International Geological Journal - Official Journal of the Carpathian-Balkan Geological Association

Trace element chemistry of low-temperature pyrites — an indicator of past changes in fluid chemistry and fluid migration paths (Eger Graben, Czech Republic)

Pages: 117 - 132

Authors: JIRI ZACHARIAS, JIRI ADAMOVIC, ANNA LANGROVA

Abstract: Trace element contents in six generations of low-temperature (< ~50 °C) pyrite (Py-1 to Py-6) recognized in silicified Cretaceous sandstones near Jenikov in the central Eger (Ohre) Graben, Bohemian Massif, are used to decipher late Cenozoic fluid circulation patterns in the graben. Py-1 and framboidal Py-2 are generally coeval with silica cementation, while Py-3 to Py-6 postdate this process. Py-6 forms inclusions in barite crystals, clearly separated in time from silica cementation. The average arsenic contents of 0.01, 0.15, 2.94, 3.91, 6.14 and 0.76 wt. % As for Py-1 through Py-6 and anomalous average nickel and cobalt contents in the oldest Py-6 inclusions (3.47 and 8.86 wt. %, respectively) indicate the presence of two contrasting fluid circulation patterns in the graben fill during the period of pyrite formation (?Pliocene to Recent). Early fluids (Py-1 to Py-5) are interpreted as progressive deepening, fault-driven fluids originating from acidic volcanics in the basement. The late fluids are shallow, topography-driven fluids in contact with the Tertiary lignite beds. Earlier data from structural geology allow us to explain such change in fluid circulation by regional tectonic stress rearrangement, which inhibited the activity on the Krusne hory Fault at about 400 ka.

Keywords: Eger Graben, silicification, fluid chemistry, fluid circulation patterns, pyrite, arsenian pyrite, arsenic

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