* Move raises question of how long deliveries can continue
* Union says no one suspended over the incident
* Union represents 18,000 of the mine's 24,000 workers
JAKARTA, May 30 (Reuters) - Workers at Freeport McMoRan Copper and Gold Inc 's Indonesia mine will not return to open pit mining until all investigations are completed into this month's deadly tunnel collapse, union official Virgo Solossa said on Thursday.
The company said on Wednesday it had resumed some operations at the world's second largest copper mine, in the remote province of Papua, after 28 people were killed just over two weeks ago in one of Indonesia's worst mining disasters.
The union, which represents about 18,000 of the mine's 24,000 workers, agreed at a meeting on Thursday to stick to its previous position that work would not resume until the investigations were complete, Solossa said, noting that they had begun only a few days ago.
"Everyone who is responsible for the safety, and who abused the safety systems, should be sent home while the investigation is underway," Solossa, who is based in Papua, told Reuters by telephone.
Another reason for the boycott was that no one had been suspended over the accident, Solossa added.
The union's refusal to go back raises a question mark over how much longer the Freeport mine can continue deliveries to customers.
Freeport has been drawing on stocks to keep up overseas shipments during the two-week production shutdown. Industry sources say large mining operations typically have three to four weeks of ore stockpiled at port, and around three days on site.
The global copper market has been keeping an eye on the Grasberg closure, which has helped underpin metal prices, but only a prolonged shutdown will hit world supplies, which are still seen in a small surplus this year.
Freeport suspended operations at the Grasberg complex in eastern Indonesia on May 15, a day after a training area in a tunnel, away from the site of its main operations, caved in on 38 workers, killing 28 of them.
The open-pit mine normally produces around 140,000 tonnes of copper ore a day, while underground operations yield 80,000 tonnes.