Colombian coal miners began an open-ended strike after wage talks collapsed with their employer, a company owned in part by Britain\'s Anglo American and Australia\'s BHP Billiton. Some 4,000 workers employed directly by Cerrejon, Colombia\'s largest coal exporter, and another 7,000 subcontractors began the walkout, said union representative Igor Diaz Lopez. The workers wanted a new two-year contract with pay hikes and safer working conditions to ward off mining-related illnesses, among other things. But no agreement was reached. The Labor, Mining and Energy Ministry urged the two sides to negotiate anew, and offered to help mediate. The Cerrejon mine, located in northern Colombia on the border with Venezuela, is one of the world\'s largest open pit coal mines. Last year, 34.6 million tonnes of coal were extracted from the site. The company said the strike will cost $3 million a day in lost revenue. Along with Anglo American and BHP Billiton, Xstrata of Switzerland also owns