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By I. Duckworth

P.T. Freeport Indonesia operates a mining complex located in the highlands of Papua, Indonesia. This district consists of both underground and surface operations. The East Ertsberg Skarn System (EESS) is one of the major orebodies in this district. Subsurface caving of the EESS has been carried out in a systematic series of mining lifts dating back almost 30 years. Present production is from the third lift (Deep Ore Zone), which is scheduled to peak at 80,000 mtpd during 2009, with this rate sustained through 2015. The orebody is proven below the existing caving level, with the next vertical block called the Deep Mill Level Zone (DMLZ). This paper presents an overview of the DMLZ Mine based on recent feasibility level study. The mine is being designed for a peak production rate of 29.2 million mtpy, with 1,803 total ore draw points spread over a panel caving footprint of about 1.3km by 375m. The present reserves for this mine total 501 million tonnes. Located 1,400-1,800m below the original surface, the DMLZ will be one of the deepest caving operations in the world. Production is scheduled to commence in 2015. Discussion is provided on most design aspects including; caving methodology and layouts, geotechnical predictions and risks, ore handling systems, ventilation design and associated infrastructure, high-lift pumping system, cost estimation and expenditure scheduling.

Jan 1, 2010

By LOWELL LAWRENCE

MAGNETITE minim and milling in the Eastern States continued at a low rate of production during 1934. The year's output was 50 per cent greater than in 1933, but when one considers that the 1934 output was only 1.5 per cent of the combined plant capacities of the eastern iron ore producers, the far-reaching effect of unrestricted importation of foreign ores and pig iron is apparent. The Chateaugay Ore and Iron Co., at Lyon Mountain, N. Y., produced 1.00,136 gross tons of concentrated and sintered ore up to Nov.1, when operations were closed clown. At Mineville, the Witherbee, Sherman Corp. confined its productivity to part-time operation of its Old Bed and Harmony mines front May 1 Lo Oct. 27. This period of activity was brought about by the use of Mineville ores in the recent blast made by the Green Island furnace at Troy, N. Y. The Forest of Dean property at Fort Montgomery, N, Y., has continued closed down during the year.

Jan 1, 1935

By A Jakowetz

OxianaÆs Sepon Copper Operation (part of the combined Sepon Gold and Copper Operation) is located in Savannaket Province, in southern central Lao PDR. The site is relatively remote, being some five hours inland from the Laos/Thailand border crossing on the Mekong River. The copper processing plant was designed to treat 1.3 Mtpa ROM ore to produce 60 000 tpa of copper cathode. Commissioning of the processing plant was completed in mid March 2005 with ramp up completed in January 2006 with 5260 tonnes of cathode harvested in this month. The focus of this paper is on SeponÆs unique grinding circuit. The entire grinding circuit is operated at highly acidic conditions, adding a number of different operational issues over and above those normally associated with grinding circuits. It became evident early in the ramp up, that reaching design mill throughput of 170 dry tonnes per hour with the original design would be challenging, coupled with the realisation that ceramic grinding media consumption had been underestimated. In order to lift the overall throughput of the processing plant, a significant continuous improvement process has been implemented within the grinding circuit to lift this key unitÆs production capacity. This presentation will focus on the key areas that have been addressed in the 12 month ramp up period and highlight areas for future work. Results to date have shown this improvement process to be very successful, with throughput rates in excess of 200 tph regularly achieved.

Jan 1, 2006

By S. Sundarraj

The morphological transition between columnar and equiaxed structures is an important solidification phenomenon frequently observed in castings, especially complex parts with varying cross-section, The mechanical properties and the occurrence of defects such as hot tears are strongly dependent on the structure formed in the casting. Hence, it is important to understand the conditions leading to columnar or equiaxed structures. Although extensive work has been done in modeling solidification systems, almost all of the existing models are based on the assumption that the structure formed in the casting is either purely columnar or purely equiaxed. Prediction of the columnar-equiaxed transition (CET) requires a solidification model which accounts for the formation of both columnar and equiaxed structures, along with related microscopic and macroscopic solidification phenomena. In this paper a CET model is presented which: (i) takes account of both columnar and equiaxed structures, (ii) accounts for macroscopic heat transfer coupled with microscopic phenomena such as nucleation, growth and microsegregation, (iii) satisfies solute conservation, and (iv) is easy to implement in commercial finite element and finite difference software. The proposed model predictions of CET have been validated with available experimental results for a uni-directional solidification of an aluminum-copper alloy. A sensitivity analysis has also been carried out to determine the effects of various parameters on the CET model predictions. The model is being extended to other alloy systems and more complex geometries. This work will be published in due course.

Jan 1, 1996

The May General Meeting of the Institute was held in Kelvin House, Johannesburg, on 21st May, 1969, at 4.30 p.m. Mr J. K. E. Douglas (Vice-President) was in the Chair. There were also present twenty-two Members, including Messrs F. P. Bath, M. Bareza, A. R. C. Fowler, D. M. Jamieson, C. M. Mavrocordatos, D. G. Maxwell and J. A. Nixon (Council Members), Messrs T. Davidson, G. L. Diering, E. T. Dunstan, D. E. H. French, K. Hodgson, O. A. E. Jackson, A. F. Lee, A. Louw, D. L. Starkey, R. K. Wheeler and M. Youngworth. Four Associate Members including Messrs D. Blair Hook and G. R. Still. One Student Mr N. A. Barcza. Thirteen Visitors, including Messrs S. H. Ash, D. L. G. Bayne, E. Bayne, S. Bell, W. S. Garrett, L. S. Gibbs, R. C. Hamilton, M. Maguire, D. Rose and J. D. van Niekerk. Total Present: Fourty-one. OBITUARY The Vice-President: "It is my sad duty to announce the death of the following member of the Institute: Thomas Spence Haldane, Member, who joined the Institute in 1924 and passed away on 21st December, 1968. As a mark of respect to the memory of the deceased and in sympathy with the bereaved, those present stood and observed silence for a few moments. MINUTES The Vice-President requested that confirmation of the minutes of the previous meeting be held over as they would only be appearing in the Journal of the following month. He also requested that confirmation of the minutes of the 75th Anniversary Meeting be held over. MEMBERSHIP The Vice-President: "I have much pleasure in announcing that the names of the under-mentioned candidates have been published in accordance with By-Law 5.2.2, and Council has elected them to membership of the Institute in the following grades: Members: Gideon Jacob Haumann, Peter John Cumming, Ian Stanley Dudman, Roderick Goldston Murchison. Associate Members: Francois Alwyn Beyers Fouche, Alan Marsh, Johannes Petrus van der Westhuysen, Waldo Edmund Stumpf, Ian Nicholas Ridley. Affiliates: Lutgerus Kolver Jooste, Roger Ainsley Ralph Kebble, Edward John Wainwright, Lewis William Davies. Graduate: Clive Graham Knobbs. MEMBER TRANSFERED TO A HIGHER GRADE From Student to Associate Member: Diethard Otto Eduard Fahrbach. I welcome the newly elected members to the Institute and congratulate the member who has been transferred to a higher grade." (Applause).

By Ye Junjian

The feed ore is the concentrate of low intensity magnetic separation of pyrite tailings, containing TFe47.47%, S19.41% and SiOpyrrhotite. The exploratory tests showed that using a process of flotation followed by magnetic separation could respectively obtain a sulphur concentrate of S 31.08% with a recovery of 82.89%, and an iron concentrate of TFe 59.97% and S 9.52%with a recovery of 30.93%. The reason of iron concentrates with high sulphur grade was that the sulphur grade of flotation tailings was 7.03%. So enhanced flotation for pyrrhotite was investigated in this research. Results show that when the natural pH of ore pulp varied from 5.5 to 6.0, a reagent combination of FS, LH, and BJ displayed the optimum flotation performance for pyrrhotite. After comparisons made on different flotation processing, the previous flotation flow of ?one roughing, one cleaning, one scavenging system and middling reprocessing?, was found, among others, to have the best flotation effect, as the grade and recovery of sulphur concentrate were 31.08% and 82.89%, respectively, and sulphur content of the flotation tailings was 7.03%. The above results indicated it was difficult to raise further the effect of flotation desulphurization. The authors therefore suggested that oxidizing roast should be adopted following the magnetic process for the purpose of further desulphurization. Besides, flue gas containing SO2 8.25%. And the valuable minerals are magnetite and 2 generated from roasting could be reused for sulphuric acid production. Keywords: pyrrhotite, enhanced flotation, desulphurization

Sep 1, 2012

By Chung Yu, Wang

CHINA can he roughly divided into three metallogenetic province: North China, the Yangtze Valley, and South China. In North China the old Pre-Cambrian schists and gneisses are represented by the abundance of quartz mines in which sporadic occurrences of copper, lead, zinc, gold, and silver are sometimes found in subordinate quantities. Along the Yangtze Valley and in Central China, extending eastward as far as Shantung, are found here and there intrusions of dioritic rocks, in which occur the famous contact deposits of iron ore, besides which minor quantities of copper. lead, and zinc are also found. In South China the igneous intrunsions are of granitoid type in which, or in the vicinity of which, occur in certain regions immense deposits of antimony, tungsten, tin, and mercury. Broadly speaking. most of the famous coal mines are now situated in regions north of the Yangtze River, in which occur also the sedimentary deposits of iron in contradistinction to the contact deposits of iron along the Yangtze Valley.

Jan 1, 1943

By G. Merle, David L. McKay, Elmar Randveer

"THE ENGINEERING AND TECHNICAL SERVICES department is responsible for supplying the following services:1. Administration and co-ordination of the work required for capital projects.2. Engineering, design and drafting services for inplant changes or improvements as requested by the operating• and maintenance departments.3. Rock mechanics.4. Preparation of plans and layouts required for efficient extraction of the ore as mutually agreed with the mine operating departments.5. Mine planning and long-term schedules in co-operation with the mine operating departments.6. Grade control (long term and short term) and the preparation of ore and waste removal schedules to maintain a uniform grade of mill feed. This also includes the calculation of metal reserves and metal production forecasts.7. Surveying, underground and surface.8. Operations research at the mine site.9. Industrial engineering.10. Chemical analyses and assays.11. Instrumentation.12. Environmental control.A staff of approximately 35 supervisors, engineers and scientists, and 80 technicians, supply the foregoing services. Consulting engineering and drafting firms are used to supply specialized services and technical personnel in-house at Timmins to handle overloads on capital projects under the direction of Ecstall engineers.The operating and maintenance departments depend on the engineering department to supply engineering, design and drafting services for any new facilities or for any planned alteration to existing facilities. To do this efficiently requires a high level of communication and co-operation with these departments. This has been a major factor in developing the present organization of the department shown in Figure 63.The organization is predicated on a strong central technical and engineering resource from which personnel can be assigned responsibilities for different projects, and in different areas, as the work load demands. Job satisfaction is very high because of the variety and challenge in the tasks. Additionally, participation in projects with production and maintenance personnel broadens each technical employee's knowledge of operating and maintenance problems."

Jan 1, 1974

By Thomas Kennedy, Michael Bennett

"History never repeats itself, but it often rhymes." The old aphorism reflects how the study of the past may, perhaps, be most widely valued when it can be used to improve current and future decision making. The education the authors received as geotechnical graduate students certainly impressed upon them the importance of recognizing that not all wisdom is necessarily new. Much of their graduate coursework involved reading technical papers that had introduced concepts of outstanding historical significance in the field, such as pore pressure coefficients, stress paths, and the stress history and nor- malized soil engineering model. These papers gave the authors both respect for and interest in the historical develop- ment of the field. After graduation, the authors furthered and deepened this interest by continuing to expand their knowledge of the profession through both experience in practice and the review of additional literature.

Jan 1, 2023

By H. J. Rowley

THERE are many varieties of limestone, but for the general purposes of the pulp and paper industry, two classifications are sufficient: (1) High-calcium stone, which should be quite free from impurities and contain not less then 90 per cent calcium carbonate. (2) High-magnesium stone, containing not less than 25 per cent of magnesium carbonate. Before proceeding with detail on the use of limestone and lime in the industry, a few words regarding the pulp products made in Canada are desirable. By far the largest tonnage is made by grinding spruce and balsam logs on rotating sandstones or on artificial abrasive stones of the Norton or Carborundum types. This mechanical or groundwood pulp finds its largest use in the production of newsprint paper, of which it comprises about 80 per cent of the total fibrous substance employed-the remaining 20 per cent being unbleached sulphite pulp. No limestone or lime is directly employed in making groundwood pulp, as contrasted with the chemically prepared pulps, all of which require one or the other form of the base for their processing. Sulphite pulps comprise the next largest tonnage group. They are produced by boiling, under pressure and at elevated temperatures, spruce and balsam wood in chip form in solutions of bisulphites and sulphurous acid. The usual bisulphites employed are those of calcium and magnesium. Sodium, potassium, and ammonium bisulphites give progressively better pulps, but to date, in the absence of efficient recovery methods, cost has precluded their use.

Jan 1, 1939

By Gary F. Rajala, Bruce R. Greenwood

INTRODUCTION The Empire Mine is an iron ore mining, concentrating and pelletizing facility operated by The Cleveland-Cliffs Iron Company in the Upper Peninsula of Michigan. Owners of the mine are Inland Steel, LTV Steel, Wheeling-Pittsburgh Steel and Cleveland-Cliff s. The orebody is a fine-grained, low grade iron formation with magnetite as the primary constituent. Also present are iron carbonates, iron silicates, chert, hematite, goethite and quartz. The original six concentrating lines were started in late 1963. Successive expansions of ten lines in 1967, five lines in 1974 and 3 lines in 1979 have resulted in Empire reaching a present annual capacity of 8.0 million long tons of pellets. The Empire flowsheet was developed over several years of laboratory bench testing, pilot plant testing and testing of a full-scale primary autogenous grinding circuit. Since the original flowsheet was established, modifications have been made based on pilot plant and full-scale plant tests. The present flowsheet for three sections of the concentrator consists of one stage of crushing, two stages of closed circuit autogenous grinding, two stages of magnetic separation, one stage of hydraulic concentration and two stages of flotation (rougher and scavenger). The flowsheet for the fourth section of the concentrator (Empire 4) is the same as the first three sections, except a crusher has been added to crush excess pebbles. The Empire 4 flowsheet appears in the at- tached figure. PRIMARY GRINDING CIRCUIT FLOWSHEET Empire has a total of 24 individual grinding lines. However, at the present time, Line 1 is not being used for processing crude ore. The primary mill on Line 1 is now grinding flux stone for fluxed pellet production and the secondary mill is being used as a ball mill to grind rougher flotation tailings prior to a scavenger flotation circuit.

Jan 1, 1992

By Victor J. Scaravilli

This report is based on experience developed on the construction of one contract for the Buffalo, New York subway. The Buffalo subway is under construction for the Niagara Frontier Transportation Authority and is called the LRRT-Light Rail Rapid Transit or more commonly the Metro. The Initial Route of the Buffalo subway construction started early in 1979 and is scheduled for completion in May, 1984. The initial system includes 5.2 miles of underground construction, 1.3 miles at grade for a total of 6.5 miles of subway system. A total of fourteen stations, eight underground and six at grade are included on the system. The Initial Route has a planned expansion to 17.3 miles in the future. On January 15, 1979, a Joint Venture of S & M Constructors, Inc., Solon, Ohio, James McHugh Construction Co., Chicago, Illinois, and Kenny Construction Company, Wheeling, Illinois, was awarded contract 100031, the Line Tunnels from Amherst Street to South Campus in northcentral Buffalo between Delaware Park and the State University, (see Fig. 1, Location Plan) This $35,000,000.00 contract was designed by Hatch Associates Consultants, Inc., Buffalo, N.Y. The Notice to Proceed was issued January 15, 1979 and the scheduled completion date is August 18, 1981. The project consists of two parallel rock tunnels with a minimum excavated diam of 18 ft 0 in. and a final concrete lining of 16 ft 0 in. diam. The tunnels total 14,630 linear ft. In addition to the tunnels, contract C-31 includes four shafts, an underground pump station, three cross passage connections, and other minor work items. (see Fig. 2, C-31 Project Plan and Profile) The tunnels were constructed primarily within the Bertie Formation, an approximately 50 foot thick moderately fractured to massive, dolo-

Jan 1, 1981

By Stephen Taber

JOHN C. BRANNER, Stanford University, Cal. (communication to the Secretary *).-Wideawake teachers of geology are constantly on the lookout for good illustrations of veins, especially where the processes of formation are either clearly shown or suggested. And I long ago found out that one who would learn nature's laws must despise nothing. It thus happened that in 1910, Dr. George J. Peirce of the depart-ment of botany at Stanford University called to my attention a cracked and broken yellow earthenware dish, 8 ½ in. across the top and 2 ½ in. deep, that, to the ordinary observer, seemed to be of no further use, and quite ready for the waste can. The striking thing about this dish was that the thin glaze over much of the outside surface and over the upper margin of the inside surface had been lifted in small scales, varying in. diameter from ½ cm. to 1 cm., and thrust outward and held there by some sort of white fibrous mineral. The process looked very much like one we are familiar with in the Southern States where. we often see in the winter pebbles and soil thrust out from a clay bank or lifted from a clay soil and held there supported by what is popularly known as needle-ice. Upon inquiry I learned the following facts in regard to the history of this particular dish: In the summer of 1910, it had been partly filled with a concentrated salt solution taken from one of the salterns of the Stauffer Chemical Co. at Redwood City, Cal. A qualitative analysis of the original brine showed: Present: iron, magnesium, sodium, potassium, chlorides, sulphates, nitrates (trace), bromides, carbonates, borates (trace), and considerable amounts of organic matter. Absent: calcium, lithium and iodides.

Jan 3, 1917

By Charles A. Ashburner

The existence of natural gas-springs in Pennsylvania and the adjoining States west of the crest of the Allegheny Mountains was known to the earliest settlers. Possibly the first gas obtained from a well was at Fredonia, Chautauqua County, N. Y., where a well was sunk on the bank of Canadaway Creek, near the Main Street bridge, in 1821, and sufficient gas obtained for 30 burners, the inn having been illuminated by the gas when General Lafayette passed through the village about 1821. In 1858 another well was drilled, which supplied 200 burners. A still larger one was drilled to a depth of 1200 feet in 1871. According to Mr. E. J. Crissey, Secretary of the Fredonia Natural Gas Light Company, the average monthly supply of these wells in 1880 was 110,000 cubic feet. Since 1859, when the drilling of oil-wells in Western Pennsyl-

Jan 1, 1886

By Emily Sarver

"Across all sectors and commodities, a common theme is driving progress in raw resource supply: sustainable development (SD). Over the past few decades, the mining and minerals industries for their part have undertaken significant and intentional changes at every level to become more responsible — no longer to just their shareholders, but also to the environment, to the communities in which they operate and to society at-large. Led by some of the global majors, these industries have indeed helped to define and operationalize the basic principles of sustainable development. Now in the midst of a full-on cultural shift, they are also key players in the continual effort to re-examine and calibrate practices to meet dynamic and increasingly complex objectives.SME’s technical position statementAs a home for so many technical experts and practitioners, SME has long recognized the importance of a commitment to sustainable development by the mining and minerals industries. In April 2016, the Society formally adopted a technical position on the topic following years of participation in, and support for, related activities. The full position statement appears below. It was drafted, revised and presented for approval to the board of directors by SME’s Sustainable Development Committee.Statement of Technical Position on The Mining Industry and Sustainable Development:• The National Environmental Policy Act of 1969 (NEPA) and the Surface Mining Control and Reclamation Act of 1977 (SMCRA) imposed considerable environmental restrictions on the mining industry; SME has always reinforced strict adherence to the laws.• In 2002, SME established a Sustainable Development Committee to lead its efforts in this area and to propel the organization into global prominence.• SME is a signatory to the Milos Statement of 2003 on Sustainable Development, so it is committed to providing scientific, technical, educational, and research skills in minerals, metals and fuels.• SME recognizes that SD programs adopted by the industry have a tangible return on investment through brand recognition and loyalty, facilitation of permitting, reduced occurrence of community protests and vandalism and diminished political risks.• SME actively promotes educational programs that encourage professional growth and interaction with the engineering professional community through books, articles, symposia, short courses and/or conferences on sustainable development in the mining and minerals industries.• SME has developed abundant expertise to provide balanced advice to government bodies, congressional staff and other interested organizations."

Jan 12, 2017

By D. A. Kinneberg, J. W. Donaldson, N. J. Themelis

In the Kennecott Converter Smelting process (KCS), copper concentrate pellets are smelted and converted to high-grade matte in a modified Peirce-Smith converter using oxygen-enriched air and fuel. A high-grade matte bath is produced and maintained in the converter. Periodically, the slag layer is skimmed, slowly cooled, and its copper content is recovered by milling. Ladles of matte are transferred and finished to blister copper in another converter. The gases from the Kennecott Converter contain the SO2 products of the smelting and converting processes and can be treated in an acid plant, eliminating the problem of low-concentration gases associated with the operation of the reverberatory furnace. Pilot tests at Utah Copper Division were followed by a full-scale prototype converter test at the Chino Mines Division of Kennecott Copper Corporation. The concepts of the process and the results of this campaign are presented.

Jan 1, 1976

By Dipl. -Ing. H. -J. Sager

The ‘Westerschelde Tunnel’ underpasses the estuary of the Schelde in the Netherlands. The tunnel will consist of two tubes which are driven by two hydroshields (slurry shields). The tunnels will each have a length of approx. 6.6km and a bore-diameter of 11.33 m. Demanding ground conditions had to be considered during the design of the shield machines. Loose sands, extensive clay formations and high ground water pressures of up to 6.5 bar will be encountered during the tunnel drive. The tunnelling activities will start in the middle of 1999 and are scheduled to end by the end of 2001.

Jan 1, 1999

By Paul Tyler

STRATEGICALLY situated in almost the heart of the leading fertilizer-consuming area of the United States, Tennessee long has ranked second only to Florida as a phosphate-producing state. Since 1932 its share of the national output of phosphate rock has increased steadily, and in 1937 its production mounted to an all-time record. More significant even than the increase in tonnage are the forward strides in technology. The Tennessee Valley Authority's research program has led to quasicommer-cial operations using hydroelectric power to manufacture concentrated phosphatic fertilizer that is used to further the farmer education program designed to streamline the fertilizer business and halt the appalling waste of farm land by soil erosion. Even more stimulating to chemically minded imaginations is the production of elemental phosphorus by a private company that not only has succeeded in extracting it from the phosphate rock in electric furnaces but actually has contrived to capture it and to transport it safely in tank cars. New values have been created for low-grade phosphate deposits, and the economic life of reserves has been lengthened while the waste of former years goes back into the mills for recovery of its values by modernized methods. Tennesse's phosphate-mining industry dates from the discovery of blue rock in Lewis County in December 1893. Its known reserves are of the order of 101,500,000 tons, which compares with the production of 825,099 tons in 1937; that is, 21 per cent of the phosphate-rock output of the whole nation. The total output reported from 1894 until July 1, 1938, was approximately 19,000,000 tons. Official estimates of reserves are overly conservative and evidence submitted before a joint Con-gressional committee in November 1938 places "probable" reserves at more than 6,000,000,000 tons.

Jan 1, 1939

Dr. James Douglas, who is memorialized on another page of this Bulletin, who held a place in the affections and regard of Institute members second to that of no other living roan, left in his will the sum of $100,000 for the maintenance of the Library of the American Institute of Mining Engineers. This is in addition to the $100,000 which Dr. Douglas gave during his lifetime. We believe that it is Dr. Douglas' wish that the library, the great means by which the benefits of Institute membership may be extended to those distant from headquarters, should be maintained by the Institute at the highest possible level of efficiency and serviceability.

Jan 9, 1918

By P. W. Billwiller

Abstract The Britannia Mining and Smelting Company, Limited, have replaced diamond drills with percussion drills and tungsten: carbide bits for most of their blast hole drilling operations and have thereby reduced ore breaking costs. Two-inch Carset bits .are used, with one-inch hexagonal Atlas Chippewa alloy steel in 3-foot .and 6-foot lengths. Locally made couplings of Atlas SPS 245 alloy steel connect the rods. The machines used are 31½-inch automatic leyners with lugged or anvil block chucks. For drilling holes below the horizontal, the lugged machines with special adapter rods made from 114- inch solid round Atlas SPS 245 are required. These rods are lugged at one end and a water hole is drilled for six inches into the other end. Over this rod is placed a water swivel which permits the water or air to be sent directly into the steel. A decreased cost per foot, increased footage per shift, and the use of standard equipment and crews are some of the main advantages of tungsten carbide drilling over diamond drilling. Introduction Long-hole drilling with percussion drills and sectional steel was introduced in several American mines some twenty-five years ago. It did not prove very successful, however, because the rapid gauge loss in steel bits necessitated the use of very large starter bits. This in turn rapidly fatigued the straight carbon-steel then in use, made it difficult to maintain the couplings, and resulted in a slow drilling rate. The introduction of the tungsten carbide insert bit and alloy drill still has changed this picture and opened real possibilities for the application of percussion drills to blast-hole drilling. If this type of bit had been perfected ten years ago, much of the research work and experimenting done to apply diamond drills to ore breaking would have gone toward developing the application of the tungsten carbide bit to this problem.

Jan 1, 1950