Magmatism and metasomatism in the formation of the Katugin Nb-Ta-REE-Zr-cryolite deposit, eastern Siberia, Russia: Evidence from zircon data

The world-class Katugin deposit (Eastern Siberia, Russia) in the high-F alkaline granite of the Katugin complex is located within the Early Proterozoic Stanovoy orogenic belt on the southeastern periphery of the Siberian craton. The deposit stores economic amounts of Nb, Y, Zr, REE, Ta, Th, U, and cryolite. Its formation was previously interpreted in terms of a single-stage model, but new zircon data reveal an additional stage in its history. That stage was separated in time from the magmatic activity and led to a redistribution of REE + Y and, probably, additional enrichment of rocks in these components. Zircon in the deposit area occurs ubiquitously in alkaline granite and forms zones at granite contact with cryolite veins and lenses. Four types of zircon have been identified based on their microstructure. Type I zircon with magmatic signatures makes relict cores in zircon grains and has an age of 2064 ± 5 Ma in granite and 2080 ± 10 in ores (> 20 vol% of zircon), which is coeval with the emplacement of the Katugin granite. This type of zircon exhibits positive ɛHf(t) values, from +3.3 to +1.1, testifying for a juvenile source. Type II zircon (1921 ± 11 Ma) occurs within a core at the granite-cryolite contact. Type III zircon (1900 ± 6 Ma), heterogeneous in cathodoluminescence (CL) images, overgrows Type I and II zircon grains. The zircon zones with low or no CL response are characterized by high concentrations of REE2O3, Y2O3 and P2O5. This type of zircon contains abundant multiphase (solids + fluid) and polycrystalline inclusions, with a large percentage of REE + Y fluoride and fluorocarbonate among solids and a high-density CO2-enriched fluid phase. Type IV homogeneous zircon (1909 ± 10 Ma) rims are observed in most zircon grains. Types II, III and IV zircon have negative ɛHf values, from −2.2 to −3.8. They are coeval and crystallized during high-grade metamorphism and magmatism, which accompanied the final amalgamation of the Siberian craton at 1.93–1.88 Ga. The formation of Type III zircon occurred in the presence of high-F CO2-rich fluids, possibly, coming from a mantle source, which supposedly led to redistribution and additional inputs of REE in the granite. •The world-class Katugin rare metal deposit was formed in two stages: magmatic and metasomatic.•The economic Zr mineralization was formed during the magmatic stage (2064 ± 5 Ma).•REE + Y and cryolite ores result from metasomatic stage (1904 ± 6 Ma).•Nb mineralization developed during all stag