Seafloor Massive Sulfide Research Articles

Serpentinization and its implications for ultramafic-hosted sulfide mineralization: A case study at the Tianzuo hydrothermal field, 63.5°E, Southwest Indian Ridge

Reaction of ultramafic rocks with seawater and subsequent serpentinization has been considered one of the most important factors controlling the formation of ultramafic-hosted seafloor massive sulfide (UM-SMS) deposits. However, the mineralization processes responsible for these deposits remain poorly understood, in particular because they are less abundant as compared with their basaltic counterparts. In this work, serpentinites with different alteration grades collected at the Tianzuo hydrothermal field (THF), Southwest Indian Ridge, were studied. Mineralogical and chemical analyses were performed in the secondary opaque minerals resulting from serpentinization to understand the role of this process during the formation of UM-SMS deposits. Our results show that these opaque minerals mainly consist of magnetite, hematite, pentlandite, and minor pyrite, suggestive of high but varying oxygen and sulfur fugacities. The hematite is characterized by an enrichment in Mg, Si, Ni, and Co as compared with magnetite. Pentlandite associated with hematite has elevated and consistent Ni contents as compared with that associated with magnetite. These results indicate that breakdown and decomposition of primary silicate and sulfide minerals during serpentinization has controlled the sources of ore-forming materials. Concentrations of Te are variable and show a positive correlation with Ni in pentlandite associated with magnetite or hematite, suggesting that gabbroic intrusions provided additional material to the hydrothermal system. Oxidation and sulfidation conditions are ideal for the formation of trisulfur ion S3− in THF, which can significantly improve the capability of hydrothermal fluids for leaching ore-forming metals from the wall rocks, promoting the formation of THF. In addition of reduced systems, hydrothermal fluids with high oxygen and sulfur fugacities triggered by extensive seawater infiltration can most likely also develop in ultramafic-hosted systems. These results suggest that the areas with well-developed fractures are promising candidates for further exploration of UM-SMS deposits along mid-oceanic ridges.

New Data for the Internal Structure of Ultramafic Hosted Seafloor Massive Sulfides (SMS) Deposits: Case Study of the Semenov-5 Hydrothermal Field (13°31′ N, MAR)

The internal structure of Seafloor Massive Sulfides (SMS) deposits is one of the most important and complex issues facing the study of modern hydrothermal ore systems. The Semenov-5 hydrothermal field is a unique area where mass wasting on the slope of the oceanic core complex (OCC) structure exposes the subsurface portion of the deposit and offers an exceptional opportunity to observe massive sulfides that have formed not only on the seafloor but in sub-seafloor zones as well. This paper examines the internal structure of the OCC-related Semenov-5 hydrothermal field along with analysis of the mineralogy and chemistry of different parts of sulfide deposit. The seafloor deposit is comprised of pyrite, marcasite, hematite, goethite, lepidocrocite, rare pyrrhotite, isocubanite and Co-rich pyrite. Sulfide chemistry indicates the prevailing influence of ultramafics on their composition irrespective of the spatial relation with basalt lavas. Sub-seafloor mineralization is associated with ultramafic rocks and is represented by massive and disseminated sulfides. Pyrrhotite, isocubanite, pyrite, chalcopyrite, Co-rich pyrite, quartz with rutile, quarts with hematite and Cr-spinels are fixed in massive subseafloor mineralization. The presence of Cr-spinels as well as a very high Cr content are regarded as indicators of the metasomatic nature of this part of the deposit that had formed as a result of ultramafic replacement. As a result, three zones of a hydrothermal ore-forming system have been described: massive sulfides precipitated from hot vents on the surface of the seafloor, massive sulfides formed due to replacement of ultramafics below the seafloor and disseminated sulfide mineralization-filled cracks in hosted rocks which have formed stockwork around metasomatic massive sulfides. Despite differences in the mineral and geochemical composition of sub-seafloor and seafloor mineralization, all minerals subject to the sample formed as a consequence of fluid circulation in ultramafic rocks and were linked by a common ore-forming process.

Sulfur sources for ultramafic‐hosted sulfide mineralization in the Tianzuo hydrothermal field, 63.5° E, South‐west Indian Ridge: Insights from sulfur and carbon isotopes

To date, discovered ultramafic‐hosted seafloor massive sulfide (UM–SMS) deposits are rare, remain poorly understood in terms of their genesis, and typically form along slow‐ and ultraslow‐spreading mid‐oceanic ridges. The Tianzuo hydrothermal field (THF) is the only UM–SMS deposit identified so far along the ultraslow‐spreading South‐west Indian Ridge (SWIR). This study presents new detailed mineralogical and S–C isotopic data for serpentinized peridotite, gabbro, serpentinite, and sulfide ore samples from the THF and to provide new insights into the processes that formed the deposit. Chromium‐reduced sulfur (CRS) and sulfate–sulfur (SS) in samples of serpentinized peridotite have positive δ34S values (up to 10.22‰ and 20.67‰, respectively). The CRS formed through thermochemical reduction of seawater sulfate during reactions between seawater and ultramafic rocks, whereas the SS most likely occurred as dissolved sulfate phases in seawater occupying the pore space of serpentinized peridotite after exposure at the seafloor. The serpentinite samples contain SS with δ34S values of 19.21‰–20.9‰, indicating infiltration by seawater that led to the deposition of seawater sulfate. The sulfide ores have acid‐volatile sulfur (AVS), CRS, and SS δ34S values of 10.99‰–12.07‰, 2.34‰–10.98‰, and −4.13‰ to 2.76‰, respectively, indicating that the AVS and CRS within the samples are dominated by sulfur reduced from seawater sulfate (e.g., anhydrite) and leached from the surrounding wall rocks, although the re‐oxidization of microbial‐reduced sulfur most likely generated the sulfate with low and negative δ34S values. The total carbon and total organic carbon δ13C values of the THF samples are negative and range from −21.99‰ to −0.34‰ and −26.7‰ to −21.02‰, respectively, further suggesting that the samples record microbial activity. Gabbro samples have strongly negative AVS (−10.69‰) and CRS (−7.2‰) δ34S values, indicating that microbial‐reduced sulfur derived from shallow levels in the crust was incorporated into the hydrothermal system that circulated through the deeper‐seated gabbroic units. Our results suggest that the ultramafic and gabbroic rocks, seawater, and microbial activity all provided sulfur to the THF, with well‐developed fractures and local magma supply probably being the key factors controlling the formation of this field and similar UM–SMS deposits elsewhere.

Joint Interpretation of Marine Self‐Potential and Transient Electromagnetic Survey for Seafloor Massive Sulfide (SMS) Deposits: Application at TAG Hydrothermal Mound, Mid‐Atlantic Ridge

AbstractThe self‐potential (SP) method is expected to play an important role in the exploration of seafloor massive sulfide (SMS) resources. Since the redox potential changes with depth below the seafloor, SMS deposits are the source of an electrical (source) current density, generating in turn a recordable electrical field. This electrical field can be remotely measured at and above the seafloor. By integrating this electrical field, we obtained a so‐called SP profile or map. The electrical conductivity distribution of SMS deposits is an important ingredient in the inversion of these SP data in order to distinguish between causative primary sources (i.e., associated with the SMS deposits themselves) and secondary current sources associated with conductivity contrasts below the seafloor. Such ingredient is therefore necessary to properly localize SMS deposits and eliminating ghosts associated with high conductivity contrasts. The conductivity structure of the seafloor is however unknown in most SP surveys. This study presents the first joint interpretation of transient electromagnetic and SP surveys. The field data were acquired at the Trans‐Atlantic Geotraverse (TAG) hydrothermal mound. The conductivity structure of TAG mound was obtained by inverting transient electromagnetic data. This electrical conductivity distribution is then used to invert the SP data. The obtained (primary) source current distribution delineates the geometry of the SMS deposits. The deposits are located in the center of the mound as well as at its edges, in a way that is consistent with water column data. Combining the two geophysical methods improves our ability to better decipher the fine geometry of SMS deposits below the seafloor.

A Review on Mineralogical and Geochemical Characteristics of Seafloor Massive Sulfide Deposits in Mid-Ocean Ridge and Volcanic Arc Settings: Water-Rock Interaction and Magmatic Contribution

A Review on Mineralogical and Geochemical Characteristics of Seafloor Massive Sulfide Deposits in Mid-Ocean Ridge and Volcanic Arc Settings: Water-Rock Interaction and Magmatic Contribution

Beyond deep-sea mining sublethal effects: Delayed mortality from acute Cu exposure of the cold-water octocoral Viminella flagellum.

The potential release of metals, especially copper (Cu) during mining of seafloor massive sulphides (SMS), represents a potential toxicological threat to cold-water coral (CWC) habitats. Herein, we evaluated for the first time the response of the whip coral Viminella flagellum to short-term acute Cu exposure. Nubbins of V. flagellum were exposed to Cu concentrations of 0 (control); 60; 150; 250; 450 and 600μg/L for 96h. After exposure, V. flagellum nubbins were transferred to a continuous flow-through aquarium and feed once a day for 3weeks. No immediate mortality was detected during the short-term Cu exposure. However, a delayed mortality, which was concentration dependent was observed. The first signs of tissue loss occurred after 1week of recovery in non-contaminated conditions in V. flagellum nubbins previously exposed to Cu concentrations of 60 and 150μg/L followed by nubbins exposed to Cu concentrations of 250, 450μg/L after 2weeks and 600μg/L after 3weeks. A delayed mortality impact should be considered in future Cu tolerance experiments and scenarios of deep-sea mining exploitation.

The soundscape of two deep-sea hydrothermal vent sites

Hydrothermal vents are sea floor structures where geothermally heated seawater is discharged. The high-temperature, chemically rich environment is host to uniquely adapted marine life. Vent soundscapes may contain important bioacoustic cues as well as signals enabling passive acoustic monitoring of hydrothermal vent dynamics. Proposals for deep-sea mining of seafloor massive sulfides near hydrothermal vents have elicited concern over potential environmental impacts due to disturbance from industrial activity, including changes to the soundscape. This study assesses the baseline soundscape at two sites, the Main Endeavour Field on the Juan de Fuca Ridge and the Lucky Strike vent field on the Mid-Atlantic Ridge over 12 months and 3 months respectively. To facilitate comparison with future studies at other sites, the most recently proposed standard soundscape analysis methodologies are employed, including terminology in alignment with ISO 18405:2017. In accordance with the latest soundscape standard literature, metrics quantifying the amplitude, impulsiveness, periodicity, and uniformity are reported. Spectral probability densities, percentiles, and long-term spectrograms are computed in hybrid millidecade frequency bands. Finally, a qualitative analysis is included to describe the source types contributing to the hydrothermal vent sound field.

Perspectives on exploration and extraction of seafloor massive sulfide deposits in Norwegian waters

Abstract We present a stochastic dynamic simulation model for exploration and extraction of seafloor massive sulfide (SMS) mineral deposits on the Norwegian Continental Shelf (NCS). The model is developed based on selected industry knowledge, expectations, and perceptions elicited through a participatory systems mapping session with 82 participants and 20 in-depth interviews with experts from industry, academia, and the public policy sector. Using the model, we simulate the expected ranges of resource- and economic potential. The simulation results indicate an expected commercial resource base of 1.8 to 3 million tons of copper, zinc, and cobalt, in which copper makes out the most significant part. Relating to the expected commercial resource base, we highlight a discrepancy between academic and industrial expectations, in which the academic expectations are more conservative than the industrial expectations. The corresponding net present values lie in the range of a net present loss of 970 million USD up to a net present gain of 2.53 billion USD, in which the academic expectations are projected to yield a negative net present value, while the industrial expectations are projected to yield a positive net present value. Closer investigation of the results reveals that one of the main challenges regarding SMS exploration and extraction is the initial exploration costs associated with coring operations. These costs are expected to be high with today’s exploration technology. Moreover, they occur relatively early in time compared to revenue-generating activity, which has a significant negative impact on the net present value of the industry due to discounting. Thus, a key focus of the industry should be to find ways to reduce the costs associated with coring operations and/or the time it takes from initial exploration to extraction and generation of revenue.

Numerical Simulation Study on the Relationships between Mineralized Structures and Induced Polarization Properties of Seafloor Polymetallic Sulfide Rocks

The induced polarization (IP) method plays an important role in the detection of seafloor polymetallic sulfide deposits. Numerical simulations based on the Poisson–Nernst–Planck equation and the Maxwell equation were performed. The effects of mineralized structures on the IP and electrical conductivity properties of seafloor sulfide-bearing rocks were investigated. The results show that total chargeability increases linearly as the volume content of disseminated metal sulfides increases when the volume content is below 20%. However, total chargeability increases nonlinearly with increasing volume content in vein and massive metal sulfides when the volume content is below 30%. The electrical resistivity of disseminated metal sulfides mainly depends on the conductivity of pore water. The electrical resistivity of vein and massive sulfides mainly depends on the volume content and the length of sulfides. Increase in the aspect ratio (0.36 to 0.93) of seafloor massive sulfides causes relaxation time constants and total chargeability to decrease. Relaxation time constants and total chargeability also decrease with increase in the tortuosity of seafloor vein sulfides from 1.0 to 1.38. This study is of great value for the electrical survey of seafloor polymetallic sulfide deposits.

Fragmentation Characteristics of Seafloor Massive Sulfides: A Coupled Fluid-Particle Flow Simulation

The research on the fragmentation mechanism of seabed minerals under high ambient pressure significantly contributes to the exploitation of seafloor massive sulfides (SMS). In this paper, the uniaxial compressive strength (UCS) test and triaxial compressive strength (TCS) test were carried out on two kinds of SMS samples to obtain the key mechanical properties of minerals, including cohesion, internal friction angle, compressive strength, and elastic modulus. Then, based on these mechanical parameters, the fluid-solid coupling cutting model of two SMS samples at high ambient pressure is established by using the coupling method of discrete elements and smooth particles. A mixed-bond model is selected, and the microscopic parameters are determined by a repeated calibration process. Meanwhile, the cutting force and debris information are monitored and collected in real time during the whole cutting process. The results show that under different confining pressure environments, the model shows the transformation of minerals from brittleness to ductility. The cutting force increases with the increasing ambient pressure. Due to the fluid pressure, the crushing mechanism tends to shear failure, which is more likely to produce mud and finer fragments.

Iron isotopes constrain sub-seafloor hydrothermal processes at the Trans-Atlantic Geotraverse (TAG) active sulfide mound

Sub-seafloor hydrothermal processes along volcanically active plate boundaries are integral to the formation of seafloor massive sulfide deposits and to oceanic iron cycling, yet the nature of their relationship is poorly understood. Here we apply iron isotope analysis to sulfide minerals from the Trans-Atlantic Geotraverse (TAG) mound and underlying stockwork, 26°N Mid-Atlantic Ridge, to trace hydrothermal processes inside an actively-forming sulfide deposit in a sediment-free mid-ocean ridge setting. We show that data for recently formed chalcopyrite imply hydrothermal fluid–mound interactions cause small negative shifts (<−0.1‰) to the δ56Fe signature of dissolved iron released from TAG into the North Atlantic Ocean. Texturally distinct types of pyrite, in turn, preserve a δ56Fe range from −1.27 to +0.56‰ that reflects contrasting precipitation mechanisms (hydrothermal fluid–seawater mixing vs. conductive cooling) and variable degrees of progressive hydrothermal maturation during the >20 kyr evolution of the TAG complex. The identified processes may explain iron isotope variations found in fossil onshore sulfide deposits.

Depth Profiles of Re-Os Geochemistry in Drill Cores from Hole U1530A in Brothers Volcano Hydrothermal Field, Kermadec Arc: Mobilization and Extreme Enrichment of Os by Volcanic Gas

AbstractBetter understanding metallogenesis in oceanic crust depends on costly sea-floor drilling projects in areas where metal-bearing deposits, such as sea-floor massive sulfide deposits, are currently forming. In 2018, International Ocean Discovery Program (IODP) Expedition 376 recovered drill cores from an active hydrothermal field at Brothers volcano, in the Kermadec arc. These provide insight into the formation of mineral deposits along arcs, the structure and permeability of hydrothermal sites, and the relationship between the discharge of magmatic fluids and the deep biosphere. We report whole-rock major and trace element compositions and the Re-Os isotope geochemistry of hydrothermally altered volcanic rocks in a core from Hole U1530A, extending 453 m beneath the sea floor, and unaltered volcanic rocks in cores from four other drilling sites and interpret these data to better understand subseafloor mixing of hydrothermal fluids and ambient seawater. The core exhibits more radiogenic 187Os/188Os values than typical basal values in four intervals. We propose two causal mechanisms of these radiogenic values: (1) mixing between seawater and hydrothermal fluid, associated with abundant deposition of sulfide or sulfate minerals; and (2) ingress of seawater with radiogenic 187Os/188Os values, associated with abundant chlorite and high porosity. Extreme Os enrichments up to 61.5 ppb are interpreted as the result of mobilization of Os as OsO4 or OsF6 and transport by volcanic gas, which also affected the Re-Os geochemistry of the rocks from the other Expedition 376 holes. Mobilization and transport of Os by volcanic gas may be an appreciable factor in the influx of unradiogenic Os into the ocean.

Modelling the Dispersion of Seafloor Massive Sulphide Mining Plumes in the Mid Atlantic Ridge Around the Azores

It is increasingly recognised that deep-sea mining of seafloor massive sulphides (SMS) could become an important source of mineral resources. These operations will remove the targeted substrate and produce potentially toxic plumes from in situ seabed excavation and from the return water pumped back down to the seafloor. However, the spatial extent of the impact of deep-sea mining is still uncertain because few field experiments and models of plume dispersion have been conducted. In this study, we used three-dimensional hydrodynamic models of the Azores region together with a theoretical commercial mining operation of polymetallic SMS to simulate the potential dispersal of plumes originating from different phases of mining operations, and to assess the magnitude of potential impacts. Although the model simulations presented here were subject to many caveats, they did reveal some important patterns. The model projected marked differences among sites making generalisations about plume-dispersal patterns in mid-ocean ridges difficult. Nevertheless, the models predicted large horizontal and vertical plume-dispersals above the thresholds adopted. Persistent plumes (temporal frequency &amp;gt;50%, i.e., 6 months out of 12 months) were projected to disperse an average linear distance of 10 to 20 km, cover an area of 17 to 150 km2, and extend more than 800 m in the water column. In fact, the model projected that plumes may disperse beyond the licensed mining areas, reach the flanks and summits of nearby topographic features, and extend into the bathypelagic, mesopelagic, and epipelagic environments. Modelled plume-dispersal overlaps with the predicted distribution of cold-water corals and with existing fishing activities. These potential impacts would be of particular concern in regions such as the Azores, where local populations are highly dependent on the sea for their livelihoods. The findings of this study are an important initial step towards understanding the nature and magnitude of deep-sea mining impacts in space and time.

Exploring Ocean Floor Geodiversity in Relation to Mineral Resources in the Southwest Pacific Ocean

The future extraction of mineral resources may irreversibly damage ocean floor geodiversity in the Southwest Pacific Ocean. Therefore, understanding of the spatial distribution of ocean floor geodiversity in relation to mineral resources is important. For that purpose, we first developed a geodiversity index map of the western Pacific Ocean including spatial information of openly available digital layers of four components: seafloor geomorphology, sediment thickness, bathymetry and seafloor roughness. Second, we analysed how these components contributed to the geodiversity index. Finally, correlations between three mineral resources (seafloor massive sulphides, polymetallic nodules and cobalt-rich crusts) and the geodiversity index, its components, and the ocean floor age were calculated. The results showed that the ocean floor environment and the time necessary for the formation of the three mineral resources were predominantly related to the bathymetry component and the age of the ocean floor, and to a lesser extent to the seafloor roughness, geomorphology and sediment thickness components. We conclude that the ocean floor geodiversity index and its components contribute to an improved understanding of the spatial distribution of abiotic seafloor diversity and can be optimized by using higher resolution data. We suggest that ocean floor geodiversity could be considered in future resource extraction to support responsible mining and help limit environmental damage.

3D self-potential tomography of seafloor massive sulfide deposits using an autonomous underwater vehicle

Seafloor massive sulfide (SMS) deposits contain abundant metals, such as Cu, Zn, Au, and Ag, which are of growing economic interest. Currently, the exploration of SMS deposits has entered into a new stage of resource assessment, so we need a geophysical method to rapidly obtain the 3D structure of these SMS deposits. We report here a self-potential (SP) survey performed with an autonomous underwater vehicle (AUV) at the Yuhuang hydrothermal field on the ultraslow-spreading Southwest Indian Ridge with a water depth ranging from 1300 m to 2200 m. The electric-field sensors are attached to the tail of the AUV to record the electric field approximately 50 m above the seafloor. The electric field strength is observed to reach an amplitude of 0.6 mV/m at this known SMS deposit. SP tomography is used to obtain the 3D structure of the ore body, and benchmark numerical tests are first performed on synthetic cases to optimize the inversion algorithm parameters to estimate the ore location. The 3D SP tomography reveals a south-sloping ore body, which is 100 m long in the north–south direction and nearly 200 m long in the east–west direction. The vertical extent of the ore body is approximately 100 m. These results suggest that an AUV-based SP survey and tomography are potentially useful exploration methods to characterize the geometry of SMS deposits. This method may play an important role in resource assessment in concert with other geophysical methods, such as magnetic and induced-polarization surveys.

A cost-effective three-dimensional marine controlled-source electromagnetic survey: Exploring seafloor massive sulfides

A 3D marine controlled-source electromagnetic (CSEM) survey for mapping hydrocarbons uses dozens of ocean-bottom electric (OBE) receivers deployed in a grid pattern and several transmitter towlines. This study considers seafloor massive sulfides (SMS) exploration, and the horizontal survey scale of SMS is a few kilometers, which is small compared with hydrocarbon surveys of tens of kilometers. If we apply a 3D CSEM survey using a receiver deployment on grids to map SMS, high survey costs will be incurred despite the small survey size. We have developed a cost-effective 3D marine CSEM survey that uses fewer receivers than the survey with a receiver deployment on grids to reduce survey costs for SMS. This CSEM survey uses a line of OBE receivers in the center of the survey area and several transmitter towlines. Numerical tests demonstrate that our survey (seven OBE receivers) using 80% fewer receivers than the survey with a receiver deployment on grids (35 OBE receivers) is able to accurately map SMS, obtaining a performance similar to that of the receiver deployment on grids. Then, we explore SMS in the Ieyama hydrothermal area off Okinawa, southwest Japan, using our 3D CSEM survey with a line of six OBE receivers and three transmitter towlines. The resulting 3D resistivity distribution from the observed data highlights three potential SMS zones consisting of 0.2 ohm-m low resistivity embedded into 1 ohm-m sediment.

Rock Magnetic Signatures of Hydrothermal Mineralization in the Trans‐Atlantic Geotraverse (TAG) Hydrothermal Field

AbstractThe Ocean Drilling Program Leg 158 drill holes from the Trans‐Atlantic Geotraverse hydrothermal field are investigated to understand the rock magnetic signatures of hydrothermal mineralization. A composite columnar section has been constructed through hole correlation to understand the stratigraphic variation of magnetomineralogy within the stockwork. Isothermal remanent magnetization components unmixing, first‐order reversal curve diagrams, low‐temperature magnetic signatures, and electron microscopic analyses disclose magnetic minerals of disparate occurrences related to predominating hydrothermal mineralization reactions in three broad zones: For basaltic basements, serpentinization of olivine phenocrysts during preliminary hydrothermal alteration produces magnetite, in addition to primary titanomagnetite; Chloritized and silicified zone samples contain relict titanomagnetite and exsolved magnetite that survived hydrothermal dissolution; Anhydrite and sulfide zone samples are dominated by magnetite and hematite, likely from oxidation of polymetallic sulfides due to exposure in oxidative seafloor environments during drilling. Our findings suggest that seafloor oxidation potentially modifies the magnetic properties of polymetallic sulfides in hydrothermal deposits, which applies to magnetic tomography of sophisticated subseafloor vent structures and prospecting seafloor massive sulfides (SMS) deposits therein. Meanwhile, we alert future deep‐sea mining that drilling may promote physicochemical alteration of SMS deposits, causing environmental risks. The established magnetic signatures ultimately contribute to understanding the in situ geological preservation of SMS deposits and optimizing exploitation procedures in the future.

Formation, remobilisation and alteration processes at inactive hydrothermal vents: insights from elemental analysis of Cu-(Fe-)S sulfides from TAG, Mid-Atlantic Ridge

Chalcopyrite is the main Cu mineral in mafic-hosted marine hydrothermal systems. Its trace element budget and that of its alteration products may hold valuable information on formation, remobilisation and alteration processes of the hydrothermal system. In this study, we analysed chalcopyrite from five inactive seafloor massive sulfide (SMS) sites from the TAG hydrothermal field on the Mid-Atlantic Ridge by electron probe microanalysis (EPMA) and laser ablation inductively coupled plasma mass spectrometry (LA-ICP-MS) for 24 elements. Twelve of them are discussed in detail. In general, trace element concentrations range between sub-parts per million (ppm) to several hundreds of ppm. The elements Se and Co are incorporated into the lattice at high temperatures of > 300 °C, whereas As, Ge, Ga substitute into the structure at intermediate to low temperatures. Other elements, e.g. Zn, are either accommodated into the mineral lattice or form inclusions, whereas V and Mn, which originate from seawater, get adsorbed onto the mineral surface. Idaite, chalcocite, and covellite exhibit similar trace element patterns to those of the precursor chalcopyrite. However, the secondary copper minerals show enrichment of Ag and Mo. Factors controlling the incorporation are predominantly related to changes in physicochemical conditions with the host rock composition playing only a minor role.

SANTORY: SANTORini’s Seafloor Volcanic ObservatorY

Submarine hydrothermal systems along active volcanic ridges and arcs are highly dynamic, responding to both oceanographic (e.g., currents, tides) and deep-seated geological forcing (e.g., magma eruption, seismicity, hydrothermalism, and crustal deformation, etc.). In particular, volcanic and hydrothermal activity may also pose profoundly negative societal impacts (tsunamis, the release of climate-relevant gases and toxic metal(loid)s). These risks are particularly significant in shallow (&amp;lt;1000m) coastal environments, as demonstrated by the January 2022 submarine paroxysmal eruption by the Hunga Tonga-Hunga Ha’apai Volcano that destroyed part of the island, and the October 2011 submarine eruption of El Hierro (Canary Islands) that caused vigorous upwelling, floating lava bombs, and natural seawater acidification. Volcanic hazards may be posed by the Kolumbo submarine volcano, which is part of the subduction-related Hellenic Volcanic Arc at the intersection between the Eurasian and African tectonic plates. There, the Kolumbo submarine volcano, 7 km NE of Santorini and part of Santorini’s volcanic complex, hosts an active hydrothermal vent field (HVF) on its crater floor (~500m b.s.l.), which degasses boiling CO2–dominated fluids at high temperatures (~265°C) with a clear mantle signature. Kolumbo’s HVF hosts actively forming seafloor massive sulfide deposits with high contents of potentially toxic, volatile metal(loid)s (As, Sb, Pb, Ag, Hg, and Tl). The proximity to highly populated/tourist areas at Santorini poses significant risks. However, we have limited knowledge of the potential impacts of this type of magmatic and hydrothermal activity, including those from magmatic gases and seismicity. To better evaluate such risks the activity of the submarine system must be continuously monitored with multidisciplinary and high resolution instrumentation as part of an in-situ observatory supported by discrete sampling and measurements. This paper is a design study that describes a new long-term seafloor observatory that will be installed within the Kolumbo volcano, including cutting-edge and innovative marine-technology that integrates hyperspectral imaging, temperature sensors, a radiation spectrometer, fluid/gas samplers, and pressure gauges. These instruments will be integrated into a hazard monitoring platform aimed at identifying the precursors of potentially disastrous explosive volcanic eruptions, earthquakes, landslides of the hydrothermally weakened volcanic edifice and the release of potentially toxic elements into the water column.

Seabed mining and blue growth: exploring the potential of marine mineral deposits as a sustainable source of rare earth elements (MaREEs) (IUPAC Technical Report)

Abstract The expected growth of the global economy and the projected rise in world population call for a greatly increased supply of materials critical for implementing clean technologies, such as rare earth elements (REEs) and other rare metals. Because the demand for critical metals is increasing and land-based mineral deposits are being depleted, seafloor resources are seen as the next frontier for mineral exploration and extraction. Marine mineral deposits with a great resource potential for transition, rare, and critical metals include mainly deep-sea mineral deposits, such as polymetallic sulfides, polymetallic nodules, cobalt-rich crusts, phosphorites, and rare earth element-rich muds. Major areas with economic interest for seabed mineral exploration and mining are the following: nodules in the Penrhyn Basin-Cook Islands Exclusive Economic Zone (EEZ), the Clarion–Clipperton nodule Zone, Peru Basin nodules, and the Central Indian Ocean Basin; seafloor massive sulfide deposits in the exclusive economic zones of Papua New Guinea, Japan, and New Zealand as well as the Mid-Atlantic Ridge and the three Indian Ocean spreading ridges; cobalt-rich crusts in the Pacific Prime Crust Zone and the Canary Islands Seamounts and the Rio Grande Rise in the Atlantic Ocean; and the rare earth element-rich deep-sea muds around Minamitorishima Island in the equatorial North Pacific. In addition, zones for marine phosphorites exploration are located in Chatham Rise, offshore Baja California, and on the shelf off Namibia. Moreover, shallow-water resources, like placer deposits, represent another marine source for many critical minerals, metals, and gems. The main concerns of deep-sea mining are related to its environmental impacts. Ecological impacts of rare earth element mining on deep-sea ecosystems are still poorly evaluated. Furthermore, marine mining may cause conflicts with various stakeholders such as fisheries, communications cable owners, offshore wind farms, and tourism. The global ocean is an immense source of food, energy, raw materials, clean water, and ecosystem services and suffers seriously by multiple stressors from anthropogenic sources. The development of a blue economy strategy needs a better knowledge of the environmental impacts. By protecting vulnerable areas, applying new technologies for deep-sea mineral exploration and mining, marine spatial planning, and a regulatory framework for minerals extraction, we may achieve sustainable management and use of our oceans.