The Windfall Project flowsheet is a proposed design based on laboratory-scale testwork performed at SGS Québec and SGS Lakefield, with no historical operating data available.
Report context
The Windfall Project 2023 Technical Report, dated January 2023, presents a feasibility study for the Windfall Project. The report describes a proposed process plant design with a nominal throughput capability of 3,400 tpd. The flowsheet was established on the basis of laboratory-scale testwork mainly performed at the SGS Québec and SGS Lakefield laboratories, as described in Chapter 13 of the technical report. The resulting flowsheet shows the results of this initial testwork and forms the basis for the plant design.
Processing route
Crushing, Storage and Reclaim
Ore transported from the underground mine will have an F80 of 400 mm. Each rear dump truck from Windfall Mine ramps will carry 50 tonnes per load. A run-of-mine stockpile close to the crushing plant will be primarily utilized for emergency storage. A static grizzly (400 mm), mounted above the ROM bin, and a rock breaker will be installed. Material is withdrawn from below to the vibrating grizzly where the oversize material is directed to an open circuit jaw crusher to further reduce the material to a P80 of 114 mm. A baghouse dust collection system will capture the dust created by the crushing operations. The jaw crusher product and vibrating grizzly undersized are collected on a conveyor belt that feeds the crushed ore silo. The live silo capacity is 4,010 t, or 26 hours of nominal capacity.
Grinding Circuit and Gravity Recovery
The grinding circuit will be a SABC circuit, comprised of a single variable speed SAG mill and a single variable speed ball mill. The SAG mill will operate in closed-circuit with a pebble crusher, followed by a ball mill, operated in closed-circuit with cyclones. The product particle size exiting the grinding circuit cyclone overflow will contain 80% passing 37 µm material.
A SAG mill size of Ø7.32 m x 2.82 m (Ø24' x 9.25') effective grinding length was selected with a total installed power of 2,800 kW to grind the rock to a P80 of 1 mm. The mill is operated with a charge of Ø127 mm steel balls.
A ball mill, Ø5.18 m x 9.5 m (Ø17' x 31') EGL, fitted with a trommel screen, was selected for secondary grinding. The total installed power is 4,200 kW. The ball mill will be charged with Ø50.8 mm steel balls.
The gravity circuit feed pump box at the ball mill trommel undersize will feed two gravity scalping screens via a split box. The undersized material from the screens will feed two gravity concentrators, arranged in parallel. The gold concentrate from both gravity concentrators will feed an intensive leaching reactor operating in batch mode.
Carbon-in-Pulp
Prior to leaching, the ground slurry received from the cyclone overflow will pass through a trash screen before feeding the pre-leach thickener feed box. The pre-leach thickener diameter is Ø24 m. Underflow from the pre-leach thickener at 50% (w/w) will be pumped to the leaching circuit. The leaching circuit consists of one pre-aeration tank and four leaching tanks, each 14 m in diameter, mechanically agitated, and operating in series. The CIP circuit consists of nine CIP tanks operating in carousel mode.
Adsorption, Desorption and Recovery Circuit
The gold recovery circuits are based on the processing of 7 tpd of loaded carbon with a high pressure Zadra process. Carbon elution uses a barren strip solution of 1% NaOH and 0.5% NaCN circulating through the elution column at a flow rate of two bed volumes per hour for 10.5 hours at elevated temperature and pressure. A carbon regeneration kiln reactivates the stripped carbon at a nominal temperature of 700-800°C. Three EW cells recover gold and silver from the pregnant strip solution, with a fourth EW cell dedicated to the ILR pregnant solution.
Cyanide Destruction Circuit
A cyanide destruction circuit treats the CIP tails at 50% (w/w) solids using the liquid SO2/oxygen process. The process occurs in two tanks operating in parallel, providing a total retention time of 2 hours. Liquid SO2 is added from a liquid SO2 storage tank and oxygen gas injected through cone spargers located at the bottom of the tank.
Tailings Filtration Plant
The tailings filtration plant receives Windfall Mill tailings at a nominal throughput of 154 tph (3,400 tpd at 92% availability). The plant also receives thickened sludge from the underground mine (nominal flowrate between 6.9 tph and 9.7 tph). The design includes a 20% design factor, allowing the plant to process up to 196 tph of solids. Based on varying mine backfill requirements over the LOM, filtered tailings are planned to be directed to the paste production circuit approximately 39% of the time and to dry stacking about 61% of the time. Two operating filter presses (third press is on stand-by), each with approximately 600 m² of filtration area, produce a cake at a density of 84% solids.
Key reported parameters
| Description | Unit | Value | Basis |
|---|---|---|---|
| Nominal plant throughput | tpd | 3,400 | Design criteria |
| Plant availability | % | 92 | Design criteria |
| Maximal daily throughput (with design factor) | tpd | 4,080 | Design criteria |
| Average Au feed grade | g/t | 8.06 | Design criteria, from testwork data |
| Average Ag feed grade | g/t | 4.18 | Design criteria |
| Au recovery by gravity circuit | % | 31.2 | Design criteria, from testwork data |
| Ag recovery by gravity circuit | % | 22.4 | Design criteria |
| Grind size to leaching, P80 | μm | 37 | Design criteria |
| Leaching retention time | hr | 36 | Design criteria |
| Au recovery by CIP | % | 90.0 | Design criteria, from testwork data |
| Ag recovery by CIP | % | 79.1 | Design criteria |
| Overall Au recovery | % | 93.1 | Design criteria |
| Overall Ag recovery | % | 83.8 | Design criteria |
| Residual total cyanide at plant discharge (average) | mg/L | 10 | Design criteria |
| Residual total cyanide at plant discharge (maximum) | mg/L | 20 | Design criteria |
| Final tailings slurry density target | % w/w | 48 | Design criteria |
| Tailings filtration plant design factor | % | 20 | Design criteria |
| Filtration plant capacity (design) | tph | 196.4 | Design criteria |
| Paste solid content (average over LOM) | % | 70.2 | Design criteria |
| Paste binder content (average over LOM) | % | 3.11 | Design criteria, interpolated from testwork results by Golder with 20% design factor |
| Paste binder | – | Slag/Cement (90:10) | Design criteria |
| Dry stack solid content | % | 84 | Design criteria |
Project website: https://www.goldfields.com/canada-operations.php
Technical qualifications
The design criteria values presented were derived from testwork data, benchmarked values, BBA's database or based on Osisko's requirements. The paste binder content was calculated based on interpolation of testwork results provided by Golder, with an added design factor of approximately 20% (or about 0.5% absolute). The flowsheet was established on the basis of laboratory-scale testwork, mainly performed at the SGS Québec and SGS Lakefield laboratories. The testwork results are described in Chapter 13 of the technical report. No historical operating data is presented in the recovery methods section. All flowsheet and performance data represent proposed design.
Source: NI 43-101 Technical Report, Feasibility Study for the Windfall Project, Osisko Mining Inc., January 2023. Relevant sections: Recovery Methods (Chapter 17) and Process Plant Design Criteria (Section 17.1).
Consolidated report summaries
The following former standalone pages about this operation were consolidated here on October 25, 2026. They are retained for source traceability; dates and figures reflect each report’s own effective date and may be superseded by the current information above.
Windfall Lake Gold Property — 2023 Technical Report
This report presents the proposed process flowsheet and design criteria for a nominal 1,200 t/d gold concentrator at the Windfall Lake Gold Property, based on metallurgical testwork and experience with similar mineralization.
Report context
This technical report forms part of a Preliminary Economic Assessment for the Windfall Lake Gold Property, located in Québec, Canada, prepared for Eagle Hill Exploration Corp. The metallurgical testwork was completed on several samples from the Windfall Lake gold deposit, providing sufficient data to design the appropriate process flowsheet. The report includes design criteria based on testwork results summarised in Chapter 13.0, as well as experience with similar mineralization. The plant location on the mine site was selected following an economic evaluation of several options.
Processing route
Crushing circuit
Mineralized material will be trucked from the underground mine and dumped into the primary crusher feed hopper, or onto a material stockpile that can be later reclaimed with a front-end loader. Before feeding into the jaw crusher, material will pass through a vibrating grizzly feeder that bypasses approximately 40% of the crusher feed. The grizzly feeder undersize (-18 inches) and the jaw crusher product will be collected on a common conveyor to transfer material to the crushed material stockpile. The grizzly will allow the capture and removal of any large tramp material, preventing damage to the crusher.
Grinding circuit
Mineralized material stored on the crushed material stockpile will be withdrawn with two variable speed apron feeders, each capable of feeding the concentrator at the nominal rate of 1,200 t/d at a controlled feed rate into the run-of-mine (ROM) mill. The ROM mill will operate in wet, SAG grinding mode and will be equipped with a single 2,000 hp motor. The ROM mill will discharge into a pump box, where the pulp will be pumped in closed circuit to a five-hydrocyclone cluster (cyclone size 15 inches) that controls the grinding circuit product size. The overflow from the cluster will constitute the final grinding circuit product and will flow by gravity to the flotation circuit feed conditioner. The cyclone underflow will be returned to the ROM mill feed chute.
Flotation circuit
The cyclone overflow will pass over a trash screen to remove small pieces of trash material, then enter the flotation conditioner where Potassium Amyl Xanthate (PAX), a collector to float the sulphides, will be added. The conditioner will discharge at the overflow toward the flotation circuit feedbox. The flotation circuit will be made up of four rougher and three scavenger 20 m³ flotation tank cells providing a total retention time of 48 minutes. Methyl Iso Butyl Carbinol (MIBC) will be added into the feedbox to produce a stable froth. The rougher tailings will flow to the scavenger flotation cells to minimize sulphide losses. The scavenger concentrate will be pumped back to the rougher flotation feed. The sulphide concentrate from the rougher cells will be pumped to the sulphide cyanidation circuit, while the scavenger flotation tails will be pumped to the non-sulphide cyanidation circuit.
Flotation tails leaching and CIL circuit
From the flotation circuit, the flotation tails will be pumped to the flotation tails high-rate thickener to thicken the slurry to 55% solids. The thickener overflow water will be recycled to the process water tank. The thickener underflow will be pumped directly to the non-sulphide leaching circuit where two leach tanks will operate in series, with a total retention time of eight hours. The feed pH level will be adjusted with lime to approximately 10.5. Cyanide will be added to both leach tanks. After leaching, the slurry will flow by gravity to the tailings CIL circuit comprising six CIL tanks providing 24 hours of residence time. Each CIL tank will be equipped with a single inter-stage screen and a carbon-transfer pump.
Flotation concentrate leaching and CIL circuit
The flotation concentrate will be pumped to the flotation concentrate high-rate thickener to increase the solid content to between 50 and 55% solids. The thickener overflow will be recycled to the process water tank. The thickener underflow will be pumped to the regrind mill feed pump box. The regrind mill will be an IsaMill™ M5000, and will regrind the flotation concentrate to a P80 of 12 μm. Dilution water can be added to reduce leach feed density to 50% solids. The regrind mill product will be pumped to two pre-aeration tanks (combined residence time six hours), where quick lime will be added for pH control and air will be added to reduce sulphide activity. Lead nitrate will also be added to improve gold leaching kinetics. From the pre-aeration tanks, the pulp will overflow to the first of two leaching tanks, with a total retention time of 12 hours. Slurry will then flow by gravity to the concentrate CIL circuit comprising six CIL tanks providing 36 hours of total residence time.
Carbon elution circuit and carbon regeneration
A single carbon elution and carbon regeneration 2.5-ton circuit is planned for treating both flotation circuits' loaded carbon, with each treated independently. Loaded carbon will be washed with a dilute hydrochloric acid solution to remove carbonates. Gold will be desorbed from the carbon by circulating a strip solution (caustic and cyanide) at 140°C and 550 kPa using the Zadra stripping process. The carbon elution circuit should treat a two tonne batch in approximately 12 hours, with one elution per day. The stripped carbon will go to the carbon reactivation kiln, then be discharged into the carbon quench tank of its corresponding CIL circuit. Separate carbon quench tanks are planned for each CIL circuit to avoid carbon mixing.
Electrowinning and refinery
The gold-loaded pregnant solution will be cooled to about 88°C and flow by gravity to the electrowinning flash tank. The solution will be pumped into two parallel electrowinning cells where gold is plated on cathodes. Barren solution will be pumped back to the elution column through an in-line heater for re-heating to 143°C. Loaded stainless steel cathodes and accumulated sludge will be cleaned with a high-pressure washer. Sludge will be filtered using a recessed plate filter, dried, mixed with fluxes, and fed into an electric induction furnace. Molten gold will be poured into doré moulds.
Cyanide destruction
Two dedicated cyanide destruction systems are required, one for the flotation concentrate stream and one for the flotation tails stream. Cyanide will be eliminated using the SO₂-air process with sodium metabisulphite. Copper sulphate will be added as needed to catalyze the reaction. The non-sulphide tails will be gravity fed to the combined tailings pumpbox, where they will be mixed with the sulphide circuit rejects. The tailings line is 4.5 km long and slurry will be pumped by a train of three pumps in series.
Reagents
Reagents used throughout the process include: PAX collector, MIBC frother, quicklime for pH control, lead nitrate for gold leaching kinetics, sodium cyanide for gold leaching and carbon stripping, hydrochloric acid for carbon acid wash, sodium metabisulphite for cyanide destruction, copper sulphate as catalyst, sodium hydroxide for carbon stripping and acid neutralisation, descalant to reduce calcium carbonate deposits, and flocculent for thickener settling.
Key reported parameters
| Parameter | Unit | Value | Source |
|---|---|---|---|
| Plant – General | |||
| Mineralized Material Processing Rate – Nominal | t/d | 1,150 | A |
| Concentrator Design Factor | % | 20 | C |
| Mineralized Material Processing Rate – Design | t/d | 1,500 | C |
| Production Target (dry) | t/y | 420,000 | E |
| Operating Hours per Day | h/d | 24.0 | A |
| Concentrator Feed | |||
| Au Grade – Nominal | g/t | 8.34 | A |
| Ag Grade – Nominal | g/t | 8.34 | A |
| Sulfur Grade – Nominal | % | 7.06 | I |
| Gold Recoveries | |||
| Concentrator Gold Recovery | % | 95.7 | I |
| Concentrator Silver Recovery | % | 74.4 | I |
| Grinding Circuit | |||
| Feed Size – Passing (F80) | µm | 150,000 | C |
| Final Product Target Size – Passing (P80) | µm | 70 | I |
| Bond Ball Mill Work Index – Nominal | kWh/t | 9.80 | I |
| Bond Ball Mill Work Index – Design | kWh/t | 11.50 | I |
| Flotation Circuit | |||
| Sulphide Recovery | % | 98.57 | I |
| Flotation Mass Pull | % | 25 | I |
| Total Retention Time (Rougher + Scavenger) | min | 48 | C |
| Concentrate CIL Circuit | |||
| Total Pre-aeration Time | h | 6 | C |
| Total CIL Time | h | 36 | C |
| Number of Leach Tanks | – | 2 | C |
| Number of CIL Tanks | – | 6 | C |
| Tailings CIL Circuit | |||
| Total CIL Time | h | 24.00 | C |
| Number of Leach Tanks | – | 2 | C |
| Number of CIL Tanks | – | 6 | C |
| Reagents (Design) | |||
| Grinding Media | kg/t of feed | 0.70 | C |
| Xanthate (PAX) | g/t of feed | 25.00 | C |
| MIBC | g/t of feed | 15.00 | C |
| Lime | kg/t of feed | 1.20 | C |
| Sodium Cyanide | kg/t of feed | 1.50 | C |
| Sodium Metabisulphite | g/t of feed | 1,500.00 | C |
| Copper Sulphate | g/t of feed | 225.00 | C |
Project website: https://finance.yahoo.com/news/eagle-hill-exploration-purchases-windfall-110000259.html
Note: Source codes – A: Criteria Provided by Owner; C: Soutex Recommendation; E: Criteria from Process Calculations; I: Metallurgical Test Results/Operating Data Provided by Owner.
Technical qualifications
The design criteria and process flowsheet presented in this report are based on metallurgical testwork results, as summarised in Chapter 13.0, and experience with similar mineralization. The report constitutes part of a Preliminary Economic Assessment. Several design criteria are specifically noted as assumptions from similar projects, standard industry practice, or Soutex recommendations where testwork data was not directly available. The source codes provided in the design criteria table indicate the basis for each parameter, distinguishing between owner-provided data, test results, process calculations, assumptions, and engineering design practice.
Source: Windfall Lake Gold Property, Québec, Canada – Preliminary Economic Assessment, Eagle Hill Exploration Corp., Report No. 1489360100-REP-R0009-03, Section 17.0 Recovery Methods.
