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

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 Fe 2 O 3 (16.75-57.9 wt.%) and Al 2 O 3 (11.35-16.44 wt.%) values and decreasing trends in SiO 2 (57.05-22.01 wt.%) values from the Meta-sandstone to the ferricrete. The alkali and alkaline earth elements, notably K 2 O (0.142 wt.%), Na 2 O (<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.%), TiO 2 (0.56 wt.%) and P 2 O 5 (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 metasandstone. 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 neoformed 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.

Fe-Al Phosphate Microcrystals in Pedogenic Goethite Pisoliths

“…The mottled texture resulted from unmixing and reordering of metastable oxide and hydroxide phases, while syneresis cracks and cavities were developed by dehydration of clay and Fe oxyhydroxides [31]. Fe minerals are structurally enriched during pedogenesis and often incorporated into clay minerals [29,30,43,44]. The detected clay mineral in the samples was mainly kaolinite.…”

Mineralogical and geochemical characteristics of the iron–duricrust deposit in Adi-Daero area, northwestern Tigray, Ethiopia: implication for the origin and controlling factors

“…The meta-sandstone of the Tambien group includes a sericite-quartz-feldspar schist (Gebru et al 2019) along with weakly metamorphosed reddish and brown sandstone, grit, polymictic conglomerate and minor siltstone (Tadesse 1997). Thus, weak deformation has developed a poorly defined phyllitic fabric where some mineral grains show alignment parallel to the dip of the local foliation.…”

“…Thus, weak deformation has developed a poorly defined phyllitic fabric where some mineral grains show alignment parallel to the dip of the local foliation. According to Gebru et al (2019), the grain size of the meta-sandstone varies from medium to coarse and dominant mineral is which is subrounded to subangular in shape. The colour of this unit varies from pale grey and grey to pale yellow.…”

“…Among the various types of ferricretes, iron-duricrust deposits are typically Cenozoic in age and developed on planation surfaces under seasonally dry, humid tropical to subtropical climatic conditions (Ghosh and Guchhait 2015;Kovács et al 2020). In a general sense, the absolute enrichment of iron might be either through upward movement or downward leaching of dissolved iron oxide as watertables fluctuate (Bourman 1993(Bourman , 2007Gebru et al 2019;Bourman et al 2020). Alternating reducing and oxidising conditions during water-table fluctuation leads to bleaching at depth, mottling in the zone of fluctuation, and iron oxide concentration at the upper limit of fluctuation (Bourman 1993(Bourman , 2007Bourman et al 2020).…”

“…Alternating reducing and oxidising conditions during water-table fluctuation leads to bleaching at depth, mottling in the zone of fluctuation, and iron oxide concentration at the upper limit of fluctuation (Bourman 1993(Bourman , 2007Bourman et al 2020). The upward capillary movement of iron in solution is also responsible for absolute iron enrichment in ferricretes (Bourman 2007;Gebru et al 2019). Bourman et al (2020) pointed out that the in situ ferricrete profile consists of a well-developed ferricrete near the surface, underlain by a mottled zone and a pallid zone.…”