Nevada Gold Cyanide Milling Regulation 1 For a more in depth discussion of the gold cyanide milling process, see EPA Technical Resource Document on Extraction and Beneficiation of Ores and Minerals for Gold (EPA 530R94 013) spent cyanide solution; residual cyanide; and solubilized metalcyanide When the supply of ore is exhausted, the final step in the life of a gold cyanide ...