RED LAKE

PROCESSING

Red Lake Complex | Campbell Complex

Red Lake Complex

The original mill was built in 1948 and was dismantled in early 2000. Following the high grade discovery and subsequent mine expansion, a new mill was commissioned in mid 2000 to treat the new high grade ore. The processing facilities consist of three separate plants: the Crushing Plant, Processing Plant, and Pastefill Plant.

The Crushing Plant consists of a two stage process which reduces underground ore size (12 inches to 3/8 inch). The ore is fed to the jaw crusher and then the sizing screen.

The screen oversize is crushed in the cone crusher which reports back to the screen, and screen undersize is conveyed to the Processing Plant for gold extraction.

Separate operations in the Processing Plant consist of grinding, gravity concentrating, leaching, carbon-in- pulp (CIP), carbon elution and reactivation, electrowinning, bullion smelting/refining, cyanide destruction, flotation, and concentrate handling. Three types of gold occur in the Red Lake Mine ore requiring these various unit operations.

Grinding consists of a ball mill (11.5 feet by 16 feet) in closed circuit with sizing cyclones. Coarse gold is recovered from grinding using two Knelson Concentrators. This gold is upgraded on a Deister Table and smelted into bullion on site. During 2005, the gravity circuit recovered over 55% of the gold fed to the processing plant.

Following grinding, thickened slurry is pumped to four leach tanks where gold is dissolved using a weak cyanide solution. The slurry, with the gold now in solution, flows to six CIP tanks that contain granular carbon particles that adsorb the gold. The adsorbed gold is stripped from the carbon using a heated mild caustic solution that is pumped to two electrowinning cells.

Under applied voltage and current density, the gold is electrically plated onto stainless steel cathodes in the cells. The gold is washed off and smelted into bullion on site. During 2005, the leach circuit recovered over 34% of the gold fed to the Processing Plant.

After exiting the CIP tanks, all remaining cyanide in solution is destroyed. This is accomplished using the INCO SO2 treatment process which oxidizes the cyanide component of the slurry and precipitates heavy metals. After the cyanide is destroyed, the slurry flows to the flotation circuit where a concentrate of sulphides, which encapsulates the remaining recoverable gold, is separated from the rest of the slurry stream. In the flotation circuit, chemicals are added to help the gold bearing sulphide minerals adhere to tiny bubbles of air that are added in small agitated tanks. The bubbles rise to the surface and collect in a froth layer which is removed from the surface with paddles. The concentrate is collected and excess water is removed with a thickener and then a drum vacuum filter. The gold-bearing concentrate is trucked from site for treatment in an autoclave, either at Placer Dome’s Campbell Mine, also in Balmertown, or at Barrick’s Goldstrike Mine in Nevada.

The tailings from the flotation circuit are directed to the Pastefill Plant from where the slurry is either discharged to the Tailings Management Area or mixed and sent underground for use as backfill. Slurry sent underground is first filtered before adding cement and water to form a paste. Once the proper consistency is achieved, the paste is discharged underground to flow by gravity to the mined out areas.

In 2006 good progress was made in developing the new Balmer shaft which will provide improved access to reserves at deeper levels of the mine.

Process Flow Sheet

Campbell Complex

The mill has been operating continuously since 1949.  It was originally designed to treat 360 tonnes per day, and has been upgraded numerous times over the years to the current capacity of 1,850 tonnes per day.  The processing consists of crushing, grinding, gravity recovery, flotation, pressure oxidation, cyanide leach, CIL, CIP recovery and pastefill.

The crushing plant is a 3 stage process which reduces underground ore size to approximately ½” in size.  The ore is fed to a jaw crusher, then to a standard cone crusher, then to a sizing screen.  Screen oversize is then fed to a short head cone crusher, which then reports back to the screen.  Screen undersize is conveyed on to the grinding circuit.

The grinding circuit is a 2 stage process, with an open circuit rod mill (9 feet by 12.5 feet) followed by a ball mill (12.5 feet by 15.5 feet) in closed circuit with sizing cyclones.  Coarse gold is recovered from grinding using a Knelson Concentrator.  The gold is upgraded on a Deister Table, and smelted into bullion on site. 

Following grinding, the slurry is fed to the flotation circuit, where a sulphide concentrate is produced.  In the flotation circuit, chemicals are added to help the gold bearing sulphide minerals adhere to tiny bubbles of air that are added to the bottom of small agitated tanks.  The bubbles rise to the surface and collect in a froth layer which is removed from the surface with paddles.  The concentrate is collected and excess water is removed with a thickener.    This concentrate is then mixed with concentrate from the Red Lake Mine, and passes into the pressure oxidation circuit.  The flotation tails pass on to the cyanide leach circuit.

In the cyanide leach circuit, thickened slurry is fed through five leach tanks where gold is dissolved using a weak cyanide solution.  The slurry, with the gold now in solution, flows to six CIP tanks that contain granular carbon particles that adsorb the gold from solution.  The carbon, along with the gold adsorbed onto it, is then fed into the CIL tanks.