Characterisation of two kaolin facies from Ediki, Southwest Cameroon

Abstract

Sand-rich (ESR) and sand-poor kaolin (ESP) facies from Ediki, Southwest (SW) Cameroon, have been mineralogically and geochemically characterised in order to elucidate on their emplacement and degree of kaolinization. The mineralogical assemblage comprised quartz, kaolinite, muscovite, microcline, goethite and anatase. ESP registered a sharp peak at 3620 cm-1 and two weak inflections between the doublets at 3652 and 3670 cm-1, whereas only one clearly resolved peak at 3620 cm-1 was observed for ESR. Quartz interference at 1023, 791 and 682 occurred in both samples. Laths, irregular platelets and flakes with swirl texture and corroded edges characterized ESR whereas loose stacks and flakes displaying a seemingly preferred orientation was observed in ESP. Low alumina content, CIA and high Si2O3:Al2O3 ratio coupled with relative enrichment of K over the other alkali and alkali earth metals was observed in both samples. The results infer partial kaolinization processes, low to moderate degrees of crystallinity and significant quartz contamination in both kaolin facies. The difference in mineralogy and geochemistry between the two facies is ascribed to physical controls on weathering (inferred porosity, permeability and inclination of the lithologic units) rather than the degree of chemical alteration. Key words: Cameroon, kaolin facies, characterization, kaolinization.