Zircon geochronology, Hf isotope, and rare earth element geochemistry of the Apdong Nb-Ta deposit in North Korea

The Apdong Nb-Ta deposit is hosted within the syenite and in the Hoamsan area in the northern part of the Imjingang Belt in North Korea. Our new sensitive high-resolution microprobe zircon U-Pb results reveal two stages of Neoproterozoic to Ordovician inherited cores (887 Ma to 465 Ma) and Silurian emplacement and mineralization (425.5 +/- 7.4 Ma) events. The zircon grains from the Apdong syenite show typical magmatic or textureless and sponge-like hydrothermal domains. These textural analyses supported the rare earth element characteristics obtained from the laser ablation-induced coupled plasma mass-spectrometry analyses (LA-ICP-MS). Neoproterozoic magmatic activities reportedly occur in the Pyeongnam Basin, Imjingang Belt [present study], Gyeonggi Massif, and Okcheon metamorphic belt in the central part of the Korean Peninsula and China (North China Craton, Qinling Orogenic Belt, and South China Craton). Notably, the Caledonian mineralization events in the southeastern part of the South China Craton coincided with emplacement and mineralization ages from the Apdong syenite (425.5 +/- 7.4 Ma). The LA multi-collector ICP-MS Hf isotope of zircons from the Apdong syenite yielded positive initial epsilon Hf values plotted along the Neoproterozoic crustal evolution path, indicating that the host rock of Nb-Ta ore was formed from the pre-existing Neoproterozoic source. The source materials of Neoproterozoic intrusives in the central part of the Korean Peninsula were generally derived from Meso-proterozoic depleted mantle sources. Considering the previously reported Hf isotopic results, the involvement of pre-existing crustal materials is more prominent in the Neoproterozoic intrusives in the southern part of the central Korean Peninsula, i.e., the Gyeonggi Massif, than in the northern part of the central Korean Peninsula, such as the Imjingang Belt and Pyeongnam Basin in the northern part of the central Korean Peninsula.