Unlike most platinum operations based primarily on Merensky and UG2 ore, Mogalakwena mines the Platreef, where palladium is slightly more abundant than platinum and grades are more variable.

The Platreef in the northern limb of the Bushveld Complex is predominantly a pyroxenitic PGE-Cu Nibearing package with a hanging wall of Main Zone gabbronorite and a footwall of Transvaal Supergroup in the south and Archaean granite and gneiss in the north. The Platreef varies from 400 m thick in the S to <50 m in the north.

The Platreef is heterogeneous and although predominantly pyroxenitic includes peridotites and norite cycles with anorthosite in the mid to upper portion of the Platreef in the south. Zones of intense serpentinisation may occur throughout the Platreef. Country rock xenoliths <1500 m long, are common. In the south, these are typically hornfelsed banded ironstones, shales, mudstones and siltstones whereas further north the xenoliths are typically dolomitic or calc silicates.

The Platreef generally shows lower PGE grade than the Merensky Reef and UG-2 chromitite. Overall grade is typically 4g/t where footwall is dolomite, but commonly 1-2 g/t elsewhere with intersections sometimes >10g/t. Grade may be bottom loaded e.g. Tweefontein, top-loaded e.g. Drenthe or be evenly distributed e.g. Overysel. Different styles of mineralisation occur within different sectors of the Platreef. For example, immiscible droplets accumulated in some structural traps or footwall depressions, good PGE grade is associated with dolomitic xenolithic rafts and zones of serpentinisation, and skarn type mineralisation occurs in the central sector where dolomite forms the footwall.

Sulphides may reach 20% in some intersections, with overall grades of 0.1-0.6% Cu and Ni. Massive sulphides are localised, commonly, but not exclusively towards the contact with footwall metasedimentary rocks. Magmatic sulphides are disseminated or net-textured ranging from a few microns to 2 cm grains of pyrrhotite and pentlandite with chalcopyrite and minor pyrite. Much of the sulphide is associated with intergranular plagioclase, or quartz-feldspar symplectites, along the margins of rounded cumulus orthopyroxenes. Composite grains of pyrrhotite, pentlandite and chalcopyrite are rimmed by, or associated with other trace sulphides including galena and sphalerite. The PGE’s occur as PtFe, Pt3Sn and variable Pd or Pt tellurides, bismuthides, arsenides, antimonides, bismuthoantimonides and complex bismuthotellurides.

The current infrastructure consists of five open pits, namely the Sandsloot, Zwartfontein, Mogalakwena South, Mogalakwena Central and Mogalakwena North pits. The mining method is open pit truck and shovel, and the current pit depths vary from 45 metres to 245 metres. The ore is milled at the new North Concentrator and at the older South Concentrator.

Ore is reduced in size with the aid of crushing and milling. Water is added to produce a pumpable slurry.

The separation of the valuable content from the ore takes place in flotation cells where reagents are added to an aerated slurry to produce high-grade PGMbearing concentrate.

Use of electric furnaces to smelt concentrate to produce a sulfur-rich matte with gangue impurities removed as slag.

Converter slag is reduced in an electric furnace to recover PGMs and base metals for recycling back to the converter.

Oxygen-enriched air is blown through a topsubmerged lance converter to oxidise sulfur and iron contained in furnace matte to SO2 gas and slag respectively. The resulting converter matte is slow-cooled to concentrate PGMs into a metallic fraction.

Crushed converter matte is milled and the PGM fraction is separated magnetically. This is pressure leached to yield a solid final concentrate that is sent to PMR. Base metal-rich non-magnetic solids and leach solution are processed further in the base metal refinery.

The SO2 gas is converted to SO3 by passing it over catalytic beds and the subsequent addition of water produces 98% sulfuric acid which is sold to fertiliser manufacturers.

Base metal-rich solids are leached in high-pressure autoclaves and contacted with MCP leach solution to yield separate nickel and copper streams.

The separate nickel and copper streams are purified. During this process cobalt sulfate is recovered.

Nickel and copper metal cathodes are produced by passing electrical current through the separate purified stream.

Excess sulfur in solution is neutralised with sodium hydroxide and crystallised to form a sodium sulfate product.

Final concentrate is dissolved using hydrochloric acid and chlorine gas. PGMs are sequentially separated and purified to yield platinum, palladium, iridium, rhodium, ruthenium and gold. Osmium is precipitated as a salt.