Marble-hosted ruby deposits from Central and Southeast Asia: Towards a new genetic model

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Trace elements investigated by electron microprobe analysis (EMPA) have been combined with oxygen isotopic composition of pink, red and other colored spinels (blue, purple, brown, orange, lavender) hosted by marbles and found in placers from Luc Yen and An Phu deposits, Yen Bai province, North Vietnam. The deposits are those from Nuoc Ngap, Cong Troi, Bai Son and different placers from the An Phu area. Trace elements such as Fe-Zn-Cr-V in red and pink gem spinels permit to separate those from Cong Troi and those from the others deposits of the An Phu area. Spinels from Cong Troi have low to extremely low Zn (< 500 ppm) and high Fe contents (3,000 to 16,000 ppm) while those from An Phu area are Zn-rich (up to 11,000 ppm). Iron is the dominant element for the other colored spinels whereas Zn, Cr and V contents are extremely variable. The Bai Son blue spinel is Fe-rich (5,000 to 7,200 ppm) with some V (950 to 1,830 ppm), Cr (270 to 480 ppm), Co (240 to 400 ppm) and Ni (550 to 950 ppm). The O-isotope composition of the whole spinels ranges between 12.1 and 24.2‰ (n = 25). Within each deposit, the range of δ18O values for red, pink and colored spinels is usually similar. However, the red and pink spinels from An Phu present two distinct sets of δ18O values, respectively between 13.2 to 17.0‰ (n = 7) and 22.5< δ18O < 24.2 (n = 5). Those from Cong Troi are from 14.8 to 17.7‰ (n = 3) and their range overlaps that of An Phu. The use of O-isotopes is not useful for distinguishing between the deposits, but the low to extremely low Zn content of the Cong Trois spinels is a discriminant. The variation of δ18O values (12.1 <δ18O < 24.2‰) of the whole spinels indicates that the oxygen isotopic compositions of the metamorphic fluids were probably buffered by the local δ18O values of the impure host marbles.ReferencesChauviré B., Rondeau B., Fritsch E., Ressigeac Ph., Devidal J.-L., 2015. Blue spinel from the Luc Yen district of Vietnam. Gems & Gemology, 51, 2-17.D'Ippolito V., Andreozzi G.B., Hålenius H., Skogby H., Hametner K., Günther D., 2015. Colour mechanisms in spinel: cobalt and iron interplay for the blue colour. Physics and Chemistry of Minerals, 42, 431-439.Garnier V., 2003. Les gisements de rubis associés aux marbres de l’Asie Centrale et du Sud-est: genèse et caractérisation isotopique. PhD thesis INPL, Nancy, France, 373p.Garnier, V., Ohnenstetter, D., Giuliani, G., Maluski, H., Deloule, E., Phan Trong Trinh, Pham Van Long, Hoang Quang Vinh, 2005. Age and significance of ruby-bearing marbles from the Red River shear zone, northern Vietnam. The Canadian Mineralogist, 43, 1315-1329.Garnier V., Giuliani G., Ohnenstetter D., Fallick A.E., Dubessy J., Banks D., Hoang Quang Vinh, Lhomme Th., Maluski H., Pêcher A., Bakhsh K.A., Pham Van Long, Phan Trong Trinh, Schwarz D., 2008. Marble-hosted ruby deposits from central and Southeast Asia: towards a new genetic model. Ore Geology Reviews, 34, 169-191.Giuliani G., Fallick A.E., Garnier V., France-Lanord Ch., Ohnenstetter D., Schwarz D., 2005. Oxygen isotope composition as a tracer for the origins of rubies and sapphires. Geology, 33(4), 249-252.Giuliani G., Fallick A.E., Boyce A.J., Pardieu V., Pham Van Long, 2017. Pink and red spinels in marble: trace elements, oxygen isotopes, and sources. The Canadian Mineralogist, 55, 743-761.Hauzenberger C.A., Häeger T., Baumgartner L.P., Hofmeister W., 2001. High-grade metamorphism and stable isotope geochemistry of N-Vietnamese gem-bearing rocks. In: Proceedings of the Workshop on gems and minerals of Vietnam, Hanoi, 124-138.Hauzenberger C.A., Bagola C., Häeger T., Muellen C., Nguyen Ngoc Khoi, Le Thi Thu Huong, 2014. Mineralogy and petrology of the An Phu marble hosted spinel and corundum deposit, Luc Yen, N-Vietnam. In Proceedings of the 4th International Gem and Jewelry Conference, Chiang Mai, Thailand, 76-78.Kleišmantas A., Daukšyte A., 2016. The influence of Vietnam and Sri Lanka spinel mineral chemical elements on colour. Chemija, 27, 45-51.Kretz R., 1983. Symbols for rock-forming minerals. American Mineralogist, 68, 277-279.Le Thi Thu Huong, Häeger T., Hofmeister W., Hauzenberger C., Schwarz D., Pham Van Long, Wehmeister U., Nguyen Ngoc Khoi, Nguy Tuyet Nhung, 2012. Gemstones from Vietnam: An update. Gems & Gemology, 48, 158-176.Malsy A., Klemm L., 2010. Distinction of gem spinels from the Himalayan mountain belt. Chimia, 64(10), 741-746.Malsy A., Karampelas S., Schwarz D., Klemm L., Armbruster T., Tuan Do Anh, 2012. Orangey-red to orangey-pink gem spinels from a new deposit at Lang Chap (Tan Huong - Truc Lau), Vietnam. The Journal of Gemmology, 33, 19-27.Pham Van Long, Hoang Quang Vinh, Garnier V., Giuliani G., Ohnenstetter D., Lhomme,T., Schwarz D., Fallick A.E., Dubessy J., Phan Trong Trinh, 2004. Gem corundum deposits in Vietnam. Journal of Gemmology, 29, 129-147.Pham Van Long, Pardieu V., Giuliani G., Nguy Tuyet Nhung, Pham Thi Thanh Hien, Pham Duc Anh, Nguyen Ngoc Khoi, Hoang Quang Vinh, 2014. Gemmological characteristics of spinel from Luc Yen, Yen Bai. Journal of Geology, 340, 29-36.Pham Van Long, Pardieu V., Giuliani G., 2014. Update on gemstone mining in Luc Yen, Vietnam. Gems & Gemology, 49, 233-245.Pouchou J.L., Pichoir F., 1991. Quantitative analysis of homogeneous or stratified microvolumes applying "PAP" In Electron Probe Quantification (K.F.J. Heinrich & D.E. Newbury eds.). Plenum Press, New York, USA, 31-75.Valley J.W., 1986. Stable isotope geochemistry of metamorphic rocks. Reviews in Mineralogy, 16, 445-481.Yui T.F., Khin Zaw, Wu C.-M., 2008. A preliminary stable isotope study on Mogok ruby, Myanmar. Ore Geology Reviews, 34, 182-199.

Section: Geological Settingmentioning

confidence: 99%

Trace elements and oxygen isotopes of gem spinels in marble from the Luc Yen - An Phu areas, Yen Bai province, North Vietnam

Long¹,

Giuliani²,

Fallick³

et al. 2018

Self Cite

“…(After Chauvire et al, 2015) All of the gem deposits are located in the Lo Gam zone. The Lo Gam formation consists of a sedimentary series metamorphosed into marble, gneiss, calc-silicates, micaschist, and amphibolite which are sometimes intruded by granitic and pegmatitic dykes (Leloup et al, 2001;Giuliani et al, 2003;Garnier et al, 2008). The marbles are mainly calcitic and interlayered with Al-, V-, and Cr-rich amphibolites.…”

Section: Location and Geologic Backgroundmentioning

confidence: 99%

Study of impurity in blue spinel from the Luc Yen mining area, Yen Bai province, Vietnam

Hường¹,

Haeger

Phan

2017

In this paper, we present the main impurities in natural blue spinel from the Luc Yen mining area in Yen Bai province, Vietnam. Together with identifying impurities and their valence, we have taken into account the site of some impurities in the MgAl 2 O 4 spinel structure by using sensitive techniques, including electron microprobe analysis (EMPA), UV-Vis-NIR, electron spin resonance (ESR), and X-ray absorption (XAS

“…All of the 11 ore bodies are located in the lower part of Ngoi Chi formation (PR 1 nc 1 ) (Pham Van Long et al, 2004;Garnier et al, 2008;Tran Xuyen, 1988) (Figure 1). The formation was observed comprising of sillimanite schist (± biotite, garnet), quartz-biotite schist (± sillimanite, garnet), garnet schist (± biotite), biotite gneiss lens, and small amphibolite vein.…”

Section: Geology Of Bao Ha Graphite Depositmentioning

confidence: 99%

Mineralogical characteristics of graphite ore from Bao Ha deposit, Lao Cai Province and proposing a wise use

Thao

Hien²,

Anh³

et al. 2017

Graphite, especially, high quality graphite can be used in many industrial applications including metallurgy, batteries, fuel cells, and refractories. In 2011, Vietnam Ministry of Natural Resources and Environment issued a mineral exploration license to explore Bao Ha graphite deposit, Bao Yen district, Lao Cai Province. The studied samples were taken from 3 drill holes of the Bao Ha largest ore body. Different methods including light microscopy, X-ray diffraction (XRD), scanning electron microscopy (SEM), and carbon and sulfur analyzer were performed to identify its lithological and mineralogical characteristics as well as graphite quality, then propose a wise use of the resource. The Bao Ha graphite is characterized as disseminated flake graphite in massive form, which developed in the sillimanite schist and quartz-biotite schist of the Ngoi Chi formation. Graphite flakes occur as distorted clusters of flaky plates/flakes within 50÷500 m, which is the medium size in comparison with the general grain size of graphite flake. Graphite particle makes up 33÷43% by volume and graphitic content (Cg) makes up 10.0÷11.7 wt.%. Impurities include mainly quartz, biotite, and feldspar (combining of K-feldspar and anorthite, the primary ore) or kaolinite (the weathered ore). This graphite ore should be refined to reach an ore concentration of at least 90% Cg for domestic industries of metallurgy, batteries, thermal materials, and refractories as well as for exports.