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Petrogenesis of PGE mineralised intrusions in the floor of the northern Bushveld Complex

Maier, W. D ; Brits, A ; Grobler, D

South African journal of geology, 2022-10, Vol.125 (3-4), p.265-290 [Periódico revisado por pares]

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Título:
Petrogenesis of PGE mineralised intrusions in the floor of the northern Bushveld Complex
Autor: Maier, W. D ; Brits, A ; Grobler, D
Assuntos: Africa ; Amatava South Africa ; Bushveld Complex ; carbonaceous composition ; chromite ores ; cores ; country rocks ; drilling ; Duitschland Formation ; Economic geology ; geochemical methods ; Geochemistry ; igneous rocks ; inclusions ; intrusions ; mafic composition ; metal ores ; metals ; mineral exploration ; Mokopane South Africa ; nickel ores ; ore minerals ; petrography ; platinum group ; platinum minerals ; platinum ores ; plutonic rocks ; Rietfontein South Africa ; rock, sediment, soil ; sills ; South Africa ; Southern Africa ; Townsland South Africa ; Turfspruit South Africa ; Uitloop South Africa ; ultramafics ; xenoliths
É parte de: South African journal of geology, 2022-10, Vol.125 (3-4), p.265-290
Descrição: The floor rocks of the northern lobe of the Bushveld Complex host several sill-like mafic-ultramafic bodies. In the present paper we evaluate whole rock data generated by exploration companies for sills on the farms Townlands, Amatava, Uitloop, Turfspruit and Rietfontein, located to the north of Mokopane, in order to constrain the origin of the sills and their mineralisation. Key observations include: (i) The sills have geochemical affinities to the Lower Zone (LZ) or Lower Critical Zone (LCZ). (ii) Most sills are enriched in sulphides and platinum-group elements (PGE) relative to most other LZ and LCZ cumulates. (iii) Most PGE mineralised intrusives have been emplaced into the carbonaceous-pelitic Duitschland Formation. (iv) The sills are spatially associated with the Mokopane gravity anomaly, possibly representing a major feeder zone to the Bushveld Complex. (v) The sills show evidence for assimilation of the sedimentary host rocks in the form of locally elevated δ34S, incompatible trace element contents and the presence of carbonaceous and pelitic country rock xenoliths. (vi) There is no correlation between PGE abundance and indicators of crustal contamination. Based on these data we propose that in the vicinity of the putative Mokopane feeder zone relatively fertile, unevolved magmas ascended through the crust initially as dykes. When intersecting the relatively fissile Duitschland Formation the mode of magma emplacement changed to one of sills. This facilitated contamination with sulphide- and graphite-rich carbonate and shale, triggering sulphide melt saturation. The sulphides were locally entrained and upgraded within the sills before precipitating, likely within flow dynamic traps.
Editor: Bureau for Scientific Publications
Idioma: Inglês

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Petrogenesis of PGE mineralised intrusions in the floor of the northern Bushveld Complex

Maier, W. D ; Brits, A ; Grobler, D

Bureau for Scientific Publications

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