Density and Magnetic Susceptibility Characterization in the Basement Complex Terrain of NE Kogi State/NW Benue State of Nigeria

SUMMARY Thirty one rock samples were collected and analysed in the laboratory using spring balance to determine the densities of rocks of the Kogi-Benue NW basement complex area which has extensive lithologic variation. The dry bulk and saturated densities of the various samples were determined. The sedimentary rocks which were dominantly sandstones had values that ranged from 1.85gm/cm3 to 2.35gm/cm3 with a slight drop also between the dry bulk and saturated density. The saturated density of the sedimentary rocks was almost consistently greater than the dry bulk density by 0.008gm/cm3. Gabbro rock samples were taken as representative of the igneous rocks which in the measurement indicated high density values and appreciable content of magnetic elements. The dry bulk density of the metamorphic rocks ranged from 2.33gm/cm3 to 2.77gm/cm3 with a slight difference of 0.41gm/cm3 and dominated by schists while the igneous rocks ranged from 2.34gm/cm3 to 2.73gm/cm3 with no significant difference between the dry bulk and saturated densities. Magnetic susceptibility measurements were carried out to aid interpretation of the magnetic data and it shows a magnitude of 0.0001 to 0.00015emu ranged and from available data, it is probable that Cordierite-Tourmaline schist with a magnetic susceptibility value of 0.00015emu is higher than other metamorphic rocks in the area. The magnetic susceptibility of the gabbro igneous rock was more prominent than those of sedimentary sandstone and metamorphic rocks schists and gneisses.