Untersuchung von “Schwefelkiesknollen“ aus den Tonschichten des Kies- Abbaues bei Barleben (Sachsen-Anhalt)

Abstract

Lorenz, P., Schulz, M., Märtens, H.: Investigation of “iron disulfide nodules“ from clay sedimentsof the gravel mining area near Barleben (Saxony-Anhalt, Germany). - Hercynia N. F. 45 (2012): 33 – 49.Iron sulfide concretions are occasionally found in clay sediments of the northern plains, e.g. in theancient glacial river bed near Magdeburg (Saxony-Anhalt, Germany). Gravel mining by use of an offshorebucket chain excavator yields occasionally iron sulfide concretions. The found objects exhibit arough surface, a grey or black colour and a knobby-, kidney- or stalactite-like shape. Sometimes theconcretions are covered with rusty limonite (iron oxide hydroxides, FeO(OH)). The average density(4.60 g . cm-3) was determined by use of a pyknometer. Breaking the concretions exhibits a metallicbrass-like glossy on the fracture surface. Investigations of the elementary composition by X-ray fluorescenceanalysis (RFA) have shown that the concretions consist of 75 – 81.5 % iron(II) disulfide (FeS2).Beside magnesium, aluminium, silicium, potassium, calcium - the concentration of these elements staggeringbetween 0,5 – 6,4 % - other trace metals have been analysed, e.g. titanium, chromium, nickel,copper, zinc, tin and barium etc. Conspicuously, a high arsenic content between 48 – 338 ppm was detectedby atomic absorption spectrometry (AAS) in the investigated samples. A sedimentary formationof the iron sulfide concretions by a bacteria supported mineralization of organic matter, e.g. wood, understrongly anaerobic conditions is discussed.Key words: iron sulfide concretions, marcasite, pyrite, FeS, FeS2, pyritization, microbial iron / sulphurreduction1 Einleitun