X-RAY STRUCTURE, LUMINISCENCE AND ZONALITY OF ZIRCONS FROM SOUTH URAL

Yu.I.Pystina

URO RAN Geology, Laboratory of Regional Mineralogy

Ilmensk complex of igneous and metamorphic rocks is part of Sysertsk-Ilmenogorsk mega-anticlinorium found within East-Uralian uplift. Numerous pegmatite bodies are observed within the complex, the bodies being attributed to three major types according to their mineral composition: granitic, syenitic and miaskitic. Traditionally, pegmatites containing original rock-forming quartz are described as granitic; nepheline-bearing pegmatites as miaskitic, and alkaline feldspathic pegmatites with no quartz and nepheline contents as syenitic. Studying miaskitic pegmatites involved a thorough investigation of zircon occurring in these rocks. The mineral normally occurs as prismatic to dipyramidal crystals 0.5-6.0 cm in length. The crystals are brownish-grey and yellowish-brown in colour. Small varieties are transparent, large ones are strongly fractured, transparent or trans- lucent. A large portion of crystals show macro- and microzonality, which is in certain correlation with X-ray and luminescent properties of the mineral. It has been found that the darker zones are distingu- ished from the lighter ones by their metamict structure, weaker X-ray luminescence and Hf, Th, U, Fe, Ca impurities.