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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 David R. Mitchell, Ernest M. Spokes

INFORMATION on magnetic properties of minerals other than magnetite is scanty and some- times erroneous. Often there is no information at all. W. R. Crane's table of tractive forces published in 1901 is still the best guide in the field, but Crane's data can be used as a guide only, since he ignored such important factors as impurities in the minerals, size, and packing effect. During the 1930's work by the U. S. Bureau of Mines added greatly to knowledge of the behavior of certain minerals in a magnetic field. The USBM bulletin gave for the first time complete magnetic characteristics for magnetite and fragmentary data for a few other minerals. The work reported here covers a study of the magnetic-susceptibility relationships of the wolf-ramite series of minerals and sphalerites as related to their chemical compositions. Theories are proposed to explain divergences found from commonly accepted beliefs.

Jan 3, 1958

By Irwin Roman

In addition to projects such as those reported in parts I and II above, the Section of Geo-physics of the Federal Government has undertaken a considerable amount of fundamental research. Two such field-projects may be mentioned, one a magnetometric study in the Comstock Dis-trict of Nevada, and the other a resistivity-study of snow and ice. In addition to the field-problems, there have been two classes of research of a mathematical type. One of these has been the preparation of tables, scales, and charts for the important geophysical functions already known; the other has been the extension of the relations involved in the resistivity-problem. The magnetometric study at Spring Valley, in the Comstock District, was made for the pur-pose of determining the value of the magnetometer in extending the knowledge of a region, as ob-tained by purely geological means. The variations in the vertical magnetic intensity were mea-sured with an Askania balance at intervals of 20 feet, along lines as shown in Figure I.. These lines were 100 or 500 feet apart over an area approximately a rectangle 6000 by 7500 feet. In addition to the lines shown, two areas were selected for more intensive study. In one, short

Jan 1, 1940

By Phillip Philbin, Frank E. Senftle

A field neutron activation analysis technique suitable for determining uranium in ores has been tested. The method is based on the measurement of the 74.7 keV gamma ray from 'U. When the thorium/uranium ratio is greater than one or the vanadium is greater than 1%, a low uranium analysis is obtained. No satisfactory correction for thorium has been found, but a correction for vanadium can be deter¬mined. For ore containing greater than 0.01% uranium, the uranium can be deter¬mined with an accuracy of about 10% which is quite adequate for a field exploration technique.

Jan 1, 1972

By Henry Louis

THE work performed by, the Royal Commission on Mining Subsidence is likely to prove of permanent value, less perhaps for the conclusions it has reached and for the recommendations it has based upon these than for the admirable exposition which it affords of the law concerning mining subsidence and of the legal status of the person who has suffered damage by reason of such subsidence, as also of him whose working has caused the damage. The Commission was appointed by Royal Warrant in the middle of 1925 and delivered its final report in the middle of 1927. The terms of reference to the Commission were as follows: "To consider the operation of the law relating to the support of the surface of the land, and of buildings or works on or under the surface, by underlying or adjacent minerals; to enquire into the extent and gravity of the damage caused by subsidence owing to the extraction of minerals and the incidence of the resulting liability; and to report what steps should be taken, by legislation or otherwise, to remedy, equitably to all persons concerned, any defects or hardships that may be found to arise in existing conditions."

Jan 1, 1929

NOMINATIONS FOR OFFICERS. In accordance with the Constitution, Article VII., the following nominations have been prepared by the Nominating Committee, submitted to the Board of Directors at its October meeting, and are hereby published for the information of the members. For Director and President: Benjamin B. Thayer, District 0 For Directors and Vice-Presidents: Herbert C. Hoover, District 6 W. L. Saunders, District 0 For Directors : Reginald W. Brock, District 11 Charles W. Merrill, District 6 Albert R. Ledoux, District 0 Henry L. Smyth, District 1 D. C. Jackling, District 7 The Constitution further provides that " Any complete or partial ticket of nominees signed by any twenty-five Members or Associates of the Institute and transmitted to the Secretary by December 15 shall also be printed and circulated with the official ticket and over the names and with the recommendations of the nominators, together with an expression of opinion of the Board thereon if deemed expedient.

Jan 11, 1913

By P. A. Witherspoon, Y. W. Tsang

Normal stress-fracture closure variation and stress-dependent fluid flow rates were calculated for rock fractures of different aperture distributions. This study shows that both the mechanical and hydraulic properties of the fracture are controlled by the large-scale roughness of the rock fracture. Hence the typical large-scale undulation wavelength of the rock joint dictates the suitable sample size to be used in normal stress and fluid-flow measurements, if results due purely to sample size are to be avoided.

Jan 1, 1982

By Stefan Boshkov, Malcolm T. Wane

THE validity and accuracy of velocity measurements underground have been questioned repeatedly by those in mine ventilation work. The general disagreement on the subject is well illustrated in an AIME publication.' Although the presence of errors is readily admitted, their magnitudes are not known and often are described by practical operators merely as "great," "small," or "of no importance." The belief that errors are of academic interest only prevails because of a justifiable claim that actual volumes of air circulated are well in excess of those required by law and safe mining practices. Poor understanding of the source and nature of errors inherent in velocity measurements, coupled with questionable determination of cross-sectional area, result in faulty techniques for the purpose of expediting ventilation surveys and render doubtful the calculated volume. Often consistency of readings is confused with accuracy. A succession of check readings showing a maximum deviation of 5 pct in the measured value of velocity usually signifies nothing more than diligent application of technique in a stable ventilating current. This article discusses the errors involved in air measurements underground. Where instrument errors are presented, the treatment is confined solely to the rotating-vane anemometer, recognized as a most useful ventilation measurement tool because of its simple design and easy operation. In the following pages a positive deviation is defined as one which has to be added to the registered air velocity to obtain the true air velocity.

Jan 1, 1956

By Francis M. Walters, Irwin R. Kramer

The substitution of cobalt for part of the nickel in Invar was found by P. H. Brace1 to lower the coefficient 01 expansion. Scott1 extended the use of cobalt to alloys of higher inflection temperatures. Such alloys have a larger temperature range of low expansion than those without cobalt, and their use up to 400' or 500°C. offers decided advantages in certain applications. However, it has been found that the iron-nickel-cobalt alloys are not stable in this temperature range. Experimental Methods Two methods were used in studying the stability of the low-expansion iron -nickel-cobalt alloys. Dilatometer specimens were held at 480°C. for 9 months and the change in expansion characteristics was dctcr- mined. Filings were held for about 2 months at various temperatures and the change in structure was determined by X-ray diffraction. As shown by Table I, the alloys studied covered a wide range in nickel plus cobalt content (which determines the inflection temperature) as well as some variation in the ratio of nickel to iron (which controls the temperature of the gamma to alpha transformation). Included also are alloys containing carbon and vanadium, carbon and titanium and three with various amounts of copper. The alloys were melted in a high-frequency induction furnace with a magnesia crucible, using ingot iron, electrolytic nickel and commercial cobalt. Fifteen-pound heats were cast into iron molds after deoxidizing with silicon, or

Jan 1, 1942

By Francis M. Walters, Irwin R. Kramer

The substitution of cobalt for part of the nickel in Invar was found by P. H. Brace1 to lower the coefficient 01 expansion. Scott1 extended the use of cobalt to alloys of higher inflection temperatures. Such alloys have a larger temperature range of low expansion than those without cobalt, and their use up to 400' or 500°C. offers decided advantages in certain applications. However, it has been found that the iron-nickel-cobalt alloys are not stable in this temperature range. Experimental Methods Two methods were used in studying the stability of the low-expansion iron -nickel-cobalt alloys. Dilatometer specimens were held at 480°C. for 9 months and the change in expansion characteristics was dctcr- mined. Filings were held for about 2 months at various temperatures and the change in structure was determined by X-ray diffraction. As shown by Table I, the alloys studied covered a wide range in nickel plus cobalt content (which determines the inflection temperature) as well as some variation in the ratio of nickel to iron (which controls the temperature of the gamma to alpha transformation). Included also are alloys containing carbon and vanadium, carbon and titanium and three with various amounts of copper. The alloys were melted in a high-frequency induction furnace with a magnesia crucible, using ingot iron, electrolytic nickel and commercial cobalt. Fifteen-pound heats were cast into iron molds after deoxidizing with silicon, or

Jan 1, 1942

By Francis M. Walters, Irvin R. Kramer

THE substitution of cobalt for part of the nickel in Invar was found by P. H. Brace1 to lower the coefficient of expansion. Scott1 extended the use of cobalt to alloys of higher inflection temperatures. Such alloys have a larger temperature range of low expansion than those without cobalt, and [ ] their use up to 400° or 500°C. offers decided advantages in certain applications. However, it has been found that the iron-nickel-cobalt alloys are not stable in this temperature range. EXPERIMENTAL METHODS Two methods were used in studying the stability of the low-expansion iron-nickel-cobalt alloys. Dilatometer specimens were held at 480°C, for 9 months and the change in expansion characteristics was determined. Filings were held for about 2 months at various temperatures and the change in structure was determined by X-ray diffraction. As shown by Table I, the alloys studied covered a wide range in nickel plus cobalt content (which determines the inflection [ ] temperature) as well as some variation in the ratio of nickel to iron (which controls the temperature of the gamma to alpha transformation). Included also are alloys containing carbon and vanadium, carbon and titanium and three with various amounts of copper. The alloys were melted in a high-frequency induction furnace with a magnesia crucible, using ingot iron, electrolytic nickel and commercial cobalt. Fifteen-pound heats were cast into iron molds after deoxidizing with silicon, or

Jan 1, 1941

By N. J. Grant, D. S. Bloom

An investigation of the Cr-Mo-Ni ternary system and attendant binaries has been completed. Some changes in the binary diagrams are shown to be necessary. The 1250°C section of the ternary and the liquidus surface have been delineated. A system of invariant reactions existing above 1250°C has been suggested. BECAUSE chromium, molybdenum, and nickel are important not only as bases for alloying systems but also as major alloying additions for other refractory metals, a study of the phase diagrams is of great interest and importance. In addition there are interesting features of theoretical value, a number of which are of prime consideration in this work. The major aim was to determine the ternary phase diagram of these metals at and above 1250°C, with sufficient attention given to lower temperatures to permit an understanding of the conditions existing at 1250°C and above. To understand ternary systems it is essential that accurate information concerning the binary systems be available, which in turn presupposes thorough knowledge of the constituent elements. On the basis of this investigation not only were significant inaccuracies indicated in the binary systems but much consideration had to be given to one of the elements, that is, chromium. The observation has been made that chromium undergoes a crystal transformation at a temperature near its melting point. Much of the experimental data leading to the detection of this transformation and the effects of this hypothesis on the form of the Cr-Ni phase diagram have already been reported' . and will not be repeated here. The experimental methods employed in the investigation have also been covered.'-" he purity of the molybdenum utilized in this work showed by qualitative spectrographic analysis that chromium, copper, iron, silicon, and tungsten were present in quantities of 0.1 to 0.001 wt pct. During the course of the investigation more than 100 melts were made, weighing from 150 to 200 grams each. Each of these melts was sectioned for chemical analysis and for specimens for examination in the as-cast and various heat-treated conditions by X-ray and metallographic means. All X-ray diffraction patterns reproduced here were made using chromium Ka radiation although iron and copper targets were used on occasions during the investigation. Experimental Results Mo-Ni-System: The most recent comprehensive investigation of the Mo-Ni system was made by Ellinger' in 1942; the diagram as shown in the American Society for Metals Handbook is based on his work. The work done on the system in this investigation substantiated the general form of the diagram although some differences were observed. These are indicated by a comparison of Ellinger's diagram and Fig. 1, the latter showing the results of pertinent thermal analyses made in this research. It can be seen in Fig. 1 that the eutectic composition is

Jan 1, 1955

By Edward Sayre

IN shaft sinking for coal mines, the cost item greatly influences the method adopted. This holds true especially when soft material must be traversed. The average life of a coal mine is short. This is clue either to the limited area of the coal basin or to the great expense of maintenance and haulage underground when the entries are extended a considerable distance from the hoisting shaft. Therefore, the engineer in opening a coal mine is confronted with the fact that the cost must be kept within certain bounds else the venture will prove unprofitable. For this reason he may be prohibited from adopting certain safe, but expensive, methods that are used in sinking caissons for foundations, driving transportation tunnels, or other work of permanent construction. A common method of sinking through difficult ground employs the aid of a steel shoe pushed ahead of the shaft timbers. Another is the drop-shaft method. These two methods were used in sinking the main shaft and the air shaft of the Eagle No. 3 mine, at Des Moines, Ia., and the following data show the relative success and cost of the two methods of sinking under the same conditions. A drill log of the material to be penetrated was as follows (see Plate 1, Fig. .1)

Jan 9, 1916

By A. E. Gorum, I. Cornet

Fatigrle of ionic crystals has been studied primarily in magnesinm oxide. under cyclic stress dislocations move irrreversibly; they multiply; slip bands form and grow; cracks mucleate and propagnte, and failure occurs. The use of ionic crystals such as MgO is advantageorus in such investigations because they are optically transparent. Individual dislocation Intersections with {100} surfaces may be observed with a standard microscope, using etch-pit techniques. Slip, deformation, crack .formation, and fracture in MgO crystals under cyclic stress are compared with cotrresponditzg processes in metals. ThE effect of cyclic loading in metals has been studied for many years. The appearance of slip lines is readily observed and the ensuing fracture may also be seen. From these observations it is possible to predict the behavior of a material and make an educated guess as to what is happening internally, but the actual changes taking place within the structure are not readily apparent. If one could obtain a material in which the individual glide components could be observed, it would be invaluable in determining the actual slip distribution resulting from cyclic loading as well as the distribution of slip in the neighborhood of a growing crack. Such a material is magnesium oxide. Dislocation arrays may be observed by means of etch pits

Jan 1, 1961

By R. W. Baldwin

As used in geophysical exploration, the term overvoltage applies to secondary voltages set up by a current into the earth which decay when the current is interrupted. These secondary effects may be measured by pick-up electrodes. The term induced polarization has often been employed to describe this same phenomenon. In its own operations Newmont Exploration Ltd. commonly uses the word pulse. The basis of this method in prospecting is that metallic particles, sulfides in particular, give a high response, whereas barren rock, with certain exceptions, gives a low response. Overvoltage has been tried in searching for many types of mineral occurrence but has been most successful in outlining the widespread disseminated mineralization associated with porphyry coppers. History:' Newmont Mining Corp. has been interested in overvoltage since 1946, when Radio Frequency Laboratories of Boonton, N. J.. drew the company's attention to phenomena observed in the laboratory. At the instigation of A. A. Brant further model studies were undertaken, and the first tests were performed in 1947. Tests at San Manuel, Ariz., in 1948 were very encouraging, clearly demonstrating that the method could be used to distinguish scattered sulfides at depth. H. 0. Seigel followed up the San Manuel work with a study to determine the phenomena involved.'

Jan 1, 1960

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 Walter C. Smith, O. J. Seeds

METALLIC bismuth was known in the Middle Ages and the name is supposed to come from the German Wismut. The origin of the German name is uncertain. References to bismuth are found in the writings of Valentine, Paracelsus, and Agricola between 1450 and 1550. Early specimens of bismuth were very impure and often were confused with antimony, tin, and zinc. About the middle of the eighteenth century, J. H. Pott, C. J. Geoffroy, and Torbern Bergman succeeded in producing fairly pure bismuth and showed it to be an elementary metal similar in many respects to lead. H. S. Washington has estimated that bismuth occurs in the earth's crust about as abundantly as tungsten and silver; i.e., to the extent of 10-6 or 10-7 pct. It is found as native metal, both alone and associated with tin, copper, and other metals, and in a large variety of ores. The important ores are the sulfide (bismuthinite), the oxide (bismite), and the carbonates (bismutite and bismutosphaerite) . Other occurrences of bismuth are in the vanadate (pucherite), the selenide (guanajuatite), the telluride (tetradymite), and in many complex sulfides, arsenides, and antimonides. Bismuth minerals have been found in many parts of the world but very few of the bismuth deposits have been of economic value, the oxide ores from parts of China being the exception. The major portion of the bismuth production of today is the so-called by- product bismuth. Bismuth often occurs in ores mined and treated primarily for other metals, and during the treatment of these ores

Jan 1, 1953

By R. L. Perrine

This paper shows how stability theory can be used to optimize solvent recovery of oil. Application of the theory leads to definition of the limiting conditions required for stable displacement to occur. One of these conditions is that the size of a solvent "slug" must at least equal a prescribed minimum. The criteria to be satisfied are miscibil-ity and stability. Stability implies that no viscous fingering will occur and that mixing will be caused only by a dispersion process. Miscibility implies that complete recovery will be obtained from the swept regions. Thus, for any specified set of reservoir conditions, an optimum use of solvent is defined. INTRODUCTION The early outlook for solvent flooding as a means to increase oil recovery was very favorable. Some laboratory results indicated that a "slug" containing perhaps 2 to 3 per cent of a hydrocarbon pore volume could be successful. However, other data suggested as much as 30 per cent would be required. The difference is of considerable economic importance. A theoretical explanation for these divergent results has been advanced by the author.1,2 Stability theory defines conditions for two distinct flow regimes. In stable displacement, solvent and oil become mixed by a dispersion process, and the solvent requirement is small. On the other hand, unstable displacement can degenerate into viscous fingering. The practical result is a considerable increase in the extent of mixing and, thus, in the solvent required. The present paper shows how to use stability theory to optimize solvent recovery of oil. Oil is usually considered to be displaced by a small amount, or a slug, of solvent. Gas in turn follows solvent. Any fingering will permit contact of nearly solvent-free gas and oil, leading to immiscibility and reduced recovery. Thus, our optimum is defined by two restrictions — stable flow and miscibility. Although an immiscible solvent process could prove more profitable than any miscible process, such processes lie outside the selected definition of an optimum. The usefulness of computations based on the present work will depend on the validity of the general theory. Because the important idealizations required tend to minimize the predicted solvent requirement, the results should state correctly the limiting conditions required. Therefore, theoretical calculations should have practical value. This paper first reviews several principles that result from stability theory. The following section describes use of these ideas in relatively simple systems which symmetry makes appear one-dimensional. Of particular importance is the step-by-step design of 3 stable minimum-solvent slug. The use of stability theory in cases of multi-dimensional displacement is discussed and, finally, suggestions are given for simplified practical application of the theoretical results. PRINCIPLES OF STABILITY THEORY The use of perturbation methods to derive stability conditions has been shown by the author.l The discussion is presented in terms of the fractional concentration of solvent in the single hydrocarbon phase. Quite generally, any disturbance can be represented as a Fourier series, of which only the least stable term need be considered. Denoting this term at time t = 0 by cn,

By H. A. Wahl

This paper presents methods of designing hydraulic fracture treatments in formations saturated with slightly compressible liquids. Howard and Fast describe the fluid-loss control resulting from the viscosity and compressibility effects of the reservoir fluid in terms of a fracturing fluid coefficient. However, for horizontal fractures, this coefficient is applicable to infinitely thick reservoirs. These methods of evaluating fluid loss from horizontal fractures during treatment differ from previous methods in that: (I) formation thickness is incorporated in the velocity function describing the rate of fluid loss to the formation; and (2) for a given thickness the relative position of the fracture to the horizontal boundaries of the reservoir or any interrnediate permeability barrier is incorporated in the design procedure. This theory is applied to several actual and hypothetical field cases. The results of these calculations demonstrate that the eflect of formation thickness on fluid loss from horizontal fractures may result in fractures several times larger than predicted by other methods. INTRODUCTION Hydraulic fracturing has been the dominating well-stimulation technique during the last decade. From the time it was commercially available, fracturing has had a very favorable success ratio compared to other stimulation methods. However, numerous wells that were successfully stimulated remained economic failures. Only in the last few years has the oil industry recognized the importance of designing treatments for each well which will yield the maximum profit. This implies that for a given set of treatment conditions the size and general physical characteristics of the fracture can be determined. One of the outstanding contributions in the field of fracture design was presented by Howard and Fast.' In their paper, three flow mechanisms that control fluid loss from the fracture to the formation are defined: (1) viscosity effects of the fracturing fluid, (2) viscosity and compressibility effects of the reservoir fluid, and (3) wall-building effects of a treated fracturing fluid. The rate of fluid loss to the formation adjacent to a fracture is shown to be a function of time. For each flow mechanism the velocity function v(t) is expressed as a constant or fracturing fluid coefficient divided by the square root of time. This form of v(t) can be used in the Carter equation, as developed in the Howard and Fasc paper, to estimate the areal extent of fractures. This equation may be written as In the following sections the effect of formation thickness on fluid loss from horizontal fractures is evaluated when the controlling flow mechanism is the viscosity and compressibility of the reservoir fluids. The major assumptions inherent in the Carter equation are brought out in subsequent mathematical developments. THE EFFECT OF RESERVOIR FLUIDS ON FRACTURE EXTENSION When a fracture treatment is performed using a fracturing fluid identical to the reservoir fluid, the only flow mechanism controlling fluid loss is the viscosity and compressibility effects of the reservoir fluids. In developing a fracturing fluid coefficient for this mechanism, Howard and Fast considered a segment of the formation bounded by a unit area on the fracture face and extending to infinity in the direction of leak-off as shown in Fig. 1(a). The direction of leak-off z is normal to the fracture face. The equation governing the linear isothermal flow of fluid into this segment is where a = Eq. 2 is a form of the diffusivity equation. It is derived from the equation of continuity, Darcy's law and Eq. 3

By T. P. Meloy

The behavior of slime-sized particles in a flotation cell is neither well documented nor well understood. In general, slimes (or 'fines' as they will be alternatively called in this chapter) have been either ignored, eliminated, or treated empirically. Recently, however, some good experimental and theoretical work has been done that leads qualitatively to a clearer understanding of the problems involved. Fines are small particles that, owing to their smallness, behave differently from larger particles of the same material. The smaller the particle, the larger is its surface-to-mass ratio. The difference in the surface-to-mass ratio for a micron-sized particle and a centimeter-sized particle is 10,000 to 1. For our purposes we shall arbitrarily define any particle less than 10 µ 10-3 cm) as being a fine. This is generally considered the upper limit of colloidal-sized particles. Recently, the field of colloidal chemistry has successfully used the concept of the double layer to explain dispersion and flocculation of fine particles in a static system. Flotation, however, is a dynamic system due both to the turbulence of the liquid and to the coursing of the bubbles through the cell. Further more, a flotation system is a heterogeneous system in which there are a number of different types of particles which interact with one another. A further difficulty is that no two flotation systems are the same for minute quantities of a variety of common chemicals will alter the behavior of the system. These reasons make reproducible experimental results that can ex- plain fine-particle behavior difficult to obtain. In spite of these experimental difficulties, millions of tons of ore containing a large amount of fines are successfully floated every year. For example, at the Morning mill of American Smelting and Refining Co., a galena concentrate that was 42% -6 µ and a sphalerite concentrate that was 33% -9 µ were floated leaving a tailing that was 27% - 9 µ.l Ores that contain fines can generally be divided into two classes. In the first are those in which the valuable mineral tends to slime, such as galena and hematite. In the other class, one or more of the gangue minerals forms the slime; a typical example is barite. Though the problems due to the presence of fines are often the same in handling the two classes of ore, the method of handling them is different because of economic considerations. Nonmetallic mineral flotation is particularly affected by slimes, by either slime-coating effects or excessive reagent consumption. Though a given gangue mineral may not float under the conditions prevailing in the flotation cell, it may still be able to adsorb the collector. I£ it also slimes, a significant

Jan 1, 1962