One miner was killed after an earthquake struck the Zofiowka coal mine in southern Poland on Saturday, the CEO of the company that owns the mine has confirmed, according to Reuters. Rescuers are working to free another trapped miner, while three others remain missing. A total of seven miners went missing following the quake, two of whom were previously rescued. Coal mining is a major industry in Poland, and the resource is the main source of energy and heating in the country.