Mineralogy of ferruginous precipitates in abandoned lignite mining region near Leknica (the Muskau Arch, western Poland): Preliminary results

摘要

The Muskau Arch, a 40 km long horseshoe-shaped belt of frontal and push moraines, originated during the Mid-Polish Glaciation. It extends from Klein Kolzig in Brandenburg, via Saxony, to Tuplice in Poland. Within the push moraines, Neogene lignite and clay, deposits occur. They were exploited up to the end of the 1980s. Abandoned excavations are recently infilled with water, thus forming large anthropogenic lake district. Due to unique geological and biological value, as well as educational and geotouristic attraction, the creation of trans-boundary geopark in this area is planned (Badura et al., 2003; Kasiriski et al., 2004). Because of the oxidation of sulphide--containing lignite, many of these lakes, especially at the teknica area, are of acidotrophic type, with very low pH values. As a consequence, numerous ochreous precipitates form. The aim of this study was mineralogical characteristic of these sediments - precipitated from ponds, as well as stream and spring waters of this area. For this purpose, mineralogical investigations (XRD + SEM-EDS), combined with chemical analyses of the waters were carried out. The analysed waters are highly mineralized (electrolytic conductivity ranges from 750 up to 2800 mu S/cm), acidic (pH 2.5-4.0) and characterized by very high Fe and sulphate concentrations, reaching 495-1880 mg/dm~3, respectively. Ca contents get close to 280 mg/dm~3, and Mg 80 mg/dm~3. Concentrations of Na, K and chloride are relatively low (usually few mg/dm~3), bicarbonate is absent. The precipitated sediments are reddish-brown and orange in colour. They occur on the pond banks, streambeds, and built up spring bowls. Very high porosity, diversified surface morphology and presence of numerous plant remnants (leaves, stalks etc.) are typical for the precipitates.