Abstract
Interpretation of Aeromagnetic and Radiometric Data covering the basement region of Benue-Niger confluence was executed to delineate major structures and other geologic frame works of mineral interest. The study area which hosts the Benue-Niger confluence also encloses two major geologic units which are basement complex and sedimentary basins. The Aeromagnetic data set comprising sheet 227 (Koton-Karfe), 247 (Lokoja) and 267 (Idah) was enhanced to reveal geologic structures while radiometric data was analysed to map lithology and zones affected by hydrothermal alterations. A set of mathematical algorithms was used to enhance the data for interpretation. First Vertical derivatives, Analytical Signal and Euler deconvolution filters were applied to the Aeromagnetic data while Ratio and Ternary images of the three radiogenic elements were obtained for the radiometric data. Magnetic signatures from the TMI showed a mixture of high and low susceptibility below koton-karfe due to intrusion of oolitic iron ore within the sedimentary formation. Lokoja regions recorded highest susceptibility of 165 nT due to magnetic signatures emanating from exposed basement rocks. The southern Idah regions recorded relatively low susceptibility. Result of First Vertical Derivative revealed near surface mineral potent structures labelled F1 – F8, cringing surface features B1, B2 and B3. Analytical signal revealed high amplitudes range of 0.174 to 0.579 cycles for magnetic sources majorly at the basement regions, while low amplitude range of 0.021 to 0.157 cycles were recorded around the sedimentary regions. Euler depth analysis revealed shallower depth to sources in the basement and deeper depth to sources in the sedimentary regions due to thick overburden. Radiometric signatures from the K/Th ratio map revealed portions around Latitude 8°00’ NW and 7°30’ SW shaded in pink colour and having values above known threshold of 0.2 %/ppm to be hydrothermally altered. Mapping of lithology from Ternary map revealed K-Feldspar mineral bearing rocks dominated the NW and SW regions, while sandstones, ironstones, mudstones, shale, alluvium and other fluvial sedimentary lithologies dominated the sedimentary North-east and South-Eastern regions. The western regions (NW and SW) hosted the major structures in form of magnetic lineaments trending NE-SW and E-W which also coincided with regions delineated to be hydrothermally altered and apparently represents the most prospective regions of mineralisation in the study area.
Highlights
Geophysical methods are often the most essential and effective tools for probing the earths subsurface for mineral exploration and other geophysical investigations of economic importance
Worthy to note is a high susceptibility lithology around Latitude 7°15’ at the lower part of the study area within the fika sandstone under which lies the lowest susceptibility which comprise a region of high overburden due to erosion. 4.2 Result of Analytical signal The Analytical analysis showed high amplitude of susceptibilities across the field, though majorly within the basement regions but some isolated structures were discovered to be located within the sediments such as that between Latitude 8°00’ and 8°15’ above and within Koton-karfe
The contacts between geological formations were seen as a fold (F1) at the middle portion of kotonKarfe where the southern Nupe/Bida basin terminated at the edge of Western Nigeria basement
Summary
Geophysical methods are often the most essential and effective tools for probing the earths subsurface for mineral exploration and other geophysical investigations of economic importance. Amongst the various Geophysical methods for mapping the earth, Air-born geophysical methods (Aeromagnetic and Radiometric) offers a cost effective and time saving means of surveying large areas and delivering high resolution data that could help delineate mineral hosting geologic frame works with high accuracy and precision. Radiometric data when analysed can shows variation and concentrations of radioelements (K, Th and U) which helps in mapping lithology and providing evidence of hydrothermal alterations. Solid minerals of economic value such as gold, marble, limestone, iron ore and gemstones are scattered across the vast land mass that make up the state.
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