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By David Court, Rab Brown

The paper discusses the work in progress on the construction of the extension of the High Speed Rail line from the Channel Tunnel into the centre of London UK known as the “Channel Tunnel Rail Link” (CTRL), and particularly on contract 250 which involves the construction of two 5.3Km tunnels 7.15m diameter constructed with two EPB convertible tunnelling machines underneath the densely populated area of East London. In addition the paper will look at an innovative Alliance that has been formed between the Contractors and the Client’s Engineer involved in the construction of the London Tunnel Contracts

Jan 1, 2003

By Steve Kral

The Northwest Mining Association (NWMA) has been an advocate for the U.S. mining industry since 1895. For several decades, the organization has represented mining members located mostly in the Northwest and some southwestern Canadian provinces. Today, though, the NWMA?s membership is located in 42 states and seven provinces and has become a national voice for the mining industry. So, during the association?s 119th and final meeting as the NWMA, a name change was announced. The organization is now called the American Exploration and Mining Association (AEMA). But that?s not all that has changed, according to the association. The new name reflects more closely the diversity and location of the AEMA?s membership. It will still be an advocate for the mining industry, dealing with land, environmental and community issues on state and federal levels. The conference, held in December 2013 in Reno, NV, attracted about 2,500 attendees. And the accompanying exhibit included 230 equipment and service suppliers in 246 booths. Technical programming ran the gamut of mining industry issues and technologies, including surface and underground mining; high technology systems and automation in mining, metallurgy and exploration; along with social issues, finance and safety. The following is a sample of some of the sessions.

Mar 1, 2014

By Trenton Cohen, Joseph McDivitt, Shimi Tzobery, Joseph Sinacori, Scott Zylstra

The 2-mile Beach Interceptor Sewer Tunnel was constructed in 1954 to then-current mining and construction standards. Due to its lifespan and deteriorating condition it is now being stabilized and rehabilitated using conventional excavation and ground support. At its southern end, below the prestigious Three Arch Bay community, the original tunnel alignment passes under a historic landslide where the tunnel was sand-backfilled and capped by bulkheads in 1957 due to severe and caving ground conditions. Video footage of the existing 21- inch clay pipe showed that the pipe is severely damaged, which could potentially cause a catastrophic pipeline failure and sewage spill into the Pacific Ocean. This paper summarizes the thorough investigation and design process, tunnel realignment construction and monitoring, and the notable cooperation between all parties to overcome the project risks.

Dec 1, 2022

By James C. Hower, B. K. Parekh

Introduction The purpose of coal preparation is to improve the quality of coal to make it suitable for a specific purpose by (1) cleaning to remove inorganic impurities; (2) sizing-crushing or screening, or both; and (3) special treatment, such as dedusting. The properties and quantities of impurities in coal are of major importance in the design and operation of steam generating equipment. Although boilers are often designed and equipped to use a wide range of coals, no boiler will perform equally well with all types of coals. All coals have certain properties that place limitations on their most advantageous use. These limitations are especially stringent for many of the older installations. Because of a general lowering of quality of raw coal in recent years, the need for coal cleaning has significantly increased. Among the factors contributing to the need for increased coal preparation are (1) increased demand for quality brought on by market and environmental requirements; (2) increased extraneous dilution caused by mine, health, and safety laws; and (3) depletion of the higher-quality coal seams. The major characteristics of coal and impurities from the standpoint of mechanical cleaning are particle size composition, generally called size consist; density differences; the relative friability of the coal and its associated impurities; hardness; and strength. Some of the other factors related to preparation are petrographic composition and rank. RANK CLASSIFICATION Coal is a general designation for a great number of solid organic minerals with different compositions and properties; all are rather rich in carbon and have a dark color, generally black. Next to mineral oil and kerogen, coal is the most important reservoir of carbon in the world. Carbon is an indispensable necessity of life as well as the main source of energy. Coals are found in stratified deposits, sometimes at great depths. All coals owe their origins to slow decomposition and chemical conversion of immense masses of organic material. As found in seams, coal is a heterogeneous mixture of organic and inorganic materials. Not only are there large differences in the properties of coal originating from different seams, but also in coal removed from different locations in a single seam. A genetic relationship exists between peats, brown coals, lignites, biturninous coals, and anthracites. As a whole, the process of coal formation, or coalification, proceeds as a continuous transformation of plant material, each phase characterized by a degree of coalification, or rank. As a measure of this rank, the carbon content or some related parameter can be used.

Jan 1, 1991

By Thomas W. Smelser

A full-scale geotechnical model of a 15-foot (4.6 m) wide coal mine entry in correlation with computer finite-element analysis (FEA) is being employed at the Bureau of Mines Spokane Research Center for basic research on roof-bolt support systems. Physical and computer modeling of various coal mine roof-bolt reinforcement systems will increase our basic knowledge of how roof supports function. This information, in correlation with computer FEA and underground verification tests, will provide a basis for establishing safer, more cost- effective roof control plans and help establish guidelines for employing fully grouted and conventional bolting systems. The basic rationale for the research, research approach, methods and equipment employed, results to date, and future research plans are described in this paper.

Jan 1, 1982

By A. F. Agnew

Discussion by A.E Agnew Strachan's paper summarizes a wealth of data on water-storage dam "incidents" published by USCOLD and ASCE in 1988, together with a review of tailings-dam incidents published by USCOLD in 1994. The data is summarized by text and 11 histograms. The histograms present a useful compilation of these data, although the patterns within the histogram blocks did not survive the Mining Engineering printing process - so their usefulness is impaired. Unfortunately, the text discussion is too cursory and does not highlight the significant relationships among the various causes of the incidents. Four paragraphs of text and Fig. 1 were devoted to water-storage dams, but the discussion is too sketchy, and Fig. 1 is unclear. Important statistics that could be uncovered are: •the total number of dam incidents tabulated were 500+, •earth embankments constituted 73% of those in operation and •incidents related to earth embankments were 75%, of which dam failures accounted for 24%, major repairs accounted for 42% and accidents accounted for 34%. Strachan concluded that "the majority of the dam failures are associated with overtopping (p. 49), and that the majority of incidents are associated with spillway and other facility structures" - although this is difficult to discern from Fig. 1. Confusion regarding Strachan's use of the terms "dam failures" and "incidents" is compounded by his use of "failures" and "accidents" in one paragraph of his Introduction section followed by his use of "incidents" in the next paragraph. Getting to the meat of Strachan's important paper, the tailings-dam incident survey (USCOLD, 1994), the connection between Figs 2 through 11 seems obscure. First, in the four paragraphs of introductory material, one learns that "incidents consisted of failures, accidents, seepage and other incidents of performance that did not meet design criteria" (p. 50). One does learn the helpful caveat that "structures not related to mill tailings were not included in the review" - so that the Buffalo Creek (West Virginia in 1972) and Aberfan (Wales in 1966) coal-mine failures, together with the ongoing metal-mine remediation work at Summitville (Colorado) do not muddy the waters of his paper. The all-too-brief discussion of the data shown in Figs. 3 through 11 (185 dams in USCOLD plus 26 dams in UNEP) reveals the following: •Figure 3: 57% of the incidents (failures and accidents) occurred with dams less than 20-m (66-ft) in height. •Figure 4: 63% of the incidents were due to failures alone (subset of Fig. 3). •Figure 5: Active dams had 82% of the accidents and 93% of the failures. •Figure 6: Types of dams (upstream, water-retention, downstream, centerline and "unknown") separated according to incidents. •Figure 7: Breaks out the incidents in Fig. 6 by failures, accidents and ground water. •Figure 8: Breaks out incidents by type (overtopping, slope stability, earthquake, foundation, seepage, structural, erosion, mine subsidence and "unknown"). •Figure 9: Separates Fig. 8 data into active and inactive dams. •Figure 10: Separates Fig. 9 data into failures and accidents. •Figure 11: Same as Fig. 8, but broken out by tailings-dam type (Fig. 6). Figures 6 and 7 show that most of the failures are associated with upstream or "unknown" types. Figure 9 shows that the leading causes of incidents for active dams

Jan 1, 2003

By Paul M. Jr. Musgrove, Thomas D. Henderson, Mark B. Nesbitt

Introduction History. Vat leaching operations began in October 1953. Since that time, about 4.2 million tpy of oxide ore averaging 0.72% copper have been treated. Economic conditions, improved operating methods, and increased production facilities have allowed the ore grade to be reduced over the years. The average ore grade was 0.84% Cu during the 1950s, 0.68% in the 1960s, and was 0.50%, or below, during the 1970s. By 1961 some 35 million tons of oxide ore had been removed from the mine, exposing the underlying sulfide ore body. A 5,000¬ tpd concentrator was constructed and put into operation to treat the sulfide ore in November 1961.1 The original crushing plants were used for both oxide and sulfide ores, but by adding a third crushing shift, six days per week, the total ore treated was raised from 12,000¬17,000 tpd. Dwindling oxide ore reserves prompted expansion of the concen¬trator to 13,500 tpd in 19672 so that exhaustion of known reserves of both ores would occur at nearly the same time. Again, no additional crushing facilities were added during the expansion. It was anticipated that the treatment rate of oxide ore would be reduced from 12,000 to about 9,000 tpd. Instead, the addition of two crushing shifts per week and improved operating procedures have increased the treatment rate to 26,500 tpd-13,000 tpd to the leaching plant and 13,500 tpd of sulfide ore treated in the concentrator. Geology. The Yerington ore body is a disseminated porphyry copper deposit where a quartz monzonite porphyry intrusive contains the major part of the ore values, with some copper mineralization found in the adjacent granodiorite and other rocks. The geology of the Yerington Mine was aptly described by J. R. Wilson (Mining Congress Journal, June 1963). The ore body is one of few porphyries where geologic conditions were optimum for the formation of an important concentration of oxidized ore with minimum economic effect of secondary enrichment. The principal mineral in the oxidized zone is chrysocolla, which irreg¬ularly occurs dispersed throughout the rock and as narrow seams along fissures. The grade of the ore in the oxidized zone is generally the same as in the primary sulfide below, although some massive concentrations do occur as vein-like fissures and as filling of breccia zones. Cuprite, tenorite, melaconite, malachite, and azurite occur but are not abundant. Lying between the chrysocolla horizon and the primary sulfide is a transition zone whose limits are irregular but seldom with vertical range exceeding 50 ft. Chalcocite, cuprite, melaconite, native copper, and chrysocolla occur superimposed on the primary sulfides. Chalcocite replacement of chalcopyrite, as well as secondary chalcocite, do occur. The primary sulfide minerals are chalcopyrite and pyrite, with minor amounts of bornite and covellite. There are no appreciable gold or silver values, and molybdenite has rarely been noted.

Jan 1, 1985

By B. W. Cavender

Innovative mining and metallurgical operating techniques or processes can be identified and developed by systematically analyzing change as it occurs within the mine, plant, technology, or industry. Sources of change to be monitored for innovative opportunities include unexpected successes or failures, incongruities between perceived and actual events, process needs, changes in perceptions, and the development of new knowledge. Innovation can be effectively organized, practiced, and managed. The perception of change as an opportunity rather than a threat is mandatory, as is the systematic measurement of innovative performance. Innovation is enhanced by specifically-designed policies regarding organizational structure and staffing, daily management practices, and compensation and incentives.

Jan 1, 1994

By Nick Barton, Khosrow Bakhtar

Two plate load tests of 1 m2 area were per- formed in a pressure tunnel at the Rocky Mountain Pumped Hydro Project. Reaction for the 250 tons loading in this 10.5 meter diameter tunnel was provided by deeply anchored, diverging rock bolts, eight per load frame. Pressure build up to 2.5 MPa was provided by circular flatjacks. Rock deformation was recorded at depths of approximately 0.3, 0.9, 1.2, 1.8 and 3.3 meters using axially located multiple position borehole extensometers. The tests were performed in representative units of massive shale and thin to medium bedded siltstone. Stress was built up in four equal steps to 2.5 MPa, held constant for one week for creep monitoring, then unloaded, reloaded and unloaded over a period of one day. The most deformable unit was the massive shale which exhibited 1.3 mm of permanent deformation at the surface after the first loading and unloading cycle, which included 0.36 mm of creep. After the second loading-unloading cycle, the permanent deformation had increased to 2.6 mm, following a maximum deformation at the surface of approximately 3.6 mm. At the maximum stress of 2.5 MPa, the tangent modulus averaged 0.4 GPa when loading, and 0.3 GPa when unloading. The thin to medium bedded siltstone exhibited only 0.17 mm of permanent deformation at the surface after the first loading-unloading cycle, which included only 0.05 mm of creep. After the second loading-unloading cycle, the permanent deformation had increased to 0.27 mm, following a maximum deformation at the surface of approximately 0.53 mm. At the maximum stress of 2.5 MPa, the tangent modulus averaged 6.2 GPa when loading and 21.9 GPa when unloading.

Jan 1, 1986

By J. Drelich

An improved experimental procedure to measure contact angle has been consolidated with coal surface preparation involving polishing with abrasive paper, alumina powder, and a cloth, followed by ultrasonic and mechanical cleaning. Specifically, the captive-bubble measuring technique has been compared with the sessile-drop technique and the former has been recommended for the examination of the hydrophobic properties of coal surfaces. Results of the research program, which is currently under way, on the examination of the effect of the nature, amount, size and distribution of mineral inclusions in coal on its wettability are briefly reviewed.

Jan 1, 1999

By Yassine Lahmadi, Edoardo Trivellato, Christian Chereau, Bénédicte Robert

Within the framework of the adaptation of the South-East European Technicentre (Technicentre Sud-Est Européen TSEE), SNCF Voyageurs appointed Pini with the project management mission (MOE) for the design and construction monitoring of a road tunnel. This investment has a dual function: during the site transformation phase, it facilitates the work logistics (and shorten traffic flows); and in the operating phase, it is intended to ease all movements on the site over the long term. This is a limited-length gallery (50 meters) to be performed in conventional excavation below Poniatowski Avenue (Paris 12e). The excavation, crossing the entire width of the boulevard, constitutes a major challenge, given the very low coverage (less than 5.5 m), and the surrounding main infrastructures. The same project mis- sion includes the design of the tunnel accesses, via reinforced-concrete frame structures. The targeted design questions several aspects of its execution framework, and particularly, continuous operation must be guaranteed to the neighboring networks during the works. The installation of an umbrella- pipe all along the excavation profile, the progression in divided sub-sections, and the implementation of a complex monitoring system are hence key elements for limiting and controlling any deformation. An exhaustive 3D finite element modelling was performed, taking into account the detailed phasing of construction (pre-support, excavation in divided section, preliminary support and definitive lining), to dimen- sion the structures, and, overall, to analyze the impacts on the neighboring structures and facilities. During the execution phase (planned for mid-2024), monitoring activities with back-analyses as close as possible to the works are planned.

Jun 23, 2024

By P. A. Cornejo

Blastings always generates induced vibrations through seismic wave, these are lost energy from the blasting and therefore causing the disturbance of slopes and structures near the blast source. Most of the components of an open pit mine have to reach a physical stability, especially during its closure process. Aiming to develop a vibration prediction model using the historical records from an open pit mine located on Peru, this research has two main focuses depending on the distance from the blast source to the structure: to protect the final slopes and to protect the villagers houses. Both are based on the Devine model of the Square Root Scaled Distance (SRSD) to predict the Peak Particle Velocity (PPV). The Mid field model, where is found mainly final slopes from the pit, limited by the failure criteria of McKenzie based on the geo mechanical properties of the rock mass. The Far field model ranges distances where are located the most community households, limited by the German rule DIN 4150 for highly sensitive structures. Both scenarios resulted on a distribution abacus to limit the weight of used explosives to get the best operational advantage and structure safety.

Mar 2, 2022

By Isabel F. Barton, MarkD. Barton, Christian A. Rathkopf

Molybdenite is the world’s principal source of rhenium (Re), a critical element in multiple high-tech applications. However, the Re contents in molybdenite vary by orders of magnitude on scales ranging from single grains to whole deposits. In order to better understand the systematics of this variation and what geochemical factors control molybdenite Re concentration, and hence overall Re resources, we examine global patterns in molybdenite Re contents through a compilation of > 3000 measurements of Re in molybdenite from > 700 mainly ore-bearing moderate- to high-temperature hydrothermal systems of different types. Our results are similar to but expand on those of earlier studies. Rhenium concentration in molybdenite has a lognormal distribution and varies systematically with type of geologic system, intrusive lithology, and Mo grade. The lowest-Re molybdenite occurs in greisens (geometric mean 1 ppm ± a multiplicative standard deviation of 9), quartz vein-hosted W-Sn deposits (2 ± 5 ppm), unmineralized granites and granodiorites (12 ± 8 ppm), intrusion-related deposits (24 ± 8 ppm), and porphyry W-Sn deposits (16 ± 11 ppm). Rhenium is most enriched in molybdenites from volcanic sublimates (23,800 ± 5 ppm), with skarn Fe and Au (560 ± 5 ppm and 540 ± 3 ppm respectively) and porphyry Cu and Cu-Au deposits next (470 ± 4 and 430 ± 7 ppm respectively). Among porphyries, skarns, and quartz vein-hosted deposits, Re is most highly concentrated in molybdenites from Cu and Au systems and its concentration decreases systematically through Cu-Mo, Mo, Sn, and W deposits. In nearly all cases, molybdenites from systems associated with intermediate igneous rocks contain more Re than molybdenites from systems of the same type with more felsic rock associations. The disparity between Re contents of molybdenite in felsic and intermediate systems is largest for porphyries, quartz vein-hosted, and skarn deposits and is near zero for subeconomic or barren granite and granodiorite Mo systems; felsic intrusion-related deposits have slightly higher molybdenite Re than their equivalents associated with intermediate intrusions. In most systems, molybdenite Re content does not correlate with metal grade, but may have an inverse correlation with Au grade in intrusion-related deposits (based on a small number of data points) and does exhibit a strong inverse correlation with deposit Mo grade. Dilution of Re through larger amounts (higher deposit grades) of molybdenite explains about 40% of this correlation, but the relative enrichment of Re in molybdenite from low-Mo deposits must also reflect some selective enrichment of Re/Mo in porphyry Cu systems compared to porphyry Mo systems. We found no evidence for secular increase or other systematic temporal variation in molybdenite Re content. The data regarding the use of molybdenite Re content as a proxy for mantle influence are ambiguous. Nearly all observed empirical correlations can be traced back to differences in redox state and sulfide concentration, the two geochemical factors identified here and by previous experimental work as the controlling influences on Re mobility under hydrothermal conditions. Hydrothermal systems with reducing conditions (W- and Sn-rich) tend to have low molybdenite Re even though compiled whole-rock data indicate that their source rocks have as much or more Re as those of more oxidized systems (e.g., Cu-rich). Vapor-phase exsolution, crustal assimilation, and mixing with external fluids may all enrich molybdenite Re concentrations in individual deposits and deposit types, but their extent and importance in overall hydrothermal concentration of Re is uncertain. Thus, it appears that the available molybdenite Re resource in an ore deposit largely depends on how the deposit’s redox and sulfidation conditions have varied over time and space during the timespan of hydrothermal activity. Oxidized, high-sulfide conditions tend to concentrate Re in molybdenite, whereas reducing conditions tend to leave Re dispersed at low concentrations in the bulk rock.

By S. Al-Thyabat

In this work, the floatability of Jordanian phosphate slime (-38 µm) was evaluated in a batch column flotation cell, 100 cm high and 5 cm inner diameter. Flotation was conducted using sodium oleate as a collector and methyl isobutyl carbinol (MIBC) as frother. Rougher flotation yielded concentrate assaying 29.19% P2O5 with 90.29% recovery at the following flotation parameters: 2.6 cm/s superficial gas velocity, 20 ppm frother dosage, 0.205 mM collector concentration and 40% weight solids. It was also found that conditioning with the same collector dosage but with a different solids weight percent gave different flotation results. However, pulp collector concentration was the key operating parameter; increasing collector dosage at the same solids weight percent decreased flotation recovery by 3%, while increasing solids weight percent at the same collector dosage increased phosphate recovery by 18%.

Jan 1, 2011

By Chee S. Theng

As the 2018 president of the Society for Mining, Metallurgy & Exploration Inc., I am pleased to present the 2018 issue of the Transactions of the Society for Mining, Metallurgy & Exploration Inc., Vol. 344. A significant portion of the contribution that we make as a professional society is the publication of professional and technical papers that accelerate the advancement of scientific knowledge and enable the transfer of technology. Communication within the mining community is the key to a successful society. This technology exchange continues a tradition that dates back to the 1871 meeting of 22 mining engineers in Wilkes-Barre, PA, that resulted in the founding of the American Institute of Mining, Metallurgical and Petroleum Engineers (AIME). Those individuals envisioned that these transaction volumes “would form a most valuable and greatly needed addition to our professional literature.” This volume fulfills that pledge. The 2018 Transactions consists of a total of 59 technical papers, encompassing all 25 papers published in 2018 in the Technical Papers Section of Mining Engineering (Vol. 70) and all 26 papers published in 2018 in Minerals & Metallurgical Processing (Vol. 35). Additionally, this volume contains 8 papers that are being published for the first time in this issue. The papers presented in this volume were written by some of the most distinguished professionals in the industry worldwide. All of the technical papers were peer-reviewed. The process of review and publication requires much hard work by authors, reviewers and our Publications staff. As the 2018 president of SME and on behalf of all our members, I would like to extend our gratitude to all whose volunteer efforts contributed to the publication of this volume. The new year brings an exciting change. The publication of Transactions will cease with this volume. Instead, our Minerals & Metallurgical Processing journal has the new name of Mining, Metallurgy & Exploration (MME), and Transactions as well as the Technical Papers Section of Mining Engineering are incorporated into MME. The journal is published in partnership with Springer Nature, and all SME members have free electronic access to the journal.

Jan 1, 2018

By R. Scheffel, R. Washnock, G. Zarate

"The second survey of global copper leaching operations has been completed, the data published in 1998 has been updated. A survey questionnaire was sent to 40 identified copper leach operations around the world including those leach properties still in operation that responded to the 1998 survey. This paper lists the results of 26 operations that responded to the survey. Selected information from the survey is represented in graphical form. INTRODUCTION Copper leaching was first performed by truck dumping huge monolithic stockpiles of ore and flooding the surface with leach solution or lixiviant with little understanding to the parameters that support optimum recovery of the metal. Heap leaching has evolved into a controlled process whereby a complex low grade ore is stacked in shallow lifts (under 10 m in most cases). The ore is usually crushed and agglomerated, conveyor stacked on an engineered containment system (leach pad) and irrigated in a controlled manner. The lixiviant chemistry is designed to extract the optimum amount of metal from the ore. At first glance, heap leaching appears to be simple in nature. In fact, it is a very complex process. A plethora of technologies such as material handling, environmental control, analytical techniques, solution chemistry, hydrology and many others contribute to the design and operation of a heap leach. Heap leaching requires an inter-disciplinary approach between geologists, mining engineers and metallurgists. Many operational factors affect heap leaching. The process must address climatic factors, flexible operation, quality control before and after leaching, physical characteristics of the ore, geology, mineralogy, reagent consumption, solution application rate and methods (wobblers or emitters), particle size, and favorable conditions for bacterial growth and survival. Predicting, troubleshooting, and optimization of leach recovery is a significant challenge when considering the number of variables involved and their interactions The survey updates many of these key operating parameters to the current state of the art. It should provide the reader an excellent benchmarking summary of these factors on a site-by-site basis."

Jan 1, 2016

By Thomas C. Shrake

The Lomas Bayas copper property is located93 km (58 miles) east of Antofagasta, Region II, Chile (Fig. 1). The deposit was discovered in 1880. The deposit produced intermittently until 1992. Production at Lomas Bayas took place in high-grade veins and breccias mined underground. During 1991, Empresa Minera Mantos Blancos SA (EMMB) optioned the property from Compania Doña Ada SA. Doña Ada maintained the right to continue mining the ores by open-pit and block-caving methods and hauling the ore to its plant located60 km (37 miles) to the north. EMMB conducted exploration and column test programs. On May 9, 1994, Compania Minera Gibraltar Ltda.(CMGL) signed a purchase option agreement to acquire the Lomas Bayas property. CMGL conducted 8,612 m(9,490 ft) of reverse-circulation drilling, 2,028 m (6,650ft) of diamond drilling, a series of metallurgical tests and geologic mapping. The company then decided to exercise its purchase option.

Jan 1, 1996

By Michael L. Ogilvie

The proportion of underground coal production as a percentage of overall Australian production has fallen in the last 10 years, with underground production remaining more or less static at about 53 Mt (58 million st). However, underground coal mining remains a viable industry in Australia, due to use of modern longwall mining systems. In 1993-1994, 26 longwalls were in operation, with total production exceeding 39 Mt/a (43 million stpy). Some of these longwalls achieve productivity levels approaching efficient opencut operations, and in some cases, they exceed them. These high-production longwall mines are not without problems when depth and distances from outcrop increase and the gas content of the seams approaches or exceeds critical limits. When gas content of a coal seam exceeds 6 m3/t (233 cu ft/st), gas flows into the mine may be sufficient to interrupt production from time to time.

Jan 1, 1995

By Vince Saporito

Miners work in dangerous terrain, around the clock, with heavy equipment. Is there room for improvement in safety and standardization in the mining industry? Recent history would suggest there is a need for action. At a 2011 Spring Thaw conference in Denver CO, one speaker commented, ?We are having a number of incidents with workers getting ?pulled? into rollers or ?trapped? at transfer points when trying to manually clean (it) while the conveyor is still in motion.? It?s a troubling thought. These actions are specifically prohibited under U.S. Mine Safety and Health Administration (MSHA) regulation 57.14202. Another official from MSHA earlier this year indicated with today?s technology and policies presently in place, ?we should not be repeating the same incidents and violations year after year as we currently do.? But we are doing exactly that.

Jan 1, 2012

By Don S. McCoy, W. Joseoph Schlitt, Donald B. Swanson

Introduction Contract miners have long played an important role in the minerals industry. Historically, these were individuals who worked as underground miners and were paid by the ton or the day. These hardy types still ply their trade in the industry. However, today the term "contract miner" generally refers to an independent contractor who supplies the people and equipment needed to conduct surface mining operations for an owner or lease holder. At one time or another, contract miners have probably handled virtually every mineral commodity from sand, gravel, and stone quarrying to mining uranium and precious metal ores. In today's market, though, contract mining appears to be concentrated in just a few areas. These include precious metal mines, various types of solid fuel operations, and reclamation of abandoned mines. This article covers market areas, contract mining organizations and services, and their advantages and disadvantages. Gold and silver mines Although exact figures are not available, contract mining represents a significant element in the precious metals segment of US mining. For gold and silver, the growth in contract mining appears to be paralleling the overall growth in mining activity itself. Nevada is the largest gold producer in the US. The latest available data (1985) on open pit gold/ silver mines is summarized in Table 1 (Nevada Division of Mine Inspection, 1986). These figures show that contractors mined nearly half of the ore in 1985. Total tonnage mined, of course, was much higher for both owners and contractors. Assuming an average stripping ratio of 2.5 to 1, the total daily mining rate for the contractors was more than 145 kt (160,000 st). This translates into a contract mining rate of about 36 Mt/a (40 million stpy) based on 250 operating days a year. This approximate 50-50 split between owner and contractor also appears to hold for the future. Metals Economics Group (1987) published a survey of 51 short-range and 54 long-range precious metal projects being considered throughout the US. Contacts with owners, requests for proposals, and past corporate philosophies all suggest that about 55% of the open pit operations scheduled for the near-term will be contract mined. This represents an estimated 26 kt/d (28.5 stpd) of ore. A similar assessment of the long-term projects indicates that about 12 kt/d (13,000 stpd), or just under 50% of the open pit tonnage will be contract mined. There are several reasons why gold and silver represent such an attractive opportunity for contract miners. One is that many properties are owned or leased by individuals or partnerships that are essentially entrepreneurial. Many of these owners or lease holders have minimal mining experience. They must therefore either rely on contract mining organizations, sell an interest in the project to another mining company that will become the operator, or hire an experienced management team. For about the same reason, junior mining companies also represent good prospects for contracting. This is because most junior companies focus on exploration. They would prefer to spend their generally limited funds on drilling programs. Thus, they tend to minimize additional capital requirements by using contract miners or farming out the property to another mining company. Another good reason for using contract miners is the size of the deposit. Many properties are so small that their reserves will not support the capital expenditures

Jan 12, 1987