Estonian graptolite argillites revisited: A future resource?

The occurrence of Cambrian to Ordovician organic-rich black shale deposits has been known in Baltoscandia, including Estonia, for a long time. The Estonian graptolite argillite (GA) shows high to very high concentrations of U (800 ppm), Mo (1000 ppm), V (1600 ppm), Ni and other heavy metals, and are rich in N, S and O, unlike normal shale. The present study provides a new estimate of the total GA tonnage in Estonia, including estimates for U, Zn and Mo. The total preserved volume of GA is about 31.92 billion m3 , while about 9.02 billion m3 has been eroded between the Estonian mainland and western islands. The total mass of GA is about 67 billion tonnes at a specific gravity of 2.1 g/cm3 . About 18.93 billion tonnes of GA has been eroded and re-deposited, including 1.8 million tonnes of U, 22.7 million tonnes of Zn, 6.6 million tonnes of Pb, 4.4 million tonnes of Mo and 13.3 million tonnes of V. In Estonian GA the total U3O8 reaches 6.7 million tonnes, ZnO 20.6 million tonnes and MoO3 19.1 million tonnes as calculated using a cell size of 400 m.