It takes a lot of power to extract traces of gold from the 60,000 tons of sludge DRDGOLD Ltd. DRD -4.05 % sends through its machinery here each day. That is something that the Johannesburg-based company hasn’t been able to count on recently. “It’s a worrying thing that you’ve got to watch all the time,” said Niël Pretorius, DRDGOLD’s chief executive. South Africa used to be one of the few countries on the continent where most people had reliable access to electricity. But a lack of maintenance and investment has pushed state-run power provider Eskom Holdings Ltd. into a daily crisis as it struggles to meet demand. Blackouts are threatening to drive Africa’s second-largest economy off a cliff, […]