Vietnam travel photos

1 Center for Gem and Gold Retìm kiếm and Identification, Hanoi, Vietnam2 IRD và CRPG/CNRS, BP đôi mươi, 54501 Vandœuvre, France3 CRPG/CNRS, Uquảng bá 2300, BPhường đôi mươi, 54501 Vandœuvre, France

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Note: We are pleased khổng lồ reproduce the following article by kind permission of Dr. Grahame Brown, Editor of TheAustralian Gemmologist.

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Reprinted from The Australian GemmologistVolume 22, Number 4, October–December 2004


Abstract

Vietnamese research in geology has indicated a high potential for gemstones in Vietphái nam & has found in this last decade numerous gem deposits, especially ruby and sapphire. In northern Vietnam, gem corundums are found in the Luc Yen, Yen Bai and Quy Chau areas, in primary deposits hosted by metamorphic rocks and in placers. In secondary deposits, ruby and sapphire are associated with gem spinel and garnet. In southern Vietnam giới, sapphires are related khổng lồ alkaline basalts, with xanh sapphires being economic. Sapphires are recovered with gem zircons & peridots in placers. Aquamarine, beryl, topaz, quartz crystals (amethyst, citrine, morion), tektite, fluorite, opal, chalcedony, jadeite, nephrite and amazonite are the other gemstones exploited in Vietnam. Ruby, sapphires & pearls provide important commercial exchanges in the gemstones markets of Vietnam and other foreign countries.

Introduction

In the late 1980s, reports emerge from Vietnam giới of a major discovery of high quality rubies in the northern part of the country, from deposits in the Luc Yen & Yen Bai areas. Ruby occurred in colluvial and alluvial sediments, and the primary source of ruby was suspected to be marble & pegmatite. Placer deposits of ruby were recovered by farmers during routine agricultural activities. Following the discovery of ruby in Luc Yen in 1987, others occurrences of gemstones were found in Thuong Xuan (aquamarine và topaz), Co Phuong (jadeite, nephrite), Thach Khoan (beryl, quartz), Quy Chau (ruby) and in the Dak Lak và Binc Thuan provinces (sapphire). After these discoveries, gemstone exploitation really started in 1988 with the establishment of Vinagemteo by the government—a state-owned company for the investigation, mining, processing, và trading of gem materials in Vietphái mạnh (Fig.1). The purpose of this paper is to realize an overview of the gemstones occurrences in Vietnam giới with a special dedication lớn ruby và sapphire.

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Figure 1. Map of Vietphái nam showing the location of gemstone occurrences.

Distribution of gemstones

Ruby and sapphire deposits

In northern Vietnam

Yen Bai mining district

The primary corundum occurrences of Yen Bai (Fig.2) occur within the high-grade metamorphic gneisses of the Day Nui Con Voi range (Psi mê Van 1996, 2003), which extends lớn the southeast from the Ailao Shan in Yunnan (China). This range is bounded by lateral strike-slip faults forming the major Cenozoic geological discontinuity in East Asia known as the Ailao Shan-Red River shear zone (Phan Trong et al. 1998, 1999, Leloup et al. 2001). The Day Nui Con Voi range is composed of high-grade metamorphic rocks with sillimanite-biotite-garnet gneisses, mica-schists with local alternation of marbles and amphibolites.

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Figure 2. Geological map of Yen Bai area with locations of ruby and sapphire deposits.

Corundum occurs as:

grey khổng lồ blue sapphires in garnet-sillimanite mica schists and gneisses which contain leucosome và leucocratic granitoidic dykes (Truc Lau gneisses and Khe Nhan meta-pegmatite); in amphibolites converted by the effect of metasomatism in biotite schists with some layers containing centimetre-sized grey lớn dark sapphires (north of Tan Huong mine, km 15 occurrence; as rubies in large marble boudins intercalated with gneiss, mica schist and amphibolite (Tan Huong drill cores). These marbles represent previous limestones intergrown with mudstones, which were sheared and metamorphosed during the tectonic activity along the Red River shear zone.
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Figure 3. Exploitation of ruby in Tan Huong mine.

The gem deposits are placers exploited along the shear zone as in Tan Huong và Truc Lau (Fig.2). In Tan Huong, ruby was found and exploited by local farmers in 1994. In 1996, the deposit was managed và exploited by the Vietnam giới National Gem & Gold Corporation (Fig.3). From 1994 lớn 1996, hundreds kilograms of rubies and star rubies were exploited illegally và sold lớn foreign dealers. The area is composed of metamorphic gneiss, micaceous-quartz schist, marble and amphibolite of the Nui Voi complex that have sầu been intruded by granites, syenites & pegmatite dykes. Ruby và spinel have sầu been found in the magmatic rocks in minor grains as well as in marbles (Nguyen Kinc Quoc et al. 1995). In placers, ruby grains are eroded but the crystals present a prismatic shape, are from 1.0 lớn 19 mm long, & range in colour from red lớn reddish & purplish to red. The main associated gem mineral are red and octahedral spinels and blue trapiche-lượt thích sapphires. In April 1997, two ruby crystals of 2.58 kg (Fig.4) và 1.96 kg (star ruby) respectively, of very high quality, were found và declared State treasure.

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Figure 4. The ruby called Star of Vietnam weighing 2.58kg that was found in the Tan Huong mine.

The Truc Lau paleoplacer consists of 10 m thiông xã of sediments overlying the bedroông chồng. The rubies and xanh sapphires are contained in a gravel layer of 5 m thickness that is overlain by a 3.5 m of quaternary sediments and solo.5 m of soil. In 2002, up to two boulders (1-2 kg) per month made of pink sapphire and star ruby were recovered from this paleoplacer.

In the Tan Dong placer (Fig.2), assemblages of xanh sapphire-margarite-plagioclase are the remainder of metasomatised pegmatites.

Luc Yen mining district

The ruby & sapphire deposits of Luc Yen (Fig, 2) are set in moderate to lớn high temperature recrystallized marble units of Upper Proterozoic-Lower Cambrian age in the eastern side of the Red River shear zone of the Lo Gam tectonic zone (Hoang Quang et al. 1999, Garnier, 2003, Pyêu thích Van 2003).

Primary ruby occurs as:

disseminated crystals within marbles with phlogopite, dravite, margarite, pyrite, rutile, spinel, edenite and graphite (Bai Da Lan, An Phu, Minch Tien, Nuoc Ngap, Luc Yen & Khoan Thong mines); veinlets associated with calcite, dravite, pyrite, margarite và phlogopite (An Phu mine);fissures with graphite, pyrite, phlogopite và margarite (Bai Da Lan mine); Minc Tien region (Fig.5).
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Figure 5. Flakes of phlogopite (brown) associated with a 1.5 cm long ruby crystal from Minch Tien area.

Secondary deposits consist of gravel concentration in karst pockets và in alluvial fans in the Luc Yen valleys (Kane et al.. 1991). The gem-bearing valleys are often narrow, small depressions ranging from 0.5 lớn 0.7 kmét vuông in area, but most common 2-3 km2. The corundums are pink, purple to lớn red (Fig.6), và blue và colourless sapphires coexist with rubies as well as with grey to brown và bi-pyramidal sapphires and trapibít rubies. Associated gem minerals include red, pink & pale blue spinel, gem chất lượng multi-colour tourmaline và garnet. The great variety & high chất lượng of the gem material recovered in the placers make the gemstone market in the center of Luc Yen town opened daily for dealers since 1987 (Fig.7).

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Figure 6. Gem-quality rubies and pink sapphires from Luc Yen deposits.

Ba Be sapphire occurrence

This is located in the Bac Kan province, 3trăng tròn km north of Hanoi (Fig.2). It is located at the proximity of the Nui Chua hoa cương và the Hoang Tri gabbro-monzonite. The colourless khổng lồ pale xanh sapphire is found in a pegmatite, composed of quartz, K-feldspar & muscovite, which intrudes schist and marble. All sapphires are opaque & cannot be used for gem cutting.

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Figure 7. The Luc Yen gemstones market.

Quy Chau mining district

This area, located 200 km south of the Red River shear zone, is formed by the Bu Khang dome (Fig.1). It consists in a broad antikhung of Paleozoic và Mesozoic sedimentary and meta-sedimentary rocks overlaying a core of micaschists, granitoids, paragneisses and orthogneisses (Nguyen Kinh Quoc et al. 1995; Jolivet et al. 1999). The northeastern part of the dome is limited by the major extensional Cenozoic shear zone of Quy Chau. This is where the corundum deposits are located.

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Figure 8. Rough ruby from Quy Chau deposit.

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Rubies and sapphires have sầu been mined since 1987 from the placer deposits of Doi Ty, Doi San, Mo Coi và Quy Hop (Pđam mê Van, 2003). The corundum occurs principally in the Quy Chau area as:

very rare và uneconomic rubies disseminated in marbles associated with pyrite và graphite;in placers which size the economic deposit. In the Doi San và Doi Ty area, granitic intrusions resulted in the injection of pegmatites and the formation of calcium-magnesium-rich skarns in the surrounding marbles, amphibolites, gneiss và micaschists. Rubies were neither observed in the skarn nor in the pegmatite. The genetic origin of this ruby has remained unclear since oxyren isotopes & fluid inclusions studies on these rubies show that they their isotopic signature was metamorphic and similar lớn that found for typical ruby-hosted marble deposits in northern Vietnam giới (Garnier, 2003; Giuliani et al., 2003a, b). The gem material consists of ruby, with smaller amount of blue to violet & orange sapphire. Ruby tends to be slightly purplish red in hue position; their crystals are usually in hexagonal prism and barrel shape (Fig.8).

In Southern Vietnam

The sapphire deposits of southern Vietnam giới consist of placers formed by the erosion of alkali-basalternative text flows (Smith et al. 1995). The sapphires present usually prismatic và pyramidal shapes. The form size of the crystals is up to lớn 2-7 mm long, but in Dak Nong, Ngoc Yeu và Da Ban areas they sometimes reach 30-40 mm in diameter. Their colour is usually dark xanh, sometimes green blue, sky xanh, & rarely honey-yellow (except in the Tien Co area in Binh Thuan province).

Several mining district were exploited from 1985 to present. These include:

The Dak Nong area (Dak Lak province)

Here the sapphires are found in weathered residual soils lying above sầu the flows và also in the river & stream fans (Tran Xuan Toan et al. 1995). Generally, the alluvial corundum corresponds khổng lồ xenocrysts found in situ in basalts (Hoang Nguyen và Flower 1998). The colour of the sapphires ranges from dark blue, through blue, green to yellow. The crystals occur as broken fragments, but with prismatic and bipyramidal shapes and dimensions of up to lớn 1.5 centimet long và 0.2-0.4 cm wide.

The Ma Lam and Da Ban area (Binh Thuan province)

The sapphires of these areas show barrel-shaped habits. The stones range from very dark blue lớn very deep blue. The alluvial corundum sometimes shows glassy-looking margins that indicate high temperature corrosion—indirect evidence of magma transport. In the Da Ban area megacrysts of dark-blue sapphires are sometimes found within alkali-basalts.

Diamond occurrences

Although diamonds are not yet discovered in the country, geological investigations in the north-western part of Vietphái mạnh & the Tay Nguyen Highland (Fig.1) provides promising areas for primary diamond discovery. Recently, the occurrences of lamproïtes (alkali lamprophyres) were reported in the Lai Chau province in the north-western part of Vietnam giới. In Tay Nguyen (Kon Tum province), kimberlite dykes are discovered và the rocks are made of olivine, phlogopite, garnet, pyrope and perovskite. In the year 2000, small grains of diamonds (smaller than 2 mm in diameter) were recovered from placers in Tay Nguyen (Pđam mê Binch, 2000). More detailed studies và investigation are still needed to lớn prove the occurrences of đá quí in Vietphái mạnh.

Emerald occurrences

Up lớn now, emerald và chrysoberyl have not yet been discovered in Vietphái nam, but the geological formations and structures in Ba Be (Bac Kan province) & Mo Ngot (Vinh Phu province) represent potential areas for emerald và chrysoberyl (Nguyen Kinh Quoc, 1995).

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Figure 9. Rough aquamarine from Thach Khoan deposit.

Beryl (var. aquamarine) và topaz occurrences

Xuan Le (Thanh Hoa province)

The first discovery of aquamarine & topaz in Xuan Le area was made in 1985 by a field geologist. Aquamarine is hosted in a swarm of pegmatites, hundreds of metres long and 0.4-5.0 m thiông chồng, which contained quartz, K-feldspar, plagioclase, muscovite, biotite and accessory minerals as blaông chồng tourmaline, colorless topaz, and zirnhỏ. The pegmatites are related to lớn the intrusion of syeno-đá hoa cương và biotite đá hoa cương. Aquamarine of high gem unique has a hexagonal prismatic shape, is sea blue-coloured, transparent và with the form size of the crystals from 5 lớn trăng tròn cm long, 1 lớn 6 centimet in diameter. These are exploited in elluvial deposits by local farmers.

Topaz in Xuan Le is related to lớn pegmatites with a reserve potential about 41.53 tons (Nguyen Kinch Quoc 1995). The topaz is exploited, mainly in placers, which yield high gem chất lượng material suitable for jewellery. Topaz crystals are usually broken by the alluvial transport, but they have sầu colourless or yellowish colors và high transparency. Accessory minerals are beryl, tourmaline, fluorite, quartz (including smoked quartz) và garnet.

After 1985, numerous occurrences of topaz were found in the Bao Loc & Tu Le areas in the Lam Dong và Yen Bai provinces, respectively.

Thach Khoan (Vinh Phuc province)

Good gem quality beryls are exploited in Thach Khoan. The crystals are transparent lớn translucent, 3-4 centimet in diameter, sometimes 10-30 cm long, & have sầu a sky-blue colour (Fig.9). In 1999, a crystal of beryl that weighed 75 kilograms, was displayed in the Geological Museum of Vietphái nam. Accessory minerals are quartz, black tourmaline, feldspar, garnet và kyanite.

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Figure 10. Rough tourmaline from the Luc Yen deposits.

Tourmaline

Tourmaline-bearing pegmatite has been reported in the region of Luc Yen (Nguyen Kinh Quoc 1995), but up lớn now gem chất lượng tourmalines have sầu not been found in situ. They occurred in alluvial gravels associated with gem-corundum or in a weathered crust. The crystals have sầu striated prisms with rounded triangular cross-sections và are variously terminated. The Luc Yen tourmaline has variable colours ranging from green, brown, blachồng to lớn yellow (Fig.10). Multicolor crystals, usually include alternating pink, purple and yellowish-green colour. Colour zoning is also commonly observed from the centre khổng lồ the periphery of the crystals, with the combination of pink, purple & dark-green colours being common.

Spinel

Gem spinels were discovered at Tan Huong, Luc Yen và Quy Chau in primary và secondary ruby and sapphire deposits. In Luc Yen mining district, and in Tan Huong mine, spinel crystals are found in dolomitic marbles together with calcite-phlogopite-humite of metamorphic-metasomatic origin. The crystals vary in form size from 1 x 1 cm to 3 x 3 cm. They have sầu octahedral khung và red lớn brownish red colour. Crystals of spinel that are recovered from placers are transparent và used for gem cutting, while bigger crystals in their host-roông chồng are usually translucent lớn opaque và used only as collector’s specimens.

Zircon

Zircon và basaltic sapphires are usually found together in placers from Kon Tum, Dak Lak, Gia Lai, Lam Dong và Binh Thuan provinces. Their colour ranges from colorless to lớn yellow, orange, brownish-orange, brownish khổng lồ reddish-brown. The habit crystals are combinations of the bi-pyramid and the tetragonal prism. Crystals are usually corroded.

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Figure 11. Cut peridot from the Tay Nguyen highlvà of Vietphái nam that range in form size from 2.35 khổng lồ 8.42ct.

Peridot

Peridot is found mainly in the Ham Rong and Bien Ho basaltic areas of the Gia Lai province (Fig.1). Peridots are collected from lherzolite xenoliths within the basalternative text flows. Gem peridot is olive-green to lớn yellowish-green (Fig.11) with crystals reaching up to lớn 2 x 4 x 4 centimet. However, most of peridot occurs in small grains that average 0.6 to lớn 1.5 cm in diameter. Today, peridot is exploited in eluvial and stream gravels by local residents. In some places, the peridot-bearing layers are reached by h& digging 5 m-deep pits.

Tektites

Tektites have been found in many places, from the north lớn the south of Vietnam. Essentially they are recovered from the highlands of the Tay Nguyen province (Kon Tum & Lam Dong) và the Phu Quoc islvà. Some occurrences are located near the border between Vietphái mạnh and Laos. Almost all of the tewktites are cut as cabochons, or carved into lớn cameos.

Pearl

Today, pearls are cultivated mainly at Cat Ba, Ha Long (Quang Ninh province), Nha Trang (Kkhô nóng Hoa province), Con Dao (Vung Tau province) và Phu Quoc (Kien Giang province) (Fig.1). The pearl farms have sầu been developed with the training and the supervision of Japanese experts. Today, the farms operate with only Vietnamese technicians. Four farms. Which are located at Cat Ba và Ha Long, belong lớn the Ha Noi Gem và Gold Corporation. Two farms in Nha Trang, và about six farms in Phu Quoc are joint-stoông chồng companies with a Japanese partners. Trial harvests have sầu produced pearls with thicker nacre & better lustre than that presently available from both Japanese & Chinese akoyas. From 2001, Vietnamese akoyas will be cultured from spat-reared stochồng, with an expected yield of 1000 kan (1 kan = 3.745 kg) by the year 2008. Vietnamese akoyas (Fig.12) range in size from 2 khổng lồ 8 milimet, và are produced in natural golden colour due lớn the good water chất lượng and protected environment in which the pearls are cultivated Blachồng South Sea pearls are now being cultured in Phuc Quoc. These vary in size from 4 to 8 milimet. In Vietphái nam, 80 per cent of the annual cultured pearl production is exported, with đôi mươi per cent remaining for the domestic markets.

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Figure 12. Removing oysters from their cages and preparing for the operation of nucleus insertion at Ha Long Bay, northern Vietphái mạnh.

Other gemstones

Quartz is one of the most abundant và widely distributed minerals in Vietnam giới. Varieties include rock crystal, amethyst, and rose quartz. Rochồng crystals and smoky quartz are found in pegmatite at Xuan Le (Tkhô giòn Hoa), Ky Son (Nghe An), Thach Khoan (Vinch Phu). Amethyst with an attractive sầu purple colour, and high transparency, is found in Don Duong (Lang Son province) and Chu Boc (Gia Lai province) . Rose quartz has been found in Da Nang, morion in Loc Tan (Lam Dong).

Jadeite và nephrite were found in Co Phuong (Son La province). It has a greenish colour và is only used for the carving of fine-art products. Agate has been found in Loc Ninch (Tay Ninh province) and is used for necklaces. Fluorite is distributed widely in Dong Pao (Lai Chau province) và Xuan Lanh (Phu Yen province) Greenish amazonite is found in syenitic pegmatites in An Phu (Luc Yen district) & in Thach Khoan (Vinc Phu province). However, the amazonite only occurs in opaque crystals that are used only for carving.

Conclusion

Up to now, the main economic deposits và occurrences of gemstones in Vietnam giới are ruby, sapphire, aquamarine & topaz. These gemstones are distributed in different metallogenetic provinces in northern Vietnam giới as ruby in the marbles from the Day Nui Con Voi metamorphic belt-Red River Fault Zone, topaz và aquamarine from the pegmatites related khổng lồ acid magmatism in the Tkhô nóng Hoa and Vinc Phuc provinces. In southern Vietphái mạnh, potential economic deposits of xanh sapphire, zircon và peridot are present in the Cenozoic basaltic igneous province. In these areas, additional new gem occurrences have sầu been found, but detailed exploration has not yet been carried out. Deposits of other minerals such as spinel, tourmaline, quartz crystals are widely distributed in the country và have sầu an important role for Vietphái mạnh gemstones industry. New discoveries of gemstones occurrences in various region of Vietphái nam suggest that in the future exploration will reveal additional deposits of economical significance.

Acknowledgements

The authors wish khổng lồ thank their many colleagues of Vietnam giới National Gem and Gold Corporation for their information on gem deposits. Mr. Hoang Quang Vinch & Bui Duc Toan from Institute of Geology are thanked for their field investigations.

Address for correspondence

Pđam mê Van Long91 Dinh Tien HoangHanoiVietphái mạnh e-mail: vggcfpt.vn

References

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