| Abstract |
Serpentinized mafic and ultramafic lithologies offer dual potential as hosts for reactive CO₂ mineralization and as natural sources of hydrogen. This study presents petrographic and SEM microanalyses of serpentinized peridotite and orthopyroxenite from Connemara, western Ireland, assessing their relevance as analogues for serpentinization-driven geothermal systems. The Dawros Peridotite shows extensive fluid–rock interaction, recorded by serpentine, amphibole, talc, carbonate, magnetite, and chromite assemblages. Orthopyroxenite, composed of enstatite with minor clinopyroxene and chromite, is pervasively altered to talc, with fluid ingress promoting local magnetite formation and magnesite veining. Amphibole–serpentine–talc–carbonate assemblages indicate widespread serpentinization and natural CO₂ mineralization, producing magnesite and dolomite from reactive Mg²⁺. Serpentinite brecciation and mesh textures suggest reaction-driven fracturing could have maintained permeability and supported fluid flow. Coexisting magnetite and carbonate veins reflect overlapping CO₂ sequestration and hydrogen-producing redox reactions. The generation of geological hydrogen is inferred to result primarily from Fe²⁺ oxidation during the formation of magnetite and serpentine from Fe-bearing enstatite (and olivine where present), while primary Fe-spinel may represent a contributory source. However, rates of H2-generation (280–310 °C) and mineral carbonation (180–200 °C) peak at distinct temperature ranges, potentially limiting concurrent operation. Incomplete transformation toward magnesite–quartz (listvenite) assemblages indicates latent mineral carbonation potential. These findings highlight how Connemara’s altered ultramafic rocks record natural processes of serpentinization and carbonation, offering insights into fluid–rock reactions relevant to CO₂ storage and resource studies. |