Siberia, Russia

Main commodities: REE
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The Tomtor ultramafic massif and related REE-Nb deposits are located in far northern Siberia, Russia, at approximately 71°N, 116° 30'E.   It lies between the Aanabar Shield to the west and the Olenyoc Uplift to the east and is located within a deep rooted 400 km long palaeorift which separates basement rocks of different ages.

The massif is a 300 sq. km ring complex in which the ore deposits are associated with a central carbonatite stock.   The massif intrudes late Neoproterozoic to Cambrian dolomites, siltstones, sandstones and tuffs and lower Palaeozoic sandstones and siltstones and is overlain by Permian coal measures, Jurassic argillites and arenites, and Tertiary to Quaternary alluvium.

The Tomtor Massif is composed of biotite-, biotite-pyroxene-nephelene, and nepheline-bearing alkaline syenites which comprise the outer 60%, or 2 to 6 km wide margin of the complex.   The central stock crops out over an area of 40 sq. km, of which 12 sq. km is carbonatite.   The syenite periphery and the carbonatite core are separated by a 1 to 3 km wide ring dyke of jacupirangite-urtite, while the carbonatite is intruded by a dyke complex of picrite, alnoite, nepheline syenite, melilitite, tinguaite, alkali trachyte and dolerite.   The rocks of the complex range in age from >700 Ma (from the jacupirangite-urtite and ring zone nepheline syenite) to 650 to 510 Ma (the carbonatite) to 410 Ma of the nepheline syenite dykes.

The ore zones comprise:  1). pyrochlore bearing carbonatite,  2). a lower ore horizon up to 300 m thick containing lodes rich in niobium and phosphorous, made up of pyrochlore and phosphorous bearing rocks within the carbonatites, volcanics, picrite dykes and country rocks, and  3). a 3 to 25 m thick upper ore horizon comprising a buried placer deposit of rich florencite-monazite-pyrochlore.   Concentrations of the economic components vary from a few tenths of a percent in the carbonatite, to a few percent in the lower ore horizon, to a few tens of percent REE and 12% Nb in the upper zone.

For detail consult the reference(s) listed below.

The most recent source geological information used to prepare this summary was dated: 1995.    
This description is a summary from published sources, the chief of which are listed below.
© Copyright Porter GeoConsultancy Pty Ltd.   Unauthorised copying, reproduction, storage or dissemination prohibited.

  References & Additional Information
   Selected References:
Kravchenko S M, Pokrovsky B G  1995 - The Tomtor Alkaline Ultrabasic Massif and related REE-Nb deposits, northern Siberia: in    Econ. Geol.   v90 pp 676-689

Porter GeoConsultancy Pty Ltd (PorterGeo) provides access to this database at no charge.   It is largely based on scientific papers and reports in the public domain, and was current when the sources consulted were published.   While PorterGeo endeavour to ensure the information was accurate at the time of compilation and subsequent updating, PorterGeo takes no responsibility what-so-ever for inaccurate or out of date data, information or interpretations.

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