Geochemical Characterization of Vertisols Developed on Granites from Kaele, North-Cameroon: Implications for REE Exploration

This paper presents the geochemical features of Vertisols developed on granites from Kaele, North Cameroun. The mineralogy of soil samples was determined by X-ray diffraction (XRD). X-ray Fluorescence (XRF) and Inductively Coupled Plasmas-Mass Spectrometry (ICP-MS) have been used to determine major and trace element including rare earth elements compositions of granite and soil samples. Granite samples consist of feldspars (orthoclase, plagioclase), quartz, biotites and opaque minerals. They have peraluminous composition and of S-type granite. They also have high contents in Ba, Cr, Sr, Zr and low REE contents with variable Eu anomaly values. The mineralogical and geochemical features of Vertisols corroborate with the parent rock nature and the intensity of weathering process. The Fe-oxide precipitation, the presence of kaolinite and calcareous nodules are responsible for significant contents in Fe2O3, Al₂O₃ and CaO, respectively. Several major and trace elements are accumulated at the bottom of the profiles. The accumulation of clay increases with REE contents from the upper to the lower horizons in Vertisols of Kaele area. LREE-enrichment in Vertisols is inherited from the parent material and probably preserved by the formation of secondary LREE-bearers. The low REE contents may result from depletion of REE rich minerals as in the parent rocks despite the REE remobilization during weathering. REEs how coherent geochemical behavior and low solubility during weathering. The variable Eu anomalies can be explained by the variable behavior of Eu-bearers while Ce anomalies exhibit the variability of the oxidation conditions. The low (La/Yb)N values and the similarity of the spectra of mass balance calculation in most of the profiles are linked to the environment which is not well drained and the homogenization of the profiles by seasonal deep surficial desiccation cracks.

Keywords: North-Cameroon; Vertisols; S-type granite; Rare earth elements; Geochemistry; Mass balance evaluation