Tracing Lithium mobility in granitic systems

Overview

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.

Methodology

Field observations and sampling in the in at least one study area (either South 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 Isotope Geochemistry Laboratory (StAIG) is equipped with a variety of solution-based and laser ablation MC-ICPMS facilities to undertake in-situ trace element and isotopic analyses of mineral phases, including zircon U-Pb geochronology and 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.

At Newcastle University, the student will have access to a variety of local and national high-performance computing facilities to enable the accurate atomic-scale simulation of Li dynamics and other properties in a variety of minerals under different geochemical conditions.

Project Timeline

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; possible 2nd field season. Initial modelling work – phase equilbria.

Year 3

Further analytical work including cassiterite Lu-Hf methods. Thermodynamic and atomistic modelling.

Year 3.5

Complete thesis writing, prepare further manuscripts for publication

Training
& Skills

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 Geochemistry Laboratory (StAIG) and BGS will provide essential analytical support for this project but all School research facilities will be made available as required.

Training in thermodynamic modelling techniques will be provided, using the various toolkits available. Travel to Newcastle to work with co-supervisor Dawson will be required for training in atomistic computational modelling. The candidate will also be required to travel to either southern Africa and/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 and Newcastle.

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

References & further reading

Gardiner NJ, Hawkesworth CJ, Robb LJ, Wainwright A, Mulder, JA, Cawood PA. 2021. Metal anomalies in zircon as a record of granite-hosted mineralization. Chemical Geology

Kendall-Langley, L.A., Kemp, A.I., Grigson, J.L. and Hammerli, J., 2020. U-Pb and reconnaissance Lu-Hf isotope analysis of cassiterite and columbite group minerals from Archean Li-Cs-Ta type pegmatites of Western Australia. Lithos, 352, p.105231.

Simons, B., et al., 2017. Fractionation of Li, Be, Ga, Nb, Ta, In, Sn, Sb, W and Bi in the peraluminous early permian Variscan granites of the Cornubian Batholith: Precursor processes to magmatic-hydrothermal mineralisation. Lithos, 278, pp.491-512.

Wolf, M., Romer, R.L., Franz, L., López-Moro, F.J., 2018. Tin in granitic melts: The role of melting temperature and protolith composition. Lithos, 310-311: 20-30.

Further Information

For any information on the project or the School of Earth and Environmental Sciences at St Andrews, please contact Nick Gardiner (nick.gardiner@st-andrews.ac.uk).

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