Mineralogy and geochemistry of sands of the lower course of the Sanaga River, Cameroon: implications for weathering, provenance, and tectonic setting

This study focuses on the mineralogy and bulk chemical composition of 19 sediment samples, collected from the Sanaga River bed, between Nanga-Eboko and the Atlantic Ocean in Cameroon, to infer provenance, weathering, and tectonic setting. The textural analysis revealed that these sediments are mainly coarse-grained sands. X-ray diffraction and heavy mineral analyses show that these sands are made of quartz, microcline, plagioclase, muscovite, ilmenite, anatase, magnetite, opaques, and epidote. The Index of Chemical Variability values (1.07-2.68) indicates that the sands are immature. The Chemical Index of Alteration (53-66 %), Plagioclase Index of Alteration (PIA; 57-75 %), and Mafic Index of Alteration (54-67 %) values revealed a moderate intensity of weathering for these sediments. According to the compositional maturity diagram, the sands are mainly litharenites. The studied sands show enrichment in light rare earth elements relative to heavy rare earth elements and a negative anomaly in Eu (Eu/Eu* = 0.32-0.83). These sands were derived from felsic metamorphic rocks dated Meso to Neoproterozoic from the Pan-African (700-1000 Ma) domain of south Cameroon. Th/U ratios (mean = 5.40; n = 19) reveal that these sands originating from felsic source rocks and are low to moderately recycled. On the tectonic discrimination diagrams, all the samples are plotted in the rift and passive margin domains, which is consistent with the tectonic history of Pan African in southern Cameroon.