The mafic rocks of the Bushveld complex: a review of emplacement and crystallization history, and mineralization, in the light of recent data

Eales, H. V.; Botha, W. J.; Hattingh, P. J.; Klerk, William J. De; Maier, Wolfgang D.; Odgers, A.T.R.

doi:10.1016/0899-5362(93)90163-k

Cited by 45 publications

(14 citation statements)

References 42 publications

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“…3). The thickest cycle may exceed 200 m, whereas the thinnest, the Merensky cyclic unit, may be on the order of 10 m (Lee 1996 Eales et al 1993). The UG2 chromitite layer forms the base of each of these sections, and the lower chromite to the Merensky Reef, the top.…”

Section: Geology Of Pge-mineralized Layersmentioning

confidence: 99%

Relationship Between Pge and PGM in the Bushveld Complex

Cawthorn¹,

Lee²,

Schouwstra³

et al. 2002

The Canadian Mineralogist

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The abundances of the platinum-group elements (PGE), and their relative proportions, are summarized for all the mines exploiting the Merensky Reef on both western and eastern limbs of the Bushveld Complex, in South Africa. Grades for the mined reef interval are uniform over 100 km of strike length, at 5-7 g/t, except for Union mine, where it is currently 8 g/t. The relative proportions of the various PGE are extremely constant over this same distance. In contrast, the platinum-group minerals (PGM) vary enormously. On a regional scale around the western limb, the mineralogy ranges from alloy-dominated in the northwest to sulfide-or telluride-arsenide-dominant in the southeast. Local features that are important in terms of mining are potholes and discordant ultramafic bodies. Comparative studies of the PGE from close to and within such structures again show constant absolute and relative abundances. Limited data on the PGE from PGE-mineralized pipes (Onverwacht, Mooihoek and Driekop) suggest that they are Pt-dominated, and have a totally different relative pattern of distribution of the PGE than that in the stratiform mineralization. The PGM in the vicinity of these pipes also tends to be dominated by alloys, and in potholes by alloys and tellurides and arsenides. Hence, on both a regional scale and very local scale associated with disturbances in the reef, there is a dichotomy between the constancy of the PGE and the variability of the PGM. These observations suggest that the primary mechanism concentrating the PGE is a first-order process, and that the evolution of the PGM is the result of secondary processes related to cooling, local changes in f(S 2 ) in the crystallization environment, and subsolidus re-equilibration. The debate as to whether the PGE are derived by fluid scavenging of a footwall succession or have accumulated from supernatant magma is reexamined, and unresolved problems pertaining to both processes are highlighted.Keywords: Bushveld Complex, platinum-group elements, platinum-group mineralogy, Merensky Reef, potholes, pipes, mineralization, South Africa. SOMMAIRELe niveau de concentration des éléments du groupe du platine (EGP), ainsi que leurs proportions relatives, sont examinés pour toutes les mines exploitant le banc de Merensky, dans les secteurs ouest et est du complexe de Bushveld, en Afrique du Sud. Les teneurs des sections exploitées de ce banc sont uniformes, entre 5 et 7 g/t, sur une distance de 100 km, sauf à la mine Union, où la teneur est présentement 8 g/t. Les proportions relatives des EGP sont d'une constance frappante sur cette distance. En revanche, les assemblages de minéraux du groupe du platine varient énormément. Sur une échelle régionale autour du secteur ouest, ces minéraux vont d'alliages dans le nord-ouest aux minéraux sulfurés ou bien aux tellurures et arséniures vers le sud-est. Les "nidsde-poule" et les venues ultramafiques discordantes sont des accidents locaux qui exercent une influence sur les activités minières. Des études comparatives des EGP près de ...

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Section: Geology Of Pge-mineralized Layersmentioning

confidence: 99%

Relationship Between Pge and PGM in the Bushveld Complex

Cawthorn¹,

Lee²,

Schouwstra³

et al. 2002

The Canadian Mineralogist

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“…The G-IX pyroxenite layer occurs at a height of 1100 m above the base of the LMZ succession in borehole H5, which is situated in the postulated distal facies of 1104 the southern sector of the western Bushveld Complex (Eales et al, 1993;Scoon and Teigler, 1994). The pyroxenite layer appears to be laterally impersistent, LCD even on a local scale.…”

Section: Discussionmentioning

confidence: 99%

“…Borehole H5 is situated within the postulated distal facies of the western Bushveld (Eales et al, 1988(Eales et al, , 1993(Eales et al, , 1994Scoon and Teigler, 1994). This is reflected in the fact that the equivalent of the 1100 m thick succession up to the base of unit G-IX in borehole H5 (Fig.…”

Section: Geological Settingmentioning

confidence: 99%

Compositional cyclicity in a pyroxenitic layer from the Main Zone of the Western Bushveld Complex: evidence for repeated magma influx

Mitchell

1996

Mineral. mag.

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Lacking the pronounced modal layering of the underlying Critical Zone, the Main Zone of the Bushveld Complex nevertheless displays well-developed cryptic layering, expressed in a series of iron-enrichment trends, each defining a unit of the order of 100 to 200 m thick. At the base of one such unit, 1100 m above the Main Zone -Critical Zone contact, a 10 m thick pyroxenitic layer was intersected in an exploration borehole from the southern sector of the western Bushveld.Within the pyroxenitic layer, mineral chemistry defines a series of five cycles of upward Mg and Cr enrichment in pyroxenes, and Ca enrichment in plagioclase. The mineral chemistry, supported by textural evidence, suggests the influx of successive surges of magma. Sustained streaming of magma gave rise to adcumulate textures in the central portion of each cycle, with orthocumulate textures at bases and tops of cycles representing waxing and waning stages of magma surges.

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“…Sharpe (1985) presented Sr-isotope evidence for density stratification in the Main Zone, and proposed that the Rustenburg Layered Suite formed from at least two isotopically different magmas. In the most recent review paper on the Bushveld Complex, Eales et al (1993) list a number of factors, such as isotopic inhomogeneity of rock units and distinctive textures, which support a crystallization model of periodic mixing of residual liquid and crystal mush with batches of fresh primitive magmas, to produce the Lower and Critical Zones, and much of the Main Zone. Only the uppermost portion of the Main Zone and the Upper Zone are seen as reflecting true differentiation (Eales et al, 1993).…”

Section: The Bushveld Complexmentioning

confidence: 99%