Multispectral remote sensing expression of lineaments and alteration minerals in part of crystalline rock units of Southwestern Nigeria: Implication on gold prospecting

Abstract

The Ilesha schist belt, the location of the research area, comprises one of Nigeria's most notable schist belts, which has attracted attention due to its considerable mineral resources, including gold deposits. Recent studies in the region have emphasized aerogeophysical mapping of geological features and the implication this has for mineral potential. However, various types of alteration and their relationships with gold deposits in the region have not received proper consideration. This research is aimed at identifying specific type of hydrothermal alteration associated with existing gold deposits in the study area as a reference to establishing new prospective zones and producing mineral prospect map of the area. To achieve this, Landsat Enhanced Thematic Mapper plus (Landsat-7 ETM+), and Advanced Space borne Thermal Emission and Reflection Radiometer (ASTER) data were utilized to define the association of lineaments and propylitic, phyllic, and argillic alteration types with Gold deposit within the study area. The processing of Landsat-7 ETM+ data were aided by applying Band ratio procedure and Principal Component Analysis (PCA). The validation was carried out using the active mining site of the study area, X-ray diffraction (XRD) analysis of some rock samples and electrical resistivity method. The results were integrated to provide information on lineaments, alteration minerals, and different types of hydrothermal alteration within the study area. Processed Landsat-7 ETM+ data delineated the structural elements as lineaments synonymous to lithologic contacts and faults/fracture zones, trending NE–SW direction, most probably controlling the alteration zones formation, distribution and localization of mineral in the country rocks of the belt. The Band ratio procedure and Principal Component Analysis (PCA) also showed that the area is rich in alteration minerals, particularly ferrous, ferric and clay minerals. ASTER multispectral analysis gave an imprint of the key alteration types within the study area, with phyllic alterations being noticeably the major alteration type associated with Gold deposits, and poses the highest prospective zone for Gold occurrence in the study area. Validation of the observed lineament dense areas with Vertical Electrical Sounding (VES) revealed highly fracture zones, thereby validating the structural framework of the study area. Also, spatial analysis involving percentage correlation evaluation carried out to compute the spatial connection between gold locations and altered zones showed that gold mine pits strongly matched with mapped altered zones with 85 percent correlation. Lastly, mineral compositions of the altered zones were confirmed by X-ray diffraction (XRD) analysis of the analyzed samples collected within the area. The research helped in understanding the spatial distribution of gold mineralisation within the study area. It is recommended that exploitation efforts be expanded to the delineated phyllic and propylitic altered zones in North, Northwestern and Northeastern part of the study area. These regions are the new probable promising site for gold potential.