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By George H. Holmes

This report describes the results of a reconnaissance survey of areas in California and Nevada considered favorable to beryllium mineralization. Pegmatite dikes, veins, intrusive sills, contact. metamorphic, and disseminated deposits as well as tactite deposits in the former major tungsten-producing districts were investigated. A general geographic pattern of beryllium mineralization was found to be concentrated along a wide belt in eastern Nevada extending from the Ruby Mountains, Elko County, south through the Fish Creek Range, Eureka County, the Snake Range, White Pine County to the Virgin Mountains in Clark County, Nev., and Mohave County, Ariz. Sporadic occurrences of beryllium are in central and southern Nevada, and in the pegmatite dikes of San Bernardino, Riverside, and San Diego Counties, Calif., and the granite masses of the southern Inyo Mountains, Inyo County, Calif. Principal company activities are centered in the Snake Range, Fish Creek Range, and the Virgin Mountains, Nev., and the Inyo Mountains, Calif. Other areas in California and Nevada have been superficially explored with results indicating either limited or widespread, but submarginal, mineralization. Although beryllium was found to occur, to some extent, in many of the deposits, mining has been hindered by the lack of a market for beryllium ores and concentrates other than standard-grade beryl and also by the erratic pattern of mineralization and the high exploration and beneficiation costs required to produce a marketable product.

Jan 1, 1963

By B. H. Kear

All the possible ways of forming simple two-dislocation boundaries in multiple slip orientations are deduced. It is shown that the principal differences in work hardening behavior of crystals plastically deformed in these orientations can he accounted for in terms of the likelihood of formation of diffuse boundaries, or deformation bands, consisting of the products of dislocation reactions of the Lomer type. Also, it is pointed out that the break-up of boundaries under the applied stress is more likely to yield interstitial jogs than vacancy jogs, whereas glide dislocations cutting throuqh dislocations trapped in particularly stable boundam'es can acquire both types of jogs. USING Frank's' grain boundary formula, Ball and Hirsch2 determined the parameters of all the possible boundaries that can be built from two sets of glide dislocations in the fee structure. This paper deduces the geometrical possibilities for the formation of these two-dislocation boundaries in the different multiple slip orientations, and discusses the role of boundaries in work hardening and in jog formation. Formation of Two-Dislocation Boundaries in Mutiple Slip Orientations. The parameters of the possible two-dislocation boundaries for any crystal orientation can be deduced most conveniently using the boundary formulae due to Amelinckx,3 in conjunction with the stereographic projection shown in Fig. 1. Suppose that slip occurs in a-BC and ß-CA. According to Amelinckx, when the two systems of glide dislocations are parallel, the rotation axis, u, of the boundary is parallel to (a x ß) and the unit normal, u, defining the boundary plane is parallel to (a x ß) x (BC x CA). On the other hand, when the glide dislocations form a crossed grid, u is parallel to (BC x CA) and u is parallel to (a x CA) x (ß x BC). In Fig. 1, (a x ß) is the pole of the great circle passing through a and ß, so that u is parallel to DC, i.e., parallel to [110]. Furthermore, (a x ß) x (BC x CA) is the pole of the great circle passing through DC and 6, so that u is parallel to [110]. Hence, when all the glide dislocations are parallel, the boundary is pure tilt with parameters u = [110], v = [ 110]. Similarly, it may be shown that the corresponding crossed grid of dislocations is a mixed boundary with u = [111], u = [111]. Consider the case of a crystal compressed in the [001] orientation. In this orientation, according to Fig. 1, there are eight available slip systems. In what follows, the different types of two-dislocation boundaries that are possible in this orientation will be examined by taking different combinations of two slip systems out of the available eight, with a-BC always one of the systems. Case (i)—Slip Systems a-BC and d-CB. The formation of a tilt boundary in (101), which consists of a crossed grid of edge dislocations with vectors BC andCB, is illustrated in Fig. 2(a). As the figure shows, slip is required in the system a-BC in one part of the crystal and in d-CB in the other part, with both sets of dislocations entering the boundary from opposite sides. The rotation axis of the boundary lies in (101), depending on the relative densities of the two sets of edge dislocations in the boundary. Case (ii)-Slip Systems a-BC and ß-CA. The two possible boundaries are shown in Figs. 2(b) and (c); boundary (b) is tilt with u = [110], u = [110], and

Jan 1, 1962

By E Widzyk-Capehart, C Hölck Teuber, S Steffen, V Rivero, O Fredes, E Sanchez, I Pedemonte, N Gonzalez

This paper summarises the research, development and initial application of a sensing platform that has the potential to monitor subsurface deformations, pore pressure and other variables simultaneously to gain a better understanding of rock mass behaviour. The platform is based on Networked Smart Markers (NSMs) devices, which, with their ability for wireless communication between individual sensors and the possibility of real-time data acquisition and processing, will assist in the development of predictive tools to better assess rock mass behaviour.A good opportunity to implement this technology is in the specific application of transitioning from an open pit mine to an underground caving operation. One of the key elements to maintaining the mining business during such a transition is having a good understanding of the unique geotechnical conditions of mutual influence created during the open pit to underground interaction. The knowledge acquisition will require the implementation of a robust platform for geotechnical monitoring, which could be enhanced by incorporating the NSMs. The integration of sensors within the NSMs would enable the collection of additional data about rock mass behaviour (ie caving propagation and crown pillar fracturing), which could be used to improve the management of mining operations and, specifically, allow the development of reliable predictive tools based on the data collected.CITATION:Widzyk-Capehart, E, Hölck Teuber, C, Fredes, O, Rivero, V, Sanchez, E, Pedemonte, I, Gonzalez, N and Steffen, S, 2016. Understanding rock mass behaviour through the development of an integrated sensing platform, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 275–284 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

The Australian Mining Industry Council is the peak mining industry representative body in the country. It is wholly funded by its member companies which comprise all of the major Australian mining houses. AMIC represents companies invo

Jan 1, 1994

By J. Engesser

A research project supported by the Minnesota Department of Natural Resources and the Iron Ore Cooperative Research Committee was undertaken to reduce the dissolution of fluoride into process water during taconite processing. Leach tests were conducted using rod mill feed samples and water containing varying concentrations of calcium and sodium. Laboratory liberation grinds were performed to evaluate fluoride rejection during grinding and magnetic separation. Tube furnace tests were conducted to evaluate fluoride volatilization during pellet induration. The results indicate that fluoride concentration of process water is a function of both calcium and sodium concentration in process water. It appears that less than 1 percent of the fluoride present in rod mill feed will dissolve in process water during grinding. More than 90 percent of the fluoride present in rod mill feed is rejected with tailings during size reduction and magnetic separation. The furnace tests demonstrate that bentonite and fluxstone (calcite and dolomite) addition to taconite concentrate during pellet production increases the amount of fluoride that volatilizes during induration. Lime hydrate addition to pellets decreases the amount of fluoride that volatilizes during pellet induration. During acid pellet production approximately three times more fluoride enters the water during induration-off-gas scrubbing than during grinding. When fluxed pellets are produced three to eight times more fluoride enters the water during off-gas scrubbing than during taconite grinding.

Jan 1, 2004

By D. F. Malan

Considerable practical knowledge and effective use of empirical evidence is required in the design of tunnel support systems. In many instances, it is unclear how individual support elements interact with fractured rock and which elements of the support system are critical in controlling and containing the movement of material proximate to the excavation. The present paper outlines a displacement discontinuity approach that allows the coupling of surface constraints, in the form of liner or mesh material, to an explicit representation of time-dependent rock discontinuity creep movements. The method is illustrated for a simple square-shaped tunnel profile in which the fracture zone is mobilized by an imposed stress field. A crucial aspect of the model is the computational treatment of the coupling between the liner material and there presentation of the fractured rock mass. This allows the response of the liner material to be assessed quantitatively in terms of the possible reduction of movement in the rock mass. The importance of installing the liner timeously after the excavation is formed is illustrated in a specific example. A number of computational difficulties in simulating liner-rock interaction mechanisms are identified.

Jan 1, 2008

By M. C. Flemings, T. S. Piwonka

Pore formation is examined analytically in cellu-larly solidified single crystals, in cylindrical castings of pure metals and alloys, and in unidirectionally solidified castings. Effects are considered of fluid flow. dissolved gas, and surface tension. Experimental results show that flow through a partially solid "mushy" aluminum alloy obeys relations similar to those applicable for flow through other types of porous beds. Flow rate is proportional to the square of the fraction liquid (fL) for fL less than 0.3. Results indicate models chosen for mathematical description of pore formation in alloy solidification are valid. ONE of the solidification variables which is influential in determining mechanical properties of castings and of wrought material produced from cast ingots is porosity. This porosity may result from shrinkage, dissolved gases, or a combination of both, and may take the form of either macroscopic pores in localized areas of the casting or microporosity evenly distributed throughout large areas of the casting. In alloys which freeze over a range of temperatures some microporosity is generally found after solidification. There has been much discussion as to whether the micropores are caused primarily by shrinkage, by gas, or by a combination of both.'-3 There has, however, been little experimental or analytical work performed to delineate the relative contributions of shrinkage and gas in causing microporosity or to quantitatively describe the influence of processing variables on microporosity. Porosity other than microporosity (e.g., center line shrinkage) has also received only limited quantitative treatment.495 The aim of this work is to examine analytically the general problem of pore formation in solidification and to perform limited confirmatory experiments. Consideration is first given to shrinkage porosity in pure and nearly pure metals (shrinkage in cellular growth, centerline shrinkage in cylinders). Next, a discussion is given of formation of shrinkage-caused microporosity in unidirectional solidification and in "mushy" solidification. Finally, influences of dissolved gas and surface tension on microporosity are examined. Numerical results are given for aluminum and an aluminum alloy. Typical examples of microporosity are shown in Figs. 1 to 3, for 1) cellularly solidified aluminum, 2) sand-cast aluminum alloy, and 3) low alloy steel. SHRINKAGE POROSITY IN PURE AND NEARLY PURE METALS 1) Cellular Growth. In cellular freezing of an impure liquid, liquid grooves may exist over a considerable length of the growing crystal.6 The cross-sectional area of the grooves decreases with increasing distance from the cell tips; the root of the groove is blunt if the liquid at this point reaches eutectic composition. As a result of volume contraction during solidification, flow occurs down the groove, parallel to the growth direction; hence, there must be a pressure drop from the groove entrance to points within the groove. The geometry of the groove is simplified to that of a circular cylinder of radius r and length L, Fig. 4, L » r, and a simple and useful limiting case is obtained. This is that, in the circular cylinder freezing at constant velocity, the pressure at the root of the groove is lower than that pressure at radius r in grooves of other geometries where r decreases continuously to a lower limit at L. As discussed below, a pore resulting from a given pressure difference

Jan 1, 1967

By G. Capello

Carboniferous mining basins are today a non-negligible source of energy. So important in fact that returns now justify high investments and costs even for those deposits that were un-economical in the past. Nowadays, if properly explored and exploited, basins previously considered non-minable due to complex structural and stratigraphical situations may be economically interesting. It is while studying a faulted basin with such features that the Authors developed the described computer-aided methodology capable of constructing a model of the physical structure of coal deposits on the basis of stratigraphical data from drillings. The aim of the procedure is to define coal reserves, the exploitation of a deposit being conditioned by the possibility of identifying zones that are technically minable. This objective is pursued by making as detailed a reconstruction as possible of the geometrical, stratigraphical and tectonic features of the coal-bearing seams of a deposit.

Jan 1, 1982

By Jiang Fan, Liu Shi, Wang Haigang

Winter-time natural convection in gravel embankments has been suggested as a technique to provide passive cooling and thereby avoid thaw-settlement of roadways located in permafrost areas. Numerical simulation by finite volume method on the proposed model is perf9rmed using the software FLUENT. A gravels model, in which the embankment is composed of stones and air, has been adopted to investigate the temperature and velocity fields in embankment. Simulation results show that in summer, a weak clockwise circulation of the pore air extending throughout most of the embankment. The pore-air motion is very weak which results in relatively straight horizontal isotherm lines. And heat transfer is mainly maintained through conduction. But in winter, pore-air velocities are higher and multiple vortexes are formed in the embankment. Natural convection then becomes the dominant influence on the isotherm shapes within the embankment. As a result of low ambient temperatures exerted on the embankment surface during winter months, an unstable air density gradient develops within the embankment. This convection increases the heat flux out of the embankment. Therefore, the winter-time convection can further reduce the temperature of the foundation soil beneath the open-graded embankment. In addition, the effects of the size of the stones within the embankment have been analyzed and compared in the gravel model. It shows that in winter, 200mm stones lead to stronger vortexes in the embankment compared with those of 60mm stones. Consequently, the zone oflow-temperature beneath the embankment is extended.

Jan 1, 2004

By F. W. Bowdish

Analysis of data on the equilibrium exchange of sodium ions from salt solutions for calcium ions, from various fractions of an oxidized calcareous iron ore from Lorraine, France, strongly suggests that the calcium may be attached to the solid by only one of its bonds. Nearly equal values were found for the equilibrium expression from data covering concentration ranges of 1000 fold for the salt and 235 fold for the ion-exchangeable calcium. Differences indicated between the exchangeable calcium contents of the slime and the sandy portions of the ore, as well as the equilibrium relationship itself, are of importance in the flotation of the ore. During an experimental program on the flotation of oxidized calcareous iron ores from Lorraine, France, ion-exchangeable calcium was found in the ore. Because this source of calcium ions, if not controlled, could thwart all efforts at flotation, an extensive study was made of the phenomenon. The part of that study reported here was to obtain data on the equilibrium established between ore solids and solutions of sodium chloride, and to analyze the data to try to understand better the physical chemistry of the exchange. The ore contains oolites of goethite and quartz grains embedded in a matrix consisting of calcite and a brown cement believed to be the residue from oxidation of the silicate minerals found in fresh unoxidized ore. When ground, a substantial fraction of the ore becomes a fine slime in which is concentrated more than half of the alumina content of the ore. It is believed that the alumina occurs as unidentified clay minerals with which most of the ion-exchange capacity of the ore is associated. A preliminary experiment on the exchange of ions from the ore for sodium ions from solutions of NaCl showed that calcium was about ten times as abundant as magnesium in the exchange solutions. Thus calcium was the predominant ion in causing difficulties with flotation, and it was the only one for which data was obtained in this study. It is believed that the omission of magnesium ion exchange from consideration does not invalidate the results. It is possible, however, that inclusion of magnesium in the analyses and calculations or its prior elimination from the samples would have improved the consistency of the results. EXPERIMENTAL Data about the equilibrium exchange of sodium from solutions for calcium from the solids were obtained using two different samples of material. The solids

Jan 1, 1963

By Edwin B. Wilson

Over the past several years, state governments have been vigorously refurbishing old health department agencies and smoke control laws in anticipation of pending federal developments. Many states now possess a mature air pollution control administrative organization and a fairly sophisticated set of regulations on air pollution, This developing network of state control legislation and regulation is the machinery which will be called upon to implement federal standards, In order to prevent the wasted effort and resources which inevitably result from hasty action, industry should be in con- tact with local and state control agencies and be familiar with lines of communication to agency representatives. Thorough knowledge of applicable laws and regulations, both current and pending, is required. Moreover, federal law and future federal air pollution control plans, should be well known. Industrial air pollution control should be geared to a long range plan which utilizes existing technology while at the same the recognizing that today's technology will be improved upon with time, Regulation, too, can be expected to become more stringent. The implications of air pollution control in the Appalachian region of the United States will be felt most strongly by the coal industry of this area. Either directly or indirectly most regulations in these states have a significant bearing on coal mining, processing, utilization or waste disposal. The extent of coal-related activity in the Appalachian States of West Virginia, Pennsylvania, Maryland, Virginia, Kentucky, and Tennessee can be observed from the data provided in Table I. This data indicates that 86 percent of active bituminous coal mines and 69 percent of bituminous coal production were accounted for by these states. The purpose of this paper is to provide information on current and proposed legislation and regulations on air pollution in the Appalachian states, The information should prove valuable not only to the coal industry but also to industry in general as a means of evaluating both pollution control action that has been taken to date and the course of future control measures. Reference information in the forms of addresses of appropriate agencies and citations to specific state laws and regulations is provided. All information is current as of February, 1969.

Jan 1, 1969

By Wing G. Agnew, John A. Johnson

"INTRODUCTION This paper is one of a series being published by the Bureau of Mines pertaining to an investigation on the use of stemming in metal mines now being conducted at the Mount Weather Testing Adit. Its purpose is to compare the amount of dust and gases produced as a result of blasting charges of dynamite (1) in drill holes, (2) in bombs, and (3) in mud-cap or adobe shots.ACKNOWLEDGMENTSValuable assistance and advice on stemming were given by members of the staff at the Bureau of Mines, as acknowledged in previous publications. 4/TEST PROCEDUREThe results used for comparison in this report are from dust and gas samples taken after blasting (1) four regular test rounds with no stemming, (2) five bomb shots, and (3) two mud-cap or adobe shots.The four rounds were the standard 26-hole test rounds designed to break 4 feet of rock. The procedure for drilling and blasting these rounds is described in Report of Investigations 3509.Before the regular test rounds were blasted, about 1,200 bounds of fine rock was placed on the steel mucking sheets that covered the end of the adit track; the wails, hack, and floor of the adit were washed thoroughly; and the fine rock on the mucking sheets was completely wetted.Each of the 5 bomb shots consisted of 10 sticks of dynamite tied together and hung at midpoint of the adit, 8 feet from the fall."

Dec 1, 1942

Jan 1, 1955

By Joseph Fry, Ralph H. Espach

In the spring of 1943, when it was evident that the Tensleep bandstone in the Elk Basin Field, Wyoming and Montana, held a large reserve of petroleum, Bureau of Mines engineers obtained samples of oil from the bottom of nine wells and analyzed them for such physical characteristics as the volumes. of gas in solution. saturation pressures or bubble points, shrinkage in volume caused by the release of gas from solution, expansion of the oil with decrease in pressure, and other related properties. The composition of the gas in solution in the oil was studied. The pressures and temperatures existing in the reservoir and the productivity characteristics of the oil wells were determined. The data obtained indicate that the oil in the Tensleep Reservoir of the Elk Basin Field has unusually varying physiral characteristics, such as a saturation pressure of 1,250 psia and 490 cu ft of gas in solultion in a barrel of oil at the crest of the structure and a saturation pressure of 530 psia and 134 cu ft of gas in solution in a barrel of oil low on the flanks. The hydrogen sulfide content of the gas in solution in the oil varies from 18 per cent for oil on the crest to 5 per cent for oil low on the flanks of the structure. Of even greater significance is the fact that these and other variable characteristics of the reservoir oil are related to the position of the oil in the structure. Many geologists and petroleum engineers have considered that all the oil in a petroleum reservoir has rather uniform physical characteristics and that equilibrium conditions prevailed in all underground accumulations of oil and gas; that such is not always so is borne out by the results of the study by the writers. INTRODUCTION The Rocky Mountain region is one in which may be found striking examples of the unusual in oil and gas accumulations, as is evident from the following: The high helium content (7.6 per cent) of the gas in the Ouray-Leadville limestone sequence in the Rattlesnake Field, New Mexico, and gases of similar helium content in other fields; 50" to 55' API gravity distillate in solution in carbon dioxide gas and recoverable through retrograde condensation, in the North McCallum Field, Colorado; the occurrence of gas, oil, or both in closely related structures contrary to the usual concepts of gravimetric segregation: the accumulation of gas and/or oil in structures closely related to other structures that apparently are more favorable but do not contain oil or gas accumulations; the high hydrogen sulfide content (as high as 42 per cent) of the gas associated with oil in some fields in the Big Horn Basin, Wyoming; and the wide range of fluid chararteristics found in the Elk Basin reservoir. Elk Basin, an interesting old oil field that has been producing oil from the Frontier formation since 1915, is situated in a highly eroded basin resulting from the erosion of the crest of an anticline and some of the underlying softer shales. The field came back into national prominence during 1943 when it became known that it was the largest single reserve of new oil discovered in the United States that year. The Tensleep sandstone was found to contain oil in November. 1942, when a well drilled to a depth of 4,538 ft (44 ft into the Tensleep sandstone) flowed oil at the rate of 2,500 B/D. By the end of 1949, 137 oil-producing wells and five dry holes had been drilled, and approximately 32 million bbl of oil had been produced. Approximately 6,000 acres may be considered productive of oil in the Tensleep Reservoir, and estimates of the oil that will be produced average 200 million bbl. The Tensleep Reservoir has further interest because it ha-greater closure than any oil field in the Rocky Mountain region; the closure of the Elk Basin anticline is variously estimated at 5.000 to 10,000 ft. of which the top 2.00 ft of the structure contained oil. SUBSURFACE OIL SAMPLING Fig. 1 is a structural map of the Elk Basin Tensleep Reservoir, on which the nine wells used in this study and the numbers correvponding to the well designations hereafter referred to are shown. Wells 1. 2, 3, 4, and 8 were tested and sampled during October and November. 1943. and Wells 5, 6. 7, and 9 during June and July, 1944. An electromagnetic type sampler developed by the Bureau of Mines and described by Grandone and Cook' was used in obtaining the subsurface oil samples. As the wells were tubed nearly to bottom, the sampler was run as far as possible in the tubing hut never below the top perforations. The following procedure was used in testing and sampling the wells: A well was shut in for at least three days, after

Jan 1, 1951

By Glenn A. Hazen

This report presents a stress investigation of four coal pillars located under two depths of cover. Each coal pillar was instrumented with ten load cells designed to measure coal pressure during initial and secondary mining. The problem considered was one of uniform triaxial stress as a large coal pillar was loaded under a thick limestone bed. Special attention was given to pillar design procedure. Unconfined uniaxial compression tests were conducted for coal specimens 7/8 in., 2-1/8 in., 3 in., and 4 in. square with length to square side ratios of 1/2, 1, 1-1/2, and 2. Stress-strain curves were recorded. Six specimens were tested at each size. Results show that a coal pillar is composed of an inner zone which is highly loaded plus a region around its perimeter which has lost its elastic strength. The bearing capacity of a coal pillar consists of elastic and crushed coal response: The failure strengths have been determined and will be useful in coal recovery, mine design, and mine safety.

Jan 1, 1975

By Richard D. Graves

Pitch from low-temperature carbonization of bituminous coal was hydrogenated at cracking conditions in a continuous bench-scale unit to produce low-molecular-weight oils and tar acids. The pitch contained 15.6 pct benzene-insoluble material, 4.0 pct hexane-soluble oil, and 80.4 pct asphaltene by weight. At 475° C, 7,500 psig, and 1.5 hours residence time, hydrogenation products, based on the weight of pitch, were about 36 pct oil boiling below 325° C, 24 pct hexane-soluble heavy oil, 17 pct asphaltene, 1 pct benzene insolubles, and 12 pct hydrocarbon gases. The yield of tar acids boiling below 250° C was 4.3 pct, and the yields of C6 to C8 paraffins, naphthenes, and aromatics were each less than 1.0 pct. The yield of tar acids was within the range of yields obtained by hydrogenation or high-temperature carbonization of bituminous coal (2 to 5 wt pct). Yields of oil boiling below 325° C increased with increased residence time or temperature. There was little or no effect of residence time on yields of alkali- soluble material which contained tar acids. Yields of hydro-carbon gases increased markedly with an increase in temperature from 475° to 500° C. Lowering the hydrogen pressure to 4,500 psig resulted in yields similar to those obtained at 7,500 psig.

Jan 1, 1962

By H. Memarian

In the last few decades, many developing countries have tried to expand and improve upon higher education, which is acknowledged to be the leading factor for development. In this respect, develiping countries have significantly increased the number of tertiary institutions and their students. These rapid expansions, along with all the benefits, have drawbacks as well. An example is the status of mining engineering education in Iran. Presently, the number of active mining engineering departments in Iran (27) is more than the sum of similar departments in Canada, Australia, the United Kingdom, and South Africa (23 altogether). Also, the number of annual mining graduates in Iran (645) is more than the cumulative graduates of the United States, Canada, the United Kingdom, and Australia (613). The expansion of mining engineering education in Iran has coincided with the closing or merging of similar mining departments, as well as a decline in the number of interested students in the industrialized world. The present study shows that the need for development and the excessive number of high school graduates, resulting from high population growth in the early 1980s, are the two primary factors influencing the significant expansion of mining engineering education in Iran.

Jan 1, 2007

By D. M. Hausen

A refractory siliceous low-grade silver ore (265 g/t Ag) from a prospect in Sonora, Mexico was investigated mineralogically and metallurgically to evaluate extraction of the silver by conventional methods. Approximately half of the silver was recoverable, occurring as coarsely crystalline acanthite (70-300 Am) that was liberated in material crushed to minus 10 mesh. The remaining silver is refractory and occurs mostly as finely locked (-2 to 0.2 Am) acanthite in cherty quartz, and as minor amounts of finely disseminated stylotypite or freibergite in fluorite. The mineralogic data have thus served to explain the 50-60% recovery of silver by flotation and cyanidation.

Jan 1, 1991

By James K. Stanley

When a plastically deformed mctal is heated to a certain temperature, it undergoes a complete change in microstructure, the consequence of which is a marked alteration of mechanical properties such as hardness, strength and ductility. This change in microstructure occurs by re-crystallization and is a process involving the formation and growth of strain-free nuclei in the deformed matrix. These nuclei continue to form with time and grow until a new grain structure replaces the cold-worked structure. The formation of the nuclei in the deformed sheet of I per cent silicon ferrite is illustrated in Fig. I. If a recrystallization is conducted iso-thermally, a nleasurement of the fraction of the matrix recrystallized plotted against time leads to an isothermal recrystallization curve, first established in 1942.1 Such recrystallization curves are shown in Fig. 4. These curves show that the recrystallization of a cold-worked metal is best considered as a rate process rather than a time independent process such as is suggcsted by the improperly named and misleading recrystallization diagrams involving deformation, temperature, and grain size.2-5 Any study of the rate of recrystallization resolves itself into a study of the component rates of nucleation and growth. The previous paper1 provided an account of the determination of the rates of nucleation; N, the number of nuclei formed per unit time per unit of unre-crystallized area, and growth, G, the radial growth in unit time, in the recrystallization of silicon ferrite (I per cent Si). A method was developed to furnish experimental data for evaluating the effect of the recrystallization variables on N and G. The mathematical analysis for the derivation of the isothermal recrystallization curve was developed for a two-dimensional case (in thin sheets where the diameter of the recrystallized grain is greater than the sheet thickness). The present paper is a continuation of the study of recrystallization of I per cent silicon ferrite begun in 1942.1 In this work the effect of the factors deformation, temperature, grain size, composition, and recovery is studied with respect to the rates of liucleation and grouth. At the same time it is shown how the cooperation of N and G affects the isothermal recrystallization curve. The study of these variables on N and G has a definite bearing on the mechanism of recrystallization and should lay a foundation for a rational theory on the subject. Procedure The procedure used in these experiments was essentially the same as that described previously but in certain details some changes were made in the interests of speed. With few exceptions, the procedure is the same for the study of all the variables. Where the procedure is different from standard manipulations attention is called to this fact.

Jan 1, 1945

By Andrew L. Mular, Robert P. Edwards

"The operation of flotation circuits is often regarded as a combination of art and science. Expert systems offer a method by which the art may be captured and supervisory control of flotation circuits fully realized. Operating knowledge, the art, can be consistently employed to enhance regulatory control through the judicious application of an expert system. Using an expert system, a supervisory control routine was developed, and success- fully implemented, in the copper flotation circuit at Brenda Mines Ltd.The expert system ran in conjunction with regulatory PI controllers on a personal computer. The expert system received assays via an on-stream analyzer and adjusted regulatory loop set points as required in real-time. From its commissioning in November, 1989, to the end of the mine 's operation in June, 1990, it was enthusiastically embraced by the operators and attained operating levels superior to those achievable manually.IntroductionExpert system (ES) software springs from research into artificial intelligence and is currently making significant inroads into business and industry. ES proponents make many attractive claims; they are a means of capturing the knowledge of experts and they can be programmed by non-programmers. To date, most uses of this software in the process industry are in off-line applications, meaning that the applications are not tied directly to operating (on-line) environments. Moreover, in on-line environments, they are typically employed as advisors and only suggest changes. Human operators are required to close-the-loop to the process. Yet, an ES should be applicable to operating environments and, if the claims of the proponents are valid, should also be better than existing tools. As an intelligent controller an ES must use the knowledge of experienced operators, apply it directly to a process and do this without the intervention of human operators. On-line applications have been successfully employed in the closed loop control of SAG circuits (Herbst et al., 1989) and flotation circuits (Hales, 1989). Harris and Kosick (1988)detail an implementation for flotation control at the Polaris Mine."

Jan 1, 1992