­ In-situ mineralisation of UK onshore igneous rocks offers significant CO ₂ storage potential

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