9:15 AM - 9:30 AM
[SCG56-02] Mineralogical and geochemical study of hydrothermal deposits beneath the seafloor at the Gondou field in the Okinawa Trough
Keywords:Submarine hydrothermal deposits, Back-arc basin
Massive and disseminated sulfide layers were recognized at Site GDUC06, which was covered with silty clay sediment and underlaid by silicified volcaniclastics. Two distinctive types of massive sulfide were recognized; the upper one is composed of sphalerite, pyrite, galena and associated with barite, while the lower one is composed of pyrite, chalcopyrite and associated with quartz, illite and chlorite. The underlaid silicified volcaniclastics layer includes pyrite. It is notable that formation of sphalerite-rich massive sulfide and chalcopyrite-rich sulfide is comparable to the black ore and yellow ore found in Kuroko-type deposits.
Similarity to the Kuroko-type deposits can be found in chemical composition of sulfide minerals. Iron content in sphalerite from the Gondou field ranges from 0.22 to 5.72 atm%, which would be comparable to the reported value from 0.07 to 0.35 atm% for the Matsumine and the Shakanai deposits of the Hanaoka mine, one of typical Kuroko-type deposits in the Hokuroku district (Shimazaki and Horikoshi, 1990)). Tetrahedrite-tennantite series occurred in the sphalerite-rich massive sulfide exhibit high As/(As+Sb) and Zn/Fe ratios, which are close to the range found in massive sulfide from the Hanaoka mine (Shikazono and Kouda, 1979). Since chemical composition of sulfide minerals is considered to reflect chemical condition such as fS2 during the formation, these similarities would provide keys to understand the mineralization processes.
This study is conducted under the framework of the Next-Generation Technology for Ocean Resources Exploration Project, Cross-ministerial Strategic Innovation Promotion Program (SIP) by the Japanese cabinet office. We are thankful to J-MARES (Research and Development Partnership for Next Generation Technology of Marine Resources Survey) for providing sediment cores used in this study.