The Mount Polley Mine employs a conventional mineral processing circuit designed for the production of copper-gold concentrate. The mill, commissioned in June 1997, integrates crushing, grinding, flotation, and dewatering stages with a throughput capacity ranging between 17,800 to 22,000 tonnes per day (tpd), contingent on ore hardness.
Processing and Recovery Methods:
1. Crushing Circuit:
– Three-stage crushing (primary, secondary, tertiary) reduces ore to 16 mm for grinding.
– Equipment:
– Primary: 1 × 42” x 65” gyratory crusher.
– Secondary: 1 × 7’ standard cone crusher.
– Tertiary: 3 × short-head cone crushers + 4 screen decks.
– Ore Handling: Crushed product stored in a 15,000 t stockpile; pebble mill feed held in a 2,000 t surge pile.
2. Grinding Circuit:
– Rod mills process crusher product at 915 t/h, reducing feed size for subsequent ball mills.
– Ball and pebble mills further grind material to 65% passing 200 mesh (flotation feed size).
– Classification: Hydrocyclones and pumps optimize particle size distribution.
– Power & Water:
– Electricity sourced via a 69 kV line from Soda Creek substation (70 km).
– Water reclaimed from tailings pond.
3. Flotation Circuit:
– Hybrid system combining column and mechanical cells for rougher/scavenger concentrate recovery.
– Regrinding and cleaning stages enhance concentrate grade.
– Flexibility: Designed to handle variations in ore head grade and oxidation.
– Reagents:
– Potassium amyl xanthate (15 g/t) – Collector.
– POLYFROTH® W22C (20 g/t) – Frother.
– Flocculant (0.13 g/t) and Lime (90 g/t) – pH control and settling aid.
4. Concentrate Dewatering:
– Thickening: Concentrate stored in surge tanks.
– Filtration: Two Larox pressure filters reduce moisture to 8% for transport.
– Storage: Conveyor system loads filtered concentrate into trucks.
5. Instrumentation & Control:
– Centralized PLC system with remote I/O stations for real-time monitoring.
– On-Stream Analyzer (OSA): X-ray spectrometer assays five process streams for metallurgical control, reducing manual sampling needs.
– Human-Machine Interface (HMI): Displays grinding/flotation circuit data for operator adjustments.
6. Concentrate Transport:
– Trucked to Port of Vancouver via Arrow Transportation Systems.
– Shipped to Asian smelters; sales contracts negotiated dynamically.
Key Technical Specifications & Innovations:
– Pebble Mill Integration: Unique use of pebble milling post-ball milling for finer grind.
– Hybrid Flotation: Combines column/mechanical cells for improved recovery flexibility.
– OSA Integration: Automated assay feedback optimizes flotation performance.
Throughput & Efficiency:
– Design Capacity: 17,800–22,000 tpd (ore hardness-dependent).
– Grinding Rate: ~915 t/h in rod mills.
– Final Concentrate Moisture: 8% (achieved via Larox filters).
Challenges & Solutions:
– Ore Variability: Circuit designed to adapt to head grade/oxidation changes via flexible flotation.
– Tailings Management: Temporary deposition in Springer Pit (permit-limited); long-term storage in TSF post-2016.
The Mount Polley circuit exemplifies a robust, conventional flowsheet with targeted innovations (OSA, hybrid flotation) to enhance operational efficiency and adaptability.
