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By R. K. Rajamani, R. Verma

In ball milling the rates of breakage vary primarily with the size distribution of powder in the mill. Using an approximate solution to the batch-grinding equation, the acceleration and deceleration of breakage rates of all individual size classes are determined when the grinding environment is varied. Experimental results with limestone and copper ore show time-dependent breakage rates under both dry and wet grinding conditions. The effect of grinding additives on breakage rates is also studied. In general, breakage rates increase for coarse sizes and decrease for fine sizes with an increase in the fines present in the mill. Such variations have strong implications in closed-circuit grinding.

Jan 1, 1992

By Enrique Llewellyn

North River Energy Company a previous subsidiary of Republic Steel Corporation commenced development of the Number One Mine in mid-1972. The mine is located in West Alabama and presently employs a total of 632 people. Production capabilities have increased to 1.4 million clean tons of steam coal per year with the newly purchased Longwall System. Washer recovery averages 57 percent. The seam being mined is the Pratt or Corona with an average height of 52 inches and an average cover of 540 feet. The immediate roof is laminated sandstone and the floor is composed of a hard fireclay. Total production out of the mine is provided to Alabama Power Company under a longtime contract.

Jan 1, 1981

By O. D. Christensen

The Carlin Trend is a 60 km (38 mi) long northwest alignment of epithermal, sediment-hosted, disseminated gold deposits. Collectively, these orebodies contained more than 620 t (20 million troy ounces) of gold. The Carlin deposit, located near the center of the Trend, has become the "type" deposit of this class. There are, however, significant differences between the individual deposits. Six subdistricts can be distinguished, based upon geographic, structural, lithologic, alteration, mineralization style, and geochemical characteristics. They are, from northwest to southeast, the Bootstrap, Bluestar-Goldstrike, Lynn, Maggie Creek, Rain and Bullion (Railroad) subdistricts. Regional Geologic Setting The Carlin District is located centrally within the Great Basin Geologic Province. Host rocks for the deposits include sedimentary units that range in age from Ordovician to Mississippian, as well as a Jurassic-Cretaceous granodiorite stock. During the Early Paleozoic, the area that is now Nevada lay along the western margin of the North American continent. A westward-thickening wedge of sedimentary units was deposited offshore in a eugeoclinal basin; these vary from continental shelf carbonates toward the east to fine-grained siliceous clastic and cherty units to the west. Tectonic activity associated with the Antler Orogeny in Late Devonian to Early Mississippian time resulted in the eugeoclinal Western Assemblage rocks being thrust as much as 140 km (90 mi) eastward over time-equivalent transitional to miogeoclinal Eastern Assemblage rocks along the Roberts Mountains Thrust fault system. The leading edge of the Roberts Mountains Thrust plate formed the emergent Antler highland from which siliceous clastic sediment, eroded from the overriding eugeoclinal rocks, was shed eastward into the adjacent foreland basin. Erosional products derived from the overthrust plate are termed the Overlap Assemblage.

Jan 1, 1987

By F. Seymour

A dynamic programming algorithm is presented that takes a series of nested phases, a fixed mining-rate schedule and a fixed plant-production-capacity schedule, and, from these, finds the mining and cutoff grade sequence that maximizes the net present value. This tool allows the mining engineer to quickly look at project sensitivity to various production capacities, commodity prices and costs. A description of the algorithm is given along with examples of how it has been used at Newmont Gold.

Jan 1, 1996

By M. J. Hughes

Kaiser Steel Corporation's Eagle Mountain operations are located in Southern California at a distance of about 130 miles east of the Corporation's steel plant at Fontana, California, and at a distance of about 225 miles from the nearest harbors which are located at Long Beach and Los Angeles, California Although the Eagle Mountain ore bodies are strategically located with respect to the steel plant and the harbor facilities, they are not of a very high grade and 'the geologic nature of the deposit makes it very difficult to mine and to concentrate. The iron ores occur as partial replacement of older zones mainly within dolomites and to a lesser extent within quartzites and quartz monzonites. The alteration was extremely variable and generally resulted in the formation of pyritic magnetic which, in part of the ore body, was leached to remove the pyrite and change the magnetite to hematite. Although the overall ore body is large, a major portion of it contains sulfur in the range of 1.0% to 5.0%. Obviously, this is too high a sulfur content for direct use in blast furnace feed.

Jan 1, 1968

By Qing Wang

A longterm overburden removal plan can be realistic and optimum only when the cost and capacity profiles off the equipment assigned to the operation are taken into consideration. Therefore, the planning should involve the proper assignment of equipment capacity by insuring a timely investment and a timely replacement policy throughout the mine life. A dynamic solution algorithm has been developed, by which all possible truck fleet alternatives are evaluated for each year off the operation. Cumulative cost off the operation is carried throughout the analysis. The optimum solution is obtained by selecting the minimum cumulative cost at the last year and tracing backward the best fleet alternative for each year. The solution provides: 1. the optimum amount of overburden to be removed each year; 2. the best fleet to be assigned to the job; and 3. the best equipment replacement policy.

Jan 1, 1989

By Roger D. Sharpe

The United States Gypsum Company operation at Plaster City, in Imperial County, California, consists of the largest gypsum quarry in the United States, a company-owned, narrow-gauge railroad and wallboard and plaster manufacturing facilities. A variety of gypsum products, including many types of wallboard, construction plasters, portland cement setting agent, and agricultural gypsum are manufactured. Gypsum is quarried from the Miocene age Fish Creek Gypsum. Evaporite minerals were deposited in a clastic-rich sabkha environment along the margin of a small embayment in the Salton Trough. The Salton Trough is a major regional structure that formed by rifting and transform faulting along the Elsinore, San Jacinto, and San Andreas fault zones. Sedimentary basins were formed between tilted fault blocks. The basins were filled by prograding alluvial fans, basin margin sabkha and marine sediments, and deltaic deposits from the Colorado River. Gypsum is exposed in the quarry on rounded hills with 250-300 feet of relief. The evaporites are up to 200 feet thick and average 125 feet in thickness. Anhydrite commonly occurs in the lower part of the evaporites under the crests of hills and beneath thick alluvial cover.

Jan 1, 1995

By H. Polat, S. Chander

Relatively large amounts of hydrocarbons such as fuel oils are often needed in the flotation of low rank coals. The amount of oil can be decreased considerably by using surfactants as promoters. The reagents that are good candidates as surfactants to promote hydrophobicity can also act as emulsifying and wetting agents. Because the physical and chemical variables influence various subprocesses in different ways, their influence on the performance parameters is complex. The results of laboratory tests are presented to show that the dual role of reagents can be judiciously exploited to increase both the recovery and grade of the clean coal. The mode and order of reagent addition is critical in enhancing their efficacy as flotation promoters. The results demonstrate the benefits of proper conditioning of the pulp prior to flotation.

Jan 1, 1999

By S. D. Van Nort

Editor’s note: This is the first of two MINING ENGINEERING articles about the Grasberg deposit. The second, focusing on open pit mine development, will appear in the April issue of the magazine. The Grasberg porphyry copper-gold deposit of Freeport Indonesia Inc. lies within the Ertsberg Mineral District in central Irian Jaya, Indonesia. The Grasberg deposit was discovered during a drilling campaign initiated in the mid-1980s. Production at the open pit de- posit commenced in December 1989. The Grasberg copper-gold ore body is contained within a young igneous complex of dioritic composition that intrudes limestones of the Tertiary New Guinea Group. Alteration is typical of porphyry copper deposits worldwide except that higher grade primary chalcopyrite with significant gold values is associated with a centrally located zone of strong quartz stockwork. Irian Jaya comprises the western half of the island of New Guinea. The Ertsberg District lies 70 km (43 miles) inland from the Arafura Sea at an altitudeof3500 to45OOm (11,480to 14,764 ft). It straddles the Papuan fold belt. This belt forms the east-west trending chain of mountains that extend the entire length of New Guinea and is the site of numerous mineral districts.

Jan 1, 1991

By L. W. Stanger, Erich U. Petersen, William J. Tafuri, Donald M. Hausen, Douglas N. Halbe

Gold mineralization at the Mercur Mine was controlled primarily by structure and secondarily by lithology in Mississippian-age sedimentary rocks. Gold was localized where Sevier-age high angle northeast-striking faults are intersected by younger northwest-striking fault zones. The Lulu Graben is a northeast- striking fault zone composed of a south-dipping master fault coupled with subsidiary or antithetic faults. The Twist Fault zone, a sinuous, low-displacement , north-striking zone of fracturing, bisects the graben. Large- tonnage disseminated ore bodies formed east of the Twist Fault zone within silty, thin-bedded, bioclastic carbonates. West of the Twist Fault zone, gold was restricted to rock near peripheral faults surrounding a subvertical collapsed pipe developed within the graben. An overlying thick carbonaceous shale capped the ore zone. Presence of abundant limited- displacement faulting and of hydrothermal jasperoid is associated with cartonate-hosted disseminated gold. Conversely, increased fault displacement and widespread brecciation are associated with reduced dissemination of gold into normally receptive carbonates.

Jan 1, 1990

By H. B. Comstock

This paper reviews the trends in supply and consumption of the principal magnesium compounds in the United States in relation to domestic requirements and world resources. The data are confined to these principal magnesium compounds: Magnesium chloride, magnesium hydroxide, precipitated magnesium carbonate, and magnesium oxide (commonly referred to as magnesia). The properties and uses of magnesium compounds are shown in various chapters of' the 2nd edition of Industrial Minerals end Rocks. 3/ The third edition of this reference is in preparation. A more recent description of properties, uses and sources of magnesium compounds appears in a Bureau of Mines publication.4/ The American Iron and Steel Institute and the Refractories Institute have published comprehensive data on the properties and uses of basic refractories. Many magnesium compounds are prepared by the producers to meet specifications set by individual consumers.

Jan 1, 1960

By A. Bayer, T. Klopfer

"As a leading global strategy consultancy, Roland Berger Strategy Consultants firmly believe that the issue of sustainability is at the core of every business activity. Thus, strategies to enhance corporate sustainability (CS) are an essential cornerstone in the consultancy's approach to develop and implement new strategic concepts for the clients. In this paper, the authors conclude that innovation is the only solution possible to guarantee growth and welfare gains while achieving sustainable development. More efficient and effective ways are necessary to enable technical and social breakthroughs. To illustrate Roland Berger Strategy Consultants's vision on CS, four selected cases from the basic resources, energy and utilities sectors are presented. They demonstrate that the implementation of a CS strategy does not only refer to CEO spheres and are by no means just a moral justification for current business practices. Rather they show that the decision to opt for these new ways also opens up multiple opportunities."

Jan 1, 2005

By David J. Kruse

Although it may be perfectly acceptable to neglect the belt's elastic behavior for many conveyor designs, this can lead to disastrous consequences for others. So how can a designer know in advance if a dynamic analysis is required? Unfortunately, in many cases it is impossible to foresee or predict dynamic problems prior to performing the actual analysis. However, a basic understanding of the principles of conveyor dynamics, as well as knowledge regarding common problem areas, can significantly help the designer make more educated decisions during the initial design stage. This paper will demonstrate how static calculations alone can incorrectly represent the true behavior of the conveyor system. It will also discuss the importance of correctly sizing and locating the take-up system to provide the most economical conveyor design. The use of capstans will also be discussed followed by two examples demonstrating their proper operation.

Jan 1, 2002

By Hisakazu Matsushita, Yoshio Yamaguchi

INTRODUCTION Shinkansen, operating 1,176km between Tokyo and Hakata, transports 340,000 passengers a day. Presently, the 466km Tohoku Shinkansen linking Tokyo and Morioka and the 270km Jyoetsu Shinkansen linking Omiya and Niigata are under construction. It is progressing smoothly and 95% of the civil and architectural construction has already been completed.

Jan 1, 1981

By S.K. SHARMA, ANKUSH GALAV, G.S.P. SINGH

This paper proposes a hydromechanically coupled numerical modeling approach to quantify the influence of various parameters on the mechanical and hydraulic performance of protective water barrier pillars (PWBP). The results are validated for two case studies having pillar widths of 16 and 42 m at cover depths of 136 and 190 m and water heads of 25 and 141 m. The outcome can be significantly helpful in the rational design of these pillars in underground coal mines.

Mar 1, 2023

By Raymond E. Kary, John W. Mcklveen

The four unit Cholla coal fired power station at Joseph City, Arizona, consumes coal from the McKinley mine located in western New Mexico. Since coals may contain relatively high uranium or thorium concentrations and may release quantities of detrimental progeny of these elements to the environs, there is concern that releases may pose an adverse environmental impact or even a health hazard to the workers. Thus, an effort was made to quantify the radionuclide content of the coal and compare the results with radionuclide concentrations already present in the vicinity of the plant. Additionally an attempt was made to assess any potential for significant enhancement of the levels of radioactivity in the environment or to plant personnel. Background gamma radiation measurements at and near the plant ranged from 8 to 12 [µ]R/hr (70 to 105 mR/yr) with a few localized anomolies measuring to 18 [u]R/hr (160 mR/yr). Levels on top of the coal storage piles decreased to ~ 6.5 [u]R/hr (60 mR/yr). Apparently the direct radiation emitted from the coal is less than the background levels in the vicinity of the plant. Measurements performed on top of several coal seams at the mine confirmed low radiation levels emanating from coal, but readings more than doubled when the overburden was monitored. Laboratory gamma spectrometry confirmed the lower amounts of natural radioactivity in the coal when compared against soil and water samples obtained in the vicinity of the plant and the overburden at the mine. In an effort to see if there is biological enhancement, animal feces was sampled. The radiation variations were found to be influenced primarily by naturally occurring potassium-40 which varied from ~ 1 to 18 pCi/gm rather than fluctuations in the uranium and thorium series. The potassium-40 concentrated in the ash were similar to the concentrations in the environs around the disposal ponds while Radium-226 concentrated in the fly ash was ~ 3 times that found in the immediate surroundings. Radon-222 gas concentrations in buildings at or near the plant ranged from 0.5 to 1.8 pCi/l and were generally lower than indoor concentrations measured in the Phoenix area. The burning of coal at the Cholla station does not appear to increase ambient levels of radioactivity found in the surrounding environs or to the workers. However, the use of byproduct fly ash for construction purposes may need to be examined.

Jan 1, 1981

By Charles T. Staniek

Following a dragline relocation at Agrico's Fort Green phosphate mine in 1986, the recovery plant experienced a significant decrease in flotation performance. Through weeks of trial and error testing, we discovered we could restore recoveries by conditioning feed at pH's higher than we had used historically. The higher pH's essentially increased flotation cell kinetics, although we still do not understand the exact mechanism at work. Armed with new-found appreciation of pH modification, we initiated a program to determine the optimum modifier for us, from both a performance and environmental perspective. Environmental considerations were important because ammonia, the standard industry modifier, is a plant nutrient and higher usage rates could affect the quality, of our recycle process water. This paper describes the research and development work spanning a 3 year period that culminated in making a major change in our reagent suite when we replaced ammonia with soda ash on a permanent full-time basis.

Jan 1, 1993

By Anthony J. Ranalli, Florentino B. Maestas, Katherine Walton-Day, Richard W. Healy

Water movement and water chemistry were monitored in the unsaturated zone at two sites in fluvial tailings deposits along the Arkansas River near Leadville, Colorado. One of the sites was remediated by the incorporation of lime and biosolids into the soil. Preliminary results, based on data collected during the 11 months following remediation, indicate that differences between the two sites can largely be attributed to heterogeneity of the deposits. Remediation has increased the alkalinity in the upper soil zone, but as of yet, there is no indication that soils at depths greater than 30 cm have been affected.

Jan 1, 2000

By R. Hogg, A. C. Maffei, D. T. Ray

Based on standard population balance models for agglomeration and size reduction processes, a simplified model has been developed to describe simultaneous growth and breakage in the flocculation of agitated suspensions. The results of semi-batch flocculation tests have been used for estimation of the model parameters and empirical relationships have been obtained to describe the effects of process variables and to establish scale-up criteria. Application of the model to the design, operation and control of continuous flocculation processes is discussed.

Jan 1, 1990

By Arthur B. Arnold, Curtis T. Scott

The Blue Mountain Tunnel is a part of the Sultan River Hydroelectric Project. The Sultan Project is in the Cascade Mountain Range, approximately 56 km (35 mi) northeast of Seattle, Washington. The geology is structurally complex, consisting of graywacke and argillite, with lesser amounts of metaigneous rocks. The tunnel, excavated with a tunnel boring machine (TBM), is 4.32 m (14 it) in diameter and 6.3 km (3.9 mi) long. The average 24 hour advance was 41 m (134 it) with a maximum of 71 m (234 it). The tunnel is essentially unlined except for 383 m (1,257 it) in a low cover area and in the rocktrap. Inspection of the tunnel after one year of operation showed it to be in good condition with only a minor amount of rock debris in the rocktrap.

Jan 1, 1987