The Reason Why Izena Hole Hosts the Large-scale Seafloor Hydrothermal Deposit Around Japanese Coastal Waters; Importance of Subseafloor Pumice Replacement Mineralization

• Published in: Resources Processing Vol. 71; no. 1; pp. 26 - 34
• Main Authors: NOZAKI, Tatsuo, ISHIBASHI, Jun-ichiro, KUMAGAI, Hidenori
• Format: Journal Article
• Language: English; Japanese
• Published: The Resources Processing Society of Japan 2024
• Subjects: Epigenetic; Izena Hole; Okinawa Trough; Pumice replacement mineralization; Seafloor hydrothermal deposit; Syngenetic
• ISSN: 1348-6012; 1349-9262
• DOI: 10.4144/rpsj.71.26

From November to December 2016, a scientific drilling cruise CK16-05 by using D/V Chikyu was performed at Hakurei Site, Izena Hole, middle Okinawa Trough to understand mainly the metallogenesis and physical property of the subseafloor sulfide body. At Hole 9026A of the deepest hole down to 180.0 mbsf, lithologies of drilling cores, in descending order, are (1) underwater debris flow deposit (pumiceous sediment), (2) hemipelagic sediment, (3) subseafloor sulfide body with two intercalated layers of hemipelagic sediment, (4) greenish hydrothermally altered clay with pyrrhotite-cubanite veins and (5) pervasive altered hydrothermally altered clay. Based on the all results of petrographic observations, chemical analyses and geophysical logging of boreholes, genesis of Northern Mound can be explained well by a classical syngeneic model, however, the subseafloor sulfide body was the most plausibly formed by “subseafloor pumice replacement mineralization”. Thus, the subseafloor replacement process (subseafloor pumice replacement mineralization) would be one of the important factors to form the large-scale seafloor hydrothermal deposit.