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By Gary J. Massoth

Are hydrothermal emissions from subduction-related volcanic arcs important to the total hydrothermal burden of the oceans? While historical observations of hydrothermal venting of fluids at mid-ocean ridgecrests, intra-plate hotspots, and backarc spreading centers are numerous, we remain poorly informed regarding the contributions from hydrothermal systems associated with oceanic submarine arcs. Here we report the chemical results from the first systematic assessment for hydrothermal activity at an intra-oceanic arc front. We discovered that 7 of the 13 submarine volcanoes that define a 260-km-long segment of the southern Kermadec arc north of New Zealand are hydrothermally active. Most significant here is that the chemical compositions of the various hydrothermal systems, inferred from back-extrapolation of observations of hydrothermal plumes, are diverse, and in many instances enriched in the concentrations of gases (e.g., CO2 and H2S) and metals (e.g., Fe and Mn) compared to effluents commonly discharged from mid-ocean ridges. If our results are generally representative of submarine arcs, whose global extent may equal one-third that of ridgecrests, the answer to our leading question could be a resounding yes in terms of both volume and chemical composition.

Jan 1, 2001

By Frans van Grunsven, Cees van Rhee, Geert Keetels

One of the obstacles during the initial phases of project development is the assessment of the environmental impact. Mining residue, consisting of fine seafloor sediments, are to be discharged subsea to mitigate the impact of these suspended particles. In order to test the effectiveness of discharging in proximity of the seabed, a numerical model is developed within the open source software package OpenFoam. Dedicated laboratory experiments for numerical model validation are discussed within this paper. INTRODUCTION Siltation is considered one of the major pressures on the environment for a seabed mining operation. Siltation is defined as the pollution of water by a high concentration of suspended sediments like clay or silt. This can be caused by two main activities during the mining process: the spill loss during the excavation and the return flow of undesired seafloor sediment after ore filtration on the ship. In a concentrated cloud, these fine particles form a so-called turbidity plume. Prediction of the size of these plumes and the created layer thickness of deposited sediment is a crucial part of the environmental impact assessment. The challenge in predicting the behaviour of these plumes is found in the wide range of scales involved in the process. At the point of origin, the turbidity plumes spread mainly under the influence of turbulent whirls created by an initial momentum and a buoyancy difference due to the presence of the suspended sediment particles. If carried by ambientcurrents, these plumes can spread for several kilometres before blending in the background.

Jan 1, 2018

By Robert R. Tarver

A long history of gold production at Nome, Alaska has resulted in long term interest in the nearshore environment as a production target. Mining by Western Gold Exploration and Mining Company offshore of Nome yielded approximately 100,000 troy ounces of gold in the period 1986 through 1990. This study was designed to determine the relationship between heavy minerals, sediments, and gold concentrations which occur in the upper meter of sediment offshore of Nome. Standard procedures were implemented for grain size analysis, heavy mineral separations, and heavy mineral frequency determination.

Jan 1, 1991

By S. W. McCandless

Since the mid 1970's, the science of remote sensing has invented and demonstrated sensors that hold unique promise for users that operate in the marine environment. Earlier, visible and infrared sensors provided images and temperature maps of surface conditions, but the 1970's introduced active (radars) and passive (radiometers) microwave sensors capable of penetrating clouds and operating day or night over the world's oceans. Space-based observation satellites permit these systems to span the globe many times each day, providing a view of the world's oceans and Arctic areas consistent with daily and, sometimes, hourly changes in the marine environment. Experimental satellites launched by NASA proved that such systems had great scientific merit, but, even more importantly, they could produce information valuable to marine transportation, fishing, and resource exploration and extraction. This latter subject includes the off-shore search and production of petroleum and natural gas resources and ocean mining as well. A few early satellites, such as GEOS-3, Nimbus-7, and most notably Seasat established that global wind fields, all weather sea surface temperature, ocean topography and sea state, and fine scale images of wave patterns, surfactants,

Jan 1, 1986

By C. W. Devey, K. S. Lackschewitz

The mineralogy and geochemistry of hydrothermally altered wall rocks from different modern basaltic- and felsic-hosted hydrothermal fields at seafloor spreading centers and convergent margins have been studied to determine the characteristics of different types of alteration and to calculate the magnitudes of elemental exchanges between seawater and wall rock.

Aug 24, 2006

By Kokichi Iizasa

Kuroko-type deposits exist in Japanese EEZ. Some of them are present in the Izu-Ogasawara oceanic island arc south of Tokyo. Major two Kuroko-type deposits occur in the area. One is the Sunrise hydrothermal field occurring on the caldera floor of Myojin knoll, which is likely to be the developed stage in sulfide mineralization. Another is present in the crater of Suiyo seamount that is the early stage of sulfide mineralization. The two deposits are here presented on the growth history based on samples recovered by Benthic Multicoring System (BMS).

Jan 1, 2002

By Stanley R. Riggs

Phosphate deposits on the southeastern U.S. coastal plain have long been the major force in world phosphate markets. World markets continue to grow, but the role of U.S. resources is rapidly declining. This situation results from a complex interaction of economic, political, and environmental factors. Causes for this ongoing erosion of the U. S. market include 1) escalating costs, 2) changes in land-use patterns, 3) environmental pressures oh conventional mining techniques; 4) exhaustion of shallow, high-grade resources in Florida, and 5) increased, low-cost production in other countries throughout the world. In fact, some agencies and commodity personnel predict that the U.S. will become a net phosphate importer early in the next century. If this projection is correct, the U.S. industry must look towards major changes in the near future in order to continue to compete in the world market. One possible change includes development and application of unconventional mining techniques to cheaply recover vast 'new' potential resources in areas with lower land-use pressures. These 'new' resources include 1) deep phosphorites within major sediment basins of the southeastern coastal plain and 2) subsurface phosphorites on the continental shelf and within the U.S. EEZ. These latter resources include extensive deposits in Onslow Bay, N.C.; broad regions offshore of Savannah, Ga. and Cape Canaveral, Fla.; and the central portion of the west Florida shelf. Little research and exploration has been

Jan 1, 1988

By Satya Nandan

• A review of the structure and mandate of the Authority – its main functions. • The different types of mineral resources found in the deep seabed – their global distribution. • The Development of Regulations for Prospecting and Exploration of Polymetallic Nodules, Cobalt-Rich Crusts and Polymetallic Sulphides including environmental regulations and guidelines. • Early constraints for deep seabed mining – Improving conditions for mining – Future prospects for mining.

By Jonguk Kim

Hydrothermal exploration aboard the R/V Onnuri was performed along the northern Central Indian Ridge (CIR) between 8°S and 12°S in January 2010. The main objectives of this first Korean research cruise on mid ocean ridge system was 1) to understand the nature of spreading segments of the northern CIR area, where no systematic survey have been operated before, by mapping and sampling of volcanic rocks and 2) to discover new hydrothermal venting along the spreading center of northern CIR. During the first leg (IR09 Leg1) bathymetric data, in ~50 km width, were collected by multibeam echo sounding system (EM120), which reveals the exact location and structure of axial rift valley of northern CIR between ~ 8°S and 17°S. Then, rock sampling and CTD casts and tows were performed in northern half of the multibeam survey area in the second leg (IR09 Leg2). The results of bathymetric survey clearly display ocean core complex between 10°S and 11°S. The ocean core complex is featured by topographic-high area with corrugated surface. Lineament of corrugations of the ocean core complex are clearly perpendicular to abyssal hill direction which are triggered by symmetric-normal faults. Symmetrical and asymmetrical segments are characterized by parallel abyssal hills and ocean core complex and/or subparallel abyssal hills, respectively. Geochemical analyses of basaltic glasses from spreading axis show geographic trend of increasing of incompatible elements north to south along the spreading axis, which might be influenced by Reunion hotspot plume. However, local but clear enrichment of incompatible elements is observed in volcanic lava from segment 2, which suggests possible local mantle heterogeneity of uncertain source. Lots of serpentinite and gabbroic rocks with coarse-grained feldspar was recovered in the ocean core complex. Ultramafic and/or mafic rocks indicate the gentle-domed block was traveled from upper mantle. Along the spreading axis of the northern CIR, significant hydrothermal plume signatures were detected by CTD castings and tows. Plume signatures were observed at all 5 surveyed segments, suggesting vigorous hydrothermal activities along the northern CIR. However, the optical signals (light transparency and backscattering) of the nearly every cast along the axial valley of the CIR showed increased background level, which might be due to higher level of suspended particles within the axial valley not only by widespread hydrothermal plumes but also by other processes like resuspension. Onboard dissolved methane analysis indicates that the greater part of the plume signals are originated from hydrothermal venting, not by resuspension. However, more detailed examination, including analyzing additional hydrothermal tracers, need to distinguish actual hydrothermal plume signature.

Jan 1, 2010

The seafloor occurrences of KODOS ferromanganese nodules can be classified into four facies based on the morphological types of nodules recovered and seafloor photographs. Facies A, B, and C are relatively unimodal whereas Facies D is bimodal in the size distribution of nodules. Both Facies A and B are highly covered by sediments, but Facies B is higher than facies A in nodule density. Facies C has a high density of small nodules and many traces of bioactivity. Facies D is irregular in nodule density, but occurs close to basement near scarps (Fig. 1). The transparent layer (TL) on subbottom profile records (von Stackelberg et al., 1987) is composed of three sedimentary units, which in cores are distinguished by color. The uppermost Unit I is postulated to be deposited during the past 0.21 Ma and the middle Unit II between 0.42 Ma and 0.21 Ma (MOMAF, 1997). There exists a hiatus between Unit II and Unit III. Unit III was deposited from 3.5 Ma to 1.5 Ma as determined by 10Be/9Be and/or 87Sr/86Sr dating (MOMAF, 2004). Internal textures observed on cut sections of nodules suggest four stages of nodule formation (Choi et al., 2000). The nuclei are either unbroken old nodules probably of hydrogenetic growth (1h and 2h) in Facies A and C, or nodule fragments probably of early diagenetic growth (2d) in Facies D, whereas there are both types in Facies B. The layers surrounding the hydrogenetic nodule nuclei are of hydrogenetic growth (3h and/or 4h) in Facies C, and are of early diagenetic growth (3d and/or 4d) in Facies A, B, and D. The layers surrounding the early diagenetic nodule fragments are mostly of early diagenetic growth (3d and 4d) in Facies A, B, and D. But hydrogenetic encrustations are also found as surface layers on the top in Facies B (Fig. 2).

Jan 1, 2005

By David A. Clague, James R. Hein, Robert W. Embley, Robert C. Vrijenhoek, Randolph A. Koski

We report preliminary results for a group of unique samples collected with MBARI’s ROV Tiburon on August 12, 2005. The samples were collected from the East Blanco Depression (EBD) diffuse-flow hydrothermal field, which was determined in a previous study to cover an area of at least 100 m by 80 m (Hein et al., 1999). The survey reported on here extends that field to more than 1500 m in an approximately N-S direction. The EBD, a pull-apart basin, occurs near the western end of the Blanco Fracture Zone (BFZ), which connects the Juan de Fuca and Gorda Ridge spreading centers (Fig. 1). The samples were collected from a waterdepth range of 3343-3380 m.

Aug 24, 2006

By U. Schwarz-Schampera, P. Stoffers

The main characteristics of the 2545 km Tonga-Kermadec subduction system are the subduction of the Pacific Plate and its sedimentary cover in the Tonga-Kermadec trench and the extension and rifting of the lithosphere behind the active island arc in the Lau basin - Havre Trough back-arc systems. The subduction of the Louisville Seamount chain at 25.6°S affects the tectonic and volcanic system and separates the island arc into the Tonga arc and the Kermadec arc, respectively. To the west, a Miocene island arc is represented by the Lau-Colville ridge. The crustal extension between the Lau-Colville and the Tonga-Kermadec ridge started at about 6 Ma, and induced their separation and the onset of the southward rifting since about 5 Ma. Characteristics of the Tonga-Kermadec arc system include (i) the fourthfold decrease of the subduction rate from 24 cm/a in northern Tonga to 6 cm/a in the southern Kermadec trench, mainly north of 23.5°S; (ii) the development from fast spreading in the Lau basin (16 cm/a) to slow rifting (2 cm/a) in the southern Havre Trough with the transition from spreading to rifting at 23.5°S; (iii) variations in the composition and the volume of the subducting sediments and rocks (detritus from the Samoan hotspot at the northern Tonga arc; the aseismic Louisville ridge at the southern Tonga arc; increasing terrigenous sediments from New Zealand at the southern Kermadec arc); (iv) a number of active volcanic centers younger than 1 Ma and characterized by significant shallow submarine hydrothermal systems.

Aug 24, 2006

By Sven Petersen, Iain J. Stobbs, Bramley J. Murton, Paul A. J. Lusty

"INTRODUCTIONIt is widely thought that seafloor massive sulphide (SMS) deposits, the modern analogue of volcanogenic massive sulphide (VMS) deposits, present a potential global resource for base (Cu, Zn) and precious metals (Au, Ag). In addition, SMS deposits can be enriched in ‘critical metals’ including Se, Te, Tl [1], which are essential for use in the construction of modern and green technologies. Globally over 340 high temperature hydrothermal sites have been identified at a range of ocean spreading centres [2], significant massive sulphide deposit formation has been recorded at 165 of these sites [3].To date only 13 deep sea sulphide deposits have undergone intrusive investigation (drilling or coring) and of these, only 6 sites have published tonnage estimates [2]. Almost all research and drilling of SMS deposits has been focused on active systems, the investigation of the morphology, subsurface structure and mineralogy of hydrothermally extinct seafloor massive sulphide (eSMS) deposits is almost non-existent.As such, little is known about the mechanisms that operate post-SMS formation and which have an impact on the preservation and hence resource value of SMS. Identifying these generic processes and mechanisms, and the extent to which they impact the resource grade, is critical in evaluating the global potential of SMS."

Jan 1, 2017

By Cees van Rhee, Rudy Helmons

INTRODUCTION Seafloor Massive Sulphides are typically found near the oceanic ridges at larger water depths (>1km). The physical properties of SMS, as shown in table 1, are comparable to the properties of weak rock. One of the technical challenges to enable extraction from these locations is the cutting or excavation process. Experiments have shown that the energy needed to excavate the material may increase with water depth (Alvarez Grima et al. 2015). Besides that, it is demonstrated that rock that fails brittle in atmospheric conditions can fail more or less in a plastic fashion when present in a high pressure environment, as would be the case at large water depths. The goal of this research is to identify the physics of the cutting process and to develop this into a model in which the effect of hydrostatic and pore pressures is included. The cutting of rock is initiated by pressing a tool into the rock. As a result, at the tip of the tool a high compressive pressure occurs, which leads to the formation of a crushed zone. Depending on the shape of the tool and the cutting depth, shear failures might emanate from the crushed zone, which will eventually expand as tensile fractures that can reach to the free rock surface. Through this process intact rock will be disintegrated to a granular medium. For an overview of the process (figure 1). Additionally, the presence of water in the pores of and surrounding the rock influences the cutting process through drainage effects. The most relevant effects are weakening when compaction and strengthening when dilation occurs in shearing and tension. Deformation of the rock causes the pore volume to change, resulting in a under or over pressure. As a result, the pore fluid needs to flow. The magnitude of the potential under pressure is limited through cavitation of the pore fluid, limiting further reduction of the pore pressure (figure 2). The drainage effects cause the rock cutting process in a submerged environment to show a stronger dependency of both the hydrostatic pressure as well as the deformation rate (figure 3).

Jan 1, 2018

By Peter E. Halbach, Andreas Jahn

"Co-rich ferromanganese crust deposits exist on slopes, summits and platforms of seamounts and guyots throughout the global oceans, where deep-sea currents have kept the seafloor structures more or less free of sediment for millions of years. They form by direct precipitation from cold seawater under more or less oxic conditions and consist of thin layers (2 up to 25 cm thick) covering hard substrate rocks in water depths of 800 to 5000m (Halbach and Marbler, 2009; Hein et al., 2000). Besides Mn these crusts contain interesting concentrations of minor elements (Co, Ni, Ti and Cu) and trace elements (Mo, W, Te, Ga, Pt and REEs), thus they represent significant metal deposits and promise potentially valuable additions to the world’s metal resources.The prospects for mining of this marine type of metal deposits largely depend on the grades and the scale of the potential ore resources. However, only a few percent of existing seamounts and guyots have been mapped and sampled in detail, most of them in the Pacific Ocean. Therefore, a model to estimate the geological resources based on the global seamount catalogue of Wessel (2001; revised: Wessel et al., 2009) and the empirical parameters which control the metal composition and distribution was developed."

Jan 1, 2017

By Andrew E. Grosz

The Atlantic Continental Shelf (ACS) of the United States includes about 391,000 km2 extending from the shoreline to the 200-m isobath. It varies in width from a fraction of a kilometer (offshore of southern Florida) to about 150 km (offshore of Cape Cod, MA). The contained volume, of sand and gravel is estimated to be on the order of 3-7 x 1.011 m3. Concentrations of potentially commercially important heavy minerals (HM) exist locally, particularly in high-energy depositional environments (for example in channels, tidal deltas, ridge and swale areas, and submerged former shoreline complexes). Recently completed and ongoing studies of HM assemblages in vibracore samples from the south shore of Long Island Sound, NY, offshore of Ocean City, NJ, offshore of Cape May, NJ, offshore of the mouth of Chesapeake Bay, VA, offshore of Myrtle Beach, SC (grab samples), and the ACS offshore of Florida provide the information base for this presentation (Table 1). The surficial sediments of the ACS contain local concentrations of HM that compare favorably to those in currently mined onshore deposits as shown

Jan 1, 1988

By J. W. Jamieson

"The future of the marine mining industry is tied to the resource potential of the seafloor. Everything from economic feasibility, policy decisions and environmental impact assessments to extraction techniques and mining tool design rely on an understanding of the size, composition, and distribution of the deposits. Development and regulatory decisions must ultimately be tied to not only the grade and tonnage estimates of individual deposits or groups of deposits, but also an understanding of the uncertainty of these estimates. Here, we will discuss how seafloor massive sulfide (SMS) deposit grades and tonnages are evaluated, and the sources of the uncertainties associated with these values.TONNAGE UNCERTAINTYFirst-order tonnage (size) estimates for SMS deposits are primarily determined from calculating the volumes of material that occurs as positive bathymetric features on the seafloor. The extent of sulfide mineralization on the seafloor can be determined either from visual surveys (camera-tow, remotely-operated vehicle (ROV), or human-occupied submersible surveys) or from volume calculations of bathymetric features identified from digital elevation models of the seafloor, or a combination of both methods. For bathymetric models to be used to identify deposits in the absence of visual groundtruthing, data resolution of 1 m or less is generally required to confidently identify a feature as being hydrothermal in origin (as opposed to a volcanic or tectonic feature), and therefore near-bottom multibeam data acquisition (e.g., using autonomous underwater vehicle (AUVs) or remotely operated vehicles (ROVs) is required (Fig. 1). Specific characteristics of bathymetric features, such as shape, slope angles and surface roughness can be used to identify features of hydrothermal origin (Fig. 1). However, so far, bathymetric features mapped at a resolution of ~1 m cannot be relied upon to unambiguously distinguish a sulfide mound, and the additional use of multiple AUVmounted sensors, such as magnetometers, which can be used to detect hydrothermal upflow zones, or self-potential sensors, which detect electrical fields related to the oxidation of sulfide minerals, can increase the confidence that a bathymetric feature is indeed a sulfide body, without the need for expensive and time-consuming visual surveys (c.f. Petersen et al., this volume)."

Jan 1, 2017

By Randolph A. Koski

Since 1985, numerous constructional sulfide-sulfate deposits in the form of mounds, pinnacles, chimneys, and sheets have been located between 40°45' and 41°05'N latitude in Escanaba Trough, the sediment-covered axial valley of the Southern Gorda Ridge. Single-channel seismic data indicate that three volcanic edifices up to 6 km in width penetrate as much as 500 m of turbidites that fill the valley; pillow and sheet flow lavas are exposed on the sea floor where these volcanoes breach the sediment surface. Observations from deeply towed camera systems and submersibles show that the largest hydrothermal deposits occur along the step-faulted northern flank of the central volcanic edifice and on the peripheries of steep-sided, sediment-capped hills, approximately 1 km wide and 100 m high, that rise above the valley floor. The sulfide deposits are highly oxidized, eroded, and partly buried by unconsolidated sediment; aprons of sulfide talus extend downslope from the mounds. Two types of sulfide have been sampled by dredging and submersible. The predominant mound and chimney material is pyrrhotite-rich massive sulfide with low amounts of Zn, Pb, Cd, and Ag. Coarse-grained zones with high porosity mark the location of myriad fluid channelways. Thin crusts of barite associated with pyrrhotite-rich sulfide have Au contents up to 2 ppm. Zoned fragments of polymetallic (Fe-Zn-Pb-Cu-As-Ag-Sb) sulfide dredged from a single site near 41°01'N latitude are part of a chimneylike vent structure with a

Jan 1, 1988

By Janine Lahr, Peter E. Halbach

The Manus Spreading Ridge is located within the EEZ of Papua New Guinea and lies in the Manus Basin ENE of the PNG Island and N of the Island New Britain. The divergent backarc spreading system is caused by the subduction of the Solomon plate in the South under the Bismarck plate in the North along the lineament of the New Britain trench. The rate of divergence is relatively high compared to other back arc spreading systems and amounts up to 12 cm/year [3]. Since submarine volcanism and associated hydrothermal circulation as important parts of the oceanic heat transfer system are also dependent on the rate of spreading, hydrothermal fluid venting and respective deposition of polymetallic sulfides can be expected there. In late 1985 first indications for hydrothermal activity were observed on a swell within the central rift valley of the Manus Spreading Centre during a photographic survey of the seafloor by an expedition of the Hawaii Institute of Geophysics with the American RV Moana Wave [1]. Detailed geological investigations including successful sampling were first carried out in June 1990 within the scope of the OLGA II research project (conducted by Prof. Tufar, Marburg) using the German RV Sonne equipped with a deep-sea television sledge and Tvcontrolled grab systems. Simultaneously a research cruise with the Russian RV Akademic Mstivlav Keldysh took place using the manned submersible Mir; the findings of the OLGA II cruise were immediately used for planning and organization of the Mir dives [3]. The massive sulphide samples which we used for our geochemical and mineralogical studies originate from the hydrothermal fields 1 and 2 and are from grab stations of the OLGA II expedition [4].

Sep 24, 2006

By S. Kim Juniper

Ocean observatory technologies permit uninterrupted, real-time observation of dynamic seafloor environments such as gas hydrate deposits and hydrothermal vent fields that are of both scientific and economic interest. Such observations enable new discoveries of linkages between physical, chemical and biological processes and could permit continuous monitoring of environmental variables during mining operations. Ocean Networks Canada operates the NEPTUNE and VENUS cabled observatories in the Northeast Pacific Ocean. The offshore NEPTUNE observatory supports instruments at two gas hydrate sites on the continental margin off Vancouver Island, and in the hydrothermal vent fields of the Endeavour segment of the Juan de Fuca Ridge. The primary focus of the gas hydrate field observations is to understand the dynamics of the growth and stability of outcropping and sub-seafloor hydrate deposits. Outcropping hydrates at 840 m depth in Barkley Canyon have been monitored for the past 3 years with a mobile instrument platform known as Wally, which is operated over the Internet by a research group in Germany. This tracked vehicle carries standard oceanographic sensors, acoustic current metres, cameras and methane sensors. Data indicate a relationship between degassing of hydrates and tidal currents. In 2012-2013 two high-resolution sonar towers were added to the hydrate field to provide precision tracking of Wally and to monitor volume changes in the outcropping hydrate mounds. A large subsurface hydrate deposit occurs at the Clayoquot Slope site, where bottom depth is 1260 metres. Monitoring instrumentation is currently being established at this location. Gas bubble release from this deposit is being monitored by a sector scanning sonar mounted on a

Sep 14, 2011