Mineralogical aspects of CO 2 sequestration during hydrothermal basalt alteration - An experimental study at 75 to 250°C and elevated pCO 2

Alexander P. Gysi*, Andri Stefánsson

*Corresponding author for this work

Research output: Contribution to journalArticlepeer-review

60 Citations (Scopus)


The lteration of basaltic glass was studied experimentally at elevated CO 2 pressures (~10-25bar) and hydrothermal conditions (75-250°C) to determine the effects of temperature and extent of reaction (ξ) on the secondary mineral formation and compositional evolution of alteration assemblages resulting from CO 2-water-basalt interaction. At <100°C, the alteration products consisted of concentric layers of ankerite and dolomite-ankerite solid solutions (Ca-Mg-Fe carbonates) and amorphous silica. At ≥150°C, mixed Ca-Mg-Fe smectites and chlorite, calcite, amorphous silica and zeolites formed instead of Ca-Mg-Fe carbonates. Competing reactions between carbonates and clays for major divalent cations (Ca, Mg and Fe) were affected by the extent of reaction with smectites formed initially and progressively being replaced by calcite and chlorite. The basaltic glass dissolution rate and mechanism were also affected by temperature and reaction time. At lower temperatures (≤150°C), a hydrated leached layer formed on the glass surface and the mass fluxes in the system were largely controlled by the dissolution rate and mechanism of the glass, whereas at higher temperature (250°C) the dissolution rate of the basaltic glass was fast with the reactions primarily driven by secondary mineral replacement and growth. We conclude that the driving force for carbonate mineralization in basaltic glass at elevated CO 2 conditions is linked to the geochemical behavior and mobility of Ca, Mg and Fe together with the availability of Si for Al-Si-mineral formation. At <100°C, the divalent cations are available for Ca-Mg-Fe carbonate formation, whereas at ≥150°C abundant clays limit the availability of Mg and Fe resulting in calcite being the only carbonate formed. This implies a quantitatively more effective fixation of CO 2 at <100°C associated with the formation of Ca-Mg-Fe carbonates.

Original languageEnglish
Pages (from-to)146-159
Number of pages14
JournalChemical Geology
Publication statusPublished - 4 May 2012

Bibliographical note

Funding Information:
We would like to thank the members of the CarbFix project for collaboration and discussions throughout this study. We are grateful for the access at the instrumentations at the Institute of Geochemistry and Petrology at ETH Zürich, and especially the help from Eric Reusser, Jessica Langlade and Lydia Zehnder were appreciated for EPMA and XRD analyses. Useful comments by two anonymous reviewers and editor Jeremy Fein were much appreciated. This research was funded by the European Union through MIN-GRO Research and Training Network (contract number: MRTN-CT-2006-035488 ) and by the Science Institute, University of Iceland .

Other keywords

  • Basalt alteration
  • Carbonates
  • CO mineralization
  • Hydrothermal experiments
  • Reaction path
  • Water-rock interaction


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