The flotation behaviour of low grade, coarse composite particles for two porphyry copper ores was studied. Different grinding times were employed to obtain size distributions for the flotation feed (d(80)) ranging from 150 to 320 mu m. Copper containing particles in the fine to intermediate size ranges were recovered in the rougher flotation stage. The rougher tailing was then screened through a 75 mu m laboratory sieve. The +75 mu m fraction was conditioned with a longer chain collector and floated in either normal viscosity (water) or high viscosity (glycerol-water mixture) medium. The recovery of copper was analysed on an un-sized and size-by-size basis. The recovery of coarse composite copper bearing particles was found to increase in high viscosity medium, even when the liberation of copper bearing minerals was only as low as 10%. The ability to recover these types of particles may result in a reduction in energy consumption in grinding due to the ability to achieve higher overall recovery of valuable mineral at coarse particle size distribution. (C) 2011 The Society of Powder Technology Japan. Published by Elsevier B.V. and The Society of Powder Technology Japan. All rights reserved.