By Fergus Jensen

JAKARTA (Reuters) - Freeport McMoRan Copper & Gold Inc's Indonesian unit will restart open-pit mining operations at its remote Papua copper mine soon, a junior minister at the mining ministry said, after a tunnel collapse that killed 28 people.

Deputy Energy and Mineral Resources Minister Susilo Siswo Utomo also said a government probe into the tunnel collapse should end in one or two months.

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.

Several investigations are being conducted into the accident at the Grasberg mine complex, including one by the Energy and Mineral Resources Ministry and one by Freeport Indonesia using international experts.

Susilo told reporters on Monday the open-pit production would restart in the immediate future and there was no reason for it not to resume as the investigation was not being done in the production area.

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.

Some industry analysts say the mine could face a prolonged closure and further strain relations between Freeport and trade unions after a three-month strike there in late 2011.

Freeport Indonesia could not be contacted by telephone on Monday.

On Saturday, as many workers carried out maintenance work, a Freeport spokeswoman said any restarting of operations would depend on the outcome of underground safety inspections being carried out by the energy and mineral resources ministry.

A union official at Freeport Indonesia reiterated that all investigations into the cause of the collapse must be completed before mining resumes at the Grasberg complex, which also holds the world's largest gold reserves.

"The union welcomes the management's decision to resume maintenance activities in Grasberg open-pit mining, but not for production activities," Papua-based union leader Virgo Solossa told Reuters on Monday.

Late last week, Freeport Chief Executive Richard Adkerson said the company was prepared to restart production relatively quickly and had taken the first steps of getting workers back and having training briefings.

(Additional reporting by Yayat Supriatna; Writing by Michael Taylor; Editing by Muralikumar Anantharaman)