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.