Water quality and trace metal concentrations of mine water in the Western Harz Mountains

Abstract

<p>The tradition of mining in the Western Harz Mountains ranges from the Middle Ages to the 20th century. To evaluate the water-rock interactions as well as the environmental impact of trace metals, the mine water of three mining districts – Rammelsberg, St. Andreasberg and Clausthal-Zellerfeld – was investigated. The water samples were also analysed for the main ions. During the sampling campaigns pH-values and specific electrical conductivites (SEC) of the mine waters were measured. Compared to the most regions of Northern Germany, high precipitation rates (>850 mm/a) and a realatively low mineralisation of surface waters are found in the Upper Harz Mountains. The logging of temperature and SEC of spring and mine water over several months clearly showed that water mineralisation decreases with increasing precipitation rates (Bozau et al., 2017). The Devonian SEDEX deposit Rammelsberg is characterised by layer-bound ores and is famous for its non-ferrous metals. Acidification due to the oxidation of metal sulphides is rare. During the sampling campaigns only one sample of the Rammelsberg mine displayed a pH-value <3 (pH = 2.8). The majority of the measured pH-values ranges from 6.8 to 7.9. SEC values from 540 up to 2680 µS/cm were measured in the Rammelsberg mine. The adit "Ernst-August-Stollen" has a lenght of 40 km and is the biggest drainage tunnel of the mining district Clausthal-Zellerfeld. The portal of the adit is located in the triassic rocks of the Harz foreland, where SEC values from 980 to 1173 µS/cm and pH-values between 7.3 and 8.2 were measured. The SEC of the adit "Ernst-August-Stollen" ranges from 629 (inflow of the Kneseberg manhole) to 4710 µS/cm at the outflow of an oil separator into the main chanel (Bothe-Fiekert et al., 2021). The ICP-MS data of unfiltered and filtered (0.45 µm and 0.2 µm) water samples of this adit show that most of the iron (> 95 %) is transported as particulate fraction in the mine water. The mines of "St. Andreasberg" are situated on the highest elevations and receives the highest precipitation amount compared to the other two mining districts. The mine water of this area shows the lowest SEC values which range from 113 to 193 µS/cm and pH-values between 6.9 and 7.6. Due to the increased occurrence of Fe-Ni-Co arsenides in the St. Andreasberg gangue ore deposit and the association with antimony minerals, increased arsenic and antimony concentrations were observed in some water samples of this mining district. Although there are different and changing trace element concentrations in the single mines and adits, significant hydrochemical characteristics for the three mining districts are observed. Threshold limit values for drinking water were seldom exceeded during the investigations.</p><p> </p><p>