At least 59 people were killed in a gold mine blast in Gbomblora in Burkina Faso's Poni province, national broadcaster RTB reported.Fifty-five people died at the scene of the explosion, while four others succumbed to their injuries in hospitals, Xinhua news agency quoted the RTB report as saying.At least 55 other people were injured, according to the provisional toll, said the report.The cause of the explosion remained unknown, but several witnesses have said that the blast was triggered by a fire which consumed a stock of explosives used by the gold miners during their operations.An investigation was underway, said the RTB.