Using Edge Detection Techniques on Aeromagnetic Data to Delineate Structures Controlling Orogenic Gold Deposits in the Sefwi Greenstone Belt, Ghana

Abstract

The orogenic-style gold deposits in the Sefwi greenstone belt are associated with quartz veins and occur along shear zones. Edge detection techniques (i.e., analytic signal, vertical, and tilt derivatives) were employed to delineate regional planar fabrics (e.g., shear zones, faults) using aeromagnetic data. The enhancing techniques aided the delineation of NE-SW striking lineaments associated with the Kenyase-Yamfo, Hwidiem, Ketesso, Bibiani, and Afema shear zones in the study area. These shear zones are within the Sefwi belt and at the contact zones between the belt and the adjacent metamorphosed volcano-sedimentary rocks of the Sunyani-Comoé and Kumasi-Afema basins. Low-displacement N-S to NNE-SSW trends which are oblique to the NE-SW shear zones, were also delineated. The local bend and offset along the NE-SW striking faults created by the cross-cutting N-S to NNE-SSW faults serve as favourable trap zones to focus fluids migrating along these shear zones. Fry analysis of known orogenic gold occurrences in the study areas shows that the NE-SW lineaments, with an azimuth of 40°-50°, are predominant in controlling the distribution of deposits. There is also a significant structural control in the N-S to NNE-SSW direction with azimuths 0°-10° and 10°-20°.