Genesis of bensa kaolin deposit, southern ethiopia; assessment from major and trace element geochemistry of the kaolin deposit

Bensa kaolin deposit is found in Southern nation nationality and people of Ethiopia regional state which is 405km south of Addis Ababa, Ethiopia. This study presents new major and trace element chemistry of Bensa kaolin deposit to assess element characteristics during kaolinisation processes and genesis of the kaolin deposit of the area. Bensa kaolin is a result of weathering of rhyolitic ignimbrite and it shows high concentration of SiO2 ranges between 53.6 to 68.8 wt. % and Fe2O3 (4.85-7.74 wt. %) and exhibits very limited CaO (0.27-0.62 wt. %), MgO (0.14-0.31 wt. %), P2O5 (0.1-0.2 wt. %) and MnO (0.12-0.3 wt. %). The highly mobile Large ion lithophile element (LILE) Sr (23.3-60.5ppm), Rb (32.3-88.4ppm), Ba (201-593ppm) and Cs (0.54-1.67ppm) of Bensa kaolin shows depletion pattern on the Chondrite normalized spider plot whereas the immobile High field strength element (HFSE) Zr (1070-1770ppm), Hf (26.8-45.4ppm), Nb (143-30ppm), Ta (9.3-14.8ppm) and REE concentrations of Bensa kaolin samples exhibit enrichment pattern. The major and trace element concentration of Bensa kaolin indicates samples from depth >20m and from the periphery of the deposit are less mature with respect to chemistry and physical property compared with samples from the center of the deposit. The depletion of CaO, MgO, P2O5, MnO and LILE and the enrichment of HFSE of Bensa kaolin indicates the mobile elements have been removed from the system during the kaolinisation processes and it is the characteristics of supergene kaolin origin. Under very high temperature to some extent HFSE Zr can be mobilized and it can be removed from the system but the very high concentration of Zr in Bensa kaolin deposit reflect that the kaolinisation processes may have been undertook at low temperature condition.