Abstract:
Exploited magnesite bodies of the Dubravsky Massif create parts of karst-fissure aquifer confined by Carboniferous metamorphic rocks of low fissure permeability. Extensive mining progress caused considerable changes in both groundwater circulation and groundwater chemical composition of the aquifer. A model of groundwater chemical composition genesis in such complicated conditions is presented in this paper. Saturation indices (SI) for chosen minerals were computed based on speciation modelling, which indicate oversaturation of groundwater with magnesite, dolomite, calcite, and undersaturation with gypsum in all saturated zone of karst-fissure aquifer. Statistical interpretations of hydrochemical data suppose that anthropogenically unaffected groundwater, where mineralisation is slightly altered by pyrite oxidation in dolomitic environment, represents hydrogeochemical background within the aquifer. It is supposed, that azonic acid, generated by condensation of nitrogen-rich gases freeing by blast-firings in mine, accelerate magnesite and dolomite dissolution. Produced groundwater types are of higher content of NO3, Mg and TIC in comparison with background values. Estimated acceleration of karstification processes due to underground mining is about 1.5 times. In spite of detected contamination, threshold values of drinking water standard, given by the Edict of the Slovak Ministry of Health Care No. 29 / 2002 Z. z. are not markedly exceeded for tested parameters. Future possible exploitation of studied aquifer after mining termination is not excluded