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By Paul M. Vercruijsse

Deep sea mining operations by nature are performed (or planned) in challenging environments. Another typifying characteristic of deep sea mining operations is the relatively high investment cost. This combination challenges engineers to design configurations able to mine the desired production rate in an efficient way. As design choices made for individual systems impact other parts of the system, it is vital to follow an integral approach to establish the one optimal overall system. Dredging and especially dredge mining learns that the excavation system, the slurry transportation system and the processing plant cannot be considered as individual sub-systems. These systems in any ?traditional dredge mining? operation interrelate to such extend that they must be developed towards an integral solution. The nominal production, peak production and variability of these figures must match for all subsystems in the overall mining system to optimize the mining efficiency. We call this the ?game of capacities?.

Jan 1, 2011

By Tae-kyeong Yeu

KIOST has developed the pilot mining robot, named MineRo ?? from early-2011 to mid- 2012. The robot consists of two unit-modules having an identical mechanical structure and hydraulic system. One unit-module has two track systems, two pick-up devices, two crushers, one lifting pump and one thruster. The pick-up device is fitted on the frame of the track device. All actuators are driven hydraulically, which are manipulated by valves and the controllers. Each unit-module is equipped with one dual HPU of 250kW / 4,000V. PWM-16 (INNOVA AS) as hydraulic valve controller is adopted, which outputs PWM signals of 16 channels and can be used under pressure in oil-filled box. To measure angular velocity or displacement of hydraulic actuator, turbine-type flow-meters are adopted. The flow-meter has RF (Radio Frequency) type pulse detector, which extends the flow range by eliminating drag on the rotor. Two track motors, two crusher motors, lifting pump, one thruster can be controlled their velocities through feedback of the measured flow-rates. As well as the flow-rates, the states of the hydraulic system such as hydraulic pressures, temperatures, leakages are measured through a self-developed flow-pressure canister. In that canister, multi-channel amplifier boards are installed, through which the vast amount of data is acquired and transmitted to the main controller using serial communication.

Sep 14, 2011

By Steven D. Scott

Stephen D. Scott Steven Scott is a Professor of Geology, Director of the Marine Geology Research Laboratory and, until May 1997, was Chairman for 9 years of Geological and Mining Engineering, all at the University of Toronto. Steve also holds a cross appointment at the University of Western Brittany's European University Institute of the Sea in Brest, France. He was educated at the University of Western Ontario (B.Sc. and M.Sc.) and at Penn State (Ph.D.). Steve is a geologist/oceanographer specializing in base and precious metal massive sulfide deposits which he and his students have studied on five continents and on the bottom of three oceans. He was the first ore deposits geologist and first Canadian to witness "black smokers" on the ocean floor. Since 1982, he has participated on 21 oceanographic surface and submersible expeditions, many of them as Chief Scientist. His research team is currently carrying out projects in the W and NE Pacific Ocean. Steve has published more than 150 research papers and lectured in more than a dozen counties. Popularized accounts of his work have appeared in various media.. He has been honored by several awards and distinguished lectureships. Steve is President of the Canadian Scientific Submersible Facility, which operates the Canadian ROPOS robotic submersible, and is President of the International Marine Minerals Society.

Jan 1, 1998

By Gerald R. Dickens

Massive sulfide ores and Fe-Mn oxyhydroxide precipitates represent two extremes of a spatial continuum of hydrothermal deposition along oceanic ridges. Elemental variations across this continuum are of interest to economic geologists as a prospective geochemical exploration tool. Theoretical considerations suggest that certain physical and chemical parameters can be used to model compositional variations within the far-field (i.e., Fe-Mn oxyhydroxide) component as a function of distance from ridge axis; however, testing and verification of such models generally has been precluded because the few available distal hydrothermal sediment sequences have been sampled at low resolution and/or are highly diluted with biogenic components (e.g., siliceous and calcareous tests). Recent ocean drilling (ODP Leg 145; Sites 885/886) in the North Pacific successfully recovered an extensive record of "biogenic-free" distal hydrothermal precipitates from an area approximately 60 km south of the Chinook Trough at longitude 168.1 °W. Geophysical and geomorphological evidence suggests the Chinook Trough is the southern lithospheric scar marking initiation of late Cretaceous north-south rifting, implying that recovered hydrothermal materials record distal hydrothermal precipitation from the now-subducted Kula-Pacific spreading ridge. The Chinook Trough hydrothermal sequence is a continuous 15 my record of "biogenic-free" hydrothermal Fe-Mn oxyhydroxide precipitation mixed with eolian clays. It was deposited during the late Cretaceous, early Paleocene (80-65 Ma) as the perpendicular distance from ridge axis increased from 75 to 600 km. A high-resolution geochemical analysis of this hydrothermal sequence reveals distinct trends for the up-core (equivalent to increasing distance from ridge) distribution patterns of Fe, Sc, As, and rare earth elements (REE). Iron concentrations exhibit an S-shape distribution pattern with respect to increasing

Jan 1, 1994

By Kyung-Ho Park

The smelting leaching process is known as one of the most favorite methods for the processing of deep-sea manganese nodules because of its smaller environmental impact and easiness of manganese recovery. The sulphuric acid pressure leaching of the matte prepared from deep-sea manganese nodules was studied to dissolve the valuable metals. Almost complete dissolution of Cu, Ni, and Co from matte was achieved under the following conditions: leaching temperature 180°C, time 4 hours, PO2 10 kgs/cm2, acid concentration 2.5% (vol/vol), pulp density 5%, ammonium sulphate 40 g/l. Under these conditions the iron concentration of leach liquor was 0.95 g/l. Optimization of leaching parameters was carried out by statistical design of experiments using 23 full factorial matrix. The linear and interaction co-efficients were evaluated for dissolution of metal values and also for iron concentration in leach liquors.

Jan 1, 2003

By Ian Selby

Recent offshore diamond exploration has been concentrated in the SW Joseph Bonaparte Gulf. I`IW Australia. Extensive high resolution seismic and sampling surveys have been carried out in Cambridge Gulf, offshore of the mouth of the OR River and other rivers of the region. Surface-tow boomer surveys have been correlated with sampling data from vibracores and a wide diameter (1m) airlift system, providing a geological framework for the area. Although large-scale bulk sampling has not been undertaken, there has been no reported recovery of diamonds since 1993. The geology and prospectivity of a range of potential diamond traps in high energy, fluvial and transgressive depositional settings has been assessed. Potentially diamondiferous targets include (i) a shoreline apron. (ii) fluvial/estuarine channel infills and terraces and (iii) ravinement surfaces.. Although there is evidence for a long history of fluvial development and sea level changes, the majority of the investigated traps represent the result of erosion and sedimentation during and following the last interglacial. Significant volumes of unconsolidated gravels and coarse-grained sands with occasional indurated layers are present, and are locally exposed at sea beet In place s thick successions (>5m) of fine-grained overburden overlie the coarse-grained sediments.

Jan 1, 1998

By Timothy F. McConachy

Between April 2000 and April 2002, the Commonwealth Scientific and Industrial Research Organization (CSIRO) Division of Exploration and Mining has led 6 research expeditions totalling 160 days ship time in waters of Papua New Guinea, Vanuatu, Solomon Islands, Indonesia and Australia. Five expeditions were undertaken aboard the Australian research vessel Franklin following successful competitive research proposals, and the sixth used the Indonesian vessel Baruna Jaya VIII (see Table 1). In addition, two CSIRO participants joined JOIDES Resolution for the Ocean Drilling Program Leg 193 in the Manus Basin of PNG. The major scientific objective underpinning these expeditions was to locate and study present-day seafloor and sub-seafloor hydrothermal ore-forming activity in order to develop improved methods of exploring for ancient mineral deposits on land that originally formed by similar processes. The research has been supported financially by a number of Australian-based mineral companies, by Australian international aid agencies, and by appropriation funds from CSIRO, and was conducted in collaboration with researchers from Australia, Indonesia, Portugal, New Zealand, United States of America, South Korea, and the host nations. Building upon earlier successes in the 1986-1997 PACLARK-PACMANUS programs in the Woodlark and Manus Basins of PNG, we have sought to examine a wider range of geological settings in which ancient orebodies are inferred to have formed, including both volcanic and sediment-hosted environments. We have now visited volcanic arcs, fore-arc and triple-junction related submarine volcanoes, and back arc basins associated with convergent plate margins in the SW Pacific and SE Asia, as well as conceptual Mississippi-Valley-type targets associated with warm seeps at passive margins in the Great Australian Bight (see Figure 1). Surveys ranged from northern Sulawesi via far western Bismarck volcanic arc near PNG-Indonesia border, through the eastern Manus Basin and the Tabar-Lihir-Tanga-Feni chain in PNG, the western Solomon Islands festoon, the San Cristobal arc, parts of the Vitiaz arc, to the northern and southern New Hebrides arc in the Solomons and Vanuatu.

Jan 1, 2002

By Natalia Konstantinova, Kira Mizell, James R. Hein, Georgy Cherkashov

"Ferromanganese crusts and nodules from the Amerasian basin of the Arctic Ocean are characterized by a unique composition compared to crusts formed elsewhere in the global ocean (Konstantinova et al., 2017; Hein et al., 2017). One of the most significant differences from global ocean crusts is the high detrital mineral content; mass balance calculations show that it may be as high as 35% in some samples (Hein et al., 2017).These Arctic Ocean Fe-Mn crusts also typically have three distinct megascopic layers, except for thin crusts; less commonly, four layers are noted for thick crusts. The age of initiation of Fe-Mn crust growth in the Amerasia Basin varies from 14.8 Myr to 0.7 Myr ago based on the Manheim and Lane-Bostwick (1988) Co chronometer, Be isotopes, and Th excess methods (Dausmann et al., 2015; Konstantinova et al., 2017; Hein et al., 2017).Samples and MethodsFourteen Fe-Mn crust samples recovered on Russian and U.S. research cruises were chosen for analyses based on their morphology, composition, water depth, genetic type, and location in Amerasia Basin. Seven samples from four distant dredge sites along Mendeleev Ridge and seven samples from four locations on the Chukchi Borderland are included (Fig. 1). Dredge site water depths vary from 3850 to 2100 m with the deepest samples from the Chukchi Borderland. Many of the selected samples were described in previous publications (Konstantinova et al., 2017; Hein et al., 2017)."

Jan 1, 2017

By Rolf B. Pedersen, Filipa Marques

The extension of the Mid-Atlantic Ridge north of Iceland has collectively been referred to as the Arctic Mid-Ocean Ridges (AMOR). The AMOR extends from the northern shelf of Iceland, to the Siberian shelf in the Laptev Sea, passing en route through the Norwegian- Greenland Sea, the narrow gateway of the Fram Strait, and across the Eurasia Basin. The AMOR is 4000 km long and is divided into six super segments: 1) the Kolbeinsey Ridge, 2) the Mohns Ridge, 3) the Knipovich Ridge, 4) the Molloy Ridge, 5) the Lena Trough, and 6) the Gakkel Ridge. After continental rifting at 60-50 million years ago, around 2.5 million km2 of oceanic seafloor has formed by seafloor spreading - resulting in the formation of the Norwegian- Greenland Sea and the Eurasian Basin. This northernmost part of the global ridge system is anomalous in several ways: The seafloor spreading takes place at an ultraslow rate (less than 2 cm/y) with spreading rates decreasing northward to around 1 cm/y at the Gakkel Ridge - which is the most slow-spreading ridge on Earth. As a result, the volcanic activity along the northern part of the AMOR is low, the oceanic crust is unusually thin (around 3,5 km at the Knipovich Ridge, Kandilarov et al.2010), and the rift valley is deep (average water depth > 3 km). In the southern part of the AMOR, the ridge system is affected by the Icelandic plume and a hot spot below Jan Mayen. The ridge-plume interaction results in higher volcanic productivity, unusually thick oceanic crust (9-11 km, Kandilarov et al. 2012) and shallow ridge segments (1500-100 m). The AMOR also display contrasting spreading regimes, whereas some super segments are dominated by orthogonal spreading (Kolbeinsey and Gakkel Ridge) others are characterized by highly oblique spreading (Mohns and Knipovich ridges). Some ridge segment displays asymmetric spreading, like the Mohns Ridge where core complexes preferentially form along the northwestern flank. Together these variations in ridge characteristics results in large diversity of hydrothermal systems and associated mineral deposits.

Jan 1, 2018

By Alexander Malahoff

Six active Kermadec arc submarine volcanoes located between 34°S and 36°30’S were mapped and sampled by an interdisciplinary inter-institutional research team between April and July 2005 using submersibles Pisces V and Pisces IV aboard the mother ship the R/V Ka’imikai-o-Kanaloa. The purpose of the expedition was to study the relationship between hydrothermal activity, formation of hydrothermal mineral deposits, and the biodiversity of life associated with the hydrothermal vents. Of the volcanoes examined, all showed evidence of hydrothermal activity, including metal-rich plumes and helium anomalies. Only two of the volcanoes, namely Brothers and Clark, showed chimneys and surficial polymetallic sulfide deposition. Hydrothermal venting at a water depth of approximately 1,650 meters near the base of the northwest caldera wall of Brothers volcano has produced a field of chimneys, some of them seven metres high and discharging black smoker venting. Temperatures up to 300°C were measured from the active vents. Clark volcano has a double cone summit at a water depth of 875 meters. The shallowest cone has a near-summit hydrothermal vent field with five-meter tall venting chimneys with smaller structures around the periphery.

Aug 24, 2006

By Fernando J. A. S. Barriga

"Recent concerns over the availability of many mineral raw materials, and newly available technological developments, produced renewed interest in deep-sea mining. However, environmental concerns, with variable degrees of justification, are raising opposition to the concept. The forecast for the behavior of consumption versus availability of many raw materials, nearly all critical metals, arguably show that consumption will grow much faster than resource discovery onshore. Finding new sources of raw materials seems inescapable. The deep seafloor stands out as the only likely candidate.Sea Floor Mining and the EcosystemMarine mining has already started, decades ago, for diamonds, currently up to depths near 400m. Although the industry recognizes there is a footprint, it considers the footprint quite minor, because the area mined is small: in Namibia, where offshore diamond mining is now 70% of the country’s total, only 3% of the concession of 3,700 sq miles (9600km2) have been mined. As plans to mine deep-sea massive sulphide deposits and polymetallic nodules progress, the environmental concerns grow. Some of these concerns are as follows:?The deep-sea ecosystems are composed of long-lived species, with low rates of reproduction. The environment may not recover from mining on a human time scale;"

Jan 1, 2017

By Marlene Olivares Cruz

The particles that make up the deep-sea sediments have two main sources: 1) those that are created in situ from dissolved components and 2) those that are washed into the ocean in solid phases from the continents, atmosphere, space and interior of the Earth. Many particles as they sink through the water column reaches the seabed and are known as pelagic sediments with terrigenous, biogenic, authigenic, and cosmogenic components. Among the minerals found in the terrigenous fraction of pelagic sediments are quartz, clay minerals, feldspar, micas, ferromagnesians, and the biogenic fraction with remains of siliceous organisms, such as, radiolarian and diatoms. The chemical nature of marine sediments is controlled by the contribution of particulate matter derived from various sources with varying compositions for the fixing of elements during deposition and the compositional changes carried out within the sediments during diagenesis. In the last decade there have been several studies on the mineralogical composition of seabed sediments, suspended particulate materials and cores, together with paleontological and geochemical data are used for paleoclimatic and paleoenvironmental reconstructions, analyze changes in sea level, stratigraphic correlations and identify past and present sources of sediment and terrigenous input pathways and to describe the current ocean mass (Martins et al., 2001, Oliveira et al., 1998). There is also a scientific and economic interest in the authigenic fraction of pelagic sediments formed from other materials for polymetallic nodules. The study of sediments associated with polymetallic nodules helps to know the genesis, evolution and occurrence of these deposits (De Koven et al., 2003, Dubinin et al., 2008).

Jan 1, 2011

By Wiebe Boomsma

This is a framework study financed by the Maritime Innovation Programme of The Netherlands and several institutions actively involved in the research of the environmental impact of deep sea mining; IHC Mining, MTI Holland, Delft University of Technology, NIOZ, IMARES, Boskalis Westminster, AllSeas and TNO. For this framework study the following mining activities have been identified to be relevant to assess the ecological impact of a deep sea mining operation: a) excavation, b) tailings return, c) vertical transport, d) vessel operations, e) ore transport and f) general operations. For this paper, only one mining activity has been selected as an example for the assessment of ecological effects. This is one of the main activities introduced by the new technology envisaged for developing deep sea mining: tailings return.

Sep 14, 2011

By Karsten Hagenah, Tor Jensen, Jens Laugesen, Øyvind Fjukmoen, Lucy Brooks

This paper discusses operational environmental threshold levels for exploitation of mineral resources in the deep sea. Such criteria are needed to be able to monitor and control deep sea mining with respect to the stringent environmental requirements that are needed. It is recommended to use existing environmental threshold levels for comparable underwater activities. Fields of application are mainly but not exclusively seabed mining operation activities under the governance of the International Seabed Authority (ISA). The threshold levels and limits mentioned in this paper are proposed recommendations based on other activities than seabed mining but are a proven and accepted approach in other maritime industry activities. An example of such other activities with proven and accepted environmental threshold levels are Oil & Gas exploitation activities in the sea. Background The first exploitation of mineral resources in international waters is coming closer. Presently regulations for exploitation for mineral resources in the Area are being developed by the International Seabed Authority (ISA). The ISA regulations will contain the framework related to environmental monitoring of exploitation. However, the regulations will not contain operational environmental threshold levels for the Contractor.

Jan 1, 2018

By K. Vanstaen, K. M. Cooper, S. Ware, S. L. Boyd

Remediation and restoration of offshore marine habitats is a relatively new concept with attempts in European regions largely being instigated by requirements of various strategic directives including Article 2 of the Habitats Directive (1992), the EC Water Framework Directive (2000, Article 2 of the OSPAR Convention (1992) and the developing European Marine Strategy Directive. A field experiment to establish the practicality of various options for rehabilitating the seabed on the cessation of dredging has been successfully set up. The purpose of this experiment is to investigate the practicality and effectiveness of gravel seeding as a potential restorative method that can be applied at marine aggregate extraction sites following cessation of dredging. Zone 2, within Area 408 (offshore Humber) was chosen as the experimental site as there is some evidence for persistence of sand which may have resulted from screening operations at this site.

By Peter E. Halbach, Andreas Jahn

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

Jan 1, 2017

By Mayumy Amparo Cabrera-Ramírez

Polymetallic nodules are a widespread resource in the Pacific Ocean, particularly in the areas of Clarion-Clipperton (Cronan, 2000). The most abundant mineral phases are forme d by iron and manganese oxides, with minor elements such as nickel, copper, cobalt, molybdenum and rare earths elements (Cronan, 1977; Cronan and Moorby, 1981; Iyer and Sharma, 1990; Mangini et al. 1990; Banerjee et al. 1991). In the Clarion-Clipperton Zone (CCZ), several authors mention that there are three main mineral species of manganese oxides, which have been recognized and which are associated with different processes of formation: todorokita (Mn2+, Ca, Mg) Mn3 4+ O7. H2), vernadite dMnO and birnessite enriched in Fe and (Na, Ca) 0.5 (Mn4+, Mn3+) 2O4. 1.5 H2O. In nodules of hydrothermal origin have been found todorokite, birnessite, vernadite, goethite and pyrolusite. Although there are many oxides and hydroxides of manganese and iron in amorphous and microcrystalline phases that make up the bulk of the nodule (Frondel et al. 1960; Cronan 1977; Dymond 1981; Calvert and Piper, 1984; Aplin and Cronan, 1985; Martin and Lallier, 1993; Achurra et al. 2009), identifying specific mineral phases is difficult due to the intergrowth of different phases and associated detrital material.

Sep 14, 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 Mayumy Amparo Cabrera-Ramírez

Polymetallic nodules are a widespread resource in the Pacific Ocean, particularly in the areas of Clarion-Clipperton (Cronan, 2000). The most abundant mineral phases are formed by iron and manganese oxides, with minor elements such as nickel, copper, cobalt, molybdenum and rare earths elements (Cronan, 1977; Cronan and Moorby, 1981; Iyer and Sharma, 1990; Mangini et al. 1990; Banerjee et al. 1991). In the Clarion-Clipperton Zone (CCZ), several authors mention that there are three main mineral species of manganese oxides, which have been recognized and which are associated with different processes of formation: todorokita (Mn2+, Ca, Mg) Mn34+ O7. H2), vernadite dMnO and birnessite enriched in Fe and (Na, Ca) 0.5 (Mn4+, Mn3+) 2O4. 1.5 H2O. In nodules of hydrothermal origin have been found todorokite, birnessite, vernadite, goethite and pyrolusite. Although there are many oxides and hydroxides of manganese and iron in amorphous and microcrystalline phases that make up the bulk of the nodule (Frondel et al. 1960; Cronan 1977; Dymond 1981; Calvert and Piper, 1984; Aplin and Cronan, 1985; Martin and Lallier, 1993; Achurra et al. 2009), identifying specific mineral phases is difficult due to the intergrowth of different phases and associated detrital material.

Jan 1, 2011

By Derek V. Ellis

This article is a summary, with documentation and references, of recent global developments in identifying environmental issues affecting the marine mining industry. It is recognised that marine mining for various products occurs at various depths from shallow water (e.g. aggregate and diamond mining) potentially to great depths (e.g. metalliferous muds, and manganese crusts and nodules). Nevertheless there are environmental issues in common, even though the options for resolutions will vary greatly. The point of this review is to identify the issues, so that where site-specific resolutions are considered, it is possible to draw on experience with the issues elsewhere. Related mining issues, e.g. tailings effluent quality, orebody geochemistry, are mentioned where relevant but are not detailed in this article, although obviously they are a part of there solutions to the environmental issues. The environmental issues and their resolutions are important - on the basis of the ethic of not creating more impact than is inevitable, and the long-term financial and social costs at a mine-site of not getting the resolutions right.

Jan 1, 2000