Update of the Mineral Resource Estimate – Kiena Mine Complex

This report provides an update of the mineral resource estimate for the Kiena Mine Complex, incorporating historical processing data and proposed modifications for two future operational phases.

Report context

The technical report is dated January 2021 and presents an update of the mineral resource estimate for the Kiena Mine Complex, owned by Wesdome Gold Mines Ltd. The recovery methods chapter text and figures were taken directly from the 2020 Preliminary Economic Assessment (PEA) of the Kiena Mine Complex project, issued on June 17, 2020 and effective as of March 31, 2020. The 2020 MRE update does not have a negative impact on or otherwise adversely affect the mineral resource inventory that formed the basis of the 2020 PEA. The results and conclusions of the 2020 PEA are still considered current and have been carried-over for this report. Information on historical mineral processing at the Kiena mine was based on the “NI 43-101 Technical Report and Mineral Resource Estimate for the Kiena Mine Complex" in Val-d'Or, Quebec dated November 7, 2019 (Richard and Torrealba, 2019), which presented available information from Anon, 1983 and Dupont, 1996.

Processing route

The Kiena Mine processing plant became operational in September 1984. A conventional gold recovery process involving cyanidation and conventional carbon-in-pulp (CIP) was used. The principal process steps included crushing, grinding, leaching by cyanidation, gold adsorption and desorption, electrolysis, cyanide destruction, melting and casting of doré bars.

Crushing circuit

The crushing circuit starts underground with a Birdsboro Buchanan jaw-crusher, reducing the rock size to 6 inches. The former design plant throughput is 1,250 tpd, however, with the addition of a screen and cone crusher, the plant has run as high as 2,000 tpd in the past. Crushed material receiving facilities start with a 35-tonne capacity hopper equipped with a 30" x 10' vibrating feeder and a 30-inch belt conveyor, which transfers crushed material onto the existing No. 1 belt conveyor. Conveyor No. 1 transports crushed material to two coarse rock silos, each with a capacity of 600 tonnes. Material discharged from the silos is conveyed, screened and crushed to approximately 1¼" (32 mm) using a standard cone crusher (150 kW) operating in open circuit. Crushed and screened material is stored in a 1,800-tonne silo, then conveyed by vibrating feeders to the grinding circuit via a belt conveyor.

Grinding circuit

Mineralised material will be ground in a 1,000 hp semi-autogenous (SAG) mill (11'6" x 18'8") operating in open circuit, followed by a 900 hp ball mill (10'6" x 13') operating in closed circuit with two stages of cyclones for classification. If necessary, cyanide and lead nitrate can be added at the SAG mill and ball mill. The pH is controlled using quicklime in the feed to the SAG mill. Cyclone underflow is redirected to the ball mill for further grinding. Based on potential future gravity testwork, a gravity circuit (currently not shown on the process flow diagrams) may be installed and fed by a portion of the feed or cyclone underflow (to be confirmed by testwork). Cyclone overflow is pumped to a vibrating 20-mesh screen to remove trash, with screen underflow directed to a 65-ft diameter process thickener to increase pulp density.

Cyanidation

Thickener overflow is pumped to a series of three carbon column tanks where gold in solution is adsorbed by carbon. The last carbon column overflows into a carbon screen, with oversize sent to the second CIP tank and screen undersize (solution with cyanide) recycled to the grinding circuit as grinding solution. Thickener underflow is forwarded to a series of three leach tanks. Cyanide and quicklime are added to the leach feed, with lead nitrate and oxygen added to optimize gold dissolution and control pH. Retention time in the carbon columns and leach tanks is approximately 11 minutes and 36 hours respectively, based on a plant feed of 1,250 tpd.

Carbon-in-pulp process

Leach tails are pumped to the CIP circuit, composed of five CIP tanks in series. Slurry is fed at the first CIP tank. Activated carbon is fed at the last CIP tank and pumped in counter-current mode relative to the slurry. NaAu(CN)₂ molecules in solution are held by activated carbon through adsorption. Discharge from CIP tanks is pumped to a 28-mesh safety screen to recover any carbon particles. In Phase 1, slurry is sent to primary and secondary backfill cyclones, with underflow (coarse particles) sent to the backfill plant and fine particle overflow directed to the 75-ft diameter waste-thickener, from which fine slurry is sent to tailings.

Loaded carbon is pumped to the elution vessel, where gold desorption takes place using the Zadra process at 140°C and 80 psi. Pregnant solution is pumped through an electrowinning cell where gold is recovered by plating on steel wool cathodes. Cathodes are washed under pressurized water and dried sludge is melted in an induction furnace to produce doré bars.

Acid wash and carbon regeneration

Once desorption is complete, carbon is transferred to the wash vessel where it is washed with hydrochloric acid. It is then forwarded to the regeneration furnace where it is heated to 1,050°C. Finally, carbon is screened to the desired grain size for reuse.

Cyanide destruction circuit and tailings treatment

To support the planned higher tonnage in Phase 2 (year 2024 and beyond), the current process plant cyanide destruction circuit, which is not operational, will be refurbished. A filtered tailings circuit will also be added. The cyanide destruction (CND) circuit will treat thickened CIL residue slurry (tailings thickener underflow) at 60% (w/w) solids and the overflow of backfill cyclones. Addition of process water will be required to set the CND feed at 50% solids. Cyanide destruction uses the Inco SO₂/Air process.

The CND process concept considers two reaction tanks arranged in series (or parallel), providing a retention time of one hour (to be confirmed in future testwork). Liquid SO₂ is added to the tanks and process air is injected through cone spargers at the bottom of each tank to oxidize cyanide species. Copper sulphate is added to catalyze the reaction, and hydrated lime addition controls pH in each tank. An agitator in each tank ensures mixing and gas dispersion.

For the dry stack initiative, a filter plant will be installed in Phase 2. Feed to the filter plant (30 tpd capacity) at approximately 50% solids will be processed by a pre-filter thickener that increases solids to 60%. Underflow feeds a stock tank acting as buffer for the filter press circuit (two in operation, one stand-by). Dry product at 85% solids will be trucked to the tailings storage facility (TSF), and filtrate will be pumped back to the pre-filter to remove suspended solids.

Reagent systems

Reagents used in the process plant include sodium cyanide (tanker delivery, liquid, no preparation required), quicklime (truck delivery, solid, mixing tank with water addition), flocculant (bag delivery, solid, eductor and mixing tank), activated carbon (super sack delivery, solid, attrition tank mixing), anti-scalant (drum delivery, liquid, no preparation), caustic soda (tanker delivery, liquid, dilution tank), HCl (tote delivery, liquid, dilution tank), lead nitrate (super sack delivery, solid, mixing tank), liquid SO₂ (tanker delivery, liquid, pressurized system, no preparation), and copper sulphate (super sack delivery, solid, mixing tank). It is assumed that site storage capacities are sufficient for each reagent or consumable due to the lower than design throughput.

Key reported parameters

Notes: Phase 1 design values selected from highest throughput for years 2021 to 2023. Phase 2 design values selected from highest throughput for year 2024 and beyond. Grind size basis noted as based on former operation, to be confirmed in prefeasibility stage. Overall Au recovery basis noted as based on latest testwork, to be confirmed in next phase of testwork. Past throughput of up to 2,000 tpd has been processed.

Technical qualifications

The report states that due to differences in tonnage during the two operational phases, it is recommended to investigate the feasibility of using only one grinding mill (SAG or ball mill) when tonnage is less than 470 tpd, and to explore addition of variable speed drives in the mills to accommodate tonnage variations along the LOM. It is recommended to conduct an audit to validate the absence of cyanide destruction circuit during the first two years of operation. It is also recommended to investigate remaining capacity of the existing TSF to confirm need and timing for a new facility, perform a full inspection of cyanide destruction equipment available at site, and investigate location of future filter plant. More analyses and modelling are required for the new dry stack tailings management facility. A geochemical kinetic test (acid rock drainage and metal leaching) should be carried out on representative mineralized material samples from new mining zones or on representative tailings samples produced during metallurgical testing for new zones. Environmental baseline studies must be carried out early at the dry-stack location.

*Source: NI 43-101 Technical Report – Update of the Mineral Resource Estimate – Kiena Mine Complex, Wesdome Gold Mines Ltd., January 2021.*