In the so-called cyanidation-in-mill technique, the ores, ore concentrates and waste material from previous incomplete leachings which are to be leached are treated in the mill with a cyanide-containing leaching solution, gold and silver being at least partly leached. Compared with the known cyanidation-in-mill technique in the presence of hydrogen peroxide, the gold yield can be considerably increased if leaching is carried out in the presence of a peroxoborate compound. The peroxoborate may be present in solid and/or dissolved form. 10 to 60 equivalents peroxoborate are preferably used per t of the material to be leached.
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