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By H. V. S. Tingley, D. Helfant Ghose

"Ten years ago," said a mining industry personnel manager, "we used to wine and dine new mining engineering graduates. Now I can pick and choose among men with 10 years of experience." Comments like that are common throughout the industry today. During the 1970s, the US and Canada did indeed suffer from a severe shortage of mining engineers, especially experienced ones. Moreover, it seemed likely this North American shortage would worsen. Increased production of minerals and coal was pushing demand for mining engineers upwards, and there appeared to be substantial new employment prospects for them in the nascent synfuels industry. The oil majors entering the mining industry were pushing for an increased professionalization of mining management, heralding a trend towards higher intensity in the use of mining engineers. In response to the shortage, mining schools expanded their programs dramatically. By 1982, American schools were churning out more than 600 new mining engineers per year, compared to barely 200 in 1970 (Table 1). The timing of the explosion in the number of mining engineers could not have been worse. The downturn in the economy and the resulting slump in the mining industry coincided almost exactly with peak output of mining engineers. The market for mining engineers shifted from shortage to surplus with startling rapidity. The new crop of engineers, no longer courted by the mining companies, struggled to find any mining jobs. At the same time, experienced mining engineers found themselves thrown into the job market, some for the first time in decades. The current oversupply of mining engineers is assumed to be a temporary phenomenon. As the economy recovers, the demand for mining engineers is expected to pick up at least enough to absorb today's surplus. Not so, according to a recent study by Fenvessy and Schwab, a general management consulting and executive recruiting firm. In 1979, Fenvessy and Schwab was commissioned by a group of major mining companies to conduct a worldwide study of supply and demand for mining engineers to the year 2000*. The study began at the height of the North American shortage. One major objective of the study was "to identify means by which business and educational institutions may cope with and alleviate a future shortage of mining engineering talent." The findings, however, ran directly counter to expectations. The current oversupply will not disappear with economic recovery, the study concluded. In fact, the US and Canada are facing a massive oversupply that will probably last until the end of the century, unless enrollments in schools are reduced. Study Method Fenvessy and Schwab's conclusions are based on supply and demand models for mining engineers that it developed in the course of the study. Specifically, predictions for the supply of mining engineers are based on a survey of the 54 mining schools that account for about 90% of the world's annual output of mining engineering graduates. This survey asked for data on historical and projected number of graduates, obstacles to further expansion, changing trends in the use of mining engineers, and graduate career patterns. Fenvessy and Schwab developed three mining engineering supply scenarios from the survey data. The high case, considered unlikely for most of the industrialized world, is based on a continuation of the 1970's soaring growth rates. The middle case was established from the mining schools' own estimates of future growth in the number of graduating mining engineers. Finally, a "low growth" case for the US and Canada assumed that the number of graduating engineers will remain at current levels. Mining engineering demand was forecast using a complex model based on the demand for 50 major minerals. Formulas were

Jan 9, 1983

By Terrence D. Chatwin, James Hendrix

Based on the findings within their report to Congress, the US Environmental Protection Agency (EPA) announced that it had decided not to regulate mining wastes under the hazardous waste regulatory program. However, they found that some mining wastes are hazardous and may be causing environmental damage. Cyanide wastes from heap leach operations were included in this group. In evaluating the effects of cyanide use in mining one finds a significant lack of information on the fate of cyanide in soils. Cyanide attenuation and degradation of soils is important, because ground water is a major potential pathway for cyanide contamination. There is a strong potential for cyanide to be removed from solutions as it migrates through soils· by volatilization, chemical reaction, adsorption, oxidation and biological processes, but no definitive investigation has defined these mechanisms adequately to be able to predict the fate of cyanide in soils.

Jan 1, 1998

By S. C. Sun

Very little information is available concerning the magnetic properties of minerals and only recently has there been any attempt to correlate magnetic susceptibility with varying chemical composition1. The work described here covers a study of the relationship and chemical composition of both the rutile and sphene types of titanium minerals. The relationship between the magnetic susceptibility of three selected mineral specimens and the applied field strength is also presented. Experimental: The equipment and procedures used in this in- vestigation for crushing and cleaning the mineral specimens and for determining the magnetic susceptibilities were the same as that employed by Spokes and Mitchell1. The particle size of-the measured specimens was limited to 270/325 mesh.

Jan 1, 1959

The Bagdad mill, built in 1977, was de-signed for a mill capacity of 36,300 tpd. An ABC (Autogenous Mill-Ball Mill-Crusher) grinding circuit was chosen. The original mill contained three completely independent grinding circuits, each containing one 9.75 m diameter by 3.96 m long fixed speed autogenous mill, one 4.72 m diameter by 6.71 m long ball mill and one 2.13 m diameter short-head cone crusher. Total installed power per grinding circuit was 8,464 kw with 5,966 kw in the autogenous mill, 2,237 kw in the ball mill and 261 kw in the crusher. (See FIGURE I--Major Equipment Flow Diagram.) The autogenous mills were designed to be able to operate semi-autogenously but were never converted to SAG. As a result of this design, only about 4,100 kw of the designed power is utilized in the autogenous mills. The grinding circuits are closed with 2.44 m by 6.10 m double deck vibrating screens. Screen oversize is returned, by a series of conveyors, underneath the mill coarse ore stockpile to feed the crushers. Variable speed belts feed the crushers and control power draw. Crusher product reports directly to the tail end of the autogenous mill feed belt. (See FIGURE 2--Typical Crusher Feed and Product Size Distributions.) Tramp iron in the autogenous mill-crusher circuit is handled in a unique way. A magnetic sensor detects the metal. This closes a gate which directs the crusher feed onto a separate belt which bypasses the crusher and returns the material to the autogenous mill feed belt.

Jan 1, 1992

By J. L. Hoover, P. W. Conrad, J. Downey, S. Parrow, S. Rosenthal

The goal of the drill bit consumption study was to develop an equation(s) based on various components that affect drill bit wear and use that equation(s) to estimate the consumption of bits during production drilling. Drill bit data from various geographic locations were compiled and used to develop linear regression equations using the Microsoft Excel software package. Multiple drill bit consumption equations were developed and statistical analysis was used to verify the accuracy of those equations. The equations will allow mining companies to more accurately forecast drill bit consumption when evaluating new mine properties. This capability becomes increasingly beneficial to forecasting as the cost of consumables increases.

Jan 1, 2012

By Robert L. Vines

"What is past is prologue" - motto of National Archives The question of past, present, and future safety performance in the coal mining industry is not merely an academic one, or one which arises from soul-searching curiosity. It is a question involving pragmatic ramifications, and the answers, or perhaps the public perception of the answers, will have a strong impact on the public policies which influence the course of meeting the Nation's future energy demands. Those of us in the coal industry are keenly aware of the significant impact of the public reaction -- in the form of the 1969 Health and Safety Act -- to -past performance of the coal industry which it found unacceptable. That Act was revolutionary -- and it was expensive. But in finding the industry's past performance unacceptable, the public also recognized its own contributory role through having enjoyed a "buyer's market" forced on a highly competitive industry. One result was to limit the industry's resources and restrict its ability for self-improvement of its safety performance. In acknowledgement of that role, the public picked up the tab for Black Lung disability incurred prior to that time.

Jan 1, 1985

By W. J. Atkinson, E. M. Anderson

FOREWORD This paper is based on the authors' experience gained in the environmental assessment of major uranium projects in the former Department of Science and the Environment and Department of Home Affairs and Environment of the Australian Government. The authors gratefully acknowledge assistance received from colleagues within the Department of Home Affairs and Environment in the preparation of this paper. Special thanks go to Mr K.E. Thompson of the Department's Environment Division for his valuable comments and criticism. The views expressed in the paper are those of the authors alone and not the Australian Government or Dames & Moore. INTRODUCTION Uranium has been mined in Australia since 1954. A number of small scale mining and milling operations were active in the Northern Territory, in South Australia and in Queensland in the late fifties and early sixties. However, in the late sixties there was an increase in exploration activities in the expectation of an upsurge in world demand for uranium Substantial new resources were delineated in the Northern Territory, Queensland, South Australia and Western Australia. The most significant deposits were located in the Northern Territory, in what is called the Alligator Rivers Region located approximately 200 km east of Darwin. The Region is in the latitude of 13° South and thus lies within the Australian tropics (Figure 1). It consists of approximately 2.3 million hectares of natural wilderness containing much spectacular and attractive scenery. The area is noted for its abundant wildlife, particularly the waterbirds that gather on the flood-plains. Much of the vegetation is diverse and interesting. The Aboriginal population still maintains elements of the traditional way of life, and the spectacular Arnhem Land escarpment contains many of the best surviving examples of Aboriginal rock art. Numerous rich archaeological sites provide evidence of continuous human habitation for tens of thousands of years. Climatically, the Region is of the tropical monsoon type with a dry season from may to September and a "wet" from November to March. High intensity short period rainfall is characteristic, and the average annual precipitation is in the order of 1 350 mm. The monthly mean temperature ranges from 25° to 30°C throughout the year. The development of regulatory controls on uranium mining in the Alligator Rivers Region has been affected by the political status of the Northern Territory. While Australia is a federation, established as an independent self-governing country in 1901, it was not until 1978 that the Northern Territory became to any real extent self-governing. Prior to 1978, the Territory was administered through a special department of the Commonwealth (ie. the Federal Government). Under the Northern Territory (Self Government) Act 1978, administrative powers similar to those possessed by the Governments of the six founding Australian states were provided to the Territory Government. However, the Commonwealth government did not transfer to the Territory all such powers and functions, and in particular there has been, since 1978, a dual role for the Commonwealth and Territory Governments in the regulation of uranium development. Details of this role are provided later in this paper. RANGER URANIUM INQUIRY By 1973, major deposits had been discovered in the Alligator Rivers Region at Nabarlek, Ranger, Koongarra and Jabiluka. The estimated reserves and mine life expectancy of these deposits are given in Table I. Other radioactive anomalies have also been identified in the area but, as yet, they have not been delineated or evaluated. [ ] In 1974, an agreement was signed between the Commonwealth Government and Peko Mines Limited and the Electrolytic Zinc Company of Australia Limited for the joint development of the Ranger deposit. In July 1975, the Government announced a Commission of Inquiry under the provisions of the Commonwealth Environment Protection (Impact of Proposals) Act 1974, into the proposed Ranger development. The inquiry was known as the Ranger Uranium Environmental Inquiry or more commonly, the Fox Inquiry after the presiding Commissioner, Mr Justice Fox.

Jan 1, 1981

By Bob Snashall

Introduction 1300 BC, Egypt. Pharaoh, the god-king, owned all things. He was the only mine operator. As the provider of all things, Pharaoh had great expectations of his officials who gathered the wealth. Pharaoh's official, the mine foreman, was at a gold mine site to see that royal expectations were met. For the official, it could mean a promotion to the good life here and to the godly life hereafter. When he checked the haul for sufficient progress, a lot was at stake. The miner wore a loincloth, perhaps a headband and, if he was a prisoner, ankle manacles. Only an oil lamp helped illuminate the hot, dusty blackness. A fire at the base of the quartz ore face competed for scarce air. The ore so heated crumbled at the prompting of copper wedges. Confined to a crouch, the miner tossed chunks of ore onto a rope-mesh which, when loaded, was drawn up and lugged out. On the surface, the gold was ground to dust. Then it was transported by donkey caravan to the royal depot. There it was weighed, recorded, and distributed to workshops. Many minerals mined Egypt had gold mines to the south in Nubia and to the east in the desert and Sinai. Indeed, gold underwrote Egypt's prosperity. With a constant gold supply, fewer hungry hands robbed burial crypts and tombs. Gold was sacred, "the flesh of the gods." The shiny metal financed the army that policed the desert mining routes and guarded the gold caravans from Bedouin marauders. Gold theft was an offense to the gods. Anyone caught with gold `in his lunchpail,' so to speak, could say goodbye to life, both in this world and the next. In addition to gold, Egypt possessed other mined riches that allowed the Egyptian civilization to flourish. From Sinai and Nubia came copper. So abundant was the red metal that it enabled Egypt to become the supreme power, before the advent of iron. Also mined were amethyst, turquoise, feldspar, jasper, carnelian, and garnet. These were used for the rich inlay work that distinguished Egyptian jewelry and cloisonne. But Egypt's most endurable and awesome material was its stonework - for statues and obelisks and in temples, tombs, and pyramids. Stone quarrying was a vast enterprise. One expedition boasted nearly 10,000 men. These included 5000 laborer soldiers, 130 skilled quarrymen and stonecutters, and - egads! - even 20 scribes. In addition, there were thousands of officials, priests, and officers grooms. There were even fishermen, to provide the multitudes with the catch of the day. Mining methods detailed In 1300 BC, quarrying techniques had changed little since the age of the pyramids some 1300 years before. At that time, in 2600 BC, limestone was locally quarried and fashioned into the blocks of the pyramids. A basic limestone mining method was tunnel quarrying. A ramp was built up to the face of a cliff. A monkey stage was then erected on a ramp. While standing on the stage, quarrymen carved out a rectangular niche in the cliff. The niche was large enough for a quarryman to crawl into. With a wooden mallet, he hammered long copper chisels along the edges of the niche floor to free up the back and sides of the block. The quarryman climbed out of the niche and removed the stage. He then carved out a series of holes in the cliff face for what would be the bottom of the block. The quarryman pounded wooden wedges into the holes. He watered the wedges until they were soaked. The water-logged wedges expanded, splitting the stone along the line of holes. The freed-up block was then levered down from the cliff. On the ground, the blocks were placed on sledges. Men pulled these to nearby water transport. Without block and tackle pulleys, paved roads, and wheels, this was no mean feat. Each block weighed an average of 2.3 t (2.5 st). Whenever possible, the quarrying was done directly from the surface. This "open cast" quarrying also involved using chisels

Jan 2, 1987

By Jonathan Ludlow, Robert A. Jankowksi

Introduction A longwall operator can make few changes to increase output, significantly reduce respirable dust, and decrease power consumption. Reducing drum speed, and thereby cutting with increased pick penetration, is one. This article defines the benefits of deep cutting in terms of reduced dust production and power consumption. It also identifies the practical aspects of high pick penetration in terms of shearer performance and coal loading. Before examining some practical aspects of reducing drum speed and looking at the theoretical background, it is worthwhile to summarize what is meant by high penetration and deep cutting, and what potential benefits and pitfalls may be expected. Deep cutting (in the sense of high penetration rather than wide web) can be defined in one or more of the following ways: • Cutting with an average pick penetration distance higher than that used in the past. • Cutting with a pick penetration higher than the longwall operator would have used if the advantages of deep and slow cutting were not considered. • Cutting with a well-designed shearer drum below 40 rpm. All these definitions are slightly arbitrary. They are given to provide a basis for discussion and to make the point that any move towards deeper, more efficient cutting can result in operational benefits. The benefits of deep cutting appear in many different areas. The most noticeable benefit, provided suitable instruments are available, is the reduction of airborne respirable dust. During an experiment on a longwall in the Pittsburgh seam, a nearly four to one reduction in dust levels was seen when drum speed was halved. Not all studies have shown such a big reduction, but it seems that some benefit is almost always obtained when drum speed is reduced. Production rate and specific power consumption are also affected (in a positive sense) by reducing drum speed or increasing pick penetration. Although these changes may not be as spectacular as those in dust level, they contribute to the economic return of the longwall operation. Similarly, improved washability through fines reduction may have a beneficial economic effect. Cutting with shearer drums operating at lower speeds does have some possible deleterious impacts that an operator should be aware of. For example, cutting reactions - loads imposed on the picks by the coal being cut - will be increased as a deeper cut is used. Steps must, therefore, be taken to ensure the stability of the shearer and provide an adequate haulage effort. These increased cutting reactions also result in higher loads on the power transmission system (gearboxes, ranging arms, pick boxes, etc.) from the shearer motor(s) to the pick tip. These higher loads must be anticipated and provided for with the necessary hardware. In particular, extra haulage power must be provided with low drum speeds, since haulage effort required increases roughly in proportion with pick penetration. Because the drum will be rotating more slowly or will have fewer picks, the load on shearer components will also be more variable. If suitable, robust equipment is not used, this increased vibration will decrease reliability. Benefits of Deep Cutting Lower dust levels, decreased specific power consumption, and improved product washability are the most noticeable benefits of reduced drum speeds. Although the benefits will vary greatly with mining conditions and the type of coal, some examples of what can be expected are described below. Reduced Dust Levels Figure 1 shows principal results of a study on the effects of reduced drum speed conducted on a longwall in the Pittsburgh seam (Ludlow, 1981). This figure shows that average dust production was reduced by about 70% when drum speed was halved. By making some assumptions about such quantities as coal density, it is possible to apply this proportional reduction to the quantity of respirable dust liberated per ton of coal mined. When this is done, two kinds of results are obtained: • At 70 rpm, about 1 g (15 gr) of airborne respirable dust is created for every ton mined (roughly one part per million). At 35 rpm, only 0.28-0.37 g/t (3.9-5.1 gr per st) of coal mined become airborne respirable dust. • At 35 rpm, nearly four times the amount of coal may be mined before the compliance level is exceeded, compared with 70 rpm.

Jan 3, 1984

By H. Keith Henson

The purpose of this paper is to describe the possible application of two relatively new technologies: flat load cells, and improvement seeking computer programs (referred to in the literature as heuristic programs); to a very old problem, inventors control of ball mills. The combination of these two technologies seems most applicable to grate discharge mills operated closed circuit. It is possible that other applications such as controlling the inventory of autogeneous mills might also be found. Direct control of ball mill inventory has been the goal of a number of investigators over many years. Many patents and articles on the subject have claimed success, but operating installations are hard to locate. An excellent review of the advantages and problems of direct inventory control is contained in an article by Oswald and Ziegler (1). Figure 1 is a conventional representation of throughput vs. inventory with other factors such as slurry consistency and rock twee held constant. There are common sense, physical arguments? and experimental evidence supporting the existence of a unimodel curve of this twee? though direct measurement of the shape is difficult and how it moves as rock type changes is riot well known. Figure 2 represents the problem faced by all mass measurements of inventory, a tare weight of about 25 time the inventory mass. Worse yet, the tare is variable due to ball and liner wear and the Periodic addition of balls. The problem then breaks down into two parts: 1) obtaining enough mass

Jan 1, 1977

By Thomas J. DeMull

Heap leaching was introduced to the precious metals mining industry approximately two decades ago as a simple, low cost method for recovering gold and silver from ores. Since that time, operational experience has contributed to knowledge and understanding of the process, making it a reliable alternative to conventional milling processes for low grade ores. At time of this writing, dozens of heap leach operations are active producing hundreds of thousands of ounces of gold and millions of ounces of silver annually. These successes have caused the popular press to acclaim heap leaching "high-tech" gold mining, but, despite the hype, the process remains a simple one. An example of simplicity in heap leaching is the operation established in 1986 at Amax Gold's Sleeper Mine. Starting with a simple goal, namely to produce gold from sub-mill grade ore at low cost, heap leaching was rapidly implemented at Sleeper; only five months after testwork started, leaching commenced on the first commercial scale, 50,000 ton heap of low grade ore. Sized at 600,000 tons per year to produce 10,500 oz gold per year, the low grade heap operation has performed beyond expectations. During the first year of production, 881,800 tons have been leached producing 15,665 oz of gold and 35,528 oz of silver. Operating ·costs for the first year have averaged $112 per oz gold produced ( or $95 per oz if silver credit is included). Successful implementation of heap leaching at Sleeper has had a dramatic impact on ore reserves and future operations.

Jan 1, 1998

By R. W. Barbaro

The limitation of sulfur dioxide in power plant emissions dictates that sulfur in coal be reduced to the lowest possible level before combustion so as not to aggravate the emission control problem at the stack. For coal fired power plants, the methods in practice to achieve low sulfur coal include mining areas with relatively low sulfur. reducing sulfur in the mined coal through preparation techniques and blending high and low sulfur coals. A prerequisite to the successful implementation of any of these practices is the knowledge of the spatial distribution and the capability to predict sulfur values in a coal seam.

Jan 1, 1988

By Edward C. Krug

"You are to use the word ... purely for its selling power. It is a name they venerate. As a result, you can use the word ... to ... get [them] to practice, not only without shame bit with a positive glow of self-approval, conduct which, if undefended by the magic word, would be universally derided." (C.S. Lewis, The Screwtape Letters, 1982, p. 162). "We need to tear everything down over a period of time and reconstruct a whole new world, planned top to bottom. "Right now there are just way too many people on the planet [5.3 billion]. `If we had ... an ethic ... we could cut back to 250 million-350 million people. `The United States is ... a bunch of pigs ... the average citizen ... [uses] maybe 70 to 80 times as much as anyone in the Third World.` "The indigenous pople were the ones that were right! I mean, they had their own religion, their own ethics and their own technology. We just went down a wrong road. "So when he says, `We got to rebuild the whole world,' you have no doubt this is serious sentiment .... And it is finally this world view that distinguishes (Ted) Turner as a media mogul and an environmentalist. It is why Worldwatch's Lester R. Brown told me Turner was `truly a visionary. "'(Interview of Ted Turner, Audubon magazine, November-December 1991. On Dec. 28, 1991, Ted Turner was name Time magazine's "Man of the Year." Clearly, media and environmental leadership agree with Turner's openly stated beliefs.)

Jan 1, 1992

By J. Lovering, H. Wilhelm, P. Siewert

Introduction The Afton property is located 290 km (180 miles) by air east-northeast from Vancouver and 14 km (8.7 miles) west of Kamloops, a city of 60,000 people, in south central British Columbia, Canada. The mine is adjacent to the Trans-Canada Highway at an elevation of 670 m (2198 ft) above sea level. The ore body is a porphyry copper deposit that has undergone supergene alteration. The major economic minerals in the supergene zone are native copper and chalcocite with chalcopyrite and bornite in the hypergene areas. The grade is 1% with an overall copper distribution - 70% native, 25% chalcocite, and 5% chalcopyrite with bornite and covellite. The ore also contains important but variable amounts of gold and silver. The mill was designed to treat 6350 t/d (7000 stpd). Semiautogenous grinding was selected to minimize capital cost and because of the expected high clay content of the ore, which would have caused problems in a conventional crushing and screening plant. Test work indicated that a recovery of 87% was possible in a circuit incorporating both flotation and gravity separation. Flowsheet Run-of-mine ore is crushed in a 1.06 x 1.65-m (3.5 x 5.4-ft) Allis Chalmers gyratory crusher set at 228.6 mm (9 in.), closed side setting. The surge pocket, below the crusher, is emptied by a Hydrastroke feeder onto number one conveyor, which discharges onto a 180,000-t (198,416-st) coarse ore stockpile. Six Hydrastroke feeders on two conveyors withdraw the crushed material from the bottom of the pile. These two conveyors, in turn, discharge onto the belt feeding the semiautogenous mill. The live storage in the stockpile is approximately 22,000 t (24,250 st), sufficient for three days' mill feed. Primary grinding is accomplished in an 8.5-m (28-ft) diam by 3.7-m (12-ft) long Koppers (Hardinge Cascade) mill (Fig. 1) containing a 10% ball charge and driven by a 4000-kW dc variable speed motor. The mill dis¬charge is pumped by a 10 x 12 G.I.W. pump to a 1.22 x 4.88-m (4 x 16-ft) stationary screen sloped at 20°. Screen oversize returns to the semiautogenous mill (SAM), and the undersize flows by gravity to the ball mill discharge pump box. Secondary grinding is performed in a 5-m (16.4-ft) diam by 8.84-m (29-ft) Koppers overflow ball mill driven by a 3430-kW synchronous motor through an air clutch. The mill is in closed circuit with a Krebs Cyclopac containing 10 635-mm (25-in.) cyclones and the cyclone overflow, at 35% solids and 65% to 70% -200 mesh, is flotation feed. In order to limit the buildup of native copper, circulating in the secondary grinding circuit, a portion of the underflow from the cyclones is processed in a circuit containing screens, cyclones, and shaking tables to produce a finished metallic copper concentrate. Primary mill variable speed drive The overall waste to ore ratio at Afton was 4.5:1. The mining was to be done with only three shovels, which meant that it was highly unlikely that more than one of them would be in ore at any one time. The resulting inability to blend the mill feed made it impossible to prevent wide swings in the grade and grindability. The variable speed do drive motor installed on the semiautogenous mill was selected because of the extreme variability of the Afton ore body. This variability has persisted throughout the lifetime of the mine. There are times, however, when due to ore conditions, the mill is operated at full speed (78% of critical) for extended periods of several shifts duration. There are other times when the mill speed may be changed several times in a 12-hour shift due to changing ore conditions. When ore is processed that contains a fairly large proportion of fine native copper, the primary mill speed and, consequently, the tonnage may be reduced to improve the secondary grind and to maintain an acceptable grind and recovery. High clay ores require less mill speed and more dilute grinding densities. In the latter case, the slower primary mill speed also helps to minimize damage to the mill liners. Approximately 57% of the time the mill operates between 90% and 100% of full speed or between 71% and 78% of critical. The variable speed is also used for inching during mill relines.

Jan 1, 1987

By Kenneth J. Miller

A novel two-stage froth flotation process to remove pyritic sulfur from fine- size coal is described. The process consists of a first-stage, standard coal flotation step in which high-ash refuse and some of the pyrite are removed as tailings. The first-stage clean coal froth concentrate is then repulped in fresh water, and a coal depressant, a pyrite collector, and a frother are added to float the remaining pyritic material. Laboratory and pilot plant flotation results with coals from the Lower Freeport and Pittsburgh beds are given. The pilot plant test results show that up to 80 percent pyritic sulfur reduction was achieved with the Lower Freeport bed coal and up to 50 percent with the Pittsburgh bed coal. Laboratory and pilot plant results were in excellent agreement, indicating that the process is a viable means of removing much of the sulfur from some coals.

Jan 1, 1974

By Gonzalo Barrientos

Instrumentation and observation of real mine structures helped define the pressure arch at White Pine, a large copper mine in sedimentary rocks. The pressure arch, which is attributed to inherent horizontal stresses, is used in the design of mine openings.

Jan 1, 1969

By Morris Beattie

Arseno Processing Ltd. has developed process technology for the extraction of gold from refractory ores and concentrates. These ores, which do not respond to conventional extraction processes, are rapidly becoming the primary targets for mining companies wishing to become significant gold producers. It has recently been estimated that by the mid 1990's, the annual gold production from the Pacific Basin Epithermal Arc in southeast Asia could be as high as 550 tonnes. Within this area the Porgera deposit under development by Placer, Renison and MIM, and the Lihir Island deposit under development by Kennecott have been shown to be refractory and require pretreatment before the gold can be extracted. The additional deposits which are now starting to be developed in this area are also expected to require such pretreatment. The Arseno process promises to be an economical pretreatment for these ores and to result in the maximum achievable gold recovery. Numerous refractory deposits are also known in Australia, North America, China and other parts of the world. Samples from many deposits throughout the world have been tested using the Arseno process conditions and the consistently successful results have demonstrated its widespread application. The samples which have been tested include ores in which the gold is locked in pyrite, marcasite or arsenopyrite. The process is insensitive to the sulphur content of the feed. Feed materials containing from 1 % to 50% sulphur have been tested successfully with the process. In the Arseno refractory gold process, sulphide minerals are dissolved so that the contained gold becomes accessible for subs7qu7nt gold recovery. This gold recovery is achieved by cyamdat1on of the process residue. For many of the materials which have been tested, gold extractions in excess of 95% have been achieved.

Jan 1, 1998

By G. L. Alston

Rigid urethane foam can be used effectively for improving mine air conditioning systems by reducing heat and moisture transfer from mine rock to ventilating air and from mine rock to ventilation ducts, for erecting mine ventilation stoppings and overcasts, for sealings around door frames and bulkheads to prevent air leakage, for preventing spalling and sloughing of roof and rib and for erecting fire-resistant powder magazines and transformer or compression stations. Rigid urethane foam is a tough, cellular material, made by nixing diisocyanate and polyether polyol resin in accurate proportions through an applicator system, then the two chemicals react, the mixture expands thirty times its original volume with 85 to 95 percent closed cells. Within seconds, the mixture solidifies and takes a preset which will adhere to overhead or vertical surfaces. It will adhere to brattice cloth, steel, wood, concrete and rock, Excessive wetness will reduce the adherence, but in such cases adherence can be improved by preliminary application of an absorbent dust such as cement.

Jan 1, 1963

By Stephen H. E. Phillips

Geological and hydrological conditions in the strata overlying the Salado Formation vary considerably in the Carlsbad, New Mexico area. The first four shafts sunk at international Minerals and Chemical Corporation's property have been located in competent and essentially dry conditions, while other shafts on adjacent properties have had such adverse conditions that ground freezing has been chosen as the water and ground control technique for shaft sinking. At the location of the IMC No. 5 Shaft there has been extensive-erosion and salt dissolution in the Rustler Formation which has led to collapse of some zones of the strata. Both ground freezing and pregrouting were considered as alternative methods of stabilizing the extremely poor ground conditions and controlling the potentially very heavy water inflows it was decided that pregrouting the shaft was feasible and would offer substantial cost and time saving over a ground freezing technique. This paper describes the pregrouting techniques used and illustrates the requirement for flexibility in a grouting program so that it can be codified to reflect any new or additional information which is obtained during the progress of the grouting.

Jan 1, 1984

By Kailash Narayan

Atlantic Richfield Company began operating a commercial uranium solution mining project in April, 1975 in Live Oak County, 10 miles southwest of the town of George West (Figure 1). The operation is designed to produce 250,000 pounds of U303 per year and is jointly owned by Atlantic Richfield Company, Dalco and U. S. Steel. The proprietary process employed in this operation consists of injecting an alkaline leaching solution into the ore-bearing formation through a pattern of injection wells. The uranium-bearing solution is then removed through producing wells using submersible pumps in central production wells. The produced solution is pumped through a pipeline to the plant area where the uranium is extracted. The barren solution is refurbished and returned to the pattern area for reinjection. The injection field and plant site are located in the drainage of Spring Creek, a small intermittent stream tributary to the Nueces River. Land use in the area is primarily agricultural -- cattle ranching and farming -- but several producing gas fields are present in the areas as well.

Jan 1, 1976