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Rustenburg Section - Bathopele, Khomanani, Thembelani, Khuseleka, Siphumelele - Bushveld Complex

South Africa

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The Anglo Platinum, Rustenburg Section operations, located to the east of the town of Rustenburg in North West Province, South Africa, exploit ores from both the Merensky and UG2 Reefs in the Critical Zone in the southwestern section of the Western Lobe of the Bushveld Complex. The Rustenburg Section comprises 5 adjacent mines Bathopele, Khomanani, Thembelani, Khuseleka and Siphumelele (#Location: 25° 41' 11"S, 27° 19' 16"E).

For background on the geology and mineralisation of the Bushveld Complex, see the separate Bushveld Complex record.

The Merensky Reef is a regular, persistent tabular body comprising a pegmatoidal, feldspathic pyroxenitic assemblage near the top of the Upper Group of the Upper Critical Zone of the Bushveld Complex. It is defined by thin top and bottom chromitite layers and is generally around 30 cm in thickness, seldom exceeding 1 m in the Rustenburg Section, with abundant associated, and generally highly disturbed, ovoid shaped (in plan) depressions, known as "potholes" making up about 15% of its area. "Potholes" represent areas where the base of the Merensky Reef disconformably transgress down, for distances of a metre to several tens of metres, into the underlying "stratigraphy" of the Critical Zone over widths of a few metres to hundreds of metres.

Some 75% of the PGEs and base metals are within the Merensky Reef, with the remainder occurring in the hangingwall and/or footwall. The highest grade encountered is around 8 ppm PGE+Au over a mining width of 90 cm (4.82 ppm Pt, 2.04 ppm Pd, 0.66 ppm Ru, 0.24 ppm Rh, 0.08 ppm Ir, 0.26 ppm Au), 0.12% Cu, 0.26% Ni. The pegmatoidal feldspathic pyroxenite of the Merensky Reef generally contains between 3 and 10% sulphides dominated by pyrrhotite, pentlandite, chalcopyrite, pyrite and cubanite with minor sulpharsenides, galena and sphalerite. Phlogopite is usually associated with the sulphides.

PGEs are present in a variety of forms, from Pt-Pd sulphides (30%), lesser tellurides and arsenides (11%) and sperrylite (6%). PGE-Au/Ag alloys are important, as are Ru sulphides (10%), etc. The PGEs occur in three associations in decreasing order of importance i). enclosed in or attached to base metal sulphides; ii). enclosed in silicates; or iii). enclosed in or attached to chromite or Fe-oxide. The composition of PGE is very similar in the Merensky Reef and the underlying UG2 at any point. To the east of the Rustenburg Section the Merensky Reef thickens appreciably to +10m, although the mineralised width is similar, but confined to the upper margin.

The UG2 chromitite occurs between 15 and 400 m below the Merensky Reef and like the Merensky Reef, can be traced over a strike length of more than 280 km. At Rustenburg it is around 70 cm thick, but averages 97 cm overall. "Potholes" are also common in the UG2. Chromite comprises 60 to 90% of the UG2 which averages 43.5% Cr2O3. The main base metal sulphides are pentlandite and chalcopyrite, with minor pyrrhotite, pyrite, arsenopyrite, bornite, chalcocite, covellite, galena & millerite. PGEs are found in the base, centre and top of the UG2 chromitite, averaging between 3.5 and 19.5 ppm PGEs, with approximately 3.6 ppm Pt, 3.8 ppm Pd, 0.33 ppm Ru and 2.26 others. Cu & Ni are typically <1000 ppm.

The ore reserves and resources at the Rustenburg Section Mines at the end of 2005 (Angloplats, 2006) were:
    Merensky Reef,
        Proved + Probable Reserve - 50.6 Mt @ 5.63 g/t 4E (Pt+Pd+Rh+Au);
        Measured + Indicated + Inferred Resource - 111.3 Mt @ 7.54 g/t 4E (Pt+Pd+Rh+Au);
    UG2,
        Proved + Probable Reserve - 198 Mt @ 3.55 g/t 4E (Pt+Pd+Rh+Au);
        Measured + Indicated + Inferred Resource - 291 Mt @ 4.73 g/t 4E (Pt+Pd+Rh+Au).


During 2005 some 11.85 Mt of ore (57% UG2) were milled at a head grade of 4.34 g/t PGE for a recovered production of 25.6 t (0.822 Moz) Pt;   12.8 t (0.401 Moz) Pd;   3.56 t (0.114 Moz) Rh;   [47.46 t (1.53 Moz) Total PGE's];  1.43 t (0.046 Moz) Au;   6300 t Ni,   3500 t Cu.   The mine is owned and operated by Rustenburg Platinums Mines Ltd, a wholly owned subsidiary of Anglo Platinum Corporation Ltd, which is in turn 50.2% held by Anglo American plc.

The ore reserves and resources at the Rustenburg Section Mines at 31 December, 2011 (Angloplats, 2012) were:
    Merensky Reef,
        Proved + Probable Reserve - 32.9 Mt @ 5.32 g/t 4E (Pt+Pd+Rh+Au),
        Measured + Indicated + Inferred Resource - 78.1 Mt @ 6.55 g/t 4E (Pt+Pd+Rh+Au),
    UG2,
        Proved + Probable Reserve - 186.9 Mt @ 3.63 g/t 4E (Pt+Pd+Rh+Au),
        Measured + Indicated + Inferred Resource - 212.0 Mt @ 5.29 g/t PGE.

NOTE: All of the chromitites layers (7 in the Lower Group, 4 in the Middle Group and 2 in the Upper Group) of the Lower and Upper Critical Zone contain significant concentrations of PGE, although only the Merensky and UG2 are exploited primarily for PGEs. They are also the only reefs with significant associated sulphides.

The most recent source geological information used to prepare this summary was dated: 2011.     Record last updated: 10/11/2012
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.


Rustenburg Section

  References & Additional Information
 References to this deposit in the PGC Literature Collection:
Ballhaus C G  1988 - Potholes of the Merensky Reef at Brakspruit Shaft, Rustenburg Platinum mines: primary disturbances in the magmatic stratigraphy: in    Econ. Geol.   v83 pp 1140-1158
Ballhaus C G  1988 - Potholes of the Merensky Reef at Brakspruit Shaft, Rustenburg Platinum Mines: Primary Disturbances in the Magnetite Stratigraphy: in    Econ. Geol.   v83, no.6 pp 1140-1158
Barnes S-J, Maier W D and Curl E A,  2010 - Composition of the Marginal Rocks and Sills of the Rustenburg Layered Suite, Bushveld Complex, South Africa: Implications for the Formation of the Platinum-Group Element Deposits: in    Econ. Geol.   v.105 pp. 1491-1511
Harris C, Pronost J J M, Ashwal L D and Cawthorn R G,  2005 - Oxygen and Hydrogen Isotope Stratigraphy of the Rustenburg Layered Suite, Bushveld Complex: Constraints on Crustal Contamination: in    J. of Petrology   v46 pp 579-601
Kingston G A, El-Dosuky B T  1982 - A contribution on the Platinum-Group mineralogy of the Merensky Reef at the Rustenburg Platinum Mine: in    Econ. Geol.   v77 pp 1367-1384
Kingston G A, El-Dosuky B T  1982 - A Contribution on the Platinum-Group Mineralogy of the Merensky Reef at the Rustenburg Platinum Mine: in    Econ. Geol.   v77, no.6 pp 1367-1384
Lomberg K G, Martin E S, Patterson M A, Venter J E  1999 - The Morphology of Potholes in the UG2 Chromitite Layer and Merensky Reef (Pothole Reef Facies) at Union Section, Rustenburg Platinum Mines: in    S. Afr. J. Geol.   v102, no.3 pp 209-220
Naldrett A J, Gasparrini E C, Barnes S J, Von Gruenewaldt G, Sharpe M R  1986 - The upper critical zone of the Bushveld complex and the origin of Merensky-type ores: in    Econ. Geol.   v81 pp 1105-1117
Nex P A, Kinnaird J A, Ingle L J, van der Vyver B A and Cawthorn R G,  1998 - A new stratigraphy for the Main Zone of the Bushveld Complex, in the Rustenburg area : in    S. Afr. J. Geol.   v101 pp 215-223
Penberthy C J, Merkle R K W  1999 - Lateral Variations in the Platinum-Group Element Content and Mineralogy of the UG2 Chromitite Layer, Bushveld Complex: in    S. Afr. J. Geol.   v102, no.3 pp 240-250
Viljoen M J, Hieber R W  1986 - The Rustenburg Section of Rustenburg Platinum Mines Limited, with Reference to the Merensky Reef: in Anhaeusser C R, Maske S, (eds),  Mineral Deposits of Southern Africa Geol. Soc. of South Africa, Johannesburg   v2 pp 1107-1134
Von Gruenewaldt G, Hatton C J, Merkle R K W  1986 - Platinum-group element-Chromitite associations in the Bushveld complex: in    Econ. Geol.   v81 pp 1067-1079
Wilson A H, Lee C A, Brown R T  1999 - Geochemistry of the Merensky reef, Rustenburg Section, Bushveld Complex: controls on the silicate framework and distribution of trace elements: in    Mineralium Deposita   v34 pp 657-672


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