The stoppage by the company, a joint venture between Anglo American, BHP Billiton and Xstrata, concerned a month-long wage dispute which reportedly cost Bogota millions in lost royalties.

Meanwhile workers expressed concerns over the latest news. “We call on the authorities to redouble efforts to ensure our safety and that of the company,” the Sintracarbon union said in a statement, according to Reuters.

For their part, company officials didn’t assign blame to any of the armed groups in the region for the assault. Colombian security forces, however, usually accuse Revolutionary Armed Forces of Colombia (FARC) guerrillas for such violence; the Marxist insurgency’s leadership is currently in negotiations with the Colombian government in Cuba.

But despite such attacks, overall security has improved markedly across South America’s fourth-biggest country since 2000, following an influx of military hardware and technical assistance from the U.S. Since then, foreign investment has surged into the Andean country – up $16 billion from $2 billion – ahead of the world’s most potentially greatest mining-driven economic expansions.