The mechanism of the interaction of Cu-Fe sulfide minerals with aqueous potassium hydrogen n-octano hydroxamate has been deduced primarily from an XPS investigation of air-exposed fracture and abraded surfaces of cubanite, chalcopyrite and bornite conditioned in a nominally saturated solution of the collector at its unadjusted pH of similar to 9.5. For fresh surfaces of the lower Cu:Fe ratio cubanite and chalcopyrite, most of the collector was chemisorbed on the Fe in the Fe oxide patches or physically adsorbed as hydroxamic acid. On those surfaces, no multilayer Fe hydroxamate and very little collector chemisorbed on the Cu in the Fe-deficient Cu sulfide regions between the Fe oxide patches was observed. For fresh surfaces of the higher Cu:Fe ratio bornite, and for more extensively air-exposed surfaces of cubanite and chalcopyrite, collector chemisorbed to Cu started to become significant. For extensively air-exposed bornite, collector chemisorbed to Cu and multilayer Cu hydroximate were the major adsorbate species, and multilayer Fe hydroxamate remained no more than a very minor constituent. Thus, counter-intuitively, as the Fe oxide concentration at the surface increased, it was the interaction of the collector with Cu that increased. It was concluded that the collector anion exchanged with OH- in Cu-OHsurf rather than interacting directly with Cu in the surface layer of the sulfide lattice. For each Cu-Fe sulfide, extensive prior air-exposure did not markedly affect the extent of collector adsorption compared with the corresponding fresh surface. Visual inspection of the abraded surfaces revealed that each was hydrophobic after conditioning and rinsing with water. That hydrophobicity was despite the retention of Fe-O patches on the conditioned mineral surfaces, and the inclusion of some hydroxamic acid in the adsorbed species. (C) 2014 Elsevier Ltd. All rights reserved.