Submarine Hydrothermal Fluids Research Articles

Lithium isotope fractionation during submarine hydrothermal alteration processes

River water and submarine hydrothermal fluids are the two primary sources of lithium (Li) input to the ocean. However, compared to well-documented weathering processes, the behavior of Li isotopes during hydrothermal alteration processes remains obscure. In this research, we investigated the Li isotopic compositions (δ7Li) of hydrothermally altered sediments from two IODP drilling cores (C0013 and C0014) in the Iheya North Knoll of the middle Okinawa Trough. The sediments, primarily altered from volcanic clasts, exhibit a pristine δ7Li value (5.2 ± 0.7 ‰) similar to that of MORB (3.7 ± 1 ‰). Intense hydrothermal activity led to the complete conversion of primary feldspars into phyllosilicates, predominantly Mg-chlorite, at site C0013 and in the middle and deep parts of C0014. The altered samples showed a depletion of 7Li (ranging in δ7Li from −10.0 ‰ to 4.2 ‰) compared to background sediment, indicating the preferential incorporation of 6Li during the formation of secondary minerals. Furthermore, both drilling sites exhibited increasing trends in δ7Li values with depth, with the deepest samples approaching the pristine δ7Li values of unaltered volcanic rock. These trends were attributed to the significant thermal gradients present at both sites. The temperature-dependent fractionation factor of Li isotopes allowed us to estimate the alteration temperature, which yielded temperature values consistent with those obtained using the δ18O geothermometer. This finding underscores the potential of Li isotopes as a novel geothermometer tool, although further calibration work is required. Based on our research findings, we developed a dissolution-precipitation model (based on mass balance) that establishes a relationship between the δ7Li values of altered solids and hydrothermal fluids, with the aim of elucidating the relatively limited variation observed in global submarine hydrothermal fluids (ranging from 1.6 ‰ to 11.0 ‰, with an averaged value of 5.9 ± 3.0 ‰, mean ± SD). This model quantitatively depicted the strong restriction of the Li concentration in hydrothermal fluids on their isotopic compositions, as high concentrations of Li in the fluids necessitate a substantial release of Li from the solid phase, causing the fluids' δ7Li values to approach that of the bedrock. Additionally, limited fractionation factors at high temperatures further constrain the variations in the fluids' δ7Li values. Model predictions also suggest that the reported δ7Li values of hydrothermal fluids have encompassed the potential δ7Li variation, providing supporting evidence for the assumption that δ7Li values of submarine hydrothermal fluids have exhibited insignificant variations throughout Earth's history.

Submarine hydrothermal fluids facilitated the accumulation of cadmium in Lower Cambrian black shales, South China

The effects of Cd-rich venting fluids on the Cd contents and isotopic compositions of continental margin sediments remain poorly understood. Characterization of the Cd isotopic composition of sediment overprinted by venting fluids is critical, as this may provide insights into how mixing between the venting fluids and bottom waters affects the Cd isotopic composition. Our study determined the Cd isotopic compositions of Lower Cambrian metalliferous sediment deposited on the passive continental margin of the southeastern Yangtze Block, South China. The Cd is predominantly hosted in sphalerite of sulfide-bearing barite sediments, V deposits, and Ni-Mo−platinum group element (PGE) sulfide layers. The Cd isotopic compositions of samples from these three units indicate that the distribution of Cd at this type of continental margin was controlled by submarine hydrothermal activity. Following the venting of hydrothermal fluids onto the seafloor, Cd2+ reacted with a limited amount of H2S generated mainly by thermochemical sulfate reduction near the vents. This resulted in isotopically lighter Cd in the sulfide-bearing barite sediments and V deposits, which have δ114/110Cd values of 0.00‰ ± 0.13‰ and 0.00‰ ± 0.14‰, respectively. The residual dissolved Cd in the fluids migrated with the upwelling seawater and ultimately precipitated almost entirely as sphalerite in the sulfidic wedge, which resulted in Ni-Mo−PGE sulfide layers with a narrow range of high δ114/110Cd values (0.35‰ ± 0.03‰). The presence of Cd-rich venting fluids can alter the Cd contents and isotopic compositions of passive margin sediments, particularly those located within long-term stratified seawater and fault depressions. Previous studies may have underestimated the migration distance and affected areas of hydrothermal activity involving Cd-rich fluids.

Re-Os, Sr-Nd isotopic and PGE elemental constraints for the formation of mid-Proterozoic ironstones in North China Craton: Implications for the atmospheric oxygen level

The origin (hydrothermal vs. continental Fe source) and environmental implications in particular for the atmospheric oxygen level of mid-Proterozoic ironstones have been widely studied, but remain highly debated. Here, we present Re-Os, Sr-Nd isotopic and PGE elemental data for ironstones from the ∼1.7 Ga Yunmengshan (YMS) Formation in south margin of the North China Craton to address the controversy. The initial 87Sr/86Sr ratios of the YMS ironstones are ∼0.7063, which are roughly comparable with seawater values around that period, suggesting a seawater signal with minor/minimal direct contributions from submarine hydrothermal fluids. The Nd isotopic compositions (εNd(t): −6.6 to −6.0) indicate a dominantly continental crustal signal for the formation of the ironstones. The PGE patterns of the YMS ironstones are distinctly similar to those of hydrogenous Fe-Mn crusts/nodules in modern ocean, also suggesting deposition from normal seawater conditions. Importantly, the YMS ironstones give initial 187Os/188Os ratios of ∼0.6 at ∼1.7 Ga, providing critical constraints for contemporaneous seawater values. This seawater 187Os/188Os value of ∼0.6 strongly suggests a result of oxidative weathering and transportation of Os in continental crust into the ocean, implying a relatively high atmospheric oxygen level at ∼1.7 Ga.

Geochemistry, zircon U-Pb chronology and Hf isotope composition of the Heishan’gou iron deposit in the Bikou Terrane, central China: Implication for the genesis of the Yudongzi banded iron formations

The Yudongzi banded iron formations (BIFs) are widely spread in the Neoarchean Yudongzi Group of the Bikou Terrane, Central China. Their sedimentary and metamorphic ages, however, remain controversial, either their forming or reworking processes. In this contribution, we conducted an integrated study of zircon U-Pb-Hf isotope geochemistry, as well as mineral and bulk-rock geochemistry on the Heishan’gou iron deposit, the largest iron deposit of the Yudongzi BIFs, to constrain their formation and metamorphism ages, source of ore-forming material and tectonic setting. Mineral chemistry analysis indicates that the amphibolite, host-rock of the Heishan’gou deposit suffered amphibolite facies metamorphism. LA-ICP-MS U-Pb dating of zircon grains from orthometamorphic host-rocks suggests that the Heishan’gou deposit was formed at the early Neoarchean (2781 ± 43 Ma for amphibolite and 2776 ± 43 Ma for plagioclase-hornblende schist), and metamorphosed at ca. 2480 ± 26 Ma and 1818 ± 44 Ma, respectively. The low contents of aluminum, titanium and high field strength elements in BIFs suggest that they are detritus-free marine chemical precipitates. The rare earth elements (REE) and Y patterns of BIFs display seawater-like signatures with light REE depletion, and positive La and Y anomalies. Meanwhile, their positive Eu anomalies suggest that submarine hydrothermal fluid might also be involved in the precipitation of BIFs. Combined with zircon Hf isotope data and geochemical compositions of amphibolites, it is proposed that the Yudongzi BIFs should be formed at back-arc basin setting. Compared with the representative Archean continent nucleus of the Yangtze Block (Kongling Complex), the Yudongzi Complex experienced distinct crustal evolutionary history. It indicates that the Yudongzi Complex might represent the accretionary block combined to the Yangtze continental nucleus later than the Paleoproterozoic.

Rift-induced structurally controlled hydrothermal barite veins in 1.6 Ga granite, Western Bastar Craton, Central India: Constraints from fluid inclusions, REE geochemistry, sulfur and strontium isotopes studies

Expressive granitic magmatism and a complex system of fault and shear zones are the main features associated with the crustal evolution and metallogeny in the Western Bastar Craton (WBC), Central India. The barite mineralization in WBC, Central India, occurs as veins and fracture fillings along faults are activated or reactivated as a consequence of rifting of – 1.5–1.6 Ga Pranhita-Godavari (PG) basin. The barite mineralization is hosted in ca. 1.6 Ga Mul granite of WBC. We present the first comprehensive, integrated field and laboratory studies approach using structural mapping, fluid inclusion, Sulfur, and Sr-Isotope geochemistry, mineral, and REE geochemistry to characterize barite mineralization ore-forming processes, a fluid source, and structural control. The host granite is intensely altered with evidence of hydrothermal mineralization in the form of silicification and hematitisation. Both sulfide-free (Brt-I) and sulfide-bearing (Brt-II) barites occur in the study area. Besides, barites with fluorite (Brt-III) were also observed in minor concentrations. The mineralization is associated with quartz-calcite vein, and the barite is accompanied by galena, pyrite, and chalcopyrite. Petrographic observations, fluid inclusion, and isotope data suggest a bimodal evolution of the mother brine viz. the oxidative source forms sulfide-free high-salinity brine and reductive low-salinity sulfide-bearing aqueous fluid formed by interaction with reducing agent causing hydrothermal barite mineralization in the study area. The source for the hydrotherms responsible for the formation of barite and galena in association with the quartz-barite vein is, in all probability, granitic magma. Incompatible elements like Ba, Pb and volatiles like S, preferentially concentrated in late magmatic hydrothermal fluids, got emplaced along the structurally weak zones in the interior of the granite pluton. The combined 87Sr/86Sr and δ34S‰ data suggest mixing fluids from diverse sources, including magmatic, marine, and crustal fluids. Low 87Sr/86Sr (<0.707) and high δ34S(>10‰) are indicative of alteration products of granite that were subsequently mixed with submarine hydrothermal fluid mobilized through the Mesoproterozoic PG rift system. This regional rifting event provided pathways for fluid flow and ore formation along faults/fracture systems (F2 and F3 fault systems) in the host Mul granite of WBC. The F2 fault system, sympathetic to the PG rift, is deep-seated and contains mainly barites of magmatic origin besides the minor marine signature. The F3 cross faults, developed across the gneissic foliation of TTG gneisses and charnockites, can be traced to the PG basin's younger marine sediments, host barites of dominantly marine signature.The Ba ± F mineralization in the study area is a perspective for regional exploration for REE-Ba-F in central India and elsewhere in a similar geological milieu. The epigenetic-submarine hydrothermal vein-type barite mineralization hosted in granite, WBC differs from Sedex, VMS, Carlin, or Orogenic type barite deposits, which has a great deal of replicability and suitability for future exploration targeting.

Coupling of the redox history and enrichment of Ni-Mo in black shale during the early Cambrian: Constraints from S-Fe isotopes and trace elements of pyrite, South China

Black shales were widely distributed in the world during the early Cambrian. Ni and Mo are enriched in black shale and can be mined only in Guizhou and Hunan, South China. The enrichment and mineralization of Ni and Mo have always been considered. However, the genesis of the deposits still has many interpretations. The migration and precipitation of elements were controlled by redox. It is conducive to explore the genesis of Ni-Mo enrichment that clarifying the relationship between the marine redox structure and metal precipitation. Pyrite nodules were selected along the profile for Fe isotope analysis, and nodules, colloidal and granular pyrite were analyzed in situ for S isotope and trace elements in the Xiaozhuliushui (XZLS) Ni-Mo deposit, Guizhou. Results show that the Fe isotopes have a slight upward trend from the lower black shale profile to the Ni-Mo layer. The maximum values (δ56Femax = 0.63; δ57Femax = 0.94) are reached at the polymetallic layer and then decrease rapidly. The δ34S values of nodules and granular pyrite decrease first and then increase rapidly from the lower part of the black shale, through the polymetallic Ni-Mo layer to the upper part of the black shale. The Co/Ni values of nodules, granular and colloidal pyrite < 0.01, in totally. Ni, Mo, As and Se are abnormally enriched in the Ni-Mo layer. These results indicate that all pyrite were formed in sedimentary and that the formation of a polymetallic Ni-Mo layer involves hydrothermal fluid. A large volume of clastic particles and sulfate were supplied due to enhanced continental weathering. It gradually becomes relatively oxidized in the depths of the ocean, which allows the metal elements to easily migrate. Then with the addition of submarine hydrothermal fluid, which disturbs the redox balance of the system, metal precipitation and enrichment occur. Means, the enrichment of polymetallic Ni-Mo in black shale is due to the coupling of continental weathering, sedimentation and hydrothermal action.

The C-O and Zn isotopic compositions of the Laochang Ag-Pb-Zn ore bodies in the Changning-Menglian suture zone, and its geological implications

老厂矿床是昌宁-孟连缝合带内唯一大型矿床，本文报道了老厂矿床Ag-Pb-Zn矿体中Ⅰ号矿体群下部块状矿体和上部网脉状矿体的方解石C-O同位素组成，以及Ⅰ、Ⅱ、Ⅳ三个矿体群内闪锌矿的Zn同位素组成。Ⅰ号矿体群下部块状矿体和上部网脉状矿体方解石δ¹³C_PDB的范围分别为-6.17‰~2.71‰和-2.18‰~3.87‰，δ¹⁸O_PDB的范围分别为-19.57‰~-17.23‰和-22.10‰~-16.21‰；计算获得对应成矿流体的δ¹³C_CO₂为-6.16‰~1.53‰和-2.39‰~6.43‰，δ¹⁸O_H₂O分别为1.62‰~7.62‰和4.36‰~16.92‰，通过与岩浆CO₂（δ¹³C=-2‰~-8‰）和围岩灰岩（δ¹³C=-1.6‰~4.0‰）的δ¹³C值相比较，指示块状矿体成矿流体中的碳主要来自岩浆，网脉状矿体成矿流体中的碳则主要来自围岩，说明老厂矿床深部水岩反应较强。10件闪锌矿的δ⁶⁶Zn和δ⁶⁸Zn值分别为0.17‰~0.25‰和0.33‰~0.49‰，与VMS型矿床以及现代海底热液流体的Zn同位素组成重合，不同标高均一的Zn同位素组成寓示老厂矿床Ag-Pb-Zn矿体中闪锌矿形成过程中几乎未受到温度、分馏和微生物作用的影响，可以直接反映金属源区的Zn同位素组成，揭示老厂矿床Ag-Pb-Zn矿体为VMS成因，成矿金属主要来自于下石炭统海底火山作用。;The Laochang deposit is the only large ore deposit in the Changning-Menglian suture zone. In this study, the C-O isotopic compositions of calcites from the lower massive ore bodies and the upper stockwork ore bodies of No.Ⅰ ore bodies in Laochang Ag-Pb-Zn ore bodies and the Zn isotopic compositions of sphalerites from No.Ⅰ, Ⅱ, Ⅳ ore bodies are investigated. The range of δ¹³C_PDB of calcites from the lower massive ore bodies and the upper stockwork ore bodies of No.Ⅰ ore bodies is -6.17‰~2.71‰ and -2.18‰~3.87‰, respectively, and the range of δ¹⁸O_PDB is -19.57‰~-17.23‰ and -22.10‰~-16.21‰, respectively. The δ¹³C_CO₂ of the corresponding ore-forming fluids are calculated to be -6.16‰~1.53‰ and -2.39‰~6.43‰, respectively, and the δ¹⁸O_H₂O are calculated to be 1.62‰~7.62‰ and 4.36‰~16.92‰, respectively. By comparison with the δ¹³C of magmatic CO₂ (δ¹³C=-2‰~-8‰) and wall-rock limestone (δ¹³C=-1.6‰~4.0‰), it indicates that the carbon in the ore-forming fluids of massive ore bodies mainly comes from magma, while the carbon in the ore-forming fluids of stockwork ore bodies mainly comes from limestone, which further shows that there is strong water-rock reaction in the deep part of Laochang deposit. The δ⁶⁶Zn and δ⁶⁸Zn values of ten sphalerites are 0.17‰~0.25‰ and 0.33‰~0.49‰, respectively, which coincides with the Zn isotopic compositions of VMS deposits and modern submarine hydrothermal fluids. The homogeneous Zn isotopic compositions at different elevations implies that the Zn isotopic compositions of sphalerite from Ag-Pb-Zn orebodies in Laochang deposit are almost unaffected by temperature, fractionation and microbial action. And it can directly reflect the Zn isotopic compositions of the metal source, revealing the genesis type of the Laochang Ag-Pb-Zn ore body as VMS-type, and the metallogenic metal mainly comes from the Lower Carboniferous submarine volcanism.

Study on seafloor hydrothermal systems circulation flow and heat transfer characteristics

&lt;abstract&gt; &lt;p&gt;In this work, the numerical simulation study of the hydrothermal flow and heat transfer process in the porous rock under 30 MPa pressure was developed. The flow and heat transfer characteristics of hydrothermal in rocks with different porosities are studied by changing the porosity of the rock. The simulation results show that the average flow velocity decreases and the average temperature increases when the porosity decreases. The velocity field and temperature field are coupled due to the nonlinear thermophysical properties of hydrothermal. The velocity field and temperature field have strongly interacted in the range of 400–450 ℃ and the effect of temperature on velocity is gradually diminishing outside the range. Most of the fluid will be "squeezed" into the crevice and the average velocity is almost three times the no-creviced case when a crevice is present. The existence of the crevice makes the total heat flux decrease from an overall perspective, and the crevice makes a large temperature gradient at the entrance and export of the crevice from a local perspective. These results provide theoretical support for the utilization of submarine hydrothermal fluid shallow circulation heat energy.&lt;/p&gt; &lt;/abstract&gt;

A New Insight Into Seawater-Basalt Exchange Reactions Based on Combined δ18O—Δ′17O—87Sr/86Sr Values of Hydrothermal Fluids From the Axial Seamount Volcano, Pacific Ocean

The δ18O values of submarine vent fluids are controlled by seawater-basalt exchange reactions, temperature of exchange, and to a lesser extent, by phase separation. These variations are translated into the δ18O values of submarine hydrothermal fluids between ca. 0 and + 4‰, a range defined by pristine seawater and equilibrium with basalt. Triple oxygen isotope systematics of submarine fluids remains underexplored. Knowing how δ17O and δ18O change simultaneously during seawater-basalt reaction has a potential to improve i) our understanding of sub-seafloor processes and ii) the rock-based reconstructions of ancient seawater. In this paper, we introduce the first combined δ17O-δ18O-87Sr/86Sr dataset measured in fluids collected from several high-temperature smoker- and anhydrite-type vent sites at the Axial Seamount volcano in the eastern Pacific Ocean. This dataset is supplemented by measurements of major, trace element concentrations and pH indicating that the fluids have reacted extensively with basalt. The salinities of these fluids range between 30 and 110% of seawater indicating that phase separation is an important process, potentially affecting their δ18O. The 87Sr/86Sr endmember values range between 0.7033 and 0.7039. The zero-Mg endmember δ18O values span from -0.9 to + 0.8‰, accompanied by the Δ′17O0.528 values ranging from around 0 to −0.04‰. However, the trajectory at individual site varies. The endmember values of fluids from focused vents exhibit moderate isotope shifts in δ′18O up to +0.8‰, and the shifts in Δ′17O are small, about −0.01‰. The diffuse anhydrite-type vent sites produce fluids that are significantly more scattered in δ′18O—Δ′17O space and cannot be explained by simple isothermal seawater-basalt reactions. To explain the observed variations and to provide constraints on more evolved fluids, we compute triple O isotope compositions of fluids using equilibrium calculations of seawater-basalt reaction, including a non-isothermal reaction that exemplifies complex alteration of oceanic crust. Using a Monte-Carlo simulation of the dual-porosity model, we show a range of possible simultaneous triple O and Sr isotope shifts experienced by seawater upon reaction with basalt. We show the possible variability of fluid values, and the causal effects that would normally be undetected with conventional δ18O measurements.

Geochemistry of the black rock series of lower Cambrian Qiongzhusi Formation, SW Yangtze Block, China: Reconstruction of sedimentary and tectonic environments

Abstract The black rock series in the Qiongzhusi Formation contains important geochemical information about the early Cambrian tectonic and ecological environment of the southwestern Yangtze Block. In this paper, major, trace, and rare earth element data are presented in an attempt to reveal the sediment source during the deposition of the early Cambrian Qiongzhusi Formation and to reconstruct the sedimentary tectonic environment and weathering intensity during that time. The basin primarily received continental clastic material with neutral-acidic igneous rocks from a stable source and with a moderate level of maturity during the depositional period of the Qiongzhusi Formation. Furthermore, the strata were weakly influenced by submarine hydrothermal fluids during diagenesis. The reconstruction of the sedimentary environment and weathering intensity shows that P2O5 enrichment and water body stratification occurred due to the effects of upwelling ocean currents during the depositional period of the Qiongzhusi Formation. The combination of upwelling and bottom-water hydrothermal fluids led to environmental changes in the study area, from dry and hot to moist and warm. Last, the reconstruction of the tectonic environment of the Qiongzhusi Formation indicates that deposition occurred in continental slope and marginal marine environments associated with a continental arc tectonic system. These findings provide an essential basis for the comprehensive reconstruction of the early Cambrian sedimentary environment of the Yangtze Block.

Geochemical constraints on the genesis of the Ekou banded iron formation, Shanxi Province, North China

The Ekou banded iron formation (BIF) in the Wutai area is hosted within the late Archean Baizhiyan formation. The mineral assemblage is used to identify oxide and silicate facies. The oxide facies is composed of magnetite and quartz, and the silicate facies is characterized by the presence of silicate minerals. A geochemical analysis shows that the major elemental compositions are dominantly SiO2 and Fe2O3T, with very little Al2O3 and TiO2 and minor abundances of incompatible elements and transition elements. These results indicate that negligible terrigenous materials were involved in the BIF deposition. The rare-earth elements (REEs), normalized by post-Archean Australian shale, exhibit the characteristics of light REE (LREE) depletion, heavy REE (HREE) enrichment, and positive La, Y, and Eu anomalies. The Y/Ho ratios are superchondritic. These results indicate that the material that formed the Ekou BIF originated from the mixing of seawater and submarine hydrothermal fluids. A Ce anomaly deficiency and heavy Fe isotope enrichment indicate that the Ekou BIF formed in an anoxic marine environment. The δ30SiNBS-28 values for quartz in the Ekou BIF are similar to those of other BIFs with distribution ranges of modern sinters and black smokers. The δ18OV-SMOW distribution is similar to that of hydrothermal sedimentary siliceous rocks. These results suggest that the formation of the Ekou BIF was closely connected to submarine volcanic exhalation activity.

Mantle degassing of primordial helium through submarine ridge flank basaltic basement

The degassing of primordial gases from Earth's interior is evidenced by the high He3/4He ratios in submarine hydrothermal plumes, vent fluids, and rock samples with mantle origin from active hydrothermal systems in mid-ocean ridges (MOR) and subduction zone volcanism. As the largest aquifer on Earth, the uppermost 40-500 m of permeable submarine ridge flank basement (1-65 million-years-old, Myr) holds ∼2% of the ocean volume and accounts for 70% of the seafloor hydrothermal heat flux. However, the degassing of primordial gases through the oceanic ridge flank crust has not yet been directly quantified. Here, we show that high integrity hydrothermal (65°C) fluids from the sediment-buried 3.5 Myr basaltic crust from the eastern flank of the Juan de Fuca Ridge (JdFR) contain elevated 3He. The He3/4He for the basaltic fluid is 4.5 ± 0.1 Ra (relative to the air ratio), which is greatly elevated when compared to deep seawater (1.05 Ra), but is half of that observed for high-temperature vent fluids (∼8 Ra) emitting from MOR. Only a small fraction of the 3He in ridge flank fluids is derived from the entrainment of high-temperature ridge-axis fluids and is better explained by degassing of the mantle through the mantle-crust boundary. The lower than MOR He3/4He ratios indicate that radiogenic 4He originates from aged uranium and thorium decay within the mantle as well as from the ridge-flank basalts. The 3He outgassing through warm ridge flanks (4.9 to 36 mol/yr) accounts for 0.7-6% of the global 3He outgassing, exceeded only by degassing through mid-ocean ridges and subduction volcanism. The presence of mantle 3He suggests that the abiogenic methane present in the ridge flank fluids might be mantle-derived. Based on the 3He outgassing flux, a possibly mantle-derived abiotic methane production rate at the ridge flank is estimated to be 0.3–35×108mol/yr.

Rhenium-Osmium isotope systematics of an Early Mesoproterozoic SEDEX polymetallic pyrite deposit in the North China Craton: Implications for geological significance and the marine osmium isotopic record

The rhenium-osmium (Re-Os) isotopic system preserved in ancient seafloor hydrothermal sulfide deposits can be used to gain insight into the Os composition of ancient seawater. In particular, the age of sedimentary exhalative (SEDEX) deposits can be determined by measuring Re-Os isotopes in syn-depositional pyrite, a common constituent of SEDEX deposits. Here we report on the Gaobanhe sediment-hosted, polymetallic pyrite deposit which is hosted within the Gaoyuzhuang Formation in the central part of the northern margin of the North China Craton (NCC). Re-Os isotopic data from syn-depositional pyrite yield an isochron age of 1505 ± 55 Ma, constraining the timing of primary mineralization, as well as the minimum age of the host sediments to the Mesoproterozoic. Analyzed pyrite grains indicate an initial 187Os/188Os (Osi) value of 0.181 ± 0.066, suggesting that the mineralizing fluids were an admixture of seawater and submarine hydrothermal fluids, with the Os being primarily derived from seawater. The Osi value is slightly higher than that of Paleoproterozoic seawater (~0.13), suggesting that there was a radiogenic riverine flux to the oceans and that atmospheric oxygen must have been sufficiently high at that time to drive this increased, continental radiogenic Os input to the oceans. We propose that the Re-Os isotopic system, as recorded by these SEDEX deposits, may provide key insights when examining changes in the Os isotopic composition of seawater throughout the Precambrian.

A New Seafloor Hydrothermal Power Generation Device Based on Waterproof Thermoelectric Modules

Submarine hydrothermal fluids contain substantial energy, and temperature differences with the surrounding cold seawater can provide energy for seabed observations and submarine operations. This study proposes a novel hydrothermal power generation device comprising a thermoelectric converter and an energy management system. Herein, a waterproof module with high-temperature and high-pressure resistance was designed. Heating and pressurization tests were performed to verify the structure's feasibility. The overall structure of the system based on the module was then designed, and laboratory performance tests were conducted. A computational fluid dynamics simulation was used to further analyze the heat transfer model. The simulation results are consistent with experimental data, validating the simulation model's accuracy. The new device reduces its own weight and solves low heat transfer efficiency problems. This study increases the temperature difference between the two ends of the thermoelectric generator in the thermoelectric converter by 76.2%.

Origin of High Mg and SO4 Fluids in Sediments of the Terceira Rift, Azores‐Indications for Caminite Dissolution in a Waning Hydrothermal System

AbstractDuring R/V Meteor cruise 141/1, pore fluids of near surface sediments were investigated to find indications for hydrothermal activity in the Terceira Rift (TR), a hyperslow spreading center in the Central North Atlantic Ocean. To date, submarine hydrothermal fluid venting in the TR has only been reported for the D. João de Castro seamount, which presently seems to be inactive. Pore fluids sampled close to a volcanic cone at 2,800‐m water depth show an anomalous composition with Mg, SO4, and total alkalinity concentrations significantly higher than seawater and a nearby reference core. The most straightforward way of interpreting these deviations is the dissolution of the hydrothermally formed mineral caminite (MgSO4 0.25 Mg (OH)2 0.2H2O). This interpretation is corroborated by a thorough investigation of fluid isotope systems (δ26Mg, δ30Si, δ34S, δ44/42Ca, and 87Sr/86Sr). Caminite is known from mineral assemblages with anhydrite and forms in hydrothermal recharge zones only under specific conditions such as high fluid temperatures and in altered oceanic crust, which are conditions generally met at the TR. We hypothesize that caminite was formed during hydrothermal activity and is now dissolving during the waning state of the hydrothermal system, so that caminite mineralization is shifted out of its stability zone. Ongoing fluid circulation through the basement is transporting the geochemical signal via slow advection toward the seafloor.

Armoured sponge spicules from Panarea Island (Italy): Implications for their fossil preservation

A variety of calcareous and siliceous skeletal components are associated with exceptional, still active deposits of modern iron ooids off Panarea, one of the volcanic islands of the Aeolian Arc (Tyrrhenian Sea, Italy). Both ooids and skeletal components occur as loose sediments influenced by submarine hydrothermal fluid vents. Whereas iron ooids are exclusively made of goethite laminae primarily nucleated on volcaniclastic material, sponge spicules – that represent most of the siliceous skeletal component – develop laminated coatings (concretions) of varying sizes. This partial or total coating consists of regularly banded Fe‒rich layers exhibiting the same textural features and mineralogical composition (goethite) of the ooid cortex developed around inorganic cores. Spicules did not reveal any obvious attaching structure or interfingering with the surrounding coating and did not undergo bioerosion or any other evidence of biological intervention during their development. A hydrothermal origin, compatible with the general setting, is therefore proposed for these armoured sponge spicules. We believe that this unique modern case of iron concretions produced on siliceous spicules can contribute to explain other known fossil cases as well as to understand the taphonomy of this type of biogenic silica that seems rarely to have been preserved in such an extreme habitat.

Depositional environments of redox-sensitive trace elements in the metalliferous black slates of the Okcheon Metamorphic Belt, South Korea

Metalliferous black slates consisting of black slates and interbedded coaly slates in the Okcheon Metamorphic Belt of South Korea were analyzed for redox-sensitive trace elements and rare earth elements (REEs) to examine their depositional conditions. Our data show that the coaly slates have elevated concentrations of redox-sensitive trace metals (U, V, Mo, and Cr), low Mn contents, high V/(V + Ni), V/Cr, and U/Th ratios, and high total organic carbon (TOC) contents. A general tendency of positive correlation between TOC and trace metals was established. The results suggest that the coaly slates were developed under a strongly reducing environment, while the black slates were deposited under a suboxic-oxic condition. The REE patterns of the coaly slates typically show positive Eu and negative Ce anomalies compared to the North American Shale Composite reference and they are essentially inherited from submarine hydrothermal fluids under high temperature reducing condition. The enrichment of the redox-sensitive elements including V (up to 3,564 ppm) and Mo (up to 358 ppm) may have been controlled by direct hydrothermal input of metals into the rift basin from hydrothermal vents, proximal from the vent sites, as supported by textural evidences, and the metals could have been fixed from seawater by means of scavenging process via exhalative oxide particles in a hydrothermal plume. The sorption of metals from seawater under anoxic conditions into organic-rich sediments occurred as well. The metal enrichments in the black slates seem to have been achieved in somewhat similar way to black shales in South China.

The Carboniferous Shikebutai Iron Deposit in Western Tianshan, Northwestern China: Petrology, Fe-O-C-Si Isotopes, and Implications for Iron Pathways

Abstract Submarine volcanic-hosted iron deposits are important sources of iron ore in northwestern China. Here we present the petrological characteristics and coupled Fe-O, C, and Si isotope data of iron ores from the Shikebutai submarine volcanic-hosted hematite deposit in the Western Tianshan region. Several stratiform and lenticular hematite-dominated orebodies occur in Carboniferous submarine volcano-sedimentary sequences in this region. The ores are mainly composed of hematite, quartz, and minor siderite with distinct alternating iron-rich and silica-rich bands. The hematite shows δ56Fe and δ18O values in the range of –0.31 to 0.80‰ and 2.2 to 7.0‰, respectively, and the jasper yields δ30Si values of –1.90 to –1.20‰. Iron and Si were both derived from hydrothermal fluids related to submarine magmatism/volcanism. The Fe-bearing minerals in the Shikebutai deposit define distinct formation pathways. Hematite is the primary dehydrated Fe(III) oxyhydroxide, and the Fe isotope data indicate fractionation resulting from the partial oxidation of Fe(II). The O isotope data reflect inheritance from the submarine hydrothermal fluids source. Jasper was produced during coprecipitation of silica adsorbed onto the Fe(III) oxyhydroxides. The siderite-rich iron ore/volcaniclastic rock samples with a high and variable total organic carbon content (0.14–5.57%) show negative δ13C values (–3.0 to –1.1‰) and light δ56Fe values (–1.11 to –0.84‰). Our isotope data, together with the common occurrence of hematite inclusions in siderite, suggest that siderite was mainly produced by microbial dissimilatory iron reduction during diagenesis. The geologic, petrological, and isotopic data suggest that the Carboniferous Shikebutai deposit was precipitated through chemical and biogenic processes.

Magmatic Signature in Submarine Hydrothermal Fluids Vented Offshore Ventotene and Zannone Islands (Pontine Archipelago, Central Italy)

Geochemical investigations carried out on submarine hydrothermal fluids vented offshore the Pontine Islands (Tyrrhenian Sea) revealed the existence of gas vents to the W of Zannone Island and SW of Ventotene Island. The geochemical features of the CO2-rich gas samples show a clear mantle-derived signature with3He/4He of 3.72-3.75 Ra and 1.33 Ra at Zannone and Ventotene, respectively. Gas geochemistry denotes how CO2-rich gases undergo fractionation processes due to CO2dissolution to a variable extent favoring enrichment in the less soluble gas species, i.e., CH4, N2, and He. The carbon isotope composition of CO2, expressed asδ13C vs. V-PDB, ranges from -0.71 and -6.16‰ at Zannone to 1.93‰ at Ventotene. Preliminary geothermometric and geobarometric estimations indicate equilibrium temperatures in the range of 150-200°C at Zannone and &gt;200°C at Ventotene besides H2O pressures in the range of 5 bar and 20 bar at Zannone and Ventotene, respectively. Although the latest volcanic activity at the Pontine Archipelago is dated Middle Pleistocene, the combination of the new geochemical information along with geothermometric estimations indicates that cooling magmas are likely releasing enough thermal energy to form an efficient hydrothermal system.

SUSTAIN drilling at Surtsey volcano, Iceland, tracks hydrothermal and microbiological interactions in basalt 50 years after eruption

Abstract. The 2017 Surtsey Underwater volcanic System for Thermophiles, Alteration processes and INnovative concretes (SUSTAIN) drilling project at Surtsey volcano, sponsored in part by the International Continental Scientific Drilling Program (ICDP), provides precise observations of the hydrothermal, geochemical, geomagnetic, and microbiological changes that have occurred in basaltic tephra and minor intrusions since explosive and effusive eruptions produced the oceanic island in 1963–1967. Two vertically cored boreholes, to 152 and 192 m below the surface, were drilled using filtered, UV-sterilized seawater circulating fluid to minimize microbial contamination. These cores parallel a 181 m core drilled in 1979. Introductory investigations indicate changes in material properties and whole-rock compositions over the past 38 years. A Surtsey subsurface observatory installed to 181 m in one vertical borehole holds incubation experiments that monitor in situ mineralogical and microbial alteration processes at 25–124 ∘C. A third cored borehole, inclined 55∘ in a 264∘ azimuthal direction to 354 m measured depth, provides further insights into eruption processes, including the presence of a diatreme that extends at least 100 m into the seafloor beneath the Surtur crater. The SUSTAIN project provides the first time-lapse drilling record into a very young oceanic basaltic volcano over a range of temperatures, 25–141 ∘C from 1979 to 2017, and subaerial and submarine hydrothermal fluid compositions. Rigorous procedures undertaken during the drilling operation protected the sensitive environment of the Surtsey Natural Preserve.