EDIT CONTAINS 4:3 MATERIAL<br/> <br />Peru's president Ollanta Humala arrived late on Tuesday (April 10) night at a wildcat mine in the south of the country to help lead an operation to reach nine workers who have been trapped underground for the last six days.<br/> <br />As rescuers were closing in on the trapped miners, president Humala was unable to confirm to the media when the workers would be pulled to the surface.<br/> <br />The men have been stuck about 656 feet below ground since the Cabeza de Negro gold-and-copper mine partially collapsed last Thursday. They have been receiving oxygen and liquids through a giant hose in place since before the accident.<br/> <br />The cave-in spurred calls to formalize Peru's vast informal mining sector, which generates as much as $2 billion a year in income, according to private estimates.