| Author: | Apeh, Ojima Isaac |
| Title: | Development and application of a tailored gravity model for geophysical exploration of mineral resources in the Southern Benue trough of Nigeria |
| Advisors: | Tenzer, Robert (LSGI) |
| Degree: | Ph.D. |
| Year: | 2024 |
| Subject: | Prospecting -- Geophysical methods Mines and mineral resources -- Nigeria Hong Kong Polytechnic University -- Dissertations |
| Department: | Department of Land Surveying and Geo-Informatics |
| Pages: | xxv, 216 pages : color illustrations, maps |
| Language: | English |
| Abstract: | Mineral resources are useful and valuable raw materials of great economic importance to several countries of the world especially developing countries such as Nigeria. The Nigerian economy relies heavily on exploitation of mineral resources. However, exploration of minerals in Nigeria has mainly relied on seismic and well-logging, which are cost-intensive and unsustainable. These active geophysical surveys were conducted by some oil and gas companies only in areas of a high geological interest such as the Benue Trough and Niger Delta of Nigeria. Additionally, most of the exploration activities carried out in Nigeria including that of gravimetric studies have been terrestrially based, and terrestrial acquisition of data has always produced sparse network of points due to the tediousness of the methods involved. Interestingly, recent advancement in satellite gravimetry has led to the development of Global Gravitational Models (GGMs) which have brought about improved knowledge of the gravity field of the Earth. However, even the combined GGMs compiled to a high spectral resolution have a relatively limited accuracy because of inherent omission and commission errors in them. Hence, the aim of the doctoral research was to develop and apply tailored gravity data for geophysical exploration of mineral resources beneath the Southern Benue Trough of Nigeria (SBToN) as a faster, cheaper, non-destructive, and sustainable geophysical prospecting tool. In this study, the performance of five existing combined GGMs were geologically and stochastically evaluated, and then a stochastic combination technique was used to develop a tailored gravity model fitted to the local gravity field of the SBToN for comprehensive geophysical investigations, tectonic studies, and mineral prospectivity mapping. Furthermore, spatial-and spectral-domain gravity separation and gravimetric inversion techniques were applied to explore interior constituents of the Earth. Obtained results were validated by using appropriate in-situ geophysical datasets such as seismic data, borehole data, measured rock sample densities. The results demonstrate that XGM2019e_2159 global gravitational model is better than the other existing combined GGMs and hence was chosen as the referenced GGM for the development of a tailored gravity model over the study area. The methods for a spherical harmonic expansion and analysis of gravitational and lithospheric density structure models were used to produce refined Bouguer and mantle gravity maps over the whole country (Nigeria) based on the referenced GGM. These refined Bouguer gravity map reveals mainly the Moho and thermal mantle signatures beneath Nigeria. A thickly compacted sedimentary cover was found at the southwestern part of the SBToN which can serve as important habitat for minerals and could generate adequate heat and pressure suitable for the maturation of hydrocarbons. Different faulting and fracturing patterns characteristic of compressional and extensional tectonic events were found causing different crustal deformation regimes within the region. It was discovered that the well-known Abakaliki Anticlinorium within the study area resulted from a narrowing of two or more conjugate plates (margins) propelled by an upward force which pulled up some of the magmas in-between those plates. Ultimately, a rock density model of mineral-bearing rocks was produced, revealing mechanisms of tectonic events, patterns of deformation regimes, and it is quite suitable for mineral prospecting expedition over the study area. Estimated rock densities highlight metallogenic provinces with varying intercalations coinciding with some past and present producing mines. However, for a more detailed identification of different mineral constituents present in the delineated mineral-bearing rocks, it is recommended to conduct geochemical and/or petrographic analyses of rock samples collected from those locations as well as involving other available geological information. |
| Rights: | All rights reserved |
| Access: | open access |
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