"Specialized gangs assaulting moving convoys has become common," Valeria Ibarra, Antofagasta's regional coordinator of public safety, said by telephone on Thursday. "These are professionals. If they see that one company is taking security measures, they'll just move on to the next one."
The sheets of stolen copper cathode are taken to illegal yards and sold as scrap at a 30 percent discount to market prices, Ibarra said.
A common target for the thieves is Antofagasta Plc's logistics unit Grupo FCAB, which owns and operates about 700 kilometers (430 miles) of railway lines used to transport cathode and semi-processed copper known as concentrate from mines to ports.
State-owned Codelco has also reported thefts, according to a statement by the prosecutor's office in Antofagasta. Codelco didn't immediately respond to a request for comment. BHP Billiton Ltd.'s Spence and Escondida copper mines, Antofagasta's Zaldivar, Mantos Copper SA's Mantos Blancos and Yamana Gold Inc.'s El Penon have all reported smaller robberies, prosecutors said.
A new method is known as "the anchor." When trains slow down in steeper areas, gangs hook a mooring line to a pile of cathodes and throw an anchor onto the railway lines. As the train advances, the pile weighing about 350 kilos (772 pounds) is dragged off the wagon and quickly picked it up by trucks.
On Wednesday, Antofagasta's regional government set up a permanent working group that includes the police, the government, FCAB, and mining companies to address the issue and coordinate surveillance and investigations.
One of their first tasks will be to solve a mystery — why so many of the robberies happen on Thursdays. Government officials are wondering if it coincides with a change in shifts, or if it has to do with the proximity to the weekend.
Written by Laura Millan Lombrana. Edited by James Attwood and Philip Sanders.