Search Documents

By Lawrence Wright

THE occurrence of gold, gold-silver, silver-lead-zinc ores in the post-Cambrian sediments in the Black Hills of South Dakota, and their genetic relationship to the Tertiary intrusives, is well known and accepted, but the occurrence of gold in the pre-Cambrian rocks at the Homestake mine, which underlie this Tertiary gold mineralization, has given rise to differ-ences of opinion as to the period of major gold introduction into the older rocks. Fig. 1 illustrates. the distribution of mineralization along the axis of the Tertiary uplift in both pre-Cambrian and post-Cambrian rocks. The following possibilities have been presented: 1. The Homestake gold deposit was formed in pre-Cambrian time and the deposits in the overlying Cambrian sediments formed during Ter-tiary time. 2. The Homestake lode existed at the beginning of Cambrian time, but was enriched by the passage of Tertiary auriferous solutions. 3. The Homestake lode was represented by pre-Cambrian quartz-chlorite sulfide mineralization, very low in gold content and the gold superimposed on the older nearly barren mineralization during the Ter-tiary metallogenic epoch. 4. The sulfides and sulfarsenides as well as gold were deposited in both pre-Cambrian and post-Cambrian rocks during the Tertiary period. Those favoring the first proposition feel that the question is pretty well settled, while the proponents of the second theory are more flexible in their view, feeling that the amount of gold introduced in either period is still an open question. The third and fourth theories, with some modifi-cations, are supported by the proponents of the Tertiary theory, who feel that the evidence strongly favors that period. The following pages are intended to present the evidence and to give the reaction of various observers with my own comments and conclu-sions; also, the accumulated facts of observation gathered over a period of close association with the area under discussion, beginning in 1919.

Jan 1, 1936

By Henry G. Granger

It still rains in the Choco! I well remember one evening a dozen years ago, while traveling toward the town of Negua in a small champa or dug-out canoe, the rain fell so heavily that I had to work my hardest to bail out the water with a large totuma or gourd in order to keep the canoe afloat, the native boatman meanwhile plying his paddle in the stern. If any one thinks bailing is easy work, let him scoop out a quart or more at a stroke, 40 times a minute for half an hour, and I venture that he will change his opinion. These small canoes required only one paddler to make the 3 miles an hour which is the standard rate of aquatic progress on the Choco. Another time, on the Atrato river, about six o'clock in the afternoon, the rain fell so heavily that an empty gourd, 9 in. in diameter and 4.5 deep, was filled to the brim in 90 sec., timed by a watch. Such downpours are typical, but unless caught in one it is not specially noticed. These downpours seldom last more than an hour, and frequently cover only a limited area, occasionally falling on one bank of a river and not on the other. During the night-time, the rain, if gentle, will usually last until dawn, and sometimes an intermittent drizzle will keep up all day as well, although, as a rule, it rarely rains during the day. The rise of the rivers, due to the rain-fall, varies from a few inches to several feet. One night in August, 1899, the spuds of the dredge Margaret, operating on the Atrato river, showed a rise of 16 ft., and for 3 days thereafter occurred the greatest flood known in that district for 32 years. The dredge had all three spuds down, and the 2-yd. shovel dragging 011 the bottom. A 0.75-in. cable fast to a stout tree, 700 ft. away, stretched tight

Jan 1, 1909

By E. A. Barnard

ARSENIC is a very old substance. The ancients speak of it in their writings, and its use has developed very little until recent years. The ancients used it in making pigments, in medicine, and for poison. They also tell of the difficulties of handling it-an experience which is very similar to our own. Until about 10 years ago, arsenic was very cheap and was a drug on the market. About that time the boll weevil began making serious inroads on the American cotton crops, and after much investigation the Depart-ment of Agriculture developed a very successful poison for this pest, consisting of calcium arsenate. The weevil pest has continued, and as the cotton planters have become convinced that calcium arsenate is the best material to use against the weevil, the demands for it have been steadily increasing, resulting not only in a rising price of arsenic but in a very serious shortage so far as our country is concerned. So serious has this shortage become, and so vital is it to the cotton growing industry, that Congress has appointed a committee to investigate and report on the situation. A meeting of arsenic producers and consumers was held in New York last December to take stock of the situation and to see what could be done. The extreme increase in, the market price of arsenic-from 6 c. to 15 c. per lb. in less than a year-has been very harmful to the producers as well as to the consumers. Some very interesting' data were brought out at this meeting, as follows: CONSUMPTION PER YEAR, SHORT TONS Arsenate of lead 2,000 Paris green 1,200 Proprietary mixtures 750 Sheep dips : 1,000 Weed killers 1,500 Glass : 2,000 8,450 1922 Consumption as calcium arsenate 4,000 12,450 1923 Estimated consumption as calcium arsenate... 12,000 Estimated 1923 consumption 20,450

Jan 8, 1923

THE problem of reaction rates in the open-hearth process is essentially that of trying to form a fairly clear picture of the "chemical mechanisms" in the bath. Quantitative data on reaction rates would perhaps not be of much practical importance even if they were available; however, what few approximate data there are can be used in combination with data given in Chapters 16 and 17 to sketch a picture of the "chemical mechanics" of the open-hearth process that is consistent with essentially all the present available evidence. The result may later be found incorrect in many details but even so it will illustrate certain useful methods for obtaining a clearer understanding of the process. Consistent with the treatment in Chapter 15, but in simpler terms, we may say that chemical reactions in general involve the following elements or steps: 1. The reacting molecules are mixed together in space in such fashion as to favor collisions among them. 2. Units of what is usually an intermediate molecular arrangement called an activated complex are formed at a certain rate, depending on temperature and concentrations. 3. These activated complex units decompose into the reaction products (this step usually assumed to be so rapid as never to limit the over-all process). 4. In any of these steps, heat energy may have to flow into, or away from, the reaction zone to permit the reaction to proceed. 5. The products of reaction will usually have to move out of the way to permit further reaction. The temperature factor enters mainly through step 2, and its effect is very marked. (What is called temperature is really the mean energy content of all the molecules of the substance involved; at any one temperature a certain proportion of the moleculea will have much higher energy content than the mean value.) Various reaction rates measured at around room tem-

Jan 1, 1951

By P. H. Brace, N. A. Ziegler

The study of the relations between gases and metals is one of pcren-nial interest to all who are connected with the production of high-grade metallurgical products. The data reported here are the outcome of work of which the object is to determine the effects of dissolved gases upon the properties of metals and to gain a more detailed knowledge of the reactions between gases and molten metals, particularly iron, under definitely controlled conditions. We have attempted to reduce our margin of error by dealing with relatively large quantities of metal, from 4 to 13 Ih. (2 to 6 kg.), and keeping the ratio of refractories to metal as small as practicable. The ingots produced are large enough to provide adequate material for making determinations of magnetic and other physical properties. In choosing the bell-jar type of furnace we were influenced by the results of considerable experimentation along the same general line which indicated that, for the scale on which we were to work, it was important to have the furnace structure independent of the vacuum enclosure. The use of a bell-jar surrounding the entire furnace accomplishes this and also gives great freedom of observation during operation and ready accessibility for the replacements which are necessary after each run. Our choice of analytical method was made in the light of the results secured by H. M. Ryder, who used a method similar in principle for the analysis of very small quantities of gas extracted from strips of metal heated electrically in high vacuum. We have presented some selected preliminary experirnental data as being illustrative of the quantity and nature of the gases which occur in iron of different origins, but do not urgc any hypothesis at this time. The Furnace Our furnace may be described as "a high-frequency induction furnacc of the bell-jar type." It is similar in a general way to that described by Cain and Peterson1 though we have introduced certain refinements of

By G. H. Anderson

During an investigation of the copper-rich portion of the copper-silicon-iron system as part of an extensive research program on P.M.G. alloys, which was begun in 1937 in the research laboratory of the Phelps Dodge Corporation, it became apparent that the binary copper-silicon system below 7 per cent Si needed revision, therefore an investigation was undertaken. Both X-ray methods and microscopic technique were employed. Despite the many investigations that have the clarification of this system as their object, no two successive reports on the system have agreed in placement of the alpha-phase solubility limit, and uncertainty about the secondary phase first to appear has been voiced several times.3,4,5 It was therefore not surprising, when T. Isawa's6 and M. Okamoto's7 works were reported at the time we were finishing up our experimental work, to find essential disagreement between their results and ours. But when C. 5. Smith's latest work on the copper-silicon systema was published just as we were finishing our laboratory report, it was indeed gratifying to find that the latter's diagram and ours checked in all essential features, except the temperature of the peritectoid line above 830" C. Many attempts were made to retain the beta phase during the present investigation, but none was successful. Isawa,6 however, reports that he has been able to obtain X-ray photograms of the beta phase. The structure, he states, is body-centcrcd cubic with a lattiee constant of 2.848 ,&. at 7.2 per cent Si. Okamoto7 and Smith8 both use the designation Kappa for the hexagonal phase, and to avoid confusion this designation will he adhered to in the present paper. Preparation of Samples The alloys were melted in vacuum in a high-frequency furnace. from copper cathodes containing 99.98 per cent Cu, and specially refined silicon supplied by The Electro Metallurgical Co. This silicon is stated

Jan 1, 1940

By G. H. Anderson

During an investigation of the copper-rich portion of the copper-silicon-iron system as part of an extensive research program on P.M.G. alloys, which was begun in 1937 in the research laboratory of the Phelps Dodge Corporation, it became apparent that the binary copper-silicon system below 7 per cent Si needed revision, therefore an investigation was undertaken. Both X-ray methods and microscopic technique were employed. Despite the many investigations that have the clarification of this system as their object, no two successive reports on the system have agreed in placement of the alpha-phase solubility limit, and uncertainty about the secondary phase first to appear has been voiced several times.3,4,5 It was therefore not surprising, when T. Isawa's6 and M. Okamoto's7 works were reported at the time we were finishing up our experimental work, to find essential disagreement between their results and ours. But when C. 5. Smith's latest work on the copper-silicon systema was published just as we were finishing our laboratory report, it was indeed gratifying to find that the latter's diagram and ours checked in all essential features, except the temperature of the peritectoid line above 830" C. Many attempts were made to retain the beta phase during the present investigation, but none was successful. Isawa,6 however, reports that he has been able to obtain X-ray photograms of the beta phase. The structure, he states, is body-centcrcd cubic with a lattiee constant of 2.848 ,&. at 7.2 per cent Si. Okamoto7 and Smith8 both use the designation Kappa for the hexagonal phase, and to avoid confusion this designation will he adhered to in the present paper. Preparation of Samples The alloys were melted in vacuum in a high-frequency furnace. from copper cathodes containing 99.98 per cent Cu, and specially refined silicon supplied by The Electro Metallurgical Co. This silicon is stated

Jan 1, 1940

By Maurice Ewing

THE purpose of this paper is to present the results of the application of the earth-resistivity method of subsurface investigation to the problem of locating seams of anthracite coal beneath a mantle of soil and subsoil. Details are given of the successful use of this method in locating the outcrops of anthracite seams in actual prospecting. The presence of the outcrop of an anthracite seam is indicated at points where electrical resistivity tests showed relatively low readings. The reason for, this is that in some localities the resistivity of anthracite was found to be about 0.0001 megohm-cm. compared to 1 to 200 megohm-cm. for shales and sandstones. For two reasons it is believed that the data sum-marized in this paper should be of particular interest. In the first place, most of the interpretations of the resistivity survey have been checked by subsequent drilling and some by the removal of the overburden and the exposing of the anthracite seams. It is infrequent that the oppor-tunity for checking results so thoroughly is given. In the second place, the fact that recent commentators 1.2.1 on the application of geophysical methods to mining have concluded that direct prospecting for anthracite and other types of coal is not promising makes the good results obtained more significant. So far as the authors can learn, the only previous experiment with electrical methods in the Pennsylvania anthracite field was one made by Sherwin F. Kelly in 1922, when he used the self-potential method at Wilkes-Barre4. The profile he made does not show a very marked correlation with the geologic cross section. Kelly points out that stray currents from electric motors in the mines undoubtedly affected his results, but the experience of the present authors with stray currents from mining machinery suggests the possibility that the potentials measured by Kelly were due almost entirely to this effect.

Jan 1, 1936

By Arthur Green

A GROUP of 13 cities situated in Los Angeles and Orange counties in Southern California is engaged in constructing an aqueduct to carry water from the Colorado River at a point near Parker, Arizona, to a distribution point sear Riverside, California. The aqueduct will have a total length of approximately 241 miles, and is designed to deliver 1605 cu. ft. of water per second, or a little more than one billion gallons per day. The aqueduct crosses a barren, desert waste and the project includes approximately 91 miles of 16-ft. tunnel. The large amount of tunnel driving that has been done in this country in the past few years has resulted in some remarkable developments in equipment and methods. The building of the Colorado River Aqueduct, with its 91 miles of tunnels, has called on the best engineering knowledge in the country. New and better equipment has been designed for all phases of the work, and this equipment has been coordinated and adapted to the various conditions with a high degree of efficiency. The result has been that records for tunnel driving have been set under adverse natural conditions that exceed the estimates for progress under good conditions. All of the tunnels in the main aqueduct, except the Valverde and Bernasconi at the western end, have a finished diameter, inside the concrete lining, of 16 ft. Fig. 4 shows a section of the tunnel with the concrete lining in place. Fig. 5 illustrates the finished tunnel in three typical sections. The standard tunnel grade is 3.432 ft. per mile in the 16-ft. tunnels, but the Valverde and Bernasconi tunnels have a steeper grade and a finished diameter of 15 ft. 3 in. The rough bore of the large main aqueduct tunnels averages 12.95 solid cubic yards of material per foot of advance in timbered sections and 10.76 solid cubic yards per foot in unsupported sections.

Jan 1, 1936

By S. R. B. Cooke, H. S. Choi, I. Iwasaki

In magnetic taconite of the East Mesabi range, quartz, magnetite, and cummingtonite (OH}(Fe, Mg)(Si4O11)2) are the three major ore-forming minerals.' Fine grinding and magnetic separation of the taconite leads to a concentrate analyzing 64 to 65 pct Fe and 8 to 9 pct insoluble; the gangue content of the concentrate arising from the presence of locked magnetite-gangue particles, and of occluded gangue particles in magnetic floccules. To further upgrade such taconite concentrates, flotation appears to offer a particularly promising approach. To evaluate its effectiveness in separation, a knowledge of the flotation characteristics of each mineral comprising the concentrate becomes desirable. The floatability of magnetite and of quartz have already been reported in a previous paper,2 in which the flotation characteristics of the two minerals were correlated with the electrokinetic properties at the mineral-solution interfaces. Since cummingtonite has somewhat intermediate chemical composition between the above-named oxides, the electrokinetic and the flotation behavior of this mineral becomes of interest for both practical and fundamental reasons. In the present article the results of electrophoretic mobility measurements and of Hallimond tube flotation tests on cummingtonite are reported and are compared with those of quartz and magnetite. MATERIALS AND METHODS A sample of cummingtonite-rich taconite, received from the Mitchell pit, near Babbitt, Minn., was crushed and ground through 100 mesh, and the product was fractionated magnetically into three portions. First, a drum-type laboratory cobber was used to separate a highly magnetic portion, consisting mainly of free, but also containing locked, magnetite particles. The cobber tailing was then passed in two stages through a Franz isodynamic separator. The middle fraction was isolated, and, upon examination petrographically, was ascertained to be principally cummingtonite. The 100 to 150 mesh fraction of this sample was selected for the present study. It was cleaned by leaching briefly with hot, dilute HC1 and then by rinsing repeatedly with demineralized water. A ground and elutriated fraction of -5p cummingtonite was used for the electrophoretic measurements.

Jan 1, 1961

By F. Cadena

Hiwassee Darn, now under construction by the Tennessee Valley Authority on the Hiwassee River, a tributary of the Tennessee River, will require aggregate for approximately 800,000 cu. yd. of concrete. Near the damsite deposits of natural sand or gravel are not available and graywacke, a rock that is found in abundance, suggested itself as a likely source of manufactured aggregate. Graywacke is a metamorphosed sandstone composed principally of a mixture of quartz (65 per cent), mica (25 per cent), and feldspar (10 per cent). Other minerals are present in negligible amounts. The rock varies in different parts of the quarry from very fine to a coarse grain containing particles of about ¼ in. maximum size, although the bulk of the deposit is medium grain. Extensive tests showed that graywacke would be suitable as a source of both coarse and fine aggregates. The aggregate plant available for use at Hiwassee Dam consisted of the coarse-aggregate and sand plant used on the Norris project. The coarse-aggregate plant had also been used at Chickamauga Dam. Although most of this plant equipment is now in use at Hiwassee, the present flowsheet is not only different from that at Norris and Chickamauga but is also unique as compared to the flowsheet of the average crushed-stone aggregate plant. It is hoped that this paper will show the importance of proper arrangement of equipment if the optimum in flexibility and capacity is to be attained. Flowsheet Rock is ioaded by 3-yd. electric shovels into 12-yd. dump trucks, which carry the rock to the primary crusher, a 42-in. Superior McCully gyratory unit set at 4¾ in. (Fig. 1). The primary crusher discharges directly onto a 42-in. inclined belt conveyor, which carries the product to a surge storage pile with a maximum live storage capacity of approximately 3000 tons. A concrete tunnel under this storage pile houses the feed end of a 36-in. belt conveyor (conveyor B) fed by a 36 by 66-in.

Jan 1, 1942

By A. Hellawell

Binary alloys of compositions intermediate between solid-solubility limits and eutectic compositions have been completely separated into primary phases and eutectic by freezing unidirec-tionally at very slow rates (10-6 to 10-5 cm per sec). The alloys examined were Pb-1 wt pct Ag, Al-20 wt pct Cu, and Al-42 wt pct Cu. The compositions and proportions were close to those expected from the phase diagrams and provided information about the solid/liquid interface at certain free zing rates. DURING the directional freezing of an alloy the solute distribution is controlled by the efficiency of mixing in the liquid,'" whereas diffusion in the solid state is of negligible importance. It is known3 that mixing by convection is very efficient, but complete segregation is only achieved at very slow freezing rates4-6 or with forced stirring in the liquid. ' Yue9 and Yue and clark10 have previously illus- trated partial separation of primary phases in alloys close to eutectic compositions. In the present work, taking binary alloys of compositions intermediate between the limits of solid solubility and eutectic compositions, it has been possible to achieve complete separation of the primary phases by directional freezing at very slow rates. METHODS AND RESULTS The alloys concerned were Pb-1 wt pct Ag, A1-20 wt pct Cu, and A1-42 wt pct Cu. As may be seen from the relevant diagrams,11 these alloys should segregate into approximately equal proportions of primary solid solutions and alloy of eutectic compositions. Specimens, -12 cm long and 1 cm wide, were frozen in horizontal tubes by withdrawal from a furnace. The lead alloy, prepared from materials of 99.999 pct purity, was sealed into evacuated Pyrex tubes and the aluminum alloy of similar purity contained in graphite boats under vacuum. The molten alloys were seeded with some 3 cm of solid to prevent irregular initial freezing rates and the last portions to freeze were ignored. At the slow freezing

Jan 1, 1965

By A. S. Nowick, W. A. Goering

INspite of considerable interest in the kinetics of ordering of the alloy Cu3Au there is no direct information available on the activation energy for atom movements in this alloy, such as that obtainable by radioactive tracer-diffusion studies or by internal friction measurements. Accordingly, this alloy was examined to find out whether it displays an internal friction peak resulting from stress-induced ordering, similar to that studied extensively in other alloy systems.1-3 Measurements of the internal friction as a function of temperature were made in a torsion pendulum similar to that described by Ké.8 Wire specimens 0.032 in. diam and 11 in. long were used. The wire, obtained in the cold-drawn condition,* was annealed at 900C in a quartz tube to obtain a large grained sample, and then mounted in the torsion pendulum furnace. Internal friction is reported here as the lag angle, 4, which is equal to the logarithmic decrement divided by .ir. Fig. 1 shows the internal friction at three frequencies (the frequency given for each curve is the value measured at the peak). The data for these curves were obtained on cooling one specimen from 460C to just above the critical temperature for long-range ordering, which is about 390C for this alloy. In this way, the internal friction is measured under conditions where the alloy is in the disordered condition throughout the run. The curves obtained at frequencies of 2.15 and 1.29 cps show peaks in the range of measurement. The corresponding peak for the 0.78-cps curve is estimated, from the shift of this curve relative to the others, to be located slightly below the critical temperature (at 385C). The fact that the peak can be observed above the critical temperature is good evidence for the belief that it is a stress-induced ordering phenomenon similar to that which is observed in other disordered alloys. The fact that the peaks in Fig. 1 are not the same

Jan 1, 1959

By F. Cadena

Hiwassee Darn, now under construction by the Tennessee Valley Authority on the Hiwassee River, a tributary of the Tennessee River, will require aggregate for approximately 800,000 cu. yd. of concrete. Near the damsite deposits of natural sand or gravel are not available and graywacke, a rock that is found in abundance, suggested itself as a likely source of manufactured aggregate. Graywacke is a metamorphosed sandstone composed principally of a mixture of quartz (65 per cent), mica (25 per cent), and feldspar (10 per cent). Other minerals are present in negligible amounts. The rock varies in different parts of the quarry from very fine to a coarse grain containing particles of about ¼ in. maximum size, although the bulk of the deposit is medium grain. Extensive tests showed that graywacke would be suitable as a source of both coarse and fine aggregates. The aggregate plant available for use at Hiwassee Dam consisted of the coarse-aggregate and sand plant used on the Norris project. The coarse-aggregate plant had also been used at Chickamauga Dam. Although most of this plant equipment is now in use at Hiwassee, the present flowsheet is not only different from that at Norris and Chickamauga but is also unique as compared to the flowsheet of the average crushed-stone aggregate plant. It is hoped that this paper will show the importance of proper arrangement of equipment if the optimum in flexibility and capacity is to be attained. Flowsheet Rock is ioaded by 3-yd. electric shovels into 12-yd. dump trucks, which carry the rock to the primary crusher, a 42-in. Superior McCully gyratory unit set at 4¾ in. (Fig. 1). The primary crusher discharges directly onto a 42-in. inclined belt conveyor, which carries the product to a surge storage pile with a maximum live storage capacity of approximately 3000 tons. A concrete tunnel under this storage pile houses the feed end of a 36-in. belt conveyor (conveyor B) fed by a 36 by 66-in.

Jan 1, 1942

By G. H. Clevenger

THE reagents now used in flotation consist of various acids or salts, which may be either electrolytes or non-electrolytes, dissolved in water and some substance or combination of substances which function as collecting or frothing agents. At times the only dissolved salts present are those naturally occurring in the water used. The general effect of the electrolyte is to greatly sharpen the separation between the gangue and the concentrate. Examples of this are: The use of sulphuric acid with zinc ores; and of sodium carbonate or calcium oxide (line) with silver-gold ores. Crude pyroligneous acid is also sometimes used when available. Various oxidizing agents, such as permanganates, bichromates, etc., are added in the selective flotation of lead-zinc ores. Many other reagents for performing certain specific functions, either real or imaginary, have been proposed, and a number of them have been tried upon a working scale. The wild orgy of experimentation which is now going on in flotation exceeds even that which followed the introduction of the Washoe process for the treatment of Comstock ores, when, among other things, sage-brush tea and tobacco juice were reagents added to the pans. Out of all this will, of course, eventually come a more or less standard practice for the treatment of each class of ore. Omitting a discussion of the functions of frothing and collecting agents, the reagents used in flotation for this purpose may be classified under five general heads: (1) Essential oils; (2) fixed or fatty oils;. (3) alcohols and their combinations with organic acids; (4) coal tar and its refined products; (5) petroleum and its refined products. A flotative agent of some kind is required in flotation as now practiced. A single reagent, as, for example, certain. of the essential oils, may perform the dual function of frothing and collecting agent, or a mixture of substances may be required.

Jan 9, 1916

By J. S. Levine

A series of four displacement experiments has been run in a large alundum core. Flow potential distribution in each liquid phase was measured continuously through oil-wet and water-wet capillary barriers, using a null-point pressure balance, and saturated distribution was determined from electrical resistivity measurements. A method has been devised for calculating the effective (and relative) permeability to each phase at any time and at any point in the flow system for the transient displacement process. Relative permeability points have been calculated and average curves drawn for oil displacing water and water displacing oil. The values of dynamic capillary pressure have also been determined. Data have been substituted into the generalized Buckley-Leverett fractional flow equation and a comparison between actual and theoretical breakthrough recoveries is shown. Displacement experiments have been performed in the laboratory for many years in an effort to determine the effect of a number of parameters on multiphase flow in porous materials. In the literature of petroleum technology, Wyckoff and Botset' were among the first to develop the relative permeability concept and to show experimentally that oil, gas, and water can flow simultaneously through a porous medium in a precise way governed by certain fluid properties, by the relative saturation of each fluid, and by characteristics of the medium itself. Somewhat later, Leverett2 and Hassler, Brunner, and Deahl11 developed some theoretical concepts of capillary behavior in porous materials. The work of Buckley and Leverett3 presented a theoretical analysis of immiscible liquid displacement based on the equation of continuity and the Darcy equation for viscous flow of each fluid. Subsequent investigators attempting to verify the Buckley-Leverett equation have, in general, deliberately neglected the capillary pressure term or have performed experiments in such a manner that it could be neglected. Terwilliger, et al4 in 1951, obtained agreement between theory and experiment for the constant rate displacement of water by gas in a long vertical sand column. Rapoport and Leas5 have investigated the

Jan 1, 1955

By R. C. Schmidt, B. E. Kennedy

The Mont Klahoyo magnetite deposit is located about 600 km (373 miles) northwest of Abidjan, Ivory Coast. During an exploration period ending in 1977 an international joint venture group investigated the deposit and proved reserves of 670 Mt (739 million short tons) grading 36% iron. The deposit occurs at the northeast end of the Baoubly-Kiriao chain of Precambrian iron formations with associated amphibolites, pyroxenites, and gneisses of the Liberian Shield. The ore body is represented by a highly metamorphosed banded quartz-magnetite iron formation with alternating beds of iron silicates and quartz-magnetite. Amphibolite-pyroxenites and sillimanite-cordierite-garnet gneisses form hanging and footwall rocks. The iron formation has been folded into an elongated, overturned 2-shaped major drag fold with axes trending and plunging approximately northeast. Beds are vertical or dip steeply to the southeast. The ore zone has an average thickness of 130 m (427 ft) and outcrops intermittently over a distance of approximately 5.5 km (3.4 miles). Based upon detailed studies of drill cores and the results of ore dressing test work, eight stratigraphic units, identified as K- 1 to K-8, are recognizable in the iron formation. Four interbedded units are low grade silicate zones (silicate facies) while the remaining quartz-magnetite units are oxide facies, representing the important Mont Klahoyo deposit ores. Ore-bearing "K" units are subdivided further into 11 ore types, based upon their specific lithologies, iron content, and concentration characteristics. Identification of these ore types proved particularly useful to mine planning and flowsheet design. A cap of oxidized material overlies the primary quartz- magnetite iron formation, but no enrichment has occurred. It is thought that the Mont Klahoyo iron formations were deposited chemically in a volcanic environment as a siliceous iron formation with volcanism the primary source of iron and silica. Metamorphism converted the siliceous iron formation to a coarse-grained, quartz-magnetite-silicate iron formation.

Jan 1, 1983

By D. K. Crampton

INTERNAL stress and season cracking in brass have been studied for many years and the technical literature contains many data on various phases of the subject. A résumé of the literature shows certain fairly well established points upon which various authors are mostly agreed: 1. Season cracking is primarily caused by the presence of relatively high internal stresses, or possibly in some cases by external stresses, or both. 2. A specific corrosion is also essential to season cracking: Certain agents, particularly mercurous salts, mercuric salts and ammonia salts; have such a specific corrosive effect. 3. The tendency to season crack under given conditions increases with increasing zinc content, brass containing less than 20 per cent zinc being relatively immune. 4. In alpha brass the season cracks are intercrystalline; in alphabeta brass they lie between the two constituents; and in beta brass they are transcrystalline. 5. The ordinary impurities or added elements in special brasses have little or no effect on the tendency to season crack. 6. Internal stresses can be eliminated, or at least reduced to a safe 'limit by annealing treatments at temperatures that do not produce visible microstructural changes or appreciable softening of the worked brasses. There are, however, some points in connection with the phenomenon of season cracking which have not been thoroughly investigated, or wherein different authors and investigators are not entirely in agreement. The investigations described in this paper were undertaken to determine: 1. The correlation between mercurous nitrate tests and actual season cracking on long-time atmospheric exposure. 2. The quantitative effect of type and degree of drawing operations on the intensity of internal stress and on the tendency to season crack in brass tubes. 3. The possibility of drawing high-brass tubes in such a manner as to prevent the occurrence of harmful stresses rather than to find a remedy for such stresses once having obtained them.

Jan 1, 1930

THE problem of reaction rates in the open-hearth process is essentially that of trying to form a fairly clear picture of the "chemical mechanisms" in the bath. Quantitative data on reaction rates would perhaps not be of much practical importance even if they were available; however, what few approximate data there are can be used in combination with data given in Chapters 16 and 17 to sketch a picture of the "chemical mechanics" of the open-hearth process that is consistent with essentially all the present available evidence. The result may later be found incorrect in many details but even so it will illustrate certain useful methods for obtaining a clearer understanding of the process. Consistent with the treatment in Chapter 15, but in simpler terms, we may say that chemical reactions in general involve the following elements or steps : 1. The reacting molecules are mixed together in space in such fashion as to favor collisions among them. 2. Units of what is usually an intermediate molecular arrangement called an activated complex are formed at a certain rate, depending on temperature and concentrations. 3. .These activated complex units decompose into the reaction products (this step usually assumed to be so rapid as never to limit the over-all process). 4. In any of these steps, heat energy may have to flow into, or away from, the reaction zone to permit the reaction to proceed. 5. The products of reaction will usually have to move out of the way to permit further reaction. The temperature factor enters mainly through step 2, and its effect is very marked. (What is called temperature is really the mean energy content of all the molecules of the substance involved; at any one temperature a certain proportion of the molecules will have much higher energy content than the mean value.) Various reaction rates measured at around room tem-

Jan 1, 1964

By R. P. Rothwell

The milling of silver ores has arrived at a great degree of perfection in the mining districts of our Western States and Territories, and I hare thought the record of the practical results obtained at the present time, in a few of the principal districts, would prove of value arid interest to many of our members, both at home and abroad. An American silver mill is composed, in descending order from where the ore is dumped, of: 1st. A rock-breaker, usually of the Blake or Alden pattern; 2d. The battery of stamps, the number of which varies from 5 to 120, generally in batteries of 5 or 10 heads, so arranged that a single battery may stand while the others are running; 3d. The tanks where the crushed ore settles (if it is a met stamping-mill), or of a drying-floor if the crushing is done dry; 4th. Amalgamating pans ; 5th. Settling pans ; 6th. Agitators or pans in which mercury escaping in the tailings is caught; 7th. Blanket sluices, over which the tailings run, and where mercury and unamalgamated sulplides are saved. A reference to the engravings (see plate), which show one of the latest forms of an 80stamp silver-mill run by a turbine water-wheel, will show clearly the arrangement of the several parts. THE ONTARIO, UTAH, SILVER MILL. One of the best examples of a silver-mill, and at the same time one of the most successful concerns in the West, is the mill of the Ontario Silver Mining Company, near Salt Lake, in Utah. This mill treats the ore from the Ontario mine, ore which at present is very base, being composed of zinc, lead, and silver sulphides and silver chloride in a quartz gangue. This ore has become baser as the mine attained greater depth, though the vein holds its own, or rather increases, both in thickness and richness. The mill is managed in a skilful and economical manner, though the necessity for

Jan 1, 1880