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By Frederik P. Agterberg

This paper deals with frequency distributions in the field of mineral resource evaluation when a grid is superimposed on the study area and metallogenetically significant attributes are coded with respect to the cells of the grid. It is shown that the parameters of a negative binomial distribution for frequency of mineral deposits per cell can be derived from the parameters of a gamma distribution for the coded attributes. It is also shown that an exponential model for spatial correlation of cell values and Matheron's discrete Gaussian model for indirect transfer functions may provide a suitable methodology for relating cell value distribution to cell size.

Jan 1, 1977

By H. A. Wriedt

At 500°C (932°F) the range of y' iron nitride is from 5. 77 + 0.03 wt pct N (in coexistence with a iron) to 5.88 * 0.03 wt pct N (in coexistence with E iron nitride). Stoichiometric "Fe,N" (5.900 wt pct N) is near the upper extreme of possible compositiom. The depe-dence of nitrogen activity (expressed as pnh,/Ph,) on nitrogen content is described satisfactorily by a "Langmuir" isotherm: At even the highest nitrogen concentrations, less than 0.18 pct of' the nitrogen atoms present are impositions of disorder. Past investigations1-4 of the Fe-N system have left only details of the thermodynamic behavior of the y' nitride, "Fe,N9', to be studied. The present investigation was made to establish more precisely than hitherto the limits of composition and the relation between composition and nitrogen activity at 500°C. EXPERIMENTAL TECHNIQUE The compositions of nitrides in equilibrium with various NH, + Hz mixtures at 500°C were determined from the weights gained by 0.02-in.-thick (4.0 to 4.5 g) strips of purified iron* when the nitrides were formed A description of the gas generation and furnace system has been published.5 Cracking and blistering during conversion of the original solid iron at 550°C injected considerable porosity into the strips without causing their disintegration. The time for complete conversion was significantly lowered by periodically reducing partly nitrided specimens in hydrogen and then reexposing them to the nitriding gas. Gas mixtures producing single-phase were used in the equilibrations at 500°C. Equilibrium was regarded as existing when the specimen weight was not detect-ably affected by further exposure to the same conditions. The gas compositions and nitrogen activities at which y' transformed to a iron (lower activity limit) and to E iron nitride (upper activity limit) were redetermined during the investigation. A specimen was equilibrated in an NH, + Hz mixture at 500°C and then exposed to a s1ightly different gas. When equi- librium had been reestablished the gas was again changed slightly. At each stage of this repeated process, while the specimen was reacting with the gas, the variation of its weight with time was observed. The onset of phase transition was marked by an abrupt change in the amount and rate of weight gain or loss. The specimens were weighed outside the furnace, in air and at room temperature, on a balance with 0.05 mg precision. When it was found that the specimens were oxidizing at a significant rate during the weighing, a series of timed weighings was made with each specimen, starting 1 min after its exposure to air. RESULTS AND ANALYSIS The gain in specimen weight from oxidation during weighing was linear in the logarithm of time between 1 min and about 2 hr, Fig. 1, later becoming linear in the cube root of time. In the logarithmic period, nitride specimens oxidized two to three times as fast as

Jan 1, 1970

By P. Nicholls

Patent records show that the attempt to improve the burning of fuel by mixture or pretreatment with chemicals dates back to the early years of the last century. By 1845 English and French patents had included the specific beneficiations of elimination or reduction of smoke, soot and clinker; reduction of the ashes; elimination of sulphur fumes; increase of the rate of burning; increase of the time a given charge of fuel would last; and, in most patents, a saving of fuel. The earlier patents specified additions up to 80 lb. or more per ton of fuel, but after 1860 the quantity was seldom more than 4 lb. There is no record of the extent to which these patents were commercialized, but after 1874 many American patents were assigned to companies specializing in treatment of coal, so it is probable that the products were marketed on a considerable scale at least as early as that date. From 1900 on, many proprietary products were marketed under the general name of "fuel savers," the principal sales being in small packages for the use of householders; savings of from 10 to 40 per cent of the coal were promised. Starting with 1927, the use of proprietary or other mixtures of chemicals was extended to power plants and to treatment of coals at the mines, the claims of saving of fuel being subordinated to those of general improvement and, in particular, to reduction of clinker-ing. Such expectations are attractive and a number of companies experimented with or adopted the practice. There were reports of improved operation, but, apparently, few were confident enough that these improvements were due to the salts to publish the results of tests or their records of operation. There are no data on the yearly tonnage of coal treated but indirect reports suggest that it has been relatively large. Since its establishment in 1910, the U. S. Bureau of Mines has continually received inquiries about these products. At the request of other governmental departments it made tests in 1910, 1916 and 1930, using certain proprietary products applied according to the instructions of the vendors; these tests were made with eastern coals in domestic and

Jan 1, 1938

By P. Nicholls

Patent records show that the attempt to improve the burning of fuel by mixture or pretreatment with chemicals dates back to the early years of the last century. By 1845 English and French patents had included the specific beneficiations of elimination or reduction of smoke, soot and clinker; reduction of the ashes; elimination of sulphur fumes; increase of the rate of burning; increase of the time a given charge of fuel would last; and, in most patents, a saving of fuel. The earlier patents specified additions up to 80 lb. or more per ton of fuel, but after 1860 the quantity was seldom more than 4 lb. There is no record of the extent to which these patents were commercialized, but after 1874 many American patents were assigned to companies specializing in treatment of coal, so it is probable that the products were marketed on a considerable scale at least as early as that date. From 1900 on, many proprietary products were marketed under the general name of "fuel savers," the principal sales being in small packages for the use of householders; savings of from 10 to 40 per cent of the coal were promised. Starting with 1927, the use of proprietary or other mixtures of chemicals was extended to power plants and to treatment of coals at the mines, the claims of saving of fuel being subordinated to those of general improvement and, in particular, to reduction of clinker-ing. Such expectations are attractive and a number of companies experimented with or adopted the practice. There were reports of improved operation, but, apparently, few were confident enough that these improvements were due to the salts to publish the results of tests or their records of operation. There are no data on the yearly tonnage of coal treated but indirect reports suggest that it has been relatively large. Since its establishment in 1910, the U. S. Bureau of Mines has continually received inquiries about these products. At the request of other governmental departments it made tests in 1910, 1916 and 1930, using certain proprietary products applied according to the instructions of the vendors; these tests were made with eastern coals in domestic and

Jan 1, 1938

By C. K. Leith

AT the outset I would like to make it clear that I do not enter this discussion in a controversial spirit, but in an attempt to contribute something helpful to an understanding of a difficult problem. I have too high regard for the sterling quality of the work of the men who have studied this subject in detail to offer anything in the way of essential contradiction to their statements of fact. Difference of opinion arises from differing valuation of the possible alternative hypothesis which these facts suggest. Some degree of recrystallization in limestone contact zones has been recognized by many investigators. Earlier investigators, for the most part, assigned an important, if not the most important, role to recrystallization in development of these zones. With the growing recognition, of introduction of ores and gangue materials into the contact zone from igneous rocks through the medium of primary magmatic solutions, there has been a tendency to ascribe to this process most, if not all, of the chemical and mineralogical characteristics of the contact zone. This has involved a correspondingly diminished emphasis on recrystallization of substances already there as a factor in the process, and in some cases even the complete elimination of this hypothesis. From detailed study of a few contacts, casual observation of others, and a general familiarity with the literature, some of us have been led in recent years to raise the question whether the pendulum has not swung too far away from recrystallization toward direct introduction from igneous sources, and to argue for more recognition of the part played by recrystallization.1 The inevitable sequence has been that those of us who have taken this view have been charged, at least by inference, with emphasizing recrys-tallization to, the total exclusion of the alternative process. Scientists, like other men, like to classify and pigeon-hole views under simple and definite designations, leaving out qualifications which would tend to make the classification more difficult to state. This has made the problem seem more definite and simple, but has tended to obscure the fact that the disagreement is primarily not one relating to essential facts, but one of

Jan 6, 1914

By A. L. Holley

The general usage of engineers, manufacturers, and merchants, is gradually, bat surely, fixing the answer to this question. In every country rails, boiler-plates, and machinery bars, whether hard or soft, are almost universally called steel, when they are made from cast ingots. Other names for the softer steels, such as " homogeneous metal,'' "Bessemer iron," " Martin iron," and the like, have failed to obtain general recognition. The meaning of the term steel, before it was enlarged to cover newly developing varieties, has been traced, by a recent writer, down through Percy, Shakspeare, and the Bible, in a most interesting manner, from an archœological point of view. Undoubtedly, it did characterize hardness arid other qualities imparted by carbon. It is within the memory of most of us, that all steels were tool steels, and that the soft, structural varieties were introduced—varieties which harden but little, which bend cold, and which, in many physical properties, are akin rather to wrought-iron than to tool-steel. But, since both the hard and the soft steels are made by the same processes, and have their great, distinguishing structural feature in common, viz., homogeneity resulting from fluidity, it has come to pass, despite every other proposed nomenclature, that all the compounds of iron which have been cast in malleable masses, are called steel, the term wrought-iron being still confined to malleable iron made from pasty masses, and hence laminated in structure. No inconvenience has been found, so far, in distinguishing between the more or less carburized products, in general, by the terms " highsteel," "low-steel," "tool-steel," etc., and, in particular, by prefixing the percentage of carbon and other ingredients, to the terra steel. Steels which contain distinguishing ingredients other than carbon, are called "chrome-steel," "titanium-steel," and the like, just as variously compounded bronzes are called " phosphor bronze," " aluminium bronze," etc. Thus the combination of several words or symbols, and figures, may completely disclose the characters of the metal, in terms that are subject to no misunderstanding. But inasmuch as several high metallurgical authorities and clever writers have of late proposed to disturb this natural and somewhat settled nomenclature, it seems important to consider the claims of the various classifications. I shall attempt, in this paper, to show

By Evert Hoek

Summarising a conference is never an easy task, but I will try to keep my comments brief and to the point. There are a number of lessons which we have learned from our deliberations together during these past three days, and I will try to give you my impressions of these lessons and of their practical implications in open pit mining. The first thing that has become increasingly obvious during these discussions is that it is no longer acceptable to offer an 'Act of God' as an excuse for a major slope or tailings dam failure. Disasters such as that at Aberfan in the United Kingdom have focussed the world's attention on the activities of the mining industry and the report of the commission set up to investigate the Aberfan disaster clearly showed that adequate knowledge was available and that failure to apply this knowledge did not qualify as an 'Act of God'. The courts and the world's press are certain to impose increasingly harsher penalties and criticism on those held responsible for major failures, particularly of tailings dams, in the future. One of the major problems in applying available knowledge to slope problems is that attempts to apply this knowledge are frequently left too late. To provide an engineering solution in the case of a slope in an advanced state of failure is an almost impossible task, and it is essential that those responsible for the stability of a slope must learn to recognise signs of distress at an early enough stage for effective remedial measures to be taken. As our ability to solve slope problems improves, the time at which slope stability problems are considered in a mining project must move forward to a stage at which these problems can be anticipated and dealt with before they arise. Conferences such as this are important in that they enable us to exchange ideas and advance our knowledge to a level at which such predictive engineering will be possible. It has been encouraging to hear of mining projects such as the Bougainville Copper operation where slope stability studies were carried out as part of the overall evaluation programme and it is hoped that this will become a more common procedure in the future. Providing a safe slope in an opencast mine obviously costs money, either in terms of the reduced ore to waste ratio given by flat slopes or because of the cost of stabilization techniques such as drainage or the use of rock anchors. An optimum slope design will provide maximum safety at minimum cost but achieving this optimum is not an easy task. Any one of us could design a slope which would be stable to the end of time, but it is probable that that slope would be so flat as to be totally uneconomic in most open pit mining situations. On the other hand, if the overall economics of a mining project are so critical as to require slope angles which the engineer responsible for these slopes considers to be unsafe, it is his duty to make us could design a slope which would be stable to the end of time, but it is probable that that slope would be so flat as to be totally uneconomic in most open pit mining situations. On the other hand, if the overall economics of a mining project are so critical as to require slope angles which the engineer responsible for these slopes considers to be unsafe, it is his duty to make

Jan 1, 1971

By R. F. Krueger, L. C. Vogel, P. W. Fischer

Previous studies have shown that the permeabilities of sandstone cores are markedly reduced following exposure to drilling fluid and subsequent clean-up with oil at high-pressure gradients. Laboratory experiments reported in this paper indicate that permeability damage from drilling mud or water can be substantially avoided through use of an initial low-pressure gradient followed by gradually increasing gradients during clean-up by reverse oil flow. On the other hand, attempts to improve the permeability of damaged Berea and oil formation cores with high-rate oil backflush (simulated well stimulation) and low-rate clean-up gave erratic results. Essentfully complete permeability repair was achieved in most of the fresh water-damaged cores from Miocene and Pliocene oil-producing formations; only minor improvement was noted generally in tests with both water-and mud-damaged Berea sandstone. Field well stimulation treatments using high-rate back-flush resulted in long-term productivity improvement when production was brought in at gradually increasing production rates and then restricted to a steady value less than the maximum possible rate. Wellbore plugging at high production rates correlated with increasing solids content in the produced oil. Observations and results from these tests agree with current concepts that formation damage in water-sensitive rocks results from movement and bridging of formation fines, rather than from clay swelling alone. INTRODUCTION Many laboratory studies1-g have shown that the permeabilities of sandstone cores are often markedly reduced following exposure to fresh water or water-base drilling mud filtrate. However, work with cores in the restored state has demonstrated that, although permeabilities to water may be very low for sandstones containing hy-dratable clays, flow of oil can often restore a substantial portion of the effective permeabilities to oi1.Neverthe- less, water invasion into water-sensitive sandstone cores results in varying degrees of permanent reduction in permeability to oil.24' Based on field data, Wade's statistical study" of well completion effectiveness also indicated a correlation between productivity damage and water invasion during completion. Similar damage can result from fluid invasion during workover. Nowak and Krueger' and Bertness4 observed in their early work (1951-53) that formation damage in water-sensitive sandstones was associated not only with swelling of expandable clays but also with movement of dispersed particles. Subsequent work by Monaghan et al." (1959), Atwood'' (19641, Mungan" (1965) and Gray and Rex'" (1965) has led to general acceptance of the hypothesis that permeability damage in water-sensitive formations is caused by migration of finely dispersed minerals and bridging in "brush heap" arrangements at pore constructions. In laboratory studies, Monaghan et al.' found the use of chemicals to be of only minor value for repairing formation damage. Atwood? however, was successful in substantially repairing damage in a number of low-permeability cores using an n-hexanol flush. In the field, except for treatments with acids, the use of chemical washes to reduce wellbore damage has had limited and sporadic success and generally is unpredictable. A statistical analysis of stimulation treatments in silt-blocked wells has shown that physical manipulation of wash materials is more important than chemical composition." The recent work reported on formation damage in water-sensitive sands brings to mind the results of some unpublished exploratory work done in 1954 in connection with drilling fluid studies.' This laboratory work and subsequent field stimulation treatments indicated a beneficial effect of controlled pressure drawdown and the associated production rate on formation clean-up. This paper reports the results of this work and more recent supplemental experiments on the clean-up of water-sensitive sandstones damaged by water or filtrate invasion. PERMEABILITY RECOVERY AFTER DAMAGE BY DRILLING MUD APPARATUS AND TEST SAMPLES A drilling mud circulating system was used to expose cores to simulated wellbore conditions. The mud flow system is the same as that described by Krueger and Voge17 except that no provision was made for scraping

By B. H. Bergstrom, W. Mitchell, C. L. Sollenberger

D. W. Fuerstenau (Associate Professor of Metallurgy, Dept. of Mineral Technology, University of California, Berkeley, Calif.) and D. A. Sullivan, Jr. (with the University of California) — Messrs. Bergstrom, Sollenberger and Mitchell have shown in two excellent papers that the energy per unit mass required for the breaking of spheres is inversely proportional to the size modulus of the fragments of the broken spheres. They found that the fragments of spheres broken within a steel enclosure were finer than those produced by breaking spheres encased in gelatin. This results from utilization of part of the strain energy at fracture for secondary breakage. For spheres not encased in gelatin, these authors found that after fracture the fragments of the spheres possess kinetic energy amounting to 45% of the strain energy needed for initial fracture. Breakage of a sphere in gelatin results in waste of this kinetic energy, whereas breakage inside the steel container makes use of this kinetic energy for further size

Jan 1, 1962

By J. Szekely

A rrlethod is presented for the estitnation of oxygen pickup by teettzed molten steel streams. Of the mechanisrt~s considered for oxygen absorption, physical entrainment appeared to be the most significant. The estent of this physical entrainment may be calculated by the application of boundary layer theory. It was found that the values of oxygen pickup thus predicted were in wry good agreement with data reported in the literature, in the case of short, well-defined metal streams. This entrainment model does not provide an adequate description of oxygen pickup by long streams, exoosed to external winds and where breakup of the streatn is likely. WheN molten steel is teemed into a mold or tundish it will absorb oxygen contained in its environment. Recently interest has been expressed in the measurement and possible prediction of the extent of this oxygen absorption: this interest owes its existence to two principal factors: a) the desirability of providing a quantitative assessment of the role played by the absorbed oxygen in impairing the quality of (vacuum degassed. stainless, or continuously cast) steel; b) the need for providing guidelines for stream protection methods. The purpose of this communication is to suggest a simple method for the prediction of oxygen absorption by continuous metal streams and to compare the predicted values with the data available in the literature. It is hoped that this method may provide at least an initial framework for the interpretation of additional data that might become available. FORMULATION Consider a continuous metal stream falling into a molten metal pool as depicted in Fig. 1. This system may absorb oxygen due to the following two mechanisms: 1) physical entrainment of gases (including oxygen) into the molten pool where reactions. thus absorption, will occur; 2) mass transfer (convec:tive diffusion) of oxygen to the metal stream. 1) Physical Entrainment. The physical entrainment may be calculated by using the concept of the diaplace-ttzent tlzickness of the laminar boundary layer, which will be stated briefly in the following.&apos; When a fluid flows past a solid surface, a portion of the fluid close to the surface is retarded due to fric-tional forces. This region in which the velocity of the fluid differs from that in the main stream is called the boundary layer. An illustration of this is given in Fig. 2 where it is seen that the thickness of the boundary layer increases as we move along in the x direction. In the laminar region, when Re, < 10&apos; the thickness of the boundary layer is given by the following relationship: f =4.64 Re;1" [1] where 61 is the boundary layer thickness, x is the length along the leading edge, Us is the velocity of the free stream, (i is the viscosity of the fluid (gas in this instance).

Jan 1, 1970

An appropriation of $4000 was made to the United Engineering Society for the support of the work of the Engineering Council. It was resolved that the proposed amendments to the Constitution, regarding requirements for membership, be sent to the membership without comment thereon by the Board of Directors. Forty-one members, and three associates were elected. The status of two junior members was changed to member. The resignation of one member was accepted. The dues of nineteen members who are engaged in active duty with the Allied armies were remitted. B. B. Thayer was elected a member of the Board of Trustees of the United Engineering Society for a period of three years, to succeed himself. John H. Janeway was elected a member of the Library Board for a period of four years, to succeed himself. George C. Stone was elected a member of the Library Board in place of E. F. Roeber, deceased. E. Gybbon Spilsbury was elected representative of this Institute on the John Fritz Medal Board of Award, to succeed himself. J. Parke Channing was elected a member of the Engineering Council for a period of three years, to succeed himself.

Jan 1, 1918

By Cleland N. Conwell

Intermittent coal mining has been conducted in Alaska for over a century. The first report of coal in Alaska was by the Veechy expedition of 1826 and 1827. Whaling ships used coal from Corwin Bluff near Cape Beaufort during the early and latter parts of the 19th century. The first coal mine in Alaska-and probably the oldest in the Pacific coast of North America-was opened by the Russians at Port Graham on the southwest tip of the Kenai Peninsula. The mine was operated from 1855 until 1867 when the United States took possession of Alaska. From 1880 to 1915 coal mining was carried on intermittently at several localities including Unga Island, Herendeen Bay, Chignik Bay, Kachemak Bay, and several points along the Yukon River. Small coal mines along the Yukon River provided fuel for the river steamers traveling from St. Michaels to Whitehorse. The area of sustained coal production began with the completion of the Alaskan Railroad from Anchorage to the Matanuska coal field in 1916 and to the Nenana field in 1918. Coal production continued to increase until 1953, at which time the oil and gas fields in Cook Inlet were developed. Oil and gas eventually replaced the Matanuska coal as a means of providing heat and power. The military in the Anchorage area shifted from coal to oil in 1967 causing a decrease in production. The increased demand for electric power in the Fairbanks area offset the decline and coal production started to increase. In 1969-1970 the Golden Valley Electric Assn. (GVEA) constructed a mine-mouth power plant 70 miles southwest of Fairbanks near Healy and a power line to Fairbanks. Location of Coals in Alaska Coals are found in all geographical subdivisions of Alaska. Coal in Alaska ranges in age from Carboniferous to Tertiary, and grade from lignite through anthracite. Fig. 1 shows the locations of Alaskan coal fields. The only fields that have been developed extensively are the Matanuska and Nenana. Fig. 2 illustrates the annual production of coal in Alaska and the ratio of underground to strip mining.

Jan 1, 1973

By J. H. Scaff, H. C. Theuerer

Germanium may be reversibly converted from n to p type by heat treatment. Data for the conversion and the associated changes in resistreatment.tivity are given and the results are interpreted in terms of changes in the donor-acceptor balance. MEANS for controlling the electrical properties of germanium in a predictable manner are of interest because of the increasing utilization of this element as the semiconducting material in electrical devices. Since both the mechanism and the magnitude of the electrical conductivity depend upon the kind and quantity of impurities present, the conductivity usually is adjusted by first carefully purifying the germanium, and then, by standard alloying procedures, adding the elements desired. The elements usually added are from the third or fifth periodic groups depending upon whether p- or n-type germanium is desired. However, in the development of germanium rectifiers during the war, it was found that it was possible also to modify reversibly the conductivity of germanium and even to produce conversion from n to p type by heat treatment.1,5 Since then a detailed study of this effect has been made. The data are presented in this paper and an explanation is offered for the effects observed. Preparation and Experimental Procedure The method used in preparing the germanium ingots for this investigation has been previously described.&apos; The method consists essentially of (1) reduction of GeO2* and (2) preparation of a 50-g ingot from the reduced material. Graphite containers are used in both steps. In the first step the GeO2 is reduced in hydrogen at 650 °C to form a sponge germanium which, to assure complete reduction and to obtain massive materials, is fused subsequently in the reduction furnace by gradually raising the temperature to 1000°C. The button of germanium thus obtained corresponds to a yield of 99.8 pct. The final ingot is prepared by fusion of the germanium button in a helium atmosphere. A cylindrical crucible in a vertical silica tube furnace is employed and the crucible is heated by an external induction coil. The ingot is solidified from the bottom upward by raising the induction coil at a constant rate with power to the coil kept at a fixed value. In such ingots, segregation is normal and most of the impurities are concentrated in the last region of the ingot to freeze. It follows then that the major portion of the ingot is purer than it would have been if freezing had occurred in a random fashion. Moreover the orderly advance of the freezing surface during solidification establishes in the ingot a succession of surfaces of constant composition, if it is assumed that the liquid is homogeneous and that diffusion in the solid is negligible. Therefore, some information on the distribution of impurities in the ingot may be acquired by determining the shape of the solid-liquid interface at different stages of solidification. This is of importance because the concentration of impurities will be seen to affect the response of germanium to heat treatment. Such information is difficult to acquire by direct means, for the impurities responsible for the electrical properties of germanium prepared in this way are present

Jan 1, 1952

By George M. Enos, Robert J. Anderson

An impoRtant factor affecting the rate and nature of corrosion of metals and alloys is the film, or coating, formed on the surface; and this may accelerate or retard corrosive action once started. The formation of films and coatings is intimately associated with the chemical composition and physical constitution of both the metal and the corroding medium. A film or coating may be either the corrosion product resulting from oxidation; that is, an oxide or salt, or a deposition of suspended matter from the corroding media upon the surface of the metal, or a mixture of both. The coating may adhere tightly or loosely to the surface of the corroded metal. In short, a film or coating is the reaction product of the corroding medium and the metal, which adheres to the surface of the metal and with which may be intermingled material from the attacking media not concerned in the chemical reactions. As the terms film and coating are used by different writers for very different things, distinction is made between the two, by the present writers, on the basis of thickness. Thus, a film is defined as a corrosion product or deposition, on the surface of a corroded metal, that is of such thickness that it cannot be measured by the metallurgical microscope. A coating, on the other hand, is of such thickness that it can be measured. If the resolving power of the 2-mm. (equivalent focal length) apochro-matic oil immersion objective (N.A. 1.4) is taken as the limit of the microscope, the limiting resolution is two lines that are 0.0002 to 0.0004 mm. apart. It is thus possible to measure coatings that are greater than 0.0002 to 0.0004 mm. thick. This thickness is equivalent to 50,000-

Jan 1, 1925

INTRODUCTION TO SAMPLING THEORY Before specifically discussing mineral sampling and sampling procedures, let us briefly consider broader and more universal concepts of modem sampling theory. A sample is de- fined as a representative part or a single item from a larger whole, being drawn for purpose of inspection or shown as evidence of quality. In modem theory the sample is a part of a statistical population whose properties are studied to gain information about the whole. The theory of sampling is built around the concept that if enough representative units of a larger overall population are selected without bias, the average value of the units will approximate that of the total population. Modem theory attempts to answer the question of how many samples are enough, given certain limits and constraints, and seeks to apply methods of sample selection and of estimation that provide, at the lowest possible cost, estimates that are precise enough for the purposes at issue. In order to meet these objectives the designer of a sample survey must rely heavily upon statistical theory. Statistics has been defined as the collection, presentation, analysis, and interpretation of numerical data. Statistical methods are primarily concerned with making valid inferences about a population based upon samples taken from the population. For most statistical applications, the total sample is in terms of number of items, attributes, or things; whereas mineral samples are usually in terms of weight or volume of mineral particles. Certain steps are involved in a well designed sample survey without regard to the particular field of application. Because the desired characteristics of an unmined mineral deposit can- not be known other than by sampling, we will consider these principle steps in terms of a mineral sample survey: 1) Clear definition of the objectives of the survey. In the case of mineral sampling this step is so apparent as to be almost ridiculous. However, it is surprising how often the overall objective of a sampling program is overlooked when decisions are made on a day-today basis. 2) Definition of the population to be sampled. The word population is used to designate the aggregate from which the sample is chosen. A sampling program may be designed to determine the grade of a single stope within a mine, the grade of a particular zone within a complex ore body, or the total value and extent of a mineral deposit. Since mineral sampling is usually done in phases, it is well to

Jan 1, 1980

By Perry Harrison

THE increased use of sintering for the beneficiation of iron ores and the reclaiming of flue dust creates a lively interest in sintering costs and, economics. The character of material sintered and geographical location of plants so radically alter sintering costs and economics that it is well to understand at least the basic elements which control such changes. The following cost factors are believed to be roughly approximated for large-scale Dwight-Lloyd &apos;continuously operated sinter-machine installations located anywhere. PER CRUDE TON Labor, supplies and repairs 0.15 Power 6.5¢ X kw-hr. rate ? Plant overhead and administration 0.05 Depreciation per ton annual capacity 0.05 Fuel: 6 per cent coke breeze or equivalent minimum ? 1 per cent coke breeze additional for each 5 per cent free and combined water in ore or dust ? Ignition distillate at 0.6 gal. per ton ? PER SINTER TON Royalty on Ore 0.10 Royalty on Flue Dust 0.15 PER CRUDE TON "Winter expense"; i. z., the cost of the five months enforced idle . period for plants tied in to Great Lakes transportation season 0.03 Using the foregoing data, it is possible to roughly approximate the cost of efficient sintering at any location for. any ore, viz:

Jan 1, 1932

By R. R. Nash, W. F. Sheely

Experiments were conducted on magnesium monocrystals in order to collect quantitative information on the mechanisms which limit the rate of basal slip. Using critical shear stress and creep data, activation energies for creep at low aid at high temperatures were derived. The activation energy at low temperatures is the same as that for jog formation and the activation energy at high temperatures agrees with that for climb. COTTRELL has suggested that at low temperatures, the expansion of dislocation loops under stresses near the yield strength is limited by the rate at____ which the expanding loops can cut the "forest" of dislocations passing through the glide planes.&apos; On the basis of this mechanism, seeger2 has derived expressions for low-temperature creep and for the relation of flow stress of single crystals to temperature. In the work reported here, the authors have performed experiments designed to obtain quantitative data on the physical properties of the dislocation intersection mechanisms operating during basal slip in pure magnesium monocrystals. Above a critical temperature, dislocations thread-

Jan 1, 1961

By Daniel L. Noble

Riparian communities are those related to, or near a natural watercourse (or sometimes of a lake, impoundment, or tidewater). Generally, riparian communities contrast sharply with the dominant vegetation type in an area, for example, the willow-birch-aspen- dominated watercourse in the Black Hills with its associated beaver- muskrat-trout habitat as compared to the dominant monotype ponderosa pine forest on either side of the drainage. Riparian ecosystems are valuable for the aesthetics, namely, varied landscape; photography and art; human awareness; diversity of plant and animal life, some of which may be unique to that habitat; cover, food, and water for associated wildlife and domestic animals; for recreation; for domestic water supply; and as natural outdoor laboratories. One major negative impact on riparian communities is hazardous chemicals from effluents from agricultural, industrial, and mining- metallurgical processes. One such chemical is cyanide, long used in the processing of gold and silver, and discharged previously directly into some of our natural ecosystems. With present environmental awareness, industry and government are attempting to minimize or eliminate this contamination. Homestake Mining Company began processing gold ore in the Lead- Deadwood area of South Dakota in 1878 and has remained in production at variable activity levels to the present time. The amount of cyanide (and heavy metals) entering the ecosystem during this time can only be crudely estimated, in part because of the variability in activity and the lack of understanding and concern about environmental pollution until the 1960&apos;s. Whitewood Creek, a tributary of the Belle Fourche River which flows into the Cheyenne River and

Jan 1, 1983

By AIME AIME

RECENT experiments in reflected sunlight photography in mine shaft&apos;s&apos; and. slopes in the McAlester, Oklahoma, coal-mining district have been so satisfactory as to indicate that such a method has definite scientific value. The entrances to abandoned deep shafts and slopes on Choctaw and Chickasaw Indian coal lands in Oklahoma are being filled or bulk-headed by the U. S. Geological Survey under Public Works Project F. P. 63-C&C. Inasmuch as these mines may be reopened at some future time when there is a demand for coal, H. I. Smith, Chief of the Mining Division, suggested that photographs of deep shafts would be of value. Such photographs would show timber details and the general condition of the walls. Photographic records of the exact status of shafts when filled will facilitate operations in reopening.

Jan 1, 1936

By Joseph Taylor

THE Ducktown district is in the extreme southeastern corner of Tennessee, its principal railroad point being Copperhill, on the Blue Ridge division of the Louisville &Nashville Railroad, midway between Knoxville, Tenn., and Atlanta, Ga. The ore deposits were discovered about 1849 and development work was begun in the early fifties. Only the "black copper? ores, products of secondary enrichment, from beneath the gossan outcrops and overlying the massive sulphide deposits, were then mined and smelted for their copper content. Upon their exhaustion, attention was directed to the treatment of the pyritic ore remaining, resulting in the devising of a, process consisting of open-heap roasting, followed by blast-furnace smelting, which was practised until 1903, when semi-pyritic smelting was-adopted. In 1908, the companies operating in the district; on account of litigation brought about by alleged smoke damage to forests and vegetation in the adjoining counties of Georgia, were compelled to erect enormous acid plants to prevent the escape of the sulphur dioxide produced in the smelting operations. The utilization of this sulphur dioxide in the, manufacture of sulphuric acid as a byproduct has added to the revenues of the companies, and at the same time has furnished a valuable source of supply of sulphuric acid to the fertilizer trade of the South, and more recently to the manufacturers of explosives for use in the production of war munitions. The steadily increasing demand for sulphuric acid for the manufacture of fertilizers and explosives, together with the decreasing imports of pyrites, from which the acid is generally produced, now makes it imperative that greatly extended resources of pyrite be developed. While the Ducktown deposits do not predominate in pyrite, they do contain an inexhaustible supply of pyrrhotite, admixed with pyrite, which can be satisfactorily employed to supplement or substitute for pyrite in acid making.

Jan 2, 1918