Located north-east of Mogok and west from Pyan Pyit.
Geologically, the area consists of igneous rocks (leucogranite, syenite) and metasedimentary rocks (mainly spinel-chondrodite marble). These marbles are tightly folded and often intruded by leucogranite and syenite forming contact zones and skarns. Many faults are observed. The Pyant-gyi area forms a natural basin south of Anyant-taung(Hmyaw-taung)
, adjacent to the primary source of gem quality spinel.
Most gems are recovered from the alluvium in the valley floor. Also, on the hillsides, using loo-dwin
, open-pit, lebin
mining methods. Rubies
are found in different types of marble which are broken apart to recover the gems embedded within.
The area is characterized by a high concentration of chromium, where chromium-rich minerals such as fuchsite
, red spinel
, chromite and other minerals are found. High chromium content is noted in blue sapphires
and in other gems.
Marbles: Mostly spinel
, some ruby
and scapolite cat's eye are found in different types of marble. Fine quality red spinels are often found associated with calcite
, and scapolite
Skarn-contact zone: Diopside
(colorless or green), scapolite
and scapolite cat's eye, fibrolite
and fibrolite cat's eye, ruby
Secondary: Most gems are recovered from the byôn
found in varying thickness (1.5 - 2 meters) in the alluvium, in the loos (loo-dwin
) and in letkya (letkya-dwin
(blue, blue-green), aquamarine
, feldspar (orthoclase
, pink orthoclase
and color-change fluorite
, pargasitic hornblende
(blue, greenish-blue, yellow, yellow/blue), scapolite
and scapolite cat's eye, spinel
, chrome-green elbaite
) and zircon
(yellow and green).
Most gems found at Pyant-Gyi are spinels
. Fewer rubies
are also found. It is reported that the largest ruby in recent years was about 80 carats of faceting grade and good quality.
are dark blue and blue-green with an undesirable blue/green overall appearance. Some of them are ruotinely heat-treated to reduce their green color component and improve their appearance. Fine quality blue sapphires are also found but they are quite rare.
Ref: Ted Themelis (2008) Gems & mines of Mogok, p. 188