Segilola Gold Project — 2019 Technical Report

This report summarizes the designed mineral processing route for the Segilola Gold Project, including crushing, grinding, gravity recovery, CIL, elution, and gold refining, as described in the 2019 Technical Report.

Report context

The Segilola Gold Project processing plant design is described in the 18 March 2019 Technical Report prepared for Thor Explorations Ltd. (Project # 3043). The design supports a nominal ore throughput of 81.3 tph, a design throughput of 84.5 tph, and an average life-of-mine annual production of 625,000 tpa. The flowsheet is based on conventional and well-proven technology.

Processing route

Plant design basis

The process plant is designed to operate 365 days per year, 24 hours per day, with a design utilization of 91.3%. Initial design was for 500,000 tpa ROM throughput, increased during the DFS to 650,000 tpa. Yantai conducted a cost adjustment exercise for the increase, estimating incremental capital costs of $2,732,000, included in the project capital estimate. The change was not fully shown in the final DFS engineering detail and was to be incorporated during front end engineering design.

Major modifications included:

• Crushing: no equipment modification; utilization increased from 38.04% to 49.45%
• Grinding: larger SAG mill, ball mill, and motors
• Leaching: larger CIL, CIL, and detox tanks, blowers, and pumps
• Power: an additional 1,200 kW generator

Crushing and stockpile

ROM ore with nominal top size of 600 mm will be delivered by haul trucks to the ROM pad, either dumped directly into the ROM bin or stockpiled. A mobile rock breaker will clear bridging on the static grizzly. The crushing circuit consists of a single-stage jaw crusher sized for 150 tph, reducing ore from 600 mm to a product top size of 160 mm, operating approximately 13 hours per day. Crushed product will be transferred to a crushed ore stockpile, then withdrawn by two apron feeders onto the mill feed conveyor. Hydrated lime for pH control will be added directly onto the mill feed conveyor.

Grinding and classification

The grinding circuit comprises a SAG mill and ball mill in closed circuit with hydrocyclones, with design throughput of 81.5 dry tph and grind product size P80 of 106 µm. The SAG mill is 5.5 m diameter by 3.0 m long, driven by a 1.2 MW motor with variable speed drive. The ball mill is 4.06 m diameter by 7.5 m long, powered by a 1.75 MW motor. SAG mill discharge passes over a trommel screen; oversize is collected, undersize gravitates to the common mill discharge sump, then to the cyclone cluster. Two-thirds of cyclone underflow returns to the ball mill feed chute and one-third reports to the gravity circuit. Cyclone overflow at 40% solids by weight and P80 of 106 µm gravitates to a vibrating trash screen to remove wood, organics, and plastics.

Gravity concentration and intensive cyanidation

One third of cyclone underflow gravitates to a Knelson concentrator scalping screen removing +2 mm material; screen oversize and remaining underflow return to the ball mill feed chute. Screen undersize reports to the Knelson concentrator for free gold recovery. The concentrator operates in batch mode; concentrate is flushed to a settling cone and drained into an Acacia reactor every 24 hours for intensive cyanide leaching. Cyanide, sodium hydroxide, and leach aid are mixed in a heated intensive cyanidation reactor (ICR) solution storage tank. Pregnant solution is transferred to the ICR pregnant solution tank, with gold recovered by dedicated electrowinning. Barren solution returns to the CIL tanks, and leached solids are washed to remove residual cyanide before returning to the ball mill feed box.

CIL plant

Gold and silver leaching occurs in a conventional CIL circuit with five leach tanks (no carbon) and five adsorption tanks containing activated carbon, allowing reduced carbon inventory and reduced locked gold. Total combined leach and adsorption residence time is 48 hours. The adsorption stage has 20 hours total residence time. Cyanide solution is dosed through a ring main into the leach feed splitter box. Loaded carbon is lifted by air lifters onto a loaded carbon screen; slurry returns as undersize, and clean carbon is discharged as screen oversize to the column. Barren carbon returning from the reactivation kiln is screened to remove fines and reports to CIL Tank 5. Leach tails gravitate to the detoxification section. A vibrating carbon safety screen recovers carbon passing through worn screens; recovered carbon is collected for return or alternative processing.

Elution and electrowinning

Loaded carbon is washed and enters the elution column. Elution is carried out at 150°C and 0.5 MPa with 5% NaOH solution, without cyanide. Elution recycle time is 6 to 8 hours, electrowinning at 2.4 V to 3.0 V and 250 A. Overall elution cycle time is 12 to 14 hours. Stripped barren carbon is heated to over 750°C in a regeneration kiln in the absence of oxygen, quenched, screened, and returned to the last adsorption tank. After elution, barren solution contains less than 2.5 g/m³ gold and stripped carbon less than 100 g/t. The elution and electrowinning circuit is designed for three tonne capacity; seven or more batches stripped per week, typically 21 tons of carbon per week.

Gold room refining

Gold sludge is washed in hot water, then leached with nitric acid to remove silver and base metals. Dried sludge is mixed with fluxes and smelted at 1,100°C to produce bullion. Bullion is stored in a vault prior to transport and refining off site, with intention to remove by helicopter to Lagos International airport.

Tailings and water

CIL tailings are treated to destroy cyanide using the SO₂ (SMBS)/air process prior to deposition in the TSF. Tailings slurry is pumped to the TSF, with return water pumped to the reclaim water tank. Water is added during grinding to achieve 75% solids in the SAG mill and 50% solids in cyclone overflow. Water demand of 163 m³/hr is met by reclaim water from TSF and clean water from the water supply dam (capacity 0.374 Mm³). The TSF supplies 40% to 100% of monthly water demand, with average 78,700 m³/month reclaimed. The TSF pond maintains minimum volume of 50,000 m³ and average approximately 71,000 m³. The water supply dam provides up to 57,850 m³/month during dry season. Raw water pond capacity is 1,000 m³, reclaim water pond capacity is 2,000 m³. Fire water consumption for two-hour duration is 144 m³, stored in a 200 m³ tank with make-up pumped at 30 m³/h.

Reagents

Cyanide solution is mixed once per day as 20% solution by mass. Lime is added to produce 5% slurry, pumped to the mill feed hopper, leach feed splitter box, and detoxification tank. Caustic soda pearls produce 20% NaOH solution for elution, electrowinning, intensive leach, cyanide make-up, and acid wash. Copper sulphate solution is made up once per day as 20% solution by mass. Sodium metabisulphite solution is made up once per day as 20% solution by mass. Activated carbon is added to the carbon quench tank for make-up. Grinding balls are delivered in 200 L steel drums and charged using an electric hoist. Diesel and LNG/CNG are delivered by road tanker. CIL air is supplied by duty/standby medium pressure compressors, with four high pressure compressors for plant and instrument air.

Key reported parameters

Technical qualifications

The 2019 Technical Report describes the process plant as designed, not as constructed or operated. The throughput increase from 500,000 tpa to 650,000 tpa was not fully shown in the final DFS engineering detail, with modifications to be incorporated during front end engineering design. No operating data, actual performance results, or current project status are reported. The elution and electrowinning circuit capacity, reagent consumption values, and recovery figures are design criteria, not measured outcomes. The report does not include pilot plant results, metallurgical testwork details, or economic analysis.

Source: Segilola Gold Project, Project # 3043, Technical Report NI 43-101, 18 March 2019, Section 17 Recovery Methods.