DRC is the world's third-largest copper producer and its top producer of cobalt, a key component in batteries for electric vehicles and mobile phones.
Mineral shipments from a Congolese copper and cobalt operation majority-owned by China's Zijin Mining Group Co Ltd were returned due to overly high radiation levels, the Congolese Mines minister said in a letter seen by Reuters on Monday.
The letter, dated April 12, informed the COMMUS project in which Zijin owns a 72 percent stake that the ministry had suspended its licence while it investigated the issue.
"I am informed of the return of your shipments that exported ... mineral products to South Africa on the grounds that their radioactivity content exceeds the regulatory threshold," Mines Minister Antoinette N'Samba Kalambayi said in the letter.
Zijin did not immediately respond to emailed questions. It was not possible to reach COMMUS for comment. The letter did not make clear what was in the shipments.
COMMUS, based near Democratic Republic of Congo's southern city of Kolwezi, produced 129,000 tonnes of copper and about 2,200 tons of cobalt in 2023, ministry data shows.
A separate internal directive by the ministry, seen by Reuters, outlined what steps its investigation would take. These include verifying COMMUS' compliance with export procedures and assessing what risks the presence of radioactive materials might have posed to the export chain.
Congo is the world's third-largest copper producer and its top producer of cobalt, a key component in batteries for electric vehicles and mobile phones.