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Subseafloor sulphide deposit formed by pumice replacement mineralisation

2021; Nature Portfolio; Volume: 11; Issue: 1 Linguagem: Inglês

10.1038/s41598-021-87050-z

2045-2322

Tatsuo Nozaki, Toshiro Nagase, Yutaro Takaya, Toru Yamasaki, Tsubasa Otake, Kotaro Yonezu, Kei Ikehata, Shuhei Totsuka, Kazuya Kitada, Yoshinori Sanada, Yasuhiro Yamada, Jun‐ichiro Ishibashi, Hidenori Kumagai, Lena Maeda, Shigeshi Fuchida, Tatsuo Fukuhara, Kei Ikehata, Jun‐ichiro Ishibashi, Hirokazu Kato, Masanobu Kawachi, Shinji Kawaguchi, Ryuhei Kawakida, Kazuya Kitada, Shogo Komori, Hiroshi Koshikawa, Kakda Kret, Hidenori Kumagai, Lena Maeda, Yuka Masaki, Yohei Matsui, Iona M. McIntosh, Kana Minamide, Rena Miyahara, Nobuhiro Mukae, Toshiro Nagase, Shunsuke Nakamura, Tatsuo Nozaki, Masao Ohno, Tsubasa Otake, Masafumi Saitoh, Yoshinori Sanada, Yutaro Takaya, Tomohiro Toki, Junji Torimoto, Shuhei Totsuka, Akihi Tsutsumi, Riki Uehara, Hirotaka Uza, Masayuki Watanabe, Yasuhiro Yamada, Takahiro Yamagishi, Hirofumi Yamamoto, Toru Yamasaki, Kotaro Yonezu,

Geochemistry and Elemental Analysis

Abstract Seafloor massive sulphide (SMS) deposits, modern analogues of volcanogenic massive sulphide (VMS) deposits on land, represent future resources of base and precious metals. Studies of VMS deposits have proposed two emplacement mechanisms for SMS deposits: exhalative deposition on the seafloor and mineral and void space replacement beneath the seafloor. The details of the latter mechanism are poorly characterised in detail, despite its potentially significant role in global metal cycling throughout Earth’s history, because in-situ studies require costly drilling campaigns to sample SMS deposits. Here, we interpret petrographic, geochemical and geophysical data from drill holes in a modern SMS deposit and demonstrate that it formed via subseafloor replacement of pumice. Samples from the sulphide body and overlying sediment at the Hakurei Site, Izena Hole, middle Okinawa Trough indicate that sulphides initially formed as aggregates of framboidal pyrite and matured into colloform and euhedral pyrite, which were replaced by chalcopyrite, sphalerite and galena. The initial framboidal pyrite is closely associated with altered material derived from pumice, and alternating layers of pumiceous and hemipelagic sediments functioned as a factory of sulphide mineralisation. We infer that anhydrite-rich layers within the hemipelagic sediment forced hydrothermal fluids to flow laterally, controlling precipitation of a sulphide body extending hundreds of meters.