Some information from heavy-mineral concentrates from Melechov massif

Geoscience Research Reports 44, 2011 (GRR for 2010), pages 172–176

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Abstract

In the granites of Melechov massif, the most important minerals which were documented in heavy-mineral concentrates only are tourmaline (scoryl) and uraninite. U-Th-Pb age of uraninite from Kouty granite according to EMPA is 280 Ma, i.e. significantly lower than cooling age of the granite; this discrepancy probably cannot be explained by the observed uraninite alteration. in the close proximity (< 20-40 /jm) of uraninite only secondary minerals and some accessories (zircon, monazite, apatite) are preserved and the secondary minerals often form concentric aureoles, which indicates that intensive radiation damage helped to the destruction of primary minerals. Measurements of radioactivity of heavy-mineral concentrates from eluvia of granites and paragneisses indicate that monazite is the most important source of radiation in the weathered rock; in the Melechov granite, also contribution of apatite and perhaps uranium bound to limonite seem to be significant.