Current utilization and hydrochemical characteristics of geothermal aquifers in the Bjelovar sub-depression

The Bjelovar sub-depression is situated in the north-western part of Croatia, on southwestern margin Pannonian Basin System where favourable geothermal conditions exist. Thermal waters are used for recreation, balneotherapy, space heating, directly as sanitary water and electricity production. Geophysical, geological borehole data were to determine types reservoirs. In addition, several campaigns conducted sample from Daruvar spa, Velika-1 Krečaves locations isotope (δ18Ο δ2H) physico- chemical (EC, T, pH, DO, Na+, K+, Mg2+, NH4+, Ca2+, SO42-, Cl-, Br-, F-, SiO2 H2S) analyses their hydrochemical characteristics. Two major reservoirs determined: (i) ‘basement – BM’ reservoir, (ii) ‘basin fill BF’ reservoir. BM reservoir consists Palaeozoic Mesozoic sediments composed of: fractured/karstified carbonate and/or fractured/fissured crystalline/metamorphic rocks. BF ‘Lower Pannonian’ ‘Upper coarse fine-grained sand, sandstones marls. aquifers most important ones study area. stable δ2H δ18O indicate that monitored thermal have a meteoric origin, but without recent replenishment. Monitored belong mixed types, Na-ClHCO3 Na-HCO3 deep basin CaMg-HCO3 type shallower parts. area has great potential. estimated total available power Križevci, spa 70.5 MWt, only 28 % this used. Since predominant activity agriculture, resources could lead modern agricultural development consequently contribute increasing standard living local population. However, additional geophysical, geological, hydrogeological investigations at number new potential required estimate resources.