The illegal miners had left their mark. Tools, explosives, sacks and ropes lay beside chopped power cables some 2,300 ft (700 meters) below ground in AngloGold Ashanti's Obuasi mine in Ghana. They had chiseled off anything they suspected might conceal gold ore, including support structures like shaft pillars. Known as galamseyers, illegal miners have disrupted commercial operations in several mines in Ghana and are costing mining conglomerates millions of dollars in Africa's second biggest gold miner after South Africa. “The galamseyers are destroying the mine ... as a result our cost of doing business has skyrocketed,” said Aboagye Ohene-Adu, a manager at Obuasi in charge of community and social development. There are about 10,000 illegal miners operating on the surface and underground at the loss-making concession. Gold was discovered at Obuasi in 1897 and the mine was long one of the world's richest in terms of yield per tonne of ore. But output has been declining since the 1990s. The mine produced 360,000 ounces of gold in 2007, down from a maximum of 900,000 ounces before the takeover of its parent company Ashanti Goldfields by South Africa's AngloGold four years ago. Company officials told Reuters during a tour of the 8 km (5 mile) long site that galamsey activities rose “tenfold” in recent months and became more violent, with attacks against workers and company property. “Under the guise of galamsey, which in itself is an illegality, they commit robbery and other serious crimes which negatively impact our operation,” Ohene-Adu said. “They deliberately dig under high-tension power poles to prevent sealing the holes through blasting. They destroy shafts and ventilation pipes ... their activities endanger lives of company workers both on the surface and underground.” In January, 37 miners were trapped underground for about 22 hours after illegal miners stole a power cable, causing an explosion and a fire. There is danger for the galamseyers as well. At least six illegal miners, aged between 14 and 20, died at Obuasi in the last month, officials said. But this does not deter those who say this is the only living they have, and a good one thanks to high gold prices. “It's worth the risk,” said Chogu Musah, who monitors gold markets.