ABSTRACT
A distinctive attribute of Basement Complex terrain is the widespread occurrence of structural features. Explicating these structural features such as faults, fractures, foliations, fissures, folds and joints of the Basement Complex terrain are panaceafor hydrogeologic, engineering and environmental studies as well as for minerals resources exploration programs. Despite the growing interest in acquiring data for solving geophysical and geological problems, there is dearth of information on seriously examined remarkably data for subsurface structural features in the study area from available literature. Hence, this study is designed to carry out mapping of basement structural features of Igarra and its environs (Longitudes 6°00ʹ and 6°30ʹE and Latitudes 7°00ʹ and 7°30ʹN) using magnetic methods.
Magnetic methods involving Aeromagnetic and Ground magnetic surveys were used. Aeromagnetic survey is a common type of geophysical survey which is carried out using a magnetometer aboard or towed behind an aircraft. Aeromagnetic data of Auchi sheet (sheet 226) was acquired from the Nigerian Geological Survey Agency (NGSA). Ground magnetic field survey carried out with a hand-held magnetometer were taken in Igarra along ten (10) traverses at 20 m intervals each measuring 1560 m, 740 m, 720 m, 540 m, 620 m, 980 m, 260 m, 1400 m, 2,260 m and 800 m. Also in Ososo along two (2) traverses were surveyed at 20 m and 5 m measuring 2,340 m and 155 m respectively. Aeromagnetic and ground magnetic data were processed and interpreted using Oasis Montajversion 6.4.2 (HJ), Surfer ™ Version 13.0., Georient, Grapher 11 and ArcGIS version 10.5 software and these helped to define the lithological boundaries and structural features.
The processed aeromagnetic maps showed that major structural bodies delineated are oriented in the NE-SW and WNW-ESE directions. The results obtained were presented in form of graphs, maps, charts, plots, curves and profiles. The 3 Dimensional Euler deconvolution and radial spectral analysis applied to locate and estimate the depths to magnetic and heat sources; magnetic sources shows varying depth ranges from 50 to 1500 m. Ground magnetic delineated in situ; Migmatite, Quartz-Biotite-Schist, Garnet schist, Quartzite, Mica schist, Porphyrictic granite and Granite gneiss. From combined results of the study area, consistent structural map was generated showing the probable positions and trends of the suspected fractured/a faulted zone as well as other basement structures were produced. All the anomalies delineated are believed to be potential targets for subsequent exploration activities to determine the viability for exploitation. This suggests that the major fractures and faults in the study area are deep within the basement formation since the spectral analysis enhances the anomalies associated with deep magnetic sources at the expense of the dominating intermediates magnetic sources.
