ANALYSIS OF AEROMAGNETIC DATA OVER MUTUM ... - RJEAS

Research Journal in Engineering and Applied Sciences (ISSN: 2276-8467) 1(2):142-148Analysis of Aeromagnetic Data Over Mutum-Biyu and Environs, North–Eastern, NigeriaAnalysis of Magnetic DataThe aeromagnetic data used for this paper wasobtained as controlled maps of total magneticintensity on a scale of 1:100,000 compiled byGeological Survey of Nigeria (GSN 1975). It consistsof sheets 213, 214, 234, 235, 254, 255, 256 and 257.The survey was conducted along NW-SE profileswith a spacing of 2 km and a nominal tie line spacingof 20 km and an average flight elevation aboveterrain of 150 m. The geomagnetic gradient wasremoved using the International GeomagneticReference Field Formula (IGRF) of the 1 st January,1974. The magnetic map was digitized at an equalinterval of 2cm x 2 cm in the N-S and E-W grid linesgiving a data matrix of (56 x 112). To eliminateregional field, a plane surface has been fitted to thedata by multi-regression least-square analysis, andexpression for the regional obtained was:-T(x, y) = 7770.55 + 1.742x-0.178y (1)Where x and y are unit of spacing of the digitizedmagnetic data.The regional field values were subtracted from theobserved data, and the obtained residual field overthe area is shown on Figure.4.The points sampled on the square grid represent theTotal Magnetic Intensity (TMI) values which werecontoured (Fig. 3).NGidan ShanuBantajiWuriuTapareGassolBagunleAmarGargaleKatsinaBakundiMutum BiyuManjiGundumaJalingoIwereYarima GamtsinKamZogon kombiGarin ShegeGurumpawaMonkinTolaMbagarAngwamKiriLegendContourTown0 20 40 60 KmFig3.Total magnetic intensity map (Cont Inter.40nTMonkinBanguleJalingoGidan ShanuMutum BiyuAmarManjiGundumaIwereZogon KombiTolaMbagarGassolGarin ShegaGargaleGurumpawaWuriuYarima GamtsinLegendKatsina KamAngwamContourBantajiTownTapareBakundiKiriFig.4. Residual magnetic map of the area (Cont. Int.80nT)From the residual magnetic map, lineaments/fractureswere traced parallel to the closures of the magneticanomalies; the length depends on the direction andthe length of magnetic anomalies. The azimuthdiagram (Rose diagram) was obtained from thestructural map. The residual lineaments map deducedindicated that 60% have NE-SW; 19% NW-SE; 13%E-W and 11% N-S direction as illustrated by azimuthdiagram showing the magnitude and direction (Figure5). These fracture directions are in line with the Pan-African and Pre-Pan-African deformational episodein the area. It could also be related to those developedin the pre-existing zones of weakness, which are alsoin alignment to the major lineaments of Africa(Grant, 1978 and Ekweme, 1994)Relating the lineaments; high density of lineamentsoccur in the eastern part of the area, in the oldergranite and gneiss-migmatites complex, and has beenintruded by igneous rocks and basalts of CameroonVolcanic Line(CVL), while the less dense lineamentsoccurred in the western part which is dominated bysedimentary rocks. Most high magnitude lineamentscould be attributed to deep seated fractures, while thelow magnitude fractures could be attributed toshallower weathered zones in the study area. Thefractures observed on the field range from open tomineralize; few of them are shown on the plate.To obtain the residual, regional field were calculatedusing a visual basic program, the regional field werecomputed from the observed data and the residualmagnetic values obtained were contoured (Fig. 4).145