Centerra Gold Inc.

Processing

The flowsheet for the Öksüt Mine is based on an 11,000 tpd heap leach operation. It includes primary crushing, screening and secondary crushing, heap stacking and cyanide leaching, carbon adsorption, carbon stripping and regeneration, electrowinning and refining.

Run-of-mine ore is delivered by 40 tonne haul trucks to the primary crusher. The ore is dumped on the stationary grizzly installed over the truck dump hopper. Oversize rocks are handled by a rock breaker. The ore is withdrawn from the dump hopper via an apron feeder. The feed is delivered to the jaw crusher via a scalper. Scalper oversize feeds the 1.5 metre x 2.0 metre jaw crusher that reduces the rock size to minus 150 millimetre prior to being conveyed by a 1.4 metre wide x 95.5 metre long belt conveyor to the secondary crushing circuit, along with the scalper undersize. A self-cleaning belt magnet has been installed over the conveyor belt feeding the secondary crusher building. A metal detector installed after the belt magnet identifies any remaining piece of metal and the conveyor can be stopped to allow manual removal by an operator.

The product from the primary crushing circuit feeds a 2.4 metre wide x 6.1 metre long double-deck screen. The screen oversize will feed a 600 kW cone crusher while the screen undersize reports with the cone crusher product and is transported by a 1.1 metre wide x 50.7 metre long belt conveyor to a radial stacker after quicklime has been added to the crushing circuit product. A 10,000 t capacity stockpile is able to be formed by the 1.1 metre wide x 39 metre long stacker installation.

The crushed ore is trucked from the crushing facility to the heap leach pad. The leach pad is being developed in three phases and is designed to accommodate up to 40 Mt crushed ore.

The heap is irrigated with a diluted cyanide solution recirculated from the ADR plant, via a network of piping covering the surface area under leach. The barren leach solution is pumped from the barren tank at the ADR plant to the area under heap leach. The cyanide concentration of the barren solution is adjusted prior to pumping, and the pH is controlled so that HCN gas formation is inhibited. The solution is filtered to remove carbon fines prior to distribution over the area under leach to minimize emitter plugging. It is pumped by means of three centrifugal pumps installed in series. The first pump covers operation for the first three years of operation, which is the end of Phase 1, while the second pump will be required from year four onwards. The third pump is a spare.

The irrigation distribution piping consists of a 300 millimetre diameter main header made of carbon steel from the barren pumps discharge to the heap perimeter followed by high-density polyethylene (“HDPE”) ending at the ore panels to be irrigated. Drip emitters are used to provide irrigation. A typical panel piping arrangement includes a 300 millimetre diameter HDPE header starting from the main header and running for 190 metres along the 250 metre side of the panel while four lateral pipes spaced at every 62.5 metres branch from the header. Each lateral pipe includes a 150 millimetre butterfly valve, a pressure gauge, and 75 metres of a 150 millimetre diameter HDPE pipe followed by 75 metres of a 100 mm diameter HDPE pipe. Emitter lines branch at every 500 millimetres on the pipes and emitters are spaced at every 762 millimetres on the emitter lines.

The pregnant leach solution flows by gravity through a network of collection pipes at the base of the heap to the pregnant leach solution pond prior to being pumped to the ADR plant for precious metals recovery.