LIMA, Nov 11 (Reuters) - Peru's top copper and zinc miner, Antamina, said that a partial labor stoppage had not hurt its production, but the union striking for a second straight day on Tuesday said output was likely down by at least 90 percent.
Zinc prices rose on Tuesday in part on concerns the strike would further tighten global supply, but the stoppage appeared not to significantly affect copper prices amid expectations of a surplus next year.
The mine, in the Peruvian highlands region Ancash, produces about 30 percent of Peru's copper and 20 percent of its zinc.
"Our production has not been affected," said Martin Calderon, an Antamina spokesman.
The union SUTRACOMASA, which represents more than half of Antamina's labor force, said production has dropped drastically.
"What we've heard from workers in operations is that at most the mine is producing 10 percent," said Hernan Robles, a SUTRACOMASA spokesman.
Unionized workers dominate areas key to production, including extraction, transportation and shipping, Robles added.
Unionized workers are demanding a bonus to offset shrinking proceeds from a revenue-sharing agreement. Profit at Antamina has been hit this year by falling production and weak global metal prices.
Antamina said the strike would not likely dent 2014 output further.
"Our contingency plan allows us to maintain our productive rhythm estimated for this year," said Calderon, who declined to specify how much Antamina had expected to produce in 2014.
In the first nine months of 2014, Antamina's copper production slipped 16 percent to 273,411 tonnes, while its zinc output fell 20 percent to 194,233 tonnes.
Antamina is owned by BHP Billiton Plc and Glencore Xstrata Plc, which each have 33.75 percent stakes. Teck Resources Ltd holds 22.5 percent and Mitsubishi Corp 10 percent.
Reporting by Mitra Taj; editing by Matthew Lewis