This report details the proposed processing facilities for the Volcan Project, designed as a conventional heap leach operation with a nominal throughput of 60,000 tonnes per day.
Report context
This technical report is dated July 15, 2025, and presents a preliminary economic assessment and NI 43-101 technical report for the Volcan Project. The process plant design, flowsheet, and associated criteria described herein are based on engineering work completed by Ausenco in 2022. The proposed plant is designed to operate 24 hours per day, 365 days per year, treating a life-of-mine feed of 293.2 million tonnes over 14 years.
Processing route
Overview
The process plant includes primary crushing, an overland conveying system, a coarse material stockpile, secondary crushing and screening in closed circuit, tertiary crushing using high-pressure grinding rolls (HPGR), agglomeration and heap stacking, heap leaching, a SART plant, and an adsorption, desorption, and recovery (ADR) circuit employing carbon-in-column (CIC) technology with desorption, regeneration, and a refinery.
Primary Crushing
The primary crushing circuit will consist of a single gyratory crusher designed to treat 60,000 tonnes per day. Run-of-mine material will be delivered to one of two dump locations by 220-ton mine haul trucks. The dump pocket is sized with a 484-tonne capacity. The primary crusher discharges to a surge pocket, also of 484-tonne capacity, which is equipped with an apron feeder to regulate withdrawal of primary crushed material to the overland conveying system.
Overland Conveying
Primary crushed material will be conveyed on the overland conveying system to the coarse material stockpile. The overland conveying system includes a sacrificial conveyor equipped with a tramp metal magnet and metal detector, followed by two flights of overland conveyors with a total length of 6,571 metres. The system is sized for a design capacity of 3,928 tonnes per hour.
Coarse Material Stockpile and Reclaim
Primary crushed material will discharge from the overland conveying system to the stockpile, which is located adjacent to the secondary and tertiary crushing plant. The stockpile has a live capacity of 31,250 tonnes, providing 10 hours of independent operation of the secondary and tertiary crushing plant in the event of a primary crusher outage. Coarse material will be reclaimed from the stockpile by three feeders onto the reclaim conveyor. The reclaim feeders will normally operate simultaneously but have the capacity for two feeders to deliver the crushing plant nominal capacity of 3,125 tonnes per hour. The reclaim conveyor will also receive recirculating secondary crusher product for a total design capacity of 6,863 tonnes per hour.
Secondary Crushing and Screening
The reclaim conveyor will deliver the primary crushed material together with the recirculation from the secondary crushing circuit. The feed will be distributed to two double-deck, banana-type vibrating screens with apertures of 90 mm and 55 mm. The oversize material from each screen will discharge to a 745.7 kW secondary cone crusher at a nominal rate of 1,558 tonnes per hour each. The discharge of the secondary crushers will be recirculated back to the secondary screen feed. The undersize material (less than 55 mm) from the bottom screen deck will discharge to the secondary crushing product conveyor, which feeds the tertiary crushing feed bin.
Tertiary Crushing
The tertiary crushing feed bin has a capacity of 1,302 tonnes, providing 20 minutes of residence time. Secondary crushed material will be reclaimed from the feed bin by two feeders, each regulating feed to one tertiary HPGR crusher at a nominal rate of 1,953 tonnes per hour. Each HPGR will have 2-metre diameter and 2-metre length rolls and will be equipped with two 2,800 kW drives. HPGR edge product (25% of the total) will discharge to two edge product recirculation conveyors, which discharge to the secondary crusher product conveyor. Each HPGR will discharge centre product to a product conveyor, each feeding an HPGR product flake breaker at a nominal 1,563 tonnes per hour. The flake breakers will discharge to the tertiary crusher product conveyor, which feeds the agglomeration feed bin. HPGR centre product will be 80% passing 9.5 mm.
Agglomeration
The agglomeration feed bin will have a live capacity of 3,125 tonnes, providing 1 hour of residence time. Tertiary crushed material will be reclaimed from the feed bin by three feeders, each regulating feed to an agglomeration drum at a nominal rate of 1,041 tonnes per hour. There will be a total of three agglomeration drums, each with a residence time of 60 seconds. Cement for binding the agglomerate will be added to each agglomeration drum feed at a rate of 4 kg per tonne of crushed material. Lime for maintaining pH during the heap leach cycle will also be added to each agglomeration drum feed at a rate of 4 kg per tonne. Barren solution will be added to each agglomeration drum to attain a final agglomerate moisture of 6%. The dimensions of the agglomeration drums will be 4 metres in diameter and 13 metres in length. The agglomeration drums will discharge to the agglomeration product conveyor, which feeds the heap leach stacking system.
Heap Leaching
The heap leach will be a permanent, multi-lift pad placed on an impermeable base with a drainage layer and piping to recover solution from the base of the pad. The nominal area under leach will be 480,000 square metres, and the mass under leach will be 7.2 million tonnes. The heap will be constructed using a conveyor stacking system at a nominal rate of 3,125 tonnes per hour. Each lift of 10 metres in height will have a leach time of 120 days at a nominal irrigation rate of 10 litres per hour per square metre. The maximum height of the heap will be 110 metres.
The solution ponds will be located in the area downslope from the leach pad. The ponds will be connected by shallow overflow ditches to allow extreme event overflow from the pregnant leach solution (PLS) pond to the barren solution pond, and then to the event solution pond. The event pond has a nominal capacity of 210,000 cubic metres and is not sized to provide long-term storage of solution, but to maintain appropriate levels in the other ponds in case of heavy precipitation events. The barren solution discharging from the adsorption system will be collected in the barren solution pond, which has a 90,000 cubic metre capacity. High-strength cyanide solution and antiscalant will be added to the suction sides of the barren solution pumps by metering pumps. Steel headers for the barren solution will run to the leach pad from the barren solution pumps. Strainers and filters will be installed on the barren solution headers to minimise plugging of the drip emitters by fine particles.
The heap will be irrigated with barren solution through buried drip lines and collected in the drainage piping system installed within a layer of drainage material (coarse crushed) placed over the geomembrane liner at the base of the heap. The drainage pipes will transport the solution to the PLS pond, which has a capacity of 170,000 cubic metres. Pumps will pump the PLS solution directly to the absorption facility.
SART Plant
SART is a chemical process that enables the selective recovery of copper, zinc, and silver cyanide complexes from the pregnant leach solution. The principal benefit of utilising SART is to recycle the cyanide back into the leaching circuit while generating a copper concentrate as a by-product. The SART process recovers above 90% of copper associated with cyanide in the PLS, producing a copper concentrate grade greater than 40%. If silver is present in the pregnant solution, it will precipitate together with copper. Gold does not precipitate in the SART process, with losses usually under 1% to the copper concentrate.
For copper removal from the cyanide leach solution, it is necessary to reduce the solution pH to below 4.5 by the addition of sulphuric acid to promote dissociation of the copper cyanide complexes, and subsequently, with the addition of sodium hydrosulphide, to precipitate the copper in solution as copper sulphide. The cyanide that was complexed with copper and that has been released after copper dissociation becomes available as free cyanide in the SART effluent solution, which is then available for gold recovery at the heap pad, reducing the overall cyanide consumption. The cyanide recovery occurs in the primary reactor or precipitation reactor, where the product reports to the copper thickener by gravity.
The copper thickener underflow is transferred to the copper filter feed tank, where copper slurry is neutralised with sodium hydroxide (50% NaOH) to a pH of 11.0. Horizontal plate and frame filters are used to filter the copper concentrate with a copper content higher than 45%. Copper filter cake is dried prior to bagging in maxi sacks ready for storage and transportation to market.
The copper concentrate thickener overflow, containing the recovered free cyanide, is neutralised to a target pH of 10.5 by the addition of lime in a sealed neutralisation reactor tank. The overflow from the neutralisation tank flows by gravity to the gypsum thickener, where flocculant is added. The underflow of the gypsum thickener is recirculated until a target solids percentage is obtained, after which it is filtered in a plate and frame filter before final disposal. The gypsum thickener overflow stream at pH 10.5 and containing the regenerated cyanide flows to the PLS pond.
All process equipment containing low pH solutions are covered with ventilation systems that draw air from the process equipment to a gas scrubber to prevent the escape of hydrogen sulphide (H2S) and hydrocyanic acid (HCN) to the environment. Operation of the SART plant is anticipated to begin one year after the start of heap leach operations. The concentration of copper in the leach solution inventory will increase gradually over this time, and operation of the SART plant before a sufficient level of copper in solution is reached is neither economical nor required.
Adsorption, Desorption, and Recovery (ADR)
The carbon-in-column (CIC) adsorption facility will consist of three trains of five up-flow, open-top, carbon steel columns. Each column will contain 6 tonnes of carbon. A carbon safety vibrating screen will be installed on the barren solution discharge of each train. Any fugitive carbon will be collected and recovered in tote bins.
Pregnant leach solution, pumped at a nominal flow rate of 4,692 cubic metres per hour, equivalent to 1,564 cubic metres per hour per train, will gravity flow through the columns. The gravity flow is counter-current to the carbon, continuing until the carbon contained in the lead column achieves the design gold load of 1.5 kg of gold per tonne of carbon. The loaded carbon will be pumped to the desorption section for gold recovery. Stripped and regenerated carbon will be pumped from the desorption section to Column 5 of each CIC train. Carbon will then be transferred sequentially up the adsorption train from Column 5 to Column 1, counter-current to the descending solution flow. Carbon transfer will be conducted using recessed impeller pumps at a rate of 63 cubic metres per hour.
Loaded carbon from the CIC circuit is later pumped to the loaded carbon screens, where carbon is washed and discharged by gravity into one of two washing vessels. The carbon from the screens is fed into the top of the acid wash vessel, with excess water drained to the floor sump after the complete batch of carbon has been transferred. The carbon in the wash vessel is soaked with prepared cyanide solution, then rinsed with water to remove copper loaded on the carbon. After rinsing, diluted hydrochloric acid is circulated through the wash vessel to remove contaminants. The washed loaded carbon is then transferred to one of two strip vessels.
Carbon stripping uses the split Anglo-American Research Laboratories (AARL) process, which consists of a soak with prepared cyanide strip solution prior to up-flow pumping of tail elution solution from the previous strip batch. One of two strip vessels is loaded with acid-washed carbon and excess water drained to the floor sump. Cyanide soak solution is heated by a propane-fired solution heater and pumped to the strip vessel. Stored tail elution solution from the previous batch is then pumped via a heat recovery heat exchanger and the propane-fired solution heater and flows through the strip column in up-flow. Solution exiting the strip vessel is cooled in the heat recovery exchanger, then reports to the electrowinning feed tank. Once the stored elution tail solution is exhausted, elution continues with heated water, with the solution exiting the strip vessel reporting to the elution tail solution tank for storage in preparation for the next strip cycle.
Gold is recovered from the solution by electrowinning (EW), where it is deposited onto stainless steel wool cathodes as a weak bonded sludge. This sludge is periodically washed off the cathodes and accumulates at the bottom of the EW tank, from where it is pumped to a plate and frame filter. The filtered gold sludge is transferred to trays, which will be periodically loaded into the mercury retort to remove mercury prior to smelting. The retorted sludge is mixed with fluxing materials, then loaded to the smelting furnace. The charge is smelted, then poured into bar moulds, after which the doré bars are cleaned, weighed, and stamped for final destination.
A percentage of the stripped carbon from the elution vessel will be reactivated by thermal regeneration. Carbon is pumped from the bottom of the strip column to a dewatering screen ahead of the carbon rotary kiln. Well-drained carbon feeds the horizontal rotary kiln, reaching a target temperature of 750 degrees Celsius in an inert environment, after which it is cooled by water quench. From the quench tank, carbon is pumped to a carbon sizing screen to remove carbon fines. The fines will be periodically filtered in a plate and frame filter and bagged for sale to recover any gold content present. The carbon sizing screen oversize and stripped carbon which has not been regenerated is combined and returns to the carbon-in-column circuit.
Reagents and Materials Handling
Cyanide will be delivered to site in briquettes contained within ISOTainers. ISOTainers will be received in escorted convoys and placed in a designated storage area. As required, ISOTainers will be presented at the cyanide preparation facility and connected by flexible hoses. Cyanide solution preparation will be carried out by circulating solution from a mix tank through the ISOTainers until the briquettes are fully dissolved, then pumping remnant solution from the ISOTainer to the mixing tank, with a final water rinse prior to disconnecting of the flexible hoses. After preparing solution from each ISOTainer, the solution strength will be confirmed by sampling, and the batch of prepared solution will be pumped to the cyanide solution storage tank. The preparation process can then be repeated with another ISOTainer. Empty ISOTainers will be stored in a designated storage area and backloaded as return freight on the escorted cyanide convoy.
Liquid reagents, including hydrochloric acid, sodium hydroxide, sulphuric acid, and antiscalant, will be received in bulk tank trucks and pumped to storage tanks, from where they will be distributed to various process circuits via individual metering pumps. Lime and cement will be received in dry bulk tanker trucks and will be pneumatically transferred to storage silos adjacent to the agglomeration plant, from where the products will be metered to use points by screw feeders. Other solid reagents, such as flocculant, will be received in maxi sacks, mixed with fresh water to their solution strength setpoints in separate mixing tanks, and stored in holding tanks before being added into the process circuits at various points using metering pumps.
All reagent solutions will be prepared and stored in bermed containment areas with separate berms for acidic and alkaline reagents. The reagent storage tanks will be equipped with level indicators and instrumentation to ensure that spills do not occur during preparation or operation. Ventilation, fire, and safety protections will be provided at the facilities.
Key reported parameters
| Description | Units | Criteria | Basis |
|---|---|---|---|
| LOM feed to plant | Mt | 293.2 | Design |
| Life of mine | years | 14 | Design |
| Plant throughput | kt/d | 60 | Design |
| Solids specific gravity | – | 2.7 | Design |
| ROM bulk density | t/m3 | 1.7 | Design |
| Average moisture | % | 2 | Design |
| Bond ball work index | kWh/t | 16.2 | Design |
| Average head grade Au | g/t | 0.63 | Design (forecast) |
| Average head grade Cu | g/t | 550 | Design (forecast) |
| Recovery Au (to doré) | % | 63.9 | Design (forecast) |
| Recovery Cu (to solution) | % | 18.0 | Design (forecast) |
| Primary crushing availability | % | 70 | Design |
| Secondary crushing availability | % | 80 | Design |
| Tertiary crushing availability | % | 80 | Design |
| Agglomeration and leach stacking availability | % | 80 | Design |
| Wet processing availability | % | 95 | Design |
| Primary crusher quantity | # | 1 | Design |
| Primary crusher type | – | Gyratory | Design |
| Coarse stockpile live capacity | t | 31,250 | Design |
| Secondary crusher quantity | # | 2 | Design |
| Secondary crusher type | – | Cone | Design |
| Secondary screening configuration | – | Closed circuit | Design |
| Secondary screens quantity | # | 2 | Design |
| Screen bottom deck aperture | mm | 55 | Design |
| Tertiary crusher quantity | # | 2 | Design |
| Tertiary crusher type | – | HPGR | Design |
| HPGR product edge recycle | % | 25 | Design |
| Agglomerator type | – | Drum | Design |
| Agglomeration drums quantity | # | 3 | Design |
| Agglomeration residence time | s | 60 | Design |
| Final agglomerate moisture | % | 6 | Design |
| Heap leach type | – | Permanent | Design |
| Lift height | m | 10 | Design |
| Maximum heap height | m | 110 | Design |
| Irrigation rate | L/h/m2 | 10 | Design |
| Piled bulk density | t/m3 | 1.5 | Design |
| Leaching cycles | # | 1 | Design |
| Total primary leach cycle duration | d | 120 | Design |
| Leaching ratio (total) | m3/t | 1.92 | Design |
| Residual moisture (dry basis) | % | 10 | Design |
| Au in PLS | ppm | 0.4 | Design |
| Au in barren | ppm | 0.02 | Design |
| CIC columns per train | # | 5 | Design |
| CIC trains | # | 3 | Design |
| Loaded carbon grade | g Au/t | 1,500 | Design |
| SART plant feed flow rate | m3/h | 800 | Design |
| Cu content target in PLS | ppm | less than 300 | Design |
| Water consumption | m3/t | 0.15 | Design estimate |
| Total water consumption | Mm3/a | 3.31 | Design estimate |
| Total power consumption | kWh/t | 4.98 | Design estimate |
Project website: https://www.tiernangold.com/project/volcan-gold-project/overview/
Technical qualifications
This report is a preliminary economic assessment and NI 43-101 technical report. The process plant has been designed in accordance with engineering practices for heap leach plants. Where data were not available at the time of flowsheet development, Ausenco's criteria for the sizing and equipment selection are based on comparable industry applications, benchmarking, and the use of modelling and simulation techniques. The report presents forecast feed grade and recovery data as design criteria; no historical operating data or testwork results from the Volcan Project itself are provided in the recovery methods section of this technical report.
Source: NI 43-101 Technical Report and Preliminary Economic Assessment, Volcan Project, July 15, 2025, Sections 17.1 through 17.5.3.
