Abstract: A process for beneficiating a finely ground ore containing sulfide minerals of copper and nickel by selective flotation to produce a copper concentrate and a copper-nickel concentrate comprises pulping the ore with water to form a slurry, conditioning the slurry with an aqueous solution of SO.sub.2 (H.sub.2 SO.sub.3) equivalent to from about 2 to about 4.5 pounds of SO.sub.2 per ton of dry ore for a time sufficiently long to maximize depression of the nickel minerals while maximizing activation of the copper minerals, wherein the conditioned slurry contains about 30 wt. % to about 35 wt. % solids, adding a collector and a frother to the conditioned slurry, subjecting the conditioned material to a rougher flotation stage to produce a rougher copper concentrate and a rougher tailings, conditioning the rougher tailings with additional collector and with Ca(OH).sub.