The Cerro Corona process plant is a conventional crush-grind-float circuit producing a copper-gold concentrate.
Report context
This technical report, dated 2021, describes the Cerro Corona mineral processing facilities. The life of mine plan is built on a throughput assumption of 800 t/hr or 6.7 Mt/a with an availability of 91.32%. The document presents the designed flow sheet, recent upgrades completed or in progress through 2021, and projected plant requirements for the first five years of the Mineral Reserve life of mine plan (2022–2028). Plant improvement or optimisation projects recently completed or in progress are noted.
Processing route
Crushing circuit
The crushing circuit includes two independent lines, one on duty and one spare, to supply an overland conveyor feeding the SAG mill. Each line has a Lokotrack LT-140E and Abon Sizer as a primary crusher that receive coarse material with a top size of 1 m. Fine ore from the mine (-9") is fed through a belt conveyor to a 300 t hopper in each line. From the hopper, a 42" apron feeder sends the ore to a 50" Abon Sizer crusher that reduces the ore size from 6" to 4". The crushed ore is then conveyed by a 55" belt feeder to the 42" overland conveyor.
The inclusion of two crushing lines removes the need for an intermediate crushed ore stockpile, which is required by the high clay content and wet characteristics of the ore.
Grinding circuit
The grinding area includes a 24' x 14.5' SAG mill that reduces the ore size to a 1" particle, and a 20' x 34' ball mill working in a closed circuit with a 26" hydrocyclone nest that reduces the ore particle size to 80% passing the 140–160 µm mesh range. The pulp is discharged into a conditioning tank which is fed to the flotation plant. A cone crusher was implemented to process pebbles from the SAG mill, with the product fed back to the ball mill.
Flotation circuit
The flotation plant includes a rougher stage of seven 160 m³ Outokumpu flotation cells. This stage is designed to recover 85%–90% of the copper and 65%–70% of the gold. The rougher flotation tails are thickened in a 36.6 m diameter thickener to a density of 45–52% solids and then piped to the tailings storage facility (TSF).
The concentrate is processed through two stages of cleaning cells of different size to deliver a concentrate of 20% copper and 30 g/t gold. The cleaning circuit also includes four regrind mills and five 50 m³ Outokumpu cleaner-scavenger flotation cells. The cleaner tails from this circuit are piped to the TSF.
A Falcon gravity concentrator is included for the recovery of gold in iron from the rougher concentrate, which is then sent to the final concentrate thickener. The tailings from the gravimetric process continue to the cleaning flotation circuit.
Concentrate handling
The final concentrate is thickened in a 16 m diameter thickener to 63% solids and then pumped to a fully automatic Metso filter. Concentrate with 7–9% moisture is stored in a dome with a 5,000 t capacity before loading into 30 t trucks. The concentrate is transported in seven vehicle convoys over 380 km to Salaverry port, where it is loaded in ships for export to copper smelters in Japan and Germany.
Recent plant upgrades and development
Several plant improvement or optimisation projects were recently completed or remain in progress as of the 2021 report date.
Gravity circuit reconfiguration: The existing Falcon gravity concentrator was recently reconfigured for incorporation into the concentrate regrind circuit recirculating load instead of being fed rougher concentrate. This provides an opportunity for multiple passes of coarse gold to be presented to the concentrator due to recirculation of gold through the regrind circuit hydrocyclones, with the aim to increase gravity recovery.
Replacement of Abon MMD Sizers: The original primary crusher Abon Sizers are nearing the end of their serviceable life. Replacement of both Abon Sizers with upgraded MMD Sizers with higher hardness rock crushing capacity was in progress, with one of the two units replaced at the end of 2021. The second original Abon MMD Sizer was scheduled to be replaced in 2022.
SAG mill grates configuration change: During 2019 and 2020, Cerro Corona engaged Fluor to review the set-up and performance of the comminution circuit. One of the recommendations made to increase capacity was to increase the aperture and open area of the SAG mill discharge grates. Following trials undertaken in 2020 and 2021, all the discharge grates were replaced with larger apertures of 50 x 34 mm, targeting a throughput increase of approximately 4 t/hr.
Key reported parameters
| Parameter | Unit | Design | Projected (2022–2028 range) | Basis |
|---|---|---|---|---|
| Throughput | t/hr | 800 | – | Life of mine plan assumption |
| Annual throughput | Mt/a | 6.7 | 6.725–6.744 kt | Life of mine plan assumption |
| Plant availability | % | 91.32 | – | Design assumption |
| Crushing top size feed | m | 1 | – | Design |
| SAG mill dimensions | ft | 24 x 14.5 | – | Design |
| Ball mill dimensions | ft | 20 x 34 | – | Design |
| Hydrocyclone diameter | in | 26 | – | Design |
| Grind size (80% passing) | µm | 140–160 | – | Design |
| Rougher flotation cells | m³ | 7 x 160 Outokumpu | – | Design |
| Rougher Cu recovery | % | 85–90 | – | Design |
| Rougher Au recovery | % | 65–70 | – | Design |
| Final concentrate grade (Cu) | % | 20 | – | Design |
| Final concentrate grade (Au) | g/t | 30 | – | Design |
| Cleaner-scavenger cells | m³ | 5 x 50 Outokumpu | – | Design |
| Final concentrate thickener diameter | m | 16 | – | Design |
| Final filter moisture | % | 7–9 | – | Design |
| Concentrate storage dome capacity | t | 5,000 | – | Design |
| Truck capacity | t | 30 | – | Design |
| Transport distance to port | km | 380 | – | Design |
| Plant power draw | MWhr | – | 173,828–174,833 | Projected from life of mine plan |
| SAG grinding media | t/a | – | 2,013–2,152 | Projected from life of mine plan |
| Ball mill grinding media | t/a | – | 4,234–4,303 | Projected from life of mine plan |
| Lime consumption | t/a | – | 18,790–21,392 | Projected from life of mine plan |
| Frother consumption | t/a | – | 24.44–60.52 | Projected from life of mine plan |
| Collectors consumption | t/a | – | 84.73–184.82 | Projected from life of mine plan |
| Flocculants consumption | t/a | – | 97.38–119.27 | Projected from life of mine plan |
| New raw water withdrawal | kt/a | – | 4,200 | Projected from life of mine plan |
| Plant employees | number | – | 312–381 | Projected from life of mine plan |
| SAG mill grate aperture (post-trial) | mm | 50 x 34 | – | From 2020–2021 trials |
| Throughput increase from grate change | t/hr | approx. 4 | – | Target from trials |
Project website: https://www.goldfields.com/reports/rr_2009/tech_cerro.php
Technical qualifications
Processing risks identified in the report include:
- Major equipment failure: Catastrophic failure of key equipment items (crushers, grinding mills, flotation tanks) could lead to significant plant downtime until repairs are completed. Risk minimisation includes dedicated on-site maintenance, critical spares, contingency operational plans, fire suppression systems, and insurances. Decisions associated with asset management, critical spares, and insurances are outside the responsibility and accountability of the Qualified Person.
- Plant operational management: Decisions made daily by plant management and operators can directly impact plant performance; for example, processing at higher throughput could result in coarser grind size and lower recoveries. Such decisions are outside the responsibility and accountability of the Qualified Person.
- Operating costs, plant consumables and reagents: Processing costs represent a significant cost element. Assumptions are required concerning consumables consumption rates, unit prices and inflation rates. Metallurgical testing on future Mineral Reserves and recent plant performance provides guidance. Cerro Corona does not allow for a discreet operating cost contingency in forecasts, which is considered reasonable. Consumables, commodity pricing and inflation are subject to external influences outside the control of the Qualified Person. Operational decisions by plant management or unexpected variances in ore nature could impact reagent and consumables usage rates.
- Processing long term stockpiles: The life of mine plan includes accelerated pit mining with subsequent long-term storage of lower grade ores in stockpiles for treatment in the last part of the processing life. Material in storage may be subject to partial oxidation or weathering, potentially impacting flotation recoveries and costs. A 4% reduction in copper grade of stockpiled ore has been allowed for based on testwork to date. It is possible that impacts may be higher than expected. Testwork and studies are ongoing to better understand this potential issue.
*Source: Cerro Corona , 2021 Technical Report, Section 17 Recovery methods*
