Pyant Gyi mine (Pyan Gyi), Pein-Pyit (Painpyit; Pyan Pyit), Mogok Township, Pyin-Oo-Lwin District, Mandalay Region, Myanmar
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 and letkya-dwin mining methods. Rubies and spinels 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, scapolite and scapolite cat's eye are found in different types of marble. Fine quality red spinels are often found associated with calcite, mica, and scapolite.
Skarn-contact zone: Diopside (colorless or green), scapolite and scapolite cat's eye, fibrolite and fibrolite cat's eye, ruby, sapphire, spinel, andalusite, kornerupine (emerald-green), montebrasite, poudretteite and hackmanite.
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): apatite (blue, blue-green), aquamarine and goshenite, chrysoberyl, danburite, diopside, feldspar (orthoclase, pink orthoclase, moonstone, sanidine), fluorite and color-change fluorite, garnet (almandine and grossular), johachidolite, hackmanite, montebrasite, pargasite, pargasitic hornblende, poudretteite, quartz, ruby, sapphire (blue, greenish-blue, yellow, yellow/blue), scapolite and scapolite cat's eye, spinel, tourmaline (rubellite, schorl, 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.
Most sapphires 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