The decarbonisation of the global economy is a pressing challenge in which Geoscience will play a key role. The transition to renewable power generation and storage will require a significant uptick in the sourcing of key metals over the next few decades, in particular lithium (Li), a key component of Li-ion batteries. The World Bank estimates a 965 % increase in global Li demand by 2050, far exceeding current known supplies, hence a new and urgent focus in better understanding and exploring for Li-bearing deposits, which have hitherto been poorly studied.
Geologically, Li is principally found associated with the intrusion of silica-rich granites and pegmatites. These deposits form when hydrothermal fluids exsolve from highly-evolved Li-bearing magmas, driving the extraction of fluid-mobile metals, and their transportation, concentration, and precipitation as ore minerals. However, the nature of Li-bearing systems in terms of: (i) magmatic source rocks, and initial Li endowment; (ii) Li behaviour during melting and crystallization; and (iii) Li partitioning from magma into hydrothermal fluids, is poorly understood, hindering models of Li deposit formation and development of new exploration tools.
This PhD is a multidisciplinary study which addresses the Li mobility in magmatic-hydrothermal systems by linking modelling and empirical approaches, applied to key Li deposits. It builds on recent work by the supervisory team and the establishment of new analytical facilities at St Andrews:
(i) Laser ablation ICP-MS laboratory plus electron microprobe allows in-situ analysis of metals including Li, and radiogenic isotopes U-Pb and Hf, in granite mineral phases, and possibly ore minerals, to determine magma source and track metal contents through the system. A recent study by supervisor Gardiner (Fig. 1A) shows how such an approach can trace tin mobility in similar systems.
(ii) Melt-modelling putative source rocks using new thermodynamic models (Fig. 1B), to explore the nature of crustal source at different P, T, H2O contents, to tackle the critical question of initial Li endowment, and how Li partitions into the melt. Supervisor White, a core contributor to Thermocalc software, is a world expert in phase equilibria modelling.
(iii) Constraining the partitioning of Li into aqueous hydrothermal fluids during granite cooling, and favourable conditions under which economically valuable Li deposits precipitate, by developing computational thermodynamic models in Geochemists Workbench and other tools (SupPHREEQC, GEMS; Fig. 2) under the guidance of supervisor Stüeken.
(iv) Atomistic modelling of Li mobility, stability and other important properties in a range of magmatic-hydrothermal systems based on density functional theory and molecular dynamics. Supervisor Dawson has significant expertise in the modelling of Li transport and Li-based materials for a range of technological applications, including Li-ion batteries.
The student will undertake fieldwork on a well characterised Li deposit: the Sinceni pluton in Swaziland, with the possibility of also studying the Greenbushes pegmatite in Western Australia. They will develop methods for the analysis of Li and other metals in key minerals to characterize the systems in terms of metal zonation and Li-hosting minerals. This empirical data will constrain both the thermodynamic and atomistic modelling of both magmatic Li source rocks to understand Li mobility during melting and evolution, and the temperature evolution of hydrothermal fluids with variable Li-enrichments to determine under what conditions (e.g. fluid pH, salinity, and major ionic composition) Li minerals precipitate.
The ultimate goal of the project is to characterize the mobility of Li in the studied examples, the role of source and whether ordinary crustal abundances of Li are sufficient to generate economic deposits, and the nature of Li during magmatic evolution and vapour saturation, to build widely applicable genetic models. The multi-disciplinary approach used in this project has the potential to transform our understanding of such systems, and the results will be of wide interest to petrologists, economic geologists, and exploration companies. Better characterization of Li-bearing granitic systems will ultimately help in their exploration and extraction, helping ensure new supplies of this metal key to the decarbonisation of society.