The Westwood Mine processing circuit is a comprehensive gold recovery system utilizing cyanidation with carbon adsorption, built upon a refurbished Doyon Mill facility. The circuit was significantly upgraded between 2011-2013 to optimize gold recovery from Westwood ore.
Processing Flow and Equipment:
1. Ore Handling:
– Underground ore is transported 2.5km by truck to the mill
– Single-stage jaw crusher (1.07m x 1.22m) with grizzly feeder
– Belt conveyor system to mill bins (2,800 dmt capacity each)
2. Grinding Circuit:
– 2,700 HP SAG mill in closed circuit with primary hydrocyclones
– 1,000 HP ball mill with secondary hydrocyclones
– Target grind size: 80% passing 53 microns (270 mesh)
3. Gravity Recovery:
– Secondary cyclone underflow feeds gravity circuit
– Equipment includes Sweco screen, 30″ Knelson concentrator, shaking table
– Gravity concentrate sent directly to refinery
– Tailings return to grinding circuit
4. Leaching and Adsorption:
– 55 hours total retention time at 3,106 tpd nominal rate
– Circuit breakdown:
• Primary leach tanks: 4.7 hours
• CIL tanks: 6.6 hours
• Secondary leach tanks: 31.3 hours
• CIP tanks: 12.1 hours
5. Gold Recovery:
– Acid wash vessel and high-pressure Zadra stripping reactors
– Two parallel electrowinning cells
– Gold sludge filtered, dried, and smelted into doré bars
– Carbon regeneration kiln for reactivation
– Carbon attrition system for fresh carbon preparation
6. Tailings Management:
– SO2/Air cyanide destruction process
– Two parallel detox reactors
– Split between paste backfill plant and Doyon open pit disposal
– Buffer tank with 14 hours capacity for backfill feed continuity
7. Paste Backfill System:
– Two 2km pipelines (feed and return)
– Designed for 144.6 tph maximum (operating at 70 tph)
– Two circuits for simultaneous stope filling
– Water recovery system to mill
Key Operational Parameters:
– Annual throughput: 1,100,000 tpy (after optimization)
– Mill availability: 96%
– Operating weeks/year: 52
– Design capacity: 2,425 tpd
Reagent Consumption (annual):
– Cyanide: 945,000 kg
– Quick lime: 5,640,000 kg (combined mill and environmental)
– SO2: 1,118,000 kg
– Slag/cement: 8,273,000 kg (backfill)
– Grinding media: 1,805,000 kg
Innovations and Notable Features:
– Refurbishment of 1970s Doyon Mill with modern equipment
– Optimized throughput increased capacity from 850,000 to 1,100,000 tpy
– Dual-purpose tailings management (backfill and pit disposal)
– Sophisticated paste backfill system with water recovery
– Comprehensive cyanide destruction circuit
Technical Challenges and Solutions:
1. Zinc Recovery Consideration:
– Initial assessments showed potential for zinc recovery
– Subsequent studies deemed uneconomical
– Solution: Process high-grade zinc ore through cyanidation only
2. Tailings Management:
– Existing Doyon tailings facilities nearing capacity
– Solution: Utilize Doyon open pit (11.3 MCUM capacity)
– Environmental criteria met for pit disposal
3. Throughput Optimization:
– Original design capacity of 850,000 tpy
– Solution: Circuit upgrades increased to 1,100,000 tpy
4. Power Management:
– Mill represents 8% of total milling cost
– Solution: Adequate contract with Hydro-Quebec (30,000 kW max)
Water Management:
– Primary source: Tailings management facility and Doyon system
– Secondary source: Bousquet River
– Annual treatment: 4.0-4.5 MCUM in HDS plant
– Water recycling from backfill plant to mill
The processing circuit demonstrates a well-integrated system combining modern gold recovery techniques with efficient tailings management and backfill production, all while maintaining environmental compliance through comprehensive cyanide destruction and water treatment systems.
