A horizontal tunnel or drive, open to the surface at one end, which is used as an entrance or access to a mine.


The analysis of the proportions of metals in ore, or the testing of an ore or mineral for composition, purity, weight or other properties of commercial interest.


Materials that facilitate one or more chemical reactions without being consumed in the reaction themselves. Platinum group metals serve as catalysts within the catalytic converters used in automotive exhaust and pollution control systems and, where so indicated, within similar applications in petroleum refining or other chemical processes.


A mineral processing product that generally describes the material that is produced after crushing and grinding ore, effecting significant separation of gangue (waste) minerals from the metal and/or metal minerals, and discarding the waste and minor amounts of metal and/or metal minerals. The resulting “concentrate” of metal and/or metal minerals typically has an order of magnitude higher content of metal and/or metal minerals than the beginning ore material.


A gently sloped underground excavation constructed for purposes of moving mobile equipment, materials, supplies or personnel from surface openings to deeper mine workings.


An estimate of the percentage of waste or low-grade mineralized rock which is included with the ore as part of normal mining practices in extracting an ore body.


A major horizontal access tunnel used for the transportation of ore or waste.

Filter cake

The PGM-bearing product that is shipped from the Company’s base metal refinery to a third-party toll refinery for the final extractive stages in the refining process.


The underlying side of a fault ore body or mine working, especially the wall rock beneath an inclined vein, fault or reef.


The average metal content, as determined by assay of a volume of ore. For precious metals, grade is normally expressed as troy ounces per ton of ore or as grams per metric tonne of ore. One troy ounce per short ton is equivalent to approximately 34.3 grams per tonne.

Mafic rocks

Igneous rocks composed chiefly of dark, ferromagnesian minerals in addition to lighter-colored feldspars.


A processing plant that produces a concentrate of the valuable minerals or metals contained in an ore. The concentrate must then be treated in some other type of plant, such as a smelter, to effect recovery of the pure metal. Term used interchangeably with concentrator.

Mineralized material

A mineralized body which has been delineated by appropriately spaced drilling and/or sampling to support a general estimate of available tonnage and average grade of metals. Such a deposit does not qualify as a reserve until a comprehensive evaluation based upon unit cost, grade, recoveries, and other material factors conclude legal and economic feasibility.


That part of a mineral deposit which could be economically and legally extracted or produced at the time of reserve determination.


The platinum group metals collectively and in any combination of palladium, platinum, rhodium, ruthenium, osmium, and iridium. References to PGM grades for the Company’s mine operations include measured quantities of palladium and platinum only. References to PGM grades associated with recycle materials typically include palladium, platinum, and rhodium.


The percentage of contained metal actually extracted from ore in the course of processing such ore.


A layer precipitated within the Stillwater Layered Igneous Complex enriched in platinum group metal-bearing minerals, chalcopyrite, pyrrhotite, pentlandite, and other sulfide materials. The J-M Reef, which the Company mines, occurs at a regular stratigraphic position within the Stillwater Complex. Note: this use of “reef” is uncommon and originated in South Africa where it is used to describe the PGM-bearing Merensky, Upper Group 2, and other similar layers in the Bushveld Complex.


The final stage of metal production in which residual impurities are removed from the metal.


That part of a mineral deposit which could be economically and legally extracted or produced at the time of the reserve determination.


A vertical or steeply inclined excavation for the purposes of opening and servicing an underground mine. It is usually equipped with a hoist at the top which lowers and raises a conveyance for handling personnel and materials.


Heating ore or concentrate material with suitable flux materials at high temperatures, creating a fusion of these materials to produce a melt consisting of two layers with a slag of the flux and gangue (waste) minerals on top and molten impure metals below. This generally produces an unfinished product (matte) requiring refining.


A localized area of underground excavation from which ore is extracted.


The portion of the mined material that remains after the valuable minerals have been extracted.

Ultramafic rocks

Igneous rocks composed chiefly of dark, ferromagnesian minerals in the absence of significant lighter-colored feldspars.