Fusing satellite imagery and ground geochemical data to map alteration zones for gold exploration in western Nigeria

Abstract

As alteration mapping is vital in identifying signatures of specific mineral deposits, this study aimed to map alteration zones associated with orogenic gold mineralization in the Wawa area using remote sensing and geochemical data. Sentinel-2 satellite images were fused with an ALOS PRISM panchromatic image for spatial resolution enhancement. Image processing methods such as color compositing, band rationing, thresholding, and principal component analysis were used for hydrothermal alteration mapping. Field investigations, major, and trace element geochemical analysis of samples were applied for results validation. The findings showed that the significant lithologies in the Wawa area are migmatite, granite gneiss, quartzite, amphibolite/amphibole schist, phyllite, and granites. Gold occurs as micro-veins within amphibolite/amphibole schist and granite gneisses in close association with pyrite. Significant alterations observed at/around the gold mining sites are clay and iron oxide. There is increased alteration intensity at apparent contact zones between granite gneisses and schists. Geochemical data support the findings that most existing gold mining sites are within intense iron oxide and clay alteration zones, and that gold pathfinder elements such as Cu, As, Pb, and Ni occur anomalously within vein quartz and amphibolitic rock samples from the alteration zones in the Wawa area. Future exploration targets for orogenic gold in the Wawa area should be concentrated within similar alteration zones with no gold mining sites.