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Analysis of recent airborne gravity and magnetic data for the interpretation of basement structures underneath the south–western Benue trough using source edge detector filters

Abdullahi Mukaila, Kumar Raj, Idi Bello Yusuf, Singh Upendra Kumar, Abba Adamu Usman

Acta Geophysica

2023

Vol. 71, no. 4

1595--1606

We present the detail basement and trends of geological structures associated with the Mesozoic-Cenozoic volcanism in the south–western region of the Nigerian Benue trough using recent gravity and magnetic anomalies of the region. The analysis aimed at recognizing and mapping the basement structure that controlled the distribution and source host of hydrocarbon and other economic mineral resources in the region. The structural recognition and mapping is done on the basis of the utilization of the Tilt Angle (TA) and Total Horizontal Derivative of the Tilt Angle (THDTA) of gravity and magnetic data. From these techniques, we have been able to identify and mapped out those edges of anomalous sources due to the gravity and magnetic data that are in association with the basement geological structures of the area. Based on the mapped structural trends, it is observed that the basement structures derived from both the gravity and magnetic anomalies correlated well with the zones of volcanic rocks around Gboko and area between Lefin and Oturkpo. The two locations are sitting over gravity and magnetic highs suggesting high density and susceptibility material below the subsurface. The Euler deconvolution method suggested depths between 1 and 5 km from both gravity and magnetic data. Deeper basement of anomalous sources are suggested between 3 and 5 km. The 1 km depth interprets the regions of basement highs or corresponding to intrusive zones.

1D resistivity inversion technique in the mapping of igneous intrusives; a step to sustainable quarry development

Nwachukwu M. A., Nwosu L. I., Uzoije P. A., Nwoko C. A.

Journal of Sustainable Mining

2017

Vol. 16, iss. 4

127--138

The use of trial pits as a first step in quarry site development causes land degradation and results in more failure than success for potential quarry investors in some parts of the world. In this paper, resistivity, depth and distance values derived from 26 Vertical Electric Soundings (VES) and 2 profiling inversion sections were successfully used to evaluate a quarry site prior to development. The target rock Diabase (Dolerite) was observed and it had a resistivity range of 3.0 x 10⁴ - 7. 8 x 10⁶ Ω-m, and was clearly distinguishable from associated rocks with its bright red color code on the AGI 1D inversion software. This target rock was overlain by quartzite, indurate shale and mudstone as overburden materials. The quartzite, with its off-red colour, has a resistivity range of 2.0 x 10³-2.9 x 10⁵ Ω-m, while the indurate shale, with a yellowish-brown colour, showed resistivity values ranging from 6.1 x 10² - 2.8 x 10⁵ Ω-m. Topsoil was clayey, with a resistivity range from 8 - 8.6 x 10²u Ω-m and depths of 0.3-1.8 m, often weathered and replaced by associated rocks outcrops. The diabase rock, in the three prospective pits mapped, showed thicknesses of between 40 and 76 m across the site. The prospective pits were identified to accommodate an estimated 2,569,450 tonnes of diabase with an average quarry pit depth of 50 m. This figure was justified by physical observations made at a nearby quarry pit and from test holes. Communities were able to prepare a geophysical appraisal of the intrusive body in their domain for economic planning and sustainability of the natural resource.