Mount Milligan mine life boost to 2035: design and tailings notes for engineers
Reviewed by Tom Sullivan
First reported on MINING.com
30 Second Briefing
Centerra Gold has secured British Columbia Environmental Assessment Office approval to run the Mount Milligan open-pit copper-gold mine to 2035, authorising an 11% throughput increase to 66,500 tonnes of ore per day, an 80-hectare expansion of the disturbance area and a 26-metre raise of the tailings storage dam to 1,121 metres above sea level. The amendment also permits a revised haulage route, new site infrastructure 155 km north of Prince George, and updated reclamation and closure plans. A recent pre-feasibility study envisages potential operation to 2045, with annual output of 150,000 oz gold and 69 million lb copper from reserves of 483.2 million tonnes at 0.28 g/t Au and 0.16% Cu.
Technical Brief
- EAO approval follows a nine‑month review of Thompson Creek Metals’ application and supporting impact assessments.
- Review scope covered water and fish habitats, air quality, noise and quantified safety risk to nearby communities and First Nations.
- Mount Milligan currently employs about 600 people, with additional construction jobs expected during expansion works.
- Regional economic contribution from the expansion phase is estimated at up to C$450 million.
- A February 2024 agreement sees Royal Gold provide US$125 million in cost support for its metal stream.
- That Royal Gold deal previously enabled a two‑year extension of operations ahead of the latest approval.
- Proven and probable reserves total 483.2 Mt containing 4.4 Moz Au and 1.7 Blb Cu.
- PFS forecasts production to 2042 at around 150,000 oz gold and 69 Mlb copper per year, subject to further permits.
Our Take
With Mount Milligan’s copper and gold grades at 0.16% Cu and 0.28 g/t Au, the extended life to at least 2035 suggests Centerra is betting on economies of scale and stable metal prices rather than grade upside, which aligns with several other low-grade, bulk-tonnage copper items in our 487 Mining stories.
The 26 m tailings dam height increase and 80 ha disturbance expansion in British Columbia place Mount Milligan among the more materially altered existing operations in our Projects-tagged coverage, signalling that regulators are currently willing to permit significant brownfield modifications where economic benefits (C$450 million regionally) and existing employment are demonstrable.
Royal Gold’s US$125 million cost-support payment tied to Mount Milligan underscores how streaming and royalty players are increasingly being used to de-risk life extensions at mature copper-gold assets, a pattern that recurs across other copper and gold pieces in our database even when headline capex is not disclosed.
Prepared by collating external sources, AI-assisted tools, and Geomechanics.io’s proprietary mining database, then reviewed for technical accuracy & edited by our geotechnical team.
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