(Updates with one-week timeline on rescue, new quotes)

By James Nelson

HUNTINGTON, Utah, Aug 7 (Reuters) - Six miners remained trapped deep in a collapsed mine in Utah late on Tuesday as frustrated rescuers said it could take up to a week to reach the men -- if they are still alive -- and even longer to get them out.

No contact has been made with the miners, stranded 1,500 feet (475 metres) below the surface, in the 36 hours since the Crandall Canyon Mine caved in on Monday -- though officials say the six men could survive for weeks in an underground chamber.

A bitter dispute erupted over the cause of the accident, with the mine's owner insisting an earthquake was responsible after geologists had said seismic activity detected at the same time was probably caused by the cave-in itself.

Rescue crews were forced to retreat from what was seen as the fastest way to reach the miners, using an abandoned mine shaft, after falling rock made it too dangerous, and had moved only some 310 feet (100 metres) closer since the cave-in.

Early in the day, Bob Murray, president and chief executive of Murray Energy Corp, said it could take three days to reach the men. But he extended the timeline to one week after scant progress on Tuesday.

"There is absolutely no way that through our underground rescue effort we can reach the vicinity of the trapped miners for at least one week at the earliest," Murray told reporters at nightfall. "We are back to square one, back to the same area we were yesterday."

But rescue work outside the mine continued around the clock and could reach the miners in 48 hours if successful, he said.

Some 135 rescuers and mine employees used equipment placed on the side of the mountain by helicopter to drill directly downward toward the trapped men, hoping to at least provide them ventilation and water.

Bulldozers were clearing a path to bring in sonar equipment that could establish communication with the trapped men, said Al Davis, a spokesman for the Mine Safety and Health Administration.

EXPERTS DOUBT EARTHQUAKE THEORY

Harley Benz, scientist in charge of the National Earthquake Information Center in Golden, Colorado, said that a conclusion over whether there was an earthquake at the central Utah vicinity of the mine was still several days and possibly weeks away.

"To date our analysis of the seismic data really suggests that what we observed was a mine collapse," said Benz.

The mine is located some 140 miles (225 km) south of Salt Lake City in a rugged, high desert plateau dotted with towering rock formations that is known for its mining industry and has seen its share of tragedy.

For some, Monday's incident brought back memories of the 1984 Wilberg Mine disaster, which killed 27 miners in the worst coal-mine fire in Utah's history.

Dozens of reporters camped on mountain roads near the rescue operation and in the nearest town of Huntington residents waited anxiously for word. Children plastered signs on their school fences reading "God Bless Our Miners."

Questions were also raised about whether the cave-in occurred during a dangerous operation known as retreat mining, where pillars of coal are used to hold up the mine roof, then removed.

Murray has denied that retreat-mining was being used at the time of the collapse.

Concerns about mine safety in the United States rose last year when 12 miners were killed in an explosion at International Coal Group's Sago mine in West Virginia.

In response, Congress passed the Mine Improvement and New Emergency Response Act, which President George W. Bush signed into law last year. (Additional reporting by Dan Whitcomb in Los Angeles and Stacey Joyce, Bill Trott and Doina Chiacu in Washington)

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