Security forces have seized 120,000 tons of China-bound iron ore at a Pacific port in the grip of a powerful drug gang, according to Mexican officials. Six Chinese nationals were also arrested while 124 heavy machines, including bulldozers, were confiscated as authorities try to determine the ore’s origin.

More than 400 federal agents, police and military personnel swarmed nearly a dozen sites around Lazaro Cardenas this week, seizing the undocumented minerals, Federal Commissioner Alfredo Castillo said. The Mexican Navy first took over the Michoacan port in Q4 2013, officials added, to fight the operation run by The Knights Templar drug cartel.

Michoacan state, Mexico’s top iron ore producer, has hosted fighting between The Knights Templar and armed vigilantes which has evolved into one of President Enrique Pena Nieto’s top security concerns. Other cartels, including the Zetas in northern Mexico, have diversified into mining revenues in one of Latin America’s most heavily geologically-endowed nations.