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Nkomati |
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Mpumalanga, South Africa |
| Main commodities:
Ni Cu Co PGE PGM Au
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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All papers now Open Access.
Available as Full Text for direct download or on request. |
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The Nkomati Ni-Cu-Co-PGE deposit is located within the Bushveld age Uitkomst Complex, an 8 x 1 km and up to 650 m thick, NW-SE trending, flat lying, poorly layered, sill like, 2025 Ma mafic body of harzburgite, gabbro, pyroxenite and gabbro-norite. Nkomati is approximately 325 km east of Rustenburg. The deposit is also some 75 km to the east of the south-eastern lobe of the main 2050 Ma Bushveld Complex, with which it is believed to be genetically associated. It plunges at around 4 degrees to the NW and cuts basement rocks of the Transvaal Supergroup, including quartzite, shales (in part graphitic), the Malmani Dolomite and Archaean granitoids.
The Uitkomst Complex concordantly intrudes dolomite/chert of the Malmani subgroup and shales/quartzites of the Timeball Hill formation at the base of the Transvaal Supergroup. It lies unconformably on an Archaean basement, as a NW-SE tubular shaped body, bounded by two NW-SE trending fracture systems.
The Uitkomst Complex comprises:
• Basal Gabbro (6 to 15 m thick), which is possibly an earlier sill, overlain by
• a sulphide bearing Lower Pyroxenite (50 to 90 , averaging 35 m) containing sedimentary xenoliths,
• Chromititic Peridotite/harzburgite (30 to 60 m),
• Massive Chromitite Unit (up to 10 m),
• Main Peridotite/harzburgite (±300 m),
• Upper Pyroxenite (65 m),
• Upper Gabbro-norite (±250 m) and
• Upper Gabbro Unit (50 m)
The Uitkomst complex contains three disseminated, sulphide mineralised zones hosted by the Basal Gabbro and Lower Harzburgite, namely the Basal Mineralised Zone (BMZ) within the Basal Gabbro; the Main Mineralised Zone (MMZ) within the Lower Pyroxenite Unit and the Chromititic Pyroxenite Mineralised Zone (PCMZ) within the chromititic peridotite for a resource in 2005 of 139 Mt @ 0.49% Ni, 0.19% Cu, 0.02% Co and 1.04 g/t PGE+Au. In addition, the peridotite unit contains the Peridotite Mineralised Zone (PRDMZ) which is a low-grade disseminated sulphide mineralisation zone not yet (in 2023) included in the mine’s Mineral Resource base.
Massive sulphide mineralisation was found in the immediate footwall of the Complex, within the Transvaal sediments and the Archaean Nelshoogte granite gneiss. This orebody, now mined out, consisted of three lenses separated by mafic/ultramafic intrusions and was accessed by means of two vertical shafts and a decline. The initially exploited orebody, the MSB, had an initial reserve of 2.86 Mt @ 2.04% Ni, 1.13% Cu, 0.10% Co, 1.65 g/t Pt, 4.18 g/t Pd, 0.16 g/t Rh, 0.18 g/t Au. The 2005 resource of the MSB was 13.2 Mt @ 2.98% Ni, 0.97% Cu, 0.17% Co, 5.62 g/t PGE+Au.
The dominant sulphide minerals are pyrrhotite, pentlandite and chalcopyrite. Cobalt is mostly in solid solution in the pentlandite, and the PGMs occur as separate minerals, with merenskyite being dominant. The chromite is contained within the Massive Chromitite Unit in the open-pit area.
The Combined Mineral Reserves for the mine and expansion project in Dec 2004 including the MSB and MMZ zones was: 51.7 Mt @ 0.52% Ni, 0.2% Cu, 0.03% Co, 1.15 g/t PGE+Au.
The total Mineral Resource at the end of 2023 for both the Main Mineralised and Chromititic Peridotite Mineralised zones (African Rainbow Mines Mineral Resources and Mineral Reserves Report, 2023) were:
Measured Mineral Resource - 72.9 Mt @ 0.32% Ni, 0.12% Cu, 0.02% Co, 0.89 g/t 4E,
Indicated Mineral Resource - 94.62 @ 0.37% Ni, 0.15% Cu, 0.02% Co, 0.98 g/t 4E,
Measured + Indicated Mineral Resource - 167.51 Mt @ 0.35% Ni, 0.14% Cu, 0.02% Co, 0.94 g/t 4E,
Inferred Mineral Resource - 46.35 @ 0.40% Ni, 0.13% Cu, 0.02% Co, 0.97g/t 4E,
NOTE: 4E = platinum + palladium + rhodium + gold. Prill split: Pt: 26%; Pd: 63%; Rh: 7%; Au: 5% (based on Measured and Indicated grades).
The Chromititic Peridotite Mineralised zone in Open Pit 3 contained Oxidised Massive Chromitite ore for: 0.18 Mt @ 23.28% Cr2O3
The Nkomati mine was a joint venture between African Rainbow Mines (50%) and LionOre (50%). In 2007, Nornickel acquired LionOre Mining and its share of the Nkomati JV. The underground mine was placed on care and maintenance in 2015. In November 2023, Nornickel transferred its 50% interest in the joint venture, held by its South African subsidiary, Norilsk Nickel Africa Proprietary Limited, to African Rainbow Mines who then assumed responsibility for care and maintenance of the mine.
The most recent source geological information used to prepare this decription was dated: 2005.
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.
Nkomati
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de Waal S A and Armstrong R A, 2000 - The age of the Marble Hall diorite, its relationship to the Uitkomst Complex, and evidence for a new magma type associated with the Bushveld igneous event : in S. Afr. J. Geol. v103 pp 128-140
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de Waal S A and Gauert C D K, 1997 - The Basal Gabbro Unit and the identity of the parental magma of the Uitkomst Complex, Badplaas, South Africa: in S. Afr. J. Geol. v100 pp 349-361
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de Waal S A, Gauert C D K 1997 - The Basal Gabbro Unit and the Identity of the Parental Magma of the Uitkomst Complex, Badplaas, South Africa: in J. of African Earth Sciences v100, no.4 pp 349-361
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de Waal, S.A., Maier, W.D., Armstrong, R.A. and Gauert, C.D.K., 2001 - Parental Magma and Emplacement of the Stratiform Uitkomst Complex, South Africa: in The Canadian Mineralogist v.39, pp. 557-571.
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Gauert C D K, de Waal S A, Wallmach T 1995 - Geology of the Ultrabasic to Basic Uitkomst Complex, Eastern Transvaal, South Africa: An Overview: in J. of African Earth Sciences v21, no.4 pp 553-570
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Hammerbeck E C I, Schurmann L W 1998 - Nickel: in Wilson M G C, Anhaeusser C R, (eds), The Mineral Resources of South Africa Council for Geoscience, Pretoria pp 471-482
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Kenyon A K, Attridge R L, Coetzee G L 1986 - The Uitkomst Nickel-Copper Deposit, Eastern Transvaal: in Anhaeusser C R, Maske S, (eds), Mineral Deposits of Southern Africa Geol. Soc. of South Africa, Johannesburg v2 pp 1009-1017
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Maier W D, Gomwe T, Barnes S.-J. , Li C, Theart H, 2004 - Platinum Group Elements in the Uitkomst Complex, South Africa: in Econ. Geol. v99 pp 499-516
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Maier, W.D, Prevec, .A., Scoates, J.S., Wall, C.J., Barnes, S.-J. and Gomwe, T., 2018 - The Uitkomst intrusion and Nkomati Ni-Cu-Cr-PGE deposit, South Africa: trace element geochemistry, Nd isotopes and high-precision geochronology: in Mineralium Deposita v.53, pp. 67-88.
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Theart H F J and de Nooy C D, 2001 - The Platinum Group Minerals in two parts of the Massive Sulphide Body of the Uitkomst Complex, Mpumalanga, South Africa: in S. Afr. J. Geol. v104 pp 287-300
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Trubac, J., Ackerman, L., Gauert, C., Durisova, J. and Hrstka, T., 2018 - Platinum-Group Elements and Gold in Base Metal Sulfides, Platinum-Group Minerals, and Re-Os Isotope Compositions of the Uitkomst Complex, South Africa: in Econ. Geol. v.113, pp. 439-461
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Yudovskaya, M., Naldrett, A., Woolfe, J., Costin, G. and Kinnaird, J., 2015 - Reverse compositional zoning in the uitkomst chromitites as an indication of crystallization in a magmatic conduit: in J. of Petrology v.56, pp. 2373-2394.
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