Geochemical behavior of elements in granite-derived weathering profiles from Mayo-Darle, North Cameroon: Implications for rare metal enrichment. Journal Of African Earth Science.

This study investigates two weathering profiles (PN1 and PY1) developed on compositionally distinct granitic parent rocks in the Mayo-Darl´e area (North Cameroon) to assess mineralogical, geochemical, and geomorphological controls on rare-metal enrichment under tropical weathering conditions. PN1, formed on a mid-slope Atype granite, and PY1, developed on a summit I-type granite. Both profiles display a typical regolith succession from saprock to lateritic horizons, yet recording contrasting weathering trajectories. Petrography, X-ray diffraction (XRD), and whole-rock geochemistry show that the A-type granite hosts abundant accessory minerals bearing high-field-strength elements (HFSE) and rare earth elements plus yttrium (REY)—rutile, cassiterite, ferro-columbite, thorite, zircon, monazite, xenotime, euxenite, and fluorcerite—favoring residual enrichment in PN1. In contrast, the I-type granite contains more reactive phases (ilmenite, titanite, allanite) that undergo hydrolytic alteration, enhancing trace-element mobility in PY1. Mass-balance calculations and enrichment factors (EF) indicate strong retention of Sn, Nb, Th, and REY in PN1, particularly within saprock and lower saprolite, whereas PY1 shows vertical redistribution and near-surface enrichment, especially of light rare earth elements (LREE). Microtextural evidence (skeletal ilmenite, replacement textures), together with weathering indices—the chemical index of alteration (CIA), index of lateritization (IOL), and plagioclase index of alteration (PIA)— support these contrasting weathering regimes. Topographic position modulates drainage efficiency and element residence time, reinforcing lithological controls. These results demonstrate that accessory mineral stability, primary microtexture, and slope-driven hydrology jointly govern Nb–Th–Sn–REY fractionation in tropical regoliths, providing a process-based framework for rare-metal exploration in deeply weathered granitic terrains.