Multiple crystallization of zircon in the Sakharjok rare-earth element-zirconium deposit, Kola Peninsula

120 Zircon is characterized by striking typomorphic features (morphology, anatomy, chemical composi� tion), which allow the reconstruction of conditions and stages of its crystallization in different geological processes (magmatic, postmagmatic, and metamor� phic). Therefore, the study of these features could be very informative in deciphering the sequence and duration of geological and, especially, oregenerating processes. The Sakharjok deposit is presently one of Russia's most promising complex sources for zirconium, rare� earth elements (REEs), and yttrium (1). The Sakhar� jok alkaline massif is located in the western part of the Keivy terrane (Kola Peninsula). The latter is made up mainly of Late Archean basic to felsic metavolcanics and metasediments lying on the tonalite-trondhjemite-gra� nodiorite basement of the Central Kola block, as well as intraformational intrusions of alkali granites. The Sakharjok Massif is restricted to the southern part of the Western Keivy alkaline granite massif. This is a fis� suretype intrusion consisting of alkali gabbroids (essexites), nepheline syenites, and alkali syenites (2). The alkaline magma intruded as extended (>7 km long) steep dikelike bodies along vertical faults between alkaline granites and gneiss diorites. The massif has maximal width (1.5-2 km) in its northern part. Its western and southwestern parts are occupied by alka� line syenites, while the eastern part is made up of nepheline syenites with large (up to 80 × 200 m in size) blocks of alkaline gabbroids. Petrographically, they are represented by very abundant trachytoid mesoand leucocratic (most abundant) lepidomelane-egirine syenites, porphyritic ferrohastingsite syenites devel� oped in the marginal parts of the massif, and pegma� toid lepidomelane-ferrohastingsite syenites that occur as lenslike bodies in the trachytoid syenites.