A common origin for Thai/Cambodian rubies and blue and violet sapphires from Yogo Gulch, Montana, U.S.A.?

Palke, Aaron C.; Wong, Jacqueline; Verdel, Charles; Ávila, Janaína N.

doi:10.2138/am-2018-6164

Cited by 29 publications

(32 citation statements)

References 46 publications

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“…In a Fe versus Ga/Mg diagram [14], all measured corundum samples were plotted to "metamorphic" and "plumasitic" population fields ( Figure 6), clearly away from the "magmatic" blue sapphires that are found within syenite pegmatites of Ilmen Mountains (see again [6,17]). However, these trace-element diagrams should be used with the caution and possibly revised, since it was found that some of the sapphires from magmatic deposits could be plotted in the "metamorphic field" [46,47]. It is probably important to refine these plots using solely data of gem-quality samples and to group them by color (e.g., plot sapphire and rubies separately), taking into account that most of trace elements used for these are corundum chromophores (e.g., Fe, Ti, Mg, Cr, V).…”

Section: Comparison Of Chemical Data With Sapphires From Other Geologmentioning

confidence: 99%

Origin of Blue Sapphire in Newly Discovered Spinel–Chlorite–Muscovite Rocks within Meta-Ultramafites of Ilmen Mountains, South Urals of Russia: Evidence from Mineralogy, Geochemistry, Rb-Sr and Sm-Nd Isotopic Data

Sorokina

Rassomakhin²,

Nikandrov³

et al. 2019

Minerals

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Blue sapphire of gem quality was recently discovered in spinel–chlorite–muscovite rock within meta-ultramafites near the Ilmenogorsky alkaline complex in the Ilmen Mountains of the South Urals. More than 20 minerals were found in the assemblage with the blue sapphire. These sapphire-bearing rocks are enriched in LREE and depleted in HREE (with the negative Eu anomalies) with REE distribution similar to those in miascites (nepheline syenite) of the Ilmenogorsky alkaline complex. 87Sr/86Sr ratios in the sapphire-bearing rocks varied from 0.7088 ± 0.000004 (2σ) to 0.7106 ± 0.000006 (2σ): epsilon notation εNd is −7.8. The Rb-Sr isochrone age of 289 ± 9 Ma was yielded for the sapphire-bearing rocks and associated muscovite. The blue sapphires are translucent to transparent and they have substantial colorless zones. They occur in a matrix of clinochlore-muscovite as concentric aggregates within spinel-gahnite coronas. Laser Ablation-Inductively Coupled Plasma-Mass Spectrometry (LA-ICP-MS) analyses showed values with trace elements typical for “metamorphic” blue sapphires, with Ga/Mg < 2.7, Fe/Mg < 74, Cr/Ga > 1.5 (when Cr is detectable), and Fe/Ti < 9. Sapphires overlap “metasomatic” at “sapphires in alkali basalts” field on the FeO–Cr2O3–MgO–V2O3 versus FeO + TiO2 + Ga2O3 discriminant diagram. The sapphires formed together with the spinel-chlorite-muscovite rock during metasomatism at a contact of orthopyroxenites. Metasomatic fluids were enriched with Al, HSFE, and LILE and genetically linked to the miascite intrusions of Ilmenogorsky complex. The temperature required for the formation of sapphire–spinel–chlorite–muscovite rock was 700–750 °C and a pressure of 1.8–3.5 kbar.

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Section: Comparison Of Chemical Data With Sapphires From Other Geologmentioning

confidence: 99%

Origin of Blue Sapphire in Newly Discovered Spinel–Chlorite–Muscovite Rocks within Meta-Ultramafites of Ilmen Mountains, South Urals of Russia: Evidence from Mineralogy, Geochemistry, Rb-Sr and Sm-Nd Isotopic Data

Sorokina

Rassomakhin²,

Nikandrov³

et al. 2019

Minerals

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“…Studies of the BGY sapphires and ruby in alkali basalts (figure 4) focused on solid inclusions Baldwin et al, 2017;Palke et al, 2018), trace element geochemistry (Peucat et al, 2007), oxygen isotopes (Yui et al, 2003;Giuliani et al, 2005) (Rakotozamizanany et al, 2014) to show that the gem corundum may have different magmatic and metamorphic origins. Within a single gem province in Australia, variations in color observed for corundum found ~10 km apart suggest the existence of multiple sources for the gemstones (Sutherland et al, 1998a;Sutherland and Schwarz, 2001).…”

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confidence: 99%

Geology of Corundum and Emerald Gem Deposits: A Review

Giuliani¹,

Groat²

2019

G&G

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The great challenge of geographic origin determination is to connect the properties and features of individual gems to the geology of their deposits. Similar geologic environments can produce gems with similar gemological properties, making it difficult to find unique identifiers. Over the last two decades, our knowledge of corundum and emerald deposit formation has improved significantly.The mineral deposits are classically separated into primary and secondary deposits. Primary corundum deposits are subdivided into two types based on their geological environment of formation: (1) magmatic and (2) metamorphic. Magmatic deposits include gem corundum in alkali basalts as in eastern Australia, and sapphire in lamprophyre and syenite as in Montana (United States) and Garba Tula (Kenya), respectively. Metamorphic deposits are divided into two subtypes (1) metamorphic deposits sensu stricto (in marble; mafic and ultramafic rocks, or M-UMR), and (2) metamorphicmetasomatic deposits characterized by high fluid-rock interaction and metasomatism (i.e., plumasite or desilicated pegmatites in M-UMR and marble, skarn deposits, and shear zone-related deposits in different substrata, mainly corundum-bearing Mg-Cr-biotite schist). Examples of the first subtype include the ruby deposits in marble from the Mogok Stone Tract or those in M-UMR from Montepuez (Mozambique) and Aappaluttoq (Greenland). The second subtype concerns the sapphire from Kashmir hosted by plumasites in M-UMR.Secondary corundum deposits (i.e., present-day placers) result from the erosion of primary corundum deposits. Here, corundum is found in the following types of deposits: eluvial (derived by in situ weathering or weathering plus gravitational movement), diluvial (scree or talus), colluvial (deposited at the base of slopes by rainwash, sheetwash, slow continuous downslope creep, or a combination of these processes), and alluvial (deposited by rivers). Today, most sapphires are produced from gem placers related to alkali basalts, as in eastern Australia or southern Vietnam, while placers in metamorphic environments, such as in Sri Lanka (Ratnapura, Elahera) and Madagascar (Ilakaka), produce the highest-quality sapphires. The colluvial Montepuez deposit in Mozam bique provides a huge and stable supply of clean and very highquality rubies. Primary emerald deposits are subdivided into two types based on their geological environment of formation: (1) tectonic-magmatic-related (Type I) and (2)tectonic-metamorphic-related (Type II). Several subtypes are defined and especially Type IA, hosted in M-UMR, which accounts for about 70% of worldwide production (Brazil, Zambia, Russia, and others). It is characterized by the intrusion of pegmatites or quartz veins in M-UMR accompanied by huge hydrothermal fluid circulation and metasomatism with the formation of emerald-bearing desilicated pegmatite (plumasite) and biotite schist. Type IB in sedimentary rocks (China, Canada, Norway, Kazakhstan, and Australia) and Type IC in granitic rocks (Nigeria) are of minor importance.T...

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“…The sapphires from kyshtymites are also plotted to the "metamorphic" field on Fe/Mg vs. Ga/Mg diagram by Peucat et al (2007) and [35,36] (Figure 8). Blue sapphires within kyshtymites overlap the "metasomatic" fields on FeO -Cr2O3 -MgO -V2O3 vs. FeO + TiO2 + Ga2O3 discriminant diagram ( Figure 9) by [35] as in case of those sapphires within Ilmen syenite pegmatites, Ilmen sapphires within meta-ultramafic rocks, sapphires from Blue sapphires within kyshtymites overlap the "metasomatic" fields on FeO - (Figure 9) by [35] as in case of those sapphires within Ilmen syenite pegmatites, Ilmen sapphires within meta-ultramafic rocks, sapphires from Gortva syenite xenoliths within alkali basalts [38], and sapphires from lamphrophiric dyke in Yogo Gulch [39]. Gortva syenite xenoliths within alkali basalts [38], and sapphires from lamphrophiric dyke in Yogo Gulch [39].…”

Section: Mineralogy Geochemistry Solid Inclusions and Uv-vis-nir-smentioning

confidence: 99%

“…Blue sapphires within kyshtymites overlap the "metasomatic" fields on FeO -Cr2O3 -MgO -V2O3 vs. FeO + TiO2 + Ga2O3 discriminant diagram ( Figure 9) by [35] as in case of those sapphires within Ilmen syenite pegmatites, Ilmen sapphires within meta-ultramafic rocks, sapphires from Blue sapphires within kyshtymites overlap the "metasomatic" fields on FeO - (Figure 9) by [35] as in case of those sapphires within Ilmen syenite pegmatites, Ilmen sapphires within meta-ultramafic rocks, sapphires from Gortva syenite xenoliths within alkali basalts [38], and sapphires from lamphrophiric dyke in Yogo Gulch [39]. Gortva syenite xenoliths within alkali basalts [38], and sapphires from lamphrophiric dyke in Yogo Gulch [39]. [40] with extended "magmatic/syenitic" field with plotted corundum-sapphire within kyshtymites (red circles), Ilmen sapphires within syenite pegmatites (yellow triangles) [2], and within the meta-ultramafic host rocks (blue circles) [3].…”

Section: Mineralogy Geochemistry Solid Inclusions and Uv-vis-nir-smentioning

confidence: 99%

“…The data on sapphires associated with xenoliths in alkali basalts (Gortva in Slovakia-green star; Loch Roag in Scotland-yellow star) were modified after Uher et al (2012) [38]. The data on sapphires associated with ultramafic lamprophyre dike in Yogo Gulch (USA) (black triangles) are after [39]. Blue dotted line shows the extension of "magmatic/syenitic" sapphire field.…”

Section: Mineralogy Geochemistry Solid Inclusions and Uv-vis-nir-smentioning

confidence: 99%

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Corundum Anorthosites-Kyshtymites from the South Urals, Russia: A Combined Mineralogical, Geochemical, and U-Pb Zircon Geochronological Study

et al. 2019

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Kyshtymites are the unique corundum-blue sapphire-bearing variety of anorthosites of debatable geological origin found in the Ilmenogorsky-Vishnevogorsky complex (IVC) in the South Urals, Russia. Their mineral association includes corundum-sapphire, plagioclase (An61–93), muscovite, clinochlore, and clinozoisite. Zircon, churchite-(Y), monazite-(Ce), and apatite group minerals are found as accessory phases. Besides, churchite-(Y) and zircon are also identified as syngenetic solid inclusions within the sapphires. In situ Laser Ablation Inductively Coupled Plasma Mass Spectrometry (LA-ICP-MS) U-Pb zircon geochronology showed the ages at about 290–330 Ma linked to the Hercynian orogeny in IVC. These ages are close to those of the syenitic and carbonatitic magmas of the IVC, pointing to their syngenetic origin, which is in agreement with the trace element geochemistry of the zircons demonstrating clear magmatic signature. However, the trace element composition of sapphires shows mostly metamorphic signature with metasomatic overprints in contrast to the geochemistry of zircons. The reason for this discrepancy can be the fact that the discrimination diagrams for sapphires are not as universal as assumed. Hence, they cannot provide an unambiguous determination of sapphire origin. If it is true and zircons can be used as traces of anorthosite genesis, then it can be suggested that kyshtymites are formed in a magmatic process at 440–420 Ma ago, most probably as plagioclase cumulates in a magma chamber. This cumulate rock was affected by a second magmatic event at 290–330 Ma as recorded in zircon and sapphire zoning. On the other hand, Ti-in-zircon thermometer indicates that processes operated at relatively lower temperature (<900 °C), which is not enough to re-melt the anorthosites. Hence, zircons in kyshtymites can be magmatic but inherited from another rock, which was re-worked during metamorphism. The most probable candidate for the anorthosite protolith is carbonatites assuming that metamorphic fluids could likely leave Al- and Si-rich residue, but removed Ca and CO2. Further, Si is consumed by the silicification of ultramafic host rocks. However, kyshtymites do not show clear evidence of pronounced metasomatic zonation and evidence for large volume changes due to metamorphic alteration of carbonatites. Thus, the obtained data still do not allow for univocal reconstruction of the kyshtymite origin and further investigations are required.

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A common origin for Thai/Cambodian rubies and blue and violet sapphires from Yogo Gulch, Montana, U.S.A.?

Cited by 29 publications

References 46 publications

Origin of Blue Sapphire in Newly Discovered Spinel–Chlorite–Muscovite Rocks within Meta-Ultramafites of Ilmen Mountains, South Urals of Russia: Evidence from Mineralogy, Geochemistry, Rb-Sr and Sm-Nd Isotopic Data

Origin of Blue Sapphire in Newly Discovered Spinel–Chlorite–Muscovite Rocks within Meta-Ultramafites of Ilmen Mountains, South Urals of Russia: Evidence from Mineralogy, Geochemistry, Rb-Sr and Sm-Nd Isotopic Data

Geology of Corundum and Emerald Gem Deposits: A Review

Corundum Anorthosites-Kyshtymites from the South Urals, Russia: A Combined Mineralogical, Geochemical, and U-Pb Zircon Geochronological Study

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