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By R. W. Gurry

When a steel in the austenitic state, with all its carbon in solution, is maintained, at constant temperature, in contact with a gas that removes the carbon from the surface, yet without otherwise altering the composition of the steel, the change in weight of the specimen, after any period of exposure, is a direct measure of the amount of carbon it has then lost. The purpose of the present paper is to show how, by application of established mathematical reasoning based on the fundamental diffusion law and on certain postulates, this loss of weight yields a complete picture of the distribution of carbon throughout a specimen of regular shape after any period of exposure, with all the accuracy required in any practical occurrence of decarburization. Precisely the same is true for the gain in weight during the reverse process of carburization, or for the gradual gain or loss of any element, so long as the steel comprises only a single phase at temperature, provided always that the experimental conditions conform to the postulates. The change in carbon content from surface to center of the specimen is always continuous, when everything is in solution, even though under the microscope the decarburized zone (or carburized rim) may appear to be sharply defined. The experimental procedure is described and some typical results are presented, which are then interpreted by application of the diffusion law. Experimental Procedure Initially an endeavor was made to follow the gain of weight during the process of carburization in a hydrogen-toluene atmosphere, but it was soon found that the specimen became coated with graphite, which could not be removed without some loss of metal; therefore it was decided to continue carburization until the steel was saturated throughout, to remove all graphite from the surface of the specimen, and then to follow the loss of weight during decarburization in a moist hydrogen atmosphere at the same temperature as that used for carburizing. The carburizing procedure has been described in an earlier paper;' it suffices to state here that the carburization lasted about I40 hr. at 760°C. (1760°F.) and 44 hr. at iiio°C. (2030°F.), these periods being long enough-—on the basis of the calculations presented later—to ensure that the specimen was about 99.9 per cent saturated at each temperature. The specimen was a cylinder about 3.8 cm. long and 0.475 cm. in diameter; the materials were carbonyl iron, a commercial low-metalloid iron, and a steel with 3.6 per cent nickel and the usual proportion of other elements. The fully carburized specimen, after cooling at the top of the furnace tube, was placed in a lathe and sandpapered to remove all graphite; then the diameter was measured with a micrometer caliper, and the initial weighing (corresponding to complete saturation) was made. By means of a

Jan 1, 1942

By Stephen Taber

A vein may be defined as an aggregation of mineral matter, more or less tabular or lenticular in form, which was deposited from solution and is of later origin than the inclosing rock. This definition differs from the one found in many text-books in that no assumption is made as to the origin of the space occupied by the vein or the manner in which the mineral matter was deposited. In the present paper the writer purposes to discuss the mechanics of vein formation, and does not wish to begin by begging the question. The origin of ore deposits has been diligently investigated in recent years, but, while much has been written concerning the chemistry of the process, the physical side of the question has received less attention. The source of the ore minerals; the chemical composition of ore-bearing solutions; the relative importance of magmatic and meteoric waters as agents of concentration; and the causes of mineral precipitation have all been discussed at length. On the other hand, little has been written concerning the mechanics of vein formation, and the theories given in text-books today are essentially the same as those developed by the early Cornish and Saxon miners. Early investigators often regarded both veins and dikes as igneous in origin, but today the theory that vein minerals have been deposited from solutions, either liquid or gaseous, is firmly established. The latter view is supported by the fact that many vein-forming minerals are not found in unaltered igneous rocks; by evidence obtained in the laboratory regarding the solubility of minerals; by the presence of many ore minerals in hot-spring waters; by the occurrence of some veins in regions consisting exclusively of unaltered sedimentary rocks; by evidence as to the temperature at which some minerals are formed; and by the absence of mineral segregation due to difference in specific gravity. There is still, however, much difference of opinion as to whether certain tabular-shaped masses should be classed as veins or as dikes. Some of the earlier investigators have also advocated the theory that veins are contemporaneous in origin with the inclosing rock, while others have believed the vein minerals to represent a recrystallization or transforma-

Jan 1, 1920

By Dan G. Cojocariu, E. Ene-Danalache, I. Huber-Panu

A general model which represents not only batch but also continuous flotation in multi-cell machines is presented. This model considers both the size distribution and the distribution of flotabilities in a size class for valuable mineral particles in the pulp. The general expression is shown to reduce to several previously reported models. In addition, a number of new models are found to arise for different specific assumptions concerning the flotability distribution and/or the size distribution of the particles undergoing flotation. Several of these new models are tested experimentally using laboratory-scale batch and pilot-scale continuous data. Model parameters are estimated from this data and a comparison of calculated recoveries and those experimentally determined are presented. Finally, the influence of the feed rate, aeration rate and valuable mineral content of the feed on the recovery is examined.

Jan 1, 1976

By J. E. Warren

The mathematical problem considered by the author1 can be given another physical interpretation which is of some practical significance. The alternative physical problem involves the approximate behavior of a single well which is producing at a constant rate through an axially symmetric, horizontal fracture of infinite flow capacity which is located at the center, top or bottom of a uniformly thick, horizontal, homogeneous, anisotropic reservoir of infinite lateral extent which contains a single, slightly compressible fluid. Using Coats' asymptotic results, the wellbore pressure in the fractured system is given by the following equation.

By S. D. Strauss

The marketing of nonferrous metals and of the ores and concentrates from which these metals are recovered is a fascinating trade, international in character, sensitive to every change in the economic tide, and complex in its organization. Each individual metal has its own marketing mechanism; no two are exactly alike. The differences sometimes are a matter of tradition rather than of necessity, but usually they have developed because of the very nature of the problems of producing or consuming the individual metal. This description, because of limitations of space, can do no more than indicate the major aspects of the trade and touch lightly on the marketing structure of each metal. The dictionary states that a market is a "meeting of people for selling and buying." In the case of nonferrous metals this meeting may occur on a half-dozen different occasions between the time the ore has been first mined and the time the refined metal is available for use by industry; or it may not occur at all until after the metal itself has been rolled, drawn, stamped, cast, or forged into a useful semifabricated shape. To illustrate: A Chilean miner may sell his small ore production to a custom mill, which produces concentrates that are sold to an ore dealer, who finances shipments of the concentrate to a custom smelter, which buys them for conversion into blister, to be subsequently refined into electrolytic copper (sometimes by a refinery having no corporate ties with the custom smelter) and sold. Conversely, aluminum production is mostly by integrated concerns that mine bauxite, convert it to alumina, smelt that to produce aluminum, and then fabricate that into semifinished or even finished products before title to the material changes hands for the first time. Some nonferrous ores are not converted into metal at all but are sold by the miners or dealers directly to the ultimate consumers. A good example would be chrome ores used by the chemical industry. And of course a substantial part of the commerce in nonferrous metals is in scrap, which is the reconversion into useful form of metals that have long since been mined and smelted. Thus, one-third of all the lead used in the United

Jan 1, 1964

By T. Okubo

Gold is generally recovered from silver anode slime by electrolysis in the final step of the copper anode slime treatment. In the present investigation, rapid and direct hydrometallurgical separation and recovery of gold in the early step of the process is studied. Gold is recovered just after the elimination of copper and selenium from copper anode slime. The studied process consists of: (a) oxidizing roasting for selenium elimination, (b) sulfuric acid leaching of the calcine for copper removal, reduction of gold in the liquor by the use of proper reductant such as hydrogen peroxide (production of gold powder), (el nitric acid treatment of gold powder for further purification and (f) melting and casting of gold. Laboratory and miniplant testwork showed that the extraction ratio of gold by chlorine leaching was 99 % up and four nine gold ingot could be recovered without electrolyses.

Jan 1, 1984

By Samuel L. Hoyt

Cemented tungsten carbide, a product of a branch of metallurgy which has never possessed more than a relatively minor interest and importance, has recently commanded the attention of engineers, industrialists, financiers and men of business. New methods, new opportunities, new goals, never before considered, have suddenly been brought within the scope of practical realization. It is these results that attract the interest of the world, but we, as engineers and metallurgists, will have equal interest in the product itself and in that branch of metallurgy from which it comes. It seems appropriate, therefore, to speak today on Hard Metal Carbides and Cemented Tungsten Carbide, as the latter represents one of the outstanding developments of recent date in non-ferrous metallurgy. We are interested in the hard metal carbides as a group of related metallic substances and in cemented tungsten carbide as the leading representative of the metallurgy of this group. The literature of this general field is limited, and, bearing this in mind, it seems advisable to attempt to cover the field broadly and to correlate the subject matter, rather than to present a detailed account of any one of its phases. Our annual lecture lends itself admirably to this plan. The quickened interest in cemented tungsten carbide, once its potentialities were recognized, the many sides to the problem of developing the manufacture and use of this new product, and the desire to economize as much as possible in the time of development, have brought many into this work, both in this country and abroad, notably the Osram Lamp Co. and Friedrich Krupp in Germany and the General Electric Co. in this country. It would be presuming too much to attempt to speak too broadly of the present state of the art and science of the hard metal carbides and my remarks arc guided largely by the work done in the General Electric Co., and by our associates in the Carboloy Co. Even here the activities of many in these two groups have centered around the utilization of cemented tungsten carbide, which is outside the scope of this talk. To those whose work is represented in this lecture, it is my pleasant duty to acknowledge their assistance and advice. To Dr. Zay

Jan 1, 1930

By R. M. Schuster, F. M. Benavides

A plan is prepared to develop and operate a four mine complex over a 30-year period. The mining complex is in the vicinity of two existing processing plants and the most economical means of transporting the raw minerals to either or both of these processing plants is sought. The mines and processing plants are all within a radius of 5.6 km (3.5 miles). Existing transportation facilities consist of county and state roads and federal highways as well as haul roads in some areas. A navigable river meanders through the area under study and there are two railroad systems servicing the area. The analysis shows the economic and operational feasibility of using an overland conveyor in lieu of other means of transportation.

Jan 1, 1983

By Frank T. Wheby

The cost of tunneling is highly sensitive to the rock characteristics through which the tunnel is to be driven. These characteristics affect in a major way the rates at which tunnels and shafts can be driven and the degree to which the openings must be supported to maintain them in a permanent stable condition. Tunnel and shaft design and cost criteria have been computerized, permitting estimates of tunnel-shaft systems to be made directly from inputs of rock mechanics characteristics and other data. Curves of quantities of steel, rock bolts, and other rock support items as related to tunnel size and rock quality designation are presented. An illustrative example of the use of the program in calculating the cost of a hypothetical tunnel system is included.

Jan 1, 1971

By John R. Low

A number of cases of low-temperature, intergranu2ar brittle fracture of metals containing small amounts of certain impurities, have now been identified. Some degree of understanding of this phenomenon exists for the simpler binary systems of a metal and a single impurity, but the profound effects of other impurities and alloying elements in modifying this type of behavior remain unexplained. Current research in this area is reviewed and some of the newer techniques of investigation which should make possible a more quantitative study of the structure and composition of grain boundaries in impure metals are described. To indicate the subject matter of this lecture, we may begin by reviewing the experimental observations concerning low-temperature intergranular brittleness in impure metals, particularly those examples in which the embrittlement appears to result from what has been called "equilibrium grain boundary segregation."' These are the systems in which it has been impossible, at least up to now, to detect the presence of any second phase film at the brittle interfaces. When second phase films are present they are usually readily detectable by fractographic methods, often appearing as epitaxial films in geometric or dendritic patterns. An example is shown in Fig. 1 for the case grain boundary carbides in a sensitized stainless steel which failed by intergranular brittle fracture at 78?k2 In contrast to this type of embrittlement there are numerous examples of low-temperature intergranular embrittlement in which the fractographs are essentially featureless, for example, that of an oxygen-embrittled iron shown in Fig. 2. The only second phase particles visible are the small, widely separated, round oxide particles typical of the bulk material. The fracture surface is extremely smooth and the fracture path appears to follow the intergranular interface without deviation. This type of fractograph also implies that crack propagation has occurred without plastic deformation at the crack tip, since localized slip or twinning ahead of the crack would be expected to distort the interface and be readily visible in the fractograph. Such indications are occasionally seen in these fractographs, but are not characteristic. A second example of this type of fractograph is shown in Fig. 3, which is from a temper-embrittled, carbon-free, Fe-Cr-Ni alloy containing Sb, broken at 1OO?C.3 The similarity to the oxygen embrittled iron case will be apparent. In the case of the temper embrittled Cr-Ni ferrite containing antimony, it is possible to remove the embrittlement by suitable thermal treatment. The grain boundaries may then be examined by thin film transmission in the electron microscope for the material in both the nonembrittled condition and in the embrittled condition. Two boundaries are shown in dark-field transmission in Fig. 4, one in the nonembrittled

Jan 1, 1970

By Stanley Herold

As an accompaniment to the interesting papers which discuss the practical aspects of forced drive, or flooding, in our oil fields, and to others which deal with laboratory or field tests on the same subject, a few remarks on the theoretical principles concerned may not be considered inappropriate at the present time. Without claiming to have had the field experience which some of you certainly possess I venture to present some of the results of an analytical investigation upon this method of increasing the recovery of oil from our natural reservoirs. I firmly believe that these results will accord with your experience. I shall confine the present discussion to the consideration of a perfectly ideal situation Let us assume that the productive formation lies perfectly horizontal, that it is of uniform thickness, of perfectly homogeneous texture, and that it contains oil with gas in solution, and no water, throughout a definite, although undefined, lateral extent. We shall furthermore assume that the pressure existing within the reservoir as thus specified, is such that some of the gas is in the free state, spread uniformly throughout, in the form of minute bubbles within the pores of the formation. We now have an ideal reservoir subject to the peculiar action of capillarity as described by the French physicist Jules Jamin. In all directions within the reservoir we see these bubbles of gas, separated by globules of oil which tend to remain in the capillary channels that connect the pores. The action of these bubbles and globules under the application or release of pressure has been fully described by Jamin.1 Most of our oil fields in the Mid-Continent and Eastern districts are subject to this action of capillarity: The fact that the actual reservoir is often far from being ideal in the manner specified above does not preclude the, influence of this phenomenon. The oil, existing under a pressure exerted by the compressed gas, is securely locked in place

Jan 11, 1926

By Emil Gathmann

Steel as it is poured, or teemed, into the mold for forming the ingot may be broadly separated into two divisions; i.e., effervescing or gassy steel, also termed evolution steel, and non-effervescing or killed steel, also termed solution steel. Between these primary divisions there are various types having the characteristics of both divisions but really nut belonging to either; such steels are termed semi-piping, rising, or wild, as the type may be. True effervescing steel should contain large volumes of gases, which are evolved while the metal is being teemed from the ladle nozzle into the mold, and continue to escape while the temperature of the steel is falling prior to its solidification the top of the ingot remaining liquid, due to the evolution of gases, until an ingot skin of considerable thickness has been formed. These gases consist principally of hydrogen, carbon monoxide, nitrogen, and ammonia. It is generally understood that nitrogen gases are the first evolved and these form the skin blowliolcs, troublesome at times, in the solidifying ingot. Ingots made of effervescing steel will always contain a large number of blowholes. Such blowholes are not deemed objectionable in certain products if they occur well inside the ingot where they will not be subjcct to oxidation upon cooling, reheating, and rolling or forging of the ingot. Very little top or bottom discard is taken from this type of ingot, as pipes, or large shrinkage cavities, at the upper portion of the ingot do not usually occur, the difference in volume between the liquid and the solid steel (6 to 10 per cent.) being compensated by the innumerable blowholes distributed throughout the body of the ingot. Of the 40,000,000 tons of steel made in the United States during the year 1919, at least 35,000,000 tons of ingots were made of gassy or semi-gassy steel. Killed, or solution, steel is termed true piping steel from the characteristic pipe or shrinkage cavity that usually occurs in the uppermost central portion of the ingot.

Jan 1, 1922

By Emil Gathmann

Steel as it is poured, or teemed, into the mold for forming the ingot may be broadly separated into two divisions; i.e., effervescing or gassy steel, also termed evolution steel, and non-effervescing or killed steel, also termed solution steel. Between these primary divisions there are various types having the characteristics of both divisions but really nut belonging to either; such steels are termed semi-piping, rising, or wild, as the type may be. True effervescing steel should contain large volumes of gases, which are evolved while the metal is being teemed from the ladle nozzle into the mold, and continue to escape while the temperature of the steel is falling prior to its solidification the top of the ingot remaining liquid, due to the evolution of gases, until an ingot skin of considerable thickness has been formed. These gases consist principally of hydrogen, carbon monoxide, nitrogen, and ammonia. It is generally understood that nitrogen gases are the first evolved and these form the skin blowliolcs, troublesome at times, in the solidifying ingot. Ingots made of effervescing steel will always contain a large number of blowholes. Such blowholes are not deemed objectionable in certain products if they occur well inside the ingot where they will not be subjcct to oxidation upon cooling, reheating, and rolling or forging of the ingot. Very little top or bottom discard is taken from this type of ingot, as pipes, or large shrinkage cavities, at the upper portion of the ingot do not usually occur, the difference in volume between the liquid and the solid steel (6 to 10 per cent.) being compensated by the innumerable blowholes distributed throughout the body of the ingot. Of the 40,000,000 tons of steel made in the United States during the year 1919, at least 35,000,000 tons of ingots were made of gassy or semi-gassy steel. Killed, or solution, steel is termed true piping steel from the characteristic pipe or shrinkage cavity that usually occurs in the uppermost central portion of the ingot.

Jan 1, 1922

INTRODUCTION The preceding chapters have brought us to a point in the mineral appraisal process where the composited sample values can now be used to estimate the grade and tonnage of the total mineral deposit. There are many techniques whereby drill hole composites and/or other sample data are used to assign grade and estimates to the surrounding rock. Matheron and his students have properly called such techniques extension functions. Before embarking upon a detailed discussion of extension functions, it is necessary that we take time to consider the concept of geostatistics as advocated by George Matheron who developed the "Theory of Regionalized Variables," which he published in 1962 (Matheron, 1971). The concept of regionalized variables has important application in the techniques of mineral appraisal. The position or location of a mineral sample within a deposit can be almost as important as its value. Geostatistics, when defined as "the application of the theory of regionalized variables* to the study of mineralized volumes of rock," takes into consideration the position as well as the magnitude of the value of the sample. The principles of geostatistics, as outlined by Matheron, represent a major step forward in the mineral evaluation process, because they provide a sound theoretical and practical basis for quantifying the geological concepts of (1) area of influence of a sample, (2) the continuity or lack of continuity of mineralization within the ore body, and (3) the lateral changes in mineralization according to the trend direction of an ore body and its orthogonal components; or in other words, a measure of the anisotropy of the deposit. Royle (1971) has defined the objects of geostatistic as being: "1. To estimate the most likely value of blocks of ore, or the values of the whole deposit; and 2. to estimate the errors of such estimates. This latter is important as, in addition to providing a check on unwarranted optimism, it shows where more valuation work may be needed." Because of the great importance of these concepts in mineral evaluation, an introduction into the theory of regionalized variables, and the study of a practical approach to its application is outlined here. REGIONALIZED VARIABLES VS. RANDOM VARIABLES Classical statistics, as discussed in earlier chapters, grew out of the study and application of probability theory. Probability is concerned with the outcome of random events and therefore classical statistics is built upon the theory of random variables, i.e., the probability of independent events. The validity of most statistical inferences depends upon sample randomness being assured for unbiased results. Where independent events cannot be assumed the results of statistical inference becomes suspect. On the other hand, geostatistics is concerned with variables that have position in space as well as magnitude, hence the term regionalized variables. Mineral deposits are not the only field to which the theory of regionalized variables is applicable. Many natural phenomena that demonstrate a relationship between change in magnitude and position in space are amenable to application of geostatistical techniques. Mineral deposits vary greatly in their geosta-

Jan 1, 1980

By W. A. McCurdy, Joseph W. Leonard, William F. Lawrence

INTRODUCTION Utilization from the Point of View of the Preparation Engineer The primary interest of the coal preparation engineer is in process design, operation, and maintenance to produce an acceptable product that can be sold at the greatest possible profit. Because of emphasis upon these interests, attention to other potential values of coal is sometimes neglected. The intent of this chapter is to alert the preparation engineer to the utilization possibilities of the product as well as the tributary coal flow moving through a modern coal preparation plant. The basis for any unrealized potential derives directly from the coal seam itself. Most coal seams consist of coal bands and benches sandwiched together in layers that differ visually from each other in physical structure and luster. Randomly selected physical and chemical ranges determined from layers of coal in a single seam can easily differ by as much as 30 Hardgrove grindability indices, 0.30 of a specific gravity point, 20 percentage points of ash, 6 percentage points of dry volatile matter, and 10 percentage points of total su1fur.l Similar wide variations exist for calorific value, seam moisture content, and, undoubtedly, for any other conceivable coal test parameter that might be used for comparative purposes. These observations all point to the long-established fact that coal is not homogeneous, as conventional analytical methods might tend to indicate, but is instead a highly heterogeneous substance.

Jan 1, 1979

C. Q. PAYNE, New York, N. Y. (written discussion*).-The method adopted by Mr. Lennox is a very interesting test of the practical application of Mr. Gates' crushing-surface diagram to a greet variety of gold and copper ores. His method of dealing with the material below 200-mesh is also a distinct contribution to the subject, although, as he suggests, it seems likely that some microscopic measurement of this material may be advisable before the mesh reciprocals of its group particles can be dealt with as accurately as can those coarser than 200-mesh. In examining the general results shown in Table 3, it is somewhat puzzling to perceive why Calumet &, Hecla jig tails should show a crushing resistance 3 - times greater than that of the ore from the Ray Consolidated copper mine. The latter is, I believe, an altered. Pinal schist

Jan 10, 1918

J. T. LITTLETON, JR., ? Corning, N. Y. (written discussion?).-This. discussion will add little that has not been brought out but will show how the problems encountered in the Corning Glass Works were overcome. The chief points of consideration in any equipment are, first, the work the equipment is called upon to do; second, the installation; and, third, the man who will use it. These three points should determine the type of apparatus adopted. If only rough measurements, merely a little better than the eye, are desired, the cost of the instruments should be considered; but if accurate temperature control is necessary, the cost of the equipment deserves only small consideration. There is no question that the real problem for any factory is the installation, making sure that the elements really give the temperatures desired; also, the instruments must be so designed that any man can use them.

Jan 12, 1919

By David R. Mitchell, Ernest M. Spokes

MINING ENGINEERING, page 373, March 1958, vol. 211) S. C. Sun: This article by Spokes and Mitchell deserves high commendation. For many years mineral dressers have been at a loss to explain the variation in magnetic susceptibility of the same mineral species obtained from different localities. In fact, they do not even have a list of accurately measured data on the specific magnetic susceptibility of weakly magnetic minerals to consult. Experience as a university teacher has firmly convinced me that the average student has more difficulty in acquiring a satisfactory knowledge of magnetism than of any other branch of mineral dressing. This is almost entirely because the subject has been treated far too much from a strict practical standpoint and far too little from a fundamental one. It is no exaggeration to state that almost all the published theoretical discussions are based on the experimental results of manufactured chemicals and alloys, but not of naturally occurring minerals. In an attempt to remedy this state of affairs, the author of this article not only set up a new magnetic balance in the Department of Mineral Preparation of The Pennsylvania State University, but also performed work of fundamental value, thus pointing the way to further research. This is evidenced by the fact that an investigation of the magnetic susceptibilities of manganese minerals was recently completed by S. G. Watt under the direction of David R. Mitchell, now acting dean of the College of Mineral Industries of the Pennsylvania State University. D. J. Cook is studying the magnetic susceptibility of titanium minerals under my supervision. It is hoped that our research program can be continued for several years and that similar investigations will be initiated at other universities and research institutions. Ernest M. Spokes (author's reply): The discusser has touched the heart of a pedagogical problem in the field of minerals beneficiation—students do not understand magnetism and, as a result, neither do the graduate engineers. Only recently has the average course in engineering physics started teaching the fundamentals of magnetism, as they are understood in modern physics, in addition to the classical treatment of the mathematical aspects of magnetic phenomena. It is to be hoped that this increasing instruction in fundamentals will improve our understanding and inspire research to determine more of the basic magnetic data that are essential if we are to see improved methods of separation by magnetism.

Jan 1, 1959

By F. S. McNicholas

IN the writer's opinion the term "block caving" has been rather loosely applied to a general principle of mining, and therefore detailed classification of caving methods and draw, together with the characteristics required for each method, will fill a desired need. Selection of caving method should be made only after a study of all governing conditions, such as size of orebody, lateral and vertical extent of ore-body, attitude, treatment demands, possible resultant pressures, and cost and profit comparison of methods. Successful caving methods can be classified under six main headings: (1) Full-protected block caving, (2) semi-protected block caving, (3) unprotected block caving, (4) full-panel caving, (5) half block-panel caving, (6) block-panel caving. The methods and factors governing choice of method are shown in Table I. Full-protected Block Caving Full-protected block caving consists of develop-ing, undercutting, and drawing to exhaustion a block of ore of predetermined size without coordination of mining or draw with adjoining areas. The block is mined and drawn as an independent unit (Fig. 1). Full-protected block caving demands that mining and draw cannot be done against unconsolidated capping in adjoining caved and exhausted blocks. Two sides of block are against solid. Caved capping must be allowed to consolidate for a suitable period, usually not less than one year. Pillars may be left in lieu of consolidated capping (Fig. 2). The advantages of full-protected block, caving are: (1) A definite area is developed, mined, and drawn as a unit so that all work may be completed, the block drawn to exhaustion in the minimum length of time, and the area then abandoned. (? Production is not restrained because of coordina1, on with adjoining areas. (3) Records of draw and caved reserve of ore are good. Upon abanwnment of the block, accountability for production is closed out with no carry-over to adjoining areas. The disadvantages of full-protected block caving are: (1) Side dilution from the draw adjacent to the consolidated capping may be serious, particularly where capping does not consolidate sufficiently in the allotted time. (2) Boundary weakening is needed on the solid sides of the block except in weak rocks. (3) Maximum cantilever and compression effect to aid caving and fragmentation may not be secured since the draw should proceed from the solid to the consolidated capping to minimize side dilution. However, undercutting from the loose (caved capping) to the solid with a slight initial draw in the same manner will develop cantilever effect. (4) A period of at least one year, more is usually desirable, must be allowed for caved capping ,to consolidate before mining the adjoining block, depending upon the characteristics of the capping. (5) Capping may not consolidate sufficiently in the time that can be allowed. Full-protected block caving is indicated where: (1) The ground is weak and heavy and workings

Jan 1, 1952

By Edmund Kirby

This meeting marks the point at which the long-standing dissatisfaction with the mineral-land laves, the innumerable protests against them, and the many isolated efforts to obtain relief, have developed into a general movement for the: revision. That part of the mining industry which is affected by these laws has three general organizations to speak for it: the American Institute of Mining Engineers, Mining and Metallurgical Society of America, and the American "A Mining Congress: all of which are represented in this meeting. In the series of able and thoughtful presented here, prominent men have discussed the evils of the present laws aid some of the reforms which should be made in them. We all appreciate fully the ultimate value of these studies; but we are also painfully aware of the fact that discussion of this kind has been going on for a quarter of a century without any other effect than a steady increase in the mass of printed records stored on library shelves. In order to get any practical result we must induce an indifferent government at Washington to act, and to do this we must unite in pushing some practical plan whereby it may act in a simple and effective way and with the least possible amount of criticism or opposition. The actual question before us is not whether the mining laws are bad; for their evils and absurdities are not only beyond discussion but also beyond the resources of a temperate and dignified vocabulary. It is not what particular changes ought to be made; for it is premature to make specific recommendations until there is some one to listen to them. Moreover, we all know that there are wisdom and experience enough available, and awaiting that time, for the creation of a code which would be a model to the mining world. The practical question now is, how to obtain the revision; and since the American Mining Congress has of late restricted its attention to this phase of the problem I wish as one of its representatives here to present its views upon the matter.

Jan 6, 1914