The gem mines have been operated for centuries.
The principle rocks are ruby-bearing marble, ruby-titanite-diopside marble, pure marble, graphite-phlogopite marble and others. The ruby-bearing marble bands vary in width from 1.5 to 3 meters and are whitish to bluish-white with medium to coarse-grained texture. Rubies
are found in the marble, in the loos (twisted holes), together with sphene
Intensive hard-rock gem mining started around 1974 and by 2000 more than 20 joint ventures were mining with no signs of its depletion.
Ref: Ted Themelis (2008) Gems and Mines of Mogok, p. 228