Crystal Chemistry of Zircon and Monazite: Crystal Structure, Major and Trace Elements, and Radiation Damage

• Main Author: Zaman, Md. Mashrur
• Other Authors: Antao, Sytle
• Format: Doctoral or Postdoctoral Thesis
• Language: English
• Published: Graduate Studies 2015
• Subjects: Geology; Mineralogy; XRD; Crystal; Arctic
• Online Access: http://hdl.handle.net/11023/2328; https://doi.org/10.11575/PRISM/25497

This study investigates the crystal structural variations and their relation to chemical composition and radiation effects of detrital zircon and monazite, and the elevated radionuclide concentrations in zircon and monazite-rich heavy mineral deposits in Cox’s Bazar, Bangladesh. Several experimental techniques such as electron-probe micro-analysis (EPMA), single-crystal X-ray diffraction (SCXRD), synchrotron high-resolution powder X-ray diffraction (HRPXRD), gamma-ray spectroscopy with hyper-purity germanium detector (GRS-HPGe), and gravity, magnetic, and electrical mineral separators have been used to carry out this research. In addition, several software programs including SHELX, WinGX, GSAS-EXGUI, Crystal Maker, and Gamma-W have also been applied for data processing and analysis. The unit-cell parameters for the eight zircon samples vary linearly with increasing unit-cell volume, V. The detrital zircon sample 7:PIF (Perry Island Formation) from the Canadian Arctic Islands has the lowest unit-cell parameters and bond distances, ideal stoichiometric composition, and is unaffected by α-radiation damage. Thus, sample 7:PIF is chemically and structurally pure zircon. Sample 8 from Jemaa, Nigeria shows the significant change throughout the synchrotron HRPXRD trace and reveals the largest structural parameters after the Rietveld refinement. Samples 1 to 7 show very good correlations between the V and Zr and Si apfu contents. They received α-radiation doses which are lower than ~3.5 × 1015 α-decay events/mg. Substitutions of other cations at the Zr and Si sites control the variations of structural parameters for samples 1 to 7. The sample 5 shows relatively long unit-cell parameters and bond distances because the Zr site accommodates other cations that have higher ionic radii. Geological age increases the radiation doses in zircon and it is also related to the V. The a and b unit-cell parameters for monazite samples 1, 2, 3, and 4 vary systematically with V, although each monazite sample contains several cations that ...