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Lamprophyric dykes from the Bushveld Complex: Tracers of precious metal sources in the South African mantle lithosphere? Geology, Geochemistry – PhD (Funded)


About This PhD Project

Project Description

Supervisors:
Dr Hannah Hughes, University of Exeter (main supervisor)
Dr Jens Andersen, University of Exeter (co-supervisor)
Prof Kip Jeffrey, University of Exeter (co-supervisor)
Dr Grant Bybee, University of the Witwatersrand (co-supervisor)
Dr Iain McDonald, Cardiff University (co-supervisor)

Additional supervisors/mentors:
Prof Judith Kinnaird, University of the Witwatersrand (co-supervisor)
Prof Chris Hawkesworth, University of Bristol (co-supervisor)

Location: Camborne School of Mines, Penryn Campus, University of Exeter, Cornwall

Project Description:

A suite of lamprophyric dykes has recently been described cross-cutting the Bushveld Complex of South Africa (Hughes et al., 2016) – the largest layered intrusion in the world and famously mineralised in Cr, V and the platinum-group elements (PGE). Despite the Bushveld Complex being one of the classic areas for igneous and economic geoscience research worldwide, surprisingly little is known about the provenance of the magmas that formed it and the metal budgets they carried. The lamprophyre dykes cross-cutting the Bushveld are substantially younger than the Bushveld Complex itself (Hughes et al., in prep) and are thought to have been derived from very small degree partial melts of the subcontinental lithospheric mantle (SCLM).

The primary aim of the PhD project is to use time-integrated radiogenic isotopic compositions of these lamprophyres to investigate changes in the sub-Bushveld SCLM composition over nearly 2 billion years. A secondary aim of the project is to ascertain the controls on PGE behaviour and geochemistry in both mantle source regions and lamprophyric magmas – a paradox of lamprophyric rocks (and kimberlites) is that their PGE (and Au) abundance is higher than would be expected given that they represent very low degrees of partial melting (McDonald et al., 1995). This observation contradicts ‘traditional’ partial melting models thought to dictate the ‘fertility’ of mantle-derived magmas for PGE and Au. By contextualising PGE geochemical data with the petrography, mineral chemistry and isotopic compositions of the lamprophyres (and comparing these with appropriate mantle/mantle-derived lithologies), the PhD studentship will identify the processes governing the distribution of these elements in the SCLM and the role that might have played to produce the metal inventory of the Bushveld Complex.

This PhD project will establish the radiogenic isotopic and PGE characteristics of the lamprophyre dykes, and contrast them with analyses of kimberlites and other lamprophyres, and thereby develop an integrated model for their petrogenesis. Thus the objectives of the studentship are to:

1. Gain insights into the precious metal budget of the SCLM through time.
2. Assess the extent to which the distribution of metals in the continental mantle influenced the distribution and characteristics of major mineralised metal deposits in and around the Bushveld Complex.
3. Develop PGE as a tool for understanding lamprophyric rock petrogenesis.
The project will provide training in petrology and in situ analyses (including SEM, EPMA and LA-ICP-MS), geochemistry (major and trace elements by ICP-OES and XRF, ICP-MS, and PGE by NiS fire assay with ICP-MS, and isotopic techniques relevant for Sm-Nd, Rb-Sr and/or Lu-Hf systems). The student will be encouraged to undertake additional training courses as required by the needs of the project or their own specific interests (for example in ArcGIS, FieldMove, ioGAS, and R). The student will be based at the Penryn Campus of University of Exeter but will also spend time in South Africa (including the University of the Witwatersrand in Johannesburg and selected field and mine locations around the Bushveld Complex).

References

Hughes, H.S.R. et al. 2016. Applied Earth Science, 125(2), 85-86.
McDonald, I. et al. 1995. Geochimica et Cosmochimica Acta, 59(14), 2883-2903.

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