Trace element behaviour in soils developed along the slopes of Mt. Cameroon, West Africa

A geochemical study of trace elements in soil profiles developed on basaltic parent materials of unknown ages along the slopes of Mt. Cameroon was carried out. The study objectives included vertical description of element dispersion, element mobility and relating element distribution to weathering intensity. Twenty five soil samples from 6 sites (between 30 to 1017 m a.s.l.) were collected and analysed for trace element concentrations by ICP-MS technique. The weathering status of these soils, (derived from chemical weathering indices) indicate that the most weathered profiles are located at higher elevations with lower mean annual precipitation. Higher losses in Cu, Co and Zr in the moderately weathered profiles in the zones of high leaching are linked to the comparatively higher dissolution of Fe-bearing minerals such as magnetite to which resulted in higher Fed/FeT ratios. Organic matter may account for low mobility of Cu and Pb, while for Zn, the Mn-Al system may control Zn retardation at low elevations. Ni and Sr were highly mobilised at all elevations while Pb, Rb and Sr showed evidence of atmospheric deposition. Comparatively higher inputs of dust-derived minerals in the lower elevation could also affect the distribution of TE. Suggestions are therefore made for the existence of an inflection point within this elevational bracket marked by incongruent dissolution of primary silicate minerals (particularly Feminerals)