Developing methods for the location and characterisation of Li-bearing geothermal waters in Cornwall

Domestic production of lithium is central to the UK’s industrial strategy. This will facilitate the energy transition and will be essential to safeguard lithium supply against geopolitical developments. To this end, two different styles of lithium extraction are being developed in Cornwall: (1) open-pit ‘hard-rock’ lithium mining at two locations in the St Austell Granite and (2) Li-enriched geothermal fluids produced through fracture-controlled fluid-rock interaction and flow. The latter resource is being evaluated for Direct Lithium Extraction (DLE) at multiple locations.

The work undertaken here will largely concern the geothermal lithium resource. In an early phase of research, the petrophysical properties of significant lithologies will be investigated, focusing on variation due to alteration around fractures. This will involve measuring the permeability, porosity, and electrokinetic properties (streaming potential and zeta potential) of core plugs; impedance spectrometry will also be carried out. Additionally, petrographic imaging, focused ion beam SEM imaging, and a combination of micro- and nano-CT scanning will be performed. Information gained in this phase of work will enhance interpretation of geophysical data and feed into prospectivity modelling. A subsequent phase of this research will, therefore, concern the analysis of pre-existing geophysical data, plus the acquisition and processing of new, pertinent geophysical measurements. Furthermore, petrophysical characterisation will permit modelling of the expected geophysical signatures of prospects of varying size, geometry, and potentially effective grade.

The formation and behaviour of the Cornish geothermal lithium resource will also be explored. Geochemical study will elucidate the chemical development of lithium-bearing groundwaters and may suggest the physicochemical consequences of water extraction at different rates. Self-potential signals will be used to recognise patterns of groundwater flow, feeding into a broader model of Cornish geothermal circulation.

Considering Cornwall as a case study, this work is expected to inform regional prospectivity for lithium-bearing geothermal brines; it could also enhance estimates of the geothermal energy potential of the region.