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THAT the march of civilization has synchronized with progress in the art of utilizing minerals is a proposition that needs no proof. It is a truism. Historians conveniently divide the time that the earth has been inhabited into the Stone Age, the Bronze (more accurately the Copper) Age, and the Iron Age. As archeologists are not entirely in accord as to dates, and as a few centuries make no difference whatever to this particular story, it may be approximated that the Age of Copper began about 8000 years B.C. and that it gave place to the Age of Iron about 1000 years B.C. The logic of this succession-stone, copper, iron-lies in the fact that copper first displaced stone, then iron displaced copper as the standard material out of which the utensils, implements, and weapons, the utilitarian articles of antiquity, were made. After the advent of iron, the mining and smelting of copper continued. Copper and bronze found use particularly in objects of artistic and ornamental nature; but the superior qualities of iron for many purposes were recognized. Useful manufactures of those days consisted principally of knives, hammers, chisels, spear-heads, arrow-heads, and battle-axes. First these were made of stone, then of copper and bronze, then of iron-particularly as there was plenty of iron ore, and the metallurgy was comparatively easy of accomplishment. Of course, the periods of transition dragged slowly. Definite as were the three Ages dominated by the mineral substance from which they get their names, ten or fifteen centuries probably elapsed from the time the first iron was smelted in a small charcoal furnace until it became the accepted material from which to shape a battle-axe. Contrast this with the pace of modern progress. In a brief span, half a dozen more or less deserving candidates for the distinction of having their name

Jan 1, 1933

By W. H. Newhouse

DURING the past few years the writer has been impressed by the close relation of many epigenetic orebodies with anticlinal structures. In the literature on ore deposits there is occasional mention that an oreshoot or district is on an anticline, but in most of the descriptions no weight or significance is attached to the relation, and usually the fact is concealed in a mass of structural detail. A few writers have stressed the relationship in a few districts or on a certain type of deposit. Church, Spurr, Butler, Stahl and Schuette have called attention to certain features, but the general extent of such a correlation has not been made known in any publication that the author has seen. A recent article1 on the localization of ore deposits, by well-known geologists, does not consider this common association. The author has seen in the field a number of the structural features described, and in addition has made a fairly complete review of the literature. This paper presents enough of the examples found to show the frequency of the relation to anticlines, and since only a few deposits on synclines are known, all of these of any importance of which the writer knows are mentioned. With certain qualifications which are discussed later, epigenetic ore deposits of replacement or vein type are mostly found where local upwarps of the earth's crust have taken place. Where formations antedating the ore deposits are present in the proper attitude to demonstrate vertical warping (i. e., more or less horizontal beds) the structural feature on which a mineral district, or mineralized area is located is almost always anticlinal, or domelike in nature. Some or even most of the ore deposits in a given district may be on the flanks of the upwarp, but few major districts are located definitely on downwarped areas. Synclinal basins within certain limits of size appear to be unfavorable to the type of fracturing that admits ore-bearing solutions.

Jan 1, 1931

By Martin Berman

The Bureau of Mines has investigated the mineral matter content of 38 American coals using X-ray fluorescence. Measurements of the Ka intensity for magnesium, aluminum, silicon, sulfur, calcium, and iron permit the determination of those elements as well as an indirect determination of the ash con-tent of the coals. The percentage of each of the six elements was corrected for absorption by all six elements as well as by hydrogen, carbon, nitrogen, and oxygen. It made little difference whether the values used for hydrogen, carbon, and nitrogen were obtained from chemical analysis or whether average values for all coals were used. In all cases, oxygen was obtained by difference. The correction for absorption by all these elements involved the inversion of a 6 X 6 matrix and was performed by computer. Assuming that the elements magnesium, aluminum, silicon, calcium, and iron were present in the ash as oxides, the quantity of ash was determined. The results for the mineral elements as well as for ash and oxygen were in good agreement with chemical results. Particle size was found to have a significant effect on fluorescence intensities. A study of size effects was made for pyrite particles, since the sulfur content of coals is of particular interest. Theoretical equations were derived and verified relating the intensity to particle size. It was found that the coal samples must be ground to less than 2 microns. Sulfur appears in several forms in coal, and the effect of sulfur form on intensity was investigated. It was found that the Ka intensity was independent of sulfur form but the Kß intensity varied with the type of sulfur. Thus, the Ka intensity was used for determination of the quantity of sulfur present. Utilization of the sulfur KB intensity did not permit a determination of the proportions of sulfur forms present in coal. However, for synthetic mixtures of cystine and pyrite in carbon black, measurement of sulfur Ka and Kß permit determination of each constituents from measurements of sulfur intensities alone.

Jan 1, 1968

By M. Gensamer

ALTHOUGH a large number of X-ray photograms of cold-rolled steel have been published, two circumstances have led to the experimental work reported in this paper. The first is that no complete study, making use of the pole-figure method of Wever1, has been made of cold-rolled low-carbon steel. Wever has published pole figures of mild steel sub-jected to plane parallel deformation1,2 and undoubtedly he has applied the method to cold-rolled mild steel, but the authors have not found these data published. Kurdjumow and Sachs3 have applied the method to the study of rolling and recrystallization textures in electrolytic iron; their results will be referred to later. The reason for this dearth of papers using the pole-figure method is obvious; a greater number of photograms and more analytical work (although this work is quite simple and straight-forward) are required to construct a pole figure than most investigators have felt worth while, despite the fact that no other method of which the authors are aware will satisfactorily depict the orientations of the crystal-lites in a polycrystalline aggregate. The second circumstance that led to the work reported in this paper was the appearance of a paper by Wayne A. Sisson4 on the same subject. In his valuable study of the factors influencing the development of pre-ferred orientations in cold-rolled mild steel, Sisson made one observation that required confirmation; that is, that at some stage of the rolling proc-ess the type of preferred orientation changed from the type that gives a photogram characterized as a "six-point" X-ray pattern to that known as a "four-point" pattern. A similar observation had been made by Tam-mann and Heinzel5, who studied the orientations developed in the rolling of steel by the specular reflection of light from the etched surface of rolled samples. These workers also found that the type of preferred orientation

Jan 1, 1936

By Charles S. Barrett, L. H. Levenson

Since 1925, when the preferred orientations in compressed aluminum were first determined1,2 the orientations have been described as a fiber texture in which a face diagonal, [110], of the face-centered cubic lattice is parallel to the compression axis. Subsequent experiments have seemed to confirm this texture,3-5 and a number of theories (recently summarized in references 6 and 7) have been proposed to explain it and to relate it to the behavior of single crystals during compression.3,8-11 The experiments reported in this paper prove that the orientations are not adequately described as quoted above—i.e., as a [110] fiber texture—although this is a first approximation to the actual texture. They also show that the texture cannot be thought of as a stable orientati011 that is reached and maintained after a sufficient amount of deformation. The actual texture, when studied in detail at successive stages of compression, indicates that a hitherto unsuspected range of orientations is present, both in the polycrystalline metal as a whole and in various individual grains in its interior, and that a state of dynamic equilibrium exists within this range. The reasons for the failure of previous theories to predict the actual texture become obvious when the heterogeneous nature of the flow is considered. In addition to the deformation texture, the manner of its development, and its theory, this paper presents data on the following related subjects: the identity of strain markings in aluminum; the orientation changes in aluminum single crystals during compression and a comparison of these with the conditions in individual grains of a polycrystalliile specimen; the origin of asterism ill deformed single crystals, which heretofore has been regarded as a distortion localized at the surfaces or slip planes; and the relation of plastic strain in individual grains ill all aggregate to the strain of the whole.

Jan 1, 1940

By Leon H. Nelson

Several factors which affect the segregation and solidification of killed hot-topped steel ingots are: (1) pouring temperature, (2) volume in the hot top, (3) taper in the ingot, (4) pouring rate by varying the nozzle size, (5) segregation of several elements, (6) moving ingots before completely solidified. In most of this discussion, segregation will be measured in terms of carbon variation only. All the data given are results on S.A.E. 1040 analysis of fully killed steel direct-poured in hot-topped molds giving 20-in, square ingots. Thus the variables of analysis and ingot size and contour are eliminated. Segregation results are all on the rolled-bloom size, not on the ingot itself. They are results from plant-control work and not results of special research on ingot segregation. Pouring Temperature The temperature (or, more correctly, the amount of superheat above the liquidus-solidus) of the steel entering the ingot is, of course, one of the most important factors influencing segregation and solidification. Table 1 gives the average segregation of a number of heats of S.A.E. 1040 steel with normal pouring temperatures of 2775" to 2825" F. The table also gives some data on segregation in hot heats (pouring temperature 2840" to 2870" F.) and in cold heats with some skull (poured at 2725" to 2760" F.). The results in Table 1 are on steel ingots with 20-in. square cross section and 60 in. long to the hot top. The ingot weighs 7100 lb. and the hot top contains 14.3 per cent of the total ingot volume and 11.2 per cent of the total ingot weight. The results are from drillings after rolling the ingots to bloom size. Segregation results obtained on the bloom are probably not as great as they would be in the ingot itself, since heating the ingots for rolling can perhaps cause some migration of carbon from regions of high and low carbon to those of average carbon content.

Jan 1, 1937

By H.A. Schwartz

From time to time, one of the authors has had occasion to investigate the graphitizing reaction and has published the results mainly as discussion' of the work of other investigators. In view, therefore, of the diversity of both observations and interpretation, it seemed well to attempt, a revision of the entire subject in the Research Laboratory of the National Malleable Castings Co. The work consisted of a careful study of a single, impure, iron-carbon alloy. The material, which may be considered typical low-carbon white cast iron of the malleable industry, was an air-furnace iron of the following composit,ion: carbon 2.30 per cent., silicon 1.20 per cent., manganese 0.29 per cent., phosphorus 0.156 per cent., sulfur 0.048 per cent. The freezing range extended from 1213' to 1132' C., the latter figure agreeing with Gontermann's data.2 We have attempted to define the equilibrium diagram of this alloy, in the stable condition as related to the mctastable diagr,aui,- from a temperature somewhat below the euteetic freezing point to a temperature l>clow Arl and for a graphitic-carbon content from practically notliing to the original total rarbon of the specimen (see Fig. 6). More csp~c~ially we desired to locate the line in the stable diagra~n corrcspo~idi~lg to thc Ac, line of the metastable syst,ern, which is designated by analogy, thc At, line (t, from tcrnpcr carbon); also to dctermirle the locat'ion of A tm witah respect, to Acm t,o~vard their lowcr extremities at Arl in ordei to determine whether or not graphitization is completed by th~ separation of an iron-carbon entectoid analogous to pearlite in the iron-cementite system. This would involvc furthcr a colnparison of thc locations of Ihc stablc and met.astable 41 points. As the carbon concelltrations of thc solid solutions of the two syste~~ls are probably not, identical, an explanation of t>lieir differences and of thc,

Jan 1, 1923

By C. T. Aimone-Martin, V. L. Rosenhaim

The response of two structures to blast-induced ground vibrations were evaluated and compared in order to quantify the impact of different blasting operations, hard rock and soft rock blasting, upon the structures movements. The first instrumented structure was a residential type, located in the operational area of a coal mine, were blasting is conducted in soft rocks, such as siltstone and coal, with compressive strength ranging from 20 to 50 MPa. Blasting is characterized by low benches, with hole lengths averaging 5.5 m (18 ft) and low powder factors, 140 to 210 g/m3 (0.236 to 0.354 lb/yd3), resulting in very little horizontal movement of the rock during the blast. The second structure was a commercial building, located in a basalt quarry (compressive strength between 109 and 180 MPa), where blasting is conducted in 12 m (39.4 ft) benches with powder factors ranging from 200 to 350 g/m3 (0.337 to 0.590 lb/yd3). Velocity sensors were placed on the structure walls to measure wall displacements and calculate blast-induced strains in the walls, and these results were compared with the driving ground excitations. The calculated strains were compared with the limits of rupture of the cement grout used as mortar between bricks and as wall coating, considered to be the weakest material in the structure composition. The blast-induced response of existing cracks in the structures were also measured using displacement gages and compared to the daily influence of weather fluctuations, such as changes in temperature and humidity, on crack movement. The results show that for the same levels of ground motions the structures present different movement, resulting in distinct levels of induced strains on the walls depending on the geology. The influence of long-term temperature and humidity variations on crack movements on both structures is very similar, during the same seasons of the year. Crack response to long-term weather changes is 2.5 to 3.5 times greater than blast influences.

Jan 1, 2015

By Frank L. Gaddy

Falls of roof account for over 50% of the fatalities that occur in coal mines in the US. Thus, roof control is one of the more important phases of underground mining. In reality, the control of roof influences the system of mining and is a major determinant of the width and spacing of working places, operations at the mining face, ventilation control, and surface subsidence. Frequently, the control of roof is the largest single cost item. Roof control is a never-ending task, not only at the working face and throughout sections where men are working, but along haulways and air- ways that must be maintained for the life of the mine. This is because roof, even the hest of roof, slowly deteriorates, so it must be frequently examined, with corrective support applied when needed. As coal is excavated, stresses are set up in the roof because the previous equilibrium is upset, resulting in pressures that cause fractures and slight movements that are frequently hard to detect. Unless the immediate roof, in the excavated area, is given support by artificial means, it might fall or there might be a succession of falls, varying from a thin scale to several feet, depending on the nature of the top. Exceptions to this are those rare mines, or sections of mines, with hard, strong, nonweathering roof that requires no support. GENERAL CLASSIFICATION OF ROOF There are two broad types of roof as far as support is concerned: the immediate roof above the coal and the main roof. Artificial support for mining purposes is only concerned with the immediate roof as nothing except large blocks of solid coal, or massive concrete, will support the main roof. The immediate roof is generally a few feet thick but call vary from inches to 6.1 m (20 ft) or more. There are examples of where there is no imrncdiate roof as the massive main roof lies directly on the coal

Jan 1, 1981

By H. A. Schwartz

From time to time, one of the authors has had occasion to investigate the graphitizing reaction and has published the results mainly as discussion' of the work of other investigators. In view, therefore, of the diversity of both observations and interpretation, it seemed well to attempt, a revision of the entire subject in the Research Laboratory of the National Malleable Castings Co. The work consisted of a careful study of a single, impure, iron-carbon alloy. The material, which may be considered typical low-carbon white cast iron of the malleable industry, was an air-furnace iron of the following composit,ion: carbon 2.30 per cent., silicon 1.20 per cent., manganese 0.29 per cent., phosphorus 0.156 per cent., sulfur 0.048 per cent. The freezing range extended from 1213' to 1132' C., the latter figure agreeing with Gontermann's data.2 We have attempted to define the equilibrium diagram of this alloy, in the stable condition as related to the mctastable diagr,aui,- from a temperature somewhat below the euteetic freezing point to a temperature l>clow Arl and for a graphitic-carbon content from practically notliing to the original total rarbon of the specimen (see Fig. 6). More csp~c~ially we desired to locate the line in the stable diagra~n corrcspo~idi~lg to thc Ac, line of the metastable syst,ern, which is designated by analogy, thc At, line (t, from tcrnpcr carbon); also to dctermirle the locat'ion of A tm witah respect, to Acm t,o~vard their lowcr extremities at Arl in ordei to determine whether or not graphitization is completed by th~ separation of an iron-carbon entectoid analogous to pearlite in the iron-cementite system. This would involvc furthcr a colnparison of thc locations of Ihc stablc and met.astable 41 points. As the carbon concelltrations of thc solid solutions of the two syste~~ls are probably not, identical, an explanation of t>lieir differences and of thc,

Jan 1, 1923

By William E. Ford, Edward Salisbury Dana

A. Hexagonal Division 1. Normal Class (13) Beryl Type 2. Hemimorphic Class (14) Zincite Type 3. Pyramidal Class (15) Apatite Type 4. Pyramidal-Hemimorphic Class (16) Nephelite Type 5. Trapezohedral Class (17) B. Trigonal or Rhombohedral Division 1. Trigonal Class (18) Benitoite Type 2. Rhombohedral Class (19) Calcite Type 3. Rhombohedral-Hemimorphic Class (20) Tourmaline Type 4. Trirhombohedral Class (21) Phenacite Type 5. Trapezohedral Class (22) Quartz Type 6. Other Classes (23) 7. Other Classes (24) Mathematical Relations of the Hexagonal System 119. The HEXAGONAL SYSTEM includes all the forms which are referred to four axes, three equal horizontal axes in a common plane intersecting at angles of 60") and a fourth, vertical axis, at right angles to them. Two sections are here included, each embracing a number of distinct classes related among themselves. They are called the Hexagonal Division and the Trigonal (or Rhombohedral) Division. The symmetry of the former, about the vertical axis, belongs to the hexagonal type, that of the latter to the trigonal type. Miller (1852) referred all the forms of the hexagonal system to three equal axes parallel to the faces of the fundamental rhombohedron, and hence intersecting at equal angles, not 90". This method (further explained in Art. 169) had the disadvantage of failing to bring out the relationship between the normal hexagonal and tetragonal types, both characterized by a principal axis of symmetry, which (on the system adopted in this book) is the vertical crystallo raphic axis. It further gave different symbols to faces which are crystallographally identical. It is more natural to employ the three rhombohedra1 axes for tri- gonal forms only, as done by Groth (1905), who includes these groups in a Trigonal Syslem; but this also has some disadvantages. The indices commonly used in describing hexagonal forms are known as the Miller-Bravais indices, since the were adopted by Bravais for use with the four axes from the scheme used by Miller in the other crystal systems.

Jan 1, 1922

By P. A. Vukmanic, M. Gensamer

Only recently has it been realized that preferred orientations are common in hot-rolled steels. In a recent paper, N. P. Gossl stated that hot-rolled mild steel exhibits a texture different from that characteristic of cold-rolled steel. No complete study of these hot-rolling textures has been reported using the pole-figure method of Wever. The material used in the work reported in this paper was the same material used by Gensamer and Mehl2 in a recent study of preferred orientations in cold-rolled steel, to which reference may be made for the composition and thermal history of the steel. Automobile-body sheet bar 1/4 in. thick was hot-rolled at two temperatures, 780' and 910' C. (1436' and 1669' F.). These temperatures refer to the temperature of the furnace in which the steel was heated; after each pass the steel was returned to the furnace and held there long enough to return to temperature. Although no accurate method was used to measure the temperature after each pass, it was estimated by color that only a slight drop in temperature occurred. In order to determine the effect of any preferred orientation that might have persisted through the normalizing treatment, one specimen at each temperature was rolled in the same direction as the original working direction and the other at right angles to it. The total reduction in each case was 85 per cent, the specimens having been reduced from 0.250 to 0.0375 in. in five passes. Final cooling was in air. Pinhole reflection photograms were taken of all four specimens, with the rolling direction vertical and the X-ray beam at an angle of 7' with the transverse direction (the transverse direction is defined as that direction in the rolling plane perpendicular to the rolling direction). These photograms, taken with a Mo target at 35 kv., are reproduced in Figs. 1, 2, 3 and 4. They show that a more pronounced texture was developed by the low-temperature rolling (780' C.), and that of the two

Jan 1, 1937

By H. A. Baumann, A. J. Rostosky

EVER since the first installation of wet-washing methods of coal preparation, the removal of the water added by the washing process has created serious technical and operating problems. The rapid development and widespread adoption of wet washing has necessitated a corresponding development of dewatering methods and equipment. The amount of water retained by coal varies with the size of the coal. The moisture that is largely on the surface of the particles is easily shaken off coarse coal; thus coarse coal can be dried comparatively easily and quickly. Fine coal presents a larger surface area than does coarse coal, so its capacity for retaining moisture is greater. In fine coal, moisture below about 5 per cent is held between the coal particles and its removal is difficult. Draining and drying of the finer sizes is a major problem at many washeries. Two common problems of coal-washing practice that are intimately connected with dewatering and drying are the clarification of washery water and the prevention of stream pollution. The first field has been studied from many angles, including the use of coagulating and settling agents followed by vacuum filters to remove the solids, and the use of sludge tanks with dewatering screens incorporated therein. In many districts, the disposal of sludges into streams has been stopped by law. The lack of space for impounding sludges has created problems of disposal in other districts. Reduction in moisture means a saving in freight costs as well as the elimination of difficulties in unloading and storing. Excess moisture in coal causes it to freeze in localities where severe climatic conditions prevail. Excess water in coals to be used in the production of coke and manufactured gas has a chilling effect on the walls of the oven or retort. Dryness of coal is important in producing good briquettes. CLASSIFICATION OF MOISTURE Moisture in coal can be classified as inherent and surface moisture. Inherent moisture is regarded as a part of the true coal substance, having been present in the original vegetal matter from which coal was

Jan 1, 1943

By W. E. Remmers

The fact that gray iron increases in volume, cracks and distorts upon repeated heating and cooling is rather conlmon knowledge. In ingot molds, Diesel engine pistons, carburizing boxes, continuous furnace parts, grate bars, stoker parts, and all castings that are subjected repeatedly to high and low temperatures, the phenomenon of growth presents a vital problem. Ingot molds distort and produce cracks which result in seams or laps and later appear as defects in the finished product. The heads of Diesel pistons frequently fail by cracking in a stellar shape. This is attributed usually to the result of permanent growth. Distortion and change of dimension of furnace parts frequently renders them entirely unusable. In chain grate stokers, mechanical difficulties frequently are caused by the growth of the links. In proper operation these links should never attain a temperature sufficiently high to start growth; nevertheless, some have grown in. on an 8-in. length when improperly operated. Even though the phenomenon is generally known there still exists a deficiency in the explanation of the mechanism of this growth. The field of investigators of this subject has a decided variation in opinion concerning the causes. The problem is of sufficient importance therefore to warrant further consideration. Review of Published Work Since the published work, particularly the European, contains much detail, only the outstanding results and conclusions of the investigators will be reviewed. The pioneering investigations of Outerbridge in 1904 and 1905 brought forth the conclusion that growth was not a function of chemical or crystallographic changes but was a result of the formation of fine hair cracks. These cracks are supposedly due to a nonuniformity of thermal expansion and contraction which ruptures the structure of the material. More recently Benedicks and Lofquist presented a purely mechanical theory, which is similar to that of Outerbridge. These investigators believe the temperature gradient from the outside to the center of the cast piece causes a contraction of the outer layers on passing

Jan 1, 1931

By C. O. Fairchild

THE meaning of temperature control can be extended to cover not only the control of temperatures' but also the control of processes through a knowledge of the temperatures involved. In this sense it has a very wide interest. A list of the industries in which temperature control is used in one way or another would cover nearly the entire industrial field. This discussion will be confined to the field of high temperatures. In practically all industries involving operations at high temperatures, pyrometers are used or men are paid for their ability either to estimate temperatures or gage an operation by some physical or chemical change or condition dependent on temperatures. As progress is made in the development of instruments and of methods for measuring temperature, some of these highly skilled artisans are learning the use of a new tool. Many processes have been, in recent years, improved by means of exact measurement thus substituted for estimation, but in a great many industries the pyrometer has had practically no opportunity to demonstrate its usefulness. The perfecting of instruments must be accompanied with a dissemination of the knowledge that new instruments are available and can be economically used. The demand at present, however, is ahead of the supply, and many industries are handicapped by the want of pyrometers. One of the highest paid skilled tradesmen of the present time is the man in the steel rolling mill who knows when proper working temperatures are attained. The metallurgist in his development of steels is continually demanding closer adherence to given temperature ranges in the processes, and the pyrometer is rapidly becoming indispensable. Properties of the finished products are being correlated with working temperatures and so closely that in some cases even the pyrometer is taxed to give the required accuracy. The greatest progress has been made in those industries in which the lower temperatures are used, particularly below 500° C. In this lower range automatic control has been highly developed.

Jan 9, 1919

By Meng Wang

"In this study, multiple methods that include geological surveying, laboratory studies, and numerical modeling have been used to study the deformation characteristics of a “deep inclined rock roadway with weak planes” (DIRRWP). Failure of the DIRRWP was found to be triggered initially by the shearing of the rock near the weak plane. The movement of the failed rock resulted in reduced confinement of the deeper rocks, and causing the failure of the supporting units and the severe deformation of the surrounding rocks. Hence, it is concluded that DIRRWP stability is affected predominantly by rocks near the weak plane. Corresponding control strategies for DIRRWP deformation were proposed: (1) greater support intensity is necessary to maintain the stability of the whole DIRRWP; (2) additional support is needed for rocks near the weak plane to reduce the potential of failure; (3) to increase the bearing capacity of the floor strata, as the floor needs to be supported; and (4) a supplementary support technique should be considered for cases of large deformation. The case study presented here indicates that the proposed control strategies can significantly reduce the potential of failure in rocks near the weak plane, thus preventing severe deformation of the DIRRWP.INTRODUCTIONAs shallow seams are mined out, the cover depths in most Chinese coalmines have become increasingly greater. Deep cover in a coalmine is considered to occur when the cover depth exceeds 800 m (Sun, Chen, and Miao, 2018). The loading and failure behavior of rocks in a deep cover setting are quite different from those in a shallow cover setting owing to the increase in in-situ stress, temperature, and hyperosmosis (Lobanova, 2008; Zhang et al., 2013). For instance, experience shows that bulking and dilating deformation in deep roadways is much greater than that which occurs in shallow roadways (Hou and Yang, 2018; Zhang et al., 2016). In addition, anisotropic behavior and thickness deviation of coal measure rocks, combined with the appearance of weak planes (e.g., faults, joints, and coal cleats) in coal and/or rocks, can significantly affect the stability of an underground roadway (Ghazvinian et al., 2013; Sun, Chen, and Miao, 2018). The presence of weak planes can significantly complicate displacement and stress transmission in nearby rocks. Additionally, tensile, compressive, and/or shearing failure in rocks near weak planes can be easily caused by high in-situ stresses in deep roadways; such failures may lead to further severe deformation of the surrounding rocks, resulting in roof falls and rib spalling (Kamata and Mashimo 2001; Wu, Ohnishi, and Nishiyama, 2004). A typical failure of the so-called “deep inclined rock roadway with weak planes” (DIRRWP) is shown in Figure 1. Severe deformation can be found near the weak plane. In this study, a plane or thin layer of rock/coal parting that can significantly reduce the strength of the surrounding rocks—and thus affect roadway stability—is defined as the weak plane."

Jan 1, 2019

By D Clarke, R Simpson

The Main lode in the Anwia Gold deposit is difficult to interpret due partly to the fact that three separate grid and drill hole orientations exist over the area and partly due to a lack of understanding of the controls on the high-grade mineralisation. Scattered high gold grades and multiple veining orientations add to the confusion. Sectional interpretations of the lode are often misleading due to the multiple orientations of drilling. Initial attempts to define a high-grade constrained geological model were not successful due to the inability to establish any geological continuity that would hold together in three dimensions. As a consequence the initial geostatistical domaining for the Main lode at Anwia comprised a simple broad mineralised envelope split by the weathering profiles. Subsequently an analysis correlating subjective qualitative logging information with grade plus utilisation of LeapfrogTM software, together with extensive geological re-interpretation resulted in the definition of a coherent high-grade shoot within the Main lode. The resource was re-estimated including this new domain as a high-grade hard boundary. Estimations on both models were carried out using uniform conditioning, which is a recoverable resource estimation methodology that estimates tonnages and metal above a series of cut-offs for SMU (selective mining unit) sized blocks. This paper compares the tonnages and metal contents that are calculated from the two estimation runs, both at a zero cut-off and a series of higher cut-offs. The results confirm that the estimation methodology has been implemented correctly as the tonnage and metal content at zero cut-off is the same for both models. The resource tabulations and grade tonnage curves predicted by the two models highlight the differences that can occur at higher cut-offs when realistic high-grade domaining is implemented. The results also reinforce the point that recoverable resource models are intended to address selectivity issues and are not substitutes for good geological modelling. Recoverable resource techniques, such as uniform conditioning, will not correctly estimate high-grade zones that have not been explicitly modelled.

Jan 1, 2006

By Norman Pilling

The micrographic analysis of silicon steels is possible if a dilute solution of nitric acid and methyl alcohol in nitrobenzol is used. The action of this reagent differs from that of sodium picrate in that there is no persistent deep-seated staining and the solution is used cold. THE technical difficulties hampering the metallographic analysis of silicon steels are chiefly the result of the extreme corrodibility of these alloys. The addition of silicon to iron in increasing quantities, up to about 6 per cent., rapidly increases the susceptibility of the alloy to chemical attack, not only in acid solution, but in water. This renders the preparation of metallographic sections very difficult, because of a non-selective attack upon the finely polished surface by the water used as a lubricant in polishing. This water attack masks the true structural details revealed by suitable etching reagents. It is thus necessary to use alcohol as a polishing lubricant in the last stages of preparation and to avoid all etching reagents having an aqueous base. A specific reagent for the identification of iron carbide in ferrous alloys, and the one hitherto used almost exclusively by metallurgists, is an alkaline aqueous solution of sodium picrate, which stains this constituent selectively. Its application to silicon steels has not proved successful, as its distinctive selective action is more or less completely hidden by the general attack of the aqueous solvent on the silico-ferrite, greatly accentuated by the fact that this reagent must be used at its boiling temperature (105° C.). Thus, a powerful metallographic aid to the study of the higher silicon alloys, such as transformer steels, is lost. A new reagent has been developed for the purpose of overcoming this difficulty. It is with some hesitation that the list of etching reagents, already overburdened, is increased, but the properties of this new reagent are advantageous in several ways and a definite field for it may be found in the metallography of ferrous alloys.

Jan 1, 1924

By D. W. Fuerstenau, G. D. Gumtz

Use of the discretized batch-grinding model for the simulation of locked-cycle grinding tests from batch-grinding data is illustrated. The simulated results were compared with actual locked-cycle experimental data for the dry grinding of dolomite. To illustrate the utility of this simulation method, a number of relationships between operating and performance parameters were generated, including relations between batch grinding and the Bond test, the production rate and the circulating load, and the production rate and the product size. A large amount of testing is done each year in the mineral industry for use with grinding unit cperations, and much of the experimental test data is obtained by the tedious locked-cycle testing procedure. In addition to being experimentally complex and requiring large amounts of sample, the very nature of the locked-cycle experiment yields results that cannot readily be interpreted. The attempts that have been made to model comminution systems during the last few years may provide a better and simpler way to obtain and analyze grinding test data; these models involve elements of both fitting to "model equations" and deterministic representations.1-1 The traditional engineering design techniques for comminution systems have relied mainly upon large amounts of industrial operating data that have been correlated with locked-cycle grinding data.',' Bond's empirical mill-design procedure involving locked cycle testing remains the most generally available method to this day. The purpose of the present paper is to show how much more useful data can be obtained from a simple batch-grinding experiment that provides information which subsequently can be utilized with population balance models of the grinding process to simulate locked-cycle behavior. These simulation results can, of course, be used in Bond's general design scheme. However, the combination of batch-grinding tests and the population balance model allows many more conditions to be considered than do single laboratory tests under specific locked-cycle conditions. The use of these simulation techniques for prediction of locked-cycle behavior represents one of the first practical applications for the simulation method in comminution.

Jan 1, 1971

By R. R. Fernández

Newmont Mining Corporation has been processing refractory gold ores by roasting since January 1995. The ores are refractory due to the association of the gold with iron sulfides, namely pyrite and marcasite, and the presence of carbonaceous components and is oxidized in an oxygen-enriched gaseous atmosphere. The structural characteristics of the calcine have a strong influence on the eventual recovery of gold by cyanidation. These characteristics are strongly dependent upon the roasting conditions, mainly the roasting temperature. Originally, the sulfides and carbonaceous matter were oxidized at a temperature that typically ranged between 535 and 560 °C. Controlling the roasting temperature within the lower and narrower range of 510 to 515 °C produced a calcine with a larger surface area(e.g. higher porosity), which resulted in a gold recovery increase of3.3 percent in 2001 equivalent to 5.1 million dollars of additional gross revenue. The new strategies of operating at temperatures never tested before are discussed. It constituted a great challenge to the control room operators for the lower operating temperature falls much closer to the ignition temperature of the sulfide ore and smaller and more frequent adjustments in operating parameters were needed to improve and maintain high gold recoveries. Based on the encouraging results that were achieved in 2001, a decision was made to install a “smart” process control system because the roaster temperature control was performed by manual inputs from the control room operators. The development and implementation of the control system to reduce or eliminate the temperature variability between the different control room operators commenced in June of 2002 and was fully operational by the end of October. Lower roaster temperatures were achieved (500 to 505 °C), which resulted in further increase of gold recovery by about two percent. The overall recovery increase equated to 8.0 million dollars of additional revenue for the first 10 months of 2002.

Jan 1, 2003