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Two of the problems long associated with the complete extraction of level pillars in the wide ore bodies of Broken Hill have been: (1) The high cost of maintaining level gangways through areas of slow subsidence to provide adequate trucking roads for the transport of sand filling; and (2) The difficulty and high cost of completely filling depleted areas. This paper deals with the experiments conducted to devise an apparatus for transporting, with the aid of compressed air, sandfill from the underground sand passes to the stopes and describes the sand blower which has been developed. This apparatus has to a large degree overcome the difficulties and removed much of the hazard associated with the rapid extraction of level pillars.Special attention is drawn to the sizing analysis of the sand and to the fact that it is not dry material. It was early found that these factors were determinants in the design and development of the apparatus described.Acknowledgment is made to the General Manager of Broken Hill South Limited for permission to present this paper, to the engineering department for assisting in the design of the apparatus, and to the underground staff for their co-operation in training the operators and in bringing to success this method of stope filling.PREVIOUS FILLING METHODSThe South Mine, with a monthly production of approximately 32,000 tons of lead-sHver-zinc sulphide ore by cut-and-fill mining methods, requires about 11,000 cubic yards of filling per month. With the exception of a small and variable quantity of developmental mullock, all this filling is...

Jan 1, 1941

By G. A. Mallory

"The South Bay Division of Selco Mining is located fifty-four miles northeast of Ear Falls Ontario on Confederation Lake. The concentrator operates five days a week and processes six hundred tons per day of copper zinc silver sulphide ore. The concentrator is comprised of crushing, grinding, differential flotation, thickening and drying circuits. The major constituents of the concentrator feed are: chalcopyrite 7%, sphalerite 20%, pyrrhotite 3%, pyrite 25 - 30% and felsitic volcanics 40 - 50%. The mine went into production in March 1971 with an anticipated three year life and is now scheduled for closure in the summer of 1981. Recent mine production has been limited to three cut and fill stopes which have widely varying ore grades, therefore mill feeds vary from 0.25 to 4% copper, 3.5 to 27% zinc, 0 to 0.4% lead and 15 to 30% iron.In mid 1977 Selco negotiated a six month rental purchase agreement with Outokumpu Instruments Canada Limited for a five stream analyser system. The Minexan 202 probes were the first Outokumpu probe type analysers installed in Canada although Outokumpus' Courier systems are well known. Installation of the system took place in April 1978 and after numerous hardware faults the six month evaluation began in August. By December it was obvious that the Minexan 202 probes with proportional detectors did not have adequate resolution to determine low copper values in either of the tailings streams. Outokumpu offered to replace the tailings analysers with a new prototype solid state detector probe the following summer. The evaluation on the five Minexan 202 probes continued until August 1979 when the new solid probe was installed. The Minexan S (solid state) probe was evaluated with the three remaining Minexan 202 probes until December 1979 when Selco elected to purchase the system."

Jan 1, 1981

By K Palmer, G J. Artmont

Alluvial gold is an ideal exploration tracer to bedrock source and indicator of bedrock mineralisation style because: (i) gold occurs in a wide range of deposit types, (ii) primary composition is sensitive to style of mineralisation, and (iii) it is a heavy resistate mineral that is readily preserved and easily sampled. In regional exploration of the Central Ranges of Irian Jaya, alluvial gold mineralogy has been applied to maximise the information return from panned concentrate sampling and to focus exploration effort. Primary gold is a solid solution of Au+Ag¦Cu¦Hg, ¦ trace Pd, Te, and Sb. In general Ag¦Hg increase and Cu decreases with inferred decreasing temperature of formation, and gold from particular mineralisation styles has signature compositions that can be used as indicators of bedrock mineralisation type. Furthermore, the abundance of alluvial gold is an indicator of the economic potential of a catchment. The convergent continental-oceanic plate geology of the Central Ranges is conducive to a wide range of mineralisation styles. Mineralogy of gold in ophiolite, skarn, porphyry, mesothermal vein and possible VHMS environments is characterised from alluvial and bedrock samples, and the use of gold mineralogy in prospecting at regional scale through prospect definition to drilling is demonstrated.

Jan 1, 1995

By Antonio Karzulovic, Ricardo Sepulveda, Manuel Schellman

Mantoverde Division of Empresa Minera Mantos Blancos S.A., Anglo American Chile, developed an open pit mine to exploit copper oxide ore. Mantoverde mine is located in the Province of Chañaral, Northern Chile, about 1,020 Km far from Santiago. Currently, the East wall of the mine is reaching the condition of final pit. To evaluate the possibility of a pit optimization on this wall a geotechnical study was performed, including slope stability analyses by limit equilibrium and numerical methods. As a result of this geotechnical evaluation, it was decided to allow a probability of failure of 12% for instabilities affecting up to 600,000 tonnes, and use steeper slopes on the East Wall of the mine. This paper describes this geotechnical evaluation and how the results of the stability analyses were used to define a flexible slope design, which allows modification if the observed slope behaviour deviated from the expected one.

Jan 1, 2006

By Brandon T. Buschmeier, Sonia S. Swift, Michael P. Walker, Frederic Masse

"Ground improvement has undoubtedly become a cost-efficient and effective solution to support the development of poor soil sites. Ground improvement elements, such as Controlled Modulus Columns (CMCs), replace piles by improving the subsurface soils and reducing settlement. As ground improvement becomes more popular, the applications become more creative and ground improvement is being used to control settlements under large structures with tight settlement tolerances.In this paper, we will discuss the use of CMCs to support two (2) large industrial warehouses where soil conditions would normally lead to the use of deep foundations and a structural slab, grade beams, and hung utilities to prevent excess settlement. Each of the sites we will discuss had poor soil conditions in the form of very soft or compressible soil, heterogeneous fill of varying thickness, and environmental contamination. At each site, we developed a design that would allow for the use of Controlled Modulus Columns (CMCs) with a Load Transfer Platform (LTP) in place of the previously-proposed deep foundations. The use of the CMCs also allowed for the use of spread footings and slab on grade construction. The benefits of this value-engineering approach include economy in the foundation system, risk mitigation by not disturbing contaminated soils requiring expensive removal, and ease of access for future sub-slab upgrades with new tenants. Additionally, the use of recycled concrete aggregate as an LTP is more environmentally friendly than placing structural slabs with heavy steel reinforcement.Designing for the settlement of large warehouses is challenging because it requires changing how we typically perform our designs. For most structures, the slab loads are relatively light when compared to the footing loads, whereas for warehouses, the slab is heavily loaded compared to the relatively light footing loads. Thus, it becomes essential to perform three-dimensional analyses to confirm that the proposed CMC layout will provide uniform support of the slab and footing across a variety of loading scenarios (loaded bays vs unloaded or travel bays). The complexity of the designs for these warehouses generated interest in conducting large area load tests over a grid of multiple columns. The performance of the area load tests provided invaluable information on the effectiveness of the LTP and CMC spacing. In this paper, we present a general description of CMC ground improvement, the differences between ground improvement and traditional pile foundations, our typical design methodology for CMC design, and the modifications to that methodology for warehouses."

Jan 1, 2017

By A. S. Adams

A glance at the list of papers1 that have been published since 1920 on the general subject of flotation suggests the variety of ideas that exist regarding the underlying cause of the phenomenon. Among these ideas, we find several coherent theories, but none that adequately and completely explain the phenomenon. Ralston2 and Bains3 suggested an electrical theory which has to do with the attachment of mineral particles to a bubble by the attraction of unlike electrical charges. This theory has its root in the fact that a bubble of air in pure water is electrified in such a way that the surfacc is negatively charged while the body of the water is positively charged. This result, which was first discussed by Helmholtz, also obtains when the water contains anything except a high concentration of hydrogen ions, or ions which are trivalent or tetravalent. The theory also holds that the mineral particles have positive charges on their surfaces, and so there is attachment between bubble surface and mineral particles by the old law of electrostatics, which states that unlike charges attract. Contact Angle and Oil Attraction The contact angle—the angle formed by a fluid-fluid boundary when both are in contact with a solid-—has been indicted several times for complicity in the phenomenon of flotation. This angle is supposed to indirectly measure the surface energy of a solid. Thus if we have two fluids in contact with a solid, we may express the difference between the two fluid-solid tensions as equal to the fluid-fluid tension times the cosine of the angle between the two fluids.4 If the two fluids are in contact with the solid, this is, no doubt, an excellent way of establishing relative surface energies. However, in flotation, we deal with substances which are not wetted by water. What assurance have we, then, that the angle

Jan 1, 1928

By W. N. Brown

One of the seemingly eternal problems with which we are frequently faced is that of providing adequate and economical warehousing facilities to store large quantities of bulk product. Seasonal consumption, transportation, marketing, and other factors very often dictate extensive product warehousing requirements for an operation geared for steady, year-around production of a material requiring weather protection during storage. Fertilizers such as potash and urea are examples of such products; the consumption of these materials is extremely heavy in the early spring at which time the materials must be placed in the soil, whereas, for obvious operating efficiencies, production is more or less constant for a given operation throughout the year.

Jan 1, 1961

By A. F. Meger

Coal treatment by oil spraying receives special attention at the Georgetown plant for the dividends it pays in satisfying present customers and attracting new markets. Customer satisfaction requires care, quality control, and use of suitable oils. REPRESENTED here are the ideas and varied experiences of many people in the Hanna Coal CO. who have helped develop, over a number of years, an efficient and flexible method for spraying controlled amounts of oil on coal. Since the Georgetown preparation plant began operations early in 1951, oil treatment of coal has received special attention. It is believed that oil treating will satisfy present customers and also attract new markets. The first step in developing the new method of oil spraying was the construction of a dust cabinet for testing 50-lb samples of treated coal with the available oil sprays on the market. Tests results were tabulated for both indoor and outdoor storage. The graph, Fig. 1, shows results of the original tests made with a 700-sec residual blend and a 500-sec lubricating oil on Georgetown stoker coal of 1¼x3/8-in. size.* The advantages of better price, improperly blended can raise havoc. Some.,pale oils also, although odorless when delivered, give off a sweet sickening odor when atomized under pressure. It is recommended that all products be tested before they are used. There is a specific place for all spraying oils. For example, at a power plant a severe dust condition exists around the stockpile area and in parts of the plant. The cheapest spraying oil made, regardless of odor, will do an excellent job in this case and will save the company 3 to 5c per gal or more. Domestic trade, on the other hand, must be carefully handled to prevent complaints about odor, and the only way to do this is to stay with the proved products after the odor tests have been made. The preparation plant at Georgetown has facilities to handle either tank car or tank truck deliveries. Steam is available at the unloading point if the weather is severe, and there is an indicator at the unloading point to prevent overflowing the 20,000-gal underground storage tank. Systematic test samples are removed from each delivery and sent to the lubrication engineer to insure quality control. Fig. 3 illustrates the chutes in which smaller sizes of coal are treated. Fig. 4 shows the entire spraying system. Buried in the ground is a 20,000-gal tank with immersion heaters grouped around the feeder line to insure adequate gravity flow to the pump under all conditions of weather. Oil flows to a 500-gal preheating tank where the temperature is kept about 150°F by six 1½-kw immersion heaters thermostatically controlled. Hot oil is fed through a self-cleaning disc-type filter to the hydraulic pump. Valves and piping make it possible to transfer oil from one tank to another or to drain the lines for maintenance purposes. All this equipment is below ground level in a covered pump room,

Jan 1, 1955

By P. R. Swann, R. M. Fisher, W. R. Duff

Observations by transmission electron microscoPy of the microstructures in quenched Fe-A1 alloys provide the basis for revision of the Fe-A1 phase diagram. The diagram is characterized by first-order transitions between the disordered ferromagnetic a! solid solution and the two ordered phases FeAl and Fe3Al. However, second-order transitions showing corre-luted fluctuations in the degree of order near the critical temperature occur between the paramagnetic a! and FeAl and the FeAl and FeAl phases. ELUCIDATION of the true nature of the Fe-A1 equilibrium diagram has proven to be an extremely challenging problem as evidenced by the fact that six quite different versions of the iron-rich portions have been published since 1958.&apos;-6 The most recent diagram shown in Fig. 1 was proposed by Rimlinger6 based on X-ray diffraction analysis and dilatometry. He shows the single-phase fields of the ordered phases of the types FeAl(L20) and Fe3A1(D03) and the disordered bcc Fe-A1 solid solution, a, separated from one another in every case by large two-phase regions. Thus, he implies that in Fe-A1 alloys ordering always occurs via a classical phase transition. In contrast to this view, theoretical studies3&apos;" have concluded that the transitions a — FeAl and FeAl — Fe3A1 should be second- or higher-order in character. A further revision of the Fe-A1 diagram of state is presented in Fig. 2 based on our previous8,9 and current observations by transmission electron microscopy of the microstructures found in quenched specimens. The average quenching rate was 50,000°C per sec and although this was sufficiently rapid to prevent Fe3A1-type ordering below -550°C it was not sufficient to suppress ordering of the type FeAl in the temperature range -650" to 800°C. However, ordering during the quench is easily recognized since the FeAl phase formed during holding at temperature rapidly develops large antiphase domains whereas FeAl formed during quenching has a very fine domain size, -50Å diam. Each symbol in Fig. 2 indicates the result of a micro-structural examination of specimens heat-treated (-1 hr) until equilibrium was established. The results will be discussed in the order of the points, A - Dl marked on both diagrams with reference to the phase fields, critical temperature, and "transition" ranges, respectively. The dark-field micrograph corresponding to point A is shown in Fig. 3 and was obtained using a 111 reflection of the Fe3A1 structure which reveals both a&apos;/4<111> and a&apos;/2<100> antiphase domain boundaries.10 The structure observed in this specimen is typical of single-phase Fe3A1 and shows no evidence for FeAl or any other additional phase. The dark-field micrograph shown in Fig. 4 corresponds to point B on the two diagrams. It was taken with a 100 FeAl reflection which reveals a/2(111) domains and exhibits the typical structure of single-

Jan 1, 1970

By F. J. Smit

The Tintic Division of Kennecott Copper Corporation operates the Burgin Mine in the East Tintic District near Eureka, Utah, approximately 75 miles south of Salt Lake City. The Division was organized in 1963 to develop concealed replacement orebodies in the area located by Bear Creek Mining Company, Kennecott&apos;s domestic exploration subsidiary. Several accounts of the discovery of these orebodies and the general geology of the area have been given (1, 2). The ore is very complex and of varying degrees of oxidation and alteration. The principal metal values are lead, zinc, silver, and cadmium. The Burgin No. 2 shaft was sunk in 1963 to provide access for mining the orebodies. Much of the ore mined after this shaft was sunk was high grade and shipped directly to smelters, but concurrently it was recognized that concentration would be required to upgrade the lower grade ore in the deposits. Accordingly, in January 1967, authorization was received to construct a 500 tpd concentrator. From the beginning it was expected that the characteristics of the mill feed would vary widely and unpredictably as mining progressed. This paper summarizes the characteristics of the ore, the test work upon which the plant design was based, the engineering and construction, and the present operation of the facility eighteen months after startup. ORE CHARACTERISTICS The Burgin ore is a complex assemblage of minerals from replacement of limestone. The replacement and alteration occurred in at

Jan 1, 1970

By D P. Blair

Rio Tinto’s Hope Downs Operations are currently mining iron ore in their South Central Pit. Prior to the commencement of mine operations, Hope Downs carried out an extensive archaeological investigation and identified an ancient rock shelter lying within the proposed mine boundaries. The site is significant to the traditional owners/custodians of the land in this part of the Pilbara, and thus the final pit design was changed to preserve the rock shelter, which now lies 30 m outside the mine boundary. In order to further preserve this ancient dwelling from blast-induced damage, blast design procedures were improved over time to minimise the vibration impact when blasting close to the shelter. Blasting and vibration monitoring commenced in May 2008 using pyrotechnic delay sequences and normal-direction firing. In October 2009 electronic delays were used to reverse-fire blasts close to the shelter in order to create a damage zone between the initiating holes and the rock shelter. A detailed statistical analysis of the vibration data shows a reduction in the higher levels of vibration for blasts fired after October 2009, which is most likely caused by the created damage zone. In May 2010, a site-specific vibration model was developed and implemented, and based on Monte Carlo waveform superposition. This model was used to give a further insight and improvement to the blast delay sequences when blasting close to the shelter. However, such models are expensive to implement and have limitations, which reduces their potential for estimating the probability of getting an excessive vibration due to a given blast design. In this regard, it is more realistic and significantly less expensive to use a recently developed probabilistic analysis based on simple charge weight scaling. This analysis shows that there was a higher probability of exceeding prescribed vibration limits at the rock shelter for blasts fired before October 2009 than there was for blasts fired after October 2009.

Nov 8, 2011

By L. Kühnel, H. Lieberwirth

Confined bed comminution in High Pressure Grinding Rollers (HPGR) and Vertical Roller Mills (VRM) is gaining substantial attention in many applications. Previously used mainly for milling coal or construction materials, HPGR and VRM have started to complement or even replace tumbling mills in ore beneficiation. Materials like coal or clinker are relatively homogenous, however, in comparison to metal ores and wall rocks. This characteristic poses a new challenge to the confined bed comminution but also an opportunity. Fuerstenau and Abouzeid have investigated the selectivity in comminution of a mixture of particles of different strength in a particle bed. The median particle size and particle size distribution (PSD) of the two constituents used were kept constant. Only the proportion of the two constituents was modified. The competence of a material is, however, also a function of particle size. Smaller particles tend to be more competent than larger ones of the same material. If selective comminution is applied on ores, this size influence has to be understood. The paper presents research results on this topic based on experimental investigations with model materials as well as with natural particles, which were stressed in a piston-die press. It appeared that the comminution result depends substantially on the material characteristics and the composition of the mixture. Conclusions will be drawn for the application in future applications of selective comminution in mineral processing. Keywords: Confined bed comminution, HPGR, VRM, piston die press, particle size

Jan 1, 2020

By Z. Gxowa, L. H. Chown, U. Curle, G. Govender

This work evaluates the deformation behaviour, at warm working temperatures, of green particle-reinforced aluminium composites produced by powder blending in a high-energy ball mill. The work focuses on metal matrix composites (MMCs) based on the 2124-Al alloy, reinforced with 10 or 15 vol.% SiC and metal matrix nanocomposites (MMNCs) based on the 2124-Al alloy, reinforced with 5 or 10 vol.% Al2O3. Three batches for each powder were blended and powder properties such as particle size distribution (PSD) and shape were consistent after blending. It was observed that a more uniform distribution of the reinforcement phase in the aluminium alloy matrix was achieved in 2124-Al/Al2O3 than in 2124- Al/SiC composites. The powders (unreinforced 2124-Al and blended) were initially over-aged at 350°C for 2 hours to reverse any natural ageing that may have occurred prior to use. The over-ageing was incorporated to improve compressibility of the powders with the aim of achieving green compacts with higher integrity. Uniaxial compression tests performed at ambient temperature on a Gleeble® 3500 thermomechanical simulator were unsuccessful as the green compacts fragmented. Engineering stress-strain curves showed that green compacts of unreinforced 2124-Al, 10%SiC MMC and 5%Al2O3 MMNC deformed in a similar manner at ambient temperature and had the same compressive fracture stress of approximately 170 MPa. When the deformation temperature was increased from ambient to warm working temperatures (170–280°C) it was observed that electrical resistance heating (the heating mode of the Gleeble®) of unreinforced Al alloy, MMC and MMNC green compacts did not occur. This was attributed to the high electrical conductivity of aluminium, which resulted in poor heat generation due to the low electrical resistance in the samples. It was presumed that the small sample size (d=8 mm, h=12 mm) also caused rapid heat loss. After further experimentation, the green compacts were heated successfully by insulating the samples to retain heat. It was found that at 280°C, increasing the soaking time from 6 to 20 minutes decreased flow stress and improved plastic flow in the 2124-Al/10%SiC green compact.

Jan 1, 2016

By Ruirui Wei, Mingrui Yang, Xuewei Lv

Calcium ferrite, as the main bonding phase in the sintering process, greatly influences the property of sintered ore. Ultrasonic vibration has been widely applied to the treatment of metals to improve the properties of metals. In this work, ultrasonic vibration was introduced into the calcium ferrite and numerical simulation was carried out by solving the Rayleigh-Plesset equation to investigate the influence of ultrasonic conditions, including frequency, power and initial radii of cavitation bubbles on the cavitation bubbling behavior in calcium ferrite melt. The results indicated that lower ultrasonic frequency, higher power, and an appropriate initial radius of bubble promotes ultrasonic cavitation.

Mar 1, 2018

By Floyd C. Kelly

A. HUltgren, .Söderfors, Sweden (written discussion*).—From the results obtained in his own experiments as well as those of Austin and of Grube Mr. Kelley derives a general law, expressed tentatively in the following words: "whenever two metals are brought into intimate contact at a temperature at which diffusion takes place, a comparatively rapid, or abnormal, grain growth results." It is suggested that,, in order adequately to represent the facts, this definition should he restricted by the following qualifications: a and b are the two metals, b diffusing into a. A. At the temperature in question a should exist as phase a 1 having a limited solubility for b. B. The supply of b by diffusion should be sufficient, in view of the rate of diffusion into a 1, to increase the concentration of b above the saturation value in a 1 so as to cause a new phase a2 to form. (7. The phase a2 should have a range of solubility for 6, thus rendering continued diffusion possible. D. In order that the columnar grains may be preserved in the structure the phase a2 should, of course, not suffer transformation on cooling. The phenomenon thus defined may be described as progressive transformation by diffusion. Its mechanism would appear to he as follows: Fig. 17 shows a portion of the equilibrium diagram a-b, Fig. 18 the distribution of b in solution after various periods of diffusion, Fig. 19 represents the structure in cross-section of a cylindrical rod of a at the end of heating period 3. 1. The first effect of diffusion of b into a will be to establish a concentration gradient in phase a1 (1, Fig. 18). When the saturation value for the temperature of the experiment (m, Fig. 17) is reached at the surface, nuclei of, a2 of composition n will form here, and later develop into a continuous layer. Assuming that diffusion proceeds without irregularities and that transformation at any point sets in without lag—i. e., in the moment saturation is exceeded—the transformation a1-a2 will advance inwards on a cylindrical surface concentric with the surface of the rod. The discontinuity of composition at the transformation surface in the position it happens to have at the end of the treatment (3, Fig. 18) will be preserved at room temperature, if the cooling is not particularly slow, and be recorded in the structure as a marked, smooth line, in agreement with Grube&apos;s and the author&apos;s observations. The shape of the distribution curves in Fig. 18 is also corroborated by the analyses given by Grube. 2. During diffusion, since the secondary phase a2 is always in immediate contact with the saturated part of the primary phase a1, there should be very little lag in the transformation. This means that the first a2 grains formed should grow in preference to the formation of independent nuclei; in other words, columnar growth results. It does not seem necessary to assume, with Green,&apos; whose conception of the phenomenon

Jan 1, 1929

By Floyd C. Kelly

A. HUltgren, .Söderfors, Sweden (written discussion*).—From the results obtained in his own experiments as well as those of Austin and of Grube Mr. Kelley derives a general law, expressed tentatively in the following words: "whenever two metals are brought into intimate contact at a temperature at which diffusion takes place, a comparatively rapid, or abnormal, grain growth results." It is suggested that,, in order adequately to represent the facts, this definition should he restricted by the following qualifications: a and b are the two metals, b diffusing into a. A. At the temperature in question a should exist as phase a 1 having a limited solubility for b. B. The supply of b by diffusion should be sufficient, in view of the rate of diffusion into a 1, to increase the concentration of b above the saturation value in a 1 so as to cause a new phase a2 to form. (7. The phase a2 should have a range of solubility for 6, thus rendering continued diffusion possible. D. In order that the columnar grains may be preserved in the structure the phase a2 should, of course, not suffer transformation on cooling. The phenomenon thus defined may be described as progressive transformation by diffusion. Its mechanism would appear to he as follows: Fig. 17 shows a portion of the equilibrium diagram a-b, Fig. 18 the distribution of b in solution after various periods of diffusion, Fig. 19 represents the structure in cross-section of a cylindrical rod of a at the end of heating period 3. 1. The first effect of diffusion of b into a will be to establish a concentration gradient in phase a1 (1, Fig. 18). When the saturation value for the temperature of the experiment (m, Fig. 17) is reached at the surface, nuclei of, a2 of composition n will form here, and later develop into a continuous layer. Assuming that diffusion proceeds without irregularities and that transformation at any point sets in without lag—i. e., in the moment saturation is exceeded—the transformation a1-a2 will advance inwards on a cylindrical surface concentric with the surface of the rod. The discontinuity of composition at the transformation surface in the position it happens to have at the end of the treatment (3, Fig. 18) will be preserved at room temperature, if the cooling is not particularly slow, and be recorded in the structure as a marked, smooth line, in agreement with Grube&apos;s and the author&apos;s observations. The shape of the distribution curves in Fig. 18 is also corroborated by the analyses given by Grube. 2. During diffusion, since the secondary phase a2 is always in immediate contact with the saturated part of the primary phase a1, there should be very little lag in the transformation. This means that the first a2 grains formed should grow in preference to the formation of independent nuclei; in other words, columnar growth results. It does not seem necessary to assume, with Green,&apos; whose conception of the phenomenon

Jan 1, 1929

By Mehdi Razavi

Scope of the Study The possibility and risk associated with mining two stopes at the same time The influence of Creighton Fault on the stability and dilution The effect of irregular shape of stope walls on overall stope stability and ore dilution The support requirements for proposed mining plan

Oct 1, 2010

By A. W. Hamilton

If you don&apos;t know a gauss from a grasshopper, you may be better off than you, think, particularly if you&apos;re an ore dressing engineer charged with the responsibility of selecting magnetic equipment for minerals separation and beneficiation. Gauss is a unit of measure for a magnetic field. It indicates the number of imaginary lines of force per square centimeter or per square inch radiating from a magnet. In discussing the strength characteristics of a magnet, we have come to speak of a magnetic field of 800 gauss, for example, meaning 800 lines of force per square centimeter. Gauss became the standard for selecting drum type separators many years ago under an arbitrary set of circumstances. The standard has continued to this day even though magnetics applications engineers have long considered it inadequate. The configurations of the older gauss meter were such that the most accurate and convenient readings on a drum type separator could be made at distances greater than one inch. So, an arbitrary distance of two inches was established and that two inches became the standard. Since then, it has become commonplace to specify magnetic strengths for drum separators according to average gauss readings at two inches; for example 500 gauss average at two inches, 750 gauss average at two inches and so on, even though gauss readings at two inches have much less to do with the separating and beneficiating function of a given application than was formerly believed. The standard was adopted as a means of gauging the strengths of electromagnetic drum type separators, for they were the only ones around at the time. These machines were usually designed with no magnetic considerations other than that the material to be separated should be agitated vigorously and the magnetic fields should be deep and strong. Drums built this way performed well enough, so it seemed logical to measure their magnetic strengths. Hence, gauss at two inches. Now, new improvements in magnetic techniques have made average gauss measurements at 2 inches positively obsolete.

Jan 1, 1971

"""Hazard"" is the general expression used by safety engineers to denote risk, or the danger to property or human beings from the contingencies peculiar to different industries. Where a business, family, or individual is subjected to possible financial loss from any particular hazard, it is customary and is considered good practice to insure for reimbursement of possible loss. Accordingly, we take out insurance for earthquakes, for fire, for accidents, etc., and are charged a different premium for each. The premium rate is based on our relative exposure to the hazard in comparison to the total loss to our particular class of business in our geographical location over a given period.Insurance, then, must be considered as the experience of a group rather than of an individual, and any individual may be fortunate or unfortunate over stated periods. Through the law of averages, the probability of loss because of exposure to hazard is becoming more accurately measured as experience is accumulated and data are analyzed.Lion human life came to have a financial value in the eyes of the law, and employers were held liable for losses through accidents to employees while on duty, insurance companies began to underwrite the accident risks of the different employers and divided them into classes based on the amount of risk involved. Premiums for compensation insurance are based on relative exposure, which is measured by pay roll. The premium is rated in proportion to the severity of losses established by statistical studies.' It soon became evident that the accident experience of employers in the some industry varied widely; that is, there were good and bad risked in the same line of business. This resulted in ""experience rating"" of premiums, meaning thereby that an employer with experience in accident cost was premium rated in proportion to his losses over a stated period (usually three or more years)."

Feb 1, 1926

By Bernie W. Martin, Raymond Leray, Christian Criado

Aguas Argentinas,1 a consortium managed by Lyonnaise des Eaux of France and operator of the world’s biggest privatized water supply and waste water collection system for the City of Buenos Aires, a city of 9 million people, was faced with the daunting task of providing new service to 1.6 million more people in the first five years of their 30 year concession. Aguas Argentinas elected to use the Negotiated Compressed Process - NCP - for the fast track implementation of a 15000 meter, 3,5 meter diameter tunnel, a key component of the infrastructure master plan. NCP was developed by Klohn Crippen for the $200 million international railway tunnel between Canada and the United States. The conceptual design of the project was performed by Safege Montgomery-Watson, who engaged Klohn Crippento assist with the NCP, the preparation of the tender documents, and implementation of theproject during construction. The process included the purchase by the client Aguas Argentinas of two sophisticated 4 metre diameter earth pressure balance tunnel boring machines from Herrenknecht of Germany. Construction of the tunnel is being performed by the consortium Wayss & Freytag (Germany) and Sollazzo Hnos S.A. (Argentina). The water tunnel is being built with a one pass, bolted segmented gasketed reinforced concrete liner. The purpose of this paper is to describe a transferable methodology for this innovative contracting procedure, the project organization and quality control plan for this important world class tunnel project which is designed to service one of Latin America’s largest metropolitan areas.

Jan 1, 1997