Oyu Tolgoi consists of a series of deposits containing copper, gold, and silver. The deposits stretch over 12 kilometres, from the Hugo Dummett North Zone in the north through the adjacent Hugo Dummett South Zone, down to the Oyut Deposit, extending to the Heruga Deposit in the south.

With considerably higher mineral grades than the open pit, underground deposits have always been the key to Oyu Tolgoi’s overall profitability. Over 80 per cent of Oyu Tolgoi’s total value lies deep underground. It is one of the best copper-gold ore bodies in the world.

The Oyu Tolgoi underground project (Underground Project) is a significant development project aiming to access and mine the high-grade orebody at the upper lift of Hugo North. Average copper grades of 1.66 per cent are expected over the mine life.

The depth and fragmented nature of the ore bodies make them well suited both geotechnically and economically to the block caving method of mining – which involves digging below the orebody and collecting falling ore.

Rio Tinto is a global leader in block caving. While the upfront capital cost of block caving is considerable, it delivers much lower operating costs than other underground mining methods.

The Underground Project involves sinking a total of 6.1 kilometres across five shafts and mining 203 kilometres of tunnel at a depth of 1.3 kilometres underground. Other supporting infrastructure includes crushing and materials handling and surface facilities.

General information on Oyu Tolgoi underground development

Key facts about Oyu Tolgoi underground mine:

  • 80 per cent of Oyu Tolgoi’s value lies beneath the surface
  • Mining method: Block caving
  • Operations: The mine will work 365 days a year with two 12-hour shifts.
  • The total conveyor length (13.2 kilometres) is as long as the distance from the Sukhbaatar Square to Tolgoit station.
  • The depth of the deepest shaft is equivalent of 12 Blue Sky Towers
  • Total length of tunnels over the life of Hugo North Lift 1 – 203 kilometres (mostly with a height of 5.5m and a width of 5m)

What is block caving?

The block caving method of mining uses the force of gravity to extract ore from an underground deposit. A series of lateral tunnels are developed under the deposit with an undercut level and extraction level. The ore is undercut creating a void which allows the rock above to fall under its own weight into draw bells.

Loaders on the extraction level then remove the fallen rock from the draw points, allowing more rock to feed into the draw bell and as the void created by the initial undercut propagates up through the deposit.

Learn more about the Oyu Tolgoi Underground Development from this poster.