Search Documents

By Eduardo Poltronieri Trés, Anderson Denadai Thomazini, Rodrigo Boyer Fernandes, Francisco de Assis Dutra Macedo, Gilvandro Bueno, Maycon Athayde, Rossano Augusto Pilon Nunes

The earliest industrial application of high pressure grinding rolls (HPGR) at comminution was in 1984 in the cement industry. Since then, the equipment has been widely applied in mining activities. Despite the rapid spread across the industry, several challenges are still present in the equipment’s application, especially considering the complex ore breakage behaviour reported for this process. The pellet feed’s HPGR comminution was recognized as fundamental to efficiently increase the particle surface area (e.g., blaine specific area, BSA) at a lower energy and water consumption level (Chapman et al. in J Southern Afr Instit Mining Metall 113:407–413, 2013). The present study considers a novel milling process applying only HPGR as a re-regrind stage after concentration. The amount of successive ground product recirculation into the machine to achieve the required particle size for the pelletizing process was investigated. The study compared the ball wet milling process with the innovative processing technology for hematite–goethite ores. Green pellet balling and induration processes were simulated in bench and pilot scale. The milling results showed a considerably steep increase in BSA after each recirculation step into the HPGR, although compared with the ball-milled product the size fraction <45 μm% increased a modest five percentage points after three recirculation cycles, remaining steady until the last recirculation step. As a result, the green pellet generated presented higher concentration of pellets between 10 and 16 mm (%10-16 mm), with a higher drop number than typically observed when produced with ball-milled feedstock. Consequently, on the induration process, a higher pellet deformation was observed during the pot grate loading. Despite that, the fired pellets still presented an outstanding performance in cold crush strength (CSS) considered suitable to an industrial application.

ITEC Environmental Colorado has begun reprocessing the tailings from old mining sites near Boulder, CO. And if the technology behind ITEC&apos;s pilot project at Gold Hill proves successful and profitable, the company plans to launch similar reprocessing operations in other parts of the state. The pilot project is under the watchful eye of state and federal authorities. They hope the technology becomes the answer to cleaning up old mining sites throughout the West. Remining and environmental cleanup on an economic basis, then, are ITEC&apos;s hopes in one the most environmentally conscious counties in the state. Clean up the mine dump sites and recycle the land, for a profit. In June 1998, ITEC Mineral Inc., ITEC Environmental Colorado&apos;s Canadian parent, acquired the Gold [ ] Hill Mill facility in Boulder County. Included in the acquisition was 4.4 hm2 (11 acres) containing the Gold Hill Mill and 283 hm2 (700 acres) of additional properties adjacent to the facility. ITEC estimates that there are about 910 kt (1 million st) of dump rock in the area. That is enough to make the operation viable. ITEC will sell the metals recovered through its reprocessing operations. However, due to low metals prices, ITEC is not expecting to make much money on the recovery of precious and base metals. Instead, the company plans to resell the reclaimed land for residential and commercial development or open space. The Gold Hill Mill site is the first of 17 sites in Colorado that ITEC Mineral hopes to clean up and recycle the land. Most notable among the sites is the historic Central City/Black Hawk mining district, which ITEC believes holds considerable potential. The Gold Hill Mill is located 14 km (9 miles) west of the city of Boulder and less than a half mile from the small town of Gold Hill. The mill was. last operated in 1992. The operation was forced to close that year due to environmental and cash flow problems. Gold Hill is in the middle of a region with more than 32 Mt (35 million st) of mine tailings. Independent geologists have&apos; established the average grade of the Gold Hill mine tailings to be 4.5 to 5.3 g/t (0.13 to 0.155 oz/st) of gold and 28 to 44 g/t (0.83 to 1.29 oz/st) of silver. According to these studies, the Gold Hill mine tailings are five times richer in precious metals than the tailings of the Norebec Manitou property in Canada that ITEC is also remining, reclaiming and restoring. Upon acquiring the mill, ITEC undertook a refurbishing program that included adding a second ball mill. This increased the Gold Hill Mill&apos;s capacity to 180 t/d (200 stpd). The operation employs 15 people. "The Gold Hill Mill site will demonstrate the efficiency of our integrated remining, reclaiming and restoration process," said Maxine Stewart, president of Denver, CO -based ITEC Environmental. "The abundance of similar mine sites in Colorado presents a number of opportunities to bring the benefits of the ITEC system to other communities around the state." Holly Huyck is technical advisor to the Clear Creek Watershed Advisory Group. She said: "ITEC is cleaning up an orphan mine site that otherwise would continue to contaminate the Boulder Creek watershed with acid and excess metals. This is a win-win situation: ITEC gains marketable minerals while it reclaims mined land and helps to improve the watershed."

Jan 1, 1998

By K. Kavouridis

On 30 April 2004, a large scale slope failure incident occurred at the external waste dump facility of the South Field Mine, in the Western Macedonia Lignite Center, Greece. This landslide involved the mobilization of waste overburden material (that was continuously deposited for the last 20 years) in the order of 40 Mm3, while the material that moved outside the boundaries of the waste dump was in the order of 3 Mm3. The factors that led to failure as well as the procedures and measures taken in order to stabilize the failure and resume normal operations at the South Field Mine are presented and discussed. Emphasis is given to the impact on mine operations and the cost related to resuming of normal production operation as well as to implementing important modifications and improvements of the materials handling system.

Jan 1, 2006

By John W. Amos, John A. Christophersen

The Deister No. 7, "77" and "88" Coal Washing Tables have been used by the coal industry in the cleaning of finer sizes of coal (-1/2") since washing of coals became necessary. This paper will deal with the in-plant use of the CONCENCO "88" Deister Coal Washing Table, along with a brief description of the Deister Refuse Superscalper. Efficient in-plant operation of the Deister Coal Washing Table can be accomplished by the adjustment of six basic variables. These variables are: 1. Headmotion 2. Feed 3. Riffle Pattern 4. Dressing Water 5. End Elevation Adjustment 6. Side Tilt Adjustment VARIABLE NO. 1 HEADMOTION The reciprocating movement of the "88" Table is developed within the headmotion entirely by rotating eccentric weights. Four parallel shafts each carry pairs of eccentric weights (Figure 1-A). The shafts are geared together with gears of 2 to 1 and 1 to 1 ratios, so that the two shafts in vertical alignment which carry the small eccentric weights operate at twice the speed of the other two shafts. The other two shafts are also in vertical alignment with each other and carry large eccentric weights. As power is supplied to one high-speed shaft, once each revolution the forces produced by the large eccentric weights are reinforced and then opposed by the small eccentric weights in a horizontal plane. The direction of movement of the table decks is reversed much more sharply at the forward end than at the backboard end of the stroke, causing material to move toward the refuse end of the table. Because in the vertical plane all centrifugal forces oppose each other and cancel out, there is no vertical movement and virtually no impact to the support steel. The "88" Coal Washing Table is suspended by wire-rope cables from three overhead steel beams, and operates with a perfectly uniform and exact differential motion curve in every stroke (Figure 1-B). The decks, being attached to the headmotion, are reciprocated in a parallel line from the head- motion to the refuse corner at speeds varying from 260-300 strokes per minute. Both length of stroke and speed are set at the factory for the coal characteristic desired and should not be changed. A 3 HP motor is mounted on the top of the headmotion and uses 3 V-belts to transmit driving power to the headmotion. The headmotion must be kept running on a horizontal plane. Punch marks are provided on the side and end of the main frame for use in leveling the motion (Figure 1-C). In leveling the motion, the work must always be done with two cables. To level the long side of the headmotion both front or both rear cables are raised or lowered to bring motion back to level. To level side to side, both right side cables or left side cables are raised or lowered to bring motion back to level VARlABLE NO. 2 FEED When tabling different size coals, each deck of a "88" DIAGONAL-DECK Coal Washing Table will handle feeds as described in figure 2-A.

Jan 1, 1988

By Sertaç Dündar, Bilgehan Kekeç, Arif Emre Dursun, Niyazi Bilim

"Estimation of rock drillability is vital for mining and boring operations. For this purpose, many researchers have developed various models and equations to estimate rock drillability. Most of these models aim to determine the drillability of rock and the penetration rate by using the physical and mechanical properties of rocks. Although drillability primarily depends on rock properties, other parameters have an impact on drillability as well. One of these parameters is the rotation speed of the bit. This study investigates the effect of rotation speed of the bit on drilling performance. Drilling tests were performed in the laboratory using rotary core drilling and a diamond drilling machine. The relationships between the physical rock properties and the penetration rate were investigated on 15 different rock types and four different rotation speeds were applied to determine the effect of rotation speed of bit on drilling. The uniaxial compressive strength, density, and P wave velocity show strong correlations with the penetration rate. In addition, if the values of the physical and mechanical properties of the rock increase, the effect of the rotation speed on the penetration rate decreases, i.e., increasing the rotation speed of the bit slightly affects drillability on hard and solid formations. 1. Introduction Drilling is one of the most essential operations in the mining industry, beginning from the exploration phase and continuing throughout all stages of production to the end of mine life (Taheri et al. 2016). In addition, drilling is widely using in the construction industry and other engineering operations. Various drillholes (blastholes, injection holes, borehole, diamond wire holes in natural stone mines, etc.), are needed during development and production activities in underground and open-pit mines as well as in dam, tunnel, road construction and sewage systems. For effective drilling operations, it is first necessary to gather information about the formation to be drilled. Drilling should then be performed after selecting appropriate drilling equipment and drilling parameters (thrust, pressure, rotational speed, flushing). Prediction of the drillability of rocks is vital for planning and performing the drilling process. Although, drilling is affected by several factors, the most important ones are related to the geological and mechanical properties of formation (Protodyakonov 1963, Paone et al 1969, Tandanand and Unger 1975, Pathinkar and Misra 1976, Rabia 1985, Perrin et al 1977). Determining the penetration rate is vital for planning a project and calculating the operation costs. The prediction of drilling affects the selection of drilling equipment, the efficiency of drilling equipment, project costs and the process of drilling operations."

Jan 1, 2017

By Ralph J. Holmes

INTRODUCTION Although sampling techniques used by the mineral industry continue to improve, sampling is still an area which is often neglected. Frequently, sampling and sample preparation requirements are left to personnel who do not fully appreciate the significance and importance of sampling. Consequently, plant evaluations are often based on seriously biased samples, leading to mass balance problems and incorrect assessments of plant performance. The basic rule for correct sampling is that each particle of ore or concentrate must have an equal probability of being collected and becoming part of the final sample for analysis. If this is not the case, bias is easily introduced and the sample is not representative. For example, when ore is travelling on a conveyor belt, the lumps may come to the surface. Consequently, a grab sample taken from the top layers only will contain a greater proportion of lumps, i.e., the sample is biased. There seems little point in making major investments in precise analytical equipment, if the sample provided to the analytical laboratory is not representative in the first place. This paper describes the sources of plant sampling errors, reviews the methods of estimating their variance, presents some worked examples, and provides some practical advice for reducing sampling errors and their variance. SAMPLING BASICS It is generally accepted that the discharge point of an ore or concentrate stream is the most suitable sampling location. The stream can be intersected at regular intervals, and representative samples, referred to as increments, can be obtained by taking a complete cross-section of the ore stream. On the other hand, sampling devices that take part of the stream on an intermittent or continuous basis, e.g., a bleed from a pipe, may introduce serious bias, and should be avoided at all cost. Increments may be taken at completely random times or tonnages during the sampling operation, in which case it is called "random sampling". However, as shown below, random sampling results in the largest sampling variance, so it is preferable to divide the ore or concentrate stream up into strata of equal time or mass and take one increment from each stratum. This operation is called stratified sampling and may be either systematic sampling, in which increments are taken at the same point in each stratum, or stratified random sampling in which the increments are taken at random within each stratum. Systematic sampling results in the smallest sampling variance, provided periodic variations in quality or quantity are not present which may coincide with, or approximate to, any multiples of the proposed sampling interval. In such cases, it is strongly recommended that stratified random sampling within fixed time or mass intervals be carried out.

Jan 1, 1991

By Daniel Su

This paper describes recent ground control challenges encountered at the longwall recovery areas of one of Bailey Mine?s two longwall faces and the proactive measures taken by CONSOL management and engineering to mitigate them. The challenges derived primarily from the following causes: (1) irregular roof coal and draw slate thickness, (2) presence of thick sandstone at the recovery area and extremely weak rocks below the sandstone, (3) close proximity to a regional anticline, (4) low shield set pressure and tip load, and (5) ineffective primary roof support that led to progressive failure of the headgate roof. The presence of the anticline contributed to extensive fracturing of the sandstone. Excessive pot-out in advance of the shields frequently occurred near mid-face due to the presence of thick draw slate and irregular roof coal near the recovery area. This, in turn, resulted in face heights that exceeded the maximum reach of the shields. Subsequently, during longwall meshing, when the advance rate slowed considerably, fractured sandstone would often break loose, causing the shields to yield, thereby reducing the height and inhibiting shearer movement. To improve the headgate and face conditions within the longwall recovery area, several actions were taken, including: (1) assessing site-specific roof geology by conducting in-mine roof coring around the recovery areas and by mapping immediate draw slate and roof coal thicknesses within surrounding entries, (2) increasing pump pressure and thus shield set pressures (3) diligently monitoring shield set pressures and longwall extraction horizon, (4) installing additional cable bolts and roof screening to prevent progressive failure of the immediate headgate roof, (5) fully-grouting supplemental cable bolts to improve headgate support stiffness, and (6) gluing the headgate roof within the recovery areas with polyurethane. As a result of these collective efforts, longwall recovery delays at Bailey Mine were reduced from 21 days in 2006 to nearly zero in 2009.

Jan 1, 2009

By J. DeYoung

Weak demand for metals and consequent low metal prices resulted in continuation of the depressed state of US mineral exploration activity through 1983. Data collected by Resources for the Future Inc. and The Pennsylvania State University for a cooperative study on mineral exploration activity indicate that US exploration in 1983 fell by as much as 25% from 1982 levels. Precious metals remained the focus of most exploration efforts, as gold and silver prices remained attractive compared to base metals. Reports of 1983 domestic exploration and development activities in several industry journals indicates that about 85% to 90% of those projects were directed primarily at gold and silver. Gold exploration included work by several companies on Carlin- type disseminated gold deposits in Nevada, geological prospecting and drilling in the Wenatchee Gold Belt in Washington, and interest in lode and placer gold properties in California, especially by several small Canadian firms. Precious metals exploration projects were also reported in Alaska, Arizona, Colorado, Montana, New Mexico, Oregon, South Dakota, and Utah. There was also tome precious metal exploration activity in the eastern US. Development continued at the Ropes gold mine near Ishpeming, MI, and companies explored historic gold-producing areas in the Southeast. Some exploration for nonprecious metals took place last year. Stratabound copper-silver deposits were examined in western Montana, and US Borax continued exploring molybdenum resources in the Misty Fjords area in Alaska. Work on these projects during 1983 may have been stimulated by time limits on the availability of certain federal lands for exploration more than by projected improvements in metal markets. During 1983, several papers were published on mineral exploration strategies and the future of US exploration. David Watson of Raymond Kaiser Engineers, in a paper presented at the 1983 AMC Mining Convention, forecast increased exploration activity for gold and silver because of world economic conditions. He added that antimony, manganese, chromium, graphite, mercury, tantalum, tin, and barite are also likely targets based on their limited domestic reserve availability. He cited concern over reported subsidized mineral production by foreign producers and US regulatory and land-planning policies as retarding mineral exploration activity. Douglas Cook of Freeport Exploration Co., at the same meeting, presented a paper that showed that a 1950-75 period of vigorous exploration has been followed by a period where acquisition has replaced exploration as the predominant means of acquiring new mineral properties. At a December IIASA conference on "The Economics of Mineral Exploration," in Vienna, Austria, A. Rose and R. Eggert of The Pennsylvania State University pointed out that recent exploration decisions tend to rely more on evaluating production costs and comparing them with existing deposits, rather than on return of

Jan 5, 1984

By Nelson R. Shaffer

Glamorous, burgeoning biotechnology and mundane industrial minerals would at first glance seem to share little in common, but in truth, modern biotechnology depends on many minerals. Biotechnical processes also can be used in industrial mineral extraction and processing. Biotechnology is broadly defined as the application of biological organisms, systems, or processes to manufacturing and service industries. Genetic engineering has reinvigorated one of mankind&apos;s oldest sciences, biotechnology, into a booming business. Many modern processes depend on microorganisms cultivated under very stringent conditions in bioreactors. Minerals from carbonate, sulfate, chloride, nitrate, phosphate, and silicate families are used to provide essential nutrients and to regulate growth conditions (such as pH) in order to assure optimal growth of organisms. Certain cells or enzymes perform better when immobilized upon or within solids, and minerals are often used to immobilize cells, especially in continuous process. Minerals are also used extensively in separating and purifying products of biotechnology. Diatomite, zeolites, and silica are especially useful in purification processes. Industrial minerals also are commonly used to clean up large volumes of process water that must be treated. Biotechnology can be employed in exploration, extraction, and processing of geologic materials and in reducing mining or other environmental problems through bioremediation. Microbes have been shown to solubilize certain elements and so promote extraction of heavy metals, phosphate, aluminum, potassium, and even rare earth elements. In a related technique, unwanted materials such as pyrite impurities can be leached microbially to produce cleaner products in sand and clay industries. Microbial actions can modify surface characteristics and so enhance certain ceramic properties. Certain organisms can accumulate useful elements from dilute sources; others can transform unusable chemical species to more useful forms. Deterioration of stone, concrete, and even glass or brick, can be accelerated by microorganisms. Control of such biodeterioration could improve long-term performance of industrial mineral products. Microbial processes have shown promise in improving several mine-related problems. Certain bacteria help remove clays from phosphate slimes and other suspensions. Others are used to degrade cyanide or other organic chemicals such as floatation aids. Cells immobilized on clays have been especially efficacious in bioremediation. Biotechnology industries, like the industrial minerals industries, encompass huge ranges of materials and processes. Costs of products from these industries range from pennies to thousands of dollars per unit, and their products are vital for maintaining modern life styles. Many biotechnical processes depend upon industrial minerals and certain biological processes can be harnessed to do useful tasks in the minerals field. The interplay of industrial minerals and biotechnology is important today, and as biotechnology advances, its interaction with the industrial minerals industry can only increase.

Jan 1, 1995

By P. F. Ziemkiewicz

This project evaluated the performance of nine passive treatment methods by studying 137 treatment units in eight eastern states. Performance was normalized according to construction cost, projected service life and tons of acid load treated. Results were dimensioned as $/tons of acid load treated/year. These costs were then compared to those of chemical treatment. Sites that achieved acid load reductions at costs below those of chemical treatment were considered successful. In addition to evaluating the performance of the treatment methods, this paper describes the various passive treatment systems, their applications and performance data for individual treatment units.

Jan 1, 2003

By M. A. Sochocky

Rod mills were developed, as a logical substitute for the rolls crusher when larger tonnages had to be handled, on a continuous basis. Today, with even larger tonnages to process, the trend is to install larger equipment, automate the plant and develop the highest availability possible, in order to cut costs. The rod mills, because of design limitations in size and speed 1&apos;2, are not able to meet these new requirements. The autogenous mill was a timely development and serves as an excellent alternative for ores that are suitable to this type of grinding. When ores are not amenable to autogenous grinding, selection of a flowsheet is dictated by liberation characteristics and unit operations to be used for mineral recovery.. The following alternatives are available: (a) Multiple rod mills, capable of drawing no more than 2000 HP each, followed by ball mills. (b) Gyradisc crusher followed by two stages of ball mill grinding.3 (c) Tertiary crushing followed by closed circuit single stage ball mills grinding to approximately -100 mesh, as in the copper industry. (d) Tertiary&apos; crushing followed by two-stage, ball milling. Each stage will operate in closed circuit with either screens or cyclones. It is this last alternative, particularly as it

Jan 1, 1972

By S. Fairis Samuelson

Boling Dome. a piercement salt dome in the Texas Gulf Coast basin is (was) the single largest deposit of native sulfur in the Western world. Total sulfur production has been over 81.000,000 long tons and the mine is still in production. Data from over 60 years of operation and 8.000+ wells reveal a salt dome rich in history as well as minerals. Sulfur mineralization and production correlate well with caprock structure and morphology. The occurrence of Mississippi Valley-type deposits in fracture zones is notable in some areas and may warrant additional study. DISCOVERY AND PRODUCTION HISTORY Boling Dome is located in the south- east corner of Wharton County, Texas, 60 miles south-west of Houston. It is a piercement type dome in the Houston diapir province. It was discovered in 1922 when the county surveyor noticed sour gas seeps along the San Bernard River (Haynes. 1942). Several companies including Gulf Production Company. Humble, Texas Company, Sun and others quickly began drilling for oil and gas. Traces of native sulfur were reported in cuttings from many wells penetrating the caprock, but the first commercial quantities of sulfur were not found until Gulf Production&apos;s E.M. Chase 3 and 4 wells were drilled in 1927. Texas Gulf Sulphur, then mining sulfur at Gulf Dome in Matagorda County, secured the sulfur rights from Gulf for $3 million in cash and half of the profits after expenses for development and construction of plant and townsite were met (Haynes, 1942). The drilling results from 200 or so Wells revealed a massive deposit destined to become the largest single source of native sulfur in North America. Original reserves were estimated at just over 46 million long tons and were increased in later years. Production by the Frasch method was begun by Union Sulphur in 1928, and continued by Texas Gulf Sulphur Co. in 1929, and Duval Sulphur Co. and the Baker Williams Co. in 1935. Union produced 8,009 long tons, Duval produced 571,123 long tons, and Baker Williams produced 1,453 long tons. Through its deal with Gulf, Texasgulf acquired the largest and best mineralized portion of the dome and has produced 88,544,466 long tons through 1990, and production is planned for several more years. That amount of sulfur is equivalent to a cube measuring 1,152 feet on each side, or a sulfur highway 1 foot thick, 20 feet wide and 14,479 miles long. Peak production averaged 8,376 ltpd in 1948. A price war between North American sulfur producers and Mexican sulfur producers in 1956, followed by the recession of 1957 and 1958 (Haynes, 1959) coupled with a rapid increase in mining depth to below 700 feet began a gradual production decline that was never reversed (Figures 1 and 2).

Jan 1, 1992

By Ronald O. Harma

Iron ore pellets made from concentrates produced from low grade iron ores are the primary iron bearing feedstock for iron making in North American blast furnaces. Steelmakers are demanding increasingly higher quality to provide for improved blast furnace productivity, efficiency, product quality and environmental compliance. Unfortunately, this higher quality iron ore product must be produced from the vast deposits of low grade iron ores that are becoming increasingly poorer in quality with regard to mineral liberation and ease of concentration. Since some of these low grade iron ores require grinding to as fine as 90% -500 mesh (25 microns) for liberation and since more of the silicious gangue and other minor undesirable constituents must be removed to provide the higher quality, we have come to depend on flotation to do the added work. Flotation technology and other preflotation unit operations must improve to meet these increasing demands. In many cases, flotation equipment, reagents and circuit operating performance have improved little during the last two to three decades. Mechanical flotation cells have grown from 14 cubic meters (500 cubic feet) to over 84 cubic meters (3000 cubic feet) to help reduce capital and operating costs; however, flotation metallurgical performance has not improved, Column flotation has only recently shown promise in improving metallurgical performance for iron ore rougher flotation. Previous column flotation success was mainly in scavenger and cleaner flotation steps for treating minerals other than iron ore. Although some new flotation chemicals have been developed for removal of silica and other minor constituents under widely varying mineralogical scenarios, recovery of iron mineral has not improved. The operation and control of flotation circuits have become more challenging because of the increasing workload on flotation. Better sensing, process control and operation of flotation circuits are essential as we go forward. Iron ore upgrading by flotation can be classified into either anionic or cationic methods. Anionic flotation of either iron oxide or silicious gangue is accomplished by collector type, pH control and selective chemical activation . Similarly, cationic flotation of silica or iron oxides is accomplished by collector type, activation and/or pH control. Removal of other minor constituents is achieved by using specialty chemicals under controlled conditions for preflotation, co-flotation or post flotation steps. Generally, anionic flotation is used for floating cleanly liberating crystalline oxidized iron ores such as hematite, specularite and martite. Earthy and hydrated oxides such as hematite and geothite can be upgraded with either anionic or cationic collectors after controlled dispersion of slimes or prior removal of slimes. Anionic flotation of silicious waste can be achieved by calcium activation of silica. For magnetic iron ores small amounts of locked silica particles (middlings) can be removed by cationic silica flotation, which is the only method in commercial use in North America today. Historically the efficiency of these iron ore flotation processes has been restricted by the loss of fine iron particles (minus 500 mesh) to the tailings product. New technology is required to overcome this loss and improve overall flotation performance. Development of technology for more selective separation of silica and other minor undesirable constituents from iron ore will provide both quality and cost benefits to the iron and steel producers. Development of future iron ore production in North America will face stiffer technical challenges. These new and undeveloped iron ore deposits are largely oxidized (non-magnetic) and by nature contain more slimes and other undesirable constituents. Unless other new technology evolves, flotation will be the major treatment process required to upgrade these difficult low grade iron ores.

Jan 1, 1993

By Milton H. Ward

The percentage of exploration dollars flowing out of the industrialized countries continues at an all-time high, and this shift in risk money is justified (Samuels, 1990; Bosson, 1977). Clearly, the odds of discovery are greatly enhanced if exploration is pursued in an untrampled and geologically more prospective environment. Unfortunately, such major unexplored areas of the developed world are shrinking rapidly, not just because the lands have already been tested, but primarily because they have been withdrawn from exploration. Experience, however, has shown that foreign investment is not without risks. These include problems that result from working in isolated areas, a lack of infrastructure, untrained workers and an absence of a solid geological data base. While the likelihood of once-feared expropriation is now low, mining enterprises still must take precautions to gain the support of their constituencies, including a variety of governments (local, provincial and central), workers, environmentalists, cultural organizations and local landowners. Is foreign exploration worth the risk? In most cases, Yes! But maintaining tenure and long-term success in a less developed country is only likely with good planning and the use of appropriate safeguards. These include measures such as buying country-risk insurance, building multinational relationships, forming joint investments, developing a broad customer base and seeking local investors in the company (Cobbe, 1979). The primary theme of this lecture is: How a company handles its constituency is critical to long-term tenure in a foreign country. Ideally, a multinational mining company would be so effective in dealing with the local people and managing its relationship with the host government that it would become a preferred employer, preferred over its competitors and over local companies. Historical overview Our earliest ancestors lived in Africa three to four million years ago. The Paleolithic or Old Stone Age, about 500,000 years ago, marked the beginning of mining in its earliest form (Gregory, 1980; Wolf, 1984). Various types of rocks and stones were used for tools and weapons, with flint being the preferred resource for implements. Initially, these materials were collected as stones (eoliths) lying on the surface. Then they came from excavations of flint in limestone beds that were exposed in river banks or naturally occurring excavations. Later, more formal mining developed. No doubt tribes of the Old Stone Age experienced conflict over rights to eoliths, food and land. The question of who owns the land and has rights to its contents and what is fair value for extraction is still the subject of intense debate and, occasionally, open conflict. As time passed, the search for useful minerals required migration from one area to another. Later, voyages from Europe to the New World and travels to other remote regions were funded and supported by absentee investors, kings and such (Rogers, 1976). The primary objective of such funding was to obtain gold, silver, food stuffs and other commodities that could be collected from the new countries. This is still the objective of foreign investment.

Jan 1, 1994

In 1991, US mine production of barite decreased 3.4%. Barite consumption, sold or used by grinding plants, decreased by 11.7%. Imports also decreased by 15.4% over 1990. World mine production increased I%, according to the US Bureau of Mines. The value of domestically produced barite, f.o.b. mine, increased 3.3% according to the Bureau. The declared value c.i.f. US port of all imported crude barite during 1991 increased from $40.61/t ($36.84/st) in 1990 to $42.35/t ($38.42/st), the Bureau stated. Nevada was the leading producer of barite with 78% of the total, followed by Georgia and Missouri. It is estimated that 75% of the domestically mined barite was used as a weighting agent in drilling fluids. The remaining 25% was used in barium chemicals, glass or as a filler. Most of the production from Missouri, Georgia and Tennessee was used in the non-oilfield sector. Of the total barite used by grinding plants and chemical manufacturers, it is estimated that 93% was used in drilling fluids. The remaining 7% was in the non-oilfield sector, including barium chemicals and fillers in paper, plastics and glass. Tonnage consumed in the drilling fluids market decreased due to the lower average rig count during 1990. The average number of rotary rigs operating was 860. That was 14.9% less than the 1990 average of 1010 in the US. Crude barite imports were 138 kt (152,000 st) less than 1990 or 15.4%. Imports accounted for 70% of the (ap¬parent) barite consumed in the US. During 1991, China continued to be the leading exporter of crude barite ore to the US with 85.1 %. India followed with 14.8%. About 97.5% of the imported barite ore was used in the oilfield sector. Ground barite imports decreased from 56.7 to 46.2 kt (62,500 to 51,000 st) 1991. Mexico was a major exporter to the US, accounting for 75.3% of the total ground barite imports. Canada shipped 23.7%, while other countries accounted for less than 1 %, primarily for the nonoilfield market. During 1991, the number of grinding plants supplying the drilling fluids market along the Gulf Coast was reduced from 12 to 10. Baroid Drilling Fluids completed its mining program at the Rossi Mine near Dunphy, NV.

Jan 1, 1992

By Stephen C. Tadolini, Thomas M. Barczak

Western mines have had limited choices for standing support. Wood cribs were often too soft and unstable. The introduction of the Can support in the early 1990’s provided a very effective alternative and remains the dominant form of tailgate support. Water-filled prestressing cells are now used to cap the Can and preload it to provide an active roof load. The Cluster Prop, consisting of three timber wedge props bundled together, provides more capacity than an equivalent sized Can support and improves transport efficiency. However, the Cluster Prop is less stable and does not maintain a consistent load throughout its loading profile. Pumpable roof supports are another alternative support, but they have not been proven in high deformation environments. Alternative supports are also being used in longwall recovery operations. These include the Rocprop and Omni Prop, which are extendable support systems. They also provide active roof loading which can be beneficial in these applications. Specialty supports, such as the Sand Prop and Spider Prop, have also been introduced into western longwall operations. This paper compares the performance characteristics of these various support systems.

Jan 1, 2005

By Larry Murphy, Mohammad R. Jafari, David M. Giel, Sharat K. Kalluri

"Built in 1940’s to provide a key roadway arterial between New York and Boston, the Heroes Tunnel is the only highway rock tunnel in the state of Connecticut and is part of the Wilbur Cross Parkway. This 365.0 m long tunnel consists of two barrels, each with two lanes of traffic, and carries over 71,000 vehicles per day. For nearly 70 years, the tunnel has seen millions of vehicles pass through but time has taken its toll and now the tunnel lining, ventilation system and radial section joints are significantly deteriorated and in need of rehabilitation. Owned and maintained by the Connecticut Department of Transportation (CTDOT), CTDOT initiated a unique managed approach to mitigate the risk, social impacts and financial implications associated with rehabilitation of this tunnel. This new approach consists of performing field inspection and conducting a comprehensive study to explore six rehabilitation options, including construction of new tunnels and enlarging the existing tunnels. The main criteria for this study are: Impact on traffic and the resulting delay cost; Construction cost; Construction duration; and Construction complexity. This paper will present the results of the alternative study. PROJECT BACKGROUND Location and Importance Heroes Tunnel is located in the State of Connecticut within the Town of Woodbridge and the City of New Haven near the Town of Hamden border. Heroes Tunnel is the only true highway tunnel in the State of Connecticut. The tunnel is part of the Wilbur Cross Parkway (Route 15), a scenic connection between Hartford and New York. Originally constructed and opened to traffic in 1949, the tunneled portion of the parkway passes through the West Rock Ridge. The tunnel was originally named West Rock Tunnel, but was re-designated as Heroes Tunnel in 2003. Route 15 is a vital roadway within the State transportation infrastructure. In the vicinity of Heroes Tunnel, Route 15 carries approximately 71,000 vehicles daily. Locally, Route 15 provides access to residences, shopping centers, and points of interest, as well as other state roadways. Regionally, Route 15 connects New York to the Hartford area and serves as an alternate expressway route to I-95 and I-91. The tunnel is approximately 365.0 m long and passes through the West Rock Ridge. West Rock Ridge is an 11.3 km long rock ridge located on the west side of New Haven. A network of suburban streets abuts the mountain on all sides and a seasonal paved park road climbs to the crest of the ridge. Figure 1 depicts the tunnel topography and location."

Jan 1, 2016

Drainage and erosion control often become problems at mine reclamation projects. An example of this was an abandoned surface uranium mine on the south Texas plains. Engineers with the Texas Railroad Commission solved these and other problems with a three-dimensional geomatrix erosion-control matting at the 69-hm2 (170-acre) site, about 70 km (45 miles) southeast of San Antonio. Enkamat, manufactured by Akzo Nobel Geosynthetics, was installed to reinforce the grass waterways that handle runoff from the reclaimed mine. Reclamation was completed in the spring of 1992. Bill Walker is regional manager for Erosion Control Systems. He worked with the contractor to identify an erosion control product that complied with the project&apos;s design and installation parameters. "Use of erosion control matting enabled us to reduce erosion control costs," said Mark Rhodes, with the Texas Railroad Commission. "Also, the erosion control material was more aesthetically compatible with the reclaimed landscape." The commission&apos;s design called for a terrace ditch to be constructed midway up the reclaimed spoil slope to catch and collect water. Commission engineers selected spoil slopes, ranging from 5% to 8%, to build reinforced grassed waterways to drain the collected water from the terrace ditches. This was done instead of dropping the water at steeper slope location in rip rap- or concrete-lined channels. Enkamat&apos;s three-dimensional geomatrix of heavy nylon monofilaments is 95% open space that aids root growth. Its root-reinforcement system resists the hydraulic lift-and-shear forces created by high-volume discharges of water. In addition, fine eddy turbulences are prevented from isolating and uprooting individual roots and clumps of vegetation. Enkamat is flexible and lightweight. This makes it easy to install. And, because grass grows into it over time, it "disappears" after installation. Between 12,540 and 14,200 m2 (15,000 and 17,000 sq yds) were installed in the waterway using 150-mm (6-in.) staples to fasten the matting, said contractor Dale Blackstock. "It was easy to use; no problem at all to put down." Blackstock selected Enkamat from a list of eight different channel lining materials described as acceptable in the commission&apos;s design specifications. The design specifications were based on the results of channel-lining performance tests conducted by the Texas Department of Transportation. Rhodes said that the commission&apos;s Abandoned Mine Land Reclamation program had installed Enkamat on other abandoned uranium mines and on an abandoned surface lignite mine near Austin. "Pretty much all of our installations of Enkamat have worked out well," he said. "There have been no failures. The reinforced grass waterways have performed as designed."

Jan 1, 1998

By E. P. Fahrenthold, K. E. Gray

Introduction Brine reservoirs along the Texas and Louisiana Gulf coasts are currently under study to investigate the technical and economic viability of production wells designed to extract methane gas in solution. The effect of well pressure drawdown on reservoir rock and associated overburden material is important to well performance predictions and the analysis of potential subsidence problems. Consequently a series of compaction tests have been conducted on sandstone and shale cored from a test well drilled near Hitchcock, Texas, in order to determine the variation of mechanical properties to be expected over the producing life of the formation. Previous Work The referenced tests are part of an extended study of geopressured-geothermal reservoir behavior, including compaction (Jogi, Gray, Ashman, and Thompson, 1981 and Jogi, Kalra, Gray, and Thompson, 1981) and creep (Thompson, Jogi, Gray, and Richardson, 1981) tests of reservoir rock and related reservoir performance studies (Rago, Okhuma, Seperhnoori, and Thompson, 1985). Recent work has considered the nonlinear constitutive behavior of sandstone (Fahrenthold and Gray, 1985 and 19861, while additional experimental work is reported here. Geological structure and composition of the Hitchcock field from which the core samples were obtained is discussed by Light (1985). Experimental Procedure Compaction tests were conducted on cylindrical cores, nominally 2.75 inches in length and 2 inches in diameter, with independent control of the axial, confining, and pore pressures. Axial and radial deformation of the samples were measured in tests over a range of effective stress states expected to develop over the reservoir lifetime. The term effective stress as used here refers to the algebraic difference of the total stress and pore pressure, with compression taken as positive. Three types of compaction tests were conducted on the sandstone. In the uniaxial tests, axial total stress and radial strain were held constant as the pore pressure was reduced, similating one dimensional compaction which may occur during reservoir depletion. In the triaxial tests, radial total stress and pore pressure were held constant as the axial total stress was increased, duplicating conventional rock compaction test procedures. In the pore pressure drawdown tests, axial and radial total stresses were held constant while the pore pressure was reduced, in order to investigate differences in sample response to mechanical and pore pressure loading. Compaction tests were also conducted on shale material obtained from the reservoir overburden. The field coring process provided few consolidated shale sections sufficiently large to allow preparation of samples with the dimensions described above. With additional attrition during sample preparation of this brittle material, ultimate yield of the coring effort was limited. The few available samples were tested in uniaxial and triaxial tests similar to those described above. The use of displacement transducers to measure sample deformation avoided the difficulty of strain gauge installation on this material. Test Results The sandstone and shale both demonstrated nonlinear stress-strain behavior, with hysteresis and residual strain present upon unloading. Polynomial interpolation of the stress-strain curves was used in the calculation of incremental values for the loading and unloading moduli. Figures 1 and 2 show example axial effective stress-axial strain curves for triaxial tests conducted on sandstone and shale samples. The figures plot incremental stress and strain variables, defined as deviations from the state of prestress to which the sample was subjected. The state of prestress was varied between tests in order to investigate material behavior over the entire stress and strain space of interest. Tables 1 and 2 give the incremental moduli (Young&apos;s modulus and Poisson&apos;s ratio) as a

Jan 1, 1986

The latest resource estimate for the Caspiche gold/silver/copper project in the Maricunga region of Chile was released by gold explorer Exeter Resource Corp. The resource is low grade, but bulk minable and drilling to date has shown a NI 43-101 compliant inferred resource of 1,117 Mt (1.23 billion st) grading 0.55 g/t (0.016 oz/st) gold, 3.81 g/t (0.111 oz/st) silver and 0.22 percent copper. Exeter said these findings make the in situ metals amounts of 609 t (19.6 million oz) of gold, 4.4 kt (137 million oz) of silver and 4.84 billion lbs of copper, which the company relates as 33.7 million gold equivalent ounces using assumed metal prices of $23.33/g ($800/oz) for gold, 35 cents/g ($12/oz) for silver and $2/lb for copper. The deposit is almost midway between Barrick?s Cerro Casale gold deposit and Kinross? Refugio Mine. In a statement Exeter chairman Yale Simpson said ?This updated resource estimate places Caspiche firmly among the world?s largest gold-copper discoveries in recent years and clearly supports our decision to aggressively drill the property, despite the global economic decline. ?We expect that the very substantial copper and silver credits will be extremely important, and will markedly impact the potential viability of Caspiche. Specifically, using metal prices of US$2/lb copper, $23.33/g ($800/oz) gold and 35 cents/g ($12/oz) silver, the 4.84 billion lbs of copper and 4.2 kt (137 million oz) of silver are equivalent to 376 kt and 62 t (12.1 and 2 million oz) of gold, respectively. ?Our recent drilling has defined what appears to be a coherent higher grade central zone associated with a definable early stage diorite intrusion. We expect this zone will be important in developing various mining and economic models for the project,? Simpson said. Exeter is still drilling the deposit to expand the re-source estimate further to the southeast and at depth and to upgrade the higher grade central zone to the indicated category. Simpson said, ?Exeter intends to enhance the value of Caspiche by continuing to de-risk the project through ongoing exploration, metallurgy, engineering, water and environmental studies. These studies will continue through the next 12 months and will lead to a conceptual development study. A timeline for the release of that study is being formulated. The project budget for the next 12 months is C$14 million.? Mineweb reported that Caspiche is likely too big of a deposit and at too high of altitude for Exeter to handle alone. Exeter will be looking to other majors, or perhaps the Chinese, to help develop this huge orebody. But, in the meantime, it also has its high grade Cerro Moro deposit in Argentina, which could be brought to production relatively quickly and at relatively low cost.

Jan 1, 2009