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By David E. Lindorff

The impact of surface coal mining on the geologic materials and ground water in different geologic settings is being investigated by the Illinois State. Geological Survey at three abandoned surface mines in Illinois. At a site near Ottawa in La Salle County, the overburden prior to mining consisted largely of pyritic shale; sand was the major component of the overburden and spoil at a mine near Coal City, Grundy County. Clays, lacustrine silts, and some shale and limestone were the dominant premining overburden materials at a mine near Harrisburg, in Saline County. Ground-water elevations at Coal City and Harrisburg are approximately at premining levels, whereas at Ottawa they are near the base of the spoil. Ground-water quality has deteriorated at all three sites, especially at Ottawa and Harrisburg.

Jan 1, 1981

By James T. Tanner

Mica is a generic term that applies to a group of complex aluminosilicate minerals that have a sheet or plate-like structure and with different chemical compositions and physical properties. All micas form flat six-sided monoclinic crystals with remarkable cleavage parallel to the direction of the large surfaces, which permits them to be split into optically flat films; as thin as 1µm in thickness in some cases (Rajgarhia, 1987). Some micas are more easily split than others. For example, muscovite mica found in pegmatites is more easily split into thin films than is phlogopite. Mica found in mica schist is not as easily delaminated as mica found in weathered pegmatites. According to Dawson (1 949), the commercially important mica minerals are: Muscovite-potassium mica (colorless to pale green and ruby) Biotite-magnesium-iron mica (dark brown to black) Phlogopite-magnesium mica (pale yellow to dark brown) Vermiculite-hydrated biotite or magnesium-iron-mica (bronze yellow flakes) Lepidolite-potassium-lithium mica (pale lilac to deep purple) Some micas of less importance are: Zinnwaldite-lithium-iron mica (gray to smoky brown) Roscoelite-vanadium-potassium-magnesium mica (various shades of green and brown) Mica, principally muscovite, is widely used for industrial applications because of its exceptional physical, chemical, electrical, thermal, and mechanical properties (Table 1). Phlogopite and vermiculite follow muscovite in importance. Biotite finds very little commercial application at the present time. Commercially, mica is used in a number of forms. These forms and their description follow: Sheet mica refers to books of mica either mined from hard rock (pegmatites) or from loosely consolidated clayey material formed from the weathering of pegmatites and alaskites. These books can be readily split into thin film or splittings with specific thicknesses ranging from 0.0031 to 0.10 mm (Davis, 1985). Quality sheet mica is graded into 10 quality classifications (Tables 2 and 3). Books of mica that are flawed with excess inclusions, cracks, or folds (A mica) are called scrap mica and are either ground into commercial products by a dry or wet process. Built-up mica was developed in 1894 as a result of the cost and scarcity of sheet mica, and because many satisfactory electrical parts could be made from it (Preston, 1971). This type mica is formed by layering pieces of mica splittings upon one another and binding them together with inorganic or organic binders. These sheets are then pressed together under high temperature. Mica for this process is produced from pieces of sheet mica too small to be punched into electrical parts (Davis, 1985). Reconstituted mica is mica paper produced by forming a mat of very thin delaminated flakes of scrap mica. This mat is usually impregnated with an organic binder, but is also available unimpregnated. It is dried at 110°C. The mica for this process is either produced from the trimmings of a sheet mica operation or from blocks of A type mica (Davis, 1985, Chapman, 1983). Ground mica constitutes by far the largest use of mica, both quantitatively and application wise. It is produced by grinding and sizing scrap mica (also mica concentrate) obtained from five sources, 1) trimming from sheet mica, 2) A type mica blocks, 3) as a byproduct of spodumene and feldspar mining, 4) weathered pegmatites and alaskites, and 5) metamorphic schists. Synthetic mica is produced by crystal growth in a slowly cooled melt of accurately proportioned chemical oxides. Extended cooling times at a specific viscosity result in larger crystals. Many different micas have been formed by this process; however, fluorophlogopite is the most common.

Jan 1, 1994

By W. Petruk

Mineral liberations that would be obtained by grinding an ore to a specific size can be predicted by analyzing unbroken ore pieces, and mineral liberations in ground ores and mill products can be determined directly by image analysis. Predictions of mineral liberations are made by measuring size distributions and textures of mineral grains by image analysis, and using liberation models. Ground ores and mill products are analyzed to determine the proportion of mineral that is liberated, and the data are used to evaluate mineral behaviour during mineral beneficiation. The liberation data for minerals in a suite of mill products from a circuit are processed by a materials balancing technique to calculate recoveries of minerals in different types of particles throughout the circuit. The liberation-materials balance data define mineral recoveries; define the behaviour of an ore in a concentrator, pilot plant or bench test; and indicate whether recovery improvements are possible and/or feasible.

Jan 1, 1991

By E. Ben-Awuah, H. Askari-Nasab, N. Al Habib

Open pit mines are getting deeper with time and transportation expenses are increasing because of the increasing haulage distance. In-pit crushing and conveying (IPCC) is getting popular in deeper open pit mines as a suitable alternative to truck haulage because it offers a lower operating cost due to shorter haulage distance and less truck requirement. Semi-mobile in-pit crusher, currently the most popular IPCC system, is relocated every two to five years and the short-term plan needs to be updated accordingly. Short-term planning with IPCC is an area of research that has not been explored extensively yet and hardly any model can generate short-term extraction sequence considering an IPCC in place. This research work proposes a mixed integer programming model to generate short-term production plan within a time horizon of 12 months. The objective of the model is to optimally allocate shovels to minimize cost of material handling and maximize revenue subject to meeting plant requirement, maximum allowable tonnage variation and IPCC location constraints to achieve production and NPV targets set by strategic plan. The proposed model has been implemented in a hypothetical case study for verification. The comparison of results between scenarios with and without IPCC is expected to justify the use of IPCC in large open pit mines from a short to medium term perspective. A semi-mobile IPCC system with one relocation is considered in the case study.

Feb 1, 2023

By Y. J. Wang

In the mathematical analysis of electrical networks, the electrical devices are often modeled using idealized network elements such as current sources, voltage sources, and resistors. An analogous approach is outlined here for the modeling of mine ventilation networks, which can be considered nonlinear resistive networks. The modeling technique proposed uses five basic (non-reducible) elements: the H element, the Q element, the D element, the R element, and the N element. These elements are characterized by their (a) pressure gain or loss, (b) air quantity, and (c) pressure-versus-quantity relationship, each of which may be known or unknown. In addition to the definition of the basic elements, the necessary conditions for which there exists a unique solution are discussed. This is performed using theoretical developments derived from electrical circuit theory and illustrated in example networks. The proposed procedures are useful in the solution and characterization of mine ventilation networks.

Jan 1, 1996

By R. A. Wyman

"The froth flotation process was patented by E.L. Sulman, H.F.K. Pickard, and John Ballot in 1906 . . . . . . . . . .James M. Hyde installed the first froth flotation process in the U.S., about August 1, 1911, at the Basin Reduction Co. plant, Basin, Montana . . . . . . . . . .By 1914, 42 mining companies were operating or experimenting with the flotation process . . . . . . . . . .The period 1930 to 1960 saw the application of flotation spread to nonsulphide ores and become the key factor in the economic production of many industrial minerals". So states FROTH FLOTATION, 50th Anniversary Volume, published by AIME in 1962. It is interesting, to observe that the Mines Branch, now part of the Canadian Department of Energy, Mines and Resources, was established in 1907 through an act of Parliament entitled, "The Nines and Geology Act". In 1911, a mineral dressing group was formed and a laboratory was constructed. By 1921, an engineer was devoting full time to industrial mineral processing problems.

Jan 1, 1971

"INTRODUCTION In recent years, there has been increasing focus on environmental and social impacts of the extractive industries, climate change and resource scarcity. The concept of the circular economy aims to replaces the “take-make-dispose” economic model with one that eliminates waste of all kinds and is restorative by design. Such closed-loop systems implicitly aim to reduce the quantity of primary extracted materials entering the economy, thereby affecting supply and demand dynamics, hence mining industry economics. For the metals industry, the ability to engage in, or adapt to the circular economy can be heavily affected by industry structure and geographical factors. Eco-efficiency initiatives that reduce waste and environmental impact may help the mining and metals industry align with some of the goals of the circular economy. This paper focuses on base metals, and explores case studies in copper, lead and zinc. It analyzes primary and secondary metal production, and recycling. It examines company structures and how these affect engagement with the circular economy. CIRCULAR ECONOMY PRINCIPLES Ellen MacArthur Foundation (2012) describes the circular economy as “an industrial system that is restorative or regenerative by intention and design”, which “replaces the ‘end-of-life’ concept with restoration”, and “aims for the elimination of waste through the superior design of materials, products, systems, and, within this, business models”. The concept is systems focused. For materials such as metals, a series of loops are considered, including maintenance of devices, reuse, refurbishment and recycling. Potential methodologies to achieve circular economy outcomes include disassembly and reassembly of manufactured goods, leasing rather than buying major appliances, and converting to renewable energy sources. The circular economy is partially aligned with the principles of eco-efficiency, which relate to reducing the environmental impact per unit of a material produced. PRIMARY AND SECONDARY METAL PRODUCTION Base metals (copper, lead, zinc and nickel) are essential ingredients in modern economies and are key commodities produced by the global mining industry. Metal production can be categorized as primary or secondary. Primary metal comes from the processing, smelting and refining of metal content extracted from ores, while secondary production comes from metals recovered from recycled streams (e.g. recycled lead-acid batteries, copper wire scrap, etc.). Metals are stored in natural, anthropogenic in-use and anthropogenic waste stocks. An example of the stocks, flows and processes associated with global copper extraction and use is shown in Figure 1."

Jan 1, 2018

By W. W. Atkinson

This paper describes some concepts developed in a geologic data recording system at the Victoria, Nevada breccia pipe-skarn copper mine. The recording system is not fundamentally new, but represents expansion of earlier ideas. The paper is based on the philosophy that a high quality geologic data base is necessary and that it should be complete, clear, standardized, neat, quantitative, and readily useable. It may be multi-colored or simply black and white. Graphic, descriptive and quantitative recording of data is essential. A format for core logging is presented and discussed and as well as a multiple overlay system for recording data gathered in surface mapping.

Jan 1, 1983

By L. Xu

Since the establishment of the standard dust concentration of 2 mg/m3, a strong effort has been made by mining engineers and researchers to provide better dust control equipment and procedures for underground coal mines. Particular areas of success have been control of dust generation by better coal-cutting strategy, better design of water sprays for dust suppression and air movement, use of scrubbers, and improved design of face ventilation systems. A drastic improvement occurred over time such that the average dust concentrations for continuous miner operators dropped from 6.5 mg/m3 in 1968 to 1.3 mg/m3 in 1980 and for auger, cutter, longwall, and roof bolter occupations from 2.7 mg/m3 in 1973 to 1.6 mg/m3 in 1980 (Niewiadomsky, 1983).

Jan 1, 1990

By N. Ward

The Gualcamayo Mine is located in the Andes Mountains north of San Juan, Argentina (Fig. 1). A property of Yamana Gold Inc., it declared commercial production in July 2009 and has a total mineral reserve and resource base of approximately 88 t (3.1 million oz) of gold. Crushing operations for the openpit mine are located in a 13,500-m3 (477,000-cu ft) underground cavern with a ceiling height of 22 m (72 ft). More than 3,600 m (11,800 ft) of tunnels are used to access the cavern and convey the ore. The project as described in this paper relates to the design and construction of the main cavern, conveyor system exit tunnel, the mechanical system access tunnels and two 4.2-m- (13.7-ft-) diameter shafts (Ore Pass #1 and Ore Pass #2) (Fig. 2). Preliminary engineering for the project was performed by Hatch Chile. Rizzo Associates Argentina, S.A., a division of Paul C. Rizzo Associates, Inc. (Rizzo), was contracted to provide geomechanical and geotechnical support for the construction of the access tunnel system and geomechanical design and construction supervision for the cavern and shafts.

Jan 1, 2011

By J. H. Hammarstrom, S. M. Fortier, W. C. Day, S. J. Ryker, R. R. Seal

"The United States’ supply of critical minerals has been a concern and a source of potential strategic vulnerabilities for U.S. economic and national security interests for decades (for example, see Strategic and Critical Minerals Stockpiling Act, 1939). More recently, with the rapid increase in the types of materials being used in advanced technologies (Fortier et al. 2018a), and geopolitical events surrounding the supply of rare earth elements (Ting and Seaman, 2013), among other developments, the critical minerals issue has again achieved a high level of visibility within the U.S. government (Executive Order 13817 (2017)).In this paper, the U.S. Geological Survey (USGS) provides an overview of its ongoing focus on critical minerals through the agency’s core competencies in mineral information, mineral resource assessments, geologic and topographic mapping, geophysical surveys and mineral resource research. Aspects of the multifaceted critical minerals issue addressed here include:• Identifying minerals that meet the definition of “critical” provided in Executive Order 13817.• U.S. net import reliance for critical mineral raw materials.• Current status of domestic critical mineral resource assessments.• Current status of topographic and geologic mapping, and geophysical survey coverage of the United States.• The Earth Mapping Resources Initiative (Earth MRI) to support future critical mineral exploration.• Critical mineral potential of waste streams from extractive industries.Identifying minerals as criticalU.S. government agencies and other organizations use a number of existing definitions and criteria to identify a mineral or mineral material as critical, strategic or otherwise important. The executive order defined a “critical mineral” to be “(i) a nonfuel mineral or mineral material essential to the economic and national security of the United States, (ii) the supply chain of which is vulnerable to disruption, and (iii) that serves an essential function in the manufacturing of a product, the absence of which would have significant consequences for our economy and national security.” This definition is broadly consistent with that defined by the National Research Council (NRC, 2008) and may be summarized as “essential in use” and “subject to disruption of supply.” Virtually all of the dozens of critical minerals studies conducted since the 2008 NRC report have used some variation of this same definition (Hayes and McCullough, 2018)."

May 1, 2019

By Moussa Wone, William Levy, Christopher Caruso, Zachary Spera, Thomas Hennings, Richard Stacy Kinchen, PE Joel Kantola

"Owners constructing new combined sewer overflow (CSO) systems increasingly seek to have project design lives of 100 or more years in response to the growing size, complexity, and cost to construct and operate these systems. However, a codified and universally accepted approach to achieving this goal in the United States does not currently exist since service life prediction is a relatively new technical field. This paper discusses how the 100-year design life requirement was met for the design of tunnels, drop shafts, and diversion structures in the DC Clean Rivers Program (DCCRP). The authors identify some commonly referenced publications, present the testing framework used by the program manager to characterize the CSOs, review the design criteria used to guide the 100-year design life development, and establish guidelines to be considered by program managers and designers when implementing similar extended design life requirements in other CSO control programs.INTRODUCTIONLike many older cities in the United States, the sewer system in the District of Columbia consists of both combined sewers and separate sanitary sewers. When the capacity of a combined sewer is exceeded during storm events, the excess flow, which is a mixture of sewage and storm water runoff, is discharged to the District’s receiving water bodies (Anacostia River, Potomac River, and Rock Creek) and tributaries through outfall structures. This excess discharge during storm events is called a combined sewer overflow or CSO. A total of 53 CSO outfalls for the combined sewer system are listed in DC Water’s National Pollutant Discharge Elimination System (NPDES) Permit issued by the U.S. Environmental Protection Agency (EPA). The DC Clean Rivers Program (DCCRP) will reduce the number of CSO outfalls into the Potomac and Anacostia Rivers and decrease flooding in DC neighborhoods during extreme rain events by capturing, storing, and conveying diverted CSOs to the Blue Plains Advanced Wastewater Treatment Plant."

Jan 1, 2016

By E. Farrokh

CSM and NTNU models are among the most commonly used models in TBM performance evaluation. Due to increasing application of TBM in different tunneling conditions, modification became necessary for these models. Sensitivity analyses on these two models indicate that both models are very sensitive to machine characteristics. Analyses performed on CSM database for cutter load and penetration rate prediction indicate while the r-square of the CSM model is reasonably high for the predicted cutterload, the r-square value for the penetration is low. In order to increase prediction capability of CSM model for penetration rate the model was reevaluated using non-dimensional analysis and the original database of Colorado school of mines. NTNU model is evaluated using Monte Carlo simulation and regression analysis. The results of analyses indicate that the majority of the variation of the penetration in NTNU model can be explained by only three parameters. This might indicate that the effects of other factors are overshadowed and it is worthy to reevaluate NTNU model using original database and more updated statistical methods to avoid overlapping of different parameters correlations.

Feb 23, 2014

By J. Seiter

Mining has always been among the most hazardous of occupations, and with the increasing demand for coal and minerals, safety in mines assumes even greater importance. Worldwide, underground miners are being exposed to noise and respirable dust hazards associated with roof bolt drilling. These hazards are now being understood to cause irreparable damage to the health of miners. The objective of this research was to discover if a Polycrystalline Diamond Cutter (PDC) drill bit generates less respirable dust and hazardous noise than a competing Tungsten Carbide (WC) bit, in dry vacuum drilling. In order to control the drill parameters the drilling tests have been conducted in a laboratory setting. The results were met by determining the quantities of dust and noise generated using each drill bit and analyzing those levels by using monitoring devices and software to collect the data. This paper includes information on experiment setup, equipment used, drilling parameters, and data collected. The test results suggest that there are noticeable trends that the PDC bits produce less dust than WC bits but more testing is needed to substantiate these trends.

Feb 23, 2014

By W. A. Crosby

All mine operators using explosives want to maximize explosive performance while minimizing blasting costs. Use of bulk explosive products such as AN/FO, heavy AN/FO, slurries and emulsions has greatly improved blasting efficiency over the years. Many operators have improved energy output from these products by adding aluminum. A major problem facing them is the fluctuation in aluminum price. The question therefore becomes, when is it economically advantageous to use aluminum in bulk products? This paper answers this question by first reviewing the energy output from the main types of aluminized and non aluminized bulk mixed explosives and then by showing the relationship between the different products on a cost and energy basis. The paper finally presents examples of charts and tables which will aid mine operators to conveniently select the most economically correct bulk explosive, including the level of aluminum addition.

Jan 1, 1991

By A. E. Ketler

Powerful, yet inexpensive, personal computers running Windows-95 operating systems provide powerful mine-wide monitoring capabilities when properly engineered. Long awaited conductivity over LAN, phone and Internet links provide new dimensions for sharing information throughout an operator's organization, in- deed around the world. On-line data analysis, archival data storage and historical trend viewing generate shared inputs to production, safety and maintenance personnel. Five years in development, Rel-Tek's new EZ-Trol/W-DX system was engineered around the pilfalls of a Windows environment. It now offers higher speeds, 3D animated graphics and long distance telemetry - all with better reliability than ever before possible. The ubiquitous DDS utility inherent in most Windows was discarded in favor of a lightning fast RAM format. Several ponderous interpretive programs were redesigned into a single compiled entity, thus avoiding the overhead from message conversion, handshaking and transfer. To make the system user friendly, a 'Wizard" utility helps operators set up and reconfigure their systems on site. In-mine data acquisition telemetry was also re- vamped, incorporating a unique noise avoidance scheme, dubbed the "DX" bus - enabling longer distances and higher reliability. 12- bit analog conversion provides the enhanced resolution needed for field scaling auto-cal sensors. By mid '96, eight EZ-TROLMI- DX systems were up and running, several for more than a year. Factory updating and assistance are possible over a phone or Internet link. Our factory testing of components routinely includes actual operation at 2400 BAUD over 14 miles of twisted pair wires.

Jan 1, 1997

By James W. Derrick

General widespread interest in fine coal cleaning circuits did not occur in the United States until the mid 1960's. Up until this period the relatively low price for which bituminous coal was sold did not justify for many operators the capital and maintenance costs associated with the beneficiation and drying of fine coal. However, with current growing interest in this area, the introduction of new types of process equipment along with modifications to existing components is occuring to maximize the recovery of coal fines. In 1973 Derrick Manufacturing Corporation introduced high frequency screening machinery into the coal industry. The first design consisted of a 4 ft. wide 18 ft. long single deck screen frame with three 100 mesh woven wire screen surfaces divided by repulping troughs for the addition of wash water. In addition, a special slotted rubber dewatering deck was installed on the discharge end of the unit to assure adequate dewatering of the screen oversize. This panel had nominal 25 mesh X 3.0" slotted openings. The machine was also equipped with a special high speed-low amplitude (3600 RPM .032" % AMP.) integral vibrator.

Jan 1, 1983

By Gabriel Böde Jimenez Leon, Michael Karmis, Christopher Newman, Zach Agioutantis

"When utilizing high recovery underground mining methods, such as longwall or high-extraction room-and-pillar mining, the movement and deformation of the overburden propagate toward the surface and may affect the integrity of overlying surface streams (Peng et al, 1996). Published studies cite three major mechanisms of subsidence as most likely to impact streams: displacement, slope and strain. While subsidence-induced vertical displacement cause little structural damage to the stream bed, it may create adverse drainage and stream flow issues as the subsidence trough allows for ponding (Dawkins, 2003). Subsidenceinduced changes to the slope, or tilt, of a stream may have adverse effects on water flow. As the stream enters the subsidence trough, the gradient increases providing potential erosion control problems. When exiting the subsidence trough, a reduction of the gradient may inhibit stream flow, causing localized ponding (Peng, 2008). While vertical displacement and tilt both may have detrimental effects to surface streams, the resulting strains have been documented as being the most damaging to surface streams and structures causing distortion, fractures, or failure (Singh, 1992). When stream beds are subjected to high tensile strain, tensile cracks may form at the surface level allowing for the direct loss of stream flow through fissures. When stream beds are located in areas of high compressive strain, rock layers forming the stream bed can fail as the stream bed ruptures, upward, blocking stream flow or having the stream diverted into the fracture zone at the base (Iannacchione, et. al., 2010).Recent investigations on the effects of underground mining on surface bodies of water suggest that to determine the degree of stream impact one must also consider the geologic structure and thicknesses, surface topography, watershed drainage areas, width of river bed and rate of mining. Due to the complex nature and number of parameters affecting surface streams, subsidence modeling tools and software packages should be implemented throughout all stages of subsidence planning, prediction and control. The Surface Deformation Prediction System (SDPS) utilizes the influence function for the calculation of final subsidence deformations with respect to the angle of influence, supercritical subsidence factor as a function of the percent hard rock, edge effect offset distance, and surface topography. Developed more than 25 years ago, SDPS has been continually updated with new analysis and prediction features, providing a reliable and versatile program for subsidence management methodologies. Most recently, the program has been updated to evaluate the effect of varying surface topography in the prediction of horizontal displacements, referred to as ground strain, allowing for the accurate three-dimensional representation of surface deformations in mountainous terrain (Agioutantis and Karmis, 2014). Ground strain has become one of the predominant deformation indices used in the evaluation of potential damage to surface structures (Karmis et al., 1995). Ongoing work with SDPS software seeks to investigate the calculation of ground strain in SDPS and its ability to accurately and realistically predict damage to surface streams due to underground mining operations."

Jan 1, 2015

By H. Fayed

Froth flotation technology is the backbone of the minerals pro-cessing industry where minerals are concentrated by selective separa-tion; either direct or in-direct flotation. In direct flotation useful minerals are conditioned to become hydrophobic (water-repellant) and attach to air bubbles while impurities (non-useful particles) remain in water. The hydrophobic particles are transported by air-bubbles to the top froth (foam) layer in flotation tank which can be removed as a concentrate. There are many factors that controls this selective separation process such as: particle’s degree of hydrophobicity, size, mass loading, air holdup and bubble size distribution. Turbulent fluctuation of the slurry in the tank is another important factor that controls the collisions rate between particles and bubbles and hence attachment rates. The turbu-lent fluctuations are measured by the local distribution of turbulent dissipation rates. Conventional flotation machines are restrained by residence time of the slurry that is about 3-5 minutes that results in a large footprint and limits the capacity of flotation plants. The designers of conventional flotation machines try to reduce the footprint of flota-tion tank by scaling up the flotation machines to increase plant throughput. The scale-up process reduces the specif power consump-tion and the local distribution of shear rates and turbulence dissipation rates. This scale-up results in a larger mean bubble size and lower particle-bubble attachment rates.

Feb 1, 2023

By Charles A. Beasley

Increased technical and legislative analysis by all parties of interest could result in more efficientand better directed regulatory legislation in the mining industry. Efforts to forestall or frustrate legislation through massive lobbying and public relations efforts are seldom effective over time and often lead to more stringent and far reaching legislation than necessary. The Federal Coal Mine Health and Safety Act of 1969 is perhaps an outstanding example of such insufficiences; a future example may well be regulatory surface mine legislation. Although a lack of extensive hard data seldom enables rapid or sophisticated analysis early in the legislative process, even preliminary analysis may be sufficient. Simple statistical analyses of available data, assessment of the legislative rationale, and subjective appraisal of other non-quantifiable constraints to improved mine safety. An average of 115 underground fatalities at an exposure frequency rate of 0.67 can be reasonably expected in the immediate future, under existing levels of technology, degree of regulation, and economic conditions. If gross unrefined estimates of 6 preparation plant, 5 surface, and 30 strip mining fatalities are assumed, the total fatality industry level could be expected to approximate 156 Serious professional, economic, and technical constraints within the the industry probably preclude any major decrease of these accident levels within the near future

Jan 1, 1972