Search Documents

By Raymond E. Zimmerman

Abstract-The Swirl Cyclone developed in Japan, although based upon the same principles as the standard cyclones for heavy-media or water-only cyclones for cleaning coal, is novel in that it is invested with the apex on top, discharging rejects at the top, and clean coal at the bottom. It also uses a variable air vent tube for controlling the vortex. Tests conducted indicate that its efficiency is not only as sharp as standard cyclones but it also performs using a much coarser grain magnetite, promising higher magnetite recovery. The author describes the results of tests conducted in Japan on a very difficult coal.

Jan 2, 1978

By R. H. Lynn, T. C. Craig

During the year 1933, in the Texas Panhandle, 113 oil wells were completed, adding 33,337 bbl. to the daily potential of the field. The field potential on Jan. 1, 1933, as determined by the Texas Railroad Commission, was 149,260 bbl., with a daily allowable production of 41,000 bbl. The potential was raised gradually, until on July 16, 1933, it reached 155,344 bbl. with a daily allowable of 55,000 bbl. This potential and allowable was maintained over a period from July 16, 1933, to Sept. 8, 1933, when the potential was reduced to 136,893, with a daily allowable of 43,727 bbl. Since Sept. 8, 1933, there has been a gradual increase, until on Jan. 1, 1934, the field potential reached 159,740 bbl. with a daily allowable of 42,000 bbl. Of this amount 26,429 bbl. arc "marginal oil" and 2682 bbl. are exempt on account of water. Deepening of Wells During the year 64 wells were deepened, increasing their total oil production 9631 bbl. per day. Of this amount the Gray County granite wash contributed 9256 bbl. from 57 wells. It has been found in many places that the granite wash carries an additional oil pay from 50 to 75 ft. below sea level. The majority of the wells that were .drilled during the early development in Gray County encountered their oil above sea level. When the wells producing from the upper horizon have become unprofit-

Jan 1, 1934

By M. G. Fowler

A GENERAL decline in copper production for most American producers occurred during the past year as a result of shortage in available labor. Few noteworthy technical developments have been reported; undoubtedly, many changes and improvements have been made but have not been reported because of lack of time. During the war years through 1944 the pressure for sustained high production has been of prime importance and during 1945, with slackening of production, many operators were faced with the problem of catching up on repairs and maintenance of plants, with inadequate labor supply. In hydrometallurgy there were some important developments that undoubtedly will be reported during 1946. Several operators in the Southwest have instituted experimental leaching programs to exploit low-grade oxidized and mixed ore bodies. The Bureau of Mines is conducting pilot-plant experimental work to determine the possibility of producing a satisfactory sponge iron at an attractive cost from deposits of iron ore and coal in Arizona. The sponge iron would be used for the production of cement cop¬per. The cell house of the Inspiration Consolidated Copper Co. at Inspiration,

Jan 1, 1946

By Howard N. Eavenson

AN analysis of the bituminous coal situation by an authority who traces the production, mining, safety, markets and labor trends in comparison with other fuels. BEFORE 1918 the production of coal experienced a steady growth, with slight recessions in ouput in only twelve years (1837, 1841, 1852, 1855, 1861, 1874, 1876, 1889, 1894, 1905, 1909, 1914), and in each of these cases the loss was recovered in the following year and the increase continued. In each decade the output was doubled. Prices, while not high, allowed some profit. In 1918 during World War I, an output of 580 million tons was reached and with the exception of 1923 this total was not again reached until 1942, in World War 11. Losses of output in this period were much greater than ever before; in 1932 the total was 270 million tons less than in 1918 or 1923, and the loss after 1923 was not recovered until 1942. The greatest output was 631 million tons in 1947.

Jan 1, 1950

By Kenneth S. Ritchie

THE discovery well of the world's -deepest oil producing structure, University 1-B of Group No. One Oil Corporation, in the Big Lake oil field, Reagan County, Texas, has had a remarkable record. The well is outstanding for the following reasons: (1) It is the world's pioneer well to produce. oil in commercial quantities from a structure 8500 ft. below the earth's . surface; (2) this well was the only. producer from the 8500-ft. pay for a period of 17 months and 24 days; (3) the flow of the discovery well has been free from-the customary changes at the casinghead, with the exception of putting on a back-pressure of 185 lb.; and, (4) the well's daily production of oil and gas increased rather steadily for 17 months and 18 days from an initial of 40 bbl. per day to a maximum of 2926 bbl. per day, and then six months later, after a period of decline and self-readjustment to subsurface changes caused by six more deep producers, the well set its real record for one day's production of oil at 2950 bbl

Jan 1, 1931

By Rich Akerman

as 1866, I wish to assure both these gentlemen that I had not seen the section when I designed mine, :md even if I had, I should not have then dared to put it forth as a standard for English rail makers; tind the soundness of my opinion has a simple but conclusive proof in the statement made concerning the extra price which was at that time required for their production. I need not say that I highly approve of the original Welch section, for it is in principle similar to the design which I made ufteen yeam subsequently; and from a professional point of view I would fully concecle to Mr. Welch the credit of first designing the modern steel-rail section. From com- mercial, matter of tict, and practical point of view, he was, however, before his time by many years; or to put it in another way, rail making was ten years behind its time when the new metal steel was first introduced for rails. If his design has been incorrectly identified with my name (as the sections are similar in principle, though they differ in thickness of flange and web), I beg to say (1st) that I much regret the misun- Understanding which has arisen through no fault of niine, aud (2d) that no confusion has been intentionally created by me. It is a pity that the section designed so long ago has not been made public at an earlier date, as it would make a really goal stand- and pattern, anil even now be quite equal to present requirements. In conclusion, I wish to say that I have never desired to claim any invention or novelty by the publication of my sections; they Were put forth as being such as English railmakers could and would produce at the ordinary market. price, and as being the best and most suitable to be so obtained. Had Mr. Welch or Mr. Holley put forward theirs ten or fifteen years ago, I should have been the first to recommend theru. In fact I should have been glad to see their narnes associated with rail patterns in their own country, in the same way as mine has been. PROFESSOR RICH. AKERMAN, STOCKHOLM, SWEDEN: i AGREE with your (Mr. Sandberg's) views that it is too early yet to stipulate only one definite chemical composition in the rails. Such a stipulation, I think, might he justified, if it were not for the manganese; but this metal changes the properties of the iron aud steel in tho same direc- tion ae carbon, silicon. and phosphorus, by increasing its tensile strength, stiffness, hardness, and brittleaess. If the iron and steel does not only contain carbon and manganese but also phosphorus,

Jan 1, 1881

By A. E. WALKER

SOME eighty years have elapsed since the discovery of the Clifton magnetite deposit. For a few years about the time of the Civil War it was mined for iron ore. most of which was smelted on the property. Since risen the small exposures of ore in the old cut. test pits, and on the dumps have been examined by various prospectors. The M. A. Hanna Co. first became interested in the possibilities of the deposit when we discovered the large area of strong magnetic anomalies caused by the margnetite bed, indicating a size that would support a commercial operation. In 1940 we made a detailed magnetometer survey of the area. and the deposit was diamond-drilled. The main ore lied was found to be 1500 ft. long, to average 60 ft. thick, and to dip southeast at an angle of about 40 deg. The thickness of the bed is irregular in wavy folds both along the strike. and down the dip. Faults occur at both raids of the main deposit.

Jan 1, 1943

By Kenneth Cotingham

Many factors joined in reducing drilling activity in Ohio in 1942. Conservation Order M-68 was important, but other things, such as operators and members of drilling crews joining the armed services and going into war plants, had an important part. The reduction in number of completions was considerable. In 1941, the total of wells drilled was 1561 but in 1942 the total was 1008. The total initial daily open flow discovered by the 701 gas wells drilled in 1941 was 492,000 M cu. ft., whereas the open flow of the 471 gas wells completed in 1942 was 314,488 M cu. ft. The total initial daily production of the 333 oil wells drilled in 1941 was 10,300 bbl., and in 1942 the 181 oil wells had a total daily initial of 7570 bbl. The average daily initial per gas well therefore was somewhat less in 1942 when compared with the preceding year, but the initial per ail well increased about 36 per cent over 1941. General Activity The total depth of the 652 oil and gas wells drilled in 1942 was 1,597,000 ft. The most active county was Perry, where 63 oil wells were drilled, most of them in Clayton township. In Morgan County. where 43 gas wells were drilled, the greatest activity was in York and Marion townships. Medina County was third in number of wells drilled, although of the total of 33 gas wells in the county, 26 were in the new Hinckley township pool. The total initial open flow of these 26 wells was 39,202 M CU. ft., and was considerably larger than from any other single area. Muskingum was an active county, particularly Washington and Wayne townships, in each of which seven gas wells were drilled, and Blue Rock and Harrison townships, in each of which five gas wells were drilled.

Jan 1, 1943

By Kenneth Cotingham

Many factors joined in reducing drilling activity in Ohio in 1942. Conservation Order M-68 was important, but other things, such as operators and members of drilling crews joining the armed services and going into war plants, had an important part. The reduction in number of completions was considerable. In 1941, the total of wells drilled was 1561 but in 1942 the total was 1008. The total initial daily open flow discovered by the 701 gas wells drilled in 1941 was 492,000 M cu. ft., whereas the open flow of the 471 gas wells completed in 1942 was 314,488 M cu. ft. The total initial daily production of the 333 oil wells drilled in 1941 was 10,300 bbl., and in 1942 the 181 oil wells had a total daily initial of 7570 bbl. The average daily initial per gas well therefore was somewhat less in 1942 when compared with the preceding year, but the initial per ail well increased about 36 per cent over 1941. General Activity The total depth of the 652 oil and gas wells drilled in 1942 was 1,597,000 ft. The most active county was Perry, where 63 oil wells were drilled, most of them in Clayton township. In Morgan County. where 43 gas wells were drilled, the greatest activity was in York and Marion townships. Medina County was third in number of wells drilled, although of the total of 33 gas wells in the county, 26 were in the new Hinckley township pool. The total initial open flow of these 26 wells was 39,202 M CU. ft., and was considerably larger than from any other single area. Muskingum was an active county, particularly Washington and Wayne townships, in each of which seven gas wells were drilled, and Blue Rock and Harrison townships, in each of which five gas wells were drilled.

Jan 1, 1943

By AIME AIME

A PAPER recently presented before the Anthracite Section of the A. I. M. E. by S. J. Phil- lips, Mine Inspector, Fifth Anthracite District, Department of Mines of Pennsylvania, covering the water hazards in the anthracite coal mines of the Lackawanna River Valley, was especially timely because the conditions there are duplicated to a large extent in the Wyoming Valley, which is traversed by the Susquehanna River with its many large tributary streams. Also, in the southern anthracite field, where there are a number of large creeks, similar pumping problems and mine water hazards will in time be presented if mining is continued to its conclusion.

Jan 1, 1936

By John K. Berry

The handling and disposal of mine water is a much larger problem than is apparent at first glance. Many more tons of water are removed from underground coal mines in the United States each year than tons of coal. In the old anthracite region of Pennsylvania the average was around 36 tons of water for each ton of coal produced, while bituminous mines average about 5 or 6 tons. Water encountered in the mines may come from several different sources. In mines with light cover and without a firm solid roof, rain may seep directly into the workings. This is also true of deeper mines where pillar falls have broken the roof to the surface. The top under creek beds is generally faulty and broken and water comes through the roof at this point. Deeper mines are frequently overlain by water-bearing strata and pillar breaks and faulty top can admit water, while places running to the dip often accumulate water which comes up through the bottom. In all cases, except where passing under a year-round stream, the amount of water made is usually pretty closely connected with the weather-more water during the rainy season, less in the dry, although the deeper a mine is, the longer it is before changes in rainfall are felt. Another source of water, not connected with seasonal changes, is old water, accumulated over a period of time in abandoned workings of the mine, or from flooded adjacent mines. Here the water filters through the coal, the parting, or comes up through cracks in the bottom. Similarly, core holes, drilled to prospect the property, can be a source of unexpected water and modern safety requirements for dust-allaying water at the working faces can turn a pleasant working area into a soggy mess over the weekend if the system is not properly maintained and operated. Why water must be disposed is obvious. If allowed to accumulate, sooner or later the mine will fill up, or at least it will become "roofed" in low places, blocking ventilation and traffic. But it must also be controlled long before it reaches this stage. Water standing in the working faces is unpleasant for the men who have to work there and also cuts down on the amount of work they can do, as they must watch where they step all the time. It is especially unpleasant in low coal.

Jan 1, 1973

By Carl M. Fellman

LABOR disputes caused considerable turbulence in the coal mining industry during 1946. As an outcome of these disputes, a definitely fundamental change in safety procedure was instituted: establishment of safety regultions for coal mines through the agency of agreements between the miners' union and the agency or agencies operating the coal mines. Although a temporary plan at present, the future will determine the. extent to which it may become permanent. Notwithstanding the turmoil in the industry extending through much of the year, the safety record for the first eleven months of 1946 was the best in the history of the industry for that period. The fatality rate for 1946 is lower than in any other year in the history of coal mining in the United States. This follows a pattern inasmuch as new low coal-mine fatality records were also made in 1945, 1944, and 1943. The five-year period 1942 to 1946 inclusive has a coal-mining fatality rate far lower than any other five-year period in the history of the industry. It is significant that this period exactly coincides with the operation of Federal coal mine inspection which got under way early in 1942.

Jan 1, 1947

By A. W. Gauger

SMELTING of iron ore, manufacture of steel, and the fabrication of ferrous metal products are all processes that require energy. Charcoal was adequate, to supply this energy for the relatively simple processes of the early iron-masters. In the fourth decade of the nineteenth century, anthracite and bituminous coal and later coke supplanted charcoal for the smelting of iron. So far as the chemical phases of the process were concerned, charcoal was an ideal iron-furnace fuel. It had practically no sulphur, and its ash, besides being low in quantity, consisted chiefly of lime and alkalies, thus supplying a part of the flux required for smelting the ore. The ash of coal and coke on the other hand, being largely silica, had itself to be fluxed with bases added to the charge. Physically, however, coke proved to have many advantages over charcoal, which could not be used in the furnaces of today. The chief reason, however, for the change from charcoal to coke was the impossibility of maintaining an adequate wood supply.

Jan 1, 1941

By Persifor Frazer

CONTENTS. PAGE 1. Committee House of Commons Report (1843).......521 2. Clark (1880).............521 3. Schröder and Schertel (1884).... . 521 4. Committee House of Lords Report (1887).......523 5. Vita (1890).............524 6. Irvine (1890-1)............524 i. Cramer (1891)............525 8. Bailey. Cohen. Tatham and Hartog (1891))......525 9. Morrison (1891)............525 10. Brunner (1891)............525 11. Bell (1892).............585 12. Oades (1892).............526 12a. Purcell (1892)............526 13. Sennett (1892)............526 14. Bulier (1892).............526 1.7. Wiesner (1892))...........526 16. Thomson (1892)............530 17. Fletcher (1892)............530 18. Committee Engineers' Club Report (1892).......530 19. Cohen and Hefford (1892)..........531 20. Discussion Soc. Chem. Ind. (1893). ..532 21. Reuss (1893).............532 22. Thomson (1894—5) ...........535 23. Clowes and Feilmann (1895). ...536 24. Callan (1895)...........536 2.5. Wright (1895)............536 25A. Mabery (1895)............536 26. Re- (1896). ..........536 27. Herman (1896)............ 537 28. Cohen and Russell (1896).......... 537 29. Dennstedt and A hrens (1896). ..537 30. Cohen (1897). ...........537 31. Drehschmidt (1897)........... 538 32. Pfeiffer (1898). .........538 33. Fritzche (1898)............ 540 34. Ost and Wehmer (1899)........... 540 35. Donkin (1899). .........541 36. Beilby (1899)............. 643 37. Berthelot (1900)............ 544

Jan 1, 1908

By C. E. Shoenfelt

There was a notable decrease in drilling operations in 1940 in all of the Rocky Mountain states except Montana, where the two large fields on the Canadian border, Cut Bank and Kevin-Sunburst, were espe-cially active. The expanding markets for Montana natural gas made necessary the more intensive development of such fields as Rowdoin, Cedar Creek and Devon. While there were no important oil and gas discoveries in 1940 in any of the Rocky Mountain states, a few small pools were opened, which may constitute separate areas but may prove with later development to be extensions of old fields. Some of the old fields were extended and deeper pay zones were discovered in others. These have given the areas greatly increased oil reserves and therefore are just as important as the discovery of new fields. The more important of the developments in 1940 are given, by states, in the following paragraphs. Colorado Hiawatha Field, Moffat County.—The Mountain Fuel Supply Co. began the development at Hiawatha of its oil reserves, which were discovered in about 1929, and late in the summer oil began moving from the field by truck to the shipping point at Rock Springs, Wyoming. The Hiawatha field of northwestern Moffat County was discovered in 1927 by the Sormir Petroleum Co., with the completion of No. r Florence Wilson for 4,5,000,000 cu. ft. of gas a day from a Wasatch sand lens at 2200 it. In later development of the field, oil showings were reported in several wells but no development of this resource was undertaken until 1940, when a test of the oil possibilities was started with the release in April of a location for No. 5-A Wilson on the S\W. SW. NW. of sec. 23-1zN-1ooW., on the east side of the field. The Well had an initial production of 327 bbl. of oil a day pumping from three Wasatch (Tertiary) sands between 2005 and 2540 ft. It was drilled to 2562 ft., where the 65/8-in. casing was cemented and gun-perforated at 2005 to 2125 ft., 2260 to 2335 ft. and 2513 to 2540 ft. At the end of the year, this well was averaging zoo bbl. of oil per day, pumping. Two other wells were drilled for oil on Hiawatha during the summer—one a small well of 60 bbl. per day and the other a small gas well. Powder Wash Field, Moffat County.—The development of the Powder Wash field in northwestern Colorado was resumed in 1940 by the Mountain Fuel Supply Co., with the release of a location for No. 2-A Musser in the CWL.NW.SE. of sec. 4-1rN-97W. The Powder Wash field was discovered in 1931 by the Mountain Fuel Supply Co. and the discovery well, No. I Musser, on C.NW. of sec. 5-IIN-97W., was completed at 2152 ft. in the Hiawatha member of the nonmarine Wasatch for-mation for an open flow of 34,000,000 cu. ft. of gas per day under a natural pressure of 685 lb. per sq. inch. Oil was discovered in the Powder Wash field on Nov. 26, 1936, in the company's No. I Carl Allen on the NE.SW.SE. of sec. 32-12N-97W. The oil production was

Jan 1, 1941

By C. E. Shoenfelt

There was a notable decrease in drilling operations in 1940 in all of the Rocky Mountain states except Montana, where the two large fields on the Canadian border, Cut Bank and Kevin-Sunburst, were espe-cially active. The expanding markets for Montana natural gas made necessary the more intensive development of such fields as Rowdoin, Cedar Creek and Devon. While there were no important oil and gas discoveries in 1940 in any of the Rocky Mountain states, a few small pools were opened, which may constitute separate areas but may prove with later development to be extensions of old fields. Some of the old fields were extended and deeper pay zones were discovered in others. These have given the areas greatly increased oil reserves and therefore are just as important as the discovery of new fields. The more important of the developments in 1940 are given, by states, in the following paragraphs. Colorado Hiawatha Field, Moffat County.—The Mountain Fuel Supply Co. began the development at Hiawatha of its oil reserves, which were discovered in about 1929, and late in the summer oil began moving from the field by truck to the shipping point at Rock Springs, Wyoming. The Hiawatha field of northwestern Moffat County was discovered in 1927 by the Sormir Petroleum Co., with the completion of No. r Florence Wilson for 4,5,000,000 cu. ft. of gas a day from a Wasatch sand lens at 2200 it. In later development of the field, oil showings were reported in several wells but no development of this resource was undertaken until 1940, when a test of the oil possibilities was started with the release in April of a location for No. 5-A Wilson on the S\W. SW. NW. of sec. 23-1zN-1ooW., on the east side of the field. The Well had an initial production of 327 bbl. of oil a day pumping from three Wasatch (Tertiary) sands between 2005 and 2540 ft. It was drilled to 2562 ft., where the 65/8-in. casing was cemented and gun-perforated at 2005 to 2125 ft., 2260 to 2335 ft. and 2513 to 2540 ft. At the end of the year, this well was averaging zoo bbl. of oil per day, pumping. Two other wells were drilled for oil on Hiawatha during the summer—one a small well of 60 bbl. per day and the other a small gas well. Powder Wash Field, Moffat County.—The development of the Powder Wash field in northwestern Colorado was resumed in 1940 by the Mountain Fuel Supply Co., with the release of a location for No. 2-A Musser in the CWL.NW.SE. of sec. 4-1rN-97W. The Powder Wash field was discovered in 1931 by the Mountain Fuel Supply Co. and the discovery well, No. I Musser, on C.NW. of sec. 5-IIN-97W., was completed at 2152 ft. in the Hiawatha member of the nonmarine Wasatch for-mation for an open flow of 34,000,000 cu. ft. of gas per day under a natural pressure of 685 lb. per sq. inch. Oil was discovered in the Powder Wash field on Nov. 26, 1936, in the company's No. I Carl Allen on the NE.SW.SE. of sec. 32-12N-97W. The oil production was

Jan 1, 1941

By John B. Hastings

THE occurrence of such a large amount of gold in the Hartsel granite, even though the surmised existence of similar areas is not new, brings freshly to mind the pegmatite type of magmatic differentiation lately brought again to attention by occurrences at Silver Peak, Nev., described by Spurr; and in Alaska, described by both Spurr and Brooks. In both localities graunitic rocks or dikes are thought to pass into metalliferous quartz-veins. An interesting association in this connection is the occurrence of diamonds in residual pegmatitic clay of San Juao de Chapado, Brazil, described by Derby :1 (P. 142) "Bodies of pegmatite are quite common in the older rocks of Brazil, both in the. diamond regions and elsewhere, occurring not only in the gneiss and granite, but in the schistose series as well. Those that have been examined are dike-like in their mode of occurrence and granitic in composition." (P. 143) "The question of the eruptive or secretionary origin of pegmatites has long been a subject of discussion among geologists. . . . The recent studies . . . seem to have clearly established that most if not all of them are essentially eruptive masses, though possibly modified in some way by aqueous agencies. Even before becoming acquainted with the literature of the subject this view had seemed to me to be the only acceptable one as regards the typical pegmatites of Brazil." What is pegmatite ? J. F. Kemp says ". . . veins or dikes-it is an open question which is the more correct term-are met formed of very coarsely crystalline aggregates of the same minerals that constitute granite. These are called pegmatite and in them is the home of graphic granite, the curious intergrowth of quartz and feldspar, such that a cross fracture of the blades of quartz suggests cuneiform characters. . . . In regard to the larger veins or dikes it seems improbable that true igneous fusion could have afforded such coarsely crystalline aggregates, and so we are forced to assume such abundance of steam and other vapors, i.e, mineralizers, as to almost, if not quite, imply solution."

Jan 5, 1908

By AIME AIME

DREAMS do come true at times, although it is evidently better to believe in engineers than to "believe in fairies" if most dreams are to be translated into fact. It was a fine dream that David H. Moffat had when he projected a railway directly west from Denver; a dream of opening a new empire in northwestern Colorado, and of quickening transportation from the Middle West to the Pacific slope. But Moffat had been a miner and had become a banker. He knew that dreams, untranslated into works, benefit no one and pleasure only the dreamer, so he employed an engineer, H. A. Sumner, to study and plan the route to be followed by the rails. Previous main lines had run to the north, the Union Pacific, or the south, the Santa Fe. The Denver and Rio Grande, it is true, wriggled its way bravely across Colorado but, in order to reach a point 74 miles in an airline west of- Denver, travelled 281 miles following two canyons and crossing Tennessee Pass at 10,240 ft. Valuable as such a road is, it could never accomplish what Moffat had in mind. It was known that no low pass could be found directly west of Denver but up to 9000 ft. the topog-

Jan 1, 1925

By J. Mizrahi, A. M. Baniel, A. Mitzmager, S. Star

This article gives an account of the latest developments in the use of TBE for sink-float separation of silicate minerals. A number of minerals for which the process has been tested and found suitable are reviewed. Specific examples are discussed in relation to the particular problems of sink-float separation and recovery of TBE as compared with non-silicate minerals. The economic aspects are outlined. Silica and silicates comprise the most common and abundant group of minerals, and since they are present in variable amounts in most ores, they constitute an appropriate subject for the review and discussion of the recent developments in the use of TBE for mineral concentration. The silicates considered as a group have an extremely wide range of chemical and physical properties. Some of these properties, which are common to all minerals, are of importance to concentration by TBE and are discussed in some detail in this paper, as well as the development of methods and apparatus for concentration and recovery of TBE and several examples of concentration of silicates. PROPERTIES OF MINERALS WITH RESPECT TO CONCENTRATION BY TBE The properties considered as most important to concentration by TBE are specific gravity, structure, surface and shape. The specific gravity of a mineral is a fundamental property and is constant between very close limits for the same species of different sources if particles are pure and free from cavities or cracks. In many species, however, solid inclusions and changes in chemical composition due to replacement of elements cause variations in the specific gravity. The plagio-clase series of feldspars between albite and anorthite illustrate this point (specific gravity from 2.60 to 2.77). Fig. 1 shows the specific gravity distribution of some of the common silicate minerals.' The highest specific gravity is about 4.7 (zircon) and the lowest is 2.0 (sepiolite), with most of them ranging between 2.6 and 3.5. Although most of the silicates given in Fig. 1 are found as constituents of rocks, those generally considered as rock making minerals are comparatively few. They include quartz, feldspars, nephelite, sodalite, leucite, mica, pyroxenes, amphiboles, chrysolite, kaolin, talc and serpentine. These minerals may appear in igneous rocks as coarse crystals in granites, syenites and diorites or as very fine grained dispersions in basalt and felsite. When the latter rocks occur in an ore, their specific gravities depend on the minerals present and structure. The same is true for the sedimentary and metamorphic rocks (sandstones, shales, gneiss, slate, schists). A comparison of specific gravities for the minerals listed in Fig. 1 with that of TBE (see Table I) shows that the important rock-forming minerals, with the exception of pyroxenes, amphiboles and chrysolite (olivine), lie in the specific gravity range of less than 2.96 and can therefore be separated by TBE. The ore structure is important both in determining the apparent specific gravity and the efficiency of TBE recovery. The structure can be compact (as in

Jan 1, 1963

By Maynard H. Jameson

Earlier investigations of the potential-drop-ratio method of electrical prospecting have indicated that under suitable conditions this method is well adapted to the location of formation boundaries in stratified ground. A description of this development was given several years ago by H. Lundberg and Th. Zuschlag.l The curves published by these authors for the potential-drop-ratio variation above a horizontal contact indicated a definite relation of the position of the curve peak to the depth of the interface. The theory underlying this relation was subsequently studied by Z. Mitera in greater detail,' and the theoretical deductions were compared with the results of tank experiments. The investigations available at this writing were confined to studies of horizontal formation boundaries. It is the purpose of this paper to extend the scope of the previous work to the problem of dipping layers. Theory Consider the case of three media of different resistivities, whose interfaces are not parallel. If a point-source is located in one of these interfaces, its images do not lie in a straight line, but on the circumference of a circle whose center is at the hypothetical junction of the interfaces. R. F. Aldredgea determined the relation that exists between the degrees of dip of the two interfaces and the distances between the various images and the point for which the potential is to be found. As seen in Fig. I, three media of resistivities PO, p1, and p2 are involved, and the source I is located at the interface of the media Coo) and (p1). The perpendicular depth of the lower interface is h, 0 is the dip, R is the distance between source I and potential point P, and r is the distance between the images and that point. To distinguish between images lying above the ground interface and those below, the notation "odd" and "even" images will be employed; images below the ground interface will be termed "odd" and those above "even." The following relations govern the distances between either kind of images and the potential point: EvEn Odd Ta — R r1 - [rl] - [RS + 4h(h + R sin 01½ r, = [r] =. [R1 + 4h cos 0)2(h + -R sin 0)1½ ri - [r3] ={r3} [R* + 4h(4 cos2 0 - i)1 (h + R sin 0)l½ r4 = [r4] = [R2 + 4h(4 cos $ cos 30)1 (h + R sin 0)]½ r, — [r4] - [R2 + 4h(4 cos9 R cos 20 + cos 48)2 (h + R sin 01½ I RI + 4h[2 cos 30(4 cos2 0 - I)12 (h + R sin 8)1 ½ rn - [r4] - [R2 + 4hlf(cOs 0)18(h + R sin R)l½ As previously pointed out, the images of the source are on the circumference of a circle. If the angle of dip is 0, the angle measured from the horizontal to the first image is 28; to the second image it is 48, and so on. Since the limit of the reflecting interface is at its outcrop, the last possible

Jan 1, 1946