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By Gene E. McClelland

4.1 INTRODUCTION Metallurgical testing is required on any ore, waste or tailing material before amenability to heap leaching treatment can be accurately determined. The amount of testing necessary to determine and optimize heap leach amenability and conditions for any feed material is determined by the ore type, grade, size of deposit, and the overall financial commitment a particular company is willing to make. It is very easy to either "under-test" or "over-test" a particular deposit or feed material. A good heap leach testing program will provide the necessary design information without "bogging" down in too much detail. The three basic stages of ore testing include: • Preliminary--bottle roll tests and small column percolation leach tests; • Detailed--larger column tests, different feed sizes, and feed size optimization; and • Pilot-Scale--Column or field heap. The following subchapters describe the stages of heap leach testing necessary to put a viable property into production. 4.2 PRELIMINARY METALLURGICAL TESTING The two types of preliminary tests that can be undertaken include bottle roll or cyanide agitation tests and small column leach tests. Each of these is described below, along with information about what the test results provide in terms of furthering knowledge of ore qualities. 4.2.1 Bottle Roll Tests The first step in a heap leach testing program is preliminary bottle roll tests at a relatively coarse feed size to determine the ore's leachability. Bottle roll tests are usually conducted on reverse circulation drill cuttings samples (= 1/4 inch (6 mm) in size). Bottle roll tests provide initial information about precious metal recovery, recovery rate, and reagent requirements. The recovery results are to be considered maximums because attrition grinding creates fines and liberates recoverable values that would not be liberated from the material during a static leach. Bottle roll tests can be conducted on up to 25 lb (11 kg) ore charges of up to two inches (50 mm) in size. However, the coarser the feed the more attrition grinding occurs during rolling.

Jan 1, 1988

By S Jahn, M Noel, E M. Rykaart, M Pau

Three soil cover test areas were constructed on waste rock backfilled into the Lichtenberg Pit, near Ronneburg Germany. A fourth, uncovered area was included as a control. Each test area measures 50 m by 65 m, and was constructed using full-scale equipment and construction practices. Extensive material sampling and testing was included as part of the construction. Devices were installed in each plot to monitor meteorology, infiltration, run-off, interflow, soil moisture, soil temperature, and soil pore gases. Boreholes were completed in each area and instrumented for temperature, pressure and pore gas sampling to a depth of approximately 60 m. Data from the monitoring instruments have been collected since July 2000, and have been comprehensively analysed and modelled on two occasions. The paper presents an overview of the test area design and instrumentation and the results of the two comprehensive data reviews. The reliability of the various monitoring methods is discussed and experience with several innovative methods is reviewed. The difficulties encountered in modelling the data set using common soil physical models are discussed.

Jan 1, 2003

By V. B. Achanti

Reliability of the compressive strength of a coal seam determined in the laboratory is often subjected to debate. Effects of the coal seam's inherent characteristics, specimen preparation, testing procedure, testing condition, and a number of tests often result in drastic variation of the strength data. This paper deals with the development of a testing procedure for determination of coal seam compressive strength in the laboratory. Coal samples from two different coal seams were tested. First, the inherent characteristics of each coal seam such as coal structure, Hardgrove Orindability Index (HOI), Slake Durability Index, proximate analysis, and mechanical properties namely Young's modulus and Poisson's ratio were determined to categorize them in terms of their characteristic severity liable to produce variable strength data in typical laboratory tests. Second, two commonly used laboratory specimen shapes namely; cylindrical and cubical, were tested to determine which shape produced the least variation of data and reproducible strength values. Third, four loading rates within the static testing range (Le. 0.007 MPa/s (1.0 psi/sec), 0.07 MPa/s (10 psi/sec), 0.34 MPa/s (50 psi/sec), and 0.7 MPa/s (100 psi/sec)) were used to determine an ideal loading rate. Finally, the number of test samples required to produce strength data within the acceptable standard deviation, considering coal seam characteristics were established.

Jan 1, 1996

By Tim McMahon

"A slurry is any combination of liquids and solids where solids make up more than 10 percent of the mixture. Mining operations create various types of slurries from processes such as dewatering, bitumen extraction in oil sands, concentrator plants, milling operations, tailings, lime addition and so on. The mines then transport these slurries through pipelines (Fig. 1).Slurry valves are used when the mine needs to transport ore a long distance and there are no other viable transportation methods, such as roads or railroads.Severe service valves must be used in slurry applications and they must be tested to ensure reliability. This article describes how Emerson designs and tests its Fisher valves for use in mining slurry applications.Slurry pipeline valvesWithin a slurry pipeline system, valves are required as part of the pumping stations, choking stations and isolation stations. There may be multiple pumping stations depending on the length of the pipeline or the terrain it crosses. Choking stations are used to reduce the velocity and the pressure in the pipeline, either before a pumping station or at the end of the pipeline, and to ensure the pipeline does not slack (remains full and pressurized). Isolation stations exist so that a pig (a device sent through a pipeline to clean or inspect the pipe) can be inserted or removed from the pipeline.Typical valves used in a slurry pipeline are severe service ball valves. The valves use floating balls that are held between the seats and are not pinned or permanently attached to the shaft that rotates the ball. The inside diameter of the ball typically matches the pipeline inside diameter, enabling the pipeline to be cleaned or inspected with a pig.They can be built to accommodate the high pressures required for the typical slurry pipeline. These pressures can require up to ASME Class 2500 valves and flanges. The valves can get qlarge, up to NPS 36 inches.Specialized segmented ball valves and slurry knife gate valves are also used in some slurry applications when pressures are lower, in the ASME Class 150-300 range."

Sep 1, 2019

By E. H. Kelton

THE purposes of this paper are to describe the use of adjustable cut and draw tools as a control test of drawing properties and to point out that no other well-known test or combination of tests determines this quality in zinc and zinc alloys. Rolled zinc has been used for making drawn articles, particularly battery cans, for many years. The development of rolling treatments satisfactory for, these purposes followed the usual course of trial and error experimentation depending upon cooperation with customers to determine what type of material was suitable. A quick test of drawing quality was highly desirable, of course. Scleroscope hardness and temper,1 having no apparent relation to drawing quality, were used simply to check the duplication of rolling treatment and grade of metal. The dynamic ductility1 test, on the other hand, was believed to be so like the drawing operation as to provide a reliable index and came to be taken as the criterion of good drawing properties. Faith in this test was strengthened by the fact that metal having the highest ductility was more satisfactory for operations, such as the manufacture of battery cups, that required several redraws. No distinction was made at that time in specifying metal as to whether it was to be subjected to simple cut and draw, redrawing or forming operations. It developed, however, that in some grades of metal the highest ductility did not coincide with the most satisfactory quality when the material was used for a single draw.

Jan 1, 1934

By S. Gomez, P. A. Bebswa, A. N. Mwale

"The research aimed at improving the way screen performance analysis is conducted using a model that accounts for most feed and design parameters in its formulation. Thus, the aim was to validate the fine screen model that was developed at the Centre for Minerals Research (CMR) unit at the University of Cape Town. Fine wet screening is increasingly becoming an important application in fine grinding operations. Minera Saucito, a lead-zinc Mexican mine has replaced hydrocyclones with eight stacks of five decker derrick screens to close the ball mill in their concentrator plant. The five decker stacks have improved the overall plant throughput by 20% and have had the ball mill circulating load reduced considerably. As a continuous plant optimization process, a number of surveys were carried out to assess the performance of the 75 µm panel aperture installed screens. The surveys were conducted at seven different feed rates to the entire nest of screens to collect performance data. Using the fine screen model to analyze the results, it is found that as the feed rate increase, the sharpness of separation reduces. The CMR fine screen model was fitted to these results. The model fits the plant data with good accuracy. Simulated results based on this model are also presented.INTRODUCTION The potential of high frequency vibrating screens has long been identified as an alternative to hydrocyclones in grinding applications (Rogers and Brame, 1985). However, high frequency vibrating screens have had two main disadvantages, low capacity and high wear rates (Kelley and Mckeon, 2005; Teknikk, 2009). Current vibrating screen technology overcomes these challenges by multiple deck screen design and use of wear resistant urethane materials for panel construction (Kelley, 2007; Valine and Wennen, 2002). For a example, the Derrick screen’s material of construction is a tensionable urethane that provide high open area ranging between 35 to 45% with considerably reduced blinding (Valine and Wennen, 2002). Thus, there has been an increased uptake by the mining industry in the use of wet fine vibrating screens closing the ball mill as the final classification stage in the comminution circuit (Barkhuysen et al., 2010; Frausto, Ballantyne et al. 2017; Pelevin and Lazebnaya, 2009; Teknikk, 2009). Even though there is a number of models in existence, none of these models adequately predict the performance of high frequency vibrating screens (Karra, 1979; Rogers, 1982; Subasinghe et al., 1990; Trumic and Magdalinovic, 2011). Recently Mwale et al., (2016) developed a model for predicting the performance of high frequency vibrating screens using the partition curve properties. The input parameters of the model include screen open area (??) in m2, tonnage feed rate (????) (tph) and the weight fraction of solids (??) in the feed for a given panel aperture size. The model was developed based on data collected from a single deck industrial size derrick screen, in a pilot setup. The work presented in this paper is an attempt to test this model using data collected from Minera Saucito concentrator, an industrial plant whose comminution circuit is shown in Figure."

Jan 1, 2018

By F. Calizaya, S. Bhattacharyya

"INTRODUCTION Mechanized underground mines often suffer from noise overexposure. Noise levels are usually above the Permissible Exposure Limit (PEL) where underground fans are used. Sound levels in active workings can reach 121 dB(A), especially when fans are not equipped with silencers. Use of silencers seldom ensure PEL for various reasons. Overexposure of noise induces permanent hearing loss among mine workers. Recent field studies by a NIOSH-funded research project at six coal and non-coal mines revalidated the findings. The University of Utah has undertaken laboratory studies to reduce fan noise at the source. A new silencer prototype with varying noise dampening material has been designed and tested. The silencer and an associated extension which can be repacked with different dampening materials were used in various configurations. Attempts were made to simulate field conditions where installations are quick and not perfect. The test results are presented here. NOISE IN UNDERGROUND MINES Noise induced hearing loss (NIHL) is a chronic problem in the mining industry. In spite of regulations being in place and elaborate hearing protection programs under way, hearing loss is prevalent among the mine workers (Bise, 2001). All production and support machinery in mining generate loud noise often beyond the approved exposure level. Researchers in the U.S. have identified auxiliary fans as one of the major sources of noise that can create noise exposure levels up to 121 dB(A), which is one of the highest in the mining operation (Bauer, 2006). Studies have demonstrated substantial reduction of noise level by using silencers. Adequate fan selection and proper utilization of silencers in auxiliary fans have great potential of abating the problem. In hard rock mines, auxiliary fans are used in blower configuration to ventilate development headings and large production stopes, and also to ventilate underground shops, crushers, conveyor transfer points, etc. Typical duct diameters in hard rock mines vary from 0.91 m to 1.21 m. Silencers are often omitted for cost reduction. In coal mines auxiliary fans are used in exhaust configuration with rigid ducts 0.61- 0.76 m in diameter (Hagood, 1982 and Moreby, 2009) to ventilate working faces in gate-roads and main entry developments. Sometimes, stone dusters are added at the discharge end to dust the roof, ribs and floor. AUXILIARY FANS AND SILENCERS Auxiliary fans are relatively smaller in size than the main fans and often have high rotational speeds (1800 -3000 rpm). Fans are selected based on pressure-quantity requirements and space restrictions only. Noise emissions are rarely considered during the selection stage. Installation of fans, ducts and other accessories is mainly based on best practices, which often do not include noise control. As a result, the operation of an auxiliary or local ventilation system normally produces excessive noise."

Jan 1, 2018

By Jurgen Hahn

The paper reports on both, the design and decision making for the filters in a backfill plant in Europe as well as more then 10 years of operation and maintenance experience of the vacuum disc filters installed. It begins with the first step, the filter sizing based on a sample provided by the customer, followed by the commissioning of the filter units and reports on the development of the filter performance during the following 10 years of operation. Based on the physical properties of the sample and the process targets of the client for the backfill plant, the paper shows the logic steps taken in the laboratory to ensure the target moisture, determine the required filtration area and filter size as well as the selection of the ancillary units and the formulation of the performance guarantee. The paper discusses some issues with filter operation during the commissioning phase and the actions taken. Finally, the paper concludes by highlighting the gradual change over the more than 10 years of operation and how this change affected filter performance and operating costs.

Feb 1, 2024

R.. B. T. KILIANI, New York, N. Y.-I do not care to discuss Mr. Taggart's paper in the light of theory, as that has been very well done by Prof. Bell,1 but I should like to criticize some of his conclusions, in the light of actual operating practice at plants all over the country. 1. Mr. Taggart's first conclusion is that in crushing average ore, the character of the gangue has little effect on the efficiency of the mill. This, I believe, is not in accordance with the usual practice, since in crushing a hard ore the capacity will be much reduced below what it would be with a softer ore, while the power consumed will be practically independent of the character of the ore, being proportional only, to the load of ore and balls in the mill. 2. Mr. Taggart's second criticism is that the Hardinge mill is not suitable for grinding soft, tough material. In answer to this I might mention that the mill is being used for grinding tough, dnctile material, such as metallic aluminum, and also for grinding licorice root. 3. He says that the ball-mill works more efficiently on material of intermediate size, say 1/2 to 3/4 in., than on either coarser or finer feed.. This is true as to coarser feed. For the most efficient work, I believe that a ball-mill should be fed with material not coarser than 1 1/2 in.; it' will handle material up to 3 and even 4 in., but the reduction from 3 or 4 in. to 1 1/2 in. can be done much more cheaply and efficiently by rolls or disk crushers than in the ball-mill. 4. As to Mr. Taggart's fourth conclusion, that a greater ratio of reduction can be expected with feed of an intermediate size than with a coarse feed, I have not enough information to express an opinion. 5. His next conclusion is that steel balls are much more efficient crushing media than pebbles. Steel balls are undoubtedly more efficient for crushing coarse feed. On fine material they are also more efficient as to tons per horsepower crushed to 10-mesh, but on fine material I think it will be found that flint pebbles are cheaper than cast-iron balls, per ton of ore, although there will be a saving in power per ton by using cast iron instead of flint. The increased cost of crushing with cast iron will be due to the higher cost of iron at the present time. 6. Mr. Taggart's sixth conclusion coincides with present practice, that steel balls will grind as fine or finer than pebbles when working on the same feed.

Jan 1, 1918

JOHN W. BELL, *Montreal, Quebec, Canada (communication to the Secretary?). The test results in Mr. Taggart's paper will, I am sure, be recognized as a notable contribution, and of great assistance in the study of the performance of the Hardinge mill. I regret, however, being obliged to note that Mr. Taggart still retains. such confidence in the Kick-Stadler method of computing the ?relative mechanical efficiency" of crushing machines. The Rittinger-Kick graph submitted by Mr. Gates and the tests made at McGill University disclosed precisely the same fundamental defect in the Kick-Stadler theory. Consequently, I have been obliged to recalculate in terms of Rittinger surface units the results obtained in the 28 rock-crushing tests cited by Mr. Taggart, in order to find- out what the relative efficiencies really were. In order to show the large discrepancies between the Stadler and Rittinger R. M. R's, the most, efficient result disclosed by each method is represented by the number 100, and the R.. M. E.'s for the other tests have been recalculated on this basis. The results will be found in Table 1. Personally, I look forward to the time when we shall cease to talk about "relative mechanical efficiency" and merely refer to the "efficiency" of a crusher. All that is required to accomplish this is to agree on a standard method for determining the "crushing constant" of a given rock and a standard method for calculating the efficiency. The figures in the fourth column of Table 1 have been derived by assuming a constant of 2,000 for the quartzite crushed in the Yale tests. The Stadler method sometimes indicates changes in efficiency produced by, changes in operating conditions, as I pointed out in a paper describing rock-crushing tests made at McGill University. It is, however, not enough to determine that certain changes increase or decrease efficiency; surely it is equally important to determine the magnitude of these variations. By examination of Mr. Taggart's results, I have been obliged to conclude that the size of feed and amount of reduction greatly influence the Stadler R. M. E. figures, that they are positively misleading. It should be mentioned that since the majority of the tests have been made at the least efficient feed rates, and since, moreover, it is one of the evidently very important factors affecting efficiency, it is possible that different results might be obtained by a high-tonnage feed series, and that

Jan 8, 1917

Discussion of the paper of H. M. WARREN, A. S. BIESECEKER and E. J. POWELL, presented at the New York meeting, February, 1916, and printed in Bulletin No. 110, February, 1916, pp. 181 to 193. R.. V. NORRIS, Wilkes-Barre, Pa.-For many years the power requirements of breakers designed in the Anthracite. Region have been based on calculations made from indicator diagrams taken during operation, with various sections of machinery idle; these, while giving reasonably accurate figures, gave no intimation of the peak loads which have been shown so clearly in the paper. The high-speed flywheel for breaker rolls is new and shows a remarkable saving in peak power required, besides eliminating the stalling of the rolls from overload. The figures given are so far in advance of anything previously published that they will undoubtedly be used as a basis for future breaker design. It is to be hoped that the authors will continue this investigation and extend their paper by a description of the motors found best suited for this work. WILLIAM KENT, Montclair, N. J.-I notice on p. 187 reference is made to one of the difficulties being the starting torque, and it is proposed to use roller or ball bearings in order to decrease the high starting torque. I suggest that. before the roller or ball bearings are put in, an investigation be made as to the amount of the starting torque, as shown by wattmeter measurements and as to what the starting torque ought to be, theoretically, according to the energy formula; that is, how much starting torque is required to accelerate the rotating mass in a given number of seconds up to full speed. Having secured this information it may be found the amount to be saved by roller bearings is not very great. If it appears that roller bearings will not greatly decrease the starting torque, the next thing to be done is to have a special design of motor in which there is a field that can be made very strong at the start, by the use of extra poles or other means, and the next thing that may be done is to increase the speed from 10,000 r.p.m. to 25,000, which can be done with wire-wound flywheels, especially if the wires are made of vanadium steel.

Jan 5, 1916

By Robert A. Macinnes, Peter Moon, John P. Pappone

"This paper, in presenting the results of the application of the assessment centre method at Texasgulf Canada Ltd., illustrates a novel "" in-use"" technique for manpower training in the mining industry.IntroductionMining history is full of examples of what goes wrong when human judgment fails-disasters, floodings, loss of life and property. We must, therefore, assume the importance of selecting competent people for supervisory responsibility. This article de scribes a method for assessing supervisory ability, its first application in Canadian mining and the result s obtained over the past six years. It is known as the assessment centre method."

Jan 1, 1981

By A. Dave Mackintosh

In 2001, at the CIM AGM in Quebec, a paper discussing poor ground conditions in a newly opened area at Agrium?s Vanscoy Potash Operation?s, suggested load transfer around old workings as a possible reason for the early room failure. High closure rates are expected in deeper regions however the rapid failure of walls immediately behind the face resulted in protective guards being mounted on and behind the borer. The high closure and early rib failure continued well past any reasonable distance to be explained by load transfer around old workings and investigations continued into possible reasons other than simply depth. Detailed investigations into the mineralogy and crystal fabric of the ore zone provided one possibility, which combined with a changed borer cutting profile are now believed to have contributed greatly to the poor conditions.

Apr 1, 2005

By S Hapugoda, J R. Manuel, M J. Peterson, A Poliakov, E Donskoi

The occurrence and deportment of manganese in a number of ferromanganese and Mn-bearing iron ore samples from supergene-upgraded deposits, as well as from magnetite banded iron formation (BIF) and magnetite skarn deposits, was characterised in order to provide a basis for improved understanding of the processing characteristics of different ore types and investigate the potential for development of a robust geometallurgical classification for Mn-oxide ores. An understanding of the Mn mineralogy in mixed Fe-Mn deposits is necessary to inform any attempt to separate the Fe and Mn during beneficiation and to understand and predict the behaviour of lump and fine ore products during processing.A suite of analytical techniques was utilised, including hand sorting of lump ore particles, optical microscopy, X-ray fluorescence (XRF)/inductively-coupled plasma mass spectrometry (ICP-MS) chemistry, X-ray diffraction (XRD), scanning electron microscopy (SEM)/electron probe microanalysis (EPMA) and gas and solid phase pycnometry, in order to elucidate manganese mineralogy, mineral chemistry and mineral textures. Manganomelane group minerals (eg cryptomelane, hollandite), pyrolusite and lithiophorite were the most common manganese oxides in the samples examined. From the microprobe work, there was evidence of probable substitution of Mn, as well as Al and Si, into the structures of goethite and hematite. Manganomelane minerals were often intimately associated with goethite, in particular, and a clarification of this association and the associated Si and Al impurities is fundamental for improved understanding of beneficiation and sintering behaviour of Mn-oxide ores. Due to the poor or very fine crystallinity of some supergene manganese deposits and of some Mn oxide minerals, in particular the extent of overlapping peaks and their variable mineral chemistry, XRD was a problematic technique to equivocally determine Mn mineralogy.For lower-grade, earthy, poorly microcrystalline ores the mineralogical and textural association between mixed Mn, Fe and Al (¦ Si) phases was also critical. The deportment and potential separation of these elements in these deposits, especially Al, was complex, as they were characterised by forms of æhydrousÆ cryptomelane with higher levels of Fe-Al-Si substitution, as well as intimate intergrowths of ochreous-earthy goethite (probably aluminous in part) with cryptomelane, lithiophorite and/or kaolinite.Trace amounts of alkali elements in ferromanganese deposits were considered likely to be preferentially structurally associated with Mn oxides, while lateritic deposits with significant amounts of lithiophorite could contain elevated levels of deleterious impurities; Co and Ni in particular.A combination of solid and gas phase pycnometry proved to be a useful technique for broadly discriminating hematitic, goethitic and mixed Mn oxide-goethite lump particles based upon differences in their envelope and apparent densities. Based upon these preliminary results and ongoing Raman spectroscopy work on manganese deposits sensu stricto, Raman spectroscopy is a technique considered to have promise during targeted research to better link the optical and compositional properties of ferromanganese ore particles. CT-scan (computed tomography scan) analysis could also be combined with Raman spectroscopy and pycnometry to link mineral composition, mineral texture, ore particle textures and particle porosity/permeability to the high-temperature processing behaviour of lump and fines products.CITATION:Peterson, M J, Hapugoda, S, Manuel, J R, Donskoi, E and Poliakov, A, 2013. Textural characterisation of manganese minerals to improve the geometallurgical characterisation of ferromanganese and iron ores, in Proceedings Iron Ore 2013 , pp 281-300 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 12, 2013

By Kathryn A. Mrotek

The textural growth patterns of nodules from two areas in the North Pacific and the South Pacific are characterized by mottled, columnar and compact-type zones. Amorphous material (mainly iron and manganese hydrox-ides) is a botryoidal-forming phase in the mottled and columnar zones. Crystalline material (platy crystals of birnessite and crystallites of todo-rokite) is found primarily in the mottled zones on botryoidal structures or as long-protruding structures growing onto that portion of the nodule in contact with the underlying sediments. The long-protruding mottled zones contain little or no biogenic debris, suggesting that these zones grew un-interruptedly within the underlying sediments. The coalition of spheroidal knobs comprising some of the nodules also suggests a relatively long residing time within the sediments. It appears that crystalline material (the usual host to associated valuable metals) forms in a quiet environment and as a result of direct nodule association with the underlying sediments.

Jan 1, 1982

By Thomas P. Meloy

The understanding, quantification and use of locked particles. Specifically discussed is the use of Textural Transforms (Meloy, 1991) for the implementation of the Interfacial Area Conservation hypothesis (Meloy, 1984); the quantification of the locked particles as a function of fragment to inclusion size ratio; and the selection of set points.

Jan 1, 1991

By Franz Wever

ACCORDING to Tammann,1 the explanation of the effect of mechanical deformation in producing changes in the properties of metals is one of the most important problems of physical metallurgy, taking rank with the study of the constitution of alloy systems; and this problem has long attracted-the attention of practitioner and scientist alike. Its solution was not advanced materially until Tammann2 set up his translation hypothesis with its crystallographic basis, while other hypotheses, such as the amorphous metal hypothesis of Beilby3 and Rosenhain,4 have been shown by more intensive studies to be less and less satisfactory. The principles of the Tammann translation hypothesis have proved to be useful even up to today and in spite of all of the recent accumulation of experimental data, while the differences of opinion which have arisen relate to the extent to which the hypothesis accounts for the observed changes in properties and to what extent further assumptions are necessary. Stimulated by the proposals of Tammann, there soon developed a lively experimental activity which aimed at the elucidation of the structural or crystallographic changes produced by the mechanical deformation of metals. Parallel movements of crystal "blocks" along definite crystal slip planes had already been observed by lowing and Rosenhain5 in 1900, in metals which had been moderately deformed but without shedding light on the crystallographic nature of the processes accompanying more severe deformation. The solution of this important problem was not advanced until a much later date, or until the methods of X-ray crystal analysis had become available. Shortly after the discovery of the diffraction of X-ray by crystals, symmetrical diffraction effects were

Jan 1, 1931

By W. D. Keller

Scan electron micrographs, SEM's, will be shown of representative refractory clays from Missouri deposits, with counterparts from other localities. The story is in the pictures, ("1000 words in each picture"), but clay types include the following. Plastic, semi-plastic, and semi-flint "fire clays" of Missouri have textures which appear to retain certain relic texture of ball clay. Flint clay is composed of tightly interlocking packets, sheaves, and books of kaolinite. Diaspore and boehmite mineral textures characterize those "clays". Surface-boulder diaspore shows very pronounced recrystallization and crystal enlargement from original, unexposed first-grade diaspore.

Jan 1, 1977

FOR the benefit of those of our members who may be asked what they know about Mr. Hoover's connec-tion with the Kaiping coal mines in China and who will naturally wish to appear thoroughly well informed on the subject, we reprint below an authoritative state-ment, recently made to the Japan Advertiser, by Tang Shao-yi, former premier of China, now retired to his country home at Tang Chia. "Information has reached me at my retreat that persons in America and China insinuate that Herbert Hoover acted dishonorably in dealings involving the Chinese Engineering and Mining Company a quarter of a century ago. I be-lieve myself the only Chinese living who was closely iden-tified with that company during Mr. Hoover's connection. My uncle founded the company and my family always has been a large shareholder and, therefore, I possess direct knowledge of its history. "I am actuated in this statement by a sense of justice and also gratitude for Mr. Hoover's acts in rescuing my family during the Boxer uprising. Mr. Hoover's record in China is clean and honorable, highly creditable and in many ways remarkable. Legal action brought in London in 1905 occurred after Mr. Hoover left the company. There were not any charges against Mr. Hoover and he was not a de-fendant in the lawsuit, but an important witness whose testimony helped the Chinese shareholders to save their property.

Jan 5, 1928

By E. H. Mohr

AT the McGill concentrator of the Nevada Consolidated Copper Co., all flotation operations have been carried out in Forrester cells since November, 1926. In respect to cost of operation, the new cell has proved to be superior to the Callow, which it supplanted, and its incorporation in the flow sheet has resulted in a marked improvement in the metallurgy. Before citing the advantages of the new machine over the old, it should be explained that the Forrester has not only replaced the Callow, but it has made possible the elimination of a number of tables as well. When Callow cells were in use, table concentration preceded flotation. The ball mill pulp was elevated, by means of air lifts, to roughing Wilfley tables situated two floors directly above the flotation floor. On an intermediate floor were additional tables which cleaned the concentrate from those above. The finished table concentrate constituted approximately 60 per cent. of the total mill production, and contained about 40 per cent. of the recovered copper. The table tailings were returned to the classifiers, the overflow from which went to the flotation cells and the oversize to the ball mills. As soon as the Forrester cells were installed, this tabling operation was discontinued. The ball mill pulp now discharges into the classifiers direct, without the intermediate tabling. It was impracticable to employ the present flow sheet when Callow cells were in use, for the reason that unless the greater part of the heavy mineral was first removed, it accumulated on the mats and adversely affected the flotation operation. By tabling ahead of flotation, it was practicable to maintain the concentrator at 10 to 20 per cent. greater capacity (depending up on the pyrite content of the ore) than was possible by flotation alone. This was due to the necessity for finer grinding in the latter case. Even though the table concentrates contained only 6 to 8 per cent. copper con- tent, the low smelting costs made it advantageous to operate at high mill capacity, at the cost of low grade of product. STANDARD SECTION EQUIPMENT With the old-flow sheet, a standard section consisted of four ball mills and classifiers, one air lift, 20 roughing tables, 10 cleaner tables, 12 primary

Jan 1, 1928