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By B. C. Allen

Grain-boundary gvoocing was studied irz chronziu?n. molybdenum, tungsten, and the solid-solution alloys, Cr-35Re. Mo-33Re, and W-25Re at 0.6 to 0.9 of the absolute liquidus temperature under an inevt atmosphere , foveign nzetal zlapor, and liquid metal. The controlling mechanism of matter transport was deduced frolr groove size and shape. kinetics of growth, and cotnparisoz with theoretical relatiotzships derived by Mullins. Grooves in chowzizon formed prittzarily by volume diffusion tkrongk kelium or argon at 1 atm pressure and by e1)apovation-condensatiotz in a static vacuum. Groozles in the other nzetals and alloys forrned priniarily by sirface diffusion, the coefficients of which were calculated. Carbon was found to decrease the acti7:ation energy for surface diffusion on molybdenun. Sitrface diffusizities weve sinzilav for iWo-0.0ZC and Mo-33Re. The presence of about 1 -?nm pressure of silver or tin vapor did not affect the neckanis)n of grooz;e formation. In liquid titz or silz:er, pain bolindary gvooves formed by zolume diffusion in the liquid. BASED on theories of ullins," the mechanisms of grain-boundary grooving have been determined for low-melting metals such as copper in an inert atmospheres or in liquid lead.4 The purpose of this investigation was to study grain-boundary grooving in the refractory Group VI-A metals, chromium, molybdenum, and tungsten, and the bcc solid-solution alloys, r-35e, 0-33e,= and -25e,' at 0.6 to 0.9 of included to see whether Mullins' theories were applicable to them as well. EXPERIMENTAL WORK The materials chromium, molybdenum, tungsten, Cr-35Re, Mo-33Re, and W-25Re were in the form of 0.050-cm-thick sheet assaying 99.98 pct or better. The nominal carbon level was generally 30 ppm. The oxygen + nitrogen + hydrogen content was -50 ppm. Mo-33Re and W-25Re were prepared by powder-metallurgy methods and supplied by Chase Brass and Copper Co. The remaining materials were arc-cast. Chromium and Cr-35Re were prepared at Battelle by arc melting, extruding, swaging, and rolling. Mo-0.003C was supplied by Climax Molybdenum Co., and Mo-0.02C and tungsten by Universal Cyclops Corp. As a source of liquid metals, tin and silver granules assaying 99.98 pct were used. Spectrographic analyses indicated the presence of -100 ppm each of iron and silicon. Vacuum melting reduced the combined gas content to c5 ppm (2.60,, 0.9N2, 0.4H2 in tin and l.602, 0.7N2, and c0.04H2 in silver). Specimens were prepared for grain-boundary grooving. Coupons 0.5 by 1.5 cm with a small hole in one end, or substrates 1.5 by 1.5 cm, were cut from sheet. The specimens were annealed in containers of the same material to provide a vapor-solid equilibrium as well as to protect them from gaseous impurities. Outgassing was done at 2 x 10"5 mm for 15 to 30 min at 1150°C for chromium and Cr-35Re, 1750°C for molybdenum and Mo-33Re, and 2600°C for tungsten and W-25Re. Then recrystallization to a stable grain size of about 0.5 mm was accomplished by annealing at least 1 hr at 1600°C for chromium, 1800°C for Cr-35Re, 2350°C for molybdenum, and 2300°C for Mo-33Re in a rhenium-element resistance furnace under 1 atm of static argon or helium. The atmosphere was gettered by tantalum radiation shielding. Tungsten and

Jan 1, 1967

By David R. Mitchell

IT is impossible to mention by name all the men and organizations that contributed to this volume. The original manuscripts of the chapters contained acknowledgments of various lengths, but space limitations make it impossible to print them. Suffice it to say that virtually everyone active in coal preparation in the United States contributed directly or indirectly to the contents of the volume. Special thanks are given to manufacturers of preparation machinery for their courtesy and willingness to furnish data, photographs and drawings. I am extremely grateful to Lupo Cinco, Alfred C. Arnold, Alfred E. Flowers, James M. Krese, J. H. Kelley, E. E. Vaccaro, E. J. Sandy, Edward Steidle, Jr., Joseph Fiedorek, David Scanlon, and Joseph T. Weber, former mining engineering students who contributed much of their leisure time for proofreading, checking references, and drafting, and without whose assistance it would have been difficult to prepare the manuscripts for publication this year. All sizes are for round-hole screens and tons are 2000 pounds, unless otherwise stated or indicated. Much of the manuscript material was prepared and edited during the war year of 1942 and I wish to offer my sincere thanks to contributors for their willingness to cooperate during these trying times. No doubt errors and omissions will be found in this book and for these I ask the readers' kindly indulgence.

Jan 1, 1943

By J. E. Metcalfe

Proceedings of the Fourth Empire Mining and Metallurgical Congress, Great Britain 1949. Part II published at the Offices of the Congress in London, England, 1139 pp. The price of these proceedings is £ 2. The parts may be purchased separately at a cost of £ 1 each.-Part I of this book covers a report of the organizing committee, the inaugural meeting and presidential address, banquet at Guildhall, welcome by Sir Richard Livingstone at Oxford. and final session. Technical session and papers are also covered in Part I. Part II covers such topics as coal, present-day trends in mineral dressing and metallurgy. Mining Engineer's Survey Manual. By J. E. Metcalfe. Published for "Mine & Quarry Engineering" by Electrical Press, London, 1951. 341 pp., illus., charts, diagrs., tables, 8 ¾ x 5 1/ in., cloth, 30s., available from Percival Marshall & Co., Ltd., London, and British Book Centre, 122 East 55th St., New York 22, N. Y. Beginning with a brief treatment of surveying fundamentals and a discussion of the correlation of surface and underground surveys, this practical manual continues with descriptions of surveying practice both above and below ground including stopes, inclined shafts; etc. Space is devoted to sampling and valuation, geological considerations, and descriptions of modern surveying instruments. The organization of survey operations is covered in the last chapter.

Jan 1, 1952

THE following employment items are made available to AIME members on a nonprofit basis by the Engineering Societies Personnel Service, Inc., operating in cooperation with the Four Founder Societies. Local offices of the Personnel Service are at 8 W. 40th St., New York 18; 100 Farnsworth Ave., Detroit; 57 Post St., Son Francisco; 84 E. Randolph St., Chicago 1. Applicants should address all mail to the proper key numbers in care of the New York office and include 6c in stamps for forwarding and returning application. The applicant agrees, if placed in a position by means of the Service, to pay the placement fee listed by the Service. AIME members may secure a weekly bulletin of positions available for $3.50 a quarter, $12 a year. MEN AVAILABLE Engineer, 43, married. Sixteen years' experience mining. Desires permanent position mine superintendent. Broad knowledge all types underground mining and shaft sinking. Construction and milling experience. Prefer North American continent but will accept foreign. Presently located Australia but available May 1, 1953. M-706. POSITIONS OPEN Mining Engineer with broad exploration experience, young, single status, and must be in excellent physical condition, as nature of work will be under very primitive conditions. Salary about 25 pct more than applicants last salary rate plus travel expenses and living allowance. Duration until July 1953. Location, Burma. Y7498.

Jan 1, 1952

By W. H. Bassett

One of the difficulties for many young engineers is the acceptance of responsibility. Even though they start as assistants to older men, they hesitate to offer positive opinions. They often make reports of observations and leave the boss to draw his own conclusions. If they happen to be in a position where they are not reporting to a senior engineer, and it is necessary to take the final responsibility for a decision, they try to get someone to help out and either assume or share such responsibility. Generally this is the result of want of confidence in one's self and fear that something may happen to go wrong and bring about criticism. Frequently diffidence is the principal factor. Young men come to me with reports on work that has been well done and well written up, who are evidently laboring under an intense desire to drop through the floor or to make a rapid' exit in some other way because of want of confidence. In my own early experience a consulting job came in that required considerable investigation. The man who was handing his place over to me mentioned my good fortune and I replied that the work would be interesting and I could handle it all right but feared the responsibility, which seemed considerable. He was an

Jan 1, 1932

THE following employment items are mode available to AIME members on a nonprofit basis by the Engineering Societies Personnel Service, Inc., operating in cooperation with the Four Founder Societies. Local offices of, the Personnel Service are at 8 W. 40th St., New York 18; 100 Farnsworth Ave., Detroit; 57 Post St., San Francisco; 84 E. Randolph St., Chicago 1. Applicants should address all mail to the proper key numbers in care of the New York office and include 6c in stamps for forwarding and returning application. The applicant agrees, if placed in a position by means of the Service, to pay the placement fee listed by the Service. AIME members may secure a weekly bulletin of positions available for $3.50 a quarter, $12 a year. POSITIONS OPEN Mining Engineer with some engineering training, capable of doing mapping, surveying, exploration, geology and transit work. Location, New York State. Y7333. Mineral Dressing Engineer, B.S. Mining or Chemical Engineering, age to 35. Must have knowledge of flotation. Duties will be in applied research and field evaluation of cationic and anionic flotation agents. Salary, $3500 to $7000 depending on experience. Location, Chicago. R-8971. Geological Draftsman, 25 to 30, with some experience in working with a geologist. Salary, $5100 a year. Location, New York, N. Y. Y7153.

Jan 1, 1952

By W. B. Lilienthal

A considerable saving in time and money has been effected by use of a specially designed stainless steel container for laboratory drilling mud test work. This container involves use of a standard tall-form stainless steel beaker for service in which the mud sample is heated to an elevated temperature and maintained there for protracted periods of time, while undergoing agitation to facilitate mixing of mud components. Agitation is accomplished by rotating the filled containers on motor-driven rollers within an oven. Several porcelain balls are generally placed in the containers to further improve agitation. Soft glass containers (.Mason jars) were used in this service in early work, and were found to be unsuitable for the following reasons: 1. Poor resistance to thermal shock. 2. Containers could withstand only relatively low pressures. 3. Accidental breakage in handling. 4. Chemical deterioration and subsequent mud contamination from reaction of high pH muds with the glass at elevated temperatures. Pyrex containers were also considered, but, inasmuch as they provided improvement only in items 1 and 4 listed above the additional cost was not believed to be justified. A scale drawing of the container is shown in the figure illustrating details in cross-section. A pressed stainless steel lid was fabricated to match the rolled edge of the beaker

Jan 1, 1950

By Frederick B. Brien

DEVELOPMENT of uranium extraction techniques over the past ten years has been spectacular. Rapid progress has been made by applying chemical, physical, and engineering fundamentals for the purpose of devising simpler processes, developing continuous procedures, reducing reagent consumption, improving final products, simplifying analytical methods, and treating more refractory ores and ores of lower grade. Since the source of many valuable metals in future will be of necessity from lower grade ores of a complex nature, and since hydrometallurgical processes are often the only means of treating such materials, these recently developed techniques will be of increasing importance. Leaching: A great deal has been published about the important role of ion exchange resins in purifying and concentrating leach solutions. Recent applications indicate that the resins will be very useful in simplifying leaching procedures of ores containing two or more valuable metals.1 The valuable metals may be differentially adsorbed by careful control of the oxidation-reduction potential of the pregnant liquors. For example, treatment of vanadium- uranium ores at present may involve salt roasting, water leaching, acid leaching, carbonate leaching, and intermediate fusions. Use of a single acid leach may now be possible, followed by a two-stage ion exchange technique, comprising initial adsorption of hexavalent uranium and rejection of tetravalent vanadium. The solution is then oxidized, producing pentavalent vanadium, which is later readily adsorbed and stripped into a separate eluate.

Jan 9, 1957

By P. Nelson, K. L. Gunsallus, A. R. Ingraffea, J. F. Beech

INTRODUCTION Fracture toughness, KIC, is an intrinsic material property and is a measure of the energy required to create new surface area in a material. Fracture toughness measurements can be made for a wide range of rock types (Ouchterlony, 1980). As a measure of energy of comminution, fracture toughness might be used for more sensitive predictions of Tunnel Boring Machine (TRM) performance than are possible with other index measures in current use. This paper describes part of an ongoing, comprehensive, analytical/experimental program aimed at evaluation of KIC in such a role. The program includes efforts to: 1. Provide a firm analytical basis for a test specimen geometry: the core-derived short-rod. 2. Develop simple, inexpensive testing equipment and techniques. 3. Evaluate the accuracy of the above by testing rock and other materials and comparing the measured fracture toughness with those obtained by other methods. 4. Measure fracture toughness of a substantial number of different rocks from three ongoing TBM projects. 5. Compare fracture toughness results with other strength measures. 6. Compare all test results with observed TBM performance in the three projects. Presented here are summaries of all but the last of these efforts. Comparative evaluation of KIC as a more senstive rock property for TBM performance prediction will be the subject of the oral presentation and a subsequent paper.

Jan 1, 1982

By M. Semchyshen, G. A. Timmons

P. A. Beck (University of Illinois, Urbana, 111.)—An interesting result of this work is the fact that in cold rolled molybdenum sheet complete loss of work hardening is obtainable on annealing, without change in texture. The retainment of the cross-rolling texture on soft-annealing is particularly significant, since this is essentially a single orientation texture, where texture retainment could be achieved by only one of the two niechanisms which produce this effect in aluminum,16 namely by recrystallization in situ. Recrystallization in situ was originally discovered by Collins and Mathewson (1940) and by Crussard (1944) as a phenomenon taking place on annealing in relatively mildly deformed single crystals of aluminum. It now appears to be a major (in many cases the major) mechanism of annealing of severely cold rolled poly-crystalline material, not only in aluminum,le but in metals as different in character as beryllium," tita- nium,'" and molybdenum. All these data now confirm the general validity, at least for more or less pure metals, of the interpretation of the annealing process given a few years ago by Smith.'" The whole question of recrystallization is now reopened. Indeed, it appears that recrystallization, as defined traditionally, may not occur at all, since at the time "deformed material" is absorbed by "recrystallized grains," it has already become completely strain free by recovery and "recrystallization in situ."

Jan 1, 1953

By R. K. Govila, E. H. Parkison

THE interplanar angles for hcp metals vary with c/a ratio, and therefore must be computed separately for each particular metal or alloy. Manual computation of these angles is laborious and time consuming, and for this reason computer programs have been developed to accomplish this task.1"3 However, these programs have certain disadvantages. For example, they require prior knowledge and understanding of ALGOL or FORTRAN languages. Further, they will not print out specific angles but instead give all angles between given limits—thus program2 prints out a total of 26,649 angles between planes with indices and in the range from (4 4 4) to (4 4 4) for any given c/a ratio. The purpose of this note is to present a simple and inexpensive computer program for accomplishing this task. This program is written in BASIC language4 which does not require any prior knowledge of computer programming, and is ideally suited for nonprofessional programmers. It also provides flexibility for the user by allowing him to select any indices for as many or few planes as desired for any given c/a ratio. The computer program proposed below is based on the relationship in which + is the angle between any two planes and . TO illustrate use of the program, consider the problem of calculating the interplanar an-

Jan 1, 1970

By H. R. Hanley

ONE of the most important contributions to the art of electrolytic zinc production-has been the aluminum cathode. This has been used in all major production: since its commercial development in 1916. The literature is replete with important contributions, some of which may have been replaced by better ones, but thus far there appears no other metal to take the place of aluminum as cathode material. Credit for this innovation goes to Sherard Cowper Coles, of England. When experi-menting on the extraction of-zinc from Broken Hill ore at Hayle, Cornwall, in 1893, he introduced the aluminum cathode, and in 1895 obtained British Patent-No. 20073. The reason for this dominant position of aluminum as cathode mate-rial in zinc sulphate electrolytes is its unique surface, to which electro-deposited metals usually do not tightly adhere. The metal must be of high purity for best results. It is possible to develop a starting-sheet method by which thin electro-deposited sheets of cathode zinc are made and stripped from a smooth aluminum plate. Such thin sheets of cathode zinc may be used as arc tine copper sheets in standard electrolytic copper-refinery practice. However, complications arise because of extreme warping of the zinc starting sheet after a .few hours of deposition, and thus special arrangements must be made to compensate for this abnormality.

Jan 1, 1938

By W. H. Davitt

While it is true that taxes, especially income taxes, whether they be federal, state, or local, are not usually thought of as a "cost" of doing business, it is equally true that these tax costs do reduce the distributable profits just as much as the cost of power, supplies, or labor. Therefore, the consideration given to taxes is often as important as that given to other costs. Hopefully you will recognize that, within certain limits, taxes can be controlled to an economic advantage. The tax laws as now imposed are quite complex. Many of these laws and the regulations thereunder involve many factual determinations, technical considerations, and specialized valuations that can best be made by people trained in the specific area concerned. A substantial amount of a tax liability turns on the proper consideration given to issues involving facts and principles which are peculiarly engineering in nature. The importance of these "engineering" issues in tax administration has been significantly increased in recent years by our rapidly advancing technology, automation, stepped-up mineral and oil exploitation, new industries such as electronics and nuclear power, and the extension of percentage depletion to all minerals. These specialized requirements incorporated in the law are so technical that full consideration can not be given by people with a non-engineering background.

Jan 7, 1974

MEMBERS-QUALIFICATIONS AND ELECTION 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 he 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 be 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 at least ten Members 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 be may belong.

Jan 1, 1938

Application of Kutter's Formula to Gases Discussion of paper by F. ERNEST BRACKETT, presented at the Pittsburgh Meeting and issued, as Pamphlet No. 1578-A-F, with MINING AND METALLURGY, June. 1926. C. S. WITHERELL, New York, N. Y. (written discussion).-There is no reason to doubt that the relationship between the rate of flow and the impelling force of all fluids can be expressed by a general typical equation . that takes cognizance of all relevant factors such as density, viscosity (or its reciprocal mobility) and nature of channel-walls. Most fluids that are commonly conveyed by flow in confined channels are so highly mobile that they may be considered non-viscous, hence for these fluids the factor of viscosity does not need to appear in the equation. Water is the outstanding example of this class of fluids and its dynamic behavior has been so thoroughly investigated that proven formulas pertaining thereto, be they rational or empirical, would naturally serve as prototypes for the other non-viscous fluids. As non-viscous fluids can be classed all gases and vapors, most unsaturated aqueous solutions, gasoline, alcohol, etc. Viscous fluids comprise those that have a sluggish flow such as most. oils, tar, molasses, etc., the high viscosity of which is due to shearing resistance between molecules; a force that must be taken into account in figuring the flow of fluids of this class.

Jan 10, 1926

Application of Kutter's Formula to Gases Discussion of paper by F.-ERNEST BRACKETT, presented at the Pittsburgh Meeting and issued, as Pamphlet No. 1578-A-F, with MINING AND METALLURGY, June. 1926. C. S. WITHERELL, New York, N. Y..(written discussion).-There is no reason to doubt that the relationship between the rate of, flow and. the impelling force of all fluids can be expressed by a general typical equation that takes cognizance of all relevant factors such as density, viscosity (or its reciprocal, mobility) and nature of channel-walls. Most fluids that are commonly conveyed by flow in confined channels are so highly mobile that they may be considered non-viscous, hence for these fluids the factor of viscosity does not need to appear in the equation. Water is the outstanding example of this class of fluids and its dynamic behavior has been so thoroughly investigated that proven formulas pertaining thereto, be they rational or empirical, would naturally serve as prototypes for the other non-viscous fluids. As non-viscous fluids can be classed all gases and vapors, most unsaturated aqueous solutions, gasoline, alcohol, etc. Viscous fluids comprise those that have a sluggish flow such as most oils, tar, molasses, etc., the' high viscosity of which is due to shearing resistance between molecules, a force that must betaken into account in figuring the flow of fluids of this class.

Jan 10, 1926

By Everette Lee DeGolyer

FIFTEEN thousand barrels of oil daily, the production of the United States 75 years ago, amounted to more than 90 per cent of world supply. Russia and Romania, neither of which produced as much as one thousand barrels daily, were the only other suppliers in substantial quantity. The adolescent oil industry of the United States, a dozen years old in 1871, was still confined to the Appalachian region. Wells were drilled by cable tools; many of them were "kicked down" by manpower with a spring pole; and depths were measured in hundreds rather than thousands of feet-a 1000-foot well was a deep well. Casing was an innovation, come into general use only a few years previously and still so new as to be subject to bitter patent litigation. Crude oil was packaged in wooden barrels and shipped by flat boat and barge on the creeks and rivers and by railroad. Such pipe lines as existed were only a few miles long. There were many refineries. Pittsburgh, Cleveland and the Atlantic seaboard were refining centers. Refineries were very small, however, and their operations consisted essentially in simple fractionation by distillation and treating for quality. The products in demand were burning oil or kerosene and lubricating oils. Oil was not yet used as fuel and gasoline was a nuisance to the refiner.

Jan 1, 1947

By J. H. Frye, S. G. Holder, E. E. Stansbury

Internal friction studies on annealed and cold-worked pure silver and alloys of silver with 4.5 atomic pct each of Cd, Sn, and Sb are reported. Small amounts of cold work, introduced by stretching pure silver, decrease the internal friction; large amounts of cold work, by wire drawing, cause this decreased internal friction to rise. Results of severol anneoling histories on the room-temperature in-ternal friction indicate a rather complex recovery and recrystallization behavior. A rather system-atic alloy effect is observed for the elements of Period V-B in silver in both the annealed and cold-worked states. DURING recent years internal friction measurements at very small stress levels have been interpreted in terms of structural models and mechanisms occurring within the metal or alloy.These measurements have been made over wide ranges of frequency of vibration and of temperature. While the effects of impurities, alloying, and plastic deformation have been studied by numerous investigators, no investigations of the effect of a series of solutes related by their position in the Periodic Table on a given solvent seem to have been reported. The present paper reports internal friction measurements on silver and on certain silver-base solid solutions to determine the values of room-temperature internal friction associated with varying amounts of plastic deformation and after different annealing

Jan 1, 1957

By E. M. Wise

THE properties required of gold alloys for jewelry are not well standardized, due in part to problems peculiar to certain branches of the jewelry industry, in part to the individual preference of the fabricator and to his willingness to cope with certain difficulties in manufacture, which arise with the use of certain alloys. GENERAL REQUIREMENTS In general, the properties desired may be classed as follows: 1. Color should conform to the dictates of good taste and smart style. 2. Corrosion resistance and tarnish resistance should be good. This is to a considerable extent determined by the carat. Resistance to such corrosive agents as mercuric chloride as well as certain depilatories is unreasonable to expect and difficult to meet. 3. Strength and hardness must be adequate to maintain the delicate contours of finely modeled jewelry. 4. Wear resistance must be great enough to resist abnormal wear, such as is encountered by a wedding ring in a lifetime of wear. 5. Ductility must be sufficient to permit the fabrication of drawn shells, tubes and difficult shapes. Material having a yield point of not less than 60,000 lb. per sq. in., an ultimate strength of 100,000 lb. per sq. in., and an elongation of 40 per cent. is desirable. 6. Melting point should be between 800° and 1200° C.

Jan 1, 1928

By W. H. A. Timm

Lake Dufault Mines, Limited, is located ten miles north of Noranda, Quebec, Canada. Following discovery of a copper-zinc orebody late in 1961, metallurgical investigations of diamond drill core were conducted by Lakefield Research Limited during 1962 and 1963. These were followed by pilot-plant tests in May and June of 1964, utilizing underground development ore. Milling operations commenced on August 16, 1964, and reached rated capacity of 1300 tpd by October 1, 1964. Since that time, tonnage was gradually increased to a maximum of 1400 tpd and since January 1, 1968, gradually decreased to the present rate of 1100 tpd due to an increase in the hardness of the ore. The ore milled from start-up until January 1968, was mainly massive sulfides, consisting of a complex mixture of iron, Copper, zinc, and minor amounts of lead sulfides with important associated values in gold, silver and cadmium (average specific gravity of 3-8). From January 1968 until the present, the ore being processed is described geologically as a boxwork of sulfide stringers of chalcopyrite, pyrite, and pyrrhotite with some local dissemination in siliceous rhyolite (average specific gravity 2.9) supplemented by the massive copper-zinc ore. The limited size of the orebody and the mining method employed (open stoping by blasthole and slash benching methods) would have

Jan 1, 1970