The influence of oxygen bubbling on the impedance of a natural galena electrode in alkaline solution without xanthate was studied. As in the absence of oxygen, the unusual potential dependence of the impedance may be explained by the growth of an oxidized film. This confirms that the anodic reaction contributing to the formation of a mixed potential at the surface of mineral particles during their flotation is the oxidation of galena forming a film. The distortion of the impedance behaviour in the presence of oxygen related to its reduction, the cathodic reaction forming the mixed potential, is qualitatively explained in the light of the new approach by changes in the film structure and perturbations in the transport vacancies in the film due to the presence of new reactions at both its interfaces. The appearance of a constant phase element (cpe) for only the most cathodic potentials also leads us to propose new insights for the origin of cpe at solid electrodes.