Operations in the world’s deepest gold mine in South Africa were halted after 164 cases of coronavirus were detected.
The Mponeng mine, like all the others in the country, resumed operations last month after being closed in March as part of a national foreclosure.
It was operating at 50% of its capacity, but some workers reportedly expressed concerns about their safety.
Most people who tested positive had no symptoms.
They were all placed in isolation, according to the mine owners, AngloGold Ashanti.
The company said 650 workers were tested after a first case was detected last week.
South Africa has the highest number of coronavirus cases in Africa – 21,343. It has recorded 407 deaths – less than Egypt and Algeria.
How deep is the mine?
The Mponeng mine, about 75 km (50 miles) southwest of Johannesburg, extends up to 4 km below the surface of the Earth.
Electronic tracking is used when minors are missing, and this system has been “useful for quickly locating primary or close contacts” of those who tested positive, said the owners.
Operations at the mine were “temporarily halted” to complete the tracing of contacts and “to disinfect the workplace,” AngloGold Ashanti said in a statement.
BBC World Service Africa editor Will Ross said the epidemic, which follows another in a platinum mine, will be of concern to the South African government as well as businesses.
The mines in South Africa, where people often work in the immediate vicinity and deep underground, have often been the epicenters of other communicable diseases such as tuberculosis and HIV.
Despite years of relative decline, South Africa remains one of the world’s largest producers of gold and the sector is a vital part of the national economy.