A combined isotope and chemical approach to determining the origin of brines in salt mines

The paper presents a summary of isotope and chemical studies on the origin of brines in four Polish salt mines (three in Zechstein salt domes and one in a Miocene formation). Stable isotope content of brines encountered in mines depend on the origin of waters and on the processes of isotope exchange. These processes may be classified as primary, i.e., those occurring in the salt rock, and secondary, i.e. those occurring in a mine. The primary processes are dissolution of, and isotope exchange with hydrated salt minerals. The secondary processes are evaporation in a mine and molecular exchange with the water vapour in the mine air. The secondary processes may lead to great shifts of the original isotope contents, which make the identification of some brines ambiguous. Particular identification problems are encountered in mines with wet exploitation and/or in the case of leaks of a low flow rate at places of a difficult access. The presented case studies prove that in spite of some ambiguities the isotope methods are very useful in solving the identification problems. (author)