Geology, geochemistry, and genesis of Kindia region's bauxite deposits (Guinea, West Africa)

Debele and Balaya bauxite plateaus are two of the tabular plateaus of Kindia bauxite province; where the bauxites ore are found upper Ordovician and Silurian formations in the southern part of the Guinean Paleozoic Bové Basin which is situated east of the West African Craton. Previous works revealed the existence of two types of bauxite on these two plateaus: the lateritic bauxites formed in situ and the sedimentary bauxites redeposited. Although the reworking characters of these sedimentary bauxites is obvious, their genetic relationship with the surrounding lateritic bauxites and Silurian schists has remained confused. To contribute to this geological task, this work deals with the petrographical, mineralogical and geochemical investigation on the different type of bauxites on Balaya and Debele plateaus. Mineralogical analysis and petrological study revealed that the mineralogy is almost identical in both lateritic and sedimentary bauxites of Balaya and Debele plateaus. Gibbsite, goethite and aluminous goethite are the major mineral components; anatase, rutile, diaspore and kaolinite are minor minerals, with zircon and clastic quartz as accessory minerals in the bauxites. Whole rock and trace elements analyses show that the main components of the bauxites ore are Al2O3, SiO2, Fe2O3, and TiO2. Trace elements investigation indicates that Ti, Cr, Ga, Nb, Th, V, Zr, Y, and REEs were immobile and specifically enriched; whereas alkalis and alkaline earth metals along with P, Sm and Tb were depleted in bauxites during lateritization. Geochemical paths of dismantlement, immobile element ratios (Zr vs Hf, Nb vs Ta and Yb vs Lu; and Cr/Ni) and REE patterns of the sedimentary and lateritic bauxites indicate that they were all originated from the Silurian argillites, aleurolites and aleuropelites of Telimele Suite through an indirect bauxitization, and that the gibbsite are products of the desilication of the kaolinite by a deep lateritization. Thus, Balaya and Debele sedimentary bauxites were formed from the lateritic bauxites by redeposition through different mechanical transportations. Pearson correlation and UCC-normalized trace elements patterns revealed that T-bearing and Fe-bearing minerals are the carrier for HREE, HFS, Sn, U, Ga, W and Y and Mo, Cu, Pb, As, Sb, Bi, respectively. P-bearing minerals and kaolinites could have played signifiquent roles in LREE concentration, but the possible presence of authigenic minerals of strontium bearing the LREE are expected.