Abstract
Gold ores can be categorized into two types - free milling and refractory. Free milling ores are those easy to process by simple gravity techniques or direct cyanidation. Refractory ores, on the other hand, are difficult to treat and require pre-cyanidation processes to liberate the gold. Underlying the difficulty of processing refractory gold ores is their mineralogy. This type of ore may have, (1) gold in intimate association with and locked in sulphide minerals, (2) gold associated with carbonaceous matter capable of adsorbing aurocyanide and (3) gold in solid solution with other minerals. This paper reviews the mineralogy of carbonaceous gold ores, the characteristics of carbonaceous matter associated with gold ores and the mechanism of aurocyanide adsorption by carbonaceous matter and activated carbon. In addition the paper describes the various pre-cyanidation treatment methods for carbonaceous refractory gold ores namely, (1) flotation and depression, (2) blanking, (3) the use of activated carbon or resin in leach, (4) roasting, (5) chemical oxidation and (6) bioleaching.
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