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By Peter Halbach

Within the frame of the German-Indonesian cooperative Bandamin research project two short cruises (7 station days each) were carried out which led to the Flores-Banda basin located north of the active volcanic arc. This basin is part of a large island-arc subduction-collision system resulting from a complex plate tectonic situation in which three major plates collide with each other. The eastern part of the Sunda-Banda convergent margin also includes the transition from subduction of oceanic lithosphere to collision of the Australian continental crust with the arc. This transitional part is cut and displaced by various large obliquely striking fault systems. Thus, the south eastern and eastern arc segments represent geological conditions which are suitable for the development of hydrothermal convection and potential mineral precipitation. Our study area lies north of the transitional section between Flores and Wetar. We started with a high-resolution bathymetric mapping of 240 km2 in a region some 36 km north of the island of Lomblen. A small submarine neovolcanic ridge was discovered striking approximately NW-SE and consisting of several submarine volcanic structures. In the northwest of the study area, the active subaerial Komba Volcano (Batu Tara) marks the youngest continuation of the ridge system examined. From the ridge we collected fresh and hydrothermally altered volcanics with disseminated sulfides (pyrite, pyrrhotite, markasite, and chalcopyrite), together with ferrugenous gossans.

Jan 1, 2004

Although Mn, Fe, Cu, Ni, and Co have been the main interests since the ferromanganese nodules had been found, the other major components such as Si and Ca might be very important controlling factors in the processing due to the locally variable content. It is because of the fact that SiO2 and CaO are added to decrease the smelting temperature in the reduction-smelting method for manganese nodule processing. We have compiled the 707 chemical data for KODOS (Korea Deep Ocean Survey) ferromanganese nodules, which have been acquired from 1994 to 2001 and have been also standardized from 2001 to 2003 to avoid the discrepancy between the data sets. All 707 chemical data were used for the hierarchical cluster analysis to get the elemental correlations and also classified by the morphological types. The averages from each station were classified by the facies groups (Fig. 1) and the localities. Then all data are plotted on the SiO2-CaO-MnO phase diagram at 1773°K to compare with the best compositional area in the nodule smelting. Variations and distributions of SiO2 and CaO as well as those of Mn, Fe, Cu, Ni and Co in KODOS ferromanganese nodules were also reviewed. The mineral phases assigned by the cluster analysis are CFA (Carbonate Fluorapatite), Fe-oxide, Al-silicate, and Mn-oxide. MnO contents are generally higher than SiO2 contents in most of the morphological types except for the Is- and It-type. The Dt- and Tt-type show wider range and the E-types show high anomaly in their CaO contents. The stations which belong to facies group A and B show generally higher MnO contents than SiO2 contents, however, the stations of facies group C and D show wide range in their MnO and SiO2 contents.

Jan 1, 2004

By J. W. Jamieson

INTRODUCTION Hydrothermal vents that form seafloor massive sulfide (SMS) deposits represent unique biodiversity hotspots that host many species that are found only at these sites. The destruction of these habitats remains one of the greatest environmental risks associated with proposed mining of SMS deposits. For this reason, there is a growing movement to protect active vent sites from direct and indirect effects of seafloor mining (Van Dover et al., 2018). Mitigating the adverse effects of mining on these ecosystems may prove to be one of the greatest challenges facing the marine minerals industry. At the same time, there is increasing evidence that inactive or extinct hydrothermal systems, which do not host the density or diversity of animals typical of active vents, may constitute a significant proportion of the SMS resource potential on the seafloor. Mining inactive SMS deposits may therefore present an extractive opportunity that does not necessitate the disturbance or destruction of active vent habitats. However, if mining of SMS deposits is to take place only at inactive vent sites in order to protect active vent ecosystems, a clear definition of what defines a site as active or inactive is necessary. ACTIVE AND INACTIVE SEAFLOOR MASSIVE SULFIDE DEPOSITS Our understanding of the number of inactive deposits, their size and grades, and how they are preserved on the seafloor remains limited, largely due to the challenges associated with finding these deposits. Over 90% of all hydrothermal vent fields discovered so far are hydrothermally-active. Almost all of these sites were discovered through the detection of chemical anomalies associated with active hydrothermal venting via water column surveys. Inactive sites have no associated hydrothermal plume, and thus the well- established plume survey exploration method is not effective. As a result, very few truly inactive sites inactive sites have been discovered. Alternative exploration methods, such as spontaneous potential (SP) surveys, magnetic surveys, and high-resolution mapping are required (Cherkashev et al., 2013; Jamieson et al., 2014; Tivey and Johnson, 2002). As methods for locating inactive deposits continue to develop, our understanding of the distribution and resource potential of these deposits will increase, and the focus of resource exploration will shift from active to inactive vent sites. However, for now, most exploration and deposit development activities remain focused on active vent fields.

Jan 1, 2018

By Raymond A. Binns

Exploration for high-value massive sulfide deposits on the ocean floor typically commences with a search for chimney fields in appropriate geological settings, followed by collection and assaying of standing chimneys. Individual chimney fields are generally too small in aggregate volume to constitute viable resources in their own right. Unless numerous small fields occur in reasonably close proximity, presence of plentiful sub-seafloor mineralization with acceptable metal tenor is the more likely requirement for potential exploitation. Expensive drilling is required to prove up mounds of collapsed chimneys, or dilatory sheets and veins or replacements of massive/semimassive sulfide (?stockworks? or ?manto?-like bodies) in underlying host rock. Where multiple targets have been defined, as many parameters as possible are desirable to help rank them for drilling.

Jan 1, 2011

By Julian Malnic

Various natural, commercial, engineering and operational factors govern the evolution of approaches taken in the exploration for Seafloor Massive Sulphides (SMS) and in delineating the resource. These stages are prerequisites to the proposed mining of SMS deposits. This paper presents and analyses these factors from the view of an SMS exploration company that is pioneering the exploration of this rich alternative source of zinc, copper and gold. Current exploration practices developed by Marine Scientific Research (MSR) workers for SMS deposits are expected to give way to industry-generated methods as the SMS exploration industry gathers momentum. The exploration process falls into three phases that are described below: Prospecting (locating targets), Indicating Resources, and Measuring Mineral Resources Considerable streamlining of the SMS exploration process will accelerate the rate of discovery. The economics of SMS mining are projected to be superior to comparable terrestrial mining operations in both operating cash cost and capital terms.

Jan 1, 2001

By R. C. Newell

The primary objective of this study was to establish the fate and distribution of material rejected during marine aggregate dredging, and the extent to which this is associated with spatial changes in biological community composition. Two actively dredged sites in the southern North Sea (Licence Areas 430 and 106) were selected in order to provide a comparison of impacts between sites subjected to different levels of dredging intensity and of contrasting environmental conditions. Dispersal of material rejected during the dredging process was monitored by means of acoustic doppler current profiling techniques (ADCP). Composition of the substratum and benthic invertebrate assemblages were investigated by the analysis of seabed grab samples. It was found that dredging in both areas had an impact on seabed bathymetry in the form of dredge furrows and also led to a reduction of the coarse gravel-sized components of the worked area. Sand sized particles were shown to increase in the surface deposits of both dredged areas. This is likely to reflect both the removal of coarse particles as cargo and the settlement of finer particles rejected during overboard screening. Dispersion and settlement profiles of material rejected by dredging vessels suggested that the majority of the suspended sediment load resulting from overboard screening settles to the seabed within 500 m. Some evidence of suspended sediment loads above background levels were noted at distances of up to 2 km from the working vessel. Analysis of the particle size composition of the deposits, along the axis of transport of material from the dredged sites, suggested that the impact on the sediment composition outside the boundaries of the dredged sites is dependent on the strength and direction of net sediment flux at the seabed. Benthic invertebrate communities within the dredged zones of both areas were found to differ significantly from communities in nearby undredged deposits. A major suppression of species richness and abundance was noted in the dredged sectors of both sites when compared to control locations. A ?footprint? of potential impact on the benthic fauna was noted in samples taken along the axis of sediment transport at distances of up to 1750m outside the boundaries of Area 430. In contrast, impacts on benthic community structure at Area 106 appeared to be confined to the immediate vicinity of the dredged zone itself. This apparent difference in impacts, beyond the boundaries of the dredged sectors between the two study sites, was thought to be a reflection of the smaller quantities of material rejected at Area 106 and the weak seabed sediment flux which is characteristic of this area. These findings, along with those of numerous dredging impacts studies, were then used to make generalised predictions of macrobenthic community recovery following marine aggregate extraction in a variety of seabed habitats.

Jan 1, 2004

By Ivo Dreiseitl

Bottom sediment sampling by means of a box corer, as a direct method of deep seabed exploration for polymetallic nodules, is the most comprehensive way to obtain various types of geological information on points forming a network of stations. However, direct information is lacking from areas separating those stations and has to be approximated by interpolation or extrapolation, which leads to uncertainties. Sediment sampling with a gravity or piston corer can provide information on the superficial, up to 4 m thick, part of the sedimentary cover. As opposed to box coring, gravity or piston coring provides no information on nodule abundance. Information for unsampled areas can be gained by application of remote techniques of exploration. The techniques of choice in visualising nodule-rich fields, nodule-free areas, hard rock outcrops and other obstacles for seafloor mining involve using sonar and continuous deep sea (CDS) camera. Seafloor mapping can be rendered with two major sonar types: the side scan sonar used to obtain seafloor imagery and multibeam sonar for bathymetric data; the two types are usually combined and work with an intermediate frequency profiler. Photo-profiling by means of a deep sea towed camera provides a series of seafloor photographs, each supplemented with information on the area covered by each frame, including the nodule abundance. Remote techniques have been quite frequently applied by the Interoceanmetal Joint Organization (IOM) in nodule field exploration. Recently, geoacoustic techniques (side scan sonar + profiler) and CDS were applied for exploration of IOM?s first prime area H11 (5372 km2) on 6 transects. During the IOM-2009 cruise, a total of 295 km of geoacoustic transects and 344 km of photo-transects were surveyed. The data obtained were processed with the aid of earlier information produced by multibeam sonar surveys. The aim of this paper is to demonstrate the advantages of remote techniques, particularly with regard to application of the towfish device, for geological and geotechnical applications in exploration for polymetallic nodules.

Sep 14, 2011

By James R. Hein

Manganese nodules from the Cook Islands (CI) Exclusive Economic Zone (EEZ) are compositionally different from other nodule fields. CI nodules have relatively high cobalt concentrations and low nickel, copper, and manganese concentrations (e.g. Hein and Petersen, 2013). This reflects the predominantly hydrogenetic (seawater source) origin for metals in the CI nodules versus dual seawater-pore water sources for most other nodules. The concentrations of many critical and strategic metals have not been previously analyzed for CI nodules, so comparisons with other nodule fields have been limited. To address this, we analyzed a set of nodules distributed throughout the CI EEZ for a complete set of 67 elements, including all of the metals that may be of economic interest, such as the rare earth elements (REEs), yttrium, tellurium, niobium, zirconium, tungsten, titanium, and others (see selected elements in Table 1). In addition, we recalculated the tonnages of nodules and contained metals from nodule abundance areas (in square kilometers) determined by GIS ArcMap calculations based on JICA/MMAJ (2001) nodule distributions. The nodule tonnage calculated and summed from each abundance sector yields a total inferred resource estimate of 9.66 billion tonnes of nodules covering an area of 1.21 million square kilometers; using a cut-off of 6 kilograms of nodules per square meter, yields a median tonnage of 8.59 billion tonnes of nodules covering 687,647 square kilometers (Table 2).

Sep 14, 2011

By Tatiana ?. Sedysheva, Vladimir V. Ivanov, Michail E. Melnikov, Irina A. Pulyaeva

"INTRODUCTIONHydrogenetic 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 [3, 4 - 8]. Now, commercial interests gain more and more attention. Mining systems are being developed which involve fragmentation of the crusts and their separation from the substrate. The effectiveness of such activities greatly depends on physico-mechanical characteristics of the crusts and rocks on which they form. This determines the importance of the engineering geological study of the objects.This article comprises the results of the engineering geological studies of the crusts samples (72 samples) and their underlying rock substrates (75 samples), which were carried out during the research cruises 6-06, 6-07, 6-08, 6-13 (2006-2013) on the Magellan Seamounts guyots in the Western part of the Pacific Ocean by the specialists of the State Scientific Centre Yuzhmorgeologia [10 - 13, 19, 20]. The authors of the article directly participated in the studies mentioned above.MethodsEngineering geological studies were carried out on board of the research vessel Gelendzhik and in the laboratories of NPA «Sevmorgeologiya». The studies involved the determination of the following parameters:"

Jan 1, 2017

By Mark D. Hannington

Seafloor polymetallic sulfides have been found in diverse volcanic and tectonic settings on the ocean floor at water depths ranging from 3700 meters to <1500 meters. More than 100 occurrences of hydrothermal mineralization have been documented (including Fe-oxide deposits, Mn-crusts, metalliferous sediments, and massive sulfides), but high-temperature hydrothermal activity and large accumulations of polymetallic sulfides are known at fewer than 20 different sites. Chemical analyses of samples from these deposits indicate that they contain important concentrations of Cu, Zn, Ag, and Au, comparable to those of massive sulfide deposits on land. However, the lack of sufficient data concerning the distribution, size, and bulk composition of seafloor deposits precludes a meaningful assessment of their resource potential.

Jan 1, 1994

By Jun Lu

Compared with land mineral resources investigation, as well known, it is more important for marine geologists to get image data (e.g. photographs, video tapes and various charts) because they are often hard to reach deep seabed directly. In the past years a plenty of image data which are in various forms have been accumulated. In contrast with both digital and character data managing the image data by using database is just unfolding and it will be a trend for marine mineral resources investigation. GIS (Geography Information System) offers another useful means of processing image data, especially geological data. GIS is characterized by processing vector data (e.g. point, line and polygon), but newer versions of GIS software package are also able to process raster data (e.g. photographs etc.). The present author made a presentation on marine mineral image database during 25th UMI, but that system runs under DOS environment and dealt with only mineralogy. Recently a new system which integrates Oracle image database with GIS (ArcView version 3.1) has been developed. This system runs under Windows NT environment. In the network environment Server/Client mode is adopted, and over 200 basic subdatabases (tables)are located on Server; operating interfaces are located on several clients so that several persons can operate the system simultaneously. The whole system involves five types of marine mineral resources: manganese nodules, cobalt-rich crusts, polymetallic sulfides, phosphorites and gas hydrates. The data of every type of marine mineral resources described above are distributed among five units and several blocks. The units and blocks are described below:

Jan 1, 2000

By T. E. Sedysheva

The study of Co-rich manganese crusts has reached the level which allows to start prospecting works in the observable future, and furthermore, probably, exploitation of ore deposits. In this connection, among other goals, the necessity to analyze a distribution of ore bed parameters in details is quite urgent. Foremost, these are crust thicknesses in connection with landforms and elements of submarine mountains relief. This report is based on representative sampling made in course of research cruises run by SSC Yuzhmorgeologiya over guyots of the Magellan Seamounts. Crustal covers could overlie seafloor surfaces which are confined to a various landforms and elements of relief under the condition, that they are free of sediments. These are planed parts of a summit surfaces, edges, spurs, rectilinear parts of slopes, intermountain saddles and volcanic edifices. It is known, that crustal thicknesses are different at a various forms of relief [1]. We processed statistically the data around crustal thicknesses, which were sampled by dredging and submersible drilling (Tables 1, 2).

Jan 1, 2010

By Sven Petersen

The southern Mid-Atlantic Ridge (SMAR) is one of the least-explored spreading centers in the world with respect to hydrothermal activity. In the past 8 years research focused mainly on the ridge segments close to Ascension Island, discovering hydrothermal fields as far south as 14°20?S (Haase et al., 2007; German et al., 2008; Tao et al., 2011). However, the vast majority of the SMAR ridge axis has never been thoroughly investigated for hydrothermal activity. In the spring of 2013 we used segment-scale AUV deployments as well as conventional CTD surveys to identify areas of hydrothermal activity along 16 mid-ocean ridge segments between 13° and 33°S, thereby covering close to 5 % of the global ridge axis in a single cruise. During cruise MSM25 of the German research vessel Maria S. Merian, we tested longrange (>100 km lines per dive) AUV deployments of GEOMAR?s AUV ABYSS (a Remus 6000 vehicle) along the spreading axis for their capability to locate active venting in a fast and efficient way on regional surveys. Since the missions covered long distances,

Sep 14, 2011

By Irina Melekestseva

The Cu-Zn massive sulfides from the basalt-hosted Semenov-2 hydrothermal field (13°31.13´ N, 44°59.03´ W, MAR) are enriched in Au (22?188 ppm) and Ag (127?1787 ppm) [Ivanov et al., 2008] and elevated contents (ppm) of Se (269?289), Sn (123?125), and Sb (72?75). These may indicate heterogeneous substrate rocks and possible ultramafic rocks. Based on phase analysis, 70% of the gold in the massive sulfides is free. LA-ICPMS analysis has shown that the main carrier of the invisible gold is covellite (22.51? 226.64 ppm). Covellite is also characterized by elevated contents of Se, Mo, Sn, Te, Au, Bi, As, Ag, Sb, Tl, and Pb relative to the primary sulfides.

Sep 14, 2011

By Ian J. Graham

Brothers volcano, in the southern Kermadec Arc, is host to two hydrothermal vent fields with very different geology, permeability, vent fluid compositions and mineralogy (see de Ronde et al. and Ditchburn et al. this volume). The NW caldera site contains mineral deposits (sulfide chimneys and crusts), which are either Cu-rich (?magmatic?) or, more commonly, Zn-rich (?epithermal?). The lower cone site, in contrast, is characterized by native sulfur mounds and spires. It has been proposed (see de Ronde et al. this volume) that the metals, especially Cu and possibly also Au, enter the hydrothermal system via injection and degassing of magma and/or the dissolution of metal-rich glasses. They are then transported rapidly upwards via magmatic volatiles along long (c. 2.5 km), narrow (c. 300 m diameter) pipes, consistent with evidence of vent fluids forming at higher than hydrostatic pressures, at relatively shallow depths. The NW caldera and cone sites may represent stages along a continuum between magmatic-hydrothermal and water/rock-dominated end-members. In this context, investigation of melt inclusions in conjunction with other geochemical and petrological research was carried out to ascertain the metal transporting conditions that may have led to mineral deposition and ore formation. Sixteen melt inclusions in plagioclase were analyzed for their chemical compositions from a typical cone dacite sample using LA-ICPMS at the University of Tasmania. The inclusions are typically glassy and commonly occur with other inclusions such as apatite, clinopyroxene, zircon, magnetite, sulfides and/or low-density fluids (Fig. 1). Major (XRF) and trace element (ICPMS) analyses were performed on whole rock samples collected during the 2005 Shinkai 6500 expedition. Haase et al., (2006) has also reported EPMA glass analyses from cone dacites, which may be used for comparison (Table 1). [ ]

Jan 1, 2010

By Julian Malnic

The emerging marine minerals exploration and mining industry is currently focused mainly on the technical elements for its success such as developing exploration and mining technologies. However, in one sense, the technical challenges are quite soluble whereas those arising in the fields of the environment and public opinion could present this new generation of miners with problems that are far more difficult to overcome. One need only look at the issues currently faced by mining projects on land to see how powerful the new forces of so-called ?civil society? are in stopping mineral developments in many countries. From the geographic viewpoint, there are many countries but there is just one ocean, so the impacts experienced by any one operation are likely to have pervasive repercussions throughout the industry. A well-oiled NGO development protest lobby will see leverage in resisting this new industry and will seize on the single-ocean angle. The Australian Minerals Industry has established a voluntary Code for Environmental Management that provides an active and valuable model for satisfying the ?court of public opinion? and in delivering economic results to industry that are in current jargon, sustainable. An explanation of the Code for Environmental Management, and the reasons behind 44 companies representing more than 300 operations and 85% of Australia?s sizeable mineral production being signatory to it will be given. Participants see it as a means to future shareholder wealth.

Jan 1, 2000

By Charles L. Morgan

In June 1996, the United Nations International Seabed Authority opened shop in Kingston, Jamaica as an autonomous international organization charged with the administration of seabed mineral developments in all areas beyond national jurisdictions. The Authority is a consequence of the 16 November, 1994 entry into force of the 1982 United Nations Convention on the Law of the Sea (UNCLOS) and the 1994 Agreement relating to the Implementation of Part XI of UNCLOS. The total seabed area included within the Authority?s purview has yet to be assessed accurately, but clearly constitutes the largest single jurisdiction on the planet. The Authority is governed by legislative bodies called the Assembly and the Council and an administration called the Secretariat. The Assembly includes representatives of the 132 member states which are currently parties both to UNCLOS and to the 1994 Agreement. These member states directly fund the operations of the Secretariat. They include most of the world?s developed nations, island nations, and others among the 188 independent countries which are members of the United Nations. Notably absent are the United States and Canada, which are the only developed coastal states not represented. The Council is a 36-member subset of the Assembly representatives selected through a somewhat involved process designed to achieve a balanced representation of the specific interests of the members. Ultimate responsibility for the Authority?s actions resides in the Assembly, but most initiatives originate in the Council. Also included in the Authority are two subsidiary advisory bodies, the Finance Committee, which reviews the Secretariat?s budget, and the Legal and Technical Commission, which evaluates claims and drafts technical regulations. The Secretariat itself includes a staff of about 30, including 15 highly qualified and competent attorneys, accountants, engineers, and scientists. Details describing the composition and activities of these bodies can be found at the Authority?s website (http://www.isa.org.jm).

Jan 1, 2000

By Sabrina Warwas, Thomas Kuhn

"Due to rising prices and increasing demand of raw materials over the last years, marine mineral resources including manganese nodules have become a focus of study for industry and science. Marine ferromanganese nodules consist of micro-layers of different chemical and mineralogical composition which incorporate metals of high economic interest (Ni, Cu, Co, Zn, Mo, Li, rare earth elements; Hein & Koschinsky, 2015).The varying composition of the layers depends on different growth processes, such as hydrogenetic (metal precipitation from the water column under oxic conditions; Mn/Fe = 3), diagenetic (metal precipitation from the sediment pore water) under oxic (Mn/Fe 3-10) or suboxic (Mn/Fe = 10) conditions; (Wegorzewski & Kuhn, 2014) or hydrothermal (metal precipitation from low-temperature hydrothermal fluids; Kuhn et al., 2003).METHODSIn this study, manganese nodules from three different locations of the Atlantic Ocean (Galicia Bank; Vema-Fracture-Zone and Brazilian Basin) were analyzed for their geochemical and mineralogical composition. Detailed information about the samples are given in table 1. The geochemical and mineralogical composition of bulk nodules were determined by XRF, ICP-MS/OES as well as XRD and the single micro-layers by high resolution analyses with electron microprobe and LA-ICP-MS."

Jan 1, 2017

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

By James R. Hein

Ferromanganese oxyhydroxide crusts (Fe-Mn crusts) precipitate out of cold ambient seawater onto hard-rock surfaces at water depths of about 600-4000 m throughout the ocean basins. Fe-Mn crusts concentrate most elements in the Periodic Table above their mean concentration in the earth&apos;s crust (continental plus oceanic crust), except for the major rock-forming oxides and also notably gold and palladium. Tellurium is concentrated greater than any other element relative to its earth&apos;s crust mean (about 1 ppb). For example, mean contents of the elements heretofore known to be most enriched in crusts, Mo, Tl, Sb, Co, Mn, Bi, As, Se, and Pb are enriched 100 to 1000 times over their earth&apos;s crust mean, whereas the mean Te content in Fe-Mn crusts is enriched about 50,000 times. However, the distribution of Te in the earth is poorly known. Estimates of the mean Te content of the earth&apos;s crust range from 0.36 to 10 ppb, with 1 ppb being the most commonly cited mean content (compilations in Levinson, 1974 and Govett, 1983). If we took the highest estimate of 10 ppb, then Te would be enriched in Fe-Mn crusts five times more than the next most enriched element, or 5000 times the estimated maximum mean earth&apos;s crust.

Jan 1, 2000