Mineralogy, Geochemistry and Genesis of the Luc Yen Noble Spinel Deposit, Vietnam

Kuksa, K. A.; Sokolov, P. B.; Marakhovskaya, Olga Yu.; Gussiås, Geir Atle; Brownscombe, William

doi:10.35597/2313-545x-2019-5-3-56-69

Cited by 4 publications

(8 citation statements)

References 12 publications

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“…Sample VN is the first described example of natural purple spinel in which both Cr 3+ and Co 2+ are the prominent contributors to the coloration and are roughly equally weighted (e.g., similar absorption peak heights above background for each chromophore, resulting in a distinctly purple hue), as opposed to Cr 3+ -(Fe 2+ ,Fe 3+ )-dominant or Fe (Fe 2+ ,Fe 3+ ) alone (e.g., Schmetzer et al, 1989;Malsy and Klemm, 2010). Kuksa et al (2019) presented compositional data and a photograph of a Vietnamese spinel described as "bluish" (within the reference sample known as sample 5), which ap- with minor M Fe 3+ ), which is shown by the greater peak-trough difference in absorption spectrum (figure 10). This is evidently due to the greater visible light absorption by Cr 3+ and particularly Co 2+ per unit of concentration compared to the predominant iron chromophore, Fe 2+ (e.g., ~20× molar absorptiv-Figure 10.…”

Section: Discussionmentioning

confidence: 99%

“…One Cr-rich outlier (1111 ppma Cr and 1236 ppma Co; Chauviré et al, 2015) reported from Vietnam is vivid blue in color with no visible reddish or purplish hues, indicating that cobalt has a much higher molar absorptivity than chromium, similar to cobalt's higher molar absorptivity relative to iron (Chauviré et al, 2015). The other outlier, sample 5 of Kuksa et al (2019), has a vivid slightly purplish blue color. Purple spinel sample VN appears to be approximately compositionally intermediate between Cr-dominant pink/red spinels and Co-dominant blue spinels, whereas sample 5 is intermediate between sample VN and Co-dominant blue spinels, as shown in a plot comparing the relative concentrations of Co to Cr, and Co to Fe (figure 12).…”

Section: Chromophore Trace Elements In Spinelsmentioning

confidence: 98%

“…Therefore, the combination of elevated cobalt (17.9 ppma) and chromium (593 ppma) concentrations as the dominant chromophores result in an attractive purple color that is more saturated, with stronger red and blue hues, than spinel colored primarily by T Fe 2+ . Sample 3 from Kuksa et al (2019), a brownish purplish red spinel from Vietnam, also serves as an interesting comparison to purple sample VN. Sample 3 contained a similar concentration of Cr, slightly over half the Co concentration, and four times the Fe concentration.…”

Section: Uv-vis-nir Absorption Spectramentioning

confidence: 99%

“…Unlike sample VN, which is purple primarily due to Cr and Co, Kuksa et al's sample 3 was brownish purplish red, likely representative of a color defined primarily by Cr and Fe. Kuksa et al (2019), did not measure light absorption, so the causes of color have not been quantified.…”

Section: Uv-vis-nir Absorption Spectramentioning

confidence: 99%

“…Cobalt-enriched spinel, generally vivid blue in color, typically contains low Cr concentrations (<60 ppma; Hanser, 2013;Chauviré et al, 2015;Kuksa et al, 2019), with two outliers known from Vietnam. One Cr-rich outlier (1111 ppma Cr and 1236 ppma Co; Chauviré et al, 2015) reported from Vietnam is vivid blue in color with no visible reddish or purplish hues, indicating that cobalt has a much higher molar absorptivity than chromium, similar to cobalt's higher molar absorptivity relative to iron (Chauviré et al, 2015).…”

Section: Chromophore Trace Elements In Spinelsmentioning

confidence: 99%

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Purple Gem Spinel from Vietnam and Afghanistan: Comparison of Trace Element Chemistry, Cause of Color, and Inclusions

Belley¹,

Palke²

2021

G&G

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This study compares two purple gem spinel samples with regard to trace element chemistry and visible light absorption spectra, and presents the first reported example of a spinel with a saturated purple color caused predominantly by chromium and cobalt. Sample VN, from a placer deposit in the Luc Yen district of Vietnam, exhibited strong saturation, orange-red fluorescence in UV, and magnesite and graphite inclusions. Sample AF was from Badakhshan, Afghanistan, with light to medium saturation and containing phlogopite, amphibole, and probable fluid inclusions. UV-Vis-NIR spectra are compared along with trace element chemistry. Sample VN is colored primarily by cobalt (17.9 ppma) and chromium (593 ppma), with minor color contribution from Fe (2437 ppma), and contains significantly more cobalt than typical Cr-enriched red, pink, and purple gem spinels (<6 ppma Co). The dominant contributions of chromophores Cr 3+ and Co 2+ to the color of sample VN are responsible for its higher color saturation than that of sample AF, which is colored dominantly by Fe 2+ and Fe 3+ (3089 ppma total Fe) and contains negligible concentrations of other chromophores (<10 ppma V 3+ , Cr 3+ , and Co 2+ ). In the Vietnamese purple spinel, the relatively low Fe concentration is likely crucial in creating the attractive saturated color. This sample is enriched in Co, Ni, Cr, V, Zn, and Ga. In contrast, the purple spinel from Afghanistan is relatively impoverished in all trace elements except Fe and Mn. Sample VN represents an approximate intermediate between natural gem spinel populations colored dominantly by Cr 3+ vs. dominantly by Co 2+ . Cr 3+ -, (Fe 2+ ,Fe 3+ )-, and Co 2+ -dominant (in terms of color) gem spinels are easily differentiated by chemical composition using a discrimination plot of Co/Cr vs. Co/Fe, but this is not valid for spinel dominantly colored by V 3+ or containing significant concentrations of Fe.

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Section: Discussionmentioning

confidence: 99%

Section: Chromophore Trace Elements In Spinelsmentioning

confidence: 98%

Section: Uv-vis-nir Absorption Spectramentioning

confidence: 99%

Section: Uv-vis-nir Absorption Spectramentioning

confidence: 99%

Section: Chromophore Trace Elements In Spinelsmentioning

confidence: 99%

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Purple Gem Spinel from Vietnam and Afghanistan: Comparison of Trace Element Chemistry, Cause of Color, and Inclusions

Belley¹,

Palke²

2021

G&G

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Marble-hosted noble spinel deposits from the Luc Yen District (Vietnam): mineral equilibria involving corundum and spinel

Krivovichev,

Kuksa,

Sokolov

et al. 2024

Zapiski Vserossijskogo mineralogičeskogo obŝestva

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Thermodynamic analysis is carried out for the model systems: (1) Na–Ca–Mg–A1–Si–CO2–H2O and (2) Ca–Mg–A1–Si–CO2–H2O. In each systems the mineral equilibria involving dolomite, calcite, spinel, corundum, pargasite, hydroxylclinohumite, and diaspore are considered. A diagram of the multisystem in coordinates μH2O-μCO2is constructed. Analysis showed a significant influence of chemical potentials of water and carbon dioxide in the mineral-forming medium on stability of corundum and spinel in marbles. The conditions of the spinel formation during metamorphism of protolith consisting of carbonate sediments with evaporites lenses and terrigenous material (smectites, bauxites, etc.), are considered in detail. The conditions of the replacement of spinel by corundum during retrograde metamorphism are determined depending on the mole fraction of CO2 in the fluid and temperature at pressure of 5 kbar.

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Preiswerkite: A First Occurrence in Marble Hosting Gem Spinel Deposits, Luc Yen, Vietnam

Кривовичев

Kuksa

Sokolov³

et al. 2022

Minerals

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We report a new occurrence of preiswerkite, the rare sodium analog of eastonite, the trioctahedral mica, from marble-hosted noble spinel deposits of the Luc Yen district, northern Vietnam. It is found in marble for the first time. The preiswerkite is anhedral and associated with phlogopite, aspidolite, sadanagaite, pargasite, spinel, corundum, dolomite and calcite. The average compositions of preiswerkite is (Na0.88Ca0.08K0.01)Σ0.97(Mg2.29Al0.72Fe0.04)Σ3.05)[(Al1.95Si2.05)Σ4.00O10](OH)2. The compositions of preiswerkite have a narrow range of Mg# values (0.96–0.99) and define a preiswerkite-aspidolite solid-solution series. Compared with other occurrences, the Luc Yen preiswerkite has a low iron content, which attains 0.09 atoms per formula unit (1.53 wt.% FeO). The formation of preiswerkite is favored by the proportion of Mg, Al and Si in the precursor rocks and the increased activity of sodium and H2O in the fluid phase.

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Mineralogy, Geochemistry and Genesis of the Luc Yen Noble Spinel Deposit, Vietnam

Cited by 4 publications

References 12 publications

Purple Gem Spinel from Vietnam and Afghanistan: Comparison of Trace Element Chemistry, Cause of Color, and Inclusions

Purple Gem Spinel from Vietnam and Afghanistan: Comparison of Trace Element Chemistry, Cause of Color, and Inclusions

Marble-hosted noble spinel deposits from the Luc Yen District (Vietnam): mineral equilibria involving corundum and spinel

Preiswerkite: A First Occurrence in Marble Hosting Gem Spinel Deposits, Luc Yen, Vietnam

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