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Abstract

Structural characterization was conducted in some parts of Ago-Iwoye to better understand the basement formation for engineering, environmental, and mining studies. The ground magnetic geophysical method was employed to analyze the variations and orientation of the magnetic properties within the basement. Ten (10) magnetic profile lines were established, each approximately 200 m in length. Data were collected using a GEMS GSM 19T proton precession magnetometer and its accessories, measuring the total magnetic field intensity with a precision of about ± 0.1 nT. The residual magnetic intensity was calculated from the total magnetic intensity by deducting the International Geomagnetic Reference Field (IGRF). Additionally, two-dimensional (2-D) inverse modeling of the magnetic bodies was analytically considered based on the geomagnetic reference field. The modeling of the magnetic anomalies utilized a cylindrical body type with high precision iterations, ensuring that the Root Mean Square (RMS) error was less than 1.0%. The processed magnetic data revealed Total Magnetic Intensity (TMI) values ranging from 32912 to 33143 nT, indicating the Precambrian nature of the basement. Magnetic trend analysis showed a decline in magnetic strength along profiles 2, 3, and 4, with values of 100 nT, 12 nT, and 10 nT, respectively. The remaining profile lines indicated a positive residual anomaly with magnetic strength varying from 3 to 68 nT. Moreover, dipping basement structures were identified in profiles 1, 5, 6, 7, 8, and 10, with varying depths from 8.3 to 25.7 m. The dipping nature of the basement correlates with the extensively metamorphosed migmatite-gneiss complex underlying the study area. Furthermore, the near-surface characteristics of the dipping basement were delineated, reflecting the undulating and uneven topography of the study area. It is important to note the delineated discordant basement intrusion, which suggests the presence of buried quartz-feldspar thick veins within the gneiss as forms of intrusion. The basement structure is primarily slab-like, contrasting with the cylindrical form found in other profiles. The study provided detailed information of both the depth and structural shape of the Basement Complex in the study area. Unlike previous studies that primarily reported the depths to the basement, this research offered a comprehensive assessment by characterizing its morphology and structural features thereby enhancing the understanding of the subsurface geology. In conclusion, this study has provided fundamental structural, geological, and geophysical information that can act as a preliminary assessment for further geological, archaeological, mineral, and environmental research.

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