The first laboratory tests on biooxidation and cyanidation of gold ores in Turkey were carried out using samples of the Copler Gold Mine. Over a 3 year R&D test period, mixed bacterial/archaeal cultures improved biooxidation of the Copler ore. The highest sulphide oxidation of 87.35% over 432 h was achieved in shake flasks in the presence of the mixed culture (MODM: Sulfolobus acidophilus and Sulfolobus thermosulfidooxidans). Bioreactor tests resulted in greater dissolution rates for iron and arsenic than did shake-flask tests, which led to a greater extent of sulphide oxidation within a shorter period of time. The maximum sulphide oxidation in the bioreactor tests was 97.79% after 240 h when the EXTM (Acidianus brierleyi and Sulfolobus metallicus) mixed culture was used. After the biooxidation experiments with solids contents of 10% and 20% (w/v), the gold recovery from the oxidised ore was lower than that achieved in the presence of 5% solids (w/v) because the extent of sulphide oxidation was reduced as the pulp density increased. A strong correlation between the sulphide oxidation and gold recovery was also established. The highest gold recovery of 94.48% was achieved during cyanidation from the biooxidised ore produced from the experiment conducted using the EXTM mixed culture.