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By V. A. Luganov

The behavior of arsenopyrite under heating has been studied by many scientists. It has been already established that under heating at more than 650°C and without air access the arsenopyrite dissociates with the formation of one atom arsenic. Under vacuum the dissociation process begins at 550 DC with the formation of elemental arsenic. The residue of dissociation process contains pyrrhotite and throilitc. In the presence of pyrite, arsenopyrite dissociates under lower temperature and with a higher velocity than without it. The industrial realization of fool scale processing of arsenic bearing raw materials is possible only by the use of standard equipment and oxygen containing blast In this view the paper presents the results of the study on the effect of oxygen in the gaseous phase and its addition into the charge of pyrite in the process of arsenopyrite decomposition. Thermodynamic analyses showed that under thermal processing of arsenopyrite in the presence of pyrite and limited quantities of oxygen in the gaseous phase the formation of arsenic sulfides is possible according to the following reactions:

Jan 1, 2003

By X Hill

Throughout the 2016/2017 financial year, the NSW Resources Regulator conducted an assessment of each underground metalliferous operation across the state to assess how each operation managed the principal mining hazard of ground and strata control. The assessment considered all aspects of the mining process, including all aspects of managing geotechnical risk within drawpoints. This assessment is ongoing and, therefore, this paper is limited to the first six mines assessed in the program.In 2015 there were three fatalities in and around underground drawpoints in Australian metalliferous mines. Whilst many of the systems of work around underground development are consistent across the industry, there are large discrepancies around how each underground mining operation manage the risks associated with drawpoints.For drawpoints to be effectively managed, their management needs to be considered at the earliest stages of the mine planning process. By using downholes and adopting remote systems of work – systems that are continuing to improve with technology – the risks drawpoints posed can be greatly reduced.The assessment by the NSW Resources Regulator revealed a number of common failings across the state in the management of the risks that drawpoints pose. The assessment also observed a number of innovative practices that particular operations have adopted in the wake of serious incidents occurring within drawpoints at their operation; however, these practices have not been communicated to other operations.It is hoped the learnings from the assessment can be considered by industry and reduce the risks drawpoints pose in underground metalliferous mines.CITATION:Hill, X, 2017. Learnings from review of drawpoint management across New South Wales mines, in Proceedings 13th AusIMM Underground Operators’ Conference 2017, pp 143–150 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Oct 16, 2017

By John C. Ferm

This report contains a summary of Phase I and complete results of Phase II portions of a study of geologic factors associated with roof falls in mines on the Pocahontas #3 coal seam in southern West Virginia and southwestern Virginia. Principal objectives of Phase I was the selection of five mines that best portrayed the spectrum of roof and mining conditions and Phase II consisted of a measurement and documentation program for each of the five mines. The documentation measurement program included reconnaissance mapping, detailed mapping, joint measurements and coring roof rock. 1.2 PHASE I RESULTS The results of Phase I consisted of the selection of the following five mines for detailed study: Virginia Pocahontas #3 (Island Creek Coal Company), Bishop (Consolidation Coal Company), Shannon Branch (Allied Chemical Company), Keystone II (Eastern Associated Coal Company) and Macalpine-East Gulf (Westmorelenad Coal Company). In addition, Phase I results, which were based on questionnaire data, indicated that the kind of rock in the roof --gray sandstone, crystallized sandstone, laminated sandstone and shale, grey shale, slickensided shale, and rider seams could be associated with good and bad top areas. Also presence of vertical separations, bolt length, entry and cross-cut width, length and torque on bolts and depth of overburden seemed to be related factors. These data provided a focus for the Phase II measurement program.

Jan 1, 1975

By W. G. Willson, Y. L. Li, P. D. Rao, D. E. Walsh

The combination of high moisture and low heating value has restricted most low-rank coal (LRC) usage worldwide to mine-mouth power generation. The objective of this study was to subject two Alaska low-rank coals to hydrothermal drying to enhance their marketability in the Pacific Rim markets and to evaluate the chemical and physical properties of the dried products as a function of process conditions. Coals from Usibelli Coal Mine and the Beluga coalfield have a heating value of approximately 18.5 MJ/kg and contain about 28% moisture. Hydrothermal treatment (at 275° to 325° C) of lump coal, from the Usibelli Coal Mine and the Beluga coalfield, enhanced the heating value of the material, on an equilibrium moisture basis, from 18.5 MJ/kg to nearly 27.8 MJ/kg. The product coal, with a high heating value and only 0.2% S, is an environmentally-acceptable premium fuel; additionally, with the Hardgrove grindability index of the coal greatly improved, its value is even further enhanced. An increase in hydrothermal drying temperature promotes vesiculation of resinite. Also, ulminite reflectance increased to 0.92%, and ulminite was subjected to widespread vesiculation; this resulted in a coke-like structure indicative that the material went through the fluid stage.

Jan 1, 1993

By J. Boulton

"Nuclear energy is an established and proven energy source. Today, CANDU-PHW nuclear-electric generating stations produce over one third of Ontario's total electrical supply: safely and economically. In many parts of Canada, where economic hydro resources do not exist or are fully developed, coal and nuclear energy are the only alternatives for future large-scale electrical generating capacity.Recent analyses have suggested that, in the f ace of increasing energy demands and decreasing reserves of hydrocarbon fuels, Canada must depend on electricity to provide an expanded fraction of its energy budget. Nuclear energy is likely to play an increasing role in the generation of electricity; there are also potential applications as a supplier of process heat in industry and in the in-situ recovery of bitumen fro m tar sands.The future supply of nuclear fuel, reactor safety and radioactive waste management are briefly discussed. In each case, the benefits to be gained from a controlled expansion in the use of nuclear energy outweigh any uncertainties which may exist."

Jan 1, 1981

By S. C. Maji, U. S. Chattopadyay, S. Chaudhuri, T. Gouri Charan

India is devoid of coking coal resources, which is a vital raw material for coke making. As a result it has to import about 80% coking coal for steel making. Indian National Steel Policy, 2017 has envisaged crude steel production around 300 million tonnes Mt) by the year 2030-31 and forecasts coking coal demand of 161 Mtpa (million tonnes per annum). One way of improving the indigenous resources is to study the performance of existing washeries and to improve the clean coal recovery by adopting suitable technology. A study was carried out, mainly to focus on the fine coal circuit of an existing coking coal washery, to generate the desired quality of clean coal. The operating coking coal washery being studied is presently feeding coal from nine different sources with varying feed ash contents. The coal fines varied in ash content ranging from 19.5% - 43.6%. For treating the coal fines, the washery has operated a spiral for the past few years. Performance studies were carried out, and it was found that the spiral is not efficient in recovering the cleans. Detailed investigations were carried out on the coal fines using flotation techniques, and it was found that to achieve a low ash clean coal, the froth flotation is a much better beneficiation option than a spiral, The studies showed that the recovery of clean coal through a spiral is 67.7% at ash content of 27.0%, while flotation tests showed a recovery of 68.1% at 16.5% ash content. Keywords: Coking coal washery, near gravity material, spiral washer, froth flotation

Jan 1, 2020

By Michael J. Beus

This Bureau of Mines report describes the development of load cells for measuring compressive loads in timber and lock-bolt support systems commonly used in. coal; metal, and nonmetal mines Design and evaluation is covered in detail to insure a reliable, accurate, and practical instrumentation scheme. The load cells are relatively inexpensive and adaptable to various size support systems. User-oriented procedures are emphasized, and design equations were reduced to a series of nomographs. Laboratory evaluation, destructive testing, environmental testing, and tests to determine the effect of extraneous loads were conducted. Field performance was evaluated in conjunction with ongoing Bureau projects at a metal mine in North Idaho and a coal mine in Utah. Load cells utilizing a titanium alloy as the cell body and weldable strain gages as the strain-sensing components satisfied the basic design and performance criteria, and with minor design modifications, the load cells can be adapted to many mining applications.

Jan 1, 1974

By L. T. Matthews, C. E. Loo, R. P. Williams

The behaviour of iron ores and fluxes in the high temperature zone of a sintering bed is extremely complex. Following a review of current knowledge, an attempt is made to define relevant terminology to describe the processes that occur in this part of the bed. A deformation temperature is used to quantify the initial formation of melt, which is produced predominantly by reactions between fine particles in the sinter mix. The subsequent assimilation of larger particles is considered to depend on the reactivity of the melt and the assimilation resistance of these particles. Novel laboratory experimental techniques are used to quantify these parameters. Results demonstrate that the properties of the raw materials used have an extremely important influence on the initial processes of melt formation and assimilation and also on the nature of the sintering reactions and sinter-bonding phases.

Jan 4, 1992

By S. Nafisi

Permanent mould casting may be regarded as a near net shape manufacturing process where simple to very complex shaped engineering components are fabricated with high degree of precision in a metallic mould, In this group, High Pressure Die Casting (HPDC), have attracted more attention because of its production rate, where both liquid and semisolid metals (SSM) can be cast with high degree of precision and versatility. The SEED process, Swirled Enthalpy Equilibration Device, the new process for semi solid metals slurry production route, consists of two steps: The initial step involves extracting specified amount of heat from the molten metal to generate liquid-solid slurry, i.e, mushy structure, followed by drainage of remaining liquid to produce a compact free standing feedstock for rheocasting operation. In this paper, microstructural evolution during the process and some initial casting results of automotive components an also reported.

Jan 1, 2005

By Carlos Rabanal, Levi Guzmán

"The concern regarding grinding media consumption rates is as old as the invention of the tumbling mill. Over the years many materials and grinding media shapes have been tested. Through all this, steel grinding balls have proved to be the most effective media for comminution in tumbling mills. There have been several approaches to be able to the wear of the ball charge in any given mill, all of them based on limited empirical evidence. The mining industry still utilizes the Bond Abrasion test that was developed in the 1960´s. As shown later in this publication, this approach shows error greater than 60%. More recently, in 2007, Radziszewski from Mc Gill University has proposed a different total grinding media wear model; this model is based on decoupling the effects of the abrasion, corrosion and impact wear mechanisms. Also in 2007, Benavente, at the time with Moly-Cop Peru, presented an empirical model relating both ore properties and operational conditions that would affect the wear performance of the grinding media. For the database referred in this article, Benavente’s model shows an average error of ± 12% which represents a higher degree of improvement in comparison with previous approaches. The current paper presents recent research conducted by Moly-Cop Peru to further improve the capability of the empirical model originally developed by Benavente to estimate grinding media wear rates. The work performed included extensive determinations of the Bond Abrasion Index for different types of ores, collected at industrial grinding applications where the corresponding operational information was made available. The results of the research enabled us to build a more robust and confident model for estimating the grinding media wear rate. The average error of this new model is in the order of ± 9% which is a significant improvement over the models previously described."

Jan 1, 2014

By Harry W. Barr

Judging by the inquiries that come to Battelle, a number of companies have run into problems in determining the size and character of markets for mineral fillers in general and specialty fillers in particular. Usually these problems arise during a project to develop a new mineral filler when management suddenly realizes that a considerable sum of money will have to be spent before any profits are realized from sales of the new filler. What management needs in this case is the odds for or against the success of the development. And these odds frequently are controlled by the markets for the new filler. Basically, the problems involved in gaging markets can be simplified to how much of this new filler can be used and by whom? But there are some potential booby traps in these simple questions that should be exposed. This paper will discuss a few of these problems such as: 1. Describing the filler so that the prospective customer recognizes its possible applicability. 2. Finding; a prospective customer who can verify the filler's applicability. 3. Expanding successful test results to total industry markets. 4. Appraising competitive products, and 6. Discovering all the possible uses for the new filler.

Jan 1, 1961

By Jeremiah Cohn, Rachel L. Bauer, Catherine E. Johnson

Water is frequently used in explosive applications to increase explosive performance and reduce air overpressure. Water tamping can enhance cutting abilities of shaped charges in demolition and increase impulse of kicking or breaching charges. In explosive disposal, water is used to suppress air overpressure and reduce noise. Despite its widespread use, the specific effect of water placement, whether in front of or behind the explosive, has not been studied. This work evaluates the directional effects of water placement on blast performance using 400-gram sheet explosive charges in five configurations: no water (control), rear-only water (tamped), front-only water (pushed), water on both sides (confined), and a thin front-and-rear water layer (low mass confined) to assess reduced mass effects. Water was sealed in plastic bags and held in position with custom 3D-printed cages to ensure consistent geometry and contact. A modified ballistic pendulum consisting of a hanging steel W-beam was used to evaluate impulse transfer, with high-speed video capturing swing velocity. Air overpressure was recorded using a seismograph microphone. Rear-only water (tamping) increased beam swing velocity by 69% over the control while confinement with water on both sides increased performance by 12% at a 2:1 water-to-explosive ratio and by 50% at 4:1, though it still underperformed the tamped-only configuration. Pushed water alone did not increase beam momentum and reduced tamping effectiveness by 19% when combined. Seismograph microphone data showed that pushed and low mass confined water configurations produced some of the highest air overpressure levels (up to 139.2 dB), while tamped and control charges produced lower levels (~134–136 dB), suggesting that pushed water may amplify, rather than mitigate, air shock transmission. These findings show that water placement has a strong directional influence on blast dynamics: water behind a charge enhances energy transfer to the target, while water in front provides limited or potentially counterproductive mitigation. This study advances understanding of water–explosive interactions and will lead to more effective charge designs for breaching, disposal, and demolition.

Jan 26, 2026

By Kremena Dedelyanova, Tsvetan Damyanov, Nikolay Hristov, Evgeni Kostadinov, Lubomir Kuzev

"Spherical grinding media (balls) are the most widely used media for comminution of ores by grinding. One way to optimize the grinding process in a tumbling mill is associated with the development and testing of a new media shape. By modelling simulation study of the behaviour of two types of grinding media (balls and tetraballpebs) in the grinding process was conducted to determine the possible advantages of the new media shape. Tetraballpebs are in the shape of tetrahedrons with spherical convex walls. D305 mm and L305 mm Bond ball mill sizes were used in the experiment. They are modelled milling tetraballpebs bodies corresponding by weight to five ball sizes, namely ¾, 7/8, 1, 1¼ and 1½ inches which form the grinding media used in a Bond ball mill. They are cast steel grinding bodies. Studies carried out with both types of grinding media include equal number of milling bodies of the same weight and volume. Having thus ensured a uniform mass of the grinding media and the same number of milling bodies, all other conditions and process parameters being identical, conclusions can be drawn about the influence of the grinding media shape on the grinding process. Compared to steel balls, the tetraballpebs used in laboratory tests carried out in closed cycle by Bond ball mill and the study of the rate of grinding gave five to six per cent higher yield of a control size of minus 0.1 mm. Measurements of the Bond ball mill power consumption demonstrated that tetraballpebs grinding media achieved energy saving of 4.7 per cent for the production of one gram of the control size of minus 0.1 mm."

Jan 1, 2014

By P. T. Bissert, L. Yan, M. D. Klein

"Federal regulations require that refuge alternatives (RAs) are located within 305-m (1000-ft) of the working face and spaced at one-hour travel distances in the outby area in underground coal mines in the event that miners cannot escape during a disaster. The Mine Safety and Health Administration mandates that RAs provide safe shelter and livable conditions for a minimum of 96 hours while maintaining the apparent temperature (AT) below 35°C (95°F). The National Institute for Occupational Safety and Health used a validated thermal simulation model to examine the mechanisms of heat loss from the RA to the ambient mine and the effect of mine strata composition on the final internal dry bulb temperature (DBT) for mobile tent-type RAs. The results of these studies show that most of the heat loss from the RA to the ambient mine is due to radiation (51%) and conduction (31%). Three mine width/height configurations and three mine strata compositions were examined. The final DBT inside the RA after 96 hours varied less than 1°C (1.8°F) for the three mine width/height configurations and less than 2°C (3.6°F) for the three mine strata compositions. INTRODUCTION Following a mine disaster, workers will try to escape the mine. If their escape is futile, they can take shelter in a refuge alternative (RA). In 2008, the Mine Safety and Health Administration (MSHA) mandated RAs in mines to ensure that a safe and livable shelter is provided for a minimum of 96 hours, and that the apparent temperature (AT) does not exceed 35°C (95°F) inside the RA [1]. An ongoing concern with RAs is the potential to exceed this limit. The temperature rise inside an RA is due to the metabolic heat released by the occupants as well as heat released by the carbon dioxide scrubbing system. The National Institute for Occupational Safety and Health (NIOSH) tested a 10-person tent-type training unit RA in its Safety Research Coal Mine (SRCM) to investigate heat buildup in RAs. The 10-person capacity for the tested RA is based on 1.4 m2 (15 ft2) of floor space per miner. NIOSH-developed simulated miners, which are heat input devices that generate both sensible and latent heat, were used to represent the metabolic heat generation of an average miner (117 W) for testing in the SRCM. It was found that the number of occupants in an RA may need to be reduced based on the ambient mine temperature, which varies from mine to mine [2]. To further research temperature rise inside an RA, ThermoAnalytics, Inc. (TAI) was contracted by NIOSH to perform thermal simulations of the tested 10-person mobile tent-type RA. TAI developed a thermal model of the SRCM using RadTherm software, which incorporates a human thermal model (HTM) to represent the equivalent metabolic heat loss of a miner within the RA’s enclosed environment. The thermal model was previously validated by comparing simulation results with test results [3]. During a mine disaster in which miners would have to take shelter in an RA, mine ventilation may not be available. As such, mine ventilation was off for both the testing in the SRCM as well as in the simulations. This paper discusses the heat loss mechanisms and the effects of mine strata composition and mine width and height associated with a ten-person tent-type RA."

Jan 1, 2016

By R. L. Grayson

In 2010, MSHA began holding hearings on a new coal mine respirable dust rule, which proposes a 1.0 mg/m3 standard, a separate 0.1 mg/m3 quartz standard, and the use of single-shift samples for compliance. Small mines largely comprise the ?hot spots? where dust diseases of the lungs increased dramatically over the past decade. This paper presents findings on the feasibility of small mines? compliance with the proposed new 1.0 mg/m3 standard. It gives probabilities of noncompliance by MSHA district, seam height, and selected ?hot spot? counties. Because silicosis and respirable quartz dust appear to be the primary issues related to a recent doubling of the prevalence of dust diseases of the lungs, multiple regression models for prediction of the average total quartz content of compliance samples are given. These findings have significant implications on the need for better dust control methods.

Jan 1, 2012

By G.A. Moore, C. E. Sims

In previous publications of the writers4-7 it has been shown that vacuum extraction of steel can be carried as close to quantitative completion as desired provided the steel is in the austenitic state and sufficiellt time is allowed. For precise work, the method claims preference because the equipmelit for holding and heating the sample can be made simple, and because crucibles, boats, and other unnecessary materials can be eliminated and the blanks thus made very small. It is well known that the evolution rate of hydrogen is smaller just above the trans. formation than immediately below, as would be expected from the increase in solubility when passing into the gamma state. Many attempts have been made to obtain analyses by extraction just below the transition, using times of approxi. mately 2 hr. while it is true that the rate of evolution drops nearly to zero under these conditions, it has repeatedly been shown that the process is incomplete since on raising the temperature into the austenitic range, evolution will be resumed, usually after a, considerable induction period. The low-temperature evolution process appears to be useful in some cases for comparative tests where the residual crror may be more or less constant between samples, For general use, however, there is no guarantee that the error caused by incomplete extraction is constant; hence, the more laborious but more reliable high-temPe'atu'e Process must be used. At high temperature, an original flash evolution, similar to that at lower temperature, is first observed. After not more than an hour, the flash subsides and cvolution settles down to a regular first-order reaction rate for which the half-life* is usually of the order of a few hours for the 5/8-in. diam cylinder at 1050°C. The regular evolution may be followed for whatever period appears justified, after which the residual gas may be estimated as equal to that which was evolved in the last observed half-life period. Tests have shown that the composition of the evolved gas does not vary greatly during the progress of evolution; therefore the residual gas may safely be taken to have the same composition as the portion col-

Jan 1, 1949

By C. E. Sims, G. A. Moore

In previous publications of the writers4-7 it has been shown that vacuum extraction of steel can be carried as close to quantitative completion as desired provided the steel is in the austenitic state and sufficiellt time is allowed. For precise work, the method claims preference because the equipmelit for holding and heating the sample can be made simple, and because crucibles, boats, and other unnecessary materials can be eliminated and the blanks thus made very small. It is well known that the evolution rate of hydrogen is smaller just above the trans. formation than immediately below, as would be expected from the increase in solubility when passing into the gamma state. Many attempts have been made to obtain analyses by extraction just below the transition, using times of approxi. mately 2 hr. while it is true that the rate of evolution drops nearly to zero under these conditions, it has repeatedly been shown that the process is incomplete since on raising the temperature into the austenitic range, evolution will be resumed, usually after a, considerable induction period. The low-temperature evolution process appears to be useful in some cases for comparative tests where the residual crror may be more or less constant between samples, For general use, however, there is no guarantee that the error caused by incomplete extraction is constant; hence, the more laborious but more reliable high-temPe'atu'e Process must be used. At high temperature, an original flash evolution, similar to that at lower temperature, is first observed. After not more than an hour, the flash subsides and cvolution settles down to a regular first-order reaction rate for which the half-life* is usually of the order of a few hours for the 5/8-in. diam cylinder at 1050°C. The regular evolution may be followed for whatever period appears justified, after which the residual gas may be estimated as equal to that which was evolved in the last observed half-life period. Tests have shown that the composition of the evolved gas does not vary greatly during the progress of evolution; therefore the residual gas may safely be taken to have the same composition as the portion col-

Jan 1, 1949

By C. L. Schneider

The problem of predicting the liberation spectra produced by a closed continuous grinding circuit is of fundamental importance for the design, optimization and control of most operations in an ore dressing plant. The only known approach through which such a calculation can be performed is the population balance model equation. The latest and certainly most significant progress made in this area is the solution proposed by King (1990), which requires one textural parameter that can be measured directly from the ore being studied. The main advantage of King's solution is that it does not require the estimation of hundreds of arbitrary parameters that cannot be independently measured, as required by the existing conventional solutions. However, King's solution relies heavily on a knowledge of the detailed internal structure of the Andrews-Milm diagram (Andrews and Mika, 1975). This has never been measured for any ore. The characterization of the internal structure of the Andrews-Mika diagram requires the measurement of the liberation spectra at several progeny sizes produced by the breakage of monosize, monograde particles at several different grades. In this paper, a procedure based on magnetic fluid fractionation for generating seven narrow-size, narrow-grade samples is presented. Each of these samples was then broken into six progeny size classes in an ultrasonic mill. The one-dimensional liberation spectra of each of the 42 progeny and seven parent particle samples were then measured by image analysis. The measured linear-grade distributions are presented in this paper. The calculation of the correspondent volumetric-grade distributions is discussed.

Jan 1, 1994

By J. F. Held

In a study of the influence of cold rolling on mechani cal properties of steel, it was found that the specific rolling procedure influenced crystallographic orientation. Properties developed by several rolling modes were determined and related to crystallographic orientation. Sanzples were cold-rolled various amounts on a laboratory mill. When palm oil was used as a lubricant, the crystallographic orientation was homogeneous throughout the thickness of the samples. Other samples were rolled without lubrication. Variations in intensity of the recrystallization texture components persisted throughout more than 50 pct of the volume of these samples. When the average plastic strain ratio, which is dependent upon crystallogvaphic orientation, was plotted as a function of percent reduction, a maximum was found at 40 pct in the samples which contained the observed texture variation. No maximum was found for the samples with the homogeneous texture distribution. Other mechanical properties, such as tensile strength and yield strength, were not influenced by the variation in crystallopaphic orientation. MECHANICAL properties of steel sheets depend, in general, upon the structural properties of the steel. For example, the Petch equation describes the relationship between yield strength and grain size. Other properties, such as hardness, vary with chemical composition. The plastic strain ratio, or R value, has been found to be dependent upon crystallographic orientation . In the course of investigating the effect of cold rolling on mechanical properties, it was found that a previously reported relationship between percent cold reduction and R value was not always observed. Published data had shown that the optimum cold reduction for best R values is 70 pct for aluminum killed steel.' However, by altering the rolling conditions, the optimum reduction can be shifted to much lower values, or it can be moved to very high values. This paper describes the rolling conditions that lead to shifting of the optimum cold reduction. The effect of rolling conditions on the various structure parameters and the resulting mechanical properties are evaluated. EXPERIMENTAL PROCEDURE Samples of three low-carbon aluminum killed steels were cold-rolled various amounts on a 9-in.-diam 2-high laboratory mill. Hot-mill thermal practice and steel chemistries are listed in Table I. Steel A was rolled with palm oil lubrication and heavy reductions on each pass; i.e., a total reduction of 75 pct was ac- complished with a maximum of five passes. Steel B was rolled without lubrication, and light reductions were given on each pass. After approximately 75 pct reduction, it was necessary to use a small amount of light oil to achieve any additional reduction in thickness. Following cold reduction, the samples were box-annealed at 1300°F for 10 hr. The heating rate between 800" and 1300°F was 50°F per hr, and the cooling rate following the soak period was 50°F per hr. Tensile specimens were machined from the annealed material and these were used to measure yield strength, tensile strength, and the plastic strain ratio (R value). Recrystallization textures were determined by an inverse pole figure technique.*'3 Integrated intensities of the (110), (002), (112), and (222) reflections were recorded for those planes lying parallel to the sheet surface. Examinations were made on both surfaces of each sample, and also at various levels beneath each surface to approximately 0.010 in. depth by etching techniques. RESULTS R Values. The R values obtained in steels A and B are shown as a function of percent cold reduction in Fig. 1. No optimum cold reduction was observed in steel A, rolled with palm oil lubrication. It is likely, however, that an optimum reduction would have occurred had higher reductions than 88 pct been employed. The optimum reduction in steel B occurred at 40 pct. The behavior in both of these steels is quite

Jan 1, 1968

By D Pateman, F de Fredrick

The Bentley underground mine, which is located 60km north of Leonora, Western Australia, is owned and operated by Round Oak Minerals Pty Limited. A high-grade Zn-Cu Volcanogenic Massive Sulphide (VMS) orebody, Bentley was discovered in 2008 with production commencing in 2012. Long-hole open stoping is employed to mine the steeply dipping ore body, and in recent years the Avoca method has been adopted. This requires all development in a particular area of the mine to be completed prior to stoping commencing in a bottom up sequence. Voids are commonly backfilled with loose Run-of-Mine (ROM) waste loose rockfill (LRF); or alternatively cemented rockfill (CRF) can be used. Stopes in the 3860 AOS and 3900 AOS panels were located below previously extracted Avoca zones, with LRF situated immediately above them. These high-grade stopes were originally designed with rib and sill pillars to maintain control of the existing backfill during extraction. Due to changing factors over time, including mining economics, alternative options to achieve full extraction of the stopes were reviewed, including: • Mining small successive full height stopes which would involve drawing a blanket of LRF down with the extracted ore (stoping under waste); • Stabilisation of the existing LRF above the stopes and implementing a primary/secondary stoping sequence, with the primary stopes backfilled using a cement fill. An assessment of these options was undertaken which determined that the second full extraction method was the most beneficial to the operation, and could be achieved using a cement grout (Minova’s FB200 grout) to stabilise the LRF in conjunction with implementing a sequence where the primary stopes would be backfilled with cemented aggregate fill (CAF). Footwall drives were developed adjacent to the rockfilled stopes, allowing for the installation of horizontal grouting conduits, as well as providing access to the top of the planned 3860 and 3900 level stopes for the placement of CAF. An interval at the base of the previously rockfilled stopes was grouted at multiple horizons to achieve the required thickness, with a comprehensive quality assurance/quality control (QA/QC) process undertaken. Primary stopes were CAF backfilled via an arrangement of downhole winzes, linking the top of primary stopes to cross-cuts developed off the associated footwall drives. CAF was delivered underground through an open reticulation network that was extended to the specific levels. Overall the successful implementation of the revised mining method effectively increased ore recovery while maintaining control of overbreak and dilution, providing significant financial upside. This was achieved while maintaining effective controls in light of the changes to the risk profile. Stabilisation of the existing rockfill has allowed the extraction of stopes to full height, including the originally designed sill pillars, representing an average 23% increase in ore tonnes on the initial design, with dilution from the stope crowns averaging less than 1%. The use of CAF in association with primary/secondary stoping, eliminating the need for rib pillars, has yielded an average 47% increase in ore tonnes compared to the base case mine design.

Mar 15, 2021