1. Processing and Recovery Methods Overview
The Fort Knox Mine operates two distinct ore processing lines:
– Mill Circuit (CIP): Comprising crushing, grinding, agitated cyanide leaching, and carbon-in-pulp (CIP) recovery.
– Heap Leach (CIC): A run-of-mine (ROM) valley-fill heap leach operation with carbon-in-column (CIC) gold recovery.
Gold is recovered from both circuits via electrowinning and refined into doré bars at the on-site refinery.
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2. Mill Circuit (CIP) – Detailed Analysis
Feed & Capacity:
– Processes higher-grade ore at 36,287 t/d (40,000 stpd).
– Operates 24/7, achieving 81–83% recovery (dependent on feed grade).
Crushing & Grinding:
– Primary Crushing:
– Gyratory crusher (1.52×2.59 m, 700 hp) reduces ore to <20 cm (8 in).
– Capacity: 65,317 t/d (72,000 stpd).
– Conveyed 800 m to a 272,000 t (300,000 st) coarse ore stockpile.
– Grinding:
– SAG Mill: 10.4×4.6 m (34×15.25 ft), dual 7,000 hp motors.
– Discharge screened; oversize (“pebbles”) crushed by a 2.13 m (7 ft) cone crusher (500 hp).
– Ball Mills: Two parallel lines, each with a 6.1×9.1 m (20×30 ft) ball mill (7,000 hp) in closed-circuit with hydrocyclones.
Gravity & Leaching:
– Coarse Gold Recovery:
– Knelson concentrators recover gravity gold, processed in an Acacia reactor (high-temperature leaching).
– Gold electrowon and refined; tails returned to grinding.
– Leaching & CIP:
– Hydrocyclone overflow passes through trash screens, thickened, and pumped to seven-stage leach tanks (94,000 gallons each) with cyanide.
– CIP Circuit: Gold adsorbed onto activated carbon; loaded carbon stripped via hot caustic elution, electrowinning, and refining.
– Tails detoxified and stored in the Tailings Storage Facility (TSF).
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3. Heap Leach (CIC) – Detailed Analysis
Facilities:
– Walter Creek Heap Leach (WCHL):
– Valley-fill ROM heap leach with 15 m (50 ft) lifts.
– Impermeable synthetic liner; year-round irrigation via buried drippers.
– 416 ML solution reservoir; pumped to dual CIC circuits (61,000 L/m capacity).
– Barnes Creek Heap Leach (BCHL):
– Future expansion, similar to WCHL, with in-heap solution storage.
Operations:
– Leaching: Cyanide solution irrigates heaps; gold-laden solution processed via CIC.
– Gold Recovery:
– Activated carbon in CIC adsorbs gold; stripped and electrowon.
– Series Operation: WCHL feeds BCHL; combined pregnant solution processed in CIC.
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4. Key Technical Specifications & Innovations
– Equipment Highlights:
– SAG/Ball Mills: High-power (7,000 hp) for efficient grinding.
– Acacia Reactor: High-intensity leaching for gravity concentrate.
– CIP/CIC Circuits: Optimized carbon adsorption with elution/regeneration.
– Throughput:
– Mill: 36,287 t/d; Heap Leach: Variable (ROM-dependent).
– Recovery Rates:
– Mill: 81–83%; Heap Leach: Not explicitly stated but relies on CIC efficiency.
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5. Challenges & Solutions
– Mill Shutdown (2020): Due to TSF capacity limits; transitioned to full heap leaching (BCHL).
– Heap Leach Variability:
– Cell geometry and snow impacts addressed via flexible stacking/irrigation.
– Dual-pad system (WCHL + BCHL) optimizes solution flow.
– Power Demand:
– Mill consumes 200,000–300,000 MWh/year; heap leach less energy-intensive.
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6. Conclusion
Fort Knox employs a hybrid processing approach, combining high-capacity milling for high-grade ore and scalable heap leaching for ROM material. The integration of gravity recovery, CIP/CIC, and electrowinning ensures robust gold recovery, while future focus shifts to heap leaching post-mill closure. Operational flexibility and advanced equipment (e.g., Knelson concentrators, Acacia reactor) underscore the site’s technical sophistication.
Technical report and processing history
The following archived source profiles have been consolidated here to preserve the project’s processing history and study context.
Fort Knox Mine — 2019 Technical Report
Fort Knox Mine — 2019 Technical Report
| Company | Kinross Gold Corporation |
| Date | 2019 |
| Region | Fairbanks North Star Borough, Alaska, USA |
| Commodities | Gold |
Executive Summary
The Fort Knox Mine, operated by Kinross Gold Corporation, is an open-pit gold mining operation located in the Fairbanks North Star Borough of Alaska, USA. The facility utilizes a dual processing approach involving a high-grade mill circuit and a run-of-mine heap leach operation to recover gold from ore. The mill processes ore 24 hours per day, 365 days per year at a nominal capacity of 36,287 t/d, while the heap leach facility processes lower-grade material.
The mill circuit includes a primary gyratory crusher, a semi-autogenous mill, and two ball mills operating in closed-circuit with hydrocyclones. Gold recovery is achieved through gravity concentration using Knelson concentrators followed by cyanide tank leaching and a Carbon-in-Pulp (CIP) circuit. Typical recovery rates in recent years have been in the range of 81% to 83%.
The heap leach operation consists of the Walter Creek Heap Leach (WCHL) and the planned Barnes Creek Heap Leach (BCHL) pads. These valley-fill facilities use run-of-mine ore with cyanide irrigation and recover gold using two parallel Carbon-in-Column (CIC) circuits. The mill is planned to cease operation in late 2020 due to tailings storage facility capacity limitations, after which all ore will be directed to the heap leach pads until the end of mine life.
Website: https://www.kinross.com/operations/default.aspx
Report Date: 2019
Region: Fairbanks North Star Borough, Alaska, USA
Project Status:
Commodity: Gold
Throughput:
Mine Life:
Mine Type:
Ore type:
Fort Knox Mine: Gold Processing Circuit Overview
Overview
The Fort Knox Mine operates two distinct gold recovery circuits: a conventional mill processing line and a run-of-mine heap leaching operation. The facility processes free-milling gold ore through crushing, grinding, cyanide leaching, and carbon adsorption circuits, with final gold recovery through electrowinning and doré bar production.
Key Process Stages
- Mill Processing Line (36,287 t/d capacity): Primary crushing (1.52×2.59 m gyratory crusher), SAG milling (10.4×4.6 m with 2×7,000 hp motors), ball milling (2×6.1×9.1 m mills), gravity concentration (Knelson concentrators), cyanide leaching (7×94,000 gallon tanks), and CIP recovery
- Heap Leach Operations: Valley-fill dump leaching (Walter Creek and future Barnes Creek pads) with 15m lifts, year-round irrigation, and parallel CIC circuits (61,000 L/m capacity)
- Gold Recovery: Carbon stripping, electrowinning, and doré bar production at centralized refinery
- Tailings Management: Detoxification of mill tailings before TSF deposition; permanent on-pad storage for heap leach residues
Critical Data
| Parameter | Value |
|---|---|
| Mill Throughput | 36,287 t/d (40,000 stpd) |
| Primary Crusher Capacity | 65,317 t/d (72,000 stpd) |
| Gold Recovery | 81-83% (mill), variable (heap) |
| Cyanide Concentration | 0.15 kg/solution tonne |
| Power Consumption | 300,000 MWh/yr (mill), 80-90,000 MWh/yr (heap) |
| Water Consumption | 5.7 Mm³ annually |
| Lime Consumption | 0.33 kg/tonne ore |
| Carbon Consumption | 0.0014 kg/tonne solution |
Circuit Features
The mill features advanced gravity recovery (Acacia reactor) for coarse gold and a seven-stage leach-CIP circuit. The heap leach operation uses innovative buried drip irrigation for year-round operation in Alaska’s climate. Both circuits share centralized gold recovery infrastructure with carbon elution and electrowinning capacity.
Future Operations
Following mill closure in 2020 due to TSF constraints, all ore will transition to heap leaching on the new Barnes Creek pad, maintaining gold production through the carbon-in-column recovery system.
