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By Ralph T. Buscarello

For practical purposes, the terms "natural frequency," "resonance" and "critical speed" are synonymous. A part passing though its "critical" or "critical speed" may also be said to be "resonant" or "resonating." The vibrations of a precisely balanced part can be magnified by the structure in which it is assembled. Anyone who has driven an automobile knows that it will vibrate more at a certain speed than at others. According to the formula for centrifugal force, vibration should increase steadily with a rise in rpm. What happens instead is that the vibration not only in- creases with r m. but suddenly rises at a much higher rate through the critical speed, and then apparently smooths out as the rpm passes beyond it. To visualize what happens, consider a simple flat spring with a weight mounted at one end. When the spring is deflected by pulling down on the weight and then letting it go, the spring will oscillate, and the spring-and-weight system will vibrate at its natural frequency. If the timing or direction bf the impulses imparted to the spring did not coincide with its natural frequency, the result would be an irregular vibration that would not build up. If, on the other hand, the timing and direction of the impulses did coincide with the spring's natural frequency, the result would be a larger and larger amplitude. If the impulses were continued indefinitely, the amplitude of the spring's vibrations would go on rising [while its frequency stayed the same] until the spring broke or the amplitude of the vibrations reached an equilibrium [because frictional or other forces would tend to damp it]. Resonance magnifies the amplitude of vibrations in a relatively undamped system between 100 to 200 times over that of nonresonant vibrations. Frictional or viscous damping often reduces the magnification [from 10 to 20 times], but even with this reduction the amplitude would still be large enough to cause excessive wear, and sometimes even fractures. For example, a blower might show only 0.001 in. of vibration on the manufacturer's test stand. Installed, the blower could pass into its critical speed [the speed at which the frequency of the vibrations caused by the rotor coincides with the supporting structure's natural frequency], and the 0.001 in. of vibration could be resonated to 0.010 in., or as much as 0.020 in. The cure for such a condition would not be to lower the vibration of the blower by further balancing or better alignment but to separate the two frequencies by at least 20 to 30%.

Jan 1, 1970

By Alexander N. Winchell

"Location. The copper mines of Michigan are all in the northern part of that state on the Keweenaw Peninsula, which extends from the (Michigan) mainland for about seventy miles northeasterly toward the middle of Lake Superior. The mines occur in a belt or zone occupying the central portion of the peninsula from end to end.. The most productive mines for many years past have been those located not far from the city of Houghton in' the central part of the zone, in a section extending about ten miles southwest of Houghton and fifteen miles northeast. The most important mines in order of location, from the northeast to south¬west, are the following: Mohawk, Ahmeek, Allouez, North Kearsarge, Wolverine, South Kearsarge, Centennial, Calumet. and Hecla, Osceola, Franklin, Quincy, Hancock, Isle Royale, Superior, Baltic, Trimountain, and Champion. The first three named are in Keweenaw county and all of the others are in Houghton county. Still farther to the southwest are the Lake, Mass, Adventure, Michigan, Victoria, and White Pine mines. These are in Ontonagon county.History. The exploitation of these copper mines extends back into prehistoric times. There is little evidence that the American Indians carried on mining operations in this region in the period shortly before the advent of white men, but there is abundant evidence that the ancestors of the Indians, •or some earlier inhabitants of the region, carried on primitive mining operations. For example, Mr. S. O. Knapp, Agent of the Minne¬sota Mining Company, in the winter of 1847-48, made the first discovery of prehistoric mining. This event is described as follows by Foster and Whitney :"

Jan 1, 1920

Heap leaching for the recovery of precious metals is a comparatively new and rapidly expanding technology. The practical aspects of heap leaching are described and environmental and economic implications discussed.

Jan 1, 1984

By Verônica Scarpini Candido

Foi notado que o rejeito originado a partir do beneficiamento do caulim é rico em silico-aluminatos, apresentando assim potencial em processo de adsorção. O presente trabalho consiste em avaliar o potencial adsortivo do rejeito do caulim quimicamente tratado. Foi utilizado o corante de azul de metileno (AM) em solução aquosa para se ter o conhecimento de adsorção do rejeito de caulim in natura e calcinado a 700ºC onde ambos foram submetidos a uma ativação química com H2SO4. Após o equilíbrio da amostra do rejeito do caulim junto ao azul de metileno, suas concentrações foram determinadas por espectrofotometria. Os resultados preliminares comprovam que o rejeito apresenta uma boa capacidade adsortiva para concentração de até 50,00 mg/L de AM, demostrando, potencial para ser utilizado na remoção de corantes em tratamento de afluentes.

Oct 30, 2017

By Randall M. Wheeler

Using Computer software to analyze and interpret blast vibration effects has never been so practical. Fully digital seismographs and powerful desktop and portable computers have led to the development of fast and easy to use analysis software. This workshop will focus on new Microsoft Windows-based blast vibration analysis programs developed by White Industrial Seismology, Inc. The Windows point and click graphical environment is ideal for developing full-featured and yet intuitive software.

Jan 1, 1994

By Ralph W. Edie

"IntroductionTHIS PAPER deals with chemical and mineralogical changes in wall-rocks associated with pitchblende mineralization in the Gold-fields area of Saskatchewan. The localities at which the rock specimens studied were collected, and descriptions of the various rock-types referred to, are given in a previous paper by the author (5).The geological field work upon which this paper is based was carried out while the writer was employed by the Eldorado Mining and Refining Company during the summers of 1948, 1949 and 1950. The laboratory work§ consisted largely of quantitative spectrographic analyses for both major and minor elements, supplemented by an examination of 250 thin sections of both altered and unaltered rocks.Character of the AlterationHydrothermal alteration, with associated pitchbende mineralization, is widespread in the Goldfields area of Saskatchewan. The most intense alteration is restricted to the immediate vicinity of fault or breccia zones, but large areas are affected to a minor extent.In detail, the relationship between alteration and pitchblende mineralization is complex, as individual veins do not in general have separate alteration halos. Pitchblende generally occurs in gash-like calcite veins or stringers in wide, fractured zones associated with faulting. Large, lenticular and tabular masses of slightly to intensely altered rock occur in the same wide fracture zones as the mineralized veins. However, vein deposition appears to be-long to a later fracturing period, after hydrothermal alteration was more or: less completed. Generally, the veins transect and are confined to highly altered rock, but on the other hand many highly altered zones intersected in diamond drill-core are barren of mineralized veins."

Jan 1, 1953

By B Watson

The ConSep ACACIA Reactor is a device, which utilises a high intensity cyanidation process to achieve very high, usually near total, recovery of gold from gravity concentrates. The process utilises a fluidised bed and a chemical oxidant to enhance the gold dissolution kinetics to the point where the bulk of the dissolution occurs in a few hours. For convenience and security, most plants operate a 24-hour turn around. The product from the process is in the form of cathode gold ready for smelting by traditional means. The ConSep ACACIA Reactor performs a two-fold role. Firstly it increases gravity gold production, leading to a decreased CIP feed grade. Secondly, it removes slow leaching components from the plant leaching circuit. This two fold benefit leads to the following efficiencies: enhancement of the dissolution kinetics; enhancement of the adsorption kinetics; reduction of the gold load reporting to the carbon; a significant reduction of the ægold in circuitÆ lockup; and removal of slow leaching entities which can also result in a lowering of the required cyanide concentrations in the leaching circuit and a subsequent reduction in overall cyanide consumption. The above benefits are discussed in this paper, with a particular focus on the ConSep ACACIA ReactorÆs role in removing slow leaching components, with data generated over a 21-month period. Improvement in overall plant recovery via removal of slow leaching gold species is achieved in two ways. Firstly, some of the slow leaching entities, successfully leached under intensive cyanidation, are not always fully leached under plant conditions. This results in a lowering of the solid tailing. Secondly, the faster leaching kinetics achieved in the plant as a result of the removal of slow leaching entities results in faster and more complete adsorption of the dissolved gold onto activated carbon. This results in a lowering of the solution tailings. The construction and operation of the ConSep ACACIA Reactor is simple. Apart from the reactor body, which is a proprietary design, all components of the system are æoff the shelfÆ or specific to the siteÆs requirements. In operation of the fully automated version, a PLC controls a series of valves and pumps but except for a daily changeover process the only operating component for the bulk of the time is a relatively small solution pump. The process can be totally automated giving the security of a æhands freeÆ concentrate handling process up to the point where the product is presented as cathode gold. The ConSep ACACIA Reactor was developed by Anglogold Australia (formerly Acacia Resources) for Union ReefÆs Gold Plant and has been in production since February 1999. It has proven to be a low cost, high recovery, mechanically reliable method for the processing of gold concentrates. Such has been the success of the plant, as of June 2003 there are eighteen full installations of the processing plant installed at mines owned and/or managed by Anglogold, Newmont, Placer Dome, Independence (formerly Lonrho), Sons of Gwalia and Harmony.

Jan 1, 2003

By A. M. Tunstall, N. Djordjevic, H. A. Villalobos

The damage zone behind a typical smooth-wall blast in the open pit was assessed by visually examining diamond drill core to identify blast-induced cracking, mapping core rock quality designations to identify changes in fracture frequency and conducting uphole seismic testing to determine changes in rock mass characteristics. The results from the three techniques show reasonable correlation. They suggest that major damage, in the form of fracturing of intact rock, occurs at least 7 m behind the smooth-wall blast and significant damage, in the form of opening and extension of calcite-filled fractures, at least 12 m from the blast. At greater distances the dominant damage mechanism is the loosening of existent joints within the rock mass. In the trachytes at El Soldado these damage mechanisms correspond to peak particle velocities of 2 000, 900 and 500 mm/s respectively

Jun 19, 1905

Winzes are usually sunk 9 ft. 6 in. long by 6 ft. 0 in. wide and are divided into two compartments, 4 ft. 0 in. by 5 ft. 0 in. inside the timbers. The general practice is to sink the winze to a depth of from 9 to 12 ft., put in bearers and three or four rings of timber, and then erect a sinking headframe before continuing sinking operations.GENERALThe main feature governing the design of the headframe was that all parts could be transported on timber trolleys in No. 2 Shaft. Except for some minor details the structural members consist of steam pipe. Joints are sections of steam pipe welded to one member and into which the other member fits and is held in place by a 1-in. bolt. The headframe consists essentially of two bedpieces to carry the winch and to form a seat for the four legs. The legs support the sheave bearers, the tipping door and the brace.Except during tipping operations the door is in a nearly vertical position. For tipping it is lowered to an inclined position and a hook suspended from one of the bracing members of the headframe is attached to a "D" welded to the bottom of the kibble. This causes the kibble to tip when it is lowered on to the tipping door. The capacity of the kibble is 4 cubic feet.THE HEADFRAMEThe dimensions of the headframe are:Height to top of sheave .. .. 14 ft. 10 in.Distance centre to centre of legs 4 ft. 4 in.Length of bedpieces .. .. .. .. 8 ft. 9 in.The weight is approximately 2,000 lb., the tipping door and bedpieces being the heaviest members. They weigh 240 lb. and 170 lb. respectively.One compartment of the winze is decked over, and the bedpieces, which are 8 ft. 9 in. lengths of 6 in. pipe with three short lengths of plate welded to the underside, are placed over the sinking compartment, either transversely or parallel to the winze. Three 3 inch pipes act as spreaders between them.Welded to the top of each bedpiece is a 6-in. by iHn. plate 3 ft. 0 in. long with four 4-in. by 1.5-in. slots cut longitudinally at 10 in. centres. Two 10 in. by 4-in. timbers are bolted to these plates, the distance between them being adjusted to suit the holes in the winch bedplate, which is bolted to the 10-in. by 4-in. timbers.Two short lengths of 3 in. pipe are welded to each bedpiece at 4 ft. 4 in. centres. These form the seats for the legs of the headframe, which are...

Jan 1, 1941

By S M. Gover

Estimating the probability of failure for embankments is not intuitive. It requires not only an appreciation of the strength of the embankment, but an understanding of the variability and uncertainty in the strength parameters as well. These additional aspects are, in themselves, relatively new to most practicing engineers, and therefore require some discussion.This paper discusses the concepts of probability and uncertainty, and presents a reliability-based numerical experiment, together with a literary study and collation of some of the author’s historical slope stability analyses, to investigate whether a direct relationship between safety factors and probabilities of failure exists for certain levels of uncertainty in strength parameters. In doing so, a useful tool is presented whereby knowing the safety factor of a simple slope or embankment with a consistent level of uncertainty, one can infer an approximate probability of failure.CITATION:Gover, S M, 2018. Linking safety factor to probability of failure, in Proceedings Mine Waste and Tailings Stewardship Conference 2018, pp 384–396 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 23, 2018

By K. A. Lewandowski

Agglomeration techniques are widely used by industry to form fine particles into larger masses that are easier to handle and process. One area where agglomeration is potentially useful is in heap leaching operations. With-out agglomeration, fine particles travel through the heap, clogging the spaces between the larger particles and resulting in poor leach solution flow. Poor flow of leach solution will result in long leach rates and/or decreased metal recovery. Agglomeration immobilizes the fine particles and therefore improves heap permeability to fluid flow. Additional additives (binders) are needed to prevent agglomerates from breaking up as leaching solution percolates through the heap. Type II Portland cement and lime are two well-known binders used in gold and silver leaching, but these are limited to alkaline leaching environments. Various other products have been tested as binders, including polymers. This paper summarizes the benefits of agglomeration in heap leaching and the results obtained from the testing of several different agglomeration binders in heap leaching operations.

Jan 1, 2009

By X. Q. Cao, D. S. Zhang, L. Q. Ma

To solve the support stability control problem for a coal face with large angles along both strike and dip (CLSD), the ’support-surrounding rock’ mechanical model has been developed, which takes into account the impact of the dip angle of the seam on the stability of the support in the strike direction. The mechanical relationships of the critical topple angle and critical slip angle of the support along the strike of the coal face with large dip angle and the support height, support resistance, friction coefficient, and other factors have been derived through the mechanical analysis of support stability in the strike direction of CLSDs in the free state, the operating state, and the special state. The research findings were applied to a fully mechanized CLSD in Xinji Coal Mine. The maximum underhand angle and overhand angle in strike are 42° and 25° respectively, and the maximum dip is 39°. It is calculated that during underhand mining and overhand mining, the critical support resistances for avoiding support toppling are 3723 kN and 1714 kN respectively, and the critical support resistances for avoiding slipping of the support are 7405 kN and 6606 kN respectively. Thus, the selection of type ZZ7600/18/38 hydraulic roof support for the coal face is justified. Measures to prevent sliding of the support and the installation of a limiting stop maintain the support runs in good condition and ensure safe and efficient mining of CLSD.

Jan 1, 2015

By Tom Dettweiler, Robina Sharpe, Wright. Michael

The International Seabed Authority and a number of countries have or are in the process of developing environmental impact assessment guidelines and legislation for seafloor mineral development. The formal decision to grant a project an environmental permit is based on an environmental and social impact assessment (ESIA), culminating in an environmental impact statement (EIS). The EIS needs to be supported by sufficient data upon which an assessment of impacts can be made and mitigation measures developed. Given the remote locations of many seafloor prospects, collection of sufficient environmental data to inform an EIS is often a difficult, expensive and lengthy process.

Sep 1, 2014

By R. H. Church, William E. Webb, Walter E. Pittman, James R. Boyle

As part of the Bureau of Mines health and safety research program, a short-range locator system, capable of locating miners who have become trapped following a mine accident, has been devised, The system consists of a lightweight, low-power radio transmitter incorporated into a miner's cap lamp battery and a directional receiver carried by rescuers. Prototype transmitters have been constructed, and the propagation of their signals has been investigated, The detectability of the signal in underground coal mines has also been investigated, This research indicates that a short-range location system would serve as an economical and practical means of locating miners from within the mine following an accident,

Jan 1, 1984

The trend for using larger equipment in open pit mining to achieve cost effectiveness raises the question about the optimum economic point of scale in the current world of globalization. The present paper treats this question through the prism of a new methodology of assessing the impact of the size of production equipment on the economic outcomes of coal mining ventures. The methodology incorporates a production scheduling optimization model that implements both principles of mine planning, coal quality optimization and waste deferment. The implementation of the waste deferment principle dealing with the spatial and time aspects of the mine sequence arrangement allows the adequate modeling of the optimality of production equipment scale through the use of mine investment parameters, such as, purchase and ownership costs and discounted cash flows analysis. A case study is provided to illustrate the applicability of the new methodology.

Jan 1, 2004

By H. Kudelka

Copper electrowinning at Duisburger Kupferhuette was introduced in March 1975. The electrowinning plant has a capacity of 10,000 mT of copper cathodes a year. The cuprous oxide feed material is an intermediate product of the treatment of the leach solutions, originating from chloridizing roasting of pyrite cinders. This material is characterized not only by a wide spectrum of accompanying impurities, but also by an unusually high level of precious metals. As the priority set was the production of high-purity cathodes. there was a need for developing a process which would be suited to treat complex leach liquors . The process adopted consist s of an oxidizing leach in spent electrolyte, followed by two- stage purification, By this means. a low- acid pregnant copper electrolyte is obtained free of elements detrimental to copper quality. Electrowinning is carried out at a current density of 200 A / m2 in the presence of 10 g/l zinc. The electrowon copper has a conductivity of at least 101.4% lACS and a softening temperature not exceeding 200°C, which makes it a suitable product for continuous casting and dip ?forming.

Jan 1, 1977

By R. H. Ring

The Automatic Extraction System (AES) was designed and built under a U.S. Department of Energy Contract by the National Mine Service Company in cooperation with the Lee Engineering Division of Consolidation Coal Company. The Pennsylvania State University, Mining Engineering Section, was contracted as an independent auditor of the AES performance. The AES had a rotating cutter drum like a continuous mining machine; but two hydraulically powered roof supports, four roof-bolting drills, a dust scrubber, a ventilation fan and ducting in the roof supports, semi-automatic control, an extensible chain conveyor, and other innovations led to the distinction "extraction system" as opposed to "miner-bolter" or "continuous mining" machine. After design and assembly, the AES was field tested experimentally in an underground coal mine. The in-mine performance audit was preceded by a computer simulation of the potential production for a later comparison with the actual tonnage mined by the AES. This paper describes the results of an in-mine trial and assesses the production potential of the AES.

Jan 1, 1980

By Nancy Potts, M. G. Barker, W. C. Holliman

"SUMMARYThis report on the characteristics of commercial aviation gasolines presents compilations of inspection test data furnished on their products by manufacturers of commercial grades of aviation gasoline, and special data obtained in Bureau of Mines laboratories on samples of these gasolines. Data and physical samples for the survey were submitted by 15 manufacturers on 18 grade 80, 21 grade 91/98, 22 grade 100/130, end 10 grade 115/145 aviation fuels.The inspection test data supplied by the participating manufacturers consist of octane and performance numbers, tetraethyllead content, dye color, and other characteristics usually listed in aviation gasoline specifications, such as AN-F-48a or ASTM Designation D910-47T. These data are tabulated and averaged by grades in tables 1 through 4 and, as reported, meet the AN-F-48a and similar specifications with a few exceptions. Two grade 80 gasolines show a lean-mixture octane rating slightly below 80.0, and 91/98 grade fuel shows a lean-mixture rating of 90.9 and a rich-mixture rating of 97.5, two 100/130 grade gasolines have a rich-mixture performance number slightly below 130.0, and one 115/145 grade gasoline shows a rich-mixture performance number of 144.5. However, octane and performance number averages are above the mini¬mum requirements for each grade. Tetraethyllead content in the 91/98 and 100/ 130 grades generally is above the maximum outlined in these specifications, whereas dye color for each of the four grades, with the exception of two gasolines in grades 80 and 100/130, is that designated for the particular grade. Distillation requirements, with a few exceptions at individual points, are met by gasolines of all grades. Reid-vapor-pressure, copper-dish-residue, heat-of-combustion or aniline-gravity-constant, freezing-point, and copper-strip-corrosion requirements are met by all gasolines so far as reported. No data for some of these tests wore submitted on a few of the gasolines. One gasoline, grade 115/145, shows a sulfur content greater than the specified maximum."

May 1, 1948

By Georgc E. Collins

SEVERAL years ago, I estimated the total stock of gold in the world to be about a thousand million ounces, of which rather over one-third was available for monetary uses. Robert H. Ridgway has estimated the world's production from 1493 to 1927 as slightly over this amount. Of this total, 1.5 per cent was produced between 1493 and 1850 (before the Californian and Australian goldfields began to flood the world with gold), 331/2 per cent from 1851 to 1900, and 511/2 per cent from 1900 to 1927. Allowing for loss by attrition and permanent consumption in the arts, and for loss of buried treas¬ure, my first-mentioned estimate is perhaps not far from the truth; but my estimate of the monetary stock was certainly too low. Of the total production stated by Rid-way. 28 per cent came from North America. 26.9 per cent from Africa, 1.6.8 per cent from Australasia, 12.4 per cent from South America, and 11.2 per cent from Asia. Excepting that from the African conglomerate beds, the ultimate origin of which is still the subject of controversy, by far the greater part of the total production was derived from alluvials. Weighing all contingencies, it is improbable that any such production as has been made during the last forty years will be repeated in any similar period, if the present price level is maintained. The gold standard today seems firmly established except for temporary digressions. Nevertheless, no well-informed mining engineer will venture to assert the probability that the material for its maintenance throughout future generations can be furnished.

Jan 1, 1932

Recovery of Fine Gold Particles from Philippine Gold Deposits by Enhanced Gravity Concentration and Flotation The objective of the study is to determine the applicability of enhanced gravity concentration (EGC) and flotation for gold recovery. While gravity concentration methods have long been applied to gold ores, especially to free-milling types that requires minimal beneficiation, flotation for gold recovery has not yet taken hold as a major operation in the Philippine setting. In this study, the application of EGC and flotation for gold is applied and compared to the existing methods for gold recovery. Two samples, with assays of 7.315 and 5.333 g Au/MT (samples 1 and 2, respectively) are used for this study. These samples are subjected to mineralogical studies and is found to have a gold-particle size ranging 10 to 200 microns. To verify the separation size, the mesh-of-grind (MOG) is used as the primary parameter for experimentation. Initially, the samples are stage-crushed, ground, and subjected to EGC using a Falcon SB40 Concentrator. Based on the results, the two samples showed that recovery increases with a finer MOG. The ratio of concentration (K) decreases with a finer MOG. This shows that there should be sufficient liberation of the gold values for EGC to be effective. The effect of the enhancement is to pronounce the difference in specific gravity of the minerals, promoting better separation. This is validated by the high recovery values of 86.97 per cent and 98.73 per cent exhibited respectively for samples 1 and 2 (at 54 microns). For the flotation runs, sample 2 with an average particle size of 80 per cent passing 74 microns is examined using thiocarbamate-based collectors for roughing and subsequently exhibited a recovery of 96.32 per cent. At this point, the concentration ratio (K) is noted as an important efficiency indicator for flotation process since it yielded a very low-mass and high-metal content concentrate.

Sep 13, 2010