JOHANNESBURG, Nov 28 (Reuters) – Impala Platinum IMPJ.J on Tuesday temporarily halted operations at its Rustenburg mining complex in South Africa after 11 workers died and 75 were injured in what the CEO said was “the darkest day” in the company’s history.

The Johannesburg-based platinum miner said in a statement that 86 workers were involved in the incident at its No. 11 shaft. All the injured had been admitted to four hospitals in the area. The company spokesperson said medical physicians classified 14 workers in the hospital as “high priority”.

“Today is the darkest day in the history of Impala and our hearts are heavy for the lives lost and the individuals affected by this devastating incident,” CEO Nico Muller said in a statement.

Impala said workers were being brought to the surface at the end of their shift on Monday, when the conveyance system, which carries workers up and down an underground shaft 1,000 meters (3,280.84 ft) deep, started a rapid descent.

All mining operations at the Rustenburg complex in South Africa’s North West province were suspended on Tuesday. The halt could be extended to Wednesday to allow the company to “mourn and heal emotionally”, Johan Theron, Impala’s spokesperson said.

He also said investigations into the cause of the accident had begun.

Impala’s shares in Johannesburg declined 6.74% at 0847 GMT.

South Africa has some of the world’s deepest, oldest and most costly platinum and gold mining shafts.

The deaths at Rustenberg add to the 41 fatalities that had been recorded in South Africa’s mining industry this year so far. Last year, 49 workers died in South Africa’s mines, which was the lowest number of fatalities to date, Minerals Council South Africa, the industry lobby group, said.

Spokesman Theron said he could not be precise about the impact of the stoppage on Impala’s metals output.

“It’s impossible to quantify the impact on production save to say (the) shaft on its own is a very large complex and contributes roughly 15% of Impala Rustenburg’s production,” Theron said.

“To the extent that it’s stopped for any length of time, it will have a corresponding impact on the entire company.”

(Reporting by Felix Njini and Nelson Banya; Editing by Kim Coghill, Jamie Freed, Louise Heavens and Barbara Lewis)