Sylke Hilberg

The central theme of the UNESCO Global Geopark “Ore of the Alps” in Salzburg’s Pongau region is prehistoric and historic copper mining in the Eastern Alpine Greywacke Zone. Much is known about the history and geology of the ore deposits. However, to date the effects of mining on groundwater quality is not investigated yet. From January to July 2024, monthly samples were taken from mine water outlets and analysed for field parameters, main and trace elements as well as sulphate isotopes. The quality of mine water was compared with reference stations sampled at the same time. The measurements show that the pH values of the mine water are in the slightly alkaline range, meaning that the heavy metal concentration is mostly harmless, although the mine water has significantly higher concentration than the reference water. The sulphate levels in the mine waters are significantly higher than those of the reference waters. Isotope analyses indicate that the increased sulphate levels are due to sulphide oxidation and thus to mining. Although systematic discharge measurements were not possible observations in one of the mines indicate a positive correlation between discharge and mineralisation. The study shows that historical mining continues to affect water composition. However, as the main ore is chalcopyrite and the mineralisation of the ore veins is bound to carbonates, the effects of sulphide weathering in the aquifer are buffered. The mine water remains pH-neutral to slightly alkaline, so it has only a low potential to dissolve harmful heavy metals. The study provides an overview of the current groundwater situation in the ‘Ore of the Alps’ UNESCO Global Geopark and confirms that there is no groundwater contamination risk from historic mining facilities. It thus contributes to a holistic understanding of this specific geo-heritage.

Coal mining in Upper Bavaria ended in the 1960s and the mines were flooded. This study investigates the mining-influenced water and its environmental implications in the Hausham Mine, one of many unmonitored coal mines in the region and along the northern edge of the Molasse zone in Austria, Germany and Switzerland. Water and solid samples were collected in the vicinity of the discharge area within a waste rock pile and downstream of a nearby lake. The samples were subjected to chemical and isotopic analysis, with a focus on the potential for natural attenuation. The mine waste discharge has high initial concentrations of calcium, sulfate, and iron, and elevated concentrations of nickel, zinc, and strontium. These element concentrations are significantly reduced along the flow path so that the water is environmentally safe for discharge into the Loidlsee. The reduced contaminant levels are related to the formation of secondary iron precipitates and associated sorption processes, the formation of secondary calcium carbonates, and mixing with another groundwater source. The results indicate that the carbonate-dominated sediments of the Molasse zone contribute substantially to the natural remediation of a potential environmental problem.