The semi-continuous biooxidation of a flotation concentrate of a particularly refractory Chinese gold ore was investigated. Without biooxidation, even after roasting, it was possible to recover only a little more than 46% of the gold. The ore contained sulfide minerals, clay minerals, and carbonaceous material. Approximately 58% of the gold was associated with arsenopyrite, 38% with the clay minerals and about 7% with the carbonaceous material. Two different bacterial consortia were studied for effectiveness at biooxidizing the concentrate. Both were effective and arsenopyrite oxidation was rapid. After the biotreatment it was possible to recover about 76% of the gold. Apparently the remaining non-recoverable gold is associated with the clays and the carbonaceous material.