General Geology and Structural Setting of Myanmar

Myanmar is situated in an area of complex plate tectonic setting. Myanmar has been divided into four main belts geomorphologically and tectonically (Stamp, 1925, Chibber, 1934, Tainsh, 1950, WinSwe, 1980, Maung Thein 1977, 1983 and 2000). Starting the East to these four belts are Eastern Highlands, the Central Lowlands which are sperated into force-arc and back-arc by the Central Volcanic Line, The Western Ranges (Indo-Burma Ranges) and finally the Rakhine Coastal and Offshore Islands and Northern Coastal Plains. In order to portray the tectonic framework of the regions the following names are proposed for these provinces; the Shan-Tenasserim Highland, the Central Cenozoic Belt, the Western Fold Belt, the Arakan Coastal Belt. These belts are mere reflections of the underlying stratigraphy structures in that each contains lithologically and structurally related rock groups.

Pyenglong Ruby Deposited

Drilling

The campaign was focused on defining the breccia zones indicated by surface works such as pitting, trenching, and aditting. Joy 12B and Long Year 24 dirll ridge were used in Pyenglong Project. Ninety five drill holes have been completed in the area. The first was initiated on the 8^th March, 1991. It involved slightly random holes around the open-pit mining area and 30.4 m (100 feet) spaced squar-grid holes along the breccias zone to the northeast. There were total of 95 holes and drill site were 70 sites of which 55 were inclined and 40 were vertical in October, 1995. Total depths are 4295.6 m. All are shallow, the deepest hole is 85 m I apparent thickness, and the shallowest one is only 10.6 m. Among them 43 holes hit the breccias zone or zones varying from 0.18m to 19.8 m in thickness including four holes with ruby in the breccias core.

Breccia Zone

In general, within the Mogok stone track, ruby occurs crystalline limestone, alaskite and pegmatite.

Sapphire occurs in alaskite, pegmatite and syenite. The style of major ruby mineralization at Penglong is totally different from those of the Mogok area because it is all in a breccias zone parallel to regional trend of the rocks. Pyenglong is totally different from Mogok area.

In mining area, major high-angle fault striking NNE-SSW and cross faults running N-S and NW-SE are well preserved at the open-pit mine. The strike of the breccias zone, running 60º along upstream of a small creek, varies from 1.5 m to 3 m and it widens to about 60 m to the northeast. Total length of breccias is ~480 m, forming a dyke-like body and sills and veinlets along fractures cutting through the metamorphic rocks and granites. Individual thickness of gem bearing zone are various from a few cm to 10m but not all breccias are gem-bearing; those with sandy matrix and felsic coloured breccias in particular are barren.

Gem bearing breccia is black, reddish brown and greenish yellow in colour soft clay matrix. Sometimes carbonaceous breccia where the rubies are hosted, no ruby has been fournd in the clasts of the breccias. The comparative of mica in the breccias is a prominent feature in the Penglong ruby mineralization. The most favorable characteristics of the breccia for hosting rubies are the abundance of mica and chalcedonic slabs and greenish yellow colouring of the breccia. When sun-dried the breccia hardened and its colour changes to whitish grey. Another informative feature is the scarcity of ruby in the breccias close to the clacsilicate and alaskite, where there are more spinels and more sapphire than ruby. The clasts of breccias are various metamorphic rocks, biotite granite, vein quartz, vuggy quartz, chalcedonic slabs and very few red chert. Doment clasts are quartzite, less than 2 cm to more than 1 m in length and granite, less than 2 cm to 0.3 m length. The associated minerals in the breccias are mica, talc, graphite, pink and green garnets, black and green tourmalines, limestone, pyrite and black, purple and pink spinels some which are coated with talc. According to the heavy mineral analysis, hematite is very common and zircon, rutile and sphene are also detected in ruby-bearing breccias. Under the microscope, most micas examined ate phlogophite and the others are muscovite and brittle mica called margarite. Some muscovites are green due to chlorization. Serpentine is associated with steartization structures and iron oxide is formed as the common opaque mineral. Two kind of titanium minerals, rutile and anatase, are also detected. The combination of very high relief, low to moderate birefringence, and the occurrence of twin lamellae are red coloured with rutile and zircon inclusions. The noticeable feature is the coating of ruby by serpentine, talc and margarite.

Origin of the ruby in the Pyenglong

The origin of the Mogok ruby has two alternative ideas 1. Contact metamorphism and 2. Regional metamorphism. In the Mogok area rubies are set in the marbles which from bands and lenses interbedded with gneisses. But at Pyenglong open-pit mining area, rubies are found only in breccias associated with country rock fragments, pegmatitic material some minerals mentioned above. The abundance of ruby is correlated with phlogopite mica, flattened cherty slabs and porous, low density, non clceraceous white coloured rock fragments which seem to be decalcified marble and it may be the original host rock of the rubies. This idea is supported by the presence of ruby bearing coarse-grained white marble exposed at the head of a small creek at about 250 meters lower level and 1 km to south of main pit.

Production

There were underground mining at first. Later, there was open pit mining. December, 1989 to end of March 1996, that mine produced 48,231 tons of ore, were mined out, yielding 540,550 carats of rubies including 80,997.06 carats of gem qualities.

Produce From; A New Rubby Deposite in Myanmar, its Exploration and Mining (Nyunt Htay, 19 Jun, 2010).

Pyenglong Ruby Deposited

Location and access

Pyenglong ruby deposit is near Pyenglong village in south-west of Namkhan Township, Northern Shan State. It is rather ruby mine in Myanmar. It is located at 880 meter above sea level, 23º 19’ 46” N and 97º 20’ 51” E. Pyenglong can be reached on foot Namkhan to Mong Wi village (about 26 miles), and Mong Wi village to Pyenglong area (about 25miles)(1995).

Exploration activities and initial mining

The first state started from September 1989, DGSE and MGE investigated Pyenglong area about 20 days in the Pyenglong area in the Shwe Li area. The geologists made quickly geological reconnaissance traverses prospecting for gem, particularly for ruby, in the Pyenglong area. After Sluicing of nearly 17.5 ton of soil 68.7 carats of ruby were collected at the head of small creek near Penglong village. The second state of geological survey exploration was form December 1989 to April 1990 with DGSE field party and a primary resource of ruby was discovered (93 E/6 O-188400). At the first, the ore was mined by underground mining method. On the July 1992, open-pit mining was started and built a small dressing plant close to the open pit mine. Its capacity was 50 tons per day of mine ore.

Regional Geology

Underline by metamorphic rock of Mogok Series, intruded by alaskite rocks, granite and syenite with major pegmatite and hornblende. Traditionally it was believed that the Mogok series or group was of the Archean age (La touch 1913 and Krishman, 1986). However, Searle and Ba than Haq (1964) believed that the Mogok metamorphic rocks comprising sedimentary, igneous and metamorphic rocks probably is ranging in age from Archean through Paleozoic and Mesozoic age. They also pointed out that the belt extends from Thabeikkyin-Twinnge area, west of Mogok, southward, fringing the west margin of the Eastern Highlands, up to the Golf of Mottama to the south, and from Thabeikkyin-Twinnge area, on the northwestern edge of the Shan Plateau. The belt bends northeast-ward and continue to the northeast up to Sino-Myanmar border and into the East Himalyan Syntaxis region. The belt was intruded by post orogenic granitoids, like the undeformed Kabaing granite which on dating by K/Ar method on biotite mica yielded Miocene (15Ma) age. Searle and Ba Than Haq (1964) also called the belt the Mogok belt. Maung Thein and Soe Win (1969) based on relic fossil evidence they discovered in the marbles of Kyaukse area, believed that Mogok belt includes metamorphosed Permo-Triassic limestone and overlying Jurassic strata of Shan Plateau. Myint Lwin Thein et al (1988) regarded the gneisses and marbles of Thabeikkyin- Mogok area to be metamorphosed correlatives of the Ordovician and Silurian strata of the Shan Pleteau Recent radiometric age determination by Ar/Ar step heating method, however, indicates that metamorphism of the Mogok rocks was of Oligocene to early Miocene age (Bertrand at al., 1999). However, a preliminary SHRIMP U-Pb in zircon dating of Mogok belt by Berley et al., (2003) confirmed a complex magmatic and metamorphic history ranging from Jurassic to Miocene. They reported the occurrence of Jurassic (~170Ma) zircons that have partely recrystallized during ~43 Ma (Eocene) high-grade metamorphism, and also ages between 35 and 23 Ma from syntectonic hornblende syenites and lucogranites. They also recognized its tectonic position comparable to Lahsa and Karakoram terranes of Tibet and Pakistan. Searle et al., (2007) futher constrained the tectonic evolution of the Mogok belt by U-Th-Pb dating of metamorphic and magmatic rocks which revealed the existence of two Tertiary metamorphic events, one in Paleocene(~59 Ma) and the other in late Eocene to Oligocene (from 37, possibly 47 to 29 Ma), thus excluding Archean rocks form them.

Local Geology

1. Sugary textured, white to light grey coloured quartzite partly with graphite, pyrite, some green stuff inter-bedded with schist and gneiss.

2. Very coarse to granulose textured marble containing accessory mineral including spinal, diopside, pholgophite, graphite and few pink ruby particularly in white marble, south of Pyenglong.

3. Green to grey coloured, bedded to foliated calc-silicate rocks with diopside.

4. Fine grained, well foliated, biotite-garnet gneiss inter-bedded with sillimanite-garnet-graphite schist.

5. quartzo-feldspathic gneiss and garnet-biotite augen gneiss.

Common intrusive rocks in the area are coarse-grained alaskitic rock composed of quartz and feldspar, and medium grained biotite granite so called Kabaing granit, the age of which is Late Miocene or early Pliocene (Searle and Ba than Hqa, 1964) or mid Miocene (Bertrand et al., 1999) which strike parallel to the foliation trend of the metamorphic rocks, running NE-SW direction. The granites are cut by parallel and oblique faults.

The occurrence of tin-Tungsten mineral deposits

In Myanmar, the occurrence of tin-Tungsten mineral deposits can be traced along the length in the eastern half of the country form south to north. In Kayah State, a world famous huge deposit of tin-tungsten mineral occurs at Mawchi. The distribution of of the deposits are spread out around Mawchi. Closely packed occurrence of tin-tungsten mineral deposits are found on the both side of the Shan-Yamethin boundary in the hilly region where granite intrusive occur among the sediments.

Veins quartz, grasin and pegmatite containing minerals of tin and tungsten occurs along the length of Myanmar from south to north. In all these areas, the occurrences of these mineral veins are closely associated with the intrusions of coarse grained biotite granite which constitute apportion Ranges in the Indo-Malayan mountain system. The granite bosses are distributed in the eastern half of Myanmar starting from Kawthaung the southern most extremity, wide-spreading abundantly in Mergui and Tavoy districts, Mokpalin, Yamethin and Kyaukse districts. To the East the occurrence is traced in Kayah State and western part of Shan State adjunct to Pyinmana Township. The mineralization of Tin and Tungsten are found in or around the intrusions.  These minerals occur in veins of quartz, greisens and pegmatite that traverse the granite bodies and the adjoining sedimentary rocks. Sometimes the constitute accessory minerals of some portion of granite. The denudation of these primary deposits produces eluvial deposits near the sources and alluvial deposits at distance places from the sources.

1. Primary Deposits

                a. Quartz veins and stringers traversing the granite and sedimentaries.

                b. Decompossed pegmatites containing muscovite and tourmaline and

                c. as a sergregation in greisens.

2. Secondary Deposits

                d. Elluvial deposits on the slopes of hills near the primary deposits

                e. Stream deposits and alluvial flats

                f. Deposits along the lower courses of the river.

Greisen bands are found are formed at the contact of quartz vein and the granite. The mineral constituents of the veins are cassiterite, wolframite, and other sulphide minerals such as pyrites, chalcopyrite, arsenopyrite, molybdenite, stibnite and galenite. Generally, more mineralization is found in thinner veins, sometimes, huge quartz veins and pegmatite veins are practically barren. The portion of tin and wolfram varies with the locality. But generally, the content tin decreases and that of wolfram increases with the approach to the north.

 

The Mawchi Mine

 The Mawchi mine is located at Latitude 18º 49’ 24.8”N and Longitude 97º 9’ 22.1”E in the Balhke Destrict, Hparsaung Township, Kayah State, Myanmar. It is situated 95 miles from south of Loikaw in Kayah State, at elevation of 3000 feet. The mine is round about 19 miles from Hparsaung and is situated in the Hilly region. It lies on one inch topographic map sheet of 94 F/1. The existence of the occurrence is known since the last 100 years. Several technologist had estimated the reserves from 500,000 to 700,000 tons of ore with an average content of 1 to 2% tin and wolfram.

A coarse-grained biotite granite had intruded the sedimentary rocks which were metamorphosed and termed as Mawchi series. There are the argillites, sandstone and limestone. The intrusion of granite causes the tourmalinisation of granite itself the formation of quartz veins carrying wolfram and tin and tourmalinisation of adjoining country rocks. About 70 quartz veins containing ore minerals are known to occur in the area striking from north to south and dipping vertical. These veins ate from a few inches to 8.37 feet wide and occur both in granite and the adjoining sedimentaries.  Through, G.V Hobson assumed that the Mawchi limestone is a limit of the northern extension of the veins, U Kyaw Nyein has reported the northern continuation of these veins beyond the limestone in 1963. He also traced the considerable occurrence of alluvial cassiterite along the down stream of Kempyu village.

Mining is tributie system and underground methods. The average annual production in the post war ranges to about 30 tons concentrate of 60% tin. The mineralization could possibly occur at Sawalo and Khodogale on the north and Parsalo, Mosaki and Sawkokedo on the south. The property is being operated by by Mineral Development Corporation since January, 1963. At present, the mine production was continued by M.E.H.Company, Myanmar.

Produce From: Review of Tin and Tungsten  deposits of Myanmar. (U Tin Aye and U Kyaw Nyein