Compositional characteristics and genetic affinity of the ferricrete deposit in Adi Kokeb district, northwestern Tigray, Ethiopia

Abstract

ABSTRACT The ferricrete deposit in Adi Kokeb district was investigated using field observations, petrographic studies and chemical analysis of samples for their geochemistry and mode of origin. Field observations confirmed the presence of kaolinites, thin iron bands and relict quartz veins. Petrographic studies of the samples revealed that quartz, sericite, muscovite, orthoclase feldspar and iron oxides/hydroxides are the dominant minerals. Geochemical determination of major, minor and trace elements of seventeen (17) samples were done using X-ray fluorescence (XRF). The results show a general increasing trend in Fe2O3 (16.75–57.9 wt.%) and Al2O3 (11.35–16.44 wt.%) values and decreasing trends in SiO2 (57.05–22.01 wt.%) values from the Meta-sandstone to the ferricrete. The alkali and alkaline earth elements, notably K2O (0.142 wt.%), Na2O (<0.005 wt.%), CaO (0.075 wt.%) and MgO (0.098 wt.%), are highly depleted, confirming that iron precipitation with subsequent oxidation is major process in ferricrete formation. Similarly, the minor elements such as MnO (0.17 wt.%), TiO2 (0.56 wt.%) and P2O5 (0.154 wt.%) are highly depleted, implying their weak substitution for major elements in the ferricrete. The average value of trace elements such as Ba (669 ppm), Zr (348 ppm), Sr (215 ppm), Cu (125 ppm), Zn (55 ppm) and Pb (9.5 ppm) show a relative enrichment of the ferricrete compared to ferruginous sandstone and meta-sandstone. The relatively high concentrations of Zr, Ba and Sr in the ferricrete are attributed to their presence in detrital material during weathering (Zr) and their adsorption on neo-formed kaolinite (Ba and Sr). Integration of field, petrographic and geochemical results suggest that the origin of this deposit is associated with weathering processes. Therefore, the deposit is likely to be a ferricrete.