Geochemistry of trace and rare earth elements during weathering of black shale profiles in Northeast Chongqing, Southwestern China: Their mobilization, redistribution, and fractionation

摘要: In this study, the mobilization, redistribution, and fractionation of trace rare earth elements (REE) during chemical weathering in mid-ridge (A), near mountaintop (B), valley (C) profiles (weak, weak to moderate, moderate intense stage, respectively), are characterized. Among elements, U V were depleted regolith all three profiles, Sr, Nb, Ta, Zr, Hf displayed slight gains or losses, Th, Rb, Cs, Sc remained immobile. Mn, Ba, Zn, Cu, Cr enriched at A B, but profile C. Pb, Co also saprock fractured shale zones B REEs zone along Mobility increased with increasing intensity. Normalized REE patterns based on parent revealed light (LREE) enrichment, middle (MREE), heavy (HREE) depletion patterns. LREEs less mobile compared MREEs HREEs, differentiation degree. Positive Ce anomalies higher C than B. The fractionated from other showed that changed trivalent tetravalent (as CeO2) under oxidizing conditions. Minimal was observed contrast, more resulted preferential retention LREE (especially Ce), leading considerable LREE/MREE LREE/HREE fractionation. (La/Yb)N (La/Sm)N ratios maximum values within low pH values. Findings demonstrate acidic solutions can mobilize result leaching out highly portions material transport downward into shale. overall behavior suggests solution pH, as well presence primary secondary minerals, play important roles mobilization redistribution black weathering.