The Makoro kaolin deposit, southeastern Botswana: its genesis and possible industrial applications

Abstract

Kaolin samples from the Makoro kaolin deposit in southeastern Botswana were investigated petrographically and mineralogically in order to elucidate the genesis of the deposit. Mineral identification and characterization studies were conducted using powder X-ray diffraction (XRD), differential thermal analyses/thermogravimetric analyses (DTA/TGA), and scanning electron microscopy with an energy dispersive X-ray spectrum (SEM-EDX) technique. Diagnostic tests for several possible industrial applications were performed. Kaolinite is the major phyllosilicate present in the deposit, whereas smectite occurs in minor amounts. Accessory minerals are quartz, goethite, K-feldspar and hematite. Hinckley's crystallinity index (HI) values were determined for kaolinite from the kaolin deposit. Differential thermal analysis (DTA) values obtained for dehydroxylation and mullitization temperatures are close to theoretical values. Hexagonal booklets of kaolinite as well as individual platelets are present in the Makoro kaolin. Based on granulometric and descriptive mineralogical analyses, the mineral assemblages and kaolinite morphology, the Makoro kaolin deposit is derived from the alteration of feldspathic arenites (arkose) that were deposited in a locally developed basin of Permian age. A possible freshwater and/or brackish water depositional environment is suggested. The kaolin is found to be suitable for making sanitary wares, although a beneficiation process would be required; it could also be used in the refractory and vitreous ceramic ware industries.