Submarine Hydrothermal Deposits Research Articles

Occurrence and precipitation mechanism of silver in pyrite from chimney fragments in the Edmond hydrothermal field, Central Indian Ridge

The enrichment of precious elements including Au and Ag in submarine hydrothermal sulfide deposits attracts more and more attention. Previous studies indicate that Au and Ag combine distinctly different ligands under the physico-chemical conditions of submarine hydrothermal systems, therefore, the factors controlling their precipitation may be different. In general, silver mineralization has been much less studied than gold mineralization in submarine hydrothermal sulfide deposits. The Ag mineralization process and precipitation mechanism of submarine hydrothermal sulfide deposits formed at Mid-ocean Ridges are still poorly constrained. In this study, we studied the occurrence and precipitation mechanism of Ag in sulfide deposits of Edmond hydrothermal field, located on the intermediate-spreading Central Indian Ridge (CIR).Three ore-forming stages were identified in chimney fragments collected in the Edmond hydrothermal field. The corresponding minerals are (stage I) anhydrite + barite + colloidal/porous pyrite (Py1) + fine-grained sphalerite; (stage II) marcasite; (stage III) euhedral pyrite (Py2) + coarse-grained sphalerite + chalcopyrite + isocubanite. Py1, characterized by colloidal, porous, and micro-sized anhedral morphology, was usually overgrown by marcasite, which is, in turn, surrounded by euhedral-subhedral Py2, usually coexisting with coarse-grained sphalerite, chalcopyrite, and isocubanite. Compared to marcasite and Py2, only Py1 contains abundant native silver nanoparticles. LA-ICP-MS analyses suggest that Py1 contains higher Pb, Cu, Ag, Mn, Tl, Mo, Au, and lower Co as compared to Py2. In-situ LA-ICP-MS and nanoSIMS analyses indicate that Py1 with higher Ag contents (101–586 ppm) has larger variation in sulfur isotopic compositions (0.8 to 6.6‰) than those of Py2 with lower Ag contents (0.22–15.5 ppm; δ34S values: 2.1 to 4.8‰ for Fe-rich samples and 0 to 2.8‰ for Zn-rich samples).Texture, mineral assemblage, pyrite trace element and sulfur isotopic compositions indicate a progressive decrease on the degree of fluid-seawater mixing as the temperature gradually increases during the growth of the chimneys in Edmond hydrothermal field. Phase diagram analysis indicates that the increase in pH and in particular cooling, due to the mixing of the hot hydrothermal fluid with cold seawater, can significantly decrease the solubility of Ag and be the effective mechanisms of silver precipitation. Our results suggest that mixing of hydrothermal fluid with seawater is the main Ag precipitation mechanism for submarine hydrothermal sulfide deposits formed at Mid-ocean Ridges.

In-field performance evaluation of “NMRI C-AUV #4” developed for surveying submarine hydrothermal deposits

In-field performance evaluation of “NMRI C-AUV #4” developed for surveying submarine hydrothermal deposits

Microbial Imprints on Sulfide Minerals in Submarine Hydrothermal Deposits of the East Pacific Rise

AbstractDiverse numbers of iron‐ and sulfur‐oxidizing microbes have been found in submarine hydrothermal deposits. They have played a prominent role in weathering of seafloor sulfide deposits. However, evidence for microbe‐mineral interactions in sediments is rare. Mineralogic analysis and scanning electron microscopy and energy‐dispersive X‐ray spectroscopy (SEM‐EDX) examination of sulfide deposits from the East Pacific Rise demonstrated that (1) sulfide minerals were extensively leached, with characteristic microbial dissolution pits on mineral surfaces; (2) the possible Acidithiobacillus‐like bacteria and metabolites were found closely associated with the dissolution pits in situ. The results provide direct evidence for microbial leaching on the solid mineral crystals, most likely by the contact mechanisms, in the seafloor sulfide deposits.

A seawater-sulfate origin for early Earth’s volcanic sulfur

Mass-independent fractionation of sulfur isotopes (MIF-S)—as recorded primarily in pre-2.5 billion years ago (Ga) sedimentary rocks—has been interpreted as evidence of photolysis of volcanic SO2 in an anoxic troposphere. Here, I present thermodynamic and kinetic calculations, combined with data on the geology, mineralogy and chemical and isotopic compositions of modern and Archaean (3.8–2.5 Ga) aged volcanic samples from different tectonic settings, to examine early Earth’s sulfur cycle. Based partly on the similarities between submarine hydrothermal deposits and arc volcanic rocks in pyrite (FeS2) abundances and sulfur isotopic compositions (for example, the presence of both positive and negative δ34S values), I conclude that degassing of sulfur (mostly as SO2) into the atmosphere has been carried out primarily by subaerial eruptions of oxidized, arc-like magmas since at least 3.5 Ga. The generation of volcanic SO2 requires plate tectonics and the involvement of sulfate-rich seawater, which requires large exposed lands and an oxygenated atmosphere. I propose that the MIF-S signatures in sedimentary rocks were created by ultraviolet photochemical reactions between SO2 from explosive volcanic eruptions and O2 in the stratosphere, above an oxygen-rich troposphere, or by high-temperature reactions between organic compounds and sulfate in the oceans. Formation of mass-independent isotope fractionation of sulfur signatures recorded in Archaean sedimentary rocks could have occurred in an oxygen-rich atmosphere, according to thermodynamic and kinetic calculations and analysis of Earth’s early sulfur cycle.

Special topic: Toward geophysical exploration for submarine hydrothermal deposit

2008年に始まった文部科学省による「海洋資源の利用促進に向けた基盤ツール開発プログラム」（2011年度に「海洋資源利用促進技術開発プログラム」へと名称を変更，以下，基盤ツール）を契機に，日本国内における探査技術の開発が始まった。物理探査誌でも2011年の64巻4号において，基盤ツール等で開発中であった探査手法に関する特集「海底熱水鉱床探査の未来」が組まれ，会員の皆さまに当時の最新の開発動向を紹介した。2014年度からは内閣府戦略的イノベーションプログラムによる次世代海洋資源調査技術「海のジパング計画」（以下，「海のジパング計画」）が始まり，熱水鉱床のみならず，コバルトリッチクラストやレアアース泥など，様々な海洋金属資源に関する成因研究が始まると共に，様々な探査技術の開発も並行して行われた。「海のジパング計画」における探査技術開発では，大学や研究機関による研究開発のみならず，それらの技術移転あるいは民間企業が主導する技術開発が行われると共に，実海域において民間企業による調査航海が行われたことが大きな特徴であり，それらの技術的な成果は「海底熱水鉱床調査技術プロトコル」としてまとめられた。また，環境を持続的に利用するため，近年では海底資源開発に関する海底環境への影響を評価することが非常に重要になってきたため，環境影響評価に関する調査手法・評価技術の構築も課題の一つとなった。この「海のジパング計画」は2018年度で終了し，探査技術の開発の一つの大きな区切りを迎えた。

Growing Professionals in Science and Technology of Korea’s New Marine Industry Sector

With consideration to research nature, scope of available materials and industrial feature, we investigate cultivation of professionals in the three new marine industries such as marine energy, marine bio-industry and submarine hydrothermal deposits development. More specific, we investigate trends of marine science and technology manpower at the national level in Korea nurturing policy to forecast mid and long term expert manpower demand and to respond to trends and forecasts of major fields. Cultivation of necessary professionals is an essential prerequisite for growth of new marine industry and its contribution to national economy. Because the new marine industry was recently introduced, the established system and policies for professionals in science and technology did not reflect demand for this new industry, which requires improvement. Since new marine industry is a new field, it is difficult for customized talent to be supplied directly from existing manpower training system. Therefore, it is necessary to cultivate talented people with fused thinking and ability. In the existing system, it is necessary to strengthen efforts to develop professional manpower with fusion competence, and it is also necessary to make policy efforts to build a new system such as cooperation process.

Zinc and lead isotope variation in hydrothermal deposits from the Okinawa Trough

The study of submarine hydrothermal vent deposits from the Okinawa Trough (OT) is of important significance for understanding hydrothermal mineralization characteristics in incipient back-arc basins. Zinc and lead isotope compositions of hydrothermal deposits from the OT show large variation. Mixing of Pb derived from local volcanic rocks and sediments in different proportions is the major cause of Pb isotope variation. Compared with the hydrothermal deposits from the Middle Okinawa Trough, samples from the Southern Okinawa Trough contain a larger proportion of sediment-derived Pb. Incorporation of continental crust-derived Pb into the hydrothermal circulation also affected the Pb isotope compositions of hydrothermal sulfides from the OT. The Zn isotope compositions of the OT hydrothermal deposits reflect Zn is mainly sourced from the local volcanic rocks and kinetic fractionation is remarkable during sphalerite precipitation. Zinc isotopes may be of potential use in ore exploration and discovery of new active hydrothermal vents.

Geochemistry and origin of Dehoo manganese deposit, south Zahedan, southeastern Iran

Dehoo manganese deposit is located 52 km to the south of Zahedan in Sistan and Baluchestan Province, southeastern Iran. This deposit that lies in the central part of the Iranian Flysch Zone is lenticular in shape and lies above the micritic limestone-radiolarite cherts of the upper Cretaceous ophiolite unit. It is hosted within the reddish to brown radiolarite cherts and in places interlinks with them, so that the radiolarite chert packages play a key role for Mn mineralization in the region. Investigated ore-paragenetic successions and the geochemical characteristics of the Dehoo deposit were studied by means of major oxide, trace, and rare earth element (REE) contents that provide information as to the mineral origin. Strong positive correlations were found between major oxides and trace elements (Al2O3-TiO2, r = 0.95; TiO2-MgO, r = 0.94; Fe2O3-Al2O3, r = 0.90; MgO-Al2O3, r = 0.84; MgO-Fe2O3, r = 0.88; Fe2O3-TiO2, r = 0.91; Fe2O3-K2O, r = 0.74; Al2O3-K2O, r = 0.69; Al2O3-V, r = 0.72; TiO2-V, r = 0.73, and MgO-V, r = 0.69) that testify to the contribution of mafic terrigenous detrital material to the deposit. Chondrite-normalized REE patterns of all ore samples are characterized by negative Ce (0.06–0.15, average 0.10) and slightly positive Eu (0.29–0.45, average 0.36) anomalies. Based on ratios of Mn/Fe (average 56.23), Co/Ni (average 0.33), Co/Zn (average 0.38), U/Th (average 3.40), La/Ce (average 1.45), Lan/Ndn (average 2.16), Dyn/Ybn (average 0.33), and light REE/heavy REE (average 8.40; LREE > HREE), as well as Ba (average 920 ppm) and total REE contents (average 6.96 ppm) negative Ce and positive Eu anomalies, Dehoo could be considered a predominantly submarine hydrothermal Mn deposit complemented by terrigenous detrital mafic material.

Volatile element isotopes of submarine hydrothermal mineral deposits in the Western Pacific

AbstractThe abundance and isotopic compositions of volatile elements trapped in fluid inclusions of submarine hydrothermal mineral deposits in Western Pacific subduction zones (Okinawa Trough, Izu‐Bonin arc, Mariana Trough, and Lau Basin) and in Kuroko ores in northeastern Japan are presented. The helium isotopic compositions corrected for air contribution of the Okinawa and Mariana troughs, ranging 4.49–7.68 Ra are lower than those of the Izu‐Bonin and Lau Basin, 7.62–8.91 Ra. This characteristic might reflect the differences in regional tectonic setting. The Okinawa and Mariana troughs are related to back‐arc spreading with strong graben sedimentary signature, whereas the Izu‐Bonin arc is associated with island arc magmatism. The arc contribution to the Lau Basin volcanism is significantly strong, even though it is assigned to back‐arc spreading. Nitrogen isotopes can also be explained by a similar hypothesis, whereas argon and carbon isotopes cannot be used to discriminate tectonic setting. δ13C–CO2/3He and δ15N–N2/36Ar diagrams elucidate the source of carbon and nitrogen. The MOR‐type mantle contributions to carbon are mostly smaller in the Okinawa and Mariana troughs (ranging 0.06–8.9% with the average of 2.4%) than in the Izu‐Bonin and Lau Basin (2.1–25% with the average of 7.7%). The sedimentary contributions to nitrogen are larger in the Okinawa and Mariana troughs (11–65% with the average of 35%) than in the Izu‐Bonin and Lau Basin (4–24% with the average of 15%), and the Kuroko samples agree well with the latter. Carbon and nitrogen fluxes are again higher in Okinawa trough than in Izu‐Bonin arc.

Development of the Acoustic Research Technology with the Towed Sub-Bottom Profiler for the Discovery of Submarine Hydrothermal Deposits

Development of the Acoustic Research Technology with the Towed Sub-Bottom Profiler for the Discovery of Submarine Hydrothermal Deposits

Evidence for Hydrothermal Activity in the Earliest Stages of Intraoceanic Arc Formation: Implications for Ophiolite-Hosted Hydrothermal Activity

Forearcs within intraoceanic arcs preserve a record of earliest arc volcanism that took place at the initiation of subduction. In this study we have investigated the submarine section of the Bonin Ridge, which forms part of the Izu-Bonin intraoceanic arc and/or forearc system. The crustal stratigraphy of this forearc is found to have many similarities with suprasubduction zone ophiolite sequences, including the occurrence of sheeted dikes overlain by depleted tholeiites and/or boninitic magmatism. We propose that the Izu-Bonin forearc is potentially analogous to suprasubduction ophiolites. Hydrothermal alteration, together with sulfide disseminations, is exposed on some of the subaerial Bonin Islands. Based on geologic observations, the hydrothermal activity appears, in general, to have been contemporaneous with the boninite and boninitic andesite host volcanics. The sulfide mineral assemblage associated with the hydrothermal alteration is dominated by pyrite accompanied by minor chalcopyrite, sphalerite, and pyrrhotite. These sulfides are mainly found as disseminations in pillow breccias and hyaloclastite, or along the margins of dikes, but are also found as sulfide nodules in hydrothermal clay-rich zones. This forearc mineral assemblage contrasts with the Pb-rich mineralization associated with the Quaternary submarine hydrothermal deposits found along the main Izu-Bonin arc. Hydrothermal alteration in the Eocene Izu-Bonin forearc represents the style of hydrothermal activity generated by magmatism immediately after the initiation of intraoceanic subduction. Similarities in the style of hydrothermal activity and in the stratigraphy of the hosting volcanic sequence imply that the Bonin Ridge can be regarded as an in situ (i.e., not obducted or dismembered) analogue for a suprasubduction ophiolite including Cyprus-type massive sulfide deposits.

Deep Sea Mining of Submarine Hydrothermal Deposits and its Possible Environmental Impact in Manus Basin, Papua New Guinea

The Manus back-arc basin host three distinct well known submarine hydrothermal deposits of Vienna Wood, Pacmanus and Onsen sites. The Vienna Wood site is a typical Cu-Zn type of mineralization consisting predominantly of pyrite, marcasite, sphalerite, wurtzite and chalcopyrite. The Pacmanus site is a polymetallic type of mineral deposit consisting of sphalerite, chalcopyrite, bornite, wurtzite, pyrite, marcasite, enargite, tennantite, galena, Pb-As-Sulphosalt, gold, covellite, digenite and chalcocite. The Onsen site is the first deep sea acid sulfate type of mineralisationconsisting ofenargite, covellite, chalcopyrite, pyrite and marcasite.The Papua New Guinea (PNG) Government has granted exploration license to Nautilus Mineral Cooperation to explore for submarin e hydrothermal deposit in the Manus Basin. It has done extensive exploration around the existing hydrothermal depos its of Vienna Wood, Pacmanus and Onsen site. This has resulted in the discoveries of well over twenty hydrothermal deposits (Solwara 1 to Solwara 20). Nautilus Minerals has done resource drilling on Solwara 1 and Solwara 12 deposit due to its polymetallic type of mineralization and its geochemicalsimilarities to the Pacmanus site. From resources drilling, Nautilus Minerals reported an indicated and inferred mineral resource of 1030 kt and 1540 kt respectively for the Solwara 1 project at 2.6% Cu equivalent cut off grade. The PNG government has granted mining lease (ML154) to Nautilus Minerals to mine the Solwara 1 deposit in January 2012. If mining activity commences at the Solwara 1 site then Nautilus needs to address possible environmental impacts of water usage and discharge, water quality, sedimentation and dewatering and preservation of hydrothermal vent communities.

Distribution of the main ore elements in the Tumurtijn-ovoo Fe–Mn–Zn skarn deposit, Mongolia

The submarine hydrothermal Tumurtijn-ovoo skarn deposit contains large concentrations of Zn related to sphalerite, Mn predominantly hosted in jacobsite and bustamite, and Fe mainly fixed in jacobsite, magnetite, and andradite. The quantitative distribution of these ore elements was studied with special emphasis on the Zn-bearing Mn-rich upper part of the skarnbody. Here, Zn is negatively correlated with Fe, but positively with Mn. The Mn/Fe ratio of the main skarn type reflects whether sphalerite is associated either with jacobsite or magnetite. In vertical direction, Zn shows minima–maxima distributions that imply stratiform mineralization. This genetic concept is in agreement with the sedimentary characteristics of the deposit as deduced from conformable marble–skarn alternations in the transitional zone between marble and skarn and from internal laminations within the skarn. In the Zn-rich skarn sections lateral differentiations have been recognized. Highest values of Zn content and the Mn/Fe ratio are spatially correlated and are interpreted to represent ore centres. Large ore centres show elongated contours and are suggested to be formed along synsedimentary faults. Analogically, the lateral differentiations within the Zn-free, Mn-poor, and quartz-rich lower part of the skarnbody have been studied using the Fe content and the Mn/Fe ratio. It could be ascertained that the position of the ore centres changed with time from the lower to the upper skarn.

Interpretation of Mineral Zoning in Submarine Hydrothermal Ore Deposits in Terms of Coupled Fluid Flow-Precipitation Kinetics Model

Major minerals (sulfates, sulfides, quartz) are distributed in different parts of submarine hydrothermal ore deposits. For instance, the abundance of barite increases stratigraphically upwards in the massive orebodies of the Kuroko deposits (black and yellow ores), while quartz is abundant in the lower parts (siliceous ore). The different distribution of barite and quartz in the Kuroko deposits can not be accounted for by thermochemical equilibrium calculations based on the precipitation due to mixing of ascending hydrothermal solutions with ambient cold seawater. In the present study, a coupled fluid flow-precipitation kinetics model was used to calculate the amounts of quartz, barite, and anhydrite precipitated from a hydrothermal solution mixed with seawater, assuming reasonable values for temperature, precipitation rate, fluid flow velocity, mineral surface area/fluid mass ratio (A/M), and initial concentrations of hydrothermal solution and seawater before mixing occurred. The results indicate that barite precipitates more efficiently than quartz from discharging fluids with relatively higher flow velocity, lower temperatures and under the condition of lower A/M ratios on the seafloor (black ore), whereas quartz precipitates more effectively from solutions with lower flow velocity, higher temperatures and higher A/M ratios beneath the seafloor (siliceous ore) and in the orebody (barite ore, ferruginous chert ore). Anhydrite precipitates in shallow sub-seafloor environments with lower precipitation rates and higher A/M ratios than barite and higher precipitation rates and lower A/M ratios than quartz. These results explain the observed occurrences of barite, anhydrite, and quartz in the Kuroko deposits. Namely, barite is abundant in black ore and barite ore which formed above the seafloor, anhydrite formed in high-permeability tuff breccias, and quartz formed in low permeability dacite intrusive bodies in the sub-seafloor environment.

Discovery of Yaguila Pb-Zn Polymetallic Deposit in Tibet: A Successful Case of Geochemical Prospecting

Yaguila Pb-Zn polymetallic deposit in Tibet is discovered through geochemical exploration techniques. The deposit is located in the eastern section of Longmala-Yaguila fault sag belt in the area of Nyainqentanglha Range. The ore bodies lie in the lithologic interface between tuffaceous sandstones and iron-manganese banded marbles in the Upper Carboniferous-Lower Permian Laigu formation. They occur in bedded and stratoid forms and are consistent with the attitude of strata. The paper reviews the process of discovering the deposit, and analyzes the important role of geochemical exploration in prospecting in the research area. It studies the geological characteristics of ore-forming, distribution of elements and features of anomalies, and finds out the Carboniferous- Permian is the main horizon Pb-Zn polymetallic anomalies form. The deposit type is submarine exhalative sedimentary-magmatic hydrothermal superimposition Pb-Zn polymetallic deposit. Furthermore, the paper also establishes a geology-geochemistry prospecting model for the research area and gives some suggestions to the further work, being of great significance in guiding geological prospecting in the research area.

COPPER ISOTOPE CHARACTERISTICS OF COPPER-RICH MINERALS FROM BESSHI-TYPE VOLCANOGENIC MASSIVE SULFIDE DEPOSITS, JAPAN, DETERMINED USING A FEMTOSECOND LA-MC-ICP-MS

The copper isotope ratios of chalcopyrite, secondary malachite, and native copper of metamorphosed Besshi-type volcanogenic massive sulfide (VMS) deposits from two different mines, Japan, were measured by femtosecond-pulsed laser ablation-multiple collector-inductively coupled plasma-mass spectrometry (fs-LA-MC-ICP-MS). The δ 65Cu (where δ 65Cu = [{(65Cu/63Cu)sample/(65Cu/63Cu)NIST-SRM976} − 1] × 1,000) values of chalcopyrite samples of both mines are relatively narrow (−0.34 to +0.29‰) compared to those of previously reported chalcopyrite from modern submarine hydrothermal deposits at mid-oceanic ridge settings (−0.98 to +3.14‰). However, the δ 65Cu values of chalcopyrite are slightly different between the two mines. This suggests that, although metamorphic reequilibration may have reduced the original range of copper isotopes, premetamorphic δ 65Cu characteristics of both mines are generally preserved. The chalcopyrite samples of one deposit might be significantly affected by dissolution during reworking processes after precipitation on the sea floor. Secondary malachite ( δ 65Cu = 2.63–2.97‰) and native copper ( δ 65Cu = 1.43–1.71‰) have higher δ 65Cu values than chalcopyrite from the same deposit. This variation is most reasonably explained in terms of a redox-controlled isotope fractionation at low-temperature conditions during secondary (weathering) processes involving the preferential incorporation of 65Cu in secondary Cu(II) solutions. It is also suggested that significant negative isotopic fractionations accompanying the reduction of Cu (II) solutions to native copper [Cu (0)] occurred.

Worldwide distribution of submarine hydrothermal deposits and their classification

Worldwide distribution of submarine hydrothermal deposits and their classification

The Best Article Award 2008 of the Society of Resource Geology was presented to Katsumi MARUMO, Tetsuro URABE, Akiko GOTO, Yoshinori TAKANO and Miwako NAKASEAMA for the following paper: Mineralogy and isotope geochemistry of active submarine hydrothermal field at Suiyo Seamount, Izu‐Bonin Arc, West Pacific Ocean. Resource Geology, 58, 220–248

The authors conducted sampling of altered rocks, sulfides and clays from a submarine hydrothermal deposit formed in a caldera on the summit of the Suiyo Seamount in the Izu-Bonin Island Arc, and carried out mineralogical and geochemical analysis for the samples. Based on these data, the genesis of the hydrothermal deposit was also discussed in the paper. This hydrothermal deposit is regarded as the first example of Kuroko-type sulfide mineralization at the volcanic front of an island arc. The samples were collected from depths of 2–9 m below the sea floor using the Benthic Multi-coring System. They are mainly altered volcanic rocks (dacite lava, pyroclastic rocks of dacite to rhyolite compositions and pumice) associated with sulfide veins and anhydrite veins/patches. The sulfides consist mainly of Zn, Cu and Pb and contain high concentrations of Au, Ag, As, Hg, Sb and Se. They show the large variation in δ202Hg/198Hg. This suggests that light Hg isotope concentrated into a vapor and then Hg precipitated by a mixing of the vapor with seawater. Lead isotope ratios of the sulfides suggest that lead is of magmatic origin and strontium isotope ratios of anhydrites suggest that strontium was derived from seawater. In addition, hydrogen isotope ratios of chlorite/montmorillonite, mica and chlorite in the active venting sites revealed that the hydrothermal water is of seawater origin. The formation temperatures of 160–270°C were estimated from oxygen isotope ratios of these minerals. The present temperature (308.3°C) in a bore hole of the active hydrothermal deposit is higher than the estimated formation temperatures of the clay minerals and anhydrite. Detailed description, analysis and discussion for Kuroko-type sulfide mineralization at the volcanic front of an island arc in this paper contributed significantly to the elucidation of the genesis of Kuroko-type deposits. For this reason, this paper was judged to be appropriate for The Best Article Award 2008.

Potassic and Ferriferous Green Clays From the Ancient Submarine Hydrothermal Deposit, with Special Reference to the Occurrence and Chemical Composition of the Clays from the Nurukawa Kuroko Deposit

Potassic and Ferriferous Green Clays From the Ancient Submarine Hydrothermal Deposit, with Special Reference to the Occurrence and Chemical Composition of the Clays from the Nurukawa Kuroko Deposit

Comparison of Modern Zn-Ba-Pb Ore Deposits at Convergent Plate Margins and Fe-Cu-Zn Deposits at Divergent Plate Margins

At divergent plate margins, black smoke forms immediately on contact of ascending hydrothermal solutions with sea water. The black smoke, consisting mainly of black ore (BO) and barite ore (BaO), is rapidly dispersed in seawater leaving behind a dominantly yellow ore (YO). At convergent plate margins, on the other hand, zinc sulfides and associated chalcophilic elements start depositing within the hydothermal mound at mesothermal temperatures, and are largely trapped there to form a mixed yellow, black and barite ore (YO-BO-BaO). The abundance of individual chalcophilic elements within the mixed ore varies by more than four orders of magnitude, with Zn-Pb-Ba-Cu-As-Sb-Cd being the elements most enriched in these deposits. The differing patterns of element deposition in these two tectonic settings is related to the temperature of the hydrothermal fluids, which is a function of water depth and therefore of tectonic setting (mid-ocean ridge vs volcanic arc). In highly sedimented basins, such as the JADE hydrothermal field in the Okinawa Trough, Pb and other chalcophilic elements are leached from the sediment by slowly migrating hydrothermal fluids to form a mixed black-yellow-barite ore (BO-YO-BaO). This type of deposit is the most enriched in Zn-Pb-Ba-As-Sb-Ag in decreasing order of element abundance. These results indicate that black ore (sphalerite plus galena) is most enriched in sedimented-hosted deposits such as the JADE deposit, is moderately enriched in submarine hydrothermal mineral deposits from convergent plate margins and is poorly enriched in submarine hydrothermal mineral deposits from divergent plate margins.