Geochemistry of Carbonatites
of the Tomtor Massif

S. M. Kravchenko*, G. Czamanske**, and V. A. Fedorenko***

* Institute of Geology of Ore Deposits, Petrography, Mineralogy, and Geochemistry, Russian Academy of Sciences,
Staromonetnyi per. 35, Moscow, 119017 Russia
** United States Geological Survey, 750 West Greenwich, Polo Alto, California 94303
*** Institute of Nonferrous Metals and Gold, Ministry of Natural Resources of the Russian Federation,
Kashirskoe sh. 129b, Moscow, 113545 Russia

Received September 13, 2001

Abstract—Carbonatites compose sheet bodies in a 300-m sequence of volcanic lamproites, as well as separate
large bodies at depths of >250–300 m. An analysis of new high-precision data on concentrations of major, rare,
and rare earth elements in carbonatites shows that these rocks were formed during crystallization differentiation
of a carbonatite magma, which resulted in enrichment of the later melt fractions in rare elements and was fol-
lowed by autometasomatic and allometasomatic hydrothermal processes. Some independent data indicate that
the main factor of ore accumulation in the weathered rock zone (also known as the “lower ore horizon” com-
prising metasomatized volcanics with interbedded carbonatites) was hydrothermal addition of Nb and REEs.
The giant size of the Tomtor carbonatite–nepheline syenite massif caused advanced magma differentiation,
extensive postmagmatic metasomatism and recrystallization of host rocks, and strong enrichment of carbon-
atites in incompatible rare and rare earth elements (except for Ta, Zr, Ti, K, and Rb) compared to the rocks of
many other carbonatite massifs. We suggest that a wide range of iron contents in carbonatites-2 can be related
to extensive magnetite fractionation at the magmatic stage in different parts of the huge massif.

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