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C. Srikantappa - One of the best experts on this subject based on the ideXlab platform.
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Corundum–leucosome-bearing aluminous gneiss from Ayyarmalai, Southern Granulite Terrain, India: A textbook example of vapor phase-absent muscovite-melting in silica-undersaturated aluminous rocks
American Mineralogist, 2010Co-Authors: Michael M. Raith, Pulak Sengupta, Ellen Kooijman, Dewashish Upadhyay, C. SrikantappaAbstract:An aluminous gneissic rock associated with high-pressure mafic and felsic granulites in the Palghat-Cauvery Shear Zone of southern India provides a classic example of quartz-absent muscovite melting. The anatectic gneiss shows a conspicuous migmatitic structure defined by closely spaced centimeter to decimeter sized, Corundum-bearing leucosomes developed in a weakly foliated mesosome of plagioclase (An 21 Ab 77 Or 2 ) and biotite (4.9 wt% TiO 2 , X Mg = 0.51–0.47). The boundaries between leucosome and mesosome domains are sharp, and no melanosome selvages are developed at the interface. Corundum occurs as euhedral crystals up to 2 cm in diameter, typically centered in the leucosome matrix of coarse-grained perthitic alkali feldspar (integrated composition: An 2 Ab 35 Or 63 ), minor relict biotite (4.2–5.1 wt% TiO 2 , X Mg = 0.48–0.46) and plagioclase (An 21 Ab 78 Or 1 ). In some domains, the mesosomes also contain elongate clusters of similarly oriented smaller Corundum plates that are intergrown with perthitic alkali feldspar, presumably replacing former kyanite blades. The textural and mineralogical characteristics and petrogenetic grid considerations indicate breakdown of muscovite through two successive dehydration-melting reactions: (1) formation of Corundum+K-feldspar-clusters via the reaction muscovite+aluminosilicate → Corundum+liquid at the sites of kyanite/sillimanite, and (2) development of Corundum-bearing leucosomes through the reaction muscovite → Corundum+K-feldspar+liquid, focused around the sites of nucleation and growth of peritectic Corundum. P - T pseudosection modeling in the Na 2 O-CaO-K 2 O-FeO-MgO-Al 2 O 3 -SiO 2 -H 2 O-TiO 2 system locates the onset and completion of the muscovite-melting reaction 2 in the steep narrow quadrivariant field Ms+Bt+Pl+Kfs+Crn+Liq, which extends from ~6 kbar, 720 °C to higher pressures. Biotite remained stable and was not involved in the melting reactions. Two-feldspar thermometry gives peak-temperatures of 800 ± 50 °C. Combined with P - T estimates for metapelitic granulites in the area, these P - T constraints appear to be consistent with a clockwise P - T evolution of the eastern Palghat Cauvery shear zone with peak P - T conditions not exceeding ca. 800 °C and 10–12 kbar. The timing of partial melting and HT-metamorphism is constrained at ~529 Ma by U-Pb spot dating of oscillatory zoned individual grains and overgrowths on detrital zircon cores included in peritectic Corundum of leucosome domains. The zircon cores indicate a Paleoproterozoic (2.5–2.0 Ga) provenance of the sedimentary protolith.
Michael M. Raith - One of the best experts on this subject based on the ideXlab platform.
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Corundum–leucosome-bearing aluminous gneiss from Ayyarmalai, Southern Granulite Terrain, India: A textbook example of vapor phase-absent muscovite-melting in silica-undersaturated aluminous rocks
American Mineralogist, 2010Co-Authors: Michael M. Raith, Pulak Sengupta, Ellen Kooijman, Dewashish Upadhyay, C. SrikantappaAbstract:An aluminous gneissic rock associated with high-pressure mafic and felsic granulites in the Palghat-Cauvery Shear Zone of southern India provides a classic example of quartz-absent muscovite melting. The anatectic gneiss shows a conspicuous migmatitic structure defined by closely spaced centimeter to decimeter sized, Corundum-bearing leucosomes developed in a weakly foliated mesosome of plagioclase (An 21 Ab 77 Or 2 ) and biotite (4.9 wt% TiO 2 , X Mg = 0.51–0.47). The boundaries between leucosome and mesosome domains are sharp, and no melanosome selvages are developed at the interface. Corundum occurs as euhedral crystals up to 2 cm in diameter, typically centered in the leucosome matrix of coarse-grained perthitic alkali feldspar (integrated composition: An 2 Ab 35 Or 63 ), minor relict biotite (4.2–5.1 wt% TiO 2 , X Mg = 0.48–0.46) and plagioclase (An 21 Ab 78 Or 1 ). In some domains, the mesosomes also contain elongate clusters of similarly oriented smaller Corundum plates that are intergrown with perthitic alkali feldspar, presumably replacing former kyanite blades. The textural and mineralogical characteristics and petrogenetic grid considerations indicate breakdown of muscovite through two successive dehydration-melting reactions: (1) formation of Corundum+K-feldspar-clusters via the reaction muscovite+aluminosilicate → Corundum+liquid at the sites of kyanite/sillimanite, and (2) development of Corundum-bearing leucosomes through the reaction muscovite → Corundum+K-feldspar+liquid, focused around the sites of nucleation and growth of peritectic Corundum. P - T pseudosection modeling in the Na 2 O-CaO-K 2 O-FeO-MgO-Al 2 O 3 -SiO 2 -H 2 O-TiO 2 system locates the onset and completion of the muscovite-melting reaction 2 in the steep narrow quadrivariant field Ms+Bt+Pl+Kfs+Crn+Liq, which extends from ~6 kbar, 720 °C to higher pressures. Biotite remained stable and was not involved in the melting reactions. Two-feldspar thermometry gives peak-temperatures of 800 ± 50 °C. Combined with P - T estimates for metapelitic granulites in the area, these P - T constraints appear to be consistent with a clockwise P - T evolution of the eastern Palghat Cauvery shear zone with peak P - T conditions not exceeding ca. 800 °C and 10–12 kbar. The timing of partial melting and HT-metamorphism is constrained at ~529 Ma by U-Pb spot dating of oscillatory zoned individual grains and overgrowths on detrital zircon cores included in peritectic Corundum of leucosome domains. The zircon cores indicate a Paleoproterozoic (2.5–2.0 Ga) provenance of the sedimentary protolith.
Gaston Giuliani - One of the best experts on this subject based on the ideXlab platform.
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Gem Corundum Deposits of Greece: Geology, Mineralogy and Genesis
Minerals, 2019Co-Authors: Panagiotis Voudouris, Gaston Giuliani, Constantinos Mavrogonatos, Ian Graham, Vasilios Melfos, Stefanos Karampelas, Vilelmini Karantoni, Kandy Wang, Alexandre Tarantola, Khin ZawAbstract: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 Minerals 2019, 9, 49 2 of 41 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 δ 18 O 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 CO 2 dominant fluids with traces of CH 4 or N 2 , and low CO 2 densities (0.46 and 0.67 g/cm 3), 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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the origin of a new pargasite schist hosted ruby deposit from paranesti northern greece
Canadian Mineralogist, 2017Co-Authors: Kandy K Wang, Ian T. Graham, Anthony E. Fallick, Elena A. Belousova, David Cohen, Gaston Giuliani, Stephen J Harris, Panagiotis Voudouris, Alan GreigAbstract:Gem-quality (cabochon) ruby-bearing occurrences (here termed PAR-1 and PAR-5) located near Paranesti, north eastern Greece have been systematically studied for the first time in this paper. Tectonically, the occurrences are located within the Nestos Shear Zone (NSZ). The NSZ separates two distinct geological units. The Rhodope Terrane is a heterogeneous unit of gneisses, mafic, ultramafic, and meta-sedimentary rocks in the hanging wall. The footwall Pangaion-Pirin Complex consists of marbles and acid gneisses of a Mesozoic carbonate platform on pre-Mesozoic continental basement. In this paper, a range of petrographic and geochemical techniques were used to determine (1) any similarities and differences to other mafic-ultramafic hosted ruby deposits worldwide; (2) distinctive geochemical fingerprints for Paranesti; and (3) the likely P-T conditions of formation. Detailed petrographic and whole-rock analyses utilizing ICP-MS, XRF, and XRD have found the Paranesti Corundum to be of a mafic/ultramafic protolith with approximately 40 wt.% SiO2, 16 wt.% Mg, 11000 ppm Cr, and 440 ppm Ni. EMPA major element analysis determined the mineral inclusions within the Corundum grains to be picotite and hercynite spinels. Pargasite is the dominant amphibole within the Corundum-bearing amphibole schist host. The surrounding non-Corundum bearing chlorite schist mainly comprises clinochlore. Petrographic examination of the mineral assemblages within the Corundum-bearing schists revealed strong fracturing and alignment (parallel to the main regional foliation) of the Corundum grains and margarite reaction rims around the Corundum. The surrounding non-Corundum amphibolites also contain anorthite, along with relict sillimanite, kyanite, and chlorite/muscovite/epidote overprinting. Detailed LA-ICP-MS trace element analysis of the color range of Corundum from the two occurrences showed the Corundum to be mainly of metamorphic origin, though pale rubies from PAR-5 suggest some metasomatic influence. The Corundum displays distinctive geochemical locality signatures, with a combination of high Cr (average 2300 ppm with 15% sample points on core positions >5000 ppm and maximum 8600 ppm); high Si (average 1400 ppm with 40% over 1500 ppm and maximum 2500 ppm), low Mg (average 30 ppm), and very low V, Ti, and Ga. Based on the literature for similar occurrences, and the mineral assemblages observed at Paranesti, the estimated P-T conditions of Corundum formation are <7 kbar and <750 °C, similar to the mafic African amphibolite-hosted rubies. This study has found the Paranesti occurrences to be most similar to the Winza, Tanzania ruby deposit, whilst there are some similarities to other high-Cr ruby deposits, primarily the Fiskenaesset, Greenland and metamorphic amphibolitic schist hosted African deposits. The Paranesti Corundum most likely formed during regional amphibolite facies metamorphism which created the Nestos Shear Zone, along with a lesser influence (primarily observed in the PAR-5 occurrence) of more localized metasomatism. Subsequent multiple greenschist facies retrogression of the occurrences resulted in the current-day host amphibole-chlorite schist assemblages.
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Origin of gem Corundum in calcite marble: The Revelstoke occurrence in the Canadian Cordillera of British Columbia
Lithos, 2014Co-Authors: Tashia Dzikowski, Jan Cempírek, Lee Groat, Gregory Dipple, Gaston GiulianiAbstract:The calcite marble-hosted gem Corundum (ruby, sapphire) occurrence near Revelstoke, British Columbia, Canada, occurs in the Monashee Complex of the Omineca Belt of the Canadian Cordillera. Corundum occurs in thin, folded and stretched layers with green muscovite + Ba-bearing K-feldspar + anorthite (An0.85–1) ± phlogopite ± Na-poor scapolite. Other silicate layers within the marble are composed of: (1) diopside + tremolite ± quartz and (2) garnet (Alm0.7–0.5Grs0.2–0.4) + Na-rich scapolite + diopside + tremolite + Na,K-amphiboles. Non-silicate layers in the marble are either magnetite- or graphite-bearing. Predominantly pink (locally red or purple) opaque to transparent Corundum crystals have elevated Cr2O3 (≤ 0.21 wt.%) and variable amounts of TiO2; rare blue rims on the Corundum crystals contain higher amounts of TiO2 (≤ 0.53 wt.%) and Fe2O3 (≤ 0.07 wt.%). The associated micas have elevated Cr, V, Ti, and Ba contents. Petrography of the silicate layers show that Corundum formed from muscovite at the peak of metamorphism (~ 650–700 °C at 8.5–9 kbar). Because the marble is almost pure calcite (dolomite is very rare), the Corundum was preserved because it did not react with dolomite to spinel + calcite during decompression. The scapolite-bearing assemblages formed during or after decompression of the rock at ~ 650 °C and 4–6 kbar. Gem-quality Corundum crystals formed especially on borders of the mica-feldspar layers in an assemblage with calcite. Whole rock geochemistry data show that the Corundum-bearing silicate (mica-feldspar) layers formed by mechanical mixing of carbonate with the host gneiss protolith; the bulk composition of the silicate layers was modified by Si and Fe depletion during prograde metamorphism. High element mobility is supported by the homogenization of δ18O and δ13C values in carbonates and silicates for the marble and silicate layers. The silicate layers and the gneiss contain elevated contents of Cr and V due to the volcanoclastic component of their protolith.
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Oxygen isotope composition as a tracer for the origins of rubies and sapphires
Geology, 2005Co-Authors: Gaston Giuliani, Anthony E. Fallick, Virginie Garnier, Christian France-lanord, Daniel Ohnenstetter, Dietmar SchwarzAbstract:Oxygen isotopic compositions of rubies and sapphires from 106 deposits worldwide, as well as heated natural Corundum, have been measured in this study. Artificially heated Corundums have the same oxygen isotopic composition as unheated material. The 18O/16O ratio of natural Corundum is a good indicator of its geological environment of formation. The consistently restricted ?18O range found for each type of deposit is explained by host-rock buffering during fluid-rock interaction. The ?18O constrains the geological source of the major type of gem-quality rubies sold on the market and brings new insight to gems found in placers. High-quality blue sapphires from Kashmir, Andranondambo, and Sri Lanka have specific oxygen isotopic ranges, but they overlap those of Mogok in Myanmar. Combined with traditional gemology techniques, oxygen isotope analysis will contribute toward defining the origin of some commercial high-value blue sapphires, especially from Kashmir.
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Gem Corundum deposits in Vietnam
The Journal of Gemmology, 2004Co-Authors: Pham Van Long, Anthony E. Fallick, Gaston Giuliani, Virginie Garnier, Daniel Ohnenstetter, Dietmar Schwarz, Hoang Quang Vinh, Thérèse Lhomme, Jean Dubessy, Phan Trong TrinhAbstract:Since 1983, gem-quality rubies have been recovered from the Luc Yen and Quy Chau mining areas in northern Vietnam. Since 1991, 'basaltic'-type blue-green-yellow ('BGY') sapphires have been mined in southern Vietnam. This article briefly reviews the history and geology of these different areas and shows the importance of marble and basalt-type deposits. Other types of Corundum occurrences are found in amphibolite, pegmatite, gneiss and metasomatite. The gemmological, chemical and isotopic characteristics of these different types of Corundum are described. The most notable features of rubies contained in marbles are that many crystals have blue colour zones, and inclusions of rutile, anhydrite and salts. The primary fluid inclusions are composed of carbon dioxide and hydrogen sulphide with native sulphur and diaspore daughter minerals. Sapphires from placers in basalts are characterized by inclusions of columbite, pyrochlore and baddeleyite. The trace element contents of Corundums allow distinction of rubies in marbles from sapphires in basalts and metamorphic rocks. Rubies have high chromium (0.54
John M. Saul - One of the best experts on this subject based on the ideXlab platform.
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LA-ICP-MS U–Pb dating of rutile inclusions within Corundum (ruby and sapphire): new constraints on the formation of Corundum deposits along the Mozambique belt
Mineralium Deposita, 2017Co-Authors: Elena S. Sorokina, Delia Rösel, Tobias Häger, Regina Mertz-kraus, John M. SaulAbstract:Direct dating of Corundum and the establishment of age constraints for Corundum crystal growth are restricted due to the absence of a geochronometer. Syngenetic mineral inclusions may help define minimum ages for Corundum growth. Here, we present results of in situ LA-ICP-MS U–Pb dating applied to rutile inclusions in Corundum from localities along the Mozambique belt. U–Pb dating of rutile inclusions gave ages of 533 ± 11 Ma (2 σ) for the Gitonga pit (John Saul ruby mine) and 526 ± 13 Ma for the Aqua Ruby mine, both in the Mangari area of Kenya, and an age of 499 ± 12 Ma for ruby from the Morogoro area, Tanzania. These ages are interpreted as cooling ages that set a minimum age for Corundum growth following metamorphism along the East-African Antarctic Orogen, and might be used for petrogenetic tracing of Corundum in placer deposits.
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LA-ICP-MS U-Pb dating of rutile inclusions within Corundum (ruby and sapphire): new constraints on the formation of Corundum deposits along the Mozambique belt
Mineralium Deposita, 2017Co-Authors: Elena S. Sorokina, Delia Rösel, Tobias Häger, Regina Mertz-kraus, John M. SaulAbstract:Direct dating of Corundum and the establishment of age constraints for Corundum crystal growth are restricted due to the absence of a geochronometer. Syngenetic mineral inclusions may help define minimum ages for Corundum growth. Here, we present results of in situ LA-ICP-MS U–Pb dating applied to rutile inclusions in Corundum from localities along the Mozambique belt. U–Pb dating of rutile inclusions gave ages of 533 ± 11 Ma (2 σ) for the Gitonga pit (John Saul ruby mine) and 526 ± 13 Ma for the Aqua Ruby mine, both in the Mangari area of Kenya, and an age of 499 ± 12 Ma for ruby from the Morogoro area, Tanzania. These ages are interpreted as cooling ages that set a minimum age for Corundum growth following metamorphism along the East-African Antarctic Orogen, and might be used for petrogenetic tracing of Corundum in placer deposits.
Dewashish Upadhyay - One of the best experts on this subject based on the ideXlab platform.
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Corundum–leucosome-bearing aluminous gneiss from Ayyarmalai, Southern Granulite Terrain, India: A textbook example of vapor phase-absent muscovite-melting in silica-undersaturated aluminous rocks
American Mineralogist, 2010Co-Authors: Michael M. Raith, Pulak Sengupta, Ellen Kooijman, Dewashish Upadhyay, C. SrikantappaAbstract:An aluminous gneissic rock associated with high-pressure mafic and felsic granulites in the Palghat-Cauvery Shear Zone of southern India provides a classic example of quartz-absent muscovite melting. The anatectic gneiss shows a conspicuous migmatitic structure defined by closely spaced centimeter to decimeter sized, Corundum-bearing leucosomes developed in a weakly foliated mesosome of plagioclase (An 21 Ab 77 Or 2 ) and biotite (4.9 wt% TiO 2 , X Mg = 0.51–0.47). The boundaries between leucosome and mesosome domains are sharp, and no melanosome selvages are developed at the interface. Corundum occurs as euhedral crystals up to 2 cm in diameter, typically centered in the leucosome matrix of coarse-grained perthitic alkali feldspar (integrated composition: An 2 Ab 35 Or 63 ), minor relict biotite (4.2–5.1 wt% TiO 2 , X Mg = 0.48–0.46) and plagioclase (An 21 Ab 78 Or 1 ). In some domains, the mesosomes also contain elongate clusters of similarly oriented smaller Corundum plates that are intergrown with perthitic alkali feldspar, presumably replacing former kyanite blades. The textural and mineralogical characteristics and petrogenetic grid considerations indicate breakdown of muscovite through two successive dehydration-melting reactions: (1) formation of Corundum+K-feldspar-clusters via the reaction muscovite+aluminosilicate → Corundum+liquid at the sites of kyanite/sillimanite, and (2) development of Corundum-bearing leucosomes through the reaction muscovite → Corundum+K-feldspar+liquid, focused around the sites of nucleation and growth of peritectic Corundum. P - T pseudosection modeling in the Na 2 O-CaO-K 2 O-FeO-MgO-Al 2 O 3 -SiO 2 -H 2 O-TiO 2 system locates the onset and completion of the muscovite-melting reaction 2 in the steep narrow quadrivariant field Ms+Bt+Pl+Kfs+Crn+Liq, which extends from ~6 kbar, 720 °C to higher pressures. Biotite remained stable and was not involved in the melting reactions. Two-feldspar thermometry gives peak-temperatures of 800 ± 50 °C. Combined with P - T estimates for metapelitic granulites in the area, these P - T constraints appear to be consistent with a clockwise P - T evolution of the eastern Palghat Cauvery shear zone with peak P - T conditions not exceeding ca. 800 °C and 10–12 kbar. The timing of partial melting and HT-metamorphism is constrained at ~529 Ma by U-Pb spot dating of oscillatory zoned individual grains and overgrowths on detrital zircon cores included in peritectic Corundum of leucosome domains. The zircon cores indicate a Paleoproterozoic (2.5–2.0 Ga) provenance of the sedimentary protolith.
