Mineralogy and geochemistry of Lobe River sediments, SW Cameroon: Implications for provenance and weathering

The Lobe River (LR) watershed basement rock, Ntem Complex (NC), south Cameroon is covered by a thick lateritic soil. To better constrain the geology of the basement rock, textural, mineralogical and bulk geochemical (major, trace, and rare earth elements) analyses were undertaken on the recent stream sediments from the LR. The aims of this study were to investigate the provenance of sediments and to determine the weathering intensity of the source area. The ternary (Al2O3-TiO2-Zr) and binary (Th/Sc-Zr/Sc) diagrams suggested high sediment recycling and sorting, indicating that the bulk hydraulic energy of the LR controls the sediment texture. Despite the diagenetic processes of K-metasomatism observed on the A-CN-K plot, the (A-K)-C-N plot, Chemical Index of Alteration (CIA), and Plagioclase Index of Alteration (PIA) indicate that the studied sediments and their source areas underwent a high degree of chemical weathering. The heavy mineral suites imply heterogeneous provenance, including igneous, metamorphic and sedimentary source rocks. The ternary diagrams and Co/Th, La/Sc, Sc/Th, Cr/V, and Y/Ni elemental ratios indicate mostly felsic source rocks with lesser contribution from mafic components. The comparison of chondrite normalized REE patterns of LR sediments with potential source rocks reveals that the sediments were derived from the Precambrian basement rocks composed of tonalitic, trondhjemitic, and granodioritic suites, with remnants derived from Archean Greenstone Belt.