São Jorge Gold Project: A Conventional Crush, Grind, and Leach Flowsheet for a Brazilian Open Pit Development

GoldMining Inc.'s São Jorge Gold Project in Pará State, Brazil, is planned as an open pit mining operation with a 2 Mtpa process plant using gravity concentration, cyanide leaching, and carbon-in-leach recovery to produce gold doré. The Preliminary Economic Assessment describes a conventional flowsheet designed around historical metallurgical test work.

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Opening

The São Jorge Gold Project is situated in the Tapajós Mineral Province within the municipality of Novo Progresso in Pará State, Brazil, approximately 70 km north of the town of Novo Progresso and accessible via the BR-163 highway. The project, held under Mineral Process No. 850.058/2002 and administered by the Brazilian National Mining Agency, is currently in the application stage for a mining concession, with the application filed on October 29, 2024, following approval of the Final Exploration Report on October 30, 2023. Environmental permitting is at an early stage, and no development timeline has been established. The project is owned by GoldMining Inc., which retained BNA Mining Solutions to prepare a Preliminary Economic Assessment evaluating a conventional open pit mining operation with on-site processing of mineralized material and production of gold doré as the target product. Mineralization at São Jorge is structurally controlled, occurring as disseminated sulfides and quartz vein systems within granitoid rocks, and the deposit remains open at depth. No Mineral Reserves have been declared for the São Jorge Project.

Critical Data

Overview

The process plant design for the São Jorge Gold Project is based primarily on metallurgical test work completed by Testwork Desenvolvimento de Processo Ltda in 2012, supplemented by historical investigations conducted by SGS Lakefield Research in 2006 and additional leaching test work completed by Testwork Desenvolvimento de Processo Ltda in 2013. The plant is designed for a capacity of 2 Mtpa, equivalent to approximately 260 t/h, treating mineralized material through conventional unit operations. These include comminution, gravity concentration, cyanide leaching with carbon-in-leach, gold adsorption, carbon elution, and gold recovery circuits. Historical test work programs conducted between 2006 and 2013 included mineralogical characterization, comminution testing, gravity recovery testing, bottle-roll leaching, kinetic leaching curves, cyanide optimization tests, and preliminary variability assessments for oxide and sulphide ores. Combined gravity and carbon-in-leach recoveries from that test work generally ranged from approximately 90% to 94%, with some tests exceeding 95% for sulphide material at finer grind sizes.

The design criteria were developed from the available historical metallurgical test work and are considered appropriate for a PEA level evaluation. The flowsheet includes primary, secondary, and tertiary crushing with stockpiling and reclaim, a ball mill with hydrocyclones producing a final product with a P80 of 75 µm, and gravity concentration treating 50% of the total hydrocyclone underflow. The gravity concentrate reports to intensive leaching with gold recovery via electrowinning. Pre-leach thickening precedes cyanide leaching and carbon adsorption through a carbon-in-leach circuit. Carbon elution uses the ADR process, and carbon handling includes regeneration. Electrowinning and smelting produce gold doré. Cyanide destruction of CIL tailings uses the SO₂/air process, followed by tailings thickening and pumping to a tailings storage facility. Reagent circuits include air and oxygen systems, and water systems cover potable water, raw water, gland seal water, and process water.

Key Process Stages

Run of mine material is delivered by haul trucks directly into the ROM bin, with an alternative arrangement allowing discharge onto a ROM pad used primarily for emergency storage and blending of saprolite and sulphide mineralized material when required by the mine plan. A variable-speed apron feeder withdraws material from the ROM bin and discharges onto a vibrating grizzly with an aperture of approximately 100 mm. Oversize material feeds a jaw crusher operating in open circuit. Crusher discharge combines with grizzly undersize and is conveyed to a double-deck screen with 60 mm and 22 mm apertures. Oversize from the first deck reports to a secondary cone crusher in closed circuit with the screen. Oversize from the second deck feeds a tertiary cone crusher, with the crushed product going to a second double-deck classification screen with 12 mm and 8 mm apertures. Undersize from the first classification screen is conveyed to the second classification screen, and oversize from both decks of the second screen returns to the tertiary crusher in closed circuit. Final product from the second classification screen is conveyed to the stockpile with a particle size below 8 mm and a P80 of approximately 5 mm. Two apron feeders with variable-speed drives reclaim material from beneath the stockpile, controlling feed rate to the grinding circuit.

Grinding is performed in a ball mill measuring 8.5 m in diameter by 5.0 m effective grinding length, operating in closed circuit with hydrocyclone classification. The cyclone underflow is divided into two streams, with 50% returning directly to the ball mill and the remaining 50% directed to the gravity concentration circuit for coarse gold recovery. Cyclone overflow with a P80 of approximately 75 µm is pumped to the pre-leach thickener and subsequently to the CIL circuit.

The gravity recovery circuit consists of one centrifugal gravity concentrator unit and one intensive leach reactor. Cyclone underflow is screened to remove material coarser than 2 mm, with oversize discharging directly to the ball mill feed. The undersize product feeds the centrifugal gravity concentrator, and tailings from the concentrator discharge to the cyclone feed pump box, returning to the grinding circuit. Gravity concentrate is pumped to the intensive leach reactor and processed in batch mode at 12-hour intervals. The concentrate is leached using a solution containing sodium cyanide, caustic solution, and leach accelerant reagents. After the leach cycle, pregnant solution goes to the gravity electrowinning circuit, and residue from the intensive cyanidation unit is pumped to the pre-leach thickener.

Cyclone overflow is pumped to a 15 m diameter pre-leach thickener to increase slurry density prior to cyanidation. Flocculant is added to the thickener feed to improve solids settling. Thickener underflow at approximately 60% solids by weight is pumped to a CIL circuit consisting of two pre-leach tanks and eight CIL tanks, providing a total residence time of approximately 24 hours. Oxygen is sparged into the leach tanks, and water is added to maintain slurry density at approximately 45% solids by weight. Sodium cyanide is added for gold dissolution, and hydrated lime maintains pH between approximately 10.5 and 11.5. Activated carbon is added to CIL Tank 6, advancing counter-currently through the circuit via interstage screens and pumps, with loaded carbon exiting from the first and second CIL tanks. Leach residue from the final tank is directed to a carbon safety screen for carbon recovery.

The cyanide destruction circuit consists of two tanks with a total residence time of approximately 200 minutes, treating slurry discharged from the CIL tanks. SO₂/air is added for cyanide destruction, with hydrated lime maintaining pH at approximately 8.5 and copper sulphate added as a catalyst. The process is designed to reduce total cyanide in solution to approximately 0.4 mg/L and WAD cyanide to approximately 0.2 mg/L. Treated slurry is pumped to a tailings thickener with flocculant added to the feed. Thickener overflow returns to the CIL circuit, and underflow is pumped to the tailings storage facility, which is designed for construction in five stages.

Loaded carbon is screened from the CIL circuit and transferred to the acid wash column, with typical gold loading of approximately 3,000 g/t in batch operation. Fresh acid is pumped from drums to the acid wash tank as required, and the carbon is rinsed with fresh water to remove acid and mineral impurities. Operating conditions include acid concentration of 2–5% HCl, temperatures from ambient to 60°C, contact time from 30 minutes to several hours, and final pH neutral. Carbon slurry is then pumped directly into the top of the elution vessel.

The selected elution process is pressure Zadra, which removes adsorbed gold and silver from loaded carbon into solution for recovery by electrowinning and smelting. A caustic cyanide solution containing 0.2% NaCN and 1% NaOH is prepared and circulated through the desorption column, entering from the bottom and exiting from the top under an operating pressure of approximately 3 kgf/cm², at a temperature of approximately 130°C, and at a flow rate of approximately 2 BVH (approximately 6 m³/h). Gold desorbs into solution during the stripping cycle, and barren carbon is transferred to the thermal regeneration feed tank using ejectors over approximately one hour. Gold-rich eluate discharges from the column and flows to the electrowinning cells.

Two electrowinning cells are installed, one dedicated to electrodepositing ionized gold recovered from the CIL circuit and the other dedicated to ionized gold from intensive leaching of the gravity concentrate. Each cell contains four cathodes and five anodes operating at 4.5 V to 6.0 V, with current density ranging from 20 A/m² to 50 A/m² and a 200-amp rectifier. The electrowinning process cycle is expected to occur over approximately 12 hours, with the total desorption and electrowinning cycle approximately 14 hours including column filling and emptying. Resulting sludge is filtered using a filter press, and the filter cake is dried in a drying oven. The dried filter cake is manually transferred to an electric smelting furnace, where gold doré bars are produced and stored in a secure vault.

Carbon regeneration begins with eluted carbon passing through a screen for dewatering and removal of fines. Oversize carbon discharges by gravity to the regeneration kiln feed hopper, while screen undersize containing carbon fines and water drains into a carbon fines tank. Regeneration occurs in a rotary kiln operating at 700°C, at a rate of 75 kg/h, with a residence time of 20 minutes, 12.5% kiln filling, and an assumed thermal efficiency of 60%. Carbon discharge enters a quench tank containing cold water, which also receives fresh carbon introduced into the process. Fresh and regenerated carbon is transferred by ejector to the final CIL tank, receiving approximately 3 t of carbon daily.

Reagent preparation and storage facilities are located within containment areas designed to accommodate volumes greater than the contents of the largest storage tank, with independent containment for each reagent system where required to avoid mixing incompatible reagents. Storage tanks are equipped with level indicators, instrumentation, and alarms, and the facilities include ventilation, fire and safety protection systems, eyewash stations, safety showers, and MSDS stations. Sumps and sump pumps are installed for spill containment and recovery. Reagent dosages are controlled through flow meters and control valves, and storage tank capacities are generally designed to provide approximately one day of operating inventory.

Process water without cyanide is stored in dedicated tanks and used throughout the plant for slurry dilution and solids density adjustment. Process water containing cyanide recovered from the cyanide destruction thickener overflow is recycled back to the CIL circuit. Fresh water is supplied to the fire suppression and gland seal water systems through a dedicated fire water tank, with the lower section reserved for fire water storage. Potable water is treated in a dedicated water treatment plant for the industrial area, with a separate treatment plant planned for camp facilities. Plant services include an air supply system distributing compressed air for instrumentation, process services, and the CIL and pre-leach circuits, with instrument air dried prior to distribution. The air compressors also supply an oxygen generation circuit using pressure swing adsorption, providing oxygen for the CIL and cyanide destruction circuits, and may bypass the oxygen generation circuit to feed the leaching circuit directly if required.

Metallurgical samplers collect feed and tailings samples to support preparation of metallurgical balances, with sampling points planned at the cyclone overflow and CIL tailings streams. Process control samplers generate samples for monitoring unit operations, with sampling locations planned for leach feed, tailings, pregnant solution to electrowinning, and barren solution after electrowinning. A weightometer is planned for the stockpile feed conveyor, with an additional weightometer on the ball mill feed conveyor. Main operational parameters, including feed rate, grinding circuit flow rates, and flows within the CIL and elution circuits, are monitored through a Programmable Logic Controller system.

Additional Interesting Data and Summary

The process plant is designed to operate 365 days per year, 24 hours per day, totaling 8,760 hours per year. The crushing circuit has an availability of 65%, yielding 5,694 operating hours per year, while the process plant has an availability of 88%, yielding 7,709 operating hours per year. Nominal feed rates are 351.25 t/h for crushing and 259.44 t/h for the process plant, with LOM total ROM throughput of 20,729,315 t.

Energy consumption was estimated based on preliminary equipment sizing. The crusher and stockpile circuit shows average power of 687.10 kW over 5,694 hours per year, totaling 3,912,347.40 kWh/year. The process plant shows average power of 6,936.00 kW over 7,709 hours per year, totaling 53,469,624.00 kWh/year. A category labeled "Others" shows 150.00 kW over 2.4 hours per year, totaling 360,000.00 kWh/year. The total estimated annual power consumption is 57,741,971.40 kWh/year, and it was confirmed by Equatorial Energia that the projected power demand can be supplied.

The workforce plan calls for the plant to operate on an 8 hour per shift schedule with 3 shifts per day and 4 teams handling rotation. The total process plant operational workforce is 22 personnel, with 11 per shift. The workforce includes a plant manager, senior metallurgist, plant superintendant, general supervisor, shift supervisors, control room operators, crushing operators, process plant operators, reagents operators, general helpers, smelter and refinery supervisor, smelter and refinery operators, shipping and receiving operator, and a driver for general service.

The PEA mine plan contemplates a 10.6 year mine life with processing of approximately 20.7 Mt of mineralized material and total mined material of approximately 109.1 Mt, resulting in a life of mine strip ratio of approximately 4.27:1. Average gold feed grade is estimated at 0.91 g/t Au with average metallurgical recovery of 90.0%, and total gold production of approximately 543.2 koz over the life of mine. The mineral resource estimate, as at January 28, 2025, totals 19,418,000 t at an average grade of 1.00 g/t Au containing approximately 624 koz Au in the Indicated category, plus 5,557,000 t at 0.72 g/t Au containing approximately 129 koz Au in the Inferred category, at a break-even cut-off grade of 0.27 g/t Au. The PEA is preliminary in nature and includes Inferred Mineral Resources, which are considered too speculative geologically to have economic considerations applied to them that would enable classification as Mineral Reserves.

Key Processes

• Primary, secondary, and tertiary crushing of ROM material with stockpiling and reclaim
• Ball mill grinding with hydrocyclone classification to P80 of 75 µm
• Gravity concentration treating 50% of hydrocyclone underflow, followed by intensive leaching and electrowinning
• Pre-leach thickening and carbon-in-leach cyanidation with an 8-tank CIL circuit
• Carbon elution using the pressure Zadra process
• Carbon handling and thermal regeneration in a rotary kiln
• Electrowinning and smelting to produce gold doré
• Cyanide destruction of CIL tailings using the SO₂/air process
• Tailings thickening and pumping to a staged tailings storage facility
• Reagent circuits including air and oxygen systems
• Water systems for potable, raw, gland seal, and process water

Source: NI 43-101 Technical Report and Preliminary Economic Assessment, São Jorge Gold Project, July 22, 2026. Project website: São Jorge Gold Project