TECHNOLOGY FOCUS - BIOTECHNOLOGY - Preferred Method: (O) further involves ensuring that both the dissolved oxygen concentration and the dissolved carbon dioxide concentration in the bioleach slurry remains above respective lower concentration limits, that are being selected to ensure that the growth of the microorganisms is not limited by a too low concentration of either the dissolved oxygen or the dissolved carbon dioxide in the bioleach slurry.The microorganisms comprise a moderately thermophilic bacterial culture. The lower concentration limit for both the dissolved carbon dioxide and the dissolved oxygen in the bioleach slurry is 0.2 ppm (parts per million). The lower concentration limit for dissolved carbon dioxide and dissolved oxygen in the bioleach slurry is 0.6 ppm and 0.5 ppm, respectively. The redox potential of the bioleach slurry is controlled within the predetermined range by controlling the concentration of dissolved oxygen and/or dissolved carbon dioxide, in the bioleach slurry. (O) includes supplying carbon dioxide and oxygen to the bioleach slurry in the form of carbon dioxide-enriched air.The bioleach slurry is acidic and includes supplying carbon dioxide to the bioleach slurry in the form of limestone. The bioleach slurry includes microorganism with enzymes in their cells which are capable of reacting with urea to release carbon dioxide, by supplying carbon dioxide to the bioleach slurry in the form of urea. The ore or its concentrate includes pyrite as an undesirable component, the redox potential being controlled in the range of 380-450 mV relative to a Ag/AgCl reference electrode, thereby inhibiting the leaching of pyrite while selectively leaching desirable sulfide minerals present in the ore or ore concentrate with a rest potential which is lower than the rest potential of pyrite. The ore or its concentrate includes chalcopyrite as a predominant sulfide component, the redox potential being controlled in the range of 830-450 mV relative to a Ag/AgCl reference electrode thereby to promote the rate and extent of chalcopyrite oxidation. EXAMPLE - No relevant example given.