* Workers lift stoppage at copper mine -Codelco * Radomiro Tomic was shut down over holiday weekend * Codelco had declared force majeure at key mine By Antonio De la Jara SANTIAGO, April 1 Workers at Codelco's Radomiro Tomic copper mine have agreed to lift their labor stoppage and return to work, the Chilean state company told Reuters on Monday morning. "The conflict has ended," a source at the company said. "Operations will start up again today." Workers shut down the Radomiro Tomic open pit mine over the long weekend, demanding the company fire managers they blame for the recent accidental death of a miner. Codelco, the world's No. 1 copper producer, declared force majeure over the weekend. The miner has not had to reprogram copper shipments but was losing a "relevant" amount of production due to the stoppage at the northern Chile mine, which produces about a fourth of Codelco's output, Chief Executive Officer Thomas Keller told reporters on Sunday. Radomiro Tomic's general manager has resigned, Keller also said on Sunday. Nelson Barria died in a March 23 landslide at the Radomiro Tomic mine. Codelco's output tumbled 5.1 percent last year due to dwindling performance at its massive, aging deposits in northern Chile, which dragged down production to its lowest level since 2008. Labor unrest, as well as accidents, extreme weather and dwindling ore grades, have curbed output at many deposits in Chile, the leading copper producer.