Changing mineralogical controls on rare earth elements (REE) enrichment during lateritic weathering of the Yasi-Kandi iron deposit, NW Iran

The mobility, redistribution, and mineralogical retention of rare earth elements (REE) during lateritic weathering remain incompletely understood, particularly regarding how REE-hosting mechanisms evolve from Fe-rich to clay-dominated conditions. Lateritic profiles developed over or associated with iron deposits provide a distinctive setting for investigating this transition because progressive weathering modifies Fe–Mn oxides, silicate minerals, and clay phases. The Yasi-Kandi lateritic iron deposit in northwestern Iran represents a natural example of this setting and comprises an upper brownish-red lateritic iron ore (BRLIO) horizon and an underlying red lateritic ore (RLO) horizon. Geochemical trends from BRLIO toward RLO show a progressive decrease in Fe 2 O 3 and increases in Al 2 O 3 , SiO 2 , TiO 2 , P 2 O 5 , REE, (La/Yb) N , and (LREE/HREE) N , indicating progressive weathering, desilication, lanthanide fractionation, and a transition from an Fe-dominated to a clay-rich weathering regime. The distribution of REE suggests an initial association with Fe–Mn oxide surfaces, followed by increasing retention within kaolinite-rich horizons during advanced weathering. Variations in Ce and Eu anomalies, together with mineralogical changes, indicate that redox conditions and secondary mineral transformations contributed to REE redistribution. The positive Ce anomaly in BRLIO is consistent with strongly oxidizing conditions and effective Ce retention by Fe–Mn oxides, whereas the stronger negative Eu anomaly in RLO reflects progressive Eu fractionation associated with advanced weathering. Overall, these relationships indicate a progressive shift in REE-hosting mechanisms from Fe–Mn oxide-associated retention toward clay-dominated retention, providing a framework for understanding REE redistribution and identifying prospective REE-rich horizons in iron-associated lateritic weathering systems.