Geochemical Feasibility of In-situ CO2 Mineralisation in the Whin Sill, Northern England, UK

In-situ carbon mineralisation is increasingly recognised as a permanent and leakage-resistant pathway for geological CO2 storage. However, its applicability to non-volcanic intrusive mafic rocks remains less well constrained than volcanic systems, despite their widespread distribution and proximity to industrial CO2 sources in the UK. This study presents a geochemically focused feasibility screening of the Whin Sill, a regionally extensive doleritic intrusion in northern England, to evaluate whether its mineralogical and geological characteristics are compatible with in-situ CO2 mineralisation. The work integrates mineralogical characterisation of representative doleritic lithologies and conceptual evaluation of CO2-water-rock interactions under subsurface conditions relevant to injection. The Whin Sill contains abundant Ca-, Mg- and Fe-bearing silicate minerals that are theoretically capable of carbonation, indicating a fundamental geochemical suitability for mineral trapping. However, its intrusive doleritic nature introduces important contrasts relative to volcanic basalts, including differences in mineral assemblages, fracture development and reactive surface area, which are expected to strongly influence dissolution kinetics, secondary carbonate precipitation, porosity evolution and injectivity behaviour. This contribution evaluates how these factors may enhance or constrain the practical feasibility of mineralisation-based storage and identifies the key geochemical and reactive-transport parameters that must be quantified to move from conceptual potential to deployable assessment. These include reaction kinetics under subsurface conditions, fracture-controlled flow behaviour and the coupling between geochemical reactions and transport processes across relevant spatial and temporal scales. The Whin Sill is therefore framed as a promising but unvalidated candidate for mineralisation-based CO2 storage in the UK. The findings define a feasibility-led research pathway centred on laboratory-derived kinetics, fracture-aware reactive-transport modelling and integration with low-carbon mineral frameworks, directly supporting the development of scalable and permanent CO2 storage in mafic rock systems.