In order to determine whether pre-oxidation results in a change in the identity of the products of the interaction of sulfide minerals with flotation collectors, chalcocite or galena surfaces that had been exposed to air were treated with diethyl dithiophosphate (DTP) or iso-butyl xanthate (BX), respectively, in a borate buffer solution of pH 9.2. The resulting surfaces were studied by means of X-ray photoelectron spectroscopy (XPS) and time-of-flight secondary ion mass spectroscopy (ToF-SIMS). The metal oxidation products formed on each mineral surface during the exposure to air were removed by immersion in water or the buffer solution alone and, to avoid this happening in collector solutions, most experiments were carried out with solutions saturated with the ion of the metal component of the mineral. Immersion of chalcocite surfaces in copper-saturated 10(-5) mol dm(-3) dithiophosphate solution for 40 s, or of galena surfaces in lead-saturated 10(-4) mol dm(-3) xanthate solution for 8 min, resulted in the formation of chemisorbed DTP or BX. Immersion of chalcocite or galena in similar DTP or BX solutions for longer periods gave rise to CuDTP or Pb(OH)BX, respectively, in addition to the chemisorbed collector. In each case, the products of interaction of the mineral with the collector were the same for freshly exposed and pre-oxidised surfaces. The results indicate that the mechanism for the fort-nation of the chemisorbed layer on the pre-oxidised surfaces would have been ion exchange with copper-oxygen or lead-oxygen species followed by reorganisation adjacent to the mineral surface, rather than dissolution of the metal-oxygen species in the aqueous medium followed by chemisorption of the collector at the oxide-free surface. (C) 2003 Elsevier B.V. All rights reserved.