Regional and fine-scale variability in composition and structure of hydrogenetic ferromanganese crusts: Geological characterization of 25 drill cores from the Marcus-Wake seamounts

Abstract

Hydrogenetic ferromanganese crusts in the northwestern (NW) Pacific seamounts are considered as potential future sources of strategic metals. The details of their regional and fine-scale variations in composition and structure are currently unknown. We attempted to characterize the variation patterns in a selected area of the NW Pacific seamounts, based on geological and geochemical analyses, which were performed with a TV-monitored drill machine and remotely operated vehicles, after full bathymetric mapping and an acoustic survey. Subsequent chemical, mineralogical, and structural analyses of the well-preserved crust cores indicated that the hydrogenetic crusts in the seamount area have similar distinct fine-scale variations throughout the growth layers from the substrate to the surface. The crust cores show almost continuous stratigraphic growth since the middle Miocene (approximately 15 Ma ago) or earlier, with significant variations in metal concentration, growth structure, and mineralogy. The fine-scale stratigraphic variations are surprisingly well-correlated across the seamount areas of approximately 1000 km apart; thus, the bulk compositional variation becomes much smaller than a secular variation when compared within the seamount area. Stratigraphic analysis is crucial for the compositional characterization of ferromanganese crusts on various scales.

Keywords:

• Ferromanganese crust
• marine mineral resource
• Northwestern Pacific
• seamount
• manganese nodule
• growth rate
• hydrogenetic
• Co-rich crust

Acknowledgement

The authors acknowledge crew and technical staff on board research cruises of R/V Hakurei, Kairei, and Natsushima for their assistance. Part of data were supplied from the sponsored projects by Ministry of Economy, Trade and Industry (METI), Japan, and Japan Oil, Gas and Metals National Corporation (JOGMEC). We acknowledge Japan Society for the Promotion of Science (JSPS) for KAKEN projects and Strategic Innovation Program (SIP) for funding to our study. Japan Agency for Marine-Earth Science and Technology (JAMSTEC), Geological Survey of Japan (GSJ/AIST), Center Adv. Mar. Core Research (CMCR) of Kochi University, Geological and Nuclear Science, New Zealand Geological and Nuclear Science (GNS), and Sumiko Resources and Development Co. Ltd. (SRED), are appreciated for discussion, collaboration and in-laboratory analyses.

Disclosure statement

No potential conflict of interest was reported by the authors.