Multi-Lithology Mineral Control on Rare Earth Element Release During Rock–Soil Weathering

Rare earth elements (REEs) are widely adopted as sensitive geochemical tracers for Earth surface critical zone processes. Clarifying how lithology and mineral assemblages jointly control REE mobilization, fractionation, and redistribution during weathering is essential for understanding surficial element cycling. Most previous investigations of REE weathering geochemistry concentrate on individual lithological profiles; furthermore, traditional statistical approaches are limited in resolving the nonlinear threshold effects of mineral phases on REE release flux. To fill this gap, this study collected rock and overlying soil samples developed from phosphorite, altered basalt, and limestone and dolomite in Liangwang Mountain, Yunnan, China. We quantified weathering intensity via the PROFILE model, evaluated REE enrichment using the enrichment factor and geoaccumulation index, and adopted major oxide principal component analysis, Pearson correlation, hierarchical clustering, and CRT (classification and regression tree) regression tree models to reveal mineral controls on light, heavy, and total REE release rates (Rm). Parent lithology dominates the inherent REE geochemical signatures of weathered soils: altered basalt and phosphorite bear high bulk REE concentrations, while limestone and dolomite possess inherently low REE backgrounds inherited in weathering products. Weathering substantially reshapes REE distribution and fractionation: silicate hydrolysis and clay adsorption produce pronounced LREE (light rare earth element) enrichment and weak positive Ce anomalies in altered basalt soils, whereas strong carbonate dissolution leads to remarkable overall REE depletion in limestone and dolomite soils. The ranking of weathering rates shifts from bedrock (limestone and dolomite > altered basalt > phosphorite) to soil (altered basalt > phosphorite > limestone and dolomite), indicating a transition from mineral dissolution control to integrated pedogenic biogeochemical regulation. Across all soil samples, HREEs (heavy rare earth elements) are preferentially leached relative to LREEs, amplifying light–heavy REE fractionation; phosphorite soils largely retain bedrock REE features owing to dominant physical weathering and weak chemical mobilization. This work constructs a complete linkage framework of parent lithology, mineral transformation, weathering progression, and REE fractionation. It highlights that lithology-specific mineral assemblages impose hierarchical nonlinear constraints on REE cycling and offers quantitative supports for investigating regional REE migration and environmental geochemical assessment within soil-water critical zones.