Search Documents

By Severn P. Brown

Search for ore continued at a feverish pace-as can be attested to by anyone who has tried to arrange for extensive diamond drilling. The stakes are high, and so is the cost as was indicated by Selco Exploration Ltd. when they announced discovery of base metal sulfides at Uchi Lake in northwestern Ontario. It was apparently their first commercial find after 15 years of exploration at a cost of more than $10 million. For the first time in many, many years the big exploration news has come from east of the Mississippi River. In January, the New Jersey Zinc Co., in an unusually worded press release, stated that they had made a major zinc discovery of 13-50 million tons of ore averaging 5-10% Zn. New Jersey's holdings are said to embrace 500 sq mi. The ore was discovered in eastern Tennessee in the upper part of the Knox dolomite of early Ordovician age. Reportedly the mineralization is at depths of 900 to 2000 ft. Currently about 20 diamond drills are working the area for New Jersey. At least nine other major companies are prospecting the region, which now includes parts of Kentucky. Five hundred thousand acres are said to be under lease. Greatest activity is clustered around Carthage, Tenn. In Missouri, the St. Joseph Lead Co. announced plans to develop a new mine in the Brushy Creek area of the "New Lead Belt." copper and zinc concentrates will be by-products.

Jan 1, 1970

By J. M. Cabal, M. Chica Olmo, J. P. Laille

One of the main goals of a simulation of a coal deposit mining is to predict a series of parameters considered by the miner to be useful, e.g. ash content, sulphur content, seam thickness etc). The idea is to simulate different ways of mining a multi-seam brown coal deposit (the Mine Puentes de Garcia Rodriguez deposit, ENDESA, Spain ), which is exploited by several bucket-wheel-excavators (BWE) . Two mining models are used: a geostatistical model which provides a numerical way of re- presenting the three-dimensional ore-body, then a deterministic model, consisting of simulating the technical aspects of the mining. The main purpose of this simulation is to show how the mining operations can be reproduced using these two techniques.

Jan 1, 1983

By G. R. Love

i\ program has been written which allows fully automatic conversion of data for X-ray intensity, as a function of time, to finished conventional pole figures. The program accepts input data in the serial order in which they are taken and is therefore immediately compatible with automatic data-acquisition devices. From these data taped instructions are prepared for the Calcomp plotter to construct ink-on-paper drawings. Because both Siemens and Norelco pole figure goniometers are used in this laboratory, the program was written for pole figure data obtained from one or more interpenetrating spiral scans during which both the polar angle, @, and the equatorial angle, a, are varied simultaneously and continuously. The reference direction for a scan, that is the point @ = 0 deg, may be chosen coincident with either the normal direction (N.D. figures) or the rolling direction (R.D. figures). In either case the plotted figures are drawn with the transverse direction (a = 0 deg) at the right and the rolling direction at the top. The full, circular, pole figure is drawn as two semicircular figures labeled "front side" and "back side". As presently constituted, the program will also accept data from circular scans taken at constant values of @. In every case the angular coordinates of each intensity entry are generated in the computer from a relatively small number of auxiliary data. The X-ray intensity data are corrected for background scattering by direct subtraction of the intensity measured with 28 set appropriately "off" the Bragg angle. It is possible to enter this correction as an additional spiral scan through the a, @ space; because the background correction does not normally vary rapidly enough to warrant this detailed a determination, the background corrections are entered as one or more auxiliary data. All data are normalized to a multiple of random intensity. The data taken in this laboratory for N.D. figures are normally taken in a reflection geometry from from sheet samples and do not extend beyond <p = 75 deg; for these data random intensity must be determined from separate experiments and entered as auxiliary information. When the auxiliary information is not available, a number is chosen to give intensity values normalized to a scale of 1 to 10. In this laboratory, R.D. figures are based upon hemispherical samples for which data are taken out to @ = 90 deg; for these data random intensity is calculated by direct numerical integration of . sin @ d@ using the trapezoidal rule and the background-corrected values of the input data. Points necessary to the construction of the pole figure are identified by simple linear interpolation between adjacent data points to determine the loci of contour lines. Points lying on a given contour are connected to one another with straight-line segments and the search-calculation-drawing sequence is patterned to assure that different contour lines do not cross, that a single line does not branch, and that lines do not end in space. However, so that there be no ambiguity in the data presentation, all contour lines end at the limits of the input data. Since the curves are constructed of straight-line segments, they are not continuous in their derivatives. However,

Jan 1, 1969

By Scott, Turner

IN 1933, the monetary metals were produced in a ratio of 6.7 oz. of silver to 1 oz. of gold, the lowest relatively for silver since the period from 1851 to 1865. At the beginning of that period, the virgin placers of California -and Australia began producing almost simultaneously; in consequence, there was an abrupt fall in the high silver side of the ratio that had prevailed through the centuries after America was discovered. The output from the Comstock and other silver-bearing lodes, located a decade after this influx of new gold began, soon restored the production ratio to its former proportion, that is, a relatively large weight of silver compared to gold.

Jan 1, 1934

By Arthur B. Yates

Diamond drilling has advanced and expanded during the past few yean. Along with this increase there has been a marked trend to rely more and more upon drilling for the outlining of ore for reserve purposes. This is especially true underground, where men have not been available for opening up ore by crosscuts, drifts and raises. During the recent heavy call upon known ore reserves, more drilling has been done for exploration and it has become expedient to drill longer lateral holes from underground and deeper holes both from surface and from exploration headings in the mines. Furthermore, these deeper holes have to be drilled closely enough to warrant calculation of "probable" if not "proven" ore, from the results obtained therefrom. Interpretation of diamond-drill results has become more precise and reliable with the growing knowledge and understanding of the geologic structures that control the geometry of ore distribution, and this has broadened the field of usefulness of the drill. All of this has created a necessity and a demand for more accurate control of the hole as to direction, a more precise and reliable method of surveying for position, and a need for better and more complete core recovery, as well as larger cores, to provide an adequate sample. At depth the control becomes more difficult and, at the same time, more important. Control A close study of drilling in various parts of the world for a period of more than 20 years has brought to light one definite rule, practically invariable; namely, that diamond-drill holes tend to deviate into a position normal to any structure existing in the rocks, such as bedding, schistosity, gneissosity, or even parting or jointing— even if the hole is started at almost any angle other than parallel with the structure. It also appears that the better developed the structure is, the more quickly will the hole get into a position perpendicular to it. It has often been said that there is a tendency for holes to "drift" in the direction of rotation. This is obviously untrue, for in a vertical hole the measure of deviation would depend upon the azimuth chosen as zero, and there is an infinite number of choices. It has been proved. however, that in homogeneous rocks there is a tendency for the hole to corkscrew, and that the direction of the spiral is the same as the direction of rotation. This may account for the belief that holes drift in that direction. Some tests have been made using right-hand and left-hand rods, and these show that no matter what the direction of rotation the hole will swing into a position perpendicular to the structure. Methods of Control The foregoing empirical rule may be used as an indirect method of control. If the prevailing structure is known, it may be advantageous to start the hole as nearly normal to it as possible, for the

Jan 1, 1946

By H. E. Lee, P. C. Feddersen

Blast-fuRnace operation at the Bunker Hill smelter deviates somewhat from common practice. Under existing conditions it is economical to operate the furnaces at "forced" capacity. The furnace feed consists chiefly of sinter and averages close to 50 per cent lead. Experience in smelting such material favors a low charge column attended by smaller proportions of coke and a low blast pressure. Under such conditions the gain in furnace tonnage greatly overbalances the somewhat higher slag losses and increased percentage of material fumed Furnace Charge The ingredients for the blast-furnace feed are stored in a group of 24 charge bins (3600 cu. ft. capacity). Each bin has two discharge chutes. Beneath each chute is a steel weighing hopper, suspended from a Fairbanks scale. The several hoppers are kept filled with the exact amount of material required to complete a furnace charge. The weighed material is discharged into a standard-gauge, bottom-dump charge car containing two compartments, each of which holds a complete charge (approximately 1½ tons). It is hauled to the blast furnace by a 44011 electric trolley locomotive. The proportionate parts of the various constituents of a representative blast-furnace charge are shown in Table 1. Table 1.—Representative Blast-furnace Charge at Bunker Hill Smelter Material Pounds Sinter.................................................. 2500 Limerock............................................... 0- 50 Coke................................................. 250-300 Scrap iron.............................................. 0-25 Settler skulls.......................................... 75 Undried zinc-plant residue................................ 0-200 Siliceous ore............................................ 25 Baghouse dust.......................................... 0-50 By-product slag......................................... 100 A variable stock tonnage of zinc-plant residue and return by-products results in fluctuations in the percentages of these materials in the blastfurnace feed. Accompanying such variations are corresponding increases or decreases in the amounts of coke, limerock and scrap iron necessary to obtain good furnace operation and adequate reduction.

Jan 1, 1937

By F. Weinberg

INTEREST is currently being directed toward grain boundary morphologies in zinc in terms of grain boundary facetingl and grain boundary energies.&apos; Some years ago the present author attempted to measure grain boundary energies in 99.999 pct purity Zn as a function of boundary angle, using the standard procedure of measuring equilibrium angles of the boundary traces at triple points. This followed an investigation he carried out on preferential melting of |H (112) Fig. 1—Electron transmission micrograph of a stacking fault, grain boundary intersection in copper. GRAIN BOUNDARY STACKING FAULT Fig. 2—Schematic representation of the intersection of Fig. 1, indicating inclination angles 0 and trace angles $. specimens were prepared by the Bollman technique in an electrolyte of 70 pct methanol, 30 pct HNO3 main-tained at -30°C. The interfacial free energy of the high angle grain boundary and of the stacking fault is assumed to be thermodynamically equivalent to the corresponding in-terfacial tensions. In terms of the true dihedral angles & between the intersecting interfaces, the equilibrium of interfacial tensions in the direction parallel to the stacking fault yields: ysF = -ygb(cos F1+ cos ±cosF2) Here, ysF is the stacking fault free energy and ygb is the grain boundary free energy, assumed equal on both sides of the intersection. Forces acting normal to the grain boundary, of the form ??gb/?F,l are assumed negligible as the grain boundary remains straight for a considerable distance on either side of the intersection. The micrograph of Fig. 1 may actually consist of several closely spaced stacking faults on the same slip plane. The actual point of intersection between the grain boundary and the first stacking fault, and the equilibrium configuration of the intersection, should not be affected by the presence of the other faults, as

Jan 1, 1970

By Edward Steidle

THAT veterans are crowding the colleges is no longer news; 78 per cent of the 1916-47 enrollment in mineral industries curricula in the United States were veterans, but the rapid comeback from an estimated 1262 total mineral industries students in 1944-45 to 11,422 in 1946-47 is almost astonishing. The figure, which includes 1008 graduate students, is a substantial increase over the previous top record of 9619 in 1938-39. A small part of the increase is caused by the larger number of women entering the field, of whom there were c 9 in 1916-47. Petroleum leads the curricula with 34.5 % of the enrollment, metallurgy is second with 28%, and mining is third with 18%. Table 1. shows all curricula offered and those accredited by ECPD. Using the Mississippi River as a dividing line, 31 colleges in the East and 27 in the West offer curricula in the mineral industries.

Jan 1, 1948

By L. K. Jetter, C. J. McHargue

The use of axis charts for representing the texture of cold-rolled thorium sheet was compared with conventional pole figures. Four texture components were deduced from the axis charts and shown to be consistent with the pole figures. It was shown that consideration of the pole figures alone could lead to an apparent component which is the average of two actually present. It was also shown that the spread about the "ideal" textures and the amount of material associated with each could be readily obtained Fom the axis chart method. BECAUSE of the crystallographic nature of the deformation mechanisms in metals, plastic flow results in the alignment of certain crystallographic directions with the primary flow directions. In the study of the "preferred orientation" thus developed, one wishes to discern the distribution of the crystallographic directions with respect to some reference direction, usually a direction related to the fabrication procedure, such as the rolling direction. The pole-figure method, introduced by ever,&apos; involves the plotting of the distribution of the poles of some family of planes on a stereographic projection which places the reference direction(s) at the north pole and/or in the center. By noting the angles between the reference directions and concentrations of poles on several such pole figures, one can deduce the crystallographic directions which are aligned with the reference directions. If the preferred orientation is relatively simple and well-developed, one to three pole figures may be sufficient for obtaining the desired information; if there are several texture components, more pole figures may be needed. A significant improvement in the method of representing the textures in wires and rods resulted from the introduction of the "inverse pole figure" or axis-distribution chart by Harris.2 Such a chart gives directly the distribution of the reference axis relative to the standard stereographic projection. There has been widespread acceptance of this method for the representation of fiber textures, and methods have been proposed for converting observed diffraction intensities into axis densities.2-6 The suggestion by Mitchell and Rowland3 and Jetter, McHargue, and williams5 that sheet textures could be represented as distributions of rolling, normal, and transverse directions have been criticized on the basis that they offer no significant advantage over a combination of two ordinary pole figures and that it has not been proved that sheet textures can be treated as quasi fiber textures.6 If the purpose of a texture determination is to study some property which is related to the orientation of a particular crystallographic plane or direction, then conventional pole figures certainly are sufficient. For example, the distribution of the slip planes in face-centered cubic metals (the (111) pole figure) serves to indicate the variation in mechanical properties of sheet. On the other hand if the study is directed at an understanding of the factors influencing texture formation, it is desirable to know not only the preferred orientation but the kind and degree of spread from it and the relative amounts of material in each component, if there are more than one. Axis charts give this information as well as the orientation distributions. Consider the procedure for deducing a texture component from a pole figure for the (111) planes

Jan 1, 1961

By D. Swan

Industrial research may be defined as a critical and exhaustive investigation to create new and better ways of doing things. The results of industrial research are new and improved products, processes, and techniques. This broad definition, of course, covers investigation of all subjects by either individuals or groups of people, and this chapter aims to examine the purpose (what research tries to do), and methods (or how research is done) as applied in the mineral industries. Concepts and History The idea or concept of organized research probably originated in the universities of Europe. There, groups of scholars banded together for discussion and application of their particular specialty to a common problem. Publication of the conclusions drawn from such investigations gave scholars in other areas the opportunity to review and criticize the work of their colleagues, and one of the hallmarks of scientific research work is the publication and criticism of the results of the investigation. It was not until the late nineteenth century that the concept of organized research for the profit of industry was recognized. During the late nineteenth and early twentieth centuries, a large number of industrial enterprises sponsored organizations to study the application of the physical sciences with the aim of making discoveries that would result in profit to the sponsoring organization. The tangible benefits accruing from these activities were so great that they, in turn, fostered several other methods for the support of organized research activities. For the large problems involving public interest, United States Government scientific re- search laboratories were set up. As the demand of smaller enterprises for research activities increased, research institutes and consulting laboratories were organized. In Europe the idea of common industry sponsorship of research centers grew and many large research organizations there were sponsored by associations of manufacturers. Finally, in the United States

Jan 1, 1959

By J. L. Bruce, G. W. Nicolson

ThE country rock of the Mavrovouni mine of the Cyprus Mines Corp. is hydro-thern~ally altered, disintegrated pillow lava, with very little tensile strength ("short" ground). In places, especially when wet, it is heavy ground, though not extremely heavy except where movement has been caused by underlying or nearby stoping operations. Damage by caving from roof or sides of galleries is not sudden but progressively faster when the size of the cave increases as a result of the fall of small pieces. CeMent and Concrete Linings During early operations, galleries in the country rock were supported by customary mine-timbering methods. Available timber, howcver, was of poor quality and of relatively high price, and replacements were frequent and expensive. Furthermore, the massive sulphide ore bodies required large volumes of fresh air for ventilation and cooling, and it was therefore desirable to provide smooth-lined galleries with low resistance for the introduction of air to the ore bodies. It was also desirable to eliminate hazards of fire in shafts and underground workings insofar as this would be practical. Cement and concrete were relatively cheap, and plans for using these in support of shafts, underground galleries, raises, and chutes, were developed steadily. Circular shafts with diameters ranging from 10 to 15 ft were adopted for all permanent shafts and airways. In places these were lined with concrete poured behind sectional pressed-steel forms especially constructed for this purpose. In other places, they were lined with precast-concrete blocks. It was found that such precast concrete of good quality could be produced on mass production scale and delivered at the mine from most favorable point of manufacture, at a cost of about 25 cents per cubic foot of concrete. This refers to prewar costs. As the use of concrete blocks in circular lined galleries was developed, it was found that there were very great advantages in the reduction of air resistance as compared with customary timber supports. After best methods had been developed, it was found that breakage and replacements were extraordinarily low, averaging only about 11\2 pct per year during a period of about 15 years. Furthermore, it has been possible to reclaim for re-use a very large percentage of the concrete blocks from abandoned galleries. During the history of the operations precast-concrete blocks have been used for lining shafts, raises, ore chutes, galleries, and shaft stations, ranging from 3 to 16 ft id. The thickness of lining has varied from 5 to 10 in.; with 12 in. thickness in a few cases. Junctions of two galleries at angles ranging from about 30 to 60° are usually made of poured concrete behind sectional forms, or of a combination of poured concretc and precast blocks. In nearly all cases it has been found advisable to make the point of the wedge at the junction, of

Jan 1, 1949

By Horace V. Winchell

This paper, embodying information acquired by the writer in his work in connection with the Geological Survey of Minnesota, is presented by permission of the State Geologist. Historical.—On November 16, 1890, the workmen of Captain J. A. Nichols, of Duluth, Minn., encountered in a test-pit on the northwest quarter of section 3, township 58, range 18, west of the fourth principal meridian, the body of soft ore now called the Mountain Iron mine. Hard ore, chiefly magnetic, had been known for many years on the Mesabi range, and explorations made by Mr. E. W. Griffin, of Minneapolis, near the falls of Prairie river in T. 56-24 and T. 56-25, and by John Mallmann, at the Mallmann explorations, T. 59-14, had revealed some hard hematite interbedded with quartzite and low-grade soft ore; but this was the first discovery of merchantable hematite on the range. Captain Nichols had been exploring more or less along the range for some two years. To him and to the Merritt brothers, of Duluth and Oneota, who, unshaken in Faith by the discouraging reports of explorers, miners, experts, and geologists, had persevered in the search for ore, great credit is due for the final success, and large rewards have accrued to them already.

Jan 1, 1893

By Oberlin Smith

The object of this paper is not so much reformatory, as historical and prophetic. History tells us that, for several months past, aluminum has, in one of its largest American manufactories, been freely nicknamed " Al" by everybody connected therewith, simply because its Christian name is too long for frequent speaking and writing. In another prominent factory, for the same reason, it is spoken of by its chemical symbol merely, pronouncing it " aye ell." These facts will, perhaps, explain the use of the final word in my title, which might otherwise seem undignified in a paper of this kind.

Jan 1, 1890

By Strathmore R. B. Cooke, Eugene L. Talbot

THE perfluoro acids and derivatives show unusual surface-active properties that qualify them as possible flotation reagents. They lower the surface tension of water from 15 to 20 dynes below that obtainable with the corresponding hydrocarbon compounds.1, 2 Fluorochemicals adsorb very strongly on solid surfaces to give films that exhibit larger contact angles than films of the corresponding hydrocarbons."&apos; * The large contact angles probably result from the terminal —CF3 group. The perfluoro acids are made by electrolysis of the corresponding carboxylic acid in anhydrous hydrogen fluoride.5 From the perfluoro acids many derivatives may be obtained, such as amides, amines, alcohols, xanthates, ethers and esters and others. Since the fluorinated analogues of the conventional hydrocarbon flotation collectors possess enhanced surface properties, a few were selected for testing. Because a survey of all possible minerals and reagent combinations would be out of the question, hematite was chosen to represent a nonsulphide system and pyrite to represent a sulphide system. The fluorinated reagents used in these experiments were prepared in the research laboratories of Minnesota Mining & Mfg. Co. Some were synthesized especially for this research. They are not available cokmercially. Separation of Nonsulphide Ores: The separation of oxides from silica has always been a challenge to the flotation industry because differences in surface properties of the minerals are normally insufficient to produce clean concentrates. Oleic acid," rosin acids,&apos; and amine salts% ave been used to considerable extent to effect separation of metal oxides and silica. The system hematite-silica was chosen to represent the nonsulphides both because of its difficulty of separation and because large tonnages of easily obtainable material are available, such as gravity concentration tailings and nonmagnetic taconites on the Mesabi Range. The wash-ore tailings used here contained approximately 35 pct iron after desliming. Samples of the material used in this work were part of the same lot used by Chang, Cooke, and Huch9 and were prepared in an identical manner. Reagents for Nonsulphide Ores: Since one of the purposes of this investigation was to compare hydrocarbons with fluorocarbons, reagents of known behavior such as oleic acid, and the alkali metal salts of certain resin acids (Dresinates), were established as standards. Hydrocarbons and fluorocarbons of comparable chain length and other experimental fluorocarbons were tried as collectors for hematite. A list of the materials used and the concentrations of their stock solutions are given in Table I. Since silica can be selectively floated from hematite by conventional reagents," a few fluorocarbon reagents were also tried for this purpose. Their composition and concentrations are given in Table 11. Most of these reagents served the dual function of collector and frother. In the case of F-11 flotation did not occur but it served as a frother when F-6 was employed as a collector. Reagent grade sulphuric acid and sodium hydroxide were used to regulate the pH. Deionized water containing less than 0.1 ppm of salts expressed as NaCl was used for all solutions and flotation tests. The pneumatic flotation cell consisted of a 350-ml fritted glass Buechner funnel with a source of filtered air which could be controlled by a needle valve." A 50-g sample of ore and 250 ml of deionized water were added to the flotation cell and stirred slowly. The reagents were added and the pulp was conditioned before air was admitted to the cell. Approximately 15 ml of the pulp were removed for pH determination before flotation was started and were then returned to the system. The pH was again measured after flotation. Air was admitted to the cell until no further flotation occurred or until the character of the float changed markedly. Both the float and the nonfloat products were filtered, dried, weighed. and assayed for iron. The cell was washed in hot water and rinsed with deionized water after each test. Occasionally the cell was cleaned with concentrated hydrochloric acid to remove iron oxide particles from the glass frit. Experimental Results: Above a pH of 8, sodium oleate was an effective collector for hematite. The emulsification of equal parts of heavy fuel oil (20"

Jan 1, 1956

F. N. SPELLER (communication to the Secretary*).-It would certainly be interesting to know more about the heat balance in this practice, but there seems to be no doubt that the net result is a greater absorption of heat where roll scale is used instead of solid metal scrap. In the experimental heats referred to, about an equal weight of pig iron or steel scrap was replaced by roll scale. This caused a reduction of about one-third in the time of blow compared with a heat of the same

Jan 6, 1917

Following the suggestion of Engineering Council and at the direction of, the President, representatives from each of the Federal Government bureaus interested in map-making were called into a conference for the purpose of coordinating all of the Government&apos;s map-making activities. This conference has now reported back to the President the results of its findings, which indicate that Engineering Council&apos;s recommendation in this matter was well founded. While the conference report states that its members were of the opinion that little duplication of effort existed, it recommends the formation of a permanent Board of Surveys and Maps. An extended review of the map-making activities, which is given as an appendix to the report, indicates that this recommendation is a logical step. The conference recommendations concerning this Board of Surveys and Maps are as follows: (1) the Board is to he com-posed of representatives of mapping bureaus to be assisted by outside engineering organizations, which have been named above; (2) the estab-lishment of an information office in one of the Government bureaus, preferably the Geological Survey, which is to be under the supervision of the Board and is to be a mapping information clearing house for the Government and outside engineering organizations; (3) copyright laws are to be so changed that copies of all. maps made in the United States and with Governmental authority, will go to the central information office; (4) the Government departments are to receive orders to cooperate, with the Board; (5) future topographic maps of all kinds are to conform with specifications for the standard topographic map; (6) the U. S. Coast and Geodetic Survey to have supervision of final adjustment of all important control data under specifications approved by Board of Surveys and Maps; (7) surveys in the form of maps and publications are to be issued as soon as possible after field work has been completed; (8) program of the Interdepartmental Committee on Aerial Surveying was approved. Outside technical and scientific organizations that are called in for consultation are to operate in an advisory capacity only, responsibility for action on Governmental work is. to rest solely with the Governmental agencies.

Jan 12, 1919

By Charles Rich, Robert Munson, Leonard Obert

Improved methods of predicting the caving characteristics of ore bodies is discussed. Experiments were conducted at Climax mine, Climax, Colo., on varied rock compositions. The cavability of adjacent areas, as well as seismic energy absorption proved to be good factors in determining cavability. Seismic velocity, core recovery, and rock quality designation (RQD) were found to be not as reliable.

Jan 1, 1977

By P. D. P. Hamilton

In any mining district where benefication of the ores is practiced, one can usually observe several types of flow sheets even though the various producers are milling ore from the same geological formations. It is obviously impossible to describe all the mills in the Porcupine district. However, the following description of some of them is of particular interest in that it shows where one mill has paid particular attention to corduroy blanket practice; one to gravity concentration of sulfides for intensive cyanidation of the values therein contained; one to flotation of values and cyanidation of this product only; and others where small variations of standard all-slime cyanidation practice prevail. In all cases it will be seen that cyanidation is the basic principle. Discussions involving the difference in the flow sheets and the reasons for them will always be of value to those interested in the art. The author of this article, however, believes that such discussions should originate from the operators of the mills under discussion. For this reason no comparisons or discussion will be included in the description of the mills mentioned. Should any reader of this article obtain information therefrom which will be of value to him in helping to solve his own particular problems, the author will consider that the article has satisfactorily served its purpose. All values mentioned throughout this article are based on the value of gold at $20.67 per ounce. Coniaurum Mines, Limited The ore of the Coniaurium mines consists of a mineralized schist and quartz containing about 2.5 per cent sulfides. Owing to the low grade of ore developed in the mine, extreme care has had to be exercised throughout the entire mining and milling operation in order that an operating profit might be obtained. The management, however, has been able to keep costs down, with the result that at present the outlook for the property is considerably brighter than it has been in the past. This is partly due to the fact that it is now known how to mine and treat

Jan 1, 1935

By J. Marin, H. A. B. Wiseman

This paper presents results of an experimental study dealing with the plastic stress-strain relations of aluminum alloy 14s-T6 subjected to combined biaxial tension and compression stresses. Plastic stress-strain relations for both constant and various types of variable stress ratios were determined and a comparison made with the simple flow theory of plasticity. THIS investigation was undertaken for two main purposes: 1—to obtain plastic stress-strain relations for Alcoa 14s-T6 when subjected to various combinations of biaxial stresses, and 2—to determine the validity of the flow theory in predicting plastic stress-strain relations for combined stresses. The biaxial stresses used were tension combined with compression. These stresses were produced by subjecting a thin-walled tube to axial tension and torsion. Various types of combined stress conditions were investigated. To provide control test data and information on the influence of biaxial stresses on the strength, the usual constant stress ratio type tests were made. These tests showed that the biaxial yield strength agrees approximately with the distortion energy theory. However, the Prager semi-empirical theory agrees best with the test results. For these constant stress ratio tests the plastic stress-strain relations were found to agree approximately with the flow theory. (For constant stress ratio the flow and deformation type theories are identical.) In view of the fact that the constant stress ratio tests cannot distinguish between the flow and deformation theories, a number of variable and special biaxial stress tests were made. These tests showed that the flow theory is inadequate, since large differences exist between the experimental and theoretical results. Special tests were also conducted to check the validity of the isotropic yielding assumption. This assumption is made in the linear-type flow theory. In these tests specimens were loaded in tension to predetermined values beyond the proportional limit stress. The tension load was removed from the specimen and the specimen was subsequently loaded in torsion to fracture. Other tests were applied with the order of torque and tension loading reversed. The nominal stress-strain curves for these two tests approximately coincide indicating that the assumption of isotropic yielding is valid. In addition, these tests verified the requirement by the slip theory of plasticity that prestraining below 140 pct of the proportioned limit stress in either torsion or tension did not influence the subsequent plastic stress-strain relations in tension or torsion. Another type of test was conducted to check the assumption that the axes of principal stress and strain coincide during plastic flow and variable stress conditions. These tests were conducted by applying combinations of axial tension, internal pressure, and torsional loads such that the axes of maximum principal stress could be rotated through 90" during the loading path. The results of those tests showed that the angle between the axes of principal stress and strain varied greatly and that the assumption of coincidence between axes of principal stress and strain is not valid. Introduction In various metal processes including forming of sheets, rolling of bars, and extrusion of rods, metals are subjected to stresses beyond the yield strength of the material. Often these stresses are not simple stresses acting in one direction, but are combined stresses acting in more than one direction. Structural and machine members are often subjected to combined stresses. To adequately determine the factors of safety for these members, it is necessary to know the plastic stress-strain relations of the material used for various combined stress conditions. Various theories have been proposed for predicting the plastic stress-strain relations for combined stress in terms of the simple tension plastic stress-strain relation for the material. To determine which theory might be adequate, test results must be obtained for various combined stress conditions, in order to compare the actual with the assumed theoretical behavior. Although there is considerable test data available for combined stress conditions in which the principal stress ratios are constant, relatively little test information is available for vari-

Jan 1, 1954

By Fred C. Bond

The Standard method of determining the crushing resistance of rocks consists of crushing prepared shapes under slow compression, and expressing the ultimate crushing resistance at the load causing failure in pounds per square inch of cross-sectional area perpendicular to the crushing force, with the height approximately equal to the diameter. One-inch cubes or cylindrical drill cores are commonly used. Cubes and drill cores are cut by a highspeed steel disk with diamond dust embedded in the edges, and running under a water spray. such a saw will cut one square inch or more of hard stone per minute. An oiled, spherical, swivel compression block of small diameter should be used to equalize the pressure. Each sample is crushed between sheets of cardboard or blotting paper extending about one-half inch beyond the edges of the stone. A cloth is wrapped around it to prevent dangerous explosive shattering. It is probably preferable to place the swivel block below the specimen, with either a rigid head or another swivel block above. Whatever the arrangement, the conditions should be selected that will develop the maximum crushing strength of the specimen, even though its top and bottom planes may not be precisely parallel. The cardboard pads may be dispensed with if the ends of the specimens are polished smooth. The use of lead pads was discontinued because of the observed tendency to split the material. The samples are weighed and measured before breaking, and the density is calculated. Cubes that contain bedding lanes or veinlets are usually placed with these vertical and parallel to the crushing force, in order to develop the maximum resistance possible. A number of compression tests were made on Canadian ores, by Forrest Nagler, of the Allis-Chalmers Manufacturing CO., and are listed alphabetically in Table I. These tests were made on one-inch cubes or on diamond-drill cores approximately one inch in diameter and One inch long. The drill cores represent virgin rock, while the cubes may have been previously weakened by explosives. compression tests have been made in the Allis-Chalmers Milwaukee Laboratory on a number of ores and other materials. These are listed alphabetically in Table 2. In test NO. 1339, on limestone from the Hanna Coal Co., comparison was made between 2 by 2-in. diamond-drill core segments and one-inch cubes cut from the cores in the same strata. Results for the cylinders are tabulated directly below those for the cubes. The bedding planes were normal to the compressive force in breaking the cylinders and parallel in breaking the cubes, which accounts for the lower strength obtained from the cylinders. The percentage of net linear compression at the ultimate pressure was measured in test No. 1055 for Fontana TV A quartzite as 0.30 for cube A, and 0.37 for cube D.

Jan 1, 1947