Stillwater & East Boulder

PGM production began at the Stillwater mine in 1986 and at the East Boulder mine in 2002. Mechanised ramp-and-fill stoping is the primary mining method at both mines. Mined ore is crushed and concentrated at processing facilities located on surface at both operations; concentrates are then transported to the Group’s Columbus Metallurgical complex in Montana, for further processing, smelting and refining.

The Stillwater mine has two principal in operation since 1986, has annual production of 250,000 to 350,000oz of platinum and palladium in concentrate and is accessed by a 580m-deep shaft and five surface portals. The eastern (Blitz) section, a major expansion project currently under development, started ore production in 2017 and is accessed via three portals.

Stillwater currently has a monthly run-of-mine (RoM) ore production level of 74,000t (2020 average). The Stillwater East expansion section will contribute to a projected monthly steady state RoM ore production of 103,000t by 2024. Ultimately, the monthly RoM production target is 110,000t in 2028.

In 2021, the Stillwater East expansion project realised 114,000oz. The current plan puts targeted production of 300,000oz for 2024. This addition will bring total Stillwater production to 600,000oz annually.

In 2021, 60% of all concentrator tailings were returned underground for backfill. The remaining 40% was sent via pipeline to Hertzler tailings storage facility (TSF) situated 11km north of Stillwater. Currently, the TSF has 4,740kt of storage remaining with expansion planned to add an additional 10,200kt of storage in 2029. The Hertzler TSF, together with the planned expansion, will provide adequate storage for current Proved and Probable Mineral Reserves.

It is estimated that current Mineral Reserves will sustain Stillwater until 2055 with the Blitz project having the potential to significantly expand Mineral Reserves beyond 2055.

A new concentrate handling system was added in 2021 as part of a new plant. The balance of the new processing facility will be commissioned in 2022.

East Boulder currently produces approximately 240,000oz per annum of platinum and palladium in concentrate. The East Boulder operation is accessed via twin 5,800m long decline tunnels.

In early 2019, the Fill the Mill project was launched to develop and provide the run-of-mine and infrastructure necessary to allow East Builder’s mill to operate at capacity, thereby increasing annual 2E PGM production by around 40,000oz. The project was completed on time at the end of 2020 with an annual run rate of 830,000t achieved in March 2021.

Currently 48% of all concentrator tailings are returned underground for backfill, with the remaining 52% sent via pipeline to a TSF adjacent to the mine site. The current storage facility has 4,600kt of storage remaining in Stages 4-6. In addition, an expansion is planned to add an additional 5,460kt of storage by 2030 at the Lewis Gulch facility. This facility, including another planned expansion, will accommodate current Proved and Probable Mineral Reserves.

Site teams are currently evaluating dry stacked tails for the Lewis Gulch facility which would essentially double the life of that facility.

It is estimated that current Mineral Reserves will sustain the East Boulder mine until 2061.