Htin-shu-taung (Oak Hill) area is characterized by its karst topography and it is located north of Zalat-taung. Gem mining (1.637 meters above sea level) is carried out in letkya-dwin
mining schemes. In the past, the Htin-shu-taung area was referred to as "Old Sapphire Mines", mentioned in the 1890s maps produced by Burma Ruby Mines Co. Ltd.
At Htin-shu-taung, mostly dark blue sapphires, and some low-to-medium quality rubies are recovered. These gems are usually fashioned as cabochons and weigh up to five carats, larger sizes are rare. Spinel and schorl are also found in the alluvium. In mid-2005, a peridot pocket was discovered in the peridot/dunite rocks at Htin-shu-taung, where fine quality and large size peridot crystals are mined.
Ref: Ted Themelis (2008) Gems & mines of Mogok, p. 181