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The first cave occurrence of orpiment (As2S3) from the sulfuric acid caves of Aghia Paraskevi (Kassandra Peninsula, N. Greece)

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Author(s): Lazarides Georgios | Melfos Vasilios | Papadopoulou Lambrini

Journal: International Journal of Speleology
ISSN 0392-6672

Volume: 40;
Issue: 2;
Start page: 133;
Date: 2011;
Original page

Keywords: Greece | Aghia Paraskevi | hypogene caves | orpiment | tamarugite | pickeringite | gypsum

ABSTRACT
Orpiment, tamarugite and pickeringite occur in close association above the surface of thermal water cave pools in the active sulfuricacid caves of Aghia Paraskevi on the Kassandra peninsula, northern Greece. Gypsum also occurs as small interstitial crystals orencrustations. Orpiment is of high significance since it has not previously been reported as a cave mineral. In addition, tamarugiteand pickeringite rarely occur in karst caves. Water from a borehole and a spring is of Na-Cl type and contains traces of CO2 and H2S.The B/Cl ratios indicate seawater participation with a possible mixing with geothermal water of meteoric origin. Oxidation of fumarolicH2S and incorporation of seawater is a possible cause for the deposition of tamarugite. Orpiment accumulated from vapors undersub-aerial conditions at low temperatures in acidic conditions through an evaporation-condensation process. Fluid cooling and/oracidification of the solution resulting from H2S oxidation were responsible for orpiment precipitation. Oxidation of H2S to sulfuric aciddissolved the limestone bedrock and deposited gypsum.
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