This work evaluates the behavior in the cyanide leaching of primary gold ore from Riacho dos Machados, central Brazil. The parameters studied were: extraction of gold/silver in different ore sizes to determine the exposition of precious metals; rare of extraction in bottle roll tests with crushed and ground ores; and the effect of addition of oxidising agents (air, oxygen and hydrogen peroxide) on gold/silver leaching. The run of mine ore contains about 7 ppm of gold and 2 ppm of silver. The gold/silver particles are of microscopic and submicroscopic sizes and 90% of the gold was extractable. The use of oxygen and hydrogen peroxide mixed with air increased the rate of gold dissolution.