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By H. G. Schneider

THE Smackover oil and gas field lies in Ouachita and Union Counties, Ark., in the south-central part of the state, in T.15 and 16S., R.15, 16, and 17W. It is 10 miles north of El Dorado, the principal business and railroad center in the south-central part of the state, and extends from the town of Smackover in all directions. Productive territory having an aggregate area of nearly 55 sq. mi. has been developed. It extends 6 miles from north to south and 12 miles from east to west. The field may be divided into two parts: the east district, which includes the area east of the town of Smackover, and the west district, which includes the area west of the town of Smackover. In relation to the neighboring productive fields of Arkansas, the Smackover field is 9 miles north of .the El Dorado oil and gas field, 8 miles slightly west of north of the East El Dorado oil and gas field, and 16 miles east of the Stephens oil field. Smackover was discovered in May, 1922, when the Oil Operators Trust drilled well No. 1 on the J. T. Murphy farm, in the southeast quarter of sec. 8, T. 16S., R.15W. This well is located almost, on the top of the Norphlet dome and was drilled to the Nacatoch sand. It had an initial open flow volume of 30,000,000 cu. ft. of dry gas per day, and a rock pressure of 950 lb. per sq. in. In July, 1922, the V. K. F. Co. completed the first oil well in sec. 29, T.15S., R.15W., on the north side of the Norphlet dome, and 3 miles north of the first gas well. This well started the active development of the north and northwest sides of the dome.1

Jan 3, 1924

By H. R. Brannon, R. J. Robinson, G. W. Kattawar

Accurate prediction of storm wave characteristics are needed for design of offshore structures. Statistical methods of random noise analysis provide techniques for predicting required wave properties. These techniques have been used to analyze and characterize storm wave profiles from Gulf of Mexico recording installations in 34, 65 and .98 ft of water. Correlations based on the results can be used to predict wave crest probabilities and wave shapes for a range of Gulf water depths and storm conditions. Example predictions of wave crest probability as a function of water depth for a particular set of storm conditions are given. INTRODUCTION Accurate predictions of wave crests and wave shapes are needed for design of offshore structures. With predictions of wave crests, platform deck elevations giving adequate protection from exposure to storm waves can be selected. Use of hydro-dynamic wave theories with the wave crest and wave shape predictions permits an estimate of the wave forces an offshore structure must withstand. Observation of ocean waves suggests use of statistical analysis for studying wave characteristics for water depths beyond the breaking wave zone; recent wave generation theories lend support to this approach. l-3 One of the most powerful methods of statistically analyzing wave profiles was introduced by Cartwright and Longuet-Higgins; most of the basic relations used were developed by Rice5.6 in studies of random noise theory. This method predicts wave crest elevation probabilities from two parameters characterizing a wave profile. The statistical approach also provides a means for predicting wave shapes. In the random noise model of a wave profile, surface elevation is represented as an infinite sum of sine waves with closely spaced frequencies and random phase angles. Power density is proportional to the sum of the squares of the amplitudes of sine waves having frequencies within a narrow band, and the distribution of power density as a function of frequency is called the power density spectrum, or power spectrum. The power spectrum characterizes an irregular sea, and hence finds use in motion studies of ships, barges and semisubmersible drilling platforms. From the power spectrum, a wave profile of any duration of time can, in principle, be calculated; this long wave profile depicts the many wave shapes to which a structure may be exposed. Thus, the statistical methods of wave analysis provide an approach to selecting wave shapes as well as wave crest elevations needed for design of offshore structures. For practical application of these techniques, power spectra and related quantities must be predicted from storm properties. Barber and Tucker 7 have reviewed correlations of wave properties and storm conditions. Their review summarizes work of Darbyshire,8 among others, in which a correlation of power spectra with wind intensity of the North Atlantic was developed. These results, plus more recent work by Pierson and Moskowitz and Kitaigorodskii,10 establish feasibility of correlation, but there is no theoretical basis for modifications extending the relations to other areas as remote as the Gulf of Mexico. Hence, to predict characteristics of Gulf of Mexico waves, a study of local observations is needed. This paper presents (1) a practical approach to computing wave profiles hat depict shapes of waves for use in force calculations, (2) a summary of relations for predicting probabilities of wave crest elevations, (3) correlations of parameters needed to apply these methods in the Gulf of Mexico and (4) examples of application of the techniques. THEORETICAL BACKGROUND The following sections summarize relations needed to calculate wave profiles and to estimate wave crest probabilities. These relations also identify quantities that must be related to storm

By J. Chipman, N. J. Grant, J. H. Walsh, T. B. King

WITH the development of adequate sampling and analysis techniques, much information has been obtained concerning the behavior of hydrogen in the steel bath during the course of steelmak-ing operations. From studies of this type it has become clear that the slag has an important role to play in determining the hydrogen content found in commercial products. A knowledge of the behavior of hydrogen in slags is necessary to round out our knowledge of hydrogen in steelmaking practice; with this information we are better able to assess practical methods of control. In this paper a method developed for analyzing slags for hydrogen content, studies of the solubility of hydrogen in synthetic slags, and studies of the variation of hydrogen content in slag and steel in industrial heats will be described. Previous Work—While very little has been done in the past to determine the hydrogen content of metallurgical slags, measurements have been made on such slag-like materials as geologic magmas and glasses. Goranson as made extensive studies of the solubility of water in natural and synthetic granites. Many workers have investigated the solubility of gases in synthetic and commercial glasses, but the recent work of Russell" is the most extensive. Russell found that the solubility of water in glass was proportional to the square root of the water vapor pressure in water vapor-oxygen mixtures. It was found that the solubility could either increase or decrease with temperature depending on the glass composition. Wentrup, Fucke, and Rief,' and Piper, Hagedorn, and Backes' have extracted hydrogen by holding a slag at 1300" and 800°C respectively in vacuum. Wentrup et al. reported hydrogen and water vapor as evolved together while Piper et al. passed the evolved gases from the hot extraction treatment over hot ferromanganese to reduce the evolved water vapor to hydrogen and, therefore, reported the analyses in terms of total dissolved hydrogen. Yavoiskii has reported hydrogen and nitrogen analyses on steelmaking slags. Dobrokhotov, Povol-skii, and Khan have studied the hydrogen content of basic open hearth steel under slags of varying viscosity. These authors reported that the hydrogen content of the steel bath increased as the fluidity of the slag was increased by the addition of bauxite. They recommended that a viscous slag be used and the steel tapped without deoxidation in the furnace to ensure a low final hydrogen content. Analysis of Slags for Hydrogen Development of Apparatus—The vacuum fusion analysis equipment described by Shields, Chipman, and Grant" was modified for the analysis of slags." This method depends upon the reduction of water in the slag to hydrogen, which is readily determined by the method used for hydrogen in steel. Preliminary experiments were made with a eu-tectic ferrosilicon melt as the reducing agent. Other experiments included the use of graphite and molybdenum crucibles. The ferrosilicon alloy bath was found to produce a thick coating on the furnace tube which could adsorb hydrogen. Graphite produced CO by the reduction of FeO, MnO, and SiO2 in such quantities that analysis for hydrogen was virtually impossible. Molybdenum, while giving a low blank value, could reduce the slag sufficiently to produce a volatile oxide which again was found to adsorb hydrogen. The arrangement finally adopted is shown in Fig. 1. The molybdenum sheet served as the induction-heated susceptor, and was separated from the escaping gases by alumina guide tubes. An outer jacket of alumina protected the quartz furnace tube, and alumina and quartz stools completed the assembly. The falling sample is shown wrapped in aluminum foil, 0.002 in. thickness, which acted as the reducing agent' This foil was careful'~ washed in acetone and an d and then dried in hot air before wrapping the weighed slag sample for charging into the apparatus. Investigation of the hydrogen content of the aluminum foil itself showed that a small quantity of hydrogen was released in vacuum, but had no relation to the weight of the aluminum charged. This quantity of hydrogen was

Jan 1, 1957

By E. E. White

In August, 1911, I read a paper before the Lake Superior Mining Institute1 on surveying and sampling diamond-drill holes. The present paper gives a more thorough descriptiou of these methods, together with a few changes and notes suggested by further experience. Since August, 1911, the methods, used constantly by the Cleveland-Cliffs Iron Co., have been developed to a higher degree of efficiency, and have given great satisfaction. Until a few years ago but little attention was paid to the determination of the actual course of drill-holes, to the accurate sampling' and analysis of the material, or to the scientific location of the drill-holes. It has now been common practice for several years in many districts to test the inclination of drillholes by etching glass tubes with hydrofluoric acid, but the direction of deviation from the vertical has not often been determined. Methods of determining the direction by means of a compass were first developed in connection with drilling in Victoria. The latest method used on the Rand in South Africa has been recently described by John I. Hoffman.2 In the same paper Mr. Hoffman describes an ingenious method of wedging-off a drill-hole so as to start new holes at several successive points. By this means a hole can be deflected in any desired direction, and the curvature can be controlled to a considerable extent, provided the rock is soft enough to permit the hole to be wedged off. Unfortunately, in the Lake Superior district, the jasper iron-formation is so hard that it is very difficult, if not impossible, to do this. I tried to deflect one hole so as to avoid drill-rods stuck in the hole, by using a

Jan 1, 1913

By Henry M. Stanley

The methods about to be described have been tested in practice, and are believed to be specially adapted to such extended topographical surveys as mining engineers in particular are sometimes called upon to execute. The assistance of Mr. H. 0. Flipper in the preparation of this paper, and his practical authorship of the second part, is hereby acknowledged. I. Photographic SuRveying. The writer was recently employed; together with Mr. H. O. Flipper, to survey the properties of the Plata-Reina de Sonora Mining and Milling Company, situated in the mining district of Las Planchas, District of Magdalena, State of Sonora, Mexico. These properties, now owned by an American corporation, of which M. W. Evans, of New Orleans, is president, and Richard A. Pomeroy is resident superintendent, are famous in the history of Mexican mining, as the place where planchus, or bolas de plata were foulld about the beginning of the last century. Ward, the English CILargh d7Affaires in Mexico from 1826 to 1828, writing at that epoch, says: "The idea [that the ores in the north of Mexico were richer than those in the south] probably originated in the discovery of the famous bolas de plata [balls of silver] of Arizona [Planchas de Plata de Arizona, a stock-ranch in northern Mexico], in the beginning of the last century, which was, and probably still is, believed in Europe to be one of those fables with which mining countries always abonnd. But the attention of the present government of Mexico having been drawn to the subject, a search was made in the viceregal archives, by order of the president, for the correspondence which was known to have taken place respecting it in the year 1736. This correspondence I have seen, and I have in my possession a certified copy of a decree of Philip the Fifth, dated Aranjuez, 28th May, 1741, the ohject of which was to terminate a prosecution, instituted by the Royal Fiscal, against the discoverers of Arizona, for having defrauded the treasnry of the duties payable upon the masses of pore silver found there. The decree states the weight of the balls, sheets and other pieces of silver discovered (bolas, planchas, y otras piezas de plata), to have amounted to 165 arroba, 8 pounds, in all, 4133 pounds; and mentions particularly one mass of pure silver, which weighed 108 arrobas (2700

Jan 1, 1892

By William P. Blake

At the August meeting of the Geological Society of America, I presented a paper on the occurrence of alunogen and bauxite upon the Upper Gila river, about 40 miles north from Silver City, New Mexico, together with observations upon the geology of that region." Inasmuch as the subject is specially interesting to metallurgists and mining engineers, and as our Transactions contain recent important papers, by Dr. Hayes, M. Laur, of France and others, upon bauxite, I venture to offer to the Institute, in more condensed form, an account of the deposits described in the paper above referred to. The only other published account of the alunogen locality which I have been able to find is a prospectus-pamphlet, issued in a small

Jan 1, 1895

By M. L. Brashears

IN the last 15 years industrial use of ground water has more than doubled, and in 1951 amounted to 5 billion gallons per day. A similar sharp increase in the utilization of ground water for irrigation and public-water supply occurred in the same period. In many areas rapid increase in withdrawal from wells has taken place almost entirely unhampered by regulatory control and with little or no integration of effort. As might be expected, the chief interest in many regions has been maximum production rather than sustained perennial yield. As a result, widespread depletion of underground reservoirs and deterioration of the quality of the water stored in them has taken place in many areas, even though total pumpage in the United States is far below ultimate potential. Of even more concern is the fact that excessive withdrawal has drawn salt water into the reservoirs beneath many heavily populated centers along the Atlantic, Gulf, and Pacific coasts, causing costly abandonment of pumping plants.1

Jan 10, 1953

By Richard D. Snouffer

Prime topics of conversation these days are the new concepts of rail haulage for bulk items such as iron ore, potash and coal. We have heard such ideas as the "integral train" and the "unit train" discussed frequently during the past two years at various AIME meetings, and progress reports have kept up a steady appearance in the technical press and in local newspapers. While no railroad has a complete "unit train" in service at this moment, one has 50 fast-discharge cars under construction and the Pennsylvania Railroad has experimented with radio-controlled motive power distributed at intervals throughout the train. To a great extent, however, the promise for greater efficiency and lower costs held out to industry by these new haulage methods is dependent not on greater speed or larger cars or more dedicated equipment alone but, rather, on the utilization of modern practices in the loading and unloading of rail cars. It is the purpose here to examine these two key steps and the up-to-date procedures and equipment they entail.

Jan 7, 1963

By Russell Millar

ACCORDING to the data of Maier and Ralston1 zinc vapor and carbon monoxide under the conditions in which they are present in a zinc condenser should, from a thermodynamic point of view, react to form zinc oxide and carbon, Zn (gas) + CO = ZnO (solid) + C. Calculations based on these results show that the gas mixture which is reducing to zinc oxide at the tempera-ture of the retort is oxidizing to zinc at the tempera-ture of the condenser. A series of experiments at the Pacific Experiment

Jan 9, 1928

By S. H. Ash

With statistics still incomplete, it appears that the safety record of the mineral industry for 1955 will do well to hold its own in comparison with 1954. On the one hand, metal mining shows an improvement in its record, due in part to intensive campaigns for preventing ground fall accidents. Coal mining, on the other hand, is showing a poorer record in 1955 than for the preceding year. While no major disasters occurred during the year, increased fatalities resulted from ground fall, haulage, and machinery accidents. It seems probable that increased job training may serve to improve the situation. Health: Utilization of diesel equipment continues to increase in noncoal mines, in spite of existing prejudice. In 1955 two types of diesel-driven tractors and one shuttle car were approved by the USBM. Where diesel engines are used controlled ventilation is mandatory in order to keep the CO content under 20 ppm, but such ventilation is not difficult to achieve with normal equipment.

Feb 1, 1956

Ocean environmental factors are an intriguing new set of parameters to be dealt with in the prospecting and exploration phases of resource development for both the continental margins and the deep ocean. While information and data gathering programs for ocean minerals would parallel onshore procedures, their costs generally run higher. Commercial Prospecting-Identification of Mining Sites Two modes of prospecting can be identified-commercia1 prospecting (in which the ultimate objective is to define potential mining sites), and scientific prospecting, which is conducted with different objectives in mind. For ocean exploration, both types of prospecting are carried out prior to the obtaining of any exclusive rights to explore and exploit a specific deposit. Deepsea's John Flipse adds: "Any commercial prospecting program should by its very nature require the freedom to search wherever minerals might occur with maximum flexibility."

Jan 4, 1975

By J. W. Bolton

THIS paper discusses some fundamental metallurgical principles involved in production of sound cast bronze. In a previous paper the writers advanced the theory that "oxidation" in bronze castings is due to incipient shrinkage, and showed the effect of reducing melting atmospheres. In the present paper the effects of certain impurities and of actual oxidizing conditions are shown. The appendix deals with the appearance of various inclusions. For many years the prevailing opinion has been that unsoundness, dark colored fractures and other phenomena accompanying porosity and weakness in bronzes are due to oxidation. The actual troubles are caused by fissures of intercrystalline type, which are often mistaken for intercrystalline films. These weaken the metal and make it porous. Grave doubt regarding the accuracy of the oxidation theory appears when several research papers presented within the last 10 years are reviewed critically. In 1919, Comstock conducted metallographic researches, attempting to identify "oxides" in synthetically prepared metals. He found that oxides of tin, aluminum, zinc, etc. are different from the intercrystalline films (or cavities) to which porosity is due. Apparently he believed that these "oxide films" may be caused by volatile oxides of zinc or of phosphorus or by dissolved gases thrown out of solution during solidi-fication of the metal. In 1923, Woyski and Boeck3 definitely questioned the accuracy of the oxidation theory and indicated the danger from reducing atmospheres. They say that "oxidation, gassing and shrinkage may produce effects very similar."

Jan 1, 1930

By R. T. Rometti, C. A. Bossard

INTRODUCTION Whenever a new mining property is developed or a new concentrator is built, considerable time, money, and planning are invested for the exploration, engineering, and construction of the required facilities. Yet, when these facilities are ready for startup, all too often insufficient time, money, and planning are invested in this critical phase of the project. Failure to plan for this phase results in untimely personnel mobilization, insufficient operator training, and inadequately prepared budget estimates, which combine to create excessive costs, lack of communication, unclear responsibility divisions, unnecessary delays, and poor production levels. Insufficient or excessive leadership, due to unclear assignment of responsibility, results in irrevocable problems within the startup team. A carefully planned and budgeted startup phase can avoid many of these problems. SCHEDULING A key element in properly planning the startup phase lies within the area of scheduling. Once the schedule has been established, planning can be greatly simplified through the expansion of each specified item. The overall project schedule should specify the date when the startup and initial operating management team will be brought onto the project. This team should be mobilized at least two years prior to the anticipated startup date, to allow sufficient time to begin to plan, assemble the startup groups for the various areas of the plant, initiate a workable communications system, and implement the development of the training program. This team is responsible for the preparation of a startup schedule, which would detail the dates for all key items associated with this phase of the project. These key items would include training program development, personnel hiring dates, prestartup plant checkout, etc.

Jan 1, 1982

By I. H. Warren, E. A. Devuyst

The selective dissolution of pyrolusite (MnO2) in presence of goethite (FeO•OH) in aqueous ammoniacal ammonium carbamate solution has been investigated: various reducing agents were studied, in particular sodium sulfite (Na2SO3,) and hydrazine hydrate (N2H4•H2O). Sodium sulfite was found to be an unsatisfactory reducing agent for both goethite and pyrolusite, for the leaching rate decreased steadily with time to an impractical level because of the limited solubility of the reactions products. Hydrazine hydrate was an effective reducing agent for pyrolusite even at low temperature, whereas goethite required much higher temperatures for any appreciable dissolution. A 1-hr leach at 35°C dissolved 90% of the pyrolusite but only 0.1% of the goethite. An activation energy of 17.0 Kcal per mole was found for the dissolution of pyrolusite with hydrazine. A reaction mechanism for the leaching of pyrolusite with hydrazine is proposed in which a reduction reaction on the surface of the mineral is the rate-determining step. The application of ammonium carbamate to the beneficiation of ilmenite is briefly described.

Jan 1, 1973

By Kendall E. Born

Production of crude oil in Tennessee during 5945 was slightly more than 6000 bbl., the lowest figure since 1916. Approximately 5500 bbl. was produced from the "Mississippi lime" in Scott and Morgan Counties. The remainder was from two wells each in Clay and Fentress Counties. Thirty million cubic feet of gas was marketed off the lease in Morgan County and about 10 million cubic feet was produced in the Jamestown field in Fentress County. The production of oil by counties is shown in Table 1.

Jan 1, 1946

By Donald Barton

Geophysical methods of prospecting taken as a whole do not seem to offer much promise to a young man planning to enter them in the future. They have come to stay, to be sure, and they will continue in at least moderate use for a long time. Domestic use of those methods presumably is at a maximum at the present time. Geophysical pros-pecting is expensive; the effects of the law of diminishing returns in efficiency in finding prospects can already, be recognized. Small oil companies, independent oil operators, and royalty buyers have been doing much geophysical work. But in face of the increasing costs of discovery of prospects and in face of the probably decreasing favorability of the prospects discovered, I expect to see a sharp drop in their use of geo-physics within the next 10 years. The major oil companies and the larger small oil companies will continue to use geophysics indefinitely, but it seems doubtful whether the very extensive domestic campaigns of a few companies will be maintained for many years, certainly not for 10 years. The use of the geophysical methods in foreign countries has not yet reached its peak, and probaby will continue to increase for several years. That peak level of activity will probably be held for 10 years, although the site of maximum activity will shift from country to country; by the end of 25 years from now, I should expect the foreign use of the methods to have leveled off to one-fourth to one-half the peak level. Foreign service in geophysics does not seem to offer an attractive career, except for men of exceptional disposition. Young men just out of college, who are willing and who can afford to spend three or four years having a fling at adventure before settling down, will find it attractive, but when their tour of foreign service is over, they probably will have harder work finding a job than when they were seniors, and their foreign experience will count for little, except for further foreign service. A few men, mainly the higher men, will have headquarters at civilized or semi-civilized cities and towns or at permanent oil-company towns, and can

Jan 1, 1938

By W. A. Ver Wiebe

It is becoming increasingly apparent that the State of Kansas contains one of the largest reserve areas for oil exploration in the United States. During the year 1936 no less than 54 new oil pools were discovered by drilling. In addition, seven gas pools were found, which may develop into oil pools when deeper horizons are tested. Several old pools increased their reserves when production was found in lower strata. The data presented in Table 2 indicate that nearly 2000 wells were drilled in the state during 1936. Of these more than 1214 found commercial quantities of oil and at least 61 found marketable quantities of gas. The data are conservative because complete results on drilling are not available for the eastern part of the state. Ellis, Rice and Russell Counties share honors with a total of 10 new pools in each. Barton County is prominent with six pools; while those counties claiming fewer new pools are Clark, Ellsworth, Harvey, McPherson, Ness, Pawnee, Rooks, Stafford and Trego. Important additions to our gas reserves were found in Finney and Haskell Counties, which are north of the extensive Hugoton gas area and may some day be part of it. At the close of the year there were 17,317 wells in the state rating as producers. By far the larger share (14,000) were classed as strippers and allowed to flow 100 per cent of their potential capacity, thus accounting for 33,500 bbl. a day. The remaining wells, capable of producing from 15 up to over 6000 bbl. per day, were limited in output according to these amounts. The largest wells having a potential of from 3000 to 7000 were allowed to flow from 2 to 3½ per cent of their official potential capacity. The percentage rises until wells of 15 to 20-bbl. capacity have a rating of slightly over 83. On the basis of these calculations the total potential capacity of all wells was 1,667,814 bbl., and the daily amount allowed was 175,851. Nine of the pools most recently opened were still unable to market their oil and were classified as "shut-in" pools. Total production for the state for 1936 was somewhat over 58 million barrels. Striking Geological Data Some interesting geological data were uncovered by deep drilling during the year. The most remarkable bit of information is the discovery

Jan 1, 1937

By Joseph W. Murray

Prior to 1950 Magma's ore production came from two parallel, steeply dipping, east-west striking mineralized faults, one called the Main or Magma vein and the other the Koerner vein, which lay about 1100 ft to the south. This vein system has been explored and mined over 9000 ft horizontally and 4800 ft vertically. In 1950 continued exploration led to the discovery and development of replacement orebodies in the Devonian limestone zones adjacent to the veins. These replacement deposits occur in the eastern part of the Magma mine and follow the strike and the 30º east dip of the host limestone. Strike length of the ore bodies varies from 250- 500 ft and thickness from 15-125 ft. The orebodies are large tabular masses with chalcopyrite and bornite being the dominant ore minerals. Hematite and pyrite are the most abundant gangue minerals. Incompetent limestone, shale, or a porphyry sill hanging wall is characteristic of portions of the replacement beds. In many instances the ore is blocky, badly fractured and intermixed with layers of limestone gouge, pyrite and hematite.

Jan 6, 1973

By Owen F. Jensen

CONSTRUCTION of a ground-water supply includes many operations, which do not end with completion of facilities. Evaluations must be made of the quality of water in various areas and the history of production. Following an analysis of geologic, hydrologic, and chemical data there must be an exploratory drilling program and a study of resulting information. When the well is completed a continuous survey of operating records and basic data is necessary, since designs for future wells are varied as more data becomes available for those already completed. As the following discussion must be limited to a single undertaking, the customary procedure will be outlined for development and construction of a ground-water supply in which more than three wells are involved. Parts of this procedure are applicable for all ground-water supplies.

Jan 11, 1954

By Frank G. Snyder

INTRODUCTION Numerous deposits of lead and zinc sulfides, often accompanied by barite and fluorite, occur in carbonate host rocks throughout central and eastern United States. So similar are the deposits in broad general characteristics that they long have been classified as Mississippi Valley type. They differ widely, however, in details such as metal ratios, age of host rock, type of ore-bearing structure, and probable time of mineralization. The theories developed to explain the source and transport of the metals are many and are known to all. The deposits have been termed telethermal on the basis of their presumably shallow occurrence and the attempt to relate the metals to the classic hydro- thermal sequence. 1t is now recognized that deposits of this type can occur at any depth; the only depth limitation is thickness of the sedimentary section. Ideas on the source of the metals also have changed, A rapidly growing body of evidence suggests that the metals were brought by concentrated brines from nearby sedimentary basins. The hypothesis preferred today by many geologists postulates that the metals were deposited during the course of normal sedimentation in depositional basins of miogeosynclinal or orthogeosynclinal type. At some time after deposition of the sediments, the metals were carried out of the basins by migrating brines; the brines moved laterally and upward into structurally high areas; they entered any reservoir-like structure, either primary or secondary in origin, that happened to be available; in this reservoir, possibly in a sulfur-rich environment, the metals were precipitated as ore minerals.

Jan 1, 1970