Genesis and characteristics of lateritic iron deposit in Mai-Kuhli area, western Tigray, northern Ethiopia

Abstract

Mai-Kuhli lateritic iron deposit is located near Shiraro town in Tigray region of northern Ethiopia. The deposit is developed at the interface between the Neoproterozic low-grade metamorphic rocks and Paleo-Mesozoic sedimentary succession. This paper characterizes the deposit based on geological, mineralogical and geochemical data. The mineralogical data was generated using X-ray diffraction (XRD) and petrographic methods while geochemical data was generated using Inductively Coupled Plasma-Mass Spectrometer (ICP-MS) and Inductively Coupled Plasma - Atomic Emission Spectrometer (ICP-AES). The deposit is mostly developed on pseudo pisolitic and mixed nodular sub horizons associated with ferruginous sandstone and mudstone. In this deposit, hematite and goethite are the dominant iron ore minerals while clay and quartz dominate the impurities. Goethite is converted to hematite following sequences from limonite →goethite→ hematite. All results indicate that in-situ weathering followed by leaching played a major role in the formation of Mai-Kuhli lateritic iron deposit. The Chemical Index of Weathering (97.96–99.97%) and Chemical Index of Alteration (76.66–99.80%) show that the host rock has experienced strong weathering and alteration under hot and humid climatic condition of subtropical-tropical zone. Relatively higher values of the immobile elements Fe, Al, Ti, Zr, Cr, V and Hf suggest their enrichment during lateritization. The parent rock composition, absorption and adsorption processes, iron concentration variation in weathering profile and degree of leaching of minerals have played a major role in the distribution of trace and REEs in the weathering profile of the deposit.