Olivine, magma and fluids: exploring the origin(s) of platinum-group element mineralization in the Main Zone of northern Bushveld Complex of South Africa.

Project Background
Long considered barren of metalliferous ore deposits, the gabbronorite dominated Main Zone of the northern limb of the Bushveld Complex of South Africa is now established as a new frontier for Ni-Cu-PGE mineralization [1]. Olivine-bearing mafic rocks are important hosts for platinum-group element (PGE) mineralization in the Troctolite Unit (TU) of the central Main Zone and the F Zone of the Waterberg Project [2,3]. Despite petrological similarities, whether these deposits represent equivalent mineralization events traceable over 60km of strike remains unclear [4]. The focus of this study is the TU which represents a short lived period of olivine stability sandwiched between 2000 m of otherwise olivine-free Main Zone cumulates. Olivine textures and absence of elevated Cr in the TU produce paradoxes for models involving conventional fractionation or magma addition [5] and reactions involving high temperature magmatic fluids offer an alternative explanation [6]. The TU has only previously been studied along a small part of its strike length. This project will characterise its petrology and mineralization fully along strike and allow a direct comparison with the Waterberg F Zone for the first time.

Project Aims and Methods
The project will aim to study surface outcrop and boreholes through the TU located at different positions along its strike. Mapping and logging will establish the lithologies present and the extent to which major stratigraphic relationships and mineralization hosts established by [7] can be traced southwards along strike. Detailed petrography using transmitted and reflected light microscopy, element mapping using SEM, and microdrilling for Sr isotopes in plagioclase will test the possible roles of new magma(s) and/or fluids in the genesis of the TU. Bulk geochemistry and combined SEM/QEMSCAN, electron microprobe and LA-ICPMS studies (Cardiff and Exeter) will establish the presence of any PGE mineralized zone(s). A systematic search for evidence of fluids (as recorded by hydrous minerals and fluid inclusions) will be made and any fluid inclusions found will be analysed via collaborative links at Bristol. Full petrological characterisation of the TU will allow a direct comparison will be made, for the first time, with the Waterberg Project’s F Zone to test suggested links between the two olivine-hosted mineralized zones. These findings will have profound implications for reconstructing the magmatic and fluid history of the northern Bushveld Complex and developing genetic models for this style of PGE mineralization.

Candidate Requirements
The candidate should have a relevant undergraduate degree in Geology or a similar discipline. The project is suited to candidates with a strong background in mineralogy and geochemistry and who have a demonstrable interest in economic geology.

CASE or Collaborative Partner
The northern Bushveld Complex is Anglo American’s most important PGE exploration area as it is projected to be the leading producer of PGE globally in coming decades. As a partner the company provide a unique level of logistical support for the project through land access and access to boreholes. The student will have an unrivalled opportunity to work alongside Anglo American geologists and engineers at Mogalakwena mine and the group’s global headquarters in London giving them a unique insight into the workings of a modern minerals company.

Training
Describe the training that the student on this project would receive, including overseas opportunities (approx.100 words)
The student will be expected to spend two field seasons in South Africa collecting data and samples for follow-up work in Cardiff and Exeter. They will be trained in: logging, sampling, petrography using transmitted and reflected light microscopy, SEM, QEMSCAN, EPMA, bulk rock geochemical analysis using ICP, ICPMS and pXRF, fluid inclusion studies and in-situ analysis of trace elements and Sr isotopes using LA-ICPMS and microdrilling and solution-basedMC-ICPMS respectively.

It is anticipated that the student will have the opportunity to attend relevant GW4+ training courses and attend UK-based economic geology conferences (MDSG, Fermor) annually, plus one overseas conference (SEG, SGA). This will allow them to establish themselves within the UK’s economic geology community and gain exposure for their work internationally.