Jury
- Prof. Max COLLINET (UNamur), président
- Prof. Johan YANS (UNamur), secrétaire
- Prof. Flavien CHOULET (Université Marie et Louis Pasteur)
- Dr Alexandre FELTEN (UNamur)
- Prof. Mohammed BOUABDELLAH (Université Mohammed IV Polytechnique)
- Prof. Nadine MATTIELLI (Université libre de Bruxelles)
- Dr Augustin DEKONINCK (UMons)
Résumé
Supergene processes are responsible for the redistribution of metals near the surface and can form economically significant mineral deposits. This PhD thesis investigates the evolution (genesis and timing) of supergene mineralization in polymetallic systems from Morocco (Anti-Atlas and Atlas) and France (Provence). The study combines field observations, petrography, geochemistry, stable isotopes analyses and experimental oxidation to provide a multiscale understanding from microscopic characterization to the regional geological evolution.
Stable Cu and Fe isotopes show singular fractionation in each deposit, which primarily depends on the primary ore isotopic composition. In addition, specific minerals (i.e., arsenates) may strongly impact Cu fractionation of later formed minerals (i.e., malachite), which can lead to extremely variable Cu isotope compositions across deposits. Hence, Cu and Fe isotopes must be considered as site specific. Experimental investigations complete geological data by quantifying oxidation rates of pyrite and galena under various conditions. These results highlight that the timing of weathering is reproductible and fit with natural examples studied in this thesis via (U–Th)/He and K–Ar geochronology. However, pyrite oxidation (4.3 µm/year) is faster than galena, which may have a catalytic effect on other sulfides in polymetallic deposits.
Overall, supergene mineralization reflects combined controls from mineralogy, host rocks, fluids, climate and tectonics. This work refines genetic models and provides new tools to describe and constrain secondary mineralization, and their potential impact on metallurgical processes.
