Idrija mercury mine is world second largest with 500 years history, and total production of 144.800 tons of mercury, which represents over 13% of the entire world production. During that time, 107.700 tons of commercial mercury have been sold and 37.100 tons of mercury was lost into the environment, which is after 20 years of mine closure still persistent in local environment. Mercury (Hg) is present in two main forms as cinnabar ore (70%) and as native Hg0 (30%). Nowadays, the main sources of Hg in Idrija are: still active mine ventilation shafts, evaporation of Hg from the heavily polluted surroundings of the former smelting plant, mineralized rock dumps of primary or partially exploited ore, outcrops of the ore deposit, and ore residues treated in various ways. Novel methodologies and approaches developed and used based on identification of mercury isotope fractionation caused by different processes and sources of Hg during formation of Idrija mine in Triassic. This will enable identification of mercury isotope ratios (IR) characteristic for different environmental Hg sources and reconstruction of Hg mass balance in wider Idrija environment, and will significantly contribute to assess dynamics and transformations of mercury between former mining and smelting operations and local environment.

The objective of this research was to study Hg isotopic compositions and evaluate Hg isotopic fractionation of different ores from the mercury mine, processed (retorted) ore, native elemental Hg0 (L) present in the mine and appeared in near-by Idrijca river, and elemental Hg0 , produced in Idrija smelting plant. Analysis has been done on Cold Vapour Generator system (CVG) coupled with MC-ICP-MS (Nu plasma II, Nu instruments Ltd, UK). Initial measurements showed huge difference in δ 202Hg values were obtained for elemental Hg0 , from -4.06 ± 0.19 ‰ in produced mercury to -0.74 ± 0.12 ‰ in the native mercury from the mine, whereas the native mercury from the Idrijca river presented δ 202Hg value of -0.35 ± 0.15 ‰. Soil core samples from different locations in the mining district were analysed and presented δ 202Hg values from -1.11 to 0.26 ‰ (2SD = 0.20 ‰). Hg isotope fingerprints in core samples close to the smelting plant show a big difference in comparison with other cores. The results, which give new information about Hg sources in Idrija mining region, will be presented.