Zambia, Africa's second-largest copper producer, has introduced a 5% import tax on raw materials which has hobbled the flow of concentrates from mines in neighbouring Democratic Republic of Congo.

"It was not possible to locate appropriate feedstock in Zambia. We are in the process of placing the plant on care and maintenance," ERG Africa said in a statement.

The miner said it was engaged with stakeholders and was exploring other sources of feed in order to resume operations.

The Chambishi Metals refinery has a capacity of 6,800 tonnes per annum of cobalt metal and 55,000 tonnes per annum of copper metal. It is the only plant in Zambia producing cobalt metal, according to the ERG's website.

On Wednesday, the president of the Mineworkers' Union of Zambia on Wednesday told Reuters that ERG planned to cut 229 jobs at the end of January.

(Reporting by Pratima Desai, writing by Zandi Shabalala; editing by David Evans)