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By H. Y. Yancey, B. M. Bird

During the past four years the experimental work in coal washing carried on by the U. S. Bureau of Mines and the University of Washington has been devoted mainly to the development of special methods for the tabling of fine sizes of coals that are difficult to wash. One important outgrowth of this investigation has been the application of hindered-settling classification to coal tabling. Although used for many years in ore dressing, the term "classification" as used here may be new to many readers. It may be defined as the separation obtained when a bed of particles is held in a uniform state of suspension in an upward current of water, either continuous or pulsating, just sufficiently strong to keep the bed in a mobile condition. A common example of this type of separation is a jig in which there is no suction stroke. When the hindered-settling classifier is used with the coal-washing table, the fine-size raw coal, instead of being fed direct to tables, as is the prevailing practice, is first fed to the classifier and grouped, according to the rate of settling against the upward current of water, into perhaps six separate products. After dewatering, each of these except the sixth, a refuse product, is elevated to a seperate feed bin arid washed on a separate table. This paper gives a brief discussion of the basis for the use of hindered-settling classification of a table feed; a description of the experimental work; a comparison of the results obtained with and without classification; and a discussion of the application of the classifier in commercial coal washing. Basis for Use oF Hindered-settling Classification of Table Feed Although theoretical reasoning might be used to justify treating a table feed by hindered-settling classification,l the simplest method of demonstrating the need of such a step before tabling is to show the

Jan 1, 1930

By John E. Miller

Absolute viscosity values for gases usually are determined with a capillary tube viscosimeter, One of the correction factors applied to the experimental data is that for nonuniformity of the capillary bore. This report contains useful analytic expressions of the nonuniformity correction for the following cases: ellipse, cone, sine wave, sawtooth wave, square wave, and the general case. The methods herein described are applied to estimate the nonuniformity of a section of stainless steel capillary tubing to be used at the Bureau of Mines Helium Research Center. Several other examples are given to illustrate the usefulness of the present results.

Jan 1, 1967

By S. J. Schatzel, K. M. Ajayi, E. N. Rubinstein, Z. Khademian

This study simulates the impact of a shale gas well casing breach near a longwall mine. Field studies are conducted to measure mining-induced permeability changes over the abutment pillar of a longwall mine, and a geomechanical model is developed in 3DEC, a three-dimensional numerical modeling code, to predict the aperture of fractures in the overburden at the study site. The predicted aperture values are used to determine mining-induced permeabilities, and the results are compared with the field measurements. These aperture values are provided as inputs into fracture flow code (FFC), which generates a stochastic discrete fracture network (DFN) model for the study site and predicts the potential shale gas flow to the mine. Results from 100 DFN realizations are statistically analyzed using the bootstrapping method to compensate for notable variation in fracture geometry. The results show a significant difference between the gas inflow for nearby panels due to increase in the induced permeability during mining of the second panel. The average gas flow to the mine was calculated as 4.72 × 10 m3/s (49 cfm) for a hypothetical breach at the Sewickley horizon during the first panel mining, 8.97 × 10 m3/s (19 cfm) for a hypothetical breach at the Uniontown horizon during the first panel mining, 2.16 × 10 m3/s (458 cfm) for a hypothetical breach at the Sewickley horizon during the second panel mining, and 8.07 × 10 m3/s (171 cfm) for a hypothetical breach at the Uniontown horizon during the second panel mining. Depending on the mine ventilation system, this could result in methane concentrations exceeding regulatory limits. Hence, these findings provide insights into the potential risk of an unconventional gas well casing breach near a longwall mine under shallow cover.

Feb 1, 2024

By Plato Malozemoff, A. M. Gaudin

IN modern practice the major portion of an ore is reduced to flotation size by fine grinding. As the result of grinding fine enough to liberate most of the minerals, a substantial portion (generally 5 to 15 per cent) of the ore is inadvertently reduced to a size much finer than that necessary for liberation. This portion of most flotation pulps is very refractory to recovery by flotation. A reduction of one-quarter or more in recovery in this range of extremely fine particles can be observed. The loss in metals caused by overgrinding is appreciable. That this loss is characteristic of very fine particles has been suspected for some time;(l)† however, it was definitely quantified only recently.(2) Definite reduction in float-ability with reduction in particle size beyond a critical size of maximum floatability can be accepted now as an established fact. Formulating the Hypothesis In looking for the cause of the ill behavior of the finest particles it may be well to consider the essential differences between fine and coarse particles. A difference that immediately comes to mind is their intrinsic difference in size and consequently in relative extent of surface. If one agrees that attachment of mineral particles to bubbles must follow direct encounter of particles with bubbles one is forced to conclude(3) that the probability of encounter between a mineral particle and a bubble varies directly as the size of the particle, provided the particle is small compared to the bubble. In other words, the finer the particle the poorer its chance of being recovered in a given time of flotation. There is an effect, implicit in this theory, which should overcome the effect of excessive fineness of the particles; namely, flocculation of the particles. The floccules can be conceived as being simply larger particles and therefore capable of becoming attached to bubbles. And, indeed, in all the cases in which a sulfide mineral of near-colloidal size was successfully floated the mineral (but not necessarily the gangue) was flocculated. Moreover, it was shown experimentally(4) that galena previously flocculated by inorganic flocculators and then added to gangue

Jan 1, 1935

By Richard N. Grigsby

INTRODUCTION The Chord property was acquired in 1975 from Roy Chord, an early prospector and miner of the area. He had staked numerous claims on the southern flank of the Black Hills in the early 19501s, and by the late 50’s, many small open pit and underground mines had been or were in operation. By the mid 1960's small tonnages of high-grade oxidized uranium ore had been mined from the property. Starting in 1975, Union Carbide conducted a series of exploration programs to determine the remaining economic potential. The previously mined areas were re-examined in order to define additional oxidized mineralization. Meanwhile, a wide-spaced drilling program was initiated to determine the potential for deeper unoxidized deposits. Through the exploration program of 1979, measured minable reserves in excess of two million pounds of contained uranium had been discovered. GEOLOGY The Edgemont District is located on the southern end of the Black Hills Uplift. A succession of pre-Cambrian to Cretaceous Formations is exposed within the core and across the flanks. The uranium host is the lower Cretaceous Inyan Kara Group which is divided into two formations, the Lakota and Fall River Formations (Figure 1). The basal Lakota Formation rests unconformably on the Jurassic Morrison Formation and consists of fluvial channel sandstones

Jan 1, 1983

By William P. Blake

(Canal Zone Meeting, November, 1910.) A DEPOSIT of manganese-ore near Tucson, Ariz., merits notice by reason of the peculiar form in which it occurs, and as a striking. example of ore-deposition by vadose upward capillary flow of metal-bearing solutions with concentration at the surface of the country-rock. This deposit occurs at the northern end of the Coyote mountains, about 40 miles west of Tucson, upon the outcropping beds of porphyritic rock, which appear to be partly-metamorphosed strata of volcanic tufa, probably of late Secondary or of Tertiary age. The strata dip northward at a low angle, and present a series of basset-edges in parallel lines of outcrop, east and west, facing the south and extending over many acres. Successive groups of these outcrops, from 5 to 20 ft. in breadth, are coated with oxides of manganese in lustrous black films and crusts, shining in the sunlight like polished ebony, and covering the whole surface of the rock above the soil. Seen at a little distance, these croppings look like solid ledges of massive and pure ore; but closer inspection and a few blows of the hammer reveal their true nature as a superficial coating allied in origin to the blackened shining surface of rocks exposed in desert-regions, familiarly known as " desert paint" or "desert varnish,"' similar to the phenomena described by me in a former paper, but much thicker and heavier. * By reason of the death of the distinguished author, this communication, probably his last communication to technical literature, is published without revision of the proofs by him. A term first given y G. K. Gilbert. See Rocks, Rock-Weathering, and Soil; by George P. Merrill, p. 256 (New York, 1897). Superficial Blackening and Discoloration of Rocks, Especially in Desert Regions, Trans., xxxv., 371 (1905).

Sep 1, 1910

By C. G. Kirkland

An apparatus for determining trace impurities in Grade-A helium by mass spectrometer methods was designed and built by the Federal Bureau of Mines. Grade-A is the designation for helium commercially produced by the Bureau. Its nominal purity is 99.995 percent. The device, following a suggestion by Deaton, concentrates the impurities in the helium by freezing them out in a coil-and-trap assembly cooled by liquid helium. A known volume of helium is passed through the trap, the concentration ratio determined, and samples of the concentrated impurities are analyzed by mass spectrometer methods. The apparatus has been in service for approximately 20 months and has satisfactorily met all requirements. Over 200 analyses were made of helium contained in conventional cylinders, obtained from the Amarillo, Exell, Otis, and Navajo Helium Plants, during the 6-month period ending March I, 1959. Total impurity concentrations, in parts per million, were as follows: Amarillo, 19.1; Exell, 17.1; Otis, 11.3; and Navajo, 6.6. Neon and nitrogen were the major impurities. Complete data are shown in table 4 in the body of this report.

Jan 1, 1960

By A. E. Hall, D. M. Mchaina

This paper outlines a proposed research project to investigate secondary sulphide ignitions. Sulphide dust explosions have resulted in loss of production and considerable capital and equipment replacement cost in Canadian mines. The practical application of laboratory test results to actual mine situations presents a complex problem and is a field requiring immediate investigation. The factors contributing to the outbreak of sulphide ignitions are not clearly understood. This indicates a need for future research to study the influence of blasting parameters, exhaust temperatures, and dust characteristics on secondary ignitions at source. The aim is to establish realistic quantities for each of the parameters and develop a model that will incorporate field and laboratory quantities. It may be possible to predict outcomes of sulphide ignitions when the parameters are known. It is also planned to study the techno-economic feasibility of the preventive and control methods. One aspect of planned future research requires quantification of some terms by obtaining measurements of pollutant concentrations and size distribution of the airborne dust in an underground environment immediately after a main blast. A blast-proof aerosol sampling package to measure the source term will be designed. This sampling package will consist of a sampling section and a shield which will be capable of withstanding a blast explosion. The accuracy in measuring the variables and combination of variables will be the main focus in this proposed study.

Jan 1, 1987

By H. R. Stahi

THE ore of the Southeast Missouri lead district consists essentially of galena in dolomitic limestone. The galena usually is in a very finely disseminated condition. The experience of recent years in the concentrating plants of the St. Joseph Lead Co. has shown that dry crushing carried to a point where about 90 per cent of the ore passes a 14-mesh screen liberates the larger portion of the galena, and minimizes further necessary reduction in rod or ball mills. Concentration practice has attempted to carry size reduction to a point where economic unlocking of the galena is obtained, without causing undue sliming of the very friable galena. While 60 per cent of the tonnage of the district is treated by the flotation process, only 40 per cent of the total concentrates is produced by that means, as efforts have always been made to keep the grade and tonnage of flotation feed as low as possible. The milling practice of the district for some years has recognized the generally accepted idea of better selective grinding in rod mills as compared with ball mills, with the attendant decrease in production of fines. The function of rod and ball mills in the various concentrating plants is the grinding of table middlings and coarse tailings that carry lead values too high to be discarded. The simplified flowsheet in Fig. I illustrates the place of grinding mills in the circuit. The arrangement of classifiers, tables and mills constitutes a closed circuit within somewhat flexible limits. In 1937 experiments were conducted in replacing the ball charge in a 6 by 4-ft. ball mill with rods 2 in. in diameter and 51 in. long. This step was taken with some hesitancy, as it was easy to picture a mass of tangled and crossed rods. However, no difficulties developed, and after a short trial period, six more ball mills were converted to rod mills. These mills are of the spur gear and pinion, belt-driven type, using in most cases a 75-hp. motor and having a 9 1/2 -in. open trunnion discharge. As ball mills, they carried a charge of 16,000 to 20,000 lb. of balls, 2 in. in original size. The feed to the mills was dewatered by dewatering wheels and introduced at 70 to 75 per cent solids, with a single scoop feeder. One change in mill design was found advisable when rods were introduced. The existing end liners had an outward flare of 3 ½ in. in 12 in. These were replaced by linings having vertical interior faces, in order to prevent undue end travel of the rods. This change gave an effective working length of 5 2 ¾ in. inside the mill. No alterations were made in the shell liners, which are of the smooth type, made of manganese steel 2 in. in original thickness. The rods at present in use are 51 in. long and 1 3/4in. in diameter. The composition has been varied at times; at present they contain 0.70 per cent carbon and 0.70 per cent manganese. Some breakage and etching occurs as the rods become small, but this is considered preferable to using softer rods, which may kink and cause tangling of the charge. The mill charges are renovated occasionally, broken pieces being removed and the charge brought up

Jan 1, 1945

By Kendall E. Born

Production of crude oil in Tennessee during 1941 was slightly more than 15,000 bbl., about the same as in the preceding year. Two thirds of the total was from the Mississippi limestone pools in Scott and Morgan Counties. About a dozen small scattered wells in Clay, Pickett, and Fentress Counties, pumped irregularly, produced approximately 5000 bbl. Natural gas was marketed from wells in Morgan and Fentress Counties for consumption in the Sunbright and Jamestown areas, respectively. The production by counties is shown in Table I. Drilling activities in the state fell to the lowest stage since 1933. Twenty-seven wells were spudded in during 1941, of which six were drilling or only temporarily suspended on Dec. 37, 1941. Of the 22 completions, four were gas wells of undetermined quantity, but are classed as commercial, and 17 were dry or near-dry holes. One well encountered oil, but it has not been tested. The total footage drilled during the year was 29,916 ft.; the average depth of wells was 1359 ft. The more important wildcats are listed in Table 2; the distribution of tests according to physiographic divisions is given in Table 3. East Tennessee.—One well was drilled to 3480 ft. in northwestern Anderson County, in the highly disturbed Appalachian area, a region long considered the most unfavorable in the state for the accumulation of oil and gas. Another test is now drilling below 2000 ft. in this general area. Cumberland Plateau.—There were two completions in the Cumberland Plateau area. One test, drilled in northwestern Scott County in an area of former Mississippi limestone production,' encountered a considerable amount of free oil at 850 ft., about the same horizon as in the old abandoned wells. No pumping tests have been made to date. A well at Oneida, Scott County, found gas at 1579 ft. in a sandy limestone of lower Mississippian age. The volume was reported doubled by a shot, although no open-flow measurement is available. Eastern Highland Rim.—Six completions on the eastern Highland Rim resulted in two small gas wells in Fentress County, which will be used to augment the supply for Jamestown. The producing horizons are shaly limestones of Ordovician (Trenton) age. Two wells in this area tested the upper part of the Knox dolomite group, one of which encountered some free oil in a sandy dolomite at 1670 to 1681 ft. A test high on a well-defined structure in Clay County found a considerable amount

Jan 1, 1942

By Kendall E. Born

Production of crude oil in Tennessee during 1941 was slightly more than 15,000 bbl., about the same as in the preceding year. Two thirds of the total was from the Mississippi limestone pools in Scott and Morgan Counties. About a dozen small scattered wells in Clay, Pickett, and Fentress Counties, pumped irregularly, produced approximately 5000 bbl. Natural gas was marketed from wells in Morgan and Fentress Counties for consumption in the Sunbright and Jamestown areas, respectively. The production by counties is shown in Table I. Drilling activities in the state fell to the lowest stage since 1933. Twenty-seven wells were spudded in during 1941, of which six were drilling or only temporarily suspended on Dec. 37, 1941. Of the 22 completions, four were gas wells of undetermined quantity, but are classed as commercial, and 17 were dry or near-dry holes. One well encountered oil, but it has not been tested. The total footage drilled during the year was 29,916 ft.; the average depth of wells was 1359 ft. The more important wildcats are listed in Table 2; the distribution of tests according to physiographic divisions is given in Table 3. East Tennessee.—One well was drilled to 3480 ft. in northwestern Anderson County, in the highly disturbed Appalachian area, a region long considered the most unfavorable in the state for the accumulation of oil and gas. Another test is now drilling below 2000 ft. in this general area. Cumberland Plateau.—There were two completions in the Cumberland Plateau area. One test, drilled in northwestern Scott County in an area of former Mississippi limestone production,' encountered a considerable amount of free oil at 850 ft., about the same horizon as in the old abandoned wells. No pumping tests have been made to date. A well at Oneida, Scott County, found gas at 1579 ft. in a sandy limestone of lower Mississippian age. The volume was reported doubled by a shot, although no open-flow measurement is available. Eastern Highland Rim.—Six completions on the eastern Highland Rim resulted in two small gas wells in Fentress County, which will be used to augment the supply for Jamestown. The producing horizons are shaly limestones of Ordovician (Trenton) age. Two wells in this area tested the upper part of the Knox dolomite group, one of which encountered some free oil in a sandy dolomite at 1670 to 1681 ft. A test high on a well-defined structure in Clay County found a considerable amount

Jan 1, 1942

A development which could prove significant was the announcement on September 18 by Lone Star Industries, Inc., Greenwich, Conn., that the Snyder process which utilizes shock phenomena to break down ore in seconds, is operational. J. R. Kringel, chairman and president of Lone Star, says this about the process: "This new approach to the comminution of ores not only provides better mineral liberation at lower capital and operating costs, but it also makes a significant contribution toward the more efficient utilization of the country's rapidly depleting mineral reserves." The Snyder process consists of loading the material into a chamber, introducing a compressible working fluid such as steam under 300-500 psi, or as low as 80 psi, and then opening a millisecond-action discharge valve, causing the material to become entrained in the expanding fluid. The mixed fluid moves through a duct toward a discharge zone at near-sonic velocity, and is subject to a variety of extreme shock phenomena which accomplish the desired size reduction and mineral liberation.

Jan 11, 1972

By H. Stillman

The International Copper Association, Ltd. (ICA) is responsible for guiding strategy and policy, and funding international initiatives that help deliver the benefits of copper around the world. ICA's technology initiative supports this mission by funding pre-competitive technology development and accelerating the commercialization of new copper-related technologies. The R&D portfolio includes some projects that defend existing applications such as plumbing tube and data cabling, but the majority of projects are designed to enable new applications for copper. The current technology portfolio is focused on leveraging copper's unique electrical, thermal, mechanical and antimicrobial properties to define and expand the role of copper in areas poised for future technological growth: reducing disease transmission, sustainable energy generation, reducing the environmental impact of production processes, and in increasing energy efficiency. Projects related to these areas are conducted at qualified external organizations including universities, early-stage firms, and large OEMs worldwide. This talk will provide an overview of ICA's technology initiative's principles, projects and partnerships to stimulate the audience to think about copper-related innovations.

Jan 1, 2007

By M B. McKevitt, W J. Shaw

The main task of grade control on a daily basis is to define the material that should be mined to a destination under various categories. This can be determined by grade, lithology, quality and blending criteria. In the case of multi-element deposits or deposits with various blending or other processing criteria the optimum selection of ore block boundaries can be quite complex. In every case the balance between ore loss and dilution must be considered when designing the ore block boundaries and this becomes a risk-based decision when using the conditional simulation model. The use of such systems allows grade control to meet specific targets, such as budget tonnages and grades and blended product specifications. Two case studies are presented: the Prominent Hill copper/gold mine and the Rapu Rapu zinc/copper mine. Mining is based on a rational grade control strategy involving a number of factors, including strong geological control, advanced geostatistical approaches, such as conditional simulation, and optimisation of the ore blocking to meet production requirements. This provides an objective, transparent and repeatable grade control strategy.

Jan 1, 2009

By A. L. Muler

Since 1956, when Broadbent and Callcott 1 proposed to analyze breakage processes by matrix methods, several authors and their co-workers have proposed various models of grinding that, in principle, could lead to fully automated grinding circuits. In particular, Meloy and Gaudin2, Gardner and Austin3, Kelsall and Reid4, Neloy and Bergstrom5, Callcott and Lynch 6, and Draper and Lynch have, by either computer simulation or by experimental data, or by a combination of the two, verified that comminution is reasonably well described by at least two functions: a selection function and a breakage function. The stage concept proposed by Callcott and Lynch6 requires that a classification matrix be included to completely describe breakage in an open circuit rod mill. The purpose of this work, portions of which are herein described, is to accumulate sufficient information on the breakage characteristics of quartz and magnetite in an open circuit rod mill, so that several of the theoretical and experimental approaches proposed in the literature can be compared with each other. Data is being gathered to compare the experimental method used by Kelsall and paid against the stage approach of Callcott and Lynch.

Jan 1, 1968

By D Morrison

Backfill is usually considered a necessary evil that contributes little to the principal objective of the operation, ore production. Consequently, it is relegated to an auxiliary role in the operation with minimal equipment and resource allocation in planning and is only superficially considered during feasibility studies. In many mines, the inadequacy of the design and operation of the backfill system ultimately leads to frequent delays, excessive costs and, in the worst cases, major instabilities which result in reduced ore production and lost or unrecoverable ore reserves. The primary objective of backfill is to prevent the progressive deterioration of mined out excavations. With the exception of narrow vein operations, it is too weak to alter the mining induced stress regime and control stress concentrations caused by stope extractions. However, the direct benefits of backfill include the possibility to consider a wider range of mining methods, recovery of 100 per cent of the planned resource and the selection of a stoping sequence that minimises the regional stability problems that cause production shortfalls in the later years of mine production. Indirectly, backfill is a practical means of solving other issues, such as waste disposal, that impact the viability of mining. In Australia, the geotechnical conditions of many mines are becoming more difficult and increased attention to the importance of backfill is warranted. This paper describes realistic aspects of backfilling and the positive impacts a well co-ordinated fill system can have on mining activities as a whole. Examples are presented where an integrated approach to backfill systems have offered significant benefits to the operation.

Jan 1, 1998

By N. L. Svensson

The model developed by Tuylor for the calculation of Polycrystalline yield strength has been applied to the case of an aggregate hawing a preferred orientation. In general this procedure requires the specification of texture by means of weighting factors applied to specific orientations. The problem to which the model has been applied is that of the yield-strength aniso-tropy of cold-rolled aluminum whose rolling texture was described as a combination of (110)[112] and (311) [112] In this case yield-strength anisotropy is defined by the rutio of yield strength measured at an angle 8 to the rolling direction to that measured along the rolling direction. The method of calculation of yield-strength ratio as a function of ? is described and the results show good agreement with experimental values. The orthotropic yield criterion suggested by Hill has been applied to the results and the strain ratio R also calculated as a function of ?. This has been compared with calculations using the method suggested by Elias, Heyer, and Smith which does not exhibit suck good agreement with observation. one deficietlcy of the method presented is that the strain ratios used by are those applying to iso-Irobic materials. The method should therefore be reg-clrded only as a first abbroximation to the prediction of anisotropy. THE problem of calculating the stress-strain characteristics of polycrystalline aggregates from the properties of single crystals has attracted attention for a number of years. The most important contributions to this study have been those due to: Sachs,' Cox and sopwith,2 Taylor,3 Kochendorfer,4 Batdorf and Budiansky,5 Calnan and Clews,6 Bishop and Hill,7,8 Kocks,9 Budiansky, Hashin, and sanders, 10 Kroner,11 Cyzak, Bow, and payne, 12 Budiansky and Wu,13 and Lin.14 While the earlier work has been largely superseded, recent developments tend to support Taylor's solution" within the restriction imposed by his assumptions. The essential features of Taylor's approach were: 1) the material is rigid-plastic; 2) each grain experiences the same strain components as the aggregate as a whole (the problem was that of uniaxial deformation with principal strain components in the ratio 3) all regions of each grain deform uniformly; 4) work hardening occurs equally on all slip systems. While Bishop and Hill7 have generally validated this approach, there has been some criticism offered. Kocks? as pointed out that since multiple slip must occur the single-crystal data must be determined from orientations arranged such that polyslip takes place. Boas and Hargreaves,15 and others, have shown experimentally that the strain distribution within grains is not uniform, the strains in the vicinity of grain boundaries being less than those in the center of the grains. Both of these criticisms can be largely offset by the suitable choice of single-crystal critical shear stress. However, for the problem analyzed below, the critical shear stress is not directly used and, consequently, these criticisms lose their importance. The more recent contributions have attempted to obtain a more complete analysis by considering an elas-toplastic material and considering interactions between grains of differing orientations. Lin14 has considered the early stages of yielding for a polycrystalline aggregate having specific regions of defined slip plane orientations. On the other hand, Budiansky and Wu13 have allowed for these interactions for randomly disposed grain orientations and have calculated the polycrystalline stress-strain curves for crystals exhibiting either elastic-ideally plastic or kinematic hardening characteristics. This work has shown that yielding commences when the macroscopic stress is 2.2 times the critical shear stress for slip in a single crystal (7,). The yield stress-strain curve then rises becoming asymptotic to a value of 3.072 7,. This is close to the value obtained by Bishop and Hill (3.06) in their confirmation of Taylor's method. This, of course, is to be expected since, at large strain values, the elastic strains are negligible and the rigid-plastic model is satisfactory. The results of Budiansky and Wu indicate that the result obtained by Taylor is 7.7 pct high at a plastic strain which is two times the elastic strain at the initiation of yield. By defining the anisotropy in terms of relative values, the ratio of yield strength at orientation ?, to that measured in the rolling direction, the effect of the discrepancy in Taylor's solution is considered to be of lesser consequence. Therefore, it is anticipated that an analysis based on Taylor's solution, which can be quite straightforward, should provide a reasonable estimation of the anisotropy of materials having a preferred orientation texture. OUTLINE OF TAYLOR'S METHOD In fee metals there are four possible slip planes (the octahedral planes) and in each there are three possible slip directions (the edges of the octahedron), that is a total of twelve possible slip systems. von Mises16 has shown that at least five independent slip systems must become operative in each grain of the polycrystalline aggregate in order to preserve continuity of strain. With this geometrical requirement as basis and the assumptions previously listed, Taylor determined the operative slip systems for a number of orientations of the tensile stress axis specified in the unit stereographic triangle. For the ith slip system, the critical shear stress

Jan 1, 1967

By J. Serra, M. Turpin, R. Alberny

A new method is proposed to obtain automatically an unbiased estimate of the interdendritic spacing A. It is shown that the structure can be built by a random distribution of a rectangular basic unit. The usual definition of the interdendritic spacing yields a value 1 which, coupled with A, gives the shape of the basic rectangular unit. A study of the relationship between dendrite arm spacing and solidification rate was conducted as a part of a research program on dendritic solidification. For any comparison between theory and experiments to be meaningful, it is necessary to measure reproducible and clearly defined spacings. Fig. 1 shows clearly that even in a fairly simple structure such measurements are difficult. if we compare photos (a) and (b), we can hardly assess which one shows the larger spacing. Moreover, the quantity to be measured can be defined in several ways. On a small scale, dendrites seem to be distributed in a very regular and ordered way. However, on a larger scale, this regularity no longer exists. The usual way to measure spacings is to pick up some rows of dendrite stalks; such measurements are obviously biased since less orderly regions are not taken into account. A more objective method is to section the picture with randomly oriented straight lines and average the measured interdendritic spacings. The purpose of this paper is to show that such measurements, which can be conducted automatically, yield objective and reproducible results which are directly related to characteristic features of the dendritic structure. I) THEORETICAL ANALYSIS 1-1) Mathematical Morphology and Function of Co-variance. Matheronl and Serra2 enlarced- the definition and geometrical meaning of the notion of covariance to encompass problems in mathematical morphology. A brief review of part of their theory can be stated as follows. Let A' be an isolated particle, and let us consider a group of two scanning points h is the vector joinlng these points, h its modulus, and a its direction. Let us also define a boolean function, k(x), whose value is 1 if x lies inside the particle and 0 if it 1s outside. The total number of events in which both points are inside A' IS the covariance Ii',(h): is the measure of the intersection of A' with the particle ALh obtained by translating A' of -h Obviously K,(O) is the volume of the particle A', or its area if A' is a two-dimensional body. The average value of K,(h), when the direction of a vector h of constant modulus is rotated, is: An important property of the covariance is illustrated on Fig. 2: if the shape of a particle shows some regularity along a direction a, K,(h) generally presents a maximum. We now consider a group A, made of many particles A' distributed in space; then k(x) is taken as the realization of a stationary random f~nction.~ The volume fraction (or fraction of area if the problem is two-dimensional) occupied by A equals the average value q of k(x): meaning "average value of"). We also replace

Jan 1, 1970

By W. H. MacLean, S. Liaghat

The Key Tuffite is a thick (0.3 m to 6 m) and laterally extensive (-10 km) cherty, sulfide-bearing tuff unit in Archean greenstones in the Matagami mining district in northwestern Quebec. It lies at the contact of the Watson Lake Group and overlying Wabassee Group volcanic rocks, and is host to major Zn-Cu volcanogenic massive sulfide deposits. The tuff component is highly altered and its volcanic precursors are not identifiable by petrographic means. The tuff is mixed with a volcanic exhalative component comprising chert, carbonate and sulfides (pyrite, pyrrhotite, and minor sphalerite and chalcopyrite). The normative mineral composition of the Key Tuffite is 33% quartz, 28% sulfides, 16% sericite, 8070 carbonate, 6% chlorite and 9% other minerals. In the vicinity of the Bell Allard and Orchan mines, the precursor tuff components are identified using immobile major and trace elements, as Watson Lake tholeiitic rhyolite (Zr/Y = 1.5 to 3.5, LaN/ybN = 1.7 to 2.8, SiO2 = 72.5 ± 1.2 wt %, and Wabassee calc-alkaline andesite (Zr/Y = 9, LaN/YbN= 4 to 8, SiO2 = 56% to 65%). Immobile element computation techniques were used to calculate mass additions and losses in the conversion of the tuff to the Key Tuffite. Average net amounts of FeP3 (27% total iron), Si02 (14%), Cao (8%), S and K2 (+ 2%), were added, Nap was removed (-2.8%), and MgO was over-all unchanged. Total net mass change was +63%, which comprises mainly exhalative additions, but also includes changes owing to hydrothermal alteration of the tuff component.

Jan 1, 1992