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By Enrique I. Acuña

Creighton Mine is part of the mining history of Sudbury with more than 100 years of operation. Currently the deeper levels of the mine are reaching the 8000 ft level without implementation of mechanical refrigeration system as a result of the use of the Natural Heat Exchange Area (NHEA) over the past decades. The NHEA of Creighton Mine is part of an old block caving area divided into 4 blocks of trenches that were used to extract the ore. Currently, it is used year round to condition the outside temperature before the airflow enters the fresh air system of the mine. As the mine is progressing deeper, underground temperatures in the lower levels are starting to approach the limit of Vale?s guidelines for working in heat. This paper presents the study developed to improve the management of the NHEA to obtain cooler temperatures at the intake of the ventilation system and outlines the impact to the mine in terms of the additional level(s) that could be operated underground without the use of mechanical refrigeration. This is another of the efforts currently under development for energy conservation and to reduce the capital and operational costs of Creighton Mine while extending the expected life of the mine.

Oct 1, 2010

By Noel H. Stearn

OF the many instruments devised for the measurement of magnetic anomalies, the ordinary dip needle, by virtue of its superior simplicity of construction, facility of manipulation, and definiteness of interpretation, seems to merit serious attention as the instrument most readily applicable to the detection of magnetic anomalies of the higher order of magnitude. In spite of the fact that it has been used for many years for the discovery of iron ore in Europe and in the Lake Superior region of America, its capabilities as a geological instrument have not yet been thoroughly plumbed. The Wisconsin Geological Survey, under Dr. W. 0. Hotchkiss, E. F. Bean, and H. R. Aldrich, has been most thorough in developing the technique of the instrument, and the results it has obtained have aroused a general interest in a more widespread use of geomagnetics as an exploration method and the dip needle as a geological instrument. The simplicity of the instrument is an especial advantage, as it can be used by anyone, regardless of his technical training; but to insure useful results not only is a knowledge of the background of geomagnetics necessary but also an understanding of the principles of the instrument itself. Principles of the Dip Needle The major feature of the dip needle is an elongated magnet suspended with fixed bearings in such a way that it can move in a single plane. If the point of suspension were exactly at the center of gravity of the magnet, the instrument would be identical with the "dip circle" or "dipping needle" of terrestrial magneticists, and as such could be used to determine variations in the inclination of the earth's magnetic field when observed in the plane of the magnetic meridian. The dip needle, however, differs from the "dip circle" or "dipping needle" in having an adjustable counterweight affixed to one end of the magnet. This counterweight serves to balance the magnet at an angle to the inclination of the earth's field when the instrument is oriented in the plane of magnetic

Jan 1, 1929

By K. Wu, X. Yuan, R. Du, C. Chao

"Lump coals are currently employed to replace part of coke in the COREX melter-gasifier for ironmaking. In order to optimize the process, the pyrolysis kinetics of Datong coal used in the COREX process was studied. A sectioning method is proposed to overcome certain shortcomings of traditional methods for studying the pyrolysis of coal. Based on the sectioning method and the characteristics of the coal pyrolysis process, the temperature range was divided into three intervals. In the first, the adsorbed gas and water of crystallization were removed; in the second, the coal was transformed into semi-coke; and finally, the semi-coke was further coked. Three models of reaction were then established to study the different stages of the pyrolysis process: an interfacial chemical reaction model, a random pore model, and internal diffusion with shrinking volume. The results showed that the experimental data fitted the models well, with all correlation coefficients (r2) exceeding 0.97. Finally, the mechanisms of reaction and kinetic parameters for each temperature range were derived, which laid a necessary foundation for optimizing the usage of non-coking coal in the COREX process. IntroductionIn view of environmental concerns and the shortage of good-quality coking coal, the COREX process was designed as a new ironmaking technology, attracting wide attention (Fang et al., 2005). In this process, lump coal and a small quantity of coke are directly charged into the melter-gasifier, where a high-quality reducing gas is generated for the reduction of the iron ore (Kumar et al., 2009). In contrast to the conventional blast furnace (BF) process, non-coking lump coal is used as the reducing agent and as the energy source, and the iron charge consists of lump ore and/or pellets, which results in the elimination of the coke oven and sintering plant as well as a decrease in investment (Kumar et al., 2009; Liu et al., 2012).Although the COREX process has made great progress, in current production practice the energy consumption greatly exceeds that of the BF, and it requires a certain amount of coke to maintain permeability of the semi-coke bed (Wang et al., 2008). In addition, the process consumes a lot of good-quality lump ore and lump coal. The pyrolysis of coal is the first step in most coal conversion processes, such as carbonization, gasification, and combustion (Aboyade et al., 2013). The reaction behaviour of lump coals in the COREX melter-gasifier is crucial, as it determines energy utilization and gas composition, as well as the metallurgical properties and particle size of the semi-coke produced (Prachethan et al., 2011; Zhang et al., 2014). In order to optimize the process and improve its competitiveness, the pyrolysis kinetics of Datong coal used in Baosteel’s COREX C-3000 facility was studied."

Jan 1, 2016

By cheng Peng-fei, TANG Hai-yan, guo Xiao-chen, LI Jing-she, Liang Yong-cang, Zhao Baojun

In the process of oxygen blast furnace, the lower coke ratio and the higher coke load make the skeleton coke more important. To understand the dissolution of coke in melting and dropping zone, the influence of FeO content, temperature and reaction time on the dissolution of coke with slag were studied by single-factor experiment. Meanwhile, the three factors and three levels orthogonal were conducted. The dissolution degrees were characterized by the weight loss ratio and diameter variation. The results showed that the weight loss ratio increased and the diameter decreased with the increase of FeO content, temperature and time. The three factors and three levels orthogonal test showed that time was the most significant factor on coke dissolution, FeO content of the second, and finally the temperature. The microstructure of coke after reaction indicated that the dissolution occurred on coke surface.

Jan 1, 2016

By J. Bouchard, Ali Vazirizadeh, R. del Villar

"The amount of water reporting to the concentrate correlates well with the solid entrainment. It is well known that the frother and collector dosage as well as the froth depth and gas rate influence the amount of water reporting to the concentrate. This is also true for gas dispersion properties such as gas holdup and bubble surface area flux. On the other hand, a positive bias rate, required to reduce hydraulic entrainment, also affects water recovery and thus the particle recovered by entrainment (depending on the their size). Up until now, the effect of the gas rate on the water recovery has been studied, but no comprehensive investigation on the gas holdup, bubble size and bubble surface area flux has yet been reported. This research precisely aims at addressing this issue. The experimental work was carried out under a constant gas flow rate to eliminate the gas volume effect, while other gas dispersion properties have been varied by modifying the frother concentration and the shearing water introduced to the frit-and-sleeve sparger. A constant froth depth and no wash water were used, in order to be able to evaluate the exclusive correlation between the water recovery and the bubble surface area flux and/or the bubble size. It is worth mentioning, that the particle size of the hydrophobic particles did not show a significant effect on the amount of water going to the concentrate. Not surprisingly, experimental results demonstrate that water recovery increases with the bubble surface area flux and with the gas hold-up."

Jan 1, 2014

By Frans van Grunsven, Cees van Rhee, Geert Keetels

One of the obstacles during the initial phases of project development is the assessment of the environmental impact. Mining residue, consisting of fine seafloor sediments, are to be discharged subsea to mitigate the impact of these suspended particles. In order to test the effectiveness of discharging in proximity of the seabed, a numerical model is developed within the open source software package OpenFoam. Dedicated laboratory experiments for numerical model validation are discussed within this paper. INTRODUCTION Siltation is considered one of the major pressures on the environment for a seabed mining operation. Siltation is defined as the pollution of water by a high concentration of suspended sediments like clay or silt. This can be caused by two main activities during the mining process: the spill loss during the excavation and the return flow of undesired seafloor sediment after ore filtration on the ship. In a concentrated cloud, these fine particles form a so-called turbidity plume. Prediction of the size of these plumes and the created layer thickness of deposited sediment is a crucial part of the environmental impact assessment. The challenge in predicting the behaviour of these plumes is found in the wide range of scales involved in the process. At the point of origin, the turbidity plumes spread mainly under the influence of turbulent whirls created by an initial momentum and a buoyancy difference due to the presence of the suspended sediment particles. If carried by ambientcurrents, these plumes can spread for several kilometres before blending in the background.

Jan 1, 2018

By H. Melama

The primary grinding stage in the Vuonos concentrator comprises a rod mill in open circuit and a semi-autogeneous mill in closed, circuit with a hydrocyclone classifier. The instrumentation of the grinding circuit is displayed in Fig. 1. All the measurements have computer interfaces and all the control circuits have been implemented by the process control computer. The crushed ore feed to the rod mill is measured by a belt-weigher and controlled by a belt-feeder. The pulp density in the rod mill is stabilized by proportioning the waterfeed at the mill inlet to the crushed ore feed. The slurry level in the pump sump is measured by a pressure transducer and it is controlled by charging the speed of the direct-current drive pump.

Jan 1, 1984

By A. S. Tawadrous

The stress field around a detonating charge in a borehole was calculated using AUTODYN for a variety of in-situ stress conditions. Calculations were conducted for zero in-situ stress, hydrostatic conditions at 100MPa, uniaxial stress conditions of 100MPa, and bi-axial state of stress with amplitudes of 200MPa and 100MPa along the axes. Two different explosives, ANFO and emulsion, were used for the calculations. It was shown that in-situ stress fields had an effect on the tensile and compressional damage zones around the blasthole, calculated on the basis of the maximum amplitude of the stress pulses in the rock after the detonation of the explosive in the blasthole. The extent of compressional damage increased around the borehole, whereas, the extent of the tensile damage decreased. The damage zones are of elliptical nature with their axes parallel to the direction of the principal stresses. The difference between the major and minor axis of the elliptical damage was not very significant in the case of the compressional damage; however it was significant in the case of the tensile damage.

Jan 1, 2007

By Andrew Dobson, Cheryl Allen, Enrique Acuña

"Totten Mine return air raise was designed with two parallel fans equipped with silencers to reduce the noise emitted from the outlets into the environment. As development and production of the mine progressed through the past years, the silencer system needed to be upgraded, and additional maintenance strategies have been necessary to meet the regulatory noise limits enforced by the province of Ontario. The current mine plan will require the fans to reach the upper limit of their capacity by Q1 2019. To achieve this operational target, additional silencing capability has been required and Totten Mine has explored alternatives to further extend the noise silencing capacity available considering the current constraints at the mine site. The alternatives included a new silencer baffle design and a new layout that have allowed doubling the length of the silencer system. Using acoustic measurement data collected on several occasions, this paper presents and discusses the performance of the various silencing systems which have been installed on the return air fans at Totten Mine.INTRODUCTION Vale Canada Limited’s Totten Mine is a base metal, underground mine extracting nickel and copper, situated in the Sudbury Basin of Ontario. The mine initiated operations at the end of 2013, and is equipped with two main return air fans and two main fresh air fans located on surface. Both fresh air and return air fans are set in a parallel arrangement to operate as integrated units and are equipped with variable frequency drives (VFDs) to allow for the remote modification of their operating set point, usually between 600 to 880 rpm, depending on the mine’s requirements. The main return air raise (RAR) fans are also equipped with dissipative baffle silencers to attenuate the noise emitted to the environment. Approximately four years ago, acoustical measurements conducted to verify compliance with the applicable regulatory criteria, and respond to noise concerns from neighboring residents, concluded that the sound emissions of the main return air raise exceeded the noise design parameters. The acoustic tones of the fans were audible offsite, at a residential location, approximately 9 km northeast of the mine site. The elevated sound levels and offsite audibility was due to degradation of the original discharge silencers from moisture and particulate being drawn from underground workings and passing through the silencer baffles. The audibility was also due to an outlet directivity pattern which directed noise towards the residential location."

Jan 1, 2019

By H Holmstr÷m, A Widerlund, M Lindvall

At the Kristineberg mine in northern Sweden sulfide-rich, poorly buffered tailings have been deposited in five impoundments located along a valley. The tailings area has been remediated by applying a combination of till cover and flooding. A new method that has been applied to parts of the tailings area is to raise the groundwater table to saturate the tailings. By increasing pH by liming, thereby reducing metal mobility, a water-covered downstream impoundment is functioning as a trap for metals released from the till-covered impoundments upstream. In this paper the efficiency of the system approach used at Kristineberg is evaluated. Progressive changes of water quality from groundwater in the upstream till-covered impoundments via surface streams within the pond system to the water in the flooded downstream pond and its outlet are described. The results show that the system approach used in the design of the remediation programme of the tailings works as planned. The sulfide oxidation rate has decreased in the till-covered impoundments, and, as predicted, there is an out-flush of old weathering products which will continue for at least five years before equilibrium is reached. The groundwater in the till-covered impoundments has high concentrations of Fe, S, Mg and Zn, but the concentrations of metals such as Cu, Cd and Pb are much lower than before the till cover was applied. The limed pond is an efficient metal trap, with concentrations as high as 2.76 per cent Zn and 0.28 per cent Cu in the calcite-gypsum sludge developed on the tailings. The outlet from the flooded pond, and thus from the whole mining area, releases small amounts of metals to the recipient in comparison to the amounts that are in movement within the mining area. During the period May to November, 13 kg dissolved Zn and 111 kg particulate Zn was released to the recipient, whereas a total of 27 000 kg was transported by surface water within the impoundment system during the same period. The results from Kristineberg show that when planning remediation of complex mining areas, it is useful to adopt a system approach in which different methods are used on different parts of the area along the flow path of the drainage water, whereas flooding of the downstream pond is the key to the performance of the entire system.

Jan 1, 2003

By John R. Bitler

The Bureau of Mines conducted this study to provide information concerning the availability of and the demand for construction-mineral aggregates in the Baltimore, Md., Standard Metropolitan Statistical Area (SMSA). The demand is discussed with reference to the area's current consumption and estimates of the area's demand for aggregates through 1990. Estimates of aggregate supply are presented in conjunction with an examination of the geology of the area, the availability of substitutes, and the effect of transportation costs. A discussion of the constraints affecting aggregate availability precedes the conclusions and recommendations. The availability of aggregates is subject to geologic, economic, and political constraints. As of January 1974, an estimated 20,100 million tons of stone was available to meet the demand projected through 1990 (188.7 million tons). An estimated 139 million tons of sand and gravel was available to meet the demand projected through 1990 (84.3 million tons). Several alternative actions are available within the area to insure the adequacy of the stone supply and to increase the supply of sand and gravel: (1) The establishment of special mineral resource zones; (2) the application of sequential land use techniques; and (3) the exploration of previously undeveloped regions.

Jan 1, 1975

By C. R. Sandberg, N. Stein, L. D. Wiener, E. B. Elfrink

this paper presents the results of a study of the slip velocity of gases rising through liquids in vertical tubes, inclined tubes, and vertical annuli. The data were obtained in gas-liquid systems which included combinations of air, propane and natural gas (over 97 per cent methane) with water, lubricating oils, and crude oils. The 214 data points obtained in this study along with 11 data points reported in the literature are incorporated in an empirical correlation which relates the mean slip velocity of gases flowing through liquids with the parameters gas rate, tube size, ratio of liquid viscosity to liquid density, gas density, liquid density, and the angle of the tube from the vertical. The average numerical deviation of the measured slip velocity data from values obtained from the correlation is 9.2 per cent. The average algebraic deviation between measured and Predicted data is 0.31 per cent, an indication that the correlation is a satisfactory representation of the data. The correlation presented in this paper will be useful primarily in the design of subsurface gas-oil separation equipment for increasing the efficiency of oil-well pumping installations. but may perhaps be extended to other situations of gases rising through liquid columns. INTRODUCTION The production of oil by pumping is often complicated by the presence of free and dissolved gas in the oil at bottom-hole conditions. This gas can be drawn into the pump barrel and result in "vapor locking" the pump, thus reducing the efficiency of the pumping operation. Large amounts of free gas may be excluded from the pump by the use of a gas-anchor, which is designed to allow the separation of free gas from the oil before it is drawn into the pump. The design of a suitable gas-anchor depends on a knowledge of the difference between the velocity of the free gas and that of the oil as the oil travels down toward the pump intake. This rate of gas rise through the oil is termed "slip velocity." AS a first step toward the full understanding of this roblem, the mean slip velocities of gases flowing through static

Jan 1, 1952

By Stanley Davidson

Introduction The ore deposit mined by Falconbridge Nickel Mines, Limited, is one of the numerous nickel-copper sulphide bodies marginal to the large oyster-shaped mass of differentiated norite in the Sudbury district, famous as the world's most important nickel producing field. The unique character of the ore deposits of the district has resulted in its intensive geological study over a period of more than fifty years. The results of these studies have given rise to a voluminous geological literature and to a great deal of controversy as to the genesis of the ores. This description of the structural geology at the Falconbridge mine is presented in the hope that it may form a small part of the chain of evidence leading to a reasonably satisfactory explanation of the ore genesis. The mine, named after Falconbridge township in which the deposit occurs, lies along the southeast margin of the norite mass which, however, is here concealed beneath a deep mantle of glacial sands and gravels averaging over 100 feet in thickness. As a consequence, the deposit was not discovered by the early prospectors, and it was not until 1916-17 that E. J. Longyear, of Minneapolis, located the ore by drilling. The discovery was foreshadowed in 1899 by the work of Thomas A. Edison, who found indications of the deposit by what is believed to have been a combination of magnetic and electrical geophysical surveys. He sank a prospect shaft over what has to date proven to be the largest and richest ore section in the mine. A wet quicksand layer at the rock surface proved impenetrable, however, and the "Edison' shaft never reached bed-rock.

Jan 1, 1946

By Robert W. Hendricks, John B. Newkirk

A simple method is described for determining the orientation of a single crystal by means of a cylindr cal X-ray camera. Orientation setting to within ±1 deg is attainable by a stereographic analysis of a single cylindrical Laue pattern produced by the originally randomly mounted crystal. Final precision adjustments which permit orientation of the crystal to within ±5 min of arc from the desired position can be made by the method of Weisz and Cole. A chart, originally Presented by Schiebold and schneider7 and which allows a direct reading of the two stereographic polar coordinates of the corresponding pole of a given Laue spot, has been recomputed to aid in the stereographic interpretation of the cylindrical Laue X-ray photograph. Detailed instructions for the use of the chart, a simple example, and a comparison with the conventional flat-film Laue Methods, are presented. 1 HE problem of determining the orientation of the unit cell of a single crystal relative to a set of fixed external reference coordinates is fundamental to most problems of X-ray crystallography and to many experimental studies of the structure-sensitive physical properties of crystalline materials. Several techniques for measuring these orientation relations have been developed which correlate optically observable, orientation-dependent physical properties to the unit cell. Examples of such procedures include the observation of cleavage faces or birefringence, as discussed by bunn,1 or the examination of preferentially formed etch-pits, as discussed by barrett.2 Each of these methods is limited, for various reasons, to an orientation accuracy of approximately ±1 deg—a serious limitation in some experimental studies. Several other limitations decrease the generality of these methods. Of these, perhaps most notable is the absence in many crystals of the physical property necessary for the orientation technique. The most widely used methods for determining crystal orientation are variations of the Laue X-ray diffraction method. Because of the indeterminacy of the X-ray wavelength diffracted to a given spot, the interpretation of Laue photographs is now limited almost exclusively to the procedure of using a chart to determine the angular coordinates of the corresponding pole for each spot. For the flat-film geometries, either a leonhardt3 or a Dunn-Martin4 chart is used in interpreting transmission patterns, whereas a greninger5 chart is used for interpreting back-reflection patterns. A less common method of interpreting flat-film transmission Laue photographs is by comparing the Laue pattern with the Majima and Togino standards,6 or with the revised standards prepared by Dunn and Martin.4 Although this last method is applicable only to crystals with cubic symmetry, it can be very rapid and just as accurate as the graphical methods. The primary limitation of all the X-ray methods mentioned is the relatively small number of Laue spots and zones which are recorded on the flat film. Often, few, if any, major poles appear, thus making interpretation tedious and sometimes uncertain. The use of a cylindrical film eliminates this problem. Schiebold and schneider7 prepared a chart by which the orientation of the specimen crystal could be determined from a cylindrical Laue photograph. However, it was only drawn in 5-deg intervals of each of the two angular variables used to identify the Laue spots, thus limiting the accuracy of orientation to about ±3 deg. An examination of this chart indicated that if it were drawn in 2-deg intervals, crystal orientations to ±1 deg would be attainable. Subsequent use of the replotted chart has confirmed this accuracy. It is the purpose of this paper to describe the redevelopment and use of this chart, and to point out its advantages and limitations. I) CAMERA GEOMETRY AND CHART CALCULATIONS The geometry of the cylindrical camera with a related reference sphere is shown in Fig. 1. The X-ray beam BB&apos; pierces the film at the back-reflection hole B, strikes the crystal at 0, and the transmitted beam leaves the camera at the transmission hole T. One of the diffracted X-rays intersects the film at a Laue spot L. The normal OP to the diffracting plane bisects the angle BOL between the incident and diffracted X-ray beams. The point P on the reference sphere can be located uniquely by the two orthogonal motions 6 and 8 on the two great circles ENWS and BPQT respectively. Because the Bragg angle 8 (= 90 - < BOP) is always less than 90 deg, P always remains in the hemisphere BENWS. Therefore, if every possible pole P is to be recorded on the same stereographic projection, it is necessary that the projection reference point be at T with the projection plane tangent to the sphere at B.* The great

Jan 1, 1963

By D. J. McAdam, G. W. Geil, D. H. Woodard, W. D. Jenkins

INTRODUCTION IN a series of papers, the authors and their associates have shown the influence of four important factors on the technical cohesion limit.3-16 By "technical cohesion limit" is meant the technically determinable resistance to fracture. The four important factors are the stress system, plastic deformation, temperature, and the strain rate. The influence of any one of these factors may be represented by a curve of cohesion limits, although only one point on the curve may represent actual fracture. As the term "fracture stress" has come into general use with the same significance as technical cohesion limit, the authors are here using the shorter term with the understanding that it does not always refer to actual fracture. The previously-mentioned series of papers contains ample evidence that plastic extension increases the fracture stress of any polycrystalline metal. In a recent paper of the series,15 moreover, it has been shown that the effect of plastic deformation on the fracture stress cannot be attributed to reorientation of internal flaws but is a work-strengthening effect, similar to the effect on the flow stress.[$] Plastic deformation of steels, however, may not only cause work hardening, but may result in additional hardness because of strain aging. Some evidence that strain aging affects not only the flow stress but also the fracture stress, has been presented in a recent paper.14 In that paper, a study is made of the influence of plastic deformation at room temperature on the fracture stress of ferritic steels at -188°C. The study is based on the results of two-stage tests. In the first stage each specimen was extended a predetermined amount at room temperature; in the second stage the specimen was tested to fracture in liquid air. In most of these tests the specimen remained in the testing machine during the interval of about one hour between the first and second stages, it was kept under a tensile load of about 500 lb and maintained at liquid air temperature. The effects of various amounts of plastic deformation on the fracture stress were thus determined and curves were obtained to represent the influence of plastic deformation at room temperature on the stress at brittle fracture in liquid air.14 Two specimens of ingot iron, however, were removed from the testing machine at the end of the first stage and several days elapsed before the specimens were tested to fracture in liquid air. As shown in Fig 8 of that paper," the points representing fracture of these specimens are far above the curve representing the results of two-stage tests without a rest interval between the stages. The evidence thus indicated that the fracture stresses of these two specimens were increased not only by the work-strengthening, but also by strain aging. The present paper presents results of further investigation of the influence of strain aging on the fracture stress. There are two kinds of aging of steel.

Jan 1, 1948

By M. E. Volin

The Ladd manganese deposits are in San Joaquin County, Calif., about 13 miles southwest of Tracy. The deposits are confined in two main areas of development, roughly about 1,700 feet apart horizontally, and known as the Ladd mine and Fabian mine, respectively. The deposits occur as interbedded lenses in the white cherts of the Franciscan formation. The ore minerals are bementite, rhodochrosite and psilomelane. As a part of the Bureau of Mines program of investigation and development of domestic mineral deposits, a development program was started. August 24, 1940, and completed on June 24, 1941. The Federal Geological Survey cooperated by mapping the geology and logging the drill cores. The program included road building, trenching, rehabilitating the mine workings, trenching underground excavation, sampling, and core drilling. The following pages mention the location, give a brief history, and note the physical features of +1-.1, district. Mine workings are sketched, the deposit is described and the plan of the project is noted. The work performed by the Bureau of Mines is explained in the concluding pages with a summary of the drill hole logs.

Jan 1, 1949

By J. Olaf Sund

"THE November issue of the Bulletin carried in it ""Origin of the New Bruns1viclc Gypsum Deposits"" by J. Olaf Sund. This paper was a digested account of a Master's thesis at the University of New Brunswick which was a very useful compendium of information of gyp-sum in New Brunswick. It was a warded the President' s Gold .Medal and the First Prize in the Graduates' Section of the Students' Essay Competition. The present writer presents his congratulations to the winner of the competition. At the same time he must comment on the use of certain terms and on certain conclusions presented in the paper.The term ""unconformable"" has been used in several places in the paper to describe the relationship of gypsum to anhydrite in various deposits in New Brunswick in a sense which is quite alien to the accepted meaning. It has long been known tl1at the gypsum at the surface or near the surface in deposits in the Atlantic Provinces has come from hydration of anhydrite by surface and ground waters. The gyp-sum must be looked upon then as an alteration or even a weathering product. It cannot in this sense be called ""unconformable"" and thus arguments using the word in the accepted sense are invalid."

Jan 1, 1960

By N Belluz, L Johnson, N Wiwoho, P Manning

The Kucing Liar skarn deposit is located in the Ertsberg mining district, which also contains other skarn deposits and the Grasberg porphyry copper û gold deposit. The Ertsberg district is located in the province of Irian Jaya, IndonesiaÆs easternmost province. Mining development began in the Ertsberg district in 1972 with the mining of the Ertsberg deposit. Daily production in the district now averages about 230 000 tonnes of ore, with the bulk of the ore coming from the Grasberg open pit and the balance from underground mining of skarn deposits. During 1998, 45 218 additional metres of drilling were conducted to delineate and understand the Kucing Liar orebody. The deposit was first intersected in drill holes in 1994 and then was intersected in underground workings located about 1000 metres from the discovery drill hole in 1995. Initially, the two intersections were thought to be different orebodies but are now realised to be different parts of the same orebody. The Kucing Liar deposit consists of magnetite û copper û gold replacement and skarn mineralisation in favorable Tertiary and Cretaceous units. The deposit is approximately 2000 metres in length and averages about 200 to 250 metres in thickness. The width varies from 400 to 600 metres. Drilling in 1998 was directed towards delineating the deposit on its NW and SE ends and to determine its down dip extension. Reserves for the deposit at the end of 1998 stand at 320 million tonnes at 1.4 per cent copper, 1.4 g/t gold, and 5.3 g/t silver. Many important questions remain to be answered concerning the relationship of the Kucing Liar orebody to the major faults in the district and to the Grasberg intrusive complex which contains the Grasberg orebody. Continued exciting developments are anticipated as work to understand the deposit by drilling and geologic study continues.

Jan 1, 1999

By M. F. Burr, F. V. Lenel, G. S. Ansell

The mechanism of materials transport was studied in a model experiment in which a silver sphere was sintered to a silver plate under an applied external stress near 800° C. For this purpose the rate of growth of the neck between the sphere and the plate which is proportional to the strain rate of the creep process involved in a neck growth was determined by measuring the change in electrical resistance of the away. This rate of neck growth will depend upon the magnitude of the applied external stress. By measuring the rate just before and just after a change in the external load and therefore the applied stress, the relationship between strain rate and stress can be derived. For material transport by slip in a pure metal it is expected that the strain rate should be proportional to the 4.5th power of the stress, while for transport by diffusional flow the strain rate should be proportional to the first power of the stress. It was found that for stresses above 5 X 10&apos; dynes per sq cm (70 psi) the exponent in the stvain rate-stress relationship was near 4.5 while for a stress of 0.7 x 108 dynes per sq cm (10 psi) an exponent of 1.8 was determined indicating that under the conditions of the experiment the transport mechanism for creep in silver shifts from diffusional flow to slip in the region of 0.7 x 106 dynes per sq cm (10 psi). The importance of these findings for an understanding of the mechanism of material transport in conventional sintering (without an external load) is pointed out. In a paper by Early et al.,&apos; the mechanism of material transport during sintering was treated as a creep process. It was pointed out that two possible types of creep processes could operate during sintering. In one of these material transport takes place by vacancy diffusion due to a gradient in chemical potential. The vacancy sinks in this diffusion process may be either grain boundaries, as in Herring-Nabarro microcreep, or regions beneath a surface of small radius of curvature. The diffusive transport may be by volume, grain boundary, or surface diffusion. In the other mechanism, creep takes place by slip, i.e., dislocation motion with its rate generally controlled by dislocation climb. One method of distinguishing between these two modes of materials transport is to investigate the creep rate, i.e., the rate of material transport as a function of stress. For material transport by vacancy diffusion, the creep rate is proportional to the stress.&apos; For creep by slip, controlled by dislocation climb, the creep rate is proportional to a power of the stress. For pure metals this power is 4.5;374 for dispersion-strengthened material a fourth power relationship can be derived.5 This difference in the stress dependence of the strain rate is illustrated schematically in Fig. 1, in which the logarithm of strain rate is plotted vs the logarithm of the stress for material transport in a pure metal by vacancy flux and by dislocation climb. The stress range in which the two types of material transport overlap would be expected to be relatively small. In the experiments described by Early and coworkers compacts pressed from spherical copper powder were sintered isothermally under an applied axial external load in a dilatometer. During sintering the magnitude of the applied external load was changed and the rate of axial shrinkage of the compact before and after the load change determined. In order to find the stress dependence of the strain rate the magnitude of the stress acting on the neck area between the spherical particles before and after the load change had to be calculated. This stress is the resultant of the stresses due both to the externally applied load and to surface tension. The stress due to surface tension is a function of the geometry of the powder compacts. It can be determined, at least for simple geometrical arrays,&apos;76 but it is difficult to obtain exact values of the stresses for actual powder compacts when only average values of particle diameters and of neck diameters between particles are available. The calculation of stress and the strain rate-stress relationship is therefore only very approximate.

Jan 1, 1968

When a mine decides to construct surface structures close to, or on undermined ground, it is required in terms of the regulations of the Mine Health and Safety Act to obtain permission from the Department of Minerals and Energy (DME). Apart from the legal requirements, the stability of the structures is crucial as damage to the structures due to surface movements could result in loss in life, equipment and/or production. This paper deals with the rock engineering aspects of a study that was conducted on one of the chrome mines in the Bushveld Complex (BC) involving the construction of plant structures on shallow undermined ground. The paper addresses the legal requirements and guidelines regarding ground stability of surface structures placed on undermined ground and the assessment of the undermined area with regard to the following: ?sources of potentially damaging surface movements ?safe mining spans ?stability of the pillars ?effect of the loading of plant structures on underground stability. Due to the irregular layout and geometry of the pillars in conjunction with a changing surface topography, numerical analysis and not the conventional tributary area theory was used to determine the imposed loads on the pillars. In order to subject the plant structures to minimum movement, the plant should be located in areas where the pillars would remain stable, the elastic deformation of the hanging wall is minimized and hanging wall failure extending to surface is unlikely to occur. The study indicates that although the depth of undermining is shallow (between 27 m and 60 m), potential damaging surface movements are not anticipated due to the stability of the pillars, competent nature of the overlying strata and negligible effect of the plant structure loading on the underground stability.

Jan 1, 2004