Travertines of Funtana Maore, Sardinia, are precipitated during CO2 degassing of calcium-magnesium bicarbonate waters flowing out of Jurassic dolomitic rocks. Diffractometric analyses show travertines to consist of predominantly calcite (up to 5.6 mole% MgCO3), with some quartz, clay minerals and Fe-oxides. On the dissolved carbonate fraction, the amount of ca, Mg, Sr, Ba, Fe, Mn, na, K, Li, SO4, PO4 and Si were determined; the same chemical parameters were analyzed in the waters depositing travertines, in addition to the major dissolved anions. from the data it can be derived: a) calcite precipitation occurs only when the solution is significantly oversaturated (SIc = 1.2); 2) the Sr amounts in travertine calcite (50-80 ppm) are comparable with those observed in the Jurassic dolomite (50-80 ppm); Ba content (in the range 10-40 ppm in the calcite of travertines and only 3 ppm in dolomite) is probably supplied to the travertine calcite by Paleozoic material through the hydrological cycle of parent solutions; c) apparent partition coefficients D Me/Ca between calcite and parent solution are 0.04, 0.19 and 0.4 for Me = mg, Sr and ba, respectively; the last D value suggests that ca-substitution does not constitute the main process for Ba incorporation into calcite.
Geochemistry of Funtana Maore travertines (Central Sardinia, Italy)
CIDU, ROSA;
1991-01-01
Abstract
Travertines of Funtana Maore, Sardinia, are precipitated during CO2 degassing of calcium-magnesium bicarbonate waters flowing out of Jurassic dolomitic rocks. Diffractometric analyses show travertines to consist of predominantly calcite (up to 5.6 mole% MgCO3), with some quartz, clay minerals and Fe-oxides. On the dissolved carbonate fraction, the amount of ca, Mg, Sr, Ba, Fe, Mn, na, K, Li, SO4, PO4 and Si were determined; the same chemical parameters were analyzed in the waters depositing travertines, in addition to the major dissolved anions. from the data it can be derived: a) calcite precipitation occurs only when the solution is significantly oversaturated (SIc = 1.2); 2) the Sr amounts in travertine calcite (50-80 ppm) are comparable with those observed in the Jurassic dolomite (50-80 ppm); Ba content (in the range 10-40 ppm in the calcite of travertines and only 3 ppm in dolomite) is probably supplied to the travertine calcite by Paleozoic material through the hydrological cycle of parent solutions; c) apparent partition coefficients D Me/Ca between calcite and parent solution are 0.04, 0.19 and 0.4 for Me = mg, Sr and ba, respectively; the last D value suggests that ca-substitution does not constitute the main process for Ba incorporation into calcite.
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