An inventory of surficial mafic rock resources for ex-situ carbon mineralization

Anthropogenic warming can be limited to 2 °C through a combination of greenhouse gas emission reductions and carbon storage, and safe, permanent carbon storage is possible through in-situ and ex-situ CO 2 mineralization of mafic volcanic rocks, where alkaline silicate minerals form stable carbonate minerals when reacted with CO 2 -saturated bicarbonate solutions. Arizona, U.S.A., hosts abundant surficial mafic rocks in three young volcanic fields, Geronimo-San Bernardino, San Francisco, and Springerville, and other distributed locations throughout the state. We present a new Mafic Rock Resource Inventory (MRRI) that categorizes geochemical, physical, and textural characteristics of a diverse suite of surficial mafic rock samples and provide a benchmark reaction dataset parameterizing the temperature, pressure, and pH conditions best suited for ex-situ mineralization in different rock types. We establish two reaction condition sets, varied in temperature, pressure, and pH where crystal-rich and glassy rocks reach maximum reaction extent and different carbonate phases are formed. Systematic ex-situ mineralization experiments on 21 diverse rock types show trends in geochemical, mineralogical, and reactivity behavior and establish maximum effective capture capacity. From this, scoria cones in three Arizona volcanic fields have a ∼62 Gt effective CO₂ storage capacity with one of the fields having a ∼42 Gt storage capacity in lava flows. Reactivity results have applications to alkaline mafic rock resources exposed globally, including producing additional effective storage capacity estimates and scaled commercialization of mafic rock ex-situ mineralization, should reaction extents be improved through advances in mineralization techniques.