Study of rare gases in geothermal waters from Herculane area, Romania

In the south-western part of Romania there is a long and deep fissure following the Cerna liver canyon as well as many transversal fissures, especially placed in the region of Herculane Spa. The geothermal water sources (springs and drillings), always accompanied by large amounts of gases, are located where these fissures cross. The presence of granite rocks at the surface is another remarkable characteristic of this area. Nitrogen and methane are the main components of emanated gases, and high helium and radon concentrations were also found. The composition of the gases was determined by using a Dempster mass spectrometer. The radon content from these gases and the rate of radon exhalation fr om the ground were determined by gamma spectrometry method. The argon isotopes were analyzed by means of a quadrupole mass spectrometer (AMP-4). In the vicinity of transversal fissures, the radon exhalation rates present higher Values from all measurements in this, area. The ratio He-4/Ne-20 > 400 is a very good indicator of the fact that these gases are not contaminated with atmospheric air and therefore the gases come from depth. The He-4/Ar-40 and Ar-40/Ar-36 ratios suggest that the helium in these sources may have a non-negligible part of primordial helium arising from the earth mantle.