A method and system for the percolation leaching of gold and silver ores applies a cyanide leaching liquid to a pile of gold and silver ore. Heap leaching, vat leaching, or the like may specifically be practiced. The cyanide leaching liquid is applied to the pile by spraying, flooding, or via a foam of oxygen gas and cyanide liquid on top of the pile. Gold and silver are recovered from the pregnant liquor. The leach rate is increased and/or the recovery of gold and silver from the ore is increased by supplying to the pile a gas containing oxygen at a significantly higher percentage than in ambient air (e.g. pure oxygen gas). The oxygen gas may be supplied to the leaching liquid, and/or into the pile itself (as with a plurality of perforated pipes adjacent the bottom of the pile).