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Jan 1, 1882

The Yanacocha Project is the first foreign investment in Peruvian mining since Cuajone (1976). Three years after the project began, it has become the largest producer of gold from heap leach operations in the world and the top producer in Latin America. The success of Minera Yanacocha (MYSA) opens a new chapter in Peruvian mining with the exploitation of its widely spread gold deposits and has attracted the interest of foreign investors in Peru's ample mineral resources. Construction began on August 1, 1992 and after twelve months of arduous work, the first gold bar was poured on August 7, 1993 from ore from the Carachugo mine. In 1993, Minera Yanacocha produced 81,000 ounces of gold and 304,000 ounces in 1994 (40% above budget). Production is expected to exceed 500,000 ounces in 1995 with the start-up of operations in the Maqui Maqui mine. This paper presents a summary of MYSA's experiences during its first two years of operations in the areas of mining, ore processing, environmental protection, loss control and community assistance. The paper also shows that MYSA's successes are not only due to the richness of the deposit, but also to the combination of a number of factors basic to the project's success, such as: an economic policy favoring investment in Peru, the availability of highly qualified local personnel to facilitate the transfer of technology from the United States and the desire and determination of the partners to carry the project forward in an initial atmosphere of uncertainty and terrorism.

Jan 1, 1996

By Paul M. Tyler

Graphite is an essential war mineral and for that reason has received much attention from the standpoint of national defense. During the World War the situation with respect to graphite supplies, though it never became acute, caused considerable concern. Even in peace time, however, graphite has aroused more interest than the actual size of the industry seems to warrant. Despite this wide interest the facts of the industry do not seem to be generally known. Often there has been an almost total disregard of the essential' economic and technical problems involved. Long ago Bastin3 made the following statement; in a Government' report: "To-day there are more abandoned mines and mills in the United States than the number in operation * * *. In the number of times' some of these properties have changed hands in the course of a few years, there is a record of misrepresentation and disappointment that can hardly be equaled in any other branch of mining; and many properties have been notoriously associated with stock manipulation of doubtful character." According to one authority fully 600 graphite mines have failed in the United States, and the record shows that of all these properties scarcely a score have ever succeeded in operating for as much as a year or two. More than 40 mines have been worked at various times in the State of New York alone and at least that many in Alabama. Throughout the country, in fact, there are scarcely a dozen States in which efforts have not been made at some time to exploit graphite deposits. At the present time the list of mines that can be classed as at all active is reduced to less than ten. Failures inevitably occur in all lands of mining, but the disheartening feature of the record of graphite mining in this country is that so few ventures have even paid back the money put into them and. that none has been a conspicuous success.

Jan 1, 1929

By Pedro A. Netto, Sergio N. Monteiro, Foluke S. de Assis, Rômulo L. Loiola, Frederico M. Margem

Banana fibers are among the lignocellulosic with great potential for use in polymer composites, such as the variety from the Musaceae family, due to its low density and good mechanical properties. In this work, epoxy matrix composites incorporated with continuous and aligned banana fibers were tested for their flexural behavior. Specimens with up to 30% in volume of fibers were bend-tested until rupture. The results showed an increase in both the composite mechanical strength and the stiffness with incorporation of these fibers. A fractographic analysis by SEM examinations a moderate adhesion mechanism between the banana fiber and the epoxy matrix. This mechanism is apparently responsible for the improved performance of the composites.

Jan 1, 2015

By R. G. Votteler, A. C. Brent

"The first in this series of two papers, on the potential of renewable electricity sources for mining operations in South Africa, investigated the internal structure of mining corporations to evaluate feasible alternative electricity sources that were identified as through earlier research. The purpose of this paper is to combine current knowledge about the external macroeconomic and the internal environments to produce a clear picture of how renewable sources of electricity could perform from the perspective of mining corporations in South Africa. The multi-attribute value theory (MAVT) approach was adapted to structure the research and results. The model was fed with real-time data provided from five different energy companies and four mining corporations operating in South Africa. The results show that the performance of hybrid versions of the currently used electricity sources (diesel generators and Eskom grid connection) with solar PV and onshore wind is favourable compared with the current sources alone. The advantage of diesel generators is significantly greater than that of the Eskom grid connection. By combining the macroeconomic influences with the MAVT results, hybrid solar PV versions are identified as having the greatest potential. In second place are hybrid wind solutions, which have the shortcoming that good wind conditions occur only in coastal regions where there are fewer mining activities. Geothermal hybrid versions are the least favourable owing to the lack of service infrastructure and high initial investment costs.IntroductionRecent developments in the macroeconomic environment necessitate an investigation of the internal structure of mining corporations to evaluate possible alternative electricitygenerating sources (Roehrl and Riahi, 2000). To be able to combine current knowledge of macroeconomic factors and the internal structure of mining corporations, the research process is presented in two papers. The first paper (Votteler and Brent, 2016) investigated the internal structure and argued that a strategic tool should be used to evaluate electricity sources from the perspective of mining corporations. The multi-criteria decision analysis (MCDA) approach was selected as the most appropriate strategic tool. Based on a literature review of previous similar MCDA approaches in energy planning, it was concluded that no adaptation of MCDA methods could be found from a corporate, mining, or South African perspective. Finally, the paper investigated the internal evaluation structure in collaboration with mining corporations, by identifying the criteria they use to evaluate electricity sources."

Jan 1, 2017

By B. Das

Waste water produced from coal preparation plants posses several problems during dewatering and solid/liquid separation. The natural sedimentation rate of the particles present in colloidal and finely divided suspended form is very slow. Flocculation technology is being applied in most of the coal washeries to recover water which is being accomplished through the use of inorganic salts, polymeric flocculants or both depending on the chemical and physical characteristics of the pollutants present in the waste water. The waste tailing water from Piperware coal preparation plant, Central Coalfield Limited (CCL), India, is highly turbid containing ~ 16000 NTU with negative surface charge in the pH range of 2 to 10. Polymeric flocculants in conjunction with fine magnetite is investigated to achieve faster settling rate with lowest level of water turbidity. The conditions affecting the interaction between the reagents and the turbid particles present in the tailings water are investigated. It is possible to bring down the turbidity of the water to < 90 NTU from very high turbid tailing water by using 2 mg/L of the polymeric flocculent in combination with 0.1 g/L of magnetite at natural pH of the tailing slurry. It has been found that finely divided positively charged magnetite particles in combination with the flocculent selectively coat the negatively charged impurities present in water and thereby increase the settling rate under the influence of a magnetic field.

Jan 1, 2014

By E. A. Rychkun

"For the last 700years of recorded economic history, man has been subjected to alternating inflationary and deflationary patterns. Through this period of time, a severe deflationary pattern has developed approximately every 55 years, creating 12recordable occurrences. Through the last two centuries, this severe deflationary phenomenon has come to be known as a depression. As these depressions have repeated themselves regularly, they are cyclic. This in turn leads to the question of whether the 13th cycle will also repeat itself in the form of a depression. As this cycle is now 51 years old, we must consider the possibility at about 1984.In analyzing a 700-year record of consumer prices in Southern England, the 55-year cycle appears to vary in shape and intensity. This varying phenomenon is due to the effect of longer cycles upon which each one ""rides "". Because each cycle effectively rides on the next largest, which in turn rides on the next largest and so on, the combined measured effect of all cycles together at any point in time is always unique. This means that anyone cycle can never repeat itself in an exact identical manner. The combined effect therefore is what we observe in the form of prices and, as cycles interact, variations in deflation are produced . The ""science"" of economics attempts to quantify and develop theory on situations which are never identical and hence can be conservatively classified as a useless predictive tool.This means that more unconventional approaches may be required to predict our economic future. In looking at previous depression cycles, it is possible to recognize similarities in human behaviour patterns and hence the resulting economic movements. These behaviour patterns create major events or influencing factors which set the scene for a major deflationary condition. The way in which these factors occur, however, is not predictable. As more and more of these similar events are identified in each cycle, we can increase our confidence on the probability of the last event occurring (a depression). By also unravelling the set of larger cycles, we can determine the potential combined effect at any point in the future.This paper presents a system of cycles ranging from 800 years to 3 years which appear to operate in our economic system. By so doing, a long-term projection into the next century can be made. Finally, the paper deals with the main controlling similarities within the depression cycle, to show that a comparison with our current cycle implies that a major deflationary collapse in the mid 1980&apos;s is virtualy inevitable."

Jan 1, 1980

By C. A. Pickles, K. Mackowiak

Black Thor chromite ore from the Ring of Fire deposit in Northern Ontario was carbothermically reduced in a microwave system to produce a ferrochromium alloy. The as-received ore contained 43.0% Cr2O3, 19.9% Fe2O3, 14.5% MgO, 13.4% Al2O3, and 7.0% SiO2. Activated charcoal was utilized as the reducing agent. Firstly, TGA/DTA and permittivity studies were carried out in order to determine the relationship between the reduction process and the microwave susceptibility. Secondly, microwave reduction experiments were performed on the chromite ore. The variables investigated were; the amount of carbon, processing time, input power and type of atmosphere. A maximum chromium grade of 76.1% and a chromium metallization of 82.7% were obtained for a processing time of 20 minutes, a power input of 800 W, and a carbon addition of 15% in an argon atmosphere.

Jan 1, 2017

By Denis Tepavac, Mark Trim

Structural performance of fiber reinforced concrete (FRC) depends on its ability to carry tensile forces after cracking. Australian Standards AS5100-2017 and AS3600-2018 are the only available design standards that establish a test procedure to determine strength and toughness of an FRC in direct tension. Direct tensile testing of fiber reinforced shotcrete samples was performed to determine if the model and guidelines in AS5100/3600 were applicable to shotcrete; all previous testing was from cast samples. In addition to direct testing, micro CT-scanning was also performed. The paper presents tests performed, results, and how the tests could be used on future projects. In addition, a brief summary is provided of the guiding structural mechanics used for estimating residual tensile strength and test methods utilized to verify those estimates.

Jun 13, 2023

By Dale Verran, Jared Orynik, Chad Sorba, David Bronkhorst

Denison Mines Corp. (“Denison”) has a 90% interest in the Wheeler River Uranium Project (“Wheeler River”) located along the eastern edge of the Athabasca Basin in northern Saskatchewan between the Key Lake mill and the McArthur River uranium mine. The project is host to the high-grade Phoenix and Gryphon uranium deposits, discovered by Denison in 2008 and 2014 respectively, which include combined Indicated Mineral Resources of 132.1 million pounds U3O8 (1,809,000 tonnes at an average grade of 3.3% U3O8). The Pre-Feasibility Study (“PFS”), completed in accordance with NI 43-101 in September 2018, is highlighted by the selection of the In-Situ Recovery (“ISR”) mining method for the development of the Phoenix deposit, with an estimated average operating cost of $4.33 (US$3.33) per pound U3O8. Phoenix is the highest-grade undeveloped uranium deposit known globally, including Indicated Mineral Resources of 166,000 tonnes at 19.1% U3O8 for 70.2 million pounds U3O8. The paper aims to provide a summary of Wheeler River and an overview of the proposed development of the Phoenix and Gryphon deposits according to the PFS completed for the Project. Further details regarding the PFS, including additional scientific and technical information are described in greater detail in the NI 43-101 Technical Report titled "Pre-Feasibility Study for the Wheeler River Uranium Project, Saskatchewan, Canada" dated October 30, 2018 with an effective date of September 24, 2018. A copy of this report is available on Denison's website and under its profile on SEDAR at www.sedar.com and on EDGAR at www.sec.gov/edgar.shtml.

Jan 1, 2020

By John C. Bowling

Many recent mine developments in North America are located in remote northern regions with extreme winter temperatures in the range of -20oF to -60°F. In addition, many locations are subject to very heavy snowfall. This paper discusses some of the key considerations in the planning and design of mine plant buildings, particularly concentrators, located in these regions. SUMMARY & CONCLUSIONS The subject is considered under three main headings: I. Building Out line and Structural Frame 2. Wall and Roof Materials 3. Foundations The plan outline of a mine plant building will naturally be governed by the scope and layout of the process equipment it contains. The selection of roof profile, on the other hand, will generally depend upon a number of factors extraneous to the process e.g. snow conditions. When these factors are considered for concentrators in cold locations, a flat or stepped roof will usually be more economical and suitable than a sloping roof. The materials normally used for the structural framework of concentrators are the same as used for other industrial buildings, namely steel, concrete and wood. Structural steel, however, is the most commonly used material for concentrators in

Jan 1, 1971

By S Hancock, B H. Brady, H Muhlhaus

The aims of this paper are to present the governing science, verify the performance and demonstrate the potential engineering applications of a computational simulator for in situ leach mining of non-ferrous minerals. Assuming that the target mineral is deposited either uniformly within rock matrixes (matrix-hosted) or on fracture walls (fracture-hosted), in situ leaching can be treated as reactive flow and transport in geological media (porous media for matrix-hosted ore deposits and fractured media for fracture-hosted ore deposits). Under this treatment, the processes of in situ leach mining for non-ferrous minerals can be quantified through several sets of equations and these coupled equations have been numerically solved. The computational simulator has been applied to the simulations of one-, two-, and three-dimensional in situ leaching cases. The computational simulator, together with laboratory and in situ leaching tests, can be used to:optimise the leaching chemistry; optimise the in situ scale mining operations; scale up the in situ scale test operation to a full-scale mining operation; and evaluate the post-mining environmental restoration plan.

Jan 1, 2000

By John O. Marsden

"This article is an attempt to capture a presentation given at the 2016 SME Mineral & Metallurgical Processing Division (MPD) Luncheon held on Feb. 24, 2016, in Phoenix, AZ. It was presented as a tongue-in-cheek, lighthearted view of several of the issues facing our industry, while identifying some of the challenges and opportunities available to new engineers entering the industry today.Disclaimer• What you are about to read includes personal preferences, biases and occasionally arbitrary opinions.• Some readers may have dissimilar opinions on the contents and/or the rank order of the lists.There are eight top ten lists offered in this article: (1) Industry realities (2) Things a metallurgical or mineral process engineering graduate should do (3) Books every metallurgist should have on their shelf (4) Things I wish I had known (5) Legends of metallurgy (posthumous, with highlights) (6) Things we’ve forgotten (7) Mineral processing innovations of the past 20 years and, finally, (8) The future? For some items, additional context or clarification is provided after the item, while for other items no further explanation is warranted and none is offered. Top 10 industry realities1. Metal price cycles.2. Bigger is better (except when it isn’t).3. Ore grades declining across the board of metals/commodities.4. Ores becoming more complex.5. Three-fold increase in capital costs between 2004 and 2015.6. Three-fold increase in operating costs between 2004 and 2015.7. Less capital availability/challenging financial markets.8. Environmental constraints increasing.9. Socio-political constraints increasing.10. The mine manager is always impossible to work with.As Table 1 shows, there was more than a three-fold increase in gold operating costs between 2004 and 2014. The increases for copper, iron ore and other commodities were similar."

Aug 1, 2016

By Mario Alvarez

Drilling with tricone drill bits is widely used in the mining industry with a direct impact on drilling safety and costs, however it can be challenging to implement a new supplier of tricone drill bits, choosing a new model of this accessory due to the normal variations of the rock mass or even due to the acquisition of new and modern drilling equipment for open pit blasting operations. This article identifies the most common mechanisms of failure in productive drill holes of tricone drill bits, both in open-pit coal and metal mines, in two South American countries. It also emphasizes the important issues that must be addressed for the optimization of the performance of these accessories, such as the correct identification of the rock mass, the drilling parameters, and the impact of autonomous drilling on new equipment with this technology. The article presents some of the successful actions to economically improve the performance of drill bits considering the close relationship in the field with the supplier's technical representatives and factory designers, as well as the commercial interrelationship between their respective business areas. The article concludes by discussing the future of tricone drill bit design development, its environmental management, and possible new advances in its manufacture.

Jan 21, 2025

By J. Fritz, V. Gangrade, J. Briton, K. M. Ajayi, M. L. Harris, G. Cole, M. Young

Mine workers using diesel-powered equipment experience the highest occupational exposure to diesel particulate matter (DPM). This problem could be aggravated in underground stone mines due to their unique ventilation challenges with the large openings for airflow. Hence, adequate ventilation in these mines requires a combination of effective ventilation planning and delivering needed air quantities using auxiliary fans and stoppings. To meet this challenge, the National Institute for Occupational Safety and Health (NIOSH) developed the Air Quantity Estimator (AQE) software as a mine planning tool to help underground mine operators estimate the air requirements necessary to dilute DPM in the main air stream to statutory levels. The major parameters required for the calculations are the engine’s horsepower, DPM emission rate, the percentage operating time, catalytic converter efficiency, and filter efficiency. In efforts to provide major updates to this software, this study describes the recent development of a revised version of the Air Quantity Estimator (AQE 2.0). With the revised version, users have access to a comprehensive database of over 40,000 pieces of equipment, can define their specific target DPM level, and can create specific equipment for a customized database, in addition to having an improved easy-to-use interface. The software output provides an estimated total airflow necessary to dilute DPM based on the projected emissions, and the user can generate a related results report. The results also provide the mine personnel with a tool to identify vehicles that are high DPM contributors and could further be used to optimize the ventilation requirement by making changes to the percentage operating time of the engine. This software provides the mine with a user-friendly tool that could help reduce the DPM exposure of workers.

Feb 1, 2023

By W. C. Hagel, J. H. Westbrook

Usittg a sectioning technique with Agl10 as the tracer, the diffusion of silver in silver-excess (45.8 at. pct Mg), near-stoichiometric (49.8 at. pct Mg), and magnesium-excess (52.0 at. pct Mg) cylinders of CsCl-type AgMg was determined from 500" to 700°C. Diffusion coefficients conform to the expression D = Do exp (-q/RT) where the respective Do values are 1.53, 0.280, and 0.134 sq cm sec-I and the Q values are 41.3, 40.6, and 38.0 kcal g-atom-&apos;. Lnttice-parameter and density measurements were performed on a more numerous assortment and wider range of compositions. Substitutional defects were found on both sides of stoichiometry. Activation energies for other rate processes in these alloys show related trends with changing composition, although silver may not be the rate-detemining species. KNOWLEDGE of diffusion coefficients is necessary for a quantitative understanding of the many rate processes (e.g., grain growth, precipitation, sintering, oxidation, or mechanical deformation) occurring in solids. Although these data are available for most metals and common alloys, they are quite limited for intermetallic compounds—a group of materials whose unique physical and mechanical properties are presently attracting great interest. From a fundamental viewpoint, diffusion in intermetallic compounds also offers several engaging aspects owing to: their ordering, the possibility of introducing large, stable concentrations of lattice defects, and the variety of bonding types and crystal structures which can be found. In the case of CsC1-type compounds, some previous work has been directed at examining the role of vacancy defects by changing their concentration compositionally. The diffusion of Co60 was measured in 0 NiAl1- and in P COA., Except for the results of Smoluchowski and Burgess, isothermal diffusion coefficients were found to pass through a minimum at the stoichiometric composi- they decreased sharply on what was reported by Bradley and co-wrkers&apos; to be the vacancy-rich (aluminum excess) side of stoichiometry. This investigation of the diffusion of Agl110 in AgMg was undertaken both as an adjunct to a concurrent study of its deformation behavior and for the purpose of obtaining information on the influence of lattice defects and temperature on diffusion in another CsC1-type intermetallic compound. Bcc AgMg remains ordered up to and melts congruently at 820°C. Solubility limits at 300°C are about 41 at. pct Mg and 53 at. pct Mg. It is one of the Hume-Rothery electron compounds with a 3/2 electron-atom ratio. Previous investigations of its properties include hardress,&apos; tenile,&apos;-&apos; electrical reistivity, and thermodyna-mic1&apos;,14 studies. Indications of a high bonding strength may be found in the large heat of mixing1&apos; and in the 6-pct vol contraction on compound formaticp, as calculated using atomic radii of l.40 and l.55a for Ag and Mg. EXPERIMENTAL PROCEDURE Alloys were prepared by the induction melting of selected fine silver (99.95) and low-iron magnesium (99.95) in magnesia crucibles under 1 atm of A. Supplied by the Handy and Harmon and Dow Chemical Cos., respectivelv. Melts were poured under argon into graphite molds providing 1 1/8-in.-diarn. by 4-in.-long ingots. These were homogenized in evacuated and argon-filled fused-silica capsules by heating for 16 hr at 750&apos;. Three 1 in.-diam. by 3/4-in.-long cylinders were machined from the mid-portion of each ingot for diffusion measurements. Three alloys, analyzing 45.8, 49.8, and 52.0 at. pct Mg were taken as representing the extremes of interest, with 49.8 at. pct Mg being very close to the stoichiometric composition of 50.0 at. pct Mg.

Jan 1, 1962

Discussion of the paper Of NOEL CUNNINGHAM, presented at the New York meeting, February, 1915, and printed in Bulletin No. 99, March, 1915, pp. 601 to 608. C. H. POIRIER, New York, N. Y. (communication to the Secretary*). -Mr. Cunningham&apos;s paper, written from the standpoint of a stamp advocate, while commenting more or less favorably upon the installation of ball mills in the Vipond plant, does not, in my opinion, give as much emphasis to the comparatively new departure as the installation of ball mills in the place of stamps justifies. This discussion is based upon my personal and intimate practical work for several years with stamp mills, and for the past three years with Hardinge ball and pebble mills. The fact that the Vipond mine contains about equal quantities of the A and B classes of ore mentioned by Air. Cunningham, and the further fact that I have had a most intimate knowledge of the working of both classes of ore in the Porcupine district in stamp mills and ball mills, justifies upholding my final decision to use ball mills in the place of stamps, and defends my present further action in now increasing the present Vipond capacity by the addition of another 6-ft. Hardinge ball mill, in which action the directors of my company concur. This is one of the strongest evidences I can possibly offer in substantiation of my opinion that the ball mill exceeds the efficiency of the stamp, both in metallurgical and mechanical economy. It is hardly fair to compare a 100-ton per clay plant with a mill handling several times this amount, yet it is my belief that the cost per ton. of grinding in the ball mill is far less than that of any stamp mill in the district, where capacities run up to 400 tons per clay.

Jan 5, 1915

By Blandford C. Burgess

Mica is an orchid among minerals. It is formed in pegmatites, one of the most bizarre of igneous formations, and is exceeded by few other minerals in the perfection it may attain as to size, color, and cleavage. First used for window glazing, as an ornament and article of trade, it has become one of the most essential insulators of electricity, heat, and shock. Most internal combustion engines use mica condensers or capacitors and such machines of war as planes, tanks, and submarines are immobile without it. The original manuscript of this guide was written in April 1943 at the peak of war emergency. It was not used because shortly thereafter a decision was made to buy on a one price basis eliminating differentials for both quality and size. This is now presented with the thought that from the standpoint of preparedness we can only consider another war imminent and every effort should be made to set up in usable form the experience gained during the Second Morld War. Colonial Mica Corp. was set up by Metals Reserve Co. as a wholly owned government agency to encourage production of domestic mica and to purchase it. It soon became the exclusive buyimg agency for such mica. The writer as Southern Manager called on all the private agencies buying mica to assist in formulating buying policies, methods, and prices. A meeting was held for that purpose in Asheville, N. C., July 20, 1942. In the general discussion the first two hours of the meeting it was decided that the following factors should be considered in pricing strategic mica: clearness, flatness, trimming, color, classification (size and quality), free splitting, hardness, and air inclusions. Most of the mica miners have been buying strategic mica, according to the mine, as No. 1, No. 2, or Nos. 1 and 2 combined. In addition to these grades of strategic mica they have been buying three lower grades of mica, electric (vegetable-stained), black-spotted and black-stained. A number of mines were named one by one and the buyers present gave their opinions as to the basis they would use in buying the sheet mica from each. It was suggested that in addition to the prices already published, prices be posted up to 10 pct higher for special quality and preparation and prices be posted 25 pct lower than the published prices for the lowest acceptable grades of strategic mica, giving the buyers authority to make intermediate prices according to the quality and preparation. It was thought desirable at the same time to announce prices for nonstra-tegic mica where such quality is being obtained in mines producing strategic mica and where it would be necessary to take the output in order to get the strategic mica. It was also suggested that the price of electric and black-spotted mica be 50 pct below the price of the lowest grade of strategic mica and the price of black-stained mica be 60 pct below the price of lowest grade strategic mica. The few experienced buyers available were employed but they were inadequate for the job and others had to be trained. All needed a guide or primer of some kind to attain systematic procedure and consistent prices in their respective buying areas. The Mica Buyers Guide was formulated for that purpose based on experience gained in the first six months of buying. The Preface to the original guide was as follows: The purpose of this guide is to serve as a text in training beginners and as a handbook for experienced buyers of the instructions which have been issued up to this time. At the meeting of prospective buyers last summer, it developed that the first essential to attain uniformity must be some kind of check sheet. Our "Mica Buyers Report" was developed for this purpose and forms the backbone of this guide. Price is determined according to size, quality and preparation. Size can be measured, but no system of measurement or machine has been devised which can be substituted for the trained eye of the buyer to deterrnine quality and preparation. Although the "One Price" system was instituted and the "Guide" not used, the buyers were required to continue making out a "Mica Buyers Report" (Fig1) with each lot of mica purchased. The form proved its value and there is no doubt that in another such emergency some similar form should be

Jan 1, 1950

By A. Baydusa, K. Barron

A theory for cutter roof failure in coal mines has been developed. It is shown that the key parameters influencing the likelihood of cutter roof failure are the rock strength, the vertical stress (depth) and the horizontal to vertical stress ratio. The support force necessary to prevent the development of this mode of failure is, in most cases, so high as to make it impractical to apply a force of such magnitude. It is, therefore, better to allow the failure to occur and to design a bolting system to support the dead weight load of the failed block. This is probably best achieved by using a yielding bolt system (such as split set bolts) which is anchored well beyond the top of the potential failure block. The maximum potential caving height determined from this theoretical approach compares favourably with field observations reported in the literature.

Jan 1, 1999

By John W. Adams

The present status of the National Bureau of Standards program is that many magnetic tapes of analog data have been recorded in four major mines. Each mine uses different types of equipment. In addition, some surface measurements of noise have been made at two additional mines. Two types of recordings have been made: (1) broadband measurements for spectral plots and (2) narrowband measurements for amplitude probability density (APD) plots. Only data from one mine (Robena #4) has been processed and was, presented at this workshop. The short-term goals are: (1) finish processing data from the other mines, (2) establish or reduce measurement system uncertainties, (3) put Robella report into final form for distribution, and (4) hold a review to determine what has been done, to distribute and to interpret the preliminary data, and to determine what still needs to be done. Long-term goals are: (1) complete final reports on each of the mine trips, (2) establish techniques for predicting noise in mines already visited and establish uncertainty bounds for these predictions, and (3) establish techniques for predicting noise in mines that have not been visited (but that use similar equipment to those visited) and also establish uncertainty bounds for these predictions. Specific factors or formats to be presented include: (A) For underground broadband measurements: 1. 300 Hz to 100 kHz spectral plots 2. 300 Hz to 384 kHz spectral plots 3. 300 Hz to 192 kHz spectral plots 4. 300 Hz to 6kHz (subject to change to 3 or 12 kHz) spectral plots (B) For surface broadband measurements: 1. 300 Hz to 6 kHz (or 12 kHz) spectral plots 2. 300 Hz to 3 kHz spectral plots (C) For underground narrowband measurements : 1. APD plots at 12 frequencies from 10 kHz to 32 mHz of magnetic field strength 2. R. M.S. and average values will be calculated based on time averaging for these plots (D) Sample spectral measurements of: 1. Roof-bolt voltages 2. Trolley wire-to-rail voltages 3. Phone line currents

Jan 1, 1973