For the second time in less than a month workers at Peru's Antamina Mine went on strike in an effort to secure pay bonuses and other benefits.

The strike is already affecting "some" operations at the project, union leader Jorge Juarez told local paper Gestion (in Spanish). However a mine spokesman told Reuters that operations were "normal".

The mine, located in Peru’s central Ancash region, turned out about one-third of Peru’s copper production in 2013, according to government figures. But this year hasn’t been as good: output from Jan. to Sept. this year plummeted 16.2 percent compared to the same time period of 2013, mining.com reported.

Antamina, which also produces a large amount of zinc, lead, and silver, is comprised of various stakeholders. BHP Billiton and Glencore each have 33.75 percent stakes in Antamina, which has a 370 kt/a production capacity. Teck Resources holds a 22.5 percent stake in the mine and Mitsubishi Corporation has10 percent.

Minerals represent 60 percent of Peru's export revenues, but lower production, falling prices and weaker demand from Asia have taken a heavy toll on earnings, dragging the nation's growth rates down from 5.8 percent last year to a forecast of 3.1 percent for 2014, based on figures from Peru’s central bank.