Interpretation of groundwater origin in the Velenje coal mine on the basis of isotope composition

Abstract

The aim of the investigation was to determine the isotopic properties of cave waters from the Velenje coal mine and define the recharge areas of individual aquifers. With regard to the oxygen isotope composition, groundwater in the Velenje coal mine can be classified into three types. Typical d18O values of the first type are around -9 ‰ and are found in surface waters in the vicinity of the mine, therefore it is supposed that these waters are recharged locally. The second type is represented mainly by waters from the lower part of the pliocene aquifer. The average oxygen composition of these waters is about -11 ‰. This isotope composition is considerably different from the isotope composition of recent waters from the mine’s vicinity, which leads to the conclusion that these are older, fossile waters. These waters also have a very high degree of mineralization and consequently conductivity. Waters of the third type have average d18O values around -10 ‰ and originate mainly from triassic dolomites. These waters could be a mixture of recent and old waters, but it is also possible that they flow into the coal mine from the higher areas of Paški Kozjak.