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By C. W. Kuttner, J. L. Gregg

ReceNtly there has been considerable interest in the production and use of extra hard alloys composed primarily of tungsten and carbon. Dr. Hoyt's recent paper1 gives a good description of these alloys and describes their performance when used as tools. There are a number of these alloys on the market sold under various trade names, and it is the purpose of this paper to describe the results of an investigation of the structure of five of these alloys by means of microscopic and X-ray methods. The samples studied were in the form of small tools or wiredrawing dies, which were either purchased or supplied as samples. They were in some cases not supplied by the original makers but were furnished by the agents in this country, and we wish to call attention to the fact that they may not be truly representative of the materials supplied under the various trade names No performance data are given and no inference as to the inferiority of one alloy as against any other is made. K. Schröter2 recently described methods for polishing alloys of this type for microscopic examination and has presented photomicrographs of several alloys. However, he did not identify their constituents or describe methods for their identification. Constituents and Their Identification As far back as 1915 attempts were made to utilize tungsten carbides commercially, but the great brittleness of these carbides made these first attempts unsuccessful. Later, successful dies were made by sintering the powdered carbides with small amounts of iron, nickel, or cobalt. Due to the high melting points of the tungsten carbides (2600" to 2800" C.), it is difficult to melt the carbides without volatilizing almost quantitatively the added element of the iron group. Inasmuch as the added metal does not exceed 20 per cent. and is usually present in much smaller amounts, some understanding of the tungsten-carbon equilibrium dia-

Jan 1, 1929

By Richard L. Gordon

Minerals long have been important commodities in international trade. As an inevitable result, the governments of the world have employed a wide variety of programs that affect the flow of trade. Roughly speaking, we may distinguish between the desire of more developed countries (MDCs) like the United States, western Europe, and Japan to control imports of minerals and the concern of less developed countries (LDCs), like India, about exploiting and exporting their minerals. The terminology used to describe different countries and the classification of specific countries into groups is unsettled and often changing. The poorest countries have been characterized as backward, undeveloped, underdeveloped, and developing. The problem seems to be in selecting a term that is both accurate and polite. Less developed seems, for reasons outlined by Hagen [pp. 51-57], the most convenient term. The borderline between an LDC and an MDC is always open to dispute. Objective measures are difficult to develop because of deficiencies in basic data, and enormous conceptual problems arise in making valid comparisons from even good data [see Hagen, pp. 7-28]. Thus, policies of the MDCs can be evaluated chiefly by using a few basic arguments for protectionist attitudes towards international trade. In dealing with the LDCs, a more far-ranging evaluation that covers general economic policy goals, the role of foreign investment, and the indirect effects of trade is required. This duality breaks down when trying to deal with the depressed areas in an MDC; here the issues are more akin to those associated with problems in an LDC. Similarly, variants of arguments used in LDCs appear in debates about foreign investments in MDCs. The whole discussion of minerals in LDCs, moreover, has obvious implications for MDCs like Canada and Australia. They, too, must face problems about the best utilization of their resources. THE RESTRICTION OF MINERAL TRADE BY DEVELOPED COUNTRIES[a] At least to some extent, the world's leading industrial nations have intervened to control the inflow of minerals. Such regulation is particularly pronounced for energy. Both the United States and western Europe employ

Jan 1, 1976

By W. R. Shimer

IN his valuable report on Finishing Temperatures and Properties of Rails, I Dr. G. K. Burgess, Chief of the Division of Metallurgy, U. S. Bureau of Standards, has begun a line of investigation which should be continued by those interested in the subject, and who have proper facilities for carrying put the work. For the past year or more the Bethlehem Steel Co. has been conducting experiments to learn the effect of rail finishing temperatures on their physical properties and microstructure and the results are here given for the consideration of those interested in the rail situation. . Considerable differences of opinion have been expressed by various authorities, in the past, as to the effect of large or small grain size and high or low finishing temperatures of steel rails on their physical properties and wearing qualities. Low finishing temperatures and, therefore, low shrinkage, have been advocated on the theory that the wearing qualities would be improved. Others have recommended high finishing temperatures. The generally accepted cause for rail failures, due to the development ,of transverse fissures, is excessive wheel pressure on hard rails. One of the causes advanced for hard rails has been that they contain too high per centages of carbon and manganese; another that the rails were finished at too low a temperature, i.e., at or near the critical point. In the experiments herein described the rails were rolled from reheated blooms. All the rail blooms were charged hot in a reheating furnace and brought up to about the original ingot-rolling temperature before rolling into rails. These rails gave better results in deflection, withstood a greater number of drops before breaking, and showed greater ductility, than. rails of identically the same composition and section which were rolled, direct from the ingot. Rails rolled from reheated blooms, finished at somewhat higher temperatures than when rolled direct from the ingot, have a different microstructure, which the writer does not believe is due so much to the difference in finishing temperatures, as to the difference in

Jan 3, 1915

By Schmidt CG

Parameters affecting gold elution using the AARL process are reviewed and critically analyzed in an attempt to optimise metallurgical efficiency and minimise costs in both current and future carbon adsorption operations. Such factors as acid washing, column geometry, elution temperatures and pretreatment reagents are discussed together with eluant water quality and eluate flowrates. Hot acid washing of carbon prior to gold elution has many benefits. Besides improving elution efficiency when eluting with regional water, a hot acid treatment preheats the carbon without causing any gold leakage. Laboratory data indicated that hot acid washing reduces the mass loss of carbon during thermal regeneration. The eluate going to either zinc precipitation or electrowinning is also relatively free of troublesome impurities (organic contaminants and ferrocyanides in particular). Because of the chromatographic character of the AARL elution where an ionic strength gradient is used to inhibit the readsorption of gold, column geometry plays a significant role. While practical considerations and capital costs may restrain the length of the elution column, high length/diameter ratios are advocated in order to promote the plug flow of column eluate. From both a metallurgical and costing viewpoint, the two significant factors affect- ing the AARL gold elution are temperature and cyanide addition. High temperature and high reagent additions within prescribed limits will improve metallurgical efficiencies, but a balance between energy and reagent costs is required in order to minimise overall elution costs. As pretreatment reagents constitute a considerable portion of the total elution costs, both the addition and consumption of sodium cyanide must be carefully considered. Lower cyanide additions may be effective in certain instances, but the more practical use of 0,6 bed volume of a 2-3 per cent NaCN reagent containing 2 per cent NaOH is advocated. This is equivalent to an addition of 20-30 kg NaCN and 20 kg NaOH per ton carbon Treated.

Jan 1, 1986

A project was funded by the Australian coal industry to investigate the mechanisms that might lead to sample bias when using cross-belt cutters, in order to help coal industry personnel to make better decisions about the purchase, maintenance and operation. It concentrated on DEM modelling of skew cutters. These are set at an angle to the belt with the intention of minimizing disturbance to the non-sampled material. Two bias mechanisms are likely to cause bias for cross-belt cutters. Waves of material are bulldozed off the belt by the upstream side of the body of square cutters and material is thrown by the leading edges of cutter blades for all types of cross-belt cutters. These mechanisms cause some parts of the load of material on a belt to be over-represented. The effects of these mechanisms cannot be made to be negligible, so cross-belt samplers cannot be trusted to produce unbiased samples, especially for segregated streams of material. However, it is possible to give a bound on the maximum likely bias. The grades of two portions of the stream can be estimated by stopping the belt and shovelling off 1/3 of the cross-section of the load on the belt into a container, concentrating on the final side of the belt and the top of the load. The remaining material should be put into another container and the difference in grade determined. The maximum likely bias is typically about 10% of this difference. For a cross-belt cutter, having an extraction ratio near to 100% is not a reliable indication that the cutter has little or no bias. Some bias mechanisms affecting cross-belt sample cutters make sample mass too high and some make it too low, so an extraction ratio near 100% can occur if two bias mechanisms are both active. Keywords: sampling, DEM simulation, sample bias, accuracy, precision

Jan 1, 2009

By Richard Hunt

BINGHAM has produced 6 per cent. of this country's copper. In total production, it ranks fourth among the copper camps of North America, the order being Butte, Michigan, Bisbee, and Bingham. In its annual production, it held that same rank until 1919, when its production was exceeded by the combined production of the Globe-Miami district of Arizona. Bingham has also been a lead camp of the first order. Utah ranks third among the lead-producing states, and its production comes largely from three camps which, in the order of their productivity, are: Bingham, Tintic, Park City. Bingham's silver production is important, but it does not rank high as a silver producer. Utah owes its rank as first among the silver-producing states to Tintic, a camp 40 miles due south of Bingham. The United States Mineral Resources reports a total production from Bingham for the period 1865-1920 having a gross value of $528,043,432. Bingham is on the eastern flank of the Oquirrh range 30 miles south-west of Salt Lake City, from which it can be reached in an hour by auto, or by the Denver & Rio Grande or the Bingham & Garfield railroads.. The automobile route is a paved road across the floor of Great Salt Lake Valley, through farming country. The Bingham & Garfield railway leaves the level of Great Salt Lake at the northern end of the Oquirrh range, and in 20 miles it climbs 2100 ft., and deposits the traveler upon a shelf cut in the side of Bingham Canyon below most of the mines, which are farther up Bingham Canyon and its tributary Carr Fork. Below lies the town, a narrow ribbon running for a couple of miles along the bottom of a canyon 2000 ft. deep-an almost impossible site for a community numbering, in prosperous times, 5000 to 7000 inhabitants drawn from all quarters of the globe. Up the canyon and down, and beneath the steep slopes nearby, and beneath the town itself, are the mining operations of over half a century.

Jan 3, 1924

By Ernest R. Woakes

Cana, originally called Santa Cruz de Cana, is situated in the province of Darien, in the Republic of Colombia, S. A. The river Cana is a tributary of the Tuyra, which flows into the Gulf of San Miguel, and thence into the Pacific Ocean some 80 rniles S.E. of the City of Panama. • The Espiritu Santo mine lies on the S. side of the Cana river at the foot of the Espiritu Santo range. The plateau of Cana has an elevation of 2000 feet above sea-level, and the mine is about 200 feet above the plateau. The map of the Darien accompanying this paper is the only correct one in existence. It was made by Lucien N. Bonaparte Wyse for the Panama Canal Co., and has been copied fur the present use, with permission, by Mr. L. G. Inglis. The dotted line on this map shows the route from the coast to Cana. As this mine was one of the most celebrated at the time of the Spanish occupation, it is only natural that there are a great many traditions and writings concerning its former workers and production. Dampier mentions it, though he does not seem to have been nearer to it than El Real de Santa Maria, the port on the Rio Tuyra, about 50 miles by road from Cana. Senor Vicente Restrepo's work, entitled Estudio sobre las Minas de Oro y Plata de Colombia, translated by C. TV. Fisher and published in New York in 1886, is, perhaps, the best treatise on Colombian mines. He has devoted a great deal of attention to the subject of the Espiritu Santo mine, and has had access to all that dealt with it in the archives of Bogota. It will be interesting to quote a few pasaages from the above work, which seemed like a romance to the writer of this paper some years ago, when he first came across the history. Being actually in Cana at the time, and knowing the present company had

Jan 1, 1900

By Ludwig Strah

"The paper outlines the history of rubber mill liners beginning with the awarding of the first North American patent rights in 1923. It includes the early-day applications and installations of the 1920s and 1930s through to their present-day application. Over-all rubber mill liner design is discussed in relation to present day installations employing rubber mill liners in various grinding applications. A brief overview is given of a manufacturer's procedures to produce rubber mill liners.IntroductionIn early 1910, it became apparent that the productive life of the silver mines in Cobalt, Ontario, could be substantially prolonged by mining lower-grade ores.The mining of lower-grade ores required the establishment of treatment facilities which initially employed jaw crushers, stamp mills, jigs and concentrating tables. The recovery of silver in other than a coarse metallic form required the additional step which was introduced at that time: the cyanidation of silver concentrates from the tables. The resultant requirement for increased and improved recovery led to the introduction of grinding mills, i.e. tube mills.Shortly after the introduction of the tube mills to the Nipissing Mine's mill in 1914, the idea of using rubber as a mill liner material was spawned. However, no action was taken due to the advent of World War I. It is interesting to note that the idea of rubber mill liners emanated from having used pieces of solid rubber tire as an emergency repair on a set of liners when a liner had broken and no immediately available spare was on site.The credit for this ingenuity and subsequent application for a patent on rubber mill liners falls to James John Denny, the mill superintendent, and Rolla Barnum Watson, the general manager of Coniagas Mines Limited. The patent application was formally made on December 3, 1921. The U.S. Patent Office issued Patent No. 1,470,597 on October 16, 1923."

Jan 1, 1982

By John D. Verhoeven, Edward E. Hucke

An experimental technique has been developed for the measurement of the rate of electrotransport to a precision of 1 pct in the molten Bi-Sn system. Results are presented across the phase diagram from 30°C above the liquidus to 520°C. A phenomenological description is presented and the data on Bi-Sn are thereby converted to the effective charge, Analysis of the data indicates the true charge of the migrating tin species in bismuth to be +1.8 at 500°C. The data agree well with the recent work of Belashchmko. fieldintensity. The resistivity of the molten Bi-Sn system is also presented. WHEN an electric field is applied to a metal, a relatively large current is produced due to the ease with which electrons move within the metal. The electric field also produces a force on the ions which might cause them to migrate. Such a migration of metallic ions has been detected under certain conditions. This electromigration of the metallic ions will be referred to herein as electrotransport. The study of electrotransport in metallic systems has a rather long history dating back to the initial work of Gerardin1 in 1861. General reviews of electrotransport in liquid and solid metals have been published by Schwarz,2 Jost,3 Seith,4 and Heumann.5 In reviewing the literature it is apparent that the theoretical developments are not yet complete. The difficulty arises in describing the momentum transfer between the migrating ions and the electrons. In addition, there is a lack of good quantitative electrotransport data at high temperatures, especially in liquid metal systems. This work was undertaken to establish quantitative electrotransport data in a liquid metal system which might serve as a critical test of the theoretical developments. The Bi-Sn system was chosen for analysis, and the rate of electrotransport was determined as a function of temperature and composition. THEORETICAL CONSIDERATIONS If all of the atoms of a metal are considered to be positively charged due to the loss of electrons to the

Jan 1, 1963

By Ralph W. Smith

DEVELOPMENT of the lime industry- in Ste. Genevieve County began in a crude way in 1840. According to information furnished by the Missouri Bureau of Geology, in the early days small vertical kilns built of stone were used, and wood was the fuel. Modern development began in 1904 when one company introduced steel shells lined with firebrick. Within a few years two more companies erected similar plants, and in 1925 a fourth company began operations. Thus there are today four lime companies at Ste. Genevieve, all operating at high capacity and with a gradually increasing production. GEOLOGY The limestone of Ste. Genevieve County, which has the chemical composition and purity required for lime burning, is the upper 80 or 90 ft. of Spergen formation. The Missouri Bureau of Geology, in its geological map of Ste. Genevieve County, gives the Spergen formation a total thickness of 160 ft., but only the upper portion is pure enough for lime burning, with an average raw-stone analysis of 98.7 per cent CaC03; 0.35 Si02; 0.3 R203; 0.35 MgCO3; 0.3 S03. The Spergen, one member of the Meramac group, Iowa series, of the Mississippian system, underlies an area approximately 12 miles long north and south, by 5 miles wide east and west (Fig. 1) in Ste. Genevieve County. The entire eastern two-thirds of Ste. Genevieve County is sedimentary, the formations dipping gently toward the east on an average grade of about 4 per cent, or 2 ½ º. Thus the outcrops of the various sedimentaries run approximately north and south. A line running west from Ste. Genevieve crosses the outcrops of the sedimentaries, ranging from the top of the Mississippian to the Ozarkian geological system in a space of 12 miles. Thus with the gentle dip of 2 ½ º the 160-ft. thickness of the Spergen formation stretches out in its outcrop so that it is approximately one mile

Jan 1, 1938

By D. Turnbull, J. E. May

THE (110) [001] texture in silicon iron is of considerable interest both from the technological and scientific points of view. Its occurrence was reported more than 20 years ago.1-4 The texture develops by means of secondary re crystallizatjon5 and can be very strong, that is, greater than 90 pct alignment even thouh the primary re crystallization texture is weak or complex. This behavior is in contradistinction to the face-centered metals which develop their strong secondary recrystalliza-tion texture from a strong primary recrystalliza-tion texture.', The microstructural changes accompanying the (110) [001] texture formation in silicon iron are as follows: When properly prepared cold-rolled sheet (i.e., 0.015 in. thick) is annealed at about 800°C, primary recrystallization occurs and a fairly stable fine-grained primary recrystallized matrix of about 0.02-mm-diam grain size is produced. The material at this stage does not have the strong (110) [110] texture. As the temperature is raised to about 900°C, relatively large grains appear in the finegrained matrix and they grow at the expense of the smaller grains to many times the sheet thickness. In time the complete sample is consumed by these large grains. This process of the growth of relatively few grains (about one in 105 primary grains) at the expense of many grains is called secondary recrystallization. Since all the secondary grains are of essentially (110) [001.] orientation, the strong texture is developed by this secondary recrystallization process. Theories of the (110) [001] texture in polycrystal-line silicon iron have been proposed by Decker and Harker and by Dunn.Decker and Harker have shown that grains initially in the (110) [001] orientation will upon annealing after cold-rolling, re-crystallize back to the initial orientation. To account for the sharp texture in silicon iron they propose that (110) [001] grains become more highly strained than grains in other orientations and therefore recrystallize first. They are then the lowest energy grains and can consume their higher energy neighbors. Grains in orientations other than (110)

Jan 1, 1959

By Bern Klein, A. Tugba Cebeci, Libin Tong

"Sensor based sorting faces two main challenges related to limited capacity/throughput and the ability of sensors to accurately discriminate based on estimated grades. This paper is aimed at improving sensor discrimination. Sensors have the ability to measure more than a single response. X-ray fluorescence (XRF) can detect and provide concentration information about a range of elements. Similarly, electromagnetic sensors (EMs) can generate magnetic susceptibility and conductivity responses over a range of frequency levels. The sensors thereby provide a response signature rather than a simply a single response that is a proxy for a metal grade. Furthermore, integrating sensor responses can improve the discrimination of metal bearing rock from waste. A study was conducted on a gold ore to assess sortability using XRF and EM sensors. A multi-variable regression approach was used to develop models that included a range of responses. Correlations improved significantly when compared to single response correlations. The approach showed that both positive and negative correlations contributed to the improved correlations. Stepwise regression simplified the models and showed that 2nd order interaction effects can be important. The approach also showed that combining different responses can improve discrimination accuracy. An important outcome of the study was that an ore that had been consider not to be sortable was determined to be sortable through the application of an approach that used the sensor responses in a more intelligent manner.INTRODUCTIONMining is aimed at recovering valuable minerals from their host rocks. Many methods are used to recover valuable minerals, and finding efficient and cost-effective ways is the key in research and production. . Ore sorting technology is fitting this definition. It not only discards waste rocks away from the concentrator but also recovers metal bearing ore particles that could be lost to the waste dump. The benefits of ore sorting include increased energy efficiency and reduced water and reagent usage in the downstream operations (Bamber, 2008; Gunson, Klein, Veiga, & Dunbar, 2012; Mazhary & Klein, 2015; Robben, Wotruba, Robben, von Ketelhodt, & Kowalzcyk, 2013)."

Jan 1, 2016

BASIC open-hearth slags have no obviously unique features when compared with slags from other metallurgical operations. Open-hearth slags form and exist at temperatures ranging from 2500 to 3100 F (1370 to 1700 C). In the course of an open-hearth heat, the liquid slag changes slowly and continuously in chemical analysis-the changes reflecting changes in temperature, changes in metal analysis, solution of charged materials, solution of feed additions, and solution of refractories. Throughout the process, the slag performs specific primary functions that are responsible for a large measure of the technical and economic importance of basic open-hearth steelmaking. It is intended in this chapter to present the chemical reactions by which the primary functions of basic open-hearth slags are carried out, to describe the physical and chemical principles governing the extent to which these reactions proceed and can be regulated, and finally to indicate the limitations imposed on other features of the process by the fulfillment of the primary functions. Basic open-hearth slags perform three primary functions. First and foremost, the slag provides a means of removing phosphorus from the liquid metal. The ability to remove phosphorus is largely responsible for the widespread use of the basic open-hearth process. Second, the slag serves as a controlling factor in transferring the oxygen required for the other oxidizing reactions. Third, the slag provides a means of eliminating some sulfur from the open-hearth bath. While the extent of sulfur removal is not comparable to that of phosphorus, the ability to remove some sulfur contributes much to the value of the process. The effectiveness with which the slag fulfills its functions varies with temperature and composition. Since operating temperatures are fixed largely by the specified nature of the product and the equipment, .the speed and extent to which the functions of the slag are carried out depend largely on its composition. The necessity for regulating slag composition to accomplish the re-

Jan 1, 1964

By W. L. Dennen, W. W. Wirth

Research looking toward the reduction of the cost of roof support by substitution of longer-life materials for wooden timber is fully justified by the fact that roof support is an important element of all production costs. Permanent or semipermanent roof support will reduce the expense of timber-maintenance crews during steady operations, but even more markedly during idle periods. The management, therefore, is faced with the important problem of timber renewals, which in times of regular operation are frequently obscured by more urgent problems of production. Increased use of timber in the Anthracite Region of Pennsylvania is caused mainly by increased percentage of coal obtained from robbing areas, which requires more timber for safety than development work, and maintenance of long haulageways through crushed ground despite the fact that less coal is transported over them. The timber reserve in the immediate vicinity of the mines has been depleted to such an extent that it is necessary to secure 70 per cent of the timber requirements from distant sources. Originally, mine timbering in this region was done by largely utilizing round props or legs with round collars. The whole cross section of the tree from which timber was cut was utilized by forming the joints between the legs and the collars with saw and adze, using plank or round saplings for lagging behind the legs and over the collars to prevent material falling between them. The Mine Inspectors' report of 1898 records an important digression from the use of round timber, when two tunnels at the Babylon colliery, near Pittston, Pa., were timbered with 12 by 12-in. square timber sets with mud sills, through quicksand for distances of 425 and 160 ft., respectively. The timbers were lagged with 3-in. plank to control sand. An early step toward the permanent type of roof support was the installation of "brick pillars or perfect arched brick rooms" instead of

Jan 1, 1940

By Daniel Hanson

FoR most of their practical applications metals are required to withstand stresses of appreciable magnitude: indeed, it id because they possess the quality of resisting stress without becoming permanently deformed that they find such extensive use in the service of man. Metals and alloys must, in service, usually behave as elastic substances—or nearly so. It is not difficult to satisfy this condition at ordinary temperatures. Iron and its alloys, especially the steels, are at normal temperatures excellent elastic bodies, capable of satisfying most of the mechanical requirements of the engineer: where electrical, chemical or other properties are impor-tant, which cannot be met by steels, it is usually possible to find a non-ferrous alloy such as nickel, copper or aluminum, which will prove satisfactory. When the metals or alloys are not inherently sufficiently elastic, cold-working or heat-treatment may develop elastic properties to a sufficient extent for practical needs. By means of relatively simple, rapid tests we can measure such properties as elastic modulus, limit of proportionality and proof stress, upon which design can be based with confidence. The case of the soft metals, such as lead and tin, is well known to be exceptional. They possess no definite limit of elasticity, and the value of proof stress or tensile strength depends to a great extent on the speed with which the test is carried out. Design here must be based on other considerations than a well-established theory of the proportionality of stress and strain. It is now generally recognized that steels and non-ferrous alloys possess at temperatures not greatly exceeding that of the atmosphere, characteristics quite different from those existing at ordinary temperatures, and that they assume qualities similar to those of the soft metals. Not only have they no limit of elasticity, but the proof stress and the ultimate stress depend on the time of application of the load. Flow under load may persist for long periods of time, possibly indefinitely, and the determination of a true maximum stress becomes a matter of great difficulty.

Jan 1, 1939

By Neil Schofield

"The estimation of recoverable ore reserves for feasibility in precious metal deposits such as Pine Creek must account not only f or the extreme variability of the ore grade but also for the complexity of the geology. Compatible models f or both must be adopted. Further, very selective mining demands reserve estimates be based on small selection units whose individual grades cannot be estimated reliably from the exploration drilling data.Multigaussian kriging is one method based on a multivariate normal model for estimating recoverable reserves under such conditions. In this paper, a non-mathematical description of the multigaussian model is presented together with its application to the Pine Creek Gold Deposit. The results, when compared to the first year of production, are encouraging for the model but not without surprises.Together, Part 1 and Part 2 of this study combine a detailed and geologically conditioned variogram analysis with an appropriate estimation method for a highly variable low-grade gold deposit. This and other studies of gold deposits familiar to the author show convincingly both that while the appropriate geostatistical skills and techniques are necessary to tackle the question of reserves, equally important but often discounted is the need for an appropriate and compatible geological model. IntroductionThe Pine Creek gold mineralization is associated with saddle reefs, and quartz and quartz- sulphide veining within the Enterprise Anti cline. The anticlinal structure is complex and, prior to mining, the mineralization was considered to be mainly strata controlled. Grades vary up to 160 grams in l .5rn core samples with coefficients of variation in excess of three.The estimation of the recoverable reserves for such a depo sit must account for both the geological complexity and the extreme variability of the gold grade.Part 1 of this work presented the geological model for the deposit and summary statistics 0 f the gold data. A detailed structural and variogram analysis considered both gold grades and the normal score (or gaussian transform) of these gold grades for different composite sizes."

Jan 1, 1988

By W. L. Dennen, W. W. Wirth

Research looking toward the reduction of the cost of roof support by substitution of longer-life materials for wooden timber is fully justified by the fact that roof support is an important element of all production costs. Permanent or semipermanent roof support will reduce the expense of timber-maintenance crews during steady operations, but even more markedly during idle periods. The management, therefore, is faced with the important problem of timber renewals, which in times of regular operation are frequently obscured by more urgent problems of production. Increased use of timber in the Anthracite Region of Pennsylvania is caused mainly by increased percentage of coal obtained from robbing areas, which requires more timber for safety than development work, and maintenance of long haulageways through crushed ground despite the fact that less coal is transported over them. The timber reserve in the immediate vicinity of the mines has been depleted to such an extent that it is necessary to secure 70 per cent of the timber requirements from distant sources. Originally, mine timbering in this region was done by largely utilizing round props or legs with round collars. The whole cross section of the tree from which timber was cut was utilized by forming the joints between the legs and the collars with saw and adze, using plank or round saplings for lagging behind the legs and over the collars to prevent material falling between them. The Mine Inspectors' report of 1898 records an important digression from the use of round timber, when two tunnels at the Babylon colliery, near Pittston, Pa., were timbered with 12 by 12-in. square timber sets with mud sills, through quicksand for distances of 425 and 160 ft., respectively. The timbers were lagged with 3-in. plank to control sand. An early step toward the permanent type of roof support was the installation of "brick pillars or perfect arched brick rooms" instead of

Jan 1, 1940

By Henry S. Rawdon

The relation between the course, or path, of the fracture of metals and alloys, produced in service or as a result of certain laboratory tests, and the crystalline units of which such materials are composed is of utmost importance. The fracture of normal material is, in general, intracrystalline, i.e., it consists of a break across the grains rather than of a separation between them. An interorystalline fracture indicates either that the metal is of very inferior quality or that the break occurred under very unusual conditions, e.g., at a very high temperature. The usual mechanical tests, when applied to metals of the type that breaks with an intercrystalline fracture, merely measure the coherence of adjacent grains for one another and reveal little as to the real properties of the metal itself. Even such a soft plastic substance as lead, under suitable conditions, may be rendered so weak and brittle that the metal can be easily crumbled into powder by the fingers although the constituent grains have lost none of the intrinsic properties of lead. Various erroneous explanations of this behavior of lead have appeared in the scientific literature, the change being described usually as an allotropic one. The importance, in an industrial sense, of a proper explanation of this type of the corrosion of lead justifies the description of the type of metal deterioration that follows. Corroded Lead Sheathing In Figs. 1 and 2 are shown two typical specimens of corroded lead sheathing selected from materials submitted to the Bureau of Standards for examination. Fig; 1 shows a section of the sheathing of an aerial cable; Fig. 2, that of the lead covering of a subterranean feeder-line of an electric light system. In this case the deterioration had proceeded to a much great'er extent than in the case shown in Fig. 1 so that certain portions of the metal could easily be crumbled into a coarse gray powder by the fingers. This was particularly true of those portions of the sheathing

Jan 1, 1921

By Joseph C. Zelanko, Christopher Mark

During August, two eastern Kentucky coal miners died in a roof fall during retreat mining operations. They had just finished extracting one pillar block and were moving to the next one when the intersection they were standing in collapsed. Regrettably, this was not an isolated incident. Since the end of 2000, there have been 28 ground fall fatalities in U.S. coal mines. Of these, 10 occurred during pillar recovery operations. Although pillar recovery has been associated with about one third of recent ground fall fatalities, it accounts for only about 10% of U.S. underground coal production. Statistically, a coal miner engaged in pillar recovery is several times more likely to be killed in a ground fall than a miner on an advancing section of a longwall. Pillar recovery is dangerous because it creates an inherently unstable situation. Once the pillars are extracted, the roof is expected to cave. Safe pillar recovery does not mean preventing roof collapse, it means ensuring that it only occurs after the miners have completed their work and have left the area. Fortunately, there are a number of proven techniques that can greatty reduce the hazards of pillar recovery. These include better mine planning, improved roof support, and safer work procedures. The goal of this article is to describe the most significant "risk factors" associated with pillar recovery, and prescribe control techniques that, taken together, can reduce the overall risk to miners. The conclusions are based on extensive studies conducted by the National Institute for Occupational Safety and Health (NIOSH) and the Mine Safety and Health Administration (MSHA) that have included detailed analysis of every fatal retreat mining incident since 1992 (25 incidents resulting in 30 fatalities). Risk reduction strategies for pillar recovery can be divided into three main groups: Global Stability: Prevention of section- wide pillar failure; Local Stability: Prevention of roof falls in the working area; and Work procedures and worker location: Minimizing exposure to hazardous areas.

By R. K. Zipf

Recent scientific studies by researchers at the National Institute for Occupational Safety and Health (NIOSH) and the U.S. Army Corps of Engineers (USACE) presented the worst-case explosion pressures that can develop if a methane-air mixture of a certain composition and dimension accumulates and ignites within a sealed area of a mine. The Mine Safety and Health Administration (MSHA) issued its final rule on sealing of abandoned areas which considers potential explosion pressures and the risk of achieving the necessary conditions. The new MSHA seals regulation has increased the pressure design criteria an order of magnitude beyond the old standard of 140 kPa (20 psi) to 800 kPa (120 psi). However, there still are major knowledge gaps pertaining to seals and sealed areas including: (1) the composition of the sealed area atmosphere and how it changes in time and space, (2) explosion pressures that might actually develop within sealed areas, (3) engineering procedures to follow when designing seals and seal installations, and (4) guidelines to manage the atmosphere within sealed areas with monitoring or inertization. NIOSH has initiated a seals research program with collaborators from Safety in Mines Testing and Research Station (SIMTARS) in Australia, West Virginia University (WVU), the Naval Research Laboratory (NRL), and USACE. Highlights of progress so far include: (1) construction of a gas explosion tube at Lake Lynn Laboratory for studying large methane-air explosions, (2) computer simulation of the fluid dynamics of high pressure methane-air explosions, (3) development of seal analysis methods considering construction materials, reinforcement and the seal foundation, and (4) development and testing of innovative seal designs that utilize inexpensive, readily-available rock rubble to resist high explosion pressures. NIOSH researchers aim to provide sound engineering guidelines to better address the new MSHA seal regulations. DISCLAIMER: The findings and conclusions in this report have not been formally disseminated by the National Institute for Occupational Safety and Health and should not be construed to represent any agency determination or policy.

Jan 1, 2009