Application of remote sensing data in gold exploration: targeting hydrothermal alteration using Landsat 8 imagery in northern Portugal

Mapping hydrothermal alteration minerals and structural lineaments using Landsat 8 multispectral imagery provides valuable information for mineral exploration. In northern Portugal, there are several known gold occurrences, but there is the potential to identify new anomalous areas. Gold mineralization occurs in the form of quartz veins and veinlets associated with hydrothermal alteration halos. Fractures are interpreted as conduits for mineralizing fluids, where the interaction between the wall rock and hydrothermal fluids induces compositional variations. Identifying these features is one of the key indicators for targeting new prospective zones of orogenic gold mineralization in the Boticas–Chaves region. Remote sensing image processing methods such as band combinations, band ratios, and principal component analysis (PCA) were implemented to the visible, near-infrared, and shortwave infrared bands of Landsat 8. The results of this investigation demonstrate the capability of the applied imagery enhancement methods in distinguishing different features and identifying hydrothermally altered rocks. Selective PCA proved to be the most effective and reliable method to identify iron oxides and hydroxyl-bearing minerals, compared to other methods, where a simple imagery analysis has a strong influence of noise and is more challenging to interpret. Enhanced imagery allowed the identification of physiographic characteristics and extracted structural features. The combination of mapped hydrothermal alteration minerals and extracted structural features allowed us to predict potential areas for the mineralization occurrence. This investigation proves that remote sensing can be a cost-efficient and time-saving technique for mineral exploration, and its application in new areas can accurately map hydrothermal alteration and outline potential new exploration targets. © 2021, Saudi Society for Geosciences.