (REEs) in the paleo- terrigenous sedimentary rare earth deposits at the bottom of the Xuanwei Formation in the Shuizhu area, northeastern Yunnan, within the contiguous region of Sichuan, Yunnan and Guizhou. The research is expected to provide crucial clues and a scientific basis for mineral exploration and comprehensive resource utilization of the same type of sedimentary rare earth deposits in the study area and across China.Methods: In this paper, a variety of rock and mineral testing techniques including basic chemical analysis, X- ray diffraction (XRD) analysis, scanning electron microscopy (SEM) analysis, and rare earth leaching experiments were employed to conduct an in- depth mineralogical study on the paleo- continental sedimentary rare earth deposits in the Lianfeng area of Yongshan County, Zhaotong City, Yunnan Province.Results: The analysis results show that the average grade of total rare earth oxides (TREO) ranges from 0.12% to 0.21%, with the maximum content of a single sample reaching 0.23%. The ratio of light rare earths to heavy rare earths is between 1.55 and 2.88, indicating a light- rare- earth- dominated characteristic, where light rare earths account for 61%~73% of the total rare earth content. Mineralogically, the ore is dominated by clay minerals with a total content of approximately 75%, among which kaolinite is the predominant component (45%), followed by montmorillonite (36%) and chlorite (19%). The contents of other minerals are trace, and independent rare earth minerals are extremely scarce. Leaching tests and measurements reveal that the ion- adsorbed phase accounts for only 0.94%–3.86% of the total rare earths, suggesting a relatively low content of ion- exchangeable rare earths. The results indicate that the rare earth elements in the samples are likely to occur as rare- earth- enriched nanomineral particles hosted within clay minerals such as kaolinite.