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By W. M. Ma, Daniel W. H. Su, K. Centofanti, Yi Luo, W. L. Zhong, Syd S. Peng

1.1 INTRODUCTION When underground mining involves total extraction, it induces overburden strata movements. If not properly planned it causes surface subsidence and affects surface environmental conditions. Total extraction usually refers to longwall mining and room and pillar mining with pillar extraction. Surface subsidence has long been a subject of intensive research for scientists all over the world and considerable achievements have been obtained. However due to its difficulties and complicated nature, research into overburden movement has been thus far incomplete as compared to that into surface subsidence. Since surface subsidence is a manifestation of the results of overburden movement, the processes and mechanisms of overburden movement must be fully understood in order to establish the mathematical prediction models of surface subsidence. In this chapter the processes of overburden movement and its zones of movement in the overburden will be discussed. 1.2 PROCESSES OF OVERBURDEN MOVEMENT When total extraction is used, it produces a large void in the coal seam and disturbs the equilibrium conditions of the surrounding rock strata. The roof strata bend downward while the floor heaves. When the excavated area (or gob) expands to a sufficient size, the roof strata will cave. As a result, the overlying strata continue to bend and break until the piles of the fallen rock fragments are sufficiently high to support the overhanging strata. At this tie the overhanging strata no longer cave, but bend and rest on the underlying strata. Strata bending and subsidence develop upward until reaching the surface and forming a subsidence basin. The whole overburden strata and the surface subsidence basin will further go through a period of compaction and gradually become stabilized. Current knowledge regarding the process of overburden movement has been derived from several sources. One is the direct observation of the mined sections and their surfaces, another from field monitoring of strata movements in the overburden, and others from computer modeling and scale modeling in the laboratory. For example, Figs. 1.1 and 1.2 show the results of a borehole monitoring experiment (Borehole B-2) using the full profile borehole inclinometer and full profile borehole extensometer for lateral displacements and vertical subsidence, respectively (Conroy and Gyarmaty, 1983). The panel, 400 ft wide by 5000 ft long and 630 ft deep, was extracted from the Pittsburgh No. 8 seam which had an average thickness of 54 in. The face advanced from east to west. Curve A in Fig. 1.1 shows the inclination of the borehole when it was 45 ft ahead of the face at Position A (i.e., on the solid coal side). The total deviation of the borehole was 1/7000. The first shear movement occurred at 130 ft above the coal seam and appeared to have occurred along the bedding plane with large contrast of rock strata on both sides, i.e., sandstone vs. shale. When the face had passed the borehole 79 ft at Position B, the borehole deformed to assume a bow shape with a maximum deviation of 2.8 in. from the center line. Numerous shearing planes occurred and extended further upward. When the face had passed the borehole by 75 ft at position C, strata subsidence was measured. Fig. 1.2 shows that a strata separation as large as 4 ft occurred at 40 to 100 ft above the coal seam. Above this level, the strata subsided more uniformly with bedding separations within 1 to 2 in. Another example is the longwall mining with complete caving in the Soviet Union's Karaganda Coalfield (Kolebaeva, 1968). The coal seam was 6 ft thick and 154 ft deep. The immediate roof was the fine-grained sandstone interbedded with coarse-grained sandstone. Above this, there was sandy shale and shale. In order to monitor the process of overburden movement, 15 stations were established in a borehole (Fig. 1.3). The elevations of those stations were measured when the face was at various distances from the borehole. Fig. 1.3 shows the movement history of each station. For convenience of comparison, the movement history of each station was plotted on a common reference point as shown in Fig. 1.4. Clearly, the movements of strata from Station # 1 to #6 were nearly simultaneous, i.e., they behaved as a single unit. The strata from Station #7 to # 15 had differential separations, the maximum of which was 40 in. As the face passed by and moved away, strata separations in general reduced gradually. But strata separation between Stations #12 and #13 remained the same until the end of the monitoring period. The total bed separation between Station #7 and # 15 reached 11 in., approximately 18% of seam thickness, when the face was 132 ft beyond. Based on the above observations, the author developed a conceptual model of overburden movement due to underground longwall mining (Fig. 1.5). The above-mentioned two case studies illustrated that subsidence in the overburden strata propagates upward and subsidence velocity decreases from the bottom to the top. When the subsidence velocity at the surface reaches the maximum value, the subsidence velocity at the bottom portion of the overburden strata has decreased considerably and the strata have begun to compact. Bed separation occurs within a certain distance above the coal seam and reduces from the bottom to the top. When the face has moved away, bed separation reduces gradually, so that eventually some beds completely close and others partially close. Bed separation reaches the highest level when the subsidence velocity at the surface is at its maximum value. For instance in Fig. 1.4 surface subsidence velocity was maximum when the face was 38 to 44 ft past the point. At this time the total bed separation was maximum. Overall the strata directly above the opening are subjected to tension in the vertical direction. But above a certain level, all strata move nearly simultaneously. There is also significant shear movement along some bedding planes. 1.3 ZONES OF MOVEMENT INTHEOVERBURDEN After the extraction of a longwall panel or room and pillar section of sufficient width the strata in the overburden are subjected to various degrees of movement from the bottom to the top. According to the movement characteristics, the damaged overburden can be divided into four zones (Fig. 1.6). Caved Zone. After the extraction of coal, the immediate roof caves irregularly and fills up the void. The strata in this zone not only lose their continuity completely, they also lose their stratified

Jan 1, 1992

By Brendan Demich, Brendan Macdonald, Timothy J. Orr, Jason Navoyski, Jennica L. Bellanca, William J. Helfrich

Recent advances in computing, rendering and display technologies have generated increased accessibility to virtual reality. Virtual reality allows for the creation of dynamic, high-fidelity environments to simulate dangerous situations and test conditions and to visualize concepts. Consequently, numerous products have been developed, but many of these are limited in scope. Therefore, U.S. National Institute for Occupational Safety and Health (NIOSH) researchers developed a virtual-reality framework, called VR Mine, to rapidly create an underground mine for human data collection, simulation, visualization and training. This paper describes the features of VR Mine, including mine generation, simulated networks, proximity detection systems, and the integration and visualization of real-time ventilation models.

By Lee W. Saperstein

P.L. 95-87 contains explicit demands for land-use planning in its reclamation and designation sections. Both sections require recognition of local land-use plans; however, the sections are not well integrated. Accommodations to these planning requirements may be found in suggestions based on British mineral planning practice. Better links can be created among local land-use planners, the state's permitting authority and designation office, and mine designers. Mining companies should take more interest in local land-use plans and in resource inventories; states should consider devolving to local government responsibility for accepting mine permit applications and designation of unsuitability petitions.

Jan 1, 1982

By T. P. Meloy

Improvement of grade and recovery requires the use of optimum processing circuits. Critical to an optimum circuit is the set point for separation. With the introduction of the concept of circuit analysis (Meloy, 1982), it became possible to determine optimum circuits for a given task. No analysis, however, has yet been made as to the grade requirements of the larger circuits. Williams and Meloy (1982), reviewed the literature and concluded that, within the operating range, most unit operations involved in particle separation behave linearly. For the purposes of this analysis, linearity will be assumed. Grade, G, is defined as the weight of the coal mineral, C, that appears in the product, divided by the weight of the coal mineral plus the weight of the gangue mineral or waste mineral, Q, which appear in the product.

Jan 1, 1982

By Z. Zhongwei

The leaching kinetic of mechanically activated sphalerite with acid FeCl3 solution was investigated. The result has shown that mechanical pre-treatment has greatly enhanced the leaching process. Comparing with the original concentrate, the activated one can be leached more completely at relatively lower temperature with diluter FeCl3 concentration within a shorter leaching time. The activation energy for the activated concentrate is 27 KJ/mol, while for the original one is 52 KJ/mol.

Jan 1, 1995

By Lee W. Saperstein

In surface mining for coal, common practice for the disposal of preparation plant refuse is to bury it. As with surface refuse piles, these buried wastes can ignite and can also lead to ground and surface water pollution. Steps to ameliorate these problems have been devised over the years. C and K Coal Company, of Clarion, Pa., the largest Pennsylvania surface mining company, has incorporated all of these steps and added of few, of their own in their latest disposal practice. In addition to layering and compacting, C and K practices selective placement and dilution to minimize longterm problems.

Jan 1, 1977

The recovery of coarse particles has been widely recognized as being limited by the froth in mineral flotation. In response to this, FLSmidth has developed the Selective Froth Recovery (SFR) System. The SFR System is an extraction system that vacuums material from select locations within the froth and separates the recovered solids into coarse and fine fractions with a hydrocyclone. The SFR is supported and located by an actuator connected to the cell?s level control so that the suction heads are maintained at an offset distance from the slurry level. This can increase the recovery of coarse material by selectively recovering the material close to the bottom of the froth where drop-back of coarse particles typically takes place. The SFR System has been tested at two separate mine sites, and has been proven to increase the copper recovery in both trials. TEST RESULTS The SFR prototype was installed in a copper recovery circuit, on a rougher scavenger 160-m3 flotation cell. Figure 1, shows the SFR System, which consists of four conical skimmer heads that are plumbed together and share a common actuator. The SFR System, raised out of the froth prior to a test, can be seen in Figure 2. The SFR prototype was able to maintain a variety of set points using the level control to determine the slurry height.

Feb 27, 2013

By R. F. Hüttl

The restoration of surface mining landscapes requires the (re)creation of ecosystems. In Lusatia (eastern Germany), large-scale open-cast lignite mining operations generated spoil dumps widely consisting of acidified, phytotoxic substrates. Amelioration and rehabilitation measures have been developed and applied to these substrates since the 1950s. However, it is still not clear whether these approaches are sustainable. This paper reports on collaborative research work into the ecological potential of forest ecosystem development on typical minesites in the Lusatian lignite district. At first sight, pine stands on minesites along a chronosequence comprising about 35 years did not show differences when compared with stands on non-mined sites of the general region. Furthermore, with some modification, conceptual models for flora and fauna succession in forest stands on non-mined sites seem to be applicable, at least for the early stages of forest ecosystem development. For example, soil organism abundance and activity at minesites had already reached levels typical of non-mined sites after about 20-30 years. In contrast, mine soils are very different from non-mined soils of the test region. Chemically, mine soil development is dominated by processes originating from pyrite oxidation. Geogenic, i.e. lignitic, soil organic carbon was shown to substitute for some functions of pedogenic soil organic matter. Rooting was hampered but not completely impeded in strongly acidified soil compartments. Roots and mycorrhizae are apparently able to make use of the characteristic heterogeneity of young mine soils. Considering these recent results and the knowledge accumulated during more than 30 years of research on minesite rehabilitation internationally, it can be stated that minesite restoration might be used as an ideal case study for forest ecosystem development starting at "point zero" on "terra nova".

Jan 1, 2002

By Michael E. Lively

DOUG HALBE: We've talked about copper operations and gold operations. For our third section on the topic "Operating Ideas That Have Saved Me Some Bucks," we'll turn to the coal fields. Our featured speaker is, I'm almost embarrassed to say, a mining engineer, Mike Lively. Mike has 25 years' experience in the coal industry. He is currently superintendent of surface operations for Southern Ohio Coal Company, Meigs Division (AEP Company). I've read his paper, and there's some really great information here. Mike.

Jan 1, 1998

By Allan Breitenbach

Leaching has been used since the 1600s on unlined ore dumps and since the late 1970s on lined leach pads for the recovery of metals from mined ore, the latter typically called ?heap? leaching and the former ?dump? leaching. Modern day run-of-mine (ROM) or crushed ore heaps are stacked in controlled lifts on lined leach pads and irrigated with a solvent solution (dilute alkaline cyanide for precious meals, dilute sulfuric acid for base metals and uranium). Conventional lined leach pads store process solutions and any storm water, snow melt and cumulative wet season surplus water by gravity flow to external ponds. Impounding valley leach pads (also known as valley fill heaps) differ from conventional leach pads by storing various combinations of process liquid solution and surplus water within internal ponds by using the interstitial pore volume of the ore. While impounding liquids within the heap is simple in concept, impounding leach pads are more complicated for construction and containment compared to conventional leach pads with external ponds.

Jan 1, 2012

By Russell H. W. Chadwick

Reviewing events in the minerals industry, in economic geology, and in my own exploration work, I find that the most compelling subject for comment is the increasing ferment in ore deposits theory. New discoveries and continued investigations of bedded deposits of lead and zinc, copper, iron, uranium, etc., coupled with the availability of much new and significant data from sedimentary and metamorphic petrology, geochemistry, and oceanography, has led many economic geologists like myself to become disenchanted with former simplistic notions. Now disenchantment among serious people should presuppose both valid objections to the old, and valid new substitutes. I can sum up my own position and, I believe, what most of the recent writers on ore deposits theory are trying to tell us, by saying that a physico-chemical (bench science) approach to a natural science is neither correct nor useful, and that the obvious cure is a return to the study of the geology of ore deposits. More specifically, ore should be viewed merely as an unusual concentration produced, in stages, by the natural processes inherent in the geochemical cycle. In criticizing the conceptual basis of a science, one is involved simultaneously in the inherent character of the science, its subject matter, and the old and new concepts. I have found it impossible to make a clean separation along those lines. As a result, and as the title suggests, these are not-quite-random reflections on genesis, a matter near and dear to all true treasure hunters since Agricola.

Jan 1, 1967

By Ronald R. Hartman

I can recall a time 10 or 12 years ago when I spent a pleasant Sunday afternoon driving to Jim Thorpe, Pennsylvania to see a carnotite deposit that had recently been discovered. The announcement of the discovery stated that it was in the Pottsville conglomerate in a road cut along the highway. To my surprise, the highway was lined with cars and every weekend prospector for 100 miles had come to see the ?big uranium deposit of the east?. I literally had to stand in line to make a measurement with the scintillation counter I had with me. The thought at first occurred to me that this is evidence of how thoroughly the surface of the United States must have been prospected, more likely, perhaps it points out quite the opposite. A lot of time and energy was being spent in tracing the footsteps of others and a lot of time was spent looking for the obvious occurrences. The point is, that in the early days a tremendous amount of uranium exploration was carried out but few systematic surveys were made. Thorium anomalies were usually discounted after cursory surface field checks. Conversely, in airborne surveys - anomalies due to elevation changes or thin over- burden on hilltops were often investigated more thoroughly than smaller indications on hillsides and valleys. An adequate supply of uranium was nevertheless found due to the ingenuity and persistence of the geological profession and the public in general. This ?adequate? supply, like so many estimates for raw materials turned out to be far too low.

Jan 1, 1967

By Lok W. Home

INTRODUCTION Today, raise drilling (boring) has become the stan¬dard method of raising throughout the Western world. It is estimated that the majority of raise footage com¬pleted in 1977 was accomplished by the raise drilling method. Extensive replacement of the drill and shoot system by mechanized raise drilling has occurred be¬cause users have recognized one or more of the follow¬ing advantages. In a direct cost per meter comparison, mechanized raise drilling is economically more attractive than drilling and shooting. Mechanized raise drilling offers improved personnel safety over the drilling and shooting method. Mechanized raise drilling is a faster and more predictable method for excavation than is drilling and shooting. The raise cost per unit of length becomes less as the raise length increases, offering greater flexibility in the overall design of mines. Mechanized raise drilling provides a substantial reduction in labor requirements. 6) Mechanized raise drilling improves the working environment. 7) Mechanized raise drilling improves the rock in¬tegrity of round, unblasted raises. Increasing acceptance of the raise drilling technique is enhanced by continuing equipment development. Today, a wide range of machines and capabilities is available, machine drive systems have been improved, reliability has been increased, and cutter technology is being improved quite rapidly. Table 1 lists the four major manufacturers of raise drilling machines, cutters, and reamers, together with the approximate number of machines that each company had in operation at the end of 1977. Although Reed and Smith are major suppliers of reamers and cutters, they do not manufacture the drilling machines. Four or five other relatively minor suppliers have built machines, reamers, and cutters for raise drilling, but they did not have a substantial num¬ber of machines in the field at the end of 1977. MACHINES FOR MECHANIZED RAISE DRILLING There are three principal arrangements for making machine-bored raises. They include the use of standard raise drills, reversible raise drills, and blind-hole or box¬hole raise drills. Standard Raise Drills The standard raise drilling machine is set up on one mine level or on the surface, and a pilot hole is drilled from that level or surface to a level below. When the pilot hole has been drilled, the raise then is reamed back from the lower level to the upper level or the surface. This arrangement is illustrated in Fig. 1. Reversible Raise Drills The reversible raise drilling machine is set up on a lower level of the mine, and a pilot hole is drilled up¬ward to a higher level. The raise then is reamed back from the upper level to the lower level. This arrange¬ment is illustrated in Fig. 2. The machines used for this type of raise drilling normally are capable of being used as standard raise drills. Blind-Hole or Boxhole Raise Drills The blind-hole or boxhole raise drilling machine is set up on a lower level of the mine, and a full diameter raise is bored to a higher level without the use of a pilot hole. This type of machine is illustrated in Fig. 3. Drill Recommendations If access to upper and lower mine levels is equal, the standard raise drill should be used. The complexity of the equipment and associated handling procedures for boxhole drilling far outweigh any mechanical advantage or reduction in the number of operations, provided that access to an upper level is available. If there is good access to a lower level but only limited access to an upper level, the use of a reversible raise drill should be considered. If there is no access to an upper level, a blind-hole or boxhole raise drill is the only practical mechanized system. MACHINE SELECTION There are six major considerations in selecting a machine for raise drilling. These include operating range, cutter loading, machine structure and main¬tenance, drill string configuration, drive system, and automated controls. Operating Range As shown in Table 2 and Figs. 4 through 6, raise drilling machines are available for a wide range of hole sizes. Standard raise drill ratings range from raises of 0.9 m (3 ft) diam and 120 m (400 ft) length up to raises of 3.5 m (12 ft) diam and 900 m (3000 ft) length. Boxhole raise drilling machines are available for raises ranging from 0.9 m (3 ft) to 2 m (6 ft) diam with lengths up to 90 m (300 ft). Table 2 lists, among other criteria, the torque and thrust of typical machines; torque and thrust are the main criteria for analyzing the capacity of a machine. The raise sizes shown in Table 2 assume a condition of medium hard to hard rock formations and optimum cutter loading. The recommended raise size for a given machine can be exceeded when raising softer rock formations or when the operator is willing to accept a lower level of performance; the performance is related directly to the 1093

Jan 1, 1982

By Lawrence Lien

The reduced need for traditionally trained and educated personnel in the mining industry is systemic to the changing mining industry. Universities and other training institutions are meeting the traditional skill needs required by the industry, but are the skill needs going to be the same in the near future? The answer may be no. Mining is changing because of increased liabilities and costs of environmental and safety is-sues; lower grades of minerals in traditional mining activities and the advent of new bio-chemical processes and robotic equipment. More productive and economic alternatives, and larger, more sophisticated and automatic equipment, are also changing the industry. Engineering is more specific, accurate, precise and expensive. Measurement is more thorough and timely of progress, production, costs and productivity. And, the industry will likely be engaging in more undersea mining, possibly space-based processing, less human interaction and more remote control of events than was previously thought possible.

Jan 1, 2011

By Robert A. Irvine

Traditionally, cost effective gains in the capacity of material handling systems were a result of increases in equipment size. In general, the use of maximum capacity components in a system optimizes the production "costs per ton." The trend-"Bigger is Better" will continue in material handling equipment. Since it is rare for plant operators to lament an over abundance of screening capacity, one can safely predict that vibrating screens will follow this trend. Large Vibrating Screens - The Challenge Large vibrating screens represent a unique challenge for Manufacturers, Plant Designers, and Plant Operators. The inherent mode of operation for vibrating screens is self-destructive. More often than Manufacturers admit, Designers plan for, or Operators staff for, a vibrating screen succeeds and self-destructs. This is a problem. It can magnify with larger vibrating screens.

Jan 1, 1983

By R. Todd Swinderman

Variations in designs between belt cleaner systems are so wide that it is impractical to establish a dimensional stan- dard. The number of variables that affect the efficiency of belt cleaners is too great to assume a required number or style of cleaners for broad classifications of bulk solids or typical applications. The amount of carryback remaining on the belt is more dependent upon the characteristics of the bulk solid and the physical parameters of the conveyor system than it is on tonnage of material conveyed. Therefore, a performance-based standard is proposed. Three levels of cleaning performance are proposed: • Level I cleaning is general specified when concerns about carryback are not critical. Cleaning systems normally associated with achieving a Level I performance are single or double cleaner systems with one-piece blades undergoing poor to average maintenance. Frequent cleaning of the carryback that falls from the return run will likely be required. • Level II cleaning is generally specified when carry- back is of concern but does not create a safety or environmental problem. Cleaning systems normally associated with Level I1 performance are multiple cleaner systems with segmented blades undergoing the manufacturer's specified maintenance. Regular but infrequent cleaning of the carryback that falls from the return run will likely be required. • Level III cleaning is generally specified when con- cerns about carryback are critical. Concerns range from safety to environmental to product contamination. Cleaning systems normally associated with achieving a Level 111 performance are multiple cleaner systems in conjunction with at least one low- volume water spray. Scheduled inspection and the manufacturer's specified maintenance would have to be performed to maintain a high level of cleaning performance. Difficult-to-clean bulk materials may require the use of a washbox system with multiple cleaners using a combination of low-volume eater sprays to lubricate the cleaners and high-volume sprays to keep the washbox and discharge piping freely flowing. Further addition of a water and sludge recycling system reduces the amount of water that ends up in the product to a negligible amount. Very infrequent cleaning of the carryback that falls from the return run will be required. PURPOSE The purpose of this proposal is to propose a standard method for specifying belt cleaner systems based on user expectations and equipment performance over time. DEFINITION In bulk solids handling by conveyor belt, carryback is the material that adheres to the belt after the belt discharges its cargo. PROPOSED STANDARD Required Basic Good Practices There are a number of basic design and operating principles that are good practice for the selection, installation, and maintenance of belt cleaning systems on conveyors in order to achieve "standard belt cleaning performance over time. 1. The Belt Cleaning System shall be designed to meet the performance requirements based on the worst operating conditions and worst bulk solids proper- ties that are expected. 2. Each conveyor discharge point shall be designed to readily accept the manufacturer's recommended minimum number of belt cleaners. In addition, the discharge chute shall be designed to accept, with minor modifications, at least one additional cleaner if it is required.

Jan 1, 2004

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 Jodie Robertson, Isabel Barton, Cristian Caro

Prior to mining, all rocks contained in a mineral deposit must be placed in one of several categories known as ore types. Each ore type describes a different way that the rock will behave in processing. The ore type determines which process stream a particular mined unit will be sent to, sets expectations for process engineers and metallurgists, and forms the basis for recovery predictions and production estimates. At first, ore types are assigned mainly by geologists based on visible geological criteria (dominant ore mineralogy, estimated grade, rock type, alteration type). As metallurgical tests are carried out and process data accumulate, the resulting criteria may be factored into the ore typing process, typically as assays and recoverable metal using the relevant process(es). Other variables may also be incorporated into ore typing at operations if they are particularly important, such as grindability, preg-robbing, gangue reagent consumption, and the presence of especially deleterious minerals such as talc or smectite. The mine operation department may also redefine ore types and/or process destinations based on economic criteria. A “best” ore type is designated that (in theory) best describes how the rock will behave in processing. Codes representing this ore type are entered into the drill hole database, then interpreted on cross sections and level plans, and finally added to the block model. Ore types are iteratively reexamined and adjusted over the life of a project. Major difficulties in effective ore typing are (1) lack of communication between geologists and metallurgists, (2) the imprecision inherent in imposing clean categories on messy natural systems without discrete divisions, (3) the need for ore types to provide useful information for a wide range of processes, (4) difficulties in scaling up laboratory test results to mine production, and (5) conflict among geological, metallurgical, and economic criteria for ore typing.

Nov 8, 2023

By M. Zaske, E. R. Mortensen

"As mine operators continuously look for ways to improve functionality and increase the capacity of their facilities, existing process equipment is often pushed to and past its designed limitations. As a result, equipment manufacturers are asked for economical solutions to meet redefined processing needs. Newmont Mining in Nevada was faced with such a need in its carbon-in-leach (CIL) train. In a collaborative effort between Newmont and Derrick Corp., tests were conceived to assess the viability of drop-in replacement screens using a three-dimensional screen panel. The synthetic pyramid screen panel was designed to increase flux while maintaining the existing equipment footprint. The test is the end result of an ongoing research and development project that Derrick undertook in an effort to refine and upgrade its urethane screening media. The application of this new screening media is presented for this CIL application along with future plans to implement the technology in trash, safety, carbon dewatering, carbon sizing and other scalping applications.In spring 2014, Process Machinery Associates (PMA), Derrick’s local area representative, met with Newmont to discuss the operation of the in tank screens in the CIL train at Twin Creeks, near Golconda, NV. The process was originally designed for about 12+ kt/d (13,000+ stpd) but the throughput has been steadily rising since the plant was commissioned. Newmont now requires 14.5 kt/d (16,000 stpd) to be processed. The original screens were running at their maximum capacity, and Newmont required additional screening capacity to continue the upward trend in production.Physical separation by use of screening is one of mineral processing’s oldest methods. Screening media can be prone to blinding and pegging, and the necessary support structures required for finer apertures result in smaller open areas. Therefore, more screening area generally requires larger panels and, thus, larger machines, screening media that does not blind or a combination of both.In an effort to avoid larger machines, Derrick had been working on a revolutionary threedimensional panel that would add nonblinding screen area in the same footprint of an existing machine. Alpha testing of the new screen panels began at Newmont Mill 2/5 in July of 2013. It was still occurring when PMA approached Twin Creeks about beta testing a refined machine and pyramid panel. After presenting the initial results, Twin Creeks determined that an upgraded machine and pyramid panels would be a possible solution to meet production needs. The testing of a machine eliminated the risk of capital costs to Newmont and provided Derrick the opportunity to obtain additional data."

Jan 1, 2015

By Joseph G. Carleton

INTRODUCTION The increasing concern for the environment may well present far more opportunities than problems for those involved in all phases of tunneling. All too frequently in the past, environmentalists and their concerns have been cast in a negative light, as obstacles to be overcome. Often forgotten is the fact that these same environmental concerns have created a rapidly increasing demand for new tunnels. Tunnels for rapid transit projects, clean water supply, and sewage treatment have been given a boost because of environmentalists' concerns about overuse of automobiles, inadequate water supplies, and improper sewage disposal. Concurrent with increasing use of tunnels to help solve or alleviate some of our environmental problems is an obligation not to create new ones in the process. Concerns which we feel responsible tunnel owners, engineers, and contractors should address themselves to include: (1) Minimum energy consumption, both during construction and in operation of the completed project; (2) proper storage and/or disposal of the excavated material; (3) minimum disruption during the construction process - noise, traffic, unnecessarily unsightly work areas, and possible weakening of foundations of nearby structures; and (4) a finished project consistent with community and environmental goals. We are especially concerned about two things. First, the longrun implications of a project -- what's good for a few people in the short-run may be bad for most of the people in the long-run. Cutting corners to save a little money now is false economy. Second, the fact that ultimately we all share the same earth -- its water, air,

Jan 1, 1974