keywords: CET, imaging SPI, IGRF, vertical derivatives
Magnetic susceptibility in the area ranged from -689 nT to 613 nT, positive magnetic anomalies were observed at the Northern end of the area above Kwalla and Wamba in Plateau and Nassarawa States, respectively However susceptibility ware generally low below Wamba down to Akira and Katsina-Ala in Benue State. The IGRF filtered residual data for the study area was reduced to the pole (RTP) before being subjected to Vertical Derivative, Source Parameter Imaging and CET grid analysis. All these were aimed at estimating depth to magnetic rocks and delineate the lineaments within the area. The first vertical derivative that sharpens the edges of the anomalies reveals that the Northern part of the study area consist of basement rock outcrops with various degrees of deformations as seen from the distortion to the magnetic signatures which represents the Granite Gneiss at Kwalla and the Migmatite Gneiss at Wamba. Similar features were obtained around Akwana, Gboko and Katsina-Ala which depicts weathered porphyritic homblede Granite. Depth to magnetic rocks estimates within the study area is generally shallow though some noticeable depths in the range 3 – 3.5 kilometers were obtained around Akira just above river Benue and below Akwana on latitude 7º30ʹN. The phase symmetry from CET grid analysis, mapped the geologic boundaries which equally coincided with ridges within the area as thick pink bands enclosing major magnetic highs, these features are predominant within the outcrop basement rocks. Valleys were observed within regions of long wavelength anomalies which could be found from the 1VD map around Makurdi, Lafia and Akira. Lineament map obtained from CET shows linear structures that trend in the NW-SE and E-W directions these could be interpreted as veins that are host for minerals within the area, they are predominant around Kwalla in Plateau State and Wamba in Nassarawa State and also in Katsina-Ala and Gboko in Benue State.
Ajakaiye DE, Hall DH, Ashiekaa JA & Udensi EE 1991. Magnetic Anomalies in the Nigerian Continental Mass based on Aeromagnetic Surveys. Tectonophysics, 192-211. Balogun OY 2003. Senior Secondary Atlas. 2nd Ed. Longman Nigeria. Cordell L & Grauch VJS 1982. Mapping basement magnetization zones from aeromagnetic data in the San Juan Basin, New Mexico: Society of Exploration Geophysicists, 52nd Annual Meeting, Abstracts and Bibliographies, pp. 246-247. Cordell L & Grauch VJS 1985. Mapping basement magnetization zones from aeromagnetic data in the San Juan basin, New Mexico in Hinze, W. J., ed., The utility of regional gravity and magnetic anomaly maps: Society of Exploration Geophy., pp. 181-197. Likkasson OK, Ajayi CO & Shemang EM 2005. Some structural features of the Middle Benue Trough, Nigeria, modelled from aeromagnetic anomaly data. Sci. Forum, J. Pure & Appl. Sci., 8: 100-125. Nigerian Geological Survey Agency 2006. Geological Map of Nigeria, Scale: 1:2, 000, 000. Nur A, Ofoegbu CO & Onuoha KM 2003. Spectral analysis and Hilbert transform of aeromagnetic data over the Upper Benue Trough, Nigeria. Global J. Geolog. Sci., 1(2): 129 – 142. Nur A, Onuoha KM & Ofoegbu CO 1994. Spectral analysis of aeromagnetic data over the Middle Benue Trough. Journal of Mining and Geology, 30: 211 – 217. Nur A 2000. Analysis of aeromagnetic data over the Yola arm of the Upper Benue Trough, Nigeria. Journal of Mining and Geology, 36: 77 – 84. Nur A 2001. Spectral analysis and Hilbert transform of gravity data over the southwest of the Chad Basin, Nigeria. Journal of Mining & Geology, 37: 155 - 161. Nwogbo PO 1997. Mapping the shallow magnetic sources in the Upper Benue Basin in Nigeria from Aeromagnetic. Spectra, 4(3/4): 325-333. Ofoegbu CO 1984a. Interpretation of magnetic anomaly over the Lower and Middle Benue Trough of Nigeria. Geophysical Journal Royal Astronomical Society, 79, 813-823. Ofoegbu CO 1988. An aeromagnetic study of part of the Middle Benue Trough, Nigeria. J Afri. Earth Sciences, 7: 77 - 90. Offodile ME 1976. The Geology of the Middle Benue Nigeria”. Cretaceous Research, Paleontological Institute: University of Uppsala. Special Publication, 4: 1-166. Offodile ME & Reyment RA 1977. Stratigraphy of the Keana-Awe area of the Middle Benue Region of Nigeria. Bulletin Geological Institutions University Uppsala (N. S.), 7: 37-66. Osazuwa IB, Ajakaiye DE & Verheijen PJT 1981. Analysis of the structure of part of the Upper Benue Rift valley on the basis of new geophysical data. Earth Evolution Sci., 2: 126-135. Phillips JD 1997. Potential-field geophysical software for the PC, version 2.2: U.S. Geological Survey Open-File Report 97-725, 34p. (online at http://greenwood.cr.usgs.gov/pub/open-file-reports/ofr-97-0725/pfofr.htm). Reid AB, Allsop JM, Granser H, Millet AJ & Somerton IW 1990. Magnetic interpretation in three dimensions using Euler deconvolution. Geophysics, 55: 80-91.