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By F. C. Bond

B. H. Bergstrom (Allis-Chalmers Mfg. Co., Milwaukee)—In reading this article, it was difficult to follow through the example given as a starting point in the derivation of the theoretical equation which relates ball size to feed size. A discussion with F. C. Bond led to the following clarification: Bond postulates that "the breaking force exerted by a ball varies ... as the cube of its diameter . . ." and that the force in pounds per square inch required to break a particle varies ... as its diameter squared." He concludes: "It follows that when a l-in. ball breaks a 1-mm particle, a 2-in. ball will break a 4-mm particle, and a 3-in. ball a 9-mm particle." The above example can be true only for a different set of assumptions. Since the first assumption is apparently true, it is the second that must be revised. The second assumption should read that the breaking force required to break a particle varies as its diameter to the 3/2 power. This relationship was derived in the next paragraph of the article.

Jan 1, 1960

By C. M. Loeb, A. M. Gaudin, J. H. Brown

R. E. Carter (General Research Laboratory, Schenec-tady, N. Y.)—Brown, Gaudin, and Loeb in their study of intergranular comminution by heating attempt to find one explanation for all types of rock in terms of the properties of the phases present. The only necessary condition for intergranular cracking by heating is the setting up of high stresses at the grain boundaries. Such stresses may be set up in multiphase isotropic mixtures if the thermal expansions of the phases are different, in non-cubic single phases because of the anisotropy of thermal expansion in the various crys-tallographic directions, and in materials containing quartz because of the a-p' transformation at 575°C. In addition, for intergranular comminution by heating, the cooling and not the heating is most important.

Jan 1, 1960

By E. B. Mayo

David LeCount Evans (Consulting Petroleum and Mining Geologist, Wichita, Kans.)-—Not only E. B. Mayo but also W. C. Lacy, who apparently urged the preparation of this analysis, is to be commended. Regional thinking of this type is needed to assure future success in the never-ending search for new mineralized and petroliferous districts. As is usually the case, here is a regional study that will be read by the mining geologist alone. It is ironic that several of the trends established in this study have suggested themselves in northern mid-continent, detailed, and regional studies. These, where established, have offered new keys to petroleum exploration and have provided a possible basis for unraveling a number of broad generalities. The oil geologists, active in Colorado, Kansas, and Oklahoma, would find much food for thought in Mr. Mayo's projections. To be more specific: 1) The parallelism between E. B. Mayo's Texas Lineament and the Amarillo Uplift, the Wichita Complex and the Arbuckle Complex of the Texas Panhandle and Southern Oklahoma is viewed with interest and appears especially significant when compared with the similar northwest trend of the Central Kansas Uplift, a major trend of production. 2) Considering the various northeast zones of Fig. 2, and with particular reference to Mayo's C-C, the Jemez Zone is on direct line with one of several northeast-southwest controls which the present writer has been using with some success in Kansas subsurface correlations. Considering zones of shearing, with no apparent vertical displacement, but suggesting strike-slip movement, because of the staggered effect on other features which cross such trends, Mayo's philosophy presents regional possibilities for lines of weakness, considered to this time of only local significance. 3) And, finally, in an area as distant from the Southwest as central Kansas, the north-south trends of the Fiarport-Ruggles anticline, the Voshel-Hol-low Nikkel-Burrton structures, the Dayton to Stut-gart trend, the north, slightly east trend of the Ne-maha structural complex, and others all seem to approach the north-south alignments, a through f, of Mayo's Fig. 3. Mayo's employment of structural intersections to pinpoint crustal weakness, to localize igneous activity and its accompanying mineralization is not, perhaps, a new concept, but it is a 1958 model, produced by tools improved from the ever-increasing accumulation of geological observations. The use of intersecting trends in petroleum geology is not a new idea, since much production in earlier days was encountered via the straight line projections of established trends to centers of intersection. A tragedy in this age of specialization is that iron curtains have been raised between groups, all seeking raw materials, all acolytes at the altar of structural geology, but all smugly content in and protected by the ivory towers of petroleum geology, engineering geology, mining geology, and geophysics. Mayo presents basic ideas which can stimulate mid-continent structural thinking and, in the case of cen- tral Kansas. he provides a key to replace the broad and overworked simple monoclinal, sinkhole-dotted, Karst topography credo, which is not finding its share of new oil in a state where the declining discovery ratio is disconcerting. The American Association of Petroleum Geologists would do well to add E. B. Mayo to its list of Distinguished Lecturers. Evans B. Mayo (author's reply)—In reply to David LeCount Evans' comments, it is pleasing to learn that some of the elements discussed in my paper may interest petroleum geologists as well as mining geologists. This should not be surprising, however, because the lineaments make up the framework of the continent, and the oil-bearing sediments must reflect to varying degrees adjustments of basement blocks along their boundaries. A further possibility that petroleum geologists must have considered is that the slow escape of heat from buried lineaments and their intersections has aided the separation of oil from the sediments and started the migration into traps. Regarding the specific points listed by Evans, the following are suggested: 1) The branch of Texas Lineament marked 1' (Fig. 3) is thought to extend eastward through the Capitan Mts., New Mexico, through the long Tertiary dikes east of Roswell, and beyond via the Matador and Electra ranges of the Red River Uplift, Texas. Its further continuation might be the eastern flank of the Ouachita Fold Belt. The Amarillo-Wichita-Arbuckle zone of uplifts appears to continue east-southeastward the Spanish Peaks belt (3-5, Fig. 3). The northwest-trending Central Kansas Uplift would not belong to the above set, except insofar as the Central Kansas Uplift is traversed by west-northwest folds, possible continuations of the Uinta belt (5-5, Fig. 3). 2) The possible continuations into Kansas of the Jemez zone are new to me and are most welcome suggestions. 3) Most of the nearly north-south Kansan structures mentioned by Evans are unfamiliar to me, but the Nemaha Uplift itself appears to be part of a very pronounced structure traceable from the Cerralvo Fault Zone, south of the Rio Grande, through the Bend Arch, Texas, and the Nemaha Uplift, into the Pre-Cambrian of Minnesota (?). This nearly meridional zone is crossed and broken by the Rio Grande Embayment and by the Red River-Wichita Syntaxis. Petroleum geologists realize the economic importance of these features. Perhaps it is inevitable that some papers of general interest be buried in the journals of specialized groups. Moreover, papers dealing with regional, or lineament, tectonics and its applications to exploration for economic mineral deposits are as yet few in the American literature. The opportunity to advance this field is open to all those who are not ultra-conservative and who have a lively curiosity, plenty of patience, and not too many business restrictions. In conclusion, much appreciation is extended to D. L. Evans for his comments.

Jan 1, 1960

By D. D. Donald

C. J. Barber (U. S. Smelting Refining & Mining Co., Salt Lake City)—In his paper Donald describes how New Jersey Zinc Co. made surveys for a connection between the Ivanhoe and Van Mater shafts at Austin-ville, Va. Except to say that the two faces had to meet "accurately" on line and grade, Donald does not indicate the required precision. Assuming that there were 24 angles in the 11/2-mile traverse and 15 in the one-mile traverse, it can be shown that if the average error in plumbing each shaft was 230" and the average error in measuring each traverse angle was 210". then the average error at the point of -connection would have been about ±1.9 ft normal to the line between the shafts. This calculation assumes that any errors in the triangulation would be negligible compared with the errors in the plumbings and traverses, and it also neglects taping errors. With no constant errors or blunders, the latter would be important only in lines normal to the line between the shafts. To make the average error at the connection less than 1.9 ft would, therefore, require either reducing the error in the plumbings to less than ±30", or that in the traverse angles to less than ±l0", or fewer stations, or a combination of these. Referring briefly to the triangulation, because of the problem of fitting a new triangulation into older surveys of the district the orientation deserved some mention, even though the connection could have been made with an assumed bearing. It would be interesting to know how many triangles were required and what the average summation error was before making any adjustments and without considering the algebraic signs. Perhaps this is referred to indirectly in the statement that the maximum angular error distributed was 2". Turning to the shaft plumbings, it would be helpful to know how many men were employed and how long each shaft was in use. Donald says that the surface positions of W-2 and W-3 were carefully surveyed from the collar position of W-1, without indicating how this was done. The length of the backsight would be particularly important. There must have been some error in setting W-1 vertically below the stations in the headframes. How immovable were the headframes, especially the Van Mater, which appears higher than the Ivanhoe and subject to more vibration because of skip hoisting? Donald does not say whether the plumbing wires had been previously restraightened to minimize spinning (otherwise they behave like weak helical springs). The use of light steel weights is most surprising because there seem to be excellent reasons for using heavier, nonmagnetic weights. Did the shafts contain no steel sets, pipes, power cables, etc., which might attract steel? The plumbing method described by Donald was designed for deep shafts in South Africa but differed from the South African practice in two important respects. As described by Browne,6 in South Africa the line between the wires was made parallel to the long axis of the shaft, whereas in the Ivanhoe shaft the lines between the wires were diagonally across the shaft. The main reason given for the South African practice is to insure that the gravitational attraction between the wires and the rock walls is the same on both wires, and therefore does not affect the bearing of the line between them. It seems probable, however, that the effect of air currents might be minimized in the South African procedure, and might be serious with the wires in the diagonal position at the Ivanhoe shaft. In the South African case cited by Donald the wires were swinging freely (although the plumb bobs were sheltered from air currents) but in the Ivanhoe case they were dampened with the plumb bobs set in water. In the discussion of Browne's paper R. St. J. Rowland said:' It has been the practice for a long time to damp the oscillations by immersing the bobs in oil or water. The time per oscillation is thus increased, thereby extending the time taken to complete the work. The longer the suspended wire the less there is to recommend the practice . . . The theoretical time for one swing of a simple pendulum 1050 ft long is approximately 36 sec, which would be increased by dampening the plumb bob in water. Hence very few complete swings would be observed in the 5 min intervals used at the Ivanhoe shaft. In the two South African cases described by Browne, the length of plumb line in one shaft was 5425 ft, the calculated period of swing was 81.6 sec, the average actual period was 76.6 sec, and 94 complete swings were observed in 2 hr. In the other case the length of plumb line was 3116 ft, the calculated period of swing was 61.8 sec, the average period was 63.5 sec, and 86 complete swings were observed in 1 hr 31 min. Browne concluded that observations of more than 30 swings are not likely to result in sufficient gain in accuracy to be justified. Returning to the Ivanhoe and Van Mater plumbings, an objection to the method used is that all four azimuths were taken from fixed points instead of swinging wires, and that each pair of observations would— barring blunders— check closely, and so perhaps give a false feeling of security. In fact, it seems that only two azimuths were obtained from one plumbing, and not four as stated by Donald. Nevertheless, the tying in of each pair of wires from both sides of the shaft has much to commend it. Donald's description leaves the impression that if each shaft was plumbed only once, the engineers were fortunate indeed if the average error in the underground orientation was as little as 30". Because the survey was done over a period of three years, it seems likely that the plumbings were repeated, perhaps more than once. The underground traverse angles were measured by conventional methods, but because the number of angles in the overlapping traverses was not given, the angular closure given by Donald does not indicate the accuracy with which this was done. Donald's description of a method of taping lines of irregular length is welcome. The literature on taping is usually confined to lines of about one tape length, generally 100 ft. Such lines are rare in metal mining because the time, trouble, and cost of setting points at 100-ft distances underground are not warranted. (Nevertheless civil engineers may go to this expense

Jan 1, 1960

By W. E. Horst

John Dasher (Central Research Laboratory, Crucible Steel Co. of America, Pittsburgh. Pa.)— Getting spodumene to float quickly and cleanly can be a problem. The author has presented an excellent account of a valid and useful approach to the scale-up of such problem floats. This indicated advantages for doubling retention time, i.e., buying another set of flotation cells. The author states that 21 pct of the spodumene floated in 2 min in the laboratory cell, that the grade of the rougher was about 75 pct spodumene, and that the final tailing contained 4 to 12 pct spodumene in different sizes with the present cells and 1 to 9 pct spodumene with twice as many cells. About 20 years ago, this writer obtained in the laboratory the flotation of over 90 pct of this spodumene in a King's Mountain sample in 1 min at a grade of 90 pct spodumene in the rougher and a final tailing that contained only 1 pct spodumene. The methods of Norman, Ralston," and Gieseke' were used, which teach that spodumene floats quickly and cleanly if its surfaces have been properly conditioned chemically and/or mechanically prior to flotation. Although feed preparation is not discussed, the results reported indicate that it is inadequate. This writer suggests that improvements in this area might be more effective than doubling the number of cells. W. E. Horst (author's reply)—Dasher's comments are appreciated by the author and require some clarification. He suggests that improved spodumene flotation performance may be obtained by feed preparation techniques rather than increased retention time in flotation. Certainly flotation performance is dependent on feed preparation and this is an important feature in the flotation process. It is true that certain types of spodumene ores, particularly weathered ores, require more complicated feed preparation processing than clean ores to achieve the desired flotation results. It was not implied that current feed preparation techniques are the same as experienced during the scale-up investigations. Although discussion of feed preparation was omitted from the article on scale-up relationships, the important feature was that pre-treatment processing was the same for each level of operation investigated— laboratory, pilot plant, and plant scale. Under these similar conditions large differences existed in recovery for comparable time intervals in each scale of operation. It is highly probable that feed preparation techniques could be modified and thereby increase the flotation rate for each scale or all scales of operation discussed. However, modifications would have to be justified on an economic basis.

Jan 1, 1960

By R. J. Charles

F. C. Bond: This is an outstanding paper on comminution theory and represents a considerable advance in mathematical formulation. It clears the way for a discussion that should ultimately decide whether the work index should be considered as a parameter according to the Third Theory or as a constant. In the empirical differential equation dE = —Cdx/x [1] either Corn must be treated as a variable to satisfy known crushing and grinding conditions. The author has chosen the exponent n as the variable, with C as a constant. According to the Third Theory, in the general case n is a constant equal to 3/2, and C is a variable related to the work index Wi. If x is placed equal to P (the size in microns which 80 pct of the product passes) and F is the size 80 pct of the feed passes, then C equals 5 W1, and dE = 5 -5 Widx/x = 10 Wi 10 Wi w = vP vF which is the basic equation of the Third Theory. It is apparent that this integration involves the error of treating the parameter Wi as a constant, just as the author's treatment involves the error of integrating his variable n as a constant. These errors are probably relatively unimportant, considering the small range of the variables. When more is known about the factors contained in the work index, Eq. 1 can be revised as a partial differential equation. The Third Theory exponent of 1/2, or n = 3/2 in the Charles' differential equation (Eq. l), was not chosen primarily because it is the average between the Kick and Rittinger exponents; this may be merely fortuitous, since it is illogical to define truth as the average between two errors. It was first discovered from the study of a large mass of crushing and grinding data and confirmed by laboratory testing. The general correspondence of the Third Theory equation to actual crushing and grinding results over the entire size reduction range argues strongly that a fundamental phenomenon is involved. The a posteriori theoretical explanation of the constant Third Theory exponent is that the work done in breaking rock is proportional to the length of the crack tips formed. Compressive force applied to the rock results in deformation and strain energy. When this locally exceeds the breaking strength a crack tip forms, the surrounding strain energy flows to the crack tip and extends it to split the rock, with release of the energy as heat. Under rapid impact the crack tip may form before the strain has reached equilibrium, resulting in less energy expenditure and probably a coarser product. In any case, the elastic limit of a brittle material is practically the same as its breaking strength, and the work necessary to form the crack tip is the work required to break. The crack length of a ton of broken rock cannot be measured directly. However, the particle shapes of feed and product are similar, and the crack length is considered equal to the square root of one half of the new surface area formed. It is, therefore, proportional to 1/vD, where D is the equivalent product particle diameter. This is the basis of the Third Theory equation. Many secondary factors can be imposed upon the crack length breakage. These may cause the Third Theory work index to increase or decrease somewhat as the product size becomes finer. The work index is properly a parameter rather than a constant, making it an increasingly valuable practical criterion of the work input required in crushing and grinding.

Jan 1, 1959

By A. F. Henderson, C. F. Cornell, A. F. Dunyon, D. A. Dahlstrom

Ossi E. Palasvirta (Development Engineer, Oliver Iron Mining Diu., U. S. Steel Gorp.)—The authors are to be congratulated for their interesting article, which thoroughly illustrates the variables inherent in filtration of taconite concentrate. The work and the conclusions based thereon largely parallel the test work done by the writer at the Pilotac plant" and the experience gained with a commercial size agitating disk filter in the same plant. At Pilotac, however, a thorough study was also made of the effect of depolarizing (demagnetizing) the filter feed, and it is the purpose of this discussion to comment on the merits of depolarization of the magnetite concentrate prior to filtering. The work at Pilotac was done in three phases: 1) preliminary laboratory testing with a circular filter leaf of 0.047 sq ft, followed by 2) plant testing using a 4-ft diam, single-disk agitating filter that was purchased on the basis of the pilot tests on the 4-ft model. In the laboratory tests depolarization was achieved by slowly withdrawing' batches of thickened concentrate from a coil producing an alternating field of about 300 oersteds. In plant tests the standard Pilotac procedure' was employed, wherein the pulp falls freely through the depolarizing coil. The preliminary tests in the laboratory at first seemed to indicate that although depolarization of the filter feed decreases the cake moisture, it also tends to decrease the thickness of the cake, thus decreasing filtering rate. The tests with the 4-ft disk filter soon showed, however, that the compactness of the cake, attained during the form period because of depolarization, permitted a considerable decrease in drying time without any sacrifice in final moisture content. Thus, the filter could be operated at a much higher speed, and the overall capacity was higher than with magnetized feed. Because of the great compactness of the cake there was little shrinkage during the drying period, which prevented cracking and subsequent loss in vacuum. This in turn permitted operation with as thick a feed pulp as the diaphragm pumps could handle, eliminating the necessity of pulp density control. On the basis of these findings, the 6-ft agitating disk filter has been operated at 2 rpm, using feed pulps varying from 65 to 73 pct solids. Initially Saran 601 was used as medium, but it was later replaced with a relatively open, tight-twist nylon cloth. Filtering rates up to 750 lb per ft- er hr can be attained with feeds averaging about 70 pct- 270 mesh, and there is no trouble because of cracking. The cake moistures vary between 8.5 and 9.5 pct. To recapitulate, the merits of depolarizing the filter feed may be summed up as follows: 1) The well dispersed pulp shows less tendency to settle in the filter tank. 2) The homogeneous filter pool results in more even cake formation. 3) Because of absence of flocs, great compactness of cake is attained during the form period. 4) The cake does not tend to crack during the drying period. 5) A drier cake is produced. 6) A shorter drying period is necessary, permitting higher operating speed, which in turn results in increased capacity. 7) Density of the feed pulp can be kept as high as the equipment can handle. This increases capacity, since it is directly proportional to the percentage of solids in the pool. A few tests were also made to study the effect of chemical flocculants on filtration efficiency. Results showed that the effects of chemical and magnetic floc-culation were quite similar. Thus the use of a floccu-lant would impair rather than improve the filtering of magnetite concentrate. A. F. Henderson, C. F. Cornell, A. F. Dunyon and D. A. Dahlstrom (authors' reply)—We want to thank O. E. Palasvirta for his comments, particularly in view of the encouraging results obtained with demagnetized taconite concentrate. In our studies an attempt was made to evaluate the effects of depolarizing the feed to the plant filters by passing the slurry through a coil, similar to the method described by Palasvirta. Unfortunately, in our experiments there were no startling improvements in performance level, neither cake rate increase nor cake moisture reduction. However, when slow filter cycle speeds were employed, the filter cake tended to crack and the vacuum level dropped, resulting in an increase in cake moisture content. When demagnetized feed was used during slow speeds, no cake cracking was evidenced and the vacuum level remained constant. Thus the depolarizing coil was found necessary only in cases of cracking. It should be noted that most of our test work concerned a feed of 85 to 90 pct —335 mesh and about 60 pct by weight solids concentration. This contrasts with 70 pct —270 mesh and 65 to 73 pct by weight solids as noted by Palasvirta. Reviewing both sets of results, it might be concluded that depolarizing may be successfully employed to alleviate cake cracking tendencies and may markedly improve cake rates and moistures on the coarser taconite concentrates. Further investigations may disclose the exact relationship of grind and pulp density to the depolarizing action.

Jan 1, 1959

By J. L. Gillson

Andre Hubaux: In the writer's opinion, more stress should be put on field and microscope observations, as J. L. Gillson does. His discovery of relics of big labra-dorite feldspars from the Marcy anorthosite in all the other rocks is proof enough that previous field observations have been inadequate. The writer's field experience with anorthositie massifs is limited to the Egersund-Sogndal district in southern Norway; however, this is a very large and well exposed area. It seems to have so many points in common with the Adirondack region that a detailed comparison should be beneficial. This comparison was not possible 20 years ago, owing to the scarcity of geological data, at least for Norway. Both regions are now far better known—the Norway district because of the work of Professors Bugge and Barth 33-35 and especially because of the extensive field and microscopic research of P. Michot,30-35 who introduced me in the field to the problems of that region. In a particular unit of the Egersund district, a sodi-fication of the plagioclase, very similar to what Gillson calls "andesinization," has taken place. 12' The percentage of anorthite in the plagioclase has dropped from 42 to 43 pct in the original norite down to 27 pct, but never below that level. This metasomatical transformation is a part of a whole series of processes of mig-matitization which have produced, above the level of granitization, concentrations of Mg, Fe, and Ti and among them, patches and parallel bands of ilmenite and magnetite. Thus both regions present somewhat comparable features and the theories to explain them have several points in common. However, as there seem to be differences between some American conceptions and the views commonly accepted at the University of Liege, I would like to make some comments about J. L. Gill-son's article. The author speaks of the garnet as being an anti-stress mineral. However, garnet may be found in schists, where its helicitic texture, when present, demonstrates its formation during differential movement. Furthermore, the whole concept of stress and anti-

Jan 1, 1959

By B. S. Butler

A. D. Mutch (Falconbridge Nickel Mines Ltd., Ona-ping, Ontario)—This contribution is prompted by the fact that the writer has recently published an article'!' which has in part the same general conclusions as B. S. Butler's, namely, the form of the standard mineral paragenesis in hypogene deposits and the parallel transition from early high temperature acid to late low temperature alkaline or neutral solutions. Since the writer also recognizes that he is not fully qualified to discuss the formation of ore deposits as a chemical problem, this discussion will be limited to summarizing other observations and will suggest how Butler's Table II might be made more effective. The form of Butler's table is not unlike that widely used by European geologists'" in which the various minerals are related to the types of ore fluids—peg-matitic, pneumatolic and hydrothermal. Thus the decrease in temperature and change in pH of the ore-bearing fluids as recognized by Butler may also be paralleled by perhaps even greater changes in composition, density, and character. W. H. Newhouse's article:" on the sequence of hypo-gene ore mineral deposition is still one of the most complete analyses of the problem. In it he makes four major observations: 1) The order of O, S, As, Sb is the same as their increasing atomic weights and the same as their melting points. 2) The order of the metallic elements is the same as the Schuermann series. 3) The general mineralogical order is paralleled by decreasing heats of formation. 4) The order is generally in decreasing hardness, higher metal content, and higher specific gravity. The order of 0, S, As, and Bi is also the same as their relative abundance. Another point worth mentioning about this series is that As, Sb, Bi, when abundant, often substitute for sulfur in the early pyrite-like minerals, whereas later in the sequence these elements appear to act more like metals. This behavior may be a further indication of the acid character of the early fluids. C. J. Sullivan"' has attempted to show that the sequence of the metallic elements is related to the order of their melting points and has discussed the interrelationship of the different types of bonding of sulfo-phile and oxiphile elements in minerals. Items 3 and 4 might best be summarized by saying that bonding of the minerals in the series appears to be from ionic to covalent to metallic, the early minerals being light in weight, hard, and near-transparent; the intermediate minerals of intermediate weight, semi-transparent, and semi-conducting; and the end minerals heavy, soft, and malleable, opaque and good conductors. A rapid fall in temperature has been assumed to be the cause of ore deposition in many deposits. Perhaps this in turn is the effect of a rapid release of energy in the form of pressure release and change of volume, the first minerals to form being those with the highest heats of formation which absorb the released energy the most rapidly. Butler's Table II could probably be streamlined and made more effective if the listed compounds were assembled as mineralogical groups as in Dana. Thus the sulfides, arsenides, antimonides, bismuthides, and sulfa salts could be arranged in AX,, AX, A2X2, etc. groups. Since these are continuous substitution series, in which the fields of stability and the heats of formation of the various individual minerals can be fairly regarded as similar, this should be accomplished with no loss of clarity. The occurrence of the individual minerals and the precise sequence of the mineral deposition in any one deposit is probably more dependent on the concentration and relative abundance of the component elements. The assembling of geological data in tabular form such as Butler's Table II will continue to be a very effective method of studying geological phenomena. The importance of this particular problem has been pointed out by C. F. Park,% who concludes that understanding of mechanisms of the standard paragenesis and interrelated problems of mineral zoning in space and time is one of the major keys to classification of ore deposits.

Jan 1, 1959

By James M. Schopf

Gilbert H. Cady (Senior Geologist, Head of Coal Division Emeritus, Illinois State Geological Survey, Ur-bans)— Those coal mining and preparation engineers and operators who read this article will probably be most concerned with those parts which deal with the applied aspects of coal petrology in the fields of mining and technology. Actually the two categories overlap to such a degree that they are essentially one. The article appears to suggest that there are two points of veiw in the field of applied coal petrology. From one viewpoint the interest is in the attributes of the various macerals (Fig. 4)—vitrinite, exinite, and inertinite—-in terms of utilization (when the coal is burned, coked, gasified, hydrogenated, etc.). From the other point of view, assuming that the macerals do possess individuality in behavior, interest attaches to the possibility that coal of a particular type (maceral composition) can be prepared by discriminating methods of preparation and blending. Most of the 29 items listed for mining and technology can be assigned to one or the other of these two categories. Somewhat the same simplicity that resides in the items of the proximate chemical analysis is desirable for the petrologic analysis. This simplicity appears to be fairly well achieved by the group maceral device provided mineral matter is also included. At present, without fully adequate experimental substantiation, the three types of material represented by the group macerals vitrinite, exinite, and inertinite are regarded as sufficiently different in composition and properties so that the preponderance of any one type gives the coal distinctive properties provided it is not too high in rank. This appears to be increasingly true with coals of decreasing rank from medium volatile bituminous coals downward. The article reflects the great emphasis placed on the technique of descriptive coal petrology in America. Such description has resulted in a good understanding of the nature of the fundamental variability in the physical composition of bituminous coals. Such understanding has been attained very largely by the thin section technique used in coal bed profile analysis introduced by R. Thiessen after the manner suggested by the data assembled in Table 11. In contrast, the group maceral concept of coal analysis in terms of the categories indicated on the left hand side of Fig. 4 is particularly useful for broken coal analysis and applied coal petrology, in which evaluation is largely based on quantitative concepts. It is inadequately emphasized in this article that although the Thiessen procedure is suitable for the purpose of petrologic description in which texture and orientation are of critical importance, it is less well adapted to the technological uses of applied coal petrology. No doubt those persons whose interest may have been aroused in the possibilities of more refined coal preparation by this and other recent contributions to the literature of coal petrology will understand that certain technical aspects of coal petrology, particularly in the field of descriptive petrology, are still a matter of some controversy among the coal petrologists, but they will also appreciate that Schopf has made an important contribution to the field of coal petrology in America by pointing out that such petrology requires consideration of disoriented or broken coal samples and that results are expressed less in descriptive terms than in quantitative values with respect to the four types of material composing coal—-vitrinite, exinite, inertinite, and mineral matter. Unfortunately because so much American coal petrology has been descriptive of the coal in the bed there is a dearth of literature on applied coal petrology. Research and experimental data in this field are greatly needed.

Jan 1, 1959

By R. Costantini

A. Brebner (Chairman, Dept. of Civil Engineering, Queen's University, Kingston, Ont., Canada) — Under the heading of friction losses, the author, in Eq. 10, gives the relationship

Jan 1, 1962

By F. X. Tartaron

F. C. Bond (Consulting Engineer, Processing Machinery Dept., Allis-Chalmers Manufacturing Co., Milwaukee, Wis.) — Papers such as this one which deal in a lucid manner with the obscure fundamentals of comminution theory are always welcome. The author has attempted to bring together several diverse theories and handles them interestingly. However, some of the ideas expressed and conclusions drawn require critical reviewing, for which amenities alone will not suffice. The author points out that the theoretical energy required to break across crystal lattices is of the order of 1000 times the actual energy required to crush or grind, and that this energy in turn is perhaps 1000 times the measured surface energy of the new surface area produced. The energy required to grind commercially is controlled by flaws and dislocations, rather than by the inner strength of the lattice structure. The measured surface energy is only a slight residue left after the face atoms are adjusted to their new environment. The dislocations in the crystal lattice structure, with a spacing of about O.l,u, or

Jan 1, 1962

By B. H. Bergstrom, W. Mitchell, C. L. Sollenberger

D. W. Fuerstenau (Associate Professor of Metallurgy, Dept. of Mineral Technology, University of California, Berkeley, Calif.) and D. A. Sullivan, Jr. (with the University of California) — Messrs. Bergstrom, Sollenberger and Mitchell have shown in two excellent papers that the energy per unit mass required for the breaking of spheres is inversely proportional to the size modulus of the fragments of the broken spheres. They found that the fragments of spheres broken within a steel enclosure were finer than those produced by breaking spheres encased in gelatin. This results from utilization of part of the strain energy at fracture for secondary breakage. For spheres not encased in gelatin, these authors found that after fracture the fragments of the spheres possess kinetic energy amounting to 45% of the strain energy needed for initial fracture. Breakage of a sphere in gelatin results in waste of this kinetic energy, whereas breakage inside the steel container makes use of this kinetic energy for further size

Jan 1, 1962

By G. M. Schwartz, J. N. Gundersen

John W. Gruner (Professor Emeritus, College of Science, Literature, and the Arts, Dept. of Geology, University of Minnesota, Minneapolis) — It is surprising that two men as well acquainted with the taconite rocks of the Mesabi District as Drs. J. N. Gundersen and G. M. Schwartz should have concluded that the taconite of the Eastern Mesabi before the intrusion of the Duluth gabbro consisted largely of quartz and magnetite. These minerals were "locally reconstituted" into "a wide variety of silicate mineral assemblages" by the gabbro. It is well known, of course, that the silicate mineralogy of the Eastern Mesabi ('about 14 miles in length) is quite different from that of the Main Mesabi which is over 60 miles long. The change from one to the other is abrupt and cannot be attributed to any other cause than the thermal effects of the gabbro. Are we to assume or believe that the taconite of the Eastern Mesabi was radically different from that of the Main range before the gabbro metamorphosed it?

Jan 1, 1962

By B. H. Bergstrom, A. P. Cohen, D. W. Fuerstenau

B.H. Bergstrorn (Research Div., Allis-Chalmers Mfg. Co., Milwaukee, Wis.) — Fuerstenau and Cohen have concluded from our study of single particle crushing, which had suggested that the size moduli of the crushed specimens were determined by the specific energy expended independent of feed size, that the same independence with respect to feed size exists for the specific energy-product size relationship for rod mills. They present data supporting this conclusion. Our single particle crushing experiments were on single spheres of soda-lime (type of glass was not given in our study) glass for which the feed size can truly be neglected. However, the feed size cannot be neglected in any case where the effective size modulus of the feed is not too much coarser than the size modulus of the product. This can be illustrated in the second experi- ment of Fuerstenau and Cohen where the feed is considered to be the original -6 +%mesh material. However, one can also consider the product from the 7.5-min grind to be the feed for the 10, 15, 20, 25-min grinds, and the 10-min product to be the feed for the 15, 20, 25-min grinds, etc. If the specific energy-product size moduli curves are drawn for these other feeds, as shown on Fig. 3, the new curves (and some curvature is apparent) are much steeper than the -6 +%mesh feed line. The slopes of these new curves are about -1.5, —1.8 and -3.0. This observation is in accord with the observation by Bond, who states that the net specific energy input to a grinding mill is equal to the specific energy represented by the product less the specific energy represented by the feed. Bond presents, on a diagram similar to Fig. 3, a series of curves which illustrate the effect of

Jan 1, 1963

By R. C. Ferguson, B. Bernstrom

R.C. Ferguson (District Manager, Hardinge Company Inc., Hibbing, Minn.) — In the opening paragraph of Mr. Bernstrom's paper he stated that the Cascade mill performance information is preliminary. With the completion of the 1962 operating season, more reliable performance information became available. The main bearings, which had been damaged, were reconditioned at the factory. New Gatke bearing bushings with a 120° are of contact were supplied. Provision was made to introduce high pressure lubricant at two points in each bearing. New spherical bearing balls that operate in spherical seats were aligned at the factory and held in place by several setscrews to aid in installing the bearings in the field. The screws were not loosened prior to, or during, operation; therefore, the bearings operated as rigid bearings. The lubricant cooling system was changed to the cooling tower type to provide lubricating water of a suitable temperature. Another refinement consisted of installing a device to add a set percentage of soluble oil to the make-up water.

Jan 1, 1963

By Sylvia Whitehead, G. M. Schwartz, J. N. Gundersen

Sylvia Whitehead (Petrologist, The Broken Hill Propriety Co. Ltd., Melbourne, Australia) — Examination of thin sections of jaspilites from numerous banded iron formations in Australia has revealed no evidence to suggest that silicate minerals have formed by reaction between magnetite and silica. Textural relations indicate that part of the magnetite crystallized very early in the history of the rocks, probably during diagenesis, and remained stable under conditions of metamorphism altering only to hematite or limonite under conditions of oxidation and weathering. Many jaspilites also contain later magnetite which is almost certainly of metamorphic origin. Wherever magnetite is present in quartz rich bands containing little or no silicate or carbonate, it is very fine grained and occurs generally as isolated, well formed octahedral crystals or as small crystalline aggregates. These show no evidence of corrosion or reaction with the quartz even in rocks where adjacent bands contain silicate minerals of moderate to high metamorphic grade. Concerning the silicate minerals, it is reasonably certain that bands of very fine grained stilpnomelane

Jan 1, 1963

By D. Hugh Trollope, L. A. Fekete

L.A. Fekete (Project Engineer, Johnson B & Assoc. Engineers, Houston.) - The author tries to classify rock slopes in: a) homogeneous monolith, b) random, c) block-jointed systems. This may be practical at a specific mine, but it does not describe the mechanical behavior of the slopes in general. The difficulty with the problems of earth mechanics is the same, as with other structural problems: To

Jan 1, 1963

By D. L. King, C. D. Rubert, R. W. Christy, B. A. Schepman

R. W. Christy (Manager of Sales, Sanitary Engineering Equipment, Link-Belt Co.) and C.D. Rubert (Barrett, Haentjens & Co.) — Messrs. King and Schepman have presented an excellent paper which outlines the general practice in the design of thickener mechanisms. Lifting devices, controls, special applications and underflow pumping arrangements have been reviewed in detail. Pumping arrangements were illustrated which eliminate the need for an expensive tunnel beneath the thickener floor. Most of those illustrated have the common feature of a relatively long underflow suction line extending from the hopper floor to the pump located on the bridge at the periphery of the tank. The authors limit these arrangements to comparatively dilute or thin slurrys. It is implied that dense and coarse concentrates, which are difficult to pump, cannot be handled unless a tunnel is constructed. Fig. 1 shows an underflow pump arrangement which negates the need for a tunnel but which permits the operator to convey a heavy dense slurry. The pump is mounted directly on the fixed hoist platform and the impeller is located at the base of the steel center column. Priming water is not needed. The column

Jan 1, 1963

By G. E. Agar, A. L. Mular

G. E. Agar (Manager, Minerals Processing Research, International Minerals & Chemical Corp., Skokie, III.) — The author notes a discrepancy between the parameters a and ß which are the slopes of the size distribution and energy-size modulus plots respectively. The reason for the discrepancy and the systematic decrease in the magnitude of a with grinding time is abundantly clear from the work of Fuerstenau8 on dry grinding. Fuerstenau shows very clearly in his Fig. 5 that at short retention times the parameter a is the same as that obtained by sizing over the complete size range. From this figure, it is obvious that sizing to only 400 mesh gave distribution curves similar to Mular's - that is, the slope apparently decreased systematically with increased grinding. As a consequence of the improper determination of a, the magnitude of ß given by Mular must be larger than the true value. In order to demonstrate this, the following Fig. 6 was taken from Mular's paper (his Fig. 1). Fuer-stenau's results show that we can approximate the correct value of K by drawing lines parallel to the short retention time curves through the 400-mesh

Jan 1, 1963