Debre Tabor kaolin deposit is located around Debre Tabor town in Amhara region of northwestern Ethiopia. The kaolin deposit in the study area needs a detailed study to evaluate the geological, mineralogical, physical, and geochemical conditions. For this purpose, detailed geological, physical, mineralogical, and geochemical laboratory tests were performed. XRD and petrographic analysis were used to study the mineralogical composition. Geochemical analysis was determined using ICP-MS and ICP-AES. The Debre Tabor kaolin deposit is exposed along riverbanks, road cuts, hillside, and quarry sites. The laboratory results reveal that the deposit is formed from the weathering of felsic rocks mainly trachyte and tuff units. From the laboratory analysis, we found that quartz is the dominant impurities. The geological, mineralogical, and geochemical studies indicate that in situ weathering followed by leaching played a major role in the formation of the Debre Tabor kaolin deposit. The average Chemical Index of Alteration (77.98%) shows that the host rock has experienced moderate weathering and alteration under the hot and humid climatic conditions of the subtropical zone. The low bulk density (1.54 g cm −3 ) and Ce + Y + La vs. Ba + Sr plot correspond to the supergene type of formation. Based on the mineralogical, geochemical, and physical properties, Debre Tabor kaolin deposit can be used for refractory, ceramics, paper coating, and filler (paint) industries, but treatment is important to remove the existing impurities such as iron, quartz, and feldspars.
Mineralogical and geochemical variations of elements from the Adi-Daero iron-duricrust were studied using petrographic, X-ray diffraction and geochemical analyses. Petrographic studies of the samples confirmed the presence of nodular and colloform textural features. The XRD analysis showed the presence of haematite, goethite, quartz, kaolinite and ilmenite are the mineral constituents. Major-element geochemistry was determined by ICP-AES, and trace and REEs were analysed using ICP-MS. Of the major oxides, Fe 2 O 3 (6.8-72.93 wt-%) and SiO 2 (11.07-77.75 wt-%) showed significant variation with generally increasing and decreasing trends from the iron-rich duricrust to the bedrock, respectively. In the profile studied, the alkali and alkaline earth elements (Ca, Mg, Na and K) were highly depleted, suggesting that iron-duricrust near-complete leaching. Elevated values of Sr and Ba in the lower part of the profile are probably due to their abundance in the protolith material (sandstone). A considerable enrichment of V and Cr, and Zr and REEs in the iron-rich duricrust and clay-rich horizon compared to the bedrock confirms their substitution for the Feoxyhydroxides, occurring in heavy mineral phases and adsorbed onto clay minerals, respectively. The La/Y <1 indicates an acidic environment in the upper part of the profile (AD-1 to AD-6; 0.64-0.99) and La/Y >1 a basic environment in the basal part of the profile (AD-7 to AD-12; 1.13-1.58). Similarly, the (La/Yb)N ratio of samples AD-1 to AD-6 (6.81-8.05) is significantly lower than that of AD-7 to , reflecting an acidic environment. Positive Ce anomalies in the samples of AD-1 to AD-2 (1.17-1.2) are linked to the existence of cerianite due to change in oxidation state of Ce while in AD-8 and AD-9 (0.92-0.93), it is related to adsorption of Ce ions onto clay particles protolith. Therefore, the absolute enrichment of iron in the Adi-Daero iron-duricrust deposit was most likely an in situ process that involved vertical transfer from the iron-poor sandstone source rock.
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