Oil Shale, 2014, Vol. 31, No. 1, pp. 4–18 ISSN 0208-189X doi: 10.3176/oil.2014.1.02 © 2014 Estonian Academy Publishers ESTONIAN GRAPTOLITE ARGILLITES REVISITED: A FUTURE RESOURCE? SIGRID HADE * , ALVAR SOESOO Institute of Geology, Tallinn University of Technology, Ehitajate tee 5, 19086 Tallinn, Estonia Abstract. 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 con- centrations 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 m 3 , while about 9.02 billion m 3 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/cm 3 . 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 U 3 O 8 reaches 6.7 million tonnes, ZnO 20.6 million tonnes and MoO 3 19.1 million tonnes as calculated using a cell size of 400 m. Keywords: graptolite argillite, black shale, metals, resource, Estonia. 1. Introduction The occurrence of Middle Cambrian to Late Ordovician organic-rich black shale deposits in an extensive area of Sweden (alum shale [1]), the Oslo region [2], Bornholm [3], Estonia (known as graptolite argillite, “Dictyo- nema shale” [4], and kukersite as proper oil shale), Poland [5] and North- West Russia [6] has been known for a long time. Alum shale, as well as graptolite argillite, contains remarkably high con- centrations of trace metals such as U, Mo, V and Ni, but may also be locally enriched with rare earth elements (REE), Cd, Au, Sb, As, Pt [7]. The beds have historically been exploited for uranium production in Sweden and Estonia. Also, a high content of potassium, sulphur and organic matter is * Corresponding author: e-mail sigrid.hade@ttu.ee