Hongtao Shen

Zircon megacrysts from Wenchang, Hainan Island, South China, were investigated to characterize their mineralogical and geochemical properties, U-Pb age, radiation-damage state, and heat-induced spectral and color responses. We integrated electron probe microanalysis (EPMA), laser ablation–inductively coupled plasma mass spectrometry (LA-ICP-MS) U-Pb and trace-element analyses, Fourier transform infrared (FTIR), Raman and ultraviolet–visible (UV-Vis) spectroscopy, powder X-ray diffraction (XRD), and controlled heating. This approach extends previous occurrence-based descriptions of the Wenchang deposits through an integrated mineralogical, chronological, structural, and thermal-response assessment. The zircons show HREE-enriched patterns, positive Ce anomalies, Eu/Eu* values close to unity, and Th/U ratios of 0.42–1.26, supporting a magmatic affinity without identifying a specific parental melt. A weighted mean ²⁰⁶Pb/²³⁸U age of 3.78 ± 0.10 Ma (1σ) was obtained. FTIR spectra retain relatively sharp SiO₄ bending features, and five representative spectra show no resolvable broad OH-related feature at the displayed scale. Raman spectra show a narrow ν₃(SiO₄) band near 1008 cm⁻¹ with an average corrected full width at half maximum of 5.5 cm⁻¹. XRD patterns of two unheated grains contain sharp zircon reflections without a conspicuous diffuse-scattering halo. Together, these observations support retained crystalline order and weak radiation damage in the analyzed samples. Within the measured low-dose dataset, ν₃(SiO₄) full width at half maximum (FWHM) increases with accumulated alpha dose (Dα), whereas Raman band position shows no statistically significant dose-related trend. Heating weakens the broad 450–550 nm absorption as the brown samples become lighter, while treatment at 1100 °C under nitrogen produces a bluish-gray hue accompanied by broad red-region absorption. The data constrain the age, radiation-damage state, and heat-induced responses of the analyzed Wenchang zircons; their primary host, source region, and transport history remain unresolved.

Fangshankou turquoise, hosted by the Lower Cambrian phosphorus–vanadium–uranium black-shale ore system of Dunhuang, NW China, has been reported to contain anomalously high Na, Fe and Si, but the mineralogical origin of these anomalies is unknown. Micro-Raman screening combined with SEM-EDS, powder and single-crystal XRD, EPMA and LA-ICP-MS on 27 specimens shows that turquoise is intergrown at the 10–50 μm scale with cyrilovite (17.7–22.4 wt% FeO, 2.6–4.7 wt% Na₂O), a poorly crystalline unnamed NaAl phosphate phase (4.9–11.1 wt% Na₂O; diagnostic Raman band at 992 cm⁻¹), fluorapatite, collinsite, alunite, jarosite, goethite, phengite and chabazite-Na. Raman-screened turquoise contains only 2.2–6.5 wt% FeO and ≤0.8 wt% Na₂O; the higher values obtained on unscreened material arise from analytical volumes that intersect these Na- and Fe-rich phosphates, not from unusual substitution in turquoise, whose structure offers no site for Na. Screened turquoise inherits the Li–Cr–V–U signature of its black-shale host (615–1357 ppm Cr, up to 65 ppm U), whereas the origin of its moderate Si remains unresolved. Chabazite-Na in post-turquoise fractures records a late Si–Na–K-rich fluid stage. The Na-rich phosphate assemblage, not reported from other Chinese turquoise deposits, is itself a potential provenance indicator, and the results show that provenance criteria for microcrystalline turquoise must rest on phase-resolved rather than bulk analyses.

The Sar-e-Sang lapis lazuli deposit has a mining history exceeding 5000 years, producing the world’s finest lapis lazuli. Recently, gem-quality forsterite has been discovered in the marble containing spinel, dolomite, and phlogopite at the periphery of the lapis lazuli ore body at the Pitawak mine, located east of the Sar-e-Sang deposit. The mineral assemblage indicates that the protolith of this marble is dolomite with aluminous and siliceous components. These forsterite crystals occur as colorless, transparent anhedral grains, exhibiting distinct red fluorescence under 365 nm ultraviolet light. To investigate the gemological and spectroscopic characteristics of the Pitawak mine forsterite, this study conducted and analyzed data from basic gemological analysis, electron probe microanalysis (EPMA), Laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS), ultraviolet–visible absorption spectroscopy (UV-VIS), Fourier-transform infrared spectroscopy (FTIR), laser Raman spectroscopy (RAMAN), and photoluminescence spectroscopy (PL) on four forsterite samples from the Pitawak mine. The analysis results reveal that the samples indicate a composition close to ideal forsterite with a crystal chemical formula of (Mg_2.00Fe_0.02)_Σ2.02Si_0.99O₄. The trace elements present include Fe, Mn, Ca, and minor amounts of Cr and Ni. The UV-VIS spectroscopy results show that the samples possess high transmittance across the visible light range with very weak absorption bands, contributing to the colorless and transparent appearance of Pitawak mine forsterite. This phenomenon is attributed to the extremely low content of chromophoric elements, which have a negligible effect on the forsterite’s color. PL spectroscopy indicates that the red fluorescence of the samples is caused by an emission peak near 642 nm. This emission peak arises from the spin-forbidden ⁴T₁ → ⁶A₁ transition of Mn²⁺ ions situated in octahedral sites within the forsterite structure.