In 1946–1948, the former oil shale processing plant in Sillamäe was rebuilt by Soviets to extract uranium oxide from the locally mined Dictyonema argillite ore (a type of oil shale).[6][7][8] During that time, many war prisoners were employed at the construction and mining activities in Sillamäe. The uranium extraction process at the Sillamäe plant was developed in collaboration with a nearby Narva pilot plant (known as Cloth Dyeing Factory)[9] and produced mainly a 40% uranium concentrate at the onset of plant production. The local mining operations continued until 1952.