<i>In-situ</i> mineralisation of UK onshore igneous rocks offers significant CO₂ storage potential

Safe and permanent storage of CO₂ will be required to limit g¬lobal warming to 1.5 – 2 °C above pre-industrial levels. <i>In-situ</i> mineralisation of CO₂ within igneous rock formations is a rapid and secure method of geological CO₂ storage. This study uses geochemical data and novel volumetric analysis of suitable onshore mafic and ultramafic formations in the UK to determine that these rocks offer a theoretical CO₂ storage capacity of 42 to 38 000 MtCO₂ through <i>in-situ</i> CO₂ mineralisation. Mid-scenario estimates suggest the assessed formations could store ~45 years of UK industrial point-source CO₂ emissions (at 2017 levels). The Antrim Lava Group in Northern Ireland offers the largest potential storage capacity (15 to 17 300 MtCO₂), followed by the Borrowdale Volcanic Group in England (8 to 8600 MtCO₂) and the Skye Lava Group in Scotland (7 to 7800 MtCO₂). Our work demonstrates that UK onshore mafic and ultramafic formations contain significant rock volumes with favourable chemistry for <i>in-situ</i> CO₂ mineralisation. Future work should prioritise characterising effective porosity and determining the impact of alteration and formation age on the reactivity and CO₂ sequestration ratio of the prospective UK formations.