Recherche des indices de minéralisations en Tio2-Zr-th-Y-Ree dans les formations alluvionnaires de Tongo-Gandima, Betare-Oya (Est–Cameroun).

Abstract

Stream sediments were analyzed to investigate the evidence of TiO2-Zr-Th-Y and REO mineralization in alluvium and heavy mineral concentrates from Tongo-Gandima (East Cameroon) in the Lom watershed, a tributary of the Sanaga. Tongo Gandima is located between 5 °00" and 5°26" latitude North and 13°50"and 14°08" longitude East. The climate is typically the equatorial transitional type. Petrographic, mineralogical and geochemical analyses were performed on several samples (whole rocks, sediments and heavy mineral concentrates) using mineralogical (X-ray diffraction and scanning electron microscope) and geochemical methods (X-ray fluorescence and Inductively Coupled Plasmas-Mass Spectrometry). The petrographic study revealed that the bedrock consists of monzonites and granites. On average, these rocks are composed of 40% feldspars, 37% quartz, 10% biotite, 10% muscovite and accessory minerals. They are peraluminous (A / CNK˃ 1) and belong to the S-type granitoids. The high proportion of feldspars and biotite has eventually contributed to the high grades of Al2O3, Fe2O3, CaO, Ba, Sr, Th, Zn, Zr and Tr. Monzonite is more enriched in TiO2, Zr, and REE than granite. Rare earth element spectra normalized to chondrite show enrichment in light rare earths relative to heavy rare earths, negative europium anomalies, and a high degree of fractionation. The alluvial materials of Tongo-Gandima are derived from surface processes (weathering, erosion, transport and deposition) of the surrounding soils and rocks. They consist of kaolinite, quartz, muscovite, gibbsite, rutile, smectite and zircon. They are mainly classified as shale, wacke, shale and clayey sand. The most abundant major elements are SiO2 (49-69%), Al2O3 (7-18%) and Fe2O3 (2-8%). The chemical index of alteration (CIA) reveals a moderate to intense weathering of the rock, confirmed by the depletion in alkaline (Na+, K+ and Ca2+) and enrichment in Al2O3. The high Ba, Sr, Th, Zr and rare earth contents are typical characteristics of an acidic source rock and indicate a high proportion of heavy minerals. The mineralogy of the fine-grained sedimentary concentrates consists of smectite, kaolinite, gibbsite, muscovite, quartz, rutile and zircon. Heavy mineral fractions are composed of opaque minerals, biotite, zircon, rutile, anatase, tourmaline, garnet, diopside and kyanite. Concentrated sediments have high contents in TiO2 (5-29%), Zr (2000-9800 ppm), Th (5000-52244 ppm), Y (1000-9809 ppm) and ∑REE (5000-152.885 ppm). The total content in REO ranges from 0.0088 to 15.66%. These concentrates are also marked by the abundance of LREO (76-97.94%). The grades are particularly high in La2O3, Ce2O3, Pr2O3 and Nd2O3. Indeed, the rare earth deposits of the Tongo-Gandima are up to ten times more enriched in TiO2- Zr-Th-Y-REO than the source rocks. TiO2-Zr-Th-Y-REO mineralization is higher in heavy mineral concentrates. Rare earth-bearing minerals are monazite, ilmenite, apatite and zircon. This is a secondary deposit of the light rare earth type.