Interpretation of Airborne Geophysical Data of Nsukka Area, Southeastern Nigeria

Abstract

Airborne geophysical (aeromagnetic and gravity) data of Nsukka area was interpreted qualitatively and quantitatively with the aim of determining the susceptibilities of rock types, depth/mass of the anomalous bodies, possible cause of the anomalies and type of mineralization prevalent in the area. The estimated depths from forward and inverse modeling of aeromagnetic data for profiles 1, 2, 3, 4 and 5 were 1200m, 1644m, 1972m, 2193m and 2285m respectively. The respective susceptibility values were 0.0031, 0.0073, 1.4493, 0.0069 and 0.0016. These indicate dominance of iron rich minerals like limonite, hematite, pyrrhotite, and pyrite and forms lateritic caps on sandstones. SPI depth result ranges from 151.6m minimum (shallow magnetic bodies) to 3082.7 m maximum (deep lying magnetic bodies). Euler depths for the four different structural index (SI = 0.5, 1, 2, 3) ranges from 7.99 to 128.93m which are depths of shallow magnetic sources resulting from lateritic bodies in the outcrops in the study area. From the gravity data interpretation, Euler depth estimation reveals that depth to anomalous bodies ranges from 89.13 to 2296.92m. Density of the causative body obtained from modeling results for profile 1 was 1498kg/m3, which is in the range of clay material and the depth was about 923m. From models 2, 4 and 5, the densities of the causative bodies were 3523, 4127 and 3707kg/m3, while depths to the surface were about 604, 815 and 1893m respectively. These density ranges correspond to that of ironstone. From model three, the density of causative body obtained was 2508kg/m3, located at a depth of about 268m below the surface. This work has shown that Nsukka area is underlain by thick strata of shales, sandstones and ironstones, which together are suitable for ceramic production, and sufficiently thick sediments suitable for hydrocarbon accumulation.

Investigation of gravity anomalies in parts of Niger Delta Region in Nigeria using aerogravity data

“…The SPI depth result varies from -539.7 m (shallow gravity anomalous bodies) to -4276.7 m (deep lying gravity anomalous bodies). The high depths indicate thick sediment which is suitable for hydrocarbon accumulation (Wright et al, 1985, Obiora et al, 2016.…”

“…Author(s) agree that this article remain permanently open access under the terms of the Creative Commons Attribution License 4.0 International License fluids within materials affect density contrast. Gravity data can be used in many ways to solve different exploration problems, depending on the geologic setting and rock parameters (Ezekiel et al, 2013;Okiwelu et al, 2013;Obiora et al, 2016), the data when analyzed provide insight to elements of petroleum exploration and production (Johnson, 1998;Obiora et al, 2016). The density contrasts presented by the juxtaposition of sediments with shales make detailed gravity modeling in this region a valuable exercise.…”

Chemical and mineralogical properties of Lejja Nsukka iron ore deposits

“…The Ajali sandstone conformably rests on the Nsukka formation, which is the upper coal measure. The lithology is extremely reminiscent of the Mamu formation and is composed of a succession of alternating sandstone, black shale, and sandy shale, with thin coal seams at various layers [6]. Eroded remnants of this formation compose of outliers and its thickness averages 250m.…”

Mapping of subsurface structural features in some parts of Anambra Basin, Nigeria, using aeromagnetic data

“…Apart from this, further studies of hydrocarbon and mineral potentials of parts of this basin is mainly concentrated at the upper part of the basin that has shown evidence of the presence of intrusive (Ofoegbu 1984;Adetona and Abu 2013;Obiora et al 2016). However, structural evidences from previous researchers reported that mineralization in the upper part of the basin may be close to the surface, and therefore the deposits are not extensive enough to attract huge investments from big mining companies.…”