This profile is based on a January 31, 2012 NI 43-101 technical report with an effective date of September 30, 2011. The processing route comprises two ore streams , direct-leach ore (DLO) and crushed gravity ore (CGO) , with CGO crushed and gravity-concentrated before heap leaching and DLO sent directly to the heap, followed by carbon adsorption, electrowinning and smelting to produce gold doré.
Report context
The technical report prepared for Aura Minerals Inc. describes the São Vicente Mine located in the municipality of Nova Lacerda, State of Mato Grosso, Brazil. The processing section reports metallurgical design criteria, testwork results and historical production information that support the expected overall metallurgical recovery estimate. Two distinct ore types are processed through separate but integrated circuits: a crushing and gravity concentration plant for CGO and a run-of-mine heap leach for DLO. The report provides reagent consumption rates, design throughputs and equipment specifications for the crushing circuit, heap leach pads, carbon circuit and elution/electrowinning section.
Processing route
Ore streams and metallurgical design
The plant treats two ore streams defined as DLO and CGO. The estimated metallurgical recoveries from testwork and historical production are 30% for DLO and 80% for CGO. These individual stream recoveries combine to an overall metallurgical recovery of 76%. Based on average mine feed grades, the report states that the mine is expected to produce approximately 50,000 oz of saleable gold. The gravity circuit is expected to deliver approximately 40% of the gold production from the CGO stream , this 40% contribution is contained within the 80% CGO recovery and is not additive to the overall recovery figure.
Crushing circuit
The crushing circuit handles only CGO. It was designed with an operational efficiency of 72% and a design feed rate of 288 tph. Ore passes through a fixed 33.5 inch by 33.5 inch grizzly, followed by a 50-t capacity primary crusher feed bin. Oversize material is managed with a hydraulic rock claw and a mobile hydraulic rock breaker. Grizzly undersize reports to a vibrating feeder that supplies the primary jaw crusher, which operates at a closed side setting (CSS) of 6 in and a design capacity of 283 tph.
Primary crusher product is conveyed to a 12,000-t stockpile. From the stockpile discharge conveyor, a magnet and metal detector protect downstream equipment. Ore is fed to a primary two-deck vibrating screen. Oversize from this screen goes to the secondary cone crusher (CSS 1 1/7 in, design capacity 290 tph). Primary screen undersize combines with secondary crusher product, passes through a sampler and optional flow diverter, then enters a secondary two-deck vibrating screen.
The secondary screen undersize is pumped, after water addition, to the gravity concentration circuit. Oversize from the secondary screen lower deck has lime added, is conveyed to and stored in a 66-tonne silo, then hauled via 20-t trucks to the heap leach pad. Oversize from the secondary screen upper deck feeds the tertiary cone crusher (CSS 3/4 in, design capacity 186 tph). Tertiary crusher product combines with secondary crusher product and returns in closed circuit to the secondary screen.
The circuit is designed to generate a product representing 30% of the total feed as material smaller than 3.5 mm, which is fed to the gravity circuit. The remaining 70% of the crushed material, combined with gravity tails, is directed to the leach pads.
Heap leaching
The heap leach pad receives both CGO crushed material and run-of-mine DLO. Ore is stacked in 6 m lifts to a maximum designed height of 36 m. Stacking uses trucks, with subsequent ripping by bulldozers. Both ore types are pH adjusted with lime and irrigated with a weak cyanide solution.
The solution collection system at the bottom of the heaps uses reticulation with lateral pipes connected to central headers for each cell, directing solution to ditches that flow by gravity to the appropriate pregnant solution pond. Lined collection ponds and a solution detoxification circuit handle large amounts of seasonal rainfall. Excess solution is detoxified and discharged.
Reagent consumption
Reported design consumption rates for heap leaching reagents are:
- Lime: 1.5 kg/t
- Sodium cyanide (NaCN): 0.65 kg/t
Gold recovery circuit
Pregnant leach solutions are fed to adsorption columns where dissolved gold loads onto carbon. Loaded carbon is fed to an elution column for stripping. The pregnant solution from elution enters an electrowinning circuit operating with cathodes and anodes under DC current. Gold is removed from cathodes by acid digestion, then filtered. This gold is combined with gravity circuit shaking table products and fed to a diesel furnace to produce gold bullion.
Stripped carbon from the elution column goes through an acid wash column, is screened, combined with fresh carbon and returned to the carbon columns.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| DLO metallurgical recovery (estimated) | 30% | Testwork and historical production |
| CGO metallurgical recovery (estimated) | 80% | Testwork and historical production |
| Overall metallurgical recovery (estimated) | 76% | Combined from DLO and CGO estimates |
| Design plant feed rate (crushing circuit) | 288 tph | Design |
| Crushing circuit operational efficiency | 72% | Design |
| Gravity circuit contribution to CGO gold production | 40% | Expected, contained within 80% CGO recovery |
| Primary jaw crusher design capacity (CSS 6 in) | 283 tph | Design |
| Secondary cone crusher design capacity (CSS 1 1/7 in) | 290 tph | Design |
| Tertiary cone crusher design capacity (CSS 3/4 in) | 186 tph | Design |
| Primary crusher stockpile capacity | 12,000 t | Design |
| Lime consumption rate | 1.5 kg/t | Design |
| Sodium cyanide consumption rate | 0.65 kg/t | Design |
| Heap lift height | 6 m | Design |
| Maximum heap height | 36 m | Design |
| Weight fraction fed to gravity circuit (crushed CGO) | 30% | Design target, material smaller than 3.5 mm |
| Weight fraction sent to leach pads (crushed CGO) | 70% | Design |
| Final product | Gold doré (bullion) | Expected product |
Project website: https://www.juniorminingnetwork.com/junior-miner-news/press-releases/906-tsx-venture/ckg/170445-chesapeake-announces-san-vicente-3-legal-update.html
Technical qualifications
The report covers a mine in operation at the time of preparation. All recovery figures are described as estimates based on test results and historical production information. The crushing circuit parameters (throughput, efficiency, crusher capacities) are design figures, not necessarily achieved operating data. The overall recovery of 76% is a combined estimate derived from the separate DLO and CGO stream recoveries, not a direct measurement. The report does not provide full flowsheet diagrams , it references Appendix 02 for a Process Flow Diagram of the crushing circuit and Figure 17-1 for metallurgical design criteria, neither of which is reproduced in the supplied text sections. This profile uses only sections 17.0-17.2.5 (Recovery Methods) from the technical report; additional sections not supplied may contain further processing details.
Source: *São Vicente Mine , NI 43-101 Technical Report*, prepared for Aura Minerals Inc., effective date September 30, 2011, report dated January 31, 2012, sections 17.0–17.2.5.
