Rare earth elements in tropical soils, Cameroon soils (Central Africa)

Abstract

This paper presents statistical analyses and spatial interpretations of the rare earth elements (REE: La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu) distributions using geochemical database of soil compositions, and highlights future research needed in the field of REE in Cameroonian soils. Raster maps which depict spatial distributions of individual REE by the interpolation of uni-element data were carried out on the REE data. Rare earth elements were investigated in 604 soil samples from 163 Cameroonian profiles. However a wide range of natural variability in rare earth element contentsincluding the REE, LREE and HREE median content are relatively high (297.42 mg/kg, 275.11 mg/kg and 22.31 mg/kg, respectively) compared to those reported in soils from other parts of the world. The decreasing order of the REE contents in the Cameroonian soils is: Andosols > Ferralsols > Nitrisols > Plinthosols > Umbrisols > Gleysols > Vertisols > Lixisols. On the other hand, the soils developed on alkaline igneous rocks usually show great or high REE contents, ranging from 678.73 to 1148.02 mg/kg, whereas on limestones the REE contents vary from 152.48 to 1927.10 mg/kg. The soils from igneous rocks show lowe REE contents (24.35-312.59 mg/kg). In decreasing order, the REE contents are: Ce > Nd > La > Pr > Sm > Dy > Gd > Yb > Er > Tb > Eu > Ho > Lu ≥ Tm. The data presented here result from the first national-wide survey of REEs in Cameroonian soils. Ours results offer the most detailed study of surface geochemistry of REEs on Cameroonian soils and help in expanding the limited knowledge available on these elements in Cameroonian soils. However, further research is warranted to explore the strongly zone of REE contents. This will allow evaluating the potential feasibility of rare earth elements project: tonnage, ore grade (%), ore value and basket price.