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Elandsdrift, Millsell, Mooinooi, Samancor Western Chrome Mines - Bushveld Complex |
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South Africa |
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Cr
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Super Porphyry Cu and Au
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IOCG Deposits - 70 papers
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The Samancor Western Chrome Mines division, operates three mines centred around 40 km east of Rustenburg, distributed over much of a 50 km stretch of the southern rim of the Western Lobe of the Bushveld Complex in the North-west Province of South Africa. These are the Elandsdrift open pit and the two underground mines, Waterkloof-Millsell and Mooinooi.
For an outline of the setting, geology and distribution of mineralisation within the Bushveld Complex, see the Bushveld Complex overview record.
Western Chrome Mines division produces approximately 1.8 Mt of run-of-mine ore per year. The combined Western and Eastern Chrome Mines divisions of Samancor have proven reserves to a depth of 300 m, totalling 450 Mt of ore. The Eastern Chrome Mines division is developed over a 100 km section of the Eastern lobe and produces 2.2 Mt of ore per year. Samancor was an unlisted JV between South32 Limited (60%) and Anglo American Corporation (40%) in 2019.
Within the three mines different chromitite layers are being mined, a reflection of the variation in thickness and grade along trend. Dips are generally 9 to 10° to the north. At Millsell and Elandsdrift the principal layer mined is the LG6 within the Lower Critical Zone of the Bushveld Complex. LG6 is regionally 0.5 to 1.05 m thick, containing 46 to 48% Cr2O3, and is the thickest of the 7 LG series chromitites.
At Millsell LG6 is commonly around 0.80 to 0.85 m thick (but may be up to 1.15 m in potholes) with a second band, LG6A , separated by a low grade to barren parting of some 0.45 to 0.55 m thick, then the overlying 0.25 to 0.30 m LG6A. Potholes (see description and definition in Rustenburg Section PGE above) are generally <80 m in diameter. The LG6 chromitite, as mined at Millsell, averages 41.5% Cr2O3 with a Cr:Fe ratio of 1.5:1. LG6 is found within pyroxenite above the upper of the two Harzburgite units of the Lower Critical Zone. It is an accumulate-type, coarse granular chromite, comprising 97% of the band, with a 3% gangue of orthopyroxene, clinopyroxene, plagioclase and accessory biotite, quartz, sulphides, carbonate and chlorite. The chromite is generally friable, with grains varying from 50 µm to 2 mm. Contacts between the pyroxenite and chromitite may be either sharp or gradational.
In contrast, at Mooinooi the MG chromite layers, within the upper sections of the Lower Critical Zone, attain mineable widths of 1.35 to 1.5 m and 44 to 46% Cr2O3, and the LG6 bands are only present as a series of stringers.
The Cr:Fe ratio of the chromitites, decreases generally, but not regularly, upwards through the Critical zone, from around 1.50 in the LG6, to 1.43 in MG4 to 1.34 in the UG2. While the UG2 is a prime PGE source in the lobe, the lower grade Cr content means its chromite is not saleable. The number of layers and the Cr:Fe ratio both decrease towards the west within the Western Lobe.
The most recent source geological information used to prepare this decription was dated: 2001.
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.
Mooinooi Waterkloof-Millsell
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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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