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This Bureau of Mines publication contains the texts of the four papers presented at the May 6-7, 1980, seminar on the role of overburden analysis in surface mining. Coverage includes the geologic distribution of pyrite and calcareous material and its relationship to overburden sampling, overburden sampling and analysis, use of soil-overburden data in mine planning and development, and minesoil classification.

Jan 1, 1981

By J. H. Nixon

A three phase program evaluated commercial proximity warning devices, developed and designed a microprocessor-based electrostatic field measurement instrument, and utilized this instrument to investigate the electro-static fields about power lines. The Phase I program consisted of test and evaluation of these commercially available proximity devices. The evaluation results were reported in the Phase I report entitlted "Evaluation of Proximity Warning Devices II dated 22 February 1980. The Phase II program resulted in the design and development of a microprocessor-based Distributed Sensor A.C. Electrometer which measures the electrostatic field present at 17 discrete locations along a crane boom. Operator control of the measurement system allows simultaneous electric field measurements from 17 probes, print out of the electric fields measured, and data archiving on magnetic tape for post measurement analysis. Under the Phase III program, electro-static fields around a crane boom were measured by the instrument at 17 high voltage power lines of various voltages and geometries. The electric field data was processed and plotted versus boom distance from the power line. Analysis of the electric field data indicate that the distances at which a single sensor alarm will activate, vary by a factory of 3 to 1. This is due primarily to variations in boom orientation. The results also indicate that in the case of multiple power lines, a single electrostatic field sensor cannot reliably be used to determine the distance from a power line.

Jan 1, 1982

By Paula Pereira

The better the capability of accurately predicting the results of any process the less laborious and costly is the optimization or improvement of that process. Rock blasting is a process that one intends to optimize for productivity and cost. Cast or throw blasting is a particular type of rock blasting which is widely used in surface coal mines, where draglines are used to remove the overburden from the top of the coal seam, in preparation for coal mining. Usually, the more rock that is thrown by the blast to the spoil side of the cut or pit, so that the dragline does not have to handle it, the more cost-effective is the cast blasting operation. As such, from an operating cost standpoint, it is crucial to better understand and predict the performance of cast blasting. The Distinct Motion Code or DMC is a Discrete Element Model which has been under development since 1987 and has been used to predict rock motion in several types of mining operations, particularly in surface coal and gold operations.

Jan 1, 2001

By Roger E. Burleigh

In June, 1989, the U.S. Bureau of Mines, undertook a 9-day evaluation of the tin resource potential of the Sleitat Mountain tin deposit. Significant tin-tungsten mineralization is associated with quartz-topaz-white mica-tourmaline greisen alteration of a multi-unit, 57 Ma, peraluminous, granite stock which intrudes Cretaceous Kuskokwim Group flysch deposits. The granite comprises marginal biotite-, intermediate biotite-muscovite-, and central zinnwaldite-granite units, interpreted as a zoned alteration system. Major vein mineralization is confined to two east-west-trending zones of steeply oriented tabular lenses of greisen interleaved with mildly altered granite. Cassiterite is the dominant ore mineral while arsenopyrite, loellingite, wolframite, pyrite, sphalerite, chalcopyrite, and bismuth-oxides are present in minor to trace amounts. The north and south greisen zones are estimated to contain an inferred resource of 128 to 212 million lbs Sn in 28.6 million st of mineralized rock. An 1,800-lb representative bulk sample contained 0.37% Sn, 0.04% W and 17 ppm Ag and is considered an average grade estimate for the deposit. Drill testing by Cominco Alaska Exploration indicates that substantial widths of high-grade tin mineralization are included within the lower grade disseminated mineralization. Depth of deposit erosion is substantial and there exists a high probability for placer tin deposits.

Jan 1, 1991

By E. K. Stanek

The field tests involved ten coal mines in which transients were initiated on the dc system from which the parameters of the dc mine electrical power system could be determined. The data processing involved the use of a Fourier Analyzer to filter noise and fit an exponential curve to the field waveforms. From this data analysis it was possible to find the dc system resistance, inductance and time constant. The survey of nationally recognized laboratories was conducted to establish that the recommended test criteria were practical. The development of test criteria for dc fuses used in mines was based on the measurement of parameters in the field, the survey of testing laboratories, literature searches, laboratory test, etc. A computer program was written to analytically predict the parameters measured in the field. This approach has limitations but reasonable agreement with field results was obtained. A brief laboratory testing program was carried out to verify the practicality of the recommended criteria and establish the accuracy of the conclusions concerning dc fuse performance.

Jan 1, 1984

By Neil J. Mansfield

Tool manufacturers are required to provide declarations of vibration emission values in order to sell their tools within Europe. To ensure that users can compare results obtained from different manufacturers, the declared values must be obtained using a methodology as specified in the relevant test code (such as in the ISO 8662 series of standards). In most cases, the vibration emission values obtained using test codes under-estimate the vibration that an operator will be exposed to when using the tool on a work-site. A further problem with manufacturers’ data is that usually only a single value is provided for a tool. This is despite many factors affecting the vibration emission, including inserted tool type, work piece, operator technique, tool condition. New improved test codes are in the process of being developed. In order to provide guidance to users on how to interpret manufacturers’ data, a Draft CEN Technical Report (Draft CEN/TR 15350 (2005)) was developed. Part of the CEN/TR provides multiplication factors for combinations of task and tool type. For example, data obtained from electrical hammer drills (tested according to EN 60745-2-6:2003) should be multiplied by 2, for hammering applications, in order to obtain an estimate of the vibration emission during work. In response to concerns from industry, the UK trade association OPERC have, in collaboration with hire companies and tool manufacturers, established a freely accessible online database of tool emission values based on independent tests carried out under simulated work-site conditions. This paper reports some of the data obtained from electrical hammer drills, highlighting the range of emission values that can be obtained for a tool. Data from many other tool types are also included in the database. Methods Tri-axial hand-arm vibration was measured at both handles of each of 19 electrical hammer drills, in accordance with ISO 5349-1 (2001). Each tool was measured with three experienced operators and at least 5 runs were completed for each operator. Tools were tested using a range of appropriate new bits from 4 to 40 mm diameter. The minimum number of bits for a tool was 3; the maximum number was 29. 146 tool / bit combinations are reported here, representing about 2200 individual 6-axis measurements. Operators were required to drill vertically into a concrete block with a compressive strength after 28 days of 40 N/mm². Two drills (1 and 15) were battery powered; others were powered using a 110V transformer supply.

Jan 6, 2006

By D. G. Hulbert, J. H. Schubert, R. G. D. Henning

"Froth depth, along with reagent addition and aeration rate, is one of the crucial factors that can be used to control a flotation circuit. Sub-optimal setpoints and disruptions in levels have a severe adverse influence on grades and recoveries. A novel control strategy has been developed which provides exceptionally tight regulation of pulp levels. The controller observes and acts on all the flotation levels simultaneously. This provides a clear improvement over the standard approach, which is to use a set of Pl controllers. The system has been run on several industrial plants and has resulted in reduced fluctuations in level; fast responses to setpoint changes, and fast settling times after start-ups or disturbances. Testwork has shown that the improvements in level stabilisation translate into improvements in recovery and grades.IntroductionProcess control and optimization have an important influence on the economic efficiency of flotation plants. Inefficient operation can allow the wrong balance between grades and recoveries, and can also lead to adverse shifts in the grade-recovery relationship. Of all metallurgical operations, flotation loses the largest proportion of valuable material. Better operation can reduce these losses.An essential requirement of a good controller is that it should be able to stabilize and regulate the plant. Stable operation allows the performance of the plant to be observed without being obscured by the effects of disturbances and fluctuations. The optimum conditions can then be detected more easily. Good regulation can maintain operation at the optimum with proper neutralization of disturbances. Only when good stabilization and regulation are achieved can an optimizing strategy be properly applied.Froth depth, aeration rate and reagent addition are the three means by which a flotation plant is generally controlled. These control actions are effective on different time scales. Reagent addition is slower in its effect as some conditioning time is required. Since reagents are only added at the head of the circuit and at a few selected points within the banks, time is required for the effect of reagent changes to move through the circuit. Because of this slower time constant, reagent addition is more suited to process optimization and to dealing with slower changes in the process. An example of these slower changes is variation in the feed."

Jan 1, 1995

By Don] [Hinkle

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Jan 1, 1977

By Schwartz M.

Respect for mining in Botswana is long-standing. This article looks at Africa's most transparent mining regime and some of its ambitious plans. Botswana's mining industry value is forecast to average 5.2% growth from 2014-2018 with solid growth for the diamond sector and acceleration of coal production. Respect for the country's mining regime is maintained in the Fraser Institute 2014 annual survey where Botswana occupies the 26th position of 122 administrations. Botswana's transparency is illustrated by Mupane gold mine near Francistown, Ghaghoo diamond mine in the Gope area and the Morupule coal mine

Mar 1, 2015

An Integrated Study of Bubble-Particle Attachment Mechanisms

Sep 13, 2010

By M. C. Bleiweiss

Various light sources were evaluated for use in a fiber optic lighting system for mining machines. It was determined that a metal halide arc lamp was best because of its resistance to damage from shock and vibration and the high luminance of the arc. Measurements were made of the percent transmission of the ½ inch thick glass window and the fiber bundles, the total lumen output of the diffuser assembly with a known input and of the average surface luminance of the diffuser assembly. These data were then used to calculate the theoretical output of the system given an estimated input from the source. A prototype 55 watt, single-ended metal halide source was then developed. In order to provide greater efficacy and higher throughput through the fiber optic cables, a variation of the lamp with thallium iodide added to the fill was developed. The lamp was modified and a ballast was developed to allow it to hot restrike.

Jan 1, 1986

By D. Zhou, T. Hamano, Tsukihashi. F., W. -G. Seo

The thermodynamic properties for the CaO-CaF2and CaO-BaO systems were calculated by molecular dynamics (MD) simulation using Born-Mayer-Huggins type pair potential. The parameters of interatomic potential were obtained by fitting the thermodynamics properties of CaO, CaF2and BaO with the experimental data. The phase diagrams for the CaO-CaF2 and CaO-BaO systems were calculated by the thermodynamic properties obtained by MD simulation. The eutectic composition and temperature of the CaO-CaF2system calculated by MD simulation were about 28 mole per cent CaO and 1575K, respectively. The calculated eutectic point agrees very well with experimental data, which are about 22 mole per cent CaO and 1633K, respectively. Keywords: molecular dynamics simulation, thermodynamics, phase diagram, calcium oxide, calcium fluoride, barium oxide.

Jan 1, 2004

By A Bouazza, J Kodikara

In this study, 23 samples of leached ash (LA) were collected from an ash pond at Loy Yang Power Station and geotechnically characterised. The samples were collected at various depths and locations within the ash pond on two separate occasions in order to account for the full variability. The LA within the ash pond at Loy Yang Power Station (LYPS) was found to vary in texture from silt to sand, depending on the location from where the sample was collected. Samples collected near the ash pond inlet discharge point, for instance, contained more than 50 per cent sand sized particles and were subsequently classified under the Unified Soil Classification System (USCS) as silty sand (SM). Further downstream of the inlet discharge, the LA became progressively finer and was classified accordingly as elastic silt (MH) when the sand content became less than 50 per cent. Basic geotechnical testing revealed that the LA from Loy Yang Power Station was generally acceptable as a landfill cover material. The permeability of LA, however, was generally too high for prescriptive covers, (ie resistive covers that generally rely on the impervious nature of the material to control percolation). Alternative covers, generally rely on the store/release function of a capillary or monolithic barrier to prevent percolation into the landfill. Subsequently, a material that can maintain a high water storage capacity while at the same time, readily allow infiltration and evapotranspiration is required for an alternative cover. Sandy silt and silty sand are optimal soils for alternative covers, as they do not yield water to gravity forces, but do give up most of the water in their pores when subjected to high-matric suction (Kavazanjian, 2001). The effectiveness of alternative covers is ultimately assessed using computer models, such as UNSAT-H and HYDRUS-2D, to rigorously perform water balance calculations. Prior to using a computer model to determine the highest possible percolation in the worst climatic conditions, it is necessary to select the most appropriate materials. This paper suggests a method to screen available materials for use as an alternative cover material on the basis of the soil water characteristic curve (SWCC).

Jan 1, 2003

By M. Grun, A. C. Marlowe, I. Littleford

SYNOPSIS A Wirth tunnel borer owned by Anglo American Corporation completed a 1150m long tunnel some years ago and was subsequently extensively modified by Technical Development Services. In 1982 this borer provided new and particularly interesting information In the field of hard rock boring. The abrasive quartzltes traversed proved to be a challenge to the cutter manufacturer and the project team. This paper examines the problems faced, the solutions found and the lessons learnt.

Jan 1, 1983

By D van der Merwe

Tracers of known densities are used world wide in coal processing plants to evaluate plant performance. Tracers are added to the feed stream and are counted after being recovered from the product and discard streams to determine partition curves. The need to recover the tracers can be eliminated by adding radio frequency identification tags to the tracers. Readers mounted on the product and discard streams record the passing RF tracers and produce the partition curve instantly. Tests were performed with three different shaped tracers at different collieries on cyclones ranging from 510mm to 800mm in diameter. Sink and float analyses of coal samples were used to compare conventional partition curves to partition curves obtained by using RF tracers. The average amount of tracers recorded was 78% of tracers in the feed. The results indicate that the stone shaped tracers represent the results from the sink-float analyses the best. The results suggest that RF tracers can be used to evaluate cyclone circuits in the coal industry and will make it possible to evaluate a coal circuit?s efficiency without stopping a plant and waiting for laboratory analyses. Keywords Coal tracers, partition curve, radio frequency tracer, RFID

Jan 1, 2006

By E. D. Palmes

A new type of personal sampler for quantitative estimation of atmospheric concentrations of contaminant gases was first reported from this laboratory in 1972. The sampler requires no pumps or flow regulators and employs instead the motion of the gas molecules them-selves to furnish the power for sampling. Under this grant, work was completed on development of a kit for the field determination of both NO2 and NO. Detailed instructions for the preparation of the samplers and the use of the kit was supplied to the Technical Project Officer. Attempts were made to adapt the same type of sampler to the measurement of SO2 and CO. Both gas chromatographic and turbidimetric procedures for the final estimation of the S02 proved to be unsatisfactory. For CO no reagent was found which would react sufficiently rapidly with this gas to utilize the essential feature of the diffusion sampler, the maintenance of a diffusion gradient which is at least approximately numerically equal to the ambient concentration. A number of publications on use of the NO2 sampler, both at occupational and community air pollution levels, have resulted from this work.

Jan 1, 1979

By L. Chen, G. A. Brooks, S. A. Nightingale

The dissolution of alumina and magnesia has been investigated using laser scanning confocal microscopy (alumina) and a rotating finger apparatus (magnesia) to assess the effects of temperature, composition and forced convection on the rate of dissolution in CaO-SiO2-Al2O3based slags. The two techniques have differing strengths and limitations, and provide complementary methods for studying dissolution. Alumina dissolution was studied for temperatures from 1477 to 1577°C. Based upon the data, the rate controlling mechanism was thought to be mass transfer control in the slag. The diffusion coefficients for the alumina particles are estimated to be in the range 10-11to 10-10m2.s. MgO degradation for sample rotation speeds of 50 to 800 rpm at 1500 and 1530°C was studied for both congruent and incongruent dissolution. The results show that the rate of dissolution for this is primarily controlled by a diffusion mass transfer mechanism for congruent dissolution except at the highest rotation speed. For incongruent dissolution, the mechanism is much more complex, with the morphology and distribution of the spinel reaction product having a significant effect. At high speeds and prolonged times, mechanical forces played a major role in the degradation process. Keywords; kinetics, corrosion, refractories, dissolution rate, inclusions, mass transfer, slags, steelmaking

Jan 1, 2004

By L. Andrews

Nickel is recovered as a by-product of the platinum-producing process operated by Anglo Platinum. The metal is mined mainly as sulphide minerals contained in platinum ores. These pass through the concentrating, smelting and converting process route and nickel is finally recovered by electrowinning. Smelting of the concentrated ore in the electric furnace produces a melt with a high slag to matte ratio. The resulting furnace slag is granulated and later milled and floated to recover matte. A project was initiated to investigate the distribution of nickel in the slag in order to improve recovery. Slag samples were examined using a combination of chemical and mineralogical techniques. The granulated slag was found to consist mainly of a silicate glass phase, which reflects the composition of the molten slag in the furnace. Nickel occurs as free matte granules, as matte phases locked inside the glass, and in the glass phase itself. Whereas nickel in the matte is as sulphide, most of the nickel in the glass phase appears to be oxide- bound(i.e. in solid solution). Milled slag as flotation feed showed recovery-limiting features such as free matte with oxidized surfaces and unliberated matte inclusions in the slag. The biggest nickel losses, assuming no tapping problems, are in the glass phase solid solution. Only around 40% of nickel would be recovered from the slag, even under ideal conditions. Spoon and pot slag samples were also examined to see if casting and crushing would improve recovery. Although larger and therefore more easily recovered matte phases formed, nickel partitioned into crystalline silicate phases, limiting the maximum theoretical nickel recovery to 70%.

Jan 1, 2004

By Liming Yuan

Barometric pressure changes affect air density, leading to change in the mass of the gas in the gob. When the barometric pressure decreases, the volume of gas in the gob expands, while the volume of gas contracts when the barometric pressure increases, causing the gob to breathe out and in. Although the concept of gob ?breathing? is simple, its effect on spontaneous heating of coal in the gob area is not clear. In this study, computational fluid dynamics (CFD) simulations were conducted to model the spontaneous heating of coal in longwall gob area under measured barometric pressure changes. A single longwall panel using a bleederless ventilation system was simulated. If there is no barometric pressure change, the intake airflow rate is equal to the return airflow rate. When the barometric pressure changes, these two airflow rates are no longer equal, and the difference between the two airflow rates represents the airflow rate the gob breathes in and out. The effect of inflow and outflow of gas on the potential spontaneous heating in the gob was investigated using the CFD model developed in our previous study. The effect of barometric pressure changes on the spontaneous heating was found to be dependent on the gob permeability and the coal oxidation rate. The effect of barometric pressure changes on oxygen concentrations in the gob was also examined.

Jan 1, 2010

By Krishna P. Sinha

An investigation was made to determine the creep behavior of oil shale at elevated temperatures. During the first phase of the investigation, work done on creep behavior of geologic materials was reviewed and triaxial creep tests on oil shale were planned. Tests at temperatures up to 250°C and axial stress up to 3000 psi were conducted at no confinement and at confining pressures equal to 1/3 and 2/3 of axial stress. Wide variations in the elastic properties as well as creep characteristics are exhibited. Creep deformation is more pronounced at elevated temperature but no definite quantitative remarks can be made regarding effect of grade of oil shale due to wide scatter and limited number of data paints. Primary creep can be described by a power law. Secondary creep seems to be an experimental function of deviatoric stress. Teritary creep was not observed within the test duration (24 hours in most tests).

Jan 1, 1983