The Merensky Reef is generally regarded as a uniform reef type, large variations occur in reef thickness, reef composition, as well as the position of the mineralisation.

The rock-forming minerals of the Merensky Reef comprise approximately equal amounts of dark iron-magnesium silicate minerals and lighter calcium-aluminium-sodium silicate minerals (called a feldspathic pyroxenite) under- and overlain by thin (5 to 15 mm) often discontinuous layers of chrornite concentrations. The total thickness of this package is generally less than 30 cm. This zone, commonly known as the Merensky pegmatoid, contains the base metal sulfide grains and associated platinum group minerals. The Merensky Reef has been traced for 300 km around the entire outcrop of the eastern and western limbs of the Bushveld Complex, and to depths of 5 km.

The rock-forming silicate minerals of the Merensky Reef consist predominantly of orthopyroxene (- 60 per cent), plagioclase feldspar (- 20 per cent), pyroxene (- 15 per cent), phlogopite (5 per cent), and occasional olivine which lists the composition of some of the common minerals found in the Bushveld-type rocks. Secondary minerals such as talc, serpentine, chlorite and magnetite have widespread occurrence.

The base metal sulfides consist of pyrrhotite (-40 per cent), pentlandite (- 30 per cent), chalcopyrite (- 15 per cent), and trace amounts of millerite (NiS), troilite (FeS), pyrite (FeSJ, and cubanite (Cu5FeS4). The major platinum group minerals are cooperite (PtS), braggite [(Pt,Pd)NiS], sperrylite (DtAsz) and PGE alloys, although in some areas minerals such as laurite) can be abundant.

The UG-2 Reef is a platiniferous chromititc layer which, depending on the geographic ocation within the Complex, is developed some 20 to 400 metres below the better known Merensky Reef. The chromitite itself is usually 1 m thick but can vary from - 0.4 to up to 2.5 m. Thin chromitite seams (generally less than 20 cm in thickness) may be present in both the footwall and, more commonly, in the hanging wall rocks. The UG-2 consists predominantly of chromite (60 to 90 per cent by volume) with lesser silicate minerals (5 to 30 per cent pyroxene, and 1 to 10 per cent plagioclase). Other minerals, present in minor concentrations, can include the silicates: phlogopite and biotite, the oxides: ilmenite, rutile and magnetite, and base metal sulfides. Secondary minerals include quartz, serpentine and talc.

The base metal distribution follows a similar trend to that of the PGE, with mat of the values occurring in the bottom and top part of the reef. The base metal content of a typical UG-2 Reef is approximately 200 to 300 ppm nickel occurring as nickel sulfide and less than 200 ppm copper occurring as copper iron sulfide.

The platinum group minerals present in the UG-2 Reef are highly variable, but generally the UG 2 is characterised by the presence of abundant PGE sulfides, comprising predominantly laurite (RuOsIr sulfide), cooperite (PtS), braggite (Pt, Pd, NiS), and an unnamed PtRhCuS. The platinum group minerals only reach an average size of approximately 12 pm, with particles larger than 30 pm being extremely rare. Most of the platinum group minerals occur in association with the base metal sulfides and silicates. It is only the mineral laurite which exhibits a preferred association with the chromite grains. Both the grain size and associations are extremely important as these affect the metallurgical behaviour during subsequent processing.

The operation had been reorganised in 2015 into a two-mine operation from previously three mines and concentrators. The West mines consists of the Thembelani and Khuseleka shafts and East Mine consists of the Siphumelele and Bathopele shafts.

The Bathopele shafts trackless mechanised operation mines the UG2 horizon exclusively at a depth varying between 40 metres and 350 metres below surface using low-profile (LP) and extra-low-profile (XLP) equipment suites. The mining layouts applied are bord and pillar in the LP section and breast mining in the XLP section. The XLP mining section contributed 10% of total square metres produced.

The remaining Rustenburg operations have three vertical shafts (Thembelani 1, Khuseleka 1, and Siphumelele 1) and the associated declines, which transport rock, men and material. Mining occurs on both the Merensky reef and the UG2 reef horizons. The predominant mining layout on the West Mine is conventional scattered breast mining with strike pillars. The predominant mining layout at Siphumelele Mine is conventional breast stoping with strike pillars. The operating depth for the current workings is between 400 metres and 1,350 metres below surface.

All reclamation of material and equipment at the Khomanani shafts and Khuseleka 2 shaft, placed on long-term care and maintenance, was completed in April 2015.

Treatment of the ore, comprising crushing, ball milling, gravity concentration and flotation is carried out in two reduction plants, an older unit and a more modern mill erected in the last few years, while a third mill is now in course of construction to handle the increased output.

The ore is first crushed in a series of jaw crushers and fed to the primary and then the secondary ball mills which are in closed circuit with hydrocyclone classifiers. This is followed by gravity concentration on corduroy tables to separate the course particles of platinum-bearing minerals and the free metallic particles.

The tailings from the tables are returned to the mill circuit, the final pulp from here being treated in a series of thickeners before going to the flotation plant. Here banks of cells are arranged in a normal rougher-cleaner circuit which recovers most of the remaining platinum-bearing minerals.

The flotation concentrates, consisting mainly of nickel, ........