ZONALLY METAMICTIZED AND OTHER ZIRCONS FROM

• Main Authors: Conadian Mineralogist, Dorian G. W. Smith, Etqp Louise, De St. Jorre, Stephen J. B, Reed, James V. P. Long
• Other Authors: The Pennsylvania State University CiteSeerX Archives
• Format: Text
• Language: English
• Subjects: metamict zircon; chemical analyses; electron microprobe; ion microprobe; Thor Lake; Blachford Lake peralkaline complex; Northwest Territories. SOMMAIRE; Blachford Lake; Northwest Territories
• Online Access: http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.536.2174; http://rruff.info/doclib/cm/vol29/CM29_301.pdf

Zircon occurs in both the T Zone and Lake Zone of the Aphebian Thor Lake rare-metal deposits. Certain rocks contain strikingly zoned zircon, with interference colors ranging from low second order down to first-order grey. Elechon- and ion-microprobe investigations show these variations in optical characteristics to be associated with sharp changes in chemical composition. The lower-birefringence zones contain as much as 4t/o U, 4t/o Y and nearly 590 Nb, with inferred water contents up to- 14q0. In contrast, the more highly birefringent zones contain very little Y or U and only about 5Vo inferred H2O. The zonal variations in composition are considered to have brought about differences in the extent of metamictization, the hieh U-zones suffering severe but localized darnage from nuclear recoil associated with the c-particle emission. Superimposed on this recoil damage is a more pervasive but less severe metamictizarion affecting thewhole crystal and due directly to o- and p-particle emission. Analytical data tend to favor the incorporation of waler during crystallization rather than during the metamictization process. Degradation of the more metamict zones may have been further enhanced by a weakening of the zircon structure associated with sub-stantial substitution of non-formula elements, particularly the REE. These zones suffer further severe damage under the elecron beam.