Search Documents

By A. M. Abdel-Rehim

The present work reports a study of production of thorium concentrate from Egyptian monazite by decomposition of ammonium carbonate solutions containing ammonium thorium and uranyl carbonate complexes. These solutions were obtained from the processing of monazite by alkaline leaching in ball-mill autoclaves, followed by selective separation of thorium and uranium from lanthanides by autoclave leaching of the hydroxide cake obtained with ammonium carbonate - bicarbonate solutions. The separation of thorium and uranium in the form of thorium concentrate from their carbonate complexes was achieved by different methods, including neutralization of solutions at pH = 6.7 by acid, addition of alkali at pH = 11.5, heating of solution at 100°C and processing of carbonate solution with steam under pressure in steel autoclaves. Processing of solutions of thorium and uranyl carbonate complexes in an autoclave with steam causes their decomposition. Complete recovery of thorium 99.8% and 98.4% uranium recovery in thorium concentrate was attained at 120°C and steam pressure 2 atm, within 10 min. Meanwhile, the recovery of lanthanides was low and did not exceed 1.1%. The thorium concentrate produced contains 67.82% Th, 4.6% U and 3.14% REE. All methods achieve complete separation of thorium and uranium from their carbonate solutions, but the first two methods are unfavourable for the industry due to the high cost of reagents and their inability to regenerate the ammonium carbonate. The decomposition of ammonium thorium and uranyl carbonate complexes with steam under pressure is recommended for industrial application for its simplicity and the ability to regenerate the ammonium carbonate.

Jan 1, 2004

By John Songstead

INTRODUCTION The Bunker Hill mine, located at Kellogg, ID, in the Coeur d'Alene mining district, has been a major pro¬ducer of lead-zinc-silver ore since 1887. Since its dis¬covery, it has produced over 25 401 171 t (28 million st) of ore from 20 to 25 veins and ore zones. The mine now covers an area of approximately 1.609 km (1 mile) in length and 0.8 km (1/2 mile) in width and extends from 1097 m (3600 ft) above sea level to 488 m (1600 ft) below sea level. Production is presently at a rate of 1542 t/d (1700 stpd). During 1965, a new stoping method, the Bunker Hill pillar system, was developed to enable the profitable mining of large, low-grade zinc ore bodies. The system was specifically designed to in¬corporate the Atlas Copco T26GH rubber-tired loaders. High productivities were achieved, and the method was adapted for mining the higher grade stopes where large timber square sets are utilized. This results in nearly 100% extraction. GEOLOGY The area encompassing the Bunker Hill mine lies immediately south of the Osburn fault, a major east-west striking, deep-seated strike slip fault which is the dominant structural feature in the Coeur d'Alene district. The Bunker Hill forms a series of veins and mineralized zones which occur as link structures, tension fractures, and breccia zones in folded, interbedded argillaceous quartzites of the Revett and St. Regis formations of the Precambrian belt series. The Rosco ore body is predominantly a zinc ore body above the Cate fault, which is presently known to occur from the 13 level. [elevation 488 m (1600 ft)] to the 1600 level [elevation 304 m (1000 ft) ]. These ore bodies are stringer zones with at least one dominant 1.8 to 4.5 m (6 to 15 ft) wide band of ore. They dip 0.09 to 0.26 rad (5° to 15°) steeper than the local 0.61 rad (35°) dip of the Cate fault, and also deviate 0.26 to 0.52 rad (15° to 30°) in strike from the Cate. Because of the flat dip and fractured weak hanging wall, normal cut-and-fill mining has not proven practical in this ore body. The mechanized timber methods described in the next section and the Bunker Hill pillar system are the mining methods successfully used. MINING METHODS While pillar stoping and mechanized cut-and-fill stop¬ing methods were obviously superior to the widely used timber stoping methods, as far as cost and productivity

Jan 1, 1982

By Livia da Silva Mello

O objetivo deste trabalho é demonstrar que a utilização da Metodologia Six Sigma e ferramentas de controle estatístico e gestão, são eficazes para controle processo, redução custos e estabilização de processos em geral. O coque dentre os custos variáveis do Circuito Polimetálicos, representa o maior custo para a unidade de Juiz de Fora e a oportunidade em otimizar sua utilização, foi identificada a partir do levantamento de dados e benchmark realizado. Observou-se que a média do consumo específico de coque grosso + coque fino no Forno Waelz, em 2012 era em média 360 Kg/t de pó de aciaria (PAE) tratado estava muito superior a outras empresas que utilizam a mesma tecnologia para tratamento de resíduos. Definiu-se então como meta do projeto atingir 210Kg/t PAE até 2014. Passando por todas as etapas de um projeto Six Sigma: Definir, Medir, Analisar, Melhorar e Controlar, todas as ações realizadas garantiram uma melhor performance da variável: consumo específico de coque, uma média acumulada em 2013 de 212,3 Kg/t PAE e 181,5 Kg/t PAE em 2014 proporcionando um custo evitado de R$ 11,6MM para a unidade.

Sep 25, 2017

By Batterham RJ

A 'research model' can be used to investigate cause and effect relations and generally improve the understanding of extractive metallurgical processes. As such, it is a useful research technique which complements the traditional methods of laboratory and plant measurement. The procedure of model development is iterative and involves observation of the process, hypothesis of phenomena, prediction using mathematical descriptions of the phenomena and comparison of predictions with real-world measurements. Lack of agreement of predictions with real-world measurements usually indicates an inadequacy in the hypotheses and necessitates revision. Experimentation has an integral role in the process of model development but its emphasis is different from that when experimentation alone is used to study processes. Since a process as a whole is investigated by using a model, experimentation is restricted to the study of specific phenomena to aid the description of these in the model, to the characterisation of the raw materials (for initial values of the model parameters) and to the measurement of physical and chemical constants required in the model equations. Similarly, plant measurements are made for the purpose of comparison with the model predictions not to establish cause and effect relations. This makes plant experimentation much simpler and cheaper'since most measurements-can be taken during normal operation.

Jan 1, 1984

By Michael Chender

INTRODUCTION The project financing described elsewhere in this book is available to major mining companies on the basis of a strong balance sheet, a significant equity position in a project of proven feasibility, and a demonstrated ability to bring ore deposits into production. "Junior" mining companies, which are most active in Canada, Australia, the US, and South Africa, by definition do not meet these criteria. In many cases, junior companies will need to raise money simply to cover the costs of acquiring and exploring potential deposits. In what follows we will look primarily at junior financing practices in the US and Canada, although the same general principles will apply in Australia and South Africa. The principal vehicles for junior mine company financing are limited partnerships, the private placement of securities and debentures, and public offering of securities, and property deals with stronger companies, in the form of leases, earn-ins and co-ventures. The cost (in terms of dollars or equity) and, to some extent, the applicability of using these difficult approaches varies with the stage of development of the property and with the corresponding degree of risk to the investor. Much junior company fund raising is, in fact, "interim" financing in that it allows the company to improve its properties and develop its assets to the stage where more favorable financing arrangements may become available. Companies will therefore often use several of the approaches described above during the development life of a specific property. LIMITED PARTNERSHIPS Limited partnerships and syndications are a popular way of structuring the initial private financing of mine developments because of their attractive tax consequences for the well-to-do investor. Costs of exploration and development can in many countries be passed through as deductions to the limited partners, who are thus able to gamble on a possible windfall at little real cost. In addition to private Canadian funds, much German money flowed into Canadian exploration ventures on this basis, but stopped in 1982 due to economic conditions in West Germany. In the US, recent regulations have, in the great majority of cases, taken away the ability to "shelter" income in mining limited partnerships. Deductions taken by the individual investor cannot exceed the amount of money he actually has at risk. Nevertheless, the allowable deductions are still attractive and some of the major mining companies are now beginning to look at limited partnerships as a vehicle for attracting additional exploration funding. Ranchers Exploration and Development has successfully put together several drilling funds on this basis. THE PRIVATE PLACEMENT Initial funding for the acquisition and preliminary exploration of prospects is often accomplished through a private placement of unregistered securities or, where it is not a problem to carry debt on the statement, by a private placement sale of debentures. A fledgling company wishing to do a public offering may well be advised by an underwriter to accomplish a small private placement as a precondition of the larger offering. In this way, the sale of the registered securities is not inhibited by the company starting out with a debt-ridden balance sheet and no demonstrated ability to secure the additional financing generally necessary beyond the proceeds of that offering. In the US, the securities offered in a private placement are not registered with the Securities and Exchange Commission (S.E.C.) but are restricted as to their resale, and could be further restricted by a underwriting agreement

Jan 1, 1985

By R. Haecker, S. Bajic, R. Thorpe, A. Palko, M. Kalstrom

"Historically, mineral processors have used inferential data like plant instrumentation, assays, and grind sizes to monitor the performance of their plants. The ability to monitor the minerals themselves on a daily basis has eluded all but the very largest and richest of operations. The advent of a new generation of compact, robust, and user-friendly SEM-based automated mineralogy systems looks set to accomplish this, aiming to bring daily mineral monitoring of plant performance within the reach of all mills from mid-size upwards. This paper describes the use of this machine at Greens Creek Mine, a 2.5 ktpd Ag-Au-Pb-Zn operation with a complex flotation flowsheet. During the trial, the machine provided turnaround from sample collection to reporting averaging 24-36 h for key daily samples. All equipment was located within the compact mill, and proved highly reliable despite the challenging environment. Turnaround time was fast enough for metallurgists to understand, and, where possible, respond to ore and process changes while they were still happening. The plethora of data generated was filtered to a simple report whereby mill management could quickly absorb key daily mineral-based performance indicators. This paper will describe how the data was used to understand the key drivers behind metallurgical efficiency at Greens Creek, and how metallurgists began using the information to enhance daily mill performance."

Jan 1, 2014

By V. Svalbonas

Everybody has an opinion what the quality of a grinding mill head casting should be, yet extremely few take the time, or get the opportunity, to compare their opinions against fitness-for-purpose data. The real question is not how flawless the casting should/could be, but rather how long will ?this? casting survive in operation. To validate an opinion on this topic one needs either extensive historical data, or comprehensive experimental data, or preferably, a combination of both. The same data can also be used to establish the conservativeness, or lack thereof, of analytical prediction methods.

Jan 1, 2009

By K. K. Kohli, S. S. Peng, R. E. Thill

Introduction Since the adoption of the Surface Mining Reclamation and Control Act of 1977, which mandates that surface subsidence be an intergral part of the underground coal mine design, there has been a sudden rise of demand on guidelines for minimizing surface subsidence and its associated structural damages. Unfortunately there is no sufficient amount of systematic subsidence data to fill such a gap, although considerable research has been devoted to the subsidence induced damages of surface structures in the past. However, it was said that many surface subsidence surveys have been performed and monitored by coal companies during the past twenty years, and that it will be a great source of information for subsidence engineering design if they can be collected and assembled together. An effort was therefore initiated in the Department of Mining Engineering, West Virginia University, under contract with the U. S. Bureau of Mines in December 1978 to contact each individual coal company in the Northern Appalachian Coal Field for any surface subsidence survey data. After 10 months' survey, the data collected include: 17 longwall panels and 2 room and pillar sections. The data in each panel and section cover the complete set of subsidence survey raw data, underground mine layout maps, surface topo maps, geological loggings showing the stratigraphic sequences and thickness of the overburden, and if available, locations and types of surface structures. On-site visits were followed to study the surface terraines and structures. Interviews were conducted with the owners of the surface structures in most cases about, if any, the history and characteristics of damages. Most subsidence surveys started with the first panel and ended with the second or sometimes, but rarely, the third panel. The first panel may be located in a virgin area but frequently it was adjacent to (on the tailentry side) a mined-out room and pillar section. It must be noted that all of the subsidence data is restricted only to the amount of vertical subsidence and that the horizontal displacement measurement was completely ignored. Primarily due to the fact that vertical subsidence is the most striking feature in a subsidence trough, which is mistakenly considered to be the only critical contributor to surface structural damages, and that a horizontal displacement survey is much more complicated and time-consuming.

Jan 1, 1981

By H. A. Thorne

This paper describing the mining practices at the Chino mines at Santa Rita, Grant County, N. Mex., is one of a series being prepared by the Bureau of Mines on mining practices, methods, and costs in the various mining districts of the United States. The Nevada Consolidated Copper Co., Chino mine's, operates an open-cut copper mine at Santa Rita, Central mining district, Grant County, N. Mex. This mine is located about 16 miles east and slightly north of Silver City, the county seat. The ore is-transported in standard railroad cars by the Atchison, Topeka & Santa Fe Railway Co., approximately 10 miles to Hurley where it is milled. The concentrated are shipped approximately l'70 miles over the same railroad to the smelter of the American Smelting and Refining Co., at El Paso, Tex. (fig. 1)

Jan 1, 1931

THE paper on "Cross-cuts in Coal Mining," by J. J. Rutledge (published in MINING AND METAL-LURGY, February, 1927, p. 64) was brought up for discussion at the annual meeting, where the follow-ing comments were made T. D. Thomas (Lehigh Coal & Navigation Co., Lansford, Pa.) : This question has caused me a lot of worry, not in the particular district in which I am, but throughout other districts. There are always several angles to consider. If you are in a hurry to push development work, you might increase the distance between cross-cuts from 60 to 350 ft., but if you have a 40-ft. chain pillar every 60 ft. it will cut down your entry driving a whole lot. Looking at it from the ventilation angle, I agree that too many cross-cuts in entries are bad things. You have a tremendous amount of leakage, and I have seen currents starting out with 45,000 cu. ft., and after passing about 30 or 40 cross-cuts the current has dwindled down to about 18,000 or 15;000 cu. ft. The result is that the question of putting in auxiliary fans is raised. That involves several points into which I do not want to go too far, but I am in favor of not getting in too many cross-cuts, putting them in only where they are necessary: I think the state mining laws are wrong in a number of places on that, and that when you finish with a cross-cut it should be in the room. It should be well sealed on an entry. There are several ways of tightening up the cross-cuts so as not to have the great amount of leakage and wastage of: air that we now have. 'I prefer tile stopping; other people prefer cement or brick, but there is a big fac-tor to all mines, saving the mine. I checked up on the number of fans in the anthracite region and found there are 651. That was derived from the state report of 1921, and it enabled me to compute from the power the weight of the air. In the anthracite region of Pennsylvania we put in 9 tons of air to every ton of coal we get out. Tracing that back again and taking the Government's figures which they made some time ago, I found but 20 per cent of the air got to the faces where it was actually needed. That is a tremendous big loss and shows a possibility for saving, money for the various coal companies. Chairman Rice: I think what Mr. Thomas refers to was an investigation by R. Y. Williams, of the Bureau of Mines in Illinois, where a study was made of 100 typical mines, and, speaking off-hand, my recollection is that we found as little as 15 per cent of air reached the faces in one of the mines and another was as much as 50. That seems to be a reflection on the type of stoppings and general ventilation scheme.

Jan 3, 1927

By E. Berrezueta

Automatic digital phase imaging should yield unbiased and representative characterizations of gold ores. However, this is not a simple tusk due to low gold grade, fine grain size, possible complex mineralogy, nugget effect, etc. Using the same sections of a gold-rich ore, a critical test was performed using an optical microscope (OM) and an electron microscope (EM). In general, the two methods are consistent and useful for ore processing. There are some minor differences, such as the detection of very fine gold grains is enhanced by EM. Key words: Digital imaging, Gold ores, Mineralogy, Electron microscopy, Optical microscopy

Jan 1, 2003

By David Newman

"Horizontal stress can have a profound effect on the stability of an underground limestone mine. The presence of horizontal stress is usually determined once the mine has been developed and the orientation of headers and crosscuts are well established. Multiple attempts are typically made to control roof falls without re-orienting the mine. Once the decision has been made to change the orientation, pillar centers, mine opening widths, and the question of how to determine the correct orientation must be answered.A case history is presented to illustrate how geologic structure, ground conditions and roof falls in adjacent mines, the World Stress Map (Heidbach et al., 2016), in-mine measurement of “cutter” roof orientation, the orientation of strata offset (cats eyes) within borescope holes, and the diametral deviation method of determining horizontal strain from drill core were used to establish the most likely range of horizontal stress.The main headers were re-orientated in a direction parallel to the median of the range of horizontal stress. The crosscuts were angled 60° to the headers to avoid being perpendicular to the horizontal stress direction. Pillar centers and opening widths were increased in the favorable stress direction of the mains and decreased in the less favorable crosscut orientation. The major principal horizontal stress magnitude was estimated using the strain measurements from the diametral deviation method and elastic modulus obtained through testing.INTRODUCTIONOver the past decade, there has been a significant increase in the number of underground stone mining operations in the United States. As stripping ratios at surface quarries become uneconomical and reach the extent of the mineral boundary, coupled with the encroachment of urban development on previously rural mining operations, the remaining mine reserves are best accessed through underground development.Although the majority of underground limestone mines in the Midwest are in relatively flat lying deposits with minimal geologic structure, many Appalachian mines are in folded and faulted environments. Tectonic horizontal stresses associated with multiple orogenic episodes are locked in the formation and are released as the underground mine is developed.A common misconception is that horizontal stress impacts are more prevalent at shallow depths where the ratio of horizontal to vertical stress may be high. However, field observations and academic research indicates that horizontal stress conditions may be encountered at any depth due to the tectonic compression of the limestone formation (Esterhuizen et al., 2007; Dolinar and Esterhuizen, 2007; Iannacchione et al., 2003; Slaker, Murphy, and Miller, 2017; Kuhnhein and Ramer, 2004). This paper outlines mine design and layout guidelines for the mitigation of horizontal stress impacts on underground stone mining operations through a case history example. This approach to mine planning and the ability to anticipate horizontal stress can significantly improve future production of multiple levels (Newman and Newman, 2019). As underground stone production continues at deeper depths and in more geologically and geometrically complex mining conditions, an emphasis on ground control and the anticipation of horizontal stress can provide safer and more productive single and multiple level mining operations."

Jan 1, 2019

By F. Lambert

"Amok Ltd./Cluff Mining operates a uranium mine at Cluff Lake in northern Saskatchewan. The project consists of one open pit and one underground mining operation along with a full-scale milling installation.The underground stoping operations are of the narrow vein type and are done between two levels 50 m apart. The mining method is undercut with concrete backfilling. Cuts are 3.5 m in height and can be as narrow as 1.4 m in width.Stoping operations are mechanized utilizing a CT-500E electric Microscoop marketed in Canada by Teledyne. The machine is only 85 cm in width and does all the mucking in stopes. Ore passes are provided in stope roughly every 40 m to 50 m.This paper describes the utilization of the CT-500E Microscoop in the company's underground operations and provides performance data related to the experience.IntroductionThe Amok Ltd ./Cluff Mining operation is located in the northwestern corner of Saskatchewan. The project started in 1980 with open pit mining and milling operations. In 1983, an underground mining operation began production . Today, the Amok Ltd./Cluff Mining installation produces 800 tonnes of uranium per year , which originates from both the open pit and the underground mine at about the same proportion."

Jan 1, 1990

By N. Tounsi

The use of analytical modeling of continuous chip formation in conjunction with orthogonal cutting experiments was presented in the open literature to identify the coefficients of material constitutive equation within the practical range of stress, strain, strain rate, and temperature encountered in metal cutting. Identification of reliable constitutive data was hampered by a lack of a reliable model for the prediction of the primary shear zone thickness that affects directly the effective strain rate field. An original analytical model to determine the primary shear zone thickness is proposed in this paper. It is based on the mechanics governing the material flow in the primary shear zone. Based on the distribution of the hydrostatic pressure and the forces measured from orthogonal cutting tests, the model that describes the thickness of the primary shear zone is derived. To validate the model, FE simulations of chip formation using DEFORM3D were carried out for different materials and cutting conditions. The results of the analytical model are in reasonable agreement with FEM results.

Jan 1, 2006

By L. E. Krys, K. D. Harrison, C. G. Anderson

Since 1984, nitrogen-species catalyzed pressure leaching has been utilized at Sunshine Mining and Refining Company for the recovery of precious metals from a refractory sulfide concentrate. The process operates without the use of cyanide. The plant is now the only industrial-scale commercial application of this technology. Since the inception of the process, changes have been implemented to improve efficiencies and throughputs. Two of these changes, the replacement of nitric acid by sodium nitrite and a concentrate regrind, have recently been implemented. This paper discusses the development and potential mechanisms involved in these recently patented plant-process changes. A companion publication (Anderson et al., 1996) covers the plant integration and potential applicability of the technology.

Jan 1, 1997

By R. K. Singhal

Optimization of a load-haul system for a surface mine involves two processes. The first is proper selection of mining equipment compatible with the minesite job specifications and the second is an efficient utilization of this equipment. All things being equal optimal productivity and cost is achieved when the capacity of the hauling equipment is matched at all times with that of the loading equipment.

Jan 1, 1986

By A. Pawelczyk, D. Hreniak, E. Zych, W. Strek, K. Grabas, A. Ostrowski

"Nowadays recycling became an important rare earth elements (REE) source, which allows to reduce their demand for extraction from natural deposits. At present, the used fluorescent lamps and old type TV or computer monitors kinescopes are selectively collected and undergo processing in the system of recycling. It has been estimated, that utilization of such waste would be sufficient to cover the REE demand for the next 5-8 years. In the developed process, the luminophores were separated from the electronic and electronic waste materials, and processed by hydrometallurgical methods to obtain concentrated REE in form of oxides. INTRODUCTIONInternational Union of Pure and Applied Chemistry (IUPAC) defines the rare earths as a set of seventeen chemical elements, specifically the fifteen lanthanides plus scandium and yttrium. They are considered the most important indicators of the developed technologies and techniques. Rare earths are used, amongst others, for the production of magnetic and superconducting materials, ceramics, lighting, catalytic converters, advanced electronics and alloys. The demand for RE continually increases, similarly to many other primary raw materials. Globalization, the growing demand for limited resources of raw materials, the policy of the countries controlling the raw material market and the economic crisis became a spur for new programs of socio-economic development of the European Union (EU), with particular regard to EU safety for commodities in intermediary as well as long-term horizons (COM 2008), COM 2011).EU countries import most of metallic and chemical raw materials important for their economy. In 2008 a detailed program named Raw Material Initiative was announced. The increase in demand for most raw materials having special importance for the development of technology, and access to of raw materials security of supply affect the future economies of the UE member states and other developed countries."

Jan 1, 2012

By Rong Fan, Roger Smart, Ning Xu

As part of an Australian Research Council project with Newmont and Newcrest mining companies studying the influence of clay minerals on rheology, hydrodynamics and flotation response, the cryo-SEM technique has been used to capture and image the clay (low crystallinity kaolinite Q38) aggregate structures in the flotation pulp immediately after collector and before frother addition. Samples were also collected from the earliest froth phase and the froth overflow corresponding to early and later concentrates. In this technique, a copper tube is filled with the sample during operation of the cell. The tube is immediately plunged into liquid nitrogen vitrifying the water phase before it can crystallise as ice thereby retaining the structures without volume or other physical change. After sublimation of the vitrified water surface, the aggregate structures are revealed and can be compared between pulp and froth phases from clays in different feeds and flotation conditions. The images from both low-clay ore and ore with clay content reveal various levels of aggregation as predominantly edge-edge connected aggregates similar to those found in our previous studies of high-clay tailings. For the samples from the ore with clay content, more extensive edge-edge clay strings are found in the early froth phase as compared to exiting froth overflow and the pulp phase with short edge-edge connected strings. It is suggested that the strings of clay particles result from edge-edge aggregation in the Plateau borders of the bubbles before breakage during sampling and the more extensive edge-edge aggregation in early froth phase is induced by crowding in the bubble borders. The clay strings collected into the overflow concentrate are almost all broken up compared with the Froth before drop-back. The implications for entrainment and entrapment mechanisms of gangue capture in froth will be discussed.

Jan 1, 2014

By A G. Guinea

If you were reading this article in a newspaper or similar in the 1800s, you would know that the world was firmly in the grip of the Industrial Revolution. You might have been one of the families that decided that an agriculturally based existence was no longer for you, and that the promise of a factory job was more appealing and more secure. And it was. Financially at least. Not so much from a workplace safety perspective.

May 5, 2022

Discussion of the paper Of NOEL CUNNINGHAM, presented at the New York meeting, February, 1915, and printed in Bulletin No. 99, March, 1915, pp. 601 to 608. C. H. POIRIER, New York, N. Y. (communication to the Secretary*). -Mr. Cunningham's paper, written from the standpoint of a stamp advocate, while commenting more or less favorably upon the installation of ball mills in the Vipond plant, does not, in my opinion, give as much emphasis to the comparatively new departure as the installation of ball mills in the place of stamps justifies. This discussion is based upon my personal and intimate practical work for several years with stamp mills, and for the past three years with Hardinge ball and pebble mills. The fact that the Vipond mine contains about equal quantities of the A and B classes of ore mentioned by Air. Cunningham, and the further fact that I have had a most intimate knowledge of the working of both classes of ore in the Porcupine district in stamp mills and ball mills, justifies upholding my final decision to use ball mills in the place of stamps, and defends my present further action in now increasing the present Vipond capacity by the addition of another 6-ft. Hardinge ball mill, in which action the directors of my company concur. This is one of the strongest evidences I can possibly offer in substantiation of my opinion that the ball mill exceeds the efficiency of the stamp, both in metallurgical and mechanical economy. It is hardly fair to compare a 100-ton per clay plant with a mill handling several times this amount, yet it is my belief that the cost per ton. of grinding in the ball mill is far less than that of any stamp mill in the district, where capacities run up to 400 tons per clay.

Jan 5, 1915