This report describes the designed processing route for the Matupá Gold Project, based on metallurgical testwork that selected a gravity concentration and leaching circuit over direct leaching.
Report context
This technical report, dated November 18, 2022, documents the recovery methods proposed for the Matupá Gold Project. The process flowsheet was developed from conclusions presented in Chapter 13 of the same report, with the third campaign of metallurgical testing demonstrating higher performance for a gravity concentration and leaching process alternative compared with direct leaching.
Processing route
Process selection basis
The flowsheet adopted for the Matupá Project consists of a primary crushing circuit followed by a single-stage SAG mill in closed configuration with hydrocyclones, designed to produce a product with a P80 of 0.125 mm. The hydrocyclone combined underflow is split into two fractions: the first passes through a gravity concentration stage, with tailings returning to the SAG mill feed; the second fraction returns directly to the SAG mill feed.
Crushing circuit
The crushing circuit is designed for a nominal capacity of 3,562 tpd at 70% availability, representing 6,132 annual operating hours and 212 tph nominal throughput. Run-of-mine ore is hauled and dumped in stockpiles, then reclaimed by front-end loader into a crushing feed hopper equipped with a static grizzly. A vibrating grizzly feeder modulates feed rate and separates coarse and fine fractions. Coarse material flows to a primary jaw crusher, with crusher discharge and fines conveyed to a surge bin. Excess crushed material is stockpiled and reclaimed by front-end loader to a reclaim bin with vibrating feeder. The predicted crushing circuit P80 is 90 mm.
Grinding circuit
The single-stage grinding circuit includes a high-aspect SAG mill operating in closed configuration with hydrocyclones. Feed at P80 of 90 mm is reduced to a product P80 of 0.125 mm. SAG mill discharge passes through a trommel screen, with retained pebbles conveyed back to the mill feed. Trommel undersize flows to a sump and is pumped to a hydrocyclone nest. Water is added at the SAG mill feed and sump to adjust pulp dilution to 70% and 61% w/w respectively. Hydrocyclone overflow passes through a trash screen, then flows to a high-rate thickener for solids concentration to 50% prior to the L-CIL circuit.
Gravity concentration circuit
The gravity circuit comprises one centrifugal concentrator with a feed scalping screen. Feed from cyclone underflow is directed to the scalping screen; oversize at +2 mm reports to the gravity tails pump box for return to the SAG mill. Scalping screen undersize feeds the centrifugal concentrator, which operates semi-batch. Gravity concentrate is collected in a concentrate storage cone and subsequently leached by an intensive cyanidation reactor. Gravity concentrator tails also report to the gravity tails pump box.
Intensive leach reactor
Gravity concentrate is directed to the intensive leach reactor (ILR) storage cone and de-slimed before transfer. ILR leach solution, comprising NaCN, NaOH and LeachAid® (an oxidant), is made up in a heated feed tank and circulated through the reaction vessel. Leached residue is washed, with wash water recovered, and solid gravity leach tailings are pumped to the L-CIL circuit. ILR pregnant solution is treated in a dedicated electrowinning cell in the gold room, with sludge combined with carbon elution electrowinning sludge for smelting.
Pre-leach thickening
Trash screen undersize feeds the pre-leach thickener, where flocculant emulsion (35% w/v) is added at 10 g/t to increase solids concentration to 50% w/w. Thickener overflow is reused as process water throughout the plant, primarily at the cyclone feed sump.
Leaching and adsorption circuit
The leach-adsorption circuit consists of two leach tanks and six carbon-in-leach (CIL) tanks, fed by grinding circuit product at P80 of 0.125 mm and 50% w/w solids. Air is sparged to maintain dissolved oxygen at 5 mg/L. Hydrated lime adjusts operating pH to 10.5. Cyanide solution is added to the first leach tank at 620 g/t of ore. Fresh and regenerated carbon is added to the last CIL tank at 15-20 g/L of pulp. Carbon flows counter-current to slurry. Loaded carbon from the first carbon tank is separated by screen and transferred to acid washing and elution. Slurry from the last CIL tank gravitates to cyanide detoxification.
Cyanide neutralization circuit
The Detox circuit comprises two tanks with 60-minute residence time each, using the SO₂/air method to reduce weak acid dissociable cyanide (CNwad) from 100-150 mg/L to less than 2 mg/L. Reagents include sodium metabisulfite as SO₂ source, copper sulfate pentahydrate as catalyst, and hydrated lime for pH and Eh control. Air is injected through spargers. Pulp then passes through a safety screen to retain any loaded carbon for recirculation, with undersize pumped to the tailing thickener.
Carbon acid wash, elution, electrowinning and smelting
Loaded carbon is repulped and pumped to an acid washing column using 3% w/v hydrochloric acid solution to remove calcium. After rinsing, carbon is transferred to the elution column for Zadra elution using 1% NaOH and 0.1% NaCN eluent heated to 150°C, with volume equivalent to 8-10 bed volumes. Pregnant solution feeds the electrowinning stage, with solution recirculated to the eluent tank. Gold-rich cathodes are washed, filtered, dried, mixed with smelting fluxes (borax, nitrate, carbonate, silica) and smelted at 1,100°C in an LPG furnace to produce gold doré.
Carbon reactivation
After elution, carbon is reactivated in a rotary kiln at 750°C in superheated steam atmosphere. A dewatering screen separates carbon at 1 mm mesh, with oversize fed to the kiln. Kiln discharge is quenched and screened; oversize returns to the CIL circuit, undersize is stored and sold.
Tailing thickening and filtering circuit
Detox circuit tailings at 48-49% w/w solids are transferred to a high-rate thickener with flocculant addition at 25 g/t. Underflow at 60% w/w solids is pumped to a horizontal vacuum filter reducing cake moisture to 21-23% dry basis. Filtered product is transferred to disposal piles. Water from thickening, filtering, and pile runoff is recirculated within the processing plant.
Reagent systems
Reagent systems designed for the processing circuit include: sodium cyanide (98% solid, prepared as 20% w/w solution); hydrated lime (25% w/w solution); sodium hydroxide (50% w/w solution); hydrochloric acid (33% solution); sodium metabisulfite (97.5% solid, 20% w/w solution); copper sulfate pentahydrate (99.5% solid, 20% w/w solution); flocculant (35% w/w emulsion); granular activated carbon; anti-scalant; and smelting fluxes. All reagents are received and stored in appropriate facilities with safety equipment including ventilation, fire protection, eyewash stations, and spillage control.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Nominal processing rate | 3,562 tpd (1.3 Mtpa) | Design criterion |
| Crusher circuit availability | 70% | Design criterion |
| Grinding and extraction circuit availability | 92% | Design criterion |
| Filtration circuit availability | 92% | Design criterion |
| Crusher circuit nominal throughput | 212 tph | Design calculation |
| Crushing circuit annual operating hours | 6,132 | Design calculation |
| Crushing circuit product P80 | 90 mm | Predicted from simulations |
| Grinding circuit feed P80 | 90 mm | Design basis |
| Grinding circuit product P80 | 0.125 mm | Design basis |
| SAG mill feed pulp density | 70% w/w | Design addition |
| SAG mill sump pulp density | 61% w/w | Design addition |
| Pre-leach thickener solids concentration | 50% w/w | Design target |
| Pre-leach thickener flocculant dosage | 10 g/t | Design basis |
| Dissolved oxygen level in leach | 5 mg/L | Design set point |
| Leach operating pH | 10.5 | Design set point |
| Cyanide dosage | 620 g/t ore | Design basis |
| Carbon concentration in CIL | 15-20 g/L pulp | Design range |
| Detox CNwad feed concentration | 100-150 mg/L | Design range |
| Detox CNwad target discharge | <2 mg/L | Design target |
| Detox tank residence time (each) | 60 minutes | Design basis |
| Acid wash HCl concentration | 3% w/v | Design basis |
| Elution temperature | 150°C | Design basis |
| Elution solution composition | 1% NaOH, 0.1% NaCN | Design basis |
| Carbon reactivation temperature | 750°C | Design basis |
| Tailing thickener feed solids | 48-49% w/w | Design basis |
| Tailing thickener flocculant dosage | 25 g/t | Design basis |
| Tailing thickener underflow solids | 60% w/w | Design basis |
| Filter cake moisture | 21-23% dry basis | Design target |
| Recirculated water flow | 206 m³/h | Design calculation |
| Raw water consumption | 25 m³/h | Estimated |
| Raw water source | Porcão River | Identified source |
Project website: https://miningdataonline.com/property/1880/Matupa-Project.aspx
Technical qualifications
The process flowsheet described in this report is a proposed design based on metallurgical testwork conclusions from Chapter 13. The third campaign of testing demonstrated higher performance for the gravity concentration and leaching alternative compared with direct leaching, leading to its selection. Specific testwork data, performance results, and economic analyses are not included in the recovery methods chapter. The crushing circuit P80 of 90 mm is predicted based on selected ROM size distribution, equipment design, and circuit simulations. An electrowinning stage for intensive leaching pregnant solution is noted as "in analysis." All processing parameters represent design criteria unless otherwise stated, and no historical operating data from an existing plant are presented.
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Source: NI 43-101 Technical Report, Matupá Gold Project, November 18, 2022, Section 17: Recovery Methods
