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 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 stoping, utilising either raise bore or Alimak for access (<5%).

The Company processes ore from the Stillwater Mine through a surface concentrator facility (mill) adjacent to the Stillwater Mine shaft. Crushed mine ore is fed into the concentrator, mixed with water and ground to slurry in the concentrator’s mill circuits to liberate the PGM-bearing sulfide minerals from the rock matrix. Various reagents are added to the slurry, which then is agitated in a froth flotation circuit to separate the valuable sulfides from the waste rock. In this circuit, the sulfide minerals are successively floated, recycled, reground and refloated to produce a concentrate suitable for further processing. The final flotation concentrate, which represents approximately 2.0% of the original ore weight, is filtered, placed in large bins and then transported by truck to the Company’s metallurgical complex in Columbus, Montana.

Currently 64% (2020) of all concentrator tailings are returned underground for backfill. The remaining 36% is sent via pipeline to Hertzle ........