Exploration of critical elements in the concealed North Estonian basement and its Eastern Fennoscandian context

This study evaluates the mineral potential of the NE Tallinn-Alutaguse-Jõhvi Estonian Paleoproterozoic corridor, composed of amphibolite- to granulite-facies gneisses and metal-rich volcanic-sedimentary units. Mesoproterozoic rapakivi bodies were also analysed. Borehole geochemistry reveals that the Alutaguse metavolcanic suites have high concentrations of Cu (2230 ppm), Zn (2650 ppm), and Pb (4030 ppm), hosted in magnetite-rich and sulphide-graphite gneisses, similar to those found in ore systems in Sweden and Finland. Data suggest that the metalliferous Alutaguse target zones are linked to intrusive bodies and/or hydrothermal-skarn processes akin to those at Jõhvi. Automated MSCL-XYZ scanning of drill cores reveals associations of critical metals, including Ni-Co-Cr, Mo-W-Bi, Sn-Zn-Cd, Cu-Ni, Nb-Y-P, and Au-Ag-As-Sb-Bi-W-Se-Sn, identifying new prospective intervals. Analyses of the Märjamaa rapakivi pluton reveal REE concentrations of up to 3600 ppm in the Si-poor Fe-Ti-P-rich Phase I, indicating potential exploration targets. Geophysical data also highlight zones of high magnetic susceptibility, possibly inferring altered or mineralised target zones.