Characterization of the Genesis of Belessa Kaolin Occurrences, Hosaina Area, Central Main Ethiopian Rift

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Addis Ababa Universty


Belessa kaolin occurrence is situated in the Western margin of Central Main Ethiopian Rift (CMER) near Hosaina town which is about 230 km from Addis Ababa. Geology of the kaolin district is composed of Miocene to Quaternary age acidic igneous rocks consisting of pyroclastic tuff, ignimbrite and rhyolite. Based on petrographic study, the main minerals identified in these volcanic rocks include quartz, k-feldspar and plagioclase. The kaolin occurrence is located in the central part of the study area and it is associated with rhyolite. The host rock has been partly and completely transformed to kaolinite. The main aim of the present study is to characterize the genesis of this kaolin occurrence. An integrated study combining geological, mineralogical and geochemical data were carried out in order to characterize the genesis of alteration (supergene or hypogene). Data obtained from morphological study and available physical property tests were also examined to see the possible industrial applications. Moreover, Landsat 8 OLI and ASTER images were enhanced using two techniques (band ratio and band composites) to discriminate lithological units, host rock and vegetation. Spectral signature curves of Belessa kaolin are also compared with other kaolinite spectral curves to produce preliminary model of spectral curves for kaolin occurrences associated with volcanic rocks in the MER. Results from geological, mineralogical and geochemical studies indicate that supergene alteration has played a great role to the formation of Belessa kaolin. The absence of quartz veining and alteration zones with high temperature minerals implies the lack of significant hypogene alteration process. The Chemical Index of Alteration (CIA) and Chemical Index of Weathering (CIW) result also showed that the host rock has experienced a strong alteration and weathering process that resulted in the formation of kaolinite. Furthermore, the higher Ce + Y + La values correspond to the supergene type alteration. The low P and high Cr + Nb concentrations also support supergene origin. From digital image processing, ASTER RGB band combinations of (7, 2, 1), (7, 3, 1) and band ratios of 9/4 showed better contrast on geologic units, vegetation and kaolinite host rock respectively. Moreover, the comparison of kaolinite spectral reflectance curves shows that the spectral curve of Belessa kaolinite can be used as a preliminary model to the kaolin occurrences in the MER. Studies from technological properties like physical tests, chemistry, mineralogy and crystal morphology indicate that Belessa kaolin could have potential applications in paper coating, filler (in paper, rubber, plastic and paint), ceramics, pharmaceuticals and cosmetics. Key words: Applications, Belessa, genesis, kaolin, supergene, technological property.



Applications, Belessa, Genesis, Kaolin, Supergene, Technological property