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By Roberto Pimentel de Souza, Helder Zenóbio

VRD started producing pellets in 1969 with one 2-million-t straight grate plant. In the beginning of April 1973, the second unit came on stream with an additional capacity of 3 million t/a of pellets. In January 1977, the third unit started, bringing the annual capacity to 8 million t/a. In the coming year (1978-79), three more units, 3 million t each, are expected to begin production. CVRD's experience with different binders and additives is described. Over the years several kinds of pellets have been produced to satisfy market requirements. General quality information is given for each.

Jan 1, 1981

By John M. Sharp

John M. Sharp, Jr. (Assistant Professor of Geology, University of Missouri, Columbia, Mo.)-Geothermal gradient and surface temperature data anomalies are potentially useful tools in mineral exploration, These data, however, may reflect a number of geologic and hydrologic processes as well as the thermophysical properties of the geologic materials. The author presents a relatively simple model which may be of value in mineral exploration. The lack of consideration of other processes, however, limits its usefulness. For instance, because of erosion or sediment deposition over geologic time the land surface must be considered a moving boundary in such a model. Evaluation of this effect coupled with annual surface temperature and thermal conductivity variations can result in temperature profiles such as shown in [Figs. 4 to 7]. These effects and others, such as ground-water movement," must be considered and filtered from the data before proper interpretation is possible. Another assumption which should have been discussed is, why were the observed mean surface temperatures not used for extrapolation of the gradients in [Figs. 4, 6, and 7?] Conductive heat transport responds to the actual boundary (land surface) temperature, not to theoretical temperatures in the absence of perturbations. Benfield presents a theoretical model for calculating perturbations in the geothermal gradient for erosion and sedimentation. The temperature (T) at any time (t) and any depth below the surface (x) is given by [ ] where T is the mean surface temperature, G, the geothermal gradient, v, the rate of erosion (or sedimentation),[ ], the long-term rate of change of T0, and k is the thermal diffusivity of the rock. Using the author's values and a rate of erosion of 1.54 cm per yr for a period of 10,000 yr, a thermal profile as shown in [Fig. 10] will be generated. A thermal diffusivity of 0.0164 sq cm per sec was used, corresponding to a thermal conductivity of 0.0082 cal per cm per sec per C. In [Fig. 11], a sediment deposition rate of 3.0 cm per yr for a period of 1000 yr was used to generate the subsurface temperature profile. A surface temperature of 24.3°C was used, as specified in [Fig. 9, 7], was set equal to zero for both cases. Superposition on the generated profiles in [Figs. 10 and 11] of the annual surface temperature variation perturbation (which may be calculated in a number of ways) will yield profiles similar to those in [Figs. 4 and 7]. Similar profiles can also be produced by regional ground-water flow. Models like the author's can be of value in mineral exploration. Other processes, however, which affect surface temperatures and gradients must first be considered, calculated, and filtered from the data if anything but the crudest qualitative interpretation is to be made. Robert C. Edmiston (Author's reply)-Professor Sharp has raised three objections to my interpretation of the subsurface temperature data I collected at Silver Bell. These are: 1) No correction was made for erosion or sedimentation,

Jan 1, 1977

By C. M. Brinckerhoff

Safety work in mining at the Andes Copper Mining Company, Potrerillos, Chile, is divided into three parts: (1) accident prevention, (2) fire prevention and protection, and (3) silicosis prevention and control. In the company's operations a steady campaign has been waged to reduce accidents and silicosis, and to prevent fires. In the following pages the safety record for the past twelve years will be examined and the methods explained by which the accident rate was reduced. Table 1 contains yearly data pertaining to the scale of the mining operations and the accident record. Block caving is used for all ore production and the tonnage mined has averaged 30,000 short tons per day for the past seven years. Table 2 classifies 44 fatal accidents which have occurred since 1935. The leading causes of accidental death are transportation of ore and use of explosives, followed in order by persons falling, falls of ground, and by asphyxiation. In the case of serious accidents, however, the greatest cause is falls of ground, followed, in turn, by ore transportation, persons falling, explosives, and asphyxiation. Accident Prevention The improvement of the safety record was obtained by a combination of many factors. In surveying the results at Andes for the past twelve years, it is possible to select some features of the present operation which have contributed to the accident record. The most important of these are: (1) good staff planning, (2) good equipment, (3) an alert safety organization, and (4) education and selection of the workmen. GOOD STAFF PLANNING As a result of good staff planning, the mine has good working conditions, namely, good ventilation, moderate temperatures and humidity, and good lighting. These factors not only reduce accidents but also improve efficiency. In haulage work, accidents have been reduced by having traffic move in a forward direction only. The latter makes possible a one-man train crew. Trains are centrally dispatched from loading drifts which are interconnected by signal lights, so that when a train in a lateral drift is given permission to move into a main line drift, a red light signals in all other lateral drifts in that area. Good track is maintained, and safety niches are required at all switch throws. Since safety niches were provided there have been no fatal or serious accidents at such points. All main line haulage drifts are illuminated by electric lights. Haulage drifts are kept clean. Adequate clearance has been provided between cars and between cars and the sides of the haulage drifts. The 4 1/2 ton Cranby type cars are equipped with roller bearings, and the 10 ton loconlotives with trolley shoes instead of wheels. These two features are responsible for improved ore haulage conditions and contribute to greater efficiency and safety.

Jan 1, 1950

APRIL 10-Officially, spring comes to the Great Lakes on March 21 as it does elsewhere in the country but in the Superior district continued snow and freezing until late in March have caused citizens in Duluth to place their bets on April 15 for the first ore vessels if the ice breakup is left to Mother Nature. North and west of Duluth and near the eastern end of the Mesabilies the little town of Aurora, population 1100. As the little v-nosed snowplow, pride of the community, shuttled back and forth clearing Aurora's few sidewalks, the crowd in Bradich's Cafe were more interested in the impending high school state championship basketball tournament in Minneapolis than in the outcome of Erie Mining Company's petition for water rights for their proposed 10 million ton taconite concentrating plant. Such a plant would employ 4500 workmen, and at the prevailing ratio of 10 people for every mine worker in Minnesota, this would mean a 45,000 increase in population for Aurora and the vicinity in the next few years. Downstate fishermen are alarmed at the flurry of activity by the mining companies in pushing plans for large scale recovery of iron from taconite. Inconvenience to these gentlemen will be inconsequential when compared with the vast increase in payrolls for range communities. Oliver is pushing the construction of a fine ore agglomeration plant at Virginia which will give them valuable experience for projected taconite processing. Oglebay, Norton & Co. is ready to go at Beaver Bay, north of Duluth, as the right of way for a railroad from Babitt to Beaver Bay is secured as well as permission to dispose of tailing into Lake Superior at the site of the proposed concentrating plant. This company is also doing research in agglomeration at Ashland, Ky., in cooperation with other interests. The financing is yet to be worked out. Of the four possibilities for agglomerating taconite concentrate-sintering, pellitizing, nodulizing and briquetting-the prospects for pelletizing appear the most favorable., It seems likely that 60 cents per ton can be saved by this process over sintering because only 1 to 2 pct of coal is required as compared with 7 pct for sintering. One reason for the lower coal consumption is that the chemical transition of magnetite to hematite which transpires in the pelletizing process is exothermic.

Jan 5, 1950

SOUTHERN CALIFORNIA LOCAL .SECTION Executive Committee SEELEY W. MUDD, Chairman C. COLCOCK JONES, Vice-Chairman. FREDERICK J. H. MERRILL, Secretary-Treasurer, 631 Higgins Bldg., Los Angeles, Cal. RALPH ARNOLD A. B. CARPENTER The Southern California Section, held a dinner and meeting at. the Sierra; Madre Club, Los Angeles, on Friday evening, Sept. 28, 1915, at which 21 members and guests-were present. The Vice-Chairman, C. Colcock Jones; presided, in the absence of the Chairman. The amendment' to the By-Laws providing for the increase of the Executive Committee from five to seven members, having been formally presented at the annual meeting of June 18, 1915, and duly announced for consideration at this meeting, was voted on and unanimously adopted. Prof. Robert H. Richards of the Massachusetts Institute of Technology; made a short address on the subject of ore concentration. The paper on the Geology and Ore Deposits of Mojave, County, Arizona, prepared by F. C. Shrader, was presented to the meeting by the Secretary and was discussed by Allen Burris and Dr. L. D. Godshall. F. J. H. MERRILL, Secretary.

Jan 11, 1915

E. T. Dumble, Houston, Texas (communication to the Sec-retary?):—In addition to the list of publications mentioned by Mr. Schorr and those by Prof. Hofman, I call attention to the following references:— Sludi sulle Lignite, by Capacci. Turin (1890). (An excellent work.) Report of Brown Coal Industry in Germany. J. Cosmo New-berry. Department of Mines, Victoria (1892).

Jan 1, 1905

By AIME AIME

BLANDFORD. C. BURGESS, the new Chairman of the Industrial Minerals Division, took the advice of Horace Greeley in reverse-he turned his hack on San Francisco and the Golden Gate, and after a few side excursions toward Alaska and Arizona, hit the trail eastward, not for the lonesome pine, but for Spruce Pine, N. C. Born Aug. 10, 1893, in San Francisco. Burgess found his first job, shortly after finishing high school at 19, as axeman for a surveying party of engineers working for the Southern Pacific Co. in Oregon. Later he moved on up with them into Alaska. He liked the engineering profession, and decided to equip himself further so he entered the University of California in the fall of 1913. and for the next two years devoted himself to acquiring an education in civil engineering.

Jan 1, 1945

COUNCIL OF SECTION DELEGATES E H Stevens, Chairman James W Halley, Vice-Chairman George J Donaldson, Secretary The Peoples Natural Gas Co 140 Stanwix St Pittsburgh 22, Pa EXECUTIVE COMMITTEE H R Wardwell, J G Evans, H R Bianco, Harry Campbell

Jan 1, 1955

By J. E. Burke

Recent investigations have elucidated many of the phenomena of the grain growth process, but have also revealed some conflicting and unexplained results. Beck and his co-workers 1,2,3 have shown that grain growth continues with continued heating at one temperature until the average grain size approaches the thickness of the specimen. Plotting the logarithm of the average grain diameter, D, against the logarithm of the annealing time, t, they find the straight line relationship given by the equation: D = Ktm [,] with possible small deviations at short annealing times. K and n are constants at constant temperature. On the other hand, Wa1ker4 finds that, in alpha brass) the rate of growth falls off more rapidly than indicated by Eq i after long annealing, so that an equilibrium grain size is approached. Burke5 showed, using Walker's data, that time and temperature for grain growth are apparently related through an activation energy, H, according to the relationship: ] where h and tz are the annealing times necessary for the average grain size to increase from Do to D at temperatures T1 and T2 and R is the gas laws constant. In the case quoted, H had the value 60,000 cal per mol. The apparent validity of this relationship, at least up to 700°C, and the approximate value of H were later confirmed by Beck3 The results obtained by Beck Kremer, Demer and Holzworth2 for aluminum and aluminum-magnesium alloys could not be satisfied by such a relationship, since the slope of the isothermal curves increased with increasing temperature. These data indicate and Beck, Holzworth and HuV ater demonstrated expcrimentally that the only apparent factor controlling the rate of grain growth at constant temperature is the grain size. While many of the phenomena have been elucidated, a reasonably quantitative explanation of the process is lacking. There exists uncertainty even as to the primary driving force for grain growth, although there is a considerable body of indirect evidence that the interfacial energy of the grain boundary is responsible.7,8,io Making implicit use of this assumption, several authors14,16 have pointed out that grain boundaries should migrate toward their center of curvature. Harker and Parkerg have advanced this concept furthest, and show that one can expect grain boundary migration to occur only when the grain faces are curved, or when they meet at non-equilibrium angles. When the face is curved toward a grain A, for example, the atoms in the surface of grain B, on the other side of the boundary7 are on the average more surromded by the atoms of their lattice than the atoms on the surface of grain A. Because of thermal motion, the atoms at the interface will sometimes be attached to grain A and

Jan 1, 1949

CALAMINE is one of the semiminerals that have great similarity to the metals. It is a very heavy mineral earth of a yellowish color. It is found in Germany near the lead mines and in Italy in a mountain between Milan and Como. It is also found, as I have heard, in other places, as at Fosini in the territory of Siena. I believe that it is almost certain that some exists there because there are many other kinds of minerals there- about, although none is mined there in these times. But this does not mean that it could not be mined or that there is not some there that is real. Someone says that he med to melt what he could find with copper [36v]

Jan 1, 1942

By W. D. Robertson

A considerable quantity of experimental data is available on the effect of time, temperature, work-hardening and composition on the mechanical properties and corrosion resistance of aluminum alloys. There is, however, little unity of purpose or generality in most of the studies and, because the number of variables is large, the results often are not applicable to the problems that arise in practice. Furthermore, the customary expression of the effect of different variables as separate curves or as three-dimensional diagrams with time, temperature and the dependent variables as coordinates, renders the task of selecting the optimum time and temperature of precipitation treatment, with respect to their simultaneous but unequal effect on the various properties, exceedingly difficult. The introduction of precipitation treatments to raise the yield strength of 24S-type alloys has created a need for a method of correlating and summarizing the effect of time and temperature on the mechanical properties and susceptibility to intercrystalline corrosion. Correlation is particularly desirable because the choice of time and temperature is of necessity a compromise to achieve the best possible combination of properties, and the optimum conditions cannot be accurately specified unless the data are in a form in which the alternatives can be readily compared. Therefore, the work described here was undertaken to find a common relationship that would be capable of expressing the effect of precipitation time and temperature on the various properties and by means of which the relative effects could be correlated and their interpretation facilitated. REVIEW OF PREVIOUS WORK In connection with an investigation of the interrelation of age-hardening and creep performance of nickel-silicon-copper alloys, Jenkins and Bucknall1 demonstrated that the time required to attain maximum hardness and tensile strength could be expressed by a relationship of the form: t = K. 10m/T (I) where t is the time in hours and T the temperature of aging, expressed in degrees absolute, and m and K are constants. They also pointed out that this expression is analogous to that which describes the change of the diffusion coefficient D with temperature; namely, D = Ae-Q/RT (2) Later, Cohen used this relationship in studies of the mechanism of age-hardening of a silver- rich copper alloy2 and of duralumin. 3

Jan 1, 1945

By F. L. Clerc

THE lead and zinc region of SW. Missouri is interesting, not only by reason of the value of its output, which ranges in the neighborhood of ten million dollars a year, but even more because of the facilities which it offers for the study of certain forms of ore-deposits, of which the loci and genesis are somewhat obscure. Although the mineral species found in the region are few and of common occurrence, crystallization has taken place on a generous scale, and unusual forms abound in many combinations, presenting examples of pseudomorphism, paragenesis, metasomatic replacement and the action of mineral-depositing and mineral-dissolving waters. For the mineralogist, lithologist, and specialist in certain lines of metamorphism, it has peculiar attractions, while the systematic geologist will perhaps find its chief claim to attention in the simplified problem it presents, in the study of ore-deposits. In addition to the phenomena above enumerated, it presents instances of well-developed comb-structure in the ores, fissures and faults, and slickensides-features usually associated with extensive movements in the earth's crust, and believed by some authorities to prove the deep-seated origin of the ores. In connection with these occurrences, the absence of all igneous rocks from this region is noteworthy and significant. For that reason, the simplified case presented by the Joplin region, from which these rocks have been eliminated as a factor, is specially valuable. Having had unusual opportunities to watch the development of this district, I have been deeply interested in the bearing of the revelations of the Joplin mines upon questions of universal importance to the science of ore-deposits ; and it was to my great regret that the project of a meeting of the American Institute of Mining Engineers at Joplin, proposed in 1892, was

Mar 1, 1907

By R. W. Raymond

That the death of Martin Coryell, which occurred at Lambertville, New Jersey, on Monday morning, November 29th, touched the sympathies of a wide circle of professional associates and personal friends, was amply testified by the gathering at the funeral services on Friday. Like his distinguished friend and neighbor, the late Ashbel Welch, Mr. Coryell was one of those pioneers in American engineering to whom we owe the great railway and canal systems which lie at the base of our national prosperity, and who have consequently enjoyed the respect and esteem of their successors of the present generation. Martin Coryell was born July 20th, 1815, at New ope, Rucks County, Pa., and was educated principally in the schools of his native town arid of Lambertville, New Jersey, to which place he returned for permanent residence fifty years later. With the exception of a brief period in youth, during which, to restore his failing health, he learned and practiced for a few months the carpenter's trade, and another brief period, later in life, when he read law for a time in the office of B. H. Brewster, of Philadelphia, afterwards Attorney-General of the United States, Mr. Coryell may be said to have spent his life as an active civil and mining engineer. Even these two episodes can scarcely be said to have been deviations from that profession, since they served to give him more thorough preparation for constructive and administrative work. The Delaware Division Canal, the Raritan Canal, and the Brunswick Canal, are among those upon which Mr. Coryell was employed. For the Raritan Canal Company, under the superintendence of Ashbel Welch, he located the greater part of the Belvidere Railroad (now the Belvidere division of the Pennsylvania Railroad), and directed its construction from Trenton to Lambertville. He was also active as a mining engineer, being one of the early pioneers of mining in the Lake Superior copper region, and had much to do with the development of the Hazleton coalfield and the railroad which has since expanded into the Lehigh Valley system. In 1862, he removed to Wilkes-Barre, where, in 1864, he became manager of the Warrior Run Mining Company. One of the editors

Jan 1, 1887

By Joseph C. Buchen

In principle, productiorl of salt from sea water is a simple operation. The sun and wind cause evaporation of sea water trapped in ponds, and what is left is principally salt. Commercial production, however, requires consideration of many factors. First is a high consistent annual rate of evaporation, as well as large areas of suitable low-lying ground close to economical shipping facilities. The south end of San Francisco Bay has these requisites. Large ponds are built, by using clamshell dredges to build up levees to a height of approximately 3 ft. on ground usually lower than sea level, so that the water may be taken in through tide gates without pumping. Ponds are divided into extremely large concentrating ponds and smeller crystallizing ponds. Approximately ten times more area is required for concentrating than for crystallizing. The concentrating ponds are irregular in shape and size but the crystallizing ponds are rectangular and fairly regular in size, to aid in harvesting. The ocean water is taken into the first of a series of concentrating ponds and gradually moved forward from pond to pond as it increase:: in density, reaehing the crystallizing area as a saturated brine. This brine is pumped into the crystallizer at the beginning of the net evaporating season, usually in May, and further evaporation causes its sodium chloride content to deposit on the bottoms of the ponds. The brine must be drawn off and a fresh supply added from time to time to prevent other undesirable salts from depositing with the sodium chloride. Harvesting usually begins near the end of August and now is accomplished almost entirely by mechanical means. After harvesting, the salt is stored in large sbockpiles until required for shipping or refining. The greatest amount is used for industrial purposes and is shipped without any processing other than screening, but all salt for domestic use produced by the Leslie Salt Co. is refined by the racuum process, giving a produet consistently testing over 09.9 per cent sodium chloride.

Jan 1, 1938

By Joseph C. Buchen

In principle, productiorl of salt from sea water is a simple operation. The sun and wind cause evaporation of sea water trapped in ponds, and what is left is principally salt. Commercial production, however, requires consideration of many factors. First is a high consistent annual rate of evaporation, as well as large areas of suitable low-lying ground close to economical shipping facilities. The south end of San Francisco Bay has these requisites. Large ponds are built, by using clamshell dredges to build up levees to a height of approximately 3 ft. on ground usually lower than sea level, so that the water may be taken in through tide gates without pumping. Ponds are divided into extremely large concentrating ponds and smeller crystallizing ponds. Approximately ten times more area is required for concentrating than for crystallizing. The concentrating ponds are irregular in shape and size but the crystallizing ponds are rectangular and fairly regular in size, to aid in harvesting. The ocean water is taken into the first of a series of concentrating ponds and gradually moved forward from pond to pond as it increase:: in density, reaehing the crystallizing area as a saturated brine. This brine is pumped into the crystallizer at the beginning of the net evaporating season, usually in May, and further evaporation causes its sodium chloride content to deposit on the bottoms of the ponds. The brine must be drawn off and a fresh supply added from time to time to prevent other undesirable salts from depositing with the sodium chloride. Harvesting usually begins near the end of August and now is accomplished almost entirely by mechanical means. After harvesting, the salt is stored in large sbockpiles until required for shipping or refining. The greatest amount is used for industrial purposes and is shipped without any processing other than screening, but all salt for domestic use produced by the Leslie Salt Co. is refined by the racuum process, giving a produet consistently testing over 09.9 per cent sodium chloride.

Jan 1, 1938

1. How Does One Determine Whether an Ore Body Will Block-cave? Page Mark A. Smith......... 122 Harry A. Leidich........ 122 McHenry Mosier ...,.. 22 R. W. Hughes ........ 122 Sherman R. Burdick ....... 123 R. T. Gallagher........I 23 Benjamin F. Tillson...... 123 Lucien Eaton...........123 C. F. Jackson..... . .. 123 Philip B. Bucky........... 126 2. How Does One Determine the Block Dimensions and the Development Work Necessary to Make an Ore Body Cave? Mark A. Smith... 125, 127, 129 Harry A. Leidich..........126 McHenry Mosier......126, 127, 132 R. W. Hughes...........126 Sherman R. Burdick.........127 R. T. Gallagher...........127 Benjamin F. Tillson......127,131 L. E. Young............127 Robert D. Hoffman.......128, 132 Gerald Sherman..........128 Philip B. Bucky......130, 131, 132 K. S. McClellan..........132 Tell Ertl.............132 3. How Do the Forces Act and What Are the Stresses Developed in a Block That Cause It to Block-cave? Mark A. Smith.........132, 135 Harry A. Leidich........133 McHenry Mosier . .. 133 R. W. Hughes ....... 133 Sherman R. Burdick..... . 133 R. T. Gallagher..........134 C. F. . Price, Jr. ........134 Benjamin F. Tillson.........134 C. F. Jackson......134, 135,137 R. Taborelli...........135 Frank A. Ayer ... .....136 Philip B. Bucky . .........136 Rollin Farmin . . .......136 . . . Weysser.....135, 136, 137 George S. Rice...........137 4. What Determines the Procedure in Removing Caved Ore? Harry A Leidich...........137 McHenry Mosier........137,141 R. W. Hughes...........137 Sherman R. Burdick........138 R. T. Gallagher...........138 Mark . Smith...........138 Philip B. Bucky......140,141,143 C. F. B. Price, Jr..........140 R. H. Bennett...........141 C. F. Jackson..........141, 143 Gerald Sherman..........141 Tell Ertl.............141 .. .. ..................143 C. H. Shoemaker..........143 5. What Are the Criteria for Determining the Efficiency of a Block-caving Operation? Harry A. Leidich.......... 143 McHenry Mosier......... 144 R. W. Hughes........... 144 Sherman R. Burdick.......144 R. T. Gallagher . ......... 144

Jan 1, 1946

Separates of all the Technical Publications published in 1930 are available at Institute headquarters. All the papers are on file in public, university and technical libraries, and when so indicated in the list, may be found in the TRANSACTIONS. Copies of these papers have been mailed to those members of the Institute who are registered in Classes A-Mining Methods; B-Milling and Concentration; C-Iron and Steel Division; D-Non-ferrous Metallurgy; E-Institute of Metals Division; F-Coal Division; G-Petroleum Division; H-Non-metallic Minerals; I-Mining Geology; K-Mining Administration; L-Geophysical Prospecting, respectively. Other members may obtain copies by writing to the Secretary. Additional copies are sold at the rate of 1 cent per page; minimum charge, 25 cents. METAL MINING TECH¬ NICAL PUBLI- TITLE AUTHOR MEETING TRANS CATION VOLUME No. AND PAGE* 264-A.29. Quicksilver Industry in 1929. Im- L. H. Duschak San Francisco T30, 283, 312 provements in the Metallurgy of C. G. Maier and Oct., 1929 Quicksilver and Symposium on The others Present Status of the Quicksilver Industry (With Discussion) (37) 271-A.30 Observation on Ground Movement R. E. Palmer New York T30,168 and Subsidences at Rio Tinto Feb., 1930 Mines, Spain (20) 274-A.31 Development and Installation of the C. L. Berrien New York T30, 139, 166 Hawkesworth Detachable Bit (29) . Feb., 1930 276-A.32 Protective Measures Against Gas O. A. Glaeser New York T30, 129, 187 Hazards at United Verde Mine (11) Feb., 1930 287-A.33 Use and Cost of Compressed Air (12) R. S. Lewis New York Feb., 1930 314-A.34 Miami Copper Company Method of F. W. Maclennan New York T30, 39, 80 Mining Low-grade Orebody (44) Feb., 1930 319-A.35 How Human Beings Respond to W. J. McConnell New York Changing Atmospheric Conditions Feb., 1930 (9)

Jan 1, 1930

By G. C. Kuczynski

Two particles in mutual contact form a system which is not in thermo-dynamical equilibrium, because its total surface free energy is not a minimum. If such a system is left for a certain period of time, the bonding of the two particles will take place in order to decrease the total surface area, even though the temperature is lower than the melting point. This phenomenon of bonding of two or more particles with the application of heat only and at temperatures below melting point of any component of the system will be called sintering, although the powder metallurgists use this term in a broader sense, including the presence of molten phase and pressure. It is the objective of this paper to study this process and the mechanisms involved in it. This problem is of utmost importance to powder metallurgy and powder ceramics, and its technological aspects have been studied for a good many years. However, the powder metallurgical operations are too complex and include too many superimposing mechanisms, and too many variables for a direct study. It was therefore advisable for the purposes of this study to reduce the variables to a minimum. In this work the radius of the interface formed during bonding in a simple system composed of a spherical particle and a large block of the same metal was studied as a function of time and temperature. It is believed that the mechanism involved in this simple process is fundamental to any sintering operations. Previous Work J. Frenkell was the first to make a serious attempt to develop a theory of sintering. He assumed that the process consists of a slow deformation of crystalline particles under the influence of surface tension which reduces to a viscous flow where the coefficient of viscosity n is related to the self-diffusion coefficient D by the following equation 1 _ D D6kT [1] where 6 is interatomic distance, k the Boltzman constant, and T the absolute temperature. This type of viscous flow of a crystalline substance is essentially different from the ordinary plastic flow. The latter is a specific propcrty of crystals and cannot take place in amorphous bodies. According to Frenkel this viscous type of flow is due to the diffusion of the holes or vacancies arising in the lattice. He was able to derive an equation relating the growth of the interface between two spherical crystalline particles or between a particle and a semi-infinite crystal (Fig 1) to time t at constant temperature. This relationship can be written as follows: x²— 3/2 a/nt [2] where x is the radius of the interface assumed to be circular, a the original radius of the sphere and a surface tension of the material. The other assump- x tions are that x is less than 0.3 and that during the period 1 the original radius, a, of the metallic particle did not change appreciably. A. J. Shaler and J. Wulff2 followed closely the ideas of Frenkel in their theory of sintering of a mass of metallic powder. Neither Frenkel nor Shaler has validated his theoretical speculations with conclusive experimental data. Two measurements reported by

Jan 1, 1950

By J. W. Dougherty, J. M. Douglas

THE Hollinger gold mine is in the Porcupine mining division, District of Cochrane, in the northern part of the Province of Ontario. The adjacent town of Timmins, with a population of 25,119, lies 490 miles by railway north of the city of Toronto. GEOLOGY The property is situated on the northwest limb of a major syncline, which pitches northeast at approximately 50°. The principal rocks of the Hollinger area are of pre-Cambrian age and consist of altered, schistose, Keewatin lava flows intruded by stocks of schistose, quartzfeldspar porphyry generally assigned to the Algoman period. The structure of the Keewatin series is extremely complex as a result of close folding and some faulting. The schistosity, trending north 70° east and dipping steeply to the southeast, is most highly developed along a subsidiary anticline in which the major porphyry bodies occur. The ore bodies, which exhibit three principal structures, consist of quartz veins and associated pyritized wall rock. Some lodes are composed of en echelon veins, others exhibit a main quartz body with branching stringers and a third consists of a single definite lead. Gold, in a coarse visible form, may be confined to quartz in some ore bodies but in others it is finely divided and is found not only in quartz but also associated with pyrite in the adjacent wall rock. In many veins the distribution of gold is such that there are several ore sections, separated by areas of low-grade material, in the same vein although its physical appearance remains unchanged. The veins form a very complex pattern in an ore zone which in places attains a length of 6000 ft. and a width of 4000 ft. They are most abundant in the Keewatin lavas in the neighborhood of the porphyry bodies. Few of the veins are persistent for long distances, though some

Jan 1, 1940

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