Search Documents

By L. F. Engle

There continues to be a certain magic attached to the word "Automation". When properly planned for, engineered, installed, and operated, the magic truly does take place - witness certain publicized mineral processing, metallurgical, and chemical plants. They operate successfully with few people, instead of previous dozens as in similar facilities not automated. Production quality has improved. Maintenance costs have been lowered. When such welcome results are achieved, it's proved to be a function of method and procedure in establishing criteria for choosing the intelligence and control systems followed by skilled choice of the specific elements used. The criteria, the bases for decision, are associated with design, construction, startup, operations, and maintenance. How to go about automating any process system to achieve the optimum profit depends on attention to all those aspects of a project. None of them can be forgotten if maximum satisfaction is to be gained. Control loops that look wonderful on an equipment. Piping, and Instrumentation diagram can suddenly turn into costly and. annoying problems in the field if there has been too little coordination of design. Panel boards that are literally works of art just before startup can become the largest of white elephants if an air header is inadequately sized and the pneumatic control circuits are sluggish. Conveyor belt replacement costs can skyrocket if a critical discharge chute far away from immediate operator attention lacks a simple yet effective clog-chute switch. Planning, execution, and followup of the work, the skills, and function of-the automating material can make any new project a success. An integrated owner contractor, producer-engineer approach is the key.

Jan 1, 1963

By Olev Trass

The mill body is a stationary grinding cylinder inside which a number of helically grooved rollers rotate, each being suspended on a flexible axis. The feed material is repeatedly crushed between these rotors and the cylinder, with the crushing force created by radial acceleration. The mill has several internal design variables such as number, size and shape of rotors, and can be operated wet or dry. It is compact, has a high capacity, modest power consumption, and can grind many materials down to ultrafine powder. Illustrative data on product size distributions and particle shapes are given for grains, metals and minerals obtained at various operating conditions, along with initial results on grinding kinetics.

Jan 1, 1980

By D. W. H. Su

A two-year study was conducted by CONSOL in a northern West Virginia coal mine to evaluate pillar design and support requirements to improve roof control in right-hand longwall headgates subject to high in situ horizontal stresses. Horizontal stress measurements conducted within undisturbed areas of the subject mine revealed a pre-existing regional horizontal stress field with a significant difference in magnitude between the east-west maximum and the north-south minimum stresses. Three¬dimensional stress cells installed to monitor horizontal stress concentration in the headgate roof during mining revealed that a narrow (60-foot center) headgate pillar reduces the east-west horizontal stress concentration in the roof ahead of the face such that the headgate is more stable and requires less support. This 60 foot x 140-foot pillar design, which has been employed in subsequent panels, still provides adequate stress attenuation to protect future tailgates under a maximum cover depth of 1000 feet. Roof geology derived from underground roof reconnaissance and underground bolt load and roof displacement measurements confirmed the effectiveness of 12-foot long cable bolts for controlling the headgate roof subject to high horizontal stresses. With the new headgate pillar design and the supplemental cable bolts, headgate roof conditions in the subsequent panels improved significantly, longwall production delay due to adverse headgate roof condition was totally eliminated, and record coal production was achieved by the subject mine in the subsequent years.

Jan 1, 2003

ALABAMA. Aldrich, Aldrich, W. F. Anniston, Noble, A. E. Auburn, Brown, R. L. Bessemer, Abbott, C. E., Ferguson, V. Birmingham, Aldrich, T. H., Aldrich, T. H., Jr., Allen, A. W., Bowron, J., Burbidge, T. A., Crawford, G. G., Crockard, F. H., Davis, F. H, Dimmick, F: D., Ellis, E. E., Geismer, H. S., Hiller, E., Johnson, G. R, Ludwig, C. P., McCormack, G. B., McCrery, Peters, R, Jr., Phillips, W. B., Pill, J. R., RamSay, E. Coal City, Pattberg, 0. F. E-msley, Wil¬liams, E. P. Helena, Squire, J. Holt, Shook, J. W. Huntsmlle, Moss. Ironton, Hudson, J., B. Lehigh, Toulmin. Bock Bun, Garvin, J. M. Woodward, Wood¬ward, A. H.

Jan 1, 1910

By R. W. Raymond

I HAVE the pleasure of exhibiting samples of the rock in which the South African diamonds are said to occur, for which I am in debted to Mr. Franz Groeger, of Vienna, formerly an assistant of the Royal Imperial Geological Institution, whose account of the general geology of Southern Africa was contained in a recent number of the proceedings of that Institution. The rock is apparently a sort of tufa, evidently of volcanic origin. Mr. Groeger assured me that it could be seen in situ, bounded by uplifted stratified rocks; and that diamonds had been mined from it, by means of shafts, some distance below the surface. Groeger calls it "greenstone-tufa," and says of it, in the proceedings of the Geological Institution, " it breaks through the younger members of Group III [lower Trias and Jura], . . .. and crops out in oval masses, filling fissures . . ..The occurrence of this tufa is not locally limited, but has been traced and proved already over a large territory." DR. HUNT remarked that the material looked like the trass of the Rhine region. He thought it a new occurrence for diamonds. He believed diamonds to belong to ancient crystalline rocks, although these materials might be brought tip by volcanic agency, and the diamonds remain unaltered. In the volcanic rocks of Auvergne, crystals of sapphire, zircon, and spinel are found; and yet no one supposes that these minerals have been generated by volcanic agency. He had had a conversation with Bertrand de Lom on this subject, who agreed with him that these minerals, being hard and resistant,

Jan 1, 1874

Jan 1, 1913

By S. Frimpong, E. Siami-Irdemoosa, S. R. Dindarloo

"Electric and hydraulic shovels are the dominant loading machinery in surface mining operations. Despite their critical role in production and their high capital and operating costs, no reliable and comprehensive quantitative performance metric is available. In this paper, a stochastic shovel effectiveness (SSE) measure is proposed for the purpose of quantifying the performance effectiveness of these shovels. The SSE is based on the widely used method of overall equipment effectiveness (OEE) in the manufacturing industry. The OEE measures the performance effectiveness of equipment by multiplying its mechanical availability, utilization and production quality. In manufacturing processes, quality rate is the ratio of the total number of products minus the number of defective products – equivalent to the number of acceptable products – to the total number of products. The SSE similarly uses the mechanical-availability and utilization terms, but instead of quality rate it uses a new parameter named bucket rate.The variability or randomness of the input data, that is, availability, utilization and bucket rate, are further incorporated into the SSE, and a final stochastic SSE distribution is derived in the form of a probability density function. One hydraulic and one electric shovel in a surface mining operation were selected to test the validity of the proposed method. The SSE scores for the two shovels, operating continuously for one year, were derived and compared. As with the OEE, the three-parameter SSE method yielded more representative results for overall performance measurement than a single-parameter approach. Using Monte Carlo simulation, a three-parameter Weibull and a normal distribution were derived for quantifying the overall effectiveness of hydraulic and electric shovels, respectively. As a decision aid, the proposed methodology promises to render a more informative tool than traditional metrics for mine equipment maintenance and management."

Jan 1, 2015

By A. Zorychta, T. Cyrul, Z. Kleczek

INTRODUCTION Underground mining causes disturbances of the primary state of stresses. Resulting from those disturbances a loss of stability of rocks that surround excavation may occur interrupting the production and creating life danger for the personnel. One of the manifestations of such an instability is a rock burst phenomenon which mainly occurs at great depths. From the mechanical mint of view the rock burst is a loss of stability /Filcek et a1.,1984; Pietuchow and Linkow, 1976/ due to : - quasi-static stress changes in the surrounding rocks; we will call it s seam burst , - dynamic stress changes in the surrounding rocks caused by rock shocks ; we will call it roof burst. Possibility of the rock burst occurrence Is uniquely determined by the state of stresses existing in the rock mass. In the following sections of the paper we will consider different aspects of this question. Moreover distributions of displacements and failure criteria for a coal seam at longwall mining will be defined. STATEMENT OF THE PROBLEM Determination of the vertical stresses and displacements resulting from longwail mining will be based on the Budryk’s idea of a stress wave /Salustowicz, 1955/. The idea originates from the analysis of a roof plate /beam/ resting on the deformable foundation /Sean/ and subjected to the cylindrical bending. Equation of the bending lice uniquely defines vertical stresses and displacements which are induced in the seam. The equation will account only the shear force effect. Elimination of the bending moment has been shown and discussed by Zorychta and Bcrecki /Zorychta, 1985; Borecki and

Jan 1, 1986

By Douglas Anderson

In the early 1980s, a method for controlling blast vibrations other than by modifying the Scaled Distance came into use. Research studies had indicated that blast vibration could be simulated by detonating a signature hole with the vibration monitored at critical locations, and then using a computer to superpose the waveforms with varying delays. By choosing delay times that create destructive interference at frequencies that are favored by the local geology, the “ringing” vibration that excites structural elements in houses and annoys neighbors could be reduced.

Jan 1, 2008

By M. Schmellenkamp

By comparing two longwall operations, one begun in 1956 and the other in 1960, the author is able to demonstrate the increases in production and performance made possible by longwall mining. These achievements have been brought about by continuous development of longwall mining equipment and associated roof supports. Because of this progress, longwall mining is able to provide, under proper conditions, high production per man-shift, remarkable cost savings, dependable roof control, safe working conditions and truly continuous production. It may seem odd that the title of this paper is not simply "Longwall Mining" but instead "Progress in Longwall Mining." However, the word "Progress" definitely has its place in longwall mining. If it had not been for progress in the development of longwall mining equipment and roof supports, the longwall mining method would not be able to compete in production and performance with modem coal mining machines. The longwall mining method was practiced at the beginning of the century and there were several successful operations in coal fields in Illinois. In those early days of longwall mining, the coal was undercut by hand 2 to 2.5 ft at the bottom of the seam and packwalls were built in the gob to support the roof. The roof eventually subsided and the weight of the subsiding roof was used to ride the face and break the undercut coal. Utilizing natural weight to soften the coal face is still practiced in modern longwall mining; however, the packwalling method has been replaced by the caving method and the roof is now supported by yielding steel roof supports and forepoling steel headers. The purpose of these yielding-type roof supports is to provide a safe working area for the crew along the entire longwall face, to permit continuous mechanical mining across the prop free face, and to provide a strong resistance for the roof by forming an even breaking line at the gob for the roof to cave. Roof supports and associated forepoling headers should be kept as close as possible to the face in order to prevent a caving between face and supports, especially under friable roof. This means that the coal should be extracted in small slices, allowing only a narrow roof area to be exposed and unsupported. The coal planer with its relatively high cutting velocity of 75 ft per min provides such an extraction of coal and has proved its high performance under difficult mining conditions. Since 1951, several longwall faces in southem West Virginia and Pennsylvania which have been equipped with the coal planer and friction-type manual roof supports have been successfully operated. Compared to today's longwall mining, these longwall faces required such a large crew, primarily to handle the roof supports, that the actual high production per shift was charged with too high a labor cost, thereby decreasing the tons per man. Yet, even then the longwall faces outperformed the conventional mining system under the same conditions. In order to demonstrate the progress that has been made in the development of longwall mining, a comparison will be made between a longwall face in Arkansas which was installed in 1956 and a modemized longwall face started in 1960 in southern West Virginia. LONGWALL MINING IN 1956 The 320-ft longwall face was developed in a 32-in. thick coal seam near Greenwood, Ark. The method of mining the 320-ft coal block was the advancing system in which three entries on either side of the face were driven ahead of the advancing longwall face. The face was equipped with a coal planer and a Panzer conveyor; timbering was done with wooden timbers and cribs. The roof supports were set without any pattern. The crew to operate the planer and to handle the roof supports (timbers and cribs) consisted of 15 men per shift. During a period of approximately eight monthsof single shift operating time, the average tonnage produced in this relatively low seam amounted to about 263 tons of clean coal per shift. To show the development in the coal plow from then until now, it should be pointed out that the standard plow was used in this operation. The plow was equipped with rigid bottom bits which could not be adjusted if the plow started to climb, thereby leaving bottom coal to be recovered by pick hammers end causing delays in production. The height of the plow

Jan 1, 1963

By R. M. Brown, W. J. Murphy, B. M. Kapadia

An investigatiott was conducted to study the influence of nitrogen, titanium, and zirconium on the boron llardenabilzty effect in a low-carbon constructiona2 alloy steel. The experimental steels investigated exhibited a significant variation in hardenability, the variation being dependent on the interactions of boron, titanium, and zirconium with the nitrogen. Only the boron not combined with nitrogen was effective in increasing hardenability. Titanium, and with lesser effectiveness zirconium, combined with available nitrogen, thereby protecting the boron. The hardenabil-ity effect mas related to an empirical expression for the "effective" boron content, P, deduced from experimental evidence of these interactions. The hardenabzlity effect reached a maximum at about 0.001 wt pct 0, and decreased somewhat as P increased further. The physical understanding of this relationship is discussed. FOR many years boron has been added to steels to obtain high hardenability. Although a great deal of research has been conducted on boron-treated steels, certain aspects of the boron hardenability effect have not been fully understood. For instance, the magnitude of the hardenability effect has been observed to vary markedly, depending on the steelmaking technique, even when the amount of boron in the steel was essentially constant. Furthermore, the optimum amount of this element to be added has not been definitely established. A better understanding of the boron hardenability effect is essential because too small an addition of boron is likely to be ineffective, while an excessive amount can cause brittleness'' and hot shortness. The findings of earlier investigations have shown that the hardenability effect cannot be consistently related to the amount of boron added or retained in the steel. Grossmann observed that in a 0.60 pct C steel the hardenability increased to a maximum with mold additions up to about 0.0025 pct B and then decreased with larger additions. Other investigators5 likewise reported a maximum in the hardenability at about 0.003 pct B. Crafts and Lamont, however, found that in commercial open-hearth heats of medium-carbon steel the hardenability increased linearly with boron up to 0.001 pct and remained essentially unchanged with larger percentages up to 0.006 pct. Other investigators7,' also observed a rather constant hardenability effect in the range about 0.0005 to 0.0035 pct B. These observations and other evidence suggest that the effectiveness of boron in increasing hardenability probably depends, in addition to the amount, on the form of boron retained in the steel, this form being influenced by the presence of other elements. Both oxygen and nitrogen apparently exert the strongest influence on the hardenability behavior, since, at the temperature of liquid steel, boron readily combines with these elements, thereby losing its effectiveness as most experimental evidence seems to indicate. For consistent recovery of the boron effective in increasing hardenability, it is necessary that the oxygen and nitrogen in the steel be either reduced to extremely small amounts by the steelmaking practice or neutralized by combination with other elements before the addition of boron. The importance of achieving adequate deoxidation prior to the addition of boron in order to realize the full hardenability effect of boron has been sufficiently emphasized by earlier investigators. Digges and Reinhart' and others have investigated the role of nitrogen and have shown that nitrogen also interacts with boron and reduces or nullifies altogether its effect on hardenability. Moreover, their work also demonstrated that the addition of strong nitride formers such as titanium and zirconium reduce the deleterious effect of nitrogen on boron hardenability by combining with nitrogen to form stable nitrides. Another element which has a pronounced influence on the boron hardenability effect is carbon. It has been shown7'10 that the hardenability effect of boron diminishes with increasing carbon content, and becomes almost negligible at the eutectoid composition. This observation is useful in comparing the potential increase in hardenability from boron of steels with different carbon contents, but is not relevant to a study of the effects of normal steelmaking variables. The amounts of oxygen and nitrogen in steel vary with the steel composition and steelmaking practice employed. Most commercia1 low-alloy steels are fully deoxidized by the addition of silicon and aluminum, or other strong deoxidizers, which adequately protect the boron from oxidation. In addition, one or more of the elements such as titanium or zirconium are usually added, either separately or in combination with boron, in the form of complex ferroalloys, to protect boron from combination with nitrogen in the steel. However, the actual amount and type of addition employed for a given processing requirement are usually selected by trial and error, and have a rather limited range of applicability. As a result, substantial variations in the hardenability of boron-treated steels are often observed in practice, particularly when the nitrogen content of the steel is a significant processing variable. These variations might therefore be reasonably attributed to the interactions between boron, nitrogen, and titanium or zirconium present in the

Jan 1, 1969

By Michael J. Friedel

The permeability and flow capacity in unsaturated media is investigated by the Bureau of Mines for application to in situ copper leach mining at the Cyprus Casa Grande mine site. Moisture retention properties are derived and combined with scanning electron microprobe data to characterize the mineralogy, texture, pore size, distribution, and permeability of the host rock. Finite element modeling is used to derive a saturated permeability, ambient degree of saturation, and assess various injection-recovery schemes. Recommended design modifications for optimization of solution distribution and maximum recovery from the rock matrix requires either (1) the injection pressures on the order of 1500 psi and recovery wells operating in a suction mode, or (2) performing permeability enhancement, through rubblization. By producing a maximum block diameter of 4 m, injection pressures can be reduced to 500 psi with improved recovery and containment of solutions.

Jan 1, 1991

By R. L. Hopkins

Some typical thiacyclopentanes and thiacyclohexanes were synthesized to provide reference compounds needed for the identification of sulfur compounds in crude oils. Two general methods of synthesis were employed: (1) cleavage of 2-alkyltetrahydropyrans with hydrogen bromide followed by the reaction of the resulting dibromoalkanes with sodium sulfide and (2) the catlyzed reaction of cyclic ethers or 1)4-or 1)5-alkanediols with hydrogen sulfide. Both methods produced mixtures of 2-alkylthiacyclopentanes and 2-alkylthiacyclohexanes with 2-alkyltetrahydropyran as the starting material. The structures of the reaction products were established by analysis for sulfur; desulfurization; gas-liquid chromatography (GLC); mass, infrared, and nuclear magnetic resonance (NMR) spectra; and an alternate synthesis. The synthesis of the cyclic sulfides contributed substantially to the identification of 10 members of this class of sulfur compounds in crude oil.

Jan 1, 1967

By G. L. Palmer

"In 1986, anomalous sampling results for heavy minerals were obtained at various sites in Namaqualand on the west coast of the Cape Province. Drilling in 1987 at Graauwduinen penetrated up to 35 meters of heavy mineral-bearing Tertiary sands which extend several kilometers inland from the coast. The heavy mineral suite includes ilmenite, rutile, leucoxene, zircon and monazite, along with gamet, pyroxene and amphibole. Three deposits are recognized, two of which comprise the resource to be mined by Namakwa Sands Limited, a recently formed Anglo American Corporation subsidiary company.Mineable reserves in excess of 500 million tonnes have been delineated, sufficient to sustain mining for over 35 years at projected production rates. During the feasibility study, on-site investigations included test mining at various sites to assess rnineability and to provide material for metallurgical testing in a pilot plant located at the site. llmenite produced at the mine will be smelted at a new facility to be built at Saldanha Bay. Saleable products comprise titania-rich slag, pig iron, zircon and rutile.During the exploration phase, company environmental guidelines were established and monitored. The feasibility study incorporated a Class 1 Environmental Impact Report, the contents of which were made public following the principles of the Integrated Environmental Management legislation."

Jan 1, 1994

By N. W. Lord

Having recently had occasion to make a series of analyses of fire-clays for the present Ohio Geological Survey, I found that the amounts of potash and soda determined indirectly by measuring the chlorides volumetrically did not " check " with those obtained directly. Investigation with the spectroscope showed the presence of lithia in what seemed very appreciable quantities. The examination was made of a considerable number of samples, and in every case this element was found, though in varying amounts, as judged by the intensity of the spectrum. To guard against error from the impurity of reagents, the whole process was repeated, using the same reagents in corresponding amounts, but leaving ont the clay. In no case did these " blanks" show lithia; hence the presence of this element in the clays seemed to be established conclusively. In the same series of analyses, titanic acid, in amounts varying from three-tenths to nearly two per cent., was found. The presence of titanium was first observed in the Ohio clays, nearly three years ago, in the examination of clays from Logan. The occurrence of this element is, of course, not unusual in clay, but I believe that none of the published analyses of Ohio clays give it; certainly none of the former Ohio geological reports speak of its presence. The following analyses show both the above ingredients. They were made during the summer of 1883.

Jan 1, 1884

By Carleton K. Smith

Due to special job or client requirements, there will always be some variation in the philosophy of organizing and controlling construction under a project management contract. In typical cases, however, some standard procedures apply. Controls on a construction project are best described only in general terms. They should apply to the total job and can be most effective only when all pieces of the job organization fit together to support a control system for the entire project. Controls are more than a system of reports, schedules, and tabulations-they are the result of an integrated organization dedicated to getting a job done on time and within budget. One of the most important aspects of project control is the construction organization. It must include the right people, facilities, and site equipment, as well as the authority to do what's necessary to accomplish the work. This should be set up to function with as little involvement from off-site or the home office as possible. However, the jobsite construction group must work within established policies and guidelines and is subject to continuous off-site or home office monitoring. In other words, the job-site leaders need to have a clear definition of their responsibility, their authority, and the necessary people and equipment to make things happen. With that philosophy in mind, this is how Bechtel sets up a new job to be

Jan 10, 1980

By Ashok K. Sinha

The quasi-binary systems "VFe3"—VCo,—VNi,— "VCu3"and "TiFe3"—TiCo3,—TiNi3-"TiCu3"have been studied by a combination of microscopic and X-ray methods. Of the Phases encountered, eleven had close-packed ordered layer structures. Within each system, there is an approximately linear variation of the degree of hexagonality of the stacking arrangement with electron concentration, e/a. A study of eighty -four known examples of AB3 structures in transition metal alloys indicates that at e/a = 8.65 the ordered structure of the close -packed layers changes from "triangular" (AuCu3 type) to "rectangular" (SbCu3 type). At e/a < 8.65, the slope of hexagonality us e/a line increases with the group number of the A component. An interesting series of close-packed ordered structures is known to exist at the composition AB3; however, their alloy chemistry has not yet been fully understood. Dwight and Beck1 observed a correlation between position of the components in the periodic table and the type of crystal structure of the binary AB2 structures formed by transition metals. No consistent effect due to atomic size was noted and they proposed that electron concentration* predominates in In the present paper, the AB3 structures are characterized by a symbol describing the stacking and a symbol specifying the ordered layer. The stacking symbol used was introduced by Zhdanov,7 and later used in the International Tables,8 and by Beck9 in his survey of possible layer stacking structures. Alternating positive and negative integers are used to represent the number of positive (e.g., in abcabc...) and negative (e.g., in cbacba...) stacking sequences. T denotes the triangular ordering found in close-packed planes of the AuCu3 structure and R the rectangular ordering found in close-packed planes of the SbCu3 structure, Figs. 3(a) and (b). The present structure symbols are listed in Table I alongside the prototypes, where known, and other structural characteristics of AB3 phases found in the present investigation. EXPERIMENTAL The starting materials were metals of 99.9+ purity. The alloys were prepared by arc melting under argon atmosphere using a nonconsumable tungsten electrode and water-cooled copper hearth. The total weight loss upon melting and subsequent annealing was always less than 0.5 pct and hence the alloys will be referred to by their intended (unanalyzed) compositions. The alloys were homogenized and annealed at suitable temperatures in the range 750" to 1200°C, the annealing periods varying from 3 days at 1200°C to 10 days at 750°C. The heat treatments were carried out in sealed silica capsules under argon atmosphere and with a molybdenum foil cover between the alloy and the walls of the capsule. The quenched alloys were microscopically examined and reduced to powder by crushing or filing. The powders were, whenever necessary, given a stress-relieving anneal at the original annealing temperature. X-ray powder patterns were obtained with an asymmetrical focusing camera, a Guinier-deWolff focusing camera, or a Debye-Scherrer camera. Cr, Co, or Cu radiations were used. In some cases, to ensure the minimum degree of contamination, the deeply etched specimens were mounted in the asymmetrical focusing camera to obtain an X-ray pattern. Internal silicon standards were employed for lattice parameter determinations. The intensity calculations were made by using a Fortran IV program

Jan 1, 1970

By J W. Edl, F C. Wu

In instrumented model rock blasting experiments in granite blocks, best fragmentation results were obtained when delays between holes were 1 to 2 milliseconds per ft. of burden and when a rectangular shothole pattern was used with spacings larger than the burden. Effective fragmentation in multiple hole blasts seemed to depend primarily on the full development of the crack network around each hole before the charge in the next hole was detonated. The test results showed that simultaneous or almost simultaneous initiation of shotholes in bench blasting resulted in poor fragmentation.

Jan 1, 1975

By Russell Franks

IN recent years a considerable tonnage of the 18 per cent chromium and 8 per cent nickel steels has been used in lightweight high-strength structures that must be resistant to deterioration under atmospheric conditions. These steels are austenitic in character and their strength can best be increased by cold-working. Although a marked increase in tensile strength is obtained, claims have been made that the cold-worked steels do not possess fully satisfactory elastic properties. Under certain conditions, however, this has caused no great concern, because, as explained by Ragsdale,1,2 the cold-rolled steels have been widely applied for construction of lightweight, high-strength trains using spot welding for joining purposes. Ffield3 agrees that the ease with which thin sections of the cold-rolled 18-8 steels can be joined by spot welding is greatly in their favor, but that they would be more satisfactory if higher elastic properties and a higher modulus of elasticity could be obtained. He states that, as far as the mechanical properties are concerned, the straight chromium stainless steel is superior to the cold-worked 18-8 steel, and in order to illustrate, he presented the data of Fig. 1, which also give a stress-strain curve for a low-carbon 13 per cent Cr steel. Ffield? pro-posed that columbium-bearing or titanium-bearing cold-rolled 18-8 steels be given a heat-treatment (preferably for 1 hr.) in the range 400° to 600°C. to precipitate carbides in order to obtain better mechani-cal properties. Discussions by Sutton,4,5 de Ganahl,6,7 8 Krivobok and Lincoln,9 Knerr,10 and Thaden11 have given further information on the properties of the cold-rolled 18-8 steels compared with other materials used in light-weight, high-strength structures. These investigators and others point out that the ultimate tensile strength of the cold-rolled 18-8 steel can be increased to 200,000 lb, per sq. in. or higher; Krivobok et al. indicate that

Jan 1, 1940

By K Shannon, A Shaw

The Hilton and George Fisher deposits occur 22 and 24 km north of Mount Isa, NW Qld, Australia respectively. Both deposits occur as deformed Proterozoic, sediment hosted, stratiform orebodies hosting Pb-Zn-Ag (Hilton) and Zn-Pb-Ag (George Fisher) mineralisation. The two deposits are separated by approximately 2 km of strongly faulted barren shales, mudstones and siltstones along strike. Despite this, correlations between the Hilton and George Fisher deposits have previously been assumed on the basis of textural, lithological and geochemical similarities, but previously lacked specific details to prove exact stratigraphic matches.Feasibility drilling allowed broad correlations based on the position of siltstone pillars separating individual orebodies. However the position of continuous potassium-rich, siliceous and cross-fractured tuffaceous marker beds (TMBs) often used as stratigraphic markers within the Hilton Mine were initially unrecognised within the George Fisher stratigraphy where they are erratically silicified and often not cross-fractured resulting in correlations being difficult to prove. As a more detailed knowledge of TMB locations at George Fisher was gained it was possible to look for corresponding TMBs within the Hilton orebodies. Recent underground stope definition drilling at the two locations enabled specific TMBs, stratigraphic units and even individual sedimentary beds to be matched between the two locations, despite the large separation between mines.The correlation between the two deposits has implications for future exploration drilling north of George Fisher. If a specific stratigraphic horizon can be determined within one hole, positioning of further drillholes can be more accurately planned. The significance of having stratigraphic matches between Hilton and George Fisher also has implications for correlations with other Isa Valley deposits. Convincing preliminary TM and stratigraphic correlations have already been made between George Fisher and the Isa Lead Mine 24 km to the south.

Jan 1, 2002