Isotopic identification of groundwater circulation and mixing in the Legnica-Głogów Copper District mines

Identification of the conditions of circulation, mixing, origin and age of groundwater in the area of underground mining plants is necessary for the correct design of drainage systems, directions of mining exploitation and intensity of mining works. For this purpose, isotopic studies were carried out in the mines of the Legnica-Głogów Copper District (LGCD) in Poland, characterized by complex hydrogeological conditions. The observed values of δ²H, δ¹⁸O and concentrations of tritium, as well as chlorides, sulfates and main cations in 29 water samples taken from different lithostratigraphic levels (and a few historical results) were used to explain the spatial variability of the origin of groundwater flowing into the mines. A model of groundwater mixing in the mining area of the LGCD was developed. The results of the research indicate that, depending on the region, the LGCD mines contain Holocene and/or interglacial waters, pre-Quaternary waters as well as older waters, recharged in period of very warm climate - flowing into the mining workings from deeper geological strata. Isotopic studies together with the chloride content measurements confirmed the correctness of the conceptual model of groundwater circulation within the mines. Their results will be useful in further elaboration of the strategy related to dewatering and designing further mining activities.