Uranium processing at Sillamäe and decommissioning of the tailings

Black shales are found all over the world. The southeastern Baltoscandian plateau contains Cambrian and Early Ordovician black alum shales. Swedish deposits are Late Cambrian and thus the oldest in Baltoscandia. The Estonian alum shales, known as graptollite argillites or, popularly, dictyonema shales, are younger—they are Early Ordovician (Tremadoc). Economically exploitable Estonian dictyonema shales are located in the northern part of the country in an area 250 km long and 15 to 80 km wide (total area about 11,000 km2). The layer is 20-30 m deep layer on the northern border of the deposit, and 200-300 m on the southern border. The layer is 1-2 m thick in the east and 3-7 m thick in the west. Estimated resources (of the category P2) amount to 62.3 billion tons. The most promising area lies in northeast Estonia (612 km2), with estimated resources of 4.1 billion tans.