Gold predictivity mapping in French Guiana using an expert-guided data-driven approach based on a regional-scale GIS
Résumé
A comprehensive overview of the French Guiana's gold-mining activities along with a reliable gold predictivity map has been obtained as part of the 'Mineral Resources of French Guiana' GIS (3396 gold sites listed). The gold mining is almost exclusively in alluvial and eluvial deposits, with primary deposits representing only 2% of the inventoried gold sites. Most of the deposits being allochthonous, a preliminary processing of the data was necessary to draw up a set of 'in-situ' deposits sufficient for a) calculating, correlations between the primary mineralization and the controlling geologic parameters, and b) assessing the favorabilities of the different criteria -- i.e., lithostratigraphy, faults and lithostratigraphic contacts, geochemical and geophysical signatures. The processing, aimed at identifying and selecting sites close to primary sources, was based on ranking the catchment basins according to the Strahler classification. The resulting gold predictivity map combines a classical approach based on algebraic methods for processing polygon and line data, and an approach using cluster analysis for processing geochemical and radiometric data and identifying groups as marking mineralization signatures, then looking for and scoring grid pixels showing a high level of similarity. The map appears realistic. It confirms the value of the known metallotects and locates the main primary deposits; some deposits with a different geochemical and geophysical signature, however, would probably not have been picked up -- hence the importance of the model used for establishing the map. The dual approach is easily transposable to other equatorial and poorly accessible countries.