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By R. Venugopal, V. K. Saxena, A. K. Mukherjee

"Coal, iron and manganese ore samples were exposed to different ultrasonic intensities of 250, 300 and 350 W/L for five minutes and to an ultrosonic intensity of 270 W/L for different time durations of 3, 5 and 7 minutes. The ultrasonically treated samples showed reductions in D80 particle diameters of 6 percent for the coal samples, 5.95 percent for the iron ore samples and 35.63 percent for the manganese ore samples during grinding. The ultrasonic treatment was also observed to assist in reducing ash content in the coal product by 8 percent and to reduce manganese losses in rejects by about 5 percent. Ultrasonic treatment was concluded to be capable of assisting in the comminution of friable ores more prominently than the hard and porous materials.IntroductionComminution is an important unit operation in the mineral-processing, cement-making, powergeneration and pharmaceutical industries. But most of the milling technologies are considered to be energy inefficient, with less energy consumed in real size reduction and most of the energy consumed in the machine. This is more critical for the mineralprocessing industry because of the growing need to exploit lower-grade ore bodies and process rejects (Blazy et al., 1994; U.S. Department of Energy, 2005). Low-grade ores require crushing and grinding to liberate the valuable minerals, which are further separated from gangues by various beneficiation methods such as gravity separation, flotation and leaching. Various studies have been carried out to minimize energy consumption during milling by developing pretreatment methods that can initiate new fractures or improve the fracture density in materials before comminution. These studies were mainly focused on chemical additives; thermal, ultrasonic and microwave treatments; and electric disintegration (Klimpel and Austin, 1982; Norgate and Weller, 1994; Bearman, Briggs and Kojovic, 1997; Gaete-Garreton, Vargas-Hermandez and Velasquez-Lambert, 2000; Kumar et al., 2010; Wang, Shi and Manlapig., 2011, Singh et al., 2012).The fragmentation effect of ultrasonic fields in solids has been investigated since the 1950s, and Gärtner was probably the first researcher who attempted it (Gaete-Garreton, Vargas- Hermandez and Velasquez-Lambert, 2000). Sound waves can propagate in solids in the form of longitudinal waves, shear waves and surface waves, and in thin materials as plate waves.In surfaces, fractures and interfaces, various types of elliptical or complex vibrations of the particles make other waves possible. During ultrasonic-vibration treatment, cavitation bubbles nucleate, grow and collapse, generating microjets, whose impacts on the particles initiate microcracks. The ultrasonic waves can enhance the nucleation, growth and coalescence of flaws, caused by tensile or shear stress. The mechanisms operating in the materials and inducing these stresses have been identified as spall and compression-induced tensile microcracks, nucleating at preexisting flaws. These mechanisms are driven by the shock wave and cavitation effects in the surrounding fluid (Chen, Huang and Shih, 2003)"

Jan 1, 2016

By L. Zhou, D. Bahrami, Y. Xue

Underground mine fires are a threat to the safety and health of mine workers. The timely determination of the location and size of an underground fire is of great importance in developing firefighting strategies and reducing the risk of any injuries. Machine learning was used in this paper to develop a predictive model for fire location and fire size in an underground mine. The ventilation data were obtained by simulating different mine fire scenarios with MFire. The ventilation data of all airways were used as features to predict the fire location. Based on the feature importance, five airways were selected to monitor, and the airflow data of the selected airways were used to predict the fire location and fire size. An accuracy score of 0.920 was obtained for the prediction of fire location. In addition, in-depth analyses were conducted to characterize the wrong predictions with the purpose of improving the performance of the random forest model. The results show that the occurrence of fire at closely connected airways at some locations can generate misleading ventilation data for each other and the model performance can be further improved by grouping them. Fire size is another factor affecting the model performance and the model accuracy increases with increasing fire size. The result from this study can help mine safety personnel make informed decisions during a mine fire emergency.

Mar 2, 2022

By A. Moergeli, Philip Sander, John J. Reilly

"Estimating and managing the costs of complex infrastructure projects – in the planning/design and construction phases, for both owners and contractors – has been a challenge for decades. The more complex and technologically advanced the project, the greater the uncertainty, including potential risks that are important to owners and contractors, such as:• Cost risks to owners – meeting budget and schedule, maintaining public credibility.• Cost risks to contractors – profit, consequences of loss, impacts to reputation/future work.This concern has been addressed in various ways by the underground construction industry for some time (Reilly, 2001). In particular, while significant advances have been made in cost estimating for the planning and design phases (Reilly et al., 2004), that are important to agencies and political decision-makers, it is not apparent that these advances have been widely adopted for construction cost estimates. The reasons for this may relate to lowbid considerations – any method that tends to increase the contractor’s cost estimate, by including risk or likely costs, could lead to an erosion of the contractor’s competitive position – if others are not similarly required to include such costs.Different cost estimating methods produce different levels of information. Specifically, there is a large difference in the character and depth of information if a deterministic (quantities times price plus a contingency) and risk-based cost methods are used. It is this difference in character and depth of information that is the reason that risk-based cost estimating has potential value for owners and contractors. Figure 1 presents hypothetical cost results from deterministic and risk-based methods and illustrates some of these differences.In Fig. 1, the results for deterministic and risk-based cost estimates are given related to the potential profit or loss for a typical project. As is evident in this example, there is significant potential for costs to be realized that are higher than the proposal/bid value estimated using a deterministic approach, with a 15 percent probability of a loss. There is a 30 percent probability that the project will have a reduced profit. There is a 55 percent probability that the project will return a good profit. Using a risk-based approach, it is possible to better recognize this potential outcome in the bid phase and, as a consequence, develop a strategy to:"

Apr 1, 2016

By H. Zhao, R. Liao, W. Qin

Theoretically, controlling redox potential to a relatively low value and inhibiting jarosite formation on the chalcopyrite surface would be an effective strategy to accelerate the bioleaching of chalcopyrite. In this work, using limonite as seed crystals, the effects of the goethite precipitation process on the bioleaching of chalcopyrite were studied for the first time. The bioleaching results showed that the addition of limonite controlled the redox potential in an appropriate range and promoted chalcopyrite dissolution through the removal of ferric (Fe3+) ions. X-ray diffraction and scanning electron microscope analyses indicate that limonite significantly induced the goethite precipitation process and inhibited the production of jarosite. We conclude that promoting the goethite precipitation process with limonite is an effective strategy in accelerating the bioleaching process of chalcopyrite.

By R. W. Waytulonis

This paper is an update of the activities of the U.S. Bureau of Mines, other government agencies, and the automotive and truck industry concerning diesel emission control. Enacted and proposed regulations from the U.S. Mine Safety and Health Administration (MSHA) and developments in diesel emission control are presented in terms of their impact on underground coal, metal, and nonmetal mines. Mine air quality regulations proposed by MSHA may require the underground mining industry to comply with new standards. Some mines may be required to take additional actions to meet new diesel particulate and lower nitrogen dioxide exposure standards; however, the mining industry is in a position to benefit from emission controls developed for the on-highway diesel engine market. The U.S. Environmental Protection Agency (EPA) has enacted regulations to reduce emissions from on-highway diesel trucks and buses. Engine manufacturers have responded by developing cleaner burning engines. Fuel producers have responded by providing cleaner burning reformulated diesel fuel, and exhaust aftertreatment devices have been developed to provide additional emissions reductions. Bureau research and development projects seek to determine the advantages of using modern engines and fuels, and to evaluate the efficacy of new exhaust control devices on mining machines. It appears that the diesel engine will continue to be a practical power source for use in confined environments because no other available power source is as mobile and efficient.

Jan 1, 1993

By Douglas B. Silver

Study Parameters (Status as of February 1993) Time Period: 1989 -1991 151 North American Public Metal Mining Companies Fiscal not calendar year basis 85+% of Canadian and U.S. Metal Production Au, Ag, Cu, Pb, Zn, Mo, Ni, W Results are Preliminary and Research Continues Chicken Little is Alive and Well

Jan 1, 1993

By Juan P. Camus, Sergio G. Jarpa

INTRODUCTION Chuquicamata mine is a large copper open pit located in the north of Chile. It has been in production for more than 80 years and now is in the later stages of its life with declining grades and increasing haul distances. As any old mine with long established organizations and procedures, it has faced one of the most difficult managerial problems: to conduct changes. Since 1994, the new management team has been devoted to a modernization pro- gram focused mainly in restructuring business operations. downsizing the labor force and introducing a mine planning pro- cess consistent with the company's goal. The explicit identification of the latter issue has been made because of the management’s conviction about the importance of it in the profitability of the business. The mine planning process at Chuquicamata mine has evolved from an old manual technique towards a modern computarized system, however the fundamental aspects and the procedures involved in this process have been the same. For in- stance, the cutoff grades policy has not changed during the last said 20 years, regardless of the changes to grade distribution, commodity prices, plant capacities, etc. To review and rethink this process, the strategy was to work with a small group of inside engineers and the management in order to interact with several mining consulting firms. The idea was to open a discussion about the fundamental principles used in the mine planning activities and, at the same time, to explore new ideas to improve the operating practices that have been followed for a long time. Thus, the goal of this paper is to present the mine planning approach that was the result of this work and the improvements that were obtained. THE CHUQUICAMATA MINE The Chuquicamata division is one of the five operations of Codelco and is currently devoted to operating the Chuquicamata mine; a copper open pit, concentrator, smelting and refining complex. It also operates Mina Sur which consists of an open pit mine, a leaching-solvent extraction and electrowinning process. There is also a dump leaching and a Sx-Ew plant for treating the low grade suifide ore (under the cutoff grade) from the Chuquicamata mine. Prior to reviewing the mine planning process, capacities for the Chuquicamata sulfide line were 640 000 tpd of run of mine material, 160 000 tpd of ore and 4 200 tpd of concentrate. This meant a total annual movement of around 230 Mt in the mine and a treatment of 57 Mt in the concentrator with a stripping ratio of approximately 3: 1. The old exploitation strategy consisted of an "open scheme", which means that all benches must have a berm with enough space to allow the traffic of large haulage trucks. This fact implied working with a great flexibility, but the consequences were flat slope angles. One of the reasons for using this operating practice in short term planning was that the grade consistency from the pit has always been a controversial variable. Schedules were designed to meet grade targets accurately and they were modified immediately when deviations become apparent. This reality led to working with a great deal of independent pushbacks and it required flexibility in the traffic system. The cutoff grade policy has been the same for a long time and the figure was 0.5 %CUT either for sulfide or oxide ore. This was the reason why a balance was produced between the mine and the concentrator. The mine is operated principally with benches of 26 m but in the upper part of the pit there are benches of 24 and 30 m. The main production equipment is shovels of 28 and 34 yd3 along with trucks of 200 and 240 st. Regarding the crushing facilities, there are two main systems located inside the pit and an old one in the periphery, close to a stockpile and near the concentrator. In the north part of the pit there is a crusher for waste material and in the north-east area is located the ore crusher facility. Both restrict a significant area of the pit and the mine sequence is considering to move the ore crusher again to the south-east sector where it used to be located. Relating to the waste crusher, the idea is to move it up to a bench near the surface in order to use the same conveyor belt and, at the same time, liberate an important sector. THE MINE PLANNING PROCESS The objective of the mine planning process is to develop a mine plan for the life of the deposit, in harmony and consistent with the company's goal. It includes the origin and destiny of tonnages and grades from the mine(s), along with the necessary resources to carry out this plan such as: fleet requirement, consumable goods, manpower, etc. From the financial point of view, it means to establish the cash flow for each time period of the mine life. That is. the revenue, capital investment and operating cost associated with each period of the plan. The fundamental principles involved in the mine planning pro- cess have been a controversial issue for a long time. One of the reasons for these divergent views could be produced by the difficulty of modeling a complete extraction policy for a geological re- source. This particular problem has to deal with several decision variables that are time dependent. So far, there is no mathematical formulation for managing such a problem, and the approach to solve it is based on a circular analysis combined with certain heuristic tools. So, a global model rather than a formula, requires a clear understanding of mine operations as well as economic theory and its application to a non-renewable resource. In order to manage this complex problem, the mine planning process can be conveniently split off in three stages which are conceptual, feasibility and operational planning. The characteristics of each stage are basically the timeliness in which they are developed and the kind and number of variables involved. Thus, conceptual planning is devoted to the definition of key variables like: the size of the operation, mining method, extraction se-

Jan 1, 1996

Extensive testing in the past ten years has shown that where a uniform natural gamma background is present in the strata bordering the seam, the thickness of the boundary coal left in place after mining can be determined by measuring the attenuation of that radiation (Nelson and Bessinger, 1989). Measurements made by the authors in underground mines in Pennsylvania, West Virginia, Ohio, Illinois, and Kentucky, and by others in Wyoming and New Mexico, have shown the presence of such a gamma background (Nelson, 1989). Natural gamma coal thickness sensors of several configurations have been tested in mines owned and operated by the Consolidation Coal Company in Pennsylvania and west Virginia (Nelson and Bessinger, 1988).

Jan 1, 1990

By T. P. Lim, J. A. Cherry, A. J. Vivyurka, R. D. Blair

The first phase of an investigation of the chemical composition of subsurface water and the hydrochemical processes in and near the abandoned Nordic tailings at Elliot Lake, Ontario, was conducted in 1979. The Nordic area, which covers 85 hectares with an average thickness of 10 m and overlies deposits of permeable glaciofluvial sand, contains 15 million tonnes of tailings with 4-7% pyrite. Nests of standpipe piezometers installed at three locations on the tailings indicate that seepage through the tailings is predominantly downward. The water table in the tailings slopes from the north side of the tailings dam, where it is within a metre of surface to the south side near the tailings dam, where it is approximately 10 m below surface. When they were deposited during the period from 1957 to 1968, the tailings contained pore water at a pH of about 8 resulting from neutralization treatment in the mill. At the three piezometer nests, the pH increases from 3 near the water table to 7 near the bottom of the tailings. The pore water in the tailings is gradually becoming acidic because of oxidation of pyrite in the zone above the water table. The concentrations of Fe, Mn, Ni, Co, Zn and Pb are high in the shallow acidic zone and much lower in the deeper neutral zone. Concentrations of 226Ra range from 30 to 230 pCi/L. At the three sites concentrations of major ions in the permeable sand a short interval beneath the tailings indicate 226Ra presence of tailings seepage, but Ra concentrations are only 2 to 8 pCi/L. Greater downward penetration of 226Ra probably occurs in the area closer to the tailings dam. Monitoring of a network of multilevel bundle piezometers installed in permeable sand that extends southward from beneath the tailings indicates the occurrence of a plume of tailingsderived water containing high concentrations of Ca, Mg, Fe and S04 that extend 400 m downgradient from the tailings dam. The total dissolved solids decline from 20,000 at the dam to less than 500 mg/L at the identifiable downgradient periphery of the plume. A much smaller but distinct plume of water with high heavy metal concentrations and 226Ra in the range of 10 to 130 pCi/L extends from beneath the dam for a distance of 15 m. The pH of the groundwater in this heavy metal-radium plume is 4 to 5, whereas elsewhere in zone of groundwater with high dissolved solids, the pH is above 6. The results of this investigat, suggest that the heavy metals an 226 Ra are relatively immobile in the perme-

Jan 1, 1980

By Robert Jedrzejczak

The Endako Mine is an open-pit molybdenum mine located in the north central region of British Columbia, Canada, about 960 km (600 road miles) north of Vancouver. Production for the latter part of 1992 was expected to averaged 63.5 kt/d (70,000 stpd). Of that amount, 27 kt/d (30,000 stpd) was the mill feed. This production is achieved with five 11.5 to 14.5 m3 (15 to 19 cu yd) electric shovels, six Euclid R190 and two Unit Rig M120 diesel-electric haul trucks, and three 320 mm (12.25 in.) electric rotary drills. There are three ore zones delineated into pit areas: the Endako, Denak East and Denak West. Present mill feed source is the southeast stage of the Endako Pit. Stripping is carried out in the south wall stage also of the Endako Pit. The mine high grade aggregate is reduced in the primary and secondary crushing circuits before processing in conventional RM-BM-flotation circuits. The majority of the molybdenum sulfide (MoS2) is roasted on site to produce technical grade molybdenum oxide (M003). A portion is further refined and treated to yield a 99.9% pure MoS2 product.

Jan 1, 1993

By Z. Hajnal

Three years ago a research program was initiated at the University of Saskatchewan to develop seismic surveying techniques for use in the Precambrian geological environment. The success of the reflection method in many younger geological settings suggested that this is the technique which would be the most suitable for experimentation. A successful adaptation of this technique to the Shield environment would make mapping of rock formations possible to much greater depth than is possible at the present time with any other applied geophysical technique. This presentation attempts to illustrate the advances which have been made in this program and will provide some insight into future plans. The field investigations were limited to the Flin Flon basin near to the town of Flin Flon, Manitoba (Fig. 1). This area was chosen because the surface geology has been mapped in great detail and it is a very important base metal producing region. It is an ancient sedimentary basin with some characteristics similar to areas where the reflection method has been successful.

Jan 1, 1976

By John S. Cummings

Although there are many geologic situations which might be discussed at a session such as this, as I considered the problem, it became apparent to me that I should discuss a situation which has been of concern to me, and should be of concern to the geologic community. As a result, the questions which I will pose, and the criticisms, have not been arrived at quickly or easily, but have accumulated through time, to the point where I feel discussion is necessary. Very briefly let me say that my criticism of geologic mapping, of conclusions reached, and objectives or lack of such, results from my association with many areas where such studies have been completed, and resultingly my inability to comprehend the system of evidence or logic which supports extensive age-formational designations. The heart of the problem is that many conclusions resulting in geologic designations are based on weak or non-existent evidence, and such should be catagorized as hypotheses. Although the geologic community as a group does not approve or disapprove of such designations, it is evident that many or most of such designations attain a "status", and arc accepted as more or less valid statements. As will be shown, the amount of specific lithologic data provided in some quadrangle mapping projects is exceedingly slim. However, of concern herein is that the type of information presented at any stage is sufficient to warrant conclusions drawn. To see the magnitude of the problem, it is probably necessary to review some basic fundamentals upon which our geologic systems are established. The United States Geological Survey has defined a "formation" as the broad unit of geologic mapping consisting of a large and persistent stratum of one kind of rock. Obviously such a designation allows that a formation could be considered "time variant" in a horizontal as well as in a vertical context. However, other definitions enable a formation to mean units

Jan 1, 1972

By J. Yao

Synthetic indium-bearing zinc ferrite (IBZF) was mechanically activated by a tumbling mill. Subsequently, the behavior and kinetics of leaching zinc and indium from the initial IBZF and activated IBZF in sulfuric acid solution were investigated. The results demonstrate that the tumbling ball milling enhances the leaching reactivity of IBZF and increases the zinc and indium extractions. The reaction temperature and H2SO4 concentration have an important effect on leaching zinc and indium from the initial IBZF and activated IBZF. The kinetic model -ln(1-x) = kt was used to describe the kinetics of leaching zinc and indium from the initial IBZF and activated IBZF and to calculate the kinetic parameters. The tumbling ball milling causes a decrease in activation energy and reaction order, which indicates that the dissolution of IBZF after mechanical activation by a tumbling mill becomes less sensitive to temperature and H2SO4 concentration. For the zinc leaching, the activation energy decreases from 73.9 to 70.3 kJ/mol and the reaction order decreases from 0.72 to 0.70. For indium leaching, the activation energy decreases from 78.1 to 73.5 kJ/mol and the reaction order decreases from 0.82 to 0.69. It is found that the dissolution rates of the initial IBZF and activated IBZF are controlled by surface chemical reactions.

By A. Cecala, J. Noll, J. Hummer

The National Institute for Occupational Safety and Health has observed that many control rooms and operator compartments in the U.S. mining industry do not have filtration systems capable of maintaining low dust concentrations in these areas. In this study at a mineral processing plant, to reduce respirable dust concentrations in a control room that had no cleaning system for intake air, a filtration and pressurization system originally designed for enclosed cabs was modified and installed. This system was composed of two filtering units: one to filter outside air and one to filter and recirculate the air inside the control room. Eighty-seven percent of submicrometer particles were reduced by the system under static conditions. This means that greater than 87 percent of respirable dust particles should be reduced as the particle-size distribution of respirable dust particles is greater than that of submicrometer particles, and filtration systems usually are more efficient in capturing the larger particles. A positive pressure near 0.02 inches of water gauge was produced, which is an important component of an effective system and minimizes the entry of particles, such as dust, into the room. The intake airflow was around 118 cfm, greater than the airflow suggested by the American Society of Heating, Refrigerating, and Air-Conditioning Engineers (ASHRAE) for acceptable indoor air quality. After one year, the loading of the filter caused the airflow to decrease to 80 cfm, which still produces acceptable indoor air quality. Due to the loading of the filters, the reduction efficiency for submicrometer particles under static conditions increased to 94 percent from 87 percent.

Jan 1, 2015

By William Gleason

"There are signs that the commodity downturn that has battered the mining industry for the past five years is beginning to ease up. As the dust begins to settle and mining companies begin to take stock of the battle, Newmont Mining Corp. will be one that is standing strong with just a few scrapes and bruises thanks in large part to the leadership of president and chief executive officer Gary Goldberg and his right hand man and chief operating officer, Chris Robison.As he closes in on retirement (for a second time) Robison, a third-generation miner from Nevada, took time to speak with Mining Engineering about a 33-year career in which, among other things, he is credited with not just helping Newmont survive the turbulent times but with steering the company to a safer, more productive and more profitable heading.“I think we did it better than anyone else,” Robison said when asked how the company fared during the past five years. “We didn’t talk about it a lot, we just put together a strategy and we delivered.”What Newmont, the world’s second-largest gold mining company by production, delivered since Robison took the position of chief operating officer in 2013 are improvements in costs, porduction, projects and safety.Operating under the mantra of “live within your means,” Robison was pulled out of retirement from Rio Tinto and into a challenging situation at Newmont. The price of gold was in a nose dive from a high of nearly $58/g ($1,800/oz) and heading to levels closer to $38.60/g ($1,200 oz).“Newmont is a big ship that can’t be turned, but has to be steered,” said Robison. “We recognized that we had to set a new course. The direction the ship was going was great for $1,600 to $1,800/oz gold but we were chasing ounces.”Like the rest of the gold mining sector before the falling gold prices, Newmont was focused on volume and was looking for gold wherever it could be found. The slogan at Newmont in 2011 was “7 million ounces a year by 2017.”When Robison came on board it was a different reality.“We had to begin focusing on value over volume as the cornerstone of Newmont going forward,” he said."

Aug 1, 2016

By Joseph W. Murray

GENERAL DESCRIPTION The undercut-and-fill method of mining was devel¬oped by Inco Ltd. in the Sudbury district of Ontario, Canada, to deal with abnormal ground conditions en¬countered in pillar recovery. Although it is now some¬times utilized as a primary stoping method, the main application continues to be in pillar recovery. In any mining method in which fill is employed, pillar systems tend to fail gradually as stoping pro¬gresses. As a result, most pillars are completely destressed and broken by the time pillar recovery com¬mences. Control of the back in such ground becomes a major problem and is contingent on local conditions as they exist in the workplace. In most mining methods, operations such as drilling, blasting, slushing, and tim¬bering can be readily assessed and the mining cycle pre¬dicted. However, in the mining of pillars with overhand methods, the time and effort required to maintain a safe back varies to a quite unpredictable extent. For years the square-set method was the most effective means available for pillar recovery. However, in areas where bad ground was encountered, square setting was a costly and sometimes hazardous method. As the tonnage mined from pillars increased, it was apparent that a safer and less expensive approach was required. Past experience indicated that the best way to deal with broken ground was to mine from the top down. Top slicing systems were examined but were rejected due to the major sub¬sidence which resulted. However, ideas generated from studying top slicing finally developed into the present method of undercut-and-fill. This method, which has almost completely replaced square-set mining, exhibits reduced costs, has improved safety and efficiency, elimi¬nates the factor of bad ground overhead, and allows a closer prediction of the actual mining cycle. The result is more accurate scheduling of pillar production. This factor is of increasing importance as the tonnage from pillar recovery increases in relation to total mine pro¬duction. Undercut-and-fill is a method of extracting a block of ore by mining successive cuts, working from the top down. After a cut of ore is completely mined out, lami¬nated timber stringers are constructed along the sides for the full length of the cut. Round logs covered by a wire screen are laid across the stringers to form a mat. The cut is then tightly filled with hydraulically placed cemented sand fill. Mining is then resumed on the cut immediately below the mat. As the cut advances, the timber stringers are supported by round timber posts seated on the solid bottom of the cut. Drilling, blasting, muck removal, and timbering operations are repeated until all the ore in the cut has been removed. At this time, another log mat is laid and the cut is filled. This sequence is continued until the block has been mined from level to level. The basic principles of undercut-and-fill can be adapted to a variety of mining situations. It can be applied transversely or longitudinally in ore bodies of varying width, that dip from vertical to flat lying. The method can be applied using conventional equipment or it can be mechanized through the introduction of small diesel or air-powered units for muck removal. Undercut¬and-fill is a selective method, ore recovery is high, and dilution can be controlled to an acceptable level. How¬ever, it is a high-cost, labor-intensive method and as such its use is restricted to areas where the less costly meth¬ods of ground support are not successful or where bulk mining methods are not adaptable. One basic require¬ment for undercut-and-fill is an adequate source of hydraulically placed cemented sand fill and a dependable sand plant and distribution system. The success of the undercut method is to a large degree dependent on the competence of the fill placed in each of the successive cuts. In theory, the weight of the fill on each cut is supported in part by the cemented sand itself as it binds to the rough sides of the mined¬out areas next to the pillar walls, and in part by the tim¬ber support. As mining progresses beneath the mat, a downward pressure is exerted within the cemented fill and a voussoir arch develops above the mat, across the full width of the cut. This supports the major portion of the load. The log mat and posts have a double func¬tion in that they carry the remaining weight not sup¬ported by the voussoir arch and in addition prevent any pronounced settling of the fill mass. Excessive settling breaks the bond between the cemented fill and the pillar walls, eliminating the arch effect and transferring the entire load to the mat and posts. The theory of a voussoir arch forming within the cemented sand fill mass is substantiated in practice by the fact that pillars have been mined from level to level with no more significant weight on the bottom cuts than was experienced on the top cuts. In effect, as mining progresses downward, there is no additional transfer of weight from previous cuts to the cut being mined. APPLICATION OF UNDERCUT-AND-FILL Because of their size, the Sudbury ore bodies are, for the most part, mined transversely and, to a considerable extent, by filling methods. Transverse stoping blocks are designed with 9-m (30-ft) crown pillars established be¬low each level and with stopes separated by vertical rib pillars. In past years, floor pillars were left above the level as well, but present practice favors the silling of primary stopes at the base of the rail. Rib pillars are designed to meet the ground control requirements of the primary stoping methods. Local conditions and past experience generally dictate their size. Historically, since the square-set method was to be used for recovery, rib pillars were designed to accommo¬date standard 1.7-m (5'h-ft) sets. A typical rib pillar is four sets wide [6.7 m (22 ft)] when located between two square-set or cut-and-fill stopes having a width of 8.4 m (27.5 ft). When the undercut-and-fill method was de¬veloped, a mat width of two sets was adopted. This di¬vided each cut of the common four-set pillar into two

Jan 1, 1982

By T. W. Beck

Drilling into coal mine roof strata to install roof bolts has the potential to release substantial quantities of respirable dust. Due to the proximity of drill holes to the breathing zone of roof bolting personnel, dust escaping the holes and avoiding capture by the dust collection system pose a potential respiratory health risk. Controls are available to complement the typical dry vacuum collection system and minimize harmful exposures during the initial phase of drilling. This paper examines the use of a bit sleeve in combination with a dusthog- type bit to improve dust extraction during the critical initial phase of drilling. A twistedbody drill bit is also evaluated to determine the quantity of dust liberated in comparison with the dust-hog-type bit. Based on the results of our laboratory tests, the bit sleeve may reduce dust emissions by one-half during the initial phase of drilling before the drill bit is fully enclosed by the drill hole. Because collaring is responsible for the largest dust liberations, overall dust emission can also be substantially reduced. The use of a twistedbody bit has minimal improvement on dust capture compared with the commonly used dust-hog-type bit.

Jan 1, 2014

By Y. Topkaya, R. E. Johnson, B. R. Palmer, R. B. Bhappu, A. E. Clark, R. P. Bush, L. E. Schultze

The U.S. Bureau of Mines conducted copper exchange capacity (CuEC) tests for six common clays under simulated in situ leaching conditions. Regression equations were obtained from the data expressing the CuEC as a function of Cu concentration, pH, and temperature. Further testing resulted in regression equations expressing CuEC's of Na and Ca montmorillonites and attapulgite as a function of Cu concentration, pH, and the concentration of metal ions which compete with Cu for exchange sites. Using these equations, an analysis was made of the impact each clay could have on overall copper recovery. The results suggest that Ca and Na montmorillonite clays could have a major impact on Cu recovery and that attapulgite and illite clays could have a smaller, but still significant, impact. Kaolinite and ripidolite clays pose little threat to loss of copper from in situ leaching solutions. Copper losses are decreased by the presence of competing ions, and A1 and Mg have the largest impact of those ions normally present in Cu leaching solutions.

Jan 1, 1993

By S. Daniel Thompson

In underground coal mining, the specification and control of belt and bunker capacities are complicated by (1) stochastic and intermittent conveyor loading, (2) a limited ability to reduce surge at the mine face, and (3) occasional overlapping of loading from two or more mine faces on the conveyors. Recently, because of longwall mining and other factors, the capacity requirements of most mine conveying systems have risen substantially; as a result, efficient capacity design and control have become important mine planning issues. This paper reviews these design issues and their associated modeling procedures. Design considerations and modeling difficulties are also examined.

Jan 1, 1996

By Madan M. Singh

It is estimated that through 1975, there were 1.69x109 m2 (418 000 acres) of urban land threatened by potential subsidence due to mining with a value of over $12 billion (19;3 dollars; USBM, 1979). With increased coal production to meet the energy needs of the nation, both these figures may be expected to increase. Hence greater attention to controlling surface damage due to subsidence is merited. In fact, the Surface `lining Control and Reclamation Act of 1977 (SMCRA) (Public Law 95-87) mandates that underground coal mining operators "adopt measures consistent with known technology in order to prevent subsidence causing material damage to the extent technologically and economically feasible, maximize mine stability, and maintain the value and reasonably foreseeable use of such surface lands, ..." The term "subsidence," as used in this paper, implies the total phenomenon of surface effects associated with the mining of minerals, and not only vertical displacement of the surface as is sometimes inferred in the literature.

Jan 1, 1984