Adit

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

Anorthosite

Igneous rock composed almost wholly of the mineral plagioclase feldspar.

Assay

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.

Catalysts

Catalysts are materials that facilitate one or more chemical reactions without being consumed in the reaction themselves.  As referenced in this report, 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.

Close-spaced drilling

The drilling of holes designed to extract representative samples of rock in a target area.

Concentrate

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.

Crystallize

Process by which matter becomes crystalline (solid) from a gaseous, fluid or dispersed state.  The separation, usually from a liquid phase on cooling, of a solid crystalline phase.

Cut-off grade

The lowest grade of mineralized material that qualifies as ore in a given deposit.  The grade above which minerals are considered economically mineable considering the following parameters: estimates over the relevant period of mining costs, ore treatment costs, general and administrative costs, smelting and refining costs, royalty expenses, by-product credits, process and refining recovery rates and PGM prices.

Decline

A gently sloped underground excavation constructed for purposes of moving mobile equipment, materials, supplies or personnel from surface openings to deeper mine workings or as an alternative to hoisting in a shaft for mobilization of equipment and materials between mine levels.

Dilution

An estimate of the amount of waste or low-grade mineralized rock which will be mined with the ore as part of normal mining practices in extracting an orebody.

Drift

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

Ductility

Property of a solid material that undergoes more or less plastic deformation before it ruptures.  The ability of a material to stretch without fracturing.

Fault

A geologic fracture or a zone of fractures along which there has been displacement of the sides relative to one another parallel to the fracture.

Filter cake

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

Footwall

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

Gabbro rocks
(See Mafic/Ultramafic)

A group of dark-colored igneous rocks composed primarily of the minerals plagioclase feldspar and clinopyroxene, with minor orthopyroxene.

Gangue material

The non-metalliferous or waste metalliferous mineral in the ore.

Grade

The average metal content, as determined by assay of a ton of ore.  For precious metals, grade is normally expressed as troy ounces per ton of ore or as grams per metric tonne of ore.

Hanging wall

The overlying side of a fault, orebody, or mine working; especially the wall rock above an inclined vein, fault, or reef.  (Compare “footwall.”)

Hoist

See shaft

Jackleg drill

A manually operated rock drill, generally powered by compressed air, used to drill holes for blasting rock and to install ground support hardware.

Lenticular-shaped

Resembling in shape the cross section of a double-convex lens.

Lode claims

Claims to the mineral rights along a lode (vein) structure of mineralized material on Federal land; typically in the U.S. lode claims are 1,500 feet in length and 600 feet wide along the trend of the mineralized material.

Mafic rocks

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

Matrix

The finer-grained material between the larger particles of a rock or the material surrounding mineral particles.

Mill

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.

Millsite claims

Claiming of Federal land for millsite purposes or other operations connected with mining lode claims.  Used for nonmineralized land not necessarily contiguous with the vein or lode.

Mineral beneficiation

A treatment process separating the valuable minerals from the host material.

Mineralization

The concentration of metals and their compounds in rocks, and the processes involved therein.

Mineralized material

A mineralized body which has been delineated by appropriately spaced drilling and/or underground 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.

Mouat Agreement

Mining and Processing Agreement dated March 16, 1984 regarding the Mouat family.  The Mouat royalty stems back to the formation of Stillwater Mining Company at which time claims staked by the Mouats’ forebears in 1876 were leased to Stillwater Mining Company.

Net smelter royalty

A share of revenue paid by the Company to the owner of a royalty interest generally calculated based on the imputed value of the PGM concentrate delivered to the smelter.  At Stillwater Mining Company, royalties are calculated on the mineral production subject to each royalty as a percentage of the revenue received by the Company after deducting treatment, refining and transportation charges paid to third parties, and certain other costs incurred in connection with processing the concentrate at the Columbus smelter.

Norite

Coarse-grained igneous rock composed of the minerals plagioclase feldspar and orthopyroxene.

Ore

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

Outcrop

The part of a rock formation that appears at the earth’s surface often protruding above the surrounding ground.

PGM

The platinum group metals collectively and in any combination of palladium, platinum, rhodium, ruthenium, osmium, and iridium.  Reference to PGM grades for the Company’s operations include measured quantities of palladium and platinum only.

PGM rich matte

Matte is an intermediate product of smelting; an impure metallic sulfide mixture made by melting sulfide ore concentrates.  PGM rich matte is a matte with an elevated level of platinum group metals.

Reserves for which quantity and grade and/or quality are computed from information similar to that used for proven (measured) reserves, but the sites for inspection, sampling, and measurement are farther apart or are otherwise less adequately spaced.  The degree of assurance, although lower than that for proven (measured) reserves, is high enough to assume continuity between points of observation.

Reserves for which (a) quantity is computed from dimensions revealed in outcrops, trenches, workings or drill holes; grade and/or quality are computed from the results of detailed sampling; and (b) the sites for inspection, sampling and measurement are spaced so closely and the geologic character is so well defined that size, shape, depth and mineral content of reserves are well established.

Recovery

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

Reef

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, UG2, and other similar layers in the Bushveld Complex.

Refining

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

Reserves

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

Recycling
materials

Spent PGM-bearing materials collected for reprocessing from automotive, petroleum, chemical, medical, food and other catalysts.  Additionally, PGMs for recycling may be sourced from scrap electronics and thermocouples, old jewelry and materials used in manufacturing glass.

Shaft

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.

Slag

Slag is a nonmetallic product resulting from the mutual dissolution of flux and nonmetallic impurities during smelting.  A silica rich slag is a smelting slag that contains a relatively high level of silica.

Sill

(1) With respect to a mine opening, the base or floor of the excavated area (stope); (2) With respect to intrusive rock, a tabular intrusive unit that is conformable with surrounding rock layers.

Slusher

(1) An electric double-drum winch with two steel ropes attached to an open-bottomed scoop that transports (drags) ore from the rock face to a loading point, where the ore is discharged.  (2) A very selective mining method in which small ore stopes are mined using a slusher.

Smelting

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.

Sponge

A granular (shot) form of PGM.  Commonly, the form required for manufacture of many PGM-based chemicals and catalysts.

Stope

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

Strike

The course, direction or bearing of a vein or a layer of rock.

Tailings

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

Tolling

Processing of material owned by others for a fee without taking title to the material.

Troy ounce

A unit measure used in the precious metals industry.  A troy ounce is equal to 31.10 grams.  The amounts of palladium and platinum produced and/or sold by the Company are reported in troy ounces.  There are 12 troy ounces to a troy pound.

Ultramafic rocks

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

Vein

A mineralized zone having regular development in length, width and depth that clearly separates it from neighboring rock.

Wall rock

The rock adjacent to, enclosing, or including a vein, layer, or dissemination of ore minerals.