Mineral Resources Minister Gwede Mantashe has ordered a speedy investigation into the cause of a fire that killed six miners at a copper mine in Phalaborwa, Limpopo.

Mantashe visited the Palabora Mining Company mine where the miners perished after a fire broke out underground when a conveyor belt apparently caught fire on Sunday morning.

"The Department of Mineral Resources is concerned about the deaths that occurred at this mine.

"We have instructed a full investigation into the cause of the incident," Mantashe told mineworkers yesterday.

"We want to know why the conveyor belt caused the fire that killed the miners. We are working with the mine management to find out exactly what happened. A report will be released at a later stage," he said, adding that investigations of this nature typically took a month to conclude.

Mantashe also said a report on the cause of the deaths at another mine, Sibanye-Stillwater gold mine, where seven people were killed two months ago, would be released soon.

He pleaded with miners to remain calm to allow the investigations to unfold.

Mantashe was taken underground at the mine to conduct an inspection-in-loco to see the conditions under which the miners worked.

Provincial organiser of the Association of Mineworkers and Construction Union (Amcu), Moses Mqhayi, said they were happy with Mantashe's intervention.

"As Amcu we still need answers to what happened. We want all line managers at the mine to provide answers because we believe there was negligence, but we don't know who was responsible," said Mqhayi.