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Large Fe isotope fractionations in sulfide ores and ferruginous sedimentary rocks from the Kuroko volcanogenic massive sulfide deposits in the Hokuroku district, northeast Japan
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Title: | Large Fe isotope fractionations in sulfide ores and ferruginous sedimentary rocks from the Kuroko volcanogenic massive sulfide deposits in the Hokuroku district, northeast Japan |
Authors: | Otake, Tsubasa Browse this author →KAKEN DB | Yamada, Ryoichi Browse this author | Suzuki, Ryohei Browse this author | Nakamura, Shunsuke Browse this author | Ito, Akane Browse this author →KAKEN DB | Shin, Ki-Cheol Browse this author →KAKEN DB | Sato, Tsutomu Browse this author →KAKEN DB |
Keywords: | Volcanogenic massive sulfide deposit | Redox environment | Seafloor hydrothermal system | Fe isotopes | Rare earth elements |
Issue Date: | 15-Feb-2021 |
Publisher: | Elsevier |
Journal Title: | Geochimica et cosmochimica acta |
Volume: | 295 |
Start Page: | 49 |
End Page: | 64 |
Publisher DOI: | 10.1016/j.gca.2020.12.009 |
Abstract: | Anoxic seawater may have played an important role in the preservation of volcanogenic massive sulfide (VMS) deposits in the Hokuroku district, northeast Japan, which is the type locality for Kuroko-type VMS deposits. In this study, we investigated the Fe isotopic compositions of sulfide ores and overlying ferruginous sedimentary rocks in these deposits. These data, coupled with petrographic and geochemical data, enable us to investigate the key formation processes and conditions during the formation of large Kuroko-type VMS deposits. Large Fe isotope variations of ca. 4 parts per thousand (delta Fe-56) associated with negative or positive Ce anomalies characterize the ferruginous sedimentary rocks formed in the Kuroko VMS deposits and post-Kuroko hydrothermal activity. This suggests that iron (hydr)oxides were precipitated by the partial oxidation of dissolved Fe2+ derived from hydrothermal fluids in anoxic or suboxic pools in the Hokuroku Basin. Positive Eu anomalies in the ferruginous cherts closely associated with the Kuroko VMS deposits indicate formation from high-temperature hydrothermal fluids. Zincrich black ores in both the Matsumine and Fukazawa deposits have lower delta Fe-56 values, due to rapid precipitation of pyrite triggered by the mixing of hydrothermal fluids with seawater. Positive shifts in delta Fe-56 values in the ferruginous cherts from the Ezuri and Fukazawa deposits may be explained by simultaneous precipitation of ferruginous sedimentary rocks with black ores, which modified the delta Fe-56 values of the hydrothermal fluids to positive values. However, Cu-rich yellow ores show no significant Fe isotope fractionation as compared with the dissolved Fe in the hydrothermal fluids, and were likely formed by slow growth of pyrite that replaced the black ores. The difference in the abundance of sulfide ores between the Matsumine and Fukazawa deposits may reflect the duration of hydrothermal circulation. |
Rights: | ©2020. This manuscript version is made available under the CC-BY-NC-ND 4.0 license http://creativecommons.org/licenses/by-nc-nd/4.0/ | http://creativecommons.org/licenses/by-nc-nd/4.0/ |
Type: | article (author version) |
URI: | http://hdl.handle.net/2115/88089 |
Appears in Collections: | 工学院・工学研究院 (Graduate School of Engineering / Faculty of Engineering) > 雑誌発表論文等 (Peer-reviewed Journal Articles, etc)
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Submitter: 大竹 翼
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