China's Bayan Obo mine in the Inner Mongolia autonomous region — already the world's largest known rare earth deposit — may hold significantly greater reserves than the currently reported 100 million tonnes, according to a leading geologist at Peking University. The finding, rooted in new geological evidence, could have sweeping implications for global rare earth supply chains, critical mineral policy, and industries from electric vehicles to aerospace materials.

A deposit shaped by two geological eras

A 2025 study led by Yang Li, a geologist at Peking University, revealed that Bayan Obo was not formed through a single geological event. Instead, it emerged through multiple stages of carbonatite activity — a process involving volcanoes that erupt cool, runny lava composed primarily of carbonate minerals.

'Our most important finding is that Bayan Obo not only contains 1,300 million-year-old igneous carbonatite but also 430 million-year-old carbonatite, and the second phase was key to mineralisation,' Yang said in the study, published in the journal Science Advances. This younger mineralisation event, the research suggests, played a vital role in concentrating rare earth elements at the site.

Why it matters

Bayan Obo has served as the backbone of China's rare earth industry for decades. According to Yang, 'Bayan Obo's rare earth resources have been the dominant source of global rare earth production since the 1990s.' If the deposit's true geological potential is larger than reported, it would further entrench China's already commanding position in the global rare earth supply chain.

Scientists now believe the currently reported reserve figure may not capture the full underground extent of the mineralisation. The multi-stage formation process means deeper or laterally adjacent zones could harbour additional concentrations not yet formally quantified.

The competitive backdrop

The findings arrive at a moment of intense global competition over critical minerals. The United States has been working to revive domestic production at sites such as the Mountain Pass mine in California, while Japan has been exploring deep-sea mining prospects near Minamitorishima Island. Europe, too, has accelerated its Critical Raw Materials Act to reduce dependence on Chinese supply.

Any upward revision to Bayan Obo's reserve estimates would reinforce China's leverage in ongoing geopolitical negotiations over rare earth export controls, which have already rattled global supply chains for electric vehicles, defence electronics, and aerospace materials.

What's next

The research, published in Science Advances, is expected to prompt further geological surveys and potentially a formal reassessment of Bayan Obo's classified reserve figures by Chinese authorities. Analysts and policymakers in competing nations will be watching closely for any official revision, which could shift the calculus of critical mineral diplomacy for years to come.