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By K. Biswas, S. S. Peng

The stability of pillars in old mined-out districts is greatly dependent on the weathering action caused by moisture penetration into the pillar structure. Field observations in old mining districts indicated that this weathering action becomes critical in terms of the stability of the pillar if the coal seam contains parting or binder (layers of claystone or mudstone). The weathering action caused by moisture penetration over a long period of time degrades both parting and coal. However, it has been observed that the structural deterioration is more severe in parting. Moisture-penetration rates in parting and coal are different. The extent of the weathered zone in various layers of the pillar is primarily time dependent. This paper investigates, both in the laboratory and in the field, the effects of weathering action on coal and parting. In the laboratory, slake durability indices and uniaxial compressive strength tests for dry and saturated specimens are compared for coal. In the field, the in situ strength profiles for coal and parting layers are obtained, and the effect of time (in terms of the pillar age) on the strength profiles is studied An attempt was also made to establish formulae for time-dependent strengths of coal and parting.

Jan 1, 2000

By Archie M. Richardson, Carl E. Brechtel, Tom R. Kelly, Frank Feero

Recent work to upgrade the ventilation system for the el Mochito lead/zinc mine in central Honduras is discussed. Network modeling and underground measurements were used to evaluate cost-effective alternatives for achieving satisfactory ventilation in a complex and expanding underground operation. Both interim and long-term solutions were implemented to make mining possible under difficult conditions. INTRODUCTION Mining operations at the el Mochito Mine, located in the central highlands of Honduras, Central America, have been virtually continuous since the opening of the mine in 1948. Initially a high-grade silver mine, the mine has expanded along a westward trend of pipe-like orebodies to a distance of roughly one mile from two centrally located shafts. Production of the relatively large San Juan orebody at the western most extension of the mine (Paddock, 1981) led to the introduction of diesel-powered equipment; however, the ventilation infrastructure was insufficient to meet the needs of mechanized mining. A succession of owners/operators in the 1980s allowed the existing ventilation infrastructure to decay to the point that ventilation in the production areas of the mine was very poor. Environmental conditions in some working areas were not conducive to efficient ore extraction because of high dry bulb temperature, high humidity, and diesel emissions. Upon acquiring the mine in 1990, Breakwater Resources of Tucson, Arizona began an aggressive program to refurbish the mine infrastructure to complete extraction of the San Juan orebody and to allow the extension of the mine another 2500 ft to the west for extraction of the Nacional orebody. The program included increasing the capacity of the main ventilation system. This article presents a case history of the process of upgrading the ventilation system in a mine where extensive old workings cause large air leakage. This process has been one of selecting solutions to difficult technical problems that are compatible with the existing mine infrastructure and economic constraints. The initial ventilation system is described in the background section, along with ventilation projections for the mine expansion. Field characterization of the ventilation system for design verification and fan specification is then discussed. The paper describes a series of interim changes to the system to improve ventilation pending completion of new ventilation boreholes. In addition, the temperature/ heat problems in the mine are described. BACKGROUND Initial Condition of Ventilation System The ventilation system is illustrated in Figure 1, which shows the extent of mining with the main ventilation paths superimposed. Early mining around the two shafts opened up vertical connections (stopes and raises) over the entire 2420 ft (737.6 m) of vertical extent, and mining progressed to the west primarily using compressed air and electric-powered equipment. Since ventilation was not a complex problem in the original mining system, the stopes and interconnecting raises were not sealed. The San Juan orebody was much larger than the silver ore zones mined previously, being primarily zinc and other base metals. Its geometry, size, and grade allowed the use of vertical crater retreat (VCR) stoping with diesel mucking and haulage equipment. Its depth, along with the existence of warm groundwater, resulted in a mine climate problem on the lower levels. To establish a complete ventilation circuit, two vertical boreholes (Bonanza Nos. 1 and 2) had been drilled by previous owners from the surface in the vicinity of the San Juan orebody. The system design called for air to be drawn down the intake shafts, across the lower mine levels to the San Juan workings, then up through the San Juan ramps and ore passes to these two exhaust boreholes (see Figure 1). In practice, however, only the Bonanza No. 1 borehole was drawing air through the desired path. Leakage across the old upper levels from the intake shafts, the Caliche tunnel, and from intervening abandoned stopes and raises supplied most of the air flowing to the base of the Bonanza No. 2 borehole. In effect, there were two ventilation circuits in semi-parallel through the mine, of which only one was delivering appreciable air to the San Juan workings.

Jan 1, 1993

By James J. Scott

I am indeed honored to be the 1991 recipient of the Daniel C. Jackling Award. To be voted this honor by my peers in the Society for Mining, Metallurgy, and Exploration and AIME means more to me than I can truly express. Daniel Jackling's position and prominence in the mining industry first came to my attention in the fall of 1949 when I transferred from Wisconsin Institute of Technology, then a three-year school, to the Missouri School of Mines to complete my last year for a bachelor's degree in mining engineering. I played basketball in the Jackling gym and ran track on the Jackling field. I didn't know a lot about Jackling then, except he was an honored graduate of the school and, obviously, supported the school financially. Over the years, Jackling's name kept coming up. He was a man with a reputation for being a doer, a mining leader who was always a step ahead, a mining engineer who knew how to motivate men in the working place, to organize mining systems, to finance and organize corporations. to open up new, low-grade ore bodies for exploitation. If Jackling were alive today, I would expect he would bean excellent candidate to apply practical rock mechanics to his projects. Looking over the list of Jackling Award recipients, I have known many, have met many personally and had a few who were dear friends that affected my own professional life. Ab Shoemaker, '58, and I consulted at the White Pine Copper Co. on mining problems in the 1960s. We arranged for our visits to the mine to coincide so that we could collaborate on our ideas. I would rent an auto and drive for Ab. He said he was the only mining engineer in the country that had a PhD for a chauffeur. James Boyd, '67, was my mentor as regards the White Pine Rock Mechanics Program that we organized in 1963. Only through Boyd's forsight. leadership, dedication and willingness to spend money on research and development did the Practical Rock Mechnics Program at White Pine succeed. He never wavered in his support to that program or to me personally. Tom Howard, '75, was my predecessor in 1970 as Director of Mining Research for the US Bureau of Mines. When I joined the Bureau in August 1970, he had the research centers up and running. Any successes I may have had with the Bureau of Mines were due in great part to Tom's leadership and organization throughout the 1960s. Gene Cameron, '68, was my teacher at the University of Wisconsin and I remember him fondly. He was the one professor who lectured in a manner that made me welcome going to his classes each day, a truly remarkable educator. If you have come today to listen to me talk about instrumentation, rock properties, stress-strain relationships, rock mechanics theory, etc., you will be disappointed. Large volumes of data have been collected by well qualified theoreticians to define stress-strain conditions in mines. Unfortunately, very little of this data has been used by industry due to the lack of initiative and understanding by the researchers to the true problems of implementation in the industry. I hope my remarks will assist future investigators to work through the maze of operational problems so they will experience the satisfaction of seeing their research used. I fully realize that the Jackling Award is given by the Society for Mining, Metallurgy, and Exploration and is primarily offered for accomplishments in hardrock mining. I have found it impossible to separate hardrock and coal mining when I talk about "Applied Rock Mechanics." There is too much overlap and the same mechanics principles are applied to both. For example, coal mine designs have been applied to salt, trona and potash. Also, the original layout and design of White Pine Copper Mine was based on coal mine designs. Any developments to apply rock mechanics ideas must

Jan 1, 1992

By Lowell T. Harmison

I appreciate very much the invitation to speak with you and the opportunity of bringing you messages from both the Secretary of the Department of Health and Human Services and the Assistant Secretary for Health/Acting Surgeon General of the U.S. Public Health Service. I would like to take this opportunity to congratulate you (the organizers of this Conference) on identifying the critical issues in the field and assembling such a broad array of experts to address them. I would like to present a brief view of the emerging framework for health that puts into perspective some of the aspirations of the Administration and to highlight several points with regard to prevention and occupational health. The goals are: 1. To improve the overall health status of our people. (This has been and will remain the National policy regarding health.); 2. To engage the Nation in the important effort of enhancing public health. (This is not reserved exclusively for the activity of the Federal Government or for State Governments. Public health has to be a cooperative effort that brings together all of the people engaged in the process of serving the people.); and 3. To pledge that health care will not be priced out of anyone's reach because of inflation. (It is clear that there are major tasks of bringing about economic recovery in our country. One aspect of this effort is to guard against the cost of health care not being allowed to rise beyond the reach of persons who need that care.) "How will these goals be achieved and what must change in the delivery of health and medical care in our society?" There are a number of real issues as well as perceptions that adversely affect the attainment of these goals: First, The cost of medical care is soaring and the public, industry unions and other elements of our society are becoming concerned. (They recognize the problem and are demanding a solution.); Second, There is a growing concern about the priorities that have been set. (For example, the evidence that preventive interventions are the most effective approach is overwhelming, yet medicine has not yet given that a high priority.); and Third, There is the perception that physicians do too much to too many people at too great a cost and that too much and too costly technologies are used. In view of the perceptions, we all must accept some changes and the challenges that needed changes will bring. A month before the new budget went to Congress, President Reagan went on nationwide television and told the American people that, "It is time to recognize that we have come to a turning point and we are threatened with an economic calamity of tremendous proportion and the [old business as usual treatment can't save us. Together we must chart a new course]." Now eight months down the road from this and a long Spring and Summer of discussion both within the Executive Branch and in the Congress, many plans and programs and concepts have emerged. The new course has been charted and the turning point has been made. Business as usual has been put aside and the Administration's leadership has been stretched and tested in putting forth a better approach with the reality that money is tight and that old habits of delivering care are difficult to change. The Congress has now given us a look at a new health budget that takes into account some of the harsh economic realities and that does make allowances for the persistence of familiar behavior. Against this background, it is now possible to begin addressing ways to provide health services to people at a price the Nation can afford to pay. There are without question difficult decisions involved but the Administration is committed to supporting and improving health care in America. It has been the President's contention that one of the principal causes of the inflationary spiral in the country was the steady and indefensible growth of the Federal budget. The problem stems from the fact that we have been living well, but beyond our means for nearly 30 years. Now we are discovering that there is a bottom to the barrel after all. It is possible for our society to run out of things like energy (oil), water or money. The health bills must be paid -- by Government, by insurance, by parents or by someone. Each year with a bigger shopping list and more money to spend the Federal Government went into the marketplace to buy. This action altered the

Jan 1, 1981

By E. R. Reeves

The mining industry has recognized the importance of engineering controls as a primary means of preventing hearing loss. The noise control treatments most commonly observed on drills and bolters during this study were windshields, sound absorbing material, and hydraulic motor covers. These controls were evaluated on machines at underground metal mines to determine the amount of noise reduction achieved by each control. The results indicate that absorbing material has very little effect on the noise level. The noise reduction attributable to the motor covers was dependent on the material used to create the cover. Properly installed windshields were the most consistent control.

Jan 1, 2004

The world's largest hydraulic excavator was recently introduced at Syncrude's North Mine at Fort McMurray, Alberta, in Canada. O&K's 826t (910-st) behemoth RH400, with a 42-m3 (55-cu yd) bucket, is capable of loading 72.5 t (80 st) in one pass. Syncrude's Alberta operation is the nation's largest single source of crude oil. It is also the world's largest producer of oil from oil sands. Syncrude produces 205,000 bbl/day, expects to increase production to 225,000 bbl/day by 1999 and to 320,000 bbl/day by 2005. That translates to 73.5 million bbl of Syncrude Sweet Blend (SSB) produced in 1996, 82 million bbl in 1999 and 114 million bbl in 2005. The North Mine is a new development that will replace the current East Mine, to be depleted of oil sand by the end of 1999. The North Mine will feature hydrotransport, a new and unique method of transporting oil sand from the pit to the process plant. Oil sand from the truck-and-shovel operation will be processed through a double-roll crusher and placed in a cyclofeeder where it mixes with hot water. The material is then screened and transported by pipeline to the extraction plant. Hydrotransport will replace conventional conveyor transport for moving raw product from the pit. Mine development will also use two 290-t (320-st) haul trucks to compliment the fleet of existing 218-t (240-st) trucks.

Jan 1, 1998

By D. A. Day, H. L. Marsh, P. J. Stephens, C. A. Wiggins

Lightweight cellular grout backfill behind pipe-in-tunnel has been gaining increased acceptance in the tunneling industry and has proved to be both practical and economical. Two successfully constructed projects, the Upper Scioto West Interceptor Sewer (USWIS), in Columbus, Ohio and the Benbrook Pipeline Tunnel Project in Fort Worth, Texas will be discussed. The projects represent two different but successful applications of lightweight cellular grout backfill. The USWIS placed the grout behind precast reinforced concrete pipe, in water bearing limestone, and in close proximity to residential water wells. The Benbrook Project placed grout behind 6,096 meters (20,000 feet) of steel pipe from just two locations, eliminating major surface disruption typically associated with the placement of pumped concrete.

Jan 1, 1999

The most common method used for cleaning the fine fraction in today's coal preparation plants is froth flotation. Past research and practice has found that froth flotation achieves excellent separation efficiencies for fine coals having only a small fraction of middling particles. However, its efficiency decreases sharply as the concentration of middling particles increases due to the flotation of high-ash particles having a small amount of hydrophobic coal present at the coal surface. Since gravity-based processes are much more efficient at treating middlings, the application of centrifugal washing for fine coal cleaning has been studied with an emphasis on the primary cleaning of fine circuit feed. Results will be shown from a parametric study using a Falcon centrifugal concentrator which reveals that the separation performance is a function of particle size, bowl geometry, feed solids content, and feed rate.

Jan 1, 1994

By Andrzej Wala

Constantly increasing demand for energy materials and metal ores brought about tremendous progress in mining techniques which are characterised by a high degree of mechanization and concentration of works. One of the recent trends in underground mining mechanization is connected with an application of heavy machines with diesel engines [l],[2]. The introduction of diesel engines in mining all over world caused not only improvement in economic conditions but also the necessity to prevent contamination of air in the mine by toxic agents in diesel exhaust emissions. A generally used way of eliminating exhaust gases is proper ventilation of the cross cut by means of providing permanent exchange of air that would guarantee in every point of the cross cut and in every moment the decay in concentration of exhaust gases beyond threshold limit [3][4][5][6][7][8][9][10]. The present paper is an attempt to define a mathematical model describing the changes of concentration in cross cut face to which fresh air is distributed by ventilators and tubes in a forcing way. Obtained model should offer its practical adaptability to engineering calculation of the amount of fresh air needed for diluting and eliminating exhaust gases beyond threshold limit. Justness of these models has been confirmed by investigation of the growth of nitrogen dioxide concentration in air environment in some cross cut faces of Kiirunavaara iron ore mine in Kiruna (Sweden).

Jan 1, 1980

By D. W. Park

Longwall mining is considered to be the most efficient underground coal-mining technique in terms of coal extraction ratio, production rate and safety standards. Due to the increasing demand for higher coal production, the recent trends have been to use wider panels and to maintain a faster face movement. For these reasons, longwall mining can result in unexpected roof falls, excessive face convergence, shield damage and numerous maintenance problems, which can cause sudden interruption of coal production as well as serious safety hazards. Recent work at the University of Alabama has been dedicated to the development of a longwall strata-control and maintenance system that can integrate real-time shield monitoring, data presentation, analysis, forecasting and warning modules. This integrated system has been called LoSCoMS. The main objective of the system is to provide minute-by-minute stability and maintenance information such as the following: high-load, low-setting pressure, leg leakage, etc.; the analysis of various mining and geological parameters to determine past and present roof characteristics; and the forecasting of loading patterns for the following mining cycles, the next periodic weighting, etc. By using this unique system, mine operations personnel are well aware of past, present and future roof-loading patterns at the longwall face and, thus, proper safety measures can be taken ahead of time.

Jan 1, 1999

By Brian W. Hester

Ore was first discovered at the Kidd Creek mine site during the first few days of December 1963 when a diamond drill hole there cut sulfide mineralization. This event marked the end of the search started 11 years earlier with the conception of a geological idea. Economic forces provided the stimulus needed for the application of this idea but other-events, and legal considerations, also played arole in delaying the ultimate discovery. The location of Kidd Creek is shown in Fig. 1. Management of the then Texas Gulf Sulphur Co. had become concerned in 1951 at the company's declining reserves of native sulfur in Texas. This problem was to be alleviated by new discoveries and development of methods to recover sulfur from sour gas. At the time, however, the solution appeared to lie in the recovery of sulfur from pyritic ores. Canada was chosen as the best country in which to find these ores. Walter Holyk was hired in 1951 to conduct the search. By 1952, he was working in the area near Sherbrooke, Quebec, known as the "Eastern Townships" where mineralization consisting of base metal sulfides in volcanic rocks has long been known. His observations here led him to the then revolutionary conclusion that such mineralization could have formed as part of the volcanic process and not, as was generally supposed at the time, by replacement. On learning of the discovery of similar mineralization near Bathurst, NB, he moved there in the spring of 1953. He was able to utilize his new concept and found the Half-Mile Lake sulfide deposit.

Jan 1, 1991

By Gerald V. Jergensen, Edward J. Samuel

Slurry system are the principal method for storage and transportation of solids within and between concentration operations In a mineral processing plant. A slurry 1s a mixture of solid particles In water, or a chemical solution, that behaves like a liquid. The design of slurry transportation systems is generally analagous to pumping and piping water, but with a few notable exceptions: • The interaction of particle on particle affects slurry transport. • Particles often interact with the fluid, particularly when chemicals have been added to the system. • Particles have a frustrating tendency to settle from the slurry suspension, especially into locations not considered In the design. • Solids have an affinity for wetted surf aces and tend to wear them away. Slurry transportation systems Include a number of separate components, each requiring special design considerations. A systematic evaluation of each component of a slurry transfer system will help overlooking the small details that could cause operational headaches. Most slurry transport systems include: • A receiving sump or tank that provides for mixing and/or momentary storage of slurry. • A driving force.. by a pump, atmospheric pressure or gravity. • A suitable conduit for transportation.. pipes or launders. • A delivery objective.. another sump or process vessel, or distribution system to several process points. • A control strategy and design to regulate the transfer operation. The design of the slurry transportation system normally evolves through the following steps: • Finalizing the process flowsheet and establishing the weights and volumes to be handled. • Identifying and characterizing the various process fluids and slurries. • Defining critical and minimum transport velocities of fluids. • Selecting a pipe diameter (or dimensions and gradient) and

Jan 1, 1986

By D. W. Fuerstenau, P. C. Kapur

A new method is proposed for measuring the grindability of solids and the energy efficiency of grinding mills. The method is based on a similarity law of fracture mechanics for elastic materials in conjunction with the self- preserving character of the size distributions formed when feed particles are comminuted individually in compression. The single-particle grindability index reflects more closely the inherent resistance of a solid to size reduction than the grindability indices currently in vogue. The performance of grinding mills is evaluated in comparison with the single-particle breakage mode, which has the highest energy utilization or efficiency of all mechanical grinding routes. For a given set of stipulations, the performance index of the commonly used ball mill when grinding dolomite is found m he only 21%. compared to 44% for the high-pressure roll mill, a newly-invented energy-efficient mill. The difference is also reflected in the energy consumed per unit mass offines produced when closed-loop grinding circuits are simulated, which shows that the high-pressure roll mill circuit is invariably more energy-efficient than the ball mill circuit, provided the energy input per pass through the mill does not exceed a prescribed limit. Theoretical upper bounds on the yield of the ground product in a desired size range and lower bounds on the energy investment are calculated from the single-particle breakage mode which has, apart from the highest energy utilization efficiency, a minimum dispersion in size of the comminuted particles. Data on theoretical hounds for seven minerals/ores are presented. It is argued that it is unlikely that a grinding mill can be designed and a comminution circuit constructed whose performance exceeds these bench-mark values.

Jan 1, 1995

Stope width was controlled around 3.5 feet for the narrow high grade vein system at Hollister Gold Mine. Without top access, backfill material was pumped from bottom access up into stope through a series of pipes after ore had been slushed out in each mining cycle. Backfill material was changed from one layer of low strength concrete plus one layer of high strength concrete cap to one layer of low strength cellular concrete plus one layer of high strength concrete cap. Backfill cost was cut down to 30 percent during this process. To reduce the steel concrete pipe set up and tear down time which was about 2 to 3 shifts in each mining cycle, steel pipes were left in man-way between mining cycles. Cellular concrete was firstly introduced into backfilling stopes at Hollister mine in Nevada Mining. This process including concrete pump selection, pumping pipe selection, material mixing, material mechanics and quality control were fully covered in this paper. CUT AND FILL MINING CYCLE The most flexible mining method, cut and fill (Figure 1), was used to mine the high grade, narrow steep vein system on this Northern Nevada property which is located eighty miles north east of Winnemucca. Without top access, stopes were accessed through two man-ways on each end, in which people travel ladders and material transport slides were set up (Figure 2). Each mining cycle was called a cut, from 6 to 8 feet high. Overhand sequence was used. Mining cycle started with drill and blast the middle portion of the stope, then expanded towards both ends. Broken ore was slushed into mill hole located at middle of the stope and then mucked out through bottom access into main haulage. Stope length was about 300 feet, which was restricted by slushing distance. Timber man-ways and mill hole would be raised and established for backfill and ready for the next mining cycle.

Jan 1, 2011

By Kevin Sierra, Orfelinda Avalo, Julio Guizado, Edwilde Yoplac, David Martinez

Mining tailings are slurry byproducts of mineral recovery. They generate serious environmental risks due to their toxicity when exposed to water and oxygen. Studies focus on eco-friendly alternatives for mitigating these environmental impacts. Processing these tailings enables a sustainable mineral production model through circular economy practices. This study evaluates using gold mining tailings to recover gold and produce bricks. Flotation tests obtained a concentrate with 86.66% gold recovery, containing sulfides (pyrite, arsenopyrite) and a tailing with silicates and oxides suitable for brick manufacturing and ornamental pieces. This approach promotes eco-friendly solutions and a greener approach to mining operations.

Feb 1, 2024

By Donald A. Dahlstrom

INTRODUCTION Solid-liquid separation is an important and many times a critical step (or steps) in a mineral or coal processing plant. Some examples of typical critical separations are as follows: 1. Operating a seven to eight stage CCD thickening circuit to re¬cover almost all of the caustic and alumina trihydrate values in an alumina plant. This must be accomplished with highly scaling slurries, starting temperatures of over 100°C and operate on a closed circuit system. 2. Making a filter step operate to produce a proper moisture for the balling step so that the pellet furnace can produce a proper product. Bentonite addition must be minimized and a good quality filtrate must be maintained to prevent abrasion of the internal parts of the filter. 3. Operating a closed water system in a coal washing plant so that reclaimed water containing less than one percent suspended solids is produced for reuse to maintain beneficiation ef¬ficiency. Refuse solids must also be thickened so that they can be effectively dewatered to meet state disposal requirements. 4. Recovering phosphoric acid values from a slurry containing gypsum and other gangue solids at an elevated temperature. This must be done while minimizing wash water and maximizing P2O5 re¬covery while simultaneously minimizing scale problems. While solid-liquid separations are important to overall performance in the processing plant flowsheet, it is also a significant factor in plant costs. Capital and operating costs for all the solid-liquid separation steps (includ¬ing water reclamation for reuse) in such plants are probably between 10 and 20%. Energy consumption can also be important in these separations. For example, in the copper concentrator, it is the third largest category in energy consumption, after comminution and flotation. Obviously, solid-liquid separation steps in a plant demand proper atten¬tion in design in order to achieve both optimum performance and cost. Simultaneously, knowledge of funda¬mentals are important to improve results in existing plants.

Jan 1, 1986

By Howard J. Brown

The Lucerne Valley limestone mining district is in the San Bernardino Mountains, one of the major ranges in the Transverse Range Province of southern California. Several large limestone mining operations are present along the north range front in Lucerne Valley, and the area is one of the premier limestone mining districts in the country. Resources are contained in Paleozoic carbonate rocks that are part of a thick late Precambrian and Paleozoic sequence that uncomformably overlies crystalline basement. The district has been affected by multiple episodes of metamorphism and deformation, as well as by a complex sequence of late Cenozoic structural events. Detailed studies, however, have demonstrated that these rocks can be divided into formations correlatable with late Precambrian to Permian strata of the Cordilleran miogeocline. The district is the leading producer of white, high-purity calcium-carbonate products in western North America. Pluess-Staufer (California) Inc. mines and processes high-purity white limestone from extensive deposits, and is one of the largest producers of high-quality limestone fillers and extenders in the western United States. Major factors influencing the genesis of economic carbonate deposits in the district include depositional environment, post-depositional processes such as diagenesis, dolomitization and/or silicification, regional and/or contact metamorphism and associated intrusive activity, faulting, folding, uplift and erosion, and preservation from erosion. Regional geologic studies, detailed geologic mapping, intimate knowledge of stratigraphy, and recognition of complex structural relationships have proven to be invaluable tools in the discovery of high quality calcium carbonate deposits in the district.

Jan 1, 1987

By Amoussou Coffi Adoko, Shevaune Zeng, Sebastian D’Hyon, Gareth Kennedy, Eleonora Widzyk-Capehart

Inertization of coal dust with stone dust is a common control implemented within underground coal mines to mitigate the hazard of a coal dust explosion. To achieve adequate inertization, the total incombustible content (TIC) of the coal/stone dust mixture is required to meet certain percentages depending on the risk and relevant legislation. Current methods for determining the TIC of a mixture involves laboratory analysis, colorimetric comparison, or the use of portable instruments. This paper provides preliminary analysis of determination of a sample’s TIC in real-time with chemometric modelling, using portable instruments employing near-infrared (NIR).

Feb 1, 2024

By Ivor Hawkes

INTRODUCTION High energy breaking is an alternative to using ex¬plosives in underground secondary breaking operations. It also is a means of upgrading conventional hand-held breakers, manual sledge-hammer breaking, and scaling bar operations. Major areas of application are in sec¬ondary breaking over grizzlies and at drawpoints. Other applications include breaking down ripping lips in longwall seam mining, scaling in stopes and rooms, general demolition work, and roadway maintenance. There is considerable interest in high-energy impact breakers for use in primary ore breaking, but, as of 1977, all such applications have been only experimental (duToit, 1973; Joughin, 1976; Wayment and Grantmyre, 1976). EQUIPMENT Essentially, a high-energy impact hammer is a boom¬mounted pneumatically or hydraulically actuated breaker. The machine basically consists of a piston that oscillates in a housing and impacts the end of a tool or moil thrust against the rock. The force applied to the rock primarily depends upon the impact energy of the piston-the higher the impact or blow energy, the greater the force and, thus, the greater the rock break¬age. Among drill and breaker designers, a common expression for blow energy is "force of blow." Hand-held breakers are limited to blow energies of about 140 J (100 ft-lb), because the operator is unable to handle heavier machines efficiently or to absorb the recoil energy resulting from higher blow energies. How¬ever, these restrictions do not apply to boom mounted breakers; machines with blow energies on the order of 4000 J (3000 ft-lb) and higher are available commer¬cially for underground use. There is considerable evi¬dence to show that increasing the blow energy also in¬creases the efficiency of the breaking operation; i.e., more rock is broken per unit of energy expended (Grantmyre and Hawkes, 1975). Thus, there is a trend to higher blow-energy machines, particularly where high¬strength rocks are to be broken. In relation to rock breaking, the blow rate of boom¬mounted impact breakers is not as important as it is for rock drills. This is because the breaker must be moved over the work surface between blows. The blow rate is governed eventually by the power supply, and typical blow rates range between 200 and 600 blows per minute. As a general rule, light blow-energy machines have higher blow rates than heavier machines. Table 1 lists most of the boom-mounted impact breakers that were available commercially during 1977, and it gives details of the blow energies and machine weights. Restrictions are placed on the blow energy by the machine weight and size, and by the strength of the boom. Typically, boom-mounted impact hammers have a blow-energy to mass ratio of about 1.5, with lower values for lighter machines and higher values for heavier machines. In addition to supporting the hammer weight, the boom also has to absorb the recoil energy of the blow, which can be on the order of 1400 J (1000 ft-lb) for large hammers operating in a horizontal mode. Interesting exceptions to the general run of impactors are the Joy HEFTI hydraulic hammers. In these machines, the piston impacts onto a fluid cushion that is positioned between the piston and the impact tool. This approach allows very high piston velocities, over 30 m/s (100 fps), to be used without the risk of break¬ing the piston or impact tool. Steel on steel impacts must be limited to impact velocities of about 10 m/s (35 fps) due to the high impact stresses generated; thus, increased blow energies can be achieved only by increas¬ing the piston size. The Joy 514 HEFTI®, listed in Table 1, has a blow energy of 27 100 J (20,000 ft-lb), but, as of 1977, the machine has been used underground only on an experimental basis. Using a fluid cushion between the piston and the impact tool allows the use of light pistons, reducing the overall machine weight. The recoil energy, which must be absorbed by the boom for a given blow energy, is directly proportional to the piston to machine mass ratio, and operating with light pistons provides an addi¬tional benefit in reducing the requisite boom size. Both pneumatic and hydraulic hammers are avail¬able commercially. Although hydraulic hammers are a relatively recent development, they already outnumber the pneumatic machines in use. There are many reasons

Jan 1, 1982

By Sunil Jain, Jan M. Mutmansky

As coal mining evolves in this country, underground coal is being mined at greater depth and under more difficult conditions than in the past. At the same time, economic conditions make it necessary to mine more efficiently and economically. As a result, pressures on mining companies arise on two fronts and make the job of mining coal underground very difficult. Recent improvements that have been made in health, safety and productivity have come about primarily due to improvements in existing technology and better management of all the production resources. However, this trend can continue only so far and thus innovation will be needed to continue the improvement. This paper deals with a concept that, on the surface, appears to be more efficient in terms of the costs to provide ventilation. The resulting design is oriented toward increasing the ventilation efficiency through use of a unidirectional ventilation plan but it also promises to increase recovery and decrease the requirements for development entries. To analyze this ventilation concept, two mine layouts with a similar production schedule were planned in a hypothetical 1.83 m (6 ft) coal seam. The first alternative analyzed uses a traditional approach to ventilation with centrally located shafts and a bidirectional ventilation pattern. Using this system, it is necessary to use large-diameter shafts and a large number of main entries. Using the same assumptions on ventilation requirements, the second alternative utilizes unidirectional ventilation whenever possible, a smaller number of main entries and small-diameter blind-bored shafts in the bleeder areas. The comparative analysis is performed using PSU/TDMVS, a computer network analysis program that is capable of determining the ventilation power requirements at any time in the mine life and converting the costs to a present value. The economic analysis is then completed by including the shaft-sinking and entry-driving costs and the costs associated with the recovery of coal that are directly related to the change in the ventilation system. The results are summarized on a present-value basis.

Jan 1, 1987