Alluvial Sapphires from Montana: Inclusions, Geochemistry, and Indications of a Metasomatic Origin

Buter, Eric; Mertz‐Kraus, Regina; Kane, Robert E.; Mainz, Johannes Gutenberg-Universität

doi:10.5741/gems.51.4.370

Cited by 17 publications

(15 citation statements)

References 5 publications

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“…Trace element concentrations and ratios determined at high spatial resolution using Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA‐ICPMS) are of great interest for a variety of geological and environmental studies . Applications of LA‐ICPMS include paleoclimate research using inorganic and biogenic carbonates, ore deposit research, mantle petrology, gemological studies, forensic studies, archeology, and studies of soils and sediments …”

Section: Comparison Of Different Software For Data Reduction Of Tracementioning

confidence: 99%

TERMITE: An R script for fast reduction of laser ablation inductively coupled plasma mass spectrometry data and its application to trace element measurements

Mischel

Mertz‐Kraus

Jochum

2017

Rapid Comm Mass Spectrometry

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RATIONALE: High spatial resolution Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICPMS) determination of trace element concentrations is of great interest for geological and environmental studies. Data reduction is a very important aspect of LA-ICP-MS, and several commercial programs for handling LA-ICPMS trace element data are available. Each of these software packages has its specific advantages and disadvantages. METHODS: Here we present TERMITE, an R script for the reduction of LA-ICPMS data, which can reduce both spot and line scan measurements. Several parameters can be adjusted by the user, who does not necessarily need prior knowledge in R. Currently, ten reference materials with different matrices for calibration of LA-ICPMS data are implemented, and additional reference materials can be added by the user. TERMITE also provides an optional outlier test, and the results are provided graphically (as a pdf file) as well as numerically (as a csv file). RESULTS: As an example, we apply TERMITE to a speleothem sample and compare the results with those obtained using the commercial software GLITTER. The two programs give similar results. TERMITE is particularly useful for samples that are homogeneous with respect to their major element composition (in particular for the element used as an internal standard) and when many measurements are performed using the same analytical parameters. In this case, data evaluation using TERMITE is much faster than with all other available software, and the concentrations of more than 100 single spot measurements can be calculated in less than a minute. CONCLUSIONS: TERMITE is an open-source software for the reduction of LA-ICPMS data, which is particularly useful for the fast, reproducible evaluation of large datasets of samples that are homogeneous with respect to their major element composition.

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Section: Comparison Of Different Software For Data Reduction Of Tracementioning

confidence: 99%

TERMITE: An R script for fast reduction of laser ablation inductively coupled plasma mass spectrometry data and its application to trace element measurements

Mischel

Mertz‐Kraus

Jochum

2017

Rapid Comm Mass Spectrometry

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“…Thus, garnet inclusions are not strongly zoned. Comparing them with those found in sapphires from Montana (USA), the latter contain more almandine (> 40%) and less grossular (approximately 10%) 8–10 …”

Section: Resultsmentioning

confidence: 80%

“…In rubies from Soamiakatra, Madagascar, garnet inclusions (chemically identified as pyrope‐almandine) were also observed 7 . In sapphires from Montana (USA), observed garnet inclusions are composed of 47% pyrope, 42% almandine and 10% grossular (measured with microprobe) 8–10 . In two sapphires from Tanzania, garnet inclusions were observed in previous studies, 11,12 and one was identified as grossular with Raman spectroscopy and energy dispersive x‐ray fluorescence (EDXRF) 12 …”

Section: Introductionmentioning

confidence: 83%

Disambiguation of pyrope‐rich garnet inclusions in coloured sapphires from Tanzania and identification of other inclusions by Raman spectroscopy

Karampelas¹,

Hennebois²,

Bersani

et al. 2023

J Raman Spectroscopy

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Study of inclusions in gems from secondary deposits can give valuable clues on the geologic (and sometimes geographic) origin of these displaced materials. For the present study, seven gem quality fancy‐coloured sapphires from Songea, Tanzania, were selected with, rarely observed in these gems, garnet inclusions in order to better understand their formation. Therefore, Raman spectroscopy was used to study garnet, as well as rutile, aluminosilicate and mica inclusions. Garnet composition calculations were made using the MIRAGEM Raman spectra software, which was further improved for the purpose of this study. A couple of garnet inclusions were also analysed by energy dispersive X‐ray spectroscopy (EDS) attached to a scanning electron microscope (SEM). All garnet inclusions presented similar Raman spectra, thus similar chemical composition. Chemical analysis demonstrates that these are pyrope‐rich (>40%) garnets with over 30% of almandine and over 20% grossular without any detectable titanium, chromium and sodium. Calculations made using the updated/improved MIRAGEM software were able to indicate the same composition as compatible with the obtained chemical analyses. Muscovite and sillimanite were also identified using micro‐Raman spectroscopy. This inclusion scene is not similar to those described in fancy‐coloured gem sapphires from other localities. The exact geological formation of these gems is yet not understood but might be eclogite or upper mantle related.

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“…In the Fe versus Ga/Mg diagram (Figure 12a; after Peucat et al [16], Zwaan et al [89]), the majority of the analyzed corundums are scattered in the field of metamorphic sapphires, and specifically in the plumasitic sub-field. Some sapphires from Naxos island, with blue and pink color plot in the field of alluvial sapphires from Yogo Culch Montana, while blue sapphires from Gorgona/Xanthi are characterized by very low Ga/Mg ratios and thus plot slightly outside the metamorphic field.…”

Section: Comparison With Corundum Deposits Around the Worldmentioning

confidence: 97%

“…Greek corundum LA-ICP-MS analyses plotted on a (a) Fe versus Ga/Mg discrimination diagram (after Peucat et al[16], Zwaan et al[89]); (b) Cr2O3 versus Fe2O3 diagram demonstrating the fields of different African deposits (modified after Schwarz et al[90]); (c) Cr2O3/Ga2O3 versus Fe2O3/TiO2 plot demonstrating composition of diverse corundum deposits (modified after…”

mentioning

confidence: 99%

Gem Corundum Deposits of Greece: Geology, Mineralogy and Genesis

et al. 2019

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Greece contains several gem corundum deposits set within diverse geological settings, mostly within the Rhodope (Xanthi and Drama areas) and Attico-Cycladic (Naxos and Ikaria islands) tectono-metamorphic units. In the Xanthi area, the sapphire (pink, blue to purple) deposits are stratiform, occurring within marble layers alternating with amphibolites. Deep red rubies in the Paranesti-Drama area are restricted to boudinaged lenses of Al-rich metapyroxenites alternating with amphibolites and gneisses. Both occurrences are oriented parallel to the ultra-high pressure/high pressure (UHP/HP) Nestos suture zone. On central Naxos Island, colored sapphires are associated with desilicated granite pegmatites intruding ultramafic lithologies (plumasites), occurring either within the pegmatites themselves or associated metasomatic reaction zones. In contrast, on southern Naxos and Ikaria Islands, blue sapphires occur in extensional fissures within Mesozoic metabauxites hosted in marbles. Mineral inclusions in corundums are in equilibrium and/or postdate corundum crystallization and comprise: spinel and pargasite (Paranesti), spinel, zircon (Xanthi), margarite, zircon, apatite, diaspore, phlogopite and chlorite (Naxos) and chloritoid, ilmenite, hematite, ulvospinel, rutile and zircon (Ikaria). The main chromophore elements within the Greek corundums show a wide range in concentration: the Fe contents vary from (average values) 1099 ppm in the blue sapphires of Xanthi, 424 ppm in the pink sapphires of Xanthi, 2654 ppm for Paranesti rubies, 4326 ppm for the Ikaria sapphires, 3706 for southern Naxos blue sapphires, 4777 for purple and 3301 for pink sapphire from Naxos plumasite, and finally 4677 to 1532 for blue to colorless sapphires from Naxos plumasites, respectively. The Ti concentrations (average values) are very low in rubies from Paranesti (41 ppm), with values of 2871 ppm and 509 in the blue and pink sapphires of Xanthi, respectively, of 1263 ppm for the Ikaria blue sapphires, and 520 ppm, 181 ppm in Naxos purple, pink sapphires, respectively. The blue to colorless sapphires from Naxos plumasites contain 1944 to 264 ppm Ti, respectively. The very high Ti contents of the Xanthi blue sapphires may reflect submicroscopic rutile inclusions. The Cr (average values) ranges from 4 to 691 ppm in the blue, purple and pink colored corundums from Naxos plumasite, is quite fixed (222 ppm) for Ikaria sapphires, ranges from 90 to 297 ppm in the blue and pink sapphires from Xanthi, reaches 9142 ppm in the corundums of Paranesti, with highest values of 15,347 ppm in deep red colored varieties. Each occurrence has both unique mineral assemblage and trace element chemistry (with variable Fe/Mg, Ga/Mg, Ga/Cr and Fe/Ti ratios). Additionally, oxygen isotope compositions confirm their geological typology, i.e., with, respectively δ18O of 4.9 ± 0.2‰ for sapphire in plumasite, 20.5‰ for sapphire in marble and 1‰ for ruby in mafics. The fluid inclusions study evidenced water free CO2 dominant fluids with traces of CH4 or N2, and low CO2 densities (0.46 and 0.67 g/cm3), which were probably trapped after the metamorphic peak. The Paranesti, Xanthi and central Naxos corundum deposits can be classified as metamorphic sensu stricto (s.s.) and metasomatic, respectively, those from southern Naxos and Ikaria display atypical magmatic signature indicating a hydrothermal origin. Greek corundums are characterized by wide color variation, homogeneity of the color hues, and transparency, and can be considered as potential gemstones.

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Alluvial Sapphires from Montana: Inclusions, Geochemistry, and Indications of a Metasomatic Origin

Cited by 17 publications

References 5 publications

TERMITE: An R script for fast reduction of laser ablation inductively coupled plasma mass spectrometry data and its application to trace element measurements

TERMITE: An R script for fast reduction of laser ablation inductively coupled plasma mass spectrometry data and its application to trace element measurements

Disambiguation of pyrope‐rich garnet inclusions in coloured sapphires from Tanzania and identification of other inclusions by Raman spectroscopy

Gem Corundum Deposits of Greece: Geology, Mineralogy and Genesis

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