22-EPN3-016: Noble Gas Tracing the Paleo-Fluids Involved in the Origin of the Crystal Caves

Visit by Petronela Ševčíková, Slovak Hydrometeorological Institute (Italy), to TA2.18 Isotoptech Noble Gas Laboratory, Debrecen (Hungary).
Dates of visit: 27 November – 07 December 2023

Report summary: We employed Noble gasses as a tracer of past and recent fluids, that may relate to the crystal caves origin. Samples represented the early and the late crystallisation of calcites (difference in ¹⁸O) of 6 caves located in different distances from large Neogene volcanic province in central Slovakia, samples of Quartz vein from the Kremica Stratovolcano, and samples of recent thermal waters in vicinity of studied caves. The question to address in this study was, whether, and to what extent, the early crystallisation fluids were mixed with fluids from a large volcanic province 12+ km to the South of the studied caves, or whether they were local fluids equilibrated with crystalline basement.

During the analytical phase we ran into unforeseen difficulties with high background, and we spent large portion of time until the background was low enough to permit the measurements. During 10 days we were able to measure five samples, where He and Ne concentrations are reliable, but the Ar-Kr- Xe fraction is affected by the incomplete purification, which indicates the presence of hydrocarbons in the fluids. The results show very high concentration of Helium with clear crustal signal of ³He/⁴He. Among the measured samples (all calcites) two represent the early crystallization, two represent late crystallisation and one sample was not distinguished (lacked the late phase). The lowest He concentrations were recorded for one ‘early’ sample and one ‘undistinguished’ sample and the phases representing the late crystallisation returned higher He concentrations. The difference is up to two orders of magnitude.

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