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By J. M. (Mac) Beggs

With New Zealand?s ratification of the United Nations Convention on the Law of the Sea in 1996, the government of the day increased work on developing an oceans strategy to help create a governance framework for the country?s extensive existing and potential maritime territories. This project took a new direction in 2001 with the establishment of an ad hoc committee of 6 Ministers, and their appointment of a Ministerial Advisory Committee (on which the senior author served) to consult with the public, identify widely held values and inform the development of a Vision for subsequent policy development. The current second stage of the policy development process involves a working group of officials from the relevant agencies completing a stock-take of existing laws and regulations to identify overlaps and gaps that should be addressed in the third and final stage. The public consultation process revealed, as might be expected, a wide range of perspectives but a solid consensus in favour of a coherent, and balanced, framework to enable the realization of economic benefits of ocean development so long as appropriate environmental standards (broadly expressed in terms of sustainability) are not compromised.

Jan 1, 2002

By Yannick C. Beaudoin

Southern Explorer Ridge (SER) is an anomalously shallow, intermediate-rate spreading ridge located 200 kilometers off the west coast of Vancouver Island, Canada. It ranges in depth between 2600 m (deepest basins) and 1760 m (bathymetric minimum). At least 60 sulfide deposits are known to be associated with hydrothermal vent fields along the ridge. For the first time geological data, including deposit locations, collected from 15 marine expeditions to SER since 1983 have been assembled in a GIS format. GIS processing techniques were employed to plot the distribution of base metal concentrations for recovered sulfide samples. The highest base metal concentrations are found in the vicinity of the Magic Mountain site (main active vent field), and also proximal to a side scan sonar anomaly referred to as AGOR 171. Individual samples near these locations have yielded values as high as 29.3 wt\% Cu, 34.3 wt\% zinc, 0.97 wt\% Pb, 2.0 ppm gold, and 664 ppm silver. Sample paucity is the key limiting factor that prevents adequate assessment of the areas economic potential.

Jan 1, 2001

By Ye Jun

Until now, more than 200 sites of sea-floor hydrothermal activities are known on the midocean ridge but few of them are documented on South Mid-Atlantic Ridge (SMAR). This on some extent restricts our directly understanding of the hydrothermal mechanism on SMAR. In 2011, During the Cruise 22 of R/V Dayangyihao, a masive sulfide field was discovered in the center part of the first-order ridge segment that bounded between Cardno Fracture Zone and Saint Helena Fracture Zone, near 15.16°S/13.35°W, which give us an opportunity to recognize the mechanism of hydrothermal systems on SMAR directly. This newly discovered hydrothermal field, which informally called SMAR 15°S, is situated in a SE-NW offset depression of an axial neovolcanic ridge, with water depth of about 2793m. In the water column around this field, strong turbidity and temperature anomalies were detected. Ten meters high venting chimneys, hydrothermal mounds as well as a large amount of hydrothermal vent shrimps were also observed and recorded by ROV and Deep tow camera on the ocean floor. The samples we collected from this field include sulfide chimney fragments, massive sulfides and basaltic rocks. In this study, we are focusing on the mineralogy and sulfur isotope geochemistry of sulfide samples for preliminarily uncovering the geological characteristics and hydrothermal processes of this hydrothermal field.

Sep 14, 2011

By William D. Siapno

The International Marine Minerals Society has now come of age! Previously known as the International Marine Mining Society, it was an informal group without officers, by-laws or official status. Despite the lack of formal structure, the Society has cosponsored symposia both in Europe and in North America including the 16th Annual Underwater Mining Institute in Halifax, Nova Scotia, last year. The roster of members is now sufficient to emerge as a fledgling professional society. To this end an ad hoc committee was appointed to prepare by-laws stating the objectives of the Society, provide the procedures for the election of officers and other guidelines essential for the operation of the organization. This paper briefly summarizes the history of the group, the by-laws, together with membership requirements.

Jan 1, 1986

By V. Soloviev

The world?s data available on near sea-bottom gas-hydrate accumulation and deep-water fluid-discharge areas are presented in this paper. Gas-hydrate accumulation associated with fluid discharge (mud volcanoes, gas seeps, gas-saturated water seeps) is characterized by the following. First, the largest hydrate accumulations in sediments are located at shallow subbottom depths and have well-defined limits, especially in the upper subbottom part. Second, gas-hydrate formation in fluid-discharge areas is a present-day process, with the global occurrence of deep-water fluid-discharge areas numbering up to about ten thousand, and with all the seep areas being favorable for the formation of near-sea-bottom gas-hydrate accumulation. Third and principal, gas resources in the hydrates can be considered as renewable. Estimates of possible gas volume in single accumulations of hydrates and the global budget, as well as possible methods of gas utilization from such gas-hydrate accumulations are discussed in the paper.

Jan 1, 2005

By In Kwon Um

The XRF Core-Scanner system performs non-destructive analysis of elements from Mg to U, in concentrations of ppm levels on split cores with digital images. Using the AVAATECH XRF Corescanner system, we conducted high resolution element analysis of deep sea sediment cores from Clarion-Clipperton fracture zone of the northeastern Pacific to reveal recent environmental changes. Comparison of data estimated by the XRF core scanner with ICP-AES showed relatively weak correlation coefficients except Mn contents. Down-core variations of most elements seem to be matched with each other and reflect changes of sediment colors. Especially Mn/Al ratio significantly change at distinct color boundaries. The variations of Mn/Al ratio with sediment colors are suggestive of changes in redox condition and further divided into two types probably affected by activities of benthic organisms. Be isotope age datings of select core (BC08-02-13) indicate that the color boundaries are approximately coincident with late Pliocene and Pleostocene also early Pliocene and late Pliocene boundary. Keywords: XRF core scanner, High resolution, C-C zone

Jan 1, 2011

By D. S. Limpenny

Marine benthic habitats are vulnerable to the influence of a wide range of anthropogenic activities (e.g. sand and gravel extraction, dredged material disposal and trawling). Traditionally, benthic ecologists have relied on point sampling techniques such as grabs, corers and dredges to provide information on the physical nature of the substrates and their associated benthic fauna. However, information of this nature only relates to the specific point on the seabed from which the sample was collected and the interpolation of such data to predict the wider distribution of substrata and associated fauna may be unreliable. Our approach uses a range of acoustic, photographic and physical sampling methodologies to produce continuous acoustic coverage maps which can be used to assist with the interpretation of faunal distributions. This approach has been used to assess the impacts of marine sand and gravel extraction at the seabed at two sites off the east coast of England in the southern North Sea. The first study site (designated ?Area 222?) is located 20km off the southeast coast of England and was surveyed in 2001 using sidescan sonar, single beam bathymetry, seabed photography and also a 0.1m2 Hamon grab for the collection of benthos and sediment samples. The main objectives of this investigation were to provide an indication of the spatial distribution of the sediments and macrofauna in the wider area encompassing the dredged site, to evaluate the scope for the effects of marine sand and gravel extraction to extend beyond the boundaries of the site and to provide a wider geographical context for time series investigations. At this site, an acoustic basemap was utilised in conjunction with faunal sampling and photographic groundtruthing, to determine the nature and distribution of the seabed sediments and their associated features. Disturbances at the seabed arising from historic sand and gravel extraction activities were mapped, and this information was helpful in establishing biological cause and effect relationships. The acoustic basemap was also used to target biological reference sites against which the effects of adjacent man-made disturbances could be evaluated.

Jan 1, 2004

By Peter A. Rona

Hydrothermal mineralization along slow-spreading oceanic ridges and rift -zones that comprise more than half the global length of the seafloor spreading center system is related to anomalous physical and chemical conditions acting within the geologic settings that characterize early and advanced stages of opening of an ocean basin. Mineralization in the early stage of opening is represented by the Atlantis II Deep of the Red Sea. There, hypersaline hydrothermal solutions discharging as density stratified brines into an axial basin, have formed the largest massive sulfide deposit (70 x 106 metric tons) known at a spreading center. Mineralization at the advanced stage of opening is represented by two types of sites: (1) oceanic crust on the wall of a rift valley; and (2) oceanic crust exposed on the wall of a transform fault zone. The first type of site is the TAG Hydrothermal Field, located on a wall of the rift valley of the Mid-Atlantic Ridge at the top of the basaltic layer of oceanic crust. Evidence is presented for multi-stage, high- and low-temperature hydrothermal activity that produces Cu, Fe, and Zn enrichments within the thin sediment column and stratiform interlayered deposits of manganese oxides, iron oxides, hydroxides and silicates, on the seafloor. The second type of site occurs along walls of transform fault zones of the equatorial Mid-Atlantic Ridge and Carlsberg Ridge, which exhibit stockwork-type Cu-Fe sulfide mineralization

Jan 1, 1985

By Timothy F. McConachy

Magmatic-hydrothermal activity in the South-West Pacific and SE Asian island arcs during the Tertiary has created a premier copper-gold province with numerous, commercially attractive base and precious metal deposits. This activity continues to the present day, especially in submarine sectors of those arcs where modern technologies enable direct observation of ore-forming processes in action. Until recently, however, the volcanic island arcs of Indonesia escaped such attention. The Indonesia-Australia Survey for Submarine Hydrothermal Activity (IASSHA), involved three cruises with KR Baruna Jaya VIII, focused particularly on the Sangihe arc; Tomini Bay, Sulawesi, including the vicinity of isolated Colo volcano; and the Sunda Strait including the neighborhood of Krakatau volcano. IASSHA 2001 and 2003 cruises studied the arc and behind-arc sectors of the Sangihe volcanic island chain extending northwards from Quaternary volcanoes on the northeastern tip of Sulawesi, near Manado, to the Kawio Islands near the border with the Philippines (Fig. 1). This chain lies above a west-dipping Wadati-Benioff seismic zone whose subduction trench is obscured by accreted sediments and mélange, forming the Talaud-Mayu ridge. West of the main active chain and extending northwards from Manado there is a subparallel ridge (The Manado Line) surmounted by a number of high (>2000 m) seamounts of uncertain age.

Jan 1, 2005

By M. Ravindran

The Government of India started its deep seabed exploration programme during 1982. This programme was started as one of national importance and several national laboratories were involved to realize the development of requisite technologies for deepsea mining and processing. After a concentrated effort on surveying, using its own as well as hired ships, India succeeded by mid 1980s in identifying a prospective site in the Indian Ocean as an exclusive claim for development. India was registered as a Pioneer Investor and became the first country to obtain this status on 17th August 1987. India has been allocated an exclusive mine site of 150,000 km2 in the Central Indian Ocean. Our country also developed considerable expertise in the metallurgical processing for extracting metals from these nodules. The Department of Ocean Development, Government of India, the organization which is designated as the nodal agency responsible for implementing the deep seabed mining programme has drawn up a long term plan which will enable it to fulfill its obligations as a Pioneer Investor. The work toward the design and development of a mining system has been entrusted to the Central Mechanical and Engineering Research Institute, Durgapur. As a part of this programme they have developed a nodule collector and a riser system which have been tested in very shallow waters only. Since this technology development for deep sea mining applications is highly time consuming and very expensive, this programme is also being used to develop components for intermediate applications. In view of the long timeframe required for perfecting a deepsea nodule mining technology, the Government of India is also keen on developing shallow water mining systems for utilizing the placer deposits. One of the richest heavy mineral deposits in the Indian Exclusive Economic Zone is available on the west coast of South India in the state of Kerala. The coastal stretch between Kanyakumari, on the southern tip of India, and Alleppey along the west coast at a distance from the tip of approximately 210 km, there is a good multimineral reserve. The initial survey indicates that the estimated reserves in the surveyed areas are approximately as follows: Ilmenite 1.4 million tonnes Rutile 0.14 million tomes Zircon 0.13 million tomes Sillimanite 0.53 million tonnes

Jan 1, 1994

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

By Natalia Konstantinova, Kira Mizell, James R. Hein, Georgy Cherkashov, Amy Gartman, Mariah Mikesell

"Two types of metallic deposits have been found in the deep Arctic Ocean: Hydrothermal Fe, Cu, and Zn sulfide deposits form along Gakkel Ridge in the Eurasia Basin and associated ridges between Greenland and Europe; and iron and manganese oxide crusts (Fe-Mn crusts) and nodules, precipitated from seawater onto rock surfaces in the Amerasia Basin, contain many rare metals of economic interest. Fe-Mn crusts and nodules collected in the Amerasia Basin during 2008, 2009, and 2012 cruises on the USCGC icebreaker Healy are characterized by unique mineral and chemical compositions, very high Fe/Mn ratios, fast growth rates, and other unique characteristics compared to those formed elsewhere in the global ocean. These characteristics reflect temporal and spatial variations in geological, oceanographic, and climatic conditions in the Arctic Ocean and surrounding continents over the past ~15 Myr.RESULTS AND CONCLUSIONSDiscrimination diagrams show that the crusts and nodules found in the Amerasia Basin north of Alaska are hydrogenetic. However, the mineralogy is not typical for hydrogenetic Fe-Mn crusts and nodules, which usually include only amorphous Fe oxyhydroxide and ?-MnO2 (vernadite). The Arctic samples also include the Mn oxides birnessite and 10Å manganates (todorokite, buserite, asbolane), and the Fe minerals also include goethite, lepidocrocite, feroxyhyte, and ferrihydrite. This mineralogy reflects formation under lower oxygen conditions than typical for samples formed elsewhere.The Amerasia Basin crusts have a unique chemical composition compared with crusts from other areas of the global ocean. The key difference is the high Fe contents relative to Mn contents, which determines the types of trace metals hosted by the Fe-Mn oxide phases, and their concentrations. The high Fe/Mn ratios reflect the expansive continental shelves (>50% of the Arctic Ocean) and upper slopes that support redox cycling and release of Fe and other metals to bottom waters, and to the large fluvial input from North America and Siberia. Brine formation on the shelves and currents promote the distribution of the metals throughout the Amerasia Basin, including the deep basins."

Jan 1, 2017

By William J. Scott

In the last two years, C-CORE has developed a new seabed sampler directed specifically at obtaining samples from hard or compacted bottoms such as are typical of marine placer deposits. Samples are required for appraisal of concentrations of saleable commodities, and for determination of levels of biological indicators in the deposits. Recently C-CORE and the University of Victoria have been comparing the performance of the Scott/C-CORE sampler with that of the Van Veen sampler often used for biological sampling. Initial trials of the Scott/C-CORE sampler in 1992 at the WestGold mining site, Nome, Alaska, were described by Jewitt et al. at the 1993 UMI. Since that time the sampler has been modified to prevent overfilling, and to limit turbulent flow of water across the top of the sampler buckets when the sampler is recovered with partly-open buckets. The modifications included shoes to prevent sampler overfill, and flexible rubber shielding over top and sides of the sampler to prevent water circulation. Samples have been taken with both samplers in two field areas, one at Pine Cove, Baie Verte, Newfoundland, and the other near Long Pond in Conception Bay on the Avalon Peninsula, Newfoundland. In each area multiple samples were taken with both sampler types, and the samples processed immediately to establish the types and quantities of marine organisms that were present. Species identification is expected to be complete by late August.

Jan 1, 1994

By William J. Scott

In the last two years, C-CORE has developed a new seabed sampler directed specifically at obtaining samples from hard or compacted bottoms such as are typical of marine placer deposits. Samples are required for appraisal of concentrations of saleable commodities, and for determination of levels of biological indicators in the deposits. Recently C-CORE and the University of Victoria have been comparing the performance of the Scott/C-CORE sampler with that of the Van Veen sampler often used for biological sampling. Initial trials of the Scott/C-CORE sampler in 1992 at the WestGold mining site, Nome, Alaska, were described by Jewitt et al. at the 1993 UMI. Since that time the sampler has been modified to prevent overfilling, and to limit turbulent flow of water across the top of the sampler buckets when the sampler is recovered with partly-open buckets. The modifications included shoes to prevent sampler overfill, and flexible rubber shielding over top and sides of the sampler to prevent water circulation. Samples have been taken with both samplers in two field areas, one at Pine Cove, Baie Verte, Newfoundland, and the other near Long Pond in Conception Bay on the Avalon Peninsula, Newfoundland. In each area multiple samples were taken with both sampler types, and the samples processed immediately to establish the types and quantities of marine organisms that were present. Species identification is expected to be complete by late August.

Jan 1, 1994

By Ian J. Graham, Cornel E. J. de Ronde

New Zealand lies astride a convergent plate boundary that extends north-eastwards from the Taupo Volcanic Zone (TVZ) to Tonga. This boundary is marked by the Kermadec arc, c. 1200 km of which falls within New Zealand’s EEZ, and which is host to numerous volcanic edifices both on the arc and in a zone immediately behind the arc to the west. In 1999, thirteen volcanic centres in the southern 260 km of the arc were surveyed for their hydrothermal plumes with seven of them discharging vent fluids into the surrounding ocean. Three of the seven volcanic centres have had mineralised rocks recovered from them during dredging and submersible operations, namely Brothers, Rumble II West and Clark. Presentday plume data combined with mineralogical evidence indicate that the vent sites at Rumble II West and Clark are waning, although the presence of Cu-rich sulphides in samples recovered from Rumble II West suggest there may be a massive sulphide (Cu-Zn-Pb-Ba ± Au) deposit located within the caldera. Brothers volcanic centre is host to the largest polymetallic mineral deposit discovered along the Kermadec arc and has numerous, up to 7 m tall chimneys within a c. 600 x 200 m area located on its NW caldera wall. Geochemical data indicate that concentrations of base metals are variable and depend critically on sample type. When combined with mineralogical and plume data, this indicates addition of a magmatic fluid component to the vent fluids.

Aug 24, 2006

By Art Wright, Steinar L. Ellefmo, Kurt Aasly, Mike Williamson, Fredrik Søreide, Martin Ludvigsen, Michael Zylstra

Exploring for minerals on the seabed is challenging and expensive – and the ability to collect representative sub surface samples is essential. The research project MarMine led by NTNU has together with Seattle based Williamson and Associates developed and tested an ROV-based drill rig for mineral (seafloor massive sulfides and crusts) and rock sampling. The ROCS system is a single stroke drill and is simple, robust and possible to use from various larger ROVs. For the vehicle to provide a stable platform, the vertical bollard pull of the ROV and the vehicle mass are important variables. The developed drill uses a thin wall drill bit and barrel and operates at high RPM to reduce the required down weight and drilling moments. The system also contains an emergency release to be used if the core barrel is stuck. The drill is hydraulically powered with cylinders operating the tower and a rotation unit. It can rapidly be modified to provide samples from softer samples like unconsolidated material. At the Arctic Mid Ocean Ridge, a work class ROV was deployed with the drill mounted for testing at 2700 m depth in basalt rock. The recovery from the system was above 80%. Such core samples can be used for chemical analyses of metal and mineral grades, mineralogy and rock mechanical testing. The system provides a probing tool for marine mineral exploration, with low cost, low operational complexity and low risk. Proper resource estimation requires drilling deeper into the deposit, but the short core samples provided by the ROCS provide valuable a priori information planning for more extensive drilling campaigns.

Jan 1, 2017

By T. Yamazaki, T. Goto, R. Arai, N. Nakatani

The importance of cobalt-rich manganese crusts on the Pacific seamounts for possible future rare metal sources has been recognized these 30 years. The thin layer-type coverage and the micro-topographic undulation of basement affect not only the excavation efficiency but also the economy of mining venture. Because of these distribution characteristics, no economic feasibility has been recognized through the past economic analyses. On the basis of a recent geological study about seamount rocks, a possibility of by-product substrate recovery for phosphorous supply with cobalt-rich manganese crust mining has been highlighted. In the mining model, the substrate rocks are utilized as phosphates for agricultural and chemical usages. Under some preliminary technical and economic assumptions, the possibility of cobalt-rich manganese crust mining venture is examined. The results show a better economy of the venture including the substrate rock usage for phosphorous supply. Introduction Cobalt-rich Manganese Crusts and the Economic Feasibility Cobalt-rich manganese crusts on the Pacific seamounts received attention as potential sources for strategic metals such as Co, Ni, Cu, and Mn, due to their vast distribution and higher cobalt concentration than manganese nodules (Cronan, 1980; Halbach, 1982; Manheim, 1986). In the earlier stage, the geological distribution characteristics were reported (Cronan, 1984; Clark et al., 1984; Misawa et al., 1987; Pichocki and Hoffert, 1987) and a systematic feasibility of the mining was studied (Hawaii DPED, 1987).

Jan 1, 2018

By Robert G. Ditchburn

Dating seafloor mineralization at hydrothermal centres of submarine arc volcanoes is important for understanding deep-seated volcanic events that can produce deposits rich in base and precious metals. The activity ratios, 228Th/228Ra, 228Ra/226Ra (Bq.Bq-1) and 226Ra/Ba values (Bq.g-1) are used for dating barite- rich seafloor massive sulphide (SMS) in the age ranges 0.3 ? 12 years, 3 ? 35 years and 500 ? 15,000 years, respectively. Thus, the time elapsed to amass an economic deposit and, ultimately, its capacity for sustainable extraction, can be estimated. 226Ra/Ba and 228Ra/226Ra values have been measured in relatively young chimneys that were collected, 1998 to 2006, from hydrothermal sites at Brothers and Clark volcanoes (Kermadec arc) and East Diamante volcano (Mariana arc) to check these initial ratios, essential for calculating ages for older mineralization at the same sites, were not varying significantly. We found that the 226Ra/Ba value for fresh SMS mineralization at the Brothers NW caldera and East Diamante hydrothermal sites have been reasonably stable for 6 years and 2 years, respectively. At both sites, the 228Ra/226Ra value for fresh SMS has been stable for 5 years. This was established from young chimneys where the measured 228Ra/226Ra value could be corrected for radioactive decay using the age derived via the 228Th/228Ra method. However, long-term stability of the initial 226Ra/Ba and 228Ra/226Ra values has yet to be proven. These isotopes of Ra are used as a proxy for better understanding of the transfer of Ba from deep magmas to the seafloor, via the circulating fluids of the hydrothermal system.

Jan 1, 2011

By Henk van Muijen, Jan Willem de Wit

1.1 Profile IHC Holland Merwede IHC Holland Merwede is world market leader in the construction of specialist dredging equipment and large-size custom-built offshore vessels. The clients of IHC Holland Merwede include major dredging companies, oil and gas exploration groups, offshore contractors and government authorities. IHC Holland Merwede is focused on the continuous development and innovation of technology to ensure maximum performance and efficiency of its designs and constructions supplied to the dredging and offshore industries. IHC Holland Merwede has a staff of approximately 2,000 at its locations in Hardinxveld- Giessendam, Kinderdijk, Krimpen aan den IJssel, Sliedrecht, Delfgauw, Goes, Hendrik Ido Ambacht and Heusden. Besides worldwide representations, IHC Holland Merwede has branches in China, Houston (USA), India, the Middle East and Singapore. 1.2 Mission IHC Holland Merwede’s mission is to optimize value by anticipating and satisfying its client’s requirements, with efficient advanced technology solutions. The group’s aim is to be consistently at the forefront of technology development, in the business sectors in which it operates.

By Fernando J. A. S. Barriga

Exploration for active seafloor hydrothermal vent fields has been highly successful, and more than 300 such fields have been discovered to date. Some will most probably be mined, given their high metal grades (Cu, Zn, Au and others). However, the current practice detects active systems, and activity rates, not the size of the deposits. This strategy may leave undetected some of the best targets, for several reasons as follows: 1. Large hydrothermal plumes are a measure of dispersion of ore components, not of efficiency in the generation of orebodies; 2. Deposits formed a few hundred years (or more) before present will generally have ceased their activity and will not be detected by plume studies; 3. Deposits formed under a cover rock (up to a few meters of sediments, volcaniclastics, or the like) may exhibit only minor seafloor hydrothermal activity, possibly diffuse flow. Cover rocks will often host hanging wall rock alteration, expressed in geochemical and mineralogical haloes. It has been demonstrated in many instances, especially for deposits formed in the geological past, now exposed on land, that ore genesis under a cover rock is one of the most suitable processes for generating large massive sulfide deposits. One of the great challenges for submarine resource knowledge will be to develop adequate exploration strategies for sizeable orebodies, not necessarily hydrothermal vent fields, sometimes hidden under a cover rock.

Jan 1, 2011