Sibanye Stillwater Ltd. owns 87% of the Kroondal operation through its subsidiary, Sibanye Rustenburg Platinum Mines (Pty) Ltd (SRPM), following an amalgamation on January 31, 2025, which led to the dissolution of Kroondal Operations (Pty) Ltd as a separate entity.
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Summary:
The Bushveld Complex extends approximately 450 km east to west and approximately 250 km north to south. It underlies an area of some 67,000km², spanning parts of Limpopo, North West, Gauteng, and Mpumalanga Provinces.
Interlayered in the Upper Critical Zone of the RLS, the Merensky and Upper Group No.2 Chromitite (UG2) Reefs are preserved as narrow tabular structures. The Kroondal Operations are situated on the western limb of the Bushveld Complex and produce the PGMs and associated Base Metals from the mining and processing of the UG2 Reef.
PGM reef-type deposits are deposits where the PGM are the main products and Ni and Cu are the by- products (e.g., the UG-2 and Merensky reefs of the Bushveld Complex, or the J-M reef of the Stillwater Complex, Montana and the MSZ of the Great Dyke of Zimbabwe). The deposits generally contain less than 1-2% sulphide minerals and tend to form laterally relatively persistent stratiform horizons in large layered intrusions that are often relatively easy to trace once they have been intersected.
The Merensky Reef at the Kroondal Operations is mined out and will not be discussed further.
The UG2 Reef consists of the Main Seam chromitite. Overlying the UG2 Main Seam is an unmineralized pyroxenite layer, locally termed the pyroxenite parting or simply parting (UG2P). Above the pyroxenite parting (UG2P) another chromite layer, the UG2L, locally referred to as the Leader Seam, is the topmost mining mineralised lithological unit.
It is these three units which form the mineable reef portion at Kroondal Operations. The thickness of the Main Seam ranges from 65cm to 80cm, whilst the pyroxenite parting varies from 10cm to 4m, and the Leader Seam thickness varies from 12cm to 25cm. In areas where the pyroxenite parting is too wide. (greater than 250cm), then only the Main Seam is exploited. The UG2 and UGL display a mottled appearance due to the presence of large bronzite crystals within the chromite.
The UG2 and Merensky Reefs form an east-west trending open arc, with a strike varying between 90° in the east to 145° in the west. The general dip of the reef is 9° to 10°. The middling between UG2 and Merensky Reefs varies between 120m to 140 m. The dip of the encompassing regional stratigraphy also varies between 9° and 10° with a general east-west strike direction. Other dip decreases locally between 1° to 5° and increases to between 15° to 30° along a monocline trending east-west at depth. The dip decreases from 3° to 7° across the farms of Klipgat and Turffontein, also roughly striking east- west.
Mineralogy
The UG2 consists predominantly of chromite (60 to 90% by volume) with lesser silicate minerals 5 to 30% pyroxene and 1 to 10% plagioclase. Other minerals, present in minor concentrations, can include the silicates: phlogopite and biotite, the oxides: ilmenite, rutile and magnetite, and base metal sulphides. Secondary minerals include quartz, serpentine and talc. The Cr2O3 content of the UG2 Reef varies from 30 to 35%. The PGMs present in the UG2 Reef are highly variable, but generally, the UG2 is characterised by the presence of various PGM sulphides, comprising predominantly laurite (RuOslr sulphide), cuperite (PTS), braggite (Pt, Pd, NiS), and an unnamed PtRhCUS. The PGMS only reach an average size of approximately 12µm, with particles larger than 30µm being extremely rare.
Most of the PGMs occur in association with the base metal sulphides and silicates. It is only the mineral laurite that 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 major base metal sulphides constitute chalcopyrite, pentlandite and pyrrhotite. The base metal sulphides occur almost entirely within the interstitial silicate and are only very rarely enclosed within the chromite particles. The grain size of the base metal sulphides rarely exceeds 30µm.
The distribution of grades within the layer is not uniform. However, PGMs are generally concentrated at the upper and lower contacts of the main chromitite seam, with lesser concentrations in the Leader seams. The highest PGM concentration is generally recorded at the base of the UG2 Reef chromitite.
In the UG2 Reef, Cu, Ni and Sulphur values are extremely low.