Mineralisation characteristics:

• The J-M Reef is 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 between 7g/t to 40g/t over a variable thickness with economic mineralised thickness ranging from 0.9m – 2.7m and averaging 1.8m.

• Ratios of palladium to platinum in metallurgical concentrate are known to range from 3.4:1 (in situ 3.5:1) at Stillwater to 3.5:1 (in situ 3.6:1) at East Boulder.

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

• Other associated PGMs such as iridium, ruthenium and osmium occur in low quantities and are generally not evaluated by Stillwater.

• The visual identification of the J-M Reef is facilitated by the presence of approximately 0.25% to locally 3% visible associated disseminated copper-nickel pathfinder sulphide minerals.

The Stillwater (including the Blitz expansion project) and East Boulder operations are located near the towns of Nye and McLeod in Montana, USA. Both are underground PGM operations. PGM production commenced in 1986 and has largely been uninterrupted.

The operations both target the J-M Reef zone, predominantly via mechanised ramp and fill mining method (+80%). All surface infrastructure and tailings management facilities are located within Stillwater and East Boulder operation operating permits, which cover an area measuring 1,396ha.

The Stillwater operation has two principal mining sections. The current section, which has been in operation since 1986, produces approximately 380koz per annum of platinum and palladium in concentrate. The Blitz section, a major expansion project currently under development, started ore production in 2017 and is currently producing 75koz per annum. The current section of the operation is accessed by a 580m deep shaft and five portals. The Blitz section is accessed by two portals.

East Boulder has been in operation since 2002, and currently produces approximately 230Koz per annum of platinum and palladium in concentrate. The East Boulder operation is accessed via twin 5,800m long decline tunnels.

The three principal mining methods are:
• Mechanised ramp and fill (both overhand and underhand) (80 – 90%)
• Sub-level extraction by long hole, open stoping with hydraulic backfilling (10 – 15%)
• Overhand cut and fill (C&F) stoping, utilising either raisebore or Alimak for access (<5%).

Ore from the two operations is milled and treated at integrated concentrator complexes located at each operation. Concentrate smelting and refining takes place at the Columbus smelter complex, situated in the town of Columbus, Montana.

Mineral processing and capacity:
- Stillwater plant: Flotation with Design capacity of 3,100 tpd;
- East Boulder plant: Flotation with Design capacity of 1,800 tpd.