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By H. Sis

The pressure filtration behavior of dispersed and flocculated alumina slurries at high percent loadings is discussed with an objective to determine the effect of surfactant type and concentration on slurry properties. A high purity alumina powder was used as a model solid. Dispersion of the alumina was controlled by surfactants that are considered to act by electric and steric stabilizers. The effect of both the ionic and nonionic surfactants was investigated. Surface charge measurements of the slurries were carried out by electrokinetic sonic amplitude (ESA) method to understand the mechanisms. The effect of surfactant type and concentration on the kinetics of pressure filtration and final cake properties are discussed.

Jan 1, 1998

By Edward J. Karkoska

The film you see is a slow motion view of a typical half million ton taconite blast at one of Erie's mines. This blast is made up of 220 drill holes and a total of 325 thousand pounds of blasting agent. The second view of the same shot is taken by a remote control hi speed camera located 1500' directly in front of the blast. Shortly you will see some violent camera movement as the air blast shock wave strikes the camera location. As the blasting sequence progresses the rock fly becomes evident, and if you will look closely amidst the clouds of smoke, rock fragments weighing up to 1/2 ton begin to cascade into view. These missles are the chief concern of blast security. The next camera shot at 4000 frames/second vividly describes the primacord firing lines detonating the blast. Travelling at 22,000 ft./sec., this white snake of fire travels to each hole, detonating the blasting agent. Before we get into the matter of blast security, let me locate our operation for those of you not acquainted with Minnesota's iron ranges and tell you something about our company.

Jan 1, 1969

By S. K. Ghosh

This paper discusses how the information on ash composition, ash-fusion temperatures, and ash-slag viscosity can be utilized to predict slagging and fouling potentials of a particular coal. A review of several empirical parameters which are commonly in use for determining such potentials is given. Also, some guideline values for interpreting the relative propensity of slagging and fouling of various types of coal are provided.

Jan 1, 1983

By Staff

"In 2018, the total estimated value of nonfuel mineral production in the United States increased by 3 percent from 2017 to $82.2 billion. The estimated value of metals produced domestically decreased by 4 percent, and the estimated value of indusrial minerals produced domestically increased by 7 percent (Table 1).Some idle U.S. metal mines and processing facilities restarted in 2018, including two primary aluminum smelters in Indiana and Missouri, a rare-earths mine in California and a zinc mine in New York. In contrast, four iron ore mines in Minnesota and a pelletizing plant in Indiana were shut down. Increased oil and natural gas drilling activity in 2018 led to increased production of some industrial mineral commodities that are used for oil and gas drilling, including barite and industrial sand and gravel. Production of industrial minerals primarily used in infrastructure and residential construction — including, cement, construction sand and gravel, crushed stone and gypsum — increased in 2018. Overall, mining activity trended upward for the second consecutive year because of increases in oil and gas extraction and industrial mineral mining (Table 2).Mineral industry performanceDiscussion of mine production is commonly segmented according to the type of materials produced within the broad categories of metals and industrial minerals (also known as nonmetallic minerals). Industrial minerals can be further subdivided as natural aggregates and other industrial minerals. Metals tend to have higher unit values but very low production quantities compared with those of industrial minerals, such as crushed stone or construction sand and gravel, which have higher production quantities but are lower-valued materials. Therefore, for discussion and analysis of the performance of the nonfuel minerals industry, the value of production is used rather than the tonnage produced. Tonnages of natural aggregates are orders of magnitude larger than those for most other mineral commodities, thus making direct comparisons based on weight meaningless (Fig. 1)."

May 1, 2019

By J. Marsden

Lift height, overall heap height and climate all play an important role in determining precious metals leaching rates, recoveries, operating costs and capital cost requirements for heap leaching operations. The effects of these factors are not easy to predict from testwork, and this can result in unexpected delays in metal production, lower recoveries than expected and higher capital and operating costs than necessary. This paper investigates the economic impact of lift height, overall heap height and climate on heap leaching and provides criteria to assist in the design and operation of leaching facilities. Descriptions of three heap leach operations in the western USA are provided to support the discussions and conclusions.

Jan 1, 1995

By T. P. Lim, J. A. Cherry, A. J. Vivyurka, R. D. Blair

The first phase of an investigation of the chemical composition of subsurface water and the hydrochemical processes in and near the abandoned Nordic tailings at Elliot Lake, Ontario, was conducted in 1979. The Nordic area, which covers 85 hectares with an average thickness of 10 m and overlies deposits of permeable glaciofluvial sand, contains 15 million tonnes of tailings with 4-7% pyrite. Nests of standpipe piezometers installed at three locations on the tailings indicate that seepage through the tailings is predominantly downward. The water table in the tailings slopes from the north side of the tailings dam, where it is within a metre of surface to the south side near the tailings dam, where it is approximately 10 m below surface. When they were deposited during the period from 1957 to 1968, the tailings contained pore water at a pH of about 8 resulting from neutralization treatment in the mill. At the three piezometer nests, the pH increases from 3 near the water table to 7 near the bottom of the tailings. The pore water in the tailings is gradually becoming acidic because of oxidation of pyrite in the zone above the water table. The concentrations of Fe, Mn, Ni, Co, Zn and Pb are high in the shallow acidic zone and much lower in the deeper neutral zone. Concentrations of 226Ra range from 30 to 230 pCi/L. At the three sites concentrations of major ions in the permeable sand a short interval beneath the tailings indicate 226Ra presence of tailings seepage, but Ra concentrations are only 2 to 8 pCi/L. Greater downward penetration of 226Ra probably occurs in the area closer to the tailings dam. Monitoring of a network of multilevel bundle piezometers installed in permeable sand that extends southward from beneath the tailings indicates the occurrence of a plume of tailingsderived water containing high concentrations of Ca, Mg, Fe and S04 that extend 400 m downgradient from the tailings dam. The total dissolved solids decline from 20,000 at the dam to less than 500 mg/L at the identifiable downgradient periphery of the plume. A much smaller but distinct plume of water with high heavy metal concentrations and 226Ra in the range of 10 to 130 pCi/L extends from beneath the dam for a distance of 15 m. The pH of the groundwater in this heavy metal-radium plume is 4 to 5, whereas elsewhere in zone of groundwater with high dissolved solids, the pH is above 6. The results of this investigat, suggest that the heavy metals an 226 Ra are relatively immobile in the perme-

Jan 1, 1980

By A. G. Yapo, T. W. Camm

"All-in sustaining cost is a metric used by mining companies to reflect the cost of gold mining in a consistent format useful to both investors and mining professionals. Cost reporting focused on the direct cost of mining and processing ore was summarized in the non-GAAP cash cost developed by the Gold Institute in 1996. In 2013, a group of mining companies, working with the World Gold Council, developed a more inclusive approach to reporting costs designed to solve the dilemma of showing a more comprehensive reflection of recurring costs involved in producing gold, without discouraging investors. INTRODUCTION Mining today plays a key role in the development of our civilization as a source of essential raw material and provider of essential fuels, producer of jobs, and a factor in support of the international balance of monetary payment (Camm, 2014). Professionals in mining locate, develop, design and manage ore deposits in an environmentally safe and profitable manner. As mineral deposits become increasingly scarce, new challenges face the industry. A current trend is to an increased emphasis on underground mining techniques for deeper deposits. Operations are safer today than before as companies understand better their work environment and the importance of mining responsibly. A continual challenge for the industry is accurately reflecting the costs and selling price of ore. An enduring characteristic of mining is the situation where the market typically determines the price of a commodity; the main control a company has on the bottom line is to control the cost of production. An attempt to bring light and clarity on the cost of their business will give a better idea to investors on the true profitability of the mining business. Gold producers face this struggle to accurately reflect the cost of production while also seeking to attract the interest of the investment community (Hill, 2013). In order to have a consistent format to report on their production costs, leading gold producers through their alliance inside the World Gold Council (WGC), worked on the adoption of a new cost framework: the All-in Sustaining Cost (AISC) and All-in Cost (AIC). Since 1996, the traditional cash cost reporting has focused only on the mining and processing costs incurred in mining an ounce of gold, which included the costs of goods sold (labor, energy, and consumables costs) and royalties (Table 1). But cash cost reporting ignores many important aspects, like sustaining capital, general and administrative expenses, and site rehabilitation at the end of the mine life (Whelan, 2013). The cash cost was used to attract many investors into the business. In fact the high gross margin (sales minus cash costs) has been promoted the past decades by the industry instead of the net or operating margin. As a result, even when the gold price was high, nearly $1900 per ounce in August 2011, gold producers were not reporting excessive profits in their cash flow / income statements, to the disappointment and incomprehension of investors (Milstead, 2014). The truth was simply that the other costs omitted in the traditional cash cost were reducing the apparent profits."

Jan 1, 2017

By Edward S. Plotkin, Gary A. Almeraris, Thomas F. Peyton

The lining of the tunnel and shafts for a new section of New York City's- water system required extensive components to produce, deliver and place a continuous tunnel linning. The project placed approximately 153,000 CM (200,000 cy) of concrete for 5,340 M (17,520) of drill and blast 7.3 M (24 ft.) ID tunnel, located at depths of 152 M (500 ft.) to 213 M (700 ft.) . This section of tunnel will be connected to the surface water distribution system via four shafts of varying diameters ranging from 5.8 M (19 ft.) ID to 1.5 M (5 ft.) ID . All work was done beneath the streets of Manhattan under the rigid constraints of the City of New York and the Bureau of Water Supply regulations.

Jan 1, 1987

By T. R. Ley

"RELIABILITY & SAFETY – TOGETHER. REALLY? I was starkly reminded of the challenges facing by the coal industry while talking with a number of senior mining executives. One said to me: “Safety is the #1 priority in our organization but of course, dollars are very, very important!!!” A coal mine worker at the Bluefield Coal Show claimed: “We know our equipment is bleeding hydraulic fluid all over the place but all that matters is getting the coal out”. We all understand. We want our people to go home safely at the end of the day but the coal industry is bleeding – fluids, dollars and real blood. An issue getting plenty of buzz these days is equipment reliability – in mining too! Achieving an optimal return from the massive investments in equipment is a critical requirement for success within a capital intensive industry like coal mining. You can cut costs by scrimping on maintenance, scavenging used parts and downsizing. Or, you can save money by being smarter with your asset management processes. Can we afford to spend money on both safety and reliability? Is one more important than the other? Many leading edge companies from a variety of industries will tell you that you can’t just cost-cut your way to profitability - or even survival. You need to systematically improve the effectiveness of your business. Do reliability and safety both have a place in improving the performance of the coal industry? According to Ron Moore, of The RM Group, the answer is emphatically YES! Ron says: “If you believe in safety, then you MUST believe in reliability and, more importantly, have the appropriate policies, systems, practices and measures in place. If you want lower costs, you must get your processes right. Simple cost cutting will remove resources from your system without changing the underlying system design, and performance will likely deteriorate.” Figure 1 shows the 5+ year results of a large manufacturing company. When plants are running well (high Asset Utilization), then injuries are less likely. Figure 2 plots data from a number of manufacturing plants. If you want sustainably lower costs get your reliability processes right. But these are manufacturing companies, not coal mining operations! It doesn’t matter. The fundamentals still apply. Mining industry thought leaders tell us that manufacturing is 20-30 years ahead of us and we need to learn from them – and do so quickly. Leading companies, no matter the industry, think in terms of operational excellence. They see this as the meshing of people, process and technology to achieve optimal results. Safety and reliability go hand-in-hand. People and equipment are different – but only to the extent that each requires its own relevant, but related, policies, practices, systems and metrics to achieve effective performance."

Jan 1, 2016

By O. P. Burghardt

Blast furnaces of high specific throughput capacities producing 10,000 tpd of pig iron or even more, require burden materials which, because of their chemical, physical and metallurgical properties, guarantee such high performances. Meanwhile, it should be generally accepted that for evaluating the quality of iron ore pellets, it is not sufficient to know the chemical analysis and the physical properties, i.e. grain size distribution, cold compression strength and abrasion of the fired pellets. It is indispensable to determine the metallurgical properties indicated by swelling, reduction-softening under load and reducibility, as well as grain disintegration in the low-temperature range in the beginning of reduction. By introducing new test methods, and in the face of the need to meet more strict requirements, pellet producers are being confronted with steadily increasing tasks and problems which require a deepening of our knowledge of the ways and means of making high-quality iron ore pellets.

Jan 1, 1975

By I. Weir-Jones

I. Introduction The experimental work described in this paper was carried out during 1967 and 1968 in an inclined reinforced concrete adit which had been driven during 1965 and 1966 to provide primary access for a new gypsum mine. The new mine was situated near the village of Sherburn-in-Elmet in central Yorkshire in an area of extensive post-glacial plains of deltaic and lacustrine origin. These plains cover a large area of this part of Yorkshire extending inland from the coast for a distance of about 35 miles. The gypsum deposit at Sherburn dates from Permian times and it is considered" to have been associated with the western-most edges of the ancient Zechstein Sea which was also responsible for the formation of the extensive evaporite deposits in north-east Yorkshire. The gypsum deposit, which varies in thickness from 10 to 15 feet, is extremely pure and it occurs quite close to the surface; in the Sherburn area the overburden is only 120 feet thick. The proximity of the deposit to the surface, however, tends to give a somewhat false idea of the magnitude of the problems associated with its extraction. These problems were all related to the nature of the overlying strata. As has already been mentioned, the surface deposits are post-glacial and they consist of an extremely large number of thin layers of varved clays, fine silts and sands extending down to a depth of 75 feet. From the bottom of the post-glacial deposits to the seam, a distance of about 45 feet, the strata consists of a succession of marls, weak sandstones, and siltstones, which although they are inherently incompetent materials, are appreciably stronger

Jan 1, 1971

By Ping Zhang, Shahram Mozaffari, Andreas Ylmefors

The risk associated with mining induced seismicity and the related rock bursts has become one of the major threats to the safety and sustainability of mining at the Kiirunavaara mine. The causes of mining induced seismicity at the Kiirunavaara mine are very complex and have affected our understanding on the source mechanisms of seismicity and further the mitigation of the seismic risk. Detailed analysis of historical mining induced seismicity at the Kiirunavaara mine was conducted. The focus of this analysis was placed on the classification of large seismic events and the evaluation of the influential factors on the classified seismic events. 145 events with local magnitude larger than 1.5 that occurred between January 1, 2011 and March 31, 2021 were analyzed. For this analysis, seismic events located in the hanging wall were not included, as these have not been observed to cause large damages to the mine itself. It was found that the magnitude of the events had good correlation with the stress change in relation to the production location. The seismic events were classified as mining-front associated, ore-pass associated, mining-front and ore-pass associated and others, according to their hypocenter location. Most of the mining-front associated events, concentrated around the production levels and slightly above and below them, generally correlated with shear cracks, and most of them occurred when the ore flow between two production levels started. The numerical modelling showed that slip of the geological discontinuity, due to unclamping between hanging wall and footwall, could be the major causative mechanisms, which further supports this finding. The ore-pass associated events are located close to the ore passes. Large seismic events located between ore passes have the source mechanism of both fault-slip and non-shear, but events located at the outer side of ore passes were all fault-slip type. By checking with the ore pass scanning data, it was concluded that the most of the events located between ore passes could be pillar bursts. An elastic core concept has been then used to define a critical pillar width. The paper is not intended to be prescriptive but rather to initiate discussion of the possible classification of seismic events at the Kiirunavaara mine and to present new perspectives of the causes of the seismicity for improving the present seismic risk management.

Apr 26, 2022

By Gilbert Sauriol

The mining complex, which the Mines Gaspé division of Noranda Mines Limited has operated in Murdochville since 1954, includes open pit and underground mines, two mills, one leaching plant and a smelter. The under- ground mining uses predominantly a large scale room and pillar method, rooms 15 m wide, 30 m high and 300 m long being common. Ore production is effected by 4.5 m3 front-end loaders and 32-tonne trucks powered respectively by 225 and 325 kW diesels. Daily dust and gas readings show that air quality can be maintained at an acceptable level with much less ventilation than that normally specified. This paper emphasizes the point that air requirements should be based on Air Quality Standards, thus allowing an operation to benefit from favourable conditions or from improvements such as exhaust treatment, fuel alteration, etc.

Jan 1, 1983

By U. Cetin

The Nevada Test Site is located approximately 65 miles northwest of Las Vegas, NY. The site was primarily used by the Department of Energy for the field testing of nuclear weapons and contaminated by several million cubic feet of low-level radioactive wastes, heavy metals, volatile and non-volatile organics, and explosive materials. Leaching and transportation of these contaminants are creating severe environmental problems. The purpose of this study is to examine pozzolan, a natural alumina-silicate mineral, as a possible replacement of the existing impermeable barriers (clays). In the first phase of this study, radionuclide sorption characteristics of pozzolan were investigated. This paper will present the results of the sorption tests for the target radionuclides.

Jan 1, 1998

By Ross W. Whipple

Applying geophysical techniques in potential geothermal areas has received: little attention in the United States, though it is widely used and accepted in New Zealand and Italy. In those countries it has been demonstrated that geophysical surveys can be useful in locating new geothermal areas and in directing test drilling programs. Geophysical studies in a thermal region can provide structural information and, if conditions are right directly; locate subsurface hot waters. They can give indications of sub-alluvial rock types and of the thickness of alluvial cover. In certain cases they can be used to estimate the power potential of a hydrothermal system.

Jan 1, 1963

By W. C. Hellyer

The Granduc ore body is located beneath glacial terrain on the borders of British Columbia and Alaska, some 600 miles from Vancouver and 30 miles from Tidewater at Stewart, B. C. The concentrator and attendant facilities are located in wilderness country at an elevation of 2500 feet. The average annual snowfall is 65 feet. Surface facilities and ore body are linked by a 10 mile railroad haulage tunnel. This copper property has been developed by Granduc Operating Company on behalf of Newmont Mining Corporation and American Smelting and Refining Co. First production started in November, 1970. In August, 1966, Granduc Operating Company awarded an engineering and construction management contract to McKee-Swan Wooster, a joint venture of A. G. McKee of Canada and Swan Wooster Engineering Company Limited, to design a concentrator to treat approximately 7000 tons of ore per day. The isolated location of the Granduc ore body indicated comparatively high freight rates on consumable items of concentrator supplies such as reagents, grinding media, etc. A firm flowsheet for the flotation of the Granduc ores having been developed by the Danbury laboratory of Newmont Exploration Limited, attention was devoted to means of reducing operating costs. One obvious method was to reduce or eliminate the costs of steel grinding media by employing some form of autogenous grinding. two pilot plant operations were carried out at the facilities of Lakefield Research of Canada Limited, in which autogenous grinding of Granduc ores was investigated. The results of these investigations led to the selection

Jan 1, 1972

By Earl M. Frizzell

Investigation of mined land characteristics, evaluation of irrigation systems and evaluations by the mining industry determined that irrigation is a feasible method for aiding the revegetation of coal mined lands in the western arid and semi-arid regions (Sherman, et al. 1980). The various regions studied displayed a commonality of characteristics which enables, independent of the site or region, the recommendation of solid-set irrigation. Irrigation should be supplemental by complimenting natural precipitation and should be implemented on a temporary basis. For germination, the vegetation requires application of small amounts of water in a gentle, frequent, and timely manner. For the establishment phase of growth, moisture should be applied and stored in the soil either through pre-irrigation or deep irrigation.

Jan 1, 1985

By Mark P. Walsh

In recent years in situ leach mining has emerged as a viable technology for the recovery of uranium from strata in South Texas which contain relatively low concentrations of uranium ore. Because the ore bodies lie within groundwater aquifers, a significant determinant in the economics is the requirement that such aquifers be protected from contaminantion. Since ammonia is one of the constituents of the leach solutions now being field tested, one environ- mental problem to be resolved is the removal of ammonia at the end of mining. A second related question is the fate of the ammonia which is not removed by the restoration procedure. This paper considers the displacement and migration of ammonium in a flowing electrolyte with concomitant ion exchange. The ion exchange is an important feature since, during the solution mining phase, ammonium saturates the mineral exchange sites and must be removed from these sites. A mathematical model is used to simulate this process and the model is tested against the results of laboratory experiments. It is found that the simulations are adequate if an appropriate selection of parameters is made. The model is then used to investigate the effect of cation composition and concentration of the restoration medium as well as dispersion on the overall effectiveness of the process. It is concluded that increasing the concentration of monovalent ions in a solution containing a mixture of both monovalent and divalent ions decreases the adsorption selectivity of the divalent ions with respect to all monovalent ions including ammonium. Thus increasing the ionic concentration of a restoration fluid by increasing the concentration of a nonselectively adsorbed (with respect to ammonium) ion may have a very limited benefit. Dispersion attending the flow of fluids in a porous medium is also shown to be an important factor. The effect of dispersion can greatly reduce the benefits of having a displacing cation which is adsorbed selectively with respect to ammonium. Since dispersion increases almost linearly with fluid velocity, an optimum displacement rate may exist.

Jan 1, 1979

By T. J. Batchler

"INTRODUCTION A variety of standing supports are being applied in underground coal mining operations to assist in providing stable mine entries. Standing support performance requirements depend on the nature of the ground deformation behavior, and therefore require a good understanding of the interaction between the support and ground to achieve an optimum roof support system. Mining operations often employ standing support strategies that are unique to their mine. A support system that functions successfully in one situation could fail in another situation. It is important that the design and installation of the standing support systems provide the highest probability of preventing roof falls. Considerable research and development has been conducted by support manufacturers to develop standing support technologies for the mining industry. The National Institute for Occupational Safety and Health (NIOSH) researchers, with the cooperation of various support manufacturers, have developed a testing protocol that evaluates performance characteristics of these standing support systems.. Using this protocol, each of these support systems has gone through rigorous safety performance testing under controlled loading conditions in NIOSH’s Mine Roof Simulator (MRS). It is important to understand the unique performance characteristics of each type of standing support. This information allows mine operators to determine if the support system is compatible with the conditions in the mine and to compare each support system and determine if that support will provide equivalent or improved support capability. This paper provides a comprehensive summary of support performance to facilitate this objective. SUPPORT DESIGN CRITERIA AND THE GROUND REACTION CURVE Standing roof support systems are designed to prevent unplanned roof falls. The selection of the standing support is based on the interaction of the support with the surrounding rock mass, and its function is to assist the primary support system in maintaining the integrity of the immediate roof. The standing support works to control the immediate roof structure by resisting deformation that contribute to delamination of the bedded layers and displacements that lead to separation of the bolted zone from stable roof structures above the bolted horizon (Barczak, 2005). Standing supports should be installed early enough and develop sufficient capacity to bring deformation of the ground into equilibrium before a critical deformation is reached that leads to a detached block condition, at which point the standing support will be required to carry the entire dead weight of the detached rock mass to prevent a roof fall from occurring (Mucho, 1999). The ground reaction curve (GRC) can be used to assist in determining the compatibility and design requirements for a support system. It is important to understand the significance of the ground reaction relative to the support design requirements. The ultimate objective is to match the support behavior to the ground response and create equilibrium (stability) of the rock mass. This equilibrium is accomplished when the support loading intersects the ground reaction curve (Figure 1). Essentially, the ground reaction concept implies that the convergence in the mine entry is controlled by the magnitude of the support resistance. However, as a passive support, the standing support develops its loading through convergence. As such, the support needs to maintain its load capacity through the associated deformation of the ground and resulting entry convergence until the equilibrium condition is reached. This requirement causes factors such as the support stiffness, peak capacity, yielding characteristics, and stability to be fundamental to proper support design and application. NIOSH contributes to providing this understanding through full-scale performance testing of support products in the Mine Roof Simulator."

Jan 1, 2017

By W. –E. Marx, M. Faber, R. Pollak, I. Astberg

INTRODUCTION Essentially three strategies are pursued in parallel for protecting the underground working force in mining against the consequences of methane ignitions which might lead to explosions: • Sufficient ventilation for avoiding the formation of explosive methane-air mixtures. • Avoiding sources of ignition caused possibly by electrical equipment or friction. • Structural explosion protection for limiting explosion propagation to the farthest-going extent for the case that methane is fired because of failing of the above preventive measures taken. The corresponding methods taken in mechanized roadheadings with point-attack roadheaders in German coalmining are subject of this paper. VENTILATION In ventilation of roadheading sites the following is to be considered in respect of methane control: • Sufficient air flows by volume being cycled to the heading face for diluting released methane to safe concentrations. • Sufficient local air velocities for effective mixing of methane and air in the whole heading site, in particular directly on the heading face and underneath the roof. Furthermore, ventilation needs to be laid out in a way that cut- ting does not result in health affecting dust exposure at any working place. Accordingly, the ventilation systems shown on Fig. 1 including primary and, if necessary, secondary auxiliary ventilation air ducts as well as dedusters, are used in roadheadings. This equipment is run according to the following principles: • If the roadheader is at standstill, the heading face is ventilated by the free air jet from the blowing duct closest to the face. In this operation phase the deduster is shut-down. • During cutting, the exhaust of the blowing air duct is automatically closed, and the deduster is taken into operation. The in- coming fresh air is now locally discharged via a lateral orifice, or distributed by Coanda-type ducts from the primary or secondary ventilation air duct. In this way, a stable dust wall not disturbed by the jet of the air duct is formed in front of the heading face. Only the ventilation air stream taken in by suction of the close-to-face deduster is passed through the inby zone of the heading face (over approx. 20 m). The clean exhaust of the deduster is dischayed to the roadway in some distance outby. Immediately at the heading face, methane accumulations possibly released by cutting are diluted by compressed-air jets from air-movers located near the roof which assure more rapid motion of the air without distuhing the dust wall. • In the zone of overlapping of primary and secondary duct and the deduster - that zone possibly is poorly ventilated during cutting - sufficient local air speed is assured by Coanda-type ducts or additional ventilation jets for avoiding methane accumulation. The regulations of the inspectorate specifies geometrical conditions to be met with these configurations of ventilation equipment. In-seam roadways are ventilated at rates > 0,5 m/s. For dedusters, present-day ventilation air flows are of 600-800 m+/ min. Ventilation monitoring and control is assured by units for measuring methane and ventilation air flows. If pre-set thresholds are exceeded or fallen short of, these measuring units shut-down - dependent on potential hazard - any not intrinsically safe electrical equipment in the roadheading, either totally or in limited zones. In addition, CO-measuring units near the roadway en- trance serve for early detection of mine fires. In spite of this ventilation layout and the equipment used and in spite of the water spray systems on the cutting head (discussed later in this paper) several cases of methane ignition and subsequent burning off (however, no explosions) have been recorded in the recent past. Therefore, the above-described ventilation is nowadays complemented in many cases by machine-mounted ventilation equipment for the immediate surroundings of the cutting head. Ventilation of the surroundings of the cutting head Investigations carried out subsequent to the above-mentioned gas ignitions have shown that the high ventilation air speed necessary for rapid dilution of methane could not permanently be arrived at in the following zones: • The direct zone of cutting, in particular during sumping. • The floor zone above the debris, predominantly below the cut- ting head. Accordingly, VOEST ALPINE-Bergtechnik, a producer of mining machinery, in cooperation with DMT developed for point- alttack roadheaders a novel machine-mounted ventilation equipment, the Jet-Block" (AERO SAFE Jet-Block) shown on Fig. 2. This system allows to ventilate the above-mentioned critical zones with high flow speeds. One AS Jet-Block is mounted on each side of the boom approx. 0.5 m behind the cutting head. The blocks discharge compressed-air jets with high energy from 10 nozzles per block into the hazardous zones (Fig. 3). Two nozzles of each jet block are tangentially oriented toward the upper circumference of the cutting head, the others are arranged fan-like with orientation to the heading face underneath the cutting head and the debris. The nozzle array of the blocks as well as the com-

Jan 1, 1997