Thiosulphates as Precursors of Banded Sphalerite and Pyrite at Bleiberg, Austria

H. Kucha and E. F. Stumpfl
Institute of Geology and Mineral Deposits, 30-059 Krakow, Ave. Mickiewicza 30, Poland
Institute of Geological Sciences, Mining University, A-8700 Leoben, Austria

Abstract: Banded sphalerite from Bleiberg, Austria, contains ubiquitous relics of Fe-thiosulphates and Fe-sulphites up to 50 µm in size. Zn, Pb, Ni and As form admixtures ranging from a few to 12 wt.% in these compounds. It is suggested that banded sphalerite is formed by a replacement of banded thiosulphate and thiosulphite precursors. This suggestion is supported by a significant admixture of Fe 0.41–8.20 wt.%) and the presence of goethite inclusions in banded sphalerite. In contrast, crystalline ZnS intergrown with the banded variety is Ni-free and contains only 0.06–0.14 wt.% Fe.

Banded pyrite contains inclusions of Fe-thiosulphate up to 200 µm in size. These thiosulphates contain (wt.%): 0.09–1.92 Zn, and 2.67–4.02 Pb. Pyrite formed by replacement (breakdown) of Fe-thiosulphate precursors contains 3.69–3.83 wt.% Pb.

It is suggested that banded sulphides precipitate from solutions carrying sulphur with mixed valances, and crystalline sulphides grow from solutions where the dominant dissolved sulphur is in the form of sulphidic anions.

Keywords: sphalerite • pyrite • thiosulphate • thiosulphite • banding • Bleiberg, Austria

Mineralogical Magazine; June 1992 v. 56; no. 383; p. 165-172; DOI: 10.1180/minmag.1992.056.383.03
© 1992, The Mineralogical Society
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