Petrography and geochemistry of ferricrete near Shire, northern Ethiopia

B Konka,En Hussen,S Gebreselassie

doi:10.4314/mejs.v5i1.85330

Abstract

A detailed petrographic and geochemical study was conducted on ferricrete (laterite) developed on Mesozoic (?) ferruginous sandstone near Shire, Tigray region, northern Ethiopia. 30 rock samples were analyzed for major and minor elements and studied for petrographic details. Ferruginous sandstone overlying the Neoproterozoic low grade basement rocks dominantly contains quartz followed by orthoclase feldspar and iron oxides/hydroxides as cement. Residual enrichment process has resulted in the development 2-3m thick ferricrete horizon and also sub-horizons: mottled, mixed nodular and psuedo-pisolitic. Mineralogy of the ferricrete includes limonite, goethite and hematite. Arid conditions and dehydration reactions seem to have produced hematite from goethite. The ore minerals show replacement, cavity and fracture filling, remobilization and colloform textures. Si>Al>Fe is the mobility pattern observed in the ferricrete horizon though presence of secondary quartz and kaolinite are also common. Development of ferricrete is related to the climatic condition that existed during Eocene and is comparable with similar deposits in Arabian Nubian Shield (ANS). Key words : Ferricrete, Laterite, Ferruginous sandstone, Shire, Tigray, Northern Ethiopia, ANS

Highlights

In Ethiopia, minable iron deposits reported so far are very few
The mineable reserve of apatite in the deposit is about 181 mt with a grade of 3.5% (P2O5)and iron ore of 58 mt with a grade of 41.65% total iron (Wondafrash, 2010; Tadesse, 2006).Occurrence of laterite deposits are reported in Tigray region, northern Ethiopia e.g.1) occurrence of pockets of lateritic deposits near Shire (Ebrahim, 2011)
Selected samples were chosen for petrographic and geochemical analysis. 5 rock samples were chosen for thin section preparation (2 from metavolcanics and 3 from ferruginous sandstone) at Geological Survey of Ethiopia, Addis Ababa. 9 samples from ferricrete were chosen for polished sections preparation at Department of Earth Science, Mekelle University

Summary

Introduction

Three different types of deposits are reported from Ethiopia, though small in size. They include magmatic iron (Fe-Ti type) of Precambrian age from Bikilal, Melka Arba areas, banded iron formation (BIF type) of Precambrian age from Koree, Gordoma, Chago areas, and lateritic ( gossan related) iron deposits (residual type) from Melka Sedi, Garo, Gato, Billa, Gambo, and Gammalucho areas. The mineable reserve of apatite in the deposit is about 181 mt with a grade of 3.5% (P2O5)and iron ore of 58 mt with a grade of 41.65% total iron (Wondafrash, 2010; Tadesse, 2006).Occurrence of laterite (ferricrete) deposits are reported in Tigray region, northern Ethiopia e.g.1) occurrence of pockets of lateritic deposits near Shire (Ebrahim, 2011)

Methods

Results

Conclusion