The U.S. Bureau of Mines investigated treatment of gold and silver refractory ores and concentrates that respond poorly to conventional cyanidation techniques owing to the complex mineralogy of the ore. Three types of ores were investigated: gold-locked placer sands, gold locked in sulfides, and gold that is robbed from the pregnant cyanide solutions by minerals in the ore. Ore treatment was selected according to the mineral type. Increased grinding, as a treatment for gold encapsulated in quartz, raised the recovery from 43 to 97 pct. Mild air preoxidation treatment for gold locked in sulfide minerals increased the recovery from 65 to 83 pct. Carbon- in-leach treatment, for gold lost from cyanide leach solution to carbonaceous minerals in the ore, increased the recovery from 85 to 89 pct. Acid pressure leaching, as a treatment for gold locked in sulfide minerals, increased the recovery from 64 to 95 pct. Other treatments discussed are flotation, hypochlorite oxidation, and roasting.