Hopes fade for those still trapped in Freeport Indonesia mine JAKARTA (Reuters) - Freeport McMoRan Copper & Gold Inc said on Saturday that rockfalls were hampering rescue efforts after a tunnel collapse four days ago at its giant Indonesian copper mine, with hopes fading of finding alive any of the 23 still missing. Freeport closed the world's second largest copper mine on Wednesday, a day after a tunnel fell in on 38 workers undergoing training. Five are known to have died. Several of the 10 rescued are still in hospital. The Grasberg mine in West Papua is in one of the most remote regions of the Indonesian archipelago. "We continue to carry out these (rescue) efforts non-stop, 24 hours a day as quickly as can be done safely to do everything possible to save lives, but as more time passes the possibility of there being any survivors becomes less likely," Freeport Indonesia's Mine General Manager, Nurhadi Sabirin, who heads the emergency response team, said in a statement. Rockfalls were slowing rescue efforts, he said. The company is using a device to detect vibrations to help find out if any of those trapped are still alive. "This device has detected vibrations that could be consistent with a human heartbeat, but this is not conclusive and could be caused by a number of other vibrations," he said. We have not detected any other potential signs of life in the past 72 hours. The training tunnel is outside the mining area and around 500 meters (yards) from the entrance of the Big Gossan mine. A trade union leader on Friday demanded that Arizona-based Freeport keep the mine closed while it investigated the accident, which he blamed on the company. "All operational activities, including production activities, have to be stopped during the investigation process," union leader Virgo Solossa told Reuters. We think that the accident has been caused by the company's carelessness. This has to be investigated. Freeport Indonesia's President Director, Rozik Soetjipto, said in the statement that once the rescue efforts are finished, the company would launch an investigation with help from international experts and Indonesian energy and mines ministry officials. The statement made no reference to how long operations might be suspended at the mine, which also holds the world's largest gold reserves. The initial impact on supplies is likely to be minimal, as the company keeps large stockpiles at the mine site. That would change if the closure drags on. The accident could also fray already fragile relations with the union, which went on a three-month strike in 2011. On Thursday, the company and union put on hold pay talks that began on May 13. The Grasberg mine has been a frequent source of friction over how its rich resources are shared between locals, the company and Jakarta. Around 50 percent of the mine's copper is shipped to smelters that Freeport either owns or part-owns in Indonesia and the United States, analysts say. Freeport declared a force majeure on some concentrate sales about one month into the 2011 strike, freeing itself from some of its contractual supply obligations. Freeport Indonesia's sales are expected to reach 1.1 billion pounds of copper and 1.2 million ounces of gold in 2013, up 54 percent and 31 percent over 2012, respectively. Reporting by Jonathan Thatcher, Michael Taylor and Yayat Supriatna, Writing by Jonathan Thatcher; Editing by Ron Popeski