A method for leaching copper and molybdenum from an ore, residue and/or concentrate containing such, in which more than 1% w/w of the total molybdenum is present as a sulfide and in which more than 1% w/w of the total copper is present as an oxide, the method comprising the steps of: exposing the ore, residue and/or concentrate to an aqueous solution of chlorine (I)-based oxidizing species of a pH of at least 3.0; oxidizing the molybdenum by the chlorine-based oxidizing species thereby providing a treated ore, residue and/or concentrate and a reduced aqueous solution of chlorine-based oxidizing species; leaching the treated ore, residue and/or concentrate by exposing the treated ore, residue and/or concentrate to an aqueous ammoniacal ammonium carbonate solution to form a pregnant leach solution containing both copper and molybdenum; and passing the pregnant leach solution containing both copper and molybdenum to a means for metal recovery.