Factors Affecting Zircon Metamictization in Granites

Characteristics of metamict zircon and its relationship to granites are reviewed. The degree of metamictization of zircon increases with increasing acidity and alkali contents of the granites. I t is evident that zircon metammtization is caused mainly by radioactive radiation from radioactive el, ements contained in it rather than by hydro:ys[s. Introduction Metamict zircon in granitoids of south Chin~ .and in gra~dte-peg~atites of Xinjiang is closely ret~ted to. rare-eteanent ~re deposits, i.e., zircon present in granites asso,ci,ated with zare-element mineralization has ,always been metJa~nictized. The so-called metamietization of zircon refers to that the lattice of crystalline ZrSO, has been partiaBy destroyed and structurally it has turned to.wards or even completely into disorder state t'~. Character~tics of Metamict Zircon There are two ways w~aich a~e most intuitive and reliable in j~t~d'gi0a,g whaVher or to what extent the zircon kas ~een metamietized. One is X-ray po.w~ler diffraction, ,because any metaaliet zircon te~c~s to ~how X-ray iso~ropism in X-my di~fvactiom patterns (Debye patterns). That is to say, the number of re~lect~nces of metam~ct zircon decreases d~astiea,lly, while Eaeir ixttensities weal~en in the X-ray diff, r~ction patterns. CryI I [ 1 I I I I I i I i I 140