Freeport McMoRan Copper & Gold Inc's Indonesian unit will restart open-pit mining operations at its Papua copper mine soon, Deputy Energy and Mineral Resources Minister Susilo Siswo Utomo said on Monday, after a tunnel collapse that killed 28 people.

Arizona-based Freeport suspended operations at the world's No. 2 copper mine on May 15, a day after the training tunnel, away from its main operations, fell in on 38 workers.

The Grasberg mine normally produces around 220,000 tonnes of concentrated ore a day, with around 140,000 tonnes coming from open pit mining and 80,000 tonnes from underground operations.

On Saturday, a union official said between 35 and 40 percent of workers at Freeport Indonesia had returned to work to carry out maintenance work.

(Reporting by Fergus Jensen; Writing by Michael Taylor; Editing by Muralikumar Anantharaman)