Rare earth element geochemistry and resource potential of alluvial sediments from the Mugheb watershed, Cameroon volcanic line

Abstract

The significance of rare earth elements (REEs) as critical metals in modern technology has led to the assessment of Mugheb sediments as a potentials unconventional resource. Sediments have sparked significant attention as a secondary source of REEs to traditional REE-bearing ores in recent times. This study evaluates resource potential of REEs, fractionation pattern, provenance and REEs signatures in alluvial sediments of Mugheb watershed, Cameroon. This area lacks data on REEs despite growing concerns on REE enrichment in sediments and unconventional economic potentials. Sediment samples were analyzed using inductively coupled plasma-mass spectrometry (ICP-MS). Total REE concentrations (∑REE) ranged from 215.30 to 457.90 mg/kg, with a pronounced enrichment of light REEs (LREEs: 204 to 431 mg/kg) over heavy REEs (HREEs: 11.30 to 21.60 mg/kg). The findings revealed anomalous concentrations for La, Ce, Pr, Nd, Gd, and Sm, critical for permanent magnet production in electric vehicles and wind turbines. Normalized ratios of (La/Yb)N :2.67 to 4.76, (La/Sm)N :0.87 to 1.29, (Gd/YbN :2.78 to 4.25 and (Ce/Sm)N :1.07 to 2.01), indicate significant REE fractionation during sedimentation processes. The multivariate statistical analysis suggests common input sources of REEs from natural geologic processes. The significant ∑REE (215.30 to 457.90), Nd + Pr (50.60-105.90), EI/SR (8.85–12.10), Y/Y* (0.73–0.87) and REEs + Y (225.80-476.10) values suggest a possible relatively promising unconventional or conventional REE-bearing ore. Positive Ce/Ce* and negative Eu/Eu*anomalies suggest oxic to sub-oxic depositional conditions. The variable LREE/HREE ratios and negative Eu anomalies in the alluvial sediments indicate that these sediments are sourced mainly from felsic rocks with contributions mafic origins. The negative Eu anomalies also signify plagioclase fractionation in the felsic source rocks during evolution or accessory minerals framework mechanism of the sediment deposition. These results highlight alluvial sediments in contributing to global REE exploration for technology-driven economy. These findings also establish a strong basis for future pilot-scale studies and the techno-economic assessment of a possible Mugheb placer deposit system (alluvial sediments) as an emerging source of REEs for future exploration.