Precious metals producer Sibanye was the object of strongly criticism from unions, media and the government after the earthquake at its Driefontein gold mine that killed the miners.
Another miner was killed there last week.
"Seismicity is a feature of mining in the region and deep-level mining layouts and support systems have been designed specifically to cope with seismicity,” said Froneman in a presentation to investors yesterday.
At Sibanye’s Driefontein and Kloof operations west of Johannesburg, Froneman said, from 2013 to the middle of May 2018 there had been an average of 649 seismic events per year measuring between 1 and 2 magnitude on the Richter scale. In 2018 alone there had been 234 to date.
Over the same period there were an average of 84 seismic events per year that were stronger than magnitude 2.
Seismic events at the operations killed one miner in 2015, one in 2017 and now eight in 2018 in the two recent quakes.
“You cannot predict seismic events That kind of technology does not exist,” said Froneman.
The event that killed seven workers last month measured magnitude 2.2 and is being investigated to see what went so horribly wrong.
“Magnitude 2 events are not unusual and these events generally happen on seismically active structures,” said Froneman.
What was unusual in this case was that the quake shook the ground in an area that was not seismically active and the epicentre was only 25m in front of the rock face where the drilling and blasting was taking place.
The 2017 death toll in South Africa’s mines increased to 88, surpassing the 2016 figure of 73.