The discovery and geological significance of the Mantoushan ion-adsorption type heavy rare earth deposit in Dechang, western Sichuan

The Mianning-Dechang rare earth metallogenic belt is one of the most important rare earth resource areas in China. All discovered rare earth deposits are related to the carbonatite-alkaline complex that formed during the Himalayan period. It is controversial whether ion adsorption rare earth deposits exist along this metallogenic belt. In this paper, we conducted a detailed survey of Mantoushan potash feldspar granite in Dechang and verified through three shallow drill coress that the thickness of the weathering crust in this area reached 17 meters. According to the degree of weathering, the weathering crust is divided into humus, clay, full regolith, and semi-regolith. The total phase rare earth oxide (TREO) grade of the regolith crust varies between 0.07% and 0.19%, with an average of 0.12%, which is higher than the industrial grade of 0.05%. Additionally, the grades of separated quantities of rare earth oxides (SREO) range between 0.02% and 0.056%, with an average of 0.03%, which is higher than the cutoff grade of 0.02%. The partition range of heavy rare earth is between 50% and 72%, averaging at 62%. The variation of rare earth grade within the weathering crust profile exhibits two patterns: "upper low-lower high" and "upper high-lower low". The full regolith and clay layers are identified as the primary ore-bearing layers for both patterns. The Mantoushan deposit is the first ion adsorption heavy rare earth ore deposit found in the Mianning-Dechang rare earth metallogenic belt, which has great economic value and scientific significance.