The important gem mines are adjacent to Kolan range.
The rocks are ruby-titanite-diopside marble, graphite-phlogopite marble, diopside marble and others. Rubies
are recovered from brecciated zone situated at the fracture between whitish-yellowish marble and diopside marble bands. Rubies are also recovered from gem-bearing lenticular-shaped marble bands, 10 cm to over 2 meters thick, bluish-white with medium to coarse-grained texture. Associated minerals are scapolite
are found in the spinel-bearing marble. Rubies or spinels have not been found in the phlogopite-bearing marble bands.
Gem mining is performed in typical gwè-dwin
scheme. Numerous lebin
s are also in operation, where ruby
are recovered from the alluvium.
Ref: Ted Themelis (2008) Gems and Mines of Mogok, p. 232