Geological and geophysical investigations involving drill-core studies, aeromagnetic data and surface mapping at the De Wildt property in the south-eastern part of the western limb of the Bushveld Complex have revealed a highly variable UG2 chromitite layer and a wide Merensky Reef (Merensky Reef) layer. A full stratigraphic succession of the Rustenburg Layered Suite of the Bushveld Complex is not developed at De Wildt. Instead, the Lower Zone and Lower Critical Zone are not developed and the Upper Critical Zone is developed in close proximity to the Transvaal floor rocks. Numerous deformed metasedimentary xenoliths and hornfels were intersected that are interpreted to be the result of contact metamorphism during cooling Bushveld magmas. The rock succession at De Wildt has been disturbed by post-Bushveld faulting and dolerite dykes whose emplacement is interpreted to have been influenced by the adjacent Brits graben to the west.
The Merensky Reef intersected at De Wildt prospect, while exhibiting its regional characteristics of a non-pegmatoidal feldspathic pyroxenite and thick distal facies, has undergone further thickening up to about 20 m, and is marked by sub-economic PGE values. The UG2 chromitite layer exhibited lateral variation from east to west, exhibiting variation in being a single massive chromitite seam (averaging 1.10 m in thickness) into a multi-layered unit and/or consisting of only disseminated chromite and chromitite stringers within a feldspathic pyroxenite. Also, the UG2 layer is characterized by a PGE-enriched immediate footwall feldspathic pyroxenite and norite that is 4 metres in thickness. Such a thick UG2 footwall (consisting of chromitite lenses and blebs) may indicate the presence of higher than usual amounts of late-stage fluids during the fluidization processes. Prill splits of the UG2 chromitite show that the reef has a high Pt:Pd ratio of 3:1 in contrast to the common western Bushveld UG2 Pt:Pd ratio of 2:1. It is interpreted that the UG2 chromitite layer was exposed to late stage magmatic and/or meteoric fluid metasomatism with the subsequent remobilization of Pd as evidenced by the presence of replacement magnetite and quartz-biotite veins within the UG2 layer.
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/9292 |
| Date | 31 March 2011 |
| Creators | Dube, Zamani Addmore |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | application/pdf |
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