Magnetic properties and metastability of greigite-smythite mineralization in brown-coal basins of the Krušné hory Piedmont, Bohemia

Details Magnetic properties and metastability of greigite-smythite mineralization in brown-coal basins of the Krušné hory Piedmont, Bohemia Magnetic properties and metastability of greigite-smythite mineralization in brown-coal basins of the Krušné hory Piedmont, Bohemia

Mar 1992

adsabs.harvard.edu/cgi-bin/nph-data_query?bibcode=1992pepi...70..273k&link_type=abstract

Physics of the Earth and Planetary Interiors, Volume 70, Issue 3-4, p. 273-287.

Physics

29

Scientific paper

Finely dispersed forms of greigite or greigite-smythite mineralization were found in layers a hundred and more metres thick in the Miocene strata of the Krušné hory (Erzgebirge) Piedmont brown-coal basins. Under laboratory thermal treatment, a pronounced instability of greigite or greigite-smythite mineralization was revealed by the magnetic parameters, conditioned by mineralogical metastability. Thermal treatment in oxidation conditions caused the most pronounced changes in magnetic parameters in a temperature range of 320-380°C, in which a laboratory process of self-reversal of remanence was observed. The products obtained during thermal treatment were identified with the aid of X-ray diffractographs (Co-radiation, Fe-filter). When they were heated to 250°C, no substantial changes were found, while at 300°C the intensities of greigite became weaker, and pyrite and marcasite originated to its detriment. Hexagonal pyrrhotite was generated in addition to pyrite and marcasite. A total decomposition of bisulphides took place at temperatures above 400°C, accompanied by the formation of various modifications of Fe2O3, until finally at higher temperatures only α-Fe2O3 was formed.
Laboratory tests suggested self-reversal of remanence in relation to the formation of pyrrhotite. So far, greigite or greigite-smythite mineralization has been proven to exist in the Bohemian Massif solely in connection with Miocene rocks containing fossil micro-organic matter. Products of thermal alteration, pyrite, marcasite, pyrrhotite, γ-, η-, and α-Fe2O3 (or Fe3O4 depending on redox conditions) may be expected in rocks of similar genesis, but partly or completely carbonified as a result of a process of pyrolysis of the micro-organic matter.

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