The mining area at Kolan (Nine Arm's Length) has been known since the last centuries for its caves and loos (twisted holes). The gem deposit is divided into Upper and Lower Kolan. The principle rocks are ruby-bearing marble, ruby-titanite-diopside marble and others. It is a typical primary deposit where rubies
of all qualities and sizes are found in different types of marble. Fewer sapphires
and other gems are found as detritus on the loos. Systematic gem mining operations started in 1996.
Ref: Ted Themelis (2008) Gems and Mines of Mogok, p. 230