The Caraíba Mill comprises a three-stage crushing, two-stage milling and flotation concentrator designed to treat 3.2 million tonnes of copper-bearing ore per annum.
Report context
The Caraíba Mill processing operations commenced in 1979 based on a design by Milder Kaiser, a Canadian engineering, design and construction company. The concentrator has undergone decades of process optimisation performed by the Caraíba process engineering team with support from third-party consultants. The plant operates 24 hours per day, seven days per week with monthly scheduled downtime for 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% total availability. This technical report, dated 25 November 2019, provides the 2020 updated Mineral Resources and Mineral Reserves Statements for Mineração Caraíba’s Vale do Curaçá Mineral Assets, Curaçá Valley.
Processing route
Crushing circuit
Two primary crushing operations are installed. Ore from other mining sites is delivered to a surface primary gyratory crusher with nominal capacity of 1,600 t/h. Ore from underground mining is crushed underground by one of two primary jaw crushers with nominal capacity of 400 t/h each. Feed enters the primary crushing operations with maximum size of 48 inches and is discharged with maximum size of 10 inches. The blended product is conveyed to a feeder stockpile with capacity of 12,000 tonnes. The stockpile feeds two primary double deck screens configured with 100 mm aperture on the top deck and 40 mm aperture on the bottom deck. Material over 40 mm feeds one of two secondary cone crushers (seven-feet standard Symons; 1,400 t/h capacity each) set to 28 mm aperture. Screen undersize and secondary crusher products discharge onto one conveyor in open circuit configuration.
Secondary cone crusher discharge and primary screen fines are blended with tertiary crusher discharge and conveyed to seven secondary double screen decks configured with 25 mm aperture on the top deck and 16 mm aperture on the bottom deck. Tertiary crushing is performed with four standard CH660 Sandvik cone crushers (capacity 350 t/h each) set to 20 mm aperture. Oversize material passes to the tertiary crushers operating in closed-circuit configuration. Final product from the combined crushing and screening operations is 88% passing ½ inch.
Ore blending
Crushed ore is conveyed to a stacker-reclaimer system to further homogenise the ore for feeding the plant. The stacker-reclaimer system comprises a two-armed stacker and a 16-bucket-wheel reclaimer with capacities of 1,600 t/h and 1,200 t/h respectively. Crushed ore capacity of the stacker-reclaim system is currently 140,000 tonnes.
Grinding circuit
The grinding circuit consists of two identical lines operating with a primary ball mill in closed circuit with a dedicated battery of 26-inch hydro-cyclones. Each ball mill is 5.0 m by 7.6 m, charged with 90 mm diameter high chrome cast steel balls. The nominal grinding capacity of each mill is 200 t/h. 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 silos that are interconnected. Ore is delivered to the ball mill over a belt weightometer to control and measure 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.
High frequency screens and regrinding circuit
The cyclone oversize is pumped to high frequency screening operations comprising eight screens with five decks each of 105+ micron aperture. The high frequency screening coarse fraction is gravity fed to the vertical mill (STM HIG Mill HIG2300/23000) for regrinding, operating in open circuit. The HIG Mill was commissioned in September 2020. The screening operation fines combine with the regrind mill product and are pumped to flotation.
Flotation and concentrate handling
Three-stage crushing prepares a nominal 12.5 mm top size crushed feed for the ball milling circuit that also feeds the regrind mill circuit prior to flotation for recovery of copper-bearing minerals. Final flotation concentrate is filtered to a design target of 7.5% moisture and transported via highway for smelting and refining either locally at Paranapanema company in Dias D’Ávila or sold via international export markets from Salvador’s port, both approximately 475 km from the Caraíba Mill.
Key reported parameters
| Parameter | Unit | Value | Basis |
|---|---|---|---|
| Plant nominal capacity | Mt/a | 3.2 | Design |
| Plant availability | % | 91 | Design assumption |
| Primary gyratory crusher capacity | t/h | 1,600 | Nominal design |
| Underground primary jaw crusher capacity (each) | t/h | 400 | Nominal design |
| Feeder stockpile capacity | tonnes | 12,000 | Historical design |
| Secondary cone crusher capacity (each) | t/h | 1,400 | Design |
| Tertiary cone crusher capacity (each) | t/h | 350 | Design |
| Stacker capacity | t/h | 1,600 | Installed equipment rating |
| Reclaimer capacity | t/h | 1,200 | Installed equipment rating |
| Stacker-reclaim crushed ore capacity | tonnes | 140,000 | Current operating capacity |
| Ball mill dimensions | m | 5.0 by 7.6 | Installed equipment |
| Ball mill nominal capacity (each) | t/h | 200 | Design |
| Ball charge diameter | mm | 90 | Historical operating |
| Typical ball consumption | g/t | 340 | Historical operating |
| Final product passing ½ inch | % | 88 | Design specification |
| Final concentrate moisture target | % | 7.5 | Design |
| HIG Mill commissioning | – | September 2020 | Actual testwork/commissioning |
| Operations commencement | year | 1979 | Historical |
Technical qualifications
The information presented is extracted from a technical report dated 25 November 2019 covering the 2020 Updated Mineral Resources and Mineral Reserves Statements of Mineração Caraíba’s Vale do Curaçá Mineral Assets, Curaçá Valley. The report contains a process flowsheet showing major unit operations detailed in Appendix C and installed equipment listed in Table 17-3, neither of which are reproduced here. The HIG Mill commissioning date of September 2020 post-dates the report date. All processing information is derived from the original process design, historical operations since 1979, and ongoing optimisation work performed by the Caraíba process engineering team.
Source: 2020 Updated Mineral Resources and Mineral Reserves Statements of Mineração Caraíba’s Vale do Curaçá Mineral Assets, Curaçá Valley, Section 17 Recovery Methods, 25 November 2019.
