| Title | Geothermal energy prospecting in radiothermal granites in the Cairngorms, Scotland, using an integrated magnetotelluric and petrophysical approach |
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| Authors | Innes Campbell, Nathaniel Forbes Inskip, Juliane Huebert, Andreas Busch, Michael van Mourik |
| Year | 2026 |
| Conference | World Geothermal Congress |
| Keywords | |
| Abstract | The Cairngorm Pluton granites in NE Scotland emit among the highest heat-production values in the UK. While past geothermal exploration had been stifled by low heat-flow estimates, recent palaeoclimate-corrected models predict significantly higher temperatures at depth. Key uncertainties persist regarding geothermal reservoir permeability, fluid pathways, and the overall pluton structure - critical factors for achieving economical geothermal flow rates at strategically placed drill sites. Hydrothermal alteration, recognised within the Cairngorm granite, may also affect reservoir quality. Studies from analogous granitic systems suggest that hydrothermal processes along fracture networks can enhance porosity and permeability through mineral alteration and microstructural modification at depth. The effects of hydrothermal alteration in the Cairngorm granites remain unquantified. To address these uncertainties, we conducted a broadband magnetotelluric (MT) survey, a geophysical deep-sounding technique with the capability to image structures in the subsurface at several kilometres depth. We collected ~50 sites in the central Cairngorms south of Glenmore during summer 2024 and 2025. The 3D inversion of the MT data reveals north-south trending conductive zones extending to ~2.5 km depth, potentially imaging fluid-bearing fracture systems and zones of hydrothermal alteration. Our integrated approach combines 3D resistivity modelling using advanced inversion techniques with laboratory measurements of altered and unaltered granite samples to evaluate the effects of alteration on porosity, permeability, and electrical resistivity. These measurements will be correlated with the MT-derived resistivity structure to identify viable geothermal fluid pathways. This work directly contributes to de-risking Scotland's geothermal development and develops transferable methodologies for characterising crystalline geothermal reservoirs worldwide. |