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Mineralized material stored on the crushed material stockpile will be withdrawn with two variable speed apron feeders, each capable of feeding the concentrator at the nominal rate of 1,200 t/d at a controlled feed rate into the run-of-mine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

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.

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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.