Hemlo gold mine blackout: production, resequencing and risk notes for engineers
Reviewed by Joe Ashwell

First reported on MINING.com
30 Second Briefing
A 4 September power outage in Hemlo Mining’s Alimak zone is constraining underground development and exploration, delaying the planned ramp-up from about 3,800 to 4,800 tonnes per day and prompting an 8.9% share price drop to C$7.55. Scotia Capital now forecasts roughly 59,600 oz. of gold in H2, about 20% lower, though analysts expect the ounces to be deferred rather than lost as mine resequencing leverages more than 300 km of existing development. A $250,000 replacement substation, ordered pre-incident under a critical spares programme, is due in December.
Technical Brief
- Power loss was localised to the underground Alimak zone; plant and other mining areas remained energised.
- A temporary electrical bypass has been installed, enabling limited production but constraining development and exploration headings.
- Hemlo’s affected infrastructure centres on an underground electrical substation now subject to comprehensive technical assessment and expedited repair.
- A pre-ordered C$250,000 replacement substation, held under a critical spares strategy, is scheduled to arrive in December.
- Operational mitigation relies on resequencing into multiple active mining areas accessed via more than 300 km of existing development.
- Processing facilities are currently operating at roughly 40% of installed mill capacity, leaving significant headroom for future ramp-up.
- Hemlo’s resource base stands at 96.9 Mt measured and indicated at 1.55 g/t Au, totalling 4.84 Moz contained.
- Since 1985, the operation near Marathon, Ontario, has produced about 25 Moz of gold from combined open-pit and underground mining.
- A C$30 million mobile equipment investment and planned pit reopening are intended to “fill the mill” and utilise existing hoisting/processing infrastructure.
Our Take
The 20% expected drop in Hemlo gold output in the second half comes only weeks after our 25 June coverage of a 34% uplift in measured and indicated resources to 4.84 million oz, so the mine’s long‑term production case remains stronger than the near‑term operational setback implies.
Hemlo’s mill currently running at about 40% of capacity, combined with roughly 300 km of existing underground development, suggests there is substantial latent throughput that could be unlocked once the blackout‑related constraints are resolved, potentially allowing a faster catch‑up in 2026–28 than the market is pricing in after the 8.9% share price drop.
Earlier drilling updates at the Williams property (26 January) and South‑Rim (14 May) showed high‑grade gold and associated copper and sulphides, so any prolonged disruption to ramp‑up risks delaying the conversion of these exploration gains into mill feed, which is critical for justifying the recent US$30 million mobile equipment spend.
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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