Search Documents

By John Wulff, J. H. Hollomon

THE opinion has been widely held that the corrosion of alpha brass occurs by the selective solution of zinc. As late as 1939, Fink1 and Evans2 suggested that in the initial stage of the corrosion the selective solution of zinc produces copper-rich areas, which subsequently act as cathodes that facilitate the deposition of copper. Previously Abrams3 had shown that most of the copper found on corroded brass was redeposited and not residual, although he did not consider the nature of the initiation of the corrosion process. Enough data exist to indicate that any metal surface is sufficiently heterogeneous to provide the anodes and cathodes necessary for the initiation of corrosion.4,5 Thus, for alpha brass we need postulate not an initial selective solution of zinc, but only the existence of local differences in electrochemical potential. The heterogeneity responsible for potential differences may arise from oxide and other films as well as from alloy concentration gradients. Even though selective corrosion may be possible in some alloy systems, previous data on alpha brass as well as the experimental work reported in this paper do not require this supposition. Bengough and May,6 in a discussion of Abrams' paper, first suggested the addition of small amounts of arsenic (0.03 per cent) to alpha brass to prevent the redeposition of copper (dezincification). This suggestion was later substantiated by Nixon.7 In their studies of the inhibiting influence of arsenic, Evans and Fink were led to the selective-solution hypothesis in order to explain the initial corrosion of such alloys. They believed that an arsenic film covered anode areas and prevented the formation of copper-rich spots capable of acting as cathodes for the deposition of copper. They did not consider, however, the mechanism by which the arsenical film was formed. Bengough and May,8 in another publication, suggested that the commonly found gray or black arsenical film may act to: (I) carry oxygen to the brass surface, (2) increase the discharge potential of copper on brass, (3) precipitate cuprous chloride from colloidal suspension in chloride solutions. Masing9 assumed that the film found upon arsenical brass was metallic arsenic. His measurements of hydrogen overvoltage of bulk arsenic led him to believe that the inhibition of dezincification occurs because the overvoltage of a brass surface is lowered by the arsenic film. He reasoned that this film would permit the more rapid reduction of hydrogen at the cathode, which would prevent the redeposition of copper. In a recent paper,10 we have pointed out that the film formed during the corrosion of arsenical brass and copper in stagnant solutions is essentially arsenious oxide (As203),

Jan 1, 1942

RECEIPTS [Magazine Advertising $ 62,564.83 Magazine Sales 3,591.44 Totalm 66,156.27 Dues, Arrears7,032.88 Dues. Current96,839.74 Dues, New Members6,525.00 Dues, in advance 1,907.02 Initiation Fees7,584.00. Sale of Transactions3,909.03 Sale of Binding7,845.05 Sale of Special Editions 338.20 Sale of Year Book76.20 Sale of Pamphlets1,189.06 Sale of Authors' Reprints867.54 Miscellaneous Receipts62.93 Interest on Bank Balances1,712.89 Interest on General Reserve Fund337.50 Interest on Life Membership Fund557.84 Interest on James Douglas Library Fund....5,491.89 Total Receipts$208,433.04] [ ]

Jan 1, 1925

By Bruce F. Grant, Stefan F. Szasz

During 1947, a Sinclair research team was assigned to investigate thermal methods of oil recovery. The assignment was recommended by a survey of possible research approaches to increase the amount of oil that ultimately can be recovered from oil producing reservoirs. The use of heat to stimulate oil production rates by the melting of paraffin deposited in well bores can be traced back to within one or two decades of the drilling of the Drake well. The application of heat on a larger scale has been discussed by generations of oil producers. Shortly after the turn of the century, one intrepid operator is reported to have injected steam into a Pennsylvania property. After a few weeks, he apparently became discouraged and terminated his experiment. Subsequently, the literature contains references to several well-developed techniques for supplying heat to a producing well bore to melt paraffin or to reduce the viscosity of oil contained in the formation immediately around the well bore.1.?.3.4 Some early references discuss procedures to furnish heat to the reservoir,5,6 with the injection well as the heat source, thus obligating the process to maintain the entire rock mass at a temperature above that at which the desired improvement in oil recovery would occur. Another approach to reservoir heating was reported by a group of Russian technologists in 1935.7,8,9 They definitely demonstrated that combustion can occur within the porous structure of an oil-bearing sandstone. Their field experiments, however, relied less on combustion within the rock than on heat furnished by combustion of oil supplied to the injection well bore. Ignition of the air-oil mixtures in the well bore was found very difficult, and the field tests were carried on for only short periods of time. Publication of the Russian work spurred at least one independent operator in this country to try firing an air-gas injection well, on for only short periods of time. Publication of the Russian work spurred at least one independent operator in this country to try firing an air-gas injection well. The Brundred Oil Corp. reportedly obtained combustion in the sand immediately around the injection well bore, but the experiment was abandoned because of interference with normal production schedules. Injection capacity of the experimental well was greatly reduced by firing. The well was reshot and pieces of sand showing partial fusing of the quartz matrix were recovered. To the authors' knowledge no other field experiments utilizing combustion techniques for formation heating were undertaken prior to 1948, although the patent literature evidences continued interest in formation heating."'," CONCEPT OF COMBUSTION-SUPPORTED HEAT WAVE The references cited were in agreement that heat applied to a reservoir would increase recovery, but there

Jan 1, 1955

By J. D. Wheeler, H. W. Mathews

The increased activity in West Texas, which started in 1933, has continued through 1936 at a constantly accelerated rate. During 1936 there were 1442 wells completed in the area as compared with 700 in 1935 and 468 in 1934. Of these completions, 1313 were producers with a total 24-hr. potential in excess of 1,750,000 bbl. From among the 1442 wells, eight are considered to be discovery wells for new West Texas fields. New Fields Bennett.—The Bennett field, which added Yoakum County to the oil-producing counties of West Texas, was actually indicated as an oil-producing area during 1935, but the discovery well, Honolulu Oil Corporation, Ltd. and Cascade Petroleum Company's Bennett No. l, was not given a production test until April 1936. The discovery well made 15 bbl. per hour through 3/4-in. choke with a plugged-back total depth of 5264 ft. First oil in the hole was from 5088 to 5090 ft., which is several hundred feet below the top of Permian lime. Producing limits of the field are unknown, as the second test had not reached the pay at the close of the year. Henderson.—-To date indications are that the Henderson pool, in northern Winkler County, is the most prolific area opened during 1936. This field, which lies to the north of the old Hendrick pool, is producing from the same reef-type dolomitic lime producing in the older field. The Henderson field was opened by the completion of R. H. Henderson, J. B. Walton-Humble 1-A in April 1936 for a natural flow of 2306 bbl. per day through tubing. Total depth of the discovery well is 3049 ft. Later development has indicated the productive area to be a rather narrow zone running slightly west of north. Present area of from 1000 to 1500 acres has been proved for production. Keys and Emperor.—The Keys and Emperor pools in the belt of sand pools running across Winkler County appeared for the first time on State proration schedules during 1936. This report considers these pools as links in joining the belt of sand production across Winkler County, for

Jan 1, 1937

The following is an incomplete list of members and guests who called at Institute headquarters during the period Oct. 10, 1918 to Nov. 10, 1918. J. Carson Adkerson, Virginia. George H. Parsons, Hayden, Ariz. Andrew B. Armstrong, Connecticut. W. E. Pomeroy, New York. Courtenay DeKalb, San Francisco. Ezra C. Rider, Bisbee, Ariz. Clifford G. Dennis, San Francisco. H. W. Seaman, Chicago, Ill. Rudolph Emmel, Boston, Mass. William Allen Smith, Northampton. Emil Gathmann, Baltimore Md. R. K. Stockwell, Salt Lake City, Utah. Ernest S. Geary, Denver, Colo. W. G. Swart, Duluth, Minn. W. E. Hopper, Washington, D. C. Kirby Thomas, New York. W. Spencer Hutchinson, Boston, Mass. - Warren D. Thompson, Harvard Club. E. W. Kohl, Jr., Philadelphia, Pa. H. Vincent Wallace, Los Angeles, Cal. E. C. Nighman, Butte, Mont. Paul T. Benson, formerly with the Tacoma smelter, has resigned his position there to accept one with the Great Metals Mining and Milling Co. at Nespelem, Wash. Prof. Edward E. Bugbee, of the Mining Department of the Massachusetts Institute of Technology, has been granted a leave of absence to accept the position of Assistant Director of Education for the S.A.T.C. of five southern states with headquarters at Raleigh, N. C.

Jan 12, 1918

SEC 1 The membership of the Institute shall comprise seven classes, namely 1 Members, 2 Honorary Members, 3 Senior Members, 4 Associates, 5 Junior Members, 6 Rocky Mountain Members, 7 Junior Foreign Affiliates All shall be equally entitled to the privileges of membership, excepting that no member of any class whose residence shall be outside of the United States of America, except those residing in Mexico and Canada, shall be entitled to vote SEC 2 Members A person to be eligible for election or transfer into the class of Member must be at least 27 years of age and must have had at least six years' employment in the practice of engineering, mining, geology, metallurgy, or chemistry, during at least three years of which he must have held positions of responsibility in one or more of these fields This shall not apply to Rocky Mountain Members SEC 3 Honorary Members Each candidate for Honorary Membership must be recommended by the Committee on Honorary Memberships and must be elected by ballot at a meeting of the Board of Directors by the unanimous vote of the Directors present, provided, however, that the number of Honorary Members shall at no time exceed twenty Such election shall automatically act as a transfer of such member from any other class of membership to which he may belong SEC 4 Senior Members The Directors may, at the special request of any Member or Associate who has reached the age of seventy years and who has paid

Jan 1, 1952

By Lyman H. Hart

Some of the significant facts that will affect the supply and demand for metals during the next few decades are given in this presentation. This is important because the only hope for intelligent guidance of the national destiny depends upon presenting a consistent and accurate picture of basic problems. The metals problems now fomenting are only slightly less important than those precipitating the energy crisis. Admittedly, it is difficult to generate serious thinking on this subject when the world is enjoying easy access to all metals at modest prices. This is possible because of the current world capacity to overproduce, and United States credit standing, at least up to now, has permitted buying freely on world markets. Although both these vital conditions are subject to change, there is little doubt that if the U.S. financial house is kept in order, we can muddle along for a while on a generally expanding, metalbased economy. But should our credit standing be permitted to collapse, or should there be a tightening of world supplies of metals, the nation would immediately find itself in trouble. Unfortunately, clear signals indicate that both of these conditions are threatening.

Jan 4, 1973

By John Wulff, J. H. Hollomon

THE opinion has been widely held that the corrosion of alpha brass occurs by the selective solution of zinc. As late as 1939, Fink1 and Evans2 suggested that in the initial stage of the corrosion the selective solution of zinc produces copper-rich areas, which subsequently act as cathodes that facilitate the deposition of copper. Previously Abrams3 had shown that most of the copper found on corroded brass was redeposited and not residual, although he did not consider the nature of the initiation of the corrosion process. Enough data exist to indicate that any metal surface is sufliciently heterogeneous to provide the anodes and cathodes necessary for the initiation of corrosion .4,5 Thus, for alpha brass we need postulate not an initial selective solution of zinc, but only the existence of local differences in electrochemical potential. The heterogeneity responsible for potential differences may arise from oxide and other films as well as from alloy concentration gradients. Even though selective corrosion may be possible in some alloy systems, previous data on alpha brass as well as the experimental work reported in this paper do not require this supposition. Bengough and May,6 in a discussion of Abrams' paper, first suggested the addition of small amounts of arsenic (0.03 per cent) to alpha brass to prevent the redeposition of copper (dezincification). This suggestion was later substantiated by Nixon.7 In their studies of the inhibiting influence of arsenic, Evans and Fink were led to the selective-solution hypothesis in order to explain the initial corrosion of such alloys. "I hey believed that an arsenic film covered anode areas and prevented the formation of copper-rich spots capable of acting as cathodes for the deposition of copper. They (lid not consider, however, the mechanism by which the arsenical film was formed. Bengough and May,8 in another publication, suggested that the commonly found gray or black arsenical film may act to: (1) carry oxygen to the brass surface, (2) increase the discharge potential of copper on brass, (3) precipitate cuprous chloride from colloidal suspension in chloride solutions. Masing9 assumed that the film found upon arsenical brass was metallic arsenic. His measurements of hydrogen overvoltage of bulk arsenic led hint to believe that the inhibition of dezincification occurs because the overvoltage of a brass surface is lowered by the arsenic film. He reasoned that this film would permit the more rapid reduction of hydrogen at the cathode, which would prevent the redeposition of copper. In a recent paper,10 we have pointed out that the film formed (luring the corrosion of arsenical brass and copper in stagnant solutions is essentially arsenious oxide (AS208)

Jan 1, 1942

Jan 1, 1967

Jan 1, 1968

By C. D. Thurmond

Jan 1, 1968

Jan 1, 1968

Jan 1, 1967

By G. Thodos, W. F. Stevens

The point-source function introduced by Horner' us a solution to the general unsteady-state equation for the flow of fluids through porous media has been utilized to calculate pressure profiles for adjacent wells as a function of time. By trial and error, the time at which the pressure waves meet to cause interference can then be calculated. For this calculation, the time of interference is arbitrarily defined as that time when both pressure waves exhibit a pressure decrease of 25 psi ar the same point within the formation. To illustrate the method, an example involving two adjacent wells producing at different rates has been worked out and is presented in detail. INTRODUCTION The initiation of production of a new well is usually accompanied by pressure drawdown measurements in order to establish the extent and characteristics of the formation. The interpretation of such pressure drawdown data is based on mathematical developments involving a single well in an infinite reservoir. If more than one well is present in a reservoir, the possibility of interaction between wells exists. Therefore, care must be taken in interpreting the pressure drawdown data. It becomes important to be able to determine when this interaction, or interference, becomes significant. This paper presents a method for the prediction of the approximate time of interference between two such adjacent wells. The basic differential equation describing the pressure distribution existing during unsteady-state flow of a slightly compressible fluid has been solved by Hor-ner.' for a constant production rate from a circular homogeneous reservoir of infinite extent. The solution utilizes the point-source function to define the pressure at various points within the formation as a function of time. The resulting expression is: q = production rate, STB/D ,;= formation volume factor, dimension-less µ = fluid viscosity, cp k = formation permeability. md H = formation thickness, ft C - fluid compressibility, psi' F = formation porosity, dimensionless R = distance from centerline of well, ft T = production time, hours Ei(—u) = Ei-function of U Eq. 1 may be used to calculate the pressure profiles generated during production from a single well in an infinite reservoir.

By Michael Tenenbaum

Selected characteristics of nonmetallic phases were determined in low-carbon sheet steels which had been produced by various refining; deoxidizing, and casting procedures. The results showed little influence of the refining process on the quantity, distribution, size, and character of the nonmetallic phases. The quantity of inclusions was governed by the deoxidation procedures. While the mode of casting influenced the internal structure and the pattern of inclusion distribution, it had little effect on the quantity of nonmetallics. The vast majority of inclusions were under 30 µ in diam, and there was little change in size distribution during hot and cold rolling. The composition and structure of the inclusions were expained an the basis of known equilibrium phase diagrams for the appropriate systems. Additional work is needed to explain some of the observations of this paper. HENRY Marion Howe's contributions to the metallurgical profession include his many writings, the wisdom that he imparted to his students, and the inspiration that he gave to the many scholars, teachers, and industrialists who knew him personally. It was Professor Howe's intimate colleague, Albert Sauveur,1 who, in the first Howe Memorial Lecture, could have been speaking for the metallurgist of our generation as well as his own when he wrote, "...how many of us on the point of going astray were called back to the right path by Howe's guiding torch?" More than a quarter of a century later, Francis Foley,2 one of the last in the Howe Lecture series who worked directly with the great man, delivered the ultimate tribute, "...truth, in its time is so hard to identify." While Professor Howe strove to be right, "he was content if he provoked the reader to take the next step along the path to greater knowledge." Like so many of my predecessors, I sought guidance for this lecture by referring to Professor Howe's two classic texts, Metallurgy of steel,3 and Metallography of Steel and Cast Iron: the former book interpreting the facts as he saw them near the start of his career, and the latter—published 26 years later—pointing to many fertile fields for metallurgical investigation. Those of us who harvest the fruits of Henry Marion Howe's contributions to the metallurgical profession now look with wonder at the tremendous legacy he has provided. It is rewarding to study his writings and to recognize the anticipation of such aspects of modern ferrous metallurgy as: 1) Direct reduction 2) Steelmaking reactions 3) The approaches and benefits of degassing 4) Solidification mechanisms 5) Habits and behavior of nonmetallic inclusions 6) Recrystallization phenomena 7) Slip and slip propagation 8) Dislocations 9) Discontinuous deformation 10) Microscopic and macroscopic segregation

Jan 1, 1970

By R. R. Unterberger

Three different physical techniques have been used to see through or probe into rocks, so miners might know what is ahead or overhead. These are radar, sonar, and a unique type of sonar called nonlinear sonar. Five radar systems have been developed. The highest frequency used is 4300 MHz for detecting small fractures at close range. This gives the best resolution. For longest range (over 2000 m, or 6560 ft) we use the 30 MHz radar for finding faults ahead of mining or ranging to salt dome flanks. Two types of salt, dome and bedded, are recognized. Radar works well in dry (dome) salt, but not in bedded salt which contains small amounts of water. The dipole moment of water absorbs energy from the radar. Thus was born the 30 MHz radar system and sonar probing systems. These can probe to 100 m (328 ft) even into wet salt. All probing systems measure data in time, which are converted to distance by measuring the time of travel of radar or sonar through salt pillars of known thickness. Ranges of probing in salt are from less than 1 m (3.3 ft) to more than 2000 m (6560 ft). Uses of radar and sonar probing in mines include mapping the top of salt above a mine; mapping salt dome flanks; finding impurities in salt such as anhydrite, sandstone, or potash stringers; locating old boreholes in salt pillars; locating fractures in salt; and finding faults or water zones ahead of mining.

Jan 1, 1985

One of the engineering proposals in the last Congress which was of interest to engineers was the soldiers' land settlement plan proposed by Secretary Lane, under which returned soldiers, sailors and marines would be employed on construction work in the reclamation of swamp and arid lands and would thereafter be given preference in the selection and settlement of those lands. This bill failed in the fillibuster at the end of the session. It is likely that some sort of a plan for soldiers' settlement will come before the next Congress. A new bill has been written up for introduction at the next session which proposes an "infiltration method" of buying improved farms in established communities for' the soldiers' settlement purpose, under the authority and direction of the Farm Loan Board. The contrast of this bill to the one recommended by Secretary Lane is of vital importance to engineers at this time; first, because of the broad engineering improvement program that the latter bill proposes as against no engineering improvement under the infiltration plan; secondly, the community settlement plan of Secretary Lane means improvement of waste lands requiring much engineering work.

Jan 7, 1919

By M. van Swaay, C. E. Birchenall

Palladium has a large capacity for the dissolution or occlusion of hydrogen; the gas also diffuses very rapidly through the metal. Palladium thimbles are widely used in the laboratory for purification of hydrogen by diffusion. The use of palladium filters could be extended to several large-scale applications if greater stability of the permeation process could be attained. In this paper a number of aspects contributing toward this goal are discussed, and new data on solubility and diffusivity are given. Palladium sheets of 0.005, 0.010, or 0.020 in. thickness were prepared by three procedures: casting and rolling, sintering palladium powder, and sintering palladium powder to which 0.1 pct thorium oxide had been added. Half-inch diam circular specimens were cut and clamped in a stainless steel holder provided with knife edges to seal the palladium sheet with soft copper gaskets. The seals were tested for leaks at l0-5 mm Hg. No difficulties from this source were encountered even after many temperature cycles in the system. The holder was silver-soldered to Kovar-glass seals and attached to the system through glass ball joints. Each joint was sealed with Apiezon wax and was adjacent to a cold trap. In several experiments the holders were fused directly into the system, eliminating the ball joints, to show that the wax did not affect the filter. Three filter holders were supported in holes in a stainless steel cylinder, which also acted as a temperature equalizing block inside the resistance wound furnace. The measuring thermocouple was inserted in one of the holders. A potentiometric controller with control thermocouple on the furnace heater winding maintained ± 0.2oC. Electrolytic hydrogen was purified and stored as shown in the flow diagram, Fig. 1. It could be admitted to either or both sides of the palladium specimens. Only a mechanical pump was used, for even high pumping speeds would not bring the pressure on the off-gas side of the filter below 10 to 50p Hg owing to the rapid hydrogen flow through the filters. A series of steady-state permeability studies allowed identification of several conditions of permeability loss. A constant fore pressure was maintained while the low-pressure face was pumped. After enough time had elapsed for a steady flow to be established the pump was cut off, and the rate of pressure increase in a thermostated bulb was measured to determine the flow rate. The time delay method of Daynes1,9 was adopted since it offered the possibility of determining solubilities and diffusivities. For each measurement both sides of the filter were evacuated for 15 min, which gave about 10-4mm Hg residual pressure. Hydrogen was admitted to one side or the other of the filter at a fixed pressure. The pressure on the off-gas side was observed as a function of time. A

Jan 1, 1961

By R. W. Balluffi, R. Resnick

NUMEROUS investigations of chemical diffusion in a brass have been made and the results are collected in several places.1-3 This work has been mainly concerned with the determination of the chemical diffusivity as a function of composition and temperature. In 1947 Smigelskas and Kirken-dall&apos; showed that zinc and copper diffuse at different rates in face-centered-cubic brass, and since then, a number of efforts have been made to determine the intrinsic diffusivities of zinc and copper in this alloy.1, 5-9 Horne and Mehl8 in particular have recently determined the intrinsic diffusivities as functions of temperature and composition using sandwich-type couples and inert markers. Inman et al." also have determined the intrinsic diffusivities in homogeneous alloys using tracer techniques. When the present work was started, no information of this type was available. Consequently, measurements of the intrinsic diffusivities were made as a function of temperature at a constant composition of 28 atomic pct Zn with vapor-solid diffusion couples where the zinc was diffused into the diffusion couple from the vapor phase. The application of these couples to the study of diffusion in a: brass has been described previously.0,7 The temperature dependence of the intrinsic diffusivities was found to follow the relation D, = A, exp(-Hi/RT) and the values of Hzn, and Hcu, were found to be closely the same. It is emphasized, however, that the chemical dif-fusivity (D = N1D2 + N2D1) is a composite diffusivity and does not necessarily follow this exponential form. It is usually found to do so within experimental error for substitutional alloys because the heats of activation of the intrinsic diffusivities generally are not greatly different.&apos;" Also, at the onset of this work, there was no information available concerning possible unequal diffusion rates of individual components and the existence of a Kirkendall effect in alloys with other than face-centered-cubic structures. Since then, two reports indicating a Kirkendall effect in body-centered-cubic ß brass have appeared. Landergren and Mehl" have published a note describing Kirkendall diffusion experiments with sandwich-type couples. Inman et a1.9 also find a Kirkendall effect in this alloy using the tracer technique. In the present work, several aspects of the Kirkendall effect in ß brass were further investigated using vapor-solid couples. Two different couples were used, one in which the zinc was diffused into the specimen from the vapor phase and the other in which the zinc was diffused out of the specimen into the vapor phase. Briefly, the existence of a Kirkendall effect is confirmed and it is found that Dzn/Dcu = 3 at about the 46 atomic pct composition in this alloy at 600°, 700°, and 800°C. As a result of the unequal diffusion rates of zinc and copper, volume changes occur and subgrain formation is observed in the diffusion zone. In addition, significant porosity is produced by the precipitation of supersaturated vacancies. Diffusion in this alloy is therefore outwardly similar to diffusion in a brass where these effects are also observed, a Brass Experimental Methods—The use of vapor-solid couples in studying diffusion in a brass has been described in previous articles.6,7 The method briefly consists of sealing a copper specimen with Kirkendall markers initially placed on its surface in an evacuated quartz capsule along with a large zinc source of fine a brass chips and then diffusing the zinc into the specimen through the vapor phase. The zinc concentration at the specimen surface rises rapidly enough to a value near that of the a brass source so that the surface concentration may be regarded as constant during diffusion. Under these boundary conditions, values of the chemical diffu-sivity may be obtained by applying the Boltzmann-Matano analysis to the concentration penetration curve, and the intrinsic diffusivities may be obtained from Darken&apos;s5 equations when the velocity of marker movement is known. The diffusion specimens were made from OFHC copper in the form of disks 3.2 cm diam and 0.5 cm thick with faces surface-ground parallel to within +0.001 cm. Markers in the form of fine alumina particles <0.0002 cm diam were placed on the specimen surface. These specimens were then sealed in quartz capsules along with enough a brass chips of a 30.0 atomic pct Zn composition to keep the source concentration from decreasing by more than 0.3 atomic pct Zn as a result of the loss of zinc to the specimen during diffusion. The quartz capsules which were initially evacuated to a pressure of

Jan 1, 1956

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