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By V.F. Marsters

Seepages of oil in Ecuador have been known for many years. The locality first to receive attention, and still worked in a modest way, lies on the north shore of the Santa Elena peninsula, between La Puntilla and Salinas. Operations mere first conducted largely by local cdpital. Later, foreign companies acquired large blocks of land, where they have done considerable drilling. For details concerning present drilling activities in Ecuador, we are indebted to Leon Price, an Ame~ican resident engineer of Ecuador. The information solicited came to the author through the office of the American Consulatell with permission to use it. The coastal plain bordering the Province of Tumbes, Peru, continues to the northeast, but narrow on passing the Zarumilla River. From this point northward it widens toward Santa Rosa. In fact, the pampas, as shown on the official Wolf map, correspond fairly well to the areal extent of tbe coastal plain as far as Guayaquil. This is shown in a general way on the accompanying map. The author understands that the Guayaquil enlbayment is bordered on all sides by the coastal plain, as recognized at Tumbes and farther southwest, and that it can be followed without a break as far north as Palmar. This view is supported by the mapped area regarded by Mr. Price as favorable or possible oil territory. Moreover the islands in the Gulf of Guayaquil are the same geologically as the coastal edge, being composed of Tertiary sediments. The author understands also that Tertiary formations occur north of Palmar. According to a report by Mr. Cardon, of Guayaquil, Tertiary sediments are exposed in the region of San Francisco and extend to and beyond Pta. Calera. There is also reason to believe that at least the lower part of the valley of the Santiago River is occupied by Tertiary sediments, ~~hich probably border the const line and extend into the River Mini l)nsin, and into Colombia. On the south coast there are many seepages, most of them near the inner edge of the coastal plain, between Zarumilla and Santa Rosa and also between Santa Rosa and Machala. I11 the latter region are

Jan 1, 1923

By W. B. Weeks, H. K. Shearer

The year 1937 brought to south Arkansas increased drilling activity and production. Oil production amounted to 12,159,440 bbl., an increase of 1,504,500 bbl., or 14.1 per cent over 1936. This was the largest production since 1931, and the first annual increase since 1925, when the deeper sands at Smackover were developed. There were 177 wells completed during the year, with 103 oil wells, 6 gas wells, and 68 dry holes, an increase of more than 100 per cent over 1936. Of the 56 wildcat wells drilled, 52 were dry and 4 produced oil. Two new fields, one important extension and three minor extensions were discovered. The trend toward deeper drilling is shown by the fact that 97 wells were more than 5000 ft. deep, including 80 over 6000 ft. and 13 over 7000 ft., although the depth record of 7973 ft., made in 1935, was not exceeded. Geological Section Deeper and more extensive drilling during the past few years, not only in south Arkansas but also in adjacent parts of north Louisiana and east Texas, has furnished much important geological information and has brought out some very unexpected facts in regard to structural and depositional conditions in the series of formations laid down in the interval between the end of the Pennsylvanian and early Cretaceous time. It is now evident that an important basin of salt deposition existed in the Arkansas-Louisiana-Texas area, but it is still an open question whether this salt basin was contemporaneous and continuous with the even larger Gulf Coast salt basin extending from Mississippi to Mexico. The accompanying columnar section (Fig. 1) shows the producing zones and names that have been applied to the several subsurface formations, most of which have no outcrop equivalents. This is for the convenience of readers unfamiliar with recent developments, but the correlations and nomenclature cannot yet be considered final. These formations will be discussed in more detail in various papers to be published in the near future.

Jan 1, 1938

By Lawson P. Entwistle

SUMMARY ONE of the important reserves of manganiferous iron ore is at Boston Hill, near Silver City, New Mexico. The area consists of a faulted block of gently dipping Lower Paleozoic shale, dolomite, limestone and sandstone, which have been intruded by a roughly circular mass of quartz-bearing monzonite porphyry and subordinate dikes. From a noselike protuberance of the intrusion radiate many premineral faults, which have localized much of the hypogene mineralization. Three important stages of hypogene mineralization can be recognized: (1) mesitite, a manganiferous iron magnesite, (2) quartz sulphides, and (3) barite-galena. The carbonate stage is widespread but stronger near the intrusion. The quartz may have been derived from hydrothermal alteration of the igneous rocks. Barite-galena is most important in the Chloride Flat mining district, about one mile north, where argentiferous galena provided silver for the supergene ore. The hypogene carbonate, lean in iron and manganese, has been oxidized and consequently enriched by meteoric waters containing an excess of oxygen and carbon dioxide to form ore bodies of intimately mixed hematite and pyrolusite. The ore bodies, at one place attaining a length of 1600 ft., a width of 300 ft., and a thickness of 25 ft., are largely confined to areas of brecciation and to spreads from faults in Silurian dolomite beneath soft Devonian shale.

Jan 1, 1944

The Delegation of American Engineers constituted by the American Institute of Mining and Metallurgical Engineers, the American Society of Civil Engineers, the American Society of Mechanical Engineers, and the American Institute of Electrical Engineers, that visited France in December, 1918, in acceptance of the invitation extended by the Congrés General du Genie Civil consisted of the following: Representing the American Society of Civil Engineers, Major James F. Case, past president, Geo. F. Swain, vice-president, Nelson P. Lewis, treasurer, Geo. W. Tillson, past director, Geo. W. Fuller, director, A. M. Hunt. Representing the American Society of Mechanical Engineers, president, Chas. T. Main. Representing the American Institute of Electrical Engineers, past president, L. B. Stillwell. Representing the American Institute of Mining and Metallurgical Engineers past-president, E. C. Spilsbury. The delegation organized on the way over by the choice of Major James F. Case as chairman, and Geo F. Swain as secretary. On arriving at Bordeaux, the Delegation was met by Mr. S. D. Brown, associate member of the American Society of Civil Engineers; and on its arrival in Paris it was joined permanently by the following attaches: Captain P. Charton, of the French Engineers, Delegate of the Commissariat-General to accompany the Delegation and serve as liaison officer; Captain Carpenter of the American Army; and Mr. Geo. Herdt, representing the Society of Civil Engineers of France. The object of the visit was to discuss with the French engineers the large engineering, problems now facing France. Engineering problems in their restricted technical sense came up for discussion practically not at all, for the French do not need advice nor assistance along strictly scientific lines. It was in the -larger and economic aspects of engineering, to aid in building up the industries and commerce of France, that our French associates desired to learn from the experience of the American Delegation.

Jan 9, 1919

By Olin G. Bell

The year 1934 in Southwest Texas was marked by aggressive development and exploratory work and resulted in the finding of five new fields and a new producing horizon in one of the older fields. This activity is the result of a reasonable market outlet for production, on both oil and gas, and the fact that drilling and operating costs are reasonable and that possibilities of finding new productive areas are rather high. A large part of the area is prospective and very little, if any, satisfactory surface geological work can be done. This, together with the possibility of finding new productive areas, stimulates wildcatting throughout the counties under discussion. Development work continued actively in all of the newer fields. Exploratory work was most intense in Duval, McMullen, Starr and Zapata counties. The activity in Duval and McMullen counties was the result of persistent efforts to find new trends of production similar to and perhaps associated with the Government Wells group of fields. The activity in Starr and Zapata counties was stimulated by the discovery of the Sam Fordyce field in Hidalgo County as well as the continued effort to find new productive trends southeastward from some of the older fields in northeastern Zapata County and western Jim Hogg Comity. Statistics on production are shown in Tables 1 and 2. New Fields Lopeno.—The Lopeno gas field in the southwestern part of Zapata County was opened in August, 1934, by R. B. Morrison No. 1 Ramirez. This is an anticlinal structure mapable in Claiborne beds and the producing horizon is the Queen City sand at 2100 ft. in the Upper Mt. Selman. At the close of the year only two gas wells had been completed but drilling operations were in progress on several other wells and a gas line was being laid to the field so that withdrawals from the area will begin early in 1935. Comilas.—The Comitas field was opened by Merle Gunby No. 1 Haynes in a sand at 800 ft. in an area southwest of the Escobas field. The discovery well had an initial production of only about 16 bbl. of oil

Jan 1, 1935

By I. N. Zavarine

The present paper is a continuation of the work on the relationship between the magnetic and the phase transformations in carbon steels during quenching. An account was given by the author in a previous paperl† of an investigation of this relationship during a continuous quench. The experimental difficulties then encountered prevented a conclusive proof of the existence or absence of such a relationship. The conclusions of the previous paper were derived indirectly. The present paper deals with the same problem, but the method of attack is modified. The technique developed by Davenport and Bain2 in their well-known study of austenite transformation at subcritical temperature was adopted in the present investigation. They have shown that the austenite to martensite transformation can be caused to proceed at a relatively slow rate by quenching steels into a hot metal bath. Slowing down of the rate of transformation, together with an observation by Lewis3 that a eutectoid steel can be preserved in the nonmagnetic state by such quenching, pointed out a possibility of a study of both transformations under more favorable conditions than previously described. The preliminary steps were connected with the technique of the hot bath quench. To study this phase of the present work a modification of the apparatus previously described' was used. The modification consisted in the use of a hot quenching bath instead of brine, and in fixing the secondary and the primary coils of the apparatus in a stationary position in and around the bath. Tubular specimens, as in the previous investigation, were heated in a suitable furnace to a temperature in the austenitic range for the given steel and then were dropped into the quenching apparatus. The quenching bath was heated to a series of temperatures within the probable range at which the austenite to martensite transformation was expected to proceed at the slowest rate. Observations

Jan 1, 1936

By E. P. Chapman

In May 1957 a diamond drill hole intersected 40 ft of magnetite and chalcopyrite assaying 2.55% copper and 51.6% iron on the claims of Craigmont Mines Ltd. near Merritt, southern British Columbia. The subsequent drilling indicated the presence of a multi-million ton orebody averaging over 2% copper and 18% iron, the latter present for the most part as magnetite and specular hematite in approximately equal proportions. This orebody, although under shallow cover at its eastern extremity, did not come to the surface and the early drilling was done on the basis of strong coinciding magnetic and geochemical anomalies. After 4 ½ years of intensive exploration and development the property was put into production in September 1961. The new ultramodern concentrator has a design capacity of 4000 tpd but is consistently treating well over this amount. Production is currently coming from that portion of the deposit which is amenable to open-pit mining methods. By mid-1958 information regarding the importance of the Craigmont find became fairly wide- spread, and exploration in the Merritt area was greatly intensified. Numerous magnetic and geochemical anomalies have been tested by drilling with notable lack of success. Detailed geological studies of the deposit and of the area have been made by Government agencies and by private companies and such studies are continuing. Many types of geophysical methods have been employed over the Craigmont deposit in an effort to develop knowledge which would assist in the search for similar mineral concentrations in the environment in which it occurs. This paper will discuss the results of the various geophysical surveys in relation to geological conditions and ore outlines insofar as they are now known.

Jan 7, 1962

By Wilbur Nelson

Little drilling has been done in Kentucky and Tennessee in 1923, with the exception of the Kettle Creek area on the Kentucky-Tennessee line. Oil prices fluctuated between $2.86 and $1.36 Per bbl. for light oil. The Kentucky production was slightly over 8,000,000 bbl., being 1,000,000 bbl. less than during 1922. Tennessee production was approximately 8500 bbl., being a decrease of 1000 bbl, over. 1922. During 1923, the first producing well was brought in, in Clay County, Tenn. Production in Tennessee will undoubtedly increase considerably in 1924, and Kentucky production will probably increase slightly. THE year 1923 has been a dull period in oil development in Kentucky and Tennessee, with the exception of the Kettle Creek area along the Tennessee-Kentucky line, in Clinton and Cumberland Counties, Kentucky, and Clay County, Tennessee. The price of oil during the year has been so low that wildcatters have shown little interest in drilling. At the beginning of the year, light oil sold for $2.31 per barrel and medium oil for $2.06 per, barrel. Prices increased to the highest point for the year in February, when light oil brought $2.86 per barrel and medium oil, $2.61. In April, prices had declined 35 c. while in May an additional decline of 25 c. went into effect. During June, prices declined 20 c. per barrel; during July, 45 c. per barrel; remained stationary during August and September, and dropped during November and December to the low price of $1.36 per barrel for light and $1.21 for medium oil. At present, an increase of 29 c. has brought the price of light oil up to $1.55, and indications are that the price will continue to increase during the coming months. It can readily be seen that during 1923 the price of oil was such as to prevent any drilling except that necessary to hold leases and to maintain production enough to take care of overhead expenses.

Jan 3, 1924

By J. M. Hartman

ONE of the most important subjects to the blast-furnace engineer is a thorough knowledge of the conditions affecting the temperature in the different portions of the furnace. All efforts to decrease the consumption of fuel and improve the working of the furnace must be based upon it, and I may, therefore, be permitted to place before you the results of my observations, and detail the conclusions to which they have led me. Tracing the thermic conditions from below upwards we have at the bottom of a blast furnace making No. 3 iron a temperature of 2900' F., which increases slightly to a point a little below the tuyeres. In the immediate vicinity of the tuyeres the temperature is somewhat lower, owing to the entering blast; but a short distance above the tuyeres, where all the oxygen of the blast has been converted into carbonic acid, the highest temperature in the furnace must be attained. This carbonic acid is, however, almost as soon as formed, converted by the glowing coal into carbonic oxide, a process which absorb, heat, reduces the temperature, and provides the active agent for the reduction of the iron ores. In its ascent the hot carbonic oxide gradually parts with its heat, first melting the descending iron and earthy materials, which drop down to the hearth of the furnace. The limit of this zone of fusion is rather sharply defined, and the temperature above this zone suddenly decreases. In its further ascent the hot gas drives off the carbonic acid from the limestone, which causes a further absorption of heat, and finally the gas escapes at the top, at a ternperature of about 250' F. if the furnace is working well. These changes of temperature I have attempted to represent graphically,

Jan 1, 1880

By A. Eilers

NO one who has visited our Western mining districts, and studied the economical part of the beneficiation of the ores occurring all over that vast extent of country, can underrate the high importance of the above subject. By far the larger number of the districts which contain smelting ores, i. e., argentiferous and auriferous lead, or copper ores, are situated in the Great Basin, that great plateau between the Rocky Mountains on the east, and the Sierra Nevada on the west, almost the whole of which is comprised at present in the boundaries of Nevada, Utah, and part of Arizona. This region is essentially a barren country. The extreme dryness of the atmosphere permits but a scanty vegetation in the plains; and even in the detached mountain-chains running through it-generally from N. to S., or from N. W. to S. E.-there are no trees found except dwarfed pines and mahogany, at the head of sheltered ravines, and a few cottonwoods and willows, which fringe the insignificant streams, before the water sinks in the arid plains. Nearly all the mountain-chains in this region are rich in silver ores. That class of these ores which is adapted to amalgamation, and rich in silver, has been worked with profit for more than ten years. But before the advent of the transcontinental railways, mining was restricted to these ores alone, and the consumption f fuel could be met with the scanty supply of forest trees in the immediate vicinity of the mining districts. Since, however, the Union and Central Pacific Railroads have brought the Great Basin nearer to the commercial centres of the East and the Pacific coast, thus reducing the expenses of freight and labor materially, other silver deposits, containing poorer ores in greater abundance, have been rapidly taken

FRIENDS of the late Charles F. Rand presented in 1930 a sum of money from which the income is available to support various phases of the work of the Institute in which Mr. Rand was so deeply interested. At present the fund amounts to $10,900. The specific terms of the deed of gift are as follows: "The fund collected to establish a memorial to the late Charles F. Rand shall be placed in the custody of the Board of Directors of the American Institute of Mining and Metallurgical Engineers, to be set up as a trust to be known as the `Charles F. Rand Foundation,' the income of which shall each year be applied to a distinct purpose to be decided upon in that year by vote of the Board of Directors. This purpose shall be such as to promote the general welfare of the Institute and to constitute a permanent memorial of the usefulness of Mr. Rand, who for many years gave unstintingly of his time and talents in its service. "It shall be within the discretion of the Board of Directors to establish a medal to be known as the Charles F. Rand Memorial Medal to be awarded at such a time and under such rules as may be determined by the Board of Directors, for Distinguished Achievement in Mining Administration." The establishment of this medal was announced at the annual meeting in February, 1932, the term "mining" being defined in its broad sense to include metallurgy and petroleum. Robert Linton is chairman of the Charles F. Rand Foundation Award Committee.

Jan 1, 1942

By S. J. Aresco, A. A. Orning

This paper presents a scheme for determination of precision for the various steps in coal sampling, sample preparation, and analysis. It also gives resulting data on 100 American coals from various coal fields covering all ranks from lignite to low-volatile bituminous. The variances of the various steps of the process are studied as a function of the coal preparation, the top size of coal as sampled, and the ash content. To understand the variables that control the overall precision of coal sampling, sample reduction and analysis, there is need for measurement of the variances due to successive steps of the process. The purpose of the present paper is to study these variances as a function of the coal preparation, the top size of the coal as sampled, and the ash content. The sampling data included are from 100 individual preparation plants from various coal fields in the United States and cover all ranks of coal from lignite to low-volatile bituminous; various types of preparation; deep, strip and auger mines; and, in many instances, mixtures from two or more coal beds or types of mines. The collection of data is continuing, but sufficient work has been done to draw some important conclusions. Since the work was done in conjunction with the Bureau of Mines sampling of coal, the time that could be spent at any one preparation plant was limited. This, in turn, limited the number of samples that could be taken for each coal. For this reason, the results from various plants were pooled in blocks. Two major blocking categories were "raw" and "washed!' The raw coals had no preparation other than crushing and/or screening. The washed coals were prepared further by some combination of wet or dry mechanical cleaning. The categories were further divided ac-

Jan 1, 1965

By P. E. Demmler

The apparatus in which the process of bright annealing of copper wire was carried out consisted of a section of iron pipe, 6 ft. long and 3 ft. in diameter. The pipe was provided with flanges to which were bolted the end plates for sealing, also with inlet and outlet tubes to allow for the displacement of the air in the pipe by natural gas. After charging with copper wire, sealing and displacing the air, the pipe was heated to 350' C. (662" F.). It was expected that the natural gas would furnish a neutral atmosphere which would prevent oxidation and give a satisfactory bright-annealed product. It was found, however, that the outer layers of wire were discolored and not suited for the use for which they were mtended. To obtain an idea of what was taking place in the annealing furnace, skeins of the hard-drawn wire were placed in a glass tube so that all changes in appearance could be observed as they were heated to different temperatures and under varying conditions. The temperature in each case was determined by means of a thermocouple placed in the tube close to the wire. Following is a summary of the results of these experiments: 1. When the wire was heated for 1 hr. in a current of natural gas at a temperature of 350") 400") or 500" C. (662", 752", or 932" F., respectively), there was a marked darkening of the wire throughout the skein. 2. When heated for 1 hr. in natural gas at a temperature of 600" C. (1112' F.), there was no coloration, the wire remaining clean and bright. 3. When heated in natural gas to 350" C. until darkened and the treatment continued with the temperature raised to 600' C., the coloration disappeared and the wire became clean and bright.

Jan 1, 1923

By V. F. Marsters

Seepages of oil in Ecuador have been known for many years. The locality first to receive attention, and still worked in a modest way, lies on the north shore of the Santa Elena peninsula, between La Puntilla and Salinas. Operations mere first conducted largely by local cdpital. Later, foreign companies acquired large blocks of land, where they have done considerable drilling. For details concerning present drilling activities in Ecuador, we are indebted to Leon Price, an Ame~ican resident engineer of Ecuador. The information solicited came to the author through the office of the American Consulatell with permission to use it. The coastal plain bordering the Province of Tumbes, Peru, continues to the northeast, but narrow on passing the Zarumilla River. From this point northward it widens toward Santa Rosa. In fact, the pampas, as shown on the official Wolf map, correspond fairly well to the areal extent of tbe coastal plain as far as Guayaquil. This is shown in a general way on the accompanying map. The author understands that the Guayaquil enlbayment is bordered on all sides by the coastal plain, as recognized at Tumbes and farther southwest, and that it can be followed without a break as far north as Palmar. This view is supported by the mapped area regarded by Mr. Price as favorable or possible oil territory. Moreover the islands in the Gulf of Guayaquil are the same geologically as the coastal edge, being composed of Tertiary sediments. The author understands also that Tertiary formations occur north of Palmar. According to a report by Mr. Cardon, of Guayaquil, Tertiary sediments are exposed in the region of San Francisco and extend to and beyond Pta. Calera. There is also reason to believe that at least the lower part of the valley of the Santiago River is occupied by Tertiary sediments, ~~hich probably border the const line and extend into the River Mini l)nsin, and into Colombia. On the south coast there are many seepages, most of them near the inner edge of the coastal plain, between Zarumilla and Santa Rosa and also between Santa Rosa and Machala. I11 the latter region are

Jan 1, 1923

By Maurice Ewing, L. Don Leet

The most important quantitative method in seismic prospecting by refraction shooting is the method of profiles. A profile is established by firing a series of charges at various points along a straight line which terminates at the seismograph. The same data are obtained by repeatedly firing charges at one place and recording at a series of stations along the line of the profile. The quantities which are measured are the distance x from each firing position to the seismograph and the time t required for the first disturbance from each explosion to travel to the seismograph. These data are used in plotting the familiar time-distance graph. The only time-distance graphs that will be considered here are those obtained in localities where the velocity of propagation depends solely on the depth beneath the surface; that is, where there is no slope in the subsurface. The essential calculation to be made from such a time-distance graph is the determination of P(x), the maximum depth of penetration of a disturbance coming to the seismograph from a firing point at the distance x from the instrument. If the time-distance graph consists of a series of straight lines, as is often the case, the penetration P(x) can be calculated by means of formulas which appear in almost every description of seismic prospecting.' Until the present, however, the only formula that has been available for calculating P(x) for time-distance graphs which are smooth curves is one which requires an arbitrary assumption regarding the law of velocity increase with depth.2 The practice in these cases has been to approximate the curve by means of a number of straight lines and then to apply the ordinary straight-line formulas. This method clearly can yield accurate results only when a sufficiently large number of straight lines is used. The labor of computation increases rapidly when the number of lines is increased, so too few lines often are used. Further than that, there is a strong tendency to overlook the approximate nature

Jan 1, 1932

By G. H. Fancher

Improving economic conditions are reflected in the statistical picture of the petroleum and natural gas industry for 1933. Prices were better, demand was greater and the volume of production increased. The increase in the production of gas has been due mainly to the utilization of outlets to the new prolific gas fields of Potter and Tioga counties; of oil, to the growing demand for Pennsylvania grade lubricants. It should be emphasized that nowhere is volume of production more subject to control due to the extensive use of secondary methods of recovery and regional peculiarities than in Pennsylvania. A summary of developments in production for Pennsylvania in 1933 of necessity is brief. The data listed in Table 1 are all too few in number and not all that is desirable from the standpoint of accuracy. No state agency for the collection of data exists, no reports are compulsory. Nevertheless, because of the hearty cooperation of many individuals and public spirited corporations, it is believed that the data are as reliable as are obtainable at the present time. Furthermore, records of the past too often are lost, were never in existence or are fragmentary, to say the least. Illustrative of the condition is the fact that no thorough study of the oil and gas-producing regions has ever been made. The publications of the Pennsylvania Topographic and Geologic Survey upon the subject are noteworthy and valuable, especially the most recent one.' The Survey has been handicapped in the work by lack of time, personnel and funds in addition to the difficulties mentioned previously. It is obvious, therefore, that Table 1 cannot be completed for Pennsylvania. The data simply are not in existence. Officially there are 328 oil and gas pools or fields known by name and 58 distinct sands or horizons, one or more of which are productive of oil and gas in the various pools, but reliable data for only three general regions could be assembled.

Jan 1, 1934

By C. Schlumberger, M. Schlumberger

The object of this paper is to clarify the idea, so important when exploring by potential methods, of the depth of investigation attainable by electrical measurements. After defining, with some precision, .the term "depth of investigation'' in geophysics, the authors show how it is possible to regulate this depth in potential methods and to obtain an 'electrical drilling" from surface observations. They consider also the difficulties encountered in deep measurements and indicate how it is possible to reach greater depths than those having an industrial interest. Depth of Investigation The term, depth of investigation, in its general sense, is easily understood. For instance, a driller who can pull cores from a depth of 2000 m. is capable of working, with accuracy, to that depth. By means of a properly placed drill, he may locate an orebody at a depth of 1999 m., however small this orebody may be. On the contrary, the term as used in geophysics requires precise elaboration. As a matter of fact, no geophysical method, irrespective of the physical property studied (density, magnetic permeability, conductivity), can discover a very small body at a great depth because, in practice, the physical parameter upon which such a geophysical method is based is never regular enough, throughout the ground, to distinguish the feeble anomaly caused by the small, deep-lying body from the numerous anomalies due to irregularities of the encasing terrains. Aside from this question of the ratio between the size of the body being hunted for and its depth of burial, a second factor plays its role in the possible depth of investigation; that is the difference, for the parameter under consideration, between the body and its surrounding material. The greater this difference, and the more homogeneous the encasing terrains, the greater is the possible depth of investigation. This being generally established for all geophysical methods, it is possible to distinguish two main classes of these methods, from this same point of view

Jan 1, 1932

By W. J. Sharwood

(San Francisco Meeting, September, 1915) CUPELLATION is well known to be one of the most effective methods of separating silver and gold from base metals and other impurities, as well as one of the most accurate means for their estimation. In the latter application it consists in absorbing in some porous medium the fused lead. oxide formed by the oxidation of the lead "bath," which carries with it the oxides of other base metals present. It has long been recognized that small amounts of both silver and gold were removed and absorbed together with the base metals, as well as being to some slight extent volatilized, and in work of the highest accuracy a correction is made for the "cupellation loss." Thus. in the assay of bullion this is done by means of "proofs" of like composition, which are manipulated throughout in precisely the same manner as the assay pieces, and are assumed to lose or gain like amounts. In the case of certain very rich ores and commercial products the loss is adjusted by assaying the cupel itself and recovering the precious metal absorbed, but this doubles the labor and does not remedy the loss by volatilization. Arbitrary tables have been drawn up by various authorities with the object of enabling a correction to be applied without the use of a check. These have been of very limited practical use owing to the fact that a number of factors affect the losses sustained. For a fixed amount of precious metal the loss varies with the amount of lead used, with the nature and amount of the impurities, with the porosity of the cupel, with the air supply, and above all with the temperature at which cupellation is carried on. Pure silver loses relatively much more than gold, but the loss in either is diminished by au addition of the other metal. The concentration of precious metal in the litharge increases as the concentration in the lead increases, but little work has been published connecting the two. If all other conditions remain the same the actual total loss increases, but the percentage loss diminishes, with an increase in the weight of precious metal treated.

Jan 8, 1915

By J. F. Crouch

INTRODUCTION Roll front uranium has unique geologic characteristics (L,) which require specialized mining procedures. Roll front uranium occurs in arkosic sandstones with the ore zone typically less than 100 feet in thickness with up to 400 feet of overburden. The areal extent of ore is often a few thousand acres. Within the ore zone, ore grade material occurs in C and S shaped rolls, which are a few feet in width and height but may run laterally for several hundred feet. Since the total mine plan may include mining all ore, a roll front uranium mine may cover a few thousand acres. For both economic and environmental reasons, a roll front deposit is mined as a series of phases or sub-pits (3, 4) as illustrated in Figure 1. A typical sub-pit is 400 to 500 feet across. Sub-pit 1 is stripped initially and the overburden is spoiled on the surface. Depending on haul distance and overburden characteristics, stripping is done with trucks and shovels (or front-end loaders) or scrapers. When ore is encountered in sub-pit 1, mining begins, and the stripping equipment is moved to sub-pit 2, with sub-pit 2 overburden also being spoiled on the surface. When ore is encountered in sub- pit 2, sub-pit 1 mining should ideally be complete so the mining equipment can move to sub-pit 2 and sub-pit 3 overburden can be spoiled in the mined out sub-pit 1 area. Ore is mined selectively in a series of 12 to 24 inch cuts by a 2-1/2 yard backhoe on the basis of radiometric probing. For effective drainage, ditches must be maintained on the boundary of sub-pits, and mining lifts are kept as level as possible, with the orebody slightly elevated as part of general good mining practice. Waste removal in the ore zone is done by self- loading scrapers near the orebodies and by push-pull or push loaded scrapers away from the orebodies. Each self-loading scraper cut is

Jan 1, 1983

By Donald R. Williamson

Ore estimation at Cyprus Pima mine begins with estimating average copper grades for mine model blocks. Accuracy of the estimates has been checked four times in the last several years by comparing the estimates with arithmetic averages of corresponding blasthole (BH) assays. The data file now contains 3.567 estimated blockgrades and more than 10,000 blasthole assays. These data were compared by straight-line regression analysis at appropriate intervals as the body of data grew. Arithmetic averages of the estimates differed each time from arithmetic averages of the BH averages by nearly the same amount. More significantly, regression curves of the new total sets of data did not change position appreciably showing that copper grade estimates of blocks in all grade ranges from the lowest to the highest grade ores remained in error by nearly the same amount. Other studies revealed that core hole assays of the dominant ore type are biased and that that bias almost equals the error in estimation. Discovery of constancy in error indicated that regression analysis could be a means for correcting estimates of average block copper grades. A correction for estimated block grades was developed. It required determining which regression is appropriate for the particular problem, and a mechanism that is demonstrably sound. This paper describes the problem and the solution: No comparable study has been, found in the literature. Two other applications of regression analysis to metal grade comparisons are presented. Each adds a bit of support to a generalization which was suggested by correction of average block copper grades, namely, when performance of an estimate is to be evaluated, the variable taken to be the yardstick for the performance should be regressed on the estimate.

Jan 1, 1980