Competing effects of iron contamination and chalcopyrite oxidation on flotation in magnetite-bearing IOCG systems

The electrochemical behavior of iron oxide copper–gold (IOCG) ores is commonly interpreted using concepts developed for hematite-bearing systems, where ferric iron-mediated galvanic corrosion governs pulp chemistry and chalcopyrite flotation. Whether this framework applies to magnetite-bearing IOCG ores containing electrically conductive iron oxides remains unclear. Here, chalcopyrite–magnetite–quartz mixtures were ground using forged steel, 18 wt% Cr steel and 30 wt% Cr steel media, and flotation, EDTA extraction, pulp chemistry measurements and electrochemical analyses were integrated to determine the controlling mechanisms. At a fixed FT-1234 dosage of 16.4 g/t, cumulative copper recoveries after 4 min of flotation ranged from 60 to 66% in the magnetite-bearing system, lower than those previously reported for the hematite-bearing system under corresponding test conditions. Among the three grinding media tested, 18 wt% Cr steel gave the highest cumulative recovery at this flotation time. Increasing grinding-media chromium content progressively reduced iron contamination but increased chalcopyrite oxidation. Simultaneously, slurry redox potential increased with dissolved oxygen, indicating an oxygen-responsive electrochemical environment distinct from ferric iron-controlled hematite systems. Electrochemical measurements further showed greater current responses with magnetite than with hematite when coupled with grinding media and chalcopyrite, consistent with a possible contribution from magnetite conductivity. However, this comparison does not separate conductivity effects from other differences in mineral chemistry and electrochemical behaviour. Together, the results support an interpretation in which reduced iron contamination favours flotation, whereas increased chalcopyrite oxidation under more oxidizing pulp conditions counteracts this benefit. A conductivity-assisted electrochemical framework is proposed to interpret these competing effects and inform grinding-media selection in magnetite-bearing IOCG systems.