Minerals assotiations and compositional heterogeneity of zircon from miaskite-carbonatite complex of the Vishnevye mountains, South Urals

Abstract

In alkaline rocks, pegmatites and carbonatites of the Vishnevye Mountains, zircons co-crystallized with rock-forming silicates (feldspars, nepheline, annite, etc.), as well as with some other minerals (pyrochlore, magnetite, ilmenite, apatite, monazite, calcite, etc.) and cannot be ascribed to metacrystals. The morphology of zircon crystals (their cut and habit) varies from dipyramidal (in miaskites) to short prismatic (in biotite syenites), from dipyramidal to prismatic in alkaline pegmatites, and with a combination of dipyramids in carbonatites, which is explained by variation in alkalinity of mineral-forming conditions from early alkaline (miaskits) to less alkaline (syenites) and alkaline (carbonatites). Zonal and zonal-sectorial zircon crystals with variations in the HfO2 content are dominant and relatively homogeneous crystal rarely occur. In diferent zircon crystals, the HfO2 content of peripheral zones either increases or decreases and unevenly vary. Sectorial composition of zircon is mostly related to distinct HfO2 contents of peripheral zones of prisms {100}, {110} and dipyramid {111} and {221}. The reserves of zircon of are ~75 kt and possible resources are >100 kt.