Raman spectroscopy of Pb-rich tourmaline from Minh Tien, Vietnam
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| Year of publication | 2022 |
| Type | Conference abstract |
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| Description |
Natural lead-bearing tourmaline is very rare; it typically witnesses metasomatism and hydrothermal activity. In this study we characterized pink, colorless, blue and black zones in primary Pb-bearing tourmaline using electron probe micro-analysis (EPMA), LA-ICP-MS, and micro-Raman spectroscopy. Composition of tourmalines ranges from Fe-rich fluor elbaite (black tur) and Mn-enriched Na-rich fluor-liddicoatite (blue and colorless tur) to Na-bearing Pb-rich fluor-liddicoatite (pink tur). The highest Pb contents are in the pink (up to 7.94 wt.% PbO) and colorless zones (up to 5.43 wt.% PbO); lower Pb enrichment was observed in the blue (1.32–3.44 wt.% PbO) and the black zones (from 0.70–1.13 wt.% PbO). The region from 200 to 1150 cm-1 was interpreted after Hoang et al. (2011). The lead contents should affect vibrations in the region under 400 cm-1 that belongs to the X–O bond stretching. Lithium contents measured using LA-ICP-MS were non-destructively confirmed by micro-Raman spectroscopy in the tourmaline V-site O–H vibrational region (spectral range from ca. 3400 to 3650 cm-1). Bands observed in the spectral ranges 3479–3503 cm-1, 3507–3515 cm-1 and 3517–3519 cm-1 are characteristic for short-range configuration of Y and Z site occupancies around O3 anion of YLiZAlZAl-2YAlZAlZAl. For iron and lithium, characteristic interactions are the peaks between 3547 and 3552 cm-1 with configuration YLiZAlZAl-YFe*ZAlZAl-YAlZAlZAl (*=Fe2++Mn2+).The range between 3571–3578 cm-1 is likely combined result of 2YLiZAlZAlYAlZAlZAl and 3YFeZAlZAl (in Fe-rich tourmalines; black zone contains ?1.11 wt.% FeOtot). The band at 3591–3597 cm-1 is typical for arrangement 2YLiZAlZAl-YAlZAlZAl in Ca-rich tourmalines (Watenphul et al. 2016). In all samples we observed bands at 3606–3609 cm-1 (which corresponds to 3YLiZAlZAl). Conclusion: The Raman spectra in the studied tourmaline reflect well the main compositional changes at Y+Z sites but are less sensitive for X-site. Presence of Pb2+ at the X-site seems to have similar effect to Ca, no additional bands were observed. |