Search Documents

By D. W. Park

A vast majority of longwall operations in the United States use shield-type hydraulic supports to provide ground control along the longwall face. The three-dimensional finite-element technique combined with a progressive failure approach was utilized to simulate interaction between shields and surrounding strata and determine various loading conditions. In addition, a separate finite element model of the shield structure was made to study responses of each long wall shield to the different loading conditions. Shield responses under various loading conditions and the shield characteristics, such as shield stiffness, the ability of resisting horizontal forces, and the effect of shield height, were studied based on the results from finite-element analyses. The results can provide the basis of effective shield design and be used for evaluation of the shield performance. It is suggested to develop a technique incorporating the finite-element method to evaluate the real-time shield performance for the purpose of effective ground control.

Jan 1, 1992

By Rashmi Kumar, Amit Chatterjee, Sanjay Chandra

The practice of adding alloying materials to a molten bath is an integral feature of many pyrometallurgical operations. However, very little is known about the dissolution rate and solution mechanisms of solid additives in liquid melts. In foundries where large tonnages of liquid metals are handled, there is considerable interest in achieving optimum metal quality at minimum cost. This objective is influenced by several factors and the solution is often plant specific. Though the amount, sequence and mode of ferroalloy addition vary from plant to plant, various fundamental factors determine how quickly these additions dissolve in the bath. At the Ingot Mould Foundry (IMF) in TATA STEEL blast furnace hot metal is used to cast ingot moulds. The composition of hot metal desired for making ingot moulds demands addition of 20 kg each of Ferromanganese and Ferrosilicon in the 12 T transfer ladles into which the blast furnace metal is poured at the IMF. Owing to low temperature of hot metal at the IMF, casting commences immediately and complete dissolution of the ferroalloys is often not possible. To study this aspect in detail and to evolve suitable corrective measures, a mathematical model for the melting of a solid particle in a liquid metal bath was developed at TATA STEEL. The model was validated using the data available in literature. In keeping with published work, two separate dissolution periods were identified - a "shell period" and a "free dissolution period". The maximum thickness of the crust formed around a spherical particle shortly after immersion, can be obtained by using the mathematical model which has been developed. The model can also be used to investigate the effect of various parameters such as superheat of the bath, size of the particle, etc., on the maximum crust thickness and the particle melting time. On the basis of this study, the addition of ferromanganese and ferrosilicon was optimized at the IMF in Tata Steel.

Jan 1, 1996

By John D. Rockaway

Failure of the mine floor supporting coal pillars frequently occurs when the subcoal strata include "underclays" or other low strength strata. The failure process has been studied to define the response of these materials to applied coal pillar loads and to determine the applicability of bearing capacity analysis to evaluate unsafe conditions. The study has been accomplished through an investigation of both the intact and insitu geotechnical properties of the subcoal strata and through the installation of floor movement monitoring instrumentation. The results of these studies have indicated that both the shear strength of the underclay and the stratigraphy of the subcoal strata must be considered in the analysis. The shear strength was the major controlling factor determining the ultimate load carrying ability of the materials, but the thickness and stratigraphic position of the weak layers influenced the mechanism of the failure process. The methods of bearing capacity analysis were used to define pillar stability that included provisions for taking into consideration a two-layer system. Conditions assumed for a coal mine where a weak underclay overlies firmer strata. The results of the analysis compared very well with observed mine conditions, indicating marginal conditions in areas of the mine which later experienced pillar support failure. In addition, a "heave factor" was derived to predict potentially unstable floor conditions in the mines studied in detail.

Jan 1, 1979

By John D. Campbell

"IS YOUR MANAGEMENT CONTROLLOOP FUNCTIONINGMineral processors make use of hundreds of control circuits in their mills, process plants, smelters and refineries, to optimize throughput and recovery and minimize cost. This afternoon, I would like to discuss what is probably the weakest circuit in any mineral processing operation - the management control loop.In their recent book ""The Winning Streak"", Goldsmith and Clutter describe extensive research on unsuccessful companies. They conclude that ineffective control, which does not immediately identify the problems, is one of the main failings of unsuccessful companies.We will look at the three key components of control which, from the manager's point of view, ensure that the loop is complete. These three are:• measuring what's happening,• assessing its significance, Rnd• altering performance.If we compare management control to process control as shown in this first figure, ""We see that parameter sensing by the analyzer in a process circuit is analogous to performance monitoring by management in a responsibility centre. The analyzer senses temperature, pressure, flow, weight or some surrogate indicator such as colour to indicate ion concentration. For manage1nent, the performance to rnonitor is dependent upon the objectives of the responsibility centre, and the key factors which affect these objectives."

Jan 1, 1985

By L. T. Grose

The Bureau of Mines conducted a comprehensive study of the Kanab, Kolob, Kaiparowits, and Harmony coalfields of southwestern Utah to obtain additional information and to determine the potentials of these coalfields as sources of energy for steam-electric power-generating plants. Field examinations were made to ascertain the geologic structure and the stratigraphy of the coalfields, the accessibility of the coal-bearing strata, and the general nature of the coal-bearing strata and the terrain. Many mines, both active and abandoned, were examined, and key personnel in the coal industry in the area were consulted. Available analyses of southwestern Utah coals were compiled, and tentative conclusions regarding the rank and quality of the coals were drawn. Coals have been classified by rank according to the standards established by the American Society for Testing and Materials in 1964. The Parr formula for moist, mineral-matter-free British thermal units has been used to calculate the rank of each sample, except as otherwise noted. Water resources related to the areas of the coal reserves also were investigated. Existing literature and maps pertaining to the geology of the areas were reviewed. Production potentials of the coalfields and economic conditions affecting the possible utilization of the coal reserves as sources of energy for steam-powered electricity-generating plants were investigated and analyzed. The data obtained and the conclusions reached as a result of this study are included in this document. The total reserves of subbituminous A and high-volatile bituminous C coals in the fields of southwestern Utah are estimated to be at least 8 billion short tons at depths generally less than 2,000 feet. It appears likely that this estimate will be increased as additional data are made available through exploration and other investigations. Sufficient coal is available in four southwestern Utah counties to supply three or four large steam-electric plants. If the States involved grant water rights to companies planning to build steam-electric plants, the cost of producing power with coal might be attractive and might justify the construction of one or more of these plants.

Jan 1, 1967

By E. D. Gardner

"Trolley lines used in connection with electric haulage in mines are a source of danger and many lives have been lost by men accidentally coming in contact with the wires. Usually the wires in metal mines are sufficiently guarded to prevent men from touching them with their person or by pieces of steel which they may be carrying or their shoulders, while walking along the level. However, it is difficult to guard effectively the wires at loading chutes along the haulage ways and in spite of safe guards, chute tappers have been electrocuted through loading bars accidentally touching the trolley line.To overcome this danger the Calumet & Arizona Mining Co., at Lowell, Arizona formely used a hinged V-shaped trough made of 1-inch by 6-inch lumber, that was dropped over the wire in front of the chute, when the cars were being loaded. This arrangement interfered with the easy operation of the chute, and a cut-out device for the trolley line was devised by W. R. Gibson, chief electrician for the company. This cut-out is efficient easily constructed and roes not interfere with the operations at the chutes or with the motors operating on the same level.When the cut-out is open the electric current is carried past the gap by an insulated wire on the opposite side of the drift. A hinged board drops down over the ends of the trolley guard when the slide is open and Prevents anything touching the live wires. About ninety of these cut-outs are now in use in the mine,The levels under the scopes are timbered with drift sets placed 5 feet apart, and the loading chutes take up the space between two sets. All trolley wires in. the company's mines are carried 6 feet above the rails and guarded by two 1/2 by 6-inch boards placed on either side of the wire."

May 1, 1921

By M. C. Roberts

Currently, mineral producers are suffering through a major downturn in prices for their products, even though it has only been a few years since they were enjoying high prices. From an historical perspective, the current situation is another of the cyclical down-turns that often reoccur every 5 to 7 years or so. This paper uses time trend decomposition techniques to identify the cycles and statistical methods to find the duration of these cycles for a variety of mineral prices. Given some idea of how long and severe these cycles typically are, the mining industry can better plan to weather the downturns and take advantage of the upturns. For example, timing investments in new projects to take advantage of the cyclical upturns can dramatically improve project profitability.

Jan 1, 2000

By T. S. Bomar, C. J. Wood

Heavy media cyclones (HMCs) are efficient, high-tonnage devices suitable for upgrading run-of-mine coal in the 50 to 0.5 mm size range. Unfortunately, industrial HMC circuits are often not optimized due to problems such as incorrect operating pressures, poor feed distribution, excessive media contamination, mismatched components, and improper density control. To avoid these problems, operating guidelines have been provided in this article that are useful for optimizing the performance of HMC circuits. The validity of these guidelines has been assessed by means of density tracer tests carried out at several coal preparation plants.

Jan 1, 2002

By R. W. Nice

"The Similkameen Mining Company property is situated about 9 1/2 miles south and west of Princeton B.C. Owned and operated by Newmont Mining Corporation, mining is presently taking place in the Ingerbelle pit. At 15,000 tpd of 0.50% Cu ore the Ingerbelle pit is sufficient for about 8 years. Another 8 years ore supply is available from the old Granby workings of the Copper Mountain property which operated from 1927 to 1957.The pit operations commenced in late 1970 with the concentrator starting in March 1972. Designed and built by Bechtel Corporation under the supervision of Newmont the concentrator's design was based on single-stage crushing and single-stage modified autogenous grinding. The modification was installation of a crusher to crush the critical size build-up. The description of the operation follows.CRUSHERThe primary crusher is an open pocket Allis-Chalmers. 54"" x 74"" gyratory. The basic closed side setting is 8"". The crusher is fed from one side with 100 ton Electra-haul trucks. The crusher pocket discharges to a 96"" wide conveyor belt, then to a 48"" conveyor system including a stacker belt. The crushed product is piled on a stockpile with a capacity of about 30,000 live tons. This stockpile feeds the concentrator."

Jan 1, 1975

By John K. Alley

Despite the extensive use of fluorphlogopite, investigators do not agree as to its exact melting temperature. Data on other fluormicas and on related fluorsilicate systems are largely nonexistent. A knowledge of the melting temperature is necessary for the effective synthesis and use of fluorphlogo¬pite or other fluormicas. The increasing use of two- and three-mica systems to yield polycrystalline ceramics has made more urgent the need for melting temperature information concerning these other fluormicas. This report is part of a program by the Bureau of Mines to synthesize large-size or large-crystal fluorphlogopite and develop a usable reconstituted fluormica sheet. The melting temperature of fluorphlogopite, K2Mg6A12Si6020F4, was found to be 1,383° ±2° C. This temperature was found by studying single crystals of fluorphlogopite, heating behavior of glass of fluorphlogopite composition, and the actual crystallization of fluorphlogopite from a melt that had been heated above 1,430° C. The formation of forsterite or norbergite was directly proportional to the loss of volatiles during the experimentation. Many trials revealed that the only reliable seal was a thick platinum sheet with welded seams. If no volatiles were lost, neither norbergite nor forsterite were formed; fluormica was then the only product. Excellently formed crystals of forsterite with an optical sign different from ordinary forsterite were obtained during the single crystal melting experiments. These crystals resulted from a slow loss of volatiles. A congruent melting of fluorphlogopite is indicated by the data of this report; however, incongruency within a small temperature range is not precluded. A more refined method using phase equilibria-quench methods would be necessary to settle the question absolutely.

Jan 1, 1962

By Samuel Frimpong

Synthetic fuel is a liquid hydrocarbon fuel synthesized from unconventional resources, such as tar sands, heavy oil, coal, and oil shale. These unconventional resources are immense and will be a major energy source for the 21st Century as the availability of conventional crude oil and natural gas declines. The authors review the available global distributions, production data, research frontiers, and current research organizations involved in tar sands, heavy oil, coal, and oil shale. Tar sands and heavy oil is mainly deposited in Canada, Venezuela, and the United States. Oil shale reserves are found in United States, Jordan, China and Australia. Coal occurs in United States, Russia, China, Canada, and Australia. Major research and development efforts are focused on reserves identification, transportation technologies, production cost modeling, bitumen extraction process improvements, coal liquefaction technologies, elimination of pollutants, greenhouse gases, and safeguarding human health and the environment. This review forms a major source for educating the public about these important energy sources, and the need to develop environmentally sound technologies and policies for their extraction.

May 1, 2007

"Load-haul-dump machines (LHDs) are typically used in underground metal mining operations. Delays or inappropriate use of LHDs can result in production loss. Optimized LHD use is especially crucial in larger mines because longer travel distances increase heat, dust, and gas emissions, which in turn increase ventilation costs. This study, conducted at an existing Swedish sublevel cave underground mine, used discrete event simulation and the AutoMod™ DES tool to determine the ventilation costs related to using too many diesel LHDs in a production area with reduced ore pass availability. When fewer ore passes are available, ventilation costs related to operating LHDs in the production area were found to increase by as much as 200, 224, and 306% for one, three, and six LHDs in operation, respectively. ¦ KEYWORDS Discrete event simulation (DES), Loading operations, Production rate, Ventilation costs RÉSUMÉ Dans les exploitations souterraines d’extraction des métaux, on utilise généralement des chargeurs-transporteurs (LHD, de l’anglais Load-haul-dump machines). Les retards ou l’utilisation abusive des LHD peuvent entraîner une perte de production. L’utilisation optimisée des LHD est particulièrement importante dans les grandes mines en raison des longues distances parcourues, lesquelles augmentent la chaleur, la poussière et les émissions de gaz qui, à leur tour, décuplent les coûts de l’aérage. Cette étude, menée en Suède dans une mine souterraine utilisant la méthode d’exploitation en sous étages avec foudroyage, s’est basée sur la simulation à événements discrets (SED) et l’outil de SED AutoMod™ pour déterminer les coûts de l’aérage liés à l’utilisation d’un nombre trop élevé de LHD alimentés au diesel dans la zone de production, avec une disponibilité réduite de la cheminée à minerai. Lorsque les mines disposent de moins de cheminées à minerai, l’étude montre que les coûts de l’aérage liés à l’exploitation des LHD dans la zone de production augmentent respectivement de 200, 224 et 306 % pour un, trois et six LHD en fonctionnement. ¦ MOTS CLÉS coûts de l’aérage, opérations de chargement, simulation à événements discrets (SED), taux de productionINTRODUCTION Transporting material from the mine face to the dumping location requires flexible loading and hauling equipment that is able to cope with sharp curves and a complex mining environment. Load-haul-dump machines (LHDs) are designed for such an environment. Models are available to suit specific features of the working environment such as small, large, or narrow open stopes (Atlas Copco Rock Drills AB, 2007). When carrying a full load, haulage speed is higher for LHDs than for front-end loaders with the same engine size. Also, payloads are approximately 50% higher for LHDs than for front-end loaders (Atlas Copco Rock Drills AB, 2007). LHDs are capable of climbing steep (Bloss, Harvey, Grant, & Routley, 2011). The haulage distance between stope and ore pass is usually between 50 m and 400 m. LHDs are efficient for tramming distances up to 200 m (Bloss et al., 2011), whereas when loading trucks, the LHDs work efficiently when the distance is less than 100 m (Atlas Copco Rock Drills AB, 2007). The largest diesel-powered LHDs, with drive motors of up to 350 kW, can handle a payload of 21 t (Wennmohs, 2014). Most mining equipment runs on diesel fuel, which provides flexibility, high durability, and high efficiency (Pronk, Coble, & Stewart, 2009); however, other alternatives such as electric, hybrid diesel/electric, or hydrogen fuel cell machines are increasingly being developed and used. This change is due to diesel-powered machines accounting for a significant portion of the ventilation costs in the mine (Chadwick, 2008; Paraszczak, Laflamme, & Fytas, 2013). Currently, as part of the European sustainable intelligent mining systems (SIMS) project, Epiroc AB is planning to demonstrate technology for a diesel-free underground mine at Agnico Eagle’s Kittlä mine in Finland using"

Jan 1, 2019

By Chuanhong Li, Zuohua Lin, Zhancheng Guo

"Catalytic mechanism of CeO2 in combustion of coals was investigated in this paper. Catalytic combustion of four kinds of coals with different metamorphic grades by CeO2 was examined, suggesting that catalytic function of CeO2 increases with increase of metamorphic grade of the coals. One important reason for CeO2 promoting combustion of the coals is that pyrolysis of anthracite is advanced by CeO2, which not only raises the pyrolysis rate and pyrolysis conversion ratio, but increases contents of light components in pyrolysis gas; and both pore space and specific surface area of the pyrolysis char are enlarged by CeO2, which is another reason. In order to realize in situ catalysis for reducing catalyst consumption, it is crucial to increase catalyst particle number and enhance the bonding force between catalyst and coal. In addition, remarkable energy saving effect was observed when a nanometer calcium-based rare earth catalyst obtained by hydro-thermal synthesis was applied to catalytic combustion of coal injection into blast furnace.Introduction Coal combustion is acknowledged as one of the most important coal applications. Since addition of catalysts could reduce the ignition temperature of pulverized coal and accelerate the coal combustion, catalytic combustion is generally accepted as an effective measure to realize fast combustion of coal. Furthermore, different catalysts added may produce different effects on ignition temperature of coal. It is reported activity of catalysts with the same cation follows this order: OH->CO3 2->Cl->SO4 2-; while that of the catalysts which have the same anion follows: Cs+>Rb+>K+>Na+>Ba2+>Li+>Sr2+>Ca2+>Mg2+>Be2+ [1-4] .Due to the special physical and chemical structure, CeO2 plays an important role in the catalysis field. Many literatures point out that CeO2 not only has great catalytic effect on energy conversion, succeeded in catalyzing combustion of gaseous fuels such as CH4, CO, etc. but also can catalyze combustion of some liquid and solid fuels such as JP-10, black carbon, carbon deposit in the automobile exhausts and so on [5-9].Pyrolysis, the first step of combustion, directly influences ignition temperature and combustion rate of coals. So a great variety of catalysts were applied to catalyze pyrolysis of coals. And plenty of studies suggest that the alkali and alkaline-earth metal compounds inherent in the coals show apparent catalytic effect on coal pyrolysis. Meanwhile, addition of alkali and alkaline-earth metals into coal combustion process also indicates obvious catalysis effect, accelerating coal pyrolysis, improving pyrolysis conversion ratio, increasing contents of pyrolysis gases and changing composition of the pyrolysis gases [10-15].Although alkali and alkaline-earth metal compounds have good catalysis effect on coal combustion, their application in the catalysis field was limited because of their erosive attack to the combustion equipments. In contrast, CeO2, as a substitution of the traditional coal catalysts, presents widely potential application due to its good catalysis ability, non-corrosive and nontoxic. However, investigation on CeO2 catalyzing coal combustion is rarely reported. In this work, catalytic mechanism of CeO2 in coal combustion was studied, in an attempt to provide theoretical foundation for developing new catalysis technologies."

Jan 1, 2009

By R. A. Strehlow

This is the final report for U.S. Bureau of Mines contract HO-122122, which was in effect from June 30, 1972 through January 4, 1976. The work resulted in the design and construction of a large laboratory scale coal dust burner and the use of this burner to study gaseous and coal dust flammability. A new technique for determining gas phase flammability was developed and the effect of solid and gaseous suppressants on the propagation of coal dust flames was studied. In addition, a technique for measuring the C/H ratio in the flame was developed and the C/H ratio that was measured in a coal dust flame on this burner showed that the burning process was preceeded by pyroysis of the coal dust. Both experimental and theoretical studies showed that radiative trans-port is very important to the propagation of a coal dust flame.

Jan 1, 1977

By Charles E. McCarthy, MORTON T. PAWEL, E. A. GEE, FRANK S. RIORDAN

Large tonnages of the magnesium silicate mineral , olivine, are known to exist in the mountains of western North Carolina and in the Puget Sound region of Washington. The North Carolina deposits alone are reputed to contain at least 230 million tons of ore averaging 45 to 49 percent of magnesium oxide In both areas the mineral is readily accessible and can be mined by the simplest methods ; one of the largest of the Washington deposits is located at tidewater .

Sep 1, 1946

By Haragobinda Srichandan

The present study aimed to investigate the bioleaching efficiency of moderate thermophilic microorganism in a growth medium without Fe supplement on three different size fractions of spent catalyst obtained from petroleum refinery. All the experiments were conducted on shake flasks at a temperature of 65 °C and a pulp density of 10% (w/v) on three size fractions viz. 45-106 µm, 106-212 µm and >212 µm and a working volume of 100 ml comprising of 10 ml of microbial inoculums and 90 ml of Modified Kelly medium. The parameters like pH, redox potential, viable planktonic cell count and the amount of acid addition was measured and quantified on regular basis to follow the progress of the bioleaching. The pH varied much in the lag and logarithmic phase of the experiments but stabilized toward the stationary phase. The total acid additions in each batch experiment were determined the amount of Conc. H2SO4 requirement, which ranged between 683-757 kg/ton of spent catalyst. The redox potential values ranged between 625-650 mV, Ag/AgCl, but were very low ranging between 350-450 mV during initial period. The planktonic viable cell count ranged between 108-109 cells/ml active in the bioleaching system, without any toxic influence of the spent catalyst, but initially due to fall in redox potential and new environment for the microbes, their population was low. The leaching yield of Ni was found to be promising with very high leaching yield of 92-96% followed by Al as 61-62%, which means both Ni and Al leaching were favored by the moderate thermophilic bioleaching compared to the mesophilic bioleaching. There was very little difference in the leaching yield, when compared with different size fractions and hence grinding can be avoided prior to leaching. This process seems to be economical as no Fe source is supplemented together with no requirement of grinding and over all a biological process resulting for an eco-friendly process for future optimization of the metal recovery from petroleum refinery spent catalysts. Keywords: bioleaching, spent catalyst, thermophile, 9K medium

Sep 1, 2012

By W. T. Swensen

The Anaconda Company, through its wholly owned subsidiary The Anaconda Company (Canada) I,td., has investigated, optioned and partially developed a large tonnage of iron ore amenable to magnetic concentration. The reserves are located in north central Ontario and occur within a twenty-two mile belt of layered and intricately folded metamorphic rocks, close to the north contact of an igneous complex of granite and pegmatite. There are two main ore deposits. Briarcliffe is a steep to vertically dipping body 100 to 500 feet wide and over a mile long. The Two Mile Lake deposit is flat dipping and confined to an open, asymmetrical syncline; it is approximately a mile wide and 250 to 4.00 feet thick. On its flat easterly plunge, it is saucer-like in shape and is amenable to open-pitting for an east-west distance of several thousand feet. Magnetometer surveys, confirmed by drilling, indicate at least a three mile eastward extension of this deposit. Location and Access: The property is located in the Kowkash Mining District of northwestern Ontario, roughly forty-four miles north of the community of Nakina on the main line of the Canadian National Railroad. (Fig. 1) Access during the exploration period was entirely by airplane from Nakina. (Fig. 2) More recently, Nakina itself was connected to the highway network in the Longlac-Geraldton area. The property is roughly 190 miles by existing and proposed railroad from the Great Lakes waterway system. The Trans-Canada pipeline moving natural gas from western to eastern Canada passes through Geraldton roughly 70 miles south of the property. Topography: The surface features in the area are typical of a sizeable portion of the Precambrian Canadian Shield area. Many lakes, low swampy areas, and glacial moraine-type features are common in this recently glaciated area. The average elevation is between 800 and 900 feet above sea level, and the relief is probably less than 100 feet with the greater portion of the area less than 50 feet. The topographic "highs" are formed either by outcrops that were resistant to glacial erosion or by moraines, eskers and drumlins which were deposited upon the recession of the glaciers. The better mineralized zones, composed chiefly of quartz and magnetite, commonly form ridges resistant to erosion and weathering. Previous Work: Because of the obvious outcrop of the magnetite-rich beds and knowledge gained from early developments within the general region, it is conceivable that the presence of the iron formations has been known for a good many years. The area is included in studies made by L. F. Kindle* in 1929 and 1930 for the Ontario Department *Kindle, L.F., Kowkash-Ogoki Gold Area, Ontario Department of Mines Annual Report, Vol. XL, Part IV, 1931; map 40f

Jan 1, 1961

By J. -F. Blais, M. -O. Simonnot, J. Mocellin, G. Mercier, J. -L. Morel

Large quantities of ferromanganese sludge are generated as waste material by blast furnace during the manufacturing of ferromanganese. These slags are very rich in manganese, zinc and lead (5 to 40 %). These residues have been deposited in a pond in periphery of the steel industry. Considering the market value of the metals, these brownfield sites can now be considered as secondary resources. We have developed a hydrometallurgical process for selectively leaching Zn, Mn and Pb in order to produce compounds of Mn and Zn pure enough to be economically recoverable and a residue rich in Pb. Batch laboratory experiments were carried out to determine appropriate leaching conditions to maximize zinc extraction (100 %) and manganese extraction (90.0 %) with sulfuric acid and to generate a residue containing 15 to 30% of lead. This Pb residue is recyclable by another process.

Jan 1, 2015

By Ho SE, Neil Phillips G, Houstoun SM

There are numerous individual gold deposits in the Archaean greenstone belts of Western Australia, but only 26 have productions and/or quoted reserves in excess of 10 tonnes Au. Most gold production has come from mineralization in shear zones, quartz veins or stockworks in volcanic or intrusive host rocks, particularly tholeiitic basalts or dolerites metamorphosed at sub-amphibolite facies (e.g. Kalgoorlie). Significant prod- uction has also come from BIF-hosted deposits (e.g. Hill 50), and large reserves are quoted for mafic hosts at high metamorphic grade (e.g. Big Bell). Most deposits have marked structural control, great depth extension, and are characterized by zoned alteration haloes of pyritization (with Au), K-metasomatism and carbonation. On the regional scale, most larger volcanic- or intrusive-hosted deposits occur in younger (ca 2.8 b.y.) rift-phase green- stones (Norseman-Wiluna Belt). These belts also have a high prospectivity (36 kg Au/km2 of greenstone belt). Younger (ca 3.0 b.y.) and older (ca 3.5 b.y.) platform-phase green stones of the Murchison and Sodthern Cross Provinces and the east Pilbara, respectively, are progressively less prospective (14 kg Au/km2 and 0.8 kg Au/km2, respectively) and also have progressively smaller deposits. The important regional- and local-scale characteristics of most gold deposits can be explained in terms of a metamorphic- replacement model. In this model, metamorphic H2O-CO2 fluids, focussed by faults and shear zones, infiltrated host rocks and deposit gold at 350 + 50¦C and 1-2 kb, largely in response to fluid-wallrock interaction. In many large deposits, gold precipitation was synchronous with sulphidation of Fe-rich host rocks, but the diversity and abundance of smaller deposits reflects the variety of reactions precipitating gold from ubiquitous, auriferous metamorphic fluids. Regional variations in abundance and size of deposits relate to factors such as tectonic setting, alteration styles and possibly source rocks.

Jan 1, 1986

By Gang Ren, Behrooz Ghabraie

"Observational data suggest that the ground surface subsidence profile from multiple-seam longwall mining is rather different from that of single seam. Despite the increase of coal production from multiple-seam mining, available predictive methods are mostly unable to predict a reliable subsidence profile for multiple-seam extractions. In this paper, a case study of multiple-seam subsidence is modelled using physical modelling techniques. The subsidence mechanism as revealed in the physical model is explained and the differences between multiple and single-seam subsidence are highlighted. On the same case study, a commonly used influence function method (IFM) and Generalised Influence Function Method (GIFM) are utilised to predict the subsidence profile. The results are compared with predictions achieved by a newly developed predictive method based on the understanding of mechanism of the multiple-seam subsidence. Results show a significantly improved correlation between the newly developed method in comparison with the conventional IFM and GIFM. INTRODUCTIONField observations and subsidence monitoring data from multiple-seam coal mining cases show a different subsidence profile as compared with single-seam ones (Sheorey et al., 2000; Li, et al, 2007; Luo and Qiu, 2012; Unlu et al, 2013). The multiple-seam subsidence curve is generally deeper and steeper than of single-seam cases, and varies from one mining configuration to another. Various researchers had made efforts to understand the mechanism behind this phenomenon and the interaction between the two mining horizons (Li et al., 2010, Sui et al., 2014; Zhang et al., 2014). However, the mechanism of the multiple-seam subsidence is yet to be comprehensively understood (Suchowerska, 2014; Ghabraie et al., 2015b).In addition, differences between the single and multiple-seam subsidence profiles make it difficult to adapt single-seam subsidence prediction tools for predicting the subsidence over multiple-seam cases, unless significant modifications are applied This requires understanding the mechanism of the multiple-seam subsidence as the first step to achieve reliable predictive results.The mechanism of the subsidence due to a multiple-seam case study can be investigated via physical modelling. The physical model allows observing the substrata movement as well as the interaction of the two mining activities. An understanding of the mechanism of the multiple-seam subsidence can be developed based on these observations, which would provide basis for developing a subsidence prediction tool."

Jan 1, 2016