Abstract
In weathered plutonic and metamorphic rocks areas, because rock outcrops are rare due to theextensive regolith cover, geological mapping is largely based on the interpretation of airbornedata and imagery (aerial photographs, satellite images, airborne geophysics when available, etc.).In the sub-Saharan Africa, numerous village water supply campaigns were performed during thelast 40 years. Most hydrogeological and geological data from these campaigns are stored andsafeguard in country scale databases. In this study, we develop a methodology to improve theexisting geological maps in a such geological context with lithological data from the existingdatabases. These data were not used during past geological mapping; yet they provide a com-plementary access to the lithology, notably in areas where outcrops are very scarce. We propose acoherent methodology to use and validate such geological data, complementary to field obser-vations on the scarce outcrops, to cope with their uncertainties. We also show that groundwaterhydrochemistry, namely the silica content, can be of use to complete the geological mapping.Using data from 735 boreholes drilled in the Koudougou and L´eo square study area of BurkinaFaso, we validate this new methodological approach and locally propose a more accurate1:200,000 geological map.