Mining methods at Sishen are opencast mining. Coal is produced from 18 opencast mines. A modest amount of opencast coal mining continues. They followed the ore veins underground once opencast mining was no longer feasible. Coal is produced from four underground and 21 opencast mines. The ironsand ore is mined at an opencast mine at Waikato North Head. This supply was supplemented by coal from local opencast mines. Deerpark Mines was the largest opencast site. Energybuild also operates the Nant y Mynydd opencast coal site nearby. Mining is done by both opencast and underground methods. In the 1960s opencast mining took over the surrounding countryside. Future opencast mining is a possibility. Mining is done by the opencast method. It is mostly mined by opencast method. Trelewis closed in 1989 when British Coal invested in opencast operations at Cwmbargoed.