Geo-electrical resistivity investigation of iron ore mineral deposits in Mbeu area, Meru county, Kenya

Abstract

Global demand for iron or its products has risen over the years due to the growing housing, road, and railway industry and the manufacture of machinery. Studies leading to the location of more iron ore fields need to be performed in order to determine the suitability of available iron ore as a raw material for iron production. Earlier, studies carried out within Mbeu and Kimaachia areas in Meru County, Kenya, using gravity and magnetic Geophysical methods did not pick shallow deposits and discontinuous magnetite mineralization occurring in rocks and veinlets. This was attributed to relatively low density contrast and magnetic susceptibility on shallow deposits and unevenly distributed magnetite rich rocks. This, therefore, necessitated the need to integrate an electrical resistivity geophysical method that can detect isolated electrical conductors in the subsurface. This research involves the use of electrical resistivity along the areas identified around 00 06’ 24’’N and 370 50’ 49’’E. By taking measurements on the ground surface, the electrical resistivity method calculates the true resistivity of the subsurface. The potential difference that results from injecting current into the earth is measured at the surface. The ground resistivity measurements were performed by the use of the LS 2 ABEM terrameter. RES2DINV software was employed in the quantitative interpretation of the data by generating models of apparent resistivity pseudo-sections. The software carried out a least square inversion on the measured apparent resistivities and induced that the true resistivity of alluvium, rocks, and clay saturated with water ranges from 2.21 Ωm to 487 Ωm, 212 Ωm to 3000 Ωm and 2.21 Ωm to 65 Ωm respectively. A comparison between electrical resistivity levels and chargeability factors guided a quantitative characterization of the subsurface. The characterization established that the subsurface ore distribution is divided into two portions: alluvium and rocks enriched with iron ore and alluvium and rocks containing disseminated deposits of iron ore. The regions of the model identified by resistivity and chargeability values of 17.4 Ωm to 406 Ωm, 208 Ωm to 886 Ωm and 0.01 msec to 3 msec, 0.091 msec to 4.64 msec are inferred as alluvium and rocks enriched with iron ore deposits, respectively; the other regions characterized by resistivity and chargeability of 110 Ωm to 487 Ωm, 542 Ωm to 995 Ωm and 3.326 msec to 7.87 msec, 4 msec to 7.07 msec are of alluvium and rocks containing disseminated deposits of iron ore, respectively. This study has established that Mbeu iron deposits are an extensive resource occurring at deep and shallow depths in the form of grained magnetite mixed with alluvium and rocks containing magnetite. It has also been found that magnetite is the main ore in the geological formations. The ore-bearing rocks and alluvium appear at an approximate depth of 1.25 m to 65.6 m in most of the profiles and extend deep beyond the terra-meter probe depth. These results on the presence of iron ore deposits will be essential to society in that mining and extraction of mineral ores will provide employment opportunities to the locals. Taxes and royalties generated will contribute to the economic growth of the region and country.