Physicochemical and mineralogical considerations of Ediki sandstone-hosted kaolin occurrence, South West Cameroon

Abstract

Field mapping, colour, particle size distribution, pH and x-ray diffraction studies were undertaken to elucidate the genesis of Ediki kaolin. The kaolin occurs within the Mungo formation of upper cretaceous age, ascribed to the Douala sedimentary basin. The kaolin profile consists of upward coarsening sandstone – siltstone – sandstone sequence with a gradient of 35 to 40°. Texturally, the kaolin is mainly silt loam with a constitution of sand (18.1 to 24 wt.%), silt (68 to 73.3 wt.%) and clay (7 to 13.5 wt.%). The pH of the sample is acidic with values ranging from 4.8 to 5. Kaolinite and quartz are the dominant mineralogical phases whereas, muscovite + microcline and illite + goethite occur as minor and trace phases respectively. High porosity and permeability of the sandstones favoured migration of fluids which enhanced the formation of secondary diagenetic minerals. The presence of detrital feldspars and mica grains in the sandstones, were favourable parent phases for kaolinite formation. Kaolinization was further enhanced by the hot humid tropical climate, acidic pH, fairly gentle relief (40°), low K and Na concentrations (inferred from the mineralogy), as well as the low energy depositional environment. Key words: Diagenesis, kaolinization, secondary kaolins, supergene enrichment, tropical climate.