At present, there are more than 65,438+0,000 spinel occurrences found in the world, which are produced in five continents, but the origin of gem-grade spinel is quite rare (Figure 6-25).

Figure 6-25 Distribution Map of Main Spinel Producing Areas in the World

The main spinel producing areas in the world are Myanmar, Vietnam, Tajikistan, Tanzania, Sri Lanka, Thailand, Pakistan, Afghanistan, Australia, Kenya, Brazil and the United States. Among them, the red spinel and blue spinel in Myanmar, Sri Lanka and Thailand are the most famous; Afghanistan produces red spinel with large particles; Black spinel mainly comes from Thailand; Light-colored spinel is also produced near Mount Hansa in northern Pakistan, Irakaka in Madagascar and Tonduru in Tanzania. The best red, pink and orange spinels are produced in the ancient pastoral areas of Myanmar, and the best blue and purple spinels are produced in Sri Lanka and Vietnam. Most of the ancient spinels in China came from neighboring countries. In the past 30 years, some spinel occurrences have been discovered in Yunnan and Xinjiang.

(2) Output and output of main spinel deposits

Gemstone-grade spinel is mainly produced in alluvial placers, and is usually found while looking for rubies and sapphires (Figure 6-26). The discovered gem-grade spinel deposits are mainly distributed in Myanmar, Vietnam, Sri Lanka, Tajikistan in Asia and Tanzania in Africa. The geographical distribution of Asian spinel deposits is mainly located in the Himalayan metallogenic belt in eastern and central Asia. The formation of mineralized zone is mainly influenced by tectonic activities during Cenozoic Indian Ocean collision.

Figure 6-26 Distribution Map of Main Spinel Mining Areas in Southeast Asia

1. Myanmar (Southeast Asian countries)

Myanmar is the most famous producing area of spinel, especially red spinel was exported to China in ancient times, among which high-quality spinel can be compared with high-quality ruby. Spinel deposits in Myanmar are mainly distributed in Mogok and Myitkyina (Figure 6-27). Ancient animal husbandry is the most important spinel producing area in the world in the 20th century. Most of the spinels produced by threshing can reach the gem level, with rich tones and good color saturation, from deep red to orange or purple, from light powder to deep powder. Since 2003, the United States began to ban the import of Burmese gems, and the Gumu mining area was closed by the military, resulting in a sharp drop in the number of Burmese spinel in the international gem market. At present, it is difficult to obtain information about gem mining in Myanmar. However, although red spinel is also found in other producing areas, Gumu is still the best producing area of pure red spinel with small and medium particles. Myanmar spinel has an irreplaceable position in the market of pink, red and purple spinel because of its unique color saturation and hue.

There are also two deposits in Myitkyina, Kachin State, namely South Asia Color (also known as Nahmias) and Youwadi deposit. The output of spinel in Nahmias is relatively unstable. There was only a small amount of local production in the 1990s, and the output increased sharply since 2000. After 2005, mining activities decreased significantly. Spinel crystals produced in Nahmias are mostly irregular. Besides red, pink, purple and orange, they also produce blue, purple and purple spinels, and the local spinels also have 10ct. The spinel of Yuwadi deposit is mainly produced in alluvial deposits, with light pink, purple, orange and various red tones.

Figure 6-27 Geographical Distribution of Main Spinel Mining Areas in Myanmar

2. Vietnam

In the international spinel market, Vietnam has always been a stable supplier of pink and purple spinel. Spinel deposits in Vietnam are mainly distributed in Luyan area of northern Anpei province. Lu 'an County has now become a major spinel mining and trade center (Figure -268). Lu 'an not only produces a large number of pink spinel (Figure 6-29), but also produces bright purple spinel. The local red spinel is also quite famous, but the output is scarce, and cobalt blue spinel can be found occasionally.

Cong Troi is a spinel ore, which is the most economically valuable deposit in Vietnam. The spinel crystals produced by the deposit are perfect in shape and rich in color, including brownish purple to purple, pink and padparadscha spinel. Other deposits with economic value include Berlin Coal Mine located in the north of Lu 'an 10km, which produces orange-red spinel. Tan Huong mineral, about 80 kilometers away from Lu 'an, produces powder to deep purple spinel; Mingtian mine, thousands of meters north of Lu 'an, produces powder to purple spinel; Trum Chan is 0/0 km away from Lu 'an/Kloc-and produces a variety of light to medium blue spinels. In recent years, some new mineral deposits have been discovered one after another. 20 10 balrog, Anpei Province produces a large number of cobalt blue spinel. Spinel crystals have large particles, but poor transparency. In the same year, a new deposit was discovered in Langchapu, 20 kilometers southwest of Lu 'an. The spinel produced by Longchamp is dark purple, with a particle length and width of about 3cm, and some high-quality red-pink to pink-orange spinels. The most striking thing is that the deposit produces a large number of orange-red (similar to Padma) spinel. The output of various mining areas in Vietnam varies. 20 1 1 Since autumn, the output of Anpei spinel is about 200kg/ month.

Figure 6-28 Vietnam Lu 'an Spinel Market

Figure 6-29 Liu 'an Spinel, Vietnam

3. Tanzania

In 1980s, spinel was first discovered in marble near Matombo and Mahenge in Morogoro province of Tanzania, and then some spinel occurrences were discovered in Songea and uTnduru. In 2000, high-quality spinel crystals were found in white marble dikes in Ipanco area near Mahenge. Since Ipanco discovered spinel, the output has been increasing. At present, Tanzania has become the second largest producer of pink to red spinel series. Spinels produced in Mahenger area are mostly pink with good transparency (Figure 6-30). In 2007, several giant spinel crystals weighing 6~54gk were found in Ipanco area. These giant spinel crystals are opaque in the center and transparent in the periphery, which can reach the gem level. Several high-quality red-pink spinels were cut from the transparent parts of these giant crystals, and the transparency was as high as 10~50ct. In 2004, faceted gemstones and rough stones weighing 1kg produced by new mining areas in this area were exhibited in Toussaint Jewelry Fair, with rich colors, among which pink orange spinel (Padma) was the most popular.

Figure 6-30 Tanzanian Mahenge Spinel

4. Tajikistan

For centuries, the Kuh-i-Lal mine in Tajikistan has been the main producer of large spinel in the world. It is said that this mine has been mined since the 7th century, and many famous large spinels such as "black prince Ruby" and "Timur Ruby" may come from this mine. The spinel produced by this mine has large particles and high purity, and the color is mainly pink and pink, and sometimes red spinel with large particles is produced.

1989 reported that pink spinel was found in Pamirs Mountain, which is located in the northern uplift of Karakorum Mountain in Pamirs Mountain in Central Asia, with an altitude of more than 3048m m. Due to the harsh local mining conditions, the output of spinel is stable but limited. Most of the spinels produced are light to dark pink, and only a small number of flawless spinels with a general weight above 15ct will be cut into facets.

(III) Genesis and types of ore deposits

Spinel is usually associated with corundum gems, and gem-grade spinel deposits can be divided into primary ore and secondary ore according to their occurrence. Geologically, primary deposits can be divided into metamorphic rock type and magmatic rock type. Metamorphic deposits are mainly formed in the contact metamorphic zone formed by magmatic intrusion into limestone or dolomite, and spinel often coexists with forsterite and diopside. Magmatic deposit spinel is mainly produced in aluminum-rich basic magmatic rocks, and often coexists with pyroxene, olivine, magnetite, chromite and platinum group minerals. Spinel primary deposits can be divided into four types:

(1) regional metamorphic and contact metamorphic marble spinel deposit: spinel is often associated with ruby, and its parent rock is mainly carbonate metamorphic rocks, and the main components of these carbonate metamorphic rocks are calcite, dolomite, mica, perlite, amphibole, chlorite, forsterite and sphene. Carbonate metamorphic rocks are generally accompanied by the intrusion of garnet-biotite-sillimanite or biotite-kyanite schist or gneiss.

(2) Magnesium skarn spinel deposit: spinel is often associated with ruby.

(3) Alkaline pegmatite spinel deposit: spinel often coexists with sapphire.

(4) Granite pegmatite spinel deposit: mainly produces dark green and green zinc spinel.

Fig. 6-3 1 spinel rough stone from placer

Besides primary ore, secondary ore is an important source of gem-grade spinel. Spinels in secondary ores are often associated with rubies and sapphires (Figure 6-3 1).

(4) Geological characteristics of main spinel deposits.

1. Myanmar (Southeast Asian countries)

The spinel producing areas in Myanmar are mainly located in the "Gumu Gem Belt" (MMB) in mandalay province. All kinds of colored gems's particle-wrapped gem belts are famous for their high-temperature deformation in geological structures. Plastic deformation is related to the oblique collision of Eurasian plate in India, and the formation time is about Oligocene to post-Miocene. The geological structure of Gumu gem belt is complex, with many faults and great lithologic changes. In the marble stratum where rubies and spinels are produced (Figure 6-32), other biogenic minerals include muscovite, phlogopite, andalusite, nacrite, sphene, pyrite and graphite. The marble unit consists of discontinuous strata with a thickness of 300 meters. The ore bodies containing ruby and spinel are layered. The secondary spinel deposits in Gu Mo area mainly occur in the so-called "gem-bearing gravel layer". The gravel layer contains brown and yellow clay, iron oxide minerals and some sand. Spinel can be found in all corundum primary and secondary minerals.

Figure 6-32 Appearance of Marble Spinel Deposit in Gu Mo Mining Area, Myanmar

Another major mining area in Myanmar is located in Yuwadi, Kachin State. The main rocks in this mining area are white-gray marble, schist and intrusive time pulse. Spinel is produced in marble, and its associated minerals are sapphire, zircon, tourmaline, garnet, yingshi, phlogopite, muscovite, andalusite, perlite, sphene, pyrite and graphite. The spinel in the primary ore in the northern part of Yuwadi Mountain was transported and deposited for a long distance, and a placer was formed in the riverbed of Yuwadi Mountain.

2. Vietnam

1983, corundum and spinel were first discovered in Anpu, Lu 'an District, Anpei Province, Vietnam. During the period of 1987, a large-scale spinel deposit was discovered in KhoanThong area. The main ore occurrences are Nuoc Ngap, Hin Om, Khau Nghien, Vang Sao, May Thuong, May Ha, Phai Chap, Tan Lap and Lam Dong. Subsequently, the gem mining activities in the whole region began to surge. These deposits are located on the east bank of chay River and are called "old mining areas" by local miners. During the period of 1994, many new mines were discovered in the west bank of Zhaihe River, such as Tan Huong, Truklau, Tan Dong, Hoa Cuong, Cam An, Ai Bao, Ngoi Nhau and Ngoi Hop. Local miners call them "new mines" (Figure 6-33). In recent years, many new mineral deposits have been discovered in Vietnam, such as the Langchapu deposit, which is located 20 kilometers southwest of Lu 'an.

The official mining of rubies and spinels in Lu 'an began in the 1990s. Spinel deposits occur in marble units with weak deformation, located in Cenozoic metamorphic belt and South Red River shear zone, and local metamorphism is very beneficial to the formation of gem deposits. Spinel crystal is perfect, mainly octahedron, and sometimes we can see all kinds of octahedron crooked shapes. Rich in color, mainly bright red and purple. Red spinel is mainly formed in calcite-dolomite marble and coexists with calcite, pyrrhotite, phlogopite, sphene, apatite and zircon. The origin of dark blue spinel is still unknown, and some people think that its formation is related to the infiltration of external fluid into marble.

Figure 6-33 Distribution and Geological Map of Main Spinel Deposits in Vietnam

Placer is the main source of gem-grade spinel in Vietnam. Secondary deposits are mainly produced in Castel capsules filled with gravel or alluvial fans in Lu 'an ravine and related riverbeds, and sometimes spinel can be found in rice fields (Figure 6-34). Primitive open-pit mining is still the main mining method. In the secondary deposit (alluvial deposit), the minerals related to spinel are sapphire, garnet, sillimanite and quartz. The most important deposits are Truklau and Tanhuong, and Turklau deposit is located in a canyon extending to the northwest with a distance of 5 kilometers.

Figure 6-34 Spinel can sometimes be found in rice fields in Lu 'an, Vietnam.

3. Tajikistan

The Kuh-i-Lal spinel deposit in Tajikistan is located in Badakh, southwest of Pamir. The genesis of the deposit is related to ultramafic metamorphic rocks widely developed in the Golan rock series in this area. Goran rock series is composed of metamorphic sedimentary rocks, mainly biotite gneiss and migmatite, marble and calc-silicalite, as well as secondary quartzite and amphibole. Ultramagnesian rocks include "albite schist" (talc-kyanite), skarn rich in enstatite and forsterite, and skarn and schist containing sodalite and nepheline. Spinel is usually associated with ruby, but it is an exception in Kuh-i-Lal mining area, which has never produced ruby in history.

4. Tanzania

Tanzanian spinel began to be mined on a large scale in 2 1 century, and mainly produced cherry red spinel. Ipanke (primary marble deposit and nearby placer deposit) is the most important spinel deposit in Tanzania at present (Figure 6-35), which mainly produces pink spinel with high transparency, and its crystals are mostly octahedral, and the size is less than 5cm. The locally produced spinel is very similar to the spinel produced by Kuh-i-Lal in Pamir mountain area of Tajikistan.

5. Sri Lanka

Figure 6-35 Ipanko spinel deposit near Mahenge, Tanzania (giant spinel crystal was discovered here in 2007).

Sri Lanka is the oldest producing area of spinel, and the history of producing spinel here can be traced back to 2000 years ago. Spinel mainly exists in alluvial deposits, and its colors are gray, blue, green and purple. Although Sri Lanka has also produced some pink, red and blue spinel related to cobalt, the color is good, but the quality is different, and high-quality spinel is rarely produced. Most of the crystals are light in color, but sometimes starlight spinel and gray-blue-purple color-changing spinel are found in Sri Lanka.

6. China

The spinel deposit in Yunnan Province, China has been mined since 1990s. The local and famous Luan spinel deposit in Vietnam have similar geological background, which is located at the southeast edge of Ailaoshan-Honghe shear zone. Due to the strong metamorphic reaction caused by magmatism, a very complex mineralization area has been formed in this area, and it is very possible to further search for gem deposits in the appropriate host rocks and surrounding rocks of the Red River shear zone in the border area between China and Vietnam. In addition, various types of spinel deposits have also been discovered in Xinjiang, Henan and Jiangsu.

Table 6-7 lists the main spinel producing areas and their main deposits in the world.

Table 6-7 Distribution Table of Main Spinel Deposits