Spectroelectrochemical studies of the interaction of amyl xanthate solution (C5H11OCS2-) at pH 10 with mineral samples of chalcopyrite (CuFeS2), tetrahedrite (Cu12As4S13), and tennantite (Cu12As4S13) at different potentials were carried out by infrared reflection spectroscopy. The experimental data were compared with simulated results in order to evaluate in detail the composition and structure of the adsorbed layers. Two-component adsorption layers were determined on these three minerals. The first adsorption product observed spectroscopically was a cuprous amyl xanthate complex followed by an amyl dixanthogen (dimer, (C5H11OCS2)(2)) The dixanthogen was always observed together with cuprous xanthate complex. It was produced simultaneously with cuprous xanthate, on chalcopyrite and tetrahedrite, or at potential 100 mV higher than cuprous xanthate formation on tetrahedrite. The produced cuprous xanthate was placed close to the mineral interface, and its amount was limited from a submonolayer to a few monolayers, whereas the dixanthogen forms the outermost layer and a very large thickness could be achieved. There was a strong thermodynamic limitation of the formation of submonolayer coverages at the potentials close to that at which the first xanthate molecules start to adsorb. After monolayer completion the adsorbed amount was time dependent. The dixanthogen was observed at the chalcopyrite surface at submonolayer coverages at potentials very close to that calculated from the thermodynamic data for bulk phase, while for tetrahedrite and tennantite dixanthogen was produced at potentials 100 and 40 mV higher, respectively. The adsorption kinetics of two kinds of surface species were investigated. The relative amount of cuprous xanthate and dixanthogen depends on the availability of copper atoms at the interface, hence, the mobility of the atoms in the interfacial region, which is different for each of the minerals. For slower copper diffusion the produced amount of dixanthogen increases. Selective flotation separation of these three minerals on the basis of differences in optimal adsorption conditions of amyl xanthate (selective changes in mineral hydrophobicity) could be improved.