Mineralogy and geochemistry of soils developed along the slopes of Mt. Cameroon, West Africa

Changes in soil mineralogy and geochemistry are investigated in four soil profiles developed from rocks of unknown ages on an elevational gradient on the lower slopes of Mt. Cameroon. The study objectives include evaluation of weathering intensities of the profiles using proxies of weathering, description of mineralogy and major element geochemistry. Methods of study include major element analysis for <2 mm fraction by ICP-AES, quantification of secondary Fe and Al phases by extractive dissolution and determination of soil mineralogy by semi quantitative XRD. BUA, the most weathered profile is located at the highest elevation while the moderately weathered profiles (MUT and LBE) are located in lower elevations with higher rainfall. Soil pH(H2O) is highest in the most weathered profile which equally exhibits the lowest ∑bases and base saturation. Secondary extractible aluminum (Ald) followed by organic matter content explains the greatest amount of soil pH variation. The distribution of iron (Fe) components (i.e. dithionite–citrate extractible, Fed; amorphous Feo; and total, FeT) are controlled by the differential dissolution of Fe-bearing minerals and Fe-mobility at low and high altitudes. Consequently, the ratio Fed/FeT can serve as a useful indicator of weathering intensity under different climatic conditions. Al and Ti display the least relative mobility; however, Ti is comparatively more mobile especially in the low elevation sites.

► We examine the geochemistry and mineralogy of four soils along an elevation gradient.
► We compare the weathering intensities of the soils using soil indices.
► Soil Ald and organic matter both controlled by precipitation highly influences pH.
► Secondary extractible Fe forms are unsuitable as weathering indices.
► Ti is comparatively more mobile than Al especially in the low elevation sites.