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By Virginie Tilot

Recommendations have been drafted following an international multidisciplinary panel discussion organized at UNESCO/IOC by the Académie des Sciences d?Outre-Mer on 15 December 2010 conveyed, according to its mandate, to the French government and to an international pool of scientists and stakeholders. These take into consideration the relevant Provisions of the United Nations Convention on the Law of the Sea of 10 December 1982, the Rio ?Earth Summit? Convention of Biological Diversity of 5 June 1992 as well as the activities and recommendations implemented for the world?s oceans and seas, in particular by the International Seabed Authority (ISA) and the recent reports and scientific works (including those implemented by the ISA Kaplan, Ifremer, COI-Unesco). The recommendations integrate, for one of the ecosystems, the conclusions of the project of the conclusions of an IOC-UNESCO / Government of Flanders project (2004-2010) implemented by Dr. V. Tilot from 2004 to 2010, during which were published three volumes describing the referential state of the polymetallic nodule ecosystem and proposing options for the management and conservation of the nodule ecosystem in the Clarion Clipperton Fracture Zone, NE Pacific Ocean: http://unesdoc.unesco.org/images/0014/001495/149556f.pdf, http://unesdoc.unesco.org/images/0014/001495/149556e.pdf; http://unesdoc.unesco.org/images/0014/001495/149556e.pdf#223

Jan 1, 2011

By Justin C. I. Baulch, Robina Sharpe, Steven J. Downey, John P. Feenan, Kate M. Perrin

Since becoming a public company in October 2005, Neptune Minerals has continued to advance its primary aims. Major achievements in the last year have been: • Successful completion of two simultaneous New Zealand exploration programs, Kermadec 2007 (K-07) and Colville-Monowai 2007 (CM-07); • New discovery of an inactive SMS field on the Rumble II West seamount; • Focused exploration license applications over quality areas of known SMS mineralization in arc and back-arc settings in Japan, Vanuatu, Papua New Guinea (PNG), Northern Marianas Islands (CNMI), Palau, and Italy; • Granting of licenses covering some 200,326 km2 of arc and back-arc within the EEZ of PNG and the Federated States of Micronesia (FSM); • Targeting of an additional mineralization style with extensive applications in PNG covering Conical Seamount-style Au-rich epithermal mineralization; • Welcoming Newmont Mining, one of the World’s largest mining companies, as a major shareholder; • Commissioning a scoping study to investigate options for mining and processing of SMS; Marine Minerals of the Pacific: Science, Economics and the Environment UMI2007 · The University of Tokyo, Japan Baulch 2 37th Underwater Mining Institute · 15-20 October 2007 • Invitation to contribute to, and participate in, the Meteor M73/2 Tyrrhenian Sea research program. The Company has granted exploration licenses covering 263,000 km2 in New Zealand, FSM and PNG, and a further 362,000 km2 under application in Japan, PNG, Vanuatu, Northern Mariana Islands, Palau and Italy.

By Sup Hong

Herein, concept designs of two different types of mining robots are concerned, which are aimed for developments of deep seabed mineral resources: polymetallic nodules (PMN) and seabed massive sulfides (SMS), respectively. Continuous mining concepts are presented based on technical and environmental feasibility, where the environmental and functional differences for commercial productions are investigated. Needs and roles of versatile mining robots are explained as a key of continuous mining system. The functional requirements and design characteristics of mining robots to satisfy the top requirements from customers are described comparatively. Schemes of axiomatic design and quality function deployment (QFD) are utilized: functional requirements (FR) are defined, technical requirements (TR) are figured out, design parameters (DP) are derived, and degrees of importance of design parameters are evaluated. Analogy and discrepancy in remote operation methods are put side by side. A pilot scale mining robot for PMN and a commercial scale one for SMS are suggested in form of concept designs. PMN mining robot is shaped as a multiple configuration of unit robot modules in side dimension, in which the unit robot module consists of two tracks and two pick-up modules. SMS mining robot is based on a four-tracked vehicle. Main platform is mounted on the vehicle through turn-table. Excavation device consists of two-articulated boom and cutter tool. Crushing-and-pumping units are placed same in both robot platforms.

Jan 1, 2011

By Robert Goodden

It is well known that diamonds are found in Kimberlite pipes within the earth’s crust and are also discovered where erosion has released them to be concentrated by rivers in trap sites within alluvial gravels. Few people are aware however, that diamonds are now being found in significant quantities at sea. And that the rugged marine environment has ensured that the quality of diamonds in the sea is predominantly gem quality. Shortly after intrusion of Kimberlites into the host rocks of the karoo in the Cretaceous period massive erosion occurred when torrential rivers carried diamonds from their Kimberlitic source rocks down the rivers and into the sea. In the sea they have been subject to a transporting and concentrating dynamic, which has deposited them in trap sites along the West Coast of Africa for hundreds of kilometers. In the last 60 million years the sea level along the West Coast has varied in steps from the current sea level to – 300m. With time at each beach level the sea has reconcentrated the diamonds previously carried down. These old beach levels exist at roughly 10 meter intervals. Each previous sea level now provides a target for marine miners. Marine diamond mining was started 46 years ago by the first pioneer, a Texan, Sammy Collins. Collins brought the potential of marine diamonds to the attention of major mining companies. With now outmoded technology Collins had days when he recovered pockets of high grade gems worth several million dollars; an excitement hard to equal in any walk of life. Amongst marine miners there is still a strong pioneering spirit but the industry has matured and now aims to consistently produce over two million carats of gems a year. The potential resource is huge stretching up to 30 kilometers offshore along the West Coast of Africa from South Africa to Angola.

Sep 24, 2006

By H. L. Gibson, U. Schwarz-Schampera, Mark Hannington

Ancient ore deposits provide important clues for the understanding of the origin and distribution of modern submarine hydrothermal systems. An analysis of the formation conditions, tectonic settings, and preservation of ancient seafloor mineral deposits from the recent geological past to the late Archean sheds light on the time-space relationships and diversity of mineral deposit types likely to be found in the modern oceans. Microplate tectonics that characterized ancient ore-hosting greenstone belts were strikingly similar to those active in volcanic arc environments of the western Pacific today. In such complex settings, oblique collisions, opposing subduction zones, and rapid changes in stress regimes (e.g., from compressional to tensional and back to compressional) were common, causing juxtaposition of diverse styles of mineralization. The world-class base metal deposits of the late Archean Abitibi greenstone belt of Canada, for example, were formed within a relatively short time span of ~20 m.y., in response to successive arc rifting, back-arc basin development, and exhumation of accretionary complexes along major arc-parallel crustal-scale faults. Similar processes and environments are important settings for metallogenesis in modern submarine volcanic arcs. Active marginal basins of similar size and representing similar stages of evolution are well represented in the western Pacific today and contain a similar suite of mineral deposit types. Examples from the eastern Manus Basin and adjoining New Ireland Basin (PNG) and in the Lau-Tonga-Kermadec arc-backarc system illustrate these similarities. Certain gold-rich volcanogenic massive sulfide deposits at the southern margin of the Abitibi greenstone belt (e.g., Bousquet and LaRonde deposits in the eastern Blake River Gp.) may be important ancient analogs of newly discovered gold-rich black smoker deposits found along the active fronts of today's submarine volcanic arcs.

Sep 24, 2006

By R. Moss

Gold and silver are important byproducts of mining volcanogenic massive sulfide (VMS) deposits. Both metals occur in VMS deposits ranging in age from the Archean to the currently forming massive sulfides found on the ocean floor. The gold- and silver-rich deposits on the modern seafloor are geographically diverse and occur in several different tectonic settings (Figure 1a,b) including seamounts (e.g. Franklin Seamount, Papua New Guinea), unsedimented mid ocean ridges (e.g. TAG and Snakepit, Mid Atlantic Ridge), sedimented mid ocean ridges (e.g. Escanaba Trough) and back-arc basins (e.g. Manus Basin, Papua New Guinea). Interestingly, the most gold- and silver-rich deposits are found in the back-arc basins of the western Pacific, commonly associated with differentiated volcanic rocks such as the dacite-rhyodacite suite at PACMANUS in the eastern Manus Basin. This suggests that different, or more efficient, mechanisms are concentrating precious metals in such back-arc settings. Such mechanisms may include leaching of volcanics enriched in gold (e.g. rifted arc crust) or silver (e.g. continental crust) and/or the introduction of gold into a hydrothermal system by a magmatic fluid. The gold content of modern seafloor precipitates varies from a few ppb up to a high of 54 ppm reported from eastern Manus Basin (1). The Jade Deposit in the Okinawa Trough has the highest silver contents with values up to 1.1% (2). Both gold and silver are preferentially concentrated in late-stage, low temperature precipitates with zinc-rich assemblages being favoured in most cases. Gold is found as relatively pure native gold and sub-microscopic inclusions in gold-rich deposits, but occurs predominantly as sub-microscopic inclusions and possibly as solid solution in the gold-poor deposits (3). Silver occurs as rare silver minerals such as acanthite and native silver in the silver rich Jade deposit (2), but more commonly in the silver-containing minerals tetrahedrite and tennantite, as is the case in the PACMANUS deposit. Tetrahedrite is also known to be an important host of silver in ancient VMS deposits (4). More abundant sulfides can contribute significantly to the silver balance. In the silver-poor deposits at 21 N East Pacific Rise, silver is contained entirely within chalcopyrite, isocubanite, pyrite, marcasite, sphalerite/wurtzite and galena. In this case silver may be present as sub-microscopic inclusions of silver minerals or in solid solution.

Jan 1, 2011

By Andrea Koschinsky

Recent technological breakthroughs in the fields of ceramics, medicine, aerospace engineering and electronics (semi- and superconductors) are constantly creating new uses and an ongoing increasing demand for a variety of rare valuable trace metals. These so-called high-tech elements such as hafnium (Hf), titanium (Ti,) niobium (Nb), tantalum (Ta), zirconium (Zr), molybdenum (Mo), vanadium (V) and the rare earth elements (REE), many of them of strategic importance, occur inter alia at elevated and potentially economic concentrations in marine ferromanganese nodules and ferromanganese crusts, making those deep sea deposits potential future resources of these metals. As these metals are mostly present in the lattice of the manganese and iron phases, which are strongly intergrown, rather than in separate mineral phases within the nodules and crusts (Koschinsky and Hein, 2003), reductive dissolution of the host phases is a prerequisite to release and dissolve the valuable metals. To evaluate the association of these rare valuable metals with their mineral carrier phases, sequential leaching experiments were carried out on selected samples in a first step in our project.

Jan 1, 2011

By U. Schwarz-Schampera, C. Rühlemann, H. -R. Kudrass

Within 2006 BGR will conclude a contract with the UN International Seabed Authority (ISA) for the exploration of polymetallic nodules. The contract covers an area in the Pacific nodule belt between the Clarion and Clipperton fracture zones, that which is about 75.000 km2 in size at water depths between 4200 and 5000 m (see Fig. 1). Up to now, 7 consortia or state parties have acquired similar exploration “licenses” for polymetallic nodules in the central Pacific Ocean and the Indian Ocean. These licenses of the UN authority are required according to the UN convention on the law of the sea (UNCLOS) as the areas of interest are located outside of national EEZs. The “licenses” then reserve exclusive rights to the applicant for a time span of about 15 years.

Aug 24, 2006

By Irina A. Pulyaeva

Hydrogenetic Fe-Mn crusts are ubiquitous in the ocean basins and play an important role in marine mineral-deposit research because of their widespread occurrence and high concentrations of valuable and rare metals. Directed research, which started in the last quarter of the 20th century, has provided significant results, with substantial amounts of data produced on Fe-Mn crusts structure, composition, and distribution in the global ocean. Detailed study of several seamounts has given confidence about the scale of Fe-Mn crust development and their characteristics. Now, commercial interests gain more and more attention. However, at the same time some theoretical questions related to Fe-Mn crust history including controls on metal sources and concentrations have not yet been answered. Here, we present the overview of age, composition, distribution, and geological setting of hydrogenetic Fe-Mn crusts from Pacific and Atlantic seamounts and discuss the geological evolution and conditions that led to the formation of potentially economic concentrations of metals. The age, composition, and distribution of Fe-Mn crusts in the Atlantic and Pacific oceans were determined by using a Fe-Mn deposits database compiled from our original data, published papers, published databases, and other international sources. Comparative analysis of Fe-Mn deposits from the Atlantic and Pacific oceans shows that there are similarities in basic characteristics of crust formation in both oceans. Simultaneously, there are significant differences in the scale of Fe-Mn crust distribution and composition that can be explained by differences in geological settings and characteristics of the deposition environment.

Jan 1, 2011

The chemical composition of the nodules varies with the type of manganese minerals and the size and characteristics of their nucleus, but those who have an economic interest have the following composition: Mn 29%, Fe 6% Si 5%, Al 3%, Ni 1.4%, Cu 1.3%, Co 0.25%, Na 1.5%, Ca 1.5%, Mg 0.5%, K 0.5%, Ti 0.2 0.2% and Ba 0.2% (Morgan, 2000; ISA, 2002). The Pacific Rim is an area of abundant occurrence of polymetallic nodules (Glasby et al., 1980; Morgan, 2000). According to these authors, the Pacific sea floor of the Clarion-Clipperton Zone (CCZ) is one of the most interesting areas in regard to the genesis of polymetallic nodules. Their abundance in the ocean floor is very variable, as there are places where they cover more than 70% of the ocean floor. The nodules can be found at any depth, but the highest concentrations are between 4000 and 6000m (Morgan et al., 1993). In studies conducted in the EEZ of the Mexican Pacific are those made within the project "Research on the origin, process and distribution of minerals in the Pacific ocean floor in the Exclusive Economic Zone of Mexico". Within this project Rosales (1989) conducted studies on the origin, process and distribution of polymetallic nodules, finding that a number of processes give origin to nodules, being diagenesis one of the main mechanisms of elements that contribute to the nodules. Besides hydrothermal processes that are carried near the East Pacific Rise at 21° N, inputs are contributing to the nodules metallic elements and sediments, especially in regions close to the dorsal, as a greater influence hydrogenetic processes occurs westward (Rosales and Carranza, 1990). In 1993, after cruise MIMAR II, Carranza and Rosales refer that metals such as Cu, Co, Ni, Sn, Fe, Mg, Pb, Zn and Ba may have a relationship with the East Pacific hydrothermal activity and sea currents carry these metals in solution to the Clarion-Clipperton fracture area, where there are hydrogenic metals sources (Al, Fe and Mn).

Jan 1, 2011

By W. H. Pelton

Polymetallic sulphide (PMS) deposits have recently been discovered associated with hydrothermal vents on the sea floor off Vancouver Island, B.C. Visual estimates indicate reserves in excess of 1 million tons. Reliable reserve estimates have not yet been made, however, due to the extreme difficulty of drilling cores in 2 km of water. Few geophysical techniques can aid in the exploration of these deposits. There is little or no difference in radioactivity, magnetic susceptibility or electrical resistivity between the deposits and the surrounding sea floor sediments. This precludes radiometric, magnetic, electromagnetic and resistivity methods. There is a density contrast, but the logistics of gravity surveys at such depths are formidable. The physical property which shows the most contrast with the sea floor sediments, and which is perhaps one of the easiest to measure (with modern equipment) is polarizability. The induced polarization (IP) method is one of the major electrical geophysical techniques for exploring for PMS deposits on land.

Jan 1, 1985

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 Robert M. Owen

Geochemical exploration for marine placers involves the acquisition, processing, and interpretation of geochemical data. Recent technological advances such as in-situ analysis systems and microcomputers have greatly improved our ability to acquire and process data, but their full benefits cannot be realized until we also develop improved methods for reducing and interpreting large amounts of raw geochemical data. Toward this end, our research has sought to identify existing and/or develop new geostatistical techniques for use in marine placer exploration. Each technique has been tested by evaluating its performance in the analysis of existing data sets. The data sets typically include the results of chemical analyses of suites of sediment samples collected from areas of known or suspected platinum and gold placers along the Bering Sea coast of Alaska. Results to date indicate that three geostatistical methods (subpopulation partitioning analysis, comparative factor analysis, and end-member compositional factor analysis) are useful in identifying elemental groups which can serve as "pathfinders" in the search for marine placers, and are also helpful in discerning the generic geochemical basis under lying observed statistical correlations between pathfinder elements and placer minerals. Existing methods of modelling sediment dispersal patterns have been examined with a view toward adapting them to the specific problem of understanding placer formation in

Jan 1, 1986

By J. R. Woolsey

Research grants of The Marine Minerals Technology Center (MMTC) are directed toward development of the technology 'for exploration, mining, and processing of non-fuel mineral resources within the U.S. Exclusive Economic Zone. FY 1989-90 research grants are as follows: - Seafloor Gamma Measurement Data Collection System. - Free-Fall Seafloor Hard Substrate Corer. - Microtopography of Manganese Crust Deposits. - Cobalt Crust Continuum on Seamounts, EEZ, Hawaii. - Economics of Marine Polymetallic Sulfide Resources. - Graphite Furnace Atomic Absorption Spectrometer. - Depositional Models for Aggregate and Heavy Mineral Exploration. - Sand Resources of Heald and Sabine Banks, Texas. - Sources, Geometries, and Compositions of Heavy Mineral Placers. - Geostatistical Methods for Marine Placer Exploration. - Computer Aided Design for Communication and Strength Umbilicals.

Jan 1, 1989

By Kristian Drivenes, Steinar L. Ellefmo, Kurt Aasly, Ben Snook, Przemyslaw B. Kowalczuk, Rolf Arne Kleiv

"Since Ellefmo et al. (2014) published resource estimates of undiscovered seafloor massive sulfides (SMS) on the Arctic Mid-Ocean Ridge (AMOR), there has been an increased focus on establishing new knowledge about exploitation technologies for such deposits. This also includes understanding the process mineralogical properties of typical SMS deposits.The part of the AMOR that lies between Jan Mayen and the Svalbard Islands and is located within Norwegian jurisdiction and, as such, investigating the potential for mineral production from hydrothermal vent fields has been seen as strategic. The AMOR has been explored for active hydrothermal vent fields since early 2000s (Pedersen et al., 2010b). One of the active vent fields discovered, Loki´s Castle, is located in the northern part of Mohn´s Ridge. This vent field was first described by Pedersen et al., (2010a) and consists of two mounds, each approximately 100-150 m diameter and 20-30 meters high, hosting several active chimneys, up to 11 m high.Loki´s Castle has been selected as a case site in order to study the properties of typical SMS occurrences with respect to possible future deep-sea mining activities. As part of the MarMine cruise in 2016, the Loki Castle was visited and sampled for e.g. mineral characterization and mineral processing analyses. In total, more than 500 kg rock samples were collected using ROVs, and intended for further research (Ludvigsen et al., 2016). In addition to sampling mineralized rock fragments, survey data like bathymetry, magnetics and Underwater Hyperspectral Imaging (UHI) was collected using Automated Underwater Vehicle (AUV)."

Jan 1, 2017

By S. Jeffress Williams

The topic area for this paper covers the United States portion of the northern Gulf of Mexico, extending from the Rio Grande delta east to the Florida peninsula. Declaration of an Exclusive Economic Zone in 1983 expanded Federal economic jurisdiction on the continental margins from 12 to 200 nautical miles seaward from the coast. The nation-wide area of the EEZ totals 3 million square nautical miles, with approximately 186 thousand square nautical miles in the Gulf of Mexico. In the Gulf, the continental shelf has an area of 81 thousand square nautical miles, extending to a depth of 600 ft. and having widths of 6 to 120 nautical miles. Specific areas on the shelf offer the greatest potential for containing aggregate and other hard mineral resources. The primary geomorphic features along the Gulf coast include: barrier islands, chenier plains, tidal inlets, bays and lagoons, estuaries, and deltaic headlands. These features are composed of terrigenous siliclastic sediments, except for the west Florida coast, south of 29°N latitude, which is dominated by carbonate sediments. On the shelf, the primary features are linear sand shoals and associated sand sheets, relict delta lobes and channels, and banks related to salt diapirs and coral reefs. The composition and distribution of sediments in these coastal and shelf features are determined by numerous geologic factors including: seabed topography; riverine sediment discharge; sediment dispersal patterns due to currents, waves, storms and tides; tectonics and subsidence; and repeated fluctuations in sea level.

Jan 1, 1986

By M. F. Dibble

The technology available for mining of underwater mineral resources such as placers and phosphorite, typically occurring with variable amounts of overburden, has remained largely unchanged for decades. The traditional bucket ladder dredge with maximum digging depth of 48 m and monthly capacities about 500,000 m3 still reins as the only heavy duty mining system capable of working the tough materials characteristic of heavy metal placers. Attempts at adapting the bucket wheel cutter-suction dredge to these severe conditions have not yet been successful except in moving small volumes from shallow depths. High capital cost (20-30 million U.S. dollars), high cost of overburden removable, and turbidity generation for the bucket ladder are often significant negative factors in mining operations where this system remains the only viable alternative. The Japanese continue to advance the technology of their submersible dredge pump system powered by specially adapted, direct drive electric motors. Present systems are designed primarily for working surficial deposits of aggregate to depths as great as 90 meters, the pump suspended by cable from a surface vessel with an eductor pipe leading from the pump to the vessel. Such a system may prove adaptable to a variety of surficial deposits including phosphorite, shell and heavy minerals in addition to aggregate. However promising for the exploitation of surficial deposits, little advantage can be expected for the deeper buried and more difficult deposits.

Jan 1, 1986

By Akira Usui, Sayuri Kubo, Satoshi Tokeshi, Shingo Kato, Katsuhiko Suzuki, Teruhiko Kashiwabara

"INTRODUCTIONFerromanganese (Fe-Mn) crusts are a kind of marine chemical sediment composed of Fe and Mn oxy-hydroxides as well as small amounts of clastic sediments, which are ubiquitously found on the surface of slopes of seamounts and oceanic plateaus at depths from 900 to 5500 meters below sea level (mbsl). Fe-Mn crusts contain extremely high concentrations of useful minor metals such as Co, Ni, Te, REEs, and thus are expected as submarine mineral resources. Also, Fe-Mn crusts record the change of chemical compositions of seawater during last several tens million years, which allow us to obtain clues to clarify the paleoenvironmental conditions at the time of its deposition. However, occurrence, chemical compositions, microbial community and growth patterns of ferromanganese crusts are yet fully understood. Hence, a comprehensive study on the genesis of ferromanganese crusts, such as growth rates and enrichment processes of elements, is required to better understand their resource potential as well as their applications to paleoceanographic study.Based on the resource potential of ferro-manganese crust, the project entitled “Next- Generation Technology for Ocean Resources Exploration” was launched as one of the governmental projects to develop the exploration technology based on the scientific research on the submarine resources such as hydrothermal deposits (e.g., a poster by Kawada et al.), ferro-manganese crusts. We have made several research cruise to seamounts in the north-western Pacific such as Takuyo-Daigo and Takuyo-Daisan seamounts (Fig. 1) ."

Jan 1, 2017

By Alexander Malahoff

Accumulation of cobalt -rich ferromanganese crusts on Pacific seamounts located off-ridge in the Hawaiian EEZ, represents a complex process that involves geologic aging of the seamounts, geographic transportation- of the seamounts on the Pacific plate during the past 80 million years, and geochemical history of the oceans for that period. A comparative study of the building and erosion processes of the young Loihi Submarine Volcano, located south of the Island of Hawaii , and the 80 million year old Cross Seamount, located west of Hawaii , shows that both edifices show wide armchair-shaped talus chutes and intervening ridges of exposed dikes. The similarity between the observed mass wasting process on Loihi and Cross suggests that the slopes of submarine volcanoes are geologically unstable from the time of their origin on the seafloor through their entire geological history. The slopes of Cross are covered by coalesced ferromanganese crust covered talus, steep exposed dike faces, and crust covered dike ridges. A study of the stratigraphy of the crusts shows a range of thicknesses and number of unconformities present. The thickest crusts, up to 8 centimeters, are found preserved within the larger coalesced slabs along the shallower slopes of the talus chutes and along the crests of the ridges between water depths of 400 and 1800 meters. The platinum content was used in stratigraphic correlation between the crusts in the coalesced slabs and those collected from ridges with the PISCES V submersible. In the samples studied, the highest platinum content of 0.7 ppm

Jan 1, 1991

By Timothy F. McConachy

Hydrothermal fluids emanating from the seafloor rise as buoyant plumes, entraining ambient bottom sea water on the way up, until they reach density equilibrium and spread laterally in a direction that is governed by near-bottom currents. Plumes provide targets for focussing exploration for seafloor polymetallic sulfide deposits associated with active hydrothermal vents because their lateral and vertical extent is commonly orders of magnitude larger than the vent field from which they originate. Black smokers can inject on the order of 10,000 µg of particles per liter into a sea water column that normally contains only about 10 µg of particles per liter. The resulting plume should be characterized by increased particulate concentration with respect to background sea water and, therefore, provide a measurable gradient towards the source of venting. By utilizing the ability of particles to scatter light, we employed a real¬time, acoustically telemetered, nephelometer to measure this gradient, and mapped the size, shape and particle concentration of plumes at an active spreading center on the Southern Explorer Ridge at lat 49°45.6'N and long 130°16.2'W. Isopach and particle concentration data indicate the presence of two separate but overlapping plumes. The first is associated with a known vent field called Magic Mountain; the second with a new field called AGOR 171, 1.2

Jan 1, 1986