IAP2-22-357

Tracing battery metal (Li + Sn) mobility in granitic systems

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 tin (Sn), essential for solder, and lithium (Li), a key component of Li-ion batteries. A significant uptick in the sourcing of these metals is predicted, hence a new and urgent focus in better understanding and exploring for Sn- and Li-bearing deposits, the latter which have hitherto been poorly studied.

Geologically, Sn and Li are principally found associated with the intrusion of silica-rich granites and pegmatites. These deposits form either endogranitic with the extraction of highly evolved magma, or when hydrothermal fluids exsolve from such highly-evolved metal-bearing magmas, driving the extraction of fluid-mobile metals, and their transportation, concentration, and precipitation as ore minerals. However, the nature of Sn-Li-bearing systems in terms of: (i) magmatic source rocks, and initial metal endowment; (ii) Sn and Li behaviour during melting and crystallization; and (iii) metal partitioning from magma into hydrothermal fluids, is poorly understood, hindering models of Sn-Li deposit formation and development of new exploration tools.

This PhD is a multidisciplinary study which addresses battery metal mobility in magmatic-hydrothermal systems by linking modelling and empirical approaches, applied to key Sn-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 Sn and Li, and radiogenic isotopes U-Pb, Rb-Sr and Hf, in granite mineral phases (zircon, apatite), and ore minerals (cassiterite, columbite-tantalite), 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 metal endowment, and how Li and Sn partitions into the melt.
(iii) Constraining the partitioning of Sn and Li into aqueous hydrothermal fluids during granite cooling, and favourable conditions under which economically valuable Sn and Li deposits precipitate, by developing computational thermodynamic models in Geochemists Workbench and other tools (SupPHREEQC, GEMS; Fig. 2) under the guidance of supervisor Stüeken.
The student will undertake fieldwork on at least one well characterized Sn-Li deposit, either in southern Africa or Western Australia. They will develop methods for the analysis of battery metals in key minerals to characterize the systems in terms of metal zonation, metal-hosting minerals, and implications for melt metal budgets. This empirical data will constrain the thermodynamic modelling of both magmatic source rocks to understand metal mobility during melting and evolution, and the temperature evolution of hydrothermal fluids with variable metal-enrichments to determine under what conditions (e.g. fluid pH, salinity, and major ionic composition) both Sn and Li minerals precipitate.

The ultimate goal of the project is to characterize the mobility of Sn and Li in the studied examples, the role of source and whether ordinary crustal abundances of these metals are sufficient to generate economic deposits, and the nature of metal mobility 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 battery metal-bearing granitic systems will ultimately help in their exploration and extraction, helping ensure new supplies of this metal key to the decarbonisation of society.

Field observations and sampling in the in at least one study area (either southern Africa and/or Western Australia) will focus on the emplacement history of granite units using cross-cutting relationships and transects deep into the granite to build 3 dimensional views of the emplacement history and ore events.

Mineral geochemistry on zircon and other accessory phases by laser ablation ICPMS will be used to track crystallisation histories recorded by mineral growth within individual samples. A range of other in-situ and whole-rock geochemical and isotopic approaches may be undertaken. Analytical work will be carried out at the University of St Andrews and the British Geological Survey (BGS). The St Andrews Geochronology Laboratory (StAGE) and Isotope Geochemistry Laboratory (StAIG) are equipped with a variety of solution-based and laser ablation MC-ICPMS and QQQ-ICPMS facilities to undertake in-situ trace element and isotopic analyses of mineral phases, including zircon U-Pb geochronology and Rb-Sr and Lu-Hf isotope analysis, as well as whole-rock geochemical and isotopic analysis. A range of other facilities including a new electron microprobe and SEM are also available to students. The Geochronology and Tracers Facility at the BGS provides a wide range instrumentation available to students including a newly installed SELFRAG (high-voltage fragmentation system) instrument for mineral separation; laser ablation MC and SF -ICP-MS instruments, a low-Pb blank clean suite, and a state-of-the-art Isotopx TIMS for high-precision (CA)-ID-TIMS U-Pb geochronology.

Year 1

Literature review, review historic data from case studies. Initial field season (April/May) to collect samples for analysis; lab training

Year 2

Laboratory training. Collect initial geochemical and isotopic data; petrographic analysis; present results at domestic conference; 2nd field season. Initial modelling.

Year 3

Further analytical work including cassiterite Lu-Hf methods. Modelling

Year 3.5

Complete thesis writing, prepare further manuscripts for publication

The PhD student will join the Planetary Geodynamics Research Group at the University of St Andrews, and become part of a vibrant research culture in the School of Earth and Environmental Sciences, with MSc, PhD and postdocs working on a wide range of Earth Science research projects.

Full training in digital-based field mapping and sample selection will be provided, as well as in sample categorization and preparation, and geochemical and isotopic analysis. Both the St Andrews Isotope Laboratories and BGS will provide essential analytical support for this project but all School research facilities will be made available as required.

The candidate will also be required to travel to either southern Africa or Australia to conduct fieldwork supported by the supervisors. The student is also expected to attend national and international conferences to disseminate research results and to spend time away from St Andrews to integrate project partners at BGS.

The student will become part of the IAPETUS DTP, which offers a multidisciplinary package of training focused around meeting the specific needs and requirements of each of our students who benefit from the combined strengths and expertise that is available across our partner organisations