Late Cretaceous granitoids are developed in the eastern and western districts of the Gejiu ore district, but tin deposits mainly occur in the eastern district, and the reasons for the difference in mineralization between the eastern and western districts are still controversial. Considering the main factors controlling granite Sn fertility, the whole-rock geochemical characteristics of granites on both sides are compared. LA-ICP-MS zircon U-Pb analyses of the Gejiu granites yielded two age periods: the early phase from 79.2 to 83.3 Ma and the later phase from 73.8 to 75.6 Ma. The western district granites have higher zircon ε_Hf(t), CaO/Na₂O, Ba, and Sr concentrations and lower Rb/Sr ratios than the eastern district granites, indicating that the western district granites have more mantle-derived materials in the source than the eastern district granites. Results of oxygen fugacity show that the western granites have a higher oxygen fugacity condition. More depleted Ba, Sr, P, Eu and Ti characteristics with obviously negative Eu anomalies in the eastern granites also have high Rb/Sr ratios and low Nb/Ta and Zr/Hf ratios, indicating that the eastern granites experienced highly magmatic differentiation, attributed to high volatile F contents that can reduce the viscosity and solidus of magma. Combined with the differences in field observations and structural styles, on the whole, the western district granites have higher oxygen fugacities and lower F contents and magmatic differentiation than those in the eastern district granites, indicating that the western district granites are not conducive to mineralization.

The TuguanZhai rare earth deposit in Tengchong, along with the Longan and Yingpanshan deposits in Longchuan, is a significant ion-adsorption type rare earth (iREE) deposit in Yunnan, China. Previous studies mainly focused on the geochemistry of residual regolith or the migration and enrichment mechanism of rare earth elements (REEs), but lacked systematic analysis of the protoliths. To constrain this deposit and its protolith rock, called Tuguanzhai granite, we systematically integrate petrology features, petrogeochemistry, zircon U-Pb date, and artificial heavy mineral separation (AHMS). Specifically, iREE-host granites include two main periods in this area: the Early Cretaceous (112.13 ± 0.75 Ma) and the Paleocene–Eocene (52.78 ± 0.28 Ma, 48.56 ± 0.19 Ma). The former includes three types of biotite monzogranite with different grain sizes, and the latter is mainly medium-grained biotite monzogranite with local mylonitization. Geochemical features show that these granites generally share high alkalinity compositions (w(K₂O + Na₂O): 7.15 to 12.75 wt%) and potassium contents (w(K₂O): 3.89 to 8.36 wt%). The mineralized granites exhibit significantly higher concentrations of the total REEs than non-mineralized granites, along with a strong enrichment of light REEs. Moreover, the results of AHMS reveal that the REE contents of apatite, allanite, and titanite in mineralized granites are 4.98, 1.29, and 1.90 times more abundant than in non-mineralized granites, respectively. Due to REEs being released from these REE-rich minerals in humid environments, there exists significant potential for iREE formation and exploration in the Early Cretaceous granites in western Yunnan. We innovatively propose the “abundance of easily leachable minerals” as a key indicator for iREE mineralization and exploration, having found it to be better than the traditional total REE contents.