Abstract Many cop per-bearing ores use Sodium Isopropyl Xanthate (SIPX) as a flotation agent. In general, SIPX will float to some extent other minerals which may not be desirable, such as pyrite. FLEX 31 is a chemically enhanced SIPX product with many of the same properties as SIPX, but FLEX 31 has the ability to reject more pyrite from concentrates as well as improves recoveries of copper when using 50% less FLEX 31 than is required if using SIPX. Copper-activated minerals, such as sphalerite and arsenopyrite, show increased recoveries as well using FLEX 31. However, in copper separation from these minerals prior to activation, FLEX 31 performs very similarly to SIPX and does not give the best separation possible with other reagents. Tests have been performed on copper/zinc, arsenopyrite and copper/molybdenum ores.