Bauxites and Fe laterites were formed on Neogene volcanics from Fongo-Tongo region in the highlands of western Cameroon, and are distributed on plateaus, slopes and downslope surfaces. Bauxitic profiles result from intense in-situ weathering of trachytes that implied depletion of silica and labile elements from the saprolite, while alumina relatively accumulated from parent minerals pseudomorphosis by primary gibbsite formation. During ongoing lateritization and bauxite maturation, important leaching and illuviation processes resulted in secondary gibbsite crystallizations. Late incision and dissection of upper bauxitic plateau resulted in degradation and dismantling of bauxitic duricrusts with Fe-depletion and increasing silica. Compared to trachyte, bauxitic duricrusts are relatively enriched in Nb, Zr,
Lateritic weathering of Miocene volcanic rocks from western Cameroon highlands formed duricrusted bauxitic profiles. Two weathering profiles on ca. Ma basalt and ca. 16 Ma trachyte were studied using geochemical mass balance functions. Less mobile elements Ti and Zr were used as references to quantify volumetric change (strain, ε), element transfer rate (τ) and geochemical mass transfers during the bauxitization process of basalt and trachyte. Conversion of parent rocks to kaolinite and goethite rich saprolites evolved to Al-Fe rich bauxites, mostly composed of gibbsite and iron oxy-hydroxides (goethite and hematite). However, formation of Al-Fe bauxitic profiles required higher Si leaching on trachyte than on basalt. Our results document that chemical weathering of a larger thickness of trachyte than basalt has been required to form a unit meter of weathering profile, implying differential rates of rock chemical erosion and topographic decay of landscapes. Rates of chemical erosion and formation of lateritic weathering profiles in western Cameroon have been mostly controlled by drainage conditions and volcanic rocks composition (mostly SiO 2 content differences), that also resulted in contrasted landscapes evolution during the Neogene.
International audienceEstimation of the mineral resources potential is an important issue for most of developing countries. The spatial distribution of bauxites and lateritic land surfaces on the Bamiléké plateau (West Cameroon) has been investigated with a Boolean modeling process into a GIS environment on the basis of geological constraints such as elevation, rock and soil types, and landscape morphology. Field observation and SRTM (Shuttle Radar Topographic Mission) data allowed the differentiation of two lateritic land surfaces separated by a minimum altitude difference of about 60 m. These surfaces constrained by favorable rock types, slope steepness and soil types provided a potential lateritic bauxitic area of 381 km 2 (17.2% of the total study site). Field validation and the integration of legacy spatial data resulted in an area of 60.1 km 2 for potential bauxitic ores, i.e. obviously duricrusted bauxitic surfaces (with 47.8 km 2 in the upper surface and 12.3 km 2 in the lower surface). Alumina contents obtained from duricrust samples were analyzed by geostatistical methods and classical kriging interpolation to discriminate between bauxitic and ferruginous laterites. This highlighted a geochemical trend from higher alumina values on the upper surface (40–66 wt.%) to lower values on the lower surface (13–44 wt.%). Finally, our study documents two duricrusted lateritic surfaces arranged in a staircase manner and having different geochemical characteristics. The total bauxitic-rich surface is distributed in five spots throughout the study area and covers 56.2 km 2 , while ferruginous laterites occupy a spot of 3.9 km 2. GIS mapping approach of lateritic land surfaces, accounting for reliable constraints, might be promising for larger scale investigations of mineral resources in Cameroon
scite is a Brooklyn-based organization that helps researchers better discover and understand research articles through Smart Citations–citations that display the context of the citation and describe whether the article provides supporting or contrasting evidence. scite is used by students and researchers from around the world and is funded in part by the National Science Foundation and the National Institute on Drug Abuse of the National Institutes of Health.