The proposed processing plant for the Borborema Gold Project is designed to treat a biotite-garnet-schist ore through crushing, single-stage semi-autogenous grinding with gravity concentration, and carbon-in-leach cyanidation followed by cyanide detoxification and dry-stack tailings filtration.
Report context
This Technical Report Summary for the Borborema Gold Project is dated February 25, 2026. The process plant design described in the report is based on metallurgical testwork and industry best practices, with a nominal throughput capacity of 2 million tonnes per year. The ore is characterised as a combination of biotite schist, schist in quartz veins, and garnet schist, with gold distributed from relatively coarse to fine grained.
Processing route
Crushing and crushed ore stockpile
Run-of-mine (ROM) ore will be hauled and dumped in stockpiles, then reclaimed with front-end loaders into the crushing feed hopper. The hopper is equipped with a static grizzly with 0.7 m aperture to retain oversize material, which is broken by a mobile rock breaker. From the hopper, a vibrating grizzly feeder modulates the feeding flow rate at a nominal throughput of 304 t/h. The vibrating grizzly separates feed into coarse oversize and relatively fine undersize fractions. The coarse fraction flows by gravity to the primary jaw crusher chamber, while the undersize fraction, together with the primary crusher discharge, is conveyed to a surge bin. Excess crushed material, arising from different availabilities of the crushing and milling circuits, will be piled in a dedicated stockpile and reclaimed by a front-end loader to a reclaim bin with vibrating feeder that also feeds the milling circuit. The predicted crushing circuit product size P80 is 122 mm.
Grinding circuit
The single stage grinding circuit will include a semi-autogenous (SAG) mill operating in closed configuration with hydrocyclones. The SAG mill is designed with dimensions of 7.9 m diameter by 7.0 m effective grinding length, equipped with an 8 MW electric motor. The grinding circuit is designed to produce a product with P80 of 0.105 mm from a feed P80 of 122 mm. Fresh feed from the crushing plant surge bin is conveyed to the SAG mill. Discharge pulp flows to a dedicated trommel screen; material retained on the screen (pebbles) is conveyed back to the SAG mill feed, while trommel undersize gravitates to an underneath sump from which it is pumped to a nest of five hydrocyclones of 500 mm diameter. The hydrocyclone underflow is split, with one fraction flowing through the gravity concentration stage and the other flowing directly back to the SAG mill feed. Water is added at the SAG mill feed and sump to adjust pulp dilution to 72% and 60% w/w, respectively. The hydrocyclone overflow at 35% w/w solids is directed to a trash screen, with undersize flowing to the CIL circuit.
Gravity concentration and intensive leaching
The gravity circuit comprises one centrifugal concentrator with a feed scalping screen. Feed is taken from the cyclone underflow to the scalping screen. Scalping screen oversize at +2 mm reports to the gravity tails pump box, from where material is pumped back to the SAG mill feed. Scalping screen undersize is fed to the centrifugal concentrator, which operates in semi-batch mode. Gravity concentrate is collected in a concentrate storage cone and subsequently leached by the intensive cyanidation reactor circuit. The leach residue is washed and pumped to the CIL circuit. Pregnant leach solution is treated in a dedicated electrowinning cell to produce gold sludge, which is combined with sludge from the carbon elution electrowinning cells and smelted.
Leaching and adsorption circuit (CIL)
The CIL circuit will consist of one leaching tank followed by six carbon-in-leach tanks. Air is sparged into each tank to maintain dissolved oxygen for leaching. Hydrated lime is added to adjust operating pH, and cyanide solution is added to the first leach tank. Fresh carbon and regenerated carbon are added to the last CIL tank at an average concentration of 16 g/L of pulp. Carbon flows counter-currently to the slurry. Slurry from the last CIL tank gravitates to the cyanide detoxification tanks. Loaded carbon is separated daily by a dedicated screen and transferred to the acid washing and elution circuit. Total residence time for the leach and CIL circuit is designed as 30 hours, comprising 4.3 hours for leaching and 25.7 hours for CIL.
Post-leach tailings thickening and cyanide detoxification
A high-rate thickener is designed for thickening the CIL tailings, with flocculant added at 40 g/t. Thickener overflow recirculates to the grinding circuit, while underflow is pumped to the Detox circuit. The cyanide neutralisation circuit will consist of two tanks, each with 60-minute residence time, using the SO₂/air method to reduce weak acid dissociable cyanide from 63.4 mg/L to less than 1 mg/L. Reagents include sodium metabisulfite as the source of SO₂, copper sulphate pentahydrate as catalyst, and hydrated lime for pH and Eh control.
Detox tailings thickening and filtration
After detoxification, the neutralised tailings slurry is thickened again in high-rate equipment to recover cyanide-free process water. The second thickener underflow at 54% w/w solids is pumped to the filtering system. A dedicated tank equalises the daily throughput between grinding/leaching/thickening and the filtering circuit. The filtration circuit includes three horizontal vacuum filters designed to reduce cake moisture to 20-21%. Filtered product is transferred to disposal piles for dry stacking of tailings (DST). Water runoff from piles is recirculated.
Acid wash, elution, electrowinning and gold room
The elution circuit is designed as a ZADRA-type circuit under pressure (ZP) in batch operation. Loaded carbon is transferred to an acid washing column where 3% w/w HCl solution is injected at 2.2 BV/h, followed by neutralisation with 10% w/w caustic soda at 4 BV. Elution uses a solution of 1% sodium hydroxide and 0.1% sodium cyanide, heated to 110°C and injected at 2 BV/h under 300 kPa pressure. The pregnant solution feeds the electrowinning stage. Each elution cycle processes 6 tonnes of carbon, with a frequency of 5 strips per week. Gold-rich cathodes are washed, filtered, dried, mixed with smelting fluxes (borax, nitrate, carbonate, silica), and smelted in an LPG furnace at 1,100°C to produce gold doré bullion.
Water and utilities
The main raw water source will be captured wastewater from a sewage pumping station in Currais Novos, pumped at 83 m³/h to a water treatment plant. The plant includes filtration, chlorination or UV disinfection, and reverse osmosis. Rainwater dammed in the fines dike provides a reserve supply. Process water is sourced from recycled water from the CIL tailings thickener (cyanide-containing), recycled water from the detox thickener overflow, and filtrate. Two ponds are designed: a raw water pond of 5,300 m³ capacity and a cyanide-free recycled water pond of 3,000 m³ capacity. Potable water will be supplied by tank truck at an average of 30 m³/day.
Key reported parameters
| Parameter | Unit | Value |
|---|---|---|
| Nominal plant throughput | Mtpy | 2 |
| Head grade | g/t | 1.22 |
| Nominal crushing circuit throughput | t/h | 304.4 |
| Crushing circuit availability | % | 75 |
| Crushing circuit annual operating hours | h | 6,570 |
| Grinding circuit throughput | t/h | 253.7 |
| Grinding circuit availability | % | 90 |
| Grinding circuit annual operating hours | h | 7,884 |
| Crusher feed size F80 | mm | 319.5 |
| Grinding circuit feed size P80 | mm | 122 |
| Grinding circuit product size P80 | mm | 0.105 |
| SAG mill installed power | kW | 8,000 |
| Gravity recovery gold (GRG) | % | 20 (design) |
| Leach/CIL recovery gold | % | 90.1 (design) |
| Global gold recovery | % | 92.1 (design) |
| CIL residence time – leach | h | 4.3 |
| CIL residence time – CIL | h | 25.7 |
| CIL total residence time | h | 30 |
| Number of leach tanks | – | 1 |
| Number of CIL tanks | – | 6 |
| Leach feed solids | % w/w | 35 |
| Solution losses | g Au/t | 0.10 |
| Elution type | – | Zadra under pressure (ZP) |
| Elution batch size | t | 6 |
| Elution frequency | strips/week | 5 |
| Cyanide detoxification method | – | Air/SO₂ |
| Detox feed CNwad | mg/L | 63.4 |
| Detox discharge CNwad target | mg/L | <1 |
| Detox tank residence time | min | 60 per tank |
| Tailings filter cake moisture | % | 20–21 |
| Cyanide solution preparation strength | % w/w | 33 |
| SMBS solution preparation strength | % w/w | 20 |
| Copper sulphate solution preparation strength | % w/w | 20 |
| Lime milk solution preparation strength | % w/w | 20 |
| Acid wash HCl concentration | % w/w | 3 |
| Elution NaOH concentration | % w/w | 1 |
| Elution NaCN concentration | % w/w | 0.1 |
| Elution temperature | °C | 110 |
| Elution pressure | kPa | 300 |
| Gold smelting temperature | °C | 1,100 |
Project website: http://www.goldroyalty.com/portfolio/borborema/
Technical qualifications
The report states that the processing plant design is similar to several industrial operations in the gold mining industry, with the exception of the wastewater processing from the city of Currais Novos, which requires additional testing and further engineering work. The report identifies risks to raising capital including additional investment for new sewage receiving lines, and notes that possible capital reductions could include simplification of the water treatment plant provided that water accumulation in rainy seasons is consistent and reliable. The report recommends further assessment on water supply alternatives.
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*Source: Technical Report Summary – Borborema Gold Project – February 25, 2026, Sections 14 (Recovery Methods: 14.1 Process Flow Sheet Selection, 14.2 Process Design Criteria, 14.3 Process Plant Description, 14.4 Reagents, 14.5 Water and Utilities, 14.6 Conclusions and Recommendations).*
