Sunshine Silver mill expansion: capex, throughput and restart lens for engineers
Reviewed by Tom Sullivan

First reported on MINING.com
30 Second Briefing
Sunshine Silver Mining & Refining is redesigning its Idaho Sunshine mine concentrator to handle up to 2,000 tonnes per day, roughly double the 1,000 t/d throughput in its March initial assessment, ahead of a targeted late-2028 restart. The original plan envisaged US$286.9 million in capex for a 6.7‑million‑oz‑per‑year silver operation over the first five years, but a Q2 2027 feasibility study will test whether the 3.16 Mt indicated at 1,022 g/t Ag plus 6.41 Mt inferred at 776 g/t can support higher throughput. Sunshine has already raised US$310.5 million in its IPO, is dismantling the old mill, installing a new hoist, and advancing 50,000 metres of underground drilling alongside studies for a 35‑million‑lb‑per‑year antimony plant and a 10‑million‑oz‑per‑year silver‑copper refinery restart.
Technical Brief
- Sunshine raised US$310.5 million gross in its June IPO, yielding US$286.5 million net proceeds.
- Feasibility study for the mine-and-mill restart is scheduled for completion in Q2 next year, before FID.
- Company estimates full replacement of existing mine infrastructure would cost about US$600 million.
- Existing shaft and upper-level tunnel already provide underground access; a new mine entrance targets Upper Country flexibility.
- Underground infill and step-out programme totals 50,000 m, mainly upgrading inferred to indicated for the feasibility case.
- Surface exploration adds a separate 45,000 m multiyear drill plan across East Sunshine, Pine Creek and Rock Creek.
- Two parallel feasibility studies will evaluate a 35 Mlb/y antimony plant and a 10 Moz/y silver-copper refinery restart.
Our Take
The recent 60% expansion of Sunshine Silver Mining & Refining’s mineral rights in Idaho’s Silver Valley, noted in our related coverage, underpins any mill-doubling scenario by giving the Sunshine mine a much larger resource catchment to feed higher throughput over a 24-year life.
The proposed 35-million-lb-per-year antimony trioxide plant, combined with existing silver-copper refining capacity, positions SSMR as one of the relatively few North American plays in our database that could offer both precious metal and critical mineral (antimony) supply from a single Idaho hub.
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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