Journal of
GEOsciences
  (Formerly Journal of the Czech Geological Society)

Original Paper

Hydrothermal uranium-base metal mineralization of the Jánská vein, Březové Hory, Příbram, Czech Republic: lead isotopes and chemical dating of uraninite

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Abstract:
The Jánská vein is one of the important veins of Březové Hory mining district (central Bohemia, Czech Republic). Base metals were mined here since 14^th century and uranium ore during late 1950’s.
Uranium mineralization is younger than most of the base metal mineralization according to macroscopic and microscopic study. Most specimens of uraninite, obtained from archive, contain more or less abundant galena inclusions. Galena of this type is non-radiogenic as indicated by its Pb isotopic composition (ICP-MS). Its origin can be explained by remobilisation of the older base-metal mineralization during the younger, uranium-bearing mineralization event. The amount of radiogenic Pb in uraninite fluctuates from 48 up to 89.8 %. The age of theoretical end member of uraninite, calculated statistically from all measured data (for intersection ²⁰⁸Pb/²⁰⁶Pb = 0), is 269.8 ± 20.3 Ma (2σ). The only uraninite grain without galena inclusions yielded an age of 263.2 ± 8.9 Ma by chemical dating using electron microprobe. The calculated age of the uranium mineralization is in agreement with published data for other uranium deposits genetically associated with the Central Bohemian Plutonic Complex.