I strongly recommend the following article on the discrimination of hydrothermal from magmatic zircons in VMS deposits from the IPB:
Toscano, M., Pascual, E., et al. (2014): Geochemical discrimination of hydrothermal and igneous zircon in the Iberian Pyrite Belt, Spain. Ore Geology Reviews 56, 301-311.
1) The Khibiny massif (Kola, Russia): crystals up to 4 cm in diameter in natrolite veins (together with ilmenite, ancylite-Ce/La, etc.);
2) The Lovozero massif (Kola, Russia): crystals up to 3 cm in cavernous albitites (together with ilmenite, pyrochlore);
3) The Kovdor massif (Kola, Russia): crystals up to 5 cm in voids of carbonatites (together with bobierrite, kovdorskite, rimkorolgite and other phosphates);
4) Olenegorsk BIFs (Kola, Russia): small (up to 2 mm) crystals grown on pumpellyite druses together with fluorapophyllite, heulandite-Ca, chabazite-Ca and other zeolites.