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By W. Nazarewicz

The introduction of continuous papermaking in the early 1800's was the beginning of the industry as we know it today. Since that time, the majority of the paper produced has employed an acid process. However, in the mid 1960?s, European producers began a transition to an alkaline papermaking process. Early European mill conversions to alkaline papermaking begun in the 601s, accelerated during the 1970's influenced by the dramatically higher cost for OPEC energy as well as the high cost of fiber and imported filler clay.

Jan 1, 1986

By L. B. Phelps

This paper focuses on the use of an integrated mine planing software package entitled "REMINE" which was constructed to provide a project evaluation tool for analysis of remining projects. Coal remining constitutes the affecting of sites which have had a past history of mining and have a pre-existing pollutional discharge. Such sites require a Best Professional Judgement (BPJ) analysis. The program was written to provide such an analysis with flexibility in the mine plans which can be analyzed. The process required for a BPJ analysis will be detailed and mine plan simulation performed to demonstrate the analysis.

Jan 1, 1990

By Glenn H. Damon

Concern about environmental pollution goes back many centuries, but until recently most efforts to control it have been perfunctory and spasmodic, aimed largely at coal smoke and other visible pollutants. Air pollution is to a large degree a byproduct of our economic development, and scientific knowledge of the causes and character of such pollution is more extensive than the technology to handle the waste byproducts of our industrial civilization. The removal of all constituents foreign to the air from the effluents produced by an industrialized society is obviously impractical at this time. There is widespread difference of opinion regarding acceptable ambient air concentration levels for the Various pollutants produced by combustion processes, but there is basic agreement that the pollution of the atmosphere must be controlled and eventually reduced. The magnitude of the air pollution problem has been increasing rapidly because our expanding economy calls for an ever-increasing consumption of energy, and fossil fuels are a principal source of energy. For example, the consumption of electricity has been increasing at an average annual rate of approximately 8 percent over the last 10 or 1.5 years. Table 1 shows the estimated emission of the principal pollutants into the atmosphere in 1966. The approximately 90 million automobiles, trucks, and buses on American highways contribute the largest proportion of pollutants to the atmosphere, but that fact does not alter the growing problems of the coal industry. You will note that sulfur oxides, particulates, and nitrogen oxides are all products of the combustion of coal. Of these air contaminants, sulfur oxides are now receiving major emphasis in terms of research to develop effective means for control, Table 2 shows that the combustion of coal produces approximately 60 percent of the sulfur oxides discharged to the atmosphere. While the utilization of coal is the principal source of particulate matter, this is not considered as serious a problem as it was in the early part of the century because of technological developments that have produced sound methods for the removal of particulates from waste gas streams.

Jan 1, 1968

By John C. Morrisey, Harold M. Ray

With full production from the Casteel Mine in 1987 The Doe Run Company, a wholly owned subsidiary of the Fluor Corporation, encountered a significant increase of copper and iron to the Viburnum Mill. This major change of the lead, zinc, and copper metal ratios in the ore created circuit problems which adversely affected concentrate quality. Recognizing the problem, the company embarked on a metallurgical research program to include laboratory, pilot plant, and plant testing. The program developed an innovative copper prefloat process which both increased copper recovery and significantly improved concentrate quality. The process was tested and first operated at Doe Run's Brushy Creek Mill then installed at the Viburnum Mill in 1992. A brief history of development, plant operating data, and other potential applications for the patented processes will be described in the paper.

Jan 1, 1993

By A. Bhagavatula, M. Rezaee, M. J. Kiser, R. Q. Honaker

"A field study of the coal preparation plant fleet in the eastern United States was undertaken to determine if quantify of rare earth elements (REEs) present in the product streams are large enough to justify further concentration. Representative composite samples were taken from the clean product, coarse refuse, and fine refuse streams from 20 coal preparation plants. Each stream was then separated into various size and density classes and analyzed for ash and REE contents. The large database showed that coarse refuse contained the largest amount of REEs, although the ratio of heavy to light REEs was greater for the clean coal products. The concentration of REEs was also compared to that typically seen in the earth’s crust. This enrichment ratio ranged from approximately 1.5 to more than 4.0 as the ash content varied. The database also showed that a linear correlation existed between La and Ce for many REEs of interest, although there were several notable exceptions for some of the high-value REEs. INTRODUCTION Worldwide energy demand is expected to grow by as much as 37% by 2040 according to the International Energy Agency (2014). This growth, coupled with a decrease of the reliance on coal to generate energy, means that it is more important than ever for countries to secure the materials necessary to meet its energy projections. For the United States, the U.S. Energy Information Administration (EIA) predicts that total domestic electricity use will increase roughly 25%, from 3,836x109 kWh in 2013 to 4,797x109 kWh in 2040 (EIA, 2015). In the EIA’s reference case, coal’s contribution to electricity generation drops from 39% in 2013 to 34% in 2040. On the other hand, renewables share of electricity generation grows from 13% to 18% for the reference case. Compared to its current state, renewable energy electricity production is predicted to grow as little as 50% to as much as 121% over this time period, depending on the economic case being examined. This growth will largely be seen in the wind and solar sectors (EIA, 2015). The focus on viable renewable energy resources will be crucial to the future of fueling American growth. Many of the renewable energy technologies, such as wind turbines and photovoltaic films, rely on materials and supply chains outside of the United States. The lack of a reliable and low-cost domestic supply could pose a threat to the growth of the renewable energy markets in the United States. This potential vulnerability recently led the United States Department of Energy (DOE) to create a Critical Materials Strategy Report. In this report, 15 elements were identified as critical for the continued growth of the renewable energy market. Eight of these elements were rare earth elements (REEs). Five REEs (dysprosium, neodymium, terbium, yttrium and europium) were identified as highly critical and vulnerable to shortages (Bauer et al., 2012)."

Jan 1, 2016

By Norman K. Olson

Hard-rock phosphate was formerly the chief source of all phosphate in Florida. Its mining began as early as 1883 or 1884, reached a peak level in 1907 and ceased in 1966. Production began and ended in the Dunnellon area (Marion County). Nearly all the hard-rock was exported because its P205 value per unit weight is generally more concentrated than that of other phosphate rock. Maximum production, achieved in 1907, was greater than 600,000 tons; the total value for that year was more than $4,000,000. The Florida hard-rock phosphate, considered to be of middle Miocene to early Pliocene age, has an intermittent narrow, linear northwest-southeast trend. The Ocala uplift controls the phosphate distribution for more than 200 miles. Other known, isolated hard-rock areas appear to be related to minor folds on the Ocala uplift. The hard-rock phosphate deposits are a heterogeneous mass of sedimentary fluorapatite, chert and quartz with textures ranging in size from clay to boulder, and in thickness from 0 to 40 feet. Phosphate compounds, principally fertilizers, have been in oversupply since before 1968, but by the middle 1970's some experts forecast a supply-demand balance. A brighter future for exploitation of Florida hard-rock phosphate depends upon one or more of these factors: 1) depletion of present premium grades (74 percent BPL and above) of land-pebble; 2) cheaper electric power from nuclear generators for profitable electric furnace operation; 3) supply and price of sulfur; 4) manageable rail-water transportation costs; 5) development of less costly mining and separation methods; and 6) minimum competition from high-grade foreign phosphate.

Jan 1, 1972

By P. D. Nora, M. G. Ranade

A statistically designed pot grate-kiln test program was conducted to determine the agglomeration process variables necessary for increasing the low temperature disintegration resistance (LTD) and reducibility (R40) of magnetite-based Empire acid pellets. The ASTM tumble index and compression strength were to be maintained at an acceptable level. Six process variables - bentonite addition level, preheat time and temperature, firing time and temperature, and cooling rate - were investigated within the constraints of the Empire plant. The bentonite addition level and firing temperature had the largest effect on pellet properties. The results of this program were verified during a plant trial. The target firing temperature at the Empire plant has been decreased for increasing the LTD and R40 of commercially produced Empire pellets.

Jan 1, 1987

By Dale W. Norris, John A. L. Campbell

INTRODUCTION Optimization, as measured by productivity gains, is being achieved in our nation's preparation plants principally by automation, economy of scale, and reducing maintenance. Increased tonnage per unit of investment, a1 so a measure of optimization, is being achieved by breaking with tradition and increasing plant utilization, while simultaneously improving on equipment re1iabi1ity. Improved qua1ity, another measure of optimization, is being attained through technical innovation. This review will concentrate on state-of-the- art unit operations and processes, and will not discuss emerging new technologies which are covered in detail in other presentations of this symposium. It is recognized that much of what will be discussed in this paper is not unique to the fine coal circuit, but is equally applicable to the entire preparation plant. However, the areas reviewed are the principal means being used today to optimize an existing preparation plant's fine coal circuit. Prior to designing and optimizing a fine coal cleaning circuit, the question that must first be answered is, "Do we even want a fine coal circuit? This is a much more complex question than is readily apparent, as most of you recognize. It can be argued either way. In the final analysis the "bottom line" will hold (Blackmore, 1982). If your sales contract a1 lows it, and the selling price can justify it, you most assuredly want to build a fine coal circuit into your preparation plant. In general today, most new preparation plants do have fine coal cleaning circuits. The purpose of fine coal cleaning has changed with time. Some of the early applications of fine coal cleaning were to prevent stream pollution rather than to prepare a product for market (Merrill a Pennington, 1962). During the 50's, 60's and into the 70's the principal thrust of fine coal cleaning was in metallurgical coal preparation. More recently, the emphasis of the 80's is on steam coal processing. There is no consensus on what is fine coal. Traditionally, fine coal would be anything below 1/4" in size. Because of the advances being made in intermediate coal cleaning processes, i.e. heavy media cyclones and jig cleaning, this discussion will define fine coal as -28 mesh (Aplan, 1987). Figure 1 is a plot of the size ranges of a large number of U.S. bituminous coals. In general the -28 mesh fraction of a bituminous coal will be between 7% and 18% of the ROM feed with reported ranges of 5% to 40% (Aplan, 1987). Consequently, traditional fine coal cleaning is general 1 y involved with a re1 actively mi nor portion of the coal feed. Every effort is taken both in terms of mining and preparation to keep it that way because of the high cost of cleaning fines. The move away from this posture, namely, the techniques to fine grind coal to liberate pyrite is probably the biggest challenge facing fine coal processing today.

Jan 1, 1988

By Gerald M. Ellis

Introduction Gold exploration in the Dominican Republic has not received much publicity. The fact is, however, that a continuous program has been underway for some time. For the past two years, the Restauracion area of the western Dominican Republic, near the Haitian border, has been the scene of mineral exploration by the Dominican Department of Mines geologists, and later by geologists of Rosario Dominicana. The latter is a state-owned gold mining company and operator of the Pueblo Viejo open-pit gold mine. The exploration is for mineral deposits with the goal of finding another Pueblo Viejo-type deposit. Geology Exploration is being carried out in the western central Cordillera, the backbone of the Island of Hispaniola. Geology consists of quartz veins and veinlets and ramifying stringers carrying pyrite, barite, minor amounts of copper, and significant amounts of gold in places. They are associated with regional faulting in a complex of Cretaceous beds of andesites, dacites, argillites, siltstones, and shales. They are intruded by tonalites, diorites, and gabbros. Lesser amounts of zinc-lead mineralization occur in some locations. The showings appear as disseminations along the faults. To date, the work has been mostly geologic mapping - 1 to 50,000 with details on a scale of 1 to 20,000 and 1 to 10,000-stream and soil lithogeochemistry, and geophysics. Trenching and sampling were used to follow possible vein extensions. Particular emphasis has been placed on the Los Candelones district that was taken over by Rosario Dominicana. Here is where drilling has been initiated in the past months. The first hole drilled showed assays of 21 g/t (0.6 oz per st). The second hole intersected an interesting oxidized zone that reminded observers of the original Pueblo Viejo oxidized zone. A third drill hole went deeper than 75 m (246 ft), the depth to which the first two holes had been scheduled. An assay of 50 g/t (1.46 oz per st) was cut during drilling. The presence of an oxidized zone of any vertical and horizontal extent is important. This gives rise to continued exploration, as the

Jan 2, 1986

By Boris CARO VARGAS, Bernard Theron

"In early 2014, Nicholson Construction Company was awarded, together with its tunneling sister company Bessac, the Norris Cut Miami Tunnel Project. The 2.5-meters diameter segmental lined tunnel, 1600-meters long, is aimed to replace the existing 54” force main connecting the Waste Water Treatment Plant (WTP) on Virginia Key to Fisher Island. To overcome project challenges such as the highly permeable limestone of the Fort Thomson Karstic Formation (one of the most permeable formation in the World), the project team has developed State of the Art solutions: The TBM was launched with pipe-jacking technique for the first 70-meters and then converted to segment erection mode. It allows substantial schedule savings and drastically reduces the size of the circular launching shaft. The TBM, jointly designed and manufactured by Bessac and Herrenknecht, can convert from slurry to EPB mode within a few minutes. The cutters can be replaced by wet divers thanks to an innovative application in the TBM industry. PRESENTATION OF THE PROJECT The aim of this project is to replace the existing 54-inch force main pipeline which transmitted all sewage collected from Miami Beach, Surfside, Bal Harbour, Bay Harbor, North Bay Village and Fisher Island to the Central District Wastewater Treatment Plant (CDWWTP) to Fisher Island. The existing pipeline consisted of pre-stressed concrete cylinder pipe which is in poor condition in a number of locations and could be subject to sudden failure. An adjacent portion of this existing force main under the Government Cut (North Fisher Island) has already been replaced as part of a previous design-build contract and involved the installation of a 60-inch diameter fiberglass-reinforced mortar pipe installed inside a micro-tunneled casing."

Jan 1, 2016

By Gerald W. Cormick

In a complex society such as ours, the range of "negotiating" relationships is constantly increasing. These negotiating relationships have emerged as a direct result of the diffusion of power or influence to new sectors and emerging concerns. Even within organizations, the myth of the authority-based heirarchical structure has given way to the reality of constant negotiations between superior and subordinate and with peers in the organizational structure. In the broader context, the corporate organization finds it necessary to reckon and often negotiate with organized employees, suppliers, buyers, government agencies and a range of organized private interests ranging from minority groups to environmental organizations. In response to this diffusion of power and the conflicts which it has engendered, a variety of conflict avoidance, conflict managing or conflict resolution techniques has developed. The purpose of this paper is to attempt to differentiate between some of the conflict intervention approaches which have appeared "on the market", and to suggest three bases for selecting among them: 1. The "role" of the conflict intervenor; 2. How far the conflict has developed; and 3. The breadth and impact of the issues involved.

Jan 1, 1979

By B. Blaschuk

The Freeport McMoRan Bagdad Solvent Extraction (SX) circuit is the oldest plant of its kind currently in operation. The plant was commissioned in 1969 and was the second SX-EW operation to be built following the Ranchers Bluebird solvent extraction and electrowinning (SX-EW) plant near Miami, Arizona. Over the years of operation, the configuration of the SX has gone through many changes to accommodate a variety of pregnant leach solution (PLS) grades and flows. Although modifications to the original plant configuration are numerous, the Bagdad SX circuit has maintained its general form consisting of multiple long and narrow settlers. The unique configuration of the Bagdad SX circuit presents a variety of operational advantages and challenges; however, it continues to operate at a level recognized in the industry as excellent.

Jan 1, 2010

By P. Bevilacqua, M. C. Williams, T. P. Meloy

We will bet you that, without prior programming within 10 minutes, we can design and simulate a 10,000 unit operation separation circuit. We will even do it at your place. We do it all the time. [ ] There are no tricks; we do it in a spreadsheet. We do it in those user friendly spreadsheet such as Quattro Pro. Spreadsheets must be user friendly. Accountants use them as do managers, business men, lawyers, doctors and salesmen. What these users seldom realize, is how powerful a mathematical tool a spreadsheet is. Among their other capabilities, spreadsheets can do a finite element analysis. That is why they are useful for accounting. That is also why they are more useful to engineers in the mineral industry. Spreadsheets are ideally suited for the engineering problems in the mineral industry. We have used then for solving problems in: a) mine ventilation; b) circuit design and optimization of dense media, flotation and sizing; c) comminution circuit design; d) shaking tables; e) Humphrey spirals; f) sluice ways and channel flow; g) lock particle and liberation problems; h) tunnel and shaft stress problems; i) cascadograph simulation; j) complex heat transfer problems; k) flow in porous media; and sheet flotation (Figure 1). Mineral industry problems presented on or with a spreadsheet are an excellent teaching instrument, problem statement and solution tools and sales devices. Spreadsheets answer easily, quickly and reliably many mineral industry engineering problems. What makes spreadsheets so useful to the mineral industry. The short answer is: they are easy to use; mineral industry problems fit the spreadsheet format. Those reasons are part of the answer. The real answer lies with the structure of the spreadsheet itself. Essentially, a spreadsheet is a "finite element analysis" form of computer software. Many mineral industry problems are readily solved by finite element analysis techniques. While some in the mineral industry may think they have never heard of finite element analysis, most use it weekly if not daily. Any profit and loss statement is essentially a finite element instrument. In fact, any array of numbers where one number is related to another may be construed as a finite element analysis product. Finite element analysis is a common daily activity. To get an appreciation of a finite element analysis, think of a monthly sales forecast for the next year. For each product and for each month, there exists a dollar figure for the forecasted amount of sales. In the forecast statement, for a given product in a given month, there is a "box" where the forecasted figure is presented. The forecast figure in that box was arrived at through some type of formula. The formula probably required some information from other neighboring boxes in the master forecast statement. Voila, one has a finite element analysis. Today the analysis would be done in a spreadsheet. A typical mineral industry problem is ventilation in an underground mine. Think of a rectangular room and pillar mining operation. Each room has air entering at a given pressure and velocity and air leaving at another pressure and velocity. During steady state, the air entering and leaving the room is determined by conditions in the adjacent rooms. One can readily model the room and pillar mine layout in a spreadsheet, and then find the flow in and out of each room at steady state. Change the flow by moving a brattice cloth or blocking off a path way and one gets a new air flow profile. Change the numbers on the spreadsheet that reflect

Jan 1, 1993

By R. J. Sweigard, R. V. Ramani

Three case studies were undertaken to investigate the role of land use potential evaluation in reclamation planning and to determine the impact of regional differences on final land use plans. The three surface mines studied were representative of operations in the Appalachian, Interior, and Northern Great Plains provinces. The scope of the investigations included a survey of regional characteristics, a detailed investigation of the mining operations and site conditions, and an assessment of local land use planning activities in the area of the mines. Special attention was given to key factors that presently determine the use of reclaimed land. Also, for each case study, the postmining land use potential was evaluated using site planning principles. Specifically, the environmental, economic, and social impacts of several potential postmining land use plans were considered.

Jan 1, 1987

By A. V. Castelli

The provinces of Guangxi, Guizhou, Hubei (and most recently Fujian) were the prime exporters of barite during this period. Guangdong and Shandong were exporters too but not major participants. These are all primarily agricultural areas so there existed a sufficient labor force willing to work in the mines to supplement their income from farming. During the early years, barite export pushed the existing transportation systems in these provinces to operational capacity. The mines from which this barite is extracted are located about 250 to 1,400 kilometers from the sea ports. Transportation of the ore from the mines to the ports follows a net-work that includes trucking to various rail-heads where it is then shipped via freight trains to ports for loading into seagoing vessels. in some instances, the barite travels by truck or train to the Yangtze River where it is then barged to an ocean port.

Jan 1, 1990

By Lawrence Neal Post

Introduction Synthetic soda ash production began to decline in the late 1930s. This was due to high operating costs and waste disposal problems. Since soda ash was used as a major component in manufacturing glass, an alternate method of producing that chemical was necessary. A process to produce soda ash from trona was developed by FMC Wyoming Corp.'s predecessor, as well as an economical way to obtain trona. Existing trona operations are located about 40 km (25 miles) west of Green River, WY. Five operators presently mine trona in this area. FMC's property has 153 km2 (59 sq miles) leased. Its eight shafts reach 488 m (1600 ft) deep to the uniform trona deposit. The seam ranges in thickness from 2.4 to 3.6 m (8 to 12 ft). History Egyptian tombs, dating from 4000 to 3000 BC, contained mummies preserved by an embalming process using soda ash. For many years, soda ash was produced by burning marine plants, then dissolving the soluble material (sodium carbonate) from the ashes. The name soda ash is derived from this method of production. In 1791, Nicola LeBlanc developed black ash, or salt cake, from salt, sulfuric acid, coal, and limestone. This process remained in use until 1863, when Ernest Solvay developed a method for producing soda ash from salt, coke, and limestone with ammonia as a catalyst. This Solvay process was widely used. And, in the 1930s, there were 17 plants in the US alone. High plant operating costs and waste disposal problems, however, necessitated finding an alternative to the Solvay process.

Jan 10, 1985

By M. Galetakis

The difficulties that rise during the evaluation of multiple-layer lignite deposits come from the deposit structure (alternating lignite layers with intercalated material of varying thickness), as well as from the limitations of the applied selective mining. Thin layers of lignite and interbedded waste layers are grouped under specified assumptions regarding thickness and ash content, to form the exploitable blocks. However, in practice the decision for excavating a block is made under subjective constraints of different importance or by using uncertain data. Advances in Fuzzy Inference Systems (FIS) have provided a new approach to the evaluation of multiple-layer lignite deposits. FIS have the ability to handle imprecise or incomplete or linguistically ambiguous information and to incorporate them into decision-making processes. In the developed FIS (Mamdani type) new linguistic variables, concerning with working conditions, operators? experience and production were involved. The FIS was used for the estimation of quality characteristics and reserves of the exploitable lignite produced from Southern Field mine, Ptolemais (Greece).

Jan 1, 2005

By John E. Tilton

Mining is one of the oldest human activities. It goes back at least to the Bronze Age and possibly even the Stone Age. The Romans mined copper in Spain and tin in England some 2,000 years ago. The writings of Agricola in the 16th century show that mining was important in the Middle Ages. Today, more mineral commodities are mined in greater tonnages than ever before. This long and fascinating history closely tied with the economic development of the human race is one of the charms of the mining industry. It also, unfortunately, gives rise to some widespread misconceptions. Old industries are generally considered stodgy with mature and stagnant technologies. Costs tend not to decline as in newer industries, and may even increase with real wages. Costs are particularly expected to rise in the case of mining as the best mineral deposits are depleted. Thus, mining is often thought of as a sunset industry, destined to decline over time as the resource base is depleted. These perceptions have several important implications. They argue against economic policies that rely too heavily on mining and mineral processing to foster growth and development. The best and the brightest young people, along with society's other valuable resources, should be encouraged to enter newer industries. There the technological opportunities and the prospects for growth are more promising. These perceptions also suggest that the ability to compete in the mining industry depends largely on the quality of a company's or country's mineral deposits. Mining will take place first in countries with the lowest-cost deposits. Once these are exhausted, mining will shift to countries with the next best deposits. From time to time, new discoveries may also produce a shift in the location of mining, [ ] and may even for a time keep the costs and prices of mineral products from rising. Over the longer term, however, rising costs and prices are inevitable, as the world is forced to exploit poorer mineral deposits.

Jan 1, 1997

By J. Y. Kim

Silver contained in zinc calcines undergoes several phase changes as it proceeds through the leaching circuit of a roast-leach-electrowin zinc plant. In the present study, the flotation response of silver from leach residues prepared under a variety of carefully controlled operating conditions in the pilot plant has been examined. Flotation of neutral leach residue is shown to be technically viable and to merit consideration for those plants without a high acid leach circuit, but having significant silver values in the feed. Residue leach conditions must be kept slightly acidic to promote the formation of Ag2S, (Ag, CU)2S and Ag2S rims on residual unroasted sphalerite, while simultaneously avoiding the hydrolysis of soluble iron which depresses silver recovery and grade. Factors to be considered during integration of a flotation process into an electrolytic zinc plant are discussed.

Jan 1, 1990

The 70th Annual Meeting of the Minnesota Section of SME and the 58th Annual University of Minnesota Mining Symposium were held April 22-24, 1997, in Duluth, MN. About 450 attended both. The Fifth Annual Trade Expo, held during the meeting, was attended by a record 80 exhibitors. An SME short course on materials handling preceded the meeting. Iron-mining and the steel industries highlighted the meetings. Specific topics in the keynote addresses and technical sessions primarily concerned iron mining, iron- ore processing, product (taconite pellet) transportation and the steel market. Although the iron mining industry held center stage, several papers outside of iron mining were also presented. Iron mining in Minnesota contributes $1 billion to Minnesota's economy. According to the Iron Mining Association of Minnesota, more than 20,000 state jobs rely on the industry. Minnesota's iron mining industry came through tough times in the early 1980s, mostly because of worldwide competition. However, the industry has shown significant improvement in the last 15 years. A large share of the steel industry's competitiveness in the late 1990s is due to cost and quality improvements in the taconite mines. The taconite industry has become more productive, largely through the application of new technology. Since the early 1980s, Minnesota's taconite mines have nearly doubled the number of tons per worker-hour. Most of the taconite reserves in the United States are located in Minnesota's Mesabi, Vermilion and Cuyuna iron ranges. The Mesabi range alone contains an estimated 24. Gt (23.6 billion long tons) of mag- netic taconite. Since the 1950s, when taconite production first began, 1 Gt

Jan 1, 1997