While South Africa has suffered electricity shortages for more than a decade, the utility is at a crisis point and is seen as the biggest threat to the economy.
The company said it failed to reach an agreement with a client in a dispute over a mining project in Latin America, prompting it to slash its profit forecast by more than 40% for the year.
The 1,000 km (620 mile) rail line is used by miners including Glencore, MMG Ltd and South 32 to carry zinc and lead concentrate from the Mt Isa region.
Peru's environmental regulator OEFA has concluded that mining waste from the company's Cuajone mine did not spill into a river during heavy rains last week.