A Dissertation submitted to the Faculty of Science, University of the Witwatersrand,
Johannesburg, in fulfillment of the requirement for the degree of Master of Science.
2016. / An important feature of the Merensky Cyclic Unit in the Bushveld Complex is the
association of platinum group metals with narrow chromitite layers. The appearance and
removal of chromitite layers in this unit has been used to define facies types. This study
explores the hypothesis that individual chromitite layers within the Merensky Cyclic Unit
at Marikana have distinguishing major element concentrations or ratios which could
assist in tracing the continuity of the chromitite layers between facies types which is
characterized by single or multiple layers. The examination of field relationships of the
chromitite layers at the transition between facies types will be useful to improve
understanding of lithological continuity. This study has two approaches; the first being
the examination of underground exposures and petrographic analysis, and secondly by
chemical analysis of chromite grains within the chromitite layers.
No chromite mineral compositional trends or similarities were observed for grains in
chromitite layers hosted by the same silicate mineral. The mineral chemistry evidence
suggests that post cumulus processes are considered to have changed the primary
chromite compositions and that reequilibration has occurred due to reaction with trapped
intercumulus liquid. Little to no reaction with the host silicates of plagioclase and
pyroxene is envisaged. The slow cooling of the Bushveld Complex has allowed
intercumulus liquid a greater opportunity to equilibrate with the early minerals, destroying
the early magmatic history by reaction and recrystallization. The cumulate deposition
model envisaged to have formed the Merensky Cyclic unit at Marikana is by the
emplacement of several pulses of superheated magma, supported by the occurrence of
several chromitite layers within the sequence. / LG2017
| Identifer | oai:union.ndltd.org:netd.ac.za/oai:union.ndltd.org:wits/oai:wiredspace.wits.ac.za:10539/21674 |
| Date | January 2016 |
| Creators | Wansbury, Nicole Tracy |
| Source Sets | South African National ETD Portal |
| Language | English |
| Detected Language | English |
| Type | Thesis |
| Format | Online resource (177 leaves), application/pdf, application/pdf, application/pdf |
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