The Stillwater (including Stillwater West and Stillwater East sections) and East Boulder mines are underground mining operations, located near the towns of Nye and McLeod in Montana, US respectively. The mines are located within the Custer Gallatin National Forest, on the front range of the Beartooth Mountains, at elevations exceeding 2,700m above mean sea level
Statistics as at 31 December 2025
Life of mine
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Stillwater
2051
East Boulder
2060
![Platinum ingots [icon]](https://www.sibanyestillwater.com/wp-content/uploads/2020/04/icon-pgm-production-1.svg){kind=icon}
Production 2E PGM
284,069oz
![Gold dollars [icon]](https://www.sibanyestillwater.com/wp-content/uploads/2020/04/icon-gold-costs.svg){kind=icon}
All-in sustaining cost
US$1,203/2Eoz
Workforce
870
employees and contractors
For up-to-date quarterly production figures, please refer to the latest results booklet.
The mines both target the J-M Reef zone via mechanised cut and fill (80% to 90%) and sub-level extraction (SLE) (10% to 20%) mining methods.
Ore from the mines is milled and processed by integrated concentrator complexes located at each mine site. Concentrate smelting and base metals refining takes place at the Columbus metallurgical complex, situated in the town of Columbus, Montana. 2E PGM filter cake is then sent to a third-party refiner for final processing into pure metal.
The Stillwater mine has two principal mining sections: the Stillwater West section, currently on care and maintenance, and the Stillwater East section, which began ore production in 2017. The western section of the operation is accessed by a 580m deep shaft and five surface portals, while Stillwater East is accessed via three portal drives.
The East Boulder mine has been in operation since 2002 and is accessed via twin 5,800m long tunnel bored portal drives.
As at 31 December 2025, the US PGM operations had total 2E PGM Mineral Reserves of 19.4Moz and total 2E PGM Mineral Resources of 80.9Moz.
A closer look
- The JM reef was discovered in 1974 by Johns-Manville Corporation, and was developed by Manville, Chevron and LAC Minerals Ltd. with production commencing in 1986
- By 1990 the smelter was commissioned and in 1994 the Stillwater Mining Company (SMC) was listed
- In 1996, the vertical shaft at the Stillwater mine was completed
- In 2000, the Hertzler tailings impoundment was constructed
- The East Boulder mine was established in 2002
- On 23 June 2003, SMC completed a stock purchase transaction with MMC Norilsk Nickel (Norilsk Nickel), whereby a
subsidiary of
Norilsk Nickel became a majority stockholder of the company. In December 2010, Norilsk Nickel disposed of its entire ownership interest in SMC through a secondary offering of the SMC shares in the public market - From 2010, SMC operated as a NYSE listed company until May 2017 when it was delisted following its acquisition by Sibanye Gold Limited
- The PGM recycling business was established in 2010
- Sibanye-Stillwater acquired the Stillwater Mining Company in 2017, the year which also saw the first production from the Stillwater East project
- In 2024, Stillwater West production was temporarily suspended due to restructuring activities
Stillwater Mine
Key infrastructure includes the mining operations and ancillary buildings that contain the concentrator, surface workshop, warehouse, changing facilities, headframe, hoist house, sand and paste plants, water treatment, storage facilities, and offices.
The original concentrator plant was built in 1986. A new concentrate handling system was added in 2021 as part of a new plant construction. The balance of the new processing facility was commissioned in 2023.
East Boulder Mine
Key infrastructure includes the mining operations and ancillary buildings that contain the concentrator, workshop, warehouse, changing facilities, twin tunnels to access mine, sand plant, water treatment, storage facilities and offices.
Stillwater Mine
On average, 52% of all concentrator tailings are returned underground for backfill. The remaining 48% are sent via pipeline to the Hertzler TSF, situated 11km north of Stillwater mine.
The current storage facility has 3,400kt of storage remaining, with expansion planned to add an additional 10,200kt of storage from the early 2030s. The Hertzler storage facility, with the planned expansion, will have adequate storage for current Proved and Probable Mineral Reserves.
East boulder Mine
On average, 44% of all concentrator tailings are returned underground for backfill, with the remaining 56% sent via pipeline to a TSF adjacent to the mine site.
The current storage facility, with the recent 2024 expansion, has 2,274kt of storage remaining in Stage 5; with 1,700kt of storage under construction in Stage 6 of the expansion (2027). In addition, a future expansion is planned to add an additional 5,500kt of storage in the early 2030s at the Lewis Gulch facility. These expansions will accommodate tailing storage through to approximately 2044. Additional tailings storage capacity to handle the remaining Reserves is included in the LoM financials, and detailed designs will be completed in the coming years.
Following further restructuring of the US PGM operations during Q4 2024, due to low PGM prices, including Stillwater West section being placed on Care and Maintenance, the US PGM operations have stabilised and returned to profitability during H2 2025. To ensure the long term sustainability and competitiveness of these mines, the US team has embarked on an optimisation strategy to reduce AISC to approximately US$1000/2Eoz over the next two to three years. This includes studies into increased levels of mechanisation at both East Boulder and Stillwater Mines.
