Geochemical Features of the Weathered Materials Developed on Gabbro in a Semi-Arid Zone, Northern Cameroon

Investigation on the mobilization and the redistribution of major, trace and rare-earth elements (REE) was performed along a soil profile developed on gabbro in the semi-arid zone (Northern Cameroon), using mineralogical and geochemical analyses. The gabbro has high contents in Ba, Cr, V, Sr, Ni, Zn, Zr, Cu, Co and Sc. The total REE content is 49 mg/kg with strong light rare-earth elements (LREE) abundance. The Ce/Ce* and Eu/Eu* ratios are very close to 1 (0.98 and 1.02 respectively) and the (La/Yb)N ratio is very low (1.48). The weathering of the bedrock leads to the differentiation of coarse saprolite, fine saprolite, loamy clayey horizon and humiferous horizon. Among trace elements, Cr and Zr concentrations range between 50 and 150 mg/kg; Ga, Y, Co, Cu, Ni and Sc concentrations vary between 50 and 150 mg/kg while those of Cs, Hf, Nb, Rb, Sn, Ta, Th, U and Pb are below 5 mg/kg. The total REE contents vary from 62.52 to 78.81 mg/kg, with strong LREE abundance. The values of the (La/Yb)N ratio (~1.04–1.59) is low and indicate the low REE fractionation. Negative Ce anomaly (Ce/Ce* ~ 0.86) and positive Eu anomalies (Eu/Eu* ~ 1.22) are observed respectively in the middle part and the whole soil profile. Mass balance calculation reveals the leaching of Ca, Mg, K, Ba, Cr, Rb, Co, Cu, Ni, Al, Cs, Sr, U and V, and accumulation of Si, Fe, Ti, Mn, Na, P, Ga, Hf, Nb, Sn, Ta, Y, Zr, Sc, Zn and REE during the weathering

Mineralogical and physicochemical characterization of Ngaye alluvial clays (Northern Cameroon) and assessment of its suitability in ceramic production

AbstractThis study reports the physicochemical analysis of three alluvial clastic clays from the Ngaye River in northern Cameroon. X-ray diffraction, infra-red spectroscopy, scanning electron microscopy and thermal analysis are used to establish the mineralogical composition. It is found that the main clay minerals in these samples are kaolinite, muscovite-illite and smectite associated with quartz, goethite, feldspars and anatase. This mineralogical assemblage is in accordance with the chemical analysis which further confirmed the high quartz proportion. The low content in fluxing agent is indicated by the low contents in Na2O, K2O, MgO and CaO. The low content in fluxing agent and high sand proportion result in poor vitrification in ceramic testing brick obtained at 900°C, 1000°C and 1100°C. For all the firing temperatures, linear shrinkage varied from 0.7% to 2.6%, weight loss varied from 3.5% to 7%, bulk density varied from 1.6 to 1.8g/m3, water absorption decreased from 20.7% to 12.7%, and flexural strength (σ) varied from 0.60 to 2.07MPa.The Ngaye alluvial clastic clays could be used in the fabrication of bricks (commons and perforated). However, an increase of fluxing agent and clays is needed to improve the mechanical performance of the ceramic products

Origin and evolution of Ngaye River alluvial sediments, Northern Cameroon: Geochemical constraints

International audienceThe origin of Ngaye River alluvial sediments and the evaluation of the weathering degree of their source rocks are assessed using trace and rare-earth element geochemistry in three bulk sediments and their different size fractions (2000–200 lm, 200–50 lm, 50–2 lm and <2 lm). The alluvial sediments consist of two sandy clay layers at the bottom and one sandy heavy clay layer at the top. Quartz and feldspars are the main minerals in the sand fractions while kaolinite and smectite are dominant in the finest sediments. The relatively low Chemical Index of Alteration (CIA) indicates that the sediments and their potential source rocks are moderately weathered. Highest trace element contents are observed in the fine sands, which are the richest in Zr, Th, U, Sc and REE. La, Ce and Nd are the most abundant REE in this fraction. The coarse fractions are characterized by LREE-enrichment relative to HREE. The PAAS-normalized REE patterns exhibit large positive Eu anomalies (Eu/Eu à $3.1 to 3.9) in the coarse sand fraction of the sandy clay layers and strong negative Eu anomalies (Eu/Eu Ã$0.35 to 0.70) in the two sand fractions of the sandy heavy clay layer. Our results document the immaturity of the Ngaye River sediments, which derive mainly from the erosion of moderately weathered granitoids of the surrounding reliefs, and in some extent from greenstones and/or basic volcanics. The results also suggest an obvious dependence of trace and rare-earth element fraction-ation on mineral sorting and weathering in the different grain-sized fractions of the alluvial sediments

Evaluation of the mineralizing potential of the Mbengwi plutonics, Northwestern Cameroon, Central Africa

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Petrography and geochemistry of the Mesoarchean Bikoula banded iron formation in the Ntem complex (Congo craton), Southern Cameroon: Implications for its origin

Precambrian banded iron formations (BIFs) represent an important source of mineable iron, as well as an archive recording secular changes in the chemistry of the Earth’s early oceans. Here we report petrographic and geochemical characteristics of unweathered drill core samples from the Bikoula BIF, a virtually uncharacterized oxide facies iron formation, hosted in the Mesoarchean Ntem complex, southern Cameroon. The BIF is cross-cut with syenitic veins. The entire succession is highly deformed and metamorphosed under granulite facies conditions. The BIF is characterized by alternating micro-bands of magnetite, quartz and pyroxene. Sulfides (pyrite, pyrrhotite, and chalcopyrite), oligoclase, ferro-pargasite, biotite and ilmenite occur as minor phases. The presence of pyroxene, ferro-pargasite and oligoclase, relatively high contents of major elements such as Al2O3 (0.76–7.52 wt.%), CaO (1.95–4.90 wt.%), MgO (3.78–5.59 wt.%), as well as positive correlations among Al2O3, TiO2, HFSEs, LILEs and transition metals (V, Cr, Ni, Cu and Zn), suggest that the BIF protolith included a significant amount of clastic material. Several samples have preserved seawater-like PAAS-normalized REE-Y patterns, including LREE depletion, and positive La and Y anomalies. Positive Eu anomalies observed in some of the analyzed samples indicate influx of hydrothermal fluids (possibly including Fe and Si) within the basin where the BIF precipitated. However, few samples show unusual negative Eu anomalies that likely result from a large proportion of clastic contamination. The lack of Ce anomalies suggests that the Bikoula BIF was deposited in a basin that was (at least partly) anoxic or suboxic, where it was possible to transport and concentrate dissolved Fe2+

Method of choosing soils as CEB or pavement layers based on geological and environmental information and mode of treatment

During research on the geological, mineralogical, mechanical and geotechnical nature of thick layers of soils developed on the rocks of the lower zone of the southern slopes of Mount Bambouto (West Cameroon), a couple of observations were made. The mechanical behavior of soils as construction materials is linked to the nature of the parent rock and its environment of formation. Four different types of rock have been noted: trachybasalt, orthogneiss, anatexite, and biotite-hornblende granitoid. These rocks in a hot and humid mountain climate, exposed to the monsoon wind, have weathered to give soils with exploitable characteristics in compressed earth bricks (CEB) and pavement layers. This article proposes a method of choosing a soil for pavement layers and for the production of fired earth bricks / earth bricks treated or not with hydraulic binders, based on the nature of the bedrock and the climatic environment. Several formulation models have been defined. The performance, fairness, accuracy and adequacy of these models with real values were made by metric evaluation. So, it is: • Preliminary method for quickly and easily formulating masonry units in clay soil. • Preliminary method for quickly and easily formulating pavement layers in clay soil. • Simple and reliable method for choosing clay soils as construction materials from elementary geological information

Characteristics of Kaolinitic Raw Materials from the Lokoundje River (Kribi, Cameroon) for Ceramic Applications

Eight kaolinitic materials from the Lokoundje River at Kribi were sampled and investigated for their physical, chemical, mineralogical and thermal characteristics in order to evaluate their potential suitability as raw materials in ceramics. The Lokoundje kaolinitic materials are clayey to silty clayey and are predominantly composed of kaolinite and quartz. The alkali (Na2O + K2O) content ranges between 1 and 2.5 wt.%; these low values do not favor vitrification of the ceramics but may be improved through flux amendment. The presence of goethite in some samples limits their utilization in white ceramics. The minerals content, color, metallic sound, cohesion, linear shrinkage, flexural strength, bulk density, water absorption and microstructure were determined. The XRD data reveal that kaolinite and goethite were transformed, respectively, into mullite and hematite. The colors of the fired products are characteristic of their mineral assemblage. The metallic sound is indicative of low vitrification which is confirmed by the presence of cracks due to low flux contents. The cohesion is good to very good, due to the abundance of kaolinite. The physicomechanical properties increase with temperature as well as densification. The geochemical data show that the Lokoundje alluvial clays are suitable for the manufacture of white stoneware tiles