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The status and outlook for mining, in your view. Minerals remain a major part of the world’s economic foundation. The fortunes of the mining industry rise and fall with general economic trends, but mining is no less important today on a global basis than it has been historically. Certainly, portions of the industry are critically depressed — domestic copper to name one area —but other sectors are prospering. Mineral consumption, both worldwide and in the United States, has increased steadily since the Great Depression, hitting all-time highs in 2000, the last year for which I have seen data. The highly developed economy in the United States tends to obscure the continuing importance of minerals here. But in less developed nations the critical nature of minerals is obvious and well accepted. In short, although there is no shortage of problems or challenges facing mining — there never has been — mining remains an essential business with great global opportunity.

Jan 1, 2003

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 Brent Duncan, Doug Harding, Bob Stier

The 73rd Street Tunnel Project is part of “The Tunnel and Reservoir Plan” (TARP)also known as the Deep Tunnel Project, and is located in the Village of Bedford Park, County of McCook, State of Illinois. The project consists of a ø 4.42 meter × 2,060 meter long (14´-6? bore, 6,760 foot)tunnel. The completed tunnel is used as a bypass tunnel for the McCook Cup Reservoir Project. The project was awarded to Affholder Inc. of St. Louis, in 2000. The paper describes the project in which a new, high-powered open gripper type main beam machine was used in which high advance rates have been achieved using conventional muck haulage techniques. Features of the project include the installation of rock support consisting of counter-sunk rock bolts that are required to be pull-tested for strength per project specifications. Installation and testing of the bolts are done during the boring cycle. Muck haulage was done by conventional muck car train and hoisting at the construction shaft. As the site layout did not include a tail tunnel, the trains needed to be shuttled at the shaft bottom. Even with the bolting requirements and the muck haulage without a tail tunnel, the Affholder site personnel still achieved high advance rates on the 73rd Street Project.

Jan 1, 2003

By J. Cayouette

In 1995, Louvicourt mine started one of the first paste backfill operations in Canada. From 500 000 t in 1995, the annual paste backfill tonnage produced reached 800 000 t in 1999. The maximum throughput of the surface plant (including binders) is 3500 tpd with a final density of 75% to 76% solids which gives a slump of 15 cm to 17 cm. Following the start-up of the paste backfill plant, the backfill strength performance levels were well below the pilot plant’s predictions. The introduction of ferrous slag, laboratory tests on various binder ratios with or without additives, and the desliming of the tailings enabled us to optimize the mix and operation costs. Primary and secondary stopes are filled respectively with a paste containing 4.5% and 2% binders in a mixture of 20% cement to 80% ferrous slag. In certain stopes, the binder ratio may vary from 2% to 7%, but always in a ratio of 80/20. Six years after start-up, or 4.5 Mt of paste backfill later, this paper discusses the present operation and the major changes that have occurred over the years to optimize both the operation and the paste fill quality.

Jan 1, 2003

By Steve Dillingham

Blasting crews, explosive product drivers, drillers, blasters, supervisors, and salespeople all arrive daily at customer blast sites in vehicles of every type whether passenger cars, pickup trucks, or bulk trucks. The majority of these vehicles are company owned and re p re s e n t a substantial investment and risk for the company. That may explain why the costs resulting from blasting incidents is often surpassed by those involving motor vehicle accidents.

Jan 1, 2003

By Rob Morrison, Peter Cameron

"Many products and technologies have been developed from outcomes of research projects carried out by the Julius Kruttschnitt Mineral Research Centre (JKMRC). When these products and technologies are applied to the design and optimisation of blasting, comminution and separation, improvements in profitability can be realised.In 1970 Alban Lynch promoted two practical ideas to improve plant operations:• Ore and equipment properties can be separated allowing experience with one type of ore or equipment to be transferred to other types of ore and equipment. If this experience was encapsulated in a mathematical model, then these properties could be combined and used to simulate (ie. to design and to optimise) complete mineral processing circuits.• Many problems associated with scale-up from laboratory to industrial equipment could be eliminated by experimental work on full-scale equipment in the plant.Many JKMRC research projects have focussed on the development of models of unit operations in mineral processing and their application to process simulation.Models of comminution and classification developed at the JKMRC have been used since the early 1980's. Ore characterisation techniques developed to support these models are licensed world wide through JKTech. The application of comminution modelling techniques to blasting, which optimises the process feed size distribution is used in Mine-to-Mill® projects. The advances in the understanding and modelling of froth flotation over recent years have provided the opportunity for integrated ore characterisation and process optimisation from resource to product.JKMRC project outcomes often provide proven opportunities for the mineral industry to improve performance and productivity. JKTech was established in 1986 to commercialise and market the most promising outcomes and thus ensure their continuing availability to the mineral industry.They include:• Commercial software (JKSimMet, JKSimBlast and JKMetAccount).• Monographs (Comminution and Blasting).• Technologies (Mine-to-Mill® and flotation optimisation).• Hardware products (JKFrothCam, JKJetLift® and the Mineral Liberation Analyser).This paper summarises these technologies and their benefits."

Jan 1, 2003

By T Laurencont, C Unger

The Mount Morgan minesite, located approximately 40 km SW of Rockhampton in Central Queensland, comprises 270 ha of unrehabilitated land which is the currently the major source of acid mine drainage run-off and seepage to the adjacent Dee River. Additionally, the minesite hosts an Open Cut Pit which contains 9000 ML of acidic and metal-rich water. In the absence of active management of water in the pit, there is a 50 per cent probability of an uncontrolled spill occurring in future years. The development of a contingency plan for management of overflow from the pit in the short term, has incorporated findings from numerous studies relevant to the Open Cut Pit including, but not limited to, water balance, contaminant source identification, toxicity testing, water quality profiling and limnological modelling, and estimates of probability of overflow. Extensive stakeholder consultation and peer review were also undertaken during the formulation of the contingency plan. The medium-term goal of lowering the water level in the pit to reduce the current high probability (50 per cent) of uncontrolled overflow to acceptable levels of risk is proposed to be achieved by a campaign of chemical water treatment. The treated water will be discharged to the Dee River, and sludge returned to the pit. The methodologies used for the selection and development of the water treatment process, that is proposed to involve treatment with lime, are described. Water treatment is the short- to medium-term component of a long range rehabilitation plan for achieving a negative pit water balance, and sustainable management of acidic water across the whole site. Achieving this ultimate goal will involve: reducing the inputs of water to the Open Cut Pit such that the annual water balance is zero or net negative, thus removing the need for water treatment in perpetuity; maximising, by surface rehabilitation works, the quality of run-off reporting to the Dee River; and minimising the volume of acidic seepage reporting to the seepage interception system. Possible strategies for achieving this long range goal consistent with overall site rehabilitation objectives are currently being developed and costed.

Jan 1, 2003

By Atsushi Shibayama, Toyohisa Fujita, Wan-Tai Yen, Ke-jun Liu

"A gold has been leached with ammonium thiosulfate solution and several leaching conditions have been studied. The leached solution has been recovered by solvent extraction and the optimum conditions have been investigated.SUMMARYIn this investigation, a sponge gold sample (99.92% pure) has been leached with ammonium thiosulfate solution. The effects of CuSO4, (NH4)2S2O3, (NH4)2SO4, NH4OH and retention time on the gold leaching % (extraction %) and thiosulfate oxidation % (consumption %) have been studied. The copper ion acts as a catalyst in gold dissolution. On the other hand, it also accelerates oxidation of thiosulfate (consumption). It was found in this study that the best gold extraction condition was obtained at 43.2 ks with 0.8 – 1.0x103 mol/m3 (NH4)2S2O3, 30 mol/m3 CuSO4, 2.0 – 3.0x103 mol/m3 NH4OH, 0.4 – 0.5x103 mol/m3 (NH4)2SO4, pH 10±0.2 and 150 rpm. The thiosulfate oxidation was about 15% of the initial concentration."

Jan 1, 2003

By George H. Hope, Steve Ciccone

"The Red Dog Mine is both the largest known zinc reserve and the largest zinc producer in the world. The mine started in 1989, and by 1999 had increased production from approximately 300,000 tonnes per year (t/yr) of zinc concentrate to in excess of 900,000 t/yr. The VIP Mill Optimization Project further increased zinc concentrate production to 1.1M t/yr while improving both product quality and zinc recovery. The Mill Optimization project also addressed a number of issues related to risk reduction: power generation capacity, water treatment capacity and concentrate thickening. The project was faced with numerous challenges, the most daunting of which was the schedule. This US$105M project was executed, from conception to completion, inside of two years. Less than nine months elapsed from concept to delivery of materials and equipment to site. The project also faced a 100-day ice-free shipping window, the challenges of construction in an Arctic environment, and an extremely tight labour market for qualified craft personnel. These challenges were successfully addressed with several innovative approaches to project execution, including an Alliance contracting arrangement between the owner, engineer and contractor; full integration of the team; construction of modules in Anchorage; and fast-track engineering, procurement and construction.INTRODUCTIONThe Red Dog Mine, which began operations in 1989, is located above the Arctic Circle in Northwest Alaska, approximately 145 km north of Kotzebue (Figure 1). An 80-km road connects the mine site to the DeLong Mountain Transportation System (DMTS) port site. Red Dog is the largest known zinc deposit in the world, with known reserves totalling 94.5M tonnes, and is the largest zinc producer with a concentrate production rate of more than 1.1M t/yr.Open-pit mining is by typical drill, blast and load operation using moderately sized mining equipment. Ore is processed through conventional crushing, grinding, and flotation to produce separate lead and zinc concentrates. Filtered zinc and lead concentrates are trucked year-round to the DMTS port site, where they are stored in two A-frame buildings, 330 and 440 m long. A lightering barge system is used to transfer concentrate from the shallow water load-out to deep-sea vessels anchored approximately two miles offshore. Shipping is limited to a 100-day, ice-free window beginning in early July."

Jan 1, 2003

By C Ferron, R Massimi

There is approximately 240 000 tonnes of arsenic trioxide dust stored in underground chambers at the Giant Mine in Yellowknife, Northwest Territories, Canada. To minimise the amount of arsenic released to the environment, a number of closure alternatives are being considered. One alternative is to mine the dust, encapsulate it and dispose the mixture into a secured landfill. The potential leaching behaviour of the encapsulated dust was examined in a laboratory programme. Cylinders of arsenic trioxide dust mixed with cement/aggregate and bitumen were prepared. The dust content varied between zero per cent and 60 per cent of dry weight charge. The cement cylinders were tested for strength, leaching and freeze/thaw durability. The bitumen cylinders were tested for leaching only. The results show that increasing dust content in the cement cylinders negatively impacts the strength and the freeze/thaw durability of the samples. A contributing factor is likely the high water to cement ratio in the samples. Leaching tests show that arsenic release from cement cylinders increase with increasing dust content. Arsenic concentrations in leachates do reach a plateau at a certain point in time. Arsenic release from bitumen cylinders was significantly lower compared to cement cylinders. Arsenic concentrations eventually were less than 0.05 mg/L in samples containing up to 25 per cent arsenic trioxide dust. Arsenic leaching rates were found to decrease by an order of magnitude over the course of three months.

Jan 1, 2003

By J. S. Phipps, D. R. Skuse

"Aqueous slurries of fine particle size calcium carbonate are used in a diverse range of end-use products. In many cases, the end-use performance is governed by the fineness of the particle size distribution. In turn, the maximum fineness of the particle size distribution is primarily determined by the efficiency of the dispersants used during the production process. Here, we report the sodium polyacrylate mediated dispersion of calcite and kaolin. Firstly, we report a colloid chemical description of the dispersant behaviour and attribute the stabilization to both steric and electrostatic mechanisms. Secondly, we describe how the understanding developed in the first part of the study can be utilized to produce more effective dispersant systems which allow the preparation of added value, higher solids and finer particle size calcium carbonate slurry products. IntroductionConcentrated aqueous dispersions of fine particulate kaolin and calcium carbonate are used extensively in the coating of paper. Currently, more than 10 Mt of such dispersions are used annually in North America and Europe alone, and worldwide consumption is growing at around 3% per year.Generally, paper is coated to enhance its visual appearance. Firstly, coatings improve the optical properties of the blank sheet, i.e., its brightness (or whiteness), opacity and gloss. Secondly, they improve the physical properties of the sheet that will influence the quality of the final printed image, such as surface smoothness, porosity, and ink absorption. In order to achieve these aims economically, paper coatings must be applied at high speeds and with minimal drying costs.Kaolin and calcium carbonate pigments are the major components of most paper coating formulations. Particle size distributions are chosen to maximize the optical benefits that they confer, and to allow the production of formulations that can be easily pumped, handled and coated. Coating pigments are generally produced and transported as slurries, and so it is important to obtain dispersions with the highest possible solids content, both to minimize drying costs and the quantity of water transported. This paper examines the dispersant technology that is currently used in the industry and the mechanisms by which it functions, and illustrates ways in which this technology has developed and could be further improved in the future."

Jan 1, 2003

By George Hope, Brigitte Lacouture

"The Red Dog mine has increased mill throughput most years since start-up. Although flotation equipment has been added over the last 10 years, the Red Dog metallurgical performance has been restricted by a lack of adequate flotation capacity. Two reduced tonnage trials conducted in 1997 as well as numerous SAG relines have consistently indicated the potential to significantly increase both zinc concentrate recovery and grade with additional flotation capacity. Later in 1999, a new circuit was designed with increased flotation capacity while simplifying the current circuit, providing for three stages of dilution cleaning, and creating a retreat section. The purpose of the retreat section is to target the more complex particles and allow the chemical environment to be fine tuned for improved iron depression. In total, 21 Outokumpu OK50 (50 m3) mechanical flotation cells and four 3.66 mØ column cells were added to the current flotation circuit. The VIP (value improvement program) mill optimization project is also addressing thickening, water treatment, and power generation issues and has a total budget of US$105 M. Start-up of equipment was phased in to minimize the impact on current operations and the project was completed by the end of 2001. IntroductionRed Dog Operations started production in November 1989. The mine is located above the Arctic Circle in northwest Alaska. It is linked by an 80 km road to a port-site facility where the concentrate is stored. Concentrate is shipped to markets throughout the world during the one hundred days of open seas. As of January 2002, the Red Dog main pit had 38.4 Mt of reserves grading 19.2% Zn, 5.3% Pb, and 102 g/t Ag. Additional reserves and resources contribute an additional 72 Mt at 15.6% Zn, 4.2% Pb, and 78 g/t Ag. Red Dog is a Mississippian to Permian, black shale-hosted, zinc-lead-silver deposit located in the DeLong Mountains, western Brooks Range, Alaska. All the rocks associated with the mineralizing event are considered to be part of the exhalite rock package. Silicification was a dominant component of the mineralizing event and the host shale has been silicified and locally resembles a chert. The major sulphides in decreasing order of abundance are sphalerite, pyrite, marcasite and galena. Most of the deposit’s silver occurs within the crystal structure of the galena. The dominant ore mineral, sphalerite, is very fine grained to amorphous and is commonly intergrown with silica. Ore textures are massive, fragmental, chaotic, veined and rarely show classic sulphide sedimentary layering. The upper portion of the orebody has been physically and chemically weathered. Oxidation has altered the sulphides to sulphates. The zinc and iron sulphates are very soluble and are readily depleted from the weathered cap, while the lead sulphate is residual and is, therefore, enriched."

Jan 1, 2003

Newmont Waihi Operations is participating in the initiation of a community liaison forum in association with the local district council. The objective is to provide a forum for the free and regular exchange of ideas, concerns and information, and through improved communication seek to achieve a more comprehensive set of solutions to community, operating and closure issues associated with Martha Mine. A similar liaison forum has been operated on two previous occasions during earlier phases of the present mine's operation. This paper deals with the practical aspects of setting up a liaison forum to act as an effective conduit between regulators, mine operators, local businesses and the community. The mechanisms and procedures for identifying community issues and concerns are dealt with. The actions and structures required to ensure effective ongoing community 'buy in' at all levels are discussed. Corporate philosophies are addressed. Specific examples from Martha Mine, Waihi New Zealand will be used to illustrate the paper. This will include a brief explanation of previous and current community issues, Newmont Waihi's operations both at Martha Mine and the proposed Favona underground mine, and the practical issues involved in setting up a liaison forum.

Jan 1, 2003

By Randy Clarkson

"Free gold particles occur in many base metal and precious metal mines throughout the world. Occasionally mine operators are unaware of the presence of free gold particles in their ores because they have not seen free gold hand specimens or at the working face of the mine.Due to the high density and malleability of gold, large circulating loads of free gold particles can build up over time in grinding circuits. This gold is often deposited in unintended traps throughout the mineral processing system.These unidentified free gold deposits represent a serious security risk as well as inaccessible inventory of gold. Deposits of free gold particles often remain undetected by mine management until they are accidentally discovered while repairing mill equipment. The trapping and subsequent release of gold particles can frustrate attempts to calculate accurate metallurgical balances.Nuclear tracers have been used to determine the free gold recovery efficiency of gravity recovery equipment, drills, and sampling equipment (Clarkson, 1994, 1997, 1998, 1999 and Walsh, 1986, 1992). In 1995, the author used radiotracers to locate and eliminate gold traps at La Mine Doyon (Clarkson, 1997). In 1998 and 2001, the author also salted mineral processing circuits at Royal Oak's Pamour Mine in Timmins (Clarkson, 1999) and at Gold Corp’s Red Lake Mine in Ontario with radioactive gold particles.The gamma and X-ray radiation from gold's nuclear isotope (Au198) were detected through steel, in pipes, and in moving equipment with scintillometers. The radiotracers proved to be a safe, rapid and accurate method of identifying gold traps, improving security, determining the recovery efficiency of Knelson gold concentrators and estimating retention times of gold particles in various processes."

Jan 1, 2003

By Duane A. Smith

They are gone now. Gone like that long ago generation that gave them birth. The Homestake Mine, nestled in the northern Black Hills, closed in 2001 after 125 years, the longest run of any major American gold mine. The Homestake Mining Co., which guided its destiny for those many years, is gone too. It merged with Barrick Gold. The Hearst family, which guided the early destiny of both, has long since gone beyond its mining heritage and into the national and even international spotlight. The mine and the company passed from the scene with as little fanfare as heralded their birth, amid the Black Hills gold rush of the 1870s. They both grew into American mining legends, as did the town they sired and nurtured, Lead. In a real sense, the mine and the company symbolized one of the last links to a vanished world and a mining era.

Jan 1, 2003

By C E. J de Ronde, J L. Mauk

Sulfide chimney samples collected during the 1998 - 1999 R/V Atlantis û DSV Alvin 3 - 30 research cruise have been examined and classified into four types, based on common characteristics. Chimney morphology is the most important characteristic and resulted in the following groups: 1. flutes, 2. cones, 3. wide-flats, and 4. beehives. Other characteristics resulted in the classification of subgroups within the flute, cone and wide-flat groups. The combination of characteristics, including; the presence of an orifice, internal chimney fabrics, wall thickness, extent of weathering, and the presence of Alvinella worm casts, enable evolutionary trends between the different chimneys types to be established. These trends indicate that with time, flutes evolve from immature zoned chimneys with a central orifice and smooth thin-walls, into cone chimneys with thick walls and massive fabrics which have their orifices infilled by massive sulfides, and a rough exterior. Repeated mineralisation within, cones may result in the formation of wide-flat chimneys. Beehive chimneys can form at any time during chimney growth.

Jan 1, 2003

By A F. Cooper

Otago Schist in the Mount Patriarch, High Burn and Cameron Creek areas of northwest Otago grades from textural grade IIA in the east to textural grade III in the west. The entire region is of the actinolite-pumpellyite metamorphic facies. Lithologies in the area are interbedded turbidite sequences comprising pelite and psammite together with pebble conglomerate, greenschist and metachert horizons. The mineral assemblage of the schist is typically quartz-albite-epidote-actinolite-pumpellyite-chlorite-stilpnomelane-calcite. A good foliation is well defined in the area and is predominantly parallel to bedding, except in hinges of mesoscopic isoclinal folds. The structure of the area appears to be defined by a large southwest plunging isoclinal fold defined by bedding with a steeply dipping axial planar foliation. Kink folding and dextral strike-slip faulting in the area postdates the ductile phase of deformation. Pods of rhodonite, rhodochrosite, spessartine garnet, coombsite, caryopilite, Mnstilpnomelane and Ni-Cu-Zn sulphides were found in concordant metachert layers in the Mount Patriarch area. Metachert was also found in float in the Cameron Creek area. Malachite occurrences relating to copper mineralisation were also noted in a green metachert horizon on the eastern flank of Mount Patriarch. The coombsite, in only the third observation worldwide, is the most Fe-rich variety reported.

Jan 1, 2003

By Rogerio C. Guimarães, Antonio E. C. Peres

The production of phosphate concentrates (phosphate rock) from slimes represents a challenge to the phosphate industry worldwide. In Brazil, this challenge is particularly relevant due to the consistently low P2O5 grades and the igneous origin. The Brazilian phosphate deposits are made up mainly of apatite from alkaline chimneys, representing 80% of the Brazilian reserves; phosphorite deposits contribute 18% and the other sources (guano, phosphorous bauxite, and apatite from veins) reach 2%. The Brazilian industry beneficiates phosphate ores that are mineralogically more complex than those treated elsewhere. The low apatite grade, inherent to the igneous Brazilian ores, added to the mineralogical complexity due to the weathering of the rocks, has represented a permanent challenge to the Brazilian process engineers. The total measured, indicated and inferred reserves reach 3.2 million tonnes of ore with average grade 11% P2O5. The development of local technology for phosphate beneficiation started in the 1960’s. The first industrial experiences of producing phosphate rock from slimes (-44µm or -325#) fraction started at Arafertil, currently Bunge Fertilizantes SA, in Araxá, in the 1980’s. This production corresponds, nowadays, to 35% of the total production of concentrates in the company (830,000t/year) in a circuit consisting of desliming in 40mm microcyclones and concentration in flotation columns, corn starch and fatty acids being utilised as reagents. The performance of slimes flotation and the process control, at Bunge´s concentrator, were improved after the introduction of column flotation technology, in the first half of the nineties. The column flotation technology for slimes recovery was expanded to other Brazilian concentrators still in the nineties: Ultrafértil (Catalão – GO), Bunge (Cajati – SP), Fosfértil (Tapira – MG) and Copebrás (Catalão – GO). At present the Brazilian production of phosphate rock is approximately 4.5Mt/year, with a strong trend for a market increase. Genuinely Brazilian technology is utilised for the processing of slimes, the concentrates representing 11 to 13% of the overall production. The production of apatite concentrates from slimes was relevant to increase phosphate recovery and reduce costs, contributing to the growth of the fertilisers industry.

Jan 1, 2003

By Alan Jorgansen, Dave Hummer, Scott Scovira

Kennecott Energy's Colowyo Coal Mine is the largest open pit coal mine in Colorado and produces 5.5 MM tons per year. Colowyo uses the terrace mining method to recover up to seven seams of rolling coal ranging in thickness from 5 to 20 feet. Draglines are used to strip overburden ranging from 60 to 120 feet thick off two coal seams. These two seams are characterized by soft and fold fractured coal and in past practice cast blasting caused excessive coal damage. As a result, to ensure minimal coal damage and high coal recoveries, the overburden was excavated in two passes. The first pass removed the upper overburden to within 10 to 20 feet of the coal seam. The second pass removed the remaining overburden above the coal. Two-pass mining was effective in controlling coal damage, but also carried significant additional costs.

Jan 1, 2003

By J. Cygankiewicz

Efficient prevention of mine fires is impossible without predicting the self heating processes in the given geological and mining conditions. The respective forecasting method is presented in this paper based on the following assumptions: - factor deciding on fire hazard in the underground workings is the process of heating of coal from the primary rock temperature to the critical temperature when the heating rate growth rapidly - another important factor is the fire incubation time defined as time needed to achieve the critical temperature. This time is determined by balance of heat and mass in the heated coal - contact of crushed coal with oxygen in air cause some exothermic processes as : physical and chemical sorption of oxygen , oxidation reaction and evaporation of humidity Heated coal transfers its thermal energy to the environment by conductivity to the rocks and by convection to the flowing gases. The heating is possible if thermal energy generated from coal is greater then the share transferred to the environment. The paper presents the laboratory method of measurement of heat generation in adiabatic conditions. Also the mathematical model with examples of computation enabling to forecast the self heating process of crushed coal is presented.

Jan 1, 2003