An explosion at a small underground coal mine in northeast Colombia killed 21 workers on Wednesday, officials said, in the latest accident to hit Latin America's mining industry. Colombia is the world's No. 5 coal exporter, with an industry dominated by major players with open-pit mines. But some smaller mines in the Andean nation are dug underground where methane gas buildups can cause accidents. The mining regulator Ingeominas said the latest blast, in Norte de Santander province, was probably caused by methane gas and preliminary figures showed 21 fatalities.