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By Emmet K. Oslen

Kaiser Steel Corporation, the pioneer steelmaker on the Pacific Coast, was founded by the late Henry J. Kaiser. In 1944 the Company purchased from the Southern Pacific Railroad an iron ore property 200 miles east of Los Angeles known as Eagle Mountain. Today the domestic operation of Kaiser Steel Corporation consists of the iron mine at Eagle Mountain; two coal mines, one each in Utah and New Mexico; an integrated steelmaking complex at Fontana, California; and several steel fabrication and erection facilities along the west coast. Kaiser Steel also has interest in Hamersley Iron, Ltd., Australia, and Kaiser Resources, Ltd., British Columbia. Eagle Mountain Mine is located about 80 miles east of Palm Springs and adjacent to the southeast corner of Joshua Tree National Monument. The area is one of the most arid in the world averaging only two inches of rain annually. Geologically, the mine is at the western edge of the Basin and Range Province which covers about one-half million square miles of the western United States. The Province is typified by north to northwesterly trending fault block mountain ranges separated by sediment filled valleys, Production has totaled over 82 million tons of finished products since the first shipment in June, 1947. Over 500 million tons of material have been mined from the deposit to date. Eagle Mountain Mine is noted for the pioneering use of the largest and most up to date equipment to mine and process its ore. In 1961 Eagle Mountain received the first fleet of 100-ton haulage trucks in the mining industry. There were thirteen semi-trailer units in the fleet. The first 12 to 17-yard size shovel in the mining industry was placed in operation at Eagle Mountain during 1962. Rotary drilling was introduced at Eagle Mountain in 1954 to replace churn drilling. Eagle Mountain was the first major mine to use metallized slurry when three aluminum slurries were introduced for primary blasting in 1962.

Jan 1, 1972

By P. H. S. W. Kulatilake

The presence of discontinuities strongly affects the mechanical and hydraulic behavior of rock masses. Joint geometry networks play a vital role in civil, mining, and petroleum engineering projects associated with jointed rock. The need for a realistic representation of joint geometry in rock masses has been recognized. The first part of the paper shows how to build three-dimensional stochastic joint network schemes and also shows how to perform validation studies for these schemes using joint data from the Stripa mine, Sweden. Due to the existence of complex joint patterns, mechanical behavior of jointed rock masses usually exhibit scale effects and an-isotropic properties. A correct understanding of the mechanical properties (strength and deformability) of jointed rock masses is important for designing and performance estimation of structures build in and on rock masses. Beyond a certain volume, the mass proper-ties of the rock may remain essentially constant with respect to the effect of joints. This minimum volume may be used as the element size to represent the equivalent properties of a statistically homogeneous rock mass volume which contains a significant number of joints. This volume may be termed as a "Representative Elementary Volume" (REV) and may be of great importance for engineering purposes. Investigations are underway at both the 2D and 3D levels to look into the possibility of establishing relationships between REV mechanical properties and joint geometry parameters. Recently developed joint geometry modeling schemes are linked with existing distinct element codes (both 2D and 3D) to create a stochastic/deterministic stress analysis approach in achieving the goal. Results obtained so far in this direction are presented in the second part of the paper.

Jan 1, 1992

Joy Mining Machinery has developed a new generation of ultra-heavy shields for Anglo Coal Australia?s Moranbah North Mine in the Bowen Basin region of Queensland. These are the largest two-leg longwall shields yet produced by Joy. The longwall at Moranbah North posed a number of challenges, among them a thick, inclined, sometimes undulating seam with increasing depths. The result of this was the need for larger, heavier, more powerful roof supports. Knowing that future longwalls would be going deeper, mine management determined that shield yield ratings of at least 1,750 t (1,930 st) was what would be required.

Jan 1, 2011

By Paul C. Lingo

Two recent antitrust cases, coming from widely separated areas, different industries and involving wholly different facts were decided by the Supreme Court on June 7, 1965. The decisions in there two cases may well prove to be the most important and far-reaching decisions in the field of labor law that have been handed down in the last 24 years. These cases, although quite dissimilar factually, had one common element. In both, the gravamen of the antitrust violation was bottomed on the terms of labor agreements negotiated by a multiemployer group. These cases are usually referred to as Pennington1 and Jewel Teat. Since a number of references will be made to the antitrust laws, it may be well to state briefly the applicable portions. Section 1 of the Sherman Antitrust Act makes "every contract, combination in the form of trust or otherwise, or conspiracy, in restraint of trade or commerce among the several states, or with foreign nations, is declared to be illegal...". Section 2 imposes criminal sanctions against "Every person who shall monopolize, or attempt to monopolize, or combine or conspire with any other person or persons, to monopolize any part of the trade or commerce among the several states...". Under Section 4 of the Clayton Act a person who sustains damages as a result of a violation of the anti¬trust laws is entitled to recover treble damages plus costs.

Jan 1, 1966

By L. B. Bramlett

The Archean (2.65 b.y.) aged Canning Stock at Copper Mountain, Wyoming contains an average of 20 ppm U. The North Canning and Fuller deposits occur within the enriched interior of the stock. Post-Laramide development of super gene enrichment blankets occurred in wide (25- 100 m) crushed zones. Hematite and chlorite accompany pyrite and sooty pitchblende in the mineralized zones. Reduction mechanisms proposed for deposition of pitchblende are: 1) sulfides, 2) hydrocarbons, 3) bacteria, 4) the water table, or 5) some combination of these. Abundant tar- type organics appear to have preserved the enrichment blankets from degradation. Trace element and radiometric data define target zones, but exploration models focus on favorable structure.

Jan 1, 1980

By Frank W. Pereira

The Montana Talc ore body was discovered in 1983 in Montana's Gravelly Range, about 40 km (25 miles) south of Ennis. Initial drilling indicated a 910-kt (1-million st) ore body of high purity talc. Preliminary analyses on ore cuttings included chemical analysis, brightness measurements, and microscopic evaluations of the structure of the talc. Results indicated it was similar to talc currently being marketed from Montana and it would probably have good commercial value. Based on the positive test results, a test pit was made and a 180-t (200-st) sample of ore was mined. A portion of the ore was ground to various particle sizes and evaluated to determine its strengths, weaknesses, and other characteristics. The deposit is located close to the Cyprus Yellowstone deposit. It was therefore believed that Montana Talc ore may possess many of the same characteristics. Testing and analyses showed the talc to have a high purity and an extremely large surface area, even for Montanatype tales. The ore was also situated in a massive deposit, indicating low cost mining. While the lab analyses were encouraging, the true evidence would be obtained from commercial tests in the marketplace. About 91 t (100 st) of ore were ground to product specifications for pitch control, paint filler, and plastics filler. Consumers were contacted and requested to evaluate the sample talc products. A major trial for the talc as a pitch control agent was arranged at a Northeast paper mill. The trial indicated the new Montana Talc product performed as well or better than the current standard in the industry. In fact, due to a minor modification in the compaction process to make the transport of the talc easier, the product had substantially less dust than the currently used product. The operating people at the paper mill requested that management purchase this talc. Trials were also run at paint plants for use as a pigment filler. And the talc was fabricated into a number of plastics compounds. The initial product tests were largely positive and provided encouragement to proceed with the project. Different grinding mills were used and their performance evaluated. Significant data were generated by the custom grinders. They indicated how the Montana Talc ore ground and the particle size distributions produced at different grinding settings. Encouraged by the positive marketing tests, a prefeasibility study was commissioned. A talc grinding plant and mine plans were designed and capital and operating costs estimated. Initial economics showed an attractive return. The operating costs were among the lowest in the industry. The positive economics, along with the excellent results by the products in the marketing tests to the paper, paint, and plastics industries, led to the recommendation to proceed with the project. Plant construction began in June of 1985. The Montana Talc Co. (MTC) analyzed the data from the commercial tests. Based on the product's outstanding performance and the uniqueness of its high purity and platy structure, a strategy was developed to position the company as a premium talc supplier.

Jan 1, 1989

"Above ground, elevated belt conveyors that span more than 200 m (656 ft) between support points can cross valleys, rivers, forests and buildings with a minimal footprint. The cable bridge conveyor (CBC) is a new type of suspension bridge based belt conveyor system that has long spans between support points. It combines a typical belt conveyor and an improved simple suspension bridge to form a conveyor bridge. The improved simple suspension bridge places a widened bridge deck directly on suspended cables, without the need for high truss towers. The benefits include reduced cost and increase aerodynamic stability compared to conventional suspension bridges. The CBC’s compatibility with current belt conveyors allows versatility in application.A belt conveyor is a ubiquitous material handling system. Conveyors can be placed directly on ground or elevated above ground by support structures. Considerations of cost, design, environment, civil work, safety and process requirements are all factors in choosing the ground-based or elevated conveyors (Zhang, 2014). The ground-based conveyor has the lowest structural cost when the conveyor is placed on an existing road. Maintenance access is easy and straightforward. Compared to the groundbased conveyor, the elevated conveyor can cross existing buildings and structures, give passage to traffic beneath the conveyor, has a smaller footprint and requires less civil work to pass mountainous areas. The drawback of the elevated conveyor is higher structural cost, which can be compared with savings in civil work and other benefits. Conventional elevated conveyors are supported by rigid truss-type structures, with a typical span of 15 to 25 m (50 to 82 ft) between concrete support bents or steel trestles. Triangular truss, using steel pipes instead of hot rolled steel sections, is more efficient. The typical span of a triangular truss-supported conveyor is around 30 to 40 m (100 to 130 ft), while the weight is about 10 percent less than conventional box truss with a shorter span (Jennings, 2013).Long-span elevated structures based on suspension bridge is another step forward in increasing the distance between support bents, reaching 100 to 400 m (330 to 1,312 ft) and beyond. The wide distance between the support points of an elevated conveyor offers unique benefits. The conveyor can cross rivers, valleys, highways, forests and other obstacles with minimal footprint and reduced civil work. The versatility from long-span conveyors makes bulk material transportation over previously impossible terrains now a feasible option."

Jan 1, 2014

By Eduardo Poltronieri Trés, Anderson Denadai Thomazini, Rodrigo Boyer Fernandes, Francisco de Assis Dutra Macedo, Gilvandro Bueno, Maycon Athayde, Rossano Augusto Pilon Nunes

The fundamental importance of comminution by high-pressure grinding roll (HPGR) technology to efficiently increase the particle surface area lies in lower energy and water consumptions for iron ore pellet feed production. This study compared the ball wet milling process with the innovative HPGR processing technology for hematite-goethite ores. Green-pellet balling and induration processes were simulated on the bench and pilot scales.

By R. Kealey, D. Huo, Q. Zhang, Y. A. Sari

Greenhouse gas (GHG) emissions from primary mineral and metal production account for ~10% of global GHG emissions. One of the main sources of GHG emissions in mining operations is fuel consumption by haul trucks. Given their size and carrying capacity, the fuel consumption of haul trucks can approach 250 liters per hour. An average of 30% of the idle time of the trucks is spent while waiting in the queue. Inefficient truck dispatch planning can waste resources, cause dilution and elevate GHG emissions. In this research, a machine learning based truck dispatch approach was developed to dynamically route the haul trucks based on the loaded material, the road traffic, the estimated wait time, and the maintenance needs of the trucks. The GHG reduction potential of this smart fleet management approach was estimated by calculating and comparing the related carbon emissions versus scenarios using traditional fleet allocation approaches. Results suggest that this dynamic fleet allocation approach can significantly reduce GHG emissions at mineral production sites by optimizing waiting times and the overall distance travelled while achieving the same production levels.

Mar 2, 2022

By David I. Smith, Kenneth Arnold, Bryan Aweh, Vincent Falkowsk, Brian Lakin, Andy Fer

Nassau County, New York, is undertaking several projects to improve the water quality in the Western Bays of Long Island. A major step forward will be the completion of the Bay Park Conveyance Project, which will divert most treated effluent away from the Western Bays to an existing ocean outfall at the Cedar Creek Water Pollution Control Plant. The ongoing works include 3.6 miles of microtunneling, 7 miles of sliplining, 14 shafts, and a 75 MGD pump station. This paper provides an overview of the design and an update on construction progress through December 2022. The project is a collaborative effort between Nassau County, New York State Department of Environmental Conservation, the design-builder, and various consultants.

Jun 13, 2023

By John J. Schanz

The ideal entering freshman for the College of Mineral Industries possesses the necessary aptitude to complete successfully a difficult technical curriculum, has a highly developed intellectual curiosity and adequate preparation in basic mathematics, sciences, and English, is enthusiastic about pursuing a career in the mineral industries, and puts forth a good academic effort while attending Penn State. The present programs of the University?s Division of Counseling and the College of Mineral Industries are directed toward providing the College with students who will meet these requirements. At present, freshmen are admitted to the Pennsylvania State University without entrance examination if they are in the upper two-fifths of their high school classes. All Pennsylvania students in the lower three-fifths are required to take the University Aptitude Test and all out-of-state students the College Entrance Board Examinations. Such students are admitted only if they score sufficiently high on either test to indicate the ability to do satisfactorily the work of University students. Only to this extent, are native intelligence and areas of greatest aptitude known for the Freshman prior to admission, and they are, therefore, largely beyond the control of either the Division of Counseling or the College of Mineral Industries. Because all freshmen, with exceptions that are numerically minor, are required to select a curriculum before admission to Penn State, each student who presents himself for required counseling during the summer, prior to his first semester, has already made a choice of his course of study. In many instances, such choices have been made without a rational and serious consideration of the student?s abilities and interests. Through tests given between the date of admission and the date of the counselling interview, it is possible to measure these characteristics and for the Division of Counselling to advise the student of his chances of success in his chosen curriculum. If he is qualified for the curriculum he has selected, Counselling Service goes on to direct the student?s attention to those other curriculums which are in the same general area as the one he has chosen and which will also challenge his abilities and correspond to his interests, Through this counselling, the curriculums of the College of Mineral Industries, which are often less well known to high school students than others for which they are no more qualified by ability or interest, are brought to the attention of the incoming freshman.

Jan 1, 1959

By Erica McGlynn, Brian Negrea, Lance Jackson

There was no need for the people of Cleveland to ask “Where does the raw sewage go? We want to know!” because it was clear. The raw sewage was being discharged into Lake Erie during heavy rainfall events due to the outdated design of the combined sewer system. In efforts to resolve this ongoing issue for the City of Cleveland, the Northeast Ohio Regional Sewer District developed Project Clean Lake in collaboration with the US EPA. Project Clean Lake is a 25-year, $3 billion program consisting of seven large-diameter CSO storage tunnels to be constructed beneath the city’s existing infrastructure. The first four tunnels have been completed using traditional hard rock TBM excavation methods. The fifth tunnel, the Shoreline Storage Tunnel Project, presents unique challenges and complexities as it will be the first large-diameter EPB TBM to dig under the City of Cleveland. The project itself consists of one tunnel drive 14,100' (2.7 miles) in length, two pipe jacking tunnels, three large slurry wall shafts, two diversion structures, and three regulator reconstructions. Upon completion of the project, 12 permitted CSO locations along Lake Erie will be taken offline, reducing overflow volumes by approximately 350 million gallons per year. This paper will discuss the current status of construction and the chosen means and methods, including the myriad of nuanced differences between hard rock and EPB TBM tunneling methods. Particular attention will be given to the site preparation, setup, and organization; TBM assembly; and TBM launching practices.

Jun 13, 2023

By Karin Bäppler

A new polyhalite fertilizer mine is currently being developed in the UK by Anglo American Crop Nutrients. The project includes the construction of a Mineral Transport Tunnel almost 37 kms long to house a conveyor belt that will move polyhalite from the production shaft at the mine to a materials handling facility at the port. The project sets a new standard in terms of an ultra-long tunnel drive and sustainable, environmentally friendly and efcient material transport. The paper highlights in particular the . m diameter TBM in use for the construction of the ultra-long tunnelling section.

Jun 23, 2024

By Kyle Kittle, Kyle Knaeble, Albert Ruiz, Gregory Raines, Ryan Gewargis

The Chimney Hollow Reservoir Project (CHRP) is located southwest of Loveland, Colorado. CHRP is a component of the Windy Gap Firming Project, operated by the Municipal Subdistrict of the Northern Colorado Water Conservancy District. The inlet/outlet tunnel (IOT) for CHRP contains a reinforced concrete lined alve Chamber with PC membrane waterproong that was ecavated via seuential ecavation method to a diameter of feet. The IOT was ecavated using both drill and blast and road header with ground support consisting of steel sets, rock bolts, wire mesh and shotcrete. The IOT will withstand 300 feet of water head and rock ll surcharge load from the dam embankment constructed over the tunnel.

Jun 23, 2024

By D. Newman

Ground control is critical to the success of a safe and productive underground stone mining operation. The primary focus of the ground control engineer is the stability of the roof or back; development and benched pillar stability; stability of the sill pillar between vertically adjacent mining levels; and floor stability. Roof stability begins with the selection of a stable back horizon based on the presence of a thin shale parting, stylolite or other discontinuity from which the production shot can easily peel away, leaving a stable back stratum. Bed thickness, fracture spacing, jointing and the material properties of the roof strata control the room width; the decision whether to bolt the roof; the bolt length, type and diameter; and the spacing of the roof support. Horizontal stress controls the header and crosscut azimuth. The mine operator should avoid driving perpendicular to the maximum horizontal stress direction. Where this is unavoidable, narrowing the opening width, narrowing pillar centers, increasing the support density and using three-way intersections are alternatives to remediate shearing along the roof-rib interface. Stable pillar dimensions depend upon the interaction of the vertical stress resulting from overburden thickness and multiple-level interaction of overlying level or levels; the mining height during development and the final mining height after floor shots are taken during benching; the presence of faults, folds or joints passing through the pillar; and limestone lithology, recognizing that the presence of oolitic bands, shale partings, joints and bentonite beds creates zones of weakness that can destabilize an otherwise competent pillar. Floor stability is typically not a significant issue for underground stone mines because the bearing capacity of the stone typically exceeds the vertical pressure transferred through the pillar. However, floor heave can be a ground control issue where shale partings, moisture-sensitive strata, weak stone bands or horizontal stress is present. Roof stability and pillar stability problems can be initiated as the floor heave enables the pillar and roof to settle. To illustrate these ground control issues, this paper presents four case histories that are a mix of ground failures and successful mining. The focus is on the geotechnical data required for roof, pillar and floor design and stability analysis.

Jan 8, 2017

By James Corcoran, Richard McLane, Matt Neuner, Joseph DeMello, Hugh Davies

The Los Angeles County Metropolitan Transportation Authority (LA Metro) Purple Line Extension Section 1 (PLE1) is a $3.12 billion USD design-build, underground heavy rail project, connecting an existing station at Wilshire Blvd. and Western Ave. and extending 3.92 miles under Wilshire Blvd, terminating approximately 550 feet west of Wilshire and La Cienega Blvds. The project alignment runs immediately adjacent to the La Brea Tar Pits, world renowned for Pleistocene fossils and continuous seepage of asphaltum (locally known as tar) and gas in an urban setting. This paper presents a successful case history of the planning, design, and construction efforts to safely construct the bored tunnels through Reach 3 of the alignment (between Wilshire/Fairfax Station, and Wilshire/La Cienega Station), in a designated Methane Zone in the City of Los Angeles. Historical context on decades of challenges and studies is summarized. Further, this paper outlines the pro-active partnership between the Owner: LA Metro, the Design Builder: Skanska-Traylor-Shea Joint Venture, and geotechnical design services provided by Golder Associates to safely manage pressurized face tunneling through a confined gas zone near the La Brea Tar Pits. Specifically, a program of in-situ oxidation and soil gas extraction was designed to test and analyze risks associated with pressurized face TBM tunneling through the complex subsurface geological conditions, then implemented during construction. In advance of tunneling, a network of wells was used to draw air into the gas zone to oxidize the 6,500 ppm hydrogen sulfide gas, as well as determine methane recharge rate. During TBM tunneling, the wells were converted to a gas extraction system to evacuate, filter (H2S) and burn (CH4) the gas as the Tunnel Boring Machine passed, providing a preferential pathway for the gas to migrate toward extraction wells, and preventing the migration to adjacent buildings. The team extracted and treated 3,857,000 cubic feet of mostly methane gas over 40 days as the TBMs passed through the zone. Gas behavior, pressures, and concentrations were monitored not only from the extraction system, but also in basements and utility vaults along this section of the alignment.

Jun 13, 2023

By W. Zhang

"The adsorption of collector on chalcocite has been studied in situ in aqueous solutions by applying an atomic force microscopy (AFM). The AFM images show that xanthate, such as potassium ethyl xanthate (KEX) and potassium amyl xanthate (PAX), adsorbs strongly on chalcocite mainly in the form of insoluble metal xanthate, which binds strongly with the mineral surface without being removed by flushing with ethanol alcohol. The result clearly shows that the adsorption of xanthate on chalcocite is totally different from its adsorption on chalcopyrite, during which oily dixanthogen is the main adsorption product on chalcopyrite surface. AFM images also showed that increasing solution pH to 10 doesn’t prevent the adsorption of xanthate on chalcocite much and the result confirms with the fact that chalcocite floats well in a wide pH range up to 12 with xanthate being used as a collector. INTRODUCTION In flotation, the adsorption of collector on mineral surface is vital for a successful flotation process to achieve a satisfying metal recovery. Historically, many works have been carried out to clarify the adsorption mechanism of collectors on sulfides. (Gaudin and Schuhmann, 1936, Poling and Leja, 1963; Allison et al., 1972, Fuerstenau, 1982; Leja, 1982; Woods, 1984) The adsorption of xanthate on chalcocite surface in aqueous solution also attracted the interest of many researches. Gaudin and his colleagues (Gaudin et al., 1934; Gaudin and Schuhmann, 1936) studied the solubility of potassium ethyl xanthate and its reaction products in organic solvents and firstly proposed there was initially chemisorbed xanthate (X-) on chalcocite surface followed by insoluble cuprous xanthate (CuX). Allison et al. (1972) studied the reaction products of various sulfide minerals with xanthate solutions and reported that the measured rest potential of chalcocite in 6.25×10-4 M KEX solution at pH 7 was +60 mV and the reaction product of PAX on chalcocite was cuprous xanthate. Mielczarski and Suoninen (1984a, 1984b) applied the XPS and studied the adsorption of potassium ethyl xanthate on cuprous sulfide. It was reported that there was a relatively rapid formation of a well-oriented monolayer of xanthate ions followed by a slow growth of disordered cuprous xanthate molecules on top of this layer. Richardson et al. (1984) carried out an electrochemical study of chalcocite flotation with the addition of ethyl xanthate. It was proposed that cuprous xanthate and possibly cupric xanthate were adsorbed hydrophobic species on chalcocite surface due to the exchange and charge transfer oxidation reactions. Leppinen et al. (1989) applied an in-situ FTIR study of ethyl xanthate adsorption on sulfide minerals under conditions of controlled potential and they concluded that, for chalcocite, there were three different potential regions of xanthate adsorption, including chemisorption, copper ethyl xanthate formation on the surface and multilayer formation."

Jan 1, 2015

By M. A. Reyes, J. Bickson, J. R. Srednicki

Federal laws mandate the presence of refuge alternatives (RAs) in underground coal mines and provide guidelines for harmful gas removal. After an explosion, harmful gases can follow survivors into an RA and can reach a deadly concentration. Investigators from the National Institute for Occupational Safety and Health (NIOSH) tested 12 ventilation system configurations (VSCs) to purge sulfur hexafluoride (SF6) tracer gas from a built-in-place (BIP) RA in the Experimental Mine in Bruceton, PA. Using a borehole air supply, tests were conducted with airflows of 750 and 1,000 standard cubic feet per minute (SCFM). Excluding a VSC where the air inlet was 1.98 m (78 in) from the air outlet, the results show that the time to purge the SF6 concentration from 1,000 parts per million (ppm) to 25 ppm ranged from 26 to 29 minutes for an airflow of 750 SCFM and ranged from 18 to 23 minutes for an airflow 1,000 SCFM. Mines can use this information to reduce purge time in case of a mine disaster and determine which VSC to avoid. INTRODUCTION After a fire or an explosion in an underground mine, the concentration of carbon monoxide can reach a fatal level. In a mine disaster, the main goal is to escape. However, if miners cannot escape, they have to migrate to a location to find refuge and, if possible, communication, and a borehole source for a fresh air supply. To ensure survival of the miners, Federal laws mandate the presence of a refuge alternative (RA) within 304.5 m (1,000 ft) of the nearest mining face. In addition, Code of Federal Regulations Title 30 CFR Section 7 sets the guidelines for personnel tracking, RAs, and the removal of noxious gases in underground coal mines (Mineral Resources, 30 CFR, 2014). Federal regulations define an RA as a protected, secure space with an isolated atmosphere and integrated components (Mineral Resources, 30 CFR, 2014). There are three types of RAs: portable metal RAs, portable tent-type RAs, and built-in-place (BIP) RAs. A BIP RA is constructed using masonry or other stoppings to create an isolated space in a mined-out area. Blast doors are installed in one or both of the stoppings for the miners to enter the RA. Furthermore, RAs must provide the following components: breathable air, food, water, air monitoring, and harmful gas removal. Federal regulations have emphasized the mandate for breathable air and harmful gas removal in the following words: “Purging or other effective procedures shall be provided for the airlock to dilute the carbon monoxide concentration to 25 ppm” (Mineral Resources, 30 CFR, 2014). The purpose of the mine ventilation system is to provide a sufficient quantity of air to the underground mine workings, to dilute methane and other contaminants, to maintain a suitable working environment, and to prevent accidents from happening (Cheng and Wei, 2014). In addition, the organic nature of coal amplifies risks from poisonous gases, explosions, and fires (Engström et al., 2018). If an underground coal mine ventilation system fails after an explosion, the concentration of toxic gases, most notably carbon monoxide, will increase. Carbon monoxide is dangerous because it creates tissue hypoxia by binding to hemoglobin (Özmen and Aksoy, 2015).

Jan 1, 2019

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 B. G. White

Traditional interpretations of vein ore deposits in the Coeur d' Alene Mining District, such as the view that these deposits formed in a transcurrent tectonic regime during the Precambrian, are being supplanted by the view that the deposits (1) formed in low-grade metamorphic shear zones similar to those that host an important type of gold deposit, (2) display features, such as wall rock carbonate zoning and vein zoning, that are common to ore deposits elsewhere, and (3) are probably Mesozoic and possibly related to emplacement of the Idaho batholith. In recent years, new interpretations have led to major ore discoveries that are likely to extend the life of the district for decades.

Jan 1, 1998