By Nicholas Bariyo

A nationwide power outage late Monday cut off power supplies to Zambia's vast copper and cobalt mines, halting mining operations across the continent's second-leading copper producer for hours, officials said Tuesday.

The Copperbelt Energy Corp., the main supplier of electricity to the country's mines, turned on several thermal plants to meet emergency electricity needs to prevent flooding and maintain ventilation in underground shafts, CEC spokeswoman, Chama Nsabika-Kalima told The Wall Street Journal.

The outage also affected supplies in neighboring Zimbabwe, where the grid and some generation plants are interconnected with Zambia, highlighting the vulnerability of the region's ailing electricity infrastructure. Most electricity facilities in the region have deteriorated after years of inadequate investment and poor maintenance, rendering them prone to breakdowns.

"CEC has an embedded capacity of 80 megawatts of generation, which it uses to power its customers' critical operations in a situation of total grid failure, as was the case," Ms. Nsabika-Kalima said.

The outage cut off electricity from eight of Zambia's ten provinces, including the copper-mining heartlands in northern and northwestern regions, where companies such as Glencore PLC (GLEN..LN), First Quantum Minerals Ltd.(FM.T) and Vedanta Resources PLC operate mines.

The state power utility Zambia Electricity Supply Corp. said the blackout was caused by a system failure which halted generation at Kafue Gorge and Kariba North Bank Power Station. The two plants account for around 75% of Zambia's 2300 MW generation capacity. Copper mines consume more than 60% of Zambia's generated power.

Zesco said that it had stated the partial restoration of supplies early Tuesday and hoped to normalize supplies across the country by the end of the day. In 2013, a nation-wide power failure trapped hundreds of miners working in underground pits at several mines in the country.

The chamber of mines couldn't immediately disclose details of production losses from the outage.

Write to Nicholas Bariyo at nicholas.bariyo@wsj.com

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