Depth profiles of resistivity and spectral IP for active modern submarine hydrothermal deposits: a case study from the Iheya North Knoll and the Iheya Minor Ridge in Okinawa Trough, Japan

Shogo Komori,Junji Torimoto,Tatsuo Nozaki,Hidenori Kumagai,Osamu Tadai,Wataru Tanikawa,Yusuke Ohta,Lena Maeda,Yuka Masaki,Jun-Ichiro Ishibashi,Masato Makio

doi:10.1186/s40623-017-0691-6

Abstract

Submarine hydrothermal deposits are one of the promising seafloor mineral resources, because they can store a large amount of metallic minerals as sulfides. The present study focuses on the electrical properties of active modern submarine hydrothermal deposits, in order to provide constraints on the interpretation of electrical structures obtained from marine electromagnetic surveys. Measurements of resistivity and spectral induced polarization (IP) were made using drillcore samples taken from the Iheya North Knoll and the Iheya Minor Ridge in Okinawa Trough, Japan. These hydrothermal sediments are dominantly composed of disseminated sulfides, with minor amounts of massive sulfide rocks. The depth profiles of resistivity and spectral IP properties were successfully revealed to correspond well to layer-by-layer lithological features. Comparison with other physical properties and occurrence of constituent minerals showed that resistivity is essentially sensitive to the connectivity of interstitial fluids, rather than by sulfide and clay content. This suggests that, in active modern submarine hydrothermal systems, not only typical massive sulfide rocks but also high-temperature hydrothermal fluids could be imaged as low-resistivity anomalies in seabed surveys. The spectral IP signature was shown to be sensitive to the presence or absence of sulfide minerals, and total chargeability is positively correlated with sulfide mineral abundance. In addition, the massive sulfide rock exhibits the distinctive IP feature that the phase steadily increases with a decrease of frequency. These results show the effective usage of IP for developing and improving marine IP exploration techniques.Graphical abstract.

Highlights

Exploration and exploitation of submarine hydrothermal deposits in Japan is becoming increasingly important for the steady supply of metal resources to Japanese industry
Note that the present study defines the sulfide mineral content as the total sum of identified sulfide minerals without sphalerite; this is because sphalerite generally exhibits less electrical conductivity and weaker induced polarization (IP) signatures than other sulfide minerals (e.g., Shuey 1975)
In order to characterize the resistivity and IP properties of the study area, we examined the contribution of these factors to resistivity and IP properties, the factors causing lowresistivity anomalies, and the applicability of IP exploration techniques to submarine hydrothermal deposits

Summary

Introduction

Exploration and exploitation of submarine hydrothermal deposits in Japan is becoming increasingly important for the steady supply of metal resources to Japanese industry. Metallic elements such as iron, copper, lead, and zinc are usually included in these deposits as sulfide minerals, Komori et al Earth, Planets and Space (2017) 69:114 the IP effect makes the sulfide particles very conductive at high frequencies and perfectly insulating at low frequencies. Understanding of the IP effect of rock and sediment samples taken from submarine hydrothermal deposits is crucial for reducing uncertainties in interpretations of geophysical structure. The resistivity and IP signature obtained were compared to other physical, lithological, and material data, in order to examine their controlling factors

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Discussion

Conclusion