Underground production at AngloGold Ashanti’s Mponeng mine in South Africa will remain closed until further notice after 53 employees tested positive for the coronavirus, a provincial health department said in a statement on Sunday.

The mine, the deepest in the world, restarted operations on April 22 after closing entirely during a nationwide lockdown, and was operating at 50% capacity.

The department of health in Gauteng, the province where the mine is located, said in statement posted on Twitter that 53 employees at the mine had so far tested positive for the virus, and that a further 104 tests were still being processed.

“The management of the mine has indicated that the underground production will remain closed until further notice,” the statement said.

The company did not immediately respond to an email requesting comment outside of business hours.

Miners were permitted to return to 50% production capacity when the country’s lockdown, still one of the world’s most restrictive, was eased in April.

Mponeng accounted for around 7.4% of the company’s total gold production in 2019.

But some workers, especially those employed at deep mines, have raised concerns about returning to work in an environment where social distancing is difficult.

Earlier in May a labor union won a court case forcing the government to impose strict guidelines on miners to protect workers.

COVID-19 Pandemic | SA provincial statistics