Origin and evolution of Ngaye river alluvial sediments, Northern Cameroon : geochemical contraints

The 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&#8211;200 lm, 200&#8211;50 lm, 50&#8211;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 3.1 to 3.9) in the coarse sand fraction of the sandy clay layers and strong negative Eu anomalies (Eu/Eu0.35 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 fractionation on mineral sorting and weathering in the different grain-sized fractions of the alluvial sediments

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

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