This technical report describes the proposed conventional crushing, grinding and flotation processing route for the Galore Creek copper–gold deposit based on a September 2011 pre-feasibility study design.
Report context
This September 2011 technical report presents the pre-feasibility study design for the Galore Creek Copper–Gold Project located in British Columbia. The report was prepared for Galore Creek Mining Corporation, NovaGold Resources Inc., and Teck Resources Limited. The process plant design is based on processing mined material through a conventional crushing, grinding and flotation plant using standard proven processes and equipment. The plant will handle a blend of material from the various zones of the Galore Creek deposit with approximately 80% coming from the Central Zone. Although the characteristics of materials from the various zones are different, the process applied is the same, with only process conditions such as slurry densities and reagent dosages changing for the different materials.
Processing route
Primary Crushing
Run-of-mine (ROM) material will be delivered by 345 t capacity mine haul trucks to the primary crushing plant located in Galore Creek Valley. The crushing plant is designed to operate at 365 d/a with an average utilization of 70%. The truck dump hopper will have a live capacity of approximately 700 t. ROM ore will be gravity-fed to a 60 x 110 class gyratory crusher with an open side setting of 175 mm and driven by a 750 kW motor. Crushed ore will fall directly from the crusher into a 700 t capacity surge bin. A dry-type dust collection system will be installed at the transfer point from the apron feeder to the discharge conveyor.
The discharge belt conveyor will be 1,829 mm wide, approximately 500 m long and designed to carry 7,000 t/h at 3.75 m/s, driven by a 630 kW motor. Crushed material will be conveyed to a surge pile in the East Fork of the Galore Creek Valley.
Coarse Ore Surge Pile and Overland Conveyor
The coarse ore surge pile will have a total capacity of 40,000 t and a live capacity of approximately 8,000 t (1.5 hours of feed at design capacity). The conical-shaped pile will be 70 m in diameter x 27 m high with a geodesic dome to protect the ore and reduce dust emissions. Two apron feeders beneath the surge pile will transfer ore to the overland conveyor system.
The overland conveyor system will comprise three conventional belt conveyors in series. The crushed ore discharge conveyor will convey primary crushed ore from the surge pile at the west end of Galore Creek Valley’s East Fork to a transfer station adjacent to the north portal of the tunnel at the head of the East Fork. This conveyor raises 89 m over its 3,152 m length and will be driven at the head end by three 1,400 kW variable speed shaft-mounted drive units. The overland tunnel conveyor will be the second in the series, raising 200 m over its 14,577 m length and driven by six 2,500 kW variable speed shaft-mounted drive units. The stockpile feed conveyor will be the third in the system, raising 460 m over its 4,036 m length and driven by four 2,800 kW shaft-mounted drive units.
Coarse Ore Stockpile
The coarse ore stockpile will receive primary crushed ore from the overland conveyor system and provide surge capacity between the conveyor system and the mill. The conical-shaped pile will have a total capacity of 240,000 t and a live capacity of approximately 47,500 t (12 hours of feed at mill design capacity). The stockpile will be 125 m in diameter x 47 m high with a geodesic dome. Four apron feeders beneath the pile will transfer ore to the SAG mill feed conveyor, with each feeder designed to deliver one-third of the mill design capacity.
Grinding Circuit
The grinding circuit will be rated at a nominal 95,000 t/d and will be designed to handle competent ore, which will constitute the mill feed for the majority of the mine life. The SABC grinding circuit will consist of one SAG mill, three ball mills, two pebble crushers and three cyclone packs. The SAG mill will be in closed-circuit with the pebble crushers, while the ball mills will be in closed-circuit with the cyclones.
The 12.2 m diameter x 7.9 m EGL (40' x 26') SAG mill will be driven by a 26 MW gearless, variable speed drive. Process water will be added to the feed chute to achieve 60% to 70% solids in the mill feed. The steel ball size will be 5" (125 mm) diameter and the steel charge will be nominally 15%. Lime slurry will be added at a constant rate into the SAG mill to raise its pH to just below 10.
Ore will leave the SAG mill through discharge grates with 75 mm ports for pebble relief and the trommel screen. Oversize pebbles will be discharged from the trommel screen onto a double-deck vibrating screen equipped with water sprays before being conveyed to the pebble crushers.
Two belt feeders will extract the pebbles from the surge bin to feed two 750 kW cone crushers operating in parallel. The cone crushers will reduce the pebbles to 13 mm.
The undersize products from the SAG mill trommel and vibrating screen, at an 80% passing size of approximately 3,000 µm, will discharge to a pump box. Process water will be added to dilute the resulting slurry product to 55% solids. A single pump will elevate the slurry to a three-way gravity splitter that will distribute the slurry between the three ball mill circuits.
Each ball mill will be 7.9 m diameter x 11 m EGL (26' x 36') and driven by 15 MW dual-pinion low-speed synchronous drives. The ball mills will operate at approximately 32.5% ball load and generally will draw approximately 14.4 MW, although the ball mill will be structurally designed for a ball load of up to 40%. Slurry from the gravity splitter will flow to the cyclone feed pump box associated with each ball mill circuit. From the pump box, the slurry will be pumped to a cluster of ten 840 mm (53") cyclones. Cyclone overflow, at 80% passing 200 µm, will flow by gravity to the rougher flotation circuit.
Rougher Flotation and Tailings Handling
The cyclone overflows from the three ball mills, at 34% solids, will be collected in a common discharge distributor that will split the slurry into two streams feeding two banks of rougher flotation cells. Each bank will consist of eight 300 m³ rougher flotation cells, providing 23 minutes of residence time.
Rougher tailings will report to a final tails collection box, where they will be joined by floor sump discharges and other discharge streams from the mill. The combined streams will be pumped to either two-stage tailings cyclones or directly to the TSF. During summer months the underflow from the second stage cyclone will be used for tailings dam construction, while the overflows from both cyclone stages will be piped into the TSF.
Regrinding
The rougher concentrate will be reground by four 1,125 kW tower regrind mills operating in closed-circuit with a single cluster of fourteen 380 mm (15") cyclones to achieve a product grind of 80% passing 40 µm. A portion of the cyclone underflow will be split off to an enhanced-gravity concentrator that will capture any coarse metallic gold. Gravity concentrate from this concentrator will flow by gravity to the third cleaner concentrate pumps for transport to the final concentrate thickener.
Cleaner Flotation
The reground rougher concentrate will overflow by gravity to the first cleaner flotation circuit, which has a bank of six 100 m³ tank cells. The first four cells will be cleaners, and their concentrate will be collected and forwarded to the second cleaners. The last two cells will be operated as scavenger cells, with scavenger concentrate recycled to the regrind mill feed.
Tailings from the first cleaner-scavenger cells will flow by gravity through a dedicated line to the TSF for sub-aqueous deposition. The second and third cleaners will consist of a total of eight 40 m³ tank cells (five in the second cleaners and three in the third cleaners). Third-cleaner concentrate will be collected as final concentrate product, averaging 26% copper.
Concentrate Thickening and Pumping
Third-cleaner concentrate will be pumped to a high-rate thickener, where it will be flocculated and thickened to 60% solids. Thickener underflow will be pumped to two agitated storage tanks providing surge capacity.
Concentrate from the storage tanks will be pumped into a premix tank, where it will be mixed with water to the density and viscosity required by the pipeline system (52% to 57% solids by weight). The concentrate slurry will be pumped by a centrifugal pump system into a PD pump that will transfer material approximately 70 km through the concentrate pipeline to the Km 8 filter plant.
The pipeline was designed to transport 150 t/h (3,600 t/d) of copper concentrate (dry basis) at 55% solids. The pipeline will be 219 mm (8.625 inch) diameter API 5L Grade X-65 carbon steel lined with HDPE. It will be buried with a minimum of 1.6 m cover.
Filter Plant
The filter plant will consist of four 120 m² pressure filters configured to run independently. The filtration rate is estimated at 388 kg/h per square meter of filter area. Concentrate slurry solids will have a size distribution of 80% passing 40 µm and 50% passing 20 µm, with a specific gravity of 4.28.
The filtration cycle time will be approximately 13.5 minutes, comprising slurry feeding, cake pressing, air blowing, cake discharge and cloth washing. Filter cake will be discharged at nominal 8% moisture. The four filters will discharge de-watered concentrate onto a belt feeder that will meter the concentrate onto a transfer conveyor, then to a 10,000 t capacity concentrate storage shed. Concentrate will be reclaimed by front-end loader and discharged into 50 t side-dump B-train trucks for transportation to the port facility at Stewart, BC.
Key reported parameters
| Parameter | Value | Basis |
|---|---|---|
| Grinding circuit nominal capacity | 95,000 t/d | Design |
| Maximum projected mill throughput (early years) | 110,000 t/d | Design (within conveyor and equipment capacity) |
| SAG mill dimensions | 12.2 m diameter x 7.9 m EGL (40' x 26') | Design |
| SAG mill drive | 26 MW gearless, variable speed | Design |
| Ball mill dimensions | 7.9 m diameter x 11 m EGL (26' x 36') | Design |
| Ball mill drive | 15 MW dual-pinion low-speed synchronous | Design |
| Pebble crusher power | 750 kW each (two units) | Design |
| Target primary grind size | 80% passing 200 µm | Design |
| Target regrind size | 80% passing 40 µm | Design |
| Rougher flotation residence time | 23 minutes | Design |
| Rougher flotation cell volume | 300 m³ each (16 cells total) | Design |
| Tower regrind mill power | 1,125 kW each (four units) | Design |
| Final concentrate grade | 26% copper | Design (from cleaner circuit) |
| Concentrate thickener discharge solids | 60% | Design |
| Concentrate pipeline design rate | 150 t/h (3,600 t/d) dry basis | Design |
| Concentrate pipeline length | Approximately 70 km | Design |
| Concentrate pipeline operating velocity | Approximately 1.5 m/s | Design |
| Filter plant pressure filters | Four x 120 m² | Design |
| Filtration rate | 388 kg/h/m² | Design |
| Filter cake moisture | Nominal 8% | Design |
| Primary crusher type | 60 x 110 gyratory, 750 kW motor | Design |
| Primary crusher open side setting | 175 mm | Design |
| Coarse ore surge pile capacity | 40,000 t total / 8,000 t live | Design |
| Coarse ore stockpile capacity | 240,000 t total / 47,500 t live | Design |
Project website: https://www.gcmc.ca/galore-creek-project/
Technical qualifications
In the opinion of the qualified persons responsible for Section 17 of the report, the following limitations and points were noted:
- The crusher size selected would be close to its operating limit but can meet the design capacity of 95,000 t/d
- The three x 1,400 kW drives mentioned for the crushed ore conveyor are potentially marginally sized; dynamic analysis will play an important role in the design of the crushed ore conveyor and potentially could change the required operating parameter
- Having the take-up at the tail end of the SAG mill feed conveyor may be more suitable than the current design
- In the early years of operation, the mill will receive less competent, sheet-fractured rock from near the surface. The operating conditions, particularly the sizes of the grate and screen openings, will be modified to process this material. The maximum mill throughput with this ore is projected to be 110,000 t/d, which will be within the design capacity for conveyors, pumps and other process equipment
- The process design is based on the metallurgical testwork and is appropriate to the grind, flotation and recovery characteristics defined for the different ore types
Source: Galore Creek Copper–Gold Project British Columbia NI 43-101 Technical Report on Pre-Feasibility Study, September 2011, Section 17.0 Recovery Methods
