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By C. J. Johnson

As the U.S. coal industry moves into the next century, it is becoming more apparent that the effective application of new technology is the only way it can remain competitive in the energy marketplace. Examples of this emphasis are with us today in such diverse areas as face-ventilation and excavation-equipment applications. The focus of this new technology is directed toward improvements in health and safety, cost control, and productivity. Room-and-pillar mining accounts for approximately 80% of the nation's underground coal production; this percentage is not expected to decrease markedly in the near future. As such, this paper analyzes the impacts of the changing technological climate on future room-and-pillar operations by comparing a base-case section (current) to three scenarios incorporating new or emerging technology. A microcomputer-based comparative analysis will reflect the changes in section production and costs.

Jan 1, 1988

By A. M. Stone

Following the conceptual idea of a Continuous Elution Process early in 1982, the system was successfully pilot plant tested at Western Mining's Kambalda gold plant in December 1982. As a consequence of these tests the Ok Tedi elution ciruit design was changed from batch operation to continuous operation resulting in a reduction in the number of similarly sized elution columns from five operating with one standby to one operating with one standby and halving the process steam requirements. In addition to providing significant capital and operating cost savings the continuous process was simpler to operate than the batch process.

Jan 1, 1989

By Harold B. Goldman

On the basis of tonnage, the sand and gravel industry is the second largest nonfuel mineral industry in the United States. In 1990, the production of sand and gravel was 927 Mt valued at $3.4 billion. California, which leads the nation with more than 126 Mt, together with Texas, Washington, Michigan, and Ohio, account for 36% of the total production in the nation (Table 1). In commercial usage, sand applies to rock or mineral fragments ranging in size from particles retained on a No. 200 Sieve (0.074 mm openings) to those passing a No. 4 Sieve (4.76 mm openings). Gravel consists of rock or mineral fragments larger than 4.76 mm, ranging up to 88.9 mm maximum size. The construction industry consumes 97% of the sand and gravel produced; the remainder is sand used for specialized products such as glass (see chapter on Industrial Sand and Sandstone and Glass Raw Materials). Utilization The building industry uses sand and gravel chiefly as aggregate in portland cement concrete, mortar, and plaster; the paving industry uses sand and gravel in both asphaltic mixtures and portland cement concrete. Aggregate is commonly designated as the inert fragmental material that is bound into a conglomerate mass by a cementing material such as portland cement, asphalt, or gypsum plaster. Sand and gravel is also used as construction fill, road base and subbase, and decorative material. Portland Cement Concrete Aggregates: Portland cement concrete consists of sand and gravel surrounded and held together by hardened portland cement paste. Concrete mixes commonly contain 15 to 20% water, 7 to 14% cement, and66 to 78% aggregate. Sand and gravel used as concrete aggregate have to meet many requirements (Goldman and Reining, 1983). Premature deterioration of concrete has been traced in many instances to the use of unsuitable aggregates. Asphaltic Aggregate: Asphaltic mixtures used predominantly for paving consist of combinations of sand, gravel, and mineral filler (material finer than 0.076 mm), uniformly coated and mixed with asphalt produced in the refining of petroleum. Sand and gravel used as asphaltic aggregate must meet the same general physical requirements as materials used for portland cement aggregate. GEOLOGY General Requirements of Aggregates Construction aggregate has many requirements that are difficult to meet if only unprocessed material from natural deposits is used. Suitable material is composed of clean, uncoated, properly shaped particles that are sound and durable. Soundness and durability are terms used to denote the ability of aggregates to retain a uniform physical and chemical state over a long period of time so as not to disintegrate when exposed to weathering and other destructive processes. Individual particles must be tough and firm, possessing the strength to resist physical stresses and chemical and physical changes, that may cause swelling, cracking, softening, and leaching. The aggregate should not be contaminated by excessive clayey material, silt, mica, organic matter, chemical salts, and surface coatings. Physical Properties: The quality of aggregate depends upon its physical and chemical properties. These, in turn, may be inherent mineralogical and textural features of the rock or may be the effects of later changes such as tectonics, mechanical or chemical weathering, or incrustations. The physical properties most significant for concrete use are: 1) abundance and nature of fractures and pores, 2) particle shape and surface texture, and 3) volume changes which may occur because of freezing and thawing or wetting and drying. An aggregate is considered to be physically sound if it is adequately strong and capable of resisting the agencies of weathering without disruption or decomposition. Minerals or rock particles that are physically weak, extremely water absorptive, and easily cleavable are susceptible to breakdown. The use of such materials in concrete reduces strength or leads to early deterioration by promoting weak bond between cement and aggregate, or by inducing cracking, spalling, or popouts. Severely weathered, soft, micaceous, or porous materials may cause localized stresses to develop in concrete by swelling and shrinking during wetting and drying or freezing and thawing cycles. Physical Suitability of the Various Rock Types. Sedimentary rocks have a wide range in physical and chemical qualities. Sand- stones and limestones, if hard and dense, are ordinarily satisfactory, but many sandstones are friable and excessively porous and commonly are clay-bearing. Shales generally make poor aggregate material, being soft, weak, and absorptive. Most igneous rocks are satisfactory, being normally hard, tough, and dense. Tuffs and certain flow rocks may be extremely porous and have high water absorption and low strength. Metamorphic rocks differ in character. Most quartzites are massive, tough, and dense. Fine-grained marbles are usually durable, but coarse-grained marbles have low abrasion resistance. Gneisses are ordinarily very tough and durable. Some schists contain micaceous minerals that are undesirable because they are soft, laminated, and absorptive. Micaceous minerals are susceptible to splitting along cleavage planes and thereby impair particle strength and durability. Some schists and slates in particular are thinly laminated and tend to assume flat slabby shapes that lack strength-and do not pack well. Any or all of these rock types may be rendered undesirable because of harmful exterior coatings. Weathering processes, particularly the action of ground waters, deposit these coatings. The most common coatings are calcium carbonate, clay, silt, opal, chalcedony, iron oxide, manganese oxide, and gypsum. Particles with these coatings are undesirable as aggregates because the bond between particle and coating may be weak, and decreasing the strength of the aggregate-cement bond.

Jan 1, 1994

By Charles Kimbell, L. Nahai, E. Shekarchi

INTRODUCTION AND SUMMARY World mineral trade during 1960 to 1984 has shown substantial changes both in value and tonnage. Although fuel commodities dominated total mineral trade during this period, this paper will focus attention primarily on nonfuel minerals. Brazil and Australia, modest producers of iron ore in 1960, have become dominant producers and exporters, together accounting for about half of major iron ore exports in 1984, far surpassing traditional export suppliers such as Sweden. Australia has also become the largest producer and trader of bauxite and alumina, and worldwide alumina trade has increased at the expense of bauxite trade. Similarly, shipments of ferroalloys have increased more than shipments of ores such as those of chromium and manganese. Canada, retaining its first rank in world export of zinc, has become also the leading source of potash and sulfur in world trade, and South Africa has been the dominant factor in chromite, manganese and their respective ferroalloys. Developing countries' share of world copper trade has increased, with Chile maintaining first rank, but developed industrialized countries have continued to dominate production and trade of lead and zinc. Phosphate, sulfur, and potash have been the principal crude nonmetallic minerals traded worldwide. Looking to the near future, dramatic increases in export of iron ore, phosphate, potash and sulfur are not envisaged. Bauxite exports will continue to decline relative to alumina but at a slower rate than in the recent past. Zinc concentrate will continue to be exported but lead will be traded more as metal than as concentrate. For iron and steel, there will be some production shift from traditional producers to certain developing countries and recently industrializing developing countries such as Brazil, India, the Republic of Korea, and Taiwan. In the following sections dealing with specific commodities, it should be understood that information is presented only on the major forms of each commodity that move in trade, and only for a selected group of countries for each commodity or major form of each commodity. Thus, totals shown or mentioned generally represent only the totals of figures presented here and do not include estimates for minor forms of material or for countries that are not listed. However, the data provided is regarded as sufficiently complete to reflect major patterns and trends, and exclusions are there- fore not seen as affecting conclusions that may be drawn from the material provided. FUEL AND NONFUEL TRADE Values of Fuel and Nonfuel Trade The value of world export trade in major mineral commodities (ores, concentrates and scrap, crude minerals, iron and steel, nonferrous metals, nonmetallic minerals and mineral fuels) in 1983, the latest year for which comprehensive data are available, was reported by the United Nations in May 1985 to have totaled over 514 billion current U.S. dollars (Table 1). This was 79% of the historic record high of nearly $649 billion ,current dollars set in 1980, but almost 18 times the current dollar value reported for 1960. [1/] The value of these 1983 exports in constant 1960 dollars was $164 billion (Table 2), only 66% of the record 1980 high of almost $250 billion, and only about 5.7 times the 1960 dollar level.

Jan 1, 1986

By W. K. Fletcher

As part of an ongoing programme on behaviour of heavy minerals In streams, the dispersion of Au as free gold (Day and Fletcher, 1987), Sn in cassiterite (Fletcher et al, 1987) and W in scheelite (Saxby and Fletcher, 1987) have been investigated downstream of mineralization. The studies of Au and W were undertaken, in British Columbia and the Yukon Territory, respectively, in streams that are strongly influenced by spring snowmelt floods. Sn was investigated under tropical rainforest conditions in Peninnsular Malaysia.

Jan 1, 1988

By S. Horton, F. L. Stanley, P. J. Bethell

Introduction The McClure River Processing Plant is located at McClure in Dickenson County, VA. The plant was originally constructed in 1979 as a 600 st per hour facility. The plant is fed by coals from numerous mines in the area as well as a major longwall mine onsite. Coal is processed predominantly for the metallurgical coal market. The original plant was comprised of three separate processing circuits incorporating a heavy medium vessel for the coarse material (+10 mm). Intermediate sized material (10 x 0.6 mm) was beneficiated in heavy medium cyclones, with the remaining fines (0.6 mm x 0) passing to froth flotation for upgrading. The products from all three circuits were combined prior to thermal drying and then stored in silos or ground storage prior to shipment to the metallurgical coal markets. A middlings heavy medium cyclone circuit was also present to rewash the vessel and primary heavy medium cyclone rejects. The original circuit is as shown as Fig. 1 (Editor's note: All figures are reproduced at the end of this paper.) In reasonably close proximity to the McClure Plant is the much older, less efficient Moss 1 Plant, (Chance cone, table, water only cyclone, froth flotation, Fig. 2), which prior to the McClure Plant expansion was processing considerable tonnages of coal. At that time, the McClure River Plant was processing coal at the maximum possible feed rate, and the Moss 1 Plant was finding increasing difficulty in maintaining the stringent quality specifications on its major metallurgical coal accounts. Given the fact that many of the feeder coals to Moss 1 could be moved with minimal difficulty and cost to McClure, an exercise was conducted to evaluate the potential of expanding the McClure Plant. This would result in transferring coals from Moss 1, thereby increasing yield, reducing operating costs, and enabling customer specifications to be met more easily. After evaluating many possible ways of expanding the McClure Plant, we eventually settled on an approach based on the idea of Gallagher at German Creek in Australia (Gallagher, 1986). Our objective was to increase plant capacity by removing the coarser size fractions (0.60 x 0.15 mm) from froth flotation and at the same time eliminating the finer fractions (1.25 x 0.6 mm) from the heavy medium cyclone circuit, thereby allowing these circuits and therefore the plant as a whole to increase its capacity. These size fractions (0.60 x 0.15 mm from froth flotation and 1.25 x 0.6 mm from the heavy medium cyclone circuit) would be treated in a new spiral circuit. After desired evaluation of the various circuit capacities, including desliming screen, clean coal filter and thermal dryer capacities, etc., it was concluded that we should be able to maintain high levels of processing efficiency in the existing circuitry while at the same time expanding plant feed rate from a nominal 600 st per hour to 1000 st per hour, thereby achieving the objectives The circuit that was finally settled on is shown in Fig. 2. Several unique features were incorporated in this circuit in an attempt to maximize processing efficiency and reduce maintenance costs. First, the idea of a single-stage spiral circuit was abandoned in favor of a two-stage circuit incorporating rewashing the primary spiral middlings in a secondary spiral (Bethell, 88). The spirals selected were Mineral Deposits Model LD4 units. It was felt, after much previous testing, that spiral middlings rather than being a true middling gravity fraction were in fact a combination of true middlings with a preponderance of misplaced light coal and high-density rock. Consequently the insertion of this material directly into either clean coal or refuse streams (per normal practice) would only lead to loss of efficiency. The operating philosophy behind the design of the circuit was to produce the purest coal and rejects possible by adjusting the spiral splitters. Misplacement of refuse into the clean coal and vice versa would be minimized by taking a fairly large middlings cut. By reprocessing this material (10%-15% of primary spiral feed) in a secondary bank of spirals the misplaced material in the primary middlings would be reprocessed and its probability of reporting to the correct stream greatly enhanced. To minimize fines loading on the spirals, fine aperture sieve bends were to be included. A further novel feature of the circuitry is the desliming/ dewatering system. A philosophy of accepting inefficiency but forcing it to work in our favor was developed. The dewatering screens (Linatex Combis) were chosen not for their ultimate screening efficiency but for their ability to remove slimes (tolerating a fair quantity of oversize in the effluent) and their enhanced maintenance characteristics. Any oversize passing into the effluent, together with the fine coal centrifuge effluent, would pass to classifying cyclones, the objective of which was to reject to overflow (and hence froth flotation) as many fines as possible (-150 µm) without running the risk of losing coarse (1.25 x 0.15 mm) material to oversize. Hence, by a process of producing a "slime free" screen product coupled with a "coarse free" cyclone overflow, sizing efficiency could be maximized. Obviously, recirculating load had to be factored into the Combi Screen design capacity. The spiral circuit as shown in Fig. 2 was installed at McClure River in January 1988. The spiral circuit efficiency was very high immediately, and, after the normal debugging, plant capacity has been increased to the point at which we are currently processing of the order of 1100 st per hour. Test program The performance of the spiral circuit has been evaluated by two major samplings of the entire new circuit, coupled with routine bi-monthly tests on all other major components of the plant circuitry.

Jan 1, 1992

By K. A. Sauer

Blasting can create severe interference for a mine's carbon monoxide based fire detection system. At the present time, without being able to differentiate between blast and non-blast carbon monoxide, a fire detection system must either set fairly high alarm levels for its sensors, or allow frequent "false" alarms to sound during blasting. This paper will introduce current work being done which will attempt to define characteristics of the carbon monoxide concentrations time curve for blasting. The work uses drift blasting for its data base as it is one of the more common forms of blasting. Future work with the data may produce a mathematical model which can be used to monitor and identify the carbon monoxide time curve for drift blasting.

Jan 1, 1989

By Fred N. Kissell, George H. Jr. Schnakenberg

INTRODUCTION A variety of instruments are available for measuring or monitoring the performance of underground mine-ventilation systems. In general terms, the instruments may be classified as those that measure air velocity and those that measure gaseous concentrations. All costs herein are in terms of 1978 US dollars. The mention of a specific manufacturer or device is not intended to be an endorsement by the US Bureau of Mines. AIR-VELOCITY INSTRUMENTS The basic instruments used for measuring the air velocity in mines are the vane anemometer and the smoke tube. Vane Anemometer Of the air-velocity instruments, the 102-mm (4.0¬in.) vane anemometer is the most common and is available as either a low- or high-speed type. The low-speed anemometer generally is the most suitable for measuring the velocities in ordinary airways. For a rough check of the velocity in an airway, it usually is satisfactory to hold the anemometer by hand, positioning it in the center of the airway for 30 sec. However, the resultant error may be as high as 25% , and such a hand-held approach is unsuitable when accurate or reliable measurements are required. To obtain more accurate measurements, the proper procedure is as follows: 1) Since holding the anemometer by hand generally causes the instrument to read about 15% high, it is mounted on a 0.6-m (2-ft) extension rod. 2) The airway is divided into equal right and left halves. A 1-min traverse is used in each half, moving the anemometer smoothly up and down in a zigzag pattern so that the entire half is covered within the allotted minute. 3) The manufacturer's correction table is applied to the readings to adjust the velocity calculation as necessary. Whenever possible, anemometer readings should be obtained in a long straight section of airway that has a constant cross-sectional area. Bends and obstructions should be avoided, since they cause turbulence and other discontinuities in the airflow and can degrade the accuracy of the velocity measurements. Although a series of velocity measurements at one location usually corresponds to within a few percent, this is not an indication that the airflows calculated from those readings are completely accurate. One reason is that the correction table provided with the instrument generally is not for that specific instrument; instead, it represents the average correction for all such instru¬ments made by the particular manufacturer. Most cor¬rection tables specify a correction factor of from 0 to 15%, depending upon the velocity. However, even after correction, the instrument error still may range from 3 to 5%. At low velocities such as those below 0.76 m/s (150 fpm), the instrument error can be two or three times greater than this, ranging from 6 to 15%. The new ball-bearing anemometers generally perform somewhat better at low velocities than did the older conventional anemometers. Another source of error is introduced when measur¬ing the cross-sectional area of the airway or entry. Under the best of circumstances, measurement errors, instrument errors, and a host of other minor errors all combine to cause a total error of at least 10% in the velocity calculation. The vane anemometer also can be used with reason¬able accuracy to measure airflows in mine-ventilation ducts. In this application, the anemometer is mounted on a rod and is held at the center of the duct end. For a duct that is discharging air, the average velocity in the duct is 85% of the centerline reading (Northover, 1957). For a duct that is taking in air, the average velocity is 70% of the centerline reading (Haney and Hlavsa, 1976). To measure the airflow discharged from a regulator or from a small hole in a stopping or bulk¬head, a correction factor for the area is necessary. A good approach in this situation is to traverse the area of the regulator or hole, holding the anemometer with an extension rod. This provides an average velocity that is multiplied by 85% of the measured area of the regulator or hole. In all cases, the manufacturer's instrument cor¬rection table must be used and applied properly. For accurate results, the anemometer should be returned to the manufacturer for periodic cleaning and checking. If it is in daily use, the anemometer should be returned about once per year, and proportionally less frequently if the usage is less frequent than on a daily basis. Smoke Tube The smoke tube may not appeal to individuals who believe that good measurement results can be obtained only with expensive, complicated, and fragile instru¬mentation. Nevertheless, smoke works about as well as anything for the routine measurement of low air velocities in mines. The following procedure yields reasonably good results: 1) Two marks are scratched 7.6 m (25 ft) apart on the floor of the airway. 2) The smoke tube is used to release a cloud of smoke in the center of the airway, about 0.9 m (3 ft) upstream of the first mark on the floor. 3) A timed interval begins when the leading edge of the smoke cloud passes over the first mark, and the interval stops when the leading edge of the cloud passes over the second mark. 4) A factor of 20% is subtracted from the cal¬culated velocity to determine the true average velocity, providing a correction for the centerline and for the spreading effect at the front of the cloud. Velocities calculated with the preceding method generally are accurate to within 10 to 15%. In some instances, the cloud from a conventional smoke tube

Jan 1, 1982

By J. H. Rowland, A. C. Smith, K. A. Teacoach

Current regulations for fire suppression systems in underground coal mines to protect conveyor belt installations have been in place since the Coal Mine Health and Safety Act of 1969 was enacted. Over time, the coal conveyer equipment being used and ventilation conditions underground have changed significantly, particularly the width of the conveyor belts and the use of belt air at the face. The effect of these new conditions on the effectiveness of suppression systems during a fire is not known. The National Institute of Occupational Safety and Health (NIOSH) conducted a study to evaluate the effect of air velocity, water sprinkler activation temperature and a limited water application time on the effectiveness of water sprinkler fire suppression systems to extinguish large-scale conveyor belt fires. The fire tests were conducted using both new and used 1.8-m-wide, fire-resistant rubber belt that met the Mine Safety and Health Administration (MSHA) flame-resistant requirement specified in Title 30, Code of Federal Regulations, part 18, section 18.65 (also known as the 2G test). Tests were conducted using standard response sprinklers with activation temperatures of 68° C and 141° C at air velocities of 0.5 and 5.1 m/s. Two tests were conducted at both air velocities for each sprinkler activation temperature, one using a new belt and one with a used belt. The results showed that the suppression system was able to suppress the fires in ten minutes to the point that a miner could extinguish it with a fire hose. However, in several of the tests, the fire reestablished itself a few minutes after the sprinkler water supply was cut off and quickly grew out of control. This report discusses the large-scale experimental configuration, the installation specifications of the fire suppression system and the results and conclusions regarding the effect of air velocity, sprinkler activation temperature and limited water application on the suppression system performance.

Jan 1, 2010

By Rolf Hindstroom

Outokumpu Mintec started development of the pressure filter in 1991, and the first unit was delivered to Tara Mines Ltd. Ireland in 1992. The filter replaced a conventional disc filter and a thermal dryer. The replacement of the thermal dryer has improved both environmental and working conditions. The filter is currently dewatering 80,000 tons per year of lead concentrate, producing a cake with less than 6 wt % residual moisture.

Jan 1, 1995

By K. O. Johnson

Contaminant transport of mine and mill tailings is controlled by the hydrologic flow regime and the geochemical mobility of the contaminants. Contaminant' mobility is primarily determined by chemical reactions occurring within an interface zone between the tailings and soil The large geochemical differences between tailings and groundwater create a disequilibrium in the groundwater with respect to the soils when seepage from tailings enters the groundwater. Precipitation and dissolution reactions involving the major chemistry occur to return the perturbed system to chemical equilibrium between groundwater and minerals. Retardation of trace elements depends upon the chemical character of the groundwater and the adsorption substrates. In the case of uranium mill tailings, the mobility of contaminants is controlled primarily by precipitation/dissolution reactions which neutralize the pH, modify the Eh (redox potential), and produce highly adsorptive substrate for retardation of trace elements.

Jan 1, 1988

By K. P. Pavlich

Strategic planning, including the process of developing competitive strategy, is an integral part of all organizational management; from one person operations to multi-national Fortune 100 firms. The structure of that process varies from decisions and direction based upon one person's intuition to the integration of multiple strategic planning groups from each of a firm's many business units. Everyone has heard interesting strategic planning stories such as the railroad industry's long term failure to realize that they were in the transportation business and not the railroad business, the decision to "give away the razors and sell them the blades", Caterpillar's "SOQ NaP" campaign (Sell On Quality, Not On Price), or the tanker industry's eventual realization that by better managing turn-around the firm could control their largest single cost: depreciation. It is important to remember that very few strategic planning decisions are going to become Harvard Business Review case studies. That fact does not, however, diminish the need for understanding the firm's business, and actively planning how it is going to remain in business in the future!

Jan 1, 1989

By J. V. G. Middleton

The paper gives a comprehensive review of the design considerations which determined the choice of the milling plant, a description of the plant and comment on the operating experience to date. Operating experience will include inter alia a description of the mill liners installed with subsequent changes due to wear patterns, the mill inlet sealing arrangement, steel ball addition, mill outlet sump design, cyclone feed pump liner wear patterns and comment on the efficiency of the linear screens for wood chip and tramp removal. Finally a view on future trends in South African milling practice with respect to type and size of plant.

Jan 1, 1989

By W. M. Aubrey

Cobbing, as used in this; paper, refers to coarse dry magnetics separation. It is applicable when, by its practice, plant cost can be reduced or the value of its products increased by the removal of a barren or lean reject or a high grade final product. This paper attempts to describe cobbing as it is now being practiced, and also the problems that are of concern to the operator and design engineer. In preparation, 16 plants were contacted, all of which were very cooperative with their time and data.

Jan 1, 1958

By Peter Van deVelde

Many companies in North America because of economic or environmental reasons are considering reprocessing material from their waste ponds. The Japanese have developed highly specialized machines and techniques to reprocess industrial/mining wastes from settling ponds. This paper discusses the techniques and results of applying this technology to North American applications.

Jan 1, 1983

By J. D. Shenk

The White Cliffs diatomite deposit occurs in a lacustrine facies of the Quiburis Formation, an Upper Miocene to Pliocene basin-fill sediment of the lower San Pedro Valley. On-going geo-logic mapping has defined an 2.5-3.0 m (8-10 ft) thick ore zone near the mill site, several marker beds, a NNW-trending high-angle normal fault, and a NW-trending syncline. The diatomite has an average loose-weight dry bulk density of 130 kg/m3 (8 lbs/ft3) and is presently marketed outside Arizona for asphalt filler. Current development is projected to yield 3500 mt (4000 st) of finished product, with an estimated 91,000 mt (100,000 st) of finished product obtain-able from several other nearby sites.

Jan 1, 1988

By S. K. Kawatra

Although temperature is known to have a substantial effect on many processes, this parameter has been widely dismissed as insignificant for mineral comminution. For this reason, temperature effects on grinding have largely escaped notice. However, it has been observed that processing plants which are subjected to large seasonal temperature variations show a change in performance which appears to be due to changing feed temperatures. The general effect is an increase of the specific energy consumption as the temperature decreases. In autogenous mills, an increased rate of production of critical-size material has also been observed. This is due, at least in part, to changing rheological conditions in the mill, with the slurry viscosity increasing markedly at low temperatures. Mechanical changes in the rock with temperature, such as increased brittle fracture, is also responsible for a portion of the observed seasonal effect, and may account for this phenomenon being observed only in certain plants.

Jan 1, 1989

By G. G. Marino

Little comprehensive information has been reported on the behavior of room-and-pillar mines. The objective of this paper is to present case data on mine failures in the Illinois basin for use in practice. Presented are results of an ongoing study and details on the site characteristics of cases where sags have developed on the surface. Site data are reported to show the geologic, mining, and sag conditions that existed. Sags mainly develop from pillar, floor, or pillar-floor failure. The character of the sags depends upon the type of mine failure as well as the overburden response.

Jan 1, 1989

Due to the relatively remote location of the St. Anthony Mine, the high cost of transportation and milling, plus the low grade nature of the deposit, the United Nuclear Corporation began investigating methods of mechanical upgrading approximately eighteen moths ago. This investigation culminated in the installation of Model 17 and Model 18 ore sorting machines. The machines are marketed in the United States and Canada by Ore Sorters of Canada (Ltd.). The installation of this advanced technology will enable United Nuclear Corporation to fully realize the residual potential of St. Anthony.

Jan 1, 1979

By D. S. Bloswick

An investigation an4 analysis of slip/fall accidents specifically pertaining to underground coal mines was conducted. From a population of 751 accident reports, three major sources of injury which account for over 80% of the incidents have been identified. The specifics of this study are presented in this paper. Based on the results, several recommendations are made to reduce such accidents in underground mines. In addition, a brief discussion of the slip-hazard analysis laboratory at the University of Utah, which will be useful in future analyses of these accidents is presented. Work in this facility includes the simulation of certain mining activities in a controlled setting. Foot forces are measured and work methods subsequently developed to minimize the slip potential of these activities.

Jan 1, 1988