Wawa Gold Project Recovery Methods: Toll Milling Process

Source: Unnamed_Company_36 (2026)

Critical Data

Overview

The Wawa Gold Project, a Preliminary Economic Assessment (PEA) by DRA, proposes a conventional gold recovery method utilizing existing toll milling facilities within a 150 km radius of the mine site in Wawa, Ontario. The project combines open pit and underground mining, with ore processed through on-site crushing to -150 mm before trucking to one of three regional mills: Alamos Island Gold Kremzar, Alamos Magino, or Hemlo Mining Company’s Williams Mill. These facilities operate gravity-leach-CIP flowsheets, achieving an average gold recovery of 88%. The significance lies in leveraging existing infrastructure to avoid capital expenditure for a new plant, while maintaining comparable metallurgical performance. The process involves primary crushing, grinding to 85% passing 200 mesh, gravity concentration using Knelson concentrators, cyanide leaching in a carbon-in-pulp circuit, and final refining to produce gold doré bars. This approach ensures efficient gold extraction from the 6.6 Mt of total plant feed over the life of mine, with average head grade of 3.2 g/t Au. The project expects annual production of approximately 48,000 oz Au from open pits and 74,000 oz Au from underground mining, demonstrating robust recovery methods tailored to the Wawa deposit.

Key Process Stages

• Stage 1: On-Site Crushing and Sampling – Single-stage primary jaw crusher and screen process ROM material at a rate of 240 t/h over one 10-hour shift to produce a minus 150 mm product. A sample tower provides representative daily composites for metallurgical accounting via fire assay.
• Stage 2: Grinding Circuit at Toll Mill – Crushed ore is fed into a closed-circuit grinding system comprising a SAG mill (22’ × 12’, 2600 kW) and a ball mill (16’ × 21’, 2600 kW). Cyclones classify the product to 85% passing 200 mesh (approx. 74 µm), preparing the slurry for downstream recovery.
• Stage 3: Gravity Concentration – The mill discharge passes through a Knelson concentrator (30”) to recover free gold. The concentrate is upgraded on a shaker table to produce a high-grade gravity concentrate, which is then combined with the leach feed or processed separately.
• Stage 4: Cyanide Leaching and Carbon-in-Pulp (CIP) – The ground slurry is thickened to 50% w/w and fed into nine leach tanks (12.2 m × 13 m, 1,400 m³ total) with lime (pH 10.2), oxygen (15–20 ppm), and cyanide (130 ppm). Leached slurry then enters six CIP tanks (8 m × 9 m, 435 m³) where gold is adsorbed onto activated carbon.
• Stage 5: Carbon Stripping, Electrowinning, and Refining – Loaded carbon (7-ton bins) undergoes acid washing (10 m³ vessel), stripping in a 10.5 m³ vessel, and thermal regeneration in a rotary kiln (1.2 m × 11.0 m). Pregnant solution feeds three electrowinning cells (3.5 m³ each). The resulting sludge is retorted and smelted in an induction furnace to produce gold doré bullion.

Additional Interesting Data and Summary

The technical data in Section 17 details a robust yet flexible recovery strategy for the Wawa Gold Project. The on-site crushing circuit operates one 10-hour shift per day at 240 t/h, feeding a 40,000-ton ROM stockpile with a 4-day surge capacity. The crushed material is trucked in 40-ton loads (50 loads per day) over distances of 75–150 km to three candidate toll mills. Notably, the Kremzar mill (75 km) is slated for decommissioning in 2026, leaving Magino (85 km, current capacity 10,000 tpd expanding to 12,400 tpd in 2026) and Hemlo (150 km) as the primary options. Environmental considerations are managed through the toll mills’ existing tailings facilities; for example, the Hemlo flowsheet includes a paste backfill plant (150 tph) and an effluent treatment plant (600 m³/h) discharging to Frank Lake. Reagents are minimal—only anti-scale chemical for water lines—while major consumables include crusher liners and screen decks. The on-site laboratory performs fire assays and shaker tests for metallurgical accounting, ensuring accurate reconciliation with toll mill operators. From an economic perspective, utilizing existing infrastructure eliminates the capital cost of a new processing plant—estimated at tens of millions of dollars—while still achieving 88% gold recovery on a 3.2 g/t head grade. Annual production averages 122,000 oz Au (48,000 oz from open pit, 74,000 oz from underground) over a 9-year mine life. Sustainability is enhanced by avoiding greenfield construction, reducing land disturbance and embodied carbon. Future outlook: the PEA recommends further test work and studies for a potential standalone processing facility, which would adopt the same proven flowsheet (crushing, grinding, gravity, leach/CIP) but with tailored design for the Wawa ore. This staged approach de-risks the project while maintaining optionality for long-term operational control.

Key Processes: CIP/CIL, Cyanidation, Gravity Separation, SAG Mill, Ball Mill, Crushing

Target Commodities: Gold