A Cobaltite-Framboidal Pyrite Association from the Kupferschiefer: Possible Implications for Trace Element Behaviour During the Earliest Stages of Diagenesis

D. J. Large1, Z. Sawlowicz2 and J Spratt3
1 Department of Mineral Resources Engineering, University of Nottingham, Nottingham, NG7 2RD, UK
2 Institute of Geological Sciences, Jagellonian University, ul. Oleandry 2A, 30-063 Krakow, Poland
3 Department of Mineralogy, Natural History Museum, Cromwell Road, London, SW7 5BD, UK

Abstract: Cobaltite-cemented pyrite framboids are reported from the base of the Kupferschiefer in the Lubin-Sieroszowice mining district in southern Poland. In the framboids, cobaltite occurs interstitial to the pyrite crystals. The cobaltite-cemented framboids are confined to within a few cm either side of the boundary between the Weissliegendes sandstone and the Kupferschiefer laminated organic-rich shales. Textural relations and distribution of the cobaltite is interpreted as indicating that the framboids acted as a site of preferred cobaltite precipitation and that the cobaltite precipitated in response to the changing chemical environment at the Weissliegendes/Kupferschiefer contact. It is proposed that the texture may have formed as a result of desorption of Co and/or As which had been adsorbed onto the monosulphide precursors to the framboidal pyrite. Desorption during the transition to pyrite resulted in cobaltite saturation within the framboid and subsequent precipitation. The source of the Co and As was probably oxyhydroxides which exist in the upper oxic part of the Weissliegendes.

Keywords: cobaltite • pyrite • framboid • Kupferschiefer • Poland • trace elements • diagenesis

Mineralogical Magazine; June 1999 v. 63; no. 3; p. 353-361; DOI: 10.1180/002646199548574
© 1999, The Mineralogical Society
Mineralogical Society (www.minersoc.org)