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By R. L. Loofbourow, Roger V. Pierce

THE degree to which our mineral requirements are being met by mining leaner, more complex or more remote deposits is indicated by developments during 1953. Heavy capital investment, skilled technical advice, planning, and able execution are requirements for the typical venture. Producers, faced with rising costs and with softer prices, are seeking improved mining and recovery. Developments in production of iron ore are typical of the course being followed in metal and nonmetal mining. Iron ore development in the U. S. is concentrated on the spectacular work with Lake Superior taconite, while in Canada new production is expected from Labrador and output from Steep Rock, Algoma, and Newfoundland is being increased. Shipment of iron will soon be made from Venezuela.

Jan 2, 1954

By Howland Bancroft

The writer has observed that some confusion is experienced by many mining engineers in making vertical sections of ore deposits in mining properties which they have examined. Having much examination work calling for the correct interpretation of vein structure and the subsequent platting of the same on sections, it has occurred to the writer that the accompanying diagram may be of use to others who at times may be called upon to prepare numerous sections. For example, a great mass of data on strike and dip of ore bodies is collected underground in separate

Jan 1, 1915

By M. J. Sinnott, W. R. Kiessel

The creep characteristics of commercially pure titanium sheet in the annealed state, cold-worked state, and cold-worked and recovered state in the temperature range from 75' to 750°F have been determined. Titanium has been found to exhibit strain aging characteristics. The effect of strain aging on creep has been determined. A possible explanation for the poor creep properties of titanium is proposed. THE metal titanium exhibits many desirable properties but results on its creep properties have been somewhat disappointing. The creep strength is low even though the material has a very high melting point.' The present work was undertaken to determine the creep strength of titanium in various conditions; annealed, cold-worked, and cold-worked and recovered and to determine why titanium shows such relatively poor creep properties. The general procedure followed in this research consisted in obtaining the usual mechanical prop- erties such as creep strength, short time tensile strengths, and hardness on materials treated to a controlled degree of internal strain, as determined by X-ray diffraction measurements, and their subsequent interpretation in terms of this internal strain. The material used in this work was sheet stock taken from one heat of commercially pure titanium. As-received, this sheet was 0.060 in. thick. The analysis was given as 0.037 pet C, 0.023 pet Si, 0.50 pct W, 0.063 pct Ni, 0.08 pct Fe, and the remainder titanium. The oxygen and nitrogen were unreported but generally are about 0.2 pct in commercial heats. In order to put the material in a state of minimum internal strain all the sheet was given an anneal in a static argon atmosphere for 1 hr at 1600°F prior to processing and testing. The microstructure of the material after this treatment was essentially a single-phase solid solution of uniform equiaxed grains. For the studies on the cold-worked sheet, the material was reduced by rolling in a two high, 5 in. mill. Rolling was done at room temperature in passes

Jan 1, 1954

By A. E. Outerbridge

I had the honor to present to the American Institute of Mining Engineers at the Pittsburg meeting, February, 1896, a paper having the foregoing title, in which I said : " It has generally been accepted as a fact that cast-iron, under the influence of repeated shocks, becomes brittle, and will finally break under a blow which otherwise it would have withstood. It will probably surprise metallurgists, therefore, to learn that experiment disproves the supposed fact, and establishes exactly its opposite. " The result of about a thousand tests of bars of cast-iron of all grades, from the softest foundry mixtures to the strongest car-wheel metal, enables me to assert with confidence that, within limits, cast-iron is materially strengthened by subjection to repeated shocks or blows." Three tables were appended showing increase of strength

Jan 1, 1905

By H. S. McQueen

THE central Ozark region of Missouri has inter-ested geologists and mining engineers for many years. Of particular interest are the mineralized sink-hole type deposits, some of which have produced large quantities of iron ore. Deposits of coal are also known in this part of the State, and in mode of occur-rence are similar to the iron ore deposits. Occurring in the same general area, and often associated with coal, are deposits of high-grade non-plastic flint fire clay, and high alumina or diaspore clay. At present these clays are the most important materials being mined from the sink-hole type deposits. Deposits of high-grade flint fire clay have been known to occur in this region for many years, the Kelley pit near Rolla, Phelps County, being discovered in drilling for iron ore shortly after the close of the Civil War. Mining operations had disclosed at an early date masses of rough, open-textured "sandy" clay associated with the flint fire clay. Some of the hard flint clay also con-tained rounded shot-like particles of "sand." Both types of clay were considered of inferior grade and unsuited to the manufacture of fire brick. These clays were discarded in mining as value-less, in some instances being used for road metal. Some knowledge of the high alumina content of this sandy material had been obtained by 1908 1, and by 1917 the high alumina content was gen- erally known, and commercial shipments of what is now called diaspore clay were being made. These deposits of diaspore clay associated with flint fire clay form the only known deposits of commercial importance in North America. The production of diaspore and flint fire clay at present exceeds that of any former year. Statistics covering the production and value of the former were not collected prior to 1922, and the figures given below do not cover the tonnage of clay mined by companies and used in their own plants, so that the total produc-tion probably is much larger than that indicated. The figures were collected by the U. S. Geological Survey and the U. S. Bureau of Mines in cooperation with the Missouri Bureau of Geology and Mines.

Jan 6, 1928

By J. B. Stubbins, D. F. Coates, K. L. McRorie

Twenty-two pit slides that occurred in two Canadian open pit mining properties are analyzed. Information on the results of laboratory tests of the rocks and a brief description of the geological environment are also presented. One deduction from the study is that slides seem to be predictable by using established theory. This corroboration indicates that, contrary to normal mining practice, the appropriate slope angle should vary with the height of the wall. In addition, if the general ground water level around an open pit can be reduced, the appropriate slope angles of the walls could then be increased by a determinable amount. The ultimate objective of these investigations is to determine the relationship between the percentage probability of failure of any slope designed with specific strength paraheters. With this relationship it would then be possible to determine optimum slope angles. Because of changes in various economic factors, open pits are now being mined to much greater depths than previously. The need to keep stripping ratios low without endanrrerine.-- lives and equipment provides a strong incentive to determine the maximum practicable wall slopes. Applied research work is currently being conducted to establish the methods for analyzing optimum slopes.

Jan 1, 1963

By H. Hu

Observations were made on the recrystallization of a 70 pct cdd-rolled silicon-iron crystal with an initial orientation of (113) [332]. Its polygonization and recrystallization characteristics were studied. Results indicated that re crystallization tendency of the deformed crystal is much weakened by the polygonization of the matrix. Complete recrystallization in such specimens is achieved by the growth of recrystallized grains of sufficient size and of the right orientations in relation to the matrix. Evidence was also furnished which suggests that the difference in the re-crystallization tendency is a result of the difference in the severity of lattice bending rather than the difference in orientation of the deformation texture. DUNN and Koh1,2 have made an extensive study on the rolling and annealing textures in silicon-iron crystals. Their results indicated that the recrystallization tendency can be widely different in crystals with different orientations. A particularly interesting example of their results was a crystal with an initial orientation of (113) [332], which developed a deformation texture of (001) [110] after 70 pct cold-rolling. Recrystallization in this crystal took long time anneals at high temperatures. Other crystals having different orientations recrystallized very rapidly. Wiener and corcoran3 have observed the retention of the (100) [011] deformation texture in a low-temperature annealed specimen of a commercial silicon-iron alloy, corresponding to areas of light-etching low-angle boundaries in the annealed struc-

Jan 1, 1960

By R. L. Wiegel

The two questions considered in this study are: (1) what similarity is there in the liberation of magnetite from various iron formations, and (2) how is this liberation affected by the size reduction technique employed. Twelve sample suites were obtained from commercial concentrators processing magnetite iron formation in the United States, Canada, and Australia. These samples have grades in the range 15 to 45% magnetite iron and approximate mineral grain sizes o f 50 to 2000 microns. Efforts were directed at measuring the liberation characteristics of the samples obtained from the concentrators primary grinding mills. The Davis tube, a laboratory magnetic separator, was used to concentrate individual size fractions of the size reduction product to determine liberation data. These liberation data were compared with relationships calculated from a highly idealized mathematical model of liberation in a binary mineral system. The results of these comparisons have been encouraging for nine or ten of the twelve samples tested. This leads to the conclusion that for most commercial iron formations, at least with conventional rod mill size reduction, it is possible to quantitatively characterize liberation with two parameters: an effective mineral grain size and ore grade. Limited laboratory size reduction tests as well as one of two sets of liberation data from commercial primary autogenous grinding lend some support to the contention that autogenous grinding can affect mineral liberation.

Jan 1, 1976

IT will be recalled that when educational instruction for the mineral industry began at Freiberg, at the beginning of the eighteenth century, the original aim was to organize and systematize the procedures previously followed by young men in gaining familiarity with the technology then in use. There must have been many other ideas current, even then, as to just what a young man needed to learn in order to become capable of assuming responsibility for the supervision and direction of such technical work. The problem in Europe was decidedly different from that in nineteenth-century America, because some of the European mines were actually owned and operated by the governing authority and the others were supervised, regulated, and taxed by it. The American problem was the efficient performance of technical operations; the European one was regulatory supervision. It was natural, therefore, that in the development of educational processes in Europe stress was laid on those factors which conserved and protected the interests of the state. The study of mineralogy and geology, leading to correct judgments as to the workability and value of mineral deposits; assaying, which gave the means of quantitative measurements, as did surveying; chemistry, which furnished a better basis of understanding for assaying, mineralogy, and geology; and physics and mathematics, which are the bases for the understanding and efficient use of mechanical appliances, became the core of systematic instruction for the mineral industry. It was early recognized that men could learn more than was already known about all of these subjects and education took on that dichotomy which still characterizes it; the teaching of established knowledge to the unlearned, and that of extending of the bounds of knowledge, now loosely termed research, which after two and a half centuries of work still shows

Jan 1, 1941

By L. C. Weiner

For zinc single crystals, xo = 3o, a surface coating raises both the cleavage and yield strengths over a large temperature range. The "brittle temperature," associated with slip after completion of twinning, does not coincide with the point of intersection of the flow and cleavage curves, which is associated with twinning. A surface film has no effect on the brittle temperature, while it lowers the intersection temperature some 20°. For crystals, yn = 83o, a coating decreases the cleavage strength, making it temperature independent, as well as increases the brittle temperature or its equivalent, the intersection temperature, 20°. These observations are described on the basis of a dislocation-pile-up-at-a-barrier model for brittle fracture; in crystals x,, = 3o the number and distribution of twins play a vital role. IN a recent investigation on the effects of solid environments on the brittle fracture of zinc single crystals,' it was demonstrated that the presence of a surface film changes the cleavage strength of these crystals, either increasing or decreasing it, depending on the crystal orientation. An increase in cleavage strength of some 43 per cent was found for coated crystals oriented x, — 3o K = 28",* while a decrease of 48 per cent was observed with crystals X" = y» — 83". Moreover, these effects were found

Jan 1, 1959

By Bradley Stoughton

My attention was called by Prof. Henry M. Howe to the article by N. M. Wittorff, entitled Preliminary Investigation of Primary Crystallization and Subsequent Physico-Chemical Permutations in Iron-Carbon Alloys Containing More Than 4 Per Cent. of Carbon. I thereupon wrote to Mr. Wittorff and received a copy of the paper in the Russian language, with permission from him to publish a translated abstract in our Transactions, the original having appeared in the .Journal of the Russian Chemical Society, vol. xliii. (1911), in which it occupies some 78 pages, with 10 illustrations and 47 micrographs. The novelty of the data presented, and especially the scientific importance of Mr. Wittorff's deductions, as well as their value in helping to clarify our meager understanding of that useful but puzzling commodity, cast-iron, seemed to more than justify a publication of the essential facts in concise form in the English language, which has not been done previously so far as I know, although a very brief abstract has been published in German, and a somewhat more extended one in French.' When the work of translation was begun, I did not know that it bore in part upon the investigations of Ruff, which Howe is reviewing at some length at this meeting. This coincidence renders the following condensed translation of Wittorff's work, which I have prepared with the aid of Sidney Marcus as interpreter, the more appropriate here. The result of Wittorff's study is greatly to extend our knowledge of the hyper-eutectic alloys of iron and carbon, and to add several significant lines at the right-hand side of the diagram originally drawn by Bakhuis-Roozeboom, and developed by Roberts-Austen, Benedicks, Carpenter and Keeling, Upton, Goerens, and others. Some of the original lines of the dia-

Jan 1, 1913

By Allen J. Johnson

It is probable that the word "anthracite" was derived from the Greek preposition an, and the Greek word for Thrace, meaning, in combination, "toward or near Thrace." Aristotle, Theophrastus, Strabo and Pliny all mention Thrace, or Samothrace, in treatises upon stones and stone coals dating back to about 371 B.C. In 1769 Obadiah Gore, a blacksmith of Wilkes-Barre, successfully burned anthracite in his forge, the first of millions of consumers of Pennsylvania anthracite. The Anthracite Region While anthracite is found in widely scattered locations throughout the world, 99 per cent of the total production of the United States origintitles within an area of 3300 square miles in castern Pennsylvania, less than 500 square miles of which arc underlain by workable coal beds. Eminent authorities such as the United States Geological Survey agree that this Pennsylvania anthracite is the only true anthracite east of the Rocky Mountains. There is some graphitic anthracite in Rhode Island but it is not suitable for combustion; and coals from such states as Virginia and Arkansas, frequently sold as anthracite, are in reality semi-

Jan 1, 1934

By R. T. Mishler

I wish to express my keen appreciation of the article on the above subject by Coe and C1evenger.l It has been doubly interesting to me, for the reason that the experience recorded and the principles evolved practically parallel the results of similar investigations made by myself and others at The Lucky Tiger Mine, El Tigre, Sonora, Mex. An outline of the work at El Tigre may aid in confirming the principles expressed by Coe and Clevenger. El Tigre has the unenviable distinction of possessing a slime with a much lower settling rate than any recorded in the article discussed. Under most favorable conditions the settling rate is about one-third that reported for the Liberty Bell mill, and one-tenth that reported for the Nipissing, Golden Cycle, and Presidio mills. This slow settling characteristic of Tigre ore has necessitated careful investigation of settling phenomena throughout the various evolutions of the plant. Previous Settling Investigation at Tigre During construction work at the mill, the metallurgical engineer in charge, D. L. H. Forbes, ran a series of experiments on settling. His tests proved that deep settling tanks were not ordinarily necessary. The use of tanks 2 or 3 ft. in depth was suggested.2 Later experiments demonstrated that the following principles of settling applied to Tigre pulp.3 1. In settling dilute pulp, settling rates are independent of pulp depth. 2. In settling thick pulp, settling rates are approximately proportional to pulp depth.4

Jan 1, 1918

By T. M. Broderick

InveStIgations into the possibilities of economically mining and concentrating low-grade iron ores of the Lake Superior region are attracting increasing attention. Among the organizations that are carrying on the work are the United States Bureau of Mines, the State of Minnesota (which spends about $80,000 annually on problems of the iron and ferroalloy ores of Minnesota), and the State of Michigan (which spends about $10,000 annually of its iron-ore research). Several of the mining companies are also financing research. Of the states in the Lake Superior district, Minnesota has done most in iron-ore concentration. In 1930, thirty-seven concentrating plants were in operation on the Mesabi Range, beneficiating about one-third of the total ore shipped. About one-half of these plants reduced silica; the others reduced moisture or improved the structure of the ore.' Research into the possibilities of magnetic concentration of the Eastern Mesabi magnetite ores indicates that vast tonnages of that ore may be utilized at a profit in the not distant future. Magnetic concentration has also been tried at Sellwood, Ontario, on the Moose Mountain deposit, and at the Berkshire mine in Wisconsin on the magnetic ores of the Western Gogebic Range. There have been few attempts to concentrate Michigan iron ores. In order to determine the possibilities of such concentration, iron-ore research has been carried on at the Michigan College of Mining and Technology for the past few years. After a general survey of the iron ores of the state, a program of more detailed experimentation was outlined, starting with work on the Ironwood formation of the Gogebic Range. The results of this research led to the belief that gravity methods will produce fairly satisfactory concentrates from the parts of the iron formation that are made up of comparatively thick alternating beds of rather high-grade ore and lean chert. About 85 per cent of the iron and steel produced in the United States comes from ores of the Lake Superior district. The reserves of direct

Jan 1, 1935

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 J. W. Matousek, C. S. Samis

me thermodynamic properties of the components in the Cu-Ni-S ternary system have been studied by measuring the H2S/H2 ratios in a gas phase equilibrated with the molten matte at 1200°C. The measured sulficr potentials have been extended by extrapolation and combtned with previously published data to permit the thermodynamic analysis of the ternary system by integration techniques. A simplifying assumption of ideality in the Ni3Sz-CuS pseudobinary has been made. SINCE copper and nickel metals were first extracted from their sulfide ores the interaction between the two metals and sulfur has been of industrial and theoretical interest. The processes developed to extract copper and nickel have been reported periodically in the literature. The theoretical studies on the Cu-Ni-S ternary have been restricted to problems directly associated with production. It is only within recent years that the binary systems related to this ternary have been analyzed thermodynamically and mathematical devices developed to permit a corresponding treatment of the ternary system. In 1910 an investigation of the role of nickel in Cu-Ni-Fe-S mattes was reported,' It was concluded from this work that nickel is not an element replacing iron in mattes, but rather that Cu-Ni alloys behave as a single metal during the matte converting operation. The laws which govern the converting of Cu-Ni alloys were found to be the same laws as those that govern the conventional converting of copper alone. Although considerable information has been reported on the theoretical aspects of copper smelting, little data is available on the smelting of Cu-Ni ores except for phase diagrams and process descriptions. The available information on the Cu-Fe-S ternary and related systems prior to 1953 has been summarized by Ruddle.2 Since Ruddle's publication, Rosenqvist and coworkers have completed phase equilibria investigations of the Fe-S, Co-S, and Ni-S binaries,3 the Fe-S-O ternary,4 and the Cu-Fe-S-O quaternary.4 An extensive investigation of the Cu-Fe-S ternary system at smelting temperatures has been made by Krivsky and Schuhmann.5 At these temperatures, the Cu-Fe-S system is very similar to the Cu-Ni-S ternary with respect to the location of the single-phase and two-phase liquid matte regions. In the former, however, the area of immiscibility is more extensive and the region of liquid matte-liquid metal-solid metal equilibria is much more extensive. Krivsky and Schumann observed that the Cu2S-FeS pseudobinary system is, for practical purposes, an ideal mixture. This investigation has served as a valuable guide in analyzing the Cu-Ni-S ternary. EXPERIMENTAL The experimental procedure employed in this investigation was the conventional technique of equilibration of the sulfide matte with gaseous mixtures of hydrogen and hydrogen sulfide at 1200°C. The thermodynamic properties of sulfur (S2) in the gas phase are determined by means of Eq. [I] and the activity of sulfur in the matte by Eq. [2].

Jan 1, 1963

By J. J. Jakosky

All electrical geophysical methods depend for their operation upon the effects produced by the flow of an electric current. By studying these effects it is possible to predict the general axis of current flow. The greater flow of current is in the path of greatest effective conductivity; and since the effective conductivity of a mineralized zone is different from that of its surrounding envelope (usually much greater), it is possible to locate such a mineralized zone by the distribution of current. Due consideration must be given, of course, to geological structure, to type of mineralization, and to other factors. A number of methods are used to cause this flow of current, and various methods arc available for detecting the presence of such current flow and for studying its effects. In a rather detailed way, this paper will discuss the theoretical and practical phases of the inductive methods of geophysical prospecting. Electromagnetic Generation of an Electeomotive Force The inductive method is so named because the current flowing in the conductor is obtained by electromagnetic induction, instead of by the use of ground electrodes through which a current is passed as in the applied potential systems, or by direct contact with the orebody. An alternating current flowing in a coil will create an electromagnetic field around the coil. This field will have the same frequency as the current and will radiate or travel outward from the coil in closed magnetic or flux circuits. These flux circuits (in air or a homogeneous medium) will be perpendicular to the plane of the coil and will extend or travel outward with uniform velocity in every direction. Maximum feld exists in the plane of the coil. Such a coil used for transmitting or as the "energizer" will exhibit similar figure-eight characteristics to those exhibited by the direction-finding coil which will be described in detail later.

Jan 1, 1929

By C. R. Ince

The term "differential flotation" is used to denote a flotation operation in which separation is effected between two or more minerals of the same class; e. g., lead sulfide from zinc sulfide, pyrite from blende, chalco-pyrite from pyrite, chalcopyrite from blende. At present, so far as published work shows, there seem to be two theories as to the mechanics of differential flotation. The earlier and more generally accepted theory is that the so-called depressing agents alter the surface of one or more of the sulfides in the ore, either by chemical action or adsorption, so that it is no longer amenable to flotation, but that these depressed sulfides can be revived, after the unaffected sulfide has been floated, by reagents which react chemically with the altered surface and make it amenable to flotation. More recently, Professor Taggartl has advanced the theory that slime adsorption is an important factor in differential flotation. He believes that, with the proper use of a class of agents, which he calls dispersion agents and which include practically all the depressing agents, one can cause the slime to adsorb differentially on sulfide surfaces. A gangue-slime coated sulfide surface will act as a gangue particle and will not float. If, subsequently, an agent that will remove the gangue-slime coating is added, the sulfide again assumes its original surface and can be floated as an ordinary sulfide. This is the basis of the slime theory of differential flotation. Timber Butte mill at Butte, Mont., is a typical lead-zinc flotation concentrator. Neihart ore, chosen for investigation in this work, is one of the custom ores treated at that mill. Practice at Timber Butte mill in February, 1928, was as follows: A combined lead-zinc concentrate was first made using 0.2 Ib. per ton on the ore of potassium xanthate and 0.03 lb. per ton of Cleveland Cliffs oil after 1.5 lb. per ton of lime and 1 lb. per ton of calcium chloride has been added just before the ball mill. The concentrate was then thickened to 70 per cent. solids. Potassium cyanide to the amount of 0.3 lb. per ton and zinc sulfate in the quantity of 0.5 Ib. per ton were added to the thickened pulp and the whole

Jan 1, 1930

By D. M. Blacknall, N. N. Winogradoff, E. W. Williams

Low-temperature measurements of photolumines-cence were used to evaluate the progvess in materials development. Variation of the impurity type, impurity concentration, and method of growth were used to clarify the chemical origin of defects in GaAs. Melt-g~ozun, epitaxial vapor-, and solution-grown samples were studied. A comparison of measurements at 77" and 20°K shows that more defects can be observed at the lower temperature. Th'vee residual defects were identified in relatively pure GaAs. These were: silicon, copper, and a gallium vacancy-donor complex. Solution growth from a gallium solution inhibits the formation of the latter two. Eleven defects were studied and the "optical" activation energy of some of these, namely, silicon, cobalt, and chromium, has not been reported in the literature before. THE discovery of the injection laser in 1962 prompted extensive measurements of the photoluminescence of GaAs. The measurements were made at 77°K on GaAs doped with shallow impurities at various doping levels and compared with electroluminescence1'2 and absorp- tion data.374 In addition, lower-temperature studies were made on relatively pure GaAS' and on GaAs doped with oxygen,5'" manganese,' and copper.' The observation of defects* in GaAs with photolu- *The word "defects" ~efers to both chemical impurities and native defects. minescence at low temperatures makes photolu mines-cence an invaluable tool in evaluating the progress in materials development. The only previous evaluation was done at 77°K when solution-grown and melt-grown GaAs were compared.O No identification of defects was made but it was shown that some of the deep-level luminescence seen in melt-grown GaAs was absent in solution-grown GaAs. The present work extends the comparison of preparation techniques to lower temperatures and to a study of epitaxial vapor-grown GaAs. It is particularly valuable for thin epitaxial layers since they cannot be analyzed by conventional analytical techniques. In addition, by varying the impurity type and impurity concentration the chemical origin and nature of defects in GaAs was demonstrated. Eleven defects were studied in all. Three of the defects were identified as residual defects which often contaminate GaAs prepared from the melt and the vapor. Only one such defect was observed in GaAs grown from a gallium solution and this was identified as silicon.

Jan 1, 1968

By Ernest F. Burchard

The Pao deposits of iron ore are in the State of Bolivar, Venezuela, near Upata, about 30 miles south of the Orinoco River and 90 miles east of Ciudad Bolivar. They were discovered 4 or 5 years ago and have not yet been developed to the stage of mining. In March-April, 1929, the writer devoted a week to the examination of these deposits. The maps, drill records and chemical analyses presented herewith were derived from original sources, and the field photographs were made by the writer. The petrographic and metallographic data are from notes by C. S. Ross and M. N. Short, of the U. S. Geological Survey, who have kindly collaborated in these special phases of the study. The Iron Obebodies Topography and Accessibility The deposits are in a region of low mountains representing northern outliers of the Guayanan Highlands. These mountains reach altitudes of 1800 to more than 2000 ft. above sea level, as determined by aneroid barometer. The iron ore is found on mountain crests that reach altitudes of 1915 to 1930 ft., and may be followed down precipitous slopes for 200 • to 300 ft. or more. The greatest vertical range in outcrop is nearly 400 ft., and drilling has indicated that the ore extends to this depth below the surface in one place, at least. The superior hardness of the iron ore accounts for the preservation of the local mountain crests with the intermediate valleys eroded in softer granitic rock. The deposits of iron ore are reached by a private road for automobiles branching northeast from the Ciudad Bolivar-Upata road, a distance of about 12 miles. This road was used in 1928-29 by trucks for transportation of food and camp supplies, gasoline, drilling equipment, etc., but was not suitable for the transportation of iron ore. Between Ciudad Bolivar and the iron-ore area the western two-thirds of the automobile road passes through nearly level, open country known as the savanna, largely used for grazing cattle. About 96 km. (60 miles) east of Ciudad Bolivar at

Jan 1, 1931