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By C. O. Worden, C. A. Zapffe, F. K. Landgraf

SUMMARY FOLLOWING the discovery of Parke and Ham that deoxidation control of cast molybdenum can be predicated upon simple fractographic examination, a special study of that metal was undertaken to investigate those patterns ascribed to forgeability and nonforgeability. An elaborately developed system of cleavage patterns immediately rewarded the study; and they are reported here as a necessarily preliminary contribution calling attention to information which is both new in type and in origin. In general, the present observations confirm those of Parke and Ham, and Woodside; but they also disclose a wealth of detail and correlated phenomena which greatly expand the earlier information. For example, the oxide pattern of nonforgeability is found to be complex, perhaps involving as many as three distinctive patterns. And the nature of the carbide seems to be at least twofold. In addition, transgranular facets are here shown for the first time. Elaborately complex, but in a characteristic manner, these facets depict distortion in original crystal growth which provides truly extraordinary patterns. No carbide and oxide forms display themselves transgranularly, except in profile as exceedingly thin superficial films at the grain boundaries. Crystallographic features are also rare-a condition undoubtedly resulting from the great substructural distortion; but occasionally registrations are found of cleavage on {001}, and faulted areas believed to be Neumann-type deformation on {112}. INTRODUCTION Parke and Ham, 1 and again Woodside, 2 have reported that the forgeability of molybdenum cast by their vacuum-electric-arc process can be predicted with great dependability by a simple fractographic observation. They state that nonforgeability is the result of a grain boundary oxide which can be readily identified on the fracture facet at high magnification; and they convert the nonforgeable condition to a forgeable one by increasing the carbon content of the melt until the oxide structures subsequently observed in the fractograph become replaced by a second strongly marked pattern characteristic of carbide and coincidentally indicative of forgeability. Considerable importance immediately attaches to such observations: (I) because of their direct commercial application to one of metallurgy's inviting and relatively unexplored metals; (2) because of a general scientific curiosity regarding the nature of these characteristic markings; and (3) perhaps more important, because of

Jan 1, 1948

By Homer G. Turner

Coals, other than anthracite, have been so thoroughly studied under the microscope during recent years, that we now know what kinds of plants and what parts of plants form the bulk of lower rank coals from peat to bituminous coal. The microscope has also shown the state of preservation of such vegetation as well as the nature and distribution of products of plant decay. These and further details have been ascertained mainly through the employment of two methods of attack, section cutting and maceration. Anthracite has failed to respond to these methods, so well adapted to the study of lower rank coals and, therefore, has been neglected by investigators to such an extent that there is much doubt as to its microscopical characteristics. The object of this paper is to lift anthracite from its realm of obscurity by demonstrating the wealth of microscopical detail that is revealed when reflected light is used on a properly polished and etched surface and, further, to show the relationship between anthracite and bituminous coal. Technique The method adopted in this investigation is similar to that described in an earlier paper.' Because of slight modifications recently made, the process is again described. It consists, briefly, of etching a polished surface of coal with heat. Although pieces of various sizes and shapes are used, blocks of coal about 2 or 3 cm. square take the most uniform polish and are large enough to be handled with ease. Larger pieces can be used if one has the equipment for polishing them and they rnay be desirable when one wishes to study some particular form that extends for some distance through the coal. Large surfaces, however, require greater care in polishing and etching; for this reason, they are not recommended for ordinary work.

Jan 1, 1925

By Robert B. Coleman

The recent surge in demand for uranium in the US, accompanied by a significant increase in price, has stimulated the search for and development of lower grade ore bodies. At the mill, this translates into much larger throughputs and-compounded by many recently enacted environmental considerations-has made the cost of milling a critical factor in today's uranium production economics. The three conventional milling methods employed in the extraction of uranium ores are reviewed in the following sections.

Jan 10, 1978

By F. H. Rhines, A. H. Grobe

The constitution of the indium-zinc alloy series has been investigated by Wilson and Peretti,1 who determined the liquidus and eutectic temperatures by the conven-tional method of cooling curves and the eutectic composition by analyzing eutectic exudations. Recent developments affecting the availability of indium and consequent increased interest in its applications make a more complete knowledge of the constitu- tion of its alloys desirable. As a part of a program far the reexamination of the constitution of indium alloys by precision methods, the indium-zinc phase diagram (Figs. I and 2) has been redetermined in its entirety. The eutectic temperature (I43. 5°C.) reported by Wilson and Peretti has been confirmed exactly, but their value of the zinc concentration at the eutectic, 4 per cent, was found to be high; the new value is 2.8 per cent of zinc. There is also a rather large difference between the forms of the liquidus curves of Wilson and Peretti and those found in the present studies. The solidus curves herein have been located for the first time and the limits of solid solubility have been tenta-

Jan 1, 1944

By A. H. Grobe, F. H. Rhines

The constitution of the indium-zinc alloy series has been investigated by Wilson and Peretti,1 who determined the liquidus and eutectic temperatures by the conven-tional method of cooling curves and the eutectic composition by analyzing eutectic exudations. Recent developments affecting the availability of indium and consequent increased interest in its applications make a more complete knowledge of the constitu- tion of its alloys desirable. As a part of a program far the reexamination of the constitution of indium alloys by precision methods, the indium-zinc phase diagram (Figs. I and 2) has been redetermined in its entirety. The eutectic temperature (I43. 5°C.) reported by Wilson and Peretti has been confirmed exactly, but their value of the zinc concentration at the eutectic, 4 per cent, was found to be high; the new value is 2.8 per cent of zinc. There is also a rather large difference between the forms of the liquidus curves of Wilson and Peretti and those found in the present studies. The solidus curves herein have been located for the first time and the limits of solid solubility have been tenta-

Jan 1, 1944

By C. G. Grant, Wm. B. Price

This investigation of low copper-nickel silvers was untiertaken to check the work of Lèon Guillet on special brasses and to determine, more accurately, the effect of the addition of nickel on the mierostructure of the binary alloys of copper arid zinc. It was hoped that the results could be successfully applied to the practical production of low copper-nickel silvers. To explain the results of his investigations on special brasses, Lèon Guillet evolved his conception of "fictitious compositions." He states,' in his general conclusions, that on the introduction of a small amount of a third metal to a copper-zinc alloy, it enters into solid solution with the normal constituents up to saturation, but by so doing it brings the ternary alloy into a state microscopically equivalent to a binary copper-zinc alloy of fictitious composition, and physically more nearly like the latter than the brass containing copper-zinc in the ratio actually present. The physical properties of the ternary alloy, when compared to the same properties of an actual brass of the fictitious composition, are modified by the natural properties of the third element. Beyond the point of saturation, a special constituent appears and the above generalization no longer holds. For example, if a 60:40 brass has 4 per cent. of tin substituted for 4 per cent. of zinc, the actual composition would analyze 60:36:4. Assuming that 1 per cent. of tin plays the same part as 2 per cent. of zinc, the proportions of copper and equivalent zinc may be stated as 60 parts of copper and 44 parts of zinc, which, figured to 100 per cent., gives an analysis of 57.7 per cent. of copper and 42.3 per cent. of zinc, the fictitious composition for a 60:36:4 tin brass. The relation between ternary alloys containing copper and zinc together with a third metal, and the microscopically equivalent binary alloy of copper and zinc, may be expressed mathematically.

Jan 1, 1924

By Raymond B. Ladoo

ABRASIVES include the substances, natural or artificial, that are used to grind, polish, abrade, scour, clean or otherwise remove solid material, usually by rubbing action but also by impact (sandblasting, for example). They do not include abrasive tools-for instance, lathe tools and files-or polishing agents such as waxes, which act by filling pores. Detergents and cleaners whose action is chemical rather than physical are omitted although some chemical action polishes and cleaners may also contain solid abrasives; for example, many metal polishes. GENERAL CONSIDERATIONS The most important physical properties of materials that qualify them for use as abrasives are hardness, toughness (or brittleness), grain shape and size, character of fracture or cleavage, purity or uniformity. For making bonded grain abrasives such as grinding wheels, additional important factors are stability under high heat and bonding characteristics of grain surfaces. The economic factors of cost and availability are always important. No one single property is paramount for any use. For some uses extreme hardness and toughness are needed, as in diamonds for drill bits; for others, the factors of greatest importance are hardness and ability to break down slowly under use, to develop fresh cutting edges when grains become worn-for example, in garnet for sandpaper, neither highly cleavable or friable grains nor extremely tough grains

Jan 1, 1949

By R. Van A. Mills

ONE of the most important problems facing the petroleum industry is the profitable recovery of oil that is left underground by the ordinary methods of production. It is true that vast quantities of oil are being recovered from fields previously considered depleted by the pressure restoration method, the most widely applicable -and most successful means of obtaining greater recoveries that has thus far been, developed. But notwithstanding the progress that is being made in the field applica¬tion of this method there is urgent need for a better understanding of the fundamental principles that are involved. To meet this need the Petro¬leum Experiment Station of the U. S. Bureau of Mines at Bartlesville, Okla., during the past two years has conducted a series of intensive laboratory and field investigations. The larger part of the work has been carried on in the laboratory to supply the much needed information upon fundamental principles, information which few if any of the oil companies are in a position to supply for themselves. In all of this work the Bureau is endeavoring to correlate the results of laboratory investigations with those in the field, using the results of one to guide or check the other. This paper is primarily a progress report, briefly outlining the Bureau's methods of study, the laboratory and equipment in use, the preliminary problems that had to be solved in order to attack the major problems at hand, the methods of attacking some of the major problems, and some of the results of the investigations to date.

Jan 1, 1928

By O. W. Shimer, D. C. Helms, C. E. Brown

The early history and progress of anthracite stripping, from the first known operation at Summit Hill in 1821 through 1917, was covered in 1917 in a paper by J. B. Warriner,1 then chief engineer, now president of the Lehigh Navigation Coal Co., and stripping methods between 1917 and 1931 were the subject of a paper in 1931 by H. H. Otto,2 of the Hudson Coal Company. The present paper is confined to methods used today on pitching beds in the western middle and southern anthracite fields. The anthracite industry, not unlike other large industries, had been affected for more than a decade by the adverse economic conditions of the country. High development and operating costs and the competition of other fuels caused some collieries to be closed temporarily, while others were permanently abandoned. In order to obtain a larger tonnage at a lower development cost, a larger stripping program was put into effect by many companies. In 1932, stripping operations accounted for 3½ million tons, or 7 per cent of the total anthracite production of the year, and in the next 10 years this increased until more than double that amount, or over 14 per cent of the total production, was from stripping operations. These figures represent the total production of the entire anthracite region; unfortunately, the figures have not been separated from the different fields. There are some operations in the southern and middle western fields where the tonnage obtained from stripping amounts to more than 30 per cent of the total colliery production. Stripping operations on pitching beds present difficult problems. Owing to the various geological formations, a different situation is encountered in nearly every stripping pit; and because of the proximity of an overlying bed, it is very often necessary to load the entire overburden into trucks and haul it out of the pit to the dump area, although back filling and casting is done whenever possible. Beds in the areas described in this paper pitch from 20" to 90° and some are on the invert in many sharp folds and faults. Planning The more successful strippings have had adequate engineering analysis. Some work is being done without much preliminary planning, but many strippings would have failed completely if close supervision by the engineering department had not been maintained. Locations of stripping areas are determined as follows: I. By constructing cross sections over the areas and drilling sufficient diamond-drill or well drill holes to study the strata and to determine the location, thickness and pitch of the beds.

Jan 1, 1946

By Alfred E. Hunt

Tars paper is suggested by the appointment on the part of the American Societies of Mechanical and of Civil Engineers of committees upon the subjects of " Standard Tests and Methods of Testing," and " Uniform Methods of Tests of Material used in Metallic Structures," respectively, and by a study of the report of one of these committees, and other papers. Moreover, the writer has had frequent occasion to hear the complahts of tnanufacturers who furnish structural material subject to specifications, that in the tests prescribed, the number of tests required, and the methods of making

Jan 1, 1892

By R. S. Archer

BERYLLIUM has certain properties such as low density, high hardness, good corrosion resistance, low thermal expansion and fairly good electrical conductivity, which would indicate that it, is worthy of consideration as an ingredient of light alloys. It was not until recently, however, that beryllium could be produced with sufficient ease to encourage research along this line. The production of beryllium by electrolysis from a fluoride bath has now developed to the stage where it could be used commercially if there were sufficient demand for the element. Claims made in certain newspapers and technical articles in regard to the strength and corrosion resistance of the aluminum-beryllium alloys are not justified by experimental results. Moreover, beryllium is an expensive metal ($200 a pound at the time this work was done) and, on account of the nature of its ore and the consequent difficulty of its extraction, it will in all probability continue to be a relatively expensive metal, although the cost would undoubtedly be a great deal less than $200 a pound if the metal were produced on a large scale. It seemed, therefore, that low-beryllium alloys offered the greater commercial possibilities except for very special purposes. It was partly for this reason that in the present work emphasis has been placed on beryllium alloys of low beryllium content.

Jan 1, 1928

By C. E. Sims, H. M. Banta, S. L. Hoyt

OVER the past few years, metallic arc welding has been extended to steels of the hardenable type. As compared with other methods of fabrication, production has been facilitated, service performance frequently has been improved, and the overall results have been so favorable that engineers and production men have placed great emphasis on this application of welding. The metallurgist and welding engineer, however, have been confronted with new problems, since, for one reason, the harder steels are more apt to crack and special precautions must be taken if sound joints are to be procured. Some of the factors that are pertinent to this problem are metallurgical, and it is an object of this contribution to discuss steel manufacture and processing methods and to show how their control assists in reducing the hazard of cracking. By this time, the problem of cracking specifically underbead cracking, or "hard cracks," or parent-metal cracks-is well known, and a large amount of work has been published, both here and abroad, dealing with this subject.1 The tests described are made under restraint to facilitate cracking and, are so designed that a semiquantitative, or at least a relative, value of the cracking tendency is obtained. As one would expect, it has been reported that the incidence of cracking increases with the carbon and alloy content of the steel. More specifically, the cracking tendency is said to increase with the hardenability of the steel, though it is now recognized that the situation is not so simple. The phenomenon itself, on the other hand, has been but loosely described, and it is in only broad generalizations that this cracking has been related to steel metallurgy. Thus, while it has been abundantly demonstrated that the hardenable aircraft steel, S.A.E. 4130, must tend to crack when arc-welded, the problem still remains of why two lots of the same composition and the same hardenability can vary so greatly in cracking tendency, or what it is about the prior metallurgical history that so strongly affects the results. Further, while the efficacy of preheating and postheating in preventing cracking is recognized and utilized in production, the mechanism by which they function seems not to have been described. These points are thought to be significant in the production of steel for fabrication by metallic arc welding and, hence, of interest to mill and process metallurgists and welding engineers. Consequently, it is another object of this paper to discuss the mechanism of parent-metal cracking, including the influence of the condition of the steel and the control of cracking by manipulation of the time-temperature conditions during and after welding. A new method of rating the cracking. tendency is also discussed, and the results of the test are related to steel composition and structure or prior history. The work to be described was the outgrowth of work in 1940-41 at Battelle Memorial Institute 0n two projects, one

Jan 1, 1945

By Henry Rawdon

ONE of the most vital problems in the manufacture of steel at present is the occurrence of the defects that have been popularly termed "snow flakes," "flakes," or "scabs." Particularly is this the problem of many manufacturers who during the past 2 yr. have undertaken large-scale production for the first time. A study of the microstructure of such defective material throws considerable light upon the nature of these defects and is essential before measures may be taken for the elimination of the defects. Flakes do not appear to be found in the plain carbon steels; they have been found, however, in abundance in some of the simple alloy steels that are being used in such vast quantities; viz., nickel steel of the approximate composition, 0.40 carbon and 3.5 per cent. nickel, and in the chrome-nickel type. The present article summarizes the characteristic features of defective steel of the flaky type as they have been found by laboratory study of numerous specimens, and it aims to show the conditions within the metal that are favorable to the occurrence of this type of defect without entering into the details of mill practice (size of ingot, design of molds, rate of cooling, distribution of cooling stresses, etc.), all of which conditions appear to play a role in the production of these defects.

Jan 2, 1919

By Frederick N. Rhines

Pure copper that has been allowed to oxidize at an elevated temperature in the air is found to be covered with two distinguishable layers of oxide scale. The outer of these, which is very thin, is composed of cuprie oxide, while the inner layer, comprising the bulk of the scale, is made up chiefly of cuprous oxide (Fig, la). If a small quantity of an alloying element, such as silicon, is present in the copper, silica particles are found disseminated through the cuprous oxide, deposited most abundantly near the metal surface, and, in addition, silica particles occur to a limited depth within the copper itself (Fig. 1b). It is this inner layer, composetl of oxide particles precipitated in a matrix of metallic copper, that is known as the "subscale" or the zone of internal oxidation. Under a low oxygen pressure it is possible to produce the subscale without the formation of external layers of copper oxides, thus leaving the metal surface bright and apparently clean while oxidation has occurred, in fact, to a considerable depth within the metal (Fig. 2). Although little is yet known in a detailed way of the mechanism of internal oxidation, the general nature of the process is evident. By virtue of the considerable solubility of oxygen in copper,' it is possible to bring the alloying element in contact with oxygen within the metallic solid solution. If the oxide of the alloying element is more stable than cuprous oxide, the foreign oxide may form and, since most oxides are relatively insoluble in copper, it will not long remain in solution, but mill separate as a precipitate. As the metallic solute is exhausted in the zone of precipitation, oxygen that is constantly being supplied at the surface diffuses farther into the alloy and thus produces an ever-thickening shell of subscale. The distribution of the reacting elements in the subscale and adjoining zones must be somewhat as indicated in Fig. 3. The conditions requisite to internal oxidation to be anticipated are thus: (I) a solubility of oxygen in the alloy, (2) the ability of oxygen to diffuse at an appreciable rate into the alloy, (3) the possibility of the

Jan 1, 1940

By Frederick N. Rhines

Pure copper that has been allowed to oxidize at an elevated temperature in the air is found to be covered with two distinguishable layers of oxide scale. The outer of these, which is very thin, is composed of cuprie oxide, while the inner layer, comprising the bulk of the scale, is made up chiefly of cuprous oxide (Fig, la). If a small quantity of an alloying element, such as silicon, is present in the copper, silica particles are found disseminated through the cuprous oxide, deposited most abundantly near the metal surface, and, in addition, silica particles occur to a limited depth within the copper itself (Fig. 1b). It is this inner layer, composetl of oxide particles precipitated in a matrix of metallic copper, that is known as the "subscale" or the zone of internal oxidation. Under a low oxygen pressure it is possible to produce the subscale without the formation of external layers of copper oxides, thus leaving the metal surface bright and apparently clean while oxidation has occurred, in fact, to a considerable depth within the metal (Fig. 2). Although little is yet known in a detailed way of the mechanism of internal oxidation, the general nature of the process is evident. By virtue of the considerable solubility of oxygen in copper,' it is possible to bring the alloying element in contact with oxygen within the metallic solid solution. If the oxide of the alloying element is more stable than cuprous oxide, the foreign oxide may form and, since most oxides are relatively insoluble in copper, it will not long remain in solution, but mill separate as a precipitate. As the metallic solute is exhausted in the zone of precipitation, oxygen that is constantly being supplied at the surface diffuses farther into the alloy and thus produces an ever-thickening shell of subscale. The distribution of the reacting elements in the subscale and adjoining zones must be somewhat as indicated in Fig. 3. The conditions requisite to internal oxidation to be anticipated are thus: (I) a solubility of oxygen in the alloy, (2) the ability of oxygen to diffuse at an appreciable rate into the alloy, (3) the possibility of the

Jan 1, 1940

By D. Jenkins

THE Franklin Laboratory was designed mainly for the analysis of the products from the two concentrating mills situated at Franklin and Sterling Hill, the most important determinations being the zinc, iron, manganese, lime, moisture and silica contents of the ores. Within the last 4 years, however, it has been found advisable to examine most of our supplies, and therefore additional space and equipment was allotted for the examination of such substances as oils, greases, soaps, alloys, fuels, paints, explosives and water. The building as shown in elevation (Fig. 1) and plan (Fig. 2) consists of a main or routine laboratory, an experimental laboratory, a water FIG. 1.-WEST ELEVATION. analysis room and the other accessories such as stock room, library, sampling and drying rooms and office. The main laboratory is further divided into a balance room and zinc analysis room. As the greater part of our determinations are volumetric, good light is a very important factor and with this in view the interior walls of the building were constructed of white enameled brick laid in Keene cement. These also have the additional advantage that they give a clean and attractive appearance to the room. The windows are large, being 76 by 44 in. and even on very dark days the light is good throughout the whole laboratory. Our zinc titration requires a constant light and as, on many days, especially in winter, the light is variable, we installed two Artificial

Jan 8, 1917

By C. F. Wang

Manchuria in General Manchuria, called the "Three Eastern Provinces" in Chinese, forms the northeastern corner of China and is bordered by Siberia on the north and northeast, and by Korea on the east. It is a land famous in Chinese annals as the place of origin of the Ching dynasty, and in more recent times it has been an arena for diplomatic maneuvering and commercial competition between the Russians, advancing from the north, and the' Japanese from the southeast. It derives its name of "three eastern provinces" from the fact that it is divided into three provinces; Hei-

Jan 2, 1918

By Charles H. Fettke

The Bradford field of northwestern Pennsylvania and adjacent portions of New York state has attracted world-wide attention in recent years on account of the remarkable success that has been attained in the application of water-flooding as a means of increasing the extraction of oil from a pool that had almost reached the economic limit by ordinary production methods. It is one of the few large oil fields in which artificially conducted water drives have thus far proved successful, although many attempts have been made to apply them elsewhere. As detailed a knowledge as possible of the character of the producing sand in this field is therefore of considerable interest, not only from a scientific but also from a practical standpoint. Outside the Bradford field, such knowledge should aid operators in determining whether or not their sands are amenable to flooding. In the Bradford field itself flooding operations are not uniformly successful over the approximately 85,000 acres of productive area, due in many instances primarily to variations in sand conditions. A knowledge of just what these variations are would often be a great aid in overcoming the difficulties, or else would save considerable sums of money which might otherwise be wasted in experimenting in areas where the chances of success are very small. Realizing that more precise information in regard to the nature of the reservoir rock was essential to improvements in the methods of oil recovery, the Northwestern Pennsylvania Oil Producers Assn., by private subscription of its members, took a core of the Bradford sand from a well 1/2 mile west of Custer City, Pa., during the spring of 1925. The Forest Oil Co. also took a core of the same sand from a well about 8 miles east of Bradford at that time. The cores were submitted to the United States Geological Survey for study and A. F. Melcherl has published the results of porosity determinations on the Custer City core.

Jan 1, 1929

By Paul Billingsley, Augustus Locke

Certain adequately developed mining districts give complete three-dimensional patterns of ore bodies as clusters rising from roots in basement rocks with details controlled by structure of cover rocks. Examples are Goodsprings, Tintic, Bisbee, Leadville, Hedley, Eureka, Ely and Goldfield. In these and others the controlling structures in both basement and cover rock are elements of the neighboring regional structure and have been produced by rock movements in harmony with continental adjustments, which are usually steep tear faults in basement and thrust crumples in cover. Invariably the structures and movements in the districts have long geologic history and result from intersecting or superimposed deformations of different ages. Salt Lake districts show intersecting Uinta and Cordilleran elements; Colorado districts show intersecting pre-Cambrian and Tertiary elements, and Bisbee shows Tertiary superimposed on fina1 Paleozoic folding. Thus the position of districts has been determined by the patterns of North American orogenic belts, which make crossroads in Rocky Mountains and blocks of superimposed deformation in Sierra Nevada, northwest Coastand Canadian Coast Ranges. Essential function of repeated deformation is to strengthen rock, as from shale to slate to schist to gneiss, and thus make it competent to carry channels to depth with or without addition of intrusives. The essence of a mining district is the presence of such competent rocks with long-lived, deep, penetrating breaks reopened to permit passage of heat and associated products from depths to surface. It is suggested that melts such as magmas; metamorphism up to and including granitization; alteration, such as orthoclase-quartz or quartz-sericite or garnet, and also mineralization, may all be by-products of such heat escape along channels made by tectonic forces at specific foci. Magnitudes of Districts (Fig. 1) Any synthesis of ore deposits must deal with comparable units. Ore deposits are innumerable, but great ore deposits, commercially important for a generation or more, are few. The bulk of metals has come from districts of the first and second magnitudes (over $1,000,000,000 and over $250,000,000, respectively), and of these the United States and adjacent provinces of Canada and Mexico contain only 28, of which 9 are first magnitude: Butte, Coeur d'Alene, Bingham, Bisbee, Sierra Gold, in the West; Tri-State, Southeast Missouri, Michigan copper, Sud-bury, in the East. Another 28 or 30 districts are of third magnitude (over $50,000,000).

Jan 1, 1941

By Augustus Locke, Paul Billingsley

Certain adequately developed mining districts give complete three-dimensional patterns of ore bodies as clusters rising from roots in basement rocks with details controlled by structure of cover rocks. Examples are Goodsprings, Tintic, Bisbee, Leadville, Hedley, Eureka, Ely and Goldfield. In these and others the controlling structures in both basement and cover rock are elements of the neighboring regional structure and have been produced by rock movements in harmony with continental adjustments, which are usually steep tear faults in basement and thrust crumples in cover. Invariably the structures and movements in the districts have long geologic history and result from intersecting or superimposed deformations of different ages. Salt Lake districts show intersecting Uinta and Cordilleran elements; Colorado districts show intersecting pre-Cambrian and Tertiary elements, and Bisbee shows Tertiary superimposed on fina1 Paleozoic folding. Thus the position of districts has been determined by the patterns of North American orogenic belts, which make crossroads in Rocky Mountains and blocks of superimposed deformation in Sierra Nevada, northwest Coastand Canadian Coast Ranges. Essential function of repeated deformation is to strengthen rock, as from shale to slate to schist to gneiss, and thus make it competent to carry channels to depth with or without addition of intrusives. The essence of a mining district is the presence of such competent rocks with long-lived, deep, penetrating breaks reopened to permit passage of heat and associated products from depths to surface. It is suggested that melts such as magmas; metamorphism up to and including granitization; alteration, such as orthoclase-quartz or quartz-sericite or garnet, and also mineralization, may all be by-products of such heat escape along channels made by tectonic forces at specific foci. Magnitudes of Districts (Fig. 1) Any synthesis of ore deposits must deal with comparable units. Ore deposits are innumerable, but great ore deposits, commercially important for a generation or more, are few. The bulk of metals has come from districts of the first and second magnitudes (over $1,000,000,000 and over $250,000,000, respectively), and of these the United States and adjacent provinces of Canada and Mexico contain only 28, of which 9 are first magnitude: Butte, Coeur d'Alene, Bingham, Bisbee, Sierra Gold, in the West; Tri-State, Southeast Missouri, Michigan copper, Sud-bury, in the East. Another 28 or 30 districts are of third magnitude (over $50,000,000).

Jan 1, 1941