The origin and sources of the Il’mensky-Vishnevogorsky miaskite-carbonatite complex, one of the world’s largest alkaline complexes, with unique rare-metal and colored-stone mineralization and Nb, Zr, and REE deposits, are discussed in this paper. Geochemical and isotopic studies, including of Nd, Sr, C, and O isotopes, as well as estimation of PT formation conditions, of miaskites and carbonatites from various deposits of the Il’mensky-Vishnevogorsky Complex have been carried out. The Vishnevogorsky, Potaninsky, and Buldym Nb-REE deposits and the Il’mensky, Baidashevo, and Uvil’dy occurrences related to carbonatites were investigated. Their geological setting, composition, and ore resource potential are characterized. The genetic models and typical features of the Il’mensky-Vishnevogorsky Complex are considered. The rocks of the Il’mensky-Vishnevogorsky Complex were formed at T = 1000−230°C and P = 2–5 kbar. Carbonated miaskite melt was divided into immiscible silicate and carbonate liquids at T = 1000°C and P = 5 kbar. Miaskite crystallized at T = 850−700°C and P = 3.5–2.5 kbar. The formation temperature of carbonatite I of the Vishnevogorsky pluton was close to the temperature of miaskite crystallization (700–900°C). The crystallization temperature of carbonate-silicate rock and carbonatite I in the Central alkaline tract was 650–600°C. The formation temperature of carbonatite II varied from 590 to 490°C. Dolomite-calcite carbonatite III and dolomite carbonatite IV of the Buldym massif were formed at T = 575−410°C and T = 315−230°C, respectively. The geochemical features of carbonatites belonging to the Il’mensky-Vishnevogorsky Complex differ from those of carbonatites related to alkaline ultramafic rocks and are close to those of carbonatites related to nepheline syenite or carbonatites localized in linear fracture zones. A high Sr content in early carbonatites along with relatively low Ba, Nb, Ta, Ti, Zr, and Hf contents and a certain enrichment in HREE (a low La/Yb ratio) in comparison with carbonatites of the alkaline ultramafic association are typical. The geochemistry of carbonatites of the Il’mensky-Vishnevogorsky Complex corresponds to the trend of geochemical evolution of carbonatitic melts and their fluid derivatives. The Sr, Nd, C, and O isotopic compositions indicate a mantle magmatic source of the Il’mensky-Vishnevogorsky Complex and participation of moderately depleted mantle (DM) and enriched mantle EM1 in magma generation. Carbonatite and miaskite of the Vishnevogorsky pluton are related to the DM magma source, and carbonatite of the Buldym massif, to the EM1 source, probably, involved in the plume ascent.

We present results of investigation of the trace-element (REE, HFSE) and Hf isotope compositions and U–Pb age of single zircons crystallized from alkaline-carbonatite magmas of the Ilmeny–Vishnevogorsky complex (IVC) (Urals, Russia). It has been established that the geochemical characteristics of the early zircon (U–Pb age of 430–410 Ma) from alkaline rocks and carbonatites of this complex are determined mainly by the magmatic evolution of parental fluid-saturated alkaline-carbonatite melts and are highly associated with the cocrystallization of zircon and uranium-containing rare-metal minerals (gatchettolite and pyrochlore) at the final stages of the magmatic-system activity. The early zircons have a moderately depleted Hf isotope composition (εHf from +11.3 to +4.7), confirming the mantle nature of the magma source and indicating the participation of DM-like and enriched-source (probably, lower-crust component) substances in the magma generation. The considerable variations in the initial Hf isotope composition of the early zircons testify to the multistage zircon crystallization involving new portions of melts with different isotope compositions controlled by mixing of substances at their source. Late IVC zircons (250–350 Ma) have strongly disturbed “rejuvenated” isotope systems and a geochemical composition different from that of the magmatic zircons. They formed apparently at the metamorphic stage of the IVC evolution without a significant input of additional material.

Carbonatites that are hosted in metamorphosed ultramafic massifs in the roof of miaskite intrusions of the Il’mensky-Vishnevogorsky alkaline complex are considered. Carbonatites have been revealed in the Buldym, Khaldikha, Spirikha, and Kagan massifs. The geological setting, structure of carbonatite bodies, distribution of accessory rare-metal mineralization, typomorphism of rock-forming minerals, geochemistry, and Sr and Nd isotopic compositions are discussed. Dolomite-calcite carbonatites hosted in ultramafic rocks contain tetraferriphlogopite, richterite, accessory zircon, apatite, magnetite, ilmenite, pyrrhotite, pyrite, and pyrochlore. According to geothermometric data and the composition of rock-forming minerals, the dolomite-calcite carbonatites were formed under K-feldspar-calcite, albite-calcite, and amphibole-dolomite-calcite facies conditions at 575–300°C. The Buldym pyrochlore deposit is related to carbonatites of these facies. In addition, dolomite carbonatites with accessory Nb and REE mineralization (monazite, aeschynite, allanite, REE-pyrochlore, and columbite) are hosted in ultramafic massifs. The dolomite carbonatites were formed under chlorite-sericite-ankerite facies conditions at 300–200°C. The Spirikha REE deposit is related to dolomite carbonatite and alkaline metasomatic rocks. It has been established that carbonatites hosted in ultramafic rocks are characterized by high Sr, Ba, and LREE contents and variable Nb, Zr, Ti, V, and Th contents similar to the geochemical attributes of calcio-and magnesiocarbonatites. The low initial ⁸⁷Sr/⁸⁶Sr = 0.7044−0.7045 and εNd ranging from 0.65 to −3.3 testify to their derivation from a deep mantle source of EM₁ type.