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Bokoni, Ga-Phasha, Twickenham, Marula, Modikwa, Two Rivers, Mototola, Booysendal, Everest - Bushveld |
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Limpopo (Northern) Province, South Africa |
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PGE PGM Pt Pd
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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 Bokoni, formerly Lebowa, and before that Atok platinum mine is hosted by layered mafic and ultramafic rocks of the 2050 Ma Rustenburg Layered Suite, on the northen tip of the Eastern Limb of the Bushveld Complex in northern South Africa, ~50 km NNW of Steelpoort and ~80 km SE of Polokwane.
The contiguous Ga-Phasha, Twickenham, Marula and Modikwa PGE deposits are located over an interval of ~50 km to the SSE of Bokoni, all on the eastern limb of the host Rustenburg Layered Suite. Following a gap ~10 km, Two Rivers, Mototola, Booysendal and Everest PGE deposits follow the eastern limb due south over an interval of ~35 km.
For more detail on the regional setting and geological map see the Bushveld Complex overview record.
Bokoni
The Bokoni mining area covers a strike distance of 9 km, on the northern extremity of the Eastern Limb of the Bushveld Complex. The Rustenburg Layered Suite consists of mafic rocks. PGEs are derived from the Merensky and UG2 Reefs. The reefs are cut and partialy offset by northeast and east trending dykes and faults with associated
conjugated joint sets. The north-eastern portion of the mining area is located below a range of pyroxenite hills and the south-western portion is below the valley floor, overlain by black soil.
The ore reserves and mineral resources in the Bokoni mining area at 31 December, 2011 (Angloplats, 2012) were:
Merensky Reef,
Proved + Probable Reserve - 28.84 Mt @ 3.97 g/t 4E (Pt+Pd+Rh+Au);,
Measured + Indicated + Inferred Resource - 199.39 Mt @ 4.93 g/t 4E (Pt+Pd+Rh+Au),
UG2,
Proved + Probable Reserve - 37.75 Mt @ 5.37 g/t 4E (Pt+Pd+Rh+Au);
Measured + Indicated + Inferred Resource - 327.35 Mt @ 6.40 g/t 4E (Pt+Pd+Rh+Au).
Ga-Phasha
Ga-Phasha (#Location: 24° 20'S, 30° 00'E) adjoins Bokoni and Twickenham to the north and south respectively and contains both the UG2 (averages 0.74 m) and Merensky (average 1.17 m) reefs over a strike length of ~8.5 km. The host sequence of the Rustenburg Layered Suite comprises: rocks of the Critical Zone (an alternating sequences of gabbros, norites, anorthosites, pyroxenites and chromitites), and the Main Zone that consists of gabbros and ferrogabbros. The sequence mainly strikes NW-SE and dips at between 14 and 18° SW, with local steepening to nearly 20°. Economic Platinum Group Metal (“PGM”) mineralisation occurs within the UG2 Reef horizon and Merensky Reef pyroxenites, which are are separated by approximately 400 metres of mafic and ultramafic cumulate rocks. The broad tectonic setting includes north-northeast and east-west trending dykes and fault/fractures. The depth of weathering varies from less than seven metres to approximately 40 metres, especially in the valley areas. The average depth of oxidation within the Project area has been assumed to be 40 metres (Anooraq Resources, 2006).
The ore reserves and mineral resources at Ga-Phasha at December, 2005 (Anooraq Resources, 2006) were:
Merensky Reef,
Measured + Indicated Resource - 41.0 Mt @ 5.09 g/t 4E (Pt+Pd+Rh+Au);
Inferred Resource - 122.4 Mt @ 5.41 g/t 4E (Pt+Pd+Rh+Au),
UG2,
Measured + Indicated Resource - 82.2 Mt @ 6.53 g/t 4E (Pt+Pd+Rh+Au);
Inferred Resource - 185.8 Mt @ 6.47 g/t 4E (Pt+Pd+Rh+Au).
Twickenham
Twickenham separates Ga-Phasha and Marula, containing a strike length of 19 km of both the UG2 and Merensky reefs, which generally trend NNW-SSE.
The ore reserves and mineral resources at Twickenham at 31 December, 2011 (Angloplats, 2012) were:
Merensky Reef,
Proved + Probable Reserve - None,
Measured + Indicated + Inferred Resource - 163.0 @ 4.66 g/t 4E (Pt+Pd+Rh+Au),
UG2,
Proved + Probable Reserve - 77.8 Mt @ 5.39 g/t 4E (Pt+Pd+Rh+Au),
Measured + Indicated + Inferred Resource - 139.8 Mt @ 5.77 g/t 4E (Pt+Pd+Rh+Au).
Marula
At Marula, located some 50 km north of Burgersfort in Limpopo Province, both the Merensky Reef and the underlying UG2 Reef are exploited and sub-outcrop on the mine property. The mine lease encloses a strike length of ~5 km of the two reefs, which dip in a generally WSW direction at about 13° with a vertical separation of some 400 m. The UG2 consists of densely packed chromitite with a pyroxenite hanging wall and pegmatoid footwall. While one prominent dyke and a dunite pipe are present, there is minimal faulting on the property. For resource calculations the mining width of the Merensky Reef is 100 cm, and the UG2 ~60 cm. (Implats, 2012)
The ore reserves and mineral resources at Marula at 31 December, 2011 (Implats, 2012) were:
Merensky Reef,
Proved + Probable Reserve - None,
Measured + Indicated + Inferred Resource - 51.9 Mt @ 4.2 g/t 4E (Pt+Pd+Rh+Au), 4.5 g/t 6E (Pt+Pd+Rh+Ru+Ir+Au);
UG2,
Proved + Probable Reserve - 82.2 Mt @ 6.53 g/t 4E (Pt+Pd+Rh+Au), 4.69 g/t 6E (Pt+Pd+Rh+Ru+Ir+Au);,
Measured + Indicated + Inferred Resource - 50.9 Mt @ 8.8 g/t 4E (Pt+Pd+Rh+Au), 10.2 g/t 6E (Pt+Pd+Rh+Ru+Ir+Au).
Modikwa
Modikwais located along the border between the Mpumalanga and Limpopo provinces, and exploits both the UG2 and Merensky reefs at a depth of ~450 m, dipping west at ~10°. The mine lease covers a strike length of the two reefs of ~24 km. The UG2 reef is a chromitite layer with an average thickness of nearly 60 cm, with the highest grades towards its base, and is overlain by a zone that includes the three thickest chromitite layers. The reefs are folded with gentle "wave-like' undulations with amplitudes of <2 m. The north shaft area is characterised by randomly distributed potholes of different sizes. In contrast, the south shaft area contains fewer potholes. The area is more disrupted by faulting. A minimum mining cut of 102 cm is used in ore reserve calculations.
The ore reserves and mineral resources at Modikwa at June, 2011 (Angloplats, 2012) were:
Merensky Reef,
Proved + Probable Reserve - None,
Measured + Indicated + Inferred Resource - 208.8 @ 2.70 g/t 4E (Pt+Pd+Rh+Au),
UG2,
Proved + Probable Reserve - 55.43 Mt @ 4.86 g/t 4E (Pt+Pd+Rh+Au),
Measured + Indicated + Inferred Resource - 219.6 Mt @ 6.00 g/t 4E (Pt+Pd+Rh+Au).
Two Rivers
The Two Rivers platinum mine is situated on the southern lobe of the eastern limb of the Bushveld Complex, ~60 km NW of the town of Lydenburg, in Mpumalanga province. It is separated from the Modikwa mining area by the ~20 km of the Kennedy Vale project area.
The mining area at Two Rivers is underlain by rocks of the Critical Zone (Winterveld norite-anorthosite) and the Main Zone (Winnarshoek norite-anorthosite). Both the Merensky Reef and the UG2 chromitite are found within the upper Critical Zone, and are ~140 m vertically apart, separated by a series of barren norites and anorthosites. To the north of Two Rivers, at Modikwa and Marula Mines, the UG2 chromitite unit is a dominant ~60 cm thick marker sandwiched between 30 to 150 cm of footwall pegmatoid and 2 to 10 m of hanging wall pyroxenites. The UG2 chromitite comprises fine- to medium-size cumulus chromite grains with substantial quzantities of post-cumulus orthopyroxene crystals. The footwall is a coarse-grained pegmatoidal pyroxenite with sporadic chromitite blebs, lenses and stringers. The hanging wall is dominantly composed of fine- to medium grained orthopyroxenite with three or more chromitite stringers known as the UG2 leaders. In particular, the UG2 leader 2 (UL2) Cr stringer, which is 1 to 10 mm wide, occurs between 50 and 60 cm above the top of the UG2 reef contact, is significant. These leaders are poorly mineralised and form non-cohesive partings influencing hanging wall beam stability. At Modikwa, where the UG2 averages 50 to 60 cm thick, with 60 to 80 cm of hanging wall pyroxenite to the UL2 chromitite parting above it, there is significant over-break to mining width of 110 cm.
At Two Rivers, the UG2 seam is 1.2 to 1.4 m thick, and has one or two chromitite leader layers above it, which are included in the optimum mine cut, depending on their distance above the main reef band. An ideal mining cut of 185 cm applied, including some footwall dilution. There may also be some internal pyroxenite partings within the UG2 at Two Rivers, which may result in split reef facies, dividing it into two or three seams, especially in the southern-most portion of the mining area.
The strike of the UG2 at Two Rivers has a consistent north-south trend, with an average dip of 8°W. The igneous layering displays a strike-parallel ‘terracing’
similar to that developed in mines of the Western Bushveld, whereby the UG2 dips in a step-wise manner, with strike-parallel zones of shallow dip separated by more steeply dipping monoclinal zones. Over much of the area to be mined, the layer dip averages 5 to 8°, separated by narrow zones where the dip increases to 10 to 15°. These monoclinal rolls in the UG2 layering are spatially associated with pothole intersections at Two Rivers as well as dyke intrusions. Increased jointing (layer-parallel and normal), associated hanging wall instability and over break are common in the areas affected by monoclinal rolling, which tend to be localised and can be projected along strike.
Resource figures in 2007 show that for a resource grade of 5.44 g/t 6E (Pt+Pd+Rh+Ru+Ir+Au), the individual key element concentrations are 2.19 g/t Pt, 1.34 g/t Pd, 0.41 g/t Rh, 0.04 g/t Au (African Rainbow Minerals, 20076)
The ore reserves and mineral resources at Two Rivers at December, 2011 (African Rainbow Minerals, 2011) were:
Merensky Reef,
Proved + Probable Reserve - None,
Measured + Indicated Resource - 38.36 Mt @ 3.17 g/t 6E (Pt+Pd+Rh+Ru+Ir+Au);
UG2,
Proved + Probable Reserve - 39.03 Mt @ 3.54 g/t 6E (Pt+Pd+Rh+Ru+Ir+Au);
Measured + Indicated Resource - 59.33 Mt @ 4.58 g/t 6E (Pt+Pd+Rh+Ru+Ir+Au);
Mototola
Mototola is a small mining area extending over a strike length of only 3.75 km of the UG2 reef, immediately to the southeast of Two Rivers.
The ore reserves and mineral resources at Mototola at 31 December, 2011 (Angloplats, 2012) were:
Merensky Reef,
Proved + Probable Reserve - None,
Measured + Indicated + Inferred Resource - 13.0 Mt @ 3.5 g/t 4E (Pt+Pd+Rh+Au),
UG2,
Proved + Probable Reserve - None,
Measured + Indicated + Inferred Resource - 25.4 Mt @ 4.36 g/t 4E (Pt+Pd+Rh+Au).
Everest
The Everest platinum mine is located near the town of Lydenburg in Mpumalanga Province, ~13 km south of Mototola, and immediately east of the Booysendal mine. The mining area extends over ~10 km of strike length of the UG2 Reef (#Location: 24° 49'S, 30° 6'E).
The mine area is situated on the southern portion of the Eastern Limb of the Bushveld Complex. The orebody at Everest is a well-defined elongate basin-like structure of UG2 Reef lying beneath a hill and extending from surface to a depth of around 250 metres at the deepest point.
The UG2 ore reserves and mineral resources at Everest at 30 June, 2011 (Aquarius Platinum, 2012) were:
Proved + Probable Reserve - 14.59 Mt @ 3.12 g/t 4E (Pt+Pd+Rh+Au);
Measured + Indicated + Inferred Resource - 14.59 Mt @ 3.12 g/t 4E (Pt+Pd+Rh+Au),
Booysendal
The Booysendal platinum mine is located near the town of Lydenburg in Mpumalanga Province, ~12 km south of Mototola, and immediately weast of the Everest mine. The mining area extends over ~15 km of strike length of the UG2 and Merensky reefs. The mine area is situated on the southern portion of the Eastern Limb of the Bushveld Complex, and covers nearly half of the southern compartment's 37 km long strike length, abutting Anglo Platinum's large Der Brochen, along with the platinum operations of Two Rivers, Mototolo, Eastplats and Everest. The UG2 prill split at Booysendal is 58.6% platinum, 31.4% palladium, 9.2% rhodium and 0.8% gold. The reserve tickness is 145 cm. There are two UG2 mines planned - the North mine and South mine, each covering 4 km of strike and 2 km of dip.
The mineral resources at Booysendal at 30 June, 2011 (Northam Platinum Limited, 2011) were:
Merensky Reef,
Measured + Indicated + Inferred Resource, Booysendal North - 164.9 Mt @ 5.32 g/t 4E (Pt+Pd+Rh+Au);
Measured + Indicated + Inferred Resource, Booysendal South - 90.57 Mt @ 3.54 g/t 4E (Pt+Pd+Rh+Au);
UG2,
Proved + Probable Reserve, Booysendal UG2 Mine - 30.64 Mt @ 3.08 g/t 4E (Pt+Pd+Rh+Au);
Measured + Indicated + Inferred Resource, Booysendal UG2 Mine - 43.64 Mt @ 4.16 g/t 4E (Pt+Pd+Rh+Au);
Measured + Indicated + Inferred Resource, Booysendal North - 328.77 Mt @ 3.61 g/t 4E (Pt+Pd+Rh+Au);
Measured + Indicated + Inferred Resource, Booysendal South - 208.10 Mt @ 3.10 g/t 4E (Pt+Pd+Rh+Au).
The most recent source geological information used to prepare this decription was dated: 2011.
Record last updated: 22/11/2012
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.
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Mossom R J 1986 - The Atok Platinum Mine: in Anhaeusser C R, Maske S, (Eds.), 1986 Mineral Deposits of South Africa Geol. Soc. South Africa, Johannesburg v2 pp 1143-1154
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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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