Name: Stillwater and East Boulder mines.

Location: The Stillwater, including the Blitz expansion project, and East Boulder mines are located near the towns of Nye and McLeod in Montana, in the US.

Mine Owner/s: Sibanye-Stillwater.

Brief History: PGM production at Stillwater started in 1986 and has largely been uninterrupted. East Boulder has been in operation since 2002.

Brief Description: Stillwater and East Boulder are shallow to intermediate level underground platinum group metals (PGMs) mines.

Stillwater has a mine life to 2044, while the Blitz section has sufficient mineral resources to sustain production beyond 2055.

East Boulder has a mine life to 2056.

Primary Metals: Platinum and palladium (2E) PGM.

Secondary Metals: By-products of gold, rhodium, copper and nickel are recovered at the concentrators, smelter and refinery.

Geology/Mineralisation: Stillwater and East Boulder target the J-M reef zone, a magmatic reef-type PGM deposit defined as the palladium/platinum-rich stratigraphic interval, mainly occurring within a troctolite (OB-I zone) of the Lower Banded Series.

Palladium and platinum are the main PGMs, both constituting from between 15 g/t to 25 g/t over a variable thickness, with economic mineralised thickness ranging from 0.9 m to 2.7 m and averaging 1.8 m.

The visual identification of the J-M reef is facilitated by the presence of about 0.25% to locally 3% visible associated disseminated copper/nickel pathfinder sulphide minerals

Reserves: Total proven and probable reserves as at December 2018, were estimated at 46.4-million tonnes grading 17.2 g/t 2E PGM.

Resources: Total mineral resources as at December 2018, were estimated at 151.7-million tonnes grading 16.4 g/t 2E PGM.

Mining Method: Stillwater and East Boulder are both underground mines using predominantly mechanised ramp-and-fill mining – overhand and underhand. The mines also use sublevel extraction through longhole open stoping, with hydraulic backfilling; and overhand cut-and-fill stoping, using either raisebore or Alimak for access.

Major Infrastructure and Equipment: Stillwater is currently accessed through a 580-m-deep shaft and five portals. The Blitz section is accessed by one portal. Other infrastructure includes the mining operations and ancillary buildings that contain the concentrator, workshop and warehouse, changing facilities, headframe, hoist house, sand and paste plants, water treatment, storage facilities and offices.

The East Boulder mine is accessed through twin 5 800-m-long decline tunnels. Other infrastructure includes the mining operations and ancillary buildings that contain the concentrator, workshop and warehouse, changing facilities, twin tunnels to access the mine, sand plant, water treatment, storage facilities and offices.

Prospects: The Blitz project is expected to add an additional 300 000 2E PGM ounces to the existing Stillwater and East Boulder production by 2021/2022.

A new incremental project at the East Boulder mine, the Fill the Mill project is forecast to deliver about 40 000 oz/y of 2E PGM production from late 2020, over a ten-year period, through an incremental expansion of mining and certain support facilities at the mine and Columbus metallurgical complex. The incremental cost of the project is estimated at $29-million.

Contact Details:
Sibanye-Stillwater
Tel +27 11 278 9600
Email ir@sibanyestillwater.com
Website https://www.sibanyestillwater.com