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Trace element and stable isotope data from a flowstone in a natural cave of the mining district of SW Sardinia (Italy): evidence for Zn2+-induced aragonite precipitation in comparatively wet climatic conditions

Author(s): Caddeo Guglielmo Angelo | De Waele Jo | Frau Franco | Railsback L. Bruce

Journal: International Journal of Speleology
ISSN 0392-6672

Volume: 40;
Issue: 2;
Start page: 181;
Date: 2011;
Original page

Keywords: mine cave | speleothems | trace elements | stable isotopes | mineralogy | calcite | aragonite | kinetics | environmental reconstruction

A speleothem from Crovassa Azzurra, a mine cave in SW Sardinia (Italy), has been analysed for mineralogy, minor and traceelements and stable isotopes. It is composed of layers of primary calcite and aragonite, with a region of secondary calcite. The primarycarbonate is strikingly rich in Zn and Pb, presumably as the result of transport in solution from overlying Pb-Zn deposits. Immediatelybelow the transition between calcite and aragonite, concentrations of Zn, Cd and P increase. At the transition between aragonite andPb-rich aragonite, concentrations of Pb and P increase. Stable isotopes do not indicate an evolution toward drier periods for thesetwo transitions, conversely to what is normally observed in calcite-aragonite speleothems. On the contrary the combined observationof increase in P and metals derived from oxidation of sulphides and the variation of isotopic composition of aragonite and calcitesuggests that in this mine cave aragonite was deposited with increasing flowrate and thus more humid conditions. In addition, theeffect of Zn2+ or Pb2+ in inhibiting precipitation of calcite appears to have been more important than that of Mg2+.
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