An interpretation of high resolution aeromagnetic data was carried out to provide new information about the study area. Located between latitude 10°30'N and 11°00'N and longitude 8°30'E and 9°00'E, the interpretation revealed previously unknown folds and magnetic anomaly with a signature that is similar to those associated with ring complexes in the study area but without the surface manifestation that is associated with the complexes. Qualitatively interpreted as unexposed ring complex, the magnetic anomaly is underlain by cross-over of major lineaments; implying presence of weak zone that probably allowed the volcanic eruption that initiated the emplacement of the source of the anomaly. A depth that ranges from outcrop to 1200 m and from outcrop to 1800 m is respectively suggested for the unexposed ring complex and folds by the Euler deconvolution results.
Several geological and geochemical studies have been carried out in a study area that is bounded by latitude 10˚30'N and 11˚00'N and longitude 8˚30'E and 9˚00'E [
because of the sparse station density of the surveys; which additional data set would have provided. In view of the relevance of the additional data set, the aeromagnetic data of the study area and beyond, acquired in 1974 by the Geological Survey of Nigeria (at nominal flight height of 152.4 m, along N-S flight lines that were spaced at 2 Km interval), have been interpreted [
Detailed studies of the geology of the study area have been carried out [
As revealed by the geological map, the study area is largely covered by basement rocks while the rest is covered by ring complexes.
The basement rocks consist of two groups; the ancient metasediments that are considered to be older than 2000 m.y and the group that mainly consist of migmatites, granite-gneisses and Older Granites that is believed to have resulted from remobilization during the Pan-African orogeny [
The ring complexes are mainly associated with surface exposure that raised between the range of 500 and 1350 m above mean sea level (
The economic importance of the ring complexes include cassiterite and columbite that were mined in commercial quantities. Other minerals that are also associated with the complexes are wolframite, tungsten, zircon, sphalerite, thorite, etc.
The high resolution aeromagnetic (HRAM) data of the study area, named sheet 126, were sourced from the Nigerian Geological Survey Agency (NGSA). The data, covering half-degree sheet and in scale of 1:100,000, were acquired at a flight altitude of 80 m, along NE-SW flight lines that were spaced at 500 m. The effect of regional geomagnetic field (IGRF; 2004) has been removed, implying that the sourced data are HRAM anomaly or resi-
dual field. Noise was removed by upward continuation of the aeromagnetic anomaly field to a height of 125 m before producing the upward continued aeromagnetic anomaly map of the sheet, in coloured (
Punctuated by pockets of distinct magnetic anomalies, almost circular in shape, the upward continued aeromagnetic anomaly map (
The north eastern part of Banke ring complex, in
Euler deconvolution technique; used to determine depth and location of features that represent structures, is based on Euler’s homogeneity equation, where the homogeneity equation relates magnetic field to the location and depth of its sources with the equation:
The homogenous function F in Equation (1) is the observed field at location (x,y,z) caused by the anomalous source at location
The technique was applied to the upward continued aeromagnetic anomaly data to determine depth of ring complexes and folds in the study area. Structural index 2, which represents cylindrical shaped body, was chosen because magnetic field of alkaline intrusion (ring complex) can be inferred with the body [
The results of the Euler solutions indicate that the depth of the ring complexes range from outcrop to 1800 m. For the inferred unexposed ring complex, the depth range from outcrop to 1200 m. It also revealed tightest cluster of solutions along inferred folds with depth that range from 0 to 1800 m.
Results of the study revealed details that are not previously known about the study area. The map in
complexes in the study area but without the surface manifestation that is associated with the complexes. The observed magnetic anomaly underlain by cross-over of major lineaments may suggest presence of weak zone that probably allowed the volcanic eruption that initiated the emplacement of the source of the anomaly, unexposed ring complex. Because of the historical knowledge of the mining activities at the neighbouring complexes in the study area, the unexposed ring complex may be associated with economic minerals. Depth of the inferred unexposed ring complex has been revealed by the Euler deconvolution results to range from outcrop to 1200 m. It also revealed tightest cluster of solutions along inferred folds with depth that ranged from 0 to 1800 m.