Mineralogy and Texture of the Weathered Products from Silicic Lavas in the Sabga Area, North West Cameroon

摘要

Products of weathering usually clay minerals, are commonly characterized through mineralogical, chemical and geochemical analysis, emphasizing their implications in industrial applications, initiation of landslides and their impact on surface water geochemistry. In this study the vertical variations in textural characteristics and clay mineral type within weathered profiles in the Sabga area were investigated. Two exposed weathered profiles were logged from bed rock to topsoil and each horizon was sampled separately. Granulometric analysis on the samples indicated mixtures of clay, silt and sand size particles in all horizons. Smectite and kaolinite were identified by X-ray diffractometry (XRD) and scanning electron microscopy (SEM). The two logs show that the lower horizons display whitish colors with fine laminations, middle horizons are brownish and the upper horizons display dark brown colors. Graphic mean values for both sections gave values that range between 2.02 - 3.7 f with an average standard deviation value of 1.9 f , indicating that the grains are poorly sorted sand, silt and clay. SEM micrographs show laths of smectite in the lower horizons, flake s of kaolinite and laths of smectites in the middle horizons while the upper horizons show flakes of kaolinite with microlites of quartz + feldspars. XRD patterns show broad basal reflections for kaolinite at 2 θ 36.8° (3.15 ?), smectite at 2 θ 33.5° (3.34 ?), both contaminated with quartz at 2 θ 36.5° (3.32 ?) typical for these minerals.