Professor Yasuhiro Kato, Graduate School of Engineering, The University of Tokyo, and Dr. Tatsuo Nozaki and Dr. Katsuhiko Suzuki, Research and Development (R&D) Center for Submarine Resources, Japan Agency for Marine-Earth Science and Technology (JAMSTEC) have successfully determined the primary formation age of the Hitachi deposit (copper-zinc-lead sulfide deposits classified as volcanogenic massive sulfide) in Ibaraki Prefecture.
To directly date the constituent sulfide minerals included in sulfide ores, the Rhenium-Osmium (Re-Os) isotope dating method was applied and revealed that the primary formation age of the Hitachi VMS deposit is estimated to be the Cambrian (485.4 to 541 million years ago), not Early Carboniferous (323.2 to 358.9 million years ago) as had been thought. The Hitachi VMS deposit is, therefore, classified as the oldest dated ore deposit in Japan.
These results support previous studies that indicated the existence of a large age gap (hiatus) in the geologic record of 150 million years and the wide distribution of Cambrian beds in the Hitachi area. It is expected to provide important age constraints for use in reconstructing the initial tectonic history of the Japanese Islands.
Source: University of Tokyo