The Damang ore body is hosted by a north tonorth-easterly plunging antiform, developed within Tarkwaian sediments. The main Damang pit is located close to the closure of the antiform, and all other known mineralisation is located on the east and west limbs of the Damang anticline. The mine exploits fresh hydrothermal and oxide mineralisation in addition to Witwatersrand-style, palaeoplacer mineralisation.

Palaeoplacer mineralisation.
There are three gold-bearing conglomerate horizons recognised on the western limb of the Damang anticline. From footwall to hangingwall, these are known as the Star/Composite, Malta/Breccia and Gulder Reefs. There are also three gold-bearing conglomerate horizons recognised on the eastern limb, namely the Lima, Kwesie-K1 and Kwesie-K2 Reefs. These conglomerate horizons are separated by poorly-mineralised sandstone units.

The reefs are usually characterised by a fining upwards sequence of poorly to moderately sorted, clast-supported polymictic conglomerates. However, local variations are observed where the conglomerate domain is interbedded with fine to coarse grained, poorly sorted sandstones. The Star/Composite, Malta/Breccia and Gulder Reefs on the west limb and the Lima, Kwesie-K1 and Kwesie-K2 Reefs on the east limb of the Damang anticline contain higher gold grades than the poorly mineralised sandstone units, which separate the reefs. The conglomerate reefs may contain between 1.3 and 1.5 g/t gold, and the poorly mineralised sandstone units usually contain between 0.1 and 0.2 g/t gold.

Hydrothermal mineralisation.
Hydrothermal gold mineralisation at Damang occurs in pyrite and pyrrhotite alteration selvages, which are usually less than one metre wide and located immediately adjacent to en-echelon quartz veins. Gold is also associated with accessory vein minerals such as carbonate, muscovite, tourmaline, ilmenite and apatite. These alteration zones are often linked and may result in significant volumes, characterised by intense veining and gold mineralisation.

Conventional drill and blast with truck and shovel mining techniques are employed at all open pits. Load-and-haul is carried out by 90 tonne dump trucks and 14 to 20 tonne excavators in backhoe and face shovel configurations. Mining benches are blasted in 9m benches and excavated in 3m flitches. Gold mineralisation is mined selectively to cut-off grades, and segregated into grade ranges to balance the ore production and processing capacities on-site and to maximise cash-flow.

Off-highway trucks haul the ore to the ROM pad and waste to the respective planned dumps. For pits that are further from the ROM Pad, the off-highway trucks haul the ore to interim stockpiles near the pits and a fleet of 30 to 40 tonne trucks reclaim and transport the ore to the RoM Pad.

The plant is a conventional two-stage grinding circuit using SAG and ball mill combination, with pebble crusher, gravity concentration and an inline leach reactor, followed by a carbon in-leach recovery process. The average throughput of the plant is currently 13,238 tons per day (tpd), with an overall plant utilisation of 92%.

The purpose of the milling section is to produce blended leach feed with about 80% passing 125 µm. The section consists of a SAG mill (8 metres x 5.1 metres with a power rating of 5.8 MW and a ball mill (6.1 metres x 9 metres) with an identical power rating. Cyanide is added to the feed to the CIL at the trash screen under pan to maximise the gold dissolution.

Gravity gold is collected and treated by the Knelson concentrators followed by an intensive cyanidation using the ILR3000BA. The In-line Leach Reactor (ILR) was commissioned in December 2012.

A scalped stream of approximately a fifth of the cyclone underflow stream (circulating load) is fed to the gravity circuit which comprises 2x KC 48 Knelson gravity concentrators with a capacity of 200 to 400 tph. The balance of the circulating load reports to the ball mill as feed. The purpose of this section is to remove any free gold out of the circuit. The section consists of two vibratory screens, which are fitted with five-millimetre aperture screen panels to the two Knelson concentrators. The feed is introduced to the screen with the oversize reporting back to the ball mill and the undersize material is presented to the Knelson concentrators. The tails from the Knelson concentrators combine with the ball mill discharge and are presented as a feed to the cyclones. The concentrate reports to the ILR, which leaches the gold under pressure and high cyanide concentrations to yield dissolved gold; which in turn is recovered by electro winning in the gold room.

Cyclone overflow is screened to remove trash before reporting to the seven-stage CIL, via the filblast pump, which is fitted with a multimix head for oxygen injection. The cyclone overflow comprises 45% solids and is introduced onto the trash screen (0.8 millimetre apertures) and the undersize is presented as leach feed. At this stage about 30% of the gold is dissolved. Gaseous oxygen and hydrogen peroxide are dosed to CIL tanks 1 and 2, to maintain dissolved oxygen content of 14 ppm and 10 ppm for the first two tanks respectively. The slurry discharging from the last tank is screened on a horizontal linear screen (tailings screen) which is fitted with a screen cloth of 0.8 millimetre aperture. This screen recovers and returns to the CIL circuit any coarse carbon discharged accidentally. Loaded carbon is recovered from the first tank of the adsorption train and transferred to acid washing, elution, and electro winning. Cathodes are washed with high-pressure spray water and the gold sludge is recovered by filtration. The gold sludge filter cake is dried and smelted. Slurry discharging from the last adsorption tank is screened ahead of thickening and tailings disposal.