Using Sentinel-2 for Hydrothermal Alteration Mapping in West Africa

Sentinel-2 satellite imagery provides an unprecedented opportunity for geological mapping across large areas at low cost. This article explores practical techniques for applying band ratio composites to identify hydrothermal alteration zones in Birimian greenstone terrains of West Africa.

The Birimian Supergroup hosts some of West Africa's most significant gold deposits, many of which are spatially associated with hydrothermal alteration. Identifying these zones remotely — before committing to expensive field campaigns — can dramatically improve exploration efficiency.

Key band combinations for alteration mapping using Sentinel-2 include band ratios B11/B8A for clay/hydroxyl alteration, B11/B12 for iron oxide mapping, and principal component analysis of multiple bands for subtle alteration fingerprints. When combined with structural lineament extraction from band composites, these techniques can generate high-confidence target areas for follow-up field work.

Validation against known deposits in Ghana and Burkina Faso has shown detection rates of 80-90% for hydrothermal alteration assemblages visible at the 20m resolution of Sentinel-2 SWIR bands.