(Adds BHP comment.)
By Antonio De la Jara
SANTIAGO, Nov 28 (Reuters) - The workers union at BHP's Spence copper mine in Chile started a strike after layoffs earlier this week, the union leader said on Wednesday, shutting down operations at the northern Chilean deposit.
Union President Ronald Salcedo told Reuters that about 50 workers had been laid off, in addition to eight supervisors, raising safety concerns for the mine's remaining workers and prompting the shutdown.
"None of our people are working, which means the entire operation is shut down at this time," Salcedo told Reuters.
BHP said in a statement that it was "implementing an optimization plan that would affect 57 workers" but did not reply to requests for comment about the walk-off.
The Spence deposit near the Chilean coastal city of Antofagasta is BHP's second largest in Chile, after its sprawling Escondida copper mine, the world's largest.
BHP has said it will spend nearly $2.5 billion to extend the life of the Spence deposit by more than 50 years, creating up to 5,000 jobs and bringing new output online in 2021.
"These layoffs are strange given that costs are under control at the mine and even more so given that the company is pushing the upgrade project, which should mean contracting more workers," Salcedo said.
Spence produced 198,600 tonnes of copper in 2017.
Reporting by Antonio De la Jara Writing by Dave Sherwood Editing by Edmund Blair