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By R. A. Metz, James W. Clark, William C. Dixon, Kevin L. Wiley, Thomas R. Couzens

This paper is a description of certain geologic aspects of the Inspiration mining operation. It is not a geologic description of the Inspiration deposit nor an exposition of all the geologic work involved in the development and exploitation of the deposit. A few specific examples of the application of geology and geostatistics to the mining process are given to illustrate the progress that has been made in making the Inspiration Mine more efficient and cost effective, and a statement of the philosophy of geologic applications is offered.

Jan 1, 1992

By Joao Felipe Costa, Jair Carlos Koppe, Alexandre Grigorieff

Discrepancies in raw materials properties informed by both producer or consumer is a common problem in most areas of the industry. Commercial contracts in the mineral industry normally penalises the producer, if contaminants in the ore exceed established limits. In some situations, the supplier is penalised if the quality of the ore is below a contracted amount. Differences in lab analysis are due many sources of error, such as distinct practices used in two laboratories for sampling, preparation or analysis. Rigid contracts impose to the miner the use of rigorous quality control program and in these situations sampling plays a major role. Sampling theory provides the tools to analyse errors involved in sampling, preparation and analysis. This paper proposes a methodology to check the precision and accuracy of a given sampling protocol emphasising the application of Gy's sampling theory to broken ore. A procedure to measure the error on each step of the protocol is introduced and the results compared to the fundamental error measured by Gy's theory. The results show the applicability of the method and its relevance to audit sampling procedures aiming at error minimisation. The methodology is illustrated in a case study at a major coal producer in Brazil.

Jan 1, 2002

By P. K. Davis, B. Gharib

The results of a previous basic study of the flow and design characteristics of hydrocyclones demonstrated that a recovery as high as 99% with a product rating* of 0.95 can be achieved on a batch+ basis with a single, water-only cyclone if it is configured properly. The next logical step was to demonstrate continuous processing of gob for the efficient recovery of coal by means of a laboratory-size demonstration system. A project to design and construct such a single-¬cyclone system was sponsored by the US Department of Energy, which also sponsored the initial study. A recovery of 93% with a product rating of 0.89 was demonstrated. The system design and the data taken are discussed.

Jan 1, 1990

By D. W. Carson, R. J. Trembley

Thoron daughter WL&apos;s measured by alpha-spectroscopy and the Kusnetz method are about one-half those of radon daughter WL&apos;s in a uranium mine in Canada.1 A diffusion model can account for the relative concentrations.l Since the Kusnetz technique is most widely used for measuring radon daughter WL&apos;s in uranium mines, a general procedure is derived to extend this method to measurement of WL&apos;s of radon and thoron daughters in air containing their mixtures. Coté P. and Townsend M.G., 1981. A procedure is also suggested for counting radon and thoron daughters by 3-channel [a]-spectroscopy. Errors in WL(Rn) are calculated for standard radon daughter counting procedures when a-decay of both thoron and radon daughters is attributed to radon daughters alone. Providing overall counting times are short, [<]30 min, these errors are generally small. The precision of ß -counting methods is also investigated. A portable 3-channel alpha spectrometer for measurement of radon and thoron daughters in uranium mines or homes is described, Carson D.W., 1979. The computer programs for analyzing the data to give, depending on the mode employed, some or all of the concentrations RaA, RaB, RaC, ThB, ThC and WL of radon and thoron daughters by alpha spectrometric, modified Kusnetz, Rolle and Tsivolglov methods are presented.(l) A commercial apparatus, based on the above prototype, incorporating a microprocessor and built under contract to EMR is now available.(2) A number of personal radiation dosimeters for miners are now being tested in mines. One of these is the CEA dosimeter which uses the track-etch film method, Duport P., Chapuis A.M. and Pradel J., 1979. An apparatus for rapid reading of track-etch films by the spark technique has been described previously, Cross W.G. and Thomasino L., 1970 and Huang V.F., 1975. We have developed such an apparatus for rapid semi-automatic reading of films exposed to radiation from mixtures of radon and thoron daughters in CEA dosimeters. The films used, Kodak LR 115 Type II Strippable, may be stripped rapidly and easily, for counting after irradiation and developing, by use of a special punch and suction technique. The method promises to provide an inexpensive and rapid technique for reading large quantities of personal dosimeter films. However, the present CEA dosimeter has faults in design, leading to a contamination problem. Those films that show contamination cannot be read by automatic means. A commercial apparatus based on the above prototype spark counter and built under contract to EMR is now available.3 1. These computer programs are available on request. 2. Pylon Instruments, Ottawa 3. Bondar Clegg, Co. Ltd., Ottawa. REFERENCES Carson, D.W., 1979, "Canalph-3, a Portable Three-Channel Alpha-Spectrometer for Measuring the Daughter Products of Radon and Thoron", CANMET Division Report MRP/MSL 79-108 (TR). Coté, P. and Townsend, M.G., 1981, "Mixtures of Radon and Thoron Daughters in Underground Atmospheres", Health Physics, Vol. 40, pp 5-16. Cross, W.G. and Thomasino, L., 1970, "Rapid Reading Technique for Nuclear Particles Damage Tracks in Thin Foils", Radiation Effects, Vol. 15, pp 85-89. Duport, P., Chapuis, A.M. and Pradel, J., 1979, "Appareil Individuel pour lu Dosimetrie des Descendants du Radon", Advances in Radiation Protection Monitoring, IAEA Vienna, pp 435-443. Huang, Y.F., 1975, "Determination of Uranium in Minerals using Fission Tracks", M. Sc. Thesis, University of Toronto, 48 pp.

Jan 1, 1981

By R. Pakalnis

A comprehensive project has been completed at the University of British Columbia that focused on the development of a commercially competitive composite cable bolt. Laboratory evaluation consisted of pull tests, preliminary shear tests, grout column testing and scanning electron microscope evaluation of the composite cable bolt. Field implementation at five underground mines throughout Canada were completed for technical and overall performance evaluation of the new product. The project began in 1989 under the sponsorship of HDRK Ltd., a consortium of mining companies including Inco, Noranda and Falconbridge Ltd. The objective was to develop a cuttable cable bolt that would serve as support for a continuous miner within a hardrock environment (Mah, 1994). The bolt was required to be cuttable by a continuous roadheader without adverse effects to equipment, personnel and the milling process. From the beginning, the focus was to employ existing cable bolt installation technology (Goris et al., 1994) whereby the cable bolts are grouted within a 4.8-cm-diam (1.08-in.diam) or larger employing a portland cement grout having a water:cement ratio between 0.35:1 to 0.4:1.

Jan 1, 1994

By A. E. Strakele, M. W. Springett, S. N. Watowich, W. F. Matlack, E. Yeomans, S. L. Manske, B. Yeomans

The Mesquite gold deposit is a large, low-grade "disseminated" ore body located in the Chocolate Mountains 65 km (40 miles) northeast of El Centro, CA. The deposit is tabular in geometry with a gentle southwest dip, concordant to a sequence of quartzofeldspathic to mafic gneisses. The host gneisses are amphibolite grade and intruded by synkinematic leucogranite and pegmatite. Reset potassium-argon (K-Ar) dates of 32 to 38 m.y. on mineral separates from gneiss in the ore body are suspected to reflect the age of mineralization. The hypo gene mineralization was introduced with siliceous breccias and -quartz veinlets and consisted of argentiferous native gold associated with minor pyrite and other base metal sulfides. Fluid inclusion study of gangue quartz indicates that the hydrothermal system contained a 225°C (437°F) boiling, 1 wt % NaCl equivalent solution with a small amount of CO2-A high degree of post-mineral faulting and fracture has resulted in deep oxidation and has obscured the original geometry and hypo gene mineralization of the ore body.

Jan 1, 1987

By William J. McCloy, Robert L. Gamble

A coal-fired fluidized bed steam generator rated at 12.6 kg/s has demonstrated the industrial and institutional application of fluidized bed combustion by burning high sulfur coal in an environmentally acceptable manner within a populated area. Designed to provide steam for heating and cooling, the unit was placed into service at Georgetown University in Washington, DC, and has already logged 5275 hours.* The unit has consistently operated well within Washington&apos;s strict regulations governing emissions of sulfur dioxide (SO2), nitrogen oxides (NOx), and particulates. The Georgetown program, cofunded by the university and the US Department of Energy, has shown that fluidized bed combustion is a promising way to realize the full potential of coal, the nation&apos;s most abundant energy resource. In a fluidized bed steam generator, a layer of granular limestone is placed on top of a grid designed to prevent particles from falling through. Air is passed upward through the bed with sufficient force to lift and float the particles. At this point the bed material resembles a boiling liquid. Crushed coal is then introduced into the bed and ignited. When high sulfur coal is burned, limestone absorbs the SO2 produced. The operating temperature of a fluidized bed steam generator is relatively low (approximately 871°C). As a result, NO, formation is minimal. Another potential problem encountered in burning coal is fly ash, a form of particulate. A feature of the fluidized bed design, developed by Foster Wheeler Energy Corp., is a fly ash reinjection system. Fly ash is reintroduced into the bed where it is burned again, thereby enhancing fuel efficiency. Nearly all remaining fly ash is captured by a baghouse dust collector. At Georgetown, the fluidized bed steam generator and all auxiliary equipment are enclosed in a structure aesthetically compatible with the surrounding university complex. The steam generator has two separate beds that can be fired independently, and operation to date has been with one and two beds in service, based on steam load demand. During several operating periods, when the fluidized bed unit was the only boiler in service, it supplied all the steam required by the 18.5 hm2 of buildings on campus. Initially fired with low sulfur coal, the unit was quickly switched over to higher sulfur fuel which will be used most of the time.

Jan 3, 1981

By Keith S. Liddell

Gold in many ores occurs in sulphides, which, if the gold is finely disseminated, renders the ore refractory and therefore not amenable to the simple process of milling and cyanidation. Traditional methods of treatment of these refractory ores is to produce a sulphidic flotation concentrate which is roasted to form a porous calcine from which the gold is recovered by cyanidation. The roasting process imposes a constraint of a minimum sulphur grade of the concentrate on the flotation plant, which may lead to a lower gold recovery being achieved in the flotation section. Thermal decomposition of the concentrate by roasting means that the sulphur contained therein has to be treated and disposed of in an environmentally acceptable manner; and, if arsenopyrite is present in the concentrate the environ- mental aspects will be worsened. It has long been recognized that finer milling of gold-bearing materials improves the liberation of gold, especially when the gold particles are very fine. After extensive laboratory and pilot plant investigations (Liddell, Patents), a suitable mill has been developed for the mining industry by Metprotech, which is capable of producing very fine grinds (down to 90 percent passing one m if necessary). In the course of the investigations it has been found that a large number of gold-bearing materials are amenable to fine milling. A specific advantage that fine milling of sulphidic materials has over oxidative processes such as roasting and bacterial leaching is that the sulphides are not decomposed and there is therefore not a sulphur disposal problem. Furthermore, the milled sulphides can become a future sulphur feed source, and can be reclaimed if necessary. A further feature of the Metprotech process is that it is possible to add cyanide to the mill feed

Jan 1, 1988

By Daniel McConvey

Who is the Investor? -Mainly institutional, including resource funds, other mutual funds and pension funds. -Some hedge funds. -Retail investors. -How important is the reserve disclosure to these investors? -Do these investors know the difference between a reserve and a resource?

Jan 1, 2003

By Lane White

This is a truly exciting time in surface mining technology. A revolution is coming - a revolution made possible by complete mine management systems working in concert with many devices currently available or in the prototype stage. By the turn of the century, the face of surface mining will indeed be different. Imagine . . . an operatorless drill moving around a blast pattern drilling off rounds in record times ... a satellite-based positioning system and drill data combining to report diggability to a shovel operator based on the position of his shovel in a blast ... a driverless truck warning central dispatch of an impending mechanical problem and being reassigned to the shop ... an infrared detector diagnosing the problem, for which the mine management system generates a maintenance work order and, once the problem is corrected, re-dispatches the truck to the optimum shovel.

Jan 1, 1994

By Clement K. Chase, Manuel R. Lastra

Introduction The choice of using a dump or heap leaching process or a fine grinding-agitation leaching process is based on the grade and tonnage of the ore body. Low grade ore and small tonnages are best treated by a low-cost method, such as dump or heap leaching. Permeability, however, is the critical factor in a successful leaching operation, regardless of tonnage or grade. Without permeability in the leach bed, no percolation, no dissolution, no extraction, and no success are possible. Solution delivery to the ore is also essential. Solute-to-mineral contact is a requisite. The solute must be effectively strong and not be depleted in active dissolvers, such as acid, ferric iron, cyanide, and oxygen. It must also be moving across the mineral to be dissolved. No pockets of stagnant solution can be allowed. A third factor is recovery of the now-dissolved metal in the pregnant liquor. All such liquor should be gathered at a reasonable metal concentration to make further pumping and processing worthwhile. Control and recovery of pregnant solutions are probably the most ignored factors of solution mining. This stage in recovery is historically where many operations either fail or become viable. Permeability A permeable heap is normally achieved by taking into account heap building/construction and agglomeration/pelletizing. Even though heap building is critical for good permeability, it will not be discussed here. It has been described in detail by others. Instead, this analysis will concentrate on agglomeration and pelletizing. Differences between agglomeration and pelletizing are emphasized. Agglomeration is referred to when small particles are being attached to larger particles -the ore presents a complete size distribution. On the other hand, pelletizing is a process where all particles are fine (less than 850)µm or 20 mesh), as with mill tailings. The difference is important from two points of view: • Mechanical devices used to achieve the desired attaching action; and • Binder dosages. Mechanical Devices Due to the absence of large particles that fines can become attached to, pelletizing should be done in a centrifugal-action-based device, such as an inclined rotating plate, a rotary drum, or a series of belt-transfer points. In agglomeration, large particles play a part as a natural nucleus for the attaching action of fines. Hence, a tumbling action as strong as for pelletizing is not required. Common methods to accomplish agglomeration include: • Cascade belt system with either all belts moving forward or some of them moving forward and at least one moving backward; • Combination of belt plus inclined vibrating chute; • Large concrete mixer drum; and • Belt discharging directly onto stockpiled ore. The proper agglomeration system will depend basically on the size distribution of the ore and the amount and type of clays present. In all of the agglomerating systems described, the tumbling action takes place at the transfer points either from belt to belt, or from belt to inclined chute ore belt to ore pile. Usually, two or three mixing bars at each transfer point are also included to help the mixing action. Plows to move the ore around on a moving belt are also used.

Jan 11, 1984

By Jerzy Iskra, Wlodzimierz Sikora

INTRODUCTION The effect of stress concentration in coal seams leads to a sudden release in the form of rock bursts. This effect is controlled along many lines, but the most efficient methods consist in preventing the accumulation of energy in the seam or in the roof. The over- burden weight resulting from mining is the main cause of excessive stresses in a seam. An additional weighting of roof takes place due to formation of abutment loads. The accumulation of energy in the roof takes place where thick sandstone beds occur in overburden strata. An essential problem is to watch, with appropriate measurements, the stress of coal and roof rocks, and to conclude, on this basis, the degree of rock burst hazard. The methods for determining the stresses in a coal seam are quite well developed at present. Let me mention here the seismoacoustic methods, or borehole overcoring measurement methods. On the other hand, an examination of the state of stress in the roof rocks is almost impossible at the actual stage of development of the measuring technique. Hence, the model of stresses in roof was analyzed and determined theoretically. Based on this model, a technology for roof fracturing was developed which aims at destressing rock masses in a planned way. The essentials of the fracturing method consist of a controlled breaking of sandstone roof beds in order to: - prevent the excessive weight on the pillar - prevent a spontaneous breaking of roof beds at a limiting state followed by sudden energy release. High pressure fluid infusion is used to release buildup of stresses. THEORETICAL AND RESEARCH BASES According to the tests carried out by A. Kidybinski by the method of finite elements, isobars of stresses occurring in the roof over the working face are shown in [Fig. 1]. The results indicate: - the highest values of compressive stresses occur in the roof directly over the seam, at a distance of about 5 m ahead of the working face - at a distance of about 22 m above the seam there is a line of transition of compressive stresses into tensile - within the tested roof area, the highest tensile stresses occur at a vertical distance of 35 m, and at a horizontal distance of 20 m from the line of the working face. H. Gil (1) determined the pres- sure initiating the fracture of roof rocks by the formula: [ ] On the basis of results of analysis of isobars, and of the initiation of failure stress formula (1), isobars may be designed for a given roof class. Assuming for sandstones the Poisson ratio equal 0.3, a field of failure stresses presented in [Fig. 2] is obtained. In this figure it can be seen in which areas the effects of sandstone breakage may be obtained with the operation of a determined hydraulic pressure. To use formula (I), the knowledge of Rr is still necessary. This value may be determined in two ways: - taking a sample and testing it in the laboratory, if there is access to roof rocks in the existing openings, - drilling boreholes in the roof from surface and examination of the rock mass by using hydraulic breaking, if there is no access to roof rocks.

Jan 1, 1982

By S. Kesler

Rössing Uranium Limited has operated since 1976 a large open pit uranium mine and extraction plant at a remote site in the Namib desert, South West Africa/Namibia. The geology (Berning, I., et al. Economy Geology) and the technical aspects concerning mining, grade control and metallurgy have previously been described (Rössing Uranium, Mining Magazin and Whyllie, R.J.M. "Rössing Uranium reaches rated production", World Mining). The improvement of leach &apos;extraction has been reported in 1984 (Kesler, S.B. et. al. "Uranium extraction at Rössing") and the installation of a central process control system has been described (Kesler, S.B. et al. "The introduction of a central process system at Rössing"). At the beginning of 1983 a decision was made to develop a computer system for metallurgical plant optimisation which included mass and volumetric balances, analytical assays for up to 5 chemical elements and the costs for the major consumables. Within 10 months this computer system was developed and implemented. A large number of test runs were made and computer studies were undertaken. The metallurgical division now has a scientific tool for production; planning for actual comparison with plant results and for strategic investigations and decision making.

Jan 1, 1986

Production reporting is a natural computer application and is often one of the first applications implemented by new computer users. Automation of a manual reporting system is a good place for new computer users to gain computing experience because generation of basic reports - is fairly straightforward, and automation can often be justified easily on the basis of clerical cost savings. Computers are particularly well-suited for reporting applications which generally satisfy the criteria for effective computerization. Three characteristics must be present to effectively utilize a computerized system: 1) The potential application must be precisely definable. If an algorithm for data processing cannot be developed, data cannot be processed. 2) The operation to be performed must be repetitive. If a particular function is only going to be performed once, computerized systems development is probably not justified. 3) The volume of the data to be processed must be relatively large. If only a few items of data must be manipulated, manual methods are probably adequate. Although a computer can perform only a few functions (it can compute; it can make comparisons; it can rearrange data), it can perform these functions much faster and more accurately than a human being can. The ability to classify and reclassify data in a variety of ways and the ability to summarize data make the computer an ideal tool for production reporting. Production reports can be classified into three major categories, depending on their purpose. Reports can be used for (1) informative, (2) analytical, and (3) control purposes.

Jan 1, 1979

Compared to alternative ways of dealing with coal fines, oil agglomeration has always been a commercial bridesmaid and never yet a bride. Yet interest is high in the process, as shown by a number of pilot plants in operation that are funded by industry as well as government. In the past in the US, alternative ways to handle coal finer than 100 to 200 mesh included flotation, or no treatment except dewatering, or discarding the fines as waste. There are now a number of factors that tilt the economics more toward fine coal recovery. Today, the cost of mining a ton of underground coal runs from $22-30, and discarding even 10% as unrecovered fine coal is a real economic loss. A number of attempts (notably by EPRI) have been made to quantify the effect of coal cleaning on utility boiler operations. Transportation and ash handling costs, frequency of unscheduled outages, fouling and slagging problems, and boiler tube erosion are all lowered by cleaning coal. The advantage of coal cleaning on these parameters has been shown, but the dollar amount varies with many assumptions and is difficult to pin down. The message to a utility, however, has not been lost and the trend toward cleaner steam coal is accelerating. This may lead to fewer installations that only wash the coarse coal, and add back the unwashed fine coal until a maximum contractual ash limit is reached. And, as the proportion of coal fines continues to increase by continuous and longwall mining, it may become impossible to clean the coal sufficiently without cleaning the fines. Flotation and oil agglomeration are the only processes that presently deal directly with cleaning the very finest coal fractions. Flotation has proven its effectiveness in cleaning blackwater and in separating fine coal from mineral matter. It has the achievable potential for far greater pyrite rejection than is now obtained in commercial preparation plants. While flotation will continue to be the predominant method for fine coal cleaning, there are conditions and opportunities where oil agglomeration can be a

Jan 8, 1980

By Aldo F. Barsotti

The production and consumption of industrial minerals in the United States traditionally have played important roles in mining and in the supply of the bulk of basic raw materials to the economy. This diverse group of minerals extracted and consumed by a variety of industries accounts, on a weight and volume basis, for most mineral-based products consumed in our economy. Industrial minerals form the bulk of the basic raw-materials feedstock for most of the construction, agricultural, and inorganic-chemical-manufacturing sectors, and a good portion of the transportation, manufacturing, organic chemical, and service sectors of the U.S. economy. In this presentation, I discuss current estimates of the amount and value of industrial minerals mined compared with all mining in 1997. I then present a summary of 1997 production of industrial minerals by several end-use industries. This is followed by a historical perspective of the consumption of industrial minerals as a subset of all basic materials, with special emphasis on the aggregates industry. The presentation concludes with a look at the geographic distribution of industrial mineral operations in the United States and some thoughts about the future.

Jan 1, 1999

By Werner A. Ruemmele, Steven R. Wardwell

INTRODUCTION The first phase of the Los Angeles Metro Rail Project consists of 7.1 km (4.4 miles) of subway and stations running through downtown Los Angeles from Union Station to MacArthur Park. Shank-Ohbayashi has two of the tunnelling contracts on this initial phase: A-171 and A-146. Contract A-171, the Wilshire/Alvarado Line, involves tunnel construction beneath 7th Street from the 7th/Flower Station to the Wilshire/Alvarado Station. The project consists of the excavation and lining of 3000 m (9900 ft) of twin-bore, 6.7 m (22 ft) excavated diameter, 5.5 m (18 ft) finished diameter subway tunnels. Contract A-146, the 5th/Hill to 7th/Flower Tunnels, comprises 1220 m (4000 L.F.) of twin-bore tunnel identical in cross section to the tunnels in Contract A-171. The majority of the excavation on Contract A-171 is beneath city streets in a weak siltstone/claystone bedrock with cover varying between 10 m and 25 m (32 ft and 82 ft) to the street surface. Approaching the 7th/Flower Station some fine-grained alluvium is encountered. The tunnels on both contracts are excavated with an open face digger equipped shield. On Contract A-146 the tunnel alignment is a 305 m radius curve of approximately 550 m (1800 L.F.) length underneath several multi-storied buildings of various construction. Excavation is still ongoing on Contract A-146. The contractor&apos;s choice for initial tunnel support on both contracts is a system of precast concrete segments similar to what the contractor had used on 7 miles of tunnel in Phoenix, Arizona, for the Arizona Department of Highways.

Jan 1, 1989

By Alva L. Kuestemeyer, Randall J. Scott

INTRODUCTION Pincock, Allen & Bolt, Inc. (PAH) has developed a series of cost models for Western U.S. Gold Mines. The models indicate the economic potential of developing gold properties at various production rates and ore grades. Various combinations of mining and processing methods are also analyzed. The conclusions shown in this paper are taken from PAH&apos;s 600 page study titled, "Capital and Operating Cost Models for Western U.S. Gold Mines." PAH decided to develop the cost manual as a result of our perception of the industry&apos;s need for such a document. It was our impression that exploration development decisions were being made on the basis of limited economic information. PAH has compiled a substantial database on unit cost information. That database and the engineering capabilities of the firm allowed us to develop a reasonably detailed analysis of capital and operating costs and overall development economics. The study has developed a series of algorithms for underground and open pit mining, processing, G&A, and infrastructure costs. The capital and operating cost data served as a basis for performing after tax discounted cash flow analysis for the various development alternatives. For the base case scenarios, a 15% DCFROR was assumed and the required ore grade was back calculated using the computer. The ore grade versus production rate graphs summarize the economics of developing gold projects in the Western U.S.

Jan 1, 1987

By B. H. Kaye

Particle-size Distribution Specifications for Particulates. Feed to and finished products from size-reduction operations are defined in terms of the particulate sizes involved. It is also well to know whether the ultimate individual particle is being measured, or, if any aggregation or agglomeration of particles exists, whether this has been created by the size-reduction operation. The most complete description of a powder is given by its particle¬size distribution. This can be plotted in terms of cumulative percent oversize or undersize in relation to the diameters of particles, or it can be plotted as a distribution of the amounts present in each unit of diameter against the several diameters. It is common to employ a weight basis for percentage, but there are some data in the literature where frequency, or number of particles, is used. The basis of percent¬age, whether weight, frequency, or some less commonly used factor, should be specified, as also should be stated the diameter, its units, and preferably whether determined by sieve, settling velocity, or other¬wise. Fig. I presents two sets of distributions-ore cumulative and the other in unit intervals. The slopes of the 5-µ intervals of the cumulative curves are converted to percent per micron and plotted as a block, or histogram, from which smooth curves are derived. Powder A has a narrower, or tighter, size range for the bulk of its weight than powder B. Both materials have the same weights below and above the size marked by the arrow. Simpler treatments of distribution are possible. In some cases the significant value is the top size. Since the 100% point is dubious, some amount, as 95 or 98%, so specified, can be called top size. In other cases the percent on some sieve helps define coarseness. Merely stating that all, or all but a small percentage, passes a given sieve is inadequate for defining the true fineness or a material. Complete parti¬cle-size analysis to show the distribution is essential for most compari¬sons and calculations. Particle-Size Equations. A number of equations have been pro¬posed to correlate the quantity of a particulate material with its parti¬cle size to obtain a distribution relationship. &apos;s 19 In the literature it is often assumed that a powder must follow some distribution, such as the Rosin-Rammler-Bennett:20, 21

Jan 1, 1985

By Stephen G. Hardcastle

CANMET has developed a simple yet very effective tracer gas method to test the efficiency of stench gas emergency warning systems which can easily be performed by mine personnel. This test method uses sulphur hexafluoride (SF,) as a surrogate for such stench gases as ethyl mercaptan. The test has many advantages: it is non-disruptive to production because SF, is odourless, colourless; it is safe to use as it is inert and only a small volume, insufficient to reduce oxygen levels, is necessary to dope the air with a measurable concentration; and most importantly it provides definitive results to assess the adequacy of the warning system. Specific findings of these tests have included, over doping sections of the mine and subsequent production loss due to sickness, the warning being ignored, the injection period being too short, excessive dispersion, and inadequate notification times. The simple test protocol involves releasing a known volume of the SF, under similar circumstances to those of the stench gas, and then sampling for its presence downstream. These samples are collected in air-tight syringes which are then analyzed in a laboratory with a gas chromatograph. By direct proportion, between the size of the stench and tracer gas releases, it is possible to convert the SF, concentration into equivalent stench gas concentrations profiles. From these, it is possible to define, the initial arrival time of the gas, the time it takes to reach a "target" notification concentration, whether the gas peak will exceed TWAEV, STEV and CEV exposure limits, and the duration of the peak above these levels. Since 1993, this test protocol has been employed a total of eight times on four different Canadian mine properties and the results are being used to optimize the stench gas release system with respect to volume of gas used, duration of injection, and number of injection locations.

Jan 1, 1997