Geochemical characteristics of rutile-bearing mineral sands of the Nkapa Formation, Douala Sub-Basin, Cameroon: insights into source-area weathering, provenance, and tectonic setting

Coastal sedimentary basins are significant crustal architectural features with a vast accumulation potential for heavy mineral sands. These deposits are a source of titanium and zirconium, as well as rare earth elements (REEs), and are often overlooked. This study utilizes sediment geochemistry from the Douala Sub-Basin to (1) evaluate variations in elemental concentration levels with depth, (2) evaluate sediment sources and weathering conditions of the source areas, and (3) evaluate its economic potential for rutile, ilmenite, and zircon. A road cut section and six auger drill holes to depths of 2-7 m were sunk and logged. A total of 21 samples from the road cut section and 30 samples from the six drill holes were collected at 1 m intervals. They consist of fine- to coarse-grained sandy clay, clayey sand, sand, clay, and silt of varying colors reflecting different degrees of Fe oxidation and mineral weathering. Visible rutile grains with angular to rounded morphologies can be observed in the sediments. The geochemistry of the sediments shows high concentrations of SiO2, Al2O3, and Fe2O3, with low contents in TiO2, indicating a low potential for ilmenite and rutile in the area. We use factor analysis to show five factors that all point to a lithological contribution. An intense weathering of Fe-sand-rich arkose source rocks of mixed mafic and felsic igneous provenance that were formed in an arc-related collisional setting is supported by weathering indices (CIA, CIW, and PIA values > 95 and ICV values < 1) and source region characteristics.