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By I. L. Greninger

THE property of the Andes Copper Mining Co. is in the central part of the Republic of Chile, Province of Atacama, 147 km. (91.5 miles) eastward by rail from the port of Chanaral. At this point the Andean system is made up of two principal ranges. The mine is on the westerly slope of the outer, or western, range, at a mean elevation of 3250 m. (10,500 ft.). A meter-gage railroad extends from the company's port at Barquito, near Chañaral, to the reduction plant at Potrerillos. This road has a total length of 151 km. (94.0 miles), of which 93 km. (57.79 miles) are owned by the Andes Copper Mining Co. The remainder of the road is owned by the state. The company operates its trains over the portion of the road owned by the state, under an agreement with the Chilean Government. The mine is connected with the reduction plant by a meter-gage railroad, 10 km. (6.214 miles) long, which extends from the coarse-ore bins at the metallurgical plant to the underground storage bins at the mine. Tunnels make up 60 per cent. of the total length of this railroad. As is characteristic of the Andean region in Chile, the topography of the locality is extremely rough, and a number of points near the mine have elevations of from 15,000 to 16,000 feet. History of Potrerillos Mine The ore occurrence has been known for many years, and many of the claims under individual ownership were worked in a small way before the property was acquired by the present owner—the Andes Copper Mining Company. The highest grade oxide ores near the surface were mined by primitive methods and, after sorting, the product, assaying around 15 per cent, copper, was hauled by mule carts a distance of about 80 km. (49.71 miles)

Jan 1, 1929

By Francisco Cadena

The construction of Norris Dam, built by the Tennessee Valley Authority on the Clinch River, a tributary of the Tennessee River, involved the production of coarse and fine aggregate for approximately 1,000,000 cu. yd. of concrete. A hammer-mill plant for the manufacture of sand from quarried rock was indicated as the most economical method of providing this material. The abrasive character of the feed as compared to the average hammer-mill feed made it necessary to control operations rather closely, and this resulted in the accumulation of many data hearing on production and maintenance. This paper will deal only with three specific sets of data, accompanied by such general information as may be necessary to explain the conditions under which they were obtained and followed by discussions on the relation of silica content to hammer wear, comparative costs of slugger and stirrup hammers, and comparative costs of tool-steel and manganese-steel grate bars. Coarse Aggregate Aggregate for the concrete poured at Norris Dam came from a dolomite quarry within 2000 ft. of the west abutment of the dam. Geologically this rock is known as a Knox dolomite. A typical chemical analysis is given in Table 1. Table 1.—Typical Chemical Analysis Per Cent H2O, 110° F............................................. 0.02 lgnition loss.............................................. 43.56 MgO.................................................... 19.19 CaO ................................................... 29.07 Fe²O³.................................................... 0.39 Al2O³ .................................................. 1.94 SiO2..................................................... 5.75 SO2...................................................... Tr. Rock was carried by 12-yd, dump trucks to a 42-in. gyratory crusher set at 6 1/2in. The product of the primary crusher was taken by a belt conveyor to a double.-deck vibrating screen followed by a 5 1/2-ft. cone

Jan 1, 1938

By Francisco Cadena

The construction of Norris Dam, built by the Tennessee Valley Authority on the Clinch River, a tributary of the Tennessee River, involved the production of coarse and fine aggregate for approximately 1,000,000 cu. yd. of concrete. A hammer-mill plant for the manufacture of sand from quarried rock was indicated as the most economical method of providing this material. The abrasive character of the feed as compared to the average hammer-mill feed made it necessary to control operations rather closely, and this resulted in the accumulation of many data hearing on production and maintenance. This paper will deal only with three specific sets of data, accompanied by such general information as may be necessary to explain the conditions under which they were obtained and followed by discussions on the relation of silica content to hammer wear, comparative costs of slugger and stirrup hammers, and comparative costs of tool-steel and manganese-steel grate bars. Coarse Aggregate Aggregate for the concrete poured at Norris Dam came from a dolomite quarry within 2000 ft. of the west abutment of the dam. Geologically this rock is known as a Knox dolomite. A typical chemical analysis is given in Table 1. Table 1.—Typical Chemical Analysis Per Cent H2O, 110° F............................................. 0.02 lgnition loss.............................................. 43.56 MgO.................................................... 19.19 CaO ................................................... 29.07 Fe²O³.................................................... 0.39 Al2O³ .................................................. 1.94 SiO2..................................................... 5.75 SO2...................................................... Tr. Rock was carried by 12-yd, dump trucks to a 42-in. gyratory crusher set at 6 1/2in. The product of the primary crusher was taken by a belt conveyor to a double.-deck vibrating screen followed by a 5 1/2-ft. cone

Jan 1, 1938

By Louis V. Bender

THIS paper gives a short review of the installation for and the use of gas, as a. fuel, at the Anaconda Reduction Works of the Anaconda Copper Mining Co. Before putting in gas tile fuels used were pulverized coal, lump coal, coke distillate and oil. These fuels are now almost entirely eliminated. For nearly fifty years bituminous coals from Wyoming and Montana fields had been used. These coals were of a good grade, analyzing 11,300 B.t.u. and having an ash content of 12 per cent. When hydro-electric power replaced steam-driven equipment, the coal requirements were reduced; and, on account of improvements in metallurgy and/ or in furnace design, the quantity was lessened. Later, oil and distillate were introduced and used in some of the operations. All of these things tended toward the lessening of the amount of coal used, and had it not been for the increase in the size of the plant, the tonnage used would have been small when the change was made to gas.

Jan 1, 1932

This volume summarizes characteristics and the geological setting of porphyry copper deposits of the Western Hemisphere. Grouped by characteristics, porphyry copper deposits are described in six regions: Andean orogen, Appalachian orogen, Alaska, northern Cordilleran orogen, southern Cordilleran orogen, and the Caribbean. Each region has its own peculiarities of geologic setting, and those deposit characteristics that may be projected from one chapter to another will be used in reaching the conclusions from which to draw genetic models for porphyry copper deposits. The term porphyry in this volume denotes a type of ore deposit, rather than a rock classification. The classification of intrusive igneous rocks used in this volume is shown in Figs. 36a and 42 (pp. 103, 130). Some modern classifications suggest mineral-ratio definitions other than those used in this volume; however, most literature references cited are based on the classification shown in Figs. 36a and 42. The reader should be aware, therefore, that quartz monzonite in this volume contains from 35% to 65% potassuim feldspar and at least 10% quartz. A term used in this volume is defined where introduced within the context of a specific chapter. Distensional tectonic conditions are used in the sense of Cady (1972) in the Appalachian orogen, for example. Porphyry copper deposits are defined as large bodies of mineralized rock, usually including a porphyritic intrusive phase, that have copper sulfide minerals disseminated through them. The definition has no commercial connotation and is used strictly in a noneconomic sense to encompass the spectrum of copper mineralization associated with these deposits. Terms commonly accepted in the literature are not defined. Porphyry molybdenum and porphyry copper deposits commonly are distinguished by most economic geologists. The basis for the separation is summarized in one chapter of this volume. To permit the reader to more easily peruse the bibliography for any particular region, references will be found at the end of each chapter. The bibliography is not intended to be complete, but is designed to provide adequate minimum coverage for descriptions of deposits in the chapter concerned. Each entry is properly referenced in the text of that chapter to facilitate the reader's research into any particular topic. This volume is written from the point of view of the exploration geologist whose task it is to evaluate the structural, petrographic, mineralogic, and metallogenic characteristics of a porphyry copper deposit. The goal of the evaluation is to determine if, and where, concentrations of metals may exist in an igneous- hydrothermal system that includes the most complex set of geologic factors found in any of the many types of ore deposits. The successful porphyry copper geologist is simultaneously a petrographer, geochemist, structural geologist, and mineralogist. Some porphyry copper deposits have developed in volcanic arcs underlain by a Benioff seismic zone with a trench paralleling the arc. The most convincing example of a deposit known to have developed in an environment where subduction is an active process is the 3.3 m.y. (million years) old Dry Creek occurrence in the Aleutian arc (this volume). On the other hand, the younger deposits in the Cascades appear to have formed in a volcanic arc lacking both the Benioff zone and the offshore trench. Subduction is not widely accepted as an active mechanism for the period when the younger Cascade deposits formed. Subduction has also been questioned for deposits formed at a great distance from a plate boundary (e.g., Bingham). Regardless of the pros and cons regarding subduction, most deposits are associated with regional faults. Strike-slip

Jan 1, 1978

By Irwin Roman

IN studying the possibilities of a continuously recording magnetometer for use along the surface of the earth and in an airplane, the Federal Bureau of Mines was led to a study of the theoretical resolving power of magnetic observations, both in the variation of the total magnetic intensity and in each of the two components ordinarily measured. Along with this general study, an attempt was made to determine the relative worth of the total intensity anomaly and the vertical anomaly in geophysical prospecting. General considerations led to three conclusions: I. In the northern magnetic hemisphere of the earth, the total intensity anomaly is offset to the south of the vertical anomaly, for a positive anomaly (see Appendix, note I). 2. The resolving power of magnetic observations decreases rapidly with distance from the disturbing body. 3. The horizontal anomaly has little value in prediction of the disturbing body but might be useful in making a choice between bodies suggested by the vertical or total anomaly. Some of the considerations leading to these conclusions were: I. The normal intensity and the anomalous intensity are vectorially additive; hence for a positive anomaly in the northern magnetic hemisphere the total intensity will be a maximum at some point south of the disturbing body and north of the point at which the line to the disturbing body is parallel to the normal earth's field. The anomaly itself has a maximum value directly above the body. For a positive anomaly of constant magnitude, the total intensity will be a maximum when the anomaly vector is parallel to the normal vector. This is shown schematically in Fig. I (not to scale) for a magnetic distribution not restricted to a relatively thin sheet in the magnetic meridian. The normal field has a magnitude Io with vertical component Vo and horizontal component H,. Six station points along a traverse' across the body from south to north are shown at M to S. At each of these stations the normal magnetic field vector terminates at F. At each of these stations the magnetic field vector due to the disturbing body B terminates at A. The line through the station point and the point A passes through B. The magnitude of the anomaly, indicated by the length of the vector terminating at A, is proportional to some power of the distance from the station point to the disturbing body. If the' disturbing body B is a concentrated point of magnetic material, the anomaly is proportional to the inverse second power of the distance. For a uniform magnetic distribution over a line perpendicular to the observed traverse, the anomaly is proportional to the inverse first power of the distance. For surface distributions, the law of intensity is more complicated. At each field point, the total magnetic intensity T is the vector sum of the

Jan 1, 1946

By Perry G. Harrison

The increased use of sintering for the beneficiation of iron ores and the reclaiming of flue dust creates a lively interest in sintering costs and economics. The character of material sintered and geographical location of plants so radically alter sintering costs and economics that it is well.to understand at least the basic elements which control such changes. The following cost factors are believed to be roughly approximated for large-scale Dwight-Lloyd continuously operated sinter-machine installations located anywhere. Per Crude Ton Labor, supplies and repairs 0.15 Power 6.5¢ X kw-hr. rate ? Plant overhead and administration 0.05 Depreciation per ton annual capacity 0.05 Fuel: 6 per cent coke breeze or equivalent minimum ? 1 per cent coke breeze additional for each 5 per cent free and combined water in ore or dust ? Ignition distillate at 0.6 gal. per ton ? Per Sinter Ton Royalty on ore 0.10 Royalty on flue dust 0.15 Per Crude Ton "Winter expense"; i. e., the cost of the five months enforced idle . period for plants tied in to Great Lakes transportation season 0.03 Using the foregoing data, it is possible to roughly approximate the cost of efficient sintering at any location for any ore, viz: Per Crude Ton Per Ton Handled Sinter 1. Flue Dust—Steel Plant Locations Sinter recovery, 15 per cent moisture and carbon 85 per cent Labor, supplies and repairs 0.15 0.18 Power 6.5¢ X 1¢ kw-hr. 0.065 0.08 Plant overhead and administration 0.05 0.06 Depreciation per ton 0.05 0.06 Dust handling and preparation 0.10 0.12 Fuel: free, contained in dust Ignition: blast-furnace gas free Royalty 0.15 Total $0.65 Note:—Cost increased by either deficiency or considerable excess of carbon in dust.

Jan 1, 1932

By Reynold Q. Shotts

INTRODUCTION THE small domestic underfeed stoker as now designed is unusually sensitive to the coking and plastic properties of coals, and when the attempt is made to burn the high rank coking and caking coals of the Appalachian fields, serious trouble may occur. Part of the trouble may be caused by the ash content and clinkering characteristics of the particular coal in use, but more often it is the result of an excessive accumulation of coke in the form of "trees" or masses in the fuel bed. Often the zone of burning becomes so restricted that the fire goes out, and in extreme cases the fire may be lifted completely out of the fuel bed and away from the air ports. Even if the fire is preserved, excessive coking may cause response to subsequent heat demand to be slow and irregular. Coke trees seem to grow. most readily during periods of hold-fire operation, so that in order to preserve the fire in mild weather it is often necessary to set the timer for such a long operating period each hour that much unneeded and unwanted heat is developed, causing discomfort. During demand periods the fire may pick up so slowly that the intense burning which develops just before stoker cut-off causes a serious overshooting of the thermostat. Stoker coal performance tests which have been made in a number of laboratories 1, 2, 3, 4, 5 are one method of approach to the problem of selecting stoker coals. As yet these tests have not been standardized and they are expensive and time-consuming. The value of the results probably increases with the length of the test. Sherman and co-workers at Battelle Memorial Institute believe that even a one-week test is not too reliable a trial2 and it is quite likely that others will agree. A great advantage of such tests is that characteristics of coals, other than the tendency to form coke masses, may be evaluated from them. The selection of stoker coals would be greatly facilitated if there existed some simple measure of the tendency of a coal to form coke in a fuel bed. Although possessing all of the disadvantages of any small-scale laboratory test, the test for the free-swelling index of coal has been found useful for evaluating the probable effects of swelling properties upon combustion. 7 Ostborg, Limbacher and Sherman, have shown that the test can predict, roughly, the tendency of coke to accumulate in the fuel bed of a domestic stoker. They also gave instances of its value in predicting combustion behavior in some large installations. The use of the test for free-swelling index has become well established and has been adopted as a standard by the American Society for Testing Materials.8 When domestic stoker coal investigations began at the State Mine Experiment Station in the summer of 1944, it was decided

Jan 1, 1948

By Robert I. Kingman

SUFFICIENT testing has been performed with the Dutch State Mines Cyclone for thickening and desliming flotation feed at the concentrator of the National Lead Co., Tahawus, N. Y., to prove its application for this work. It is the purpose of this article to present some of the test results, operational details and advantages of cyclone thickening and classification. The metallurgy of the mill operation was described by Frank R. Milliken, assistant manager of the titanium division.l The present flowsheet for the recovery of ilmenite consists in grinding the crushing plant product in four open-end rod mills in closed circuit with mechanically vibrating screens to approximately -20 mesh. The screen undersize is treated in Crockett magnetic separators which produce three products: magnetic concentrate, nonmagnetic tailing containing ilmenite and gangue, and a Crockett slime overflow. The non- magnetic tailing is classified into eight sizer spigots products and a classifier overflow. The spigot sand products are tabled separately to produce a rough ilmenite concentrate, a middling product and a tailing. The table middlings are returned to Crockett feed. The table concentrate is dewatered and dried and further concentrated on Wetherill magnetic separators to produce the finished ilmenite concentrate.

Jan 8, 1950

By Howard N. Eavenson

From the Pittsburgh coal bed in the four states of Pennsylvania, Ohio, Maryland and West Virginia has been produced an output that, at mine prices, represents a greater value than any other single mineral deposit in the world has yielded.12 While this distinction may in a few years pass to the gold reef of the Witwatersrand, it is possible that eventually, owing to the tremendous reserves still remaining, the ultimate yield of the Pittsburgh bed will be greater than that of any other known single deposit. Considering its importance, not a great deal has been written of its early history and development as a whole; most of the accounts have been of limited localities, or, at the most, of the area within a single state. In "Coal through the Ages" the writer mentioned some references to its early history, but this study will deal not only with its history but with the character of the bed, where and why it was first developed, and its effect upon the states in which it is found. It has not been the intention to write a detailed history of the development of the seam in each locality, as neither time nor inclination were available for doing such work, but only to show the influences that tended to hasten or retard such development. In general the historical matter ends about 1830, when geological surveys began to be made. Some of the maps show data available only since that time, and the sections about coal preparation and coking have been extended to the present time to show the changing conditions. It is believed that the early history includes all published records, and many more sources than those shown in the bibliography were consulted. It is quite likely that some references to coal in this area may be found in the unpublished papers of some of our early soldiers and colonizers, which exist in several libraries, and it is hoped that some future * Dedicated to Dr. Thomas S. Baker, President Emeritus, Carnegie Institute of Technology, whose labors in promoting the International Coal Conferences and in establishing the Coal Research Laboratory have done much in showing the industry how science can be of help to it. Manuscript received at the office of the Institute Feb. 15, 1938.

Jan 1, 1938

By Howard N. Eavenson

From the Pittsburgh coal bed in the four states of Pennsylvania, Ohio, Maryland and West Virginia has been produced an output that, at mine prices, represents a greater value than any other single mineral deposit in the world has yielded.12 While this distinction may in a few years pass to the gold reef of the Witwatersrand, it is possible that eventually, owing to the tremendous reserves still remaining, the ultimate yield of the Pittsburgh bed will be greater than that of any other known single deposit. Considering its importance, not a great deal has been written of its early history and development as a whole; most of the accounts have been of limited localities, or, at the most, of the area within a single state. In "Coal through the Ages" the writer mentioned some references to its early history, but this study will deal not only with its history but with the character of the bed, where and why it was first developed, and its effect upon the states in which it is found. It has not been the intention to write a detailed history of the development of the seam in each locality, as neither time nor inclination were available for doing such work, but only to show the influences that tended to hasten or retard such development. In general the historical matter ends about 1830, when geological surveys began to be made. Some of the maps show data available only since that time, and the sections about coal preparation and coking have been extended to the present time to show the changing conditions. It is believed that the early history includes all published records, and many more sources than those shown in the bibliography were consulted. It is quite likely that some references to coal in this area may be found in the unpublished papers of some of our early soldiers and colonizers, which exist in several libraries, and it is hoped that some future * Dedicated to Dr. Thomas S. Baker, President Emeritus, Carnegie Institute of Technology, whose labors in promoting the International Coal Conferences and in establishing the Coal Research Laboratory have done much in showing the industry how science can be of help to it. Manuscript received at the office of the Institute Feb. 15, 1938.

Jan 1, 1938

By Ernest F. Burchard

Fluorspar is found in most of the states from the Rocky Mountains westward, and commercial production of the mineral has been reported from Arizona, Colorado, Nevada, New Mexico, Utah and Washington. The map in Fig. 1 indicates the general distribution of many of these deposits but it is by no means complete. In the summer of 1926 the writer examined certain deposits of fluorspar in Arizona, California, Colorado, New Mexico and Washington; in November, 1927, revisited the Jamestown, Colo., district, and in earlier years examined deposits in Colorado and New Mexico. Based on notes of his own and on descriptions and other data by H. A. Aurand, H. W. Davis, R. B. Ladoo, V. C. Heikes, W. D. Johnston, Jr., and by producers of fluorspar, he prepared the following brief descriptions of deposits and estimates of reserves of fluorspar, originally for the use of the subcommittee on fluorspar of the Joint Committee on Foreign and Domestic Mining Policy and on Industrial Preparedness respectively of the Mining and Metallurgical Society of America and the American Institute of Mining and Metallurgical Engineers. Descriptions of many fluorspar deposits in various western states and districts have been published. It is not feasible to summarize this literature here, but the appended bibliography will indicate to the interested reader what papers are available. Arizona Fluorspar has been reported as occurring in Arizona in the following localities: near Duncan, Greenlee County; near Naco, Tombstone, and Paradise, Cochise County; Black Mountain, Mojave County; 25 miles southwest of Tucson, and at Helvetia and Silver Bell, Pima County; near Mammoth mine, Pinal County; in Yavapai County, 7 miles from Aguila, and in the Bradshaw Mountains; and near Dome, Yuma County. Production has come principally from the Castle Dome district, Yuma County, with minor quantities from Greenlee, Pima and Yavapai counties. The writer examined deposits in the Castle Dome district, Yuma

Jan 1, 1934

By Ionel I. Gardescu

Natural gas influences the movement of oil through reservoir rock by affecting the physical properties of the oil and the pressure within the reservoir. The presence of gas bubbles changes the laws of flow and the distribution of forces. The problem of flow of oil and gas through a porous rock is complex, and most authors, in order to analyze their problems, have found it necessary to make or accept certain generalized assumptions. Some of these assumptions, particularly the ones dealing with capillary phenomena and moleculnr forces, have not received sufficient attention and by lack of understanding have often been misinterpreted. Herold1 has called attention to the resistance offered by gas bubbles in capillary spaces and has drawn some interesting conclusions with regard to the action of natural gas in a reservoir rock. He has duplicated an experiment of the French physicist Jamin, has interpreted his findings in terms of molar mechanics, and, from experimental observations, has made a number of assumptions which he later applies in discussing problems of natural flow and recovery of oil. The Jamin action is an assumption because it lacks a physical proof and has never been determined quantitatively. Tickel12 attempts to develop a formula expressing the work performed by a distorted bubble. H. A. Wilson, in the recent publication of the American Petroleum Institute on the function of natural gas, discusses the phenomenon in terms of classical physics. Both contributions are incomplete and offer no experimental data. This paper includes a study of the static condition of equilibrium of gas and liquid bubbles confined to capillary spaces. In order to avoid any possible confusion, it is proposed to restrict the term "Jamin action"

Jan 1, 1930

By I. L. Box

IN planning retreatment of tailings, the material to be retreated should be thoroughly investigated, tak- ing into consideration the total tonnage, the blende content, the specific gravity of the different particles, and the grinding necessary to liberate the mineral. The tailing pile is surveyed by making a closed trav-erse around the outer edges, locating the stations at points from which a considerable portion of the pile is visible. From each of these points the pile is sur-veyed by stadia and a contour map made. The yardage is then calculated from the contour interval and the area inclosed by the contours obtained with a planim-eter. A party of three men can survey an average tailing pile in one and one-half, days. In calculating tonnage it is assumed that 22 cu. ft. of tailing in place equal one ton. Sampling is done by the use of an auger with casing to prevent the hole from caving. These holes may be bored 12 to 15 ft. deep by hand, but to penetrate the entire pile some kind of power is applied to drive the casing and raise or lower the auger. The latter method is more expensive but the increased cost is more than compensated for by the value of the information obtained.

Jan 7, 1928

By W. J. Millard

It is well known that the excellent mica from Brazil played a most vital role in World War 11. Increased production from Brazil was necessary and with the assent of the Brazilian Government engineers from the united' States went down to study the problem. One of the means advocated by a former Chief of Metals and Minerals Branch of the Board of Economic Warfare, Mr. Carl Schwegler, was the use of stripping machinery. On a pegmatite dike favorable for stripping, a small number of miners could produce as much mica per day as an underground mine employing many times the same number of men. Type of Deposit Favorable The most favorable type of pegmatite for stripping is that which lies more or less parallel to the surface of the slope of a hill. Pegmatite dikes that cut directly into a hill are not suitable for stripping except where a long outcrop extends along the slope. Then just the outcrop could be stripped to some advantage. The ratio at no time should be greater than 1: 3; i.e., I cu. m. of pegmatite to 3 cu. m. of waste, unless the pegmatite was extremely rich throughout the dike. The Economics of Stripping When a mineral is badly needed to win a war, not too much heed can be paid to costs. The object is to produce rapidly and in quantity. Again, a deposit containing a superior grade of mica may be worked although the pegmatite is more costly to work than another deposit containing a considerably greater amount of poor-grade mica. For example: one deposit may have a little mica that will run 11 per cent good stain and better when trimmed and contain 2 kg, of crude mica per cubic meter of pegmatite, while another may run 0.2 per cent of good stain and better, and have a mica content of 10 kg. per cubic meter. A number of stripping projects were found in the vicinity of Raul Soares, Minas Gerais. These were sampled in the various old workings by cutting out a cubic meter of pegmatite and saving the usable mica. Because of the proximity to the surface of most stripping projects, about 34 per cent only of the mica is good for trimming. The other 66 per cent is too badly weathered to be of use. In Table I are given data collected on five properties near Raul Soares. In Table I, "value per cubic meter of pegmatite" means the value of the qualified mica obtainable. This does not include the half trimmed and splittings. By "value per cubic meter of matter" is meant the value of the qualified mica per cubic meter of material excavated; i.e. both waste and pegmatite. This is the figure that should be used to determine whether the operation will be profitable or not, as the cost of stripping is about $0.14 per cubic meter. With new machinery not subject to breakdowns, the cost per cubic meter should be around $0.10 to $0.15. To this should be

Jan 1, 1948

By W. J. Millard

It is well known that the excellent mica from Brazil played a most vital role in World War 11. Increased production from Brazil was necessary and with the assent of the Brazilian Government engineers from the united' States went down to study the problem. One of the means advocated by a former Chief of Metals and Minerals Branch of the Board of Economic Warfare, Mr. Carl Schwegler, was the use of stripping machinery. On a pegmatite dike favorable for stripping, a small number of miners could produce as much mica per day as an underground mine employing many times the same number of men. Type of Deposit Favorable The most favorable type of pegmatite for stripping is that which lies more or less parallel to the surface of the slope of a hill. Pegmatite dikes that cut directly into a hill are not suitable for stripping except where a long outcrop extends along the slope. Then just the outcrop could be stripped to some advantage. The ratio at no time should be greater than 1: 3; i.e., I cu. m. of pegmatite to 3 cu. m. of waste, unless the pegmatite was extremely rich throughout the dike. The Economics of Stripping When a mineral is badly needed to win a war, not too much heed can be paid to costs. The object is to produce rapidly and in quantity. Again, a deposit containing a superior grade of mica may be worked although the pegmatite is more costly to work than another deposit containing a considerably greater amount of poor-grade mica. For example: one deposit may have a little mica that will run 11 per cent good stain and better when trimmed and contain 2 kg, of crude mica per cubic meter of pegmatite, while another may run 0.2 per cent of good stain and better, and have a mica content of 10 kg. per cubic meter. A number of stripping projects were found in the vicinity of Raul Soares, Minas Gerais. These were sampled in the various old workings by cutting out a cubic meter of pegmatite and saving the usable mica. Because of the proximity to the surface of most stripping projects, about 34 per cent only of the mica is good for trimming. The other 66 per cent is too badly weathered to be of use. In Table I are given data collected on five properties near Raul Soares. In Table I, "value per cubic meter of pegmatite" means the value of the qualified mica obtainable. This does not include the half trimmed and splittings. By "value per cubic meter of matter" is meant the value of the qualified mica per cubic meter of material excavated; i.e. both waste and pegmatite. This is the figure that should be used to determine whether the operation will be profitable or not, as the cost of stripping is about $0.14 per cubic meter. With new machinery not subject to breakdowns, the cost per cubic meter should be around $0.10 to $0.15. To this should be

Jan 1, 1948

By John I. Yellott

SINCE the days of Newcomen and Watt, when men first sought to turn the energy of fuels to useful purposes, coal-generated steam has supplied most of the power needed for both stationary and mobile applications. The low efficiency and large water requirements of the nineteenth century steam-power plant caused many engineers to turn their thoughts toward more direct means of converting heat into power. As far back as 1791, John Barber secured an English patent on a combination' which he might well have called a "gas turbine." He proposed to generate procducer gas from coal or charcoal, to burn it under pressure in air obtained from a reciprocating compressor, and to drive a turbine wheel with the resultant hot combustion products. With the optimism characteristic of the inventor, he hoped that the turbine would not only operate his compressor but also perform useful work. There is no record that Barber ever built his machine, but if he had done so he would have learned that useful power can result from such a combination only when both turbine and compressor are highly efficient and when the temperature of the gas entering the turbine is not far below 1000°F. Hot-air prime movers continued to attract attention, and both Stirling in England and Ericsson in America2 built reciprocating engines that operated with some success upon coal-heated air. The internal-combustion engine, burning liquid fuels, supplanted the hot-air type, and, for the first time, challenged the supremacy of both the steam cycle and its familiar fuel, coal. LIQUID FUELS COMPETE WITH COAL As the increasing use of the automobile multiplied the demand for gasoline, the supply of residual fuel increased rapidly, and heavy oil declined in price to the point where it became competitive with coal. First in the marine field and later in stationary plants in areas adjacent to refineries, oil began to be widely used. Oil's greater convenience and higher heating value per pound of weight or per cubic foot of bunker space have caused it to take over much of the marine field. The introduction of the highly efficient diesel engine, capable of burning a fuel that is cheaper than gasoline, again threatened the position of coal, for the operating costs of the diesel became directly competitive with those of coal- burning equipment. In isolated power plants and smaller marine installations, the diesel provided the medium by which oil again successfully invaded fields formerly dominated by coal. The diesel engine, provided with an

Jan 1, 1946

By Walton J. Greer, System By John E. Owen

The guard electrode system measures the resistivity of formations by employing a thin disk of current which is caused to flow perpendicular to the bore hole. The control of this current disk is obtained in a brute force manner through the use of relatively long equipotential electrodes above and below the measuring electrode. The log obtained from the system is free of "lag," "plateau," "shadow," "reflection" and other distortions evident on conventional logs. The proportionate contributions of the hole size and invaded zone resistivity to the apparent resistivity reading are reduced when the mud and filtrate resistivities are lower. Thus, the guard system favors the use of conductive muds. The mathematical development of the theory is given in an appendix. Equations are derived to evaluate the effects of mud resistivity, hole size, invaded zone resistivity and depth, and the true formation resistivity. Sample logs from several provinces are reproduced and compared with conventional electric logs to illsutrate the much greater detailed lithology that can be presented by the guard electrode system. INTRODUCTION With increased ability of those in the petroleum industry to analyze formation characteristics from electrical resistivity data, there has become apparent the need for more precise measures of that parameter. The measurement of the resistivity of a homogeneous and isotropic material can be made simply when the body of the material is infinite in all dimensions and the measuring electrodes can be placed within the body. In such a case, the current leaving an electrode follows a spherical distribution and the mathematical expression for the potential level at any distance from that electrode can readily be derived.'.' If it is considered that the active electrodes are within a bore hole filled with mud of a resistivity different from that of the formation. the current does not flow in a spherical pattern near the current source or sink, and the calculations of potential levels become more difficult. The additional consideration of a section of formation invaded by mud filtrates, and thus having resistivity different from either that of the mud, the adjacent formations or of the undisturbed formation, makes the mathematical problem extremely complex. Should the vertical dimensions of the formations be considered as finite. the problem becomes so complex as to preclude reasonable solution. Yet, even these considerations have not described adequately the conditions encountered in a large proportion of the wells to be studied. In efforts to evaluate the effects of the various conditions. combinations of twn, three. and four electrode logging con- figurations of the conventional types have been used. The resulting logs have left much to be desired in some provinces. It has become apparent that the use of such configurations will not result in adequate measurements being made, particularly in cases where the formation is composed of thin sections. If all the current of a resistivity measuring circuit is made to flow through the formation opposite the exploring electrode, many of the shortcomings of the conventional measuring system are eliminated. In the guard electrode method of electrical well logging to be discussed in this paper, the current is so controlled by causing it to flow in a thin disk normal to the axis of the logging tool. EARLY HISTORY The guard electrode method of electrical well logging in its early years was a joint development by the Geophysical Research Corp. and the Amerada Petroleum Corp. The method was first experimentally investigated by means of model studies. The results of these studies indicated that current focusing systems properly applied to electrical well logging

Jan 1, 1951

By System By John E. Owen, Walton J. Greer

The guard electrode system measures the resistivity of formations by employing a thin disk of current which is caused to flow perpendicular to the bore hole. The control of this current disk is obtained in a brute force manner through the use of relatively long equipotential electrodes above and below the measuring electrode. The log obtained from the system is free of "lag," "plateau," "shadow," "reflection" and other distortions evident on conventional logs. The proportionate contributions of the hole size and invaded zone resistivity to the apparent resistivity reading are reduced when the mud and filtrate resistivities are lower. Thus, the guard system favors the use of conductive muds. The mathematical development of the theory is given in an appendix. Equations are derived to evaluate the effects of mud resistivity, hole size, invaded zone resistivity and depth, and the true formation resistivity. Sample logs from several provinces are reproduced and compared with conventional electric logs to illsutrate the much greater detailed lithology that can be presented by the guard electrode system. INTRODUCTION With increased ability of those in the petroleum industry to analyze formation characteristics from electrical resistivity data, there has become apparent the need for more precise measures of that parameter. The measurement of the resistivity of a homogeneous and isotropic material can be made simply when the body of the material is infinite in all dimensions and the measuring electrodes can be placed within the body. In such a case, the current leaving an electrode follows a spherical distribution and the mathematical expression for the potential level at any distance from that electrode can readily be derived.'.' If it is considered that the active electrodes are within a bore hole filled with mud of a resistivity different from that of the formation. the current does not flow in a spherical pattern near the current source or sink, and the calculations of potential levels become more difficult. The additional consideration of a section of formation invaded by mud filtrates, and thus having resistivity different from either that of the mud, the adjacent formations or of the undisturbed formation, makes the mathematical problem extremely complex. Should the vertical dimensions of the formations be considered as finite. the problem becomes so complex as to preclude reasonable solution. Yet, even these considerations have not described adequately the conditions encountered in a large proportion of the wells to be studied. In efforts to evaluate the effects of the various conditions. combinations of twn, three. and four electrode logging con- figurations of the conventional types have been used. The resulting logs have left much to be desired in some provinces. It has become apparent that the use of such configurations will not result in adequate measurements being made, particularly in cases where the formation is composed of thin sections. If all the current of a resistivity measuring circuit is made to flow through the formation opposite the exploring electrode, many of the shortcomings of the conventional measuring system are eliminated. In the guard electrode method of electrical well logging to be discussed in this paper, the current is so controlled by causing it to flow in a thin disk normal to the axis of the logging tool. EARLY HISTORY The guard electrode method of electrical well logging in its early years was a joint development by the Geophysical Research Corp. and the Amerada Petroleum Corp. The method was first experimentally investigated by means of model studies. The results of these studies indicated that current focusing systems properly applied to electrical well logging

Jan 1, 1951

By Charles F. Park

Mining in the Pacific Coastal Region has passed through three stages of development. First came the gold rush days, a period when gold and silver were the objects of intensive search. Second was the development of the high-grade base-metal deposits and of the smaller and more refractory precious metal deposits. And third was the modern period that covers the discovery and development of the rarer metals, of large low-grade deposits, and of the industrial and nonmetallic minerals. Brief discussions of the salient geologic features of the region and of a few of the better known mineral deposits are given. The regional geology is favorable for continued exploration and discovery of new deposits and districts.

Jan 1, 1968