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By H. E. Grand

The purpose of this paper is to outline briefly some basic principles of ground- water hydrology that have application in mine hydrology. The development of a mine below the water table pleads for accurate values to answers of hydrology problems. Such problems involve both an inflow of water without adequate drainage facilities and a deficiency of water for the required use. Methods which give acceptable quantitative values for the solution of many ground-water problems depend on rather simple geologic structures, characterized chiefly by isotropic rocks of considerable areal extent. Unfortunately, mining operations are likely to be centered where isotropic rocks are not present. Consequently, methods that attempt to show values of the storage and transmitting capacity of rocks in mining areas must be applied with caution. In spite of complex geology and apparent uniqueness of individual mines and quarries, adherence to some concepts of ground water used by -hydrologists in the study of behavior of wells should be helpful to mine operators, The work of the Ground Water Branch of the U.S. Geological Survey through its history has been confined largely to the study of ground water as a resource, In view of the increasing number of problems relating to drainage of mines, the Branch started an investigation of mine hydrology in 1945 under the direction of W.T. Stuart, Mr. Stuart and other workers are making detailed studies of specific mine areas. In the present paper an attempt is made to synthesize some facts about ground water into usable form for the typical mine operator. Mining operations that extend below the water table disturb the natural hydrologic regimen, Prior to development, the water table slopes away from the site of a mine in at least one direction, but as soon as development begins and water is removed from the mine, the mine becomes the apex of a depressed cone in the water table, causing a convergence in the flow of water toward the mine. The behavior of the cone of depression, as it tends to deepen and increase in areal extent when the mine deepens, is related to the rate of withdrawal of water necessary to keep the mine dry. The significance and nature of the cone of depression in the vicinity of pumped wells has been studied by ground-water hydrologists for years, but the cone caused by pumping water from mines has generally been less systematically appraised.

Jan 1, 1958

By Nick D. Rose

The importance of structural geology in open pit slope stability is overlooked in many mining operations due to pressures to cut costs and minimize mine personnel. As a result, mine geology staff are often unable to keep up with geological mapping of the pit slopes due to other day to day production oriented tasks. In some instances, key structural controls that contribute to slope instability may not be identified until after a slope instability has initiated, at which time it may be difficult or impossible to delineate these features in the field. Even for small slopes, understanding the engineering and structural geology of the rock mass, as well as the effects of groundwater and blasting practices, are of key importance to slope stability. Two case histories are presented as examples of mining operations that experienced slope instability with little more than anecdotal information about the structural and groundwater conditions encountered during mining. By conducting field reconnaissance, simple slope stability analyses and ongoing slope monitoring, practical remedial measures were implemented, allowing continued safe mining operation.

May 1, 2002

By George A. Morgan

The successful expansion of crude oil production begun in late 1977, led to promising development of the nonfuel minerals sector. Although actual production of nonfuel minerals was limited both in variety and in percentage of output on a world scale, the potential for expansion with a rapidly developing infrastructure was significant. The energy base was expanding with construction of two new hydroelectric powerplants in addition to the existing plant near Edea. The Song Loulou plant will have a 240-megawatt capacity, and a hydroelectric plant under construction in the northern part of the country by mainland China will have 72 megawatts of installed capacity. Inflation of between 15% and 20% resulted in a real gross domestic product (GDP) of $2.8 billion2 in fiscal year 1980 (July 31 to June 1), up 6% from that of the previous fiscal year. Petroleum became the leading export item in terms of value, surpassing coffee and cocoa exports. Mineral exports as a whole increased eightfold in value, mainly because of oil sales. Oil exports also caused a reduction in the trade deficit by nearly one-third, and the Government expected its 1980-81 budget to be balanced at $1.17 billion. The Port of Douala accounted for about 8 million tons of cargo, or 93% of total maritime traffic for Cameroon. Expansion plans for the port call for an initial increase to 5 million tons, and a cargo handling capacity of 7.5 million tons in 1985 and 10 million tons by 1990. The Port of Victoria will gain importance with the startup of an oil refinery. The country's third seaport at Kribi was used solely for timber shipments, and capacity at the Port was to triple by 1981. The Government operated its own shipping line with six oceangoing freighters. France was the dominant trading partner, accounting for 25%

Jan 1, 1982

By Tanm Engin, Ali Riza Tarakcilar, Derya Dispinar

"Nowadays, the casting industry is developing parallel with the information technologies (IT). Particularly the casting simulation software is being frequently used in foundry floors for casting quality control and optimisation. In this study, the filling and solidification analysis of a rolling roll manufactured by spherical graphite cast iron were carried out by Vulcan casting simulation software. The appropriate defect relieving suggestions were presented by anticipation of defects that may form during the casting process.IntroductionThe optimisation of a casting process has long been the most focused area in manufacturing plants. Many of the work involve not only the process itself but the cost as well. When it comes to the process, it is important to be able to control the defects that may form during casting.The casting process begins with the melting of a charge; followed by pouring into the mould cavity. One of the most important factors is the difference in the liquid/solid density which may lead to porosity. On the other hand, turbulence during filling is another significant factor in casting operations [1].During solidification, due to the density difference between liquid and solid, porosity might form which leads to crack-like defects. There are several other factors that may determine the quality of a casting such as segregation, inclusions, grain size and etc. However, porosity is one of the first parameters that can be easily determine and controlled by the help of simulation software. Simulation is a cost-effective tool in the optimization of process parameters and castings can be visually observed. Time loss and economic expenses could be minimized [2]."

Jan 1, 2012

"Decreasing gold-in-ore grades is one of the main drivers of poorer productivity and rapidly escalating unit costs. Grinding costs, water use and reagent consumption are all intimately related to the ore grade processed. Various pre-concentration technologies have been developed that can be applied at various stages of crushing prior to ore grinding. This paper will review the amenability of ores to coarse particle barren gangue rejection for fine crush sizes in the pumpable particle size range (i.e., particles between 5 mm and 0.3 mm in size). The liberation of oxide gangue achieved during crushing is evaluated by proxy using sink-float analysis and the deportments of gold, sulfur, and arsenic into sinks and floats are monitored. Amenability of gangue rejection by continuous gravity separation is evaluated after various crushing modes (vertical shaft impact crushing, cone crushing, and HPGR crushing). The potential to identify coarse particle mineral association and liberation using three-dimensional x-ray computed tomography will be discussed.INTRODUCTIONThe aim of research in this area is to explore some of the attributes which make some ores amenable to preconcentration, or rejection of a significant component of the feed mass to tailings at a coarse liberation size. Characteristics such as ore type, mineralogy, breakage pattern, particle shape, and liberation characteristics may need to be examined to identify amenability to pre-concentration amenability.It is intended to focus on continuous gangue rejection in the pumpable size range (0.3–5.0 mm) as this remains one of the key opportunities to reduce processing costs through a combination of techniques including screening (for mineral differentiation rather than size classification only) and gravity separation (using jigs). This is to be contrasted to conventional preconcentration as performed with automatic ore sorters."

Jan 1, 2016

By A. Elizabet Serna

The weak acid is a by product obtained in a pre-treatment of gases from a copper smelter prior to sulfuric acid manufacture and the main components of this weak acid are: sulfuric acid. copper, arsenic. antimony, bismuth and iron. Usually, this effluent is neutralized with lime and the solid residues are stored in a landfill as a hazardous waste. This work was directed at determining the optimal conditions to recover copper from weak acid using a cementation process before the neutralization of the effluent. The variables investigated are: Effluent temperature, iron scrap amount and acid concentration versus reaction time. The results of these experiments show that the cementation process of copper and the co-cementation of impurities such as arsenic, antimony and bismuth were in accord with the theory of the electrode potentials.

Jan 1, 1996

To reuse chromium, nickel, and molybdenum now lost in stainless and specialty steel-making wastes, and simultaneously to overcome the current environmental problem resulting from landfilling these wastes. Approach A variety of stainless and specialty steelmaking wastes are agglomerated and recharged into the plant's electric arc furnaces. How It Works Stainless and specialty steel-making wastes such as bag-house dust from the electric arc furnace, dust from the argon-oxygen decarburization unit, grinding swart, and mill scale are blended in proportion to the ratio in which they are generated. Next they are agglomerated on a pelletizer with an addition of a small amount of carbonaceous reducing agent, and air-dried in preparation for being recharged into the furnace. Some mixtures of wastes tested in the laboratory required the addition of binders and/or the use of ovens in lieu of air-drying to produce sufficient pellet strength. Although the optimal maximum particle size of wastes being pelletized is 35 mesh, somewhat larger particle sizes were satisfactorily pelletized during in-plant tests. The photograph shows a typical mixture of wastes and the pellets made from them.

Jan 1, 1981

By L. E. Murr

Preliminary studies of bacterial attachment to MoSp (molybdenite) have indicated a low correlation between dislocation density in the (0001) basal plane and the density of attached microbes. In the present investigation, poly- crystalline thin sections of CuFeSp (chalcopyrite) have been ion-etched or carefully comminuted to electron transparency and observed in the transmission electron microscope. The thinned test sections were then immersed in a culture solution in which bacterial attachment occurred. The attached bacteria were biologically stained in a uranyl acetate solution and the entire thin CuFeSp sections or tiny particles containing thin, electron transparent edges with bacteria attached were observed in the transmission electron microscope, allowing the coincidence of bacteria and their density to be directly observed in relation to lattice dislocations and crystallographic orientations of the exposed surfaces. This technique has the advantage of exposing crystallographic orientations where dislocation lines intersect the free mineral surface, and the emergence sites of dislocations could in principle be directly investigated as a possible preferential attachment site for bacteria. Bacteria morphologies were also extensively observed in the scanning electron microscope. The implications of the results are that although a strong correlation between dislocation density and distribution and bacterial attachment, density, and distribution has not been established, systematic multiplication of dislocation densities in crystalline mineral particles to be leached could enhance leaching rates by increasing the reaction rates as well as the density of attached bacteria at crystalline, metal-rich phases. Techniques for dislocation production in mineral and ore bodies and the particular implications in chalcopyrite leaching are discussed in relation to in-situ leaching where comminution is attained by explosives and the generation of strong shock waves in an ore body. The present study demonstrates the use of microanalytical and microscopic techniques in the investigation of fundamental microstructural phenomena in hydrometallurgical processes.

Jan 1, 1976

By K. Muchima, C. Siame, L. Little, B. Kaputula, Q. Mclennan

"The variability of copper mineralization at Kansanshi mine significantly affects the efficiencies of the processes used to recover copper. Quantifying this variability is therefore essential for monitoring and optimizing the performance of the concentrator, which comprises three different flotation circuits (sulphide, mixed, and oxide) and an atmospheric leach circuit. Onsite automated scanning electron microscopy with energy-dispersive X-ray spectrometry (Auto-SEM-EDS) is used to analyse routine weekly composite samples for each circuit, providing detailed analyses of bulk mineralogy, copper deportment to different minerals, mineral liberation, and associations. Weekly mineralogical trends are used to assess changes in process performance, and characterization of the copper losses has inspired a number of projects to target the specific particle types responsible for the main losses. In this paper we describe the relationship between mineralogy and plant performance at Kansanshi, and discus IntroductionKansanshi is a copper and gold mine located in the Northwestern Province of Zambia, with an annual production in the region of 250 000 t of copper and 160 000 ounces of gold. Ore mined from the epigenetic vein-hosted deposit is classified into three ore types based on the extent of oxidation and supergene enrichment. Sulphide, oxide, and mixed ore are fed to separate mineral processing circuits tailored for recovery of the dominant copper minerals in each. After comminution to a target grind size of 80% passing 150 µm, each ore type is subjected to flotation to recover the copper sulphide minerals (chalcopyrite, bornite, chalcocite, covellite). The oxide float tails and a large proportion of the mixed float tails are then treated by atmospheric leaching to extract copper from the remaining copper-hosting minerals, which include cuprite, malachite, chrysocolla, and delafossite. Some native copper is recovered by flotation and some of it is recovered by leaching. A small portion of the combined concentrate from all circuits is subjected to high-pressure leaching and the rest is sent to the smelter. Sulphuric acid produced during smelting is used for the atmospheric leach."

Nov 1, 2018

By N. O. Johnson

The Hog Mountain mine is a pyritic-gold property in the north central part of Tallapoosa County, Alabama, at an elevation of 800 ft. in the southern Appalachian region. It is 13 miles by a good secondary road from Alexander City, a station on the Central of Georgia Railroad. Since its discovery in 1839, the mine has been worked intermittently. The records of past operations are few and are scattered over a long period of time; however, available information indicates a production of approximately 12,000 oz. of gold prior to the present company's activities, which started in 1933. Additional 7844 oz. has been produced under the direction of the present management. The ore from stopes has averaged 0.200 oz. gold per ton; the ore from development, 0.136 oz. gold per ton. Silver, copper, iron and sulphur are also present but to date are of minor importance. The grade of ore in comparatively narrow veins makes necessary extreme vigilance in the methods of mining. Geology Wall Rock.—Hog Mountain consists of a quartz-diorite intrusion approximately 5000 ft. long by 1200 ft. wide. Its resistance to weathering, as compared to the surrounding schists, has led to the formation of a conspicuous ridge rising 400 ft. above the adjacent country. All the mining operations are confined within the limits of this quartz-diorite formation. Except where there is excessive shearing, either parallel or at flat angles to the quartz veins, all the walls of the stopes within the limits of the veins are strong enough to make timbering unnecessary. Where shearing exists, there may be a sloughing off of the walls, especially in the process of drawing the ore. When this occurs, stulls are placed in the stope, either while the stope is advancing, or while ore is being drawn from a completed stope. In general, very little timber is required. Veins.—The quartz veins have been deposited along fracture planes in the quartz diorite. There are 20 principal veins, all of which are roughly parallel and strike at right angles to the long axis of the formation.

Jan 1, 1937

By V Cullinan, D Buchanan

The Brunswick plant is located in Costerfield, approximately 40km east of Bendigo in central Victoria. Crushing, grinding, gravity gold concentration and flotation methods are used to produce a saleable gold concentrate and an antimony-gold flotation concentrate. This paper discusses the improvements made within the processing plant which have resulted in a 99% increase in throughput over nameplate capacity of 6 250 average tonnes per month to 12 445 average tonnes per month and increases of 12% gold (from 2007 average of 78% to 2014 average of 90%) and 16% antimony recovery (from 2007 average of 79% to 2015 average of 95%). This combined effort has resulted in an increase of equivalent gold ounces (AuEq oz) produced from 2010-2014 of 15 872 to 82 574 – a 66 702 increase.AuEq oz= Au oz +Sb t × Sb (US$/t)Au (US$/oz)CITATION:Buchanan, D and Cullinan, V, 2015. Improvements in bi-metal production at the Brunswick Plant, Costerfield, in Proceedings MetPlant 2015, pp 267–272 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 7, 2015

By K. C. Corin, M. S. Manono, R. M. Manenzhe, J. G. Wiese

"Environmental concerns necessitate the recycling of process water within mining operations. Given that recycled water is chemically different from fresh water, and collectors are added such that they adsorb at the liquid-particle interface, changes in the aqueous phase are expected to affect collector adsorption. A Finnish nickel-copper ore was floated in synthetic plant waters of varying ionic strengths and plant waters obtained at Boliden Kevitsa Mine, with aerophine and sodium isopropyl xanthate as collectors. Of the tested waters, the copper thickener overflow was the least conducive to xanthate adsorption and valuable mineral recovery. The nickel thickener overflow, standard process water, and raw water were the most conducive to xanthate adsorption. For the raw water and nickel thickener overflow, increased adsorption correlated with increased valuable mineral recovery. Further, recycling xanthate retained in water affected the selectivity of the collector and hence the concentrate grades.INTRODUCTIONFlotation is a separation process that exploits the differences in the surface properties of the particles being separated. The efficiency of separation is dependent on the degree of hydrophobicity achieved by the particles meant to be floated, which are, in most cases, valuable minerals. The hydrophobicity is in turn dependent on the adsorption of the chosen collector onto the surfaces of the floated particles (Fuerstenau, 1984; Taggart and Hassialis, 1946). Empirical findings suggest that species dissolved in solution strongly influence collector adsorption and overall flotation response (Fuerstenau and Chander, 1986). Due to environmental concerns, it is becoming more pertinent for mining plants to recycle process water and hence limit the usage of potable water. There is an interest to ensure minimal discharge of plant water into the environment, as this water is typically polluted with process reagents that may render it toxic (Levay et al., 2001).Recycled water, however, has been shown to adversely affect flotation. Reagent efficiency can be reduced due to increased suspended solids. A loss of mineral recovery can occur due to competitive adsorption between reagents and other dissolved species, loss of reagents due to precipitation, and unwanted reactions. Further, a reduction in grade can occur due to non-selective coating of reagents on valuable and gangue minerals, and hydrophobic coating of microbiological material on gangue, causing unwanted flotation. Yet despite these drawbacks, water reuse has the advantages of minimal fresh water use and reduced reagent consumption by recovering the unconsumed reagents retained in wastewaters (Bruckard et al., 2011; Levay et al., 2001; Shengo et al., 2016; Slatter et al., 2009)."

Jan 1, 2018

By F. X. Ferney

The centrifuge which will be reviewed in this dis¬cussion is the continuous solid bowl typo. As there are presently approximately 2000 of these units operating in our country, and about 200 of these in use in the coal industry, I expect that most of you are acquainted with its operating principle. How¬ever, for those who are not familiar with the machine a brief introduction is in order. The continuous solid bowl centrifuge was first successfully marketed, worldwide by the Bird machine Company in 1934. The successful development of this unit was based primarily on the invention of a drive mechanism to properly control the differential speed between the two rotating elements. This centrifuge was introduced into the coal industry immediately following the second World War. Today there are five or six additional firms' selling this machine in our country, and approximately twenty others in Europe, England and Japan.

Jan 1, 1965

By J. B. Littlefield

This study is one of a number conducted to determine the concentration of dust in the air during the complete cycle of operation in wet drilling information as to various factors connected with drilling in mining operations is considered to be of definite value in the control and prevention of air dustiness, and it is particularly desirable to ascertain What features of present-day wet-drilling operations in mine work contribute to dust disease and to remedy deficiencies when they are found. ACKNOWLEDGMENTS A testing alit through rock strata is being developed by the Mining Division of the United States bureau of Mines at Mount Weather, Va., and the tests discussed in this report were conducted there. This experimental alit in rock, constitutes a typo of laboratory where mine conditions can be closely simulated and where many of the variables likely to occur in an actual mine can be eliminated or at least controlled with reasonable effort, thus affording maximum opportunities to secure fundamental data uncomplicated by extraneous conditions. The authors wish to acknowledge the valuable assistance and cooperation of several members of the Mining Division, particularly C. F. Jackson, chief engineer, McHenry Mosier, associate mining engineer, and G. E. McElroy, supervising engineer, mine ventilation.

Jan 1, 1938

By M. Cohen, R. J. Teitel

There is considerable interest in beryllium because of its low density (1.84 g per cu cm), high modulus of elasticity (40 X 106 psi), high melting point (1280°C), and special nuclear characteristics. Moreover, it has fair resistance to corrosion and oxidation. However, the purest beryllium known to the authors is relatively brittle at room temperature, and cannot be fabricated readily. The search for improved properties leads naturally to investigations of beryllium alloys and the phase relationships upon which they are based. The present paper is concerned with the alloys of beryllium and iron, primarily from the standpoint of the equilibrium diagram. Iron was selected (1) because of its all-round importance in metallurgy, and (2) because the beryllium-iron system is known to be quite complex. The most recent diagram in the literature is that of Gaev and Sokolov,' and covers only the iron-rich end up to 16 wt pct beryllium. Beryllium markedly restricts the austenitic field, closing the gamma loop at about 0.4 wt pct (3 at. pct). On the other hand, beryllium is soluble in a-ferrite up to a maximum of 7.5 wt pct (34 at. pct) at the eutectic temperature of 1160"C. The eutectic composition lies at 10 wt pct beryllium (42 at. pct) and corresponds to a mixture of or and FeBez (called j3 in the present paper). The solid solubility of beryllium in the a phase decreases with decreasing temperature, and makes precipitation-hardening possible. These findings substantiate the earlier work of Oester-held,2 Wever and Mueller3 and Laissus.4 In addition to the FeBe2 (ß) mentioned above, Misch6 has reported on FeBes, and indicated evidence for another compound containing still more beryllium. A preliminary diagram by Gordon,5 not hitherto published, is given in Fig 1. Besides the phases previously named, there are shown a solid solution of extended range (e), a compound of limited solubility (t), and a high temperature phase (7). Beryllium is designated as 8. The t field contains the compound composition FeBea, and the f phase undoubtedly corresponds to the beryllium-rich compound found by Misch.6 The region around the { phase was proposed by R. J. Teitel based on Gordon's data. The details of the diagram are self-explanatory. It was the unusual complexity of this system that prompted the authors to undertake the present studies. By the same token, more emphasis was placed on the beryllium-rich than the iron-rich end of the diagram. Exprimental Details RAW MATERIALS The beryllium employed in this investigation was one of the purest grades available. Its chemical analysis after vacuum melting is given in Table 1. The metal assayed 99.4 wt pct beryllium. Vacuum melted electrolytic iron of purity shown in Table 1 was the source of iron.

Jan 1, 1950

By Theodore J. Barrett

[One of the earliest records of pillar removal can be found in the 16th Chapter of Judges in the Old Testament. Here we read where the mighty Sampson removed the pillars from beneath the prison house causing the collapse of the structure resulting in his own death along with the deaths of the 3,000 Philistine occupants. Our problems at the Mi Vida Mine differ somewhat from those of Sampson of old, in that it is our aim first to remove the pillars and get out from under the back before the "house falls in" and, secondly, to remove the pillars without the lose of a single life or without even a single casualty. As of January 15, 1959, the Mi Vida accident record stood at 772 days without a lost-time accident]

Jan 1, 1959

By D. E. Musgrove

The question of alternating current vs direct current has become an important consideration to the mining industry. Rising production costs demand lower investment, which, in many instances, can be realized by the use of ac mining machines. Generally ac motors, control systems, and distribution and power conversion equipment can be installed for approximately 50 pct of the first cost of their dc equivalents. This basic saving has made ac mining a serious competitor for the traditional dc mining systems. With the increased use of ac voltages underground, there has developed the problem of conveniently converting distribution voltages to usable 480-v power. Power at low voltages should not be carried for comparatively long distances, and the transformation should be made at the point of use. Otherwise, serious voltage regulation problems and objectionable line losses will occur.

Jan 5, 1955

United Engineering Society ARTHUR S DWIGHT J VIPOND DAVIES J V N Dorm Engineering Societies Library Board SIDNEY H BALL ALEXANDER C HUMPHRFYS GEORGE C STONE JOHN H JANEWAY Engineering Foundation Board H M BOYLSTON J VIPOND DAVIES GALEN H CLEVENGER Society for Promotion of Engineering Education WILLIAM KELLY ALLEN H ROGERS

Jan 1, 1923

By Jones

Extractive metallurgy in the mining industry in Western Australia has diversified and increased in the last 11 years. Before 1980, the industry mainly produced alumina, nickel, mineral sands and iron ore, with the gold industry restricted to five operating plants using Merrill-Crowe technology. In 1981 Carbon-in-pulp (C]P) plants were commissioned at Kambalda, Kalgoorlie and Meekatharra.Currently, the gold industry has some seventy CIP plants in operation, production of synthetic rutile has increased tenfold to 500 000 tpa, alumina production has doubled and production of copper, lead and zinc concentrates has begun. Other extractive metallurgy plants recover tin, niobium and tantalum, silicon, titanium dioxide and zirconia. Current proposals include vanadium, steel and rare earths.

Jan 1, 1992

By A. T. Iannacchione

Synopsis Underground stone mining Is an emerging sector of the U.S. mining industry. As this expansion takes mines under deeper cover, and as more efficient mining methods are utilized, effective stone pillar design methods will become even more Important. Current design practices are examined and a discussion of safe mine layouts is presented as a first approach towards weighing the demands for increased production against increased risk. Risks to underground stone-mine workers include rib Instabilities, pillar failures and roof falls. Seventy-two stone-mine pillar designs were examined. Pillars with width to height ratios of less than 1.5 appear more likely to fail when subjected to excessive stress levels. When width to height ratios fall below 1.0 defects in the pillars, such as through-running discon¬tinuities, can have a significant influence on stability. Discontinuity persistence, dip, material properties and orientation are also important determining factors in pillar strength. During the past three years the number of active underground stone mines in the U.S.A. has ranged between 90 and 100. This number is expected to increase as the crushed stone industry responds to growing demands for its products.1 As more of the industry moves to benefit from the advantages of underground mining production from underground stone mines is expected to increase above its current level of approximately 66 000 000 r/year. Parker2 identified four advantages of underground mining operations: (1) surface developments, zoning laws and environmental concerns are often less of an issue; (2) stripping and restoration requirements are eliminated; (3) additional reserves are often available beneath the quarry floor, under pit slopes or under an adjoining property; and (4) space is created for secondary use. Underground mines enjoy the added benefits of work in a constant underground climate, rather than in the variable surface climate, minimization of community concerns by placement of the crushing, sizing and stowing operations underground and reduction of surface vibration concerns through smaller blasts. The drawbacks of underground mining include added health and safety hazards for the stone miners, whose health can suffer from increased exposure to falls of ground, airborne contaminants and fog in large underground openings. Injuries from falls of ground in stone mines have occasionally exceeded the incidence rates for other mineral resources mined underground. 3 Existing underground stone operations, by comparison with stone operations a decade ago, mine more stone at a faster rate and with larger equipment. Because of high demand mines face increased pressure to yield more stone per production blast. A majority of the miners use the V-cut blasting pattern, which limits the depth or pull for each shot to about 4 m. Therefore, to produce more stone, either the mines must work more faces or existing faces must be enlarged. The enlargement of underground openings poses problems in the maintenance o€ strata stability, First, the widths of the mine entries partially control the amount of sag or deflection that any given roof beam can withstand before failure. This deflection can take pi ace quickly after an opening is excavated or much later as weathering processes form additional, thinner beams. Because increased deflection increases the potential for roof beam failure, there is a limit to how wide a room can safely be made. These limits depend on local geological and stress conditions and, to some extent, the cost effectiveness of roof-bolting. Given these room width limitations, underground stone mines have placed more attention on expansion of production through benching where mining thicknesses permit. The heights of rooms partially control the strength characteristics of adjacent pillars: as the room height increases for a given pillar width the pillar width-to-height ratio (w/h) decreases. In general, stone pillars are very strong, but when the width-to height ratio diminishes the potential for pillar rib instabilities and pillar failures increases (see Fig. 1). [ ] In the underground environment the desire to utilize wider rooms, higher benches and multi-level mining results in the potential for unstable ground conditions. Although the number of failed pillars is currently very low, the potential for additional failures will grow if more slender pillars are developed, especially under deeper cover, with wider mining sections and in multi-level operations. It should also be noted that the passage of time acts to decrease the strength of many existing pillars. An examination of current design practices