Experimental assessment of galena oxidation using XPS depth profiling: implications for weathering processes and supergene Pb ore formation

This study investigates the oxidation behavior of galena (PbS) using X-ray Photoelectron Spectroscopy (XPS) depth profiling. Samples of galena from three distinct geological contexts (Mississippi Valley-Type Vedrin and Engis in Belgium, and vein-type Kipushi deposit in Democratic Republic of Congo) were exposed to continuous water drip experiment for up to 5000 hours to simulate weathering processes. Results reveal that galena oxidation proceeds through the formation of thin layers of lead sulfates (anglesite), oxides, and minor carbonates, with occasional intermediate sulfide species. Oxidation rates, calculated from depth profiles, range from 0.6 to 0.9 µm.yr-1, significantly slower than those previously observed for pyrite under similar conditions (4.3 ± 0.6 µm.yr-1). Trace element substitutions show negligible influence on oxidation kinetics, whereas inclusions of other sulfides (e.g. pyrite, chalcopyrite) may accelerate the oxidation process. These findings provide quantitative constraints for extrapolating weathering rates in geological profiles and highlight the role of mineral associations, host-rock buffering, and fluid chemistry in supergene ore formation and environmental risk assessment.