Auto-Radiation Damages in Zircons of the Yastrubtsi Ore Occurrence of the Ukrainian Shield According to the Data of NMR and XRD

Abstract

By the method of XRD and high-resolution nuclear magnetic resonance (MAS NMR), the features of the structure of partially metamict zircons from Yastrubtsi ore occurrence of the Ukrainian Shield were studied. Samples 1 and 2 (depths 627 and 1069 m) belong to middle metamict zircons, and sample 3 (depth 1302.5 m) — to weak metamict zircons. The purpose of this work was to elucidate the features of the structure of partially metamictic zircons from Yastrubtsi ore occurrence of the Ukrainian Shield and the features of their recrystallization. The XRD method showed the presence of diffuse diffraction bands, which indicates the presence of an amorphous phase. For sample 3, these bands are less pronounced. After heating at T = 1100°C, these bands significantly decrease. Based on the XRD data, the degree of crystallinity and unit cell parameters of the samples were calculated. To obtain information on the local structure of the samples, spectra were obtained for the initial and annealed samples. It was shown by MAS NMR that there are regions in the initial structure in which [SiO4] tetrahedra are interconnected. These regions are designated Qn (n is the number of bridging oxygen atoms per Si atom). It has been established that the silica phase is practically absent in the zircon samples. In such samples, mainly Q1-2 and Q3 polymerization of silicon atoms occurs (for sample 3, only Q1-2 polymerization is characteristic). The MAS NMR results are in good agreement with the XRD data.