PGE mineralization in the western sector of the eastern Bushveld Complex

Gruenewaldt, G. von; Horsch, Hanna; Dickst, D.; Wet, J. de

doi:10.1007/bf01162685

Cited by 26 publications

(11 citation statements)

References 25 publications

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“…This is well illustrated by the data of Hiemstra (1986), which show that the Pd content of the upper part of the UG2 is much less than that of the lower part, even though Ir, Pt, and the other metals vary in concert throughout. Although not obvious in Hiemstra's (1986) profile, the upper UG2 typically contains much less sulfide (e.g., von Gruenewaldt et al, 1990). As pointed out by Peach and Mathez (1996), the UG2 profile is not consistent with sulfide liquid fractionation and must reflect late magmatic or subsolidus PGE redistribution.…”

Section: Pge Geochemistrymentioning

confidence: 92%

Character of the UG2 Chromitite and Host Rocks and Petrogenesis of Its Pegmatoidal Footwall, Northeastern Bushveld Complex

Mathez¹,

Mey²

2005

Economic Geology

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The UG2 chromitite and its immediate footwall have been mapped at the centimeter scale in a characteristic section exposed in a wall in the Middelpunt mine, northeast Bushveld Complex. In this region the UG2 chromitite and its coarse-grained footwall rocks are underlain and overlain by plagioclase pyroxenite. The UG2 chromitite itself is a massive, 70-cm-thick layer composed of 75 to 90 percent chromite with plagioclase as the dominant interstitial mineral. Immediately beneath the chromitite is the so-called mixed layer, a previously undescribed but distinct, mappable layer, 50 to 70 cm thick, consisting of chromite-bearing pegmatoidal pyroxenite and chromitite intimately mixed at scales of centimeters to decimeters. The mixture is chaotic with no megascopic fabric and contains in bulk about 15 percent chromite. The contact between the mixed layer and overlying chromitite is well defined but sinuous at scales of centimeters to decimeters. Based on observations of drill core and outcrop, the mixed layer appears to exist throughout the central sector of the eastern Bushveld and may be ubiquitous throughout the entire Complex. The mixed layer usually rests directly on the UG2 pegmatoid, which is a well known and widespread pegmatoidal plagioclase pyroxenite. The pegmatoid is much coarser grained than the underlying pyroxenite, but the two lithologic units are similar in terms of mineral modes and compositions. The contact between them is irregular at scales of decimeters to meters, with vertical fingers of pegmatoid extending into the pyroxenite. The mixed layer and UG2 pegmatoid contain rare lenses of massive anorthosite encased by continuous, centimeter-thick rims of chromitite.A model is proposed to account for the footwall sequence of the UG2 chromitite. In this model, the UG2 pegmatoid formed when hydrous, interstitial melt percolated up through the partially molten crystal pile, accumulated beneath the preexisting, compacted, massive chromitite, and metasomatized and partially melted the pyroxenite protolith, which upon cooling recrystallized to a coarse-grained rock. On the basis of published experiments illustrating the effect of water on melting in mafic systems, it is shown how the hydrous melt was able to penetrate the pyroxene-bearing assemblages below the chromitite but unable to partially melt the chromitite itself, which in consequence remained relatively impermeable. The anorthosite lenses in the pegmatoid mark local areas of relatively high degrees of hydration partial melting, with the anorthosite representing the crystalline residue. The mixed layer formed by gradual collapse of the base of the UG2 chromitite into the less dense, relatively fluid footwall. The mixed layer and UG2 pegmatoid are diagnostic of the UG2 chromitite, and the three lithologic units should be considered a single petrologic unit.

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Section: Pge Geochemistrymentioning

confidence: 92%

Character of the UG2 Chromitite and Host Rocks and Petrogenesis of Its Pegmatoidal Footwall, Northeastern Bushveld Complex

Mathez¹,

Mey²

2005

Economic Geology

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“…d Base-metal and platinum-group element concentrations across the concentrated towards the base and the upper contact of the layer . The sulfur concentration within the chromitite is less than 0.1 weight percent in most cases (Barnes et al 2009; with exceptional sulfide abundance of up to 2.5 volume percent observed the Messina Mine (Von Gruenewaldt et al 1990). Cawthorn et al (2005) reported that the Pt/Pd ratios are significantly different from the Eastern to the Western Limb.…”

Section: Pge-mineralization Associated With Large Chromitite Layersmentioning

confidence: 98%

Platinum-Group Element Deposits in Layered Intrusions: Recent Advances in the Understanding of the Ore Forming Processes

Godel

2015

Springer Geology

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“…The model of an original sulfide control of the PGE in the chromitites and subsequent S, Pd and Cu loss is supported by the observation that PGM in the chromitites are often associated with base metal sulfides (BMS) (McLaren and De Villiers, 1982). Further, sulfide-and BMS-rich UG2 and UG1 chromitite occurs at several localities in the Bushveld Complex, e.g., in the northern limb (''UG2-like chromitite'', Hulbert, 1983;Hulbert and von Gruenewaldt, 1982), and in the western sector of the eastern Bushveld Complex, particularly at Messina and Maandagshoek (Von Gruenewaldt et al, 1990;Gain, 1985). At Messina, the UG1 has up to 0.8% sulphide, 1287 ppm Cu and 2089 ppm Ni.…”

Section: Ore Genesismentioning

confidence: 89%

“…The relative PGE abundances in the S-rich UG2 are also somewhat different to those of the UG2 elsewhere in the Complex. Pd is relatively enriched and the IPGE, particularly Ru, are relatively depleted, resulting in higher Pd/Pt (0.72 vs 0.43) and Pd/Ru ratios (2.94 vs 1.44, Von Gruenewaldt et al, 1990;Barnes and Maier, 2002b). (ii) Some of the PGE in the chromitites (notably the IPGE and Rh) could have been concentrated by means of solid solution in chromite (Capobianco et al, 1994;Peach and Mathez, 1996;Righter et al, 2004).…”

Section: Ore Genesismentioning

confidence: 96%

Platinum-group element (PGE) deposits and occurrences: Mineralization styles, genetic concepts, and exploration criteria

Maier

2005

Journal of African Earth Sciences

163

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PGE mineralization in the western sector of the eastern Bushveld Complex

Cited by 26 publications

References 25 publications

Character of the UG2 Chromitite and Host Rocks and Petrogenesis of Its Pegmatoidal Footwall, Northeastern Bushveld Complex

Character of the UG2 Chromitite and Host Rocks and Petrogenesis of Its Pegmatoidal Footwall, Northeastern Bushveld Complex

Platinum-Group Element Deposits in Layered Intrusions: Recent Advances in the Understanding of the Ore Forming Processes

Platinum-group element (PGE) deposits and occurrences: Mineralization styles, genetic concepts, and exploration criteria

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