The 2018 PEA for the Madsen Gold Project outlines a conceptual process flowsheet based on an existing milling circuit previously operated at the site in the late 1990s, with design assumptions derived from historical operating data rather than new metallurgical testwork.
Report context
This technical report for the Madsen Gold Project is dated January 29, 2018, and documents a Preliminary Economic Assessment (PEA). The report describes a conceptual process for processing underground mine run (PMR) through an existing milling circuit that was originally installed at the Dona Lake Mine in late 1989 to early 1990, then moved to the Madsen site by Claude Resources and operated from 1997 through 1999. The mill has been shut down since 1999.
Processing route
Material handling and crushing
PMR would be hauled from the Madsen portal to a portable crusher unit on the mill apron. The sized material would be delivered into a 600 tonne storage bin located on the mill apron. PMR from the storage bin would be transported to the SAG mill via a SAG mill feed conveyor. The ore is discharged from the mine coarse ore bin using a coarse ore vibratory feeder. A weightometer is included on the SAG mill feed conveyor to measure the feed rate, and a magnet removes tramp steel from the mill feed.
Grinding circuit and gravity recovery
PMR, typically with a maximum size of 15 cm, would be reduced in a grinding circuit consisting of a primary SAG mill followed by a secondary ball mill. The SAG mill is 4 m diameter by 1.5 m long, equipped with a 260 kW wound rotor induction motor, and operates as a grate discharge mill with grate openings of about 1.3 cm. The SAG mill discharge is pumped across a 10 mesh sizing screen; oversize reports back to the SAG mill and undersize material reports to a pump box, then to a set of 38 cm hydrocyclones. Cyclone underflow reports to a 2.4 m diameter by 3.6 m long overflow discharge ball mill equipped with a 340 kW motor. The ball mill discharge joins with the SAG mill undersize to feed the hydrocyclone bank. PMR would be reduced from a top size of 15 cm down to 80% passing 100 microns in the grinding circuit.
A single Falcon concentrator is included in the underflow stream of one of the hydrocyclones in the grinding circuit to recover any coarse free gold from the mill feed. The Falcon concentrate reports to a concentrate surge tank and is then transported via pump to the refinery area. A gravity concentration table further upgrades the Falcon concentrate prior to processing in the induction furnace to produce bullion bars. Gravity concentrator tailing is returned to the cyclone feed pump box.
Pre-leach thickening
The cyclone overflow (ground feed) passes over a screen for wood and trash removal ahead of the gold recovery circuits. Slurry is thickened to about 50 percent solids in a 15 m diameter pre-leach thickener. Water removed is recycled back into the grinding process. Thickened slurry is pumped to the first tank in the cyanidation circuit at approximately 55 percent solids.
Cyanidation circuit
The cyanidation circuit consists of a series of five agitated leach tanks. The first tank is a pre-aeration tank where air is injected to pacify cyanide-consuming species in the feed. At a processing rate of 600 tonnes per day, the residence time in each of the five cyanidation tanks is about 10 hours per tank. Starting at the number 2 leach tank, sodium cyanide is stage added to facilitate the dissolution of gold. Lime is used to maintain alkalinity at about pH 11, and lead nitrate is also stage added.
Carbon-in-pulp (CIP) circuit
Slurry from the cyanidation tanks passes across a trash screen prior to being pumped to the CIP tanks. The CIP circuit consists of six agitated tanks with a residence time of about one hour for each tank at the anticipated mill feed rate. Gold is transported from the solution phase of the slurry onto the surface of activated carbon contained in each CIP tank. Carbon movement in the CIP circuit is counter flow to the slurry: carbon is advanced from tank 6 to tank 1, while slurry moves from tank 1 to tank 6. Interstage screens in each CIP tank allow carbon to remain captive while slurry flows through by gravity. Loaded carbon is removed from tank 1 and advanced to the strip circuit. Slurry depleted of gold content discharges from the last CIP tank (tank 6) and passes over a safety screen to capture any escaping carbon, then is pumped to the tailing storage area.
Elution and carbon regeneration
Loaded carbon is advanced from the number 1 CIP tank to a one tonne carbon strip vessel. Stripping is carried out under elevated temperature and pressure on a batch basis, with one tonne batches processed every 24 hours. Loaded solution from the strip circuit is advanced to the electrowinning circuit. Stripped or barren carbon is discharged and fed to a carbon re-activation kiln to burn off impurities and restore carbon activity before it is re-circulated back into the number 6 CIP tank.
Electrowinning and refining
Gold is recovered from loaded strip solution in an electrowinning cell equipped with stainless steel wool cathodes. Gold is deposited on the surface of the steel wool using electrochemical principles. The gold is washed off the steel wool and then dried. Both the dried sludge from the electrowinning process and the gravity product are melted at high temperature in an induction furnace to produce high grade doré bars containing gold with silver and other minor impurities. Bullion bars are sent to an external refiner for further upgrading.
Cyanide destruction
The report states that it has not been confirmed if cyanide destruction will be required. The assumption for this PEA is that tailings will be pumped to the existing tailing storage, where residual cyanide and metals will dissipate by natural degradation. This item is noted as requiring further modelling or testing in the next phase of work.
Tailing management
The tailings management facility at the Madsen Gold Property has been in operation since the late 1930s and has undergone several modifications. In the 1950s, containment structures were constructed using tailings. In 1997, two rock fill tailings dams were constructed to create a distinct tailings pond and a polishing pond. Subsequent modifications have been made to address stability and flood routing issues. The existing TMF was designed to withstand a 100-year rain or snow event. It is anticipated that the current available capacity in the tailings pond will need to be extended for the envisioned project.
Key reported parameters
| Parameter | Value | Units | Basis |
|---|---|---|---|
| Mill feed rate (design) | 600 | tonnes per day | Historical operating data |
| Mill feed rate (design) | 23 | tonnes per hour | Historical operating data |
| PMR top size to grinding | 15 | cm | Design assumption |
| Grinding product size | 80% passing 100 | microns | Design target |
| SAG mill dimensions | 4 m diameter x 1.5 m long | Existing equipment | |
| SAG mill motor | 260 | kW | Existing equipment |
| Ball mill dimensions | 2.4 m diameter x 3.6 m long | Existing equipment | |
| Ball mill motor | 340 | kW | Existing equipment |
| Pre-leach thickener diameter | 15 | m | Existing equipment |
| Pre-leach thickener underflow solids | 50 | % | Design target |
| Number of cyanidation leach tanks | 5 | Existing circuit | |
| Leach tank residence time per tank | 10 | hours | At 600 tpd design rate |
| Number of CIP tanks | 6 | Existing circuit | |
| CIP tank residence time per tank | 1 | hour | At 600 tpd design rate |
| Strip vessel capacity | 1 | tonne | Batch basis, every 24 hours |
| Historical gold recovery range | 90 – 94 | % | Actual operating data |
| Assumed gold recovery in PEA | 92 | % | Routinely achieved during operation |
| Mill operating cost (with contingency) | 28.27 | $/tonne milled | Estimated |
| Mill capital cost (with contingency) | 11,019,000 | $ | Estimated refurbishment |
| Power consumption | 30.0 | kWhr/tonne | Assumed |
| Power cost | 0.10 | $/kWhr | Assumed |
Project website: https://westredlakegold.com/madsen-mine/
Technical qualifications
The report states that metallurgical testing has not been completed to establish the design criteria for this PEA study. All assumptions regarding reagent consumption and mill recovery have been derived from actual operating data from the plant when it operated at the Madsen Mine from 1997 through 1999. The report notes that during the operating period, ore from the McVeigh deposit made up a portion of the mill feed and that when consistent feed came from the McVeigh deposit, historical data showed recoveries higher than 92%. The report also notes that relatively low recoveries achieved during the 1990s are attributable to fluctuations in tonnage of daily feed available and that feed came from multiple deposits including the number 1 Shaft area and the Buffalo deposit, which accounted for feed grades consistently lower than planned.
The report also states that it has not been confirmed if cyanide destruction will be required, noting that further modelling or testing is needed in the next phase of work. The existing mill has been shut down since 1999, and all electrical equipment will require testing for serviceability as a next step. The capital estimate includes an allowance for replacement and repair of electrical gear as required.
*Source: Madsen Gold Project PEA, January 29, 2018, Section 17 – Recovery Methods*
