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By Yngve Jordal, Sverker Hartwig

The IVAR Project is Norway's largest sewer project presently under construction. One part of it is an 8.1 km (26 575 ft) long, 3.5 m (11 ft 6 in.) diam tunnel, bored in one year. The tunneling project has been running smoothly; however, not everything has been easy. A few of its features are highlighted in this paper: The use of 9 0 (12 cu yd) muck cars on a double track back-up in such a comparatively narrow tunnel. Employing only four men in the tunnel, including the loco driver. A quartzite dyke - 96% quartz with 350 MPa (50 000 psi) and more compressive strength - turned out to be 640 m (2 100 ft) thick instead of the predicted 90 m (300 ft). Passing under a gaseous swamp with only same 5 m (16 ft 5 in.) of rock cover on top.

Jan 1, 1991

By Terry Eldridge, Keith MacKay, David Siddle, Luke Moger

On August 4th, 2014, a breach occurred in the Perimeter Embankment of the Tailings Storage Facility (TSF) located at the Mount Polley Mine, releasing approximately 10.6 million m3 of supernatant water, 7.3 million m3 of tailings solids, 6.5 million m3 of tailings interstitial water and 0.6 million m3of construction materials. A Temporary Upstream Rockfill Berm was constructed between August 2014 and February 2015 within the area of the tailings dam failure in order to retain the remaining tailings solids during the low flows of the winter season. The Temporary Upstream Rockfill Berm was constructed as part of the initial response phase, with the primary objective to abate the flow of tailings into the receiving environment. A secondary objective of its construction was facilitating the required investigation works downstream of the tailings dam failure. The selection of the coarse grained material used in the construction of the Temporary Upstream Rockfill Berm was based on the availability of the material (timeliness of construction) and the non-water retaining design of this initial response phase. Consequently, an alternative method was required in order to prevent further loss of mine-affected water and tailings from the TSF, as well as to provide short-term contingency water storage, during high flow conditions expected in late spring. Golder Associates Ltd. designed the 2015 Freshet Management Embankment, a deep mixing cut-off wall, to meet these site requirements, which was constructed by Mount Polley Mining Corporation and Golder Construction Inc. between December 2015 and April 2015. The works included 132 soil cement panels constructed to depths of up to 27 meters. This aspect of the works was completed using an RG25S Bauer CSM rig on a 24 hour per day, 7 day per week schedule. The cut-off wall specifications included a target unconfined compressional strength (UCS) of between 1 and 2 MPa, a maximum hydraulic conductivity of 1x10-6 cm/s, and a ductility to enable the soil cement to undergo a minimum of 5% strain without a reduction in strength or increase in hydraulic conductivity. In order to control and assure the quality of the soil cement, 2553 wet grab specimens were retrieved from the fresh soil cement panels using a project-developed sampler. Four of the soil cement panels were cored with a mud-rotary drill rig and optical and acoustic televiewers were placed into the boreholes in order to log several relevant parameters, including image, texture, relative hardness, borehole-shape, and temperature.

Jan 1, 2016

By J D. St George

Flyrock is the unexpected and undesirable projection of rock fragments during detonation of a blast and managing this risk is becoming an increasing challenge as urban development encroach toward mineral extraction sites. The basic factors associated with flyrock are discussed in relation to geology, blast design and management. Published data of historical flyrock events are investigated and compared with local information on incidents. Good agreement was found between the data sets. A computer program of flyrock was developed using projectile motion based on launch velocity and angle, rock size, shape and density. This deterministic model was coupled with a probability model to simulate blast events. The impulse time ?t of the explosive pressure was taken as the stochastic variable to replace launch velocity. The variables were calibrated to replicate field data. A simulation was executed to demonstrate the capability of the approach to defining flyrock danger zones. For a simplistic situation it was identified that an appropriate distance to be cordoned off for the blast danger zone is a radius of 120 m in front of the blast and 65 m behind.

Jan 1, 2001

By William K. Tolley

The U.S. Bureau of Mines (USBM) is currently investigating the electrochemistry of mineral flotation. A significant need in this area is greater reliability of sensors. The USBM is testing electrolytic methods to clean and condition redox-sensing electrodes to improve the reliability and extend the service life of these instruments in the harsh physical and chemical environment of mineral processing slurries. A novel method for removing scale from fouled electrodes has been developed that includes anodic polarization to 1.2 V versus the Ag/ AgC1 reference potential, followed by brief potentiodynamic conditioning. Laboratory results show that this technique removes calcarious deposits from gold sensing electrodes and returns the electrodes to useful service within approximately 10 min. Mechanical abrasion to remove the scale is thereby avoided.

Jan 1, 2010

By Sarkis G. Ampian

This late 1979 Bureau of Mines report presents current stocks and monthly consumption rates for Guyanese refractory bauxite (GRB), with emphasis on the impact of the GRB shortage on the refractory and downstream industries, general background material, and an evaluation of the situation resulting from the strike of Guyanese bauxite workers during the summer of 1979. A study by the Bureau indicated that industry stocks contained little more than a month's supply of GRB--30,000 calcined short tons (CST), at present consumption rates of 25,000 CST per month. The report was requested by the Federal Emergency Management Agency (FW) in response to refractory industry requests that the Government release GRB from the National Stockpile to minimize forecasted industry problems. The report traces the historical innovations in the high-alumina and/or bauxite-type refractory products industry, eventually leading up to fabrication of modern, high-quality firebrick and monolithic refractories.

Jan 1, 1980

By AIME AIME

ELECTRICAL methods of geophysical exploration attracted major attention at the three sessions devoted to geophysics on Monday and Tuesday. At the opening' meeting Monday morning Hans Lundberg gave the paper by himself and Folke Kihlstedt; he described the use of the Racom, discussed last year, and the method whereby it is possible to eliminate all but subsurface, effects in electrical exploration. In the discussion Theodor Zuschlag pointed out some of the theoretical considerations behind the field procedure. Karl Sundberg's paper on the effect of impregnating waters was presented by title only, and S. F. Kelly then gave an abstract of a paper on the electrical properties of ores, by J. J. Jakosky, R. N. Anderson and Clyde H. Wilson. , This dealt with an exhaustive series of laboratory tests on the variation of -conductivity of ore specimens with the frequency of the energizing current, and of the effect of moisture content in typical clays and gouges on their conductivities at various frequencies. Considerable discussion was provoked during which the authors came in for some-criticism on their measuring circuits and for their assumption that a solid conductor could be compared with linear ones. They were praised, however, for making a start toward a compilation of resistivities for ores and rocks. Dr. Slichter disagreed with them that the conductivity of an orebody was primarily capacitive. He also called attention to the fact that it was high time geophysicists adopted the standard physical expression of ohm-,centimeters or ohm-meters to express resistivities. This same point was the burden of the next paper,. "Uniform Expression for Resistivity," by Sherwin F. Kelly, presented by title only.

Jan 1, 1932

By P. W. Ware

The majority of all refined copper is consumed to produce electrical conductors. Most copper conductors are drawn into wire from 8 mm ETP copper rod produced from high purity copper cathodes. Southwire Company has more than 40 years experience using, designing, fabricating and marketing a process for continuously producing ETP copper wire rod. This process is called the SCR® (Southwire Continuous Rod) process. Today, approximately half the copper wire rod produced in the world, or more than one third of all refined copper consumed, is produced using the SCR process. Southwire has sold 75 SCR copper rod mills to metal producers and wire manufacturers around the world. Southwire is North America's largest electrical wire and cable producer. Southwire operates a 48 metric ton per hour SCR® copper rod system in Carrollton, Georgia. This allows Southwire to provide technical support for existing SCR® system customers based on first-hand knowledge. Rod fabricators and their wire customers are always striving for copper rod that improves productivity. They are looking for improved surface quality, finer wire sizes and fewer wire breaks per ton of rod drawn. This paper will present a brief history of the SCR® process, a description and recent process developments.

Jan 1, 2007

By V. V. Trusova, Shiyrav Gandandorzh, K. V. Fedotov, V. A. Domracheva

"In Russia, 1.1 million tons of mercury-containing waste are stored. The amount of mercury in soils and heaps of industrial enterprises is estimated at 3000 tons; in dumps, concentration tailings, sludge dumps of the gold mining industry up to 6000 tons have been accumulated. Mining is one of the main sources of mercury emissions in the natural environment that poses a real threat to the natural environment. At present, the process of amalgamation is prohibited and not applied in gold extraction. The application of amalgam technology in gold mining led to the accumulation of highly toxic products in the form of gold-bearing amalgam and metallic mercury, with a mercury content of dozens and even hundreds of times greater than the maximum permissible concentration for soil (1). Therefore, mercury-containing tailings constitute an ecological hazard to the environment. According to published data, at waste storage sites of industrial enterprises, up to 50 tons of mercury enter soil annually, and up to 3.5 tons pollute the air. At the same time, mercury-containing waste due to the reduction of the country's mineral resources is an additional source of mercury. Therefore, it is necessary to recycle mercury-containing waste. INTRODUCTION Paperobjective: demercurization of technogenic raw materials (amalgamation tails, discharge outlets of tailing dumps) to be recycled. Under natural conditions, the mercury usually migrates in the form of three most common compounds: elementary mercury (Hg); mercuric mercury ion (Hg+2); methylmercuryion (Hg (CH3) +. Chemical compounds Hg (II) are found in natural conditions much more often than Hg (I).The authors propose to conduct demercurization of technogenic raw materials (mercurial tailings) in two stages. At the first stage, the mercury in the form of small balls, the finest particles (drip mercury) can be extracted by applying the gravitational method. We propose a method for centrifugal processing of crushed waste in the apparatus of Itomak company, Novosibirsk, as the basis of the technological process for mercury recycling. The extraction of metallic mercury out of mercury-containing waste into commercial products, according to the technological characteristics of the Itomak apparatus, reaches 86.0% (2, 3). At the second stage, the extraction of mercury out of technogenic raw materials is performed applying a sorption method and using carbon sorbents based on fossil coals. Hard coal of the Kuznetsk Basin has been already used for industrial production of active carbons (carbon sorbents) of the KAD-iodine type, which is one of the prerequisites that determine the choice to use it for the aims of this study."

Jan 1, 2018

The system of keeping geological plans and sections for the Geco Mine at Manitouwadge, Ontario, is described. Special methods employed to save draughting time with-out sacrificing accuracy, such as the extensive use of black line prints, are discussed. The uses made of the plans and sections by the mine planning engineers in their designs of stopes, and by the blast-hole engineer in ~is preparation of blast-hole layouts, are noted. An unusual scheme for portraying the distribution of .copper, zinc and silver values within the ore zone is de-scribed. The method of estimating the grade of ore to be "blasted in each ring of blast holes is outlined, as is the method of estimating the annual ore reserves. The design of an effective but simple transparent geo-logical and mine development model, used as a display for -visitors, is discussed. A large-scale model used for the study of problems in geological structure is also de-scribed.

Jan 1, 1964

By R L. Braithwaite

Mesothermal quartz lodes in Paleozoic Greenland Group metasediments of the Reefton area have produced 67 t of gold up to 1951, and recent exploration has identified new gold resources in several deposits, including the largest past producers, Blackwater and Globe Progress. The metasediments consist of alternating sandstone and argillite, metamorphosed to lower greenschist facies and hydrothermally altered near the quartz lodes. We examined and sampled drill core from four prospects, Globe Progress, General Gordon, Merrijigs and Blackwater, to determine the mineralogical and geochemical characteristics of hydrothermal alteration in the sandstone units. The sandstones are feldspathic litharenites averaging Q65, FlO and R25, with detrital grains of quartz, feldspar, rock fragments, muscovite, biotite (mostly altered to chlorite), and trace quantities of graphite, apatite, zircon, tourmaline and titanite. Hydrothermal alteration has developed a secondary mineral assemblage of K-mica (muscovite, sericite and illite), carbonate, chlorite, pyrite, arsenopyrite and limonite. The abundance of secondary chlorite is greater at Blackwater than at the other locations studied. Features in the sediments associated with increasing hydrothermal alteration towards quartz lodes include, the development and increasing intensity of colour bleaching and carbonate spotting, increasing quantities of disseminated pyrite and arsenopyrite, and the appearance and increasing quantity and size of thin carbonate, quartz and sulphide veins. This is accompanied by increasing concentrations of sulphur, arsenic and antimony as shown in assays, and of volatiles (loss on ignition) and iron as seen in XRF analyses. We were unable to identify consistent trends in the behaviour of potassium, sodium, and calcium that are exhibited by similar mesothermal quartz lode deposits inVictoria, Australia.

Jan 1, 1998

By M. Bester, R. Carey, T. Russell, J. van Heerden

"In order to reach the goal of optimal and safe extraction of the mineral reserve, the mining industry is increasingly focusing on reconciliation across the mining value chain to ensure that the mining process occurs in a progressively more predictable manner. This will consequently improve the understanding of mine plans and their associated implementation risks, ultimately leading to increased investor confidence. In terms of geotechnical engineering, mine to design performance assessment is a critical aspect of mine to plan adherence focusing on the complex aspects influencing slope performance. A mine to design reconciliation process therefore needs to systematically track implementation and geotechnical aspects in order to review or update slope design criteria and pit layouts according to the mine planning cycle as the mine is developed. This paper describes the development and implementation of a standardized mine to design reconciliation system for operations utilizing laser scanning technology, analysis tools, as well as associated key performance indicators. Performance is evaluated on final pit boundaries in terms of geometry achieved as well as blast performance evaluation of face conditions. These aspects as well as the resulting catch berm capacity should be captured in an information system, enabling longer term trend analysis and detailed root cause analysis where unsatisfactory outcomes occur. Adverse outcomes should subsequently be incorporated into the mine’s risk management process informing risk mitigation measures including blast design adjustments, slope design changes, or rockfall protection measures. IntroductionIn order to reach the goal of optimal and safe extraction of the mineral reserve, the mining industry is increasingly focusing on reconciliation across the mining value chain to ensure that the mining process occurs in a progressively more predictable manner. This will consequently improve the understanding of mine plans and their associated implementation risks, ultimately leading to increased investor confidence. In terms of geotechnical engineering, mine to design performance assessment is a critical aspect of mine to plan adherence focusing on the complex aspects influencing slope performance. A mine to design reconciliation process therefore needs to systematically track implementation and geotechnical aspects in order to review or update slope design criteria and pit layouts according to the mine planning cycle as the mine is developed."

Jan 1, 2016

By S. Makni, S. Koppalkar, A. Bouajila

This paper reviews briefly the gravity recovery involving conventional gravity separators and centrifugal gravity separators. The advantages of semi-continuous gravity separators will be discussed. Techniques for upgrading the gravity concentrates will be addressed briefly. The research efforts in optimizing semi-continuous gravity separators will be recalled. Innovative gravity circuit for eliminating or minimizing the use of complex processing schemes will be reviewed. On-going gold gravity research at COREM has revealed that gold particle shape transformation is the main factor explaining the lower recoveries of the plant units. Efforts to devise possible remedies for improving gravity recovery at plant will be discussed.

Jan 1, 2011

By Warren M

Many Australian tunnelling and mining companies regularly investigate different methods or equipment in an attempt to keep ahead of their competition. Sometimes the result is a new approach or process which wins a tender or provides an advanced solution to a problem.The Australian Government has a policy of encouraging forward thinking among Australian companies and provides a range of incentives. One of these incentives is currently available retrospectively to 1985 - 86, and the registration process is relatively simple with only one form to be completed. Companies who investigate methods of raising productivity could be reimbursed for the costs of the investigation.

Jan 1, 1993

By W. B. Morrison

The principal factors influencing the total percent elongation of a lead-tin eutectic and several low-alloy steels which exhibit superplasticity were investigated. These factors are: a) Strain-rate sensitivity of the stress (m). b) Specimen geometry; in particular, diameter-to-length ratio (d0/l0), and surface irregularity (e.g. notches). A feature of the tensile deformation of a superplastic alloy is the early appearance of a neck which continues to extend throughout the test. As a result the total elongation is directly related to the diameter-to-gage-length ratio. The strain-rate sensitivity of the stress varies during extension, mainly because of microstruc-tural changes. A satisfactory correlation exists between the minimum strain-rate sensitivity and total elongation, as indicated in the equation shown below. Notches cause a considerable reduction in total elongation and their effect is greatest at high values of strain-rate sensitivity. An initial notch depth exists below which there is no appreciable effect on elongation. An equation relating elongation to strain-rate sensitivity and specimen geometry is proposed, THE total percent elongation of a tensile specimen is usually regarded as a measure of superplasticity. However, little attention has been given to the fact that total elongation is also a function of specimen diameter and gage length, even though the importance of geometry has long been recognized in the tensile testing of materials in which elongations are relatively small.* In the present study, the effect on superplas- tic extension of the ratio of specimen diameter to length was investigated and an analysis was made of strain distribution along the gage length. Superplastic alloys are characterized by having a flow stress sensitive to strain rate but relatively insensitive to strain.2"' In an earlier study,5 it was found that the strain-rate sensitivity of several low-alloy steels changed during the test and that the minimum value correlated best with total elongation. In the present study, the variation of strain-rate sensitivity during the straining of a lead-tin alloy was investigated. EXPERIMENTAL PROCEDURE Lead-tin eutectic alloy (32 pct Pb 68 pct Sn), made from high-purity lead and tin, was cast in the form of 1-in. diam rod. The rod was cold-rolled in stages to 0.25 in. diam and then swaged to 0.125 in. diam. Samples were cut from the rod at various stages of the mechanical working process. Tensile test specimens were then made by attaching threaded steel ends to the rods by an epoxy-base thermosetting adhesive which required a setting treatment of 2 days at room temperature. The rods were seated in the steel ends in holes approximately 0.01 in. oversize. The test pieces thus made were of various diameters and gage lengths. These were stored at a temperature of about -70°C (-94°F) until required for testing. The distribution of strain along the gage length of a specimen was determined at various stages of the tensile test. The lead-tin alloy was superplastic at room temperature and direct observations during testing were simple. The gage length was divided by reference marks into five initially equal units. These reference marks were made with ink and were reinforced during the test when the initial marks became faint. Photographs were taken, at intervals, of the deforming specimen and measurements of the elongation in each of the gage units were made on these photographs. Tests were also done on several superplastic low-alloy steels whose properties were described earlier.5 The chemical compositions of these steels are given in Table I. A diagram of the notched tensile specimen used in the steel tests is shown in Fig. 1. The specimens were tested at 900°C (1650°F) in a furnace through which a mixture of He + 2 pct H was continuously circulated.5 RESULTS Strain Distribution. Approximately 20 tests on lead-tin alloy specimens were conducted to determine the strain distribution during the test. An example is shown in Fig. 2 of the strain distribution in the gage

Jan 1, 1969

By J. C. Gerdeen

This project was a supporting effort with research contract H0230016 at White Pine Copper Company. Creep properties of White Pine rock were determined. These and properties for bolted joints were used in finite element analyses of sections of the White Pine Mine which included analysis of bed separations in the roof and sloping faults. In-situ experimental measurements were made of tension, compression, and bending of resin bolts by use of strain-gaged bolts. Evaluations of bolting effectiveness and comparisons of predicted and measured roof behavior are given.

Jan 1, 1976

By Fred W. Brackebusch

"The use of paste technology for surface tailings disposal may offer economic, technical, safety, and environmental advantages for both underground and surface mining operations. Paste is a non-Newtonian fluid having some shear strength during transport and placement. The strength is augmented after placement by consolidation, water loss, and by addition of chemicals. Economical dewatering systems are necessary to the success of surface paste tailings disposal. In an underground mine, the paste backfill plant can produce paste for surface disposal about 50% of the time because only about 1/2 of the tailings are needed for backfill. The distribution of paste to the surface stack involves expensive pumping equipment and thus a nearby location of the stack is desirable. The viscosity of paste can often be manipulated by modifying pH. Placement of the paste in a designed stack configuration depends on topographic and climatic factors as well as paste properties.INTRODUCTIONThe use of paste technology for mine backfill is becoming accepted for underground mines mainly because of ground control and economic reasons. Paste technology is just starting to be applied for tailings disposal with only a few hardrock metal mines worldwide using the technology; however, it has been used extensively for red mud disposal in the aluminum industry. The disposal of dry tailings is very attractive from environmental and safety points of view because of limited water which might potentially escape and pollute river systems. Dry stacking systems, however, are expensive because of filtration and truck transportation costs. Paste can be produced from most tailings streams by special types of thickeners. Furthermore, it can be transported in pipelines, therefore paste technology may be more economic than dry stacking but still have some of the major advantages. Understanding of paste technology has improved through experience with operating underground backfill systems in recent years and because of testwork and research programs by mining companies, consultants and equipment vendors. Thus we may be on the verge of taking a new look at tailings management using paste technology."

Jan 1, 2002

By Charles T. Holland

Miners have observed for many years that as pillars are removed in mining operations the pillar adjacent to those mined out frequently shows evidence of being compressed. Although this has been known for a long time, little or no information is available concerning how far from the mining area the pillars are affected in this manner, or how great is the magnitude of the compression, or concerning the manner or characteristic way in which the compression acts, as the mined-out area approaches the pillar under consideration. The writer made a study of pillar action in the Mona mine of the Arkwright Coal Co., partly to get some quantitative data on the deformation of coal-mine pillars. The study was not completed but it seems best to present the information that was obtained. Method of Measurement Fig. 1 shows the details of the apparatus used for measuring the deformation. This is permanently attached to the pillar. Fig. 2 shows the details of the gauge that records the deformation. This gauge is removable and was used to measure the deformation at all the stations. The recording dial is graduated in thousandths of an inch and records measurements up to one inch. Fig. 3 shows how the removable gauge is placed in the instrument. When installing the instrument in the side of the pillar, all loose coal near by was removed and a trench 4 to 6 in. deep, and approximately 1 ft. wide, was dug in the pillar. In this trench near the top and the floor, the holes holding the instrument were bored. These holes were then partly filled with thin cement and the rods were inserted. The remaining space in the holes was tamped full of cement. At this time, by carefully manipulating the permanent rods and clamps and adjustable pin, it was possible to adjust the instrument so that the removable gauge would stand true and measure any vertical deformation between the top and bottom rods. Fig. 4 is a photograph of one of the instruments installed, showing the removable gauge in place.

Jan 1, 1938

By Charles T. Holland

Miners have observed for many years that as pillars are removed in mining operations the pillar adjacent to those mined out frequently shows evidence of being compressed. Although this has been known for a long time, little or no information is available concerning how far from the mining area the pillars are affected in this manner, or how great is the magnitude of the compression, or concerning the manner or characteristic way in which the compression acts, as the mined-out area approaches the pillar under consideration. The writer made a study of pillar action in the Mona mine of the Arkwright Coal Co., partly to get some quantitative data on the deformation of coal-mine pillars. The study was not completed but it seems best to present the information that was obtained. Method of Measurement Fig. 1 shows the details of the apparatus used for measuring the deformation. This is permanently attached to the pillar. Fig. 2 shows the details of the gauge that records the deformation. This gauge is removable and was used to measure the deformation at all the stations. The recording dial is graduated in thousandths of an inch and records measurements up to one inch. Fig. 3 shows how the removable gauge is placed in the instrument. When installing the instrument in the side of the pillar, all loose coal near by was removed and a trench 4 to 6 in. deep, and approximately 1 ft. wide, was dug in the pillar. In this trench near the top and the floor, the holes holding the instrument were bored. These holes were then partly filled with thin cement and the rods were inserted. The remaining space in the holes was tamped full of cement. At this time, by carefully manipulating the permanent rods and clamps and adjustable pin, it was possible to adjust the instrument so that the removable gauge would stand true and measure any vertical deformation between the top and bottom rods. Fig. 4 is a photograph of one of the instruments installed, showing the removable gauge in place.

Jan 1, 1938

By Jack Washburn, E. R. Parker

Kinking in zinc single-crystal tension specimens was observed under conditions of low stress and high temperature. Kinking is discussed in relation to other plastic bending phenomena on the basis of dislocation theory. Experiments on the stress-induced motion of small angle boundaries are reported. KINKING was first reported by Orowan1 as a new deformation mechanism. He observed the phenomenon in cadmium single crystals loaded in compression. Glide lamellae in a local region of the rod were observed to snap over suddenly to a tilted position, resulting in a sudden shortening of the specimen. Between the tilted portion and the rest of the crystal there were fairly sharp boundaries, with the slip plane assuming approximately mirror image positions on opposite sides of these boundaries. Orowan considered the boundaries to be regions where dislocations had concentrated. Hess and Barrett' observed the formation of kinks in critically oriented zinc compression specimens. It was found that the sudden snapping over of the tilted region was not an essential part of the kinking phenomenon but rather was associated with the method of loading. Kinking was explained on the basis of the accepted mechanisms of slip and flexural glide. It was also suggested that a kink can be considered as a special type of deformation band. During a recent investigation of the effect of surface condition on creep of zinc single crystals," a similar phenomenon was observed in crystals which were loaded in tension. The specimens were 0.4 in. diam cylindrical rods with a free length of 4 in. between end connections. All of the crystals were tested at a constant load. adjusted to give an extension rate of approximately 0.05 pct per hr. Kinking, as shown in Fig. 1, occurred in some of the tests performed at temperatures above 200°C. Kinking was observed in specimens varying widely in initial orientation, scattering about a 45" angle between the slip plane and the specimen axis. The condition leading to kinking in tension appeared to be non-uniform distribution of flow along the gage length combined with the restraint imposed by the tensile load. At low temperatures and fast strain rates, the distribution of strain throughout the midsection of tension specimens was generally quite uniform; therefore, bend planes developed only near the ends as described by Miller.4 However, at high temperatures under creep conditions it was difficult to obtain specimens in which the distribution of flow was uniform. Some of the factors which may have caused differences in flow stress along the length of the crystals are: Nonuniform distribution of impurities, accidents of growth (lineage structure), slight bending or other damage during handling, surface conditions, and strain-aging characteristics due to dissolved nitrogen." Plastic flow, once started in a local region, often continued to a relatively large strain before other parts of the gage length became active. Under these conditions a series of kinks, such as those in Fig. 1, were produced. Fig. 2 illustrates how a nonuniform distribution of slip produces bending moments which- are responsible for kink formation. If no plastic bending were to occur while the rod extended by pure slip in two separate sections of the rod, it would assume a shape such as that in Fig. 2a. A specimen having this shape and being subjected to a tension load would have concentrations of stress at the concave surfaces C and lower than average stress would exist at the convex surfaces D. Therefore a bending moment is superimposed on the average stress in the regions between C and D. The positions of potential bend planes under these conditions are shown as dotted lines. Actually no such shape as Fig. 2a develops because plastic bending in the region C-D occurs simultaneously with pure slip in the intervening regions. The observed structure of a tension kink is indicated by Fig. 2b. Perhaps the best approach to an understanding of kinking as well as other related plastic bending phenomena, such as the bend planes discussed by Miller,' cell formation studied by Wood et al.,6 and polygonization,7 is consideration of the dislocation model of a bent lattice. Current theories of the slip process postulate generation or multiplication of dislocations at certain lattice imperfections. The mechanism proposed by Frank and Read8 results in continuous generation of concentric dislocation loops which spread out

Jan 1, 1953

By E. Wm. Heinrich

Glass sands fall into that extremely select category of mineral deposits that requires a fantastic degree of natural concentration (95% +) of a single component before they can even be considered as ores suitable for further refinement. The combination of geological factors that has produced such an environment of "mineralogical single-mindedness" has appeared only rarely. Factors that require consideration in the economic evaluation of a potential glass-sand deposit can be grouped into three categories: 1) geological (e.g., size, shape, structure); 2) petrographic (e.g., grain size, accessory minerals, nature of iron contaminants); 3) geographic - political (e.g., proximity to consumer, size of market, zoning restrictions). Of particular con ern is the nature of the iron contamination. Iron-bearing species appear as 1) accessory mineral grains, either detrital or authigenic, 2) cements, 3) grain coatings, and 4) quartz-grain inclusions. Selection of the cheapest form of beneficiation requires precise information on the mineralogy of the iron species and their detailed petrography. Because of the antipathetic relationships, in many parts of the United States and Canada between the geographical locations of glass plants and the geological distribution of glass sands, the selection of ac suitable source for a particular glass plant may be dichotomous. One may seek either an exceedingly pure "classic" type glass sand that is relatively distant and whose cost includes a major transportation charge or a relatively proximate and somewhat "impure" source whose cost includes a substantial fee for beneficiation.

Jan 1, 1974