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By P. A. C. De Ruiter

The Lower Cretaceous salt deposits of the Gabon Basin and Congo Basin were said down on ton of an Burly Cretaceous Lato Jurassic, continental graben fill that represent!) the rifting phase of the Afro-American continent. The salt 13 characterized by high percentages of potash and magnesium salts and the scarcity of sulphates and carbonates. The salt probably originated from a brine that was already enriched in high-soluble salts before entering the Gabon Congo basins. Their low-solubility equivalents are found in the Cuanza Basin of Angola. Commercial mining of the potash salt is only possible in those onshore areas where it is essentially undisturbed, shallow and of the right chemical composition. These conditions are net in Congo where the Holle mine produces from rich sylvinite deposits.

Jan 1, 1978

By Nobuharu Isago, Atsushi Kusaka, Kosuke Kawata

"Strong earthquakes occur frequently in Japan, and some rock tunnels have sustained severe damages on their permanent lining. Many road tunnels, which were constructed by conventional steel arch support and timber lagging method, exist in Japan and they need risk mitigation measures against earthquakes as per our empirical knowledge. Many reinforcing measures for deformed tunnels that may be effective against earthquakes are developed; however, behaviors during earthquakes are not fully understood.In this study, static loading tests and numerical analysis, which simulate a loading condition during earthquakes, were carried out to clarify the effect of the countermeasures. The Load-bearing capacity is estimated for the tunnel structures facilitated by the installment of an inverted arch; however, a joint between inverted arch and sidewall become structural weakness. Rock bolts and carbon fiber sheets have a potential able to mitigate the risks of collapse of the lining by the forces from an earthquake.INTRODUCTIONA number of rock tunnels with no apparent unfavorable ground conditions suffered severe damage, including the collapse of their permanent lining, in large seismic events such as the Chuetsu Earthquake in 2004 (e.g., Mashimo 2005). Since these tunnels were considered to exhibit the required structural strength to survive earthquakes, studies are being carried out to clarify the mechanical behavior of tunnels during earthquakes and their damage mechanism (e.g., Kusaka et al. 2009); however, the aseismic design methodology for mountain tunnels has not yet been established.In many cases of earthquake-damaged tunnels, some defects already existed, such as improper construction and deterioration of lining concrete. Although countermeasures are usually implemented against such problems, their earthquake-resistant effect was not fully understood.In this study, static loading tests and numerical analyses to reproduce these tests were carried out assuming that a rock tunnel was affected by the earthquake to clarify the mechanism of the lining damage and the effect of the countermeasures."

Jan 1, 2016

"Iron ore is the source of primary iron for the world’s iron and steel industries. Its production can be reported as crude ore, usable ore or iron content of ore. Historically, the U.S. Geological Survey (USGS) used reported crude ore production from China in tabulations of world iron ore production while other countries have typically reported their production in terms of usable iron ore. When China’s crude ore production was tabulated with usable ore production from other countries, world iron ore production totals have been overestimated by 10 percent to a high of content and may include products such as concentrates, direct-shipping ore, pellets, and sinter.• Iron content, also referred to as metal content or grade, denotes the amount of elemental iron in the crude or usable ore.BackgroundIron ores consumed in the steel industry typically require an iron content greater than 58 percent before being considered commercially usable. Iron ores that are not commercially usable must undergo beneficiation to raise the iron content. Approximately 98 percent of the world’s usable iron ore production is consumed in blast furnaces to make pig iron, which is further processed to make steel.High-grade iron ore mines can supply usable iron ore, known as direct-shipping ore, to blast furnaces, with minimal physical processing and no beneficiation. With direct-shipping ore, the reported production for crude ore and usable ore are the same. Ore from low-grade deposits must undergo beneficiation to increase the iron content before it can be used by the steel industry. In this instance, the mined material is called crude ore and post-beneficiation concentrates are called usable ore; the amount produced will be less than the crude ore amount. With the notable exceptions of countries such as Australia and Brazil, most of the world’s iron ore deposits are low-grade and require beneficiation."

Feb 1, 2017

By J. P. Matoney

The operation of a modern coal preparation plant, particularly in western Canada, is a very complex task. Most western Canadian operations are processing two or more, sometimes up to ten, different seams through the same plant. This requires a sophisticated multi-circuit plant that needs close operational control. Add the soft nature and large amounts of natural fines of western Canadian coal and you have a formidable cleaning task. To assist in the operation, programmable controllers and sophisticated control concepts are being more widely used. Two of the newest coal preparation plants in Canada have been designed by Raymond Kaiser Engineers Inc. and its Canadian subsidiary, Phillips Barratt Kaiser Engineering, Ltd. The use of programmable controllers and control systems will be illustrated by showing their application in a "typical" western Canadian coal plant. This example will cover flowsheet design, control concept systems application, and possible future uses.

Jan 1, 1983

By G. B. Walker

The success of Heavy Media Separation, the static sink-float process, is evidenced by the operation of an estimated 300 installations treating many millions of tons per year of a wide variety of mineral products ranging in value from gravel to diamonds. The static heavy media process is usually limited to the treatment of plus 1/4 inch material. Mr. Victor Rakowsky, who was largely instrumental in the development and application of heavy media separation, recognized the need for a new apparatus and process which would extend the application of heavy media into the finer size range without placing a restrictive limit on the top size of the feed. He recognized the requirement for the application of centrifugal force to augment the force of gravity in separating fines by sink-float techniques.

Jan 1, 1966

By C. Y. Haas

Of all the industrial clay minerals, attapulgite probably enjoys the widest variety of applications. A review published over three years ago by Haden and Schwint (18) cited some 80 individual uses, a list which continues to grow. In its near half-century of commercial life, attapulgite has received a generous share of research study and patent development effort, both on the part of producers as well as consumers. This work has been divided between understanding the mineral's structure or properties and applying it to specific end-uses. Naturally, information gained from the former has pointed toward opportunities in the latter. References of particular significance are cited throughout the text. Attapulgite's variety of uses derives from the unique three-dimensional structure and needle-shaped particle form of this crystalline hydrated magnesium aluminum silicate. Its inherent colloidal and sorptive properties are well known, and distinguish it from its sister clay minerals. Attapulgite is characterized by its high surface area, porosity, sorptivity, and decolorizing power. Its slips or slurries are viscous and thixotropic, however, unlike bentonite are not flocculated by electrolytes. In Table I are compared the general properties of attapulgite, bentonite, and kaolin. The properties in Table I are documented in greater detail by the wealth of scientific literature which has been published on the composition (14)(15), structure (6)(16), surface (16)(4)(22)(24), adsorption (31)(4)(5)(25), rheology (10-11)(12)(13)(26)(27)(32), plasticity (30) (31), and chemistry (23)(3)(7) of attapulgite. Attapulgite is the principal mineral constituent (70 to 80%) of attapulgite clay as it is commercially produced in the Georgia-Florida area of the United States. As mined, this clay also contains 10 to 1S% montmorillonite, sepiolite, and other clays; 4 to 8% quartz, and 1 to 5% calcite or dolomite. (18) During processing, non-clay fractions are removed so that commercial products are enriched to 85 to 90% attapulgite. By wet processing (such as practiced in the

Jan 1, 1971

By Antonio Rivera

On Nov. 13, 1985, Colombia's Ruiz volcano erupted, killing an estimated 25,000 people and burying several villages. Damages were estimated to be about $US300 million. The following is an account by SME member Antonio Rivera of the volcanic activity that led to the eruption. His account also includes a description of the geography and some geology of the affected area. Mining operations in the area were mostly unaffected, although some operations were forced to close until the roads leading to them could be repaired. Introduction The Ruiz volcano is located on the Central Cordillera of Colombia about 28 km (17 miles) southeast of Manizales, the capital of the state of Caldas. Ruiz is one of nine volcanoes that form a complex volcanic chain within the middle portion of the Central Cordillera. The Cordillera has 30 other volcanoes in the southern part of Colombia. Ruiz volcano Ruiz's elevation is 5200 m (17,060 ft). It is covered by an ice cap estimated to be 20 m (66 ft) thick at its summit, an area that covers 17 km2 (6.5 sq miles). Drainage is composed of several rivers that flow into the Magdalena River on the east and Cauca River on the west. The rivers flowing to the east are Guali, Azufrado, Lagunillas, and Recio. The rivers that flow to the west are Claro, Molinos, and Chinchina. There is a road from Manizales to El Refugio, a ski area located on the northeast flank of the volcano at 4800 m (15,750 ft) in elevation. The Ruiz volcanic complex was built in two stages. The first is a shield type of volcano (mainly lavas) formed about a million years ago. The second is a younger stratovolcano overlaying the ancient one. It consists of lavas and pyroclastics and was built over the past 500,000 years. Twenty-four eruptions of Ruiz are known to have occurred during the last 14,000 years. Its products mainly consist of lava flows, pyroclastic flows, mudflows (lahars), and directed lateral explosions. Historic eruptive record 1595 - Debris avalanche, blast, pyroclastic flows, mudflows, ash flows, and ash fall. 1828-1829 - Ashes (phreatic). 1831-1833 - Gas emissions and ashes. 1845 - Mudflows and pyroclastic flows. 1985 - Sept. 11- Fumarolic activity, phreatic eruption, ash fall, and small mudflows. 1985 - Nov. 13 - Ash and pyroclastic fall, major destructive mudflows (magmato-phreatic eruption). From 1845 through 1984, Ruiz volcano always had a slight fumarolic activity. It was restricted to the crater area. In November and December 1984, the fumarolic activity increased and the first ash emission and vapor-sulfur formation started. Small local earthquakes accompanied these volcanic activities. The volcano had a small erup¬tion on Sept. 11, 1985. It was manifested by phreatic explosions that ejected fragments of the vent and formed ash deposits 25 mm (1 in.) thick around an area 2.5 km (1.5 miles) from the crater. Fine material was blown by the wind and reached Manizales and neighboring areas, producing a small layer of ash up to 10 mm (0.4 in.) thick.

Jan 2, 1986

By H. W. Newcomen, D. R. Brox

Assessments of the stability performance of open pit highwalls have traditionally been based on consideration of surface movement rates. Although generally accepted in industry, this approach presents challenges for establishing appropriate threshold values to allow for safe mining operations and does not address the issue of total strain. Surface movement monitoring data from a limited number of open pit mining operations in North and South America has been evaluated in terms of highwall strain, rock mass quality and inferred mechanism of instability. Threshold strain levels for key stages of highwall stability proposed from previous work have been reviewed and are generally endorsed based on evaluation of additional data. An empirical highwall strain criteria for the assessment of highwall stability performance is postulated based on the observed trends in highwall strain data from the case histories presented.

Jan 1, 2004

By Angelina Anani, Nathalie Risso, Gail Heath, Dean Riley, Nilufer Akbulut, James Werner, Víctor O. Tenorio

Implementing a Digital Twin at the San Xavier Mine Laboratory (Sahuarita, AZ), requires a network redesign with a robust architecture. The goal is to create an ecosystem in where all personnel and equipment can be monitored in real-time from the University of Arizona campus, visualizing the site in a digital terrain model. A wireless mesh will help to test robots with autonomous features. Expected outcomes include data retrieval and analytics, the evolution of communications and safety protocols, tele-operation, and an innovated approach for managing the site with new supervision challenges. A timeline with expected commissioning benchmarks is also included.

Feb 1, 2024

By Rafael Moure

On April 21, 1980 the Oil, Chemical and Atomic Workers Union (OCAW) submitted a petition urging the revision of the Mine Safety and Health Administration (MSHA) permissible exposure limit to radon daughters in underground mines. This petition asks for: 1. Annual worker exposure to be lowered from the current 4 WLM/year to 0.7 WLM/year; 2. Full economic protection for workers whose exposure exceeds the proposed 0.7 WLM/ year; and 3. The primary means of lowering workers' radiation exposures shall be environmental controls. I will present the scientific rationale for the lower standard requested in our petition to the Department of Labor. [1. Radiation Exposures to Uranium Miners] Two types of radiation exposures are present in the environment of uranium mines: A. [External Exposure] to gamma sources which until 1978 was considered as negligible compared with internal alpha radiation. R. E. Utting (1), in an investigation of three Canadian uranium mines, found levels of exposures adding to an annual dose equivalent of 3 rems (30 mSv)/year. He concluded that gamma dosages may be a major fraction of the maximum permissible dose for many individual miners. The U.S. experience has shown that there is significant gamma exposure in U.S. uranium mines and, therefore, it could contribute to the total radiation exposure to the lungs in combination with internal alpha radiation. Before ventilation improvements in uranium mines, the contribution of external radiation to total lung dosage was relatively small. After improvements in ventilation, the reduction in internal radiation exposure appears to be in 1980 as low as 1/10 of the 1950 dosages. However, ventilation improvements do not affect external gamma radiation. Gamma radiation remains at the same 1950's level, and it represents today a higher proportion of the total radiation burden to the miner's lungs. MSHA regulations (57.5-47) state that if gamma exposure is below 2.0 milliroentgens per hour, then workers are not required to wear gamma dosimeters and cummulative gamma radiation records need not be kept. Assuming an exposure of 1.9 milliroentgens per hour per 173 hours/month for 12 months,a miner would accumulate a dose from external radiation of 3.9 rems/ year. This dosage would, of course, go unrecorded. MSHA, therefore, should consider a downward revision of the external radiation permissible exposure limit of 2.0 milliroentgens/hour. MSHA should make clear that this exposure level, when added to the internal exposure, does not make for sound health physics -even though the measured current levels do not approach 2.0 milliroentgens/hour. B. [Internal Exposure] to alpha radiation is still the larger contributor to lung irradiation in uranium miners. The target organ is still the lung. The parameters to be considered in determining the biological radiation load appear in Table I for radon daughters present in the upper respiratory tract (URT). TABLE I RADIATION DOSE PARAMETERS IN THE URT OF URANIUM MINERS Parameter Uranium Underground Mining [1. Quantity of the Absorbed Radon daughters (Po-218, Nuclide Pb-214, Bi-214) deposit in bronchial and lung tissue. (Measured by air concentration, Working Levels) 2. Type of Radiation Emitted Alpha Particles 3. Energy of Radiation High-Linear Energy Transfer 4. Half-life of the Nuclide Ra 222, 3.8 days in the Organ Po-218 (RaA), T1/2 = 3.1 minutes Pb-214 (RaB), T1/2 = 26.8 minutes Bi-264 (RaC), Vi = 19.7 minutes 5. Selection Factor of the Direct inhalation with mine Organ dust to be deposited in the tipper Respiratory Tract 6. Mass and Form of the Organ Especially cancer sensitive, tracheobronchial region and bronchi* 7. Distribution of the Activity Dependent on deposited dust in the Organ distribution in the Upper Respiratory Tract 8. Chemical Nature of All compounds (RaA, RaB, RaC) Incorporated Substance biologically insoluble. (Only localized, irradiation) *See Reference (2)] The parameters of Table I depend, in turn, on the demography of the exposed population, especially: 1. Age 2. Sex 3. Health Status 4. Genetic Constitution 5. Lifestyle (Smoking, Diet) Some of these demographic characteristics of uran-

Jan 1, 1981

By J. S. Hall

The productivity and fuel efficiency of iron-ore blast furnace operations has greatly increased in recent times. These improvements, particularly to the Japanese steel industry, have primarily arisen from process engineering studies of the blast furnace and associated operations such as sintering. The development of fluxed sinter based on iron-ore fines reacted to produce highly reducible, low slag sinters has contributed further to a reduction in fuel requirements. The Pilbara province of Western Australia is a significant source of these iron-ore fines supplied to the international market. Increasingly, this market is being offered high quality ores from other foreign sources. To technically assist companies in improving the processing efficiency of ores, and to improve the technical marketing of ores by modelling the processing characteristics of Australian/international ore blends, the Commonwealth Scientific and Industrial Research Organization (CSIRO) is actively assisting the industry by researching the general theme of 'iron ore from mine to metal in this paper we outline progress towards a numerical description of: a. ore deposit classification. b. Degradation during transport. c. Direct reduction of iron ore. d. Liquid bath ore reduction/smelting. e. Industrial sintering.

Jan 1, 1986

By Alan Rhodes

This study is initiated to investigate the efficiency of separation of mineral slimes using electroflotation as compared to that of column and conventional flotation techniques. Important parameters such as collector concentration, pH, current density, aeration rate, etc., have been studied. The results indicate that electroflotation can be used more efficiently in processing rutile slimes (10 µ) under certain operating conditions.

Jan 1, 1982

By E. Wm. Heinrich

Glass sands fall into that extremely select category of mineral deposits that requires a fantastic degree of natural concentration (95% +) of a single component before they can even be considered as ores suitable for further refinement. The combination of geological factors that has produced such an environment of "mineralogical single-mindedness" has appeared only rarely. Factors that require consideration in the economic evaluation of a potential glass-sand deposit can be grouped into three categories: 1) geological (e.g., size, shape, structure); 2) petrographic (e.g., grain size, accessory minerals, nature of iron contaminants); 3) geographic - political (e.g., proximity to consumer, size of market, zoning restrictions). Of particular con ern is the nature of the iron contamination. Iron-bearing species appear as 1) accessory mineral grains, either detrital or authigenic, 2) cements, 3) grain coatings, and 4) quartz-grain inclusions. Selection of the cheapest form of beneficiation requires precise information on the mineralogy of the iron species and their detailed petrography. Because of the antipathetic relationships, in many parts of the United States and Canada between the geographical locations of glass plants and the geological distribution of glass sands, the selection of ac suitable source for a particular glass plant may be dichotomous. One may seek either an exceedingly pure "classic" type glass sand that is relatively distant and whose cost includes a major transportation charge or a relatively proximate and somewhat "impure" source whose cost includes a substantial fee for beneficiation.

Jan 1, 1974

By K. D. Luxbacher, J. T. Davis

"A wind tunnel was designed to examine air flow, heat transfer and layering near an active fire at a working face. This tunnel simulates an active entry in an underground coal mine including an attached cross-cut of similar dimensions. A steel rectangular duct 1 ft. (0.305 m) tall, 3 ft. (0.914 m) wide and 10 ft. (3.05 m) long composes the main body of the tunnel and represents a mine entry. Air flow is generated by an exhausting centrifugal fan attached to one end of the crosscut. This fan was sized to supply air velocities based on Froude scaling. A 6 in. (15.25 cm) propane burner is used to simulate fires of various heat release rates at the working face. Thermocouples are used to map heat layering in the tunnel. Ports are installed for the introduction of tracer gases into and from sampling the system. Barometric, differential pressure, and temperature sensors are also included to monitor environmental conditions. Details about the design and testing of the system are presented including an overview of how the tunnel was scaled to accurately represent fire and flow phenomena. Finally, the proposed use of the tunnel for better understanding of mine fire phenomena and prevention is given. INTRODUCTION Fires in underground mines have been a concern since the dawn of mining. While technological advancements, regulations and best practices have improved both fire detection and firefighting techniques, mine fires continue to represent high risk events. From 2006 through 2015, fires accounted for 1.06% of fatalities in underground coal mines and 0.85 percent of fatalities in all underground mines in the United States (U.S. Department of Labor, 2006 to 2015). In addition to the risk of loss of life, mine fires can cause millions of dollars in equipment damages and lost production revenue. Extensive research has been conducted on how fires occur and spread in underground mines. In addition to testing conducted by government agencies such as the Mine Safety and Health Administration (MSHA) and the National Institute for Safety and Health (NIOSH) (e.g.(Liming, 2006), researchers like Verakis and Dalzell (Verakis, 1988) and Lowndes, et. al. (Lowndes, 2004) have furthered this field by studying ignitions and propagation of conveyor belt fires. While the studies of belt fires in mines are extensive, studies focused on fires at the working face are few in number. The particularly confined space and limited access to a working face, coupled with less robust, temporary ventilation controls create a unique environment that warrants special attention. Separate from studies on mine fires, the use of tracer gases to characterize flow patterns in normal mining ventilation is well established. In 1982, Timko and Thimons (Timko, 1982) outlined current and future applications of sulfur hexafluoride (SF6). However, little experimentation has been conducted to study specifically how tracer gases might be used to evaluate active mine fires and the fires’ effect on the surrounding mine environment (e.g.(Lindsay, 2014). In order to better understand the dynamics of smoke layering from a fire in an enclosed space, a small-scale apparatus was designed to map smoke layering and to examine other aspects of fire behavior at a working face. In addition to studying smoke flow around an active fire, experiments will be conducted using tracer gases in order to determine how they might be used to evaluate an underground fire."

Jan 1, 2017

By D. Arku

The increased use of sensors to facilitate automation has led to an explosion of data. As data sets grow in size, their use becomes more complex. Therefore, there is an incentive for reducing the size of the datasets, as long as this does not compromise information gleaning. With this in mind, this project explored basic aggregation as a viable alternative to amassing large amounts of data. The goal of the project was to determine if one would arrive at different conclusions had they analyzed aggregated data instead of raw data. In a mine, operational data is typically used for tracking process statistics, correlation between factors, autocorrelation and multivariate models (for a factor of choice). Therefore, this project compared results from such analyses when it was conducted with aggregated data (AD) with the results of analyses conducted with raw data (RD). The data consisted of one-minute-apart readings from a semiautogenous grinding (SAG) mill on the horsepower, feed rate (tons per hour), rotations per minute (rpm), noise, recycle (tons per hour), density (% solids) and bearing pressure (psig). This data was aggregated by averaging five and 10 continuous (one-minute) observations. Changes in statistical measures between the two approaches were typically within 5% of each other. Differences in correlation coefficients between RD and AD(s) were also within this range. Autocorrelations present within RD were preserved in AD, as long as the time lags were scaled for the amount of aggregation. Regression and neural network models were also developed for power consumption. The prediction performance of developed models was similar whether one used raw data or aggregated data. Overall, it appeared that aggregating the data based on 5- or 10-minute time spans would not have resulted in conclusions (from simple or complex analyses) being different from using raw data. In other words, whether one had used raw data or aggregated data, the conclusions would have been the same, suggesting that time domain aggregation, a common industry practice, is a good alternative to storing high-density data in this case.

By R. McCulloch

Exploration activity in metallic minerals continued to decline in Montana in 1992 as companies either reduced budgets or left the state. The number of active projects dropped another 50% from 1991. Expenditures were 3% to 6% of 1989's 28.6 million. Many of the major mining companies closed offices in Montana. Although depressed commodity prices have hurried the exodus, continuous changes in environmental regulations, as well as the Mining Law of 1872, without regard to economic effect have had the most serious impact. Many companies indicate that Third World countries present a more stable business environment than the United States. Grassroots projects are nearly non-existent, while late-stage programs continue cautiously. Exploration activity continued at the following projects: Garnet, Pegasus Gold; Southern Cross, Asarco; Elkhorn, Goldfields; 7-Up-Pete, Phelps Dodge and Canyon Resources; Miller Mountain, Pegasus Gold; Sheep Creek, Cominco American Resources; Checkerboard, Kennecott and BHP Utah International; Emigrant Creek, Pegasus Gold; and Crevise, American Copper and Nickel. All mineral activity, whether on private, state or federal land, is regulated by the Montana Department of State Lands under three classes of permits - Small Miner Exclusion Statements (SMES), Exploration Licenses and Operating Permits. A total of 230 Exploration Licenses are active in the state with 26 of those being new. However, there are only 433 projects current in Montana, with many of those in the reclaiming stage. The majority of exploration projects consist of individuals expending time rather than money on properties. The number of mines functioning under operating plans declined by one when W.R. Grace closed its Zonolite operation.

Jan 1, 1993

By Fathi Habashi

At the Duisburger Kupferhütte plant in Germany, pyrite cinder is collected from the sulfuric acid manufacturers in that country and processed to recover the nonferrous metals contained in the cinder, before charging it to the blast furnace for iron recovery. A typical analysis of the cinder is given in Table 9-1. The pyrite cinder is mixed with NaCl and treated continuously in a multiple hearth furnace. The evolved gases are scrubbed with water to form a weak acid which is used for the leaching process. Each batch requires about 2 days for leaching. The concentrated leaching solution obtained in the first 15 to 20 hr is sent for copper recovery, while that subsequently obtained, being poor ill metal content, is recycled. The residue, called purple ore, now a high-grade iron ore (61-63 % Fe); is sintered and delivered to the blast furnace.

Jan 1, 1970

By George K. Schenck

INTRODUCTION Recent advances in high-pressure water jet technology can be effectively employed in mining and tunneling. The new equipment is based on available industrial hardware such as pumps, nozzles, and rotary swivels and seals, and is compatible with present mining and tunneling techniques. Principal advantages of water-jet assisted cutting relative to standard cutting are higher production rates, lower dust levels, and reduced fines. When used on rock and coal miners, water jets mean that relatively smaller and cheaper machines can be purchased. If properly applied, the combined effect is lower cost and significantly improved health and safety. While commercial use of high-pressure water blast cutting and extraction of rock (and concrete) already has a firm foothold in Europe, application of this new technique is just beginning in America. This paper begins with current American applications of high-pressure water jets for drills, for slotting and channeling machines, and then discusses the emerging technology for initiating rock failure in conjunction with drag bits on coal plows, continuous miners and boom-type miners (roadheaders). The focus of this paper is use of high-pressure water jets for cutting rock. High-pressure water jet cutting utilizes water above 70 MPa and currently reaches to 300 MPa and above. Some informatfon is included on low pressure "wethead" coal shearers and boom miners with water pressure to about 15 MPa.

Jan 1, 1983

By James T. Tanner

Mica is a generic term that applies to a group of complex aluminosilicate minerals that have a sheet or plate-like structure and with different chemical compositions and physical properties. All micas form flat six-sided monoclinic crystals with remarkable cleavage parallel to the direction of the large surfaces, which permits them to be split into optically flat films; as thin as 1µm in thickness in some cases (Rajgarhia, 1987). Some micas are more easily split than others. For example, muscovite mica found in pegmatites is more easily split into thin films than is phlogopite. Mica found in mica schist is not as easily delaminated as mica found in weathered pegmatites. According to Dawson (1 949), the commercially important mica minerals are: Muscovite-potassium mica (colorless to pale green and ruby) Biotite-magnesium-iron mica (dark brown to black) Phlogopite-magnesium mica (pale yellow to dark brown) Vermiculite-hydrated biotite or magnesium-iron-mica (bronze yellow flakes) Lepidolite-potassium-lithium mica (pale lilac to deep purple) Some micas of less importance are: Zinnwaldite-lithium-iron mica (gray to smoky brown) Roscoelite-vanadium-potassium-magnesium mica (various shades of green and brown) Mica, principally muscovite, is widely used for industrial applications because of its exceptional physical, chemical, electrical, thermal, and mechanical properties (Table 1). Phlogopite and vermiculite follow muscovite in importance. Biotite finds very little commercial application at the present time. Commercially, mica is used in a number of forms. These forms and their description follow: Sheet mica refers to books of mica either mined from hard rock (pegmatites) or from loosely consolidated clayey material formed from the weathering of pegmatites and alaskites. These books can be readily split into thin film or splittings with specific thicknesses ranging from 0.0031 to 0.10 mm (Davis, 1985). Quality sheet mica is graded into 10 quality classifications (Tables 2 and 3). Books of mica that are flawed with excess inclusions, cracks, or folds (A mica) are called scrap mica and are either ground into commercial products by a dry or wet process. Built-up mica was developed in 1894 as a result of the cost and scarcity of sheet mica, and because many satisfactory electrical parts could be made from it (Preston, 1971). This type mica is formed by layering pieces of mica splittings upon one another and binding them together with inorganic or organic binders. These sheets are then pressed together under high temperature. Mica for this process is produced from pieces of sheet mica too small to be punched into electrical parts (Davis, 1985). Reconstituted mica is mica paper produced by forming a mat of very thin delaminated flakes of scrap mica. This mat is usually impregnated with an organic binder, but is also available unimpregnated. It is dried at 110°C. The mica for this process is either produced from the trimmings of a sheet mica operation or from blocks of A type mica (Davis, 1985, Chapman, 1983). Ground mica constitutes by far the largest use of mica, both quantitatively and application wise. It is produced by grinding and sizing scrap mica (also mica concentrate) obtained from five sources, 1) trimming from sheet mica, 2) A type mica blocks, 3) as a byproduct of spodumene and feldspar mining, 4) weathered pegmatites and alaskites, and 5) metamorphic schists. Synthetic mica is produced by crystal growth in a slowly cooled melt of accurately proportioned chemical oxides. Extended cooling times at a specific viscosity result in larger crystals. Many different micas have been formed by this process; however, fluorophlogopite is the most common.

Jan 1, 1994

By Ronald P. Wright

ARAMIDS UNDERGROUND COAL MINING

Jan 1, 1993