Deep beneath Mongolia’s South Gobi region, more than a decade of work at Oyu Tolgoi is helping unlock one of the world’s largest known copper resources.

Demand for copper is growing, driven by emerging technologies like AI data centres, renewable energy, battery storage and the electricity networks that connect them. Supply shortages are expected to grow in the years ahead, with some forecasts predicting the world could face a copper supply deficit of around 30% by 2035.

Oyu Tolgoi is projected to become one of the world’s most important new copper sources, at a time when high-quality deposits are becoming harder to find and more complex to develop.

It’s already one of the world’s most significant copper-gold operations, comprising an open pit, a major concentrator and, since early 2023, a vast underground mine.

The combined operation will produce around 500,000 tonnes of copper a year on average from 2028 to 20361 – enough for about 6 million electric vehicles annually.

More than 80% of that value lies underground. And after more than a decade of planning, design, engineering, construction, and engagement with the Government of Mongolia, the underground project is now operational.

1 The 500ktpa copper production target (stated as recoverable metal) for the Oyu Tolgoi underground and open pit mines for the years 2028 to 2036 were previously reported in a release to the Australian Securities Exchange (ASX) dated 11 July 2023 “Investor site visit to Oyu Tolgoi copper mine, Mongolia”. All material assumptions underpinning that production target continue to apply and have not materially changed.

Unlocking Oyu Tolgoi’s underground value
Discovered in 2001, Oyu Tolgoi has become one of the most technologically advanced, water efficient and safe mining complexes anywhere in the world.

The site contains a huge copper and gold resource that extends for at least 12 kilometres beneath the South Gobi Desert. It’s made up of several separate deposits, including the near-surface Oyut deposit in the centre of the mining licence area, the deeper Hugo North and Hugo South deposits, which contain the highest concentrations of copper, and the Heruga deposit to the southwest.

The vast underground Hugo North and South deposits were named after geologist Hugo T. Dummett (1940–2002), a key figure in the exploration and discovery of Oyu Tolgoi's copper–gold resources. Source: Delivering Oyu Tolgoi: Benefits and Challenges / Turquoise Hill Resources

While each deposit is different, together they make up one of the world's largest and most significant copper–gold resources.

Open pit mining at Oyu Tolgoi began in 2011, followed by first copper concentrate production from the concentrator in 2013.

The open pit established Oyu Tolgoi’s operations, but the project’s long-term future has always been underground.

And that underground journey has been our most significant effort to date.

Part of Oyu Tolgoi's secondary crusher, which is as tall as a 7-storey apartment block.

To mine the underground deposit, we’re using block caving, a technically demanding but highly efficient method of mining large, deep deposits of ore.

How the block caving process works.

We began digging shafts for the underground mine in 2005. The scope of work included sinking 5 shafts, building more than 200 kilometres of tunnels and installing a 6.7-kilometre inclined conveyor to the surface – one of the world’s largest underground conveyor systems.

Some parts of the mine reach depths of 1.3 kilometers – the same height as around 4 Eiffel Towers.
In 2009, the investment partners and the Government of Mongolia signed an Investment Agreement, initiating Mongolia’s largest industrial development to date.

Underground development paused in 2013 as the project partners worked through the project financing and related issues needed for the next phase of the project.

In 2015, the project partners agreed the project financing for the project and other commercial issues, clarifying the path forward, and work restarted in mid-2016.

During the construction, difficult ground conditions required changes to mine designs and sequencing, and COVID-19 restrictions in 2020/21 disrupted construction and contributed to shifting timelines. But design modifications and a further project reset in January 2022 helped clear the way for underground mining to begin.

Soon after, the first drawbells were fired at Hugo North, and in March 2023, sustainable underground production began 1.3 kilometres below the surface.

Since then, the underground mine has ramped up quickly.

Placing supports during Oyu Tolgoi's underground project construction.

We developed the orebody in multiple “lifts”, each several hundred metres high, like layers in a tiered cake. Within each lift, the ore is further divided into large sections called “panels” – separate mining zones that can be developed in sequence.

We initially opened around 15 drawbells – large, funnel-shaped voids blasted into the rock – each quarter, completing the first panel, Panel 0, ahead of schedule in 2024 and helping deliver record copper production.

Underground ore now makes up a growing share of concentrator feed and, because underground grades are more than 4 times higher than the open pit, the underground delivered twice the contained copper of the open pit in the first half of 2025 – making Oyu Tolgoi now a predominantly underground mine.

At the same time, developing Panels 1 and 2 continued to support the ramp-up to full underground production. In the first quarter of 2026, underground copper and gold production exceeded our plan by more than 10%, while development at Panel 2 continued ahead of schedule.

The operation also reached key infrastructure milestones, including commissioning the world’s longest conveyor-to-surface system and completing the second primary crusher – which is as tall as a 7-storey apartment block.

The underground ramp-up is strengthening Oyu Tolgoi’s broader contribution to Mongolia. To date, the operation is the largest foreign investment made in Mongolia, with over $17 billion invested in the mine and related assets since 2010.

Today, the mine supports around 17,000 workers, 97.8% of whom are Mongolian, and works with more than 500 national suppliers, with over $14 billion spent with in-country suppliers since 2010. Over that period, Oyu Tolgoi has paid US$6.1 billion in taxes, fees and other payments in Mongolia, including US$628 million in 2025.

As we continue to develop the mine, we’ve planned for staged drawpoint openings to steadily increase the underground operation’s output in the decades to come.

At full capacity, Hugo North Lift 1 is expected to supply ~95,000 tonnes per day, with the open pit contributing a further 20,000 tonnes.2

But maintaining that performance will require constant monitoring and adaptive management as we continue mining underground.

Safety has remained a constant focus throughout development and operations, reflecting the complexity and risks of large-scale underground mining. Block caving depends on disciplined systems, real-time monitoring and experienced teams to safely access deeply buried ore as underground conditions change.

At Oyu Tolgoi, that approach is supported by structured assurance processes, critical control checks, extensive workforce training, and a culture of continuous improvement.

Published Date:2026-08-19