Chalcopyrite, conditioned with sodium dicresyl dithiophosphate (DTP), was floated under standard and well-defined hydrodynamic conditions. The advancing contact angle values of the flotation feed and products were measured and the flotation response benchmarked against a calibration previously established for the chalcopyrite-amyl xanthate (MAX) system. Furthermore, the flotation response of pyrite, separately conditioned with MAX and DTP, was also evaluated under the same hydrodynamic conditions. When the advancing contact angle of chalcopyrite conditioned with DTP was the same (within 5 degrees) as that of chalcopyrite conditioned with MAX, the flotation response was, within experimental error, the same. For both chalcopyrite and pyrite, heterogeneity of the advancing contact angle within the feed size fractions was demonstrated by significant differences in contact angle values measured on the flotation concentrate and tailings size fractions. The mean contact angle of the chalcopyrite and pyrite particles remained constant, within experimental error, through both flotation and sample preparation under the test conditions. The flotation response of chalcopyrite at 2% solids (w/w) was the same, within experimental error, as that at 30% solids (w/w) in the presence of silicate gangue, suggesting non-interaction of this gangue mineral with chalcopyrite under the test conditions. The operational advancing contact angles inferred for pyrite using the calibration established for the chalcopyrite-KAX system were, however, lower than the measured feed advancing contact angles, while the maximum recovery of pyrite was also lower than for chalcopyrite for the same feed advancing contact angle values, in the contact angle range less than 80 degrees. The difference in flotation response between these two minerals for the same feed contact angle values was interpreted in terms of a difference in critical contact angle value for stable bubble-particle attachment. The critical advancing contact angle values for the pyrite size fractions were higher than values for chalcopyrite for size fractions above 20 mu m. This difference in critical advancing contact angle was attributed to the difference in mineral specific gravity between chalcopyrite and pyrite. (C) 2010 Elsevier B.V. All rights reserved.