Minerals of rare and rare-earth elements in acidic metavolcanites of the Sablegorskaya Formation (Northern Urals)

   Research subject. Metavolcanics of the Sablegorskaya Formation collected in the area of Mount Redka on the western slope of the Northern Urals (Komi Republic).

   Aim. To study the petrogeochemical composition of metavolcanics and mineral forms of Nb and rare-earth elements contained therein.

   Materials and methods. Rock samples were collected from eluvial-deluvial rubble and mine workings on the southeastern slope of Mount Redka. The analytical procedures included determination of the contents of rock-forming oxides in rocks by the classical chemical method; measurement of concentrations of rare, trace, and rare-earth elements by inductively coupled plasma mass spectrometry (ICP–MS); microprobe analysis of mineral composition.

   Results. The studied metavolcanics of the Sablegorskaya Formation belong to rhyolites and trachyrhyolites of normal and subalkaline series formed in an intraplate setting. The presence of rare-metal (Nb-rutile) and rare-earth (allanite, monazite, xenotime, nioboeschinite-Y) in the mineral composition of the rocks was established. They form a scattered dissemination of grains 20–50 μm (Aesh(Y), Xnt, Mnz) and 50–500 μm (Nb-Rt, Aln) in size. We consider their appearance to be a result of magma crystallization, autometasomatic processes, and subsequent metamorphism.

   Conclusions. The presence of rare metal and rare-earth minerals in the composition of acid metavolcanics of the Sablegorskaya Formation of the Northern Urals was established. An assumption is made about the possibility of mobilization of Th, U, Y, Nb, and REE from rhyolites and trachyrhyolites in tectonically active zones with the formation of corresponding ore occurrences.

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