Tijirit Project — Technical Report (PEA)

This preliminary economic assessment describes a conventional gravity and cyanide leaching plant designed for two production phases at the Tijirit Project in Mauritania, with an average daily throughput increasing from 2,976 tonnes in Phase 1 to 4,500 tonnes in Phase 2.

Report context

The Technical Report for the Preliminary Economic Assessment (PEA) of the Tijirit Project, Mauritania, presents process design criteria, flowsheet development, and equipment selection for a gold recovery plant. The report, dated in accordance with National Instrument 43-101 standards, is preliminary in nature and includes inferred mineral resources considered too speculative geologically to have economic considerations applied to enable categorization as mineral reserves. The proposed processing facility is designed for two distinct phases: Phase 1 processes higher-grade mineralisation from the Eleonore deposit, while Phase 2 processes lower-grade material from the Lily and Sophie mining zones.

Processing route

Crushing circuit

Run of mine (ROM) mineralised rock is delivered by 55-tonne haul trucks to the crusher feed stockpile area. Material is either directed into the crushing circuit feed hopper or stored in one of two stockpiles (divided into high-grade and low-grade material). Each stockpile has a live capacity of 6,000 tonnes and can be blended to stabilize plant feed grade when multiple pits are mined simultaneously.

ROM is fed to a 132 kW jaw crusher, with a variable speed apron feeder transferring crushed material onto the crushed rock conveyor. The apron feeder speed controls crushing circuit throughput. During Phase 1, the jaw crusher open side setting is 100 mm, producing crushed material with an 80% passing size of about 98 mm. For Phase 2, the open side setting increases to 150 mm, producing material with an 80% passing size of about 143 mm. A bag house-type dust collector controls dust emissions.

Crushed material is conveyed to a Coarse Mineralised Rock Stockpile with a live capacity of 4,500 tonnes, providing up to one day of feed during Phase 2 and one and a half days during Phase 1.

Grinding and gravity circuits

The Phase 1 grinding circuit is a single-stage arrangement consisting of a SAG mill operating in closed circuit with a hydrocyclone cluster. A re-circulating load of 400% was selected for equipment sizing. The targeted cyclone overflow size is 80% passing 105 microns. The SAG mill, with installed power of 3,300 kW, operates in open circuit configuration. SAG mill discharge passes over a trommel screen, with oversize pebbles recycled internally via a water jet system. Phase 1 does not include a pebble crusher.

For Phase 2, the circuit transitions to a two-stage SAG/ball mill arrangement. Additions include a pebble cone crusher (185 kW installed power), a ball mill (3,300 kW), a larger capacity hydrocyclone cluster, and an additional gravity concentrator. The SAG mill trommel oversize will be conveyed to the cone crusher and returned to the SAG mill. Hydrocyclone underflow is divided; one stream equivalent to fresh feed gravitates to gravity concentration, with the balance returned to the SAG mill. The ball mill trommel undersize directs to the hydrocyclone feed pump box.

The gravity concentration circuit includes a trash and oversize screen and a gravity concentrator that operates semi-continuously, using centrifugal forces to separate liberated coarse gold. Oversize material returns to the hydrocyclone feed pump box. Fluidization water removes fine low specific gravity material. After the concentration cycle, feed slurry bypasses the concentrator, and flush water pushes free gold to concentrate discharge. The concentrated free gold gravitates to the Intensive Leach Reactor circuit.

Leaching, CIL and carbon circuits

Ground mineralised rock from the hydrocyclone overflow gravitates through a trash screen to the CIL circuit. The circuit comprises seven tanks: one pre-aeration tank, one leach tank, and five CIL tanks. Total circuit residence time is 48 hours for Phase 1 and 30 hours for Phase 2, including two hours of pre-aeration. No circuit modifications are required for Phase 2 given the greater residence time requirement in Phase 1. Equipment selection includes a 910 m³ pre-aeration tank, a 2,000 m³ leach tank, and five 2,000 m³ CIL tanks.

Air is injected at tank bottoms to maintain dissolved oxygen levels. Hydrated lime slurry maintains slurry pH above 10 to prevent dangerous hydrogen cyanide gas formation. Sodium cyanide is added to the leach and first CIL tank. Activated carbon in the CIL tanks adsorbs dissolved gold, with carbon advanced counter-currently using carbon advance pumps. The fifth CIL tank receives fresh or barren carbon and discharges mostly barren slurry to the tailings thickening circuit via a safety screen to prevent fine carbon carryover.

Elution, electrowinning and gold room

Gold-laden carbon is pumped to the elution circuit, selected as AARL type. A 3-tonne acid wash column and 3-tonne elution column are included. Loaded carbon from the first CIL tank passes through a loaded carbon screen; screen undersize returns to the first CIL tank, while oversize enters the acid wash column. Hydrochloric acid dissolves carbonate scale. The elution process uses pre-soak solution prepared with sodium hydroxide and sodium cyanide, followed by heated water circulation to desorb gold into pregnant solution. A diesel-fired indirect heating system heats barren solution. Water quality requirements specify total dissolved solids below 500 mg/L, ideally below 350 mg/L, necessitating a water treatment system and anti-scalents.

The pregnant solution undergoes electrowinning in two independent cells, one each for elution pregnant solution and ILR pregnant solution. Electrowinning deposits gold on cathodes, which is washed off, dewatered in a manually operated filter press, dried, mixed with flux, and melted in a diesel-fired furnace to pour bars. No changes are required to the electrowinning and gold room circuits for Phase 2, only the frequency of electrowinning and gold pours. Barren solution from elution returns to the circuit, with a portion purged to the CIL circuit to prevent contaminant buildup. Carbon regeneration uses a rotary kiln heating carbon to about 700°C, with regenerated carbon cooled and returned to the fifth CIL tank.

Phase 2 modifications include additional reclaim feeder arrangements, a pebble crusher, a ball mill, a larger hydrocyclone cluster, and an additional gravity concentrator to accommodate increased throughput and reduced grind size.

Tailings dewatering and storage

The project uses a dried stacked tailings storage approach. Slurry from the fifth CIL tank is fed to an 18 m diameter high-rate thickener via a safety screen. The thickener concentrates tailings from 40% w/w to more than 60% w/w using flocculant. Thickener overflow is recovered as process water, with residual cyanide recycling to reduce overall cyanide consumption. Thickener underflow is pumped to a vacuum disc filter with 175 m² of filtration area. Filter cake undergoes washing to recover cyanide-containing water, with filtrate and wash water combined with thickener overflow and recycled. Filter cake is stored in a stockpile, loaded into trucks by front-end loaders, and transported to the tailings storage facility. Target filter cake moisture is less than 15% w/w. For Phase 2, thickener underflow pumps will be replaced for higher capacity, and a second vacuum disc filter with 140 m² area will be added.

The tailings stockpile is built in cells to facilitate rehabilitation, with the base not covered with a geomembrane. Preliminary tests on acid generation potential were inconclusive. Run-off water is recycled for process use.

Consumables and reagents

Reagents and consumables for the process include hydrated lime (pH control), sodium cyanide (gold leaching and barren liquor preparation), sodium hydroxide (pH control in elution and cyanide preparation), hydrochloric acid (acid wash), activated carbon (gold adsorption), flocculant (thickener), leach aid (free gold leaching), antiscalant (scale reduction in elution and electrowinning), flux (smelting), SAG and ball mill grinding media, crusher and mill liners, and filter cloths.

Intensive leaching

A separate Intensive Leach Reactor (ILR) circuit treats free gold concentrate from gravity concentrators on a batch basis. The ILR uses sodium hydroxide, sodium cyanide, hydrogen peroxide (as needed), and a leaching aid. Each batch produces ILR tailings (returned to the grinding circuit) and ILR pregnant solution (stored for electrowinning). The selected ILR unit has a 6-tonne batch capacity, requiring approximately 4 batches per week during Phase 1 and 6 batches per week during Phase 2. The ILR circuit can accommodate both phases by modifying batch frequency. The elution circuit operates on a similar batch basis, with a cycle performed approximately once daily during Phase 1 and twice daily during Phase 2.

Phase 2 modifications summary

To achieve Phase 2 throughput and grind size targets, several circuit changes are required: an additional reclaim feeder (two operating and one standby); a pebble cone crusher in the SAG mill circuit; a ball mill to convert the grinding circuit from single-stage to two-stage; a larger hydrocyclone cluster; additional gravity concentration capacity including a second trash and oversize screen and gravity concentrator; replacement of hydrocyclone feed pumps and thickener underflow pumps; and a second vacuum disc filter. The hydrocyclone feed pump box is already sized for Phase 2 throughput, and the SAG mill feed conveyor is sized for higher throughput.

Key reported parameters

Technical qualifications

The report includes a cautionary statement that the PEA is preliminary in nature, includes inferred mineral resources considered too speculative geologically to have economic considerations applied to enable categorization as mineral reserves, and there is no certainty that the PEA will be realized. Mineral resources that are not mineral reserves do not have demonstrated economic viability.

Specific technical limitations identified in the report include:

• Preliminary acid generation potential tests on tailings were inconclusive, requiring additional testing to evaluate the actual acid generation potential for each deposit.
• The tailings stockpile base will not be covered with a geomembrane, with only preliminary testing of acid generation potential conducted.
• The tailings thickener has been sized for Phase 2 throughput without modification, but thickener underflow pumps must be replaced for higher capacity.
• Phase 2 requires modifications to the grinding circuit including a pebble crusher, ball mill, and additional gravity concentration capacity.
• The SAG mill operates in open circuit configuration, with a recirculating load of 400% selected for equipment sizing.
• Trade-off studies were produced comparing three different grinding circuit scenarios and two different grind sizes (75 microns versus 105 microns) for Phase 1 to select optimal conditions for the flowsheet.

Source: Technical Report for the Preliminary Economic Assessment of the Tijirit Project, Mauritania, Sections 1.14, 17.3, 17.4, and 17.4.3.