Analyses of high resolution aeromagnetic data for structural and porphyry mineral deposit mapping of the nigerian younger granite ring complexes, North - Central Nigeria

Abstract

This study report the results of the different geophysical analyses carried out on the aeromagnetic data of north-central Nigeria with the object of delineating the occurrence and evaluate the structural influence on the emplacement of the porphyry mineral deposits of the Ring Complexes. The residual magnetic intensity extracted using Low Cut Guassian filter, from the high resolution aeromagnetic data of north-central Nigeria were filtered to remove high frequency near surface cultural noise and subsequently Reduced to Pole at Low Latitude (RTPLL) to focus anomaly peaks on the corresponding geological sources in order to resolve anomaly complexity associated with mid-latitude potential data. The data were further enhanced using upward continuation filter to extract desired magnetic responses at various continuation distances. Analytic Signal (AS), Centre for Exploration Techniques (CET) Grid and Porphyry Analyses were then carried out on the filtered, transformed and enhanced magnetic data to generate diagnostic magnetic attributes employed to map the boundaries of geologic magnetic sources, extract linear features and delineate the occurrence of porphyry mineral deposits across the study area.The AS responses defined twenty-four (24) arcuate/circular shaped AS anomalies which correspond to Younger Granites Ring Complexes in the northeast, northwest, southeast and central part of the study area from the low AS response Basement Complex rocks that host them. The CET grid analysis delineates several linear structures which generally trend NE – SW, NNE – SSW and ENE – WSW directions and their average length (500 m–17,500 m) and population (212–32) directly and inversely, respectively, correlate with the upward continuation distances. The CET porphyry analysis also delineates fifty (50) porphyry mineral deposits which vary in radial size from 300 m–4300 m. The occurrence of the porphyry mineral deposits within or in close proximity with the Younger Granite Ring Complexes which are either crosscut or flanked by the linear structures, suggests hydrothermal non-orogenic origin of the structurally controlled ring complexes and the associated porphyry mineralisation that result from phase mineralisation that accompanied Jurassic hydrothermal activities.