We have utilized electrochemistry, vibrational spectroscopy and X-ray photoelectron spectroscopy to investigate the interaction of KH n-octanohydroxamate with the sulfide minerals chalcocite, pyrite, chalcopyrite, covellite and bornite. Each of these techniques showed that a multilayer of cupric hydroxamate formed on chalcocite, bornite and chalcopyrite conditioned in the hydroxamate collector, and visual inspection revealed that this multilayer had rendered the mineral hydrophobic. Hydroxamate adsorbed to Fe atoms, co-adsorbed hydroxamic acid and some ferric hydroxamate were also observed on the ternary sulfides. Only limited adsorption of collector was observed on pyrite fracture surfaces, unlike abraded surfaces which were rendered hydrophobic by significant adsorption. These results have implications in the use of hydroxamates for the flotation of mixed sulfide-oxide and transitional ores, including the possible collection of gangue minerals in the concentrate.