The geology and structure of the Rustenburg Layered Suite in the Potgietersrus/Mokopane area of the Bushveld Complex, South Africa

Merwe, Mauritz J. van der

doi:10.1007/s00126-007-0168-9

Cited by 26 publications

(18 citation statements)

References 15 publications

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“…Therefore, it is reasonable to assume that the magmatic sequences identified in the Flatreef are representative of the magmas in most of the northern limb (south of the Hout River Shear Zone), prior to interaction with local country rocks. This is also consistent with the presence of Merensky Reef and UG-2 correlatives south of the Planknek Fault (van der Merwe 2008 ; Maier et al 2008 ). If the MU-BU sequence is bounded by unconformities with the rest of the UCZ below and the Main Zone above, and local contamination was not the trigger and source of mineralization, there is not enough magma volume in the emplaced sequence to extract PGE at the grades measured.…”

Section: Discussionsupporting

confidence: 80%

“…Key localities include those for which there is incomplete data such as Atok, Richmond in the eastern limb as well as Rustenburg, Brits, and Amandelbult in the western limb. Key localities in the northern limb should include the Grasvally and Rooipoort areas where van der Merwe ( 2008 ) and Maier et al ( 2008 ) identified Merensky and UG2 units.…”

Section: Discussionmentioning

confidence: 99%

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Strontium isotope stratigraphy through the Flatreef PGE-Ni-Cu mineralization at Turfspruit, northern limb of the Bushveld Igneous Complex: evidence of correlation with the Merensky Unit of the eastern and western limbs

et al. 2020

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The origin of PGE-Ni-Cu mineralization in the Platreef, northern limb of the Bushveld Igneous Complex (BIC), and the possible correlation with the Merensky Reef in the eastern and western limbs has been long debated. The Platreef and Merensky Reef share the same stratigraphic position in the uppermost part of the Upper Critical Zone (UCZ), near the transition to the overlaying Main Zone (MZ). However, discrepancies in interpretations have been difficult to resolve due to the effects of intense magma-country rock interaction throughout most of the northern limb succession. To address this problem, we generated a detailed stratigraphic profile of the initial strontium isotopic ratio [Sr i = ( 87 Sr/ 86 Sr) i ] in plagioclase across a Flatreef interval lacking macroscopic evidence of country rock assimilation. The in situ Sr isotopic ratios in plagioclase were determined using LA-MC-ICP-MS analysis on 37 samples from a drill core (UMT094) at the Turfspruit project. Strontium isotope stratigraphy is useful because of a well-documented shift in Sr i near the base of the Merensky Unit in the eastern and western limbs. The results show the existence of a significant shift (from Sr i = 0.7060 to Sr i = 0.7090) that matches the isotopic shift documented through the Merensky Unit in the eastern and western limbs. Thus, this new Sr isotope data indicates that the main mineralized interval of the Flatreef can be stratigraphically correlated to the Merensky Reef in the remainder of the BIC. In addition, we interpret these results as compelling evidence to suggest that the main mineralization processes in the Flatreef were likely similar to those operating in the eastern and western limbs and that interaction with local country rocks was not a necessary condition. Electronic supplementary material The online version of this article (10.1007/s00126-020-01006-3) contains supplementary material, which is available to authorized users.

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Section: Discussionsupporting

confidence: 80%

Section: Discussionmentioning

confidence: 99%

Strontium isotope stratigraphy through the Flatreef PGE-Ni-Cu mineralization at Turfspruit, northern limb of the Bushveld Igneous Complex: evidence of correlation with the Merensky Unit of the eastern and western limbs

et al. 2020

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“…A number of distinctive marker layers have been recognised in the Main Zone and include the Porphyritic Gabbro Marker, Main and Upper mottled anorthosite markers and the Pyroxenite Marker. These have been described from the Eastern Limb (Von Gruenewaldt, 1973 andMolyneux, 1974), the Western Limb (Mitchell, 1990 andMitchell et al, 1998), as well as from the Northern Limb (Van der Merwe, 2008 andAshwal et al, 2005).…”

Section: Main Zonementioning

confidence: 99%

“…It is underlain by dolomite for 9 km before transgressing onto Archaean Basement granite on northern Zwartfontein, (Fig. 18a) (Van der Merwe, 1978 and2008). The full Platreef pyroxenitic assemblage varies from about 100 metres to over 250 metres in thickness and has a variable and irregular footwall contact.…”

Section: Figure 17 (A) Geological Section and Pge Value Profile For mentioning

confidence: 99%

The Bushveld Complex -Host to the World’s Largest Platinum, Chromium and Vanadium Resources

Viljoen¹

2016

Episodes

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The geological setting of the Bushveld Complex, the world's largest layered igneous body containing most of the planet's chromium, Platinum Group Elements (PGEs) and vanadium resources, is outlined. The complex is situated in a central position on the ancient Kaapvaal Craton of South Africa, with the mineralisation contained in three large arcuate mafic to ultramafic Limbs, comprised of rocks of the Rustenburg Layered Suite (RLS). The Limbs are overlain by co-magmatic felsic rocks while the floor consists mainly of sediments of the Transvaal Supergroup. The RLS is divided into the Marginal, Lower, Critical, Main and Upper Zones with the chromium and PGE enriched layers occurring in the Critical Zone and the vanadium mineralisation occurring within titaniferous magnetitite layers of the Upper Zone. The chromitite layers are classed into Lower, Middle and Upper Groups and show a general decrease in chromium content upwards from >46% Cr 2 O 3 at the base to <42% Cr 2 O 3 at the top. This is accompanied by an increase in iron content upwards and a change in the Cr /Fe ratio from >1.5:1 at the base to <1.3:1 at the top. The Lower Group and Middle Group chromitite layers have, or are currently being, extensively mined. A noteworthy feature is the presence of PGEs in all the chromitite layers, with an increase from <0.5 ppm in the lower layers to >5 ppm in the uppermost and economically important PGE bearing chromitite layer (the UG2). The economically important Merensky Reef occurs above the UG2 near the top of the Critical Zone. It typically comprises top and bottom chromitite stringers, separated by up to 14 metres of pyroxenite and/ or pegmatoidal pyroxenite, with the best mineralisation generally being associated with the top chromitite stringer and where the two chromitite stringers are in close proximity to each other. These stringers can eventually merge towards pothole structures in places, with the top stringer transgressing downward to form a range of pothole Reef features. The nature and origin of the Merensky Reef in the Eastern and Western Limbs of the Bushveld Complex is discussed. A synthesis and interpretation of a large amount of platinum mine data from the Western Limb, highlights the great variability in the nature of the Merensky Reef in this segment. Evidence suggests that the top chromitite layer represents a magmatic unconformity resulting from thermo-chemical erosion, reconstitution and mineralisation of the immediate footwall layers that it transgressed. The Platreef, a thick, generally feldspathic pyroxenitic and harzburgitic assemblage, occurs on the eastern flank of the Northern Limb and is broadly equated with the Merensky Reef. About 21 magnetitite layers ranging from massive titaniferous magnetitite, to disseminated and weakly disseminated magnetitite occur within, or are associated with, magnetite gabbro, gabbro and diorite of the Upper Zone. The vanadium content in magnetite is highest in the lowermost magnetitite layers (over 2.2% V 2 O 5 in places) dropping to 1.6% V 2 O 5 in the over...

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“…In contrast, McDonald et al (2005) suggested that the northern limb ore-bodies are distinct from the Upper Critical Zone and propose they resulted from the mixing of Lower and Main Zone magmas. The viability of this theory has been questioned as evidence exists to suggest that the Lower Zone cumulates were consolidated, significantly cooled and tilted prior to emplacement of a later magma (van der Merwe, 1978;Kinnaird et al, 2005). The relationship (if any) between the northern limb and the Upper Critical Zone or the GNPA member and the Platreef currently remains unclear.…”

Section: Regional Geologymentioning

confidence: 99%

The mineralogy and petrology of platinum-group element-bearing sulphide mineralisation within the Grasvally Norite–Pyroxenite–Anorthosite (GNPA) member, south of Mokopane, northern Bushveld Complex, South Africa

Smith

Holwell

McDonald

2011

Applied Earth Science

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The Grasvally Norite-Pyroxenite-Anorthosite (GNPA) member is a 400 to 800 m thick cumulate package located in the northern limb of the Bushveld Complex, south of the town of Mokopane. On the farm Rooipoort it forms the lowermost unit of the magmatic stratigraphy, overlying Transvaal Supergroup sediments, whereas further south on the farm Grasvally it overlies Lower Zone rocks of the Bushveld Complex. The GNPA member is divided into three units; the Lower Mafic Unit (LMF), the Lower Gabbronorite Unit (LGN) and the Mottled Anorthosite Unit (MANO). Platinum-group element (PGE) mineralisation is closely associated with base metal sulphides (BMS) and is confined to the LMF and MANO where PGE grades range from 1 to 4 ppm (3PGEzAu). A number of distinct BMS assemblages are observed throughout the area and are interpreted to be the result of a combination of primary magmatic processes and low temperature alteration. In areas where the GNPA member is underlain by Lower Zone rocks, a pyrrhotitechalcopyrite-pentlandite sulphide assemblage dominates, representing initial orthomagmatic sulphide mineralisation. Late-stage low temperature alteration has significantly altered much of the sulphide mineralogy, producing two secondary pyrite-chalcopyrite-pentlandite¡pyrrhotite ¡millerite and pyrite-pentlandite¡millerite sulphide assemblages. The primary assemblage was variably altered by crystallisation of pyrite and millerite from pyrrhotite and pentlandite at temperatures below 230uC. Sulphide replacement was associated with the precipitation of quartz and secondary silicates. This replacement of sulphides is more prevalent towards the base of the unit where the GNPA member is underlain by quartzites. These features suggest a strong footwall control over the low temperature alteration and thus the extent of the development of the secondary sulphide assemblages.

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The geology and structure of the Rustenburg Layered Suite in the Potgietersrus/Mokopane area of the Bushveld Complex, South Africa

Cited by 26 publications

References 15 publications

Strontium isotope stratigraphy through the Flatreef PGE-Ni-Cu mineralization at Turfspruit, northern limb of the Bushveld Igneous Complex: evidence of correlation with the Merensky Unit of the eastern and western limbs

Strontium isotope stratigraphy through the Flatreef PGE-Ni-Cu mineralization at Turfspruit, northern limb of the Bushveld Igneous Complex: evidence of correlation with the Merensky Unit of the eastern and western limbs

The Bushveld Complex -Host to the World’s Largest Platinum, Chromium and Vanadium Resources

The mineralogy and petrology of platinum-group element-bearing sulphide mineralisation within the Grasvally Norite–Pyroxenite–Anorthosite (GNPA) member, south of Mokopane, northern Bushveld Complex, South Africa

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