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By D. S. Cronan

Mineral exploration problems in the S.W. Pacific are not unique to that region, but a combination of favourable circumstances render it an ideal area to attempt to solve such problems. The land area of the S.W. Pacific island nations is only a fraction of the total sea area they can claim under current International Law. Hence, they have a great need to explore and evaluate their offshore areas. For the past ten years the focus of this work has been CCOP/SOPAC which has individually and jointly with other groups initiated and maintained far reaching marine mineral exploration programmes. In association with CCOP/SOPAC the writer has obtained and analysed approximately 650 sediment samples from the S.W. Pacific region for seventeen elements. Multivariate statistical techniques have been applied to the data set. The aim has been to identify chemically anomalous sediments reflecting either sea floor mineralisation and/or mineralisation on adjacent land areas.

Jan 1, 1985

By I. Yu. Melekestseva

The Semenov hydrothermal sulfide cluster (13º31´N), consisted of five fields (Semenov-1, -2, -3, -4, and -5), was discovered in 2007 in the 30th cruise of R/V Professor Logatchev [Beltenev et al., 2007; 2009]. The hydrothermal fields are located on a seamount composed of ultramafic and mafic rocks, gabbro, plagiogranite, and their altered rocks. The Semenov cluster is considered to be the largest sulfide accumulation in the Ocean with massive sulfide (MS) resources of about 40 million tons [Beltenev et al., 2009]. MS of the Semenov-1, -3, -4, and -5 hydrothermal fields are mostly characterized by marcasite-pyrite composition whereas rich copper-zinc MS with high Cu and Zn contents (11.37?19.33 and 5.89?18.32%, respectively) and anomalous Au and Ag grades (22?188 ?127?1787 ppm, respectively) were dredged only at the Semenov-2 hydrothermal field associated with basalts (13°31.13´N, 44°59.03´W; 2360?2580 m of depths) [Ivanov et al., 2008].

Jan 1, 2010

By Wilfred Lus

Meaningful and real time environmental monitoring of marine tailings placement is a clear sign of deeper commitment to the people of PNG in regard to impacts of mining on coastal environment and marine life. Today daily mine wastes and tailings are increasingly being delivered to the seabed offshore of project sites in Misima and Lihir islands. Ramu and Simberi mining projects also plan to dispose tailings out at deep sea. As tailings leave the tailings pipe and come out into the seabed, concentrations of the cations and other potential harmful particles in the tailings stream need to be quantifiably monitored each day during the life of the refinery. For continuous monitoring of the tailing?s true chemical characteristics submarine cables connected with ocean floor observation systems consisting of deep-sea underwater video, and cation sensors and electrodes will be laid. Power transport to the tailings site and data transfer from the tailings site will be via opto-electric cables. Various data center instruments will record and manage the collected data. Observation data will be transferred in real time to stake holder?s data centers via a dedicated line from on-land stations, and then distributed to company offices and government establishments. Japan Marine Science and Technology Center, Telikom PNG, and Australian Institute of Marine Sciences will be the key advisers in this project. The main role of the observatories is to monitor and collect background seabed geochemical data prior to start of tailings disposal, during tailings disposal period, and after the life of the refinery.

Jan 1, 2001

By Alexander Malahoff

A shipboard research system capable of operating in waters of up to 2,000 meters has been designed and implemented by the Hawai'i Undersea Research Laboratory (HURL) of the University of Hawai'i. It uses a remotely-operated ocean bottom survey camera system, an ROV, the Pisces V submersible, and a submersible emergency recovery system, all aboard the 222- foot R/V Ka'imikai-o-Kanaloa. All systems are operated from the stern of Ka'imikai with a mounted Caley telearm and articulated A-frame system. The system was designed for multipurpose use of the ship for launch and recovery of the Pisces V submersible on a lift recovery line (with or without diver assistance), or night-time operations with an electro-optical cable using either the HURL ocean floor sidescan or photo and video system operated at 10 meters above the ocean floor. The 1.14-inch diameter cable is also used to operate an ROV system. The garage/ROV system can also act as a submersible rescue system with a submersible lift capability. The ship is equipped with a SeaBeam and shallow penetration sediment profiling systems. This integrated system approach to deep ocean floor research will make it possible for HURL to carry out research pro- grams on seamount ocean resources and ocean chemistry and climate in Hawai'i and the equatorial Pacific.

Jan 1, 1995

By Mikhail D. Ageev

The paper concerns with some questions of Autonomous Underwater Vehicle (AUV) control system design, which allows a motion at rough undersea terrain. The AUV advantages reveal itself completely during exploration of such objects as seamounts and reefs area. These objects are characterized by steep slopes (30 degrees and above) and chaotic situated obstacles (rock debris, pinnacles, escarpments). Uses of other technical facilities for operating in such formations are difficult, dangerous or impossible. These regions take an interest due to the presence of iron-manganese crusts. Modern AUV can estimate density of mineral by means of still camera or video recorder. For this reason the vehicle has to move with the distance of 3-5 meters from seabed. Under such conditions micro- and mesorelief presents a considerable danger for AUV. The AUV can bypass underwater obstacles in the various ways. However, in any case AUV motion will be characterized by intensive maneuvering on various speeds (from 0 up to 1.5 m/s), circular change of tractive force vector and, hence, a circular flow about the hull. So, AUV is equipped with the propulsion system, which provides free modes of motion.

Jan 1, 2003

By Dennis Sánchez Mora, John Jamieson

INTRODUCTION Work by Humphris et al., (2002); Ondréas et al., (2009); Barreyre et al., (2012); and Escartín et al., (2015) has identified active and inactive hydrothermal sites along the Lucky Strike segment. The sites that contain the largest accumulation of known sulfides are located between the north and the southern zones (Figure 1), a vent site area that is referred to as the Main Lucky Strike hydrothermal field (Escartín et al., 2015). Hydrothermal fluid outflow has been linked to a shallow fault network (Barreyre et al., 2012). However, specific constraints on fault geometries have not been determined. Other off-axis sites at Lucky Strike, such as Capelinhos (high temperature vent), and Grunnus (inactive?), as well as a low temperature vent field (on-axis), Ewan, have been described by (Escartín et al., 2015). Given the spatial relationship between the Main Lucky Strike hydrothermal field (MLSHF), and the intersection of northern rift faults with the southern rift faults, a structural analysis of this area can provide insight into the fault controls on fluid flow that leads to hydrothermal venting and sulfide precipitation. METHODOLOGY Structural data (dip direction and dip) was determined using Leapfrog Geo 4.0 software. Bathymetric data was obtained from Escartín et al., (2015) and references therein. The bathymetry was imported into Leapfrog Geo (in UTM format) and, using the structural modelling tool, individual measurements with dip direction and dip data were collected with a focus on the northern volcanic rift and the southern central volcano (Figure 2a). All measurements were taken from what the authors consider as normal faults, and to aid the determination of individual measurements a “face dip” map was constructed, where the bathymetry is colored by slope angle (Figure 2b). All measurements are simultaneously plotted on a stereonet generated by the Leapfrog Geo Software. Data were divided into northern and southern, and western and eastern zones to determine the relationship between hydrothermal venting and the structural geometries at Lucky Strike (Figure 2c). Slip measurements for individual faults were determined along the dip of the fault with a measuring tool. Net slip, heave (horizontal displacement), and throw (vertical displacement) was calculated for each of the zones.

Jan 1, 2018

By Anthony Wakefield

Dredging tends to be either horizontal or vertical. In each case solids have to be disengaged from the deposit, mobilized, acquired and elevated or translated. One means of elevation is the airlift. Elevation and translation of essentially granular material nay be by jet pump or centrifugal pump. Any of the three types may be used on its own. The airlift and jet pump may he combined for vertical transport and the centrifugal and jet pumps for predominantly horizontal. Both suction point and pipework must have a means of deployment from the surface or from a submerged vehicle or merely a diver. An airlift is an energetic system, having a source of energy and a means of storing it. It therefore will be difficult to prevent oscillation -surging. A centrifugal pump has a characteristic that bends over at low flow rate and is therefore intrinsically unsuitable for pumping solids. The result is blockage, operation at high velocity and correspondingly high wear rates or operation at low concentration of solids and correspondingly low efficiency. The jet pump is intrinsically exceptionally stable but has a low hydraulic efficiency. The jet pump-airlift hybrid prevents or reduces surging and increases system efficiency away from the optimum depth for airlift operation. Delivered solids concentration is increased. The jet pump-centrifugal pump hybrid totally prevents pipeline blockages and increases the productivity from a given pipeline size. For a given energy input the average production is typically doubled. For example, the Indian River Delaware bypassing pipeline transmits an overall day-in-day-out average of 500t/h (tonnes) of sand down a 10.86" diameter line.

Jan 1, 1998

By T. Kuhn

The Logatchev hydrothermal field is situated on the east inner flank of the rift valley of the MAR at 14°45?N and is hosted by serpentinized peridotites and minor gabbronorites while basalts are subordinate. Hydrothermal precipitates recovered from the Logatchev field during a recent R/V Meteor cruise include massive chalcopyrite chimneys, massive pyrite crusts, silicified breccias, abundant secondary Cu-sulfides, red jaspers, abundant Fe-Mn-oxyhydroxides as well as atacamite and Mn-oxides (Kuhn et al., 2004). Previous results of hydrothermal fluid studies in the Logatchev field are somewhat at odds with theoretical models of ultramafic-seawater reaction. Butterfield et al. (2003) suggested that the Fe component of orthopyroxene plays the more important role compared to olivine in ultramafic-hosted hydrothermal systems. This consideration is supported by the recovery of large amounts of Opx-rich gabbronorites and orthopyroxenites in the Logatchev field (Kuhn et al., 2004). A possible tool to constrain the contribution of the different rock types (ultramafics, mafics, MORB) to a seafloor hydrothermal system is the systematic analysis of 187/188Os ratios of the host rocks as educts and the sulfides as products. For instance, abyssal peridotites mainly display low 187/188Os ratios (<0.127); in contrast MORB and gabbronorites have radiogenic ratios of >0.13 (Snow and Reisberg, 1995), orthopyroxenite has ratios of about 0.174 (Büchl et al., 2002) and seawater has an ever higher 187/188Os of about 1 (Sharma et al., 1997). Therefore, massive sulfides predominantly leached from ultramafic rocks should have Os isotopic ratios plotting on a mixing line between the ultramafic rocks and seawater (in a 187/188Os vs. 1/Os diagram), whereas those derived from MORB, gabbronorites and/or orthopyroxenites will be plotting on different mixing lines.

Jan 1, 2004

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 Sukumar Bandopadhyay

The Marine Minerals Technology Center (MMTC) was authorized by an act of the United States Congress in 1996. The act established several marine minerals research centers in the U.S., including one at the University of Alaska Fairbanks. The Alaska MMTC is funded through the Minerals Management Service of the Department of the Interior and concentrates its research in the Arctic seas region. Recent research projects at the MMTC include, among others, application of a geographic information system (GIS) to the gold placer deposits offshore Nome, Alaska, development of a marine gold placer reserve definition model using a neural network, and development of an expert system model for submarine tailings disposal (STD) planning and decision-making. Although geostatistics remains the most prevalent method used today for ore grade estimation, researchers have made numerous improvements over the years for accurately predicting grades of ore using other estimation techniques. One such technique, the neural network, has recently emerged as an alternative to geostatistics for grade estimation purposes. A neural network is a non-linear, model-free estimator that is well-suited for noisy and/or sparse data environments. Neural networks perform best with non-linear spatial data, contrary to the stationary assumption of ordinary Kriging techniques. In the marine placer ore reserve definition model, the neural network technique was used to estimate placer gold reserves offshore Nome. This study demonstrated the utility of neural network modeling over other traditional ore reserve estimation methods, especially for high cut-off grades. Some of the relevant issues of neural network modeling were also addressed in the study. In testing, the neural network produced results that were close to those from geostatistical techniques including Kriging, polygonal, and inverse distance methods.

Jan 1, 2005

By A. Ivanova

The continental shelves occupy a vast area of Russia and contain complexes of commercial placer minerals. Of prime importance are Cenozoic placers of valuable minerals including gold, cassiterite, diamonds, chromite, platinoids, and minerals of titanium, zirconium and rare earth elements, biogenic amber and fossil ivory (1). Commercial placer minerals are associated with shelf placer formation zones (SPFZ). These zones are located at junctions of marginal orogens and shelf troughs in morphostructures where upwarping, subsidence, and sign-variable neotectonic movements are not significant. The SPFZs are characterized by ancient buried leveling planes with mantles of waste, series of wave-cut aggradation terraces on land and beneath the sea, and drowned and buried stream valleys. The occurrence of mineral placers in the SPFZs was caused by endogenic mineralization and exogenic placer hosted formation. Concentrations of commercial biogenic minerals are associated with areas of burial of biogenic material (release of resins by plants and theriofauna thanatocoenoses) and with their transition zones. Since the Oligocene, alternations in marine transgression-regression have dominated the shelf areas. This has resulted in the formation of polygenic placers. Climatic conditions are of great importance: warm and humid climate in the Paleogene-Neogene changed to colder climates in the late Pliocene (polar type sedimentation; formation of permafrost strata and sea glaciation). These events are responsible for the regularity in placer formation during the Cenozoic in which the early Cenozoic (Eocene-Oligocene-Miocene) and late Cenozoic (late Pliocene-early Pleistocene and late Pleistocene-Holocene) epochs are prominent.

Jan 1, 2004

By Robert M. Owen

Recent advances in coring technology and in the development of shipboard and/or in situ geochemical geochemical analysis systems have greatly improved our ability to collect and analyze exploration samples, particularly for marine placer exploration programs. The potential benefit of these improvements cannot be fully realized, however, until we also develop more efficient methods of data reduction and interpretation. Specifically, there is a need to provide prospectors with rapid and useful interpretations of the raw geochemical data so that they can exploit promising results and otherwise optimize the exploration program while the exploration vessel is still at sea. The goal of this project has been to identify and/or develop computer software which is capable of making the necessary data reduction calculations and which can be run on conventional desk-top computers. All work on this project has been supported through a research grant from MMTC-CSD to The University of Michigan. The first stage of this effort involved an evaluation of commercially available (i.e., "off the shelf") software to determine its suitability for use in marine placer exploration applications. Various commercial software packages, each purportedly capable of making different types of statistical and/or mathematical calculations, were tested by evaluating their performance in handling geochemical data sets representative of actual marine placer locations. These data sets include the positions and results of chemical analyses of suites of sediment samples collected from areas of known or suspected marine placers along the Bering Sea coast of Alaska. The evaluation of each commercial program involved a comparison between the results obtained from using the test program

Jan 1, 1991

By Karstein Vestgard

During the last few years autonomous underwater vehicle (AUV) technology has evolved from concept demonstrators towards commercial products. The driving forces are the move for energy exploitation towards deeper waters, naval applications and the Internet driven need for more intercontinental underwater communication cables. Other applications emerging for the future will be within environmental research and monitoring and deepwater exploration. Deepwater developments beyond the continental shelf will require the same level of survey data quality and intervention access as established for shallow water. The potential for cost savings is two folds. Firstly, there is a reduction in the survey cost it self and secondly there is a considerable cost saving by avoiding over design of subsea installations due to lack of sufficient documentation of the field. In this scenario, there is an increasing understanding that underwater robotics and in particular AUVs will play an important role in future survey and subsea engineering work. The AUV as a free swimming underwater survey sensor carrier has several advantages compared to cable controlled ROV?s and deep towed systems: The paper prepared for the ?Underwater Mining Institute 2003? on Jeju Island, Korea will focus on the HUGIN AUV concept and field results to date.

Jan 1, 2003

By Carla J. Moore

The National Geophysical Data Center (NGDC), Marine Geology and Geophysics Division and co-located World Data Center-A for MGG archives and distributes global marine sediment data from U.S. and international sources. NGDC is part of the U.S. Department of Commerce, National Oceanic and Atmospheric Administration (NOAA), National Environmental Satellite, Data, and Information Service. NGDC offers a variety of digital marine sediment data sets including sediment descriptions, textural analyses, geochemistry, paleontology, paleomagnetism, and well logs. Some data sets are compiled by outside sources and sent to NGDC for distribution; many are received under exchange agreements and through the World Data Center system. Other data sets are compiled at NGDC, frequently in cooperation with other government agencies or academic institutions. One of the best examples of the latter is the Index to Marine Geological Samples, or "Core Curators&apos; Database".

Jan 1, 1993

By Richard H. T. Garnett

The Chilean part of the archipelago of Tierra del Fuego, situated south of latitude 62o S, is within that country?s Región de Magallanes y Antártica, and separated from the remainder of Chile by the Magellan Strait. In recent geological history several phases of Quaternary age glaciers originating in the Andean and Dawinian Cordilleras eroded assumed primary gold deposits and entrained their related alluvial deposits. Piedmont glaciation extended to the east and south over m0st of the land and beyond the present-day coastline into extensive areas exposed during the resulting lowered relative sea level. During interglacials particulate gold incorporated unevenly in the widespread drift, till and moraines was fluvially released and concentrated into streams and flood gravels. Coastal erosion enriched various beaches with gold. From 1868 onwards Tierra del Fuego hosted a major gold rush whereby early, labour intensive, beach mining eventually developed into inland dredging. But continued mining activity was interrupted and then terminated by several external factors. Most miners, always seeking ?greener pastures?, joined the rush to the new discoveries in the Klondike (1896) and Nome, Alaska (1899). In 1904 the international boundary, established in 1881, became the subject of a major dispute not settled until 1984, The Panama canal?s opening in 1914 turned Tierra del Fuego, previously on the Pacific-Atlantic shipping route, into a remote backwater. World War II brought opposing foreign naval forces to the actual islands where most gold had been taken from the beaches. It also crippled the dredging industry which lost its coal supply and never recovered. Nevertheless, some small scale mining continues to this day.

Sep 14, 2011

By Nobuyuki Okamoto

The present three-year long phase of the SOPAC/Japan Deep Sea Co-operative Mineral Resources Programme [Programme], commenced in 2000. The Programme has been funded by the Government of Japan through the Japan International Co-operation Agency (JICA) and the Metal Mining Agency of Japan (MMAJ), since 1985. Field survey activities and associated data analysis and interpretation, for the Programme, has largely been carried out by the Deep Ocean Resources Development Co., Ltd. (DORD). The Government of Japan has, since 1982, recognised DORD as one of its ? Pioneer Investigators? for manganese nodules in the Clarion Clipperton Fracture Zone . Although the objective of this paper is to present the results of the drilling cruise that was conducted from December 2001 to January 2002, within the North Fiji Basin, in Fiji?s EEZ, it will also seek to provide a broad overview of the results of the cruise conducted within the Cook Islands in May to June 2000, as well as present preliminary results of the cruise conducted in the Marshall Islands in June to July 2002.

Jan 1, 2002

Clark volcano is a large volcanic center on the active arc front of the intraoceanic Kermadec arc. It is one of the two southern-most Kermadec arc volcanoes (the other being Whakatane volcano) that sits on oceanic crust before the transition to continental New Zealand, and is underlain by the 17-km-thick Hikurangi Plateau, which is presently subducting beneath the southern section of the Kermadec arc. Unusual K-rich basaltic lavas have been recovered from Clark (1.5 to 2.25 wt.% K2O), together with more typical basaltic-andesite, andesite and dacite rocks. The total volume of the Clark volcanic center is ~90 km3, calculated from the summit of the volcano down to the 2,500 m contour (which marks the inflection point of the volcano flanks with the surrounding seafloor) and comprises two separate edifices similar in size; the northern one having a volume of ~4.57 km3 and the southern one 4.43 km3. The volcano has a maximum relief of ~1,645 m from the 2,500 m contour to the summit of the shallower northern edifice shoaling to 855 m below sea level. The northern edifice is comprised of twin peaks each consisting of a constructional cone, with evidence of sector collapse having occurred between the cones. A more recent, smaller cone again has grown on the eastern flank between these summit cones. Massive, blocky lavas and coarse talus dominate the summits of the cones, with finer-grained volcaniclastic material and sediments a feature of the volcano flanks. The southern edifice is noticeably more dissected than the northern one, having a pronounced horst in the centre of the volcano bounded by 5-6 km-long faults. There is no obvious constructional cone atop the southern volcanic edifice.

Jan 1, 2011

By Akira Usui

Occurrence of hydrogenetic ferromanganese crusts has been well documented over inactive seamounts in the central and southern Pacific Ocean. It has been thus believed that the hydrogenetic crusts develop preferentially at water depths between about 800 to 2500 meters. In fact, according to the Manganese Crust Database (F. Manheim, 1988), only two occurrences are known at water depths below 5000 m out of 819 occurrences cited in the database. Unexpectedly, we found typical hydrogenetic ferromanganese crusts from deep-sea floors; 1) outcropping old volcanic basement over the Philippine Sea Plate (abandoned spreading centers and subducting old oceanic crusts) and 2) one from the slope of an abyssal hill in the Central Pacific Basin (Cretaceous deep-sea basin) at water depths ranging between 5200 to 6100 meters. We report their occurrences with submersible observations from Shinkai 6K, physical parameters (such as thickness of crusts about 2-4 cm in maximum), chemical composition, petrology of substrate, and results of Be-10 dating for some samples in comparison with typical Co-rich manganese crusts from the Central Pacific seamounts. The preliminary chemical and mineralogical analyses reveal that they are of typical hydrogenetic origin, and typical of iron-manganese oxide mineral, vernadite, slow and probably continuous growth, and lower content of Co than the Central Pacific seamount crusts. The occurrences and nature of the crusts indicate that deep-sea floors are also optimal for the growth of hydrogenetic crust even at 5000 m water depth or deeper, only if oxygenated deep waters are supplied and the sea-floor morphology keeps stable enough for significant geological time period. Additional details of chemical analyses will be prepared by November and to be shown in the conference.

Jan 1, 2001

By Toru Yamasaki

"Bimodal lithostratigrafic assemblages are of significance in volcanogenic massive sulfide (VMS)-hosted lithology. The largest deposits are either bimodal-siliciclastic or maficsiliciclastic, and the presence of a significant siliciclastic component in the host stratigraphic succession favors large VMS deposits (e.g., Franklin et al., 2005; Barrie and Hannington, 1999). In the case of modern sub-seafloor VMS deposits in arc-related settings, the majority of deposits have been discovered in association with calderas or cauldrons (Halbach et al., 1993; Ishibashi and Urabe, 1995; Iizasa et al., 1999). These features are formed by the explosive eruption of silicic volcanoes, so that silicic host rocks and/or pumiceous volcanic clasts are generally observed around the ore deposits (e.g., Binns and Scott, 1993; Fiske et al., 2001). Caldera-like and graben-like morphological features therefore attract attention in geophysical surveys. However, silicic lithologies (dacite and rhyolite) normally contain only small amount of metallic elements (e.g., a few ppm to a few dozen ppm of Cu), whereas mafic rocks, such as basalts and basaltic andesites, contain significant amounts of metals (e.g., a few hundred ppm of Cu). Thus, the origin of metallic elements in VMS deposits associate with the silicic host rock remains unclear.The Iheya North Knoll is a volcanic complex in the middle of the Okinawa Trough. It is located in a young and actively spreading back-arc basin that extends for 1200 km behind the Ryukyu arc-trench system (Lee et al., 1980; Letouzey and Kimura, 1986). Several active hydrothermal fields have been recognized in the Iheya North Knoll. Mineralization at the Iheya North Knoll is characterized by relatively juvenile features consisting of VMS deposits with associated hydrothermal alterations to various degrees. Massive sphaleriterich sulfides at this site, recovered for the first time from beneath an active seafloor hydrothermal system, strongly resemble the black ore of the Kuroko deposits of the Miocene age in Japan (Takai et al., 2011). From February 11 to March 17, 2016, the SIP CK16-01 (Exp. 908) D/V Chikyu cruise was conducted at Iheya North Knoll and the rifting center of the Iheya Minor Ridge area, middle Okinawa Trough. The Iheya Minor Ridge area is also an active hydrothermal field, located ~30 km southeast of the Iheya North Knoll. In this area, basaltic rocks are widely distributed, and drilling has confirmed that the basaltic materials continue to ~120 m below the seafloor (Kumagai et al., in prep)."

Jan 1, 2017

By D. Cronan

Both the S.W. Pacific and Caribbean island arcs are host to submarine hydrothermal mineral deposits, the former more so than the latter. In the S.W. Pacific, the whole gamut of such deposits occurs on the sea floor, sulphides, silicates, Fe and Mn oxides, whereas during the limited studies to date in the Caribbean only hydrothermal Mn oxides have been found to occur on the sea floor there in any abundance. Comparisons between the respective Mn oxides are thus the most fruitful at the present limited stage of our knowledge of Caribbean submarine hydrothermalism. Southwest Pacific hydrothermal ferromanganese oxides and their possible relationships to underlying sulphide mineralisation or bedrock anomalies (the geochemical window concept) has been a fruitful field of research in recent years. Certain element enrichments in crusts may be indicative of underlying mineralisation (Rogers et al. 2001). However, more recent studies on buried hydrothermal crusts in the S.W. Pacific (Cronan et al. 2002) have shown there to have been postdepositional diagenetic uptake of elements in them, and thus these elements cannot be used with any confidence in geochemical exploration for buried sulphide deposits unless sediment involvement can be eliminated.

Jan 1, 2002