# Mineralogy, geochemistry and microbiology insights into precipitation of stibnite and orpiment at the Daiyon-Yonaguni Knoll (Okinawa Trough) hydrothermal barite deposits

V.M. Dekov, K. Kyono, K. Yasukawa, B. Guéguen, M. Ivarsson, G.D. Kamenov, T. Yamanaka, D. Asael, M. Ishida, L.L. Cavalcante, et al.

► To cite this version:

V.M. Dekov, K. Kyono, K. Yasukawa, B. Guéguen, M. Ivarsson, et al. Mineralogy, geochemistry and microbiology insights into precipitation of stibnite and orpiment at the Daiyon-Yonaguni Knoll (Okinawa Trough) hydrothermal barite deposits. Chemical Geology, 2022, 610, pp.121092. 10.1016/j.chemgeo.2022.121092. hal-04758342

HAL Id: hal-04758342

https://hal.univ-brest.fr/hal-04758342v1

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1 Mineralogy, geochemistry and microbiology insights into

2 precipitation of stibnite and orpiment at the Daiyon-Yonaguni

3 Knoll (Okinawa Trough) hydrothermal barite deposits

4
5 V.M. Dekov<sup>a,*</sup>, K. Kyono<sup>a</sup>, K. Yasukawa<sup>b,c</sup>, B. Guéguen<sup>d,e</sup>, M. Ivarsson<sup>f</sup>, G.D.

6 Kamenov<sup>g</sup>, T. Yamanaka<sup>a</sup>, D. Asael<sup>h</sup>, M. Ishida<sup>c</sup>, L.L. Cavalcante<sup>f</sup>, Y. Kato<sup>b,c,i,j</sup>, T.
7 Toki<sup>k</sup>, J.-I. Ishibashi<sup>l</sup>

8
9
a Department of Ocean Sciences, Tokyo University of Marine Science and Technology, 4-5-7

10 Konan, Minato-ku, Tokyo 108-8477, Japan

11 b Frontier Research Center for Energy and Resources, School of Engineering, The University of

12 Tokyo, Bunkyo-ku, Tokyo 113-8656, Japan

13 c Department of Systems Innovation, School of Engineering, The University of Tokyo, 7-3-1

14 Hongo, Bunkyo-ku, Tokyo 113-8656, Japan

15 d CNRS, Univ Brest, UMR 6538 Laboratoire Géosciences Océan, F-29280 Plouzané, France

16 e CNRS, Univ Brest, UMS 3113, F-29280 Plouzané, France

17 f Department of Palaeobiology, Swedish Museum of Natural History, SE 104 05 Stockholm,
18 Sweden

19 g Department of Geological Sciences, University of Florida, 241 Williamson Hall, Gainesville,
20 FL 32611, USA

21 h Department of Geology and Geophysics, Yale University, New Haven, CT 06520, USA

22 i Ocean Resources Research Center for Next Generation, Chiba Institute of Technology, 2-17-1

23 Tsudanuma, Narashino, Chiba 275-0016, Japan

<footnote>* Corresponding author.</footnote>

<footnote>E-mail address: vdekov0@kaiyodai.ac.jp (V.M. Dekov)</footnote>
24 *j* Submarine Resources Research Center, Research Institute for Marine Resources Utilization,
25 Japan Agency for Marine-Earth Science and Technology (JAMSTEC), 2-15 Natsushima-cho,
26 Yokosuka, Kanagawa 237-0061, Japan

27 *k* Department of Chemistry, Biology and Marine Science, Faculty of Science, University of the
28 Ryukyus, 1 Senbaru, Nishihara, Okinawa 903-0213, Japan

29 *l* Kobe Ocean-Bottom Exploration Center, Kobe University, 5-1-1 Fukaeminami-machi,
30 Higashinada-ku, Kobe 658-0022, Japan

31

32

33 A B S T R A C T

34

35 Samples of active chimneys, chimney flanges and massive sulfides from the Daiyon-
36 Yonaguni Knoll hydrothermal field are composed of major barite and minor stibnite and
37 orpiment. Barite is inferred to precipitate from focused-discharge fluids composed of >40%
38 hydrothermal end-member fluid at T = 100-240°C, whereas the stibnite and orpiment are later
39 and lower temperature precipitates. The hydrothermal fluids from this field were subject of sub-
40 seafloor boiling and phase separation and, consequently, are brine-rich depleted in volatile and
41 enriched in non-volatile elements. Boiling and phase separation exerted major control on the rare
42 earth elements (REE) partitioning in the vent fluids: high-chlorinity high-temperature fluids were
43 enriched in light REE and low-chlorinity low-temperature fluids were enriched in heavy REE.
44 Y/Ho molar ratio and Ce anomaly of the vent fluids suggest that the seawater has not completely
45 reacted with the basement rocks and has not equilibrated with them. The trace element
46 concentrations in the hydrothermal deposits suggest a complex interplay among hydrothermal,
47 hydrogenetic and microbial processes. Sulfur isotope composition of the sulfides suggests that the
48 sulfide S is a mixture of both basement rock and seawater S with a higher proportion of the
49 basement rock S. The sulfate dissolved in the fluids was subjected to reduction during a slow
50 mixing of hydrothermal fluid and seawater within the chimney walls of the Tiger and Abyss
51 vents and this resulted in a heavy S-isotope composition of the vent fluid sulfate. Lead isotope
52 composition of the hydrothermal deposits indicates mixing relationships suggesting that Pb and
53 potentially other metals with similar geochemical behavior were derived from two or three
sources. The Pb isotopes in the hydrothermal deposits imply that an enriched source, either sediments or extended continental lithosphere, and a depleted source, potentially back-arc mafic volcanics, are present in the area of Daiyon-Yonaguni Knoll. Filamentous orpiment found in the deposits is supposed to be either heavily mineralized fungal hyphae or pure abiogenic biomorphs. Presence of carbonaceous matter on and around the orpiment filaments suggests for microbial activity during filament formation. The filaments experienced temperature of 209.1±37.1°C which falls within the temperature range of the Daiyon-Yonaguni Knoll vent fluids. Stability phase diagrams modeling reveals that the stability of stibnite does not depend on the vent fluid chlorinity, but depends on the vent fluid temperature: the area of stibnite stability increases with decreasing vent fluid temperature and results in stibnite precipitation at low $log_{10}a$ of $Sb_2S_4^{2-}$ and less reduced environment (Eh still <0). Orpiment is stable in a wide range of $log_{10}a$ of $H_2AsO_4^-$, in reduced conditions and at high S activity. Barite is stable in wide range of $log_{10}a$ of $Ba^{2+}$ and precipitates in slightly reduced to slightly oxic conditions.

**Keywords:** Daiyon-Yonaguni Knoll hydrothermal field; geomicrobiology; Okinawa Trough; orpiment; seafloor hydrothermal activity; stibnite

# 1. Introduction

Substantial effort has been made to elucidate the mineralogy of seafloor hydrothermal deposits since their discovery (Corliss et al., 1979; Spiess et al., 1980) and nowadays we can dare to think that we have extensive knowledge on it (e.g., Haymon and Kastner, 1981; Oudin, 1983; Koski et al., 1984; Fouquet et al., 1988; Koski et al., 1988; Hannington et al., 1991; Fouquet et al., 1993a, b; Iizasa et al., 1999; Fouquet et al., 2010; Webber et al., 2015). Although the studies of the seafloor hydrothermal deposits recognize distinct mineralogical differences among the deposits formed at mid-ocean ridges (MOR) (sedimented and unsedimented), volcanic arcs and back-arc spreading centers, they show that most seafloor hydrothermal deposits are composed of relatively simple mineral assemblages. Metal (Fe, Cu, Zn, Pb) sulfides, and Ca- and Ba-sulfates are the main constituents of these deposits, whereas silicates, oxyhydroxides, carbonates and
sulfosalts are minor minerals (Herzig and Hannington, 1995). Sulfides of metalloids (B, Si, Ge, As, Sb and Te) are rare. Therefore, seafloor hydrothermal deposits containing metalloid sulfides attract particular scientific interest because these minerals imply for uncommon conditions of precipitation (T, P, pH, Eh, ion activity and speciation).

Stibnite ($Sb_2S_3$) and orpiment ($As_2S_3$) are accessory minerals in the seafloor hydrothermal deposits according to published observations. Stibnite is mainly reported at volcanic arc [Palinuro Seamount, Aeolian Arc (Dekov and Savelli, 2004); Wakamiko Crater, Kagoshima Bay, Kyushu Island (Nedachi et al., 1991; Yamanaka et al., 2013)], back-arc [Minami-Ensei Knoll (Nakashima et al., 1995), JADE (Halbach et al., 1993; Nakashima et al., 1995) and Hatoma Knoll (Okamoto et al., 2002) at Okinawa Trough] and fore-arc [Conical Seamount, New Ireland fore-arc (Petersen et al., 2002)] settings. There is only one report on stibnite occurrence at MOR setting: Ashadze-1 hydrothermal field at the Mid-Atlantic Ridge (Firstova et al., 2016). Stibnite was also observed to form in the artificially produced hydrothermal chimneys at the Iheya-North field, Okinawa Trough (Nozaki et al., 2016). Orpiment has also been reported at volcanic arc [Suiyo Seamount, Izu-Bonin Arc (Marumo et al., 2008); off-shore Milos Island, Aegean Arc (Price et al., 2009)], back-arc [Lau back-arc basin (Petersen, 1992); JADE field, Okinawa Trough (Halbach et al., 1993; Dekov et al., 2013); Kaia Natai Seamount, Manus back-arc basin (Dekov et al., 2013)] and fore-arc [Conical Seamount, New Ireland fore-arc (Petersen et al., 2002; Herzig et al., 2003; Dekov et al., 2013)] settings only.

In 2000 during the YK00-06 *Yokosuka-Shinkai 6500* research cruise in the southern Okinawa Trough a new hydrothermal system was discovered and named Daiyon-Yonaguni Knoll (Matsumoto et al., 2001; Hsu et al., 2003). Along with the common barite, wurtzite, galena, tetrahedrite, chalcopyrite, pyrite and native sulfur, minor stibnite and orpiment were detected in the Daiyon-Yonaguni Knoll hydrothermal deposit (Okamoto et al., 2002; Suzuki et al., 2005; 2008).

Motivated by the scarce knowledge on the stibnite and orpiment precipitation at seafloor hydrothermal conditions, we investigated the stibnite-orpiment containing barite deposits and hydrothermal fluids from the Daiyon-Yonaguni Knoll hydrothermal site and report the results of our study in this contribution.

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## 2. Geologic setting

The Okinawa Trough is an intra-continental back-arc basin extending behind the Ryukyu Trench-Arc system (Fig. 1 A). The rifting of this trough located at the eastern margin of the Eurasian tectonic plate was discussed in several works (e.g., Kimura et al., 1986; Glasby and Notsu, 2003; Ishibashi et al., 2015). The lithosphere beneath the Okinawa Trough is thinned continental lithosphere with a minimum thickness of ~8 km (Nagumo et al., 1986; Hirata et al., 1991; Oshida et al., 1992; Klingelhoefer et al., 2009). Thick sediment supplied from the Yangtze and Yellow rivers covers the seafloor of the Okinawa Trough and reaches ~2 km in its southern part (Sibuet et al., 1987). The volcanic rocks sampled in the southern Okinawa Trough range from calc-alkaline andesite to rhyolite (Shinjo et al., 1999). Active hydrothermal vents were discovered close to some of the seafloor volcanic edifices and the composition of both the venting fluids and hydrothermal deposits were described in a several works (Okamoto et al., 2002; Glasby and Notsu, 2003; Gena et al., 2005).

The Daiyon-Yonaguni Knoll is one of the seamounts that delineate a volcanic belt in the southernmost part of the Okinawa Trough (Matsumoto et al., 2001) (Fig. 1 B). An active hydrothermal field, adjacent to this seamount and named after it, is located in an elongated valley (~1000 m long and ~500 m wide) covered by thick muddy sediment (Gena et al., 2005) (Fig. 1 B). Volcanic breccias were observed in the northeastern part of the hydrothermal field. Four major hydrothermal chimney-mound complexes venting hot (up to 328°C) both black and clear fluids are aligned north-south and were named Lion, Tiger, Swallow and Crystal (Konno et al., 2006; Suzuki et al., 2008; Fujiwara et al., 2015). Liquid CO₂ emissions were detected at the seafloor between the Tiger and Swallow sites (Konno et al., 2006). Diffuse venting (T ≤ 80°C) was observed in the southern part of the hydrothermal field and named the Abyss Vent (Suzuki et al., 2008).

## 3. Samples

In our efforts to shed more light on the mineralogy and geochemistry of the stibnite-orpiment containing deposits at the Daiyon-Yonaguni Knoll hydrothermal field, we selected six
samples (collected during the R/V *Natsushima* cruise NT01-05 Leg2; 2001) of active chimney and active chimney flange from the Tiger vent (Table 1; Fig. 2) (sample repository of the JAMSTEC) and investigated them. Sub-samples from macroscopically different areas of the samples (Fig. 2) were collected using a mini-drill bore with diamond bit and ground to fine powders in an agate mortar for further analyses. Thin polished sections were prepared from each sample for optical microscopy and electron microprobe investigations.

Eleven vent fluid samples (recovered during the R/V *Yokosuka* cruise YK03-05; 2003) collected from the Tiger vent (8 samples from the vent and 2 from the buoyant plume above the vent) and Abyss diffuse venting site (1 sample) using water-hydrothermal *atsuryoku* tight sampler (WHATS; developed for collecting fluid samples while maintaining gas pressure; Tsunogai et al., 2003), bag sampler, and Niskin sampler (Table 2) were filtered (0.45 µm membrane filters) and acidified immediately after recovery and analyzed in onshore laboratories later.

# 4. Methods of investigation

## 4.1. Mineralogy of hydrothermal deposits

Initially, the hydrothermal deposit samples were observed with a stereomicroscope (Nikon SMZ745T) and pictures of the major minerals that constitute the samples were acquired in natural light. The mineral composition and texture of the samples were investigated in thin polished sections by optical polarizing microscope (Nikon ECLIPSE LV100N POL) in transmitted and reflected light.

Crystal habit of the minerals that compose the studied samples was studied on small (~1x1 cm) sub-samples using a Hitachi TM3030 Plus tabletop scanning electron microscope (SEM) (V=15.0 kV, I=1850 mA, electron beam diameter 0.1 µm), after mounting of the sub-samples on aluminum stubs using carbon tape and coating them with carbon. The crystal habit was documented on secondary electron images (SEI) and the chemistry (qualitative) of the imaged minerals was probed by energy dispersive X-ray spectrometry (EDS).
Mineral chemistry (point analyses) and element distribution within the minerals (X-ray maps in major elements detected: Sb Lα, As Lα, Ba Lα, S Kα lines) were analyzed on thin polished sections (those used in the optical microscope studies) after coating them with carbon and using JEOL JXA-8230 electron microprobe (EMP) (V=15 kV, I=1.2 nA, electron beam diameter 2 µm). Standards used were CaSO₄ (S Kα), Sb₂S₃ (S Kα and Sb Lα), CaCO₃ (Ca Kα), GaAs (As Lα), As (As Lα), BaSO₄ (Ba Lα), SrSO₄ (Sr Lα), and the detection limits (in wt.%) were 0.030 for Sb, 0.013 for S (CaSO₄ standard), 0.005 for S (Sb₂S₃ standard), 0.027 for As (As standard), 0.017 for As (GaAs standard), 0.016 for Ca, 0.047 for Ba, 0.018 for Sr.

Bulk mineral composition of the finely powdered samples was determined by X-ray diffraction (XRD) analysis of random mounts using Rigaku Ultima IV X-ray diffractometer with monochromatic Cu Kα radiation with scans from 4 to 70 °2θ, with 0.05 °2θ step, and 4 s/step.
XRD patterns were interpreted by using the MacDiff software.

## 4.2. Chemistry of hydrothermal deposits

Chemistry (elemental concentrations) of the hydrothermal deposits was determined by Inductively Coupled Plasma Quadrupole Mass Spectrometer (ICP-QMS; Thermo Fisher Scientific i-CAP Q; Department of Systems Innovation, The University of Tokyo) after total sample dissolution (Kato et al., 1998; 2002; 2005; Yasukawa et al., 2014; 2020). In short, after drying the sample powders at 110°C for ~12 h, we weighed ~50 mg from each sample and put them in Teflon beakers. The samples were dissolved with HNO₃-HF-HClO₄ after heating on a hot (130°C) plate in the tightly closed beakers for 2 h. The dissolved samples were progressively evaporated at 110°C for 12 h, at 160°C for 6 h, and at 190°C until dry. The residues were subsequently dissolved in 2 mL *aqua regia* on a hot (90°C) plate for 6 h. The dissolved samples were progressively evaporated at 120°C for 2 h, then at 160°C until dry. Subsequently, the residues were dissolved by 10 mL of a 2 wt.% acid mixture consisting of HNO₃:HCl:HF (20:5:1) on a hot (90°C) plate for 3 h. The remaining residues in the solutions were removed by filtration (0.45-µm mesh, polytetrafluoroethylene membrane filters; Merck Millipore Millex®), precisely weighted and investigated by XRD. Before the ICP-QMS measurements the sample solutions were diluted to 1:50, 1:250 and 1:500 (or 1:10000, 1:50000, and 1:100000 with respect to the
sample powder, respectively) by mass using the same 2 wt.% HNO₃-HCl-HF (20:5:1) acid mixture. During the ICP-QMS measurements, spectral overlaps from oxides and hydroxides (⁴⁴Ca¹⁶O on ⁶⁰Ni, ⁴⁷Ti¹⁶O on ⁶³Cu, ⁵⁰Ti¹⁶O on ⁶⁶Zn, ¹³⁷Ba¹⁶O on ¹⁵³Eu, ¹⁴¹Pr¹⁶O and ¹⁴⁰Ce¹⁶O¹H on ¹⁵⁷Gd, ¹⁴³Nd¹⁶O on ¹⁵⁹Tb, ¹⁴⁷Sm¹⁶O and ¹⁴⁶Nd¹⁶O¹H on ¹⁶³Dy, ¹⁴⁹Sm¹⁶O on ¹⁶⁵Ho, ¹⁵⁰Nd¹⁶O and ¹⁵⁰Sm¹⁶O on ¹⁶⁶Er, and ¹⁶⁵Ho¹⁶O on ¹⁸¹Ta) were corrected following the method described by Aries et al. (2000). Samples along with the standards and blanks were analyzed as one analytical batch. To check the analytical precision and accuracy, reference standards issued by the Geological Survey of Japan [JB-2 (basalt), JB-3 (basalt) (Imai et al., 1995; Makishima and Nakamura, 2006; Lu et al., 2007) and JMS-2 (pelagic clay) (Takaya et al., 2014)] were analyzed twice within the analytical batch. The analytical errors for the unknown samples were calculated on the basis of the relative standard deviation for each element in JMS-2.

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### 4.3. Chemistry of vent fluids

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A pre-concentration method was employed for the determination of the concentrations of a set of elements (Fe, Mn, Co, Ni, Cu, Zn, Cd, Mo, Sb, Pb, U, V, Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) in the collected vent fluids using a separation procedure with the NOBIAS chelate-PA1 resin (Hitachi High-Technologies) following already published protocols (Sohrin et al., 2008; Minami et al., 2015). 2 mL of each fluid sample were weighted and the samples were adjusted to pH~6 with a buffer prior to column purification. Then, the columns were loaded with 0.5 mL of clean resin and the resin was washed with 30 mL 18.2 MΩ water, 0.5 mL 3M HNO₃, and 10 mL 18.2 MΩ water. Before the sample load, the resin was conditioned with 1 mL 2.5% HNO₃ + 120 µL of the buffer to reach a final pH~6. The sample matrix was eluted with 10 mL 18.2 MΩ water. Elements of interest (listed above) were eluted with 23 mL 3M HNO₃. The resin was washed with 20 mL 18.2 MΩ water and the columns stored for further separation procedures. We were not able to measure the As concentrations because of analytical challenges: (1) As is not retained on the NOBIAS resin; (2) As is difficult to be measured directly in the vent fluid because of the number of interferences it experiences during the Inductively Coupled Plasma – Mass Spectrometry (ICP-MS) measurements.

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The solutions with eluted elements were evaporated to dryness and re-dissolved in 2 mL ~0.28M HNO₃ for High Resolution – Inductively Coupled Plasma – Mass Spectrometry (HR-ICP-MS) measurements. Concentrations of elements in these solutions were measured with a HR-ICP-MS Element XR (Thermofisher Scientific) at Pôle de Spectrométrie Océan (PSO, IUEM, Brest, France). Indium was used as an internal standard for correcting drift of the signal and concentrations were calibrated using external calibration standards. A referenced seawater standard (CASS-6; National Research Council, Canada) and one blank were also processed following the above protocol and analyzed with the same HR-ICP-MS instrument.

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## 4.4. Sulfur isotope analysis of hydrothermal deposits and fluids

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The sulfide contained in the hydrothermal deposit samples was separated through the following procedures before the analysis of its S isotope composition:

(1) About 0.5 g of each powdered sample were weighed and put in three-necked flasks. A Pasteur pipette was attached to the tip of a tube connected to the flask and the tip was placed in Cd(CH₃CO₂)₂ solution in a test tube. N₂ gas was introduced in the system for 2-3 minutes.

(2) Fine-grained sulfide minerals were separated using selective chemical dissolution procedures. Sphalerite, pyrrhotite, and galena were reacted with 30 mL 12M HCl at 80°C in the three-necked flask. The glass stopper was tightened and N₂ gas flowed for 20-30 minutes while H₂S gas was generated during the reaction between the sulfides (sphalerite, pyrrhotite, galena) and HCl. The generated H₂S gas was fixed as CdS (yellow precipitate formed in the test tubes) and oxidized to BaSO₄. Chalcopyrite, isocubanite, pyrite, tennantite, and native sulfur were oxidized to SO₄²⁻ in mixture solution of Br₂ and HNO₃ and precipitated as BaSO₄.

(3) The N₂ gas flow was stopped, 1 mL H₂O₂ solution was added in the test tube, the tube was plugged with a rubber stopper, stirred, and left overnight.

(4) The solution was transferred from the test tube to a beaker and heated on a hot (140°C) plate until the solution amount was reduced by ~20%. If a white precipitate formed, 2 mL 6M HCl were added and the precipitate was collected by filtration.

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260 (5) The sample solution was heated to 140°C, 10 mL BaCl₂ solution was added to it and it was left overnight. Precipitated BaSO₄ was collected through suction filtration and dried at 261 110°C. 262

263 BaSO₄ recovered through the above procedures was used for measuring the S-isotope 264 composition of the sulfide in the hydrothermal deposit samples. 265

266 Sulfur isotope composition of sulfate in the vent fluids was analyzed according to the following protocol. 2 mL of each fluid sample was diluted with 10 mL 18.2 MΩ water, acidified 267 with 1 mL 6M HCl and heated at 150°C for 5 minutes. 1 mL BaCl₂ solution was added to each 268 sample solution to precipitate dissolved sulfate as BaSO₄, which was collected by filtration and 269 dried at 110°C. Recovered BaSO₄ was used for measuring the S-isotope composition of the vent 270 fluid sulfate. 271

271 0.15-0.20 mg BaSO₄ precipitate from all samples (deposits and vent fluids) were mixed 272 with 1.0-3.0 mg V₂O₅ and wrapped in Sn capsules. In a similar way, MSS-2 and MSS-3 273 standards were mixed with V₂O₅ and wrapped in Sn capsules as work standards for measurement. 274 The S isotopes were measured by EA-IRMS, the data are reported against the Canyon Diablo 275 Troilite (CDT) and expressed in per mil (‰). The analytical error of the measurements was ± 276 0.3‰. 277

278 4.5. Lead isotope analysis of hydrothermal deposits 279

280 All reagents used for sample preparation for Pb isotope analyses were Optima-grade. The 281 sample preparation was performed under a clean lab environment at the Department of 282 Geological Sciences at the University of Florida. Around 30 mg of sample powder was 283 transferred in pre-cleaned Teflon beaker and dissolved in 3 mL aqua regia on a hot (100°C) plate 284 overnight. After digestion, the solutions were evaporated to dryness and the dry residue was 285 dissolved in 1M HBr and loaded on columns packed with clean Dowex 1X-8 resin to separate Pb 286 for isotope analysis. After 3x1 mL of 1M HBr washes the purified Pb fraction was collected in 1 287 mL of 3M HNO₃. Pb isotopes were determined with Tl-normalization on a “Nu Plasma” Multi- 288 Collector – Inductively Coupled Plasma – Mass Spectrometer (MC-ICP-MS), following methods 289 described in Kamenov et al. (2004). The reported Pb isotope data for the samples are relative to
290 NBS 981 values of $^{206}\text{Pb}/^{204}\text{Pb}=16.937$ (±0.004, 2σ), $^{207}\text{Pb}/^{204}\text{Pb}=15.490$ (±0.004, 2σ),
291 $^{208}\text{Pb}/^{204}\text{Pb}=36.695$ (±0.009, 2σ).

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293 **4.6. Stability phase diagrams modeling**

294

295 In order to get insight into the conditions of abiogenic precipitation of the stibnite, orpiment
296 and barite in the studied hydrothermal chimneys we modeled Eh vs log₁₀a phase diagrams at the
297 physical-chemical conditions of three selected vent fluids (Daiyon-Yonaguni Knoll hydrothermal
298 field) using the Geochemist's Workbench 8.0 (GWB) software (based on the “thermo_minteq”
299 database) (Bethke, 2008).

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301 **4.7. Investigations of filamentous structures**

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303 Raman spectra of selected sub-samples (light orange filamentous structures and
304 surrounding dark red colloform mineral) from sample 2K1267 L1 were acquired using a Horiba
305 LabRAM HR 800 Raman spectrometer (Department of Materials and Environmental Chemistry,
306 Stockholm University), equipped with an air cooled double-frequency Nd:YAG laser operating at
307 532 nm. The selected sub-samples were exposed to a laser power of 5 mW through an objective
308 lens with 50× magnification (NA 0.42). A diffraction grating with 600 grooves mm⁻¹ was used to
309 resolve the spectra. Acquisition time was set at 2 s, with 20 scans accumulated from 0 to 4000
310 cm⁻¹ with a spectral resolution of 2 cm⁻¹.

311 The filamentous structures were further studied using a stereomicroscope (Olympus SZX2-ILLT) and an Olympus BX51 microscope with an X-cite Series 120 Q fluorescence light source.
312 The filaments were stained by CalcoFlourwhite (BioTium), a dye that binds to chitin. Before 313 staining, the samples were treated with sterile gloves and forceps to reduce the introduction of 314 exotic fluorescent particles.
315

316 An XL30 environmental scanning electron microscope (ESEM) with a field emission gun
317 (XL30 ESEM-FEG) was also used to analyze the filamentous structures. The ESEM was
318 equipped with an Oxford x-act energy dispersive spectrometer (EDS), backscatter electron (BSE)
319 detector and a secondary electron (SE) detector. The acceleration voltage was 20 kV. The
instrument was calibrated with a cobalt standard. Peak and element analyses were recorded using
the accompanying AZTEC software.

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## 5. Results

324

### 5.1. Mineralogy of hydrothermal deposits

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The hand specimens of the studied deposits were porous, fragile, greyish-black (Fig. 2 A) to blackish-grey (Fig. 2 B, E, F) with orange to white stains (Fig. 2 B-F).

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The XRD studies of bulk samples (active chimney and active chimney flange) showed that the major mineral that composes them is barite (Table 3). Only one sample of active chimney is composed of pyrite and isocubanite (Table 3). However, our stereomicroscope, optical polarizing microscope, SEM and EMP studies showed regular presence of two other minerals (stibnite and orpiment) and traces of several others (native sulfur, pyrite, gypsum, and clays). Obviously, these minerals are in quantities below the XRD detection limits: i.e., <4 wt.%. We will focus our attention on the stibnite and orpiment in the following description.

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Long (0.3 mm), needle-like, black to grey with metallic lustre stibnite forms rosettes of radiating crystals, which fill cavities and cover the surface of greyish-white to white barite (Fig. 3 A). The optical microscope (thin polished sections) and SEM observations revealed that the studied samples were composed of bunches and stacks of prismatic and tabular transparent (in transmitted light) crystals of barite overgrown by long prismatic crystals of stibnite forming rosettes (Fig. 3 B, C). The average empirical formula of stibnite is Sb<sub>1.93</sub>As<sub>0.08</sub>S<sub>3.00</sub> (average of 10 point analyses; Table 4), which suggests that its chemistry is close to the stoichiometry with a little excess in cations. Mapping of the concentration distributions of the elements (in characteristic lines) present in the studied samples showed that Sb, As and S are homogenously distributed within the stibnite crystals (Fig. 4 A, B, D, E) and the stibnite always grows on barite (Fig. 4 A-D).

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Orange filaments (Fig. 5 A) and dark red colloform aggregates (Fig. 5 B) of orpiment stain the surface of the samples and fill cracks in them. At places, yellow fine precipitates and yellow thin filaments of orpiment occur along with the orange orpiment filaments and overgrow
transparent to white barite crystals (Fig. 5 F). Orpiment mostly occurs as colloform masses (Fig. 5 D) composed of fine (<1 µm) crystals deposited on barite. Rarely, it occurs as stacks of branching filaments ~300 µm long and 20 µm wide (Fig. 5 C, E) with clear axis and two concentric zones in cross section (Fig. 5 E). Orpiment rarely contains traces of Sb and has an average empirical formula As₁.₉₈Sb₀.₀₁S₃.₀₁ (average of 19 point analyses; Table 4). The chemistry of orpiment slightly deviates from the stoichiometry with a slight deficiency in cations and slight excess in S. Orpiment and barite show homogenous distribution of the major elements that compose them (As and S, and Ba and S, respectively; Fig. 6 A-E) and only the traces of Sb in the orpiment show slight enrichment in some zones (Fig. 6 B).

The most common morphology of barite in the studied samples is tabular (match box-like; Fig. 3 D), but radial barite crystals forming rosettes (dendritic barite) among the sulfides can rarely be observed (Fig. 3 E). The average empirical formula of barite (Ba₀.₉₅Ca₀.₀₃Sr₀.₀₂)SO₄ (average of 5 point analyses; Table 4) is close to the stoichiometry with traces of Ca and Sr as isomorphic replacements for Ba. Whitish-yellow to yellow native sulfur (as closely packed rhombic crystals; Fig. 3 F), fine-grained greenish-yellow pyrite, white gypsum, and flake-like alumino-silicates (presumably clays) filling the open space among the barite crystals are rare minerals.

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## 5.2. Geochemistry of hydrothermal deposits

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Logically, the chemistry of the stibnite and orpiment separates (expected to be monomineralic according to stereomicroscope observations) differ from that of the bulk samples (Table 5). Orpiment samples along with that of stibnite are rich in As, Ca, Mg, K, Al, Ti, Fe, Mn, Zn, Pb, Bi, Hf, Ta, U, and Au (Table 5). The bulk samples as well as the stibnite sample are rich in Sb, and P (Table 5). The stibnite separate is highly enriched in Tl (Table 5). The stibnite and orpiment separates are richer in REE than the bulk deposit samples (ΣREE; Table 6). The bulk samples exhibit well-pronounced negative Ce anomaly (Ce/Ce*<1) when normalized to chondrite REE concentrations whereas the stibnite and orpiment samples show either less-pronounced negative or weak positive Ce anomaly (Ce/Ce*>1) (Table 6; Fig. 7 A). Bulk deposit samples

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379 show stronger both positive Eu anomaly (Eu/Eu*>1) and light REE enrichment relative to the
380 heavy REE (LaCN/LuCN>1) than the stibnite and orpiment separates (Table 6; Fig. 7 A).
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5.3. *Geochemistry of vent fluids*

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384 Previous works investigated the major ion chemistry of the Daiyon-Yonaguni Knoll
385 hydrothermal fluids (Suzuki et al., 2008) and in order to complete our knowledge on them, we
386 focused our attention on the trace elements chemistry of these fluids (Table 7). Although the REE
387 were studied in the Daiyon-Yonaguni Knoll fluids (Hongo et al., 2007), we extended this
388 exploration with more detailed analysis of the Tiger vent fluids and analyzed for the first time the
389 REE in the Abyss vent fluids (Table 8). In order to facilitate the interpretations of the vent fluid
390 chemistry from the point of view of possible phase separation and to consider the potential vent
391 fluid mixing with seawater, we also cite Cl and Mg concentrations in the same fluids from
392 previous work (Suzuki et al., 2008) (Tables 7, 8). Chlorine and Mg concentrations in the seawater
393 from the vicinity of the Tiger vent (Suzuki et al., 2008) are given as background values (Table 7).
394 The chemistry of the Tiger vent end-member fluid was calculated by extrapolating the data points
395 in Mg vs. Element diagrams to 0 mmol/kg Mg, considering that Mg is quantitatively removed
396 from seawater during its interaction with hot magmatic rocks of the basement (Von Damm,
397 1990).
398

398 Vent fluid with the highest chlorinity (D762 W1 F, [Cl] = 606 mmol/kg) and lowest Mg
399 concentration ([Mg] = 18.4 mmol/kg) has the highest concentrations of Fe, La, Ce, Pr, Nd, Sm,
400 Eu, Tb, ΣREE, second high concentrations of Mn, Ni and Y, and the lowest concentrations of Sb
401 (Tables 7, 8). Two other vent fluids with high chlorinity and low Mg content (D763 W2 F, D763
402 W4 F) have the highest concentrations of Zn, Pb, Cu and Cd, high contents of Fe, Mn, Ni and Sb,
403 high Eu anomalies, low concentration of V, and the lowest content of U (along with sample D762
404 W1 F) (Tables 7, 8). The chemistry of the Tiger vent end-member fluid is close to that of the
405 three vent fluids with the lowest Mg content and highest chlorinity (D762 W1 F, D763 W2 F,
406 D763 W4 F). Iron, Mn, Y and REE concentrations of the Tiger end-member fluid are close to
407 those of the vent fluid with the highest chlorinity (D762 W1 F), whereas the concentrations of
408 Zn, Pb, Cu, Ni and Cd in the end-member fluid are similar to those in the other two high-
409 chlorinity and low-Mg vent fluids (D763 W2 F, D763 W4 F) (Tables 7, 8). The Tiger end-
410 member fluid has very low Mo and V concentrations, and U content calculated to be negative
411 (Table 7).

412 The fluid of the buoyant plume above the Tiger vent has the lowest concentrations of Fe,
413 Mn, Ni, Y and REE, and the highest content of V (Tables 7, 8).

414 The low-temperature Abyss vent fluid (T = 80°C; Table 2) has a chlorinity ([Cl] = 547
415 mmol/kg) close to that of the local seawater ([Cl] = 544 mmol/kg), the highest Mn, Y, Dy, Ho,
416 Er, Tm, Yb and Lu concentrations, the lowest Pb and Cd concentrations, among the lowest Zn,
417 Mo, Sb and Co concentrations, and the lowest positive Eu anomaly (Tables 7, 8).

418 Chondrite-normalized REE distribution patterns of the Tiger venting and end-member
419 fluids show weak negative Ce anomalies, weak to strong positive Eu anomalies and enrichment
420 in the light relative to heavy REE (Fig. 7 B, Table 8). The REE distribution pattern of the Tiger
421 end-member fluid closely resembles that of the venting fluid with the highest chlorinity (D762
422 W1 F; Fig. 7 B). Chondrite-normalized REE distribution pattern of the low-temperature Abyss
423 vent fluid shows weak both negative Ce and positive Eu anomalies, and flat distribution of the
424 heavy REE (Fig. 7 B, Table 8). Y/Ho ratio of all venting fluids and of the Tiger end-member
425 fluid is between 50 and 100, and is lower than that of the previously published data for the Tiger
426 hydrothermal fluids (Y/Ho > 100, Table 8; Hongo et al., 2007).

427
428 5.4. Sulfur isotope compositions of hydrothermal deposits and vent fluids
429

430 The S-isotope composition of the sulfides from the studied Daiyon-Yonaguni Knoll
431 hydrothermal deposits varies in a narrow range (δ³⁴S*sulfide* = 4.0 - 5.3‰; Table 5), falling within
432 the range of the S-isotope composition of the Okinawa Trough hydrothermal deposits (Fig. 8).

433 The S-isotope composition of the Daiyon-Yonaguni Knoll vent fluid sulfate (δ³⁴S*sulfate* =
434 20.3 - 21.6‰; Table 7) clusters around the average seawater value (δ³⁴S*sulfate* = 20.97 ± 0.10‰;
435 Paris et al., 2013) with some scattering to slightly lighter (2 samples) and slightly heavier (2
436 samples) isotope compositions relative to that of seawater (Table 7, Fig. 8).

437
438 5.5. Lead isotope composition of hydrothermal deposits
Lead isotope data for the analyzed hydrothermal deposits are presented in Table 9. The samples show relatively limited variations in $^{206}$Pb/$^{204}$Pb (18.491 to 18.545), but wider spread in $^{207}$Pb/$^{204}$Pb (15.575 to 15.652) and $^{208}$Pb/$^{204}$Pb (38.564 to 38.951). As a result the data form a relatively steep linear trend in Pb isotope space (Fig. 9).

## 5.6. Stability phase diagrams modeling

In the modeling of Eh vs $log_{10}a$ phase diagrams for the stability of the stibnite, orpiment, barite and the most possible Sb-, As- and Ba-ions at the conditions of Daiyon-Yonaguni Knoll hydrothermal system, we used the physical and chemical parameters of three vent fluids. We chose the vent fluids with: the highest temperature (sample D759 W1 F, Tiger vent), the lowest temperature (sample D762 B F, Abyss vent), and the highest both chlorinity and metal concentrations (sample D763 W2 F, Tiger vent) (Tables 2, 7). For the modeling we used our data for vent fluid temperature, pH, hydrostatic pressure (calculated from the depth of sampling), and trace element concentrations (Tables 2, 7). Major ion concentrations, which we used, were the unpublished vent fluid chemistry on the basis of which Suzuki et al. (2008) calculated the Daiyon-Yonaguni Knoll end-member hydrothermal fluid. They were as follows:

(1) sample D759 W1 F: [Cl] = 550 mmol/kg, [SO₄] = 28.8 mmol/kg, [NH₄] = 0.14 mmol/kg, [Na] = 450 mmol/kg, [K] = 9.9 mmol/kg, [Mg] = 49.2 mmol/kg, [Ca] = 9.4 mmol/kg, [B] = 0.40 mmol/kg, [SiO₂] = 0.18 mmol/kg, [Sr] = 81.6 µmol/kg;

(2) sample D763 W2 F: [Cl] = 600 mmol/kg, [SO₄] = 13.1 mmol/kg, [NH₄] = 4.96 mmol/kg, [Na] = 454 mmol/kg, [K] = 58.0 mmol/kg, [Mg] = 22.0 mmol/kg, [Ca] = 17.8 mmol/kg, [Li] = 2.53 mmol/kg, [B] = 2.49 mmol/kg, [SiO₂] = 7.33 mmol/kg, [Sr] = 98.8 µmol/kg;

(3) sample D762 B F: [Cl] = 547 mmol/kg, [SO₄] = 23.9 mmol/kg, [NH₄] = 1.04 mmol/kg, [Na] = 456 mmol/kg, [K] = 14.4 mmol/kg, [Mg] = 45.9 mmol/kg, [Ca] = 9.6 mmol/kg, [B] = 0.72 mmol/kg, [SiO₂] = 2.65 mmol/kg, [Sr] = 84.1 µmol/kg.

## 5.7. Carbonaceous matter in the orpiment filaments
The Raman spectra of orpiment filaments (sample 2K1267 L1) are characterized by bands between 1000 and 1800 cm⁻¹, and between 2700 and 3000 cm⁻¹, denoted as first and second order regions, respectively (Fig. 10 B). These bands are typical of carbonaceous matter (Kouketsu et al., 2014; Qu et al., 2015) that suggests the orpiment filaments contain carbonaceous matter.

The two main bands occurring at approximately 1350 and 1600 cm⁻¹ in the first order region are commonly identified as disordered carbon (D) and ordered graphite (G) bands, respectively. These bands have previously been attributed as ring breathing modes of disordered carbonaceous matter, and in-plane vibrations of sp² carbon atoms (Ferrari and Robertson, 2000). Moreover, the intensity ratio between the D and G bands (I(1350)/I(1600)) has previously been used to indicate the structure order of the carbonaceous matter (Kouketsu et al., 2014; Qu et al., 2015), and the calculated value of 0.765±0.08 was obtained for the analyzed filaments.

Additionally, a deconvolution of the region between 1000 and 1800 cm⁻¹ was done. Using the FWHM-D1 value calculated, and applying the relationship determined by Kouketsu et al. (2014), the maximum temperature experienced by the filaments was calculated to be between 190-230°C.

The Raman spectra of both light orange filamentous (Fig. 10 B) and dark red colloform (Fig. 10 C) structures showed a weak band at 230 cm⁻¹, and a broad strong band at 339 cm⁻¹, which supported the electron microprobe analyses that both types of sub-samples are composed of an arsenic sulfide mineral phase. Previously, in analogous deposits from hydrothermal vents off Milos Island, similar Raman spectra were attributed to poorly to non-crystalline forms of orpiment (Godelitsas et al., 2015).

Staining with ChalcoFlourWhite under fluorescence microscopy turned out to be unsuccessful, thus suggesting that chitin is not present in the filaments.

The ESEM analyses (sample 2K1267 L1) are in support of the Raman data indicating a carbonaceous phase associated with the filaments. The carbonaceous matter occurs rather as a film coating the filaments than incorporated in them (Fig. 11).

# 6. Discussion
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500

6.1. Sequence of mineral precipitation at the Daiyon-Yonaguni Knoll hydrothermal field

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The chemistry of the major mineral in the studied deposits, barite (Table 3), is close to its stoichiometry with negligible isomorphic replacement of Ca and Sr for Ba (Table 4). The isomorphic replacements of As for Sb and of Sb for As in stibnite and orpiment, respectively, are also insignificant and the chemistries of the studied stibnite and orpiment (Table 4) practically match their stoichiometric empirical formulae. The textural relations between the major barite and minor stibnite and orpiment (Figs 3 B, C; 4 A-E; 5 F; 6 A-E) suggest that the stibnite and orpiment have precipitated after barite.

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Barite is an abundant mineral in the back-arc basin hydrothermal deposits (Shikazono and Kusakabe, 1999) and a number of studies have been focused on it (e.g., Shikazono, 1994; Shikazono et al., 2012; Jamieson et al., 2016). These studies showed that tabular large-crystal barite with smooth crystal faces precipitates from solutions with low degrees of supersaturation (saturation index below ~100) and dominates the barite deposited at the back-arc basin hydrothermal systems (Shikazono, 1994). Dendritic barite with rough crystal faces is rare (or lacking) in these deposits and forms from solutions with high degrees of supersaturation (Shikazono, 1994). It was found that dendritic barite at seafloor hydrothermal systems precipitates from fluids composed of less than 40% hydrothermal end-member fluid (and more than 60% seawater), whereas the tabular barite forms from fluids containing greater proportion of hydrothermal end-member fluid (Jamieson et al., 2016). In general, the seafloor hydrothermal barite precipitates from solutions with high flow rates (i.e., focused discharge) (Shikazono et al., 2012) and at temperatures of between 100°C and 240°C (Tokunaga and Honma, 1974; Jamieson et al., 2016).

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Our studies of the Daiyon-Yonaguni Knoll hydrothermal deposits confirm the previous observations that the tabular barite is the dominant barite morphology at the back-arc basin hydrothermal systems (Shikazono, 1994). On the basis of the knowledge gained up to now we may infer that the Daiyon-Yonaguni Knoll barite precipitated from focused-discharge fluids composed of high proportion (>40%) of hydrothermal end-member fluid and at temperatures 100-240°C. The minor minerals, stibnite and orpiment, have precipitated after barite and seem to be later lower temperature precipitates.
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## 6.2. Phase separation and trace element chemistry of the Daiyon-Yonaguni Knoll vent fluids

The chlorinities of all studied fluids from the Tiger and Abyss vents vary and are higher than that of the local ambient seawater (Table 7). The richest in chloride vent fluid (D762 W1 F) has a chlorinity ~11% higher than that of the seawater. Deviations (positive and negative) from seawater chlorinity have long been measured in seafloor hydrothermal fluids (Edmond et al., 1979; Michard et al., 1984; Von Damm et al., 1985a; Von Damm and Bischoff, 1987; Bowers et al., 1988; Butterfield et al., 1990; Von Damm, 1990; Butterfield et al., 1994; Von Damm et al., 2005) and explained with sub-seafloor boiling and phase separation (Von Damm, 1990). Analyzing the major ion chemistry of the Daiyon-Yonaguni Knoll vent fluids Suzuki et al. (2008) also ascribed their enhanced chlorinity relative to the ambient seawater to sub-seafloor phase separation.

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Sub-seafloor boiling, phase separation and emission of brine-rich (chloride-rich) fluids from the Daiyon-Yonaguni Knoll vents explain the enrichment in non-volatile elements (Fe, Mn, Zn, Pb, Cu, Cd, Ni, Y, La, Ce, Pr, Nd, Sm, Eu and Tb) and depletion in volatile elements (Sb) of the three Tiger vent fluids with the highest chlorinity and lowest Mg content as well as of the Tiger vent end-member fluid (Tables 7, 8). The lowest concentrations of Mo, V and U in the lowest-Mg (highest chlorinity) vent fluids and in the end-member fluid ([Mg] = 0 mmol/kg) (Table 7) support the knowledge that these elements are nearly quantitatively removed from the seawater during its interaction with the hot basement rocks (German and Von Damm, 2003) and their contents in a vent fluid depend on the seawater proportion in it. The calculated negative U concentration in the end-member fluid (Table 7) implies that U is not only 0 nmol/kg in this fluid, but that the end-member fluid is a sink for U from the seawater and entrains it upon fluid-seawater mixing.

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The lowest concentrations of Fe, Mn, Ni, Y and REE, and the highest content of V in the fluid of the buoyant plume above the Tiger vent (Tables 7, 8) are likely a result of removal of dissolved Fe, Mn, Ni, Y and REE from the vent fluid to plume particles (Feely et al., 1990; Ludford et al., 1996; Edmonds and German, 2004; Klevenz et al., 2011; Findlay et al., 2015) and entrainment of seawater V (Trefry and Metz, 1989), respectively.
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Although the chlorinity of the Abyss vent fluid is close to that of the ambient seawater it is yet slightly higher than it (Table 7). This implies that the Abyss low-temperature vent fluid must contain a proportion of high-temperature brine-rich vent fluid that has undergone phase separation (Von Damm and Lilley, 2004). The low Pb, Cd, Zn and Sb concentrations in the Abyss vent fluid (Table 7) are likely a result of sub-seafloor element-sulfide precipitation during fluid cooling and dilution with seawater that are typical for low-temperature diffuse venting at the seafloor (Koschinsky et al., 2002). As the most ubiquitous metal in the seafloor hydrothermal fluids, Fe, preferentially precipitates relative to the other common metal Mn on cooling (Seyfried and Ding, 1993) the low-temperature vent fluids usually appear to be enriched in Mn over Fe (Thompson et al., 1985) and this explains the highest Mn concentration in the Abyss vent fluids (Table 7).

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The highest concentrations of La, Ce, Pr, Nd, Sm, Eu and Tb in the highest chlorinity (and high-temperature) vent fluid (Tiger vent, D762 W1 F) and the highest concentrations of Y, Dy, Ho, Er, Tm, Yb and Lu in the lowest chlorinity (and low-temperature) vent fluid (Abyss vent, D762 B F) are directly related to the chlorinity and temperature control on the distribution of the REE in the vent fluids (Table 8; Fig. 7 B). Previous studies revealed (1) that in a chloride-rich hydrothermal fluid, the REE transport is facilitated by formation of chloride complexes at acidic conditions and (2) that the light REE (La-Sm) are complexed more strongly by chloride, than the heavy REE (Gd-Lu) (Haas et al., 1995). At elevated temperatures this relation (2) becomes more pronounced. The REE speciation calculations (Douville et al., 1999a) confirmed that in the hot acidic fluids of the seafloor hydrothermal systems the REE were mainly complexed by $Cl^-$ ions. Because the Cl$^-$ complexing tends to be stronger for the light REE, an increased aqueous chloride content will tend to favor these lighter elements. Therefore, the high-chlorinity high-temperature Tiger vent fluids have the highest contents of La, Ce, Pr, Nd, Sm, Eu and Tb, whereas the low-chlorinity low-temperature Abyss vent fluids have the highest contents of Y, Dy, Ho, Er, Tm, Yb and Lu within the Daiyon-Yonaguni Knoll vent field.

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Compared to the end-member hydrothermal fluids from three other sedimented seafloor hydrothermal systems (Escanaba Trough, Guaymas Basin and Middle Valley), the Daiyon-Yonaguni Knoll end-member hydrothermal fluid shows the highest Pb, La, Ce, Pr, Nd, Sm, Eu, Tb, Dy, Ho and Er concentrations, and the lowest Mn concentration (Table 10). These differences
deserve particular scientific attention involving the chemistry of the source rocks (volcanic and sedimentary) that is beyond the scope of this work.

### 6.3. Yttrium and REE insights into fluid-rock equilibrium

In most seafloor hydrothermal fluids, Y is trivalent and behaves like Ho, and it is supposed that the Y/Ho molar ratio can give important clues for the origin of the hydrothermal fluids (Douville et al., 1999a). The Y/Ho molar ratio of the studied Daiyon-Yonaguni Knoll vent fluids (50.5 - 76.4; Table 8) is between that of the southern Okinawa Trough lavas [27.6 - 31.8, basalts, andesites, dacites and rhyolites; Shinjo et al. (1999), Shu et al. (2017), Guo et al. (2018)] and North Pacific deep water (101; Nozaki et al., 1999). It seems likely that the seawater-based hydrothermal fluids of the Daiyon-Yonaguni Knoll field have not completely lost their original high seawater Y/Ho molar ratio (Bau and Dulski, 1999; Nozaki et al., 1999). This suggests that the seawater has not completely reacted with the basement rocks and has not equilibrated with them.

The REE distribution pattern of the Daiyon-Yonaguni Knoll end-member fluid (Fig. 7 B) implies the same conclusion. It not only closely matches the REE distribution pattern of the highest chlorinity Tiger vent fluid (D762 W1 F) thus, suggesting that this fluid is close to the end-member, but still shows a weak negative Ce anomaly (Fig. 7 B). This supports the assumption that the mother fluid, seawater, has not completely reacted with the basement rocks and has not completely lost its original negative Ce anomaly.

The origin of the positive Eu anomaly and the enrichment of light REE over the heavy REE when the REE concentrations are normalized to those of chondrite are discussed elsewhere (Michard et al., 1983; Michard and Albarède, 1986; Michard, 1989; Klinkhammer et al., 1994; Bau and Dulski, 1999; Douville et al., 1999a) and we will not repeat this discussion here.

### 6.4. Trace elements in the Daiyon-Yonaguni Knoll hydrothermal deposits: hydrothermal – microbial – hydrogen genetic interplay
The studied Daiyon-Yonaguni Knoll hydrothermal deposits (bulk samples and mineral separates) are rich in Sb and As (Table 5). Previous works (Douville et al., 1999b; Breuer and Pichler, 2013) found that these two volatile elements are particularly enriched in the hydrothermal fluids discharged at back-arc and volcanic arc settings. Their high concentrations in these fluids are inferred to be primarily controlled by phase separation processes and source rock types: felsic volcanic rocks and sedimentary blanket. Thus, the fluid phase separation at the Daiyon-Yonaguni Knoll vents (see 6.2) and the source rock types, felsic volcanics [calc-alkaline andesite to rhyolite; Shinjo et al. (1999)] and sediment cover (Sibuet et al., 1987) explain the high Sb and As concentrations in the hydrothermal deposits. Antimony and As are highly volatile elements and most probably separate in the vapor (low-chlorinity) during the boiling and phase separation. As the chlorinities of all studied vent fluids are higher than that of the local ambient seawater (Table 7), it seems reasonable to assume that Sb and As minerals in the Daiyon-Yonaguni Knoll deposits had precipitated in the past when the vapor phase (rich in volatiles) had dominated in the vent fluids.

Thallium is also a volatile element and its high concentration in the stibnite precipitates (Table 5) may also be explained with vent fluid phase separation and source rock types.

Gold concentrations in the bulk Daiyon-Yonaguni Knoll hydrothermal deposits (0.50 - 1.00 ppm; Table 5) fall within the range of Au content in the Okinawa Trough hydrothermal deposits (0.05 - 4.5 ppm; Fuchs et al., 2019) whereas the Daiyon-Yonaguni Knoll stibnite and orpiment samples are richer in Au (1.00 - 11.0 ppm; Table 5) than the Okinawa Trough hydrothermal deposits. However, the Au concentrations of the Daiyon-Yonaguni Knoll hydrothermal deposits (0.50 - 11.0 ppm; Table 5) are within the lower end of the Au content range of the global seafloor hydrothermal deposits (0.01 - 43.0 ppm; Fuchs et al., 2019). Almost linear correlation between Au and As concentrations (diagram available on request) suggests that (1) Au (like As) is hydrothermally derived in these deposits, (2) Au (like As) may also be contributed by direct magmatic degassing (e.g., Fuchs et al., 2019), and (3) As plays an essential role in Au intake in the As-containing sulfides (Pokrovski et al., 2021).

Higher concentrations of Fe, Mn, Zn, Pb and Bi in the orpiment samples than in the bulk samples can be explained with high hydrothermal input.
In addition to the high Au concentrations, the stibnite and orpiment samples have also enhanced U concentrations relative to those of the bulk deposit samples (Table 5). This seems controversial because unlike Au, the U is quantitatively removed (~98%) from seawater during hydrothermal circulation through the oceanic crust (Michard and Albarede, 1985; Chen et al., 1986) and, as a result, the seafloor end-member hydrothermal fluids are depleted in U. Therefore, hydrothermal contribution of U to the Daiyon-Yonaguni Knoll hydrothermal deposits had likely been negligible and the low U concentrations of the bulk samples (0.03-0.07 ppm; Table 5) seem to show that. The enhanced U concentrations in the stibnite and orpiment samples (0.12-3.96 ppm; Table 5) relative to the bulk deposits suggest that a factor other than the hydrothermal fluid controlled U concentration in the stibnite and orpiment. Previous work (Lovley et al., 1991; Mills et al., 1994) suggested that U enrichment within the TAG seafloor hydrothermal deposits is microbially mediated. The presence of carbonaceous matter associated with the filamentous orpiment and inferred microbial activity (see 6.6) imply that the elevated U content in this type of orpiment is a result of bacterial concentration of U from a seawater-dominated fluid. Thus, the enrichments of the stibnite and orpiment in two elements with different mechanisms of mobilization and fixation, Au and U, likely happened at different stages of the mineral deposition. Gold seems to have been deposited within stibnite and orpiment, and during their hydrothermal precipitation, while U has mostly likely been deposited within bacterial biofilms on stibnite and orpiment after their deposition.

Chondrite-normalized REE distribution patterns of the Daiyon-Yonaguni Knoll (bulk) deposits and one stibnite and one orpiment samples show negative Ce anomalies, positive Eu anomalies and enrichment of light relative to the heavy REE (Fig. 7 A; Table 6). These patterns resemble that of the Daiyon-Yonaguni Knoll end-member hydrothermal fluid, which slightly differs from those of the end-member fluids from other seafloor hydrothermal fields (Michard et al., 1983; Michard and Albarède, 1986; Michard, 1989; Klinkhammer et al., 1994; Bau and Dulski, 1999; Douville et al., 1999a) in possessing of a weak negative Ce anomaly (Fig. 7 B). We interpreted this feature as a result of incomplete reaction of seawater with the basement rocks and partial preservation of its original negative Ce anomaly (see 6.3). Thus, the REE distribution patterns of the discussed deposits (bulk, one stibnite and one orpiment) seem to be inherited from the end-member hydrothermal fluid (mixed or not with ambient seawater). However, two of the
orpiment samples (2K1271 L1 flange, outer bottom, Op and 2K1267 L1, Op-1) have positive Ce anomalies, highest Nd concentrations, the smallest positive Eu anomalies, and the smallest fractionation between the light and heavy REE (LaCN/LuCN) (Table 6; Fig. 7 A). Previous studies showed that positive Ce anomalies and high Nd concentrations (>100 ppm) are typical for the seafloor hydrogenetic Fe-Mn deposits (Bau et al., 2014). The origin of the positive Ce anomaly in the seafloor Fe-Mn deposits is discussed elsewhere (Bau and Koschinsky, 2009). Although we are not aware of any particular study of the REE in the seafloor hydrothermal orpiment we may assume that the observed positive Ce anomalies, high Nd concentrations, little positive Eu anomalies, and little fractionation between the light and heavy REE in the two orpiment samples (Table 6) are results of hydrogenetic influence.

Hence, the trace element contents in the Daiyon-Yonaguni Knoll hydrothermal deposits suggest a complex interplay among hydrothermal (hydrothermal input), microbial (preferential concentration) and hydrogenetic (preferential scavenging from seawater) processes.

## 6.5. Origin of S in the sulfide precipitates and sulfate reduction in the vent fluids of the Daiyon-Yonaguni Knoll hydrothermal field

The S-isotope systematics in the seafloor hydrothermal systems at arc/back-arc settings show substantial variability in δ³⁴S (Fig. 8). The wide variation in δ³⁴S is a result of S-isotope fractionation due to three processes contributing to the S budget of the hydrothermal system: (1) basement rock sulfide supplied by interaction of hydrothermal fluid with basement rocks (Shanks and Seyfried, 1987; Shanks, 2001), (2) thermochemical reduction of sulfate supplied by seawater (Shanks and Seyfried, 1987; Shanks, 2001), (3) disproportionation of SO₂ supplied by magma vapors (Kusakabe et al., 2000; Peters et al., 2021).

Sulfide S of the Daiyon-Yonaguni Knoll hydrothermal deposits has isotope composition (δ³⁴S) between those of the terrestrial mantle (basement rocks) sulfide and seawater sulfate, but being closer to the former (Table 5; Fig. 8). This suggests that the Daiyon-Yonaguni Knoll S bound in sulfides is a mixture of both basement rock and seawater S with a higher proportion of the basement rock S. The S-isotope composition of the Daiyon-Yonaguni Knoll sulfides supports the origin of sulfide S in the overall Okinawa Trough hydrothermal deposits being generally
dominated by basement rock S (Fig. 8). There are no clear indications for magmatic S supply to
the Daiyon-Yonaguni Knoll hydrothermal deposits.

The slightly heavier S-isotope composition of sulfate in one Tiger vent and one Abyss vent fluids (21.2 and 21.6‰, respectively; Table 7) than that of the seawater (δ³⁴Sₗsulfate = 20.97 ± 0.10‰; Paris et al., 2013) is similar to the heavy S-isotope composition of sulfate of the CLAM hydrothermal fluids (δ³⁴Sₗsulfate > 21.0‰; Gamo et al., 1991) and deserves some consideration. We know that sulfate reduction in a closed system causes an increase of δ³⁴S of the residual sulfate (removal of the isotopically light sulfide during sulfate reduction) with decreasing sulfate concentration (Ohmoto and Rye, 1979; Shanks et al., 1981). Thus, the S-isotope composition of the sulfate from these two Daiyon-Yonaguni Knoll vent fluids can be interpreted as a result of sulfate reduction. Sulfate reduction or sulfide oxidation depends on the rate of mixing between the hydrothermal fluid and seawater (Peter and Shanks, 1992). Slow mixing of the hydrothermal fluid and seawater in the chimney walls or within a mound favors sulfate reduction. This sulfate reduction results in S isotope fractionation approaching equilibrium values and ³⁴S-enriched sulfate resulting from a reservoir effect, as ³²S is removed to the sulfide reservoir (Peter and Shanks, 1992). Overall, it appears that the hydrothermal fluid mixed slowly with seawater within the chimney walls of the Tiger and Abyss vents that favored reduction of the sulfate dissolved in the fluids and resulted in a heavy S-isotope composition of the vent fluids.

725

## 6.6. *Sources of Pb to the Daiyon-Yonaguni Knoll hydrothermal deposits*

727

The Pb isotope data for the Daiyon-Yonaguni Knoll hydrothermal deposits form a steep array indicating mixing of two Pb end-members (Fig. 9). At the low end of the array is sample 2K1271 L1 flange, outer bottom, Op. This sample plots below regional sedimentary and volcanic rocks, towards the NHRL indicating more primitive, mantle-like source of Pb. This in turn suggests presence of more depleted Pb isotopic source, possibly back-arc mafic volcanic rocks, in the area of Daiyon-Yonaguni Knoll. Three of the samples (2K1271 L1 flange, center upper; 2K1271 L1 flange, outer bottom, Stb; and 2K1271 L1, Op) plot close to the regional lavas. This suggests that Pb and other metals in these three hydrothermal samples can be derived from the local lavas. Alternatively, the Pb isotopic compositions of these three samples can be explained

728

729

730

731

732

733

734

735

736
by mixing between the more primitive source, responsible for the isotopic composition of 737 2K1271 L1 flange, outer bottom, Op and more enriched source reflected in the rest of the 738 hydrothermal deposit samples. The enriched samples are very similar to laser ablation Pb isotope 739 data for galena and anglesite from the Daiyon-Yonaguni Knoll (Zeng et al., 2022) and plot above 740 the regional lavas indicating Pb derivation from more evolved source, potentially continental 741 lithosphere and/or sedimentary rocks. This is consistent with Pb isotope studies of other 742 hydrothermal deposits in the Okinawa Trough that also found evidence for significant 743 involvement of sedimentary Pb in the hydrothermal systems (e.g., Ma et al., 2021; Zeng et al., 744 2022). However, it is interesting to note that the Pb isotope data for the closest hydrothermal 745 fields [southern Okinawa Trough (SOT) sulfides] are very distinct from the Daiyon-Yonaguni 746 Knoll hydrothermal deposits (Fig. 9). As can be seen on the Figure 9, the SOT sulfides are close 747 to the regional sediment Pb data, thus providing direct evidence for a significant sedimentary 748 component in the hydrothermal system (Ma et al., 2021). In contrast, the Daiyon-Yonaguni Knoll 749 hydrothermal deposits are isotopically distinct from the SOT sulfides. Furthermore, the 750 hydrothermal deposits are not close isotopically to any of the available sediment samples (Fig. 9). 751 However, based on their position above the regional volcanic rocks it is most likely that another 752 enriched source, either sediments or extended continental lithosphere, is present in the area of 753 Daiyon-Yonaguni Knoll. 754

755

6.7. *Filamentous orpiment: biogenic or abiogenic?* 756

757

The morphology of the light orange filaments (Fig. 5 A, C, E) resembles microbial fossils 758 (especially, fossilized fungi) previously described at the seafloor (Ivarsson et al., 2020). The 759 longitudinal, branching filaments forming a network-like framework (Fig. 5 A, C) can be 760 compared to fossilized fungal mycelium. The consistent and distinct center of the filaments (Fig. 761 5 C, E) corresponds size-wise to known sizes for fungal hyphae. The empty core (Fig. 5 E) can be 762 the remains or cast of an initial microbial/fungal filament/hyphae. However, the concentric 763 layering in cross sections of the filaments (Fig. 5 E) implies this morphology can be a result of 764 repeated mineral deposition. Additionally, the overall features of the filaments with the rather 765 straight appearance, the 90° branching and interconnections between filaments, the distinct 766
767 tapering and variation in diameter could be explained by abiotic biomorphs, or heavily encrusted
768 fungal hyphae. Based on morphology alone we can neither rule out nor support a biological or an
769 abiotic origin of the filaments at this point. The staining for chitin was unsuccessful, thus there is
770 no solid evidence for fungal (biogenic) origin of the filaments.

771 The Raman data, on the other hand, supports the presence of carbonaceous matter
772 associated with the orpiment filaments. Thus, even though a fungal origin of the orpiment
773 filaments cannot be unambiguously supported, the presence of microbial activity can be. The
774 filaments and their close proximity appear coated by a thin carbonaceous film that may represent
775 the remains of a biofilm. The I(1350)/I(1600) value indicates that the carbonaceous matter
776 associated with the filaments present medium structural order. The calculated maximum
777 temperature experienced by the filaments (209.1±37.1°C) falls within the temperature range of
778 the vent fluids (Table 2) and indicates that the carbonaceous matter reached low to medium-grade
779 thermal maturity. This excludes the possibility of recent contamination by carbonaceous matter
780 and supports the idea that the carbonaceous matter associated with the orpiment filaments is
781 indigenous to the primary hydrothermal environment.

782
783 6.8. Stibnite, orpiment and barite hydrothermal precipitation: implications from stability phase
784 diagrams

785
786 The maximum temperature, which the GWB can consider in the modeling is 300°C.
787 Therefore, we used this temperature when modeling the stability diagrams for vent fluid sample
788 D759 W1 F (T = 323°C) (Fig. 12 A, D, G).

789 In view of the chemistry of the Daiyon-Yonaguni Knoll vent fluids (Tables 7, 8; Suzuki et
790 al., 2008), it seems plausible to assume that the major Sb- and As-ions in these fluids will be
791 chloride and sulfide. We could not obtain any stability diagrams when using Sb-chloride and As-
792 chloride ions as major Sb- and As-ions, respectively, in the vent fluid. This may mean that the
793 incorporation of these species in the GWB data base may not be correct. Therefore, we used Sb-
794 sulfide ions as main Sb-ions in the vent fluids. Using the measured Sb concentrations in the
795 Daiyon-Yonaguni Knoll vent fluids (Table 7) in the modeling, we did not get any stability field
796 of stibnite. This suggests that stibnite does not precipitate from the current vent fluids: Sb content
797 is lower than that necessary for stibnite precipitation. Therefore, we put as a variable $log_{10}a$ of the
798 main Sb-ion suggested by the GWB, $Sb_2S_4^{2-}$, along one of the axes of the diagrams (Fig. 12 A, B,
799 C).

800 On the basis of the vent fluid chemistry of the three vent fluids the GWB suggested only
801 one As-sulfide ion, but it did not yield any diagram with stability field of orpiment. The main As-
802 ion suggested by the GWB was $H_2AsO_4^-$ and we used it in the modeling. As we were not able to
803 measure the As concentrations in the vent fluids (see sub-section 4.3) we put as a variable $log_{10}a$
804 of $H_2AsO_4^-$ along one of the axes of the diagrams and investigated a wide range of $log_{10}a$: from -
805 10 to +5 (Fig. 12 D, E, F).
806

806 We assumed that $Ba^{2+}$ will be the major Ba ion in the studied vent fluids and therefore, we
807 used $Ba^{2+}$ in the modeling of barite stability (Fig. 12 G, H, I).

808 Modeling suggests that the stibnite has a limited area of stability within the
809 physicochemical conditions of the selected vent fluids (Fig. 12 A, B, C). Its area of stability does
810 not seem to depend on the vent fluid chlorinity: The area of stability of stibnite in the most
811 chloride-rich fluid, D763 W2 F, does not differ substantially from those in the other fluids (Fig.
812 12 A, B, C). Obviously, the stability of stibnite increases with decreasing temperature of the vent
813 fluid and results in precipitation at lower $log_{10}a$ of $Sb_2S_4^{2-}$ (i.e., lower Sb concentrations) and less
814 reduced environment (i.e., higher Eh, but still <0) (Fig. 12 A, B, C). In other words, the lowest
815 temperature Daiyon-Yonaguni Knoll vent fluid (D762 B F; T = 80°C) is the most probable
816 environment for stibnite precipitation.

817 Orpiment is stable (i.e., precipitates) in a wide range of $log_{10}a$ of $H_2AsO_4^-$ (i.e., As
818 concentrations) and in reducing conditions (Eh<0) (Fig. 12 D, E, F). With decreasing vent fluid
819 temperature (from 300°C to 80°C), orpiment is stable (precipitates) at slightly less reduced
820 conditions (higher Eh, but still <0) (Fig. 12 D, E, F). The differences in vent fluid chlorinity and
821 vent fluid trace metal concentrations do not seem to affect the stability of orpiment (Fig. 12 D, E,
822 F). Previous studies (Rytuba, 1984) add an additional constraint for orpiment precipitation.
823 According to them, under conditions of constant temperature and pressure, the relative stability of
824 As-sulfides is a function of S activity. Orpiment appears to be the stable As-sulfide at high S
825 activity, which suggests high S activity during the orpiment precipitation at the Daiyon-Yonaguni
826 Knoll hydrothermal site.
Modeling showed that in the high-temperature vent fluids D759 W1 F (T = 300°C) and D763 W2 F (T = 210°C), the major Ba-ion is BaCl⁺ (Fig. 12 G, H), whereas in the low-temperature vent fluid D762 B F (T = 80°C) dissolved Ba appears as Ba²⁺ (Fig. 12 I). Barite is stable in wide range of log₁₀a of Ba²⁺ (i.e., Ba concentrations) in all the three vent fluids and precipitates from slightly reduced to slightly oxic conditions (Fig. 12 G, H, I). With decreasing temperature of the vent fluid (from 300°C to 80°C), the stability field of barite slightly shifts to less reduced (more oxic) conditions (Fig. 12 G, H, I). Modeling of barite precipitation from the Daiyon-Yonaguni Knoll vent fluids shows large stability field of barite in wide temperature range (80-300°C) and extends previous knowledge that hydrothermal barite precipitates at temperatures 100-240°C (see 6.1).

837

## 7. Summary

839

The major mineral in the Daiyon-Yonaguni Knoll hydrothermal deposits is barite, which likely precipitated from focused-discharge fluids composed of a high proportion (>40%) of hydrothermal end-member fluid at T = 100-240°C. Stibnite and orpiment are minor minerals, which seem to be later lower temperature precipitates.

The Daiyon-Yonaguni Knoll vent fluids were subjected to sub-seafloor boiling and phase separation and are brine-rich (chloride-rich) enriched in non-volatile and depleted in volatile elements. Sub-seafloor boiling and phase separation exerted major control on the REE partitioning in the vent fluids, with the high-chlorinity high-temperature fluids enriched in light REE and low-chlorinity low-temperature fluids enriched in heavy REE. The Y/Ho molar ratio and Ce anomaly of the Daiyon-Yonaguni Knoll vent fluids suggest that the seawater had not completely reacted with the basement rocks and had not equilibrated with them.

The trace element contents in the Daiyon-Yonaguni Knoll hydrothermal deposits suggest a complex interplay among hydrothermal, microbial and hydrogenetic processes.

Sulfur isotope composition of the Daiyon-Yonaguni Knoll sulfides suggests that the sulfide S is a mixture of both basement rock and seawater S, with a higher proportion of the basement rock S. The hydrothermal fluid mixed slowly with seawater within the chimney walls of the Tiger
and Abyss vents which favored reduction of the sulfate dissolved in the fluids and resulted in a
heavy S-isotope composition of the vent fluid sulfate.

The Pb isotope data for the Daiyon-Yonaguni Knoll hydrothermal deposits indicate
involvement of two or even three sources of metals in the hydrothermal system. One of the
sources can be local volcanic rocks, as three of the samples show Pb isotopes close to the latter.
However, the Pb isotope data form a steep array that potentially can be explained by only two
end-members, one enriched (continental lithosphere and/or sediments) and one depleted (possibly
back-arc basalts). It is interesting to note that both of these end-members are discrete, not
identifiable in the available Pb isotope data for southern Okinawa sedimentary and volcanic
rocks.

The morphology details of the filamentous orpiment suggest that these filaments are either
heavily mineralized fungal hyphae or pure abiogenic biomorphs. Although a fungal origin of the
orpiment filaments cannot be unambiguously inferred, microbial activity (presence of
carbonaceous matter) is detected at/around them. The filaments experienced temperature of
209.1±37.1°C which falls within the temperature range of the Daiyon-Yonaguni Knoll vent fluids
and indicates that the carbonaceous matter on/within the filaments reached low to medium-grade
thermal maturity.

Modeling of stability phase diagrams suggests that the stability of stibnite does not seem to
depend on the vent fluid chlorinity, but rather on the vent fluid temperature: the area of stibnite
stability increases with decreasing temperature of the vent fluid and results in stibnite
precipitation at lower log₁₀a of Sb₂S₄²⁻ and less reduced environment (i.e., high Eh, but still <0).
Orpiment is stable in a wide range of log₁₀a of H₂AsO₄⁻, in reduced conditions and at high S
activity. The variations in vent fluid chlorinity and trace metal concentrations do not seem to
affect the stability of orpiment. Barite is stable over a wide range of log₁₀a of Ba²⁺ and
precipitates in slightly reduced to slightly oxic conditions.

881

882 Declaration of Competing Interest

883

The authors declare that they have no known competing financial interests or personal
relationships that could have appeared to influence the work reported in this paper.

885
886

887 Acknowledgements

888

889 The successful completion of this work would not be possible without the valuable support of Dr.

890 T. Tomiyama (JAMSTEC), who generously provided the hydrothermal deposit samples, Prof. Y.

891 Takahashi (University of Tokyo), who gave us the possibility to perform the SEM studies in his

892 lab, and Mrs. M. Otsuki (TUMSAT), who helped with the EMP analyses. We greatly appreciate

893 their help. The suggestions and comments by two anonymous reviewers improved the paper

894 significantly and are highly appreciated.

895

896

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1283 Tsunogai, U., Toki, T., Nakayama, N., Gamo, T., Kato, H., Kaneko, S., 2003. WHATS: a new multi-bottle gas-tight

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1285 Ueno, H., Hamasaki, H., Murakawa, Y., Kitazono, S., Takeda, T., 2003. Ore and gangue minerals of sulfide

1286 chimneys from the North Knoll, Iheya Ridge, Okinawa Trough, Japan. JAMSTEC J. Deep Sea Res. 22, 49-

1287 62.

1288 Von Damm, K.L., 1990. Seafloor hydrothermal activity: Black smoker chemistry and chimneys. Annu. Rev. Earth

1289 Planet. Sci. 18, 173-204.

1290 Von Damm, K.L., Bischoff, J.L., 1987. Chemistry of hydrothermal solutions from the Southern Juan de Fuca Ridge.

1291 J. Geophys. Res. 92, 11334-11346.

1292 Von Damm, K.L., Lilley, M.D., 2004. Diffuse flow hydrothermal fluids from 9°50′N East Pacific Rise: Origin,

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1294 S.C. (Eds), The Subseafloor Biosphere at Mid-Ocean Ridges. Geophysical Monograph Series 144, American

1295 Geophysical Union, Washington, DC. pp. 245-268.

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1297 hydrothermal solutions at 21°N, East Pacific Rise. Geochim. Cosmochim. Acta 49, 2197-2220.

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1300 Von Damm, K.L., Parker, C.M., Zierenberg, R.A., Lilley, M.D., Olson, E.J., Clague, D.A., McClain, J.S., 2005. The

1301 Escanaba Trough, Gorda Ridge hydrothermal system: Temporal stability and subseafloor complexity.

1302 Geochim. Cosmochim. Acta 69, 21, 4971-4984.

1303 Webber, A.P., Roberts, S., Murton, B.J., Hodgkinson, M.R.S., 2015. Geology, sulfide geochemistry and supercritical

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1305 2678.

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1308 4572.

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1312 Wakamiko Crater of Kagoshima Bay, southern Kyushu, Japan. J. Volcanol. Geotherm. Res. 258, 74-84.

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1314 characteristics of metalliferous sediments from the Tangyin hydrothermal field in the southern Okinawa

1315 Trough. Ore Geol. Rev. 120, 103464.
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1319 Geochemical features of Fe-Mn micronodules in deep-sea sediments of the western North Pacific Ocean:

1320 Potential for co-product metal extraction from REY-rich mud. Ore Geol. Rev. 127, 103805.

1321 Zeng, Z., Chen, Z., Qi, H., 2022. Two processes of anglesite formation and a model of secondary supergene

1322 enrichment of Bi and Ag in seafloor hydrothermal sulfide deposits. J. Mar. Sci. Eng. 10, 35.

1323 Zierenberg, R.A., Shanks, W.C., III., Bischoff, J.L., 1984. Massive sulfide deposits at 21°N, East Pacific Rise:

1324 chemical composition, stable isotopes, and phase equilibria. Geol. Soc. Am. Bull. 95, 922-929.

1325

1326

1327

Figure captions

1328

1329 **Fig. 1.** (A) Map of Ryukyu Trench-Arc system and Okinawa Trough with location of Daiyon-

1330 Yonaguni Knoll hydrothermal field (red solid square); (B) Detail map of the Daiyon-Yonaguni

1331 Knoll hydrothermal field with location of sample site (red solid dot).

1332

1333 **Fig. 2.** Studied samples from the Daiyon-Yonaguni Knoll hydrothermal field: (A) active

1334 hydrothermal chimney, sample 2K1271 L1 lower outer; (B) active hydrothermal chimney flange,

1335 sample 2K1271 L1 flange, outer top; (C) active hydrothermal chimney flange, sample 2K1271

1336 L1 flange, center upper; (D) active hydrothermal chimney flange, sample 2K1271 L1 flange,

1337 outer bottom; (E) massive sulfide, sample 2K1267 L1; (F) massive sulfide, sample 2K1267 L2.

1338

1339 **Fig. 3.** Photomicrographs of stibnite, barite, and native sulfur from the Daiyon-Yonaguni Knoll

1340 hydrothermal deposits: (A) needle-like crystals of stibnite (Stb) (stereomicroscope, sample

1341 2K1271 L1 flange, center upper); (B) thin, needle-like, radial crystals of stibnite (Stb) over

1342 prismatic, transparent crystals of barite (Bt) (thin polished section, optical microscope,

1343 transmitted plain polarized light, sample 2K1271 L1 flange, outer top); (C) rosettes of stibnite

1344 (Stb) radial crystals (SEM, SEI, sample 2K1271 L1 flange, outer top); (D) match box-like

1345 crystals of barite (Bt) (SEM, SEI, sample 2K1267 L1); (E) radial barite (Bt) crystals (dendritic

1346 barite) among coated by amorphous silica pyrite (Py) (SEM, SEI, sample 2K1267 L2); (F)

1347 rhombic crystals of native sulfur (SEM, SEI, sample 2K1267 L1).
1348
**Fig. 4.** X-ray maps and BSE image of stibnite (Stb) within barite (Bt) matrix in the Daiyon-
Yonaguni Knoll hydrothermal deposit (sample 2K1271 L1 flange, outer top): (A) X-ray scan in
Sb Lα; (B) X-ray scan in As Lα; (C) X-ray scan in Ba Lα; (D) X-ray scan in S Kα; (E) BSE
image. Color scales (right-hand side), elemental concentrations.
1350
1351
1352
1353

1354 **Fig. 5.** Photomicrographs of orpiment from the Daiyon-Yonaguni Knoll hydrothermal deposits: (A) fillaments of orpiment (orange) (stereomicroscope, sample 2K1271 L1 flange, outer top); (B) colloform orpiment (red) (stereomicroscope, sample 2K1267 L1); (C) fillaments of orpiment among thin tabular crystals of barite (Bt) (SEM, SEI, sample 2K1267 L1); (D) colloform orpiment (SEM, SEI, sample 2K1267 L1); (E) cross-section of the filament-like orpiment shown at (C), note the concentric internal structure of the filaments (SEM, SEI, sample 2K1267 L1); (F) bunches of reddish-white barite (Bt) crystals partly covered by fine yellow orpiment (Op) crystals (thin polished section, optical microscope, reflected plain polarized light, sample 2K1271 L1 flange, outer top). 1355
1356
1357
1358
1359
1360
1361
1362
1363

1364 **Fig. 6.** X-ray maps and BSE image of orpiment (Op) over barite (Bt) crystals in the Daiyon-
Yonaguni Knoll hydrothermal deposit (sample 2K1271 L1 flange, outer top): (A) X-ray scan in
As Lα; (B) X-ray scan in Sb Lα; (C) X-ray scan in Ba Lα; (D) X-ray scan in S Kα; (E) BSE
image. Color scales (right-hand side), elemental concentrations.
1365
1366
1367
1368

1369 **Fig. 7.** CI chondrite-normalized (McDonough and Sun, 1995) REE distribution patterns of the
1370 studied hydrothermal deposits (A) and vent fluids (B) from the Daiyon-Yonaguni Knoll
1371 hydrothermal field (Okinawa Trough). NPDW = North Pacific Deep Water (Alibo and Nozaki,
1372 1999).
1373

1374 **Fig. 8.** Sulfur-isotope composition (range) of selected hydrothermal deposits from mid-ocean ridges [unsedimented (mafic- and ultramafic-hosted) and sedimented], volcanic arcs and back-arc basins compared to those of studied stibnite-orpiment-containing deposits and vent fluids (sulfate S) from the Daiyon-Yonaguni Knoll hydrothermal field, Okinawa Trough. References: terrestrial 1375
1376
1377
mantle (Labidi et al., 2012), seawater (Paris et al., 2013), Galapagos Rift (Skirrow and Coleman, 1982; Knott et al., 1995), 21°N EPR (Hekinian et al., 1980; Arnold and Sheppard, 1981; Styrt et al., 1981; Kerridge et al., 1983; Zierenberg et al., 1984; Woodruff and Shanks, 1988; Stuart et al., 1994), 11-13°N EPR (Bluth and Ohmoto, 1988; Stuart et al., 1995; Fouquet et al., 1996; Ono et al., 2007), 9-10°N EPR (Ono et al., 2007), 18-21°S EPR (Marchig et al., 1990; Ono et al., 2007), Lucky Strike (Rouxel et al., 2004; Ono et al., 2007), Broken Spur (Duckworth et al., 1995; Butler et al., 1998), TAG (Stuart et al., 1994; Gemmell and Sharpe, 1998; Herzig et al., 1998; Shanks, 2001), Snakepit (Kase et al., 1990; Stuart et al., 1994), Southern MAR (Peters et al., 2010), Rainbow (Rouxel et al., 2004), Logatchev (Rouxel et al., 2004; Peters et al., 2010), Semenov (Melekestseva, 2010), Red Sea (Shanks, 2001), Juan de Fuca (Shanks et al., 1984; Shanks and Seyfried, 1987; Hannington and Scott, 1988; Stuart et al., 1994), Escanaba Trough (Shanks, 2001), Guaymas Basin (Shanks, 2001), Okinawa Trough (Lüders et al., 2001; Ueno et al., 2003; Nishio and Chiba, 2012; Kawasumi et al., 2016; Yang et al., 2020), Izu-Bonin Arc (Alt et al., 1998), Mariana Trough (Kusakabe et al., 1990), Manus Basin (Kim et al., 2004), Lau Basin (Kim et al., 2011), Kermadec Arc (de Ronde et al., 2005; 2011), Aeolian Arc (Peters et al., 2011; Petersen et al., 2014).

**Fig. 9.** Pb isotope data for the studied Daiyon-Yonaguni Knoll (DYK) hydrothermal (hydroT) deposits compared to DYK hydrothermal Pb minerals (galena and anglesite) (Zeng et al., 2022), southern Okinawa Trough (SOT) sulfides (Ma et al., 2021), and southern (S) Okinawa and Ryukyu sediments and lavas (Bentahila et al., 2008; Shu et al., 2017; Chen et al., 2019). Dotted line is the Northern Hemisphere Reference Line (NHRL), after Hart (1984). Note that the studied DYK hydrothermal deposits form a trend from the DYK Pb hydrothermal minerals to the regional lavas and one sample extending to much lower $^{207}$Pb/$^{204}$Pb and $^{208}$Pb/$^{204}$Pb toward the NHRL, for more discussion see the text.

**Fig. 10.** (A) Photomicrograph (stereomicroscope) of orpiment from the Daiyon-Yonaguni Knoll hydrothermal deposits (sample 2K1267 L1) with positions (B, C) of the sub-samples analyzed by Raman spectroscopy (see Raman spectra at panels B and C); (B) Raman spectrum of light orange filamentous orpiment containing carbonaceous matter with characteristic D and G bands in the
1408 first-order region, and bands in the second-order region; (C) Raman spectrum of dark red
1409 colloform orpiment surrounding the filamentous orpiment. Raman intensity in arbitrary units
1410 (a.u.).

1411
1412 Fig. 11. ESEM image (A) and EDS spectra (B: spectrum 136) and (C: spectrum 137) showing the
distribution of carbon as indicative of carbonaceous matter associated with the orpiment
1413
filaments (note, the major elements are As and S). 1414

1415
1416 Fig. 12. Stability phase diagrams for the chemical species (dissolved and solid) in the three
1417 selected vent fluids from the Daiyon-Yonaguni Knoll hydrothermal field: (A), (B) and (C) - Eh-
1418 log₁₀a diagrams calculated for Sb₂S₄²⁻; (D), (E) and (F) - Eh-log₁₀a diagrams calculated for
1419 H₂AsO₄⁻; (G), (H) and (I) - Eh-log₁₀a diagrams calculated for Ba²⁺.
1420
<figure><img src="image_2.png" /></figure>

Water depth (m)

122°36′E 122°40′E 122°44′E

<figure><img src="image_3.png" /></figure>

Water depth (m)
<figure><img src="image_4.png" /><figcaption>A</figcaption></figure>

1 cm

<figure><img src="image_5.png" /><figcaption>B</figcaption></figure>

1 cm

<figure><img src="image_6.png" /><figcaption>C</figcaption></figure>

1 cm

<figure><img src="image_7.png" /><figcaption>D</figcaption></figure>

1 cm

<figure><img src="image_8.png" /><figcaption>E</figcaption></figure>

1 cm

<figure><img src="image_9.png" /><figcaption>F</figcaption></figure>

1 cm
<figure><img src="image_10.png" /></figure>

<figure><img src="image_11.png" /></figure>

<figure><img src="image_12.png" /></figure>

<figure><img src="image_13.png" /></figure>

<figure><img src="image_14.png" /></figure>

<figure><img src="image_15.png" /></figure>
<figure><img src="image_16.png" /></figure>
<figure><img src="image_17.png" /></figure>

<figure><img src="image_18.png" /></figure>

<figure><img src="image_19.png" /></figure>

<figure><img src="image_20.png" /></figure>

<figure><img src="image_21.png" /></figure>

<figure><img src="image_22.png" /></figure>
<figure><img src="image_23.png" /></figure>
<figure><img src="image_24.png" /></figure>

<figure><img src="image_25.png" /></figure>
<figure><img src="image_26.png" /></figure>
$^{208}$Pb/$^{204}$Pb

39.20

39.00

38.80

38.60

38.40

38.20

38.00

37.80

15.70

$^{207}$Pb/$^{204}$Pb

15.65

15.60

15.55

15.50

18.20

18.30

18.40

18.50

18.60

18.70

18.80

<figure><img src="image_27.png" /></figure>

<figure><img src="image_28.png" /></figure>
<figure><img src="image_29.png" /></figure>

<figure><img src="image_30.png" /></figure>

<figure><img src="image_31.png" /></figure>
<figure><img src="image_32.png" /></figure>

<figure><img src="image_33.png" /></figure>

<figure><img src="image_34.png" /></figure>
<figure><img src="image_35.png" /></figure>

<figure><img src="image_36.png" /></figure>

<figure><img src="image_37.png" /></figure>

<figure><img src="image_38.png" /></figure>

<figure><img src="image_39.png" /></figure>

<figure><img src="image_40.png" /></figure>

<figure><img src="image_41.png" /></figure>

<figure><img src="image_42.png" /></figure>

<figure><img src="image_43.png" /></figure>
**Table 1**

<table><caption>Studied hydrothermal deposit samples from the Daiyon-Yonaguni Knoll hydrothermal field (Okinawa Trough).</caption><thead><tr><th>Sample ID</th><th>Vent name</th><th>Sample type</th><th>Latitude (°N)</th><th>Longitude (°E)</th><th>Depth (m)</th><th>Sampling device</th></tr></thead><tbody><tr><td>2K1271 L1 lower outer</td><td>Tiger</td><td>active chimney</td><td>24.8497</td><td>122.6992</td><td>1364</td><td>submersible, Shinkai 2000</td></tr><tr><td>2K1271 L1 flange, outer top</td><td>Tiger</td><td>active chimney flange</td><td>24.8497</td><td>122.6992</td><td>1364</td><td>submersible, Shinkai 2000</td></tr><tr><td>2K1271 L1 flange, center upper</td><td>Tiger</td><td>active chimney flange</td><td>24.8497</td><td>122.6992</td><td>1364</td><td>submersible, Shinkai 2000</td></tr><tr><td>2K1271 L1 flange, outer bottom</td><td>Tiger</td><td>active chimney flange</td><td>24.8497</td><td>122.6992</td><td>1364</td><td>submersible, Shinkai 2000</td></tr><tr><td>2K1267 L1</td><td>Tiger</td><td>active chimney</td><td>24.8489</td><td>122.7002</td><td>1366</td><td>submersible, Shinkai 2000</td></tr><tr><td>2K1267 L2</td><td>Tiger</td><td>active chimney</td><td>24.8489</td><td>122.7002</td><td>1366</td><td>submersible, Shinkai 2000</td></tr></tbody></table>
**Table 2**

Studied vent fluid samples from the Daiyon-Yonaguni Knoll hydrothermal field (Okinawa Trough).

<table><thead><tr><th>Sample ID<sup>a</sup></th><th>Vent name</th><th>Type of venting fluid</th><th>Latitude (°N)</th><th>Longitude (°E)</th><th>Depth (m)</th><th>Temperature (°C)</th><th>pH</th><th>Sampling device</th></tr></thead><tbody><tr><td>D759 W1 F</td><td>Tiger</td><td>grey smoky</td><td>24.8</td><td>122.7</td><td>1366</td><td>323</td><td>5.292</td><td>WHATS</td></tr><tr><td>D760 B F</td><td>Tiger</td><td>clear</td><td>24.8</td><td>122.7</td><td>1362</td><td>-<sup>b</sup></td><td>5.051</td><td>bag sampler</td></tr><tr><td>D762 W1 F</td><td>Tiger</td><td>grey smoky</td><td>24.8</td><td>122.7</td><td>1365</td><td>-</td><td>-</td><td>WHATS</td></tr><tr><td>D763 B F</td><td>Tiger</td><td>grey smoky</td><td>24.8</td><td>122.7</td><td>1365</td><td>210</td><td>-</td><td>bag sampler</td></tr><tr><td>D763 F F</td><td>Tiger</td><td>grey smoky</td><td>24.8</td><td>122.7</td><td>1365</td><td>210</td><td>-</td><td>-</td></tr><tr><td>D763 W2 F</td><td>Tiger</td><td>grey smoky</td><td>24.8</td><td>122.7</td><td>1365</td><td>210</td><td>4.906</td><td>WHATS</td></tr><tr><td>D763 W3 F</td><td>Tiger</td><td>grey smoky</td><td>24.8</td><td>122.7</td><td>1365</td><td>210</td><td>4.743</td><td>WHATS</td></tr><tr><td>D763 W4 F</td><td>Tiger</td><td>grey smoky</td><td>24.8</td><td>122.7</td><td>1365</td><td>210</td><td>4.842</td><td>WHATS</td></tr><tr><td>D762 N1 F</td><td>buoyant plume above Tiger</td><td>grey smoky</td><td>24.8</td><td>122.7</td><td>1359</td><td>-</td><td>6.550</td><td>Niskin sampler</td></tr><tr><td>D762 N2 F</td><td>buoyant plume above Tiger</td><td>grey smoky</td><td>24.8</td><td>122.7</td><td>1359</td><td>-</td><td>6.951</td><td>Niskin sampler</td></tr><tr><td>D762 B F</td><td>Abeyss</td><td>clear</td><td>24.8</td><td>122.7</td><td>1380</td><td>80</td><td>5.297</td><td>bag sampler</td></tr></tbody></table>

<footnote><sup>a</sup> Abbreviations in the sample IDs: W = WHATS sampler; B = bag sampler with pump; N = Niskin sampler; F = filtered.</footnote>

<footnote><sup>b</sup> No data.</footnote>
<caption>**Table 3**</caption>

Bulk mineralogy (XRD) of the studied hydrothermal deposits from the Daiyon-Yonaguni Knoll hydrothermal field (Okinawa Trough).

<table><thead><tr><td>Sample ID</td><td>Mineralogy</td></tr></thead><tbody><tr><td>2K1271 L1 outer lower</td><td>barite</td></tr><tr><td>2K1271 L1 flange, outer top</td><td>barite</td></tr><tr><td>2K1271 L1 flange, center upper</td><td>barite</td></tr><tr><td>2K1271 L1 flange, outer bottom</td><td>barite</td></tr><tr><td>2K1267 L1</td><td>barite</td></tr><tr><td>2K1267 L2</td><td>pyrite, isocubanite</td></tr></tbody></table>
**Table 4**

Mineral chemistry (EMP data) and empirical formulae of stibnite, orpiment, and barite from the studied hydrothermal deposits from the Daiyon-Yonaguni Knoll hydrothermal field (Okinawa Trough).

<table><thead><tr><th>Sample ID</th><th>#<sup>a</sup></th><th>Mineral</th><th>Sb<br>(wt.%)</th><th>S</th><th>As</th><th>BaO<sup>b</sup></th><th>SrO</th><th>SO<sub>3</sub></th><th>CaO</th><th>Total</th><th>Empirical formulae</th></tr></thead><tbody><tr><td>2K1271 L1 flange, outer bottom</td><td>10</td><td>stibnite</td><td>69.68</td><td>28.56</td><td>1.72</td><td>b.d.l.<sup>c</sup></td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>99.95</td><td>Sb<sub>1.93</sub>As<sub>0.08</sub>S<sub>3.00</sub></td></tr><tr><td>2K1271 L1 flange, center upper</td><td>5</td><td>barite</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>64.88</td><td>1.03</td><td>35.77</td><td>0.83</td><td>102.50</td><td>(Ba<sub>0.95</sub>Ca<sub>0.03</sub>Sr<sub>0.02</sub>)SO<sub>4</sub></td></tr><tr><td>2K1267 L1</td><td>19</td><td>orpiment</td><td>0.22</td><td>39.49</td><td>60.49</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>100.20</td><td>As<sub>1.98</sub>Sb<sub>0.01</sub>S<sub>3.01</sub></td></tr></tbody></table>

<footnote><sup>a</sup> Number of EMP analyses.</footnote>

<footnote><sup>b</sup> Concentrations of Ba, Sr, S, and Ca are given in oxide form as they were measured in barite.</footnote>

<footnote><sup>c</sup> b.d.l. = below detection limits.</footnote>
<table><caption>**Table 5**

Chemical (ICP-MS) and S isotope compositions of the studied hydrothermal deposits from the Daiyon-Yonaguni Knoll hydrothermal field (Okinawa Trough).</caption><thead><tr><th>Sample ID</th><th>Sb<br>(wt.%)</th><th>As</th><th>Ca</th><th>Mg</th><th>Na</th><th>K</th><th>Al</th><th>Ti</th><th>P</th><th>Fe</th><th>Mn</th><th>(δ<sup>34</sup>S<sub>sulfide</sub>)<sup>a</sup><br>(‰)</th></tr></thead><tbody><tr><td>2K1271 L1 lower outer</td><td>4.49</td><td>0.52</td><td>0.13</td><td>0.01</td><td>n.m.<sup>b</sup></td><td>0.05</td><td>0.05</td><td>0.0002</td><td>0.047</td><td>0.04</td><td>0.002</td><td>4.0</td></tr><tr><td>2K1271 L1 flange, outer top</td><td>6.29</td><td>0.45</td><td>0.09</td><td>0.01</td><td>n.m.</td><td>0.04</td><td>0.06</td><td>0.0003</td><td>0.004</td><td>0.03</td><td>0.003</td><td>5.1</td></tr><tr><td>2K1271 L1 flange, center upper</td><td>4.87</td><td>0.07</td><td>0.53</td><td>0.01</td><td>n.m.</td><td>0.01</td><td>0.03</td><td>0.0003</td><td>0.087</td><td>0.02</td><td>0.003</td><td>n.m.</td></tr><tr><td>2K1271 L1 flange, outer bottom, Stb<sup>c</sup></td><td>1.96</td><td>1.95</td><td>0.82</td><td>0.01</td><td>n.m.</td><td>0.12</td><td>0.07</td><td>0.0038</td><td>0.032</td><td>0.04</td><td>0.017</td><td>n.m.</td></tr><tr><td>2K1271 L1 flange, outer bottom, Op<sup>d</sup></td><td>0.35</td><td>5.33</td><td>0.80</td><td>0.06</td><td>0.58</td><td>0.15</td><td>0.27</td><td>0.0125</td><td>b.d.l.<sup>e</sup></td><td>0.17</td><td>0.039</td><td>n.m.</td></tr><tr><td>2K1267 L1, Op-1</td><td>0.90</td><td>3.47</td><td>0.64</td><td>0.07</td><td>0.58</td><td>0.16</td><td>0.24</td><td>0.0078</td><td>b.d.l.</td><td>0.10</td><td>0.011</td><td>5.3<sup>f</sup></td></tr><tr><td>2K1267 L1, Op-2</td><td>0.13</td><td>4.17</td><td>0.75</td><td>0.04</td><td>0.20</td><td>0.05</td><td>0.10</td><td>0.0049</td><td>b.d.l.</td><td>0.05</td><td>0.087</td><td>n.m.</td></tr><tr><td colspan="13"><em>Standards</em></td></tr><tr><td>JB-2 (measured)</td><td>0.00002</td><td>0.00026</td><td>6.84</td><td>2.69</td><td>1.43</td><td>0.32</td><td>7.41</td><td>0.77</td><td>0.038</td><td>9.69</td><td>0.168</td><td></td></tr><tr><td>JB-2 (reference)</td><td>0.00002</td><td>0.00029</td><td>6.68</td><td>2.74</td><td>1.49</td><td>0.35</td><td>7.62</td><td>0.70</td><td>0.039</td><td>9.58</td><td>0.162</td><td></td></tr><tr><td>JB-3 (measured)</td><td>0.00001</td><td>0.00015</td><td>7.17</td><td>3.12</td><td>2.12</td><td>0.61</td><td>8.75</td><td>1.01</td><td>0.125</td><td>7.94</td><td>0.134</td><td></td></tr><tr><td>JB-3 (reference)</td><td>0.00001</td><td>0.00018</td><td>6.93</td><td>3.13</td><td>2.03</td><td>0.66</td><td>9.26</td><td>0.82</td><td>0.128</td><td>8.39</td><td>0.143</td><td></td></tr><tr><td>JMS-2 (measured)</td><td>0.00045</td><td>0.00378</td><td>3.47</td><td>1.77</td><td>4.08</td><td>2.04</td><td>6.98</td><td>0.86</td><td>0.54</td><td>7.26</td><td>1.62</td><td></td></tr><tr><td>JMS-2 (reference)</td><td>0.00040</td><td>0.00356</td><td>3.43</td><td>2.02</td><td>4.37</td><td>2.28</td><td>7.66</td><td>0.84</td><td>0.58</td><td>7.65</td><td>1.78</td><td></td></tr><tr><td colspan="13"><em>Detection limits in rock (ppb)</em></td></tr><tr><td></td><td>15</td><td>45</td><td>75</td><td>3140</td><td>3140</td><td>29120</td><td>26235</td><td>1365</td><td>28570</td><td>35</td><td>1445</td><td></td></tr></tbody></table>

<sup>a</sup> Averages of two duplicate measurements.

<sup>b</sup> n.m. = not measured.

<sup>c</sup> Stb = stibnite separate.

<sup>d</sup> Op = orpiment separate.

<sup>e</sup> b.d.l. = below detection limits.

<sup>f</sup> Measured on bulk sample 2K1267 L1.

<table><thead><tr><th>Sample ID</th><th>Cu<br>(ppm)</th><th>Zn</th><th>Pb</th><th>Tl</th><th>Bi</th><th>Ba</th><th>Sr</th><th>Hf</th><th>Ta</th><th>Th</th><th>U</th><th>Au</th></tr></thead><tbody><tr><td>2K1271 L1 lower outer</td><td>736</td><td>108</td><td>54.2</td><td>301</td><td>0.09</td><td>585</td><td>1204</td><td>0.006</td><td>0.005</td><td>0.06</td><td>0.05</td><td>0.79</td></tr><tr><td>2K1271 L1 flange, outer top</td><td>880</td><td>321</td><td>69.4</td><td>278</td><td>0.20</td><td>567</td><td>968</td><td>0.004</td><td>0.002</td><td>0.02</td><td>0.07</td><td>0.74</td></tr><tr><td>2K1271 L1 flange, center upper</td><td>659</td><td>n.m.</td><td>43.0</td><td>427</td><td>0.09</td><td>328</td><td>1040</td><td>0.006</td><td>0.002</td><td>0.02</td><td>0.03</td><td>0.50</td></tr><tr><td>2K1271 L1 flange, outer bottom, Stb<sup>c</sup></td><td>301</td><td>n.m.</td><td>15.7</td><td>1769</td><td>0.13</td><td>377</td><td>2140</td><td>0.011</td><td>0.010</td><td>0.10</td><td>0.12</td><td>1.66</td></tr><tr><td>2K1271 L1 flange, outer bottom, Op<sup>d</sup></td><td>733</td><td>1681</td><td>236</td><td>n.m.</td><td>1.77</td><td>156</td><td>1187</td><td>0.024</td><td>0.017</td><td>0.07</td><td>3.96</td><td>7.75</td></tr><tr><td>2K1267 L1, Op-1</td><td>276</td><td>591</td><td>27.2</td><td>n.m.</td><td>0.32</td><td>182</td><td>1162</td><td>0.023</td><td>0.018</td><td>0.07</td><td>1.02</td><td>4.25</td></tr><tr><td>2K1267 L1, Op-2</td><td>907</td><td>1200</td><td>532</td><td>n.m.</td><td>0.91</td><td>128</td><td>1280</td><td>0.012</td><td>0.005</td><td>0.03</td><td>0.78</td><td>11.0</td></tr><tr><td colspan="13"><em>Standards</em></td></tr><tr><td>JB-2 (measured)</td><td>220</td><td>101</td><td>4.53</td><td>0.011</td><td>0.025</td><td>202</td><td>164</td><td>1.47</td><td>0.03</td><td>0.26</td><td>0.15</td><td>0.01452</td></tr><tr><td>JB-2 (reference)</td><td>219</td><td>107</td><td>4.88</td><td>0.034</td><td>0.028</td><td>215</td><td>177</td><td>1.45</td><td>0.03</td><td>0.26</td><td>0.16</td><td>0.00564</td></tr><tr><td>JB-3 (measured)</td><td>192</td><td>93.1</td><td>4.65</td><td>0.02</td><td>0.01</td><td>223</td><td>369</td><td>2.58</td><td>0.10</td><td>1.24</td><td>0.44</td><td>0.01088</td></tr><tr><td>JB-3 (reference)</td><td>179</td><td>114</td><td>4.85</td><td>0.046</td><td>0.015</td><td>239</td><td>414</td><td>2.65</td><td>0.11</td><td>1.30</td><td>0.48</td><td>0.00199</td></tr><tr><td>JMS-2 (measured)</td><td>430</td><td>139</td><td>81.4</td><td>2.68</td><td>1.27</td><td>1745</td><td>405</td><td>4.95</td><td>1.31</td><td>13.8</td><td>2.62</td><td>0.07265</td></tr><tr><td>JMS-2 (reference)</td><td>472</td><td>167</td><td>77.5</td><td>2.79</td><td>1.38</td><td>1799</td><td>435</td><td>4.88</td><td>1.42</td><td>14.2</td><td>2.77</td><td>-</td></tr><tr><td colspan="13"><em>Detection limits in rock (ppb)</em></td></tr><tr><td></td><td>975</td><td>105</td><td>2.5</td><td>0.45</td><td>2.5</td><td>4</td><td>0.35</td><td>0.05</td><td></td><td>0.25</td><td>0.25</td><td>0.45</td></tr></tbody></table>
**Table 6**

<table><caption>REE concentrations (ICP-MS) in the studied hydrothermal deposits from the Daiyon-Yonaguni Knoll hydrothermal field (Okinawa Trough).</caption><thead><tr><th>Sample ID<sup>a</sup></th><th>La<br>(ppb)</th><th>Ce</th><th>Pr</th><th>Nd</th><th>Sm</th><th>Eu</th><th>Gd</th><th>Tb</th><th>Dy</th><th>Ho</th><th>Er</th><th>Tm</th><th>Yb</th><th>Lu</th><th>ΣREE (Ce/Ce*)<sup>b</sup> (Eu/Eu*)<sup>c</sup></th><th>La<sub>CN</sub>/Lu<sub>CN</sub></th></tr></thead><tbody><tr><td>2K1271 L1 lower outer</td><td>2235</td><td>1404</td><td>98.9</td><td>181</td><td>28.8</td><td>414</td><td>16.4</td><td>1.91</td><td>12.5</td><td>1.83</td><td>6.04</td><td>1.13</td><td>6.34</td><td>0.90</td><td>4409</td><td>0.44</td><td>53.1</td><td>258</td></tr><tr><td>2K1271 L1 flange, outer top</td><td>2460</td><td>1195</td><td>64.5</td><td>140</td><td>11.8</td><td>399</td><td>12.0</td><td>0.95</td><td>5.37</td><td>0.83</td><td>2.89</td><td>0.37</td><td>2.96</td><td>0.46</td><td>4296</td><td>0.35</td><td>101</td><td>553</td></tr><tr><td>2K1271 L1 flange, center upper</td><td>2252</td><td>1218</td><td>70.4</td><td>155</td><td>9.51</td><td>531</td><td>13.9</td><td>1.26</td><td>8.02</td><td>1.13</td><td>3.75</td><td>0.84</td><td>3.57</td><td>0.69</td><td>4269</td><td>0.39</td><td>141</td><td>339</td></tr><tr><td>2K1271 L1 flange, outer bottom, Stb</td><td>2040</td><td>2611</td><td>198</td><td>546</td><td>80.1</td><td>974</td><td>45.0</td><td>5.63</td><td>36.5</td><td>6.27</td><td>15.3</td><td>2.63</td><td>19.2</td><td>2.40</td><td>6582</td><td>0.79</td><td>45.1</td><td>88.4</td></tr><tr><td>2K1271 L1 flange, outer bottom, Op</td><td>1986</td><td>4419</td><td>397</td><td>1056</td><td>144</td><td>544</td><td>91.5</td><td>13.8</td><td>79.3</td><td>14.1</td><td>39.2</td><td>5.73</td><td>32.4</td><td>5.63</td><td>8827</td><td>1.14</td><td>13.5</td><td>36.6</td></tr><tr><td>2K1267 L1, Op-1</td><td>918</td><td>2510</td><td>218</td><td>713</td><td>132</td><td>443</td><td>94.6</td><td>12.8</td><td>75.3</td><td>13.7</td><td>40.6</td><td>6.61</td><td>33.5</td><td>5.62</td><td>5217</td><td>1.32</td><td>11.5</td><td>16.9</td></tr><tr><td>2K1267 L1, Op-2</td><td>4568</td><td>5758</td><td>376</td><td>831</td><td>103</td><td>461</td><td>62.3</td><td>9.41</td><td>51.7</td><td>11.0</td><td>34.4</td><td>4.90</td><td>32.3</td><td>5.40</td><td>12308</td><td>0.81</td><td>16.3</td><td>87.8</td></tr><tr><td colspan="20"><em>Standards</em></td></tr><tr><td>JB-2 (measured)</td><td>2132</td><td>6689</td><td>1079</td><td>6171</td><td>2126</td><td>776</td><td>3099</td><td>551</td><td>3858</td><td>824</td><td>2468</td><td>367</td><td>2443</td><td>364</td><td>32946</td><td>-<sup>d</sup></td><td>-</td><td>-</td></tr><tr><td>JB-2 (reference)</td><td>2140</td><td>6390</td><td>1100</td><td>6320</td><td>2190</td><td>818</td><td>3200</td><td>579</td><td>4010</td><td>868</td><td>2580</td><td>376</td><td>2490</td><td>386</td><td>33447</td><td>-</td><td>-</td><td>-</td></tr><tr><td>JB-3 (measured)</td><td>8437</td><td>21714</td><td>3176</td><td>15952</td><td>4151</td><td>1264</td><td>4606</td><td>713</td><td>4561</td><td>926</td><td>2646</td><td>385</td><td>2461</td><td>373</td><td>71364</td><td>-</td><td>-</td><td>-</td></tr><tr><td>JB-3 (reference)</td><td>8120</td><td>20900</td><td>3140</td><td>15900</td><td>4170</td><td>1310</td><td>4770</td><td>741</td><td>4660</td><td>949</td><td>2690</td><td>380</td><td>2500</td><td>377</td><td>70607</td><td>-</td><td>-</td><td>-</td></tr><tr><td>JMS-3 (measured)</td><td>136276</td><td>164512</td><td>35906</td><td>152814</td><td>34515</td><td>8604</td><td>38855</td><td>5789</td><td>37337</td><td>7673</td><td>22405</td><td>3091</td><td>19616</td><td>2913</td><td>670306</td><td>-</td><td>-</td><td>-</td></tr><tr><td>JMS-3 (reference)</td><td>135261</td><td>159305</td><td>37381</td><td>150059</td><td>35927</td><td>9003</td><td>40093</td><td>6120</td><td>38561</td><td>8065</td><td>23274</td><td>3223</td><td>20301</td><td>3151</td><td>669725</td><td>-</td><td>-</td><td>-</td></tr><tr><td colspan="2">Detection limits in rock (ppb)</td><td>0.83</td><td>4.58</td><td>2.46</td><td>9.27</td><td>1.23</td><td>0.34</td><td>0.78</td><td>0.27</td><td>0.00</td><td>0.00</td><td>0.46</td><td>0.11</td><td>0.00</td><td>0.30</td><td></td><td></td><td></td></tr></tbody></table>

<footnote><sup>a</sup> Abbreviations Stb and Op see in Table 5.</footnote>

<footnote><sup>b</sup> Ce/Ce*=2Ce<sub>CN</sub>/(La<sub>CN</sub>+Pr<sub>CN</sub>).</footnote>

<footnote><sup>c</sup> Eu/Eu*=2Eu<sub>CN</sub>/(Sm<sub>CN</sub>+Gd<sub>CN</sub>).</footnote>

<footnote><sup>d</sup> Ce/Ce*, Eu/Eu*, and La<sub>CN</sub>/Lu<sub>CN</sub> not presented for the standards.</footnote>
<table><caption>**Table 7**

Chemical (ICP-MS) and S isotope compositions of the vent fluids from the Daiyon-Yonaguni Knoll hydrothermal field (Okinawa Trough).</caption><thead><tr><th>Sample ID</th><th>Vent name</th><th>Cl<sup>a</sup><br>(mmol/kg)</th><th>Mg<sup>a</sup></th><th>Fe<br>(nmol/kg)</th><th>Mn</th><th>Zn</th><th>Pb</th><th>Cu</th><th>Ni</th><th>Mo</th><th>Sb</th><th>V</th><th>Co</th><th>Cd</th><th>U</th><th>Y</th><th>(δ<sup>34</sup>S<sub>sulfate</sub>)<sup>b</sup><br>(‰)</th></tr></thead><tbody><tr><td>D759 W1 F</td><td>Tiger</td><td>550</td><td>49.2</td><td>825</td><td>1937</td><td>200</td><td>3.28</td><td>24.7</td><td>509</td><td>169</td><td>18.3</td><td>25.9</td><td>5.81</td><td>1.69</td><td>11.6</td><td>0.27</td><td>n.m.<sup>c</sup></td></tr><tr><td>D760 B F</td><td>Tiger</td><td>525</td><td>40.7</td><td>2161</td><td>6121</td><td>311</td><td>3.40</td><td>62.9</td><td>47.1</td><td>115</td><td>18.8</td><td>34.3</td><td>0.59</td><td>0.35</td><td>4.25</td><td>0.72</td><td>20.5</td></tr><tr><td>D762 W1 F</td><td>Tiger</td><td>606</td><td>18.4</td><td>46031</td><td>20086</td><td>148</td><td>4.81</td><td>7.97</td><td>840</td><td>130</td><td>2.25</td><td>26.4</td><td>4.67</td><td>1.35</td><td>2.01</td><td>7.57</td><td>n.m.</td></tr><tr><td>D763 B F</td><td>Tiger</td><td>583</td><td>49.4</td><td>839</td><td>1931</td><td>254</td><td>7.02</td><td>13.9</td><td>11.6</td><td>138</td><td>119</td><td>34.5</td><td>0.44</td><td>0.71</td><td>13.6</td><td>1.17</td><td>21.0</td></tr><tr><td>D763 F F</td><td>Tiger</td><td>-</td><td>-</td><td>129</td><td>1407</td><td>36.6</td><td>0.95</td><td>5.89</td><td>556</td><td>181</td><td>565</td><td>6.61</td><td>20.6</td><td>0.34</td><td>12.0</td><td>0.03</td><td>21.2</td></tr><tr><td>D763 W2 F</td><td>Tiger</td><td>600</td><td>22.0</td><td>18921</td><td>9691</td><td>26774</td><td>2698</td><td>1310</td><td>63.0</td><td>60.2</td><td>150</td><td>8.72</td><td>1.06</td><td>49.1</td><td>2.35</td><td>1.79</td><td>n.m.</td></tr><tr><td>D763 W3 F</td><td>Tiger</td><td>589</td><td>32.1</td><td>6143</td><td>12980</td><td>188</td><td>11.7</td><td>14.2</td><td>49.4</td><td>189</td><td>11.4</td><td>21.3</td><td>0.35</td><td>1.00</td><td>2.71</td><td>1.01</td><td>20.3</td></tr><tr><td>D763 W4 F</td><td>Tiger</td><td>583</td><td>30.7</td><td>15392</td><td>9088</td><td>25788</td><td>2151</td><td>1366</td><td>1196</td><td>136</td><td>135</td><td>1.94</td><td>3.09</td><td>52.0</td><td>1.19</td><td>1.21</td><td>n.m.</td></tr><tr><td>D762 N1 F</td><td>buoyant plume above Tiger</td><td>563</td><td>48.0</td><td>b.d.l.<sup>d</sup></td><td>1411</td><td>414</td><td>13.8</td><td>13.4</td><td>13.9</td><td>142</td><td>15.3</td><td>33.7</td><td>2.40</td><td>1.43</td><td>2.46</td><td>0.07</td><td>21.0</td></tr><tr><td>D762 N2 F</td><td>buoyant plume above Tiger</td><td>553</td><td>49.0</td><td>108</td><td>255</td><td>285</td><td>24.6</td><td>11.5</td><td>11.3</td><td>141</td><td>13.2</td><td>34.9</td><td>0.99</td><td>1.12</td><td>9.17</td><td>0.08</td><td>21.0</td></tr><tr><td>D762 B F</td><td>Abyss</td><td>547</td><td>45.9</td><td>2921</td><td>53286</td><td>59.8</td><td>0.95</td><td>70.3</td><td>29.9</td><td>63.2</td><td>10.5</td><td>21.8</td><td>0.49</td><td>0.32</td><td>4.56</td><td>13.3</td><td>21.6</td></tr><tr><td>Tiger end-member fluid</td><td></td><td>-</td><td>0</td><td>51907</td><td>24944</td><td>17646</td><td>2067</td><td>1202</td><td>822</td><td>84.3</td><td>78.2</td><td>3.17</td><td>2.59</td><td>46.0</td><td>-6.79</td><td>6.81</td><td>-</td></tr><tr><td>seawater<sup>e</sup></td><td></td><td>544</td><td>48</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>CASS-6 (measured)</td><td></td><td>-</td><td>-</td><td>36.1</td><td>47.4</td><td>21.3</td><td>0.12</td><td>8.93</td><td>8.14</td><td>b.d.l.</td><td>-</td><td>6.42</td><td>0.43</td><td>0.24</td><td>6.97</td><td>0.22</td><td>-</td></tr><tr><td>CASS-6 (reference)</td><td></td><td>-</td><td>-</td><td>27.4</td><td>39.7</td><td>19.0</td><td>0.05</td><td>8.18</td><td>6.99</td><td>93.4</td><td>-</td><td>9.62</td><td>1.12</td><td>0.19</td><td>12.0</td><td>-</td><td>-</td></tr></tbody></table>

<footnote><sup>a</sup> Vent fluid data used for calculation of the chemistry of the end-member hydrothermal fluid of the Daiyon-Yonaguni Knoll hydrothermal field (Suzuki et al., 2008).</footnote>

<footnote><sup>b</sup> Averages of two duplicate measurements.</footnote>

<footnote><sup>c</sup> n.m. = not measured because of insufficient sample volume.</footnote>

<footnote><sup>d</sup> b.d.l. = below detection limits.</footnote>

<footnote><sup>e</sup> Averages of two seawater samples collected in the vicinity of the Tiger vent (Suzuki et al., 2008).</footnote>
<table><caption>**Table 8**
REE concentrations (ICP-MS) in the vent fluids from the Daiyon-Yonaguni Knoll hydrothermal field (Okinawa Trough).</caption><thead><tr><th>Sample ID</th><th>Vent name</th><th>Cl<sup>a</sup><br>(mmol/kg)</th><th>La<br>(nmol/kg)</th><th>Ce</th><th>Pr</th><th>Nd</th><th>Sm</th><th>Eu</th><th>Gd</th><th>Tb</th><th>Dy</th><th>Ho</th><th>Er</th><th>Tm</th><th>Yb</th><th>Lu</th><th>Y/Ho</th><th>ΣREE<br>(ppb)</th><th>(Ce/Ce*)<sup>b</sup> (Eu/Eu*)<sup>c</sup></th><th>La<sub>CN</sub>/Lu<sub>CN</sub></th></tr></thead><tbody><tr><td>D759 W1 F</td><td>Tiger</td><td>550</td><td>0.147</td><td>0.257</td><td>0.035</td><td>0.129</td><td>0.041</td><td>0.021</td><td>b.d.l.<sup>d</sup></td><td>0.006</td><td>0.025</td><td>b.d.l.</td><td>0.009</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>-</td><td>0.096</td><td>0.85</td><td>2.66</td></tr><tr><td>D760 B F</td><td>Tiger</td><td>525</td><td>0.705</td><td>0.914</td><td>0.111</td><td>0.384</td><td>0.107</td><td>0.474</td><td>b.d.l.</td><td>0.016</td><td>0.065</td><td>b.d.l.</td><td>0.022</td><td>0.003</td><td>0.013</td><td>b.d.l.</td><td>-</td><td>0.404</td><td>0.72</td><td>23.5</td></tr><tr><td>D762 W1 F</td><td>Tiger</td><td>606</td><td>9.132</td><td>8.644</td><td>1.509</td><td>5.153</td><td>1.141</td><td>1.849</td><td>1.327</td><td>0.166</td><td>0.664</td><td>0.099</td><td>0.175</td><td>0.018</td><td>0.081</td><td>b.d.l.</td><td>76.4</td><td>4.295</td><td>0.52</td><td>4.52</td></tr><tr><td>D763 B F</td><td>Tiger</td><td>583</td><td>1.111</td><td>1.523</td><td>0.207</td><td>0.758</td><td>0.217</td><td>0.121</td><td>b.d.l.</td><td>0.031</td><td>0.125</td><td>0.017</td><td>0.032</td><td>0.003</td><td>0.018</td><td>b.d.l.</td><td>69.1</td><td>0.595</td><td>0.72</td><td>2.95</td></tr><tr><td>D763 F F</td><td>Tiger</td><td>-</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>0.001</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>-</td><td>0.001</td><td>-</td><td>-</td></tr><tr><td>D763 W2 F</td><td>Tiger</td><td>600</td><td>2.369</td><td>3.039</td><td>0.514</td><td>1.838</td><td>0.529</td><td>2.031</td><td>b.d.l.</td><td>0.068</td><td>0.265</td><td>0.036</td><td>0.069</td><td>0.009</td><td>0.047</td><td>b.d.l.</td><td>50.5</td><td>1.562</td><td>0.64</td><td>20.4</td></tr><tr><td>D763 W3 F</td><td>Tiger</td><td>589</td><td>2.251</td><td>1.790</td><td>0.363</td><td>1.353</td><td>0.345</td><td>0.438</td><td>b.d.l.</td><td>0.038</td><td>0.130</td><td>0.020</td><td>0.029</td><td>0.002</td><td>0.014</td><td>b.d.l.</td><td>52.0</td><td>0.966</td><td>0.44</td><td>6.76</td></tr><tr><td>D763 W4 F</td><td>Tiger</td><td>583</td><td>1.630</td><td>2.154</td><td>0.288</td><td>0.993</td><td>0.272</td><td>0.926</td><td>b.d.l.</td><td>0.038</td><td>0.142</td><td>0.019</td><td>0.033</td><td>0.003</td><td>0.015</td><td>b.d.l.</td><td>64.0</td><td>0.935</td><td>0.71</td><td>18.1</td></tr><tr><td>D762 N1 F</td><td>buoyant plume above Tiger</td><td>563</td><td>0.037</td><td>0.045</td><td>0.006</td><td>0.023</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>0.002</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>-</td><td>0.016</td><td>0.67</td><td>-</td></tr><tr><td>D762 N2 F</td><td>buoyant plume above Tiger</td><td>553</td><td>0.021</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>0.002</td><td>b.d.l.</td><td>b.d.l.</td><td>b.d.l.</td><td>-</td><td>0.003</td><td>-</td><td>-</td></tr><tr><td>D762 B F</td><td>Abyss</td><td>547</td><td>2.613</td><td>3.839</td><td>0.432</td><td>1.507</td><td>0.377</td><td>0.093</td><td>b.d.l.</td><td>0.104</td><td>0.702</td><td>0.177</td><td>0.532</td><td>0.086</td><td>0.549</td><td>0.085</td><td>75.4</td><td>1.623</td><td>0.80</td><td>1.31</td><td>2.52</td></tr><tr><td>CASS-6 (measured)</td><td>Tiger end-member fluid</td><td>-</td><td>0.084</td><td>0.042</td><td>0.012</td><td>0.046</td><td>0.009</td><td>0.002</td><td>b.d.l.</td><td>0.002</td><td>0.010</td><td>b.d.l.</td><td>0.007</td><td>0.001</td><td>0.008</td><td>b.d.l.</td><td>-</td><td>0.032</td><td>0.28</td><td>0.00</td></tr><tr><td>CASS-6 (reference)</td><td></td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr><tr><td>D816-WT1<sup>e</sup></td><td>Tiger</td><td>-</td><td>7.161</td><td>9.708</td><td>1.070</td><td>3.992</td><td>0.983</td><td>4.401</td><td>1.171</td><td>0.165</td><td>0.907</td><td>0.190</td><td>0.564</td><td>0.070</td><td>0.366</td><td>0.057</td><td>121</td><td></td><td>0.76</td><td></td><td></td></tr><tr><td>D816-WT2<sup>e</sup></td><td>Tiger</td><td>-</td><td>8.402</td><td>11.545</td><td>1.285</td><td>4.846</td><td>1.222</td><td>4.893</td><td>1.402</td><td>0.191</td><td>1.035</td><td>0.219</td><td>0.659</td><td>0.083</td><td>0.418</td><td>0.063</td><td>116</td><td></td><td>0.76</td><td></td><td></td></tr><tr><td>D821-WT1<sup>e</sup></td><td>Tiger</td><td>-</td><td>5.643</td><td>7.023</td><td>0.837</td><td>3.200</td><td>0.742</td><td>3.214</td><td>0.878</td><td>0.135</td><td>0.816</td><td>0.195</td><td>0.580</td><td>0.067</td><td>0.315</td><td>0.045</td><td>125</td><td></td><td>0.70</td><td></td><td></td></tr></tbody></table>

<footnote><sup>a</sup> Vent fluid data used for calculation of the chemistry of the end-member hydrothermal fluid of the Daiyon-Yonaguni Knoll hydrothermal field (Suzuki et al., 2008).</footnote>

<footnote><sup>b</sup> Ce/Ce* = 2Ce<sub>CN</sub>/(La<sub>CN</sub>+Pr<sub>CN</sub>)</footnote>

<footnote><sup>c</sup> Eu/Eu* = 2Eu<sub>CN</sub>/(Sm<sub>CN</sub>+Gd<sub>CN</sub>)</footnote>

<footnote><sup>d</sup> b.d.l. = below detection limits</footnote>

<footnote><sup>e</sup> Data from Hongo et al. (2007).</footnote>
<caption>**Table 9**</caption>

Pb isotope composition of the studied hydrothermal deposits from the Daiyon-Yonaguni Knoll hydrothermal field (Okinawa Trough).

<table><thead><tr><th>Sample ID<sup>a</sup></th><th><sup>206</sup>Pb/<sup>204</sup>Pb</th><th><sup>207</sup>Pb/<sup>204</sup>Pb</th><th><sup>208</sup>Pb/<sup>204</sup>Pb</th></tr></thead><tbody><tr><td>2K1271 L1 lower outer</td><td>18.545</td><td>15.652</td><td>38.951</td></tr><tr><td>2K1271 L1 flange, outer top</td><td>18.537</td><td>15.646</td><td>38.931</td></tr><tr><td>2K1271 L1 flange, center upper</td><td>18.522</td><td>15.622</td><td>38.807</td></tr><tr><td>2K1271 L1 flange, outer bottom, Stb</td><td>18.519</td><td>15.621</td><td>38.791</td></tr><tr><td>2K1271 L1 flange, outer bottom, Op</td><td>18.491</td><td>15.575</td><td>38.564</td></tr><tr><td>2K1271 L1, Op</td><td>18.520</td><td>15.620</td><td>38.824</td></tr><tr><td>2K1267 L1</td><td>18.529</td><td>15.638</td><td>38.896</td></tr><tr><td>2K1267 L1, Op-1</td><td>18.527</td><td>15.638</td><td>38.900</td></tr><tr><td>2K1267 L1, Op-2</td><td>18.527</td><td>15.638</td><td>38.898</td></tr></tbody></table>

<footnote><sup>a</sup> Abbreviations Stb and Op see in Table 5.</footnote>
<caption>**Table 10**</caption>

Trace and rare earth elements chemistry of the end-member hydrothermal fluids from sedimented seafloor hydrothermal systems.

<table><thead><tr><th>Hydrothermal field</th><th>Vent name</th><th>Fe<br>(nmol/kg)</th><th>Mn</th><th>Zn</th><th>Pb</th><th>Cu</th><th>Co</th><th>Cd</th><th>U</th></tr></thead><tbody><tr><td>Daiyon-Yonaguni Knoll</td><td>Tiger</td><td>51907</td><td>24944</td><td>17646</td><td>2067</td><td>1202</td><td>2.59</td><td>46.0</td><td>-6.79</td></tr><tr><td>Escanaba Trough<sup>a</sup></td><td>6X, 0</td><td>40800-58100</td><td>25000-31100</td><td>11300</td><td>1560</td><td>3200</td><td>115</td><td>115</td><td>-0.2 - 2.0</td></tr><tr><td>Guaymas Basin<sup>b</sup></td><td>South Field, East Hill</td><td>8000-180000</td><td>128000-236000</td><td>100-40000</td><td>&lt;20-652</td><td>&lt;20-1100</td><td>&lt;5</td><td>&lt;10-46</td><td>-</td></tr><tr><td>Middle Valley<sup>c</sup></td><td>Bent Hill, Dead Dog</td><td>10000-20000</td><td>63000-78000</td><td>700-1700</td><td>50-125</td><td>300-1300</td><td>-</td><td>-</td><td>-</td></tr></tbody></table>

<table><thead><tr><th>Hydrothermal field</th><th>Vent name</th><th>La<br>(nmol/kg)</th><th>Ce</th><th>Pr</th><th>Nd</th><th>Sm</th><th>Eu</th><th>Gd</th><th>Tb</th><th>Dy</th><th>Ho</th><th>Er</th><th>Tm</th><th>Yb</th><th>Lu</th></tr></thead><tbody><tr><td>Daiyon-Yonaguni Knoll</td><td>Tiger</td><td>8.855</td><td>8.708</td><td>1.530</td><td>5.278</td><td>1.242</td><td>2.947</td><td>-</td><td>0.172</td><td>0.675</td><td>0.099</td><td>0.170</td><td>0.019</td><td>0.090</td><td>b.d.l.<sup>d</sup></td></tr><tr><td>Escanaba Trough<sup>e</sup></td><td>6X, 0</td><td>0.870</td><td>1.020</td><td>0.122</td><td>0.490</td><td>0.112</td><td>0.165</td><td>0.093</td><td>0.013</td><td>0.080</td><td>0.026</td><td>0.036</td><td>-</td><td>-</td><td>-</td></tr><tr><td>Guaymas Basin<sup>e</sup></td><td>South Field, East Hill</td><td>0.670-1.470</td><td>0.620-1.590</td><td>0.063-0.143</td><td>0.216-0.390</td><td>0.029-0.053</td><td>0.228-1.530</td><td>0.017-0.030</td><td>0.003-0.005</td><td>0.015-0.017</td><td>0.003-0.004</td><td>0.005-0.011</td><td>-</td><td>-</td><td>-</td></tr><tr><td>Middle Valley</td><td>Bent Hill, Dead Dog</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td><td>-</td></tr></tbody></table>

<footnote><sup>a</sup> Von Damm et al. (2005).</footnote>

<footnote><sup>b</sup> Von Damm et al. (1985b), Campbell et al. (1988).</footnote>

<footnote><sup>c</sup> Butterfield et al. (1994).</footnote>

<footnote><sup>d</sup> b.d.l. = below detection limits</footnote>

<footnote><sup>e</sup> Klinkhammer et al. (1994).</footnote>