Atmospheric carbon dioxide is spontaneously sequestered through the weathering and subsequent carbonation of serpentinite outcrops at Montecastelli (Tuscany, Italy). The three selected studied areas consist of: i) serpentinite escarpment close to a spring water; ii) gangue materials dumped in front of the entrance of a serpentinite-hosted copper mine; and iii) the main tunnel of the serpentinite-hosted copper mine. The three sites are characterized by high humidity and the serpentinite rocks appear whitish in color, completely coated by a thin carbonate crust. XRD analyses indicated that precipitated minerals of the carbonate crust are, in different proportion, hydromagnesite, nesquehonite, manasseite, pyroaurite, brugnatellite, very often in association with aragonite. No silica (quartz, opal, chalcedony) has been detected. Serpentinite host rocks do not evidence any pervasive alteration and/or dissolution, with the exception of localized carbonate late veins. In addition, these rocks contain significant amount of brucite, not often recovered in oceanic serpentinites. The emerging waters, sampled in the three areas, have high pH, relatively high TDS (Total Dissolved Solids) and high Mg/Ca molar ratio with respect to the meteoric water, indicating that the chemical compositions are controlled by interaction of rainwater with serpentinite host rocks. Isotopic analyses (δ18O, δ2H, 87/86Sr) of rainwaters, emerging waters, serpentinites and carbonates highlighted that the carbonates have been precipitated from superficial waters circulating into the serpentinite bodies. Overall, our data point to an on-going rapid uptake of atmospheric CO2, triggered by high humidity and presence of magnesium oxide (brucite) into the rocks. At low temperature, brucite dissolves easier then serpentine minerals, as already reported in some occurrences of weathered serpentinites. This natural process introduces new application on the carbon mineralogical sequestration and its study could open new solutions for the environmental sustainability and GHG reduction.
Multiple isotope approach to unravel the sequence of water-rock interaction and hydromagnesite precipitation at Montecastelli (Tuscany)
BEDINI, FEDERICA;PERCHIAZZI, NATALE
2014-01-01
Abstract
Atmospheric carbon dioxide is spontaneously sequestered through the weathering and subsequent carbonation of serpentinite outcrops at Montecastelli (Tuscany, Italy). The three selected studied areas consist of: i) serpentinite escarpment close to a spring water; ii) gangue materials dumped in front of the entrance of a serpentinite-hosted copper mine; and iii) the main tunnel of the serpentinite-hosted copper mine. The three sites are characterized by high humidity and the serpentinite rocks appear whitish in color, completely coated by a thin carbonate crust. XRD analyses indicated that precipitated minerals of the carbonate crust are, in different proportion, hydromagnesite, nesquehonite, manasseite, pyroaurite, brugnatellite, very often in association with aragonite. No silica (quartz, opal, chalcedony) has been detected. Serpentinite host rocks do not evidence any pervasive alteration and/or dissolution, with the exception of localized carbonate late veins. In addition, these rocks contain significant amount of brucite, not often recovered in oceanic serpentinites. The emerging waters, sampled in the three areas, have high pH, relatively high TDS (Total Dissolved Solids) and high Mg/Ca molar ratio with respect to the meteoric water, indicating that the chemical compositions are controlled by interaction of rainwater with serpentinite host rocks. Isotopic analyses (δ18O, δ2H, 87/86Sr) of rainwaters, emerging waters, serpentinites and carbonates highlighted that the carbonates have been precipitated from superficial waters circulating into the serpentinite bodies. Overall, our data point to an on-going rapid uptake of atmospheric CO2, triggered by high humidity and presence of magnesium oxide (brucite) into the rocks. At low temperature, brucite dissolves easier then serpentine minerals, as already reported in some occurrences of weathered serpentinites. This natural process introduces new application on the carbon mineralogical sequestration and its study could open new solutions for the environmental sustainability and GHG reduction.I documenti in IRIS sono protetti da copyright e tutti i diritti sono riservati, salvo diversa indicazione.
