The Black Fox Complex is located with other gold deposits near the Destor-Porcupine Deformation Zone. The auriferous zones seem to be associated with an orogenic gold occurrence related to longitudinal shear zones (greenstone-hosted quartz-carbonate vein deposit). They correspond to structurally controlled, complex epigenetic deposits hosted in deformed metamorphosed terranes.

Open pit mining commenced at Black Fox in May 2009 and subsequently depleted in September 2015. Commercial production from the underground mine began in October 2011. Underground ore is accessed from a series of declines branching off from the main ramp to surface. The underground mine at Black Fox begins at bottom of the open pit (approximately 200 metres below surface) and is expected to extend to more than 800 m in depth below surface. Backfilling is done with a combination of mine waste rock mixed with a Portland cement slurry mix.

Underground mining uses three predominant mining methods: longhole stoping, cut-and-fill and shrinkage stoping. The mining method is selected based on the geometry of the orebody. Ground conditions and the stability of the hanging wall are also taken into consideration when selecting a mining method.

Longhole stopes are mined both longitudinal and transverse, with the latter being applied to ore widths greater than 10 m. Development waste is used for backfill where possible, however cemented backfill is used where adjacent stopes are planned, to minimize dilution and maximize ore recovery.

Ore mined at Black Fox is initially crushed on-site and transported by road trucks to the Black Fox mill site located 28 kilometres away, and fed via a conveyor system to the mill’s crushing circuit. The crushed product is transferred to a 1,500 tonne fine ore surge bin, and then fed into a 2,400 tonnes per day grinding circuit which includes two stages of closed circuit ball milling. The regrind mills are operated in closed circuit with five (5) secondary cyclones. The overflows from the secondary cyclones flow to a vibrating trash screen. The trash screen undersize falls into the thickener feed pump box.

The ground slurry is then pumped to a thickener for dewatering. The thickener underflow is pumped to the first of two (2) leach tanks. The solution flows by gravity from the first tank to the second. Lime slurry is added to the first leach tank for pH control.

The overflow from this leach tank flows to a series of two (2) additional leach tanks and four (4) CIL tanks, where the gold now in solution is adsorbed onto 6-12 mesh granular carbon.

Six (6) CIL tanks are present at the mill complex, however tanks #1 & #2 are currently being used as the two (2) additional leaching tanks as their inter-tank screen assemblies are not currently installed. If warranted, tanks #1 & #2 can be commissioned after installation of their interstage screens. The four (4) leach tanks and the four (4) CIL tanks provide a minimum of 36 hours of residence time. Each operational CIL tank is equipped with an interstage screen and a carbon-transfer pump and is agitated to maintain the solids in suspension. Air is injected in the bottom of the pre-aeration tank and in each CIL tank for gold dissolution. Carbon is advanced in the opposite direction to the slurry flow (counter-current) until it reaches CIL tank #3. It can then be pumped to the loaded carbon screen feeding the 3 t strip circuit. The loaded carbon oversize flows to the loaded carbon tank. Fresh and regenerated carbon is added into the last CIL tank.

The solution from the last CIL tank overflow goes to the tails surge tank on the safety screen. The screen prevents the loss of carbon in the eventuality of a failure of the last CIL tank interstage screen. The carbon is recovered at the screen oversize. The screen undersize is discharged to the tailings dam.

From the loaded carbon tank the carbon is transferred to the carbon strip vessel where the gold is removed from the carbon by a concentrated solution of caustic soda and sodium cyanide at 142°C. The pregnant solution flows out of the strip tank through a heat exchanger to an electro winning cell where the gold is plated onto stainless steel electrodes. Periodically the gold sludge is removed from the electrodes by pressure washing. It is then pumped out of the electro winning cell into a filter press where it is dewatered. On a regular basis the sludge is removed from the filter press, dried and smelted in an induction furnace before being poured to produce a doré bar. The tails from the electro winning cell are pumped into a barren solution tank. From there they are pumped through the heat exchanger and an electric inline heater back into the strip vessel. Stripped carbon is transferred from the strip vessel to an acid wash tank where scaling is removed by a 3% nitric acid wash before the carbon is sent through a carbon regeneration kiln. The kiln is operated at 700°C to remove volatile contaminants from the carbon.

The discharge from the kiln falls into a quench tank. New carbon is also added to this tank and, after attrition, it is transferred to the reactivated carbon sizing screen where fine carbon is removed. The oversize from that screen falls into the carbon conditioning tank from where it is transferred to the CIL circuit as required. The original 1 t batch strip circuit remains as an alternative stand-by circuit.