And now authorities in Kyrgyzstan say it's under their full control.
The Kumtor mine was the largest foreign investment project in the country.
Until last month it was operated by Canada's Centerra Gold.
But Kyrgyz lawmakers passed a law letting the government take control.
That follows alleged environmental and safety problems.
Conducting a media tour of the facility, the charges were summed up by the head of the country's environment and climate committee, Dinara Kutmanova.
Over a billlion tonnes of waste has been dumped, she says.
But Centerra President and Chief Executive Scott Perry says the company has never been asked to change its practices.
He says the environmental allegations are just a pretext:
"It really appears to be a concerted effort to falsely justify a nationalization of the mine. That's really concerning, I think it's sad. The leadership of Kyrgyz Republic repeatedly refused to engage with Centerra and ourselves despite many, many attempts."
Centerra has a long history of disputes with Kyrgyzstan over how to share profits from the country's biggest industrial enterprise.
Now the seizure comes after nationalist politician Sadyr Japarov won a landslide presidential election victory in January.
He has long supported nationalisation.
Officials say the mine is working as normal, and will stick to existing production targets.
Centerra has begun bankruptcy proceedings for its Kyrgyz units.
It says the legal action will prevent the government from trying to strip assets from the operations.
