Major, trace, and Rare Earth Element (REE) characteristics of the mentebteb lateritic iron deposit, northern Ethiopia

Rare earth elements (REEs) fractionation and accumulation in Mentebteb lateritic Fe deposits are the key processes with direct implications for REE exploration in weathered terrains. This study investigates the distribution, mobility, and controls on REE behavior across a lateritic weathering profile, using an integrated approach that combines petrographic analysis, X-ray Powder Diffraction (XRD), and geochemical techniques such as Inductively Coupled Plasma Atomic Emission Spectrometry (ICP-AES) and Inductively Coupled Plasma Mass Spectrometry (ICP-MS). The profile is divided into three main horizons: a lateritic iron horizon, a clay-rich lateritic horizon, and ferruginous sandstone. In the lateritic iron horizon, hematite is identified as the dominant Fe-bearing mineral, with subordinate goethite and accessory quartz, feldspar, and kaolinite. The Geochemical data reveal that REEs are differentially fractionated and enriched along the profile, with Fe-oxyhydroxides playing a major role in REE accumulation, particularly in the lateritic iron horizon. The positive correlations between Fe, Cr, V, Co, Ni, and ΣLREE/ΣHREE ratios suggest selective sorption and co-precipitation of REEs with Fe phases in the lateritic iron horizon. In contrast, the negative correlation between Al₂O₃ and these elements in the upper lateritic horizon suggests a negligible role of clay minerals in REE retention. However, Al₂O₃ exhibits variable correlations with V (r = 0.27; r = −0.37), Cr (r = 0.61; r = −0.79), Ni (r = 0.52; r = −0.48), and Co (r = 0.65; r = −0.52) in the clay-rich lateritic and ferruginous sandstone layers, indicating that clay minerals influence element mobility in the clay-rich horizon but have minimal impact in the ferruginous sandstone. REE fractionation patterns is evidenced by La/Y ratios is depleted in the lateritic iron horizon (La/Y < 1, 0.87–0.99) and enriched in the clay-rich horizon (La/Y > 1, 1.08–1.36) and ferruginous sandstone (La/Y > 1, 1.27–1.76). These variations in the REE dispersion and fractionation trends are controlled by weathering intensity, redox conditions, acid dissolution, mineral breakdown and differential solubility effects which drive leaching, complexation, and secondary enrichment processes. The observed REE behavior underscores the importance of lateritization in concentrating critical metals and provides geochemical criteria for vectoring towards REE-enriched zones. This study highlights the importance of lateritization processes in REE accumulation and provides a framework for REE exploration in weathered Fe deposits, particularly in lateritic terrains.