Dr David Holwell (University of Leicester),
Dr Iain McDonald (Cardiff University), Dr Hannah Hughes (Camborne School of Mines, University of Exeter), Professor Tom Blenkinsopp (Cardiff University), Andy Lloyd (Anglo American), Fiona Stevens (Anglo American).
The Northern Limb of the Bushveld Complex, South Africa is host to the world’s largest resource of platinum-group elements (PGE), along with significant nickel, copper and cobalt in a complex magmatic sulfide ore deposit. All of these resources are linked with environmentally-friendly technologies and energy usages in the automotive industry, with the PGE being essential components in catalytic converters (including Pd which has more than tripled in price in the past five years), and Ni, Co and Cu critical metals in Electric Vehicle batteries. As such, the northern limb of the Bushveld is likely going to play a large part in the switch to cleaner automotive technology.
The major deposit in the Critical Zone of the northern Bushveld (commonly known as the ‘Platreef’) rests directly on variable basement of Archaean and Paleoproterozoic units at surface. Down dip, it overlies Bushveld Complex Lower Zone rocks; themselves prospective for base metal sulfide mineralisation. The stratigraphy, structure, mineralization styles and metal budgets of the Northern Limb of the Bushveld Complex show important differences to the other limbs of the complex. The underlying causes behind these differences are poorly understood and no geological model exists to investigate them on anything more than a local scale.
This PhD project aims to tackle questions surrounding the controls on the emplacement of the various magmatic units, which appear to have their own, variable metal budgets and thicknesses. This focusses on processes that occur prior to and during emplacement and are critical to understanding the genetic and exploration models. The project is in partnership with Anglo American, who have been mining the Platreef via surface methods since the 1990s, and now operate the world’s largest PGE surface mining operation at the Mogalakwena Mine. Whilst the near-surface resources are reasonably well characterised, the down dip potential and extension of resources is known, but has had no research work completed on it thus far. Therefore, this PhD provides the opportunity to work on one of the world’s greatest ore deposits, with resources critical for a greener future, and at a time when exploration and mining activities in the area are expanding.
1. How did the pre-existing basement architecture and structure control the emplacement, thickness and grade of the northern limb magmas.
2. Which direction did the (potentially) sulphide-laden magmas move? Where is the feeder? Can we vector towards higher tenors and possibly more massive sulfide in feeder conduits?
3. Is the Lower Zone emplaced entirely before the Critical Zone, or is the Critical Zone a differentiated continuum/mixing zone of residual Lower Zone magma? Which Lower Zone bodies are sources of viable Ni-Co-Cu-sulfides?
4. Were the magmas emplaced with a pre-enriched cargo of base and precious metals, and if so, where did the key processes of sulfide saturation and metal enrichment happen?
5. Are Northern Limb magmas inherently more Pd and Au enriched than the rest of the Bushveld?
In order to tackle the research questions, a multi-disciplinary approach will be used whereby the PhD researcher will undertake fieldwork in South Africa and make use of an unrivalled collective resource of laboratory facilities at Leicester, Cardiff and CSM (Exeter).
A. Fieldwork in South Africa will include structural mapping (in field and drone mapping in open pit mines) of the immediate basement architecture to the Bushveld rocks, and in particular, fold structures in the Palaeoproterozoic metasedimentary rocks to tackle question 1 and 2.
B. Fieldwork in South Africa to sample extensive drill core of the shallow and deeper stratigraphy of the northern Bushveld Complex. This will include basement, Lower Zone, Lower and Upper Critical Zone, and the base of the Main Zone units. Sampling from drill core will form the basis of lab work to tackle questions 3-5 (see C-E).
C. Mineralogical and geochemical characterisation of the Lower Zone bodies along with petrological evidence of the nature of the contacts and chill zones between Lower Zone bodies and the Critical Zone to tackle question 2.
D. Mineralogical and laser ablation analysis of sulfide inclusions in early formed silicates and oxides to characterise the ‘parental’ high temperature sulfide liquid that formed Platreef mineralisation (question 4).
E. Geochemical and petrological assessment of fine grained chill zones and unmineralized rocks within the sequence to determine parental magma compositions and address question 5.
In terms of the scientific developments in understanding the northern limb specifically, and the genesis of such ore deposits more generally, the project will test and revise models of “staging chambers” during magmatic evolution; determine the fundamental directional aspects of the emplacement model; and undertake a calculation of a realistic mass balance and metal endowment of each magma, essential for any broader modelling work.
The application of this to industry includes an assessment of the metal endowment of Lower Zone stratigraphy and bodies to inform future exploration; the identification of vectors towards possible feeder systems to increase the chance of exploration success; and provide a quantitative basis to market the upside polymetallic base metal and Pd-Au value of the northern Bushveld.
This PhD forms part of a large consortium project (NL4D) funded by Anglo American involving Leicester, Cardiff and CSM (Exeter). The project runs for five years from January 2020 and will include three PhD studentships (two based at Leicester) working alongside senior researchers, postdocs and Masters students from all three universities. The PhD researcher will have access to labs at all three institutions and the opportunity to spend some extended period working at each. There will be regular interaction with Anglo American through fieldwork, internal reporting and workshops/meetings in South Africa and the UK. The PhD researcher will be encourage to present their results at national and international conferences each year, including the International Platinum Symposium in 2022 and the Biennial meetings of the SGA (e.g. Rotarua, New Zealand, 2021).
Grobler, DF, Brits, JAN, Maier, WD and Crossingham, A., 2018, Litho- and chemostratigraphy of the Flatreef PGE deposit, northern Bushveld Complex. Mineralium Deposita 54, 3-28.
McDonald I, Holwell DA. 2011. Geology of the Northern Bushveld Complex and the Setting and Genesis of the Platreef Ni-Cu-PGE Deposit. Reviews in Economic Geology 17, 297-327.
Yudovskaya, M.A., Kinnaird, J.A., Grobler, D.F., Costin, G., Abramova, V.D., Dunnett, T., Barnes, S-J. 2017. Zonation of Merensky-Style Platinum-Group Element Mineralization in Turfspruit Thick Reef Facies (Northern Limb of the Bushveld Complex). Economic Geology, 112, 1333-1365