Publications scientifiques
* (Auteur correspondant)
Paola Raissa Bassanak Ongboye
François Ndong Bidzang
Geological Journal
Tongo Gandima is an area located in the southeastern part of the Bétaré Oya Gold district (Eastern Cameroon). Geochemical investigations on rare metals (TiO 2 , Th, Y, and rare‐earth elements [REE]) were carried out on sample types (source rocks, unconsolidated fine‐grained sediments, and concentrated sediments) using X‐ray diffraction (XRD), X‐ray fluorescence (XRF), inductively coupled plasma‐mass spectrometry (ICP‐MS), and scanning electron microscope equipped with EDAX spectrometer (SEM‐EDS) methods. In this study, five layers of river terraces were selected (organic matter layer, clayey layer, fine sandy layer, coarse sandy layer, and gravel layer). One of them, the gravel layer, is mineralized. TiO 2 , Zr, and REE are more enriched in monzonites than in granites. Unconsolidated sediments derive mainly from the erosion of weathered materials developed on monzonites and granites. The mineral assemblage of fine‐grained sediments from the gravel layer is muscovite, kaolinite, quartz, rutile, smectite, and others, and the average concentrations in Th, Zr, and Y are high. Fifty concentrated fractions from the same samples were analysed separately and their mineralogy is smectite, kaolinite, gibbsite, muscovite, quartz, rutile, anatase, zircon, titanomagnetite, and ilmenite. The heavy mineral fractions are opaque minerals, biotite, zircon, rutile, tourmaline, garnet, diopside, zoisite, and kyanite. TiO 2 , Zr, Th, Y, and REE contents are high. The REE oxides (REO) total grade ranges from 0.0088 to 15.66 wt%, marked by LREO‐abundance, especially in La 2 O 3 , Ce 2 O 3 , Pr 2 O 3 , and Nd 2 O 3 . The Tongo Gandima REO deposit was classified as LREO‐dominated type. The chondrite‐normalized REE patterns exhibit strong negative Eu anomalies; their V‐shaped patterns are typical of ore varieties. The abundant TiO 2 , Zr, Y, Th, and REE might have been influenced by surface processes (peneplanation and chemical weathering) and variations in sediment grain size. SEM‐EDS data reveal that apatite with Ce‐ and La‐dominant, monazite‐(Ce), and Ce‐Mn‐bearing ilmenite are rare metal‐bearing minerals. This study demonstrates that the economic importance of the alluvial‐fluvial placers from Tongo Gandima results from their high Ti, Zr, Th, Y, and REE contents.
