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By A. Fakhimi

The effect of porosity on mechanical behavior of rock has been studied in the past using both experimental and numerical techniques. One important aspect of this study that has not received much attention is the role of void size and distribution on the mechanical behavior of rock. In this study, the CA2 computer program that is a hybrid discrete-finite element program for two-dimensional simulation of geomaterials is used. Numerical specimens with different macro-void sizes are loaded uniaxially. The Young?s modulus, Poisson?s ratio, uniaxial strength and crack initiation stress are studied. The numerical results are compared with the database of experimental tests on Plaster of Paris specimens containing Styrofoam spheres with different void sizes and porosities. It is shown that the macro void spatial distribution is partly responsible for the scatter of the experimental data. It is also shown that not-only the porosity but also the pore size can affect the deformability, crack initiation stress and rock strength.

May 1, 2009

By R. C. Bryce

"Accident prevention has been an on-going priorty for five years. In 1987, adherence to the ILCI five-star rating loss control program was started, and a first star was awarded. Extensive training programs have been undertaken to establish standard procedures and upgrade employee skills. Due to its location, Selbaie owns and rents housing in the town of Joutel and contracts a busing service to and from the mine. Employees from other areas are lodged in dormitories and fed in the site dining room. Accounting and warehousing services are carried out in efficient fashion. Employee relations are structured to provide prompt resolution of complaints and differences. No lost time due to industrial relations differences has been encountered during the history of the mine.Safety and Loss ControlAll mines are concerned and occupied with a wide range of activities to ensure the safety of its employees. Selbaie is no exception. Programs to achieve success in safety and loss control have been implanted since the start of construction and development at Selbaie and have followed three interesting stages of evolution."

Jan 1, 1990

By P. Fleming, W. Pascheto

"Rod mills processing nickel and copper ore experienced recurring failures of liner bolts. In some cases failures became very frequent, requiring constant mill intervention and consequently impacting process stability and operating costs. Investigation related to the causes of bolt failures involved a multidisciplinary approach with the participation of engineering, maintenance and operation. It included the determination of bolt failure mechanisms as well as the assessment of mechanical properties, fabrication quality and handling and installation procedures. In addition, other parameters affecting bolt performance such as mill and liner design, operating parameters and maintenance practices were studied. This paper reports the failure investigation results and proposed solutions for failure prevention. INTRODUCTIONOccasional liner bolt failures are common in rod mills. However, chronic bolt failures developed in rod mills processing nickel and copper ore caused frequent shutdowns for bolt replacement to an extent that affected process stability. At first, it was thought that the cause of recurring failures was related to bolt quality. The operation then submitted several failed bolts to failure analysis. However, it became apparent that bolt quality was unlikely to be the main cause of failures. The determination of root cause (s) then became more complex, requiring a multi-disciplinary approach to failure investigation, requiring the assessment of bolt installation methods, mill design, operating conditions and maintenance practices. The results of the metallurgical failure analysis and investigation of other possible causes of failures are reported here."

Jan 1, 2016

By G. de Alva

"Industrias Peñoles S.A. de C.V. (Peñoles) is a private enterprise and is the main silver producer in Mexico. Peñoles is a Mexican Company, and since 1887 ranks as one of Mexico's main natural resources industrial groups.Peñoles Mining Group includes six operating Companies producing mainly gold, silver, lead, and zinc. All mines are underground operations, and the ore is milled in ten concentrator plants near the mine sites. Plant throughputs range from 150,000 to 810,000 tonnes per year.This paper gives a general view of the Peñoles Mining Group, their type of deposits, mining methods, and mineral processing work practices.The paper also discusses some of Peñoles work philosophies and measures being adopted to become more competitive. Due to the small size of the deposits, the mining methods used and size of the concentrator plants are somehow different to those typically seen in large deposits. This could make the paper more interesting.IntroductionIndustrias Peñoles S.A. de C.V. (Peñoles) since 1887 ranks as one of Mexico's main natural resources industrial groups; initially in the mining field and afterwards in the metallurgical, chemicals and refractories areas.Peñoles is integrated as follows: a Mining Group; an Exploration, Engineering and Construction Groups; the Metals Group; and the Chemicals Group.Peñoles is a Mexican Corporation devoted to the location, extraction, industrialization and commercialization of natural resources under its control, performed in an efficient and responsible manner for the benefit of its shareholders, employees and the communities where it operates, through blending and managing a portfolio of sound highly profitable business, offering products and services with integral quality; leaders in their respective fields or with an outstanding presence; technologically and operatively effective, with ecological consciousness and international projection, and an image of prestigious integrity."

Jan 1, 1996

By T. Krumins, L. Zunti, R. Frischmuth

Titanium and titanium alloys are commonly selected for pressure oxidation autoclave vent piping and pressure control valve components, as well as autoclave internals, in high-temperature operations. In a vent application, titanium ignition risk is reduced by limiting oxygen concentration, and preventing high gas velocity gas impingement on surfaces. Oxygen concentration is dependent on the autoclave pressure and temperature conditions and therefore titanium ignition risk is dependent on standard operating procedures, and process control interlocks and permissive conditions. It is not uncommon for standard controls to be deficient during atypical operating conditions, or for operations to deviate from the operating procedures, increasing the potential for titanium ignition incident. Titanium ignition risk caused by elevated oxygen concentration in autoclave vent systems can be reduced with the introduction of an online autoclave overpressure calculation and the configuration of associated interlocks and permissive conditions.

Jan 1, 2014

By Paul G. Dunn

Safe rapid drift development results principally in reducing exposure of underground workers to the working face. This reduction in exposure is not achieved until either the rock walls have been suitably scaled or sufficient support has been put in place. Rapid drifting enables quicker access to orebodies (increasing returns), higher production rates and a resultant lower cost of mining. The Mining Innovation, Rehabilitation And Applied Research Corporation (MIRARCO) has been developing technology and a methodology for safe rapid drift development within the underground metalliferous mining industry. In terms of rock scaling for underground metal mines, there is still considerable use of manual and mechanical impact rock scaling techniques. Two main issues result from this approach. The first is that in highly stressed or highly fractured ground, a decision has to be made as to when sufficient scaling has taken place. This is not always easy to do and hence operator judgment is a crucial element in this approach. During a baseline study of current rock scaling practices, a wide range of scaling practices were observed within five different underground mining operations; this demonstrates the difficulty inherent in the rock scaling quality decision making process. The second issue is related to the exposure of workers to freshly created rock surfaces. In manual scaling techniques this is unavoidable and despite the best scaling practices, accidents still occur. In an attempt to provide an alternative scaling technology, MIRARCO has been investigating highpressure water jet scaling for removing loose rock as part of the drift advance process. This technology not only provides a means by which scaling practices can be engineered (remove the loose material you want to in a given rock mass condition), it is also quicker and easily automated. Automating the scaling process removes workers from exposure to freshly created rock surfaces and also enhances the application of spray-on liners through improved adhesion of these support types to the rock surface. This paper describes the water jet scaling technology research and methodology for safe rapid drifting within the underground metaliferous mining industry and highlights the key issues and major drivers behind their continued development at MIRARCO.

May 1, 2004

By Jianglan Duan, Steve L. Cockcroft, Andre B. Phillion, Carl Reilly, Daan M. Maijer

"In the aluminum alloy wheel casting process, careful design of the cooling system in the die and its operation (cooling channel timing) are critical to achieve quality and productivity goals. The problem is challenging owing to the cyclic nature of the process and the relatively large thermal mass of the die in comparison to the wheel. For a given die geometry, a set of constraints have been defined to ensure directional solidification and an objective function, based on cooling rate during solidification, has been defined to reach a target secondary dendrite arm spacing. The methodology presented in this study employs the commercial finite element package, ABAQUSTM, and an optimization module based on the open source library, Scipy. The developed methodology has been applied to a series of geometries and cooling system configurations, including a 2-D axisymmetric wheel and die assembly generated from a prototype die. Preliminary testing has shown that careful selection of the objective and constraint functions have made it possible to reach desired solidification pattern.TM- Dassault Systèmes Corp."

Jan 1, 2014

By Emilie Williams

The Mouska Mine uses primarily shrinkage mining to extract the narrow veins that contain its mineralization. Mining is currently occurring on levels 12 to 14, reaching depths of 800 m below surface. Although the mine is not considered ?deep?, no backfill is available to fill empty stopes and certain areas remain open for over 500 m in height. As only narrow sill pillars remain to separate the levels, a highstress environment is created. Seismic activity was first observed when mining reached Level 11 (600 m deep) and has steadily increased since then. Seismic activity is associated with the highly-stressed sill and rib pillars; no geological structures have demonstrated significant seismic potential to date. In response to this increase in activity, pillar dimensions have been increased with depth and dynamic ground support has been installed. Seismic and pressure monitoring have been implemented, among other types of instrumentation. The following paper further describes the challenges associated with using conventional methods in the high-stress environment typical of the Canadian Shield, as well as several solutions implemented to mitigate these risks.

Feb 1, 2008

By H. Wilhelm, W. I. van Drunick

The Anglogold Ashanti (AGA) Navachab single stage SAG mill has provided an excellent setting for incremental optimization. Over the past decades, several interventions have resulted in marked improvements in specific performance; including steel ball scat removal, re-design of the mill lifters, replacement the pebble crusher and cyclone cluster, as well as the use of a vibrating screen in place of a discharge trommel. Recent initiatives now include an operating fine DMS circuit, studies on pre-crushing of the ROM feed and also fine-screening as an alternative to hydrocyclone classification. The current optimized state of the Navachab mill allows it to operate at approximately 20% higher efficiency when compared to mills of similar shell dimensions in gold mining, treating similar ore. This paper describes the systematic improvement of the SAG circuit to its current state.

Jan 1, 2012

By J. M. Ortiz, J. Haas, W. Kracht, G. Pamparana

This work explores the effect of ore hardness variability on the design of a solar photovoltaic system with battery storage and grid backup, to operate a semi-autogenous grinding mill (SAG). First, a case of two synthetic ore populations was studied, without any consideration of spatial distribution. The mean and variance of the ore hardness (measured in specific energy consumption) of both populations were subjected to a sensitivity analysis. The operation was evaluated with one and two stockpiles. The latter allows classifying according to ore hardness to adapt the SAG energy consumption to the solar cycle. The results show that using two stockpiles allows achieving a larger autonomy (i.e., fewer energy imports) at lower total costs, especially when the difference of mean hardness between the two populations is large. The difference in variance (between the two populations) has a smaller impact on the design recommendations. Second, a case study was performed considering the spatial distribution of geometallurgical units. Two cases were considered: (a) brownfield, when there is historical information of the actual variability of the ore hardness; and (b) greenfield, when the system design relies mainly on geometallurgical modeling. Brownfield and greenfield planning result in similar sizing recommendations of the solar power plant if precise drill cores are available. In this case, geometallurgical modeling is an effective tool for forecasting the energy demand necessary for designing the power plant. INTRODUCTION Solar energy can help make mining more sustainable (Moreno-Leiva et al., 2017). With falling battery costs, an autonomous solar supply is soon to become an economical alternative in many parts of the world, even in the presence of a larger power grid (Child et al., 2017). Although this, places with high solar radiation such as the Atacama Desert in Chile, nowadays show a large potential of incorporating solar energy as a supply of energy. Many of the Chilean copper mines are in this zone making it interesting to study their compatibility and potential of integrating this renewable source to their operation. The power demand in a copper mineral processing plant is determined by the main power loads in grinding and flotation, with grinding typically the largest power consumer, especially the semi-autogenous grinding (SAG) mills (Wei and Craig, 2009). In Chile, it corresponds on average the 50% of the electrical energy consumption (COCHILCO, 2013). Solar energy production is determined by the irradiance perceived into the solar photovoltaic (PV) panels (which varies through the geographic location) and several other climatic parameters such as the current season, humidity, temperature, altitude, and others (Molina et al., 2017). Also, solar energy is only generated during the sun hours, getting to a maximum generation at a certain peak hour during midday, and finally dropping to zero during the night. This shows a cyclic parabolic profile as shown in Figure 1. Due to the SAG mill operated continuously, the power supply always must be available. During the night, to continue supplying the energy, it is necessary to complement the solar power generation with a battery energy storage system (BESS), which will act as a power backup and a buffer. For the optimal sizing of this PV- BESS system, information of the demand profile is needed (Pamparana et al., 2017). In the case of the SAG mill operation, the resulting demand relates to the ore-hardness for a specific throughput and grind size (Morrell, 2004). Therefore, for a given throughput and target grind size, a harder ore would require more power, and variable hardness results in more variable demand and a subsequent need for larger energy storage (Bueno et al., 2015). Due to the ore-hardness variability and the operation of the mill, the power demand profile in inherently variable.

Jan 1, 2019

By William C. Boggis

EKATI? Diamond mine is located 300km northwest of Yellowknife and 200 km south of the Arctic Circle in the Northwest Territories of Canada. The site is a remote tundra area with continuous permafrost and is in the Canadian Shield. EKATI? is the first diamond mine in Canada and is operated by BHP Diamonds Inc., which is a part of BHP Minerals. BHP Diamonds Inc. is an incorporated company based in Vancouver, BC. The mine is a joint venture of BHP Diamonds Inc. (51%), Dia Met Minerals Ltd. (29%), Charles E. Fipke (10%) and Dr. Stewart L. Blusson (10%). The mining area lies within the 10,960 ha land leases held by the joint venture. The total claim block covers 344,000 ha. To date over 136 kimberlite structures have been identified within the claim. Five of these provide the basis for the present mine plan with three others identified for future inclusion. At full capacity the mine will produce 4.5 million carats per year, approximately 4 % of world production and employ approximately 600 people, with over 33% being Aboriginal from the Northwest Territories.

May 1, 2001

"Chairman - To start this discussion off, I wonder if Mr. Dave Livingstone or Mr. Jeffrey of Granisle Copper would give a description of the crushing plant at Granisle since it is somewhat different from the usual plant, W. N. Jeffrey - Granisle Copper The main difference between the Granisle crushing plant and many others is the Livingstone method of putting the screens under the crushers instead of above them. This method allows a more compact arrangement and eliminates the heavy superstructure required to take care of the screen vibration when the screens are mounted above the crushers. There is a small surge bin above the tertiary crusher which takes care of the variation in circulating loads.All three crushers are gyratory crushers. There is no grizzly ahead of the primary crusher but the fines are removed from the primary crusher discharge at the first screen and sent directly to the fine ore bins. E, Thornton - Sullivan GroupDo you have any coarse ore storage outside?w. N. Jeffrey - Yes, there is about 6000 tons live storage, We have very little trouble with freezing even though it is open storage.E. Thornton - Sullivan GroupDoes rain cause any problem?w. N. Jeffrey - It sometime creates a problem because the storage area is on a slope. It is mainly a problem of keeping the drainage ditches open.Question – What is the size of the primary gyratory crusher and how does it work on run of mine size materials, in other words, do you have a problem with oversize material and how do you handle the oversize rock?w. N. Jeffrey - The primary gyratory is a 42 x 65 with a nominal open side setting of 61'. We do at times get a run of oversize material. For anything too large for the crusher to handle, we use what is known as the Esco hook, which is a type of grapple used to remove oversize rocks.The disadvantage with this equipment is that the crane is too slow. I am sure there must be better arrangements than the one we have,"

Jan 1, 1971

By Tom Setterfield

Monster Copper Resources ?Junior focused solely on IOCG deposits ?Founded by ex-WMC geoscientists ?Properties in Brazil, Wernecke Breccias (Yukon), Central Mineral Belt and Nova Scotia Nova Scotia ?JV with Wallbridge Mining Company ?Ongoing Story ?Presented as a case study in generation and implementation of IOCG exploration program

Apr 1, 2005

By T. Gonzales, S. Thakurdin

The conducting of risk reviews is an essential activity in ensuring safe operating conditions, both during project design phases and for existing facilities. The following paper presents a structured approach to the conducting of risk reviews for existing operations, including descriptions of supporting documentation and guidelines for on-site review activities. The conducting of regular site risk reviews and safety audits is crucial in ensuring the continued safe operation of existing facilities, particularly in the copper industry where numerous processes and unit operations can present catastrophic risks, both in terms of loss of life and financial liability. The structured approach presented aims to provide a logical and comprehensive analysis of risks to align safety-related facilities and procedures with current industry best practice and ensure consistency across multiple client operations. INTRODUCTION The production of copper, whether by pyrometallurgical or hydrometallurgical process routes, carries significant inherent safety risks. Production volumes are relatively large, often requiring complex processing routes, multiple production trains and a variety of supporting ancillary facilities. Furthermore, considering the relatively large size of ore reserves, copper production plants can have operational lives well beyond the typical design duration of 20 years. In this context, the conducting of regular risk reviews is essential in ensuring safe operating conditions and aligning facilities with current industry best practices. Risk reviews and safety audits can take various forms and have various areas of focus. The methodologies and approaches described below relate specifically to catastrophic risks, defined broadly as risks that carry the potential for multiple fatalities and significant financial losses. Focus is given to existing facilities and does not consider the risk-related activities such as hazard and operability (HAZOP) studies conducted during plant design. The structured approach presented aims to provide a guide for effective site- based audits and a logical analysis of risks identified. RISK CLASSIFICATION Table 1 provides a typical summary of the classification of risk types and the associated consequence categories and descriptions. It illustrates the descriptions of a catastrophic risk in terms of the broad categories of Health & Safety, Environment, Financial, Image & Reputation and Legal & Compliance. In terms of the Financial category, numeric costs ranges are often prescribed depending on the financial characteristics of the specific operation and the associated parent company.

Jan 1, 2019

By João Felipe Costa, Jair Carlos Koppe, André C. Zingano

Abstract - Traditional mine planning based on block models built with interpolation techniques such as kriging does not take into account the uncertainty associated with the estimates. These models are inadequate for short-range mine planning. In contrast, conditionally simulated models reproduce the actual variability (histogram) and spatial continuity (variogram) of the attributes of interest. Conditional simulation can be used to address the problem of measuring the uncertainty associated with an estimate. This paper outlines how the sequential Gaussian conditional simulation algorithm can be used to assess uncertainty of grade estimates and also illustrates how simulated models can be incorporated into mine planning and scheduling. A case study demonstrates the efficiency of the method in assessing risk associated with geological and engineering variables.

Jan 1, 2000

By Brian Putland, Fred Kock, Leigh Siddall

Single stage semi-autogenous / autogenous (S/AG) milling has become a common design for a variety of ore types with the advantages of being comparatively low capital cost and flexible for future expansion. The single stage SAG/AG milling option is ideal for starter projects with significant exploration and expansion potential. Currently a number of the largest SAG mills designed are installed in single stage configuration. This paper discusses the challenges associated with the process design of single stage SAG/AG milling circuits, the design flexibility required to ensure a robust circuit and the operating techniques adopted at successful installations.

Jan 1, 2012

By Sobczyk

The article will present a comparison of classifications of resources according to the JORC Code System with Polish classification, basing on system used in Eastern Europe. The differences between these classifications are significant. The information about mineral resources in Poland is not comparable to the main international system of reporting reserves like JORC, SAMREC, and PERC. Although comparisons between these systems are used, the transfer of particular categories of resources from the Polish system into a JORC category is not simple. Basing on the examples of privatization of Polish coal companies through initial public offering on the Warsaw Stock Exchange, the current practices providing guidelines how to convert resources from the Polish classification to the JORC system are described. Such independent assessment of resources is necessary for development of Mineral Expert?s Report (MER or CPR) which is an integral attachment to the prospectus.

Aug 1, 2013

By D. R. Griffiths

"Oxidation of pyrrhotite prcxiuces sulphuric acid which in turn leaches out heavy metals, resulting in acidic contaminated seepages. The establishment of a marsh on top of the pyrrhotite would result in an anaerobic sediment, which should prevent further oxidation of the pyrrhotite. Initial data indicates that concentrations of sulphates and heavy metals in the seepage water are greatly reduced. Further hydrogeological studies are required however, to determine if metal and acidic loadings to the environment have increased.L'oxidation du sulfure de fer produit de l'acide sulfurique qui a son tour attaque les métaux ayant pour resultat une contamination d'acide et de métal des eaux d'infiltration. L'etablissement d'une couverture faite de boue et de vase au-dessus du depot du sulfure de fer réduit les effets de l'oxidation.Les données initiales indiquent que les concentrations de souffre et de métaux dans les eaux d'infiltration sent grandernent réduites.Des études plus poussées sent nécessaires pour déterminer si les quantités de souffre et de métaux dans les eaux d'infiltration ont augmentées.INTRODUCITONPyrrhotite tailings are readily oxidized through a combination of precipitation and atmospheric oxygen causing acidification of the unsaturated zone above the water table. This reaction is usually catalyzed by the bacteria, Thiobacillus ferooxidans. As the pH decreases, heavy metals become more soluble resulting in contaminated seepages to ground and surface waters.By creating a marshland on top of the pyrrhotite, an anaerobic intermediate layer should form between the organic covering and the tailings, preventing the oxidation process from progressing.In September 1986, Falconbridge Limited implemented a tailing reclamation project that involved creating a marshland on top of pyrrhotite tailings. The following paper will discuss and illustrate the preliminary results obtained during the sampling period of May to September 1987."

Jan 1, 1988

By Yongteng Dong, John P. Quinn, Bradford Wesstrom, Guikuan Yue

With increasingly low-grade copper ores being mined, it is difficult to handle growing concentrations of As, Sb, Bi and/or Fe in the whole flowsheet, especially during copper electrorefining. To better elucidate the effects of those impurities on the quality of cathode deposit and/or current efficiency, a detailed speciation study of the electrolyte under industrial conditions is required to quantitatively describe their distribution in the solution, thereby facilitating their effective control and removal. In the present study, a thermodynamic model of complicated iron-arsenic-copper-sulfuric acid electrolyte under industrial conditions was developed. The main species of those elements involved in the electrolyte were first identified, and their thermodynamic data were collected and critically assessed. Those data were then used to estimate the activity coefficients of species, and to calculate the equilibrium constants from 25°C to 70°C. The developed model provides a mathematical tool that is capable of quantifying the concentrations of free ions and complexes in terms of temperature and solution composition. Finally, oxidation-reduction potential measurements were employed to validate the model. INTRODUCTION In copper electrorefining, impurities like arsenic, antimony, bismuth and/or iron can partially dissolve in the electrolyte and accumulate gradually, and eventually cause problems such as bad cathode deposit (co-deposition with copper or mechanical inclusion from the floating slime), lower current efficiency, etc., which eventually increases the operating costs. The presence of impurities may substantially reduce properties of copper products such as conductivity, corrosion resistance, mechanical properties, and leads to more energy consumption (Schlesinger et al., 2011; Jafari et al., 2017). To remove these impurities, various methods have already been proposed and applied in industrial copper production, such as solvent extraction, ion exchange, chemical precipitation, absorption by activated carbon, etc. (Cunningham et al., 1997; Navarro et al., 1999; Toyabe et al., 1987). In addition, adding reducing agents such as sulfur dioxide and trivalent arsenic could also precipitate arsenic, antimony and bismuth from copper electrolyte, by changing the distribution of impurities with various valence (Braun et al., 1976; Xiao et al., 2007). The disadvantages of those methods include high energy consumption, serious contamination, lower selectivity and efficiency, and so on.

Jan 1, 2019

By H. E. (Buzz) Neal

"Abstract - The Labrador Trough contains world-class iron deposits which have been mined since 1954. The direct shipping of Knob Lake ores were mined at Schefferville from 1954 to 1982. Concentrate production began in 1961 in the southwest end of the Trough, with three mines currently producing concentrate and pellets at a rate of 35 Mt per year. West and north of Schefferville, several billion tonnes of taconite have been outlined in fine-grained, cherty magnetite iron formation. Several deposits of highly metamorphosed magnetite-specularite iron formation are located west of Ungava Bay. Numerous studies have shown that this medium- to fine-grained iron formation can be beneficated to 66% to 68% iron. In the area from Wabush Lake to Mont-Wright, a medium- to coarse-grained friable specularite-quartz iron formation is repeated by folding to form several large deposits. In this area, three mining operations are located with reserves and resources in the order of 5 billion tonnes.The iron deposits occur within iron formation in sediments in the extensive Proterozoic geosyncline called the Labrador Trough. Several facies of iron formation within the Sokoman Formation reflect variations in chemical composition and depositional conditions. The correlation between the mineralogy and textures is discussed to illustrate the development of different types of iron ores. This band extends for about 1100 km southeast of Ungava Bay through both Quebec and Labrador. Further south, it turns southwest past the Wabush and Mont-Wright areas to within 300 km of the St. Lawrence River. The iron formation is essentially folded and faulted along most of its length. The degree of metamorphism is variable, ranging from intense in the northern and southern portions to greenschist facies in the central portion.The stratigraphy, structure and mineralogy of the producing mines are described along with the history of discoveries. Geological input is required to achieve the strict specifications of the international iron ore market."

Jan 1, 2000