This report presents the 2019 updated Mineral Resources and Mineral Reserves statements for Mineração Caraíba’s Vale do Curaçá Mineral Assets, including a detailed description of the processing facilities and recovery methods at the Caraíba Mill.
Report context
The report, dated 25 November 2019, provides the updated Mineral Resources and Mineral Reserves statements for Mineração Caraíba’s Vale do Curaçá Mineral Assets. It includes a comprehensive description of the process plant, with supporting technical details on installed equipment and operating parameters.
Processing route
General description
The Caraíba Mill was designed and built by Mill Der Kaiser, a Canadian engineering, design and construction company. Processing operations commenced in 1979 and the plant has since had the benefit of decades of process optimization work performed by the Caraíba Mill’s process engineering team with the support of third-party consultants as needed. The concentrator is operated 24 hours per day, seven days per week with monthly scheduled downtime to perform routine maintenance. In its current configuration, the plant has capacity to treat a nominal 3.2 million tonnes of copper bearing ore per annum, assuming 91% availability.
The Caraíba Mill is of a conventional three-stage crush, milling and flotation design. Three-stage crushing is used to prepare a nominal 12.5mm crushed feed for the ball milling circuit prior to being sent to flotation for the recovery of copper-bearing minerals. Final flotation concentrate is filtered to a design target of 7.5% moisture and is transported via highway for smelting and refining either (i) locally at Paranapanema company, located in Dias D’Ávila, or (ii) sold via international export markets from Salvador’s port, both approximately 475km from the Caraíba Mill.
Crushing
There are two primary crushing operations. Ore from open pit mining is delivered to the surface primary cone crusher, featuring a nominal capacity of 1,600t/h. Ore from underground mining is crushed underground by one of two primary jaw crushers with a nominal capacity of 400t/h each. Feed enters the primary crushing operations with maximum size of 48” and is discharged with maximum size of 10”.
The blended product of the primary crushing operations is transported via conveyors to an apron feeder stockpile with a capacity of 12,000 tonnes and fed to one of two secondary cone crushers (seven-foot (“ft.”) standard Symons; 1,400t/h of capacity each) set to 28mm aperture. The secondary discharge feeds two primary double deck screens, configured with 100mm gaps on the top and 40mm gaps on the bottom decks. Screen undersize passes to the collection conveyor while oversize material passes to the secondary crushers in an open circuit configuration.
Secondary cone crusher discharge and primary screen fines are blended with tertiary crusher discharge and are conveyed to the seven secondary double screen decks, configured with 25mm gaps on the top and 16mm gaps on the bottom decks. Tertiary crushing is performed with four standard CH660 Sandvik cone crushers (capacity of 350t/h each) set to 20mm aperture. Oversize material passes to the tertiary crushers operating in a closed-circuit configuration. Final product from the combined crushing and screening operations is 88% passing 1/2”.
Ore blending
Crushed ore is conveyed to the stacker-reclaimer system to further homogenize the ore for feeding the plant. The stacker-reclaimer system is comprised of a two-armed stacker and a 16 bucket-wheel reclaimer with capacities of 1,600t/h and 1,200t/h, respectively. Crushed ore capacity of the stacker-reclaim system is currently 140,000 tonnes.
Grinding
The grinding circuit consists of two identical lines operating with a primary ball mill operating in closed circuit with a dedicated battery of 26” cyclone classifiers. Each ball mill is 5.0 m by 7.6 m, charged with 90 mm in diameter high chrome cast steel balls. The nominal grinding capacity of each mill is 200 t/h each. Typical ball consumption is 340 g/t.
Blended ore from the stacker reclaimer is withdrawn through belt feeders below one of the 3,000 tonne ore surge bins on each line. Ore is delivered to the ball mill over a weightometer to monitor the mass of ore sent to each mill for metallurgical accounting purposes.
The coarse fraction from the cyclone underflow recycles to the ball mill feed chute for further grinding. Overflow from both grinding lines combines as feed to flotation, at approximately 40 to 45 percent solids and a target P65 to P70 (65% to 70% of discharge passing a screen aperture) of 105 microns.
In early 2018, a flash cell that had previously been installed to process approximately 50% of the underflow on one of the ball mills was reactivated. The objective of this program is to perform a flash flotation of liberated copper particles that do not need additional grinding. The produce of this circuit is a flash cell concentrate grading approximately 40% copper in practice that is mixed with the mill’s conventional flotation final concentrate. Flash cell tailings return to the mill feed as cyclone under flow. The cell has been shown to operate well for ores with feed grade above 2.5% copper and improving the residence time in the mill’s conventional flotation circuit. A plan to add another flash cell to the
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Plant feed capacity | 3.2 million t/a | Design, assuming 91% availability |
| Availability | 91% | Assumption |
| Primary crush (open pit) | 1,600 t/h | Nominal capacity |
| Primary crush (underground) | 2 × 400 t/h | Nominal capacity, jaw crushers |
| Apron feeder stockpile | 12,000 t | Capacity |
| Secondary crushers | 2 × 1,400 t/h | Nominal capacity, Symons 7 ft standard, 28mm aperture |
| Tertiary crushers | 4 × 350 t/h | Nominal capacity, Sandvik CH660, 20mm aperture |
| Crushed product | 88% passing 1/2” | Design |
| Stacker capacity | 1,600 t/h | Nominal |
| Reclaimer capacity | 1,200 t/h | Nominal, 16 bucket-wheel |
| Stacker-reclaim crushed ore capacity | 140,000 t | Current |
| Ball mills | 2 × 200 t/h | Nominal, 5.0 m × 7.6 m |
| Ball charge | 90 mm diameter | High chrome cast steel balls |
| Ball consumption | 340 g/t | Typical |
| Ore surge bins | 2 × 3,000 t | One per grinding line |
| Cyclone feed solids | 40–45% | Operating |
| Target grind | P65–P70 of 105 microns | Design |
| Flash cell concentrate grade | ~40% Cu | Practice |
| Flash cell underflow treated | ~50% of one ball mill | Design |
| Flash cell feed grade | >2.5% Cu | Shown to operate well above this grade |
Technical qualifications
Specific limitations from the report include the absence of detailed flowsheet diagrams within the provided text, with reference made to Appendix C for a process flowsheet showing major unit operations. The report does not provide details on flotation cell equipment specifications, reagent consumption, or metallurgical recovery data. Testwork results were not provided in the source material. The report does not include details on water balance, tailings management, or environmental controls. Actual operating data from the flash cell program were used to support the stated performance observations, but no broader plant performance data were presented.
Source: 2019 Updated Mineral Resources and Mineral Reserves Statements of Mineração Caraíba’s Vale do Curaçá Mineral Assets, Curaçá Valley, Form 43-101F1 Technical Report, 25 November 2019, Rev. F, Recovery Methods, Sections 17.1–17.4.
