Pb isotope compositions of galena in hydrothermal deposits obtained by drillings from active hydrothermal fields in the middle Okinawa Trough determined by LA-MC-ICP-MS

Totsuka, Shuhei; Shimada, Kaoru; Nozaki, Tatsuo; Kimura, Jun–Ichi; Chang, Qing; Ishibashi, Jun Ichiro

doi:10.1016/j.chemgeo.2019.03.024

Cited by 22 publications

(7 citation statements)

References 27 publications

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“…Izena Hole (Fig. 1B) has two hydrothermal sites: the JADE site on the northeastern caldera slope (Halbach et al, 1989;Ishibashi et al, 2015) and the Hakurei site on the southern caldera floor (Ishibashi et al, 2015;Totsuka et al, 2019;Morozumi et al, 2020). Iheya North Knoll (Fig.…”

Section: Geological Setting and Samplesmentioning

confidence: 99%

“…At Izena Hole, cores were obtained during D/V Chikyu Expedition 909 at the Hakurei site, from Hole C9027B on Northern mound and from Hole C9025A east of Northern mound and associated with a subseafloor sulfide body beneath the sediment (Figs. S1 and S2 and Tables S1-S3 in the Supplemental Material 1 ) (Nozaki et al, 2018;Totsuka et al, 2019). At Iheya North Knoll, cores were drilled during IODP Expedition 331 at the Original site at Hole C0016B on the eastern flank of North Big Chimney mound (Figs.…”

Section: Geological Setting and Samplesmentioning

confidence: 99%

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Microbial sulfate reduction plays an important role at the initial stage of subseafloor sulfide mineralization

Nozaki

Nagase

Ushikubo

et al. 2020

Geology

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Seafloor hydrothermal deposits form when hydrothermal fluid mixes with ambient seawater, and constituent sulfide minerals are usually interpreted to precipitate abiogenically. Recent research drilling at Izena Hole and Iheya North Knoll in the middle Okinawa Trough (East China Sea), combined with secondary ion mass spectrometry determinations of δ34S in pyrite grains, provides compelling evidence that the initial stage of subseafloor sulfide mineralization is closely associated with microbial sulfate reduction. During the sulfide maturation process, pyrite textures progress from framboidal to colloform to euhedral. Pyrite δ34S has highly negative values (as low as –38.9‰) in framboidal pyrite, which systematically increase toward positive values in colloform and euhedral pyrite. Sulfur isotope fractionation between seawater sulfate (+21.2‰) and framboidal pyrite (–38.9‰) is as great as –60‰, which can be attained only by microbial sulfate reduction in an open system. Because framboidal pyrite is commonly replaced by chalcopyrite, galena, and sphalerite, framboidal pyrite appears to function as the starting material (nucleus) of other sulfide minerals. We conclude that framboidal pyrite, containing microbially reduced sulfur, plays an important role at the initial stage of subseafloor sulfide mineralization.

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Section: Geological Setting and Samplesmentioning

confidence: 99%

Section: Geological Setting and Samplesmentioning

confidence: 99%

Microbial sulfate reduction plays an important role at the initial stage of subseafloor sulfide mineralization

Nozaki

Nagase

Ushikubo

et al. 2020

Geology

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“…no clear signs of upward zone refining based on the Cu concentrations in the subseafloor sulphide bodies; Supplementary Fig. S10 and Supplementary Table S2 ), (3) the presence of nearly unaltered hemipelagic sediment overlying the subseafloor sulphide body and (4) S and Pb isotopic compositions that differ between exhalative mound and subseafloor sulphide body signatures 24 , 34 . Instead, we propose a model in which mineralisation occurs as subseafloor pumice replacement (Fig.…”

Section: Resultsmentioning

confidence: 99%

Subseafloor sulphide deposit formed by pumice replacement mineralisation

Nozaki

Nagase

Takaya

et al. 2021

Sci Rep

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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.

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“…Studies on the rare earth elements (REEs), sulfur‐lead‐osmium‐zinc and noble gas isotopes, and the compositional characteristics of fluid inclusions of massive sulfides have shown that the endmembers of seawater, felsic volcanic rocks, and marine sediments may be the sources that formed the massive sulfides in the hydrothermal field of the OT (Halbach, Hansmann, Köppel, & Pracejus, ; Hongo & Nozaki, ; Hou, Zhang, & Qu, ; Lüders, Pracejus, & Halbach, ; Zeng et al, ; Zeng, Jiang, Qin, Zhai, & Hou, ; Zeng, Jiang, Zhai, & Qin, ; Zeng, Qin, & Zhai, ; Zeng, Zhai, & Du, ; Zhang, Zhai, Yu, Guo, & Wang, ). The Pb isotope compositions of galena in hydrothermal deposits in the middle OT also reflect that their metal sources originated from either the local volcanic rocks and/or the sediments via water–rock interactions (Totsuka et al, ). Analogously, the distinctive chemistry of the OT hydrothermal fluids is associated with the organic‐rich continent‐derived sediment deposited on the OT seafloor and the volatile‐rich dacitic‐rhyolitic (silicic) magma beneath the OT (Ishibashi et al, ; Kawagucci, ; Sakai et al, ).…”

Section: Geological Settingmentioning

confidence: 99%

Amphibole perspective to unravel the rhyolite as a potential fertile source for the Yonaguni Knoll IV hydrothermal system in the southwestern Okinawa Trough

Chen

Zeng

et al. 2019

Geological Journal

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Yonaguni Knoll IV is an active seafloor hydrothermal system containing massive Zn-Pb sulfides located in the southwestern OkinawaTrough. Previous research has suggested that the metal elements Zn and Pb were dominantly derived from the local volcanic rocks via water-rock interactions. However, it is not known whether or why the volcanic rocks are rich in these metals. Here, we performed a detailed in situ analysis of the major and trace elements in amphiboles in the rhyolite from the hydrothermal field to decipher the physical-chemical conditions of the silicic magma, including temperature (T), pressure (P), oxygen fugacity (fO 2 ), volatile contents (Cl, H 2 O) and metal contents (Pb, Zn), and investigate the behavior of the metals (Zn and Pb) during melt evolution. Our results show that the amphiboles are euhedral calcic magnesiohornblende and are in equilibrium with the hydrous and oxidized host rhyolitic melt characterized by high H 2 O melt (~5.8-6.5 wt.%), fO 2 (NNO +0.1 to +0.6) and SiO 2 melt (~71.73-72.62 wt.%) values at 761-797°C and 102-137 MPa, corresponding to an approximate depth of 3.9-5.2 km. In addition, the rare earth element (REE) patterns of the melt reconstructed from the amphiboles are analogous to those of cold-wetoxidized rhyolites. Thus, the amphiboles crystallized in a cold-wet-oxidized shallow silicic magma chamber. The high oxygen fugacity is inferred to have favored sulfur and metal enrichment in the melt. The most abundant metal in the amphiboles is Zn (237-294 ppm), and the concentrations of Pb are much lower (0.86-3.32 ppm), suggesting that Zn preferentially entered the amphibole and that Pb was retained in the melt. The Cl content of the amphiboles ranges from 0.11 to 0.25 wt.%, and accordingly, the Cl melt content estimated from the amphiboles varies from 0.15 to 0.28 wt. %. The low (Cl/H 2 O) melt ratios, which are <0.05 (i.e.,~0.02-0.04), suggest that the melt exsolved an H 2 O-rich vapor rather than a hydrosaline fluid with insufficient Cl to transport metals (e.g., Pb and Zn) into the vapor phase during degassing both in the magma chamber and during ascent. The lack of exsolved hydrosaline fluid and the high oxidation conditions resulted in the metal elements Pb and Zn remaining dissolved in the rhyolitic melt and/or partitioning into crystalline minerals upon eruption. Thus, the large volumes of rhyolitic magma that intruded into the upper crust of the Yonaguni Knoll IV hydrothermal field are a potential fertile source of these elements via leaching by heated seawater.

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Pb isotope compositions of galena in hydrothermal deposits obtained by drillings from active hydrothermal fields in the middle Okinawa Trough determined by LA-MC-ICP-MS

Cited by 22 publications

References 27 publications

Microbial sulfate reduction plays an important role at the initial stage of subseafloor sulfide mineralization

Microbial sulfate reduction plays an important role at the initial stage of subseafloor sulfide mineralization

Subseafloor sulphide deposit formed by pumice replacement mineralisation

Amphibole perspective to unravel the rhyolite as a potential fertile source for the Yonaguni Knoll IV hydrothermal system in the southwestern Okinawa Trough

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