Abstract: The Mianning-Dechang rare earth element (REE) metallogenic belt exhibits considerable resource potential. Previous prospecting was oriented to hard-rock REE deposits associated with Himalayan alkaline complexes, with ion adsorption-type REE deposits under-studied. To explore the mineralization prospect of granite weathering crusts widespread in the metallogenic belt, this study investigated the Shizishan area through multi-channel gamma-ray spectrometry, soil profile survey, and shallow drilling. One ion adsorption-type REE ore occurrence was identified in the granite weathering crust at Mosuoying. This study analyzed the radioactive response of the geological, geophysical, and geochemical profiles and ore contents, finding that the elemental contents of thorium (Th) and potassium (K) were highly indicative of REE and rare metal mineralization. Highly mineralized, industrial-scale ion adsorption-type REE deposits will likely occur when 6.25< w(Th)/w(K)< 10, w(eTh)> 37×10^-6, and w(eK)> 4.2%. As revealed by the analysis of the response of radioactive anomalies to supergene weathering, thorium anomaly halos can effectively indicate granitic plutons while potassium anomaly halos can well delineate the extent of granite weathering crusts.