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HYDROLOGY OF MEZICA (SLOVENIA) LEAD AND ZINC MINE DEWATERING AFTER MINE CLOSURE

M. Mavc, J. Prestor, S. F. Strucl

Abstract

Mining in upper Me\vza valley had more than 350 years of tradition. Lead and zinc ore deposit was developed in the triassic carbonate layers on the area of 64 km2. Until 1994, when the mining process was stopped, miners excavated about 19 million tons of lead and zinc ore and over 1000 km of galleries and pits. A crucial aspect of the Me\vzica mine was the dewatering issue. Me\vzica ore deposit is developed in Triassic carbonate rocks – limestone and dolomite. The area is of rough mountainous relief rising from 500 m a.s.l. to 2.126 m a.s.l (Mt. Peca). The hydraulic barriers of the depression cone are well known to the northern and southern side, where there are outcrops of practically impervious rocks. Boundary conditions to the east and west side could not be well defined, because there is no evident geological barrier. The mine was excavated 250 m below the regional groundwater level at 520 m a.s.l. Carbonate rocks are fissured and karstified. Catchment area is quite big 83 km2 extending over high mountains Peca, Mala Peca and \vSumahov vrh. A volume of 1,7 million m3 of mine galleries was excavated below groundwater level and on the other hand a volume of 360.000 m3 of flotation mud was deposited in those galleries. The inflowing water would make mining impossible if not dealt with properly. The discharge of groundwater to the mine was approximately 35 m3/min (580 l/s). During mining under the groundwater level the inflowing water had to be pumped, so the regional depression cone with radius between 1.300 and 5.140 m was formed.

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