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Geochemistry of Funtana Maore travertines (Central Sardinia, Italy)
No full textTravertines 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
Weathering of Pb-Zn mine tailings in PH buffered environment
No full textThe Ingurtosu Pb-Zn mine in south-western Sardinia, exhibits three main weathering processes: 1) oxidation without acidification derived from Pb and Zn sulphides; 2) oxidation with acidification derived from Fe sulphides; 3) pH buffering due to Ca and Mg carbonate dissolution. These weathering processes are followed by adsorption of metals on iron oxyhydroxides and precipitation of hydrated sulphates (sometimes carbonates). Nearly all iron sulphides and carbonate (siderite, ankerite) grains, have alteration rims made up of iron oxyhydroxides (goethite), where Zn, Cu and Pb are adsorbed after sulphide oxidation. Moreover, the occurrence of slightly weathered clay minerals confirms the low pH values are never reached. -from Author
Evolution of mineral surface during reaction: some constraints by AFM and solution chemistry
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Otavite from Montevecchio, Sardinia, Italy
No full textThe rare mineral otavite CdCO3 was found at the abandoned Pb-Zn mine of Montevecchio (SW Sardinia, Italy). Otavite occurs in the oxidised gossan, in association with aurichalcite. SEM imaging shows that otavite is composed of lenticular hollow structures containing aggregates of tiny rhombohedral crystals. Oxidation of primary Cd-bearing sulphides (sphalerite and greenockite) releases up to 24 ppm of Cd to drainage waters of the Montevecchio area. These waters are generally saturated with respect to otavite. Therefore, this mineral might play an important role in controlling Cd mobility in the environment
Le peliti dei calcari nodulari di Gutturu Pala e di altri affioramenti dell’Iglesiente (Sardegna sud-occidentale)
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In situ investigation of galena dissolution in oxygen saturated solution: Evolution of surface features and kinetic rate
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