The coalfield is composed of four main seams, only one of which, the No. 1 Seam, is currently being mined subsurface using slope mining. The No. 1 Seam has an average height of 8.5 meters (28 ft), and is located at an average depth of 80 meters (260 ft) below surface. Production over a recent 7-year stretch averaged 877,000 tons per year. Overall coalfield reserves are estimated at 5 billion tons of coal.