Source: Alan J. Nash The owner of the second-largest coal mine in the U.S. by production volume is planning for the asset's closure as retirement dates approach for several plants that burn much of the mine's fuel. Coal demand in the U.S. has been declining for years, and Arch Resources Inc. announced Feb. 9 that it would be winding down its thermal coal operations, including those at Black Thunder, a Wyoming mine that produced 12.7 million tons of coal in the fourth quarter of 2020. Black Thunder production represented about 9.7% of the coal mined in the country in that period, according to an S&P Global Market Intelligence analysis.