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By K. G. Colman

Introduction This text is intended to provide the operator and turnkey contractor with the basic data for sizing vibrating screens to be used in ore crushing plants. The basic capacities, modifying factors, etc.. used in the area requirement calculations were developed empirically and modified to their present values based upon years of practical applications. It must be pointed out that screening is much more of an art than an exact science; however. the information presented here should provide for reasonably accurate screen sizing when applied to many metallic ores. Types of Screens There are two types of screens which can be used for strictly sizing applications. These are two- and four-bearing screens; both are inclined circle-throw machines. Two-Bearing Screens The motion of a two-bearing screen is generated by unbalanced weights attached to the vibrator shaft. The body of the machine is usually supported by steel coil springs (see Fig. 8). The main advantage

Jan 1, 1985

By Biswajit Samanta, Rahul Kumar, Pranjal Pathak

The Open Pit Mine Production Scheduling Problem (OPMPSP) is a complex optimization problem that seeks to determine the best sequence for extracting mineralized material from the ground in order to maximize the Net Present Value (NPV). This process must take into account various capacity constraints, such as mining rates, processing limits, stockpiling capacities, blending requirements, and precedence constraints, which dictate the order in which blocks can be extracted. Traditionally, the OPMPSP has been formulated as a mixed integer programming problem, employing binary and continuous variables to represent the extraction of each block. However, this approach has limitations, particularly when it comes to addressing the stockpiling issue. In response, some researchers have proposed mathematical models, which offer a more accurate representation of the problem but come with their own set of challenges. In this study, an alternative approach to tackle the OPMPSP with stockpiling by employing constraint programming (CP) is explored. The method was carefully tested on the Newman1 dataset from the well-known Minelib library. The results show that the CP-based model obtained a production schedule having about 2.69 % higher NPV than the NPV of the solution, which is recorded in the Minelib Library.

Jun 25, 2023

By R. G. Church

Belle Ayr Mine was established in 1972 as the first large surface coal mine in the Powder River Basin of Wyoming. During the mid-1980s, it was eventually out-distanced in productivity by newer mines, and management recognized that the mine must recapitalize its major mining equipment and enhance its workforce flexibility in order to be competitive in the deteriorating market situation. Therefore, state-of-the-art haulage and loading equipment was placed into service, and a 12-hour rotating shift and a technician-based workforce was implemented. Belle Ayr Mine is located 29 km (18 miles) southeast of Gillette, Wyoming, in Campbell County (Figure 1). The mine is a part of AMAX Coal West, Inc., and with its sister mine, Eagle Butte, located 8 km (5 miles) north of Gillette, is a major contributor to the overall coal production of AMAX Coal Industries, Inc., headquartered in Houston, Texas. This paper addresses mine planning, recapitalization initiatives, and innovative workforce changes which propelled this large, surface coal mine to the forefront of productivity in the ever tightening low sulphur coal market.

Jan 1, 1994

By M. S. Duffy

To exploit the mineral resources of fine grained ore bodies the minerals processing industry is turning to fine grinding technology, of which tower milling has become an established part. However, compared to other mills relatively little is known about the operating mechanisms in tower mills. In all milling processes one of the keys to understanding how they work is in knowing how their grinding media move. To investigate the ball motion in tower mills a glass unit was therefore constructed and measurements taken of the movement of the grinding media. This paper describes the results from this study.

Jan 1, 1998

By Thomas V. Mullen

Some 146 kt (4.69 billion oz) of gold have been mined throughout history. Of this, 70% has been mined in this century alone, with 17% produced from 1985 through 1996 (Fig. 1 and Table 1). Until the mid-19th century, placers were the chief source of gold. Advancements in mining, metallurgy and geological thinking have resulted in underground mining (first of veins plus stockworks and later of Rand-type deposits) becoming the principal source of gold. With the demise of the South African deposits and the move towards lower grade ores, the primary source of gold will be from disseminated deposits exploited through large, open-pit mines. For the past 200 years, there has been a fairly constant ratio of about 31 g (1 oz) of gold to each person alive. If this ratio is to be maintained, annual gold production will have to rise from about 2.3 kt/a (73.9 million oz/year) to more than 3.1 kt/a (99.7 million oz/year) by the year 2000. To effect this increase, an unforeseen breakthrough in exploration or metallurgy is needed. Barring this, there will be pressure for an increase in the price of gold. This article traces the historical production of gold from 4000 B.C. - the earliest record of gold mining - to today and relates this 6,000-year record to advances in geological thinking, mining engineering and extractive metallurgy. It also proposes that man's thirst for gold, reflected in the price he will pay for gold, and his ability to find, mine and refine gold have combined to effect an equilibrium based loosely on the historical ratio of 31 g (1 oz) of cumulative gold production per each man or woman alive.

Jan 1, 1998

By Silas Li, Michael Harris-Gifford, Jason Choi, William H. Hansmire

Twin-bore tunnels with a single track in each tunnel are currently the most common subway tunnel configuration. However, a large diameter single-bore tunnel with two tracks separated by a center wall could replace twin-bore tunnels and introduce potential benefits but require necessary modifications to the subway system. In particular, a nominal 40-foot-diameter single-bore tunnel can be considered in lieu of nominal 20-foot-diameter twin-bore tunnels. This paper discusses the benefits and modifications introduced by replacing twin-bore tunnels with a single-bore tunnel, with respect to various elements of the subway related to the tunnel, stations, track, and tunnel systems.

Dec 1, 2022

By Martin C. Kuhn

The use of tritium in manufacturing and its subsequent loss to the local environment in Tucson, Arizona resulted in a great debate relative to the physiological effects of low level radiation. This paper reviews some of the facts of the release and attempts to quantify the degree of hazard encountered by the local community. Some of the difficulties in assessing the true degree of absorbed dose and the assumptions necessary for calculation purposes are presented.

Jan 1, 1981

By Michael D. Loy

This paper examines the computerization steps of United Coal Company of Bristol, Virginia. OVERVIEW Producing close to 7,000,000 tons per year, United Coal Company is one of the most interesting mining companies in the east. Their approach to mining reflects a dedication to modern technologies and extraction methodologies. With varying amounts of production coming from four divisions (a fair amount of production comes from contract operators) and over a billion tons in recoverable reserves, United rests heavily on the planning and engineering efforts of a centralized engineering group. Although each division relies on its own engineering personnel for day-to-day management and operations, long range planning and reserve management is conducted at the corporate engineering level. This group, while extremely competent and efficient, is relatively small (7 people), when compared to the needs of a large mining company.

Jan 1, 1985

By Kevin DeSomber, Scott Bird

Larger grinding mills continue to utilize large gear-driven drives or electrical wraparound drives. The panel will include presenters from operations with large mechanical and electrical drives. JIM HANDLEY: Before we get to the third and final session, I want to introduce my co-conspirator for this session, John Mansanti. John is manager of milling with Newrnont Gold Company, Carlin, Nevada, and was very active in securing participation in this innovative symposium. I'm Jim Handley and I'm with Cyprus-Amax Minerals at the Sierrita copper and molybdenum mine. Our third presentation is titled "Geared Up or Wrapped Up?" I hear this topic discussed, but never at great length. I think that's because the opinions are fairly strong and diverse, and people generally aren't reinforced properly in their arguments. The first person to enlighten us on this topic is Scott Bird. He has more than 20 years with Kennecott, is a graduate in metallurgical engineering from the University of Utah, and is currently operations superintendent and deals with this phenomenon every day.

Jan 1, 1998

By Peter J. King

Demand for both lead and zinc to the year 2000 will be characterised by modest to nil growth in mature economies, with positive 3 to 4 per cent annual growth rates in developing nations. Asia and China will feature significantly in this growth. Overall lead demand is expected to grow about 1 per cent a year, with industry becoming more dependent on the fortunes of the automotive industry as the lead-acid battery will be the only major end use to expand. Zinc will become more dependent on its main use, galvanising, as the automotive and construction industries move to high levels of dependence on corrosion prevention. Strong growth in zinc consumption in S.E. Asia, China and India is likely to feature widespread development of the continuous steel strip mini-galvanising line technology. Thank you Mr. Chairman for inviting me to this Conference. As an Australian I am honoured to be here to offer some thoughts about future trends in metal consumption -- with particular reference to the role of countries in my own neighbourhood, the developing Asian nations, including China. It is customary for a member of the producer fraternity to speak to the topic of future development. This is no doubt due to the fact that our companies are so often engaged in endeavours to determine the future prospects of the metals as essential background to massive investment decisions relating to the development of new mines and smelters. This is sometimes also applied in relation to the more painful decision of closures of aging operations. In this paper I have drawn upon recent studies by AM&S into the future of lead and zinc. While this work has been thorough and skillful, we are nonetheless left with uncertainty on a number of counts. Firstly. predictions in the past in our industry have not been all that credible. Need I remind a U.S. audience for instance of the Paley ' investigation setup by President Truman in 1950 to study U.S. copper requirements for 25 years in the future. Asarco's Simon Strauss gave those of us daring to forecast long term commodity trends a salutary reminder that the Paley Commission with all the expertise at its disposal missed the mark in its copper predictions by a very wide margin indeed. Additionally, it is difficult to take comfort from longer term economic forecasts. Too many important economic issues remain unresolved suggesting considerable caution. These include the threat of growing protectionism; low economic growth rates with stubborn unemployment levels; and levels of government expenditure at near saturation as a percentage of GDP, to name a few. However, on a more optimistic note. we can look to China, where there appears to be momentum in its economic growth; oil, where stable oil prices to the mid 1990's will contribute to inflation control; and the fact that LDC debt, while still a major issue, is declining in importance and priority. In the short time allocated to us. I wish to deal succinctly with the lead and zinc raw materials supply picture, which is one I do not believe will hold too many surprises for this audience. Following the review of raw materials supply, we will turn our attention to the changes in the pattern of demand towards the year 2000. emphasising the Asian position. In this context. I would like to focus on the theme of the changes in OECD consumption levels relative to those of the emerging nations. One area we will be paying special attention to is China.

Jan 1, 1986

By G. Machiavelli, P. Bevilacqua, G. Ferrara, T. P. Meloy

During several years of operation in Europe, South Africa and other locations, the Tri-Flo process has demonstrated substantial improvements in dense-medium dynamic-separation systems. The reasons for this improvement are: • a high-sharpness separation due to the multistage system and the application of new concepts in the design of the regeneration circuit and in the control of the medium Theology, and • the possibility of performing two cuts at different densities using a single separation device and a single regeneration circuit. This paper discusses the above points in detail with particular reference to the multistage technology (based on the circuit analysis theory) and to the control of the medium rheology (based on recent work in the modeling and simulation of the rheological behavior of dense suspensions). Concerning the multidensity separation, information is given on the new three-stage separator where the high-density separation is performed by the first stage and the low-density separation is performed by the second and third stages. This configuration (already realized in two operating plants) was selected because no particular sharpness was required at the high-density separation, while high sharpness was required at the low-density separation. However, the configuration can be inverted or a fourth stage can be added (at very low additional cost) to provide two stages for each separating density. The importance of achieving a high sharpness separation is related to minerals (industrial minerals in particular) where the density difference of the phases to be separated is very low (as in processing of lithium ores, feldspar- and others). Information is provided on plants operating in South Africa and Canada, for the beneficiation of lithium minerals and on a plant under construction in Italy for the beneficiation of feldspar. Finally, the importance of making the separation at two densities is emphasized with particular reference to coal; i.e., producing a low-ash premium coal and recovering, in the middling, a by-product without losing heating value. Also, very important for some minerals is the production of a high-grade concentrate (at the first stage) suitable for sending directly to metallurgy (e.g., chromite ores) and the production of a low-grade concentrate that can be further treated. In this way, a higher overall recovery of the valuable mineral can be achieved, and, at the same time, a reduction of the treatment costs can be obtained. All of the above applications were once considered impossible.

Jan 1, 1995

By W. V. Liu, D. Omane, H. Yu, Y. Pourrahimian

"A large-scale wildfire had broken out at Fort McMurray in Alberta, Canada during May 2016. Many oil sands mining activities were affected due to the wildfire and the associated ash emissions. In particular, ash emission generated from the fire outbreak is a huge problem during the post-fire cleanup. These emissions pose a severe health hazard to workers, environment, and global climate. The ashes emitted into the atmosphere are caused by either human activities or climate conditions. The objective of this research is to assess the effect of three different ash dust suppressants, namely water, #1 surfactants, and #2 polymers at various volumetric concentrations on ashes samples to prevent propagation of fine solid emissions into the atmosphere. It is found that both #1 surfactants solution and #2 polymers solution are effective in retaining fugitive ash dust generated from the ashes. Volumetric concentration efficiency of 0.05% of #1 surfactant and 5% of #2 polymers in 500 ml of water have been proven to provide ash dust retention efficiency greater than 99% after the spraying of these suppressants. It is also found that both #1 surfactants solution and #2 polymers solution maintain an ash dust retention efficiency higher than that of the use of only water. This confirms the merit of using chemical dust suppressants on fugitive ash dust for a longer period, which is proven by the 72-hour data from this experiment. This study gives a general view of how effective chemical suppressants on fugitive ash emissions work. INTRODUCTION On May 1st, 2016, a large-scale wildfire gutted Fort McMurray, Alberta, Canada. Many oil sands mining activities were affected due to the wildfire and the associated ash emission. Due to the wildfire, some of the biggest oil sands companies in Fort McMurray such as Royal Dutch Shell and Suncor Energy shut down their oil production, at 255,000 and 350,000 barrels per day respectively [1]. Syncrude Canada Ltd scaled down its normal production capacity level of 350,000 barrels per day [1]. This generated an estimated loss of about 1.1 million barrels of oil production per day, constituting a 30% reduction in the Canadian daily oil production, crippling the economy [2]. This loss in production by the companies translated into 0.33 % of the Alberta GDP in 2016 constituting a loss of $985 million and 0.06 % of the entire Canadian economy [3]. In 2017, it is estimated that the rebuilding and reclamation of the affected areas in Fort McMurray will add $ 1.3 billion in GDP to Alberta’s economy [3]. A population of over 90,000 people was evacuated from the location and its surroundings for health and safety reasons [4]. The fire destroyed about 2,400 structures and over 500,000 hectares of forest vegetation in Fort McMurray, leaving an estimated 232,000 tonne of post-fire ashes [5,6]."

Jan 1, 2017

By Brain W. Lawrence

Sublevel stoping generally is a large-scale open stoping method. It sometimes is referred to as long-hole or blasthole stoping. This method usually is applied to strong ore bodies that require minimal support and are surrounded by strong country rock. The ore body should be fairly regular in shape and well-defined. The dip of the footwall normally should be sufficient to allow broken ore to gravitate freely, although the method has been adapted successfully to mine some of the flatter ore bodies. Sublevel stoping is not dependent on the width of the ore body. Widths of less than 6 m (20 ft), however, make the utilization of long-hole drilling techniques more difficult. The main criteria for sublevel open stoping are competent ore and stable host rock, regular ore boundaries, and a footwall dip that exceeds the angle of repose of broken ore. Basically, the method entails providing access to the ore body at various subintervals between the main haul- age levels in order to drill and blast the intervening ore. Stope drilling is carried out from drilling drifts on the sublevels, and the ore is blasted in slices towards an open face, which generally is vertical on the downholes and may be inclined towards the open face for the up holes. The blasted ore gravitates to the bottom of the stope and is collqcted through drawpoints. Fig. 1 illustrates a typical sublevel stoping mine. The method requires extensive ore body development with relatively high capital expenditures. How- ever, much of the development is in ore, and production costs are comparatively low. Productivity rates are in the 13.6 to 27.2 t (15 to 30 st)/manshift range. The drilling, blasting, and loading operations are performed independently, and equipment utilization is high. Large outputs can be obtained with few units and limited personnel. Dilution with waste rock may occur if ore boundaries are irregular or if caving occurs, but 100% of the ore within the stope usually is recovered. Pillar recovery sometimes is a problem. It is at this point that most of the waste dilution occurs. At the time data was gathered for this report (1973), the sublevel open stoping method was used by more than 21% of the metallic ore mines in the US (9 out of 42 mines producing 1088 + t/day (1200 + stpd) and provided more than 12% of the total metallic ore production from these mines. DEVELOPMENT Access to a sublevel open stope mine is gained by a slope or shaft that is normally sunk in the footwall of the ore zone, away from any possible effects from blasting or other production operations in the stoping process. Main level interval is selected and usually varies from 45.7 to 121.9 m (150 to 400 ft), depending on the vertical extent of the ore body, the number of drawpoints required to maintain output, and the eventual stope height. The main haulage drifts are located at the bottom of the stope horizon, either directly in ore or in the footwall, with access crosscuts at intervals. Raises are driven up through the ore to connect to the level above and provide access and ventilation to the sublevel drilling drifts, which are driven horizontally in the ore for the length of the stope. Depending on the drawpoint system to be used, the stope is either undercut by a raise-and-cone system, from a scram or slusher drift, or simply provided with a drilling drift from which access is made at intervals to the main haulage level. A raise driven either at the end or in the middle of the stope (if stope access is from both ends) provides a start for opening up a vertical slot across the stope to establish a free or open face for long-hole drilling and blasting. Sublevel stoping has proved to be a relatively safe and economical system.

Jan 1, 1982

By John McMorran

An open pit mine design system should have the characteristics of being flexible, versatile, and simple. All of these characteristics are necessary for producing a dynamic mine design. In other words, a design that can be improved, updated, and implemented. Flexibility is an important characteristic due to changing times. For example, the effects of a changing economy, increased knowledge of the mineral deposit, or improvements in mining technology can result in a considerable, if not a complete change in the long range mining plans. Since the short range mining plans are based on the long range mining plans, they will-also be effected. Also, it is very important to validate the information used in the design or the design itself. This means the system should have the flexibility of being able, not only to detect, but to correct errors. Versatility is another important characteristic of a mine design system due to the wide range of situations that may appear. First, a design system must be able to handle both long and short term planning. This is necessary because of the variability in the definition of a time range. Second, a design system must be able to handle different types of deposits. Special emphasis must be placed on this issue, because many deposits, if not the majority, do not fit predefined categories such as bedded, massive, or roll-front, etc . . . Furthermore, the true test of the versatility of a design system is not only the ability to create an ultimate design but also to schedule sequences for this design. Thus, the versatility of being capable to design with a variety of time ranges, variety of deposit types, and scheduling are all important characteristics of the design system.

Jan 1, 1982

NIOSH is conducting research to reduce the silica dust exposure of workers at surface coal mines. One goal of this research is to evaluate the relationship between drilling parameters, rock strata and silica dust generation. This study involved measuring blast hole emission dust from a rotary drill rig which required sampling high concentration dust (>400 mg/m3) for silica content in a high velocity airstream. To measure dust initially, traditional sampling methods using personal sampling instruments were attempted in and around the shroud area of the drill with no success. Variations in the dust cloud concentrations under the shroud, the condition of the shroud and its orientation over the hole, and ambient air conditions prevented consistent and accurate dust measurements from being obtained. Amore consistent dust cloud is necessary for accurate measurements. An area of the drill’s dust collector system that consistently draws the emitted airborne dust from the hole is the collector tube. This tube connects the drill collector’s vacuum and dust filtration system to the shroud area. Assuming the collector system is working as designed, sampling from the collector tube would enable more consistent and accurate samples to be taken. However, current personal samplers are unable to sample in the concentrations and velocities experienced in the collector tube, so another method had to be devised. To achieve the desired results, an in-stack cascade cyclone was used. Preliminary field testing shows positive results.

Jan 1, 2003

By Meili Zhu, Qingpu Shi

High temperature, methane, dust and other disasters are getting more serious with mining depth getting deeper and the development of mechanization in underground mines. An application of a descensional ventilation to a coalface is one of the effective measures to solve the above problemes. The descensional ventilation is an venttilation that an airflow in a coalface wouuld downflow along an inclination of a coalface and the direction of the airflow is the same as coalflow. Since 1960's, the descensional ventilation has been applied to 171 coalfaces in 46 coal mines of 23 coal mine administrations in China, such as Pingdingshan , Zhongliangshan, Pubai, Huangshi coal mine administrations. Among the 171 coalfaces, there were 104 coalfaces taking 60.8% in gently inclined seam. The coalfaces in inclined seam and steep seam were individually taking 18.7 % and 20.5 %. There were 77 coalfaces taking 45 % of the total in low gassy coal mines and coal and methane outburst mine were individually taking 17% and 38%. There were 141 coalfaces taking 82.5% of the total in potential danger of dust explosion. There were 125 coalfaces taking 73.1% of the total in potential danger of spontaneous combustion. Therefore, the descensional ventilation can be used in coalfaces under different conditions in China. The practice at home and abroad shown that the application of the descensional ventilation to coalfaces has obvious results in dust control, temperature control, preventing methane accumulation at top corner angle and control of spontaneous combustion in goaf. To more safely and reliably apply the descensional ventilation to coalface and to provide a way for the development of mine ventilation technology in China, the paper will have discussions on the following problems: METHANE EMISSION AND DISTRIBUTION AT COALFACE WITH DESCENSIONAL VENTILATION Methane emission in a coalface with a descensional ventilation is an argued issue for many years. Base on the coal practice, special similar model tests and researches in China, the followings are our main comments. The Descensional Ventilation can Reduce the Methane, Accumulation at the Top Corner Angle. The measurements in six coalfaces with the downward airflow in Qinhemen Mine, Fuxin Coal Mine Administrations shown that the methane concentration at the top corner angle is often up to l% when the coalface has the upward, airflow. The max. methane concentration at the top corner angle is about 0.49 to 0.7% when the coalface has the descensional ventilation. Therefore, with the descensional ventilation, it basically solved the overlimited gas concentration at the top corner angle which is a potential danger to coal production. Because the direction of upfloating gas is opposite to the direction, of the descensional airflow, the descensional ventilation; could increase a turbulent flow mixing capacity of the methan gas and air, and reduce a possibility of methane; accumulation. Due to an air leakage in goat when the coalface with the descensional ventilation lower than an air leakage in goat when the coalface with the, ascensional ventilation, a less methane quantity will release from goat at the descensional ventialtion. It should be pointed out that due to a higher air leakage at ascensional ventilation and the direction of the air; leakage same to the direction of the natural upfloating methane in goaf, those will cause a large methane; accumulation at the top of the goaf and easy bring about, methane accumulation and overlimited methane concentration at the top corner angle with an ventilation vortexflow at the top corner angle. On the other hand, because the direction of the upfloation force function is upward, the descentional ventilation could minimize as possibility of methane accumulation at top corner angle in coal with the descensional ventiltion.

Jan 1, 1991

By Clayton J. Parr, Northcutt Ely

Mining law is essentially a branch of the law of real property. It concerns acquisition of property for extracting contained minerals, and the rights, privileges and duties that fall upon the holder thereof once the rights are acquired Accordingly, this section focuses on the procedures to be followed in acquiring state. federal and private lands, and defines briefly the nature of the rights obtained. The mining laws of Canada and Mexico are summarized, and the related subjects of minerals taxation and governmental regulation are discussed briefly. This section is not intended to be the basis for legal decisions. Rather, its purpose is to provide the engineer with an understanding of basic principles and procedures. For a detailed treatise of mining law, reference can be made to The American Law o] Mining, a five-volume set edited by the Rocky Mountain Mineral Law Foundation. The law changes constantly, especially that based on federal and state statutes, and the reader is cautioned to be alert for subsequent modifications of statutes, regulations and case law. 2.1-PRELIMINARY LAND-STATUS CHECK Often, after completion of area reconnaissance, or perhaps after receipt of a submittal, a specific more localized target area will become of interest. Usually, an intensive exploration program comprising detailed surface mapping, sampling, geophysical prospecting and drilling will be required before the mineral potential of the ground can be properly evaluated. Before an investment of this magnitude is made, however, it is advisable to obtain rights to mine ore from the property. Otherwise, knowledge of the exploration activity might greatly inflate land values, or speculators or competing mining concerns might step in. Hence, as a general rule, a land-acquisition program should be undertaken before an intensive exploration project is begun. The first step in such a program is to make a land-status check to determine whether the subject lands are available and, if so, from whom they can be obtained and by what means. 2.1.1-BUREAU OF LAND MANAGEMENT RECORDS In those states which contain large areas of federal land, basically (he western states, the primary informational source is the records of the Bureau of Land Management. These may t)e examined at the land office having jurisdiction over federal lands in the area of interest. The records for Montana and North and South Dakota are kept at the Billings (Mont ) land office; Wyoming, Nebraska and Kansas, Cliejenne, Wyo.; New Mexico, Oklahoma and Texas, Santa Fe, N M ; northern Alaska, Fairbanks, and southern, Anchorage; Utah, Salt Lake City; Nevada, Reno; Arizona, Phoenix; Colorado, Denver. There are two land offices in California, at Sacramento and Los Angeles Records for other states are kept in Washington, D C. at the office of the Director, Bureau of Land Management.

Jan 1, 1973

By Justin Brown, Michael Kobler, Dave Ragland, Bob Shufflebotham

PROJECT OVERVIEW As the sun-bronzed San Diego students strolled casually to class, mining crews from Atkinson Construction were working only 9 meters below the surface. The330 meter long, 11.3 meter diameter squat ellipse NATM tunnel is part of the9.3 kilometer Mission Valley East Extension Light Rail Transit (MVE-LRT) being constructed for the San Diego Metropolitan Transit Development Board (MTDB). The SDSU segment of the MVE-LRT was awarded to the Clark Construction Group, the parent company of Atkinson Construction for $82.7 million. URS CORP was the prime designer and Hatch Mott MacDonald performed the NATM tunnel design. The construction managers were Washington Infrastructure Services with Underground Construction Managers, EPC Consultants, and ILF Consultants. A NATM tunnel design was chosen as the most cost-effective way to minimize disruption of the university activities. The tunnel passes close to several buildings and directly below access roads, tennis courts and a baseball field. The NATM method of conventional mining uses shotcrete for ground support often reinforced with steel orplastic fibers, welded wire mesh and lattice girders. The tunnel runs from a cut and cover box up a 4.2% grade in a 217 meter radius left-hand curve with several spirals and ends at the underground station 330 meters away. The depth of cover varies from 16 meters near the west portal to nine meters at the station. The design called for a two-pass system with a primary lining of 300 mm shotcrete with lattice girders at 1 m centers and two layers of welded wire mesh. The lattice girders are used primarily for profile control and are not considered a structural element. The top heading was designed to be excavated in one of three excavation sequences depending on ground conditions and depth of cover. In sequence one excavation, the top heading is excavated in two halves with a one-meter separation. In sequence two excavation, a side gallery is advanced 8 or more meters ahead of the

Jan 1, 2003

The estimation of local recoveries, such as the local recovered tonnage of ore and its corresponding grade at a given cutoff grade, is an important problem in a selective mining operation. Multigaussian kriging provides a simple solution to this specific problem. The solution is also complete in the sense that local recoveries are estimated together with their estimation variances. It is thus possible to assess confidence limit intervals on the estimated recoveries. Multigaussian kriging has been applied to the Jerritt Canyon deposit in a most realistic situation. The various steps of the estimation procedure are presented in detail and the potential of the method is demonstrated in view of the results. The obtained results show that the estimated recoveries are in good agreement with the actual recoveries and the actual estimation errors are correctly predicted by the estimation variances. Multigaussian kriging thus appears as a useful and fully operationable tool for the mining industry.

Jan 1, 1986

By P. L. Stavenger

Principles of Operation and Mechanical Features General Mechanical Description Sieve-bend screens are high-capacity screening devices which utilize stationary, concave, wedge-bar screening surfaces. A complete sieve bend is comprised of a feed distribution chamber, a structure for holding the screen surface, and collection chambers or chutes for oversize and undersize materials. In devices used for metallurgical practice, provision is usually made for reversal of the direction of flow over the surface, either by rotating the surface or by changing the feed nozzle position. The size of the unit varies in height from 5 to 8 ft, and in width from 2 to 8 ft. The orientation of the wedge-bar surface is such that the slots between the wedge bars are perpendicular to the flow of feed material over the surface. The feed distribution means is arranged such that the flow of liquid suspension is distributed evenly and tangentially over the width of the screen surface. A variety of means are used including simple gravity weir feeds, long slotted nozzles, and a multiplicity of round nozzles. A typical gravity-fed weir type nozzle is shown in Fig. 18. Most sieve bends are fed with gravity feed in such

Jan 1, 1985