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Mogalakwena, Potgietersrust - Bushveld Complex |
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Limpopo (Northern) Province, South Africa |
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PGE PGM Pd Pt Au Ni Cu
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Super Porphyry Cu and Au
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The Mogalakwena, formerly the Potgietersrust Platinums mine, exploits the Platreef on the Northern Limb of the northeastern margin of the Bushveld Complex Northern Lobe in the Limpopo (Northern) Province of South Africa, some 240 km to the north-east of Rustenburg and 20 km NW of the town of Mokopane.
For detail on the regional setting and geological map see the Bushveld Complex overview record.
The Potgietersrus Limb extends for more than 100 km in a north-south direction. The base of the Bushveld mafic suite transgresses from the Pretoria Group quartzites and shales, through the Penge Iron Formation and Malmani Dolomite to basement granite gneiss in the north. The Lower Zone and the chromite bearing lower sections of the Critical Zone of the Complex are only fully represented in the far south. To the north they occur as disjointed masses in the basement rocks and disappears altogether near Potgietersrus.
The lowermost Bushveld unit over much of the limb is the upper sections of the Critical Zone. A sulphide bearing composite pyroxenite layer of variable thickness occurring near the base of the main layered mafic mass is known as the Platreef and hosts the important PGE deposits with associated Cu & Ni at Potgietersrus where it rests on basement. The 30 to 50 degree west dipping Platreef pyroxenite, which is not layered, has been correlated with the Merensky Reef found elsewhere in the Bushveld Complex. It has been variably and extensively contaminated by the basement, particularly iron formation, shales (graphitic in part) and anhydrite bearing dolomite, with abundant xenoliths which have significantly influenced its chemistry.
The Platreef varies from a few up to 150 m in thickness and is composed of three pyroxenite units, or 'reefs', as follows: i). the upper pyroxenite, or 'C' Reef which is usually barren; ii). the middle pyroxenite, or 'B' Reef - a coarse grained bronzitite with minor inter-cumulus plagioclase, very variable, but overall roughly equal orthopyroxene and clinopyroxene, virtually no olivine, some chromite and fair to good grades of base metal sulphides; iii). the lower pyroxenite or 'A' Reef - a highly feldspathic unit with a marked heterogenous texture and grain size, graphic plagioclase-quartz intergrowths, disseminated mineralisation and large blebs of composite base metal sulphides.
At the Potgietersrust Platinum Mine, the ore is hosted by the 'B' Reef. Four separate ore zones have been delineated based on a 3 g/t PGE cutoff. The uppermost of these zones is the thickest (2 to 39 m thick) and most consistent. Cu ranges from 0.1 to 0.25%, Ni from 0.15 to 0.35%, while PGEs vary from <0.25 to15 g/t, and locally up to 25 g/t, with a Pt:Pd ratio of around 1:1. Where Cu+Ni is from 0.2-2%, there is a strong correlation between base metals and PGEs. The PGE contents of the Platreef do not vary with the thickness of the mineralised pyroxenite.
Published ore reserves and mineral resources at the end of 2005, at a 1 g/t PGE cutoff were:
Proved + probable reserves - 335.9 Mt @ 3.23 g/t 4E (Pt+Pd+Rh+Au);
Measured + indicated + inferred resources - 2393.7 Mt @ 2.05 g/t 4E (Pt+Pd+Rh+Au).
The ore reserves and mineral resources at the Mogalakwena Mine at 31 December, 2011 (Angloplats, 2012) were:
Proved + Probable Reserve - 725.4 Mt @ 2.90 g/t 4E (Pt+Pd+Rh+Au);,
Measured + Indicated + Inferred Resource - 2785.4 Mt @ 2.18 g/t 4E (Pt+Pd+Rh+Au).
During 1999 some 56.8 Mt of ore + waste was broken and 4.535 Mt of ore were milled at a head grade of 4.03 g/t PGE for a recovered production of 6.2 t (0.20 Moz) Pt; 6.5 t (0.21 Moz) Pd; 0.43 t (0.013 Moz) Rh; [13.78 t (0.443 Moz) Total PGE's]; 0.67 t (0.022 Moz) Au; 4600 t Ni; 2700 t Cu. The stripping ratio was 7.86:1. Mill feed is based on a 2.5 g/t cutoff, while stockpiled lower grade +1.7 g/t mineralisation is counted as ore in calculating the stripping ratio (1999). The mine is operated by Potgietersrust Platinums Ltd, a wholly owned subsidiary of Anglo Platinum Corporation Ltd, which is in turn 50.2% held by Anglo American plc.
The most recent source geological information used to prepare this decription 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.
Mogalakwena (Potgietersrust)
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Selected References:
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Armitage P E B, McDonald I, Edwards S J, Manby G M 2002 - Platinum-group element mineralization in the Platreef and calc-silicate footwall at Sandsloot, Potgietersrus District, South Africa: in Trans. IMM (incorp. AusIMM Proc.), Section B, Appl. Earth Sc. v111 ppB36-B45
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Holwell D A and Jordaan A, 2006 - Three-dimensional mapping of the Platreef at the Zwartfontein South mine: implications for the timing of magmatic events in the northern limb of the Bushveld Complex, South Africa: in Trans. IMM (incorp. AusIMM Proc.), Section B, Appl. Earth Sc. v115 pp 41-48
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Holwell D A and McDonald I, 2006 - Petrology, geochemistry and the mechanisms determining the distribution of platinum-group element and base metal sulphide mineralisation in the Platreef at Overysel, northern Bushveld Complex, South Africa : in Mineralium Deposita v41 pp 575-598
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Holwell D A, McDonald I and Armitage P E B, 2006 - Platinum-group mineral assemblages in the Platreef at the Sandsloot Mine, northern Bushveld Complex, South Africa: in Mineralogical Magazine v70 pp 83-101
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Junge, M., Oberthur, T., Kraemer, D., Melcher, F., Pina, R., Derrey, I.T., Manyeruke, T. and Strauss, H., 2019 - Distribution of platinum-group elements in pristine and near-surface oxidized Platreef ore and the variation along strike, northern Bushveld Complex, South Africa: in Mineralium Deposita v.54, pp. 885-912.
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McDonald. I., Holwell, D.A. and Armitage, P.E.B., 2005 - Geochemistry and mineralogy of the Platreef and Critical Zone of the northern lobe of the Bushveld Complex, South Africa: implications for Bushveld stratigraphy and the development of PGE mineralisation: in Mineralium Deposita v.40, pp. 526-549.
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van der Merwe M J, 2008 - The geology and structure of the Rustenburg Layered Suite in the Potgietersrus/Mokopane area of the Bushveld Complex, South Africa: in Mineralium Deposita v43 pp. 405-419
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White J A 1994 - The Potgietersrus Prospect - Geology and Exploration History: in XVth CMMI Congress, Johannesburg SAIMM v3 pp 173-181
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Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge. It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published. While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo, its employees and servants: i). do not warrant, or make any representation regarding the use, or results of the use of the information contained herein as to its correctness, accuracy, currency, or otherwise; and ii). expressly disclaim all liability or responsibility to any person using the information or conclusions contained herein.
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