 4, 1953).The Ubja mine was given to Eesti Põlevkivi in 1957, but it was closed in 1959.After construction of large oil shale-fired power stations in Narva, demand for oil shale increased and consequently Eesti Põlevkivi opened the underground mines Viru (1965) and Estonia (1972) along with the open-pit mines Sirgala (1963), Narva (1970) and Oktoobri (1974; later named Aidu).