By Laura Zuckerman
SALMON, Idaho (Reuters) - Rescue teams using tiny cameras snaked through newly drilled bore holes in a collapsed silver mine have detected a void in fallen rock and debris near where they believe a miner has been trapped since last Friday.
The two drill holes also enabled search crews to pump fresh air into the opening, more than a mile beneath the surface at the Lucky Friday Mine in northern Idaho, the Hecla Mining Co. said in a statement on Wednesday.
But the size and extent of the void could not be measured, and the trapped miner, Larry Marek, 53, still has not been heard from, since the roof of a mine tunnel collapsed five days ago, the company said. His condition and exact location in the mine also remained unknown
Rescue teams cleared about 39 feet of an estimated 75-foot-long blockage of rubble in the collapsed mine corridor, and had hoped to make greater progress after bringing in to unmanned digging machines.
But unstable rock and fears of further cave-ins forced a suspension of digging operations on Tuesday.
Instead, officials initiated a backup strategy to drill and blast two alternate tunnels through solid rock -- each running more than double the length of the original rescue route.
By Tuesday night, rescue crews had advanced 24 feet along the first 220-foot alternate route, and they were planning to begin work on a second, 182-foot-long tunnel on Wednesday.
Robin McCulloch, a mining engineer for the Montana Bureau of Mines and Geology, estimated that it would take at least six to seven days to complete either of those routes. He also said temperatures in hard-rock mines a mile deep would likely well exceed 100 degrees Fahrenheit without proper ventilation.
Marek and his brother were working a vein of silver ore when a section of tunnel fell in on them for unknown reasons. Marek's brother escaped unharmed.
The accident comes as Hecla is expanding the depth of the mine to 8,000 feet. The company employs 275 workers and 100 contractors at the Lucky Friday, one of Hecla's three active mines in the United States.
(Editing by Steve Gorman and Peter Bohan)