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By Charles M. Bayer

Reading in the AIME annual reports that certain activities have been financed by the Rocky Mountain Club Fund, less senior members of the Institute may wonder. "What's the Rocky Mountain Club?" Less youthful members will not have to wonder. They will recall the Club as an intriguing, almost fantastic organization, largely of western mining men, that flared across the New York horizon, flamed brilliantly for a little more than two decades, then sputtered out of existence- glorious even in its last flash. It was the only product of its mold, a fabulous group of magnanimous men who unhesitatingly sacrificed a cherished dream for which they had raised millions of dollars so that the money, instead of creating a magnificent club house, could be used instead to save the lives of starving Belgian children in World War I.

Jan 12, 1964

By John F. Shaw

The Denver Mining Research Center headquartered at Denver, Colo., is typical of the new research units recently activated as a result of increased emphasis by the U. S. Bureau of Mines on research concerned with metal and nonmetal (except mineral fuels) ore extraction. The Denver Center, together with the recently established Minneapolis Research Center and the Offices of Mining Research at Reno and Spokane, and the older, well-known Applied Physics Research Laboratory at College Park, Md., share the responsibility for the comprehensive mining research program. The Denver Center specializes in two areas of research: (1) The development of engineering principles and mathematical techniques applicable to exploration, development and operational problems in mining, and (2) the study of rock mechanics as applied to ground control. The first area presently includes three categories: research on methods of ore sampling, mine-systems analysis, and applications of statistics to problems of mineral exploration. The second area emphasizes research in two main categories: laboratory investigations designed to develop a fuller understanding of how rock be- haves under the loads imposed by mining, and field investigations to evaluate stress-strength relation- ships in full-scale, operating mines.

Jan 3, 1962

By V. R. Garfias

Even before the arrival of Cortes in 1519, the history of Mexico was closely linked to that of its mineral production; the mining activities of the Aztecs being thus described by Clavigero, one of the early historians: In the mountains of Anahuac there abound in veins all kinds of metals, and infinite variety of other fossiliferous products. The Aztecs obtained gold from the countries of the Cohuijques, of the Mixtecas, of the Zapotecas and from various other places. They gathered that precious metal usually in gain, from the sands of the rivers, keeping a certain portion for the crown. They obtained silver from the mines of Taxco, of Tzumpango and others; however, this metal was not as esteemed by them as by other neighboring nations. They had two kinds of copper; one hard, which they used instead of iron to make sickles, lancea and all kinds of rural and military instruments and another, soft, with which they made kettles, goblets and other receptacles. This metal abounds mainly in the province of Zacatula and in that of Cohuijques, which at present is in the kingdom of Michoacan. They obtained tin from the mines of Taxco and lead from those of Izmiquilpan, located in the country of the Otomies. From the tin they made money, and the lead, we know they sold in the market places, but we ignore the uses to which they applied it. They also had mines of iron in Tlaxcala, in Taxco and in other places; but they either had not discovered them, or did not know how to make use of the metal they contained. In Chilapa there were mines of mercury, and in other places there were mines of sulphur, alum, vitriol, cinnabar, cohre and of a white earth which they esteemed highly. As regards mercury and vitriol, we do not know of what use they were to them; the other metals they used in paintings and dyes. There were then great abundance of amber and asphalt—bitumen of Judea—on the coast of the seas and many cities of that territory paid tribute of one and the other to the kingdom of Mexico. They mounted the amber in gold, and it was only used as ornament and display by them. With the asphalt they made certain perfumes. The following extracts dealing with pre-Colonial gold are taken from the famous " Cartas de RelaciÓn " to Charles V, in which Cortes described the progress of the Conquest: . . . here there came two chiefs who owned lands in the valley; one four leagues down the valley and the other two leagues up the valley and they gave me some gold necklaces of little value and seven or eight girls. . . . . . . that day I left the City of Churultecal and traveled four leagues to some villages of the City of Cuasucingo where the natives received me very well and gave me women and pieces of gold. . . .

Jan 1, 1937

By W. L. McMorris, Shiou-Chuan Sun

The Convertol process was first described in Ger- many by Muschenborn1 in 1952. In the U. S. Fraser2 reported this new process in 1953, and Brisse and McMorris-resented the results of a Convertol pilot plant at the Alpheus preparation plant in Gary, W. Va., illustrating the mechanics of the process by a series of sketches. The purpose of the present investigation was threefold: 1) to determine the relative effectiveness of various oils and hydrocarbons for recovering coal by the Convertol process, 2) to ascertain the behavior of coal pulps in this process under various operational conditions, and 3) to compare Convertol with flotation in the recovery of fine coals.

Jan 11, 1959

By R. W. Wittkopp, J. D. Stephens

In a device known as the electron-beam microprobe, the mining industry has lately acquired a sophisticated new analytical tool that can dig out answers to a broad range of questions spanning all phases of mining activity. Essentially, the microprobe is a specialized X-ray fluorescence unit that makes it possible to obtain chemical analytical data for volumes as small as 1 cup. With this capability, it can be used both for determining the composition of small inclusions in rocks or metallic products and for monitoring changes in composition that proceed from a reacting surface. At the Research Center of Kennecott's Metal Mining Division, this versatile probe has successfully solved problems in mineral operations ranging from exploration through refining. A few instances of how the probe has been applied at the Center are presented here. In Mineral Exploration-A Good Look Before Leaping Since the objective of mineral exploration is to locate deposits of materials which can be processed at a profit, the mode of occurrence of elements or minerals in the deposits is important.

Jan 1, 1970

By S. M. Runke, R. G. Meara, O&apos

The Bureau of Mines has been charged by Congress to investigate processes for the production of alumina from low-grade bauxite, alunite, and clay. As one part of the program, an investigation of the application of ore-dressing methods to improve the grade of high-silica bauxite is in progress at the Mississippi Valley Experiment Station at Rolla, Mo. This paper summarizes data obtained so far and presents detailcd results of tests on four typical samples. Mineralogy of Batjxite The name bauxite originally was used to designate the dihydrous aluminum oxide (A1203.2HzO). The designation has been retained, although the existence of a specific mineral of such composition has been disproved. The term is now applied to ores of aluminum consisting of various mixtures of the minerals gibbsite (AlzOa.3H20), diaspore (A120a.H20), and boehmite (Alr-03.H20). The predominant hydrous aluminum oxide in most American bauxite, however, is gibbsite. In some instances bauxite may be amorphous mixtures of the hydrous aluminum oxides that approximate the composition of dihydrous aluminum oxide (A1203.2Hz0). The proposed name for this material is cliachite. Gibbsite and boehmite, the trihydrate and monohydrate, are soluble in a solution of sodium hydroxide at elevated temperature and pressure, whereas diaspore is practically insoluble. The solubility of these two minerals is the basis of the Bayer process of alumina extraction. All bauxites contain certain impurities, the commonest of which, in the order of their importance, are: silica, principally as a constituent of kaolinite, and to a lesser extent as quartz; iron, as hematite, limonite, and siderite; and titanium, as ilmenite, rutile and leucoxene. Minor impurities are zircon, cobalt and nickel. Bauxite is produced commercially in Arkansas, Alabama, Mississippi, Georgia and Tennessee, but the most important deposits in the United States are in Arkansas, in the vicinity of Little Rock. History of Batjxite Beneficiatjon The literature on bauxite beneficiation is limited, but the reports of Gandrud and DeVaneyl and Clemmer, Clemmons, and Stacy2 show the possibilities of flotation as a means of beneficiating bauxite. Their work has also developed reagent combinations that are satisfactory for flotation of gibbsite.

Jan 1, 1944

By R. B. Sosman, J. C. Hostetter

We have shown in the preceding paper that practically all natural oxides of iron contain a determinable percentage of ferrous iron, and in many cases the percentage approaches that in magnetite itself. Some of these oxides are true homogeneous solid solutions. Others are not homogeneous, and can be separated magnetically into fractions. The nature and cause of this inhomogeneity in certain special cases form the subject of the present paper. Magnetic FRactionation of Oxides of Iron The magnetic fractionation of a sample of oxide can be conveniently carried out by powdering the material very fine, and exposing it at various distances from the poles of an electromagnet. The magnet that we used was specially designed1 to give a strong field together with a steep gradient outside of the poles. It is set in a frame, with the pole pieces directed downward. A glass plate can bc adjusted at various distances beneath the poles. If the fine iron oxide powder is placed just beneath the glass plate, successive portions of the powder are picked up by the magnetic attraction and are caught against the glass plate, the most magnetic portions being taken up at the greatest distance from the poles. Some natural oxides can thus be separated into several fractions of different magnetic susceptibilities. Among other natural iron oxides, we examined the powder obtained by crushing some crystals of hematite from Elba.2 We found that

Jan 1, 1918

Spencer Gulf takes off from the Great Australian Bight cutting a 200 mile deep wedge of water into the South Australia coastline. A pale winter sun shines yellowly on the choppy surface of this body of water which is progressively more salty as it approaches Port Augusta at the head of the Gulf. Once Port Augusta thrived as a grain port and the speedy clipper ships began or ended their legendary races there. On the eastern shores of Spencer Gulf, farm land spreads away from the water's edge. The western side of the gulf meets marginal grazing land of acacia tree and salt bush. Part way down the gulf, there are two industrial towns facing each other from opposite shores; Port Pirie on the east and Whyalla on the west. These towns are like half brothers, the common parent being the founders of Broken Hill Pty. Ltd., (BHP) who began lead smelting at Port Pirie and discovered iron ore near Whyalla needed for the lead smelting process. The iron deposits later became the inspiration for BHP's iron and steel business.

Jan 10, 1964

By J. E. Gruzleski, O. Knacke, M. J. Meixner

The evolution of CO from small specimens of solidifying steel was investigated using a thermobalance technique. Gas evolution begins in the temperature range between 1400" to .1450°C. This behavior is independent of the initial carbon content and the cooling rate. At a constant temperature above 1220°C, the rate of gas evolution is temperature independent. Out-gassing of the specimen is thought to proceed through small channels formed by the coalescence of bubbles between dendrites. LIQUID metals have a higher solubility for gas than the solid. During freezing, these gases form bubbles which may either escape or remain trapped in the solid. Recent work1 on the evolution of oxygen from solidifying silver showed that the gas is not liberated until a large fraction of the melt has solidified, and that the gas is evolved in an almost explosive manner. Because of the commercial importance of CO evolution in solidifying steel, a similar investigation was undertaken to study the mechanism of gas liberation in steel. EXPERIMENTAL The thermogravimetric method of Knacke and eixner1 to follow gas evolution by weight changes was employed. Weight differences of 0.1 mg could be reproducibly measured on specimens weighing 2.5 g. These specimens were taken from alloys with varying carbon contents from <0.01 to 0.11 wt pct and <0.01 wt pct of each of silicon, manganese, and aluminum. Specimens contained in 8 mm ID magnesium alumi-nate crucibles were heated to 1550°C under 1 atm of very pure (99.995 pct) CO with a tungsten resistance furnace. The specimen temperature was measured with a Pt-Pt/Rh thermocouple located directly beside the crucible. It is felt that the temperature thus measured was within 5" to 10°C of the specimen temperature since on fusion the weight of the specimen increased due to uptake of CO, and this weight increase was always observed to begin within the temperature range of 1530" to 1540°C. Even after 3 hr there was a small weight increase with time indicating that the molten specimen was not completely saturated with CO. Therefore, complete saturation was not attempted, and all specimens were simply held for 3 hr at 1550°C before cooling. Two types of cooling experiments were performed. One consisted of continuous cooling at linear rates from 5°C to 20°C per min down to 1020°C. The second type of experiment involved continuous cooling at 10°C per min to a predetermined temperature, and then holding the specimen at this temperature for a certain time. During all of these experiments, the sample weight was recorded as a function of time and temperature. OBSERVATIONS Continuous Cooling Experiments. No gas evolution was detected above 1450°C. The initial weight decrease always occurred between 1400" and 1450°C with the average at 1430°C. With further cooling, gas evolution continued to about 1150°C. Between this temperature and 1020°C no further outgassing was observed. This behavior did not seem to depend on the initial carbon content nor on the cooling rate in the range investigated. Typical patterns of gas evolution are shown in Figs. 1 and 2 for different initial carbon levels and cooling rates. The total amount of gas liberated during solidification varied with the rate of cooling. The total weight change on continuous cooling at a rate of 10°C per min

Jan 1, 1970

By C. K. McArthur

The subject of classification is so broad that this discussion is confined to what the author believes is of prime importance in connection with proper grinding and classification. The years past have witnessed many noteworthy changes in fine grinding and classification, which have been accompanied by a readjustment of ore-dressing flowsheets for the preparation of better ground and/or sized products at an expenditure of less power, steel and maintenance than formerly. Nowhere in the industry is more being done in the way of experimental work to lower costs than in grinding circuits, because, at best, grinding costs are high. Recent years have indicated that, on the average, finer grinding has a real application. Without careful preparation of the process feed, no operation can be highly efficient or successful. In an earlier paper, the findings of an extensive survey at representative concentrators were presented1. Also, in the year of 1935, a technical discussion was given by Dr. J. V. N. Dorr (Some Notes on Classification Trends in America) before the Chemical, Metallurgical and Mining Society of South Africa In both papers mentioned, much has been said regarding flowsheets, grinding and classification. The author is very familiar with these papers, having had considerable to do with the actual operation of the flowsheets, as well as large mills and classifiers in the work described. Some data from the second paper have been included in the following discussion. Circulating Load In this particular paper it seems advisable to deal with the classification phases of the work that to a major extent govern the success of any closed-circuit grinding unit. The question has often been asked in connection with a closed circuit: "What circulating-load ratio should be carried?" This is really an

Jan 1, 1939

By C. K. McArthur

The subject of classification is so broad that this discussion is confined to what the author believes is of prime importance in connection with proper grinding and classification. The years past have witnessed many noteworthy changes in fine grinding and classification, which have been accompanied by a readjustment of ore-dressing flowsheets for the preparation of better ground and/or sized products at an expenditure of less power, steel and maintenance than formerly. Nowhere in the industry is more being done in the way of experimental work to lower costs than in grinding circuits, because, at best, grinding costs are high. Recent years have indicated that, on the average, finer grinding has a real application. Without careful preparation of the process feed, no operation can be highly efficient or successful. In an earlier paper, the findings of an extensive survey at representative concentrators were presented1. Also, in the year of 1935, a technical discussion was given by Dr. J. V. N. Dorr (Some Notes on Classification Trends in America) before the Chemical, Metallurgical and Mining Society of South Africa In both papers mentioned, much has been said regarding flowsheets, grinding and classification. The author is very familiar with these papers, having had considerable to do with the actual operation of the flowsheets, as well as large mills and classifiers in the work described. Some data from the second paper have been included in the following discussion. Circulating Load In this particular paper it seems advisable to deal with the classification phases of the work that to a major extent govern the success of any closed-circuit grinding unit. The question has often been asked in connection with a closed circuit: "What circulating-load ratio should be carried?" This is really an

Jan 1, 1939

By H. C. Heard

The review by Professor J. C. Jaeger (Chapter 1) briefly summarizes and discusses a select group of papers by various workers dealing primarily with aspects of fracture in brittle rock materials. Professor Jaeger&apos;s treatment is primarily concerned with the correlation of phenomenological and theoretical failure criteria with empirical results from short duration tests at ambient temperatures and generally at low lithostatic and interstitial fluid pressures. As engineering rock mechanics becomes more concerned with new techniques of mineral exploration and production at increasingly greater depths in the crust, it is well to be aware of the effect of the environment -that of the superposed stress field upon the lithostatic and interstitial fluid pressure, the temperature and the duration of the loading upon the failure of rocks either by fracture or flow. All results to be discussed here are from laboratory tests on small homogeneous samples, thus caution should be used in the direct extrapolation of these results to large inhomogeneous rock masses having quite different boundary conditions in the earth. The purpose of this supplement is to briefly point out the major effects of these parameters as examined singly, with all others held constant, and to cite some recent results which apply to the main theme on the brittle failure of rocks. The total stress field imposed upon a small volume of porous and permeable rock in the earth&apos;s crust may be thought of as the sum of an applied differential stress, plus a lithostatic pressure, plus an interstitial fluid pressure. The differential stress portion may be completely specified by nine components, six shear and three normal. If the small volume element is in rotational equilibrium, by suitably choosing our coordinate axes we may resolve these nine components into the three principal com-

Jan 1, 1967

By K. Osseo-Asare

The DIAGRAM computer program has been used to develop stability diagrams such as Eh-pH, log [CNI-pH, and log [Me]-pH for the systems Me-CN-H 0 where Me = Au, Ag, Fe, Zn, Cu, Ni, Co. More complex 2 diagrams involving sulfur- and arsenic-containing species are also presented. With the aid of these diagrams, a discussion is presented of the solution conditions (e.g. pH, [CN], [CNS], Eh) vhich influence gold and silver extraction in cyanide solutions. Special emphasis is given to the effects of ore minerals or calcination products, such as pyrrhotite, pyrite, arsenopyrite and hematite on gold-silver dissolution. Application of the stability diagrams to solution treatment operations such as cementation is also indicated.

Jan 1, 1984

By Henry Howe

THAT the quiescence of a liquid while it is solidifying should favor the formation of columnar crystals, normal of the cooling surface, is seen readily on considering the mechanism of solidification. First; each particle of any composite liquid, whether it be an aqueous solution or a molten metal; in solidifying splits up into two parts, different in composition and hence in fusibility. One part is infusible at the, existing temperature, - and hence solidifies, and in general attaches itself to the inclosing walls of metal which have already, solidified; A, Fig. 1. The other part is, fusible at the existing temperature and hence remains molten. In the case of carbon Open steel, the part. of each drop which actually j; Sea solidifies is poorer, in carbon than the drop itself was before it began to solidify, and this impoverishment of the solidifying,. half-drop enriches . the other, half-drop in carbon, and Layer of Liquid thus. makes it unfreezable at the existing tem- Fig. 1.MECHANISM OF perature. SOLIDIFICATION. By this- mechanism there arises during solidification a " littoral" or shore layer- of liquid, B, Fig. 1, bathing the already solidified. walls, and more fusible than either those walls or the great remaining central mass of liquid or "deep sea," C, from which it separates them. It is essential that we grasp clearly this conception of a fusible littoral molten layer coating the already solidified walls and separating them from the deep sea. Meanwhile. heat is flowing rapidly outward through these walls, its escape cooling them, so that if any given particle of the deep sea metal

Jan 2, 1919

By S. A. Herres, A. R. Elsea

Temper brittleness refers to the loss in the notched-bar impact resistance encountered in most medium- or low-alloy steels when they are tempered within the temperature range of 700 to ll00°F or slowly cooled from a higher tempering temperature. Temper brittleness is important because it impairs the service properties of otherwise suitable steels over the range of hardnesses obtained at medium tempering temperatures and because it is impractical to cool pieces of large section rapidly enough from higher tempering temperatures to prevent temper brittleness. The problem of temper brittleness has always been closely associated with ordnance manufacture because armor plate and gun steels require good shock resistance and are often heat treated in heavy section. However, it is now realized that many brittle failures in structural alloy steel parts are attributable to temper brittleness, and there is little question that it contributes to the low impact resistance of alloy steels used in the hot-rolled or normalized condition which are slowly cooled from the hot-rolling or normalizing temperature. Recently Hollomonl has presented a comprehensive summary of the literature on the subject and an excellent description of the manner in which temper brittleness affects the notched-bar impact resistance and other mechanical properties of steel. Carpenter and Robertson2 have given a good analysis of the probable mechanism of temper brittleness, which is similar in many respects to the precipitation-hardening phenomenon. Fig 1 is their diagram illustrating the response to tempering of a susceptible steel. Three changes are recognized as the temperature of tempering a previously quenched steel is raised: (1) pre- cipitation occurs more rapidly and to a greater extent and the notched-bar impact value falls to a minimum; (2) coalescence of the precipitated particles begins to be effective and the impact values for both rapidly cooled and slowly cooled specimens increase; (3) the precipitate goes back into solution at higher tempering temperatures and the impact values of specimens cooled rapidly enough to retain the solution increase, while reprecipitation occurs in slowly cooled specimens and their impact values decrease again. No change must proceed to completion before the following one begins and there is overlapping in temperature ranges. Although there have been a large number of experimental investigations of temper brittleness, insufficient evidence has been accumulated to permit definite identification of the precipitate wnich causes temper brittleness nor have the specific effects on it of various alloy elements and impurities in steel been definitely established. This lack of evidence is largely a result of the lack of a suitable measure for temper brittleness. Temper brittleness is evidenced by an increase in the temperature of brittle failure of notched-bar impact specimens, but most of the data are in the form of an arbitrary susceptibility ratio of the room-temperature impact value for specimens quenched from a high tempering temper to that of similar specimens furnace cooled from the temper. It is obvious that this numerical ratio is dependent upon the type of specimen used and the specific conditions of testing rather than the characteristics of the steel. In general, manganese, chromium, and nickel alloy steels are most susceptible to temper brittleness and molybdenum has heen used to decrease

Jan 1, 1950

By S. E. Clay, G. P. Martins, P. R. Taylor

A grain model for gas-solid reactions in cylindrical pellets is formulated and solved numerically. The numerical solution demonstrates when it is safe to assume either a thin disk or a long cylinder geometry, and when the more general two dimensional geometry must be used. The numerical solution also demonstrates the solution of a two-dimensional moving boundary problem (i.e., when the reaction is diffusion controlled and the ratio of the height to diameter dictates two dimensions).

Jan 1, 1986

By John L. Walter

A sintered compact of iron containing 0.007 vol fraction of glass , prepared 6). powder rnetullurgtcal lechniques, was rolled lo foil, 0.001 in. /hick. The foil sullrples were anneuled a1 650° to 850°C in hydrogen. Pri,narj recryslullization prodtnced large grains which Lc3ere highly elongnled in the rolling direclion und which had an unusual prgferred orientation. The glass parlicles assumed a stringerlike dispersiorz on working; llie slrinyers were parallel lo the rolling direction and to the long axis of the grains. The same unusual grain structure, preferred orientation, and stringerlike dispersion of purticles are found in heal-ily rolled and annealed foil of tungsten which has heen doped wilh small amounts of aluminum, silicon, and polassiutvt. Both the proper dispersion of the particles and severe working (reductions in excess of 98 pct) are necessary to produce the elongzcted grain structure. RECENTLY, the author reported on the origin of the elongated or "nonsag" grain structure in tungsten foil which was doped with aluminum, silicon, and potassium.&apos; It was observed that particles, identified as mullite (Al6Si2Ol3), were present in the doped ingot (as sintered) and at all stages of processing from ingot to sheet or wire. It was shown that the particles, being plastic at tungsten working temperatures (up to 1550"C), underwent a "stringing out" parallel to the working di-direction. It was concluded that these strings of particles were responsible for the formation of the highly elongated interlocking grains observed in doped tungsten wire or sheet. To give further credence to this explanation of a long-observed but not understood phenomenon, it was decided to design a new system, one which was analogous to the doped-tungsten system. Thus, a bcc metal, iron, was chosen to be doped with glass which would be plastic at reasonable working temperatures for iron. The glass chosen was a #0080 Corning lime glass which melts at about 810°C. This is approximately the same fraction of the melting point of iron (0.6) as the melting temperature of mullite is of tungsten. It will be shown that all the observed unusual features of the doped tungsten are duplicated in the glass. doped iron, even to the preferred orientation of the grains in the recrystallized sheet. In the tungsten sheet the preferred orientation consists of two components, (1i3)(691) and (013)(362), neither of which has been observed as a component in textures of primary recrystallized bcc metals. EXPERIMENTAL PROCEDURE The glass, in the form of fine powder, was added to high-purity electrolytic iron powder and mixed dry. The particular composition chosen was 0.007 vol fraction of glass. After mixing, the powder was mechanically pressed to a disk 0.5 in. diam and 0.15 in. thick at a pressure of 5000 psi. The pellet was sintered, in pure dry hydrogen, for 2 hr at 8 50°C. The sintered pellet was then heated to 750°C and rolled to 50 pct reduction of thickness in two passes, with reheating between passes. The rolling temperature was then reduced to 600°C and the slab was rolled to a thickness of 0.050 in. Rolling to 0.010 in. was accomplished in several passes at 300°C. Final reductions to 0.003 and 0.001 in. were taken at room temperature. This rolling temperature schedule was similar, in terms of the fraction of the melting point, to that used in the rolling of the doped tungsten. The total reduction of thickness was in excess of 99 pct. Samples of the rolled foil were lightly electro-polished and annealed for 1 to 6 hr at temperatures of 650" to 85O°C in hydrogen. Samples for transmission electron microscopy were thinned on a Disa Electropol using AC-1 electrolyte.

Jan 1, 1968

By R. H. B. Jones

THIS paper reviews pertinent geology of the Biwabik iron formation, Mesabi Range, Minnesota. This iron formation is divisible into four members. Each member is distinctive and contains marker horizons, which are recognizable throughout all phases of alteration from lean, fresh rock to high-grade iron ore. Some beds have a larger magnetite content than others. During the process of ore genesis, which is essentially an oxidation process, the magnetite content is lowered. Alteration from iron formation to ore includes both oxidation of iron minerals and silica removal by leaching and these distinct processes progress at variable rates for different locations and structures. Magnetic intensities, of each horizon of the iron formation are dependent chiefly upon its preoxidation magnetite content, upon the subsequent degree of oxidation, upon the character of the enclosing rocks, and on the extent of fracturing, folding, or faulting. The results of a number of magnetic surveys are described and are correlated with results of drill-hole and mine exploration and development. The magnetic anomalies obtained are discussed in relation to phases of formation of ore within the iron formation.

Jan 1, 1946

NAME AND OBJECT. SEc. 1. This Institute is incorporated under the Membership Corporations law of the State of New York ; its corporate name is American Institute of Mining Engineers; and its objects are such as are stated in its Certificate of Incorporation. ARTICLE II. MEMBERS. SEC. 1. The membership of the Institute shall comprise four classes, namely 1. Members ; 2. Honorary Members ; 3. Associates ; 4. Junior Members. All members shall be equally entitled to the privileges of membership, except¬ing that Honorary Members, Junior Members, and Members and Associates whose residences shall be outside of the United States, Mexico, and Canada shall not be entitled to vote. Members and Associates residing within the United States of America, Mexico, and Canada, and not in arrears for dues, shall be entitled to vote in person at the meetings of the Institute, or, as hereinafter provided for, by letter ballot. SEC. 2. The following classes of persons shall be eligible for membership in the Institute, namely : as Members, all professional mining . engineers, geologists, metallurgists, or chemists, and all persons actively engaged in mining and metal¬lurgical engineering, geology, or chemistry ; as Associates, all persons desirous of being connected with the Institute who in the opinion of the Board of Directors are suitable.

Jan 1, 1917

By R. A. Matuszak

Abstract-Throughout the history of power excavating machines, engineers have continuously tried to shape the main drive speed-torque characteristics to provide an optimum performance from each main motion. Selection of prime mover for the various motions has been the subject of many engineering studies and most forms of energy conversion have been tried. A new form of electrical power conversion looms on the horizon as the most optimum yet. Controlled frequency operation of a squirrel cage induction motor increases the reliability of the most reliable form of energy conversion (electrical) found thus far, and improves the performance characteristics.

Jan 2, 1978