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By John A. Haggman

Philippines is a country that is richly endowed in mineral wealth. In 1988, Climax Arimco Mining Corp. (CAMC) geologists found the Dinkidi porphyry gold-copper deposit in Nueva Vizcaya province. It is the most significant mineral discovery in that country in recent times. To date, the company has defined indicated resources of 124 Mt (136 million st) of 1-g/t (0.029-oz/st) gold and 0.4% copper. This includes a high-grade core of 7.9 Mt (8.7 million st) of 6-g/t (0.175-oz/st) gold equivalent. Total contained metal is 124.4 t (4 million oz) of gold and 499 kt (1.1 billion lb) of copper. Dinkidi's discovery resulted from initial geologic reconnaissance and recognition of the intrusive complex that is exposed at surface and anomalous in its topographic expression. This was followed by systematic exploration. This includes extensive gradient array induced polarization (IP), ground magnetics, geochemical sampling and diamond drilling. This later defined a further 16 satellite porphyry targets in the Didipio region. Climax was been granted a Financial and Technical Assistance Agreement contract with the Philippine government. It allows 100% foreign ownership of mining projects. After four years of negotiations, Climax was the first company to have such an application granted. Some 120 applications from numerous international mining companies are waiting for approval following implementation of new Philippine Mining Act of 1995. Exploration history Didipio is located 200 km (125 miles) north of Manila at an elevation of about 700 m (2,300 ft) in the remote Sierra Madre mountains. This region remains mostly unexplored. The property is accessed by 25 km (15 miles) of logging track from the town of Cabarroguis, Quirino. The area experiences an average rainfall of about 3,000 mm (118 in.) a year. Most of it falls during the July-to-November typhoon season. Didipio was first recognized as a gold province in the 1970s when native Ifugao and Ilongot hunters discovered alluvial gold in the region. The region had been prospected over the years by local companies. They were mostly prospecting for alluvial gold. However, in 1988, Climax Mining geologists identified the potential of an obscure razorback ridge protruding from the alluvial valley floor. This ridge, later named Dinkidi by Climax, was the site of several small- scale tunnels. Locals had mined narrow quartz stockwork veining and sluiced soft argillic alteration zones, using irrigation canals and sluice boxes to catch free gold.

Jan 1, 1997

By John Mastoris, Kostis Dragasakis, Kostas Kouklidis, Shkurtë Gashi, Halil Berisha, Jenuz Bulica

Titan Group’s environmental policy and Sharrcem’s Corporate Social Responsibility (CSR) are the driving forces behind the development and implementation of a comprehensive Rehabilitation Plan at Dimce Quarry, which is the main raw material source for Sharrcem Cement Plant since the 1970’s, located in the municipality of Hani i Elezit in Kosovo. Based on an Environmental Impact Assessment Study and the approved Mining Plan and also on the principles prescribed in the Guidelines on Quarry Rehabilitation, released by the Cement Sustainability Initiative of the World Business Council for Sustainable Development (WBCSD-CSI), Sharrcem has adopted a quarry operation and rehabilitation process in line with the best practices in the mining and cement sector. This paper discusses the background for the development of the rehabilitation plan and the results of rehabilitation activities, as have been implemented over the last few years. The main objective of the progressive rehabilitation plan at Dimce Quarry is to restore the depleted pit and return it back to the original land owners for resettlement. To date approx. 3,4Ha of former mining area has been restored by backfilling and levelling of the depleted closed pit and returned back to owners, who have built their houses and turned it into a living area again. This Quarry has turned out to be a real composition and practical example of preserving and returning back the natural resources in a state compatible with the surrounding environment and with respect to the needs of the local stakeholders. The motivation for business to engage in rehabilitation activities in the first place lies in the belief that the development and implementation of a progressive and practical Quarry rehabilitation plan and restitution of the land will deliver significant environmental and social benefits that outweigh the long-term rehabilitation costs, while maintaining the company’s reputation.

Jan 1, 2017

By W. M. Ma, W. L. Zhong, Syd S. Peng

In a longwall section that consisted of 7 longwall panels, there were two high pressure gas transmission pipelines across the panels burying from 3 to 10 ft. below the surface. One pipeline was 20 in. in diameter while the other was 24 in. in diameter. In order to investigate the stress conditions sustained by the pipelines during underground longwall mining, strain gages were mounted on the pipelines above panel #3, #4, and #5. Survey monuments were also installed along but near the pipelines. This paper presents a subsidence prediction method and the preliminary results of the pipelines' stress conditions as affected by underground longwall mining.

Jan 1, 1986

By A. E. Halim, J. F. Brune

The 2006 Sago, Darby, and Aracoma mine disasters in the United States (US) forced the US government to implement the 2006 MINER Act and additional regulations that require all US underground coal mines to install and maintain refuge chambers to manage entrapment emergencies, in particular, fires and explosions. However, there is a debate on whether barricading in refuge chambers is a good strategy to survive such emergencies. Australian coal mines are not required to use refuge chambers and, instead, have adopted a strategy that focuses on instructing and training miners to self-escape to the surface. This paper analyzes merits and problems of using refuge chambers and self-escape to the surface to manage emergencies in fires or explosions in an underground coal mine. The authors found that the use of refuge chambers may not be the best strategy during extensive fires or when multiple explosions happen. In these situations, mine rescuers are unlikely able to extract miners who are sheltered in chambers and conversely, self-escape may save more lives than sheltering. Chances for successful self-escape are further improved by regular, externally assessed training such as Level 1 Emergency Exercises required in the Australian State of Queensland. These exercises put pressure on mine operators to ensure and maintain the effectiveness of their emergency management system.

By D. W. Struhsacker

Mineral exploration has evolved into a sophisticated science which uses powerful scientific tools to make mineral discoveries. In addition to their usefulness in performing mineral exploration, these scientific tools can assist the exploration geologist in assessing environmental conditions at exploration sites. During exploration, environmental data acquisition should focus on data collection efforts which can be easily integrated into exploration activities, and should provide information needed for pre-feasibility and preliminary engineering design studies. Environmental studies performed during exploration should also include an environmental liabilities audit and a fatal flaw analysis to assess whether there are any unresolvable environmental or regulatory issues affecting the project. Performing extensive environmental baseline studies during exploration and project evaluation is neither necessary nor recommended. This paper describes opportunities to integrate environmental data collection with mineral exploration activities. This paper also examines how political and communication issues can affect the outcome of permitting efforts, and recommends a strategy to improve the industry's ability to respond to political challenges and to communicate with the public. This strategy integrates technical and political issues, and implements programs to convince the public of the mining industry's technological achievements and its commitment to resource stewardship and environmental protection.

Jan 1, 1994

By Ryan Marsters, Adam Pring, Robin Dornfest

Raw water supply in the central Rocky Mountains often relies on trans-basin conveyance. Many of these older diversions incorporate high-elevation, miles-long tunnels driven over a century ago in hard rock. Tunnels were excavated using conventional drill-and-blast mining and weak ground was supported by timber sets and other various means. Over time, timbers rot and fail, rock quality deteriorates, and the timbers are gradually replaced by more timber, steel patches and braces, formed concrete, rock bolts, split sets, shotcrete, and other means which are commonly applied over existing support, thereby reducing tunnel cross sections, obscuring previous support systems, and rarely addressing the failing rock itself, leading to further deterioration of both the rock and the existing support. Traditional investigation techniques to assess compromised areas are often unfeasible due to access, depth, rubble and voids behind weight-bearing existing supports, confined space, poor invert conditions, poor ventilation, and flowing water. This presentation will discuss design procedures for assessing obscured ground conditions, assigning support classes which accommodate for unknowns, and implementing contractual means to address inevitable surprises or quantity overruns. Case studies include raw water supply tunnels in the Rocky Mountain region constructed between early to mid-20th century.

Dec 1, 2022

By J. Bigu

Ventilation conditions in working environments are usually studied by anemometry or, in complex cases, b using special tracer gases such as SF6 and 85Kr. in conjunction with chromatographic and radioactivity techniques, respectively. In some working environments, such as underground uranium mines, however, use can be made of the natural radioactivity environment (e.g.. 222rn. 220rn, and their progeny) to investigate mine ventilation conditions of practical interest. Theoretical studies and experimental data in several underground uranium mines and mine locations show that certain thoron progeny to radon progeny concentration ratios are very good indicators of ventilation conditions. Furthermore, the growth and decay of radon progeny and thoron progeny provide valuable information on mine air residence and clearance times. Some specific examples have been analyzed, such as bacterially-assisted uranium leaching operations in a partially enclosed stope, and the effect on the underground environment of turning ventilation fans on and off for a period of time. Air residence times and other variables of interest, determined from the mine radioactivity environment, were compared with more traditional techniques, such as anemometry and tracer gas chromatography. These studies were also extended to a wet non-uranium mine which exhibited relatively high concentrations of radon and its progeny.

Jan 1, 1989

By James R. Aggson, Verne E. Hooker

GENERAL CONSIDERATIONS The design of a mine or any underground opening in rock is similar to the design of any other structure, such as a building or a bridge, in one important way. This similarity lies in the fact that the stability of the structure is a function of the loads that will be applied during the structure's expected lifetime. In the case of an underground opening, the applied load is the product of the existing in situ stress field and the concentration of this field that is produced by the extraction of a load¬bearing material. Thus, a knowledge of the in situ stress field is considered a basic requirement in the design process and essential to the eventual stability of the underground structure (Duvall, 1976; Obert, 1972; Merrill and Peterson, 1961; Dahl and von Schonfeldt, 1976; Hedley and Wilson, 1975). The in situ stress field can be used along with the physical properties of the rock masses involved, the ge¬ometry of the various rock types, the geometry of the openings involved, and a failure criterion to evaluate structural stability of a planned mine by theoretical or numerical techniques. This same information can be used to investigate ground control problems in existing mines. In situ rock stress determinations can be separated into three categories: the determination of applied stress, also called the absolute or field stress; the deter¬mination of concentrations of the field stress near open¬ ings; and the determination of changes in rock stress as load-bearing material is removed. The applied stress field is more difficult to determine than are stress changes. Various instruments and techniques have been developed to determine applied rock stress and stress changes in rock. ABSOLUTE OR FIELD STRESSES Theoretical Considerations In the absence of actual measurements, it is often assumed that at any point, the vertical stress is equal to the weight of the overlying material. [ ] where S„ is vertical stress, S is average weight density of overburden rock, and h is depth from the surface. This is normally consistent with actual experience. The horizontal stresses are assumed to be equal and related to the vertical stress through the Poisson effect. [] where Sh is horizontal stress, S„ is vertical stress, and v is Poisson's ratio. The derivation of Eq. 2 is dependent on lateral con¬finement of the rock mass. An increasing amount of information is rapidly becoming available which indi¬cates that the in situ stress field at a particular location cannot simply be assumed to be a gravity-induced stress distribution in which the secondary principal stresses in the horizontal plane are due to confinement and Pois¬son's effect. Rather they can be a complex function of gravity loading, regional stresses, structural features, ex¬cavation geometries, and variations in surface and/or possibly basement rock topography. Furthermore, the underground principal stress dis¬tribution is not necessarily vertical and horizontal as is often assumed. The deviation of the three-dimensional stress distribution from vertical and horizontal can be due to a combination of both topographic (Hooker, Bickel, and Aggson, 1972) and structural features.

Jan 1, 1982

By Allan M. Johnson

Since 1974 researchers at Michigan Technological University have been studying mine subsidence in the Iron River District of Northern Michigan. The district, which was active from 1881-1978, has had numerous cases of subsidence. Much of the subsidence resulted from rock mass failure but some appeared to have developed primarily in the thick glacial overburden which is a typical feature of this area. This latter observation led to the recognition that some of the surface subsidence was due to piping; i .e., loss of overburden material to the mine voids by groundwater flow (Johnson and Frantti, 1978). The Sherwood Mine was the last mine to operate in the district. With its closedown scheduled for late summer of 1978, a unique opportunity to monitor the mine as it flooded was presented. It was reasoned that with the cessation of pumping, groundwater would rise in the overburden and the mine would flood. The physical characteristics of the mine were favorable for piping to occur as the mine flooded. With the permission of Inland Steel Mining Company and the support of the U. S. Bureau of Mines, a project to monitor the Sherwood Mine for piping subsidence began in June of 1978. This paper present aspects of this study pertinent to the piping-induced subsidence events which occurred at the Sherwood Mine in 1980 and 1981, including acoustic emission monitoring of the subsidence activity, hydrologic monitoring of the groundwater regime and the flooding mine, laboratory modeling of the piping mechanism, and analytic procedures which are under development.

Jan 1, 1982

By Frederick K. A1lgaier

The Bureau of Mines' Denver Research Center initiated a subsidence research program in 1978. The short ten goals of the program were to determine practical methods and equipment for measuring subsidence and demonstrate these methods by monitoring subsidence at several mines having mining, geologic and topographic variables typical of those encountered in the western United States. Data from the monitoring program would be supplied to cooperating mining companies and used by the Bureau to accomplish the long term objective of developing and validating subsidence prediction techniques applicable to mines in the West. Subsidence monitoring is being conducted at five mines in Colorado and Utah with substantially different mine plans, mining methods, depths of cover, and topography. The monitoring procedures used at each site are similar and include designing the monitoring network layout, installing the subsidence monuments, initial and periodic surveying of the monuments, and processing the survey data. The network layout, surveying methods, and types of monuments vary according to the conditions at the individual sites and the type of data being collected.

Jan 1, 1982

By Jan E. Stache

Commercial software programs are being utilized to create and maintain a mine subsidence database in conjunction with the U.S. Bureau of mines research on mine subsidence in Illinois. A three-year survey net of monitored structures in an Illinois subdivision was entered as textual information (attributes), on an existing AutoCAD drawing. These attributes can be optionally displayed on the corresponding drawing or extracted as a text file for import to a database program. The database program, dBASEIV, allows combinations of multiple database files for extensive querying capabilities. Subsurface database files can be merged with surface database files to enhance the effectiveness of surface response analyses in mine subsidence research. The geographic information system (GIS), pcARC/INFO, was chosen to integrate existing AutoCAD drawings and dBASEIV database files into a relational database with a graphical representation. The relational database allows users to update either the graphical representation or the database, with the changes being reflected automatically in its alternate format. The increased capacity, through use of a GIS, to query combinations of database files and have the results reflected graphically has significant potential for expediting mine subsidence research.

Jan 1, 1986

By JoAnn Silverstein, Eric A. Marchand

Competition between Thiobacillus ferrooxidans and non-iron-oxidizing heterotrophic bacteria was induced by the addition of glucose to a co-culture of T. ferrooxidans and A. acidophilum in an oxygen-limited environment. Iron oxidation was inhibited as dissolved oxygen was used preferentially for glucose metabolism. Furthermore, as the water became anoxic, glucose was consumed along with the oxidized iron species (Fe3+) during iron respiration resulting in a pH increase from 2.0 to 4.0. Results suggest that biologically mediated acidification of drainage water can be reversed by dispersion of an easy to degrade, soluble, and inexpensive carbon source such as glucose into the subsurface.

Jan 1, 2000

By M. Fornaro

A small size quarrying activity (3 different quarries with an overall production in blocks less than 10.000 m3/year) has been exploiting for a long time the ?Tonalite? deposit of Adamello-Presanella. In 1967, given the outstanding natural beauty of the area, a natural park has been established with the aim of preserving environmental quality and, at the same time, of providing a sustainable development to the area. Because of the potential impacts of a mining activity in such a context, a specific study has been recently carried out in order to define if and how the quarries could co-exist with the park, beyond the ?administrative results? of a classic environmental impact assessment. The paper deals with the process that drove to the conclusion that the activities are not ?a priori? incompatible with the aims of the park. In the opinion of the authors, a responsible quarry management, which must take inspiration from the care given to environment by traditional alpine productive activities (e.g. the use of water, of wood, and of the stone itself), and take advantage of modern technologies in terms of emissions and safety, can be considered not only compatible with the protected area, but even able to positively contribute to the protection of the land and environment (Barisone et al., 2001). A series of specific prescriptions, which have been adopted by the Park Authorities after this study, are also discussed in the paper: only the definition of suitable spatial and temporal limits, the adoption of effective technical practices and a strict control are considered to be able to drive this ?exceptional? activity towards the final goal of real sustainability.

Jan 1, 2007

By Gordon T. Austin

Garnet is the general name for a family of complex silicate minerals having similar physical properties and crystallizing in the isometric (cubic) system. All garnets have the same general chemical formula but vary greatly in chemical composition. The name garnet is derived from the Latin word granatus, meaning like a grain, which refers to the mode of occurrence wherein crystals resemble grains or seeds embedded in the matrix. GEOLOGY Mineralogy Chemical Properties: The general formula for garnet is A3B2(SiO4)3, whereas A can be calcium, magnesium, ferrous iron, or manganese, and B can be aluminum. ferric iron, or chromium, or rarely titanium. The formulas and names of common garnet species are: [ ] Almandite and almandite-pyrope solid solution garnets are the best abrasive types, but andradite, grossularite, and pyrope also are used. All species of garnet have been used as gemstones. The structure of garnet consists essentially of isolated SiO, tetrahedra connected by oxygen-cation-oxygen bonds through the distinct A and B group cation sites. Within this structure magnesium, ferrous iron, and manganese easily interchange and substitute for each other in the A cation position, and calcium does so less readily. Additionally, aluminum, femc iron, and chromium substitute for each other to a limited extent in the B cation position. This ability to substitute or exchange ions without changing the crystal structure is called isomorphism, and garnet is one of the finest examples of a isomorphous series. Because of this isomorphism there is complete solid solution between certain garnet species but not between others. Fig. 1 illustrates these solid solution relationships. Some rare species of garnet are known that illustrate the wide range of cation substitution that the garnet crystal structure can accommodate. They include: [ ] These rare species are not of interest for industrial applications, but can be of interest to mineralogists and the gem industry. Physical Properties: Garnet displays the greatest variety of color of any industrial mineral. Garnets have been found in all colors except blue. For example, grossularite can be colorless, white, gray, yellow, yellowish green, various shades of green, brown, pink, reddish, or black. Andradite garnet can be yellow- green, green, greenish brown, orangy yellow, brown, grayish black or black. Pyrope is commonly purplish red, pinkish red, orangy red, crimson, or dark red; and almandite is deep red, brownish red, brownish black or violet-red. Spessartite garnet can be red, reddish orange, orange, yellow-brown, reddish brown, or blackish brown. A few garnets exhibit a color-change phenomenon. They are one color when viewed in natural light and another color when viewed in incandescent light. Because of the great variation in color of garnet within each species and similarities in color between garnets of different species it is recommended that garnet identification not be based on color alone. The Mohs hardness of garnet varies from 6.5 to 9.0. Grossularite and uvarovite have a hardness of 6.5 to 7.5; andradite is 6.5 to 7.0; and pyrope, almandite, and spessartite are 7.0 to 7.5 in hardness. There are reports of almandite having a hardness of between 8.0 and 9.0. As with hardness, the specific gravity of garnet varies considerably. The specific gravity may be as low as 3.2 or as high as 4.3 depending on chemical composition. Garnet crystallizes in the isometric system with rhombic dodecahedra and trapezohedra the most common forms. Crystals also form in combinations of dodecahedra and trapezohedra or either of these in combination with hexoctahedra. Crystals can have cubic or octahedral faces, but these are rare. Under favorable conditions of formation garnet will crystalize in nearly perfect forms that rival study models. Garnet also forms as irregular blebs, grains, knots, or masses, with or without distinguishable crystal faces, and as coarse- or fine-grained granular masses that appear to be totally lacking in crystal form. The fracture of garnet also shows great variation. In some garnets, particularly those that are well crystallized and glassy in appearance, the fracture is subconchoidal to conchoidal. Other, more poorly crystallized garnets exhibit a fracture that can only be described as uneven. Garnet occasionally has an indistinct dodecahedral cleavage. Certain species of garnet from specific locations have a pronounced laminated structure consisting of planes of weakness along which parting takes place. This parting may resemble cleavage, but since it is mechanical and not related to crystal structure it is not true cleavage. The optical properties of garnet are sensitive to even small changes in chemical composition or strain in the crystal structure. For this reason each species does not have a single index of re- fraction (IR) but has a range of 1Rs. Uvarovite in its pure form should have an IR of 1.870, but in nature samples vary from 1.74

Jan 1, 1994

By Bernard L. Merlo

INTRODUCTION Modern mine management is constantly striving to develop improved mining methods which will not only increase productivity, but will also provide a safer work environment and make the most efficient use of our natural resources. Progress can be seen in this area by tracing mining methods through history. Work that was originally done with hand tools progressed with the age of mechanization to conventional mining, matured to continuous and longwall mining, and the advent of short¬wall mining, a combination of continuous and longwall, has recently been seen. This new method of shortwall mining provides a promising method for safe and ex¬pedient coal extraction. This study focuses upon the planning, design de¬velopment, and operation of the first producing short¬wall unit in the US which was operated in the Pittsburgh coal seam in northern West Virginia. MINE DESCRIPTION The mine is located in northern West Virginia at Grant Town in the heart of the high volatile Pittsburgh coal seam. Originally opened in 1901, the mine has be¬come one of the largest in the US, encompassing an area of approximately 103.6 sq km (40 sq miles). The seam being mined was the high volatile Pittsburgh seam which ranged in thickness from 1.8 to 2.96 m (6 to 91/2 ft). Three types of mining methods were employed: con¬tinuous mining, longwalling, and shortwalling, with each type accounting for 50%, 30%, and 20% of total pro¬duction, respectively. A total of 630 contract and super¬visory personnel were employed to produce the mine's designed annual tonnage of 1.8 Mt (2 million st). There were ten producing sections, eight continuous miners, one longwall, and one shortwall, operating a total of 22 unit shifts per day. Eight shafts, varying in depth from 80.2 to 194.2 m (263 to 637 ft) provided entrance to the Pittsburgh coal seam. These shafts were used for ventilation, portaling, coal hoisting, supply, and emergency escape hoisting. Ventilation was achieved by means of three exhaust fans which provided 707.9 m3/s (1.5 million cfm) of air to the mine and removed approximately 141 584 m3 (5 mil¬lion cu ft) of methane per 24 hr period. The room-and-pillar method was used for secondary recovery with designed barrier blocks between panels of 61 m (200 ft) in width. A double row of blocks was left around each gob area to provide efficient bleeder action

Jan 1, 1982

By David M. Spatz

Anyone who scans the modern literature will realize that concepts of leadership have changed during the past few years. And like change in so many areas of our culture, change has been rapid in the perception of leadership. Many traditional leadership traits are still highly regarded and many of the longstanding personal qualities that improve leadership abilities continue to be effective. In the past, though, leaders could rely on dominance, intimidation and fear to accomplish their goals through the actions of others. In contrast, effective leaders today build relationships, provide vision and guidance, and strive for communication, cooperation, trust and employee satisfaction. Earnest leadership involves moral issues like honesty, integrity, fairness, empathy and respect. Modern leaders guide, facilitate and coach, rather than command and direct. But how well equipped are managers in the mining industry to meet the leadership challenges that lie ahead? More importantly, is he or she becoming a better leader? This article outlines steps to becoming a more effective leader. Management consultants stress that the changes that lie ahead will demand swift organizational adjustments and managers who are equipped to lead during times of change (Boyett and Conn, 1991; Hesselbein et al., 1996; White et al., 1996 and Kotter, 1997). Becoming a better leader begins with self-assessment and a commitment to unify all who depend on one's leadership abilities. Simply defined, leadership is leading others. Contrary to common practice, leadership is not about advancing one's own career but about bringing out the best in others. The beauty of modern leadership, however, is that the path of serving others creates synergies. They benefit everyone, including the leader, those the leader manages, upper management and company shareholders.

Jan 1, 1998

By I. H. Warren, F. A. Forward, D. E. Pickett, Ernest Peters, Alvin H. Ross, I. M. Masters, N. P. Finkelstein, R. Derry, A. W. Fletcher

In this section the chemical, physical, and mechanical principles of hydrometallurgical processes are developed and reviewed. Plant practice is not discussed other than to note the metals which are processed using the various systems that are available. These notations will permit the reader to refer to the appropriate section in Part II of the Handbook for specific details on a particular metal or mineral. The equipment used to accomplish the desired unit operation is de¬scribed. Comparative data are presented to illustrate performance characteristics of unit operations, process, and equipment. The economic efficiency of individual processes is outlined. Some of the chapters contain material that is covered in detail in other sections of the Handbook Such chapters are developed only sufficiently to indicate the specific application of the techniques to hydrometallurgical processes. In this section considerable cross-referencing to the other related sections has been done.

Jan 1, 1985

By James M. Barker, Richard O. Y. Breese

The recognition of perlite as a distinct volcanic glass, and of the arcuate fractures that often characterize these natural glasses, dates back at least to the late 19th century and perhaps into the 18th century (Howell, 1974). Some authors suggest that recognition of perlite dates considerably further into antiquity, perhaps to the 3rd century BC (Caley and Richards, 1956). Most recent definitions identify perlite by the presence of vit¬reous, pearly luster and by the presence of characteristic concentric or arcuate perlitic fractures. As discussed more fully below, arcuate fractures in perlite need not be megascopic. The textures of perlite which commonly occur in deposits range from dense to highly vesiculated to pumice-like. Thus, the classical definition of perlite is descriptively restrictive compared to the natural range of textures and neglects to address the issues of genetic origin and geologic occurrence. In spite of the petrological usage of the term perlite, the in¬troduction of expanded perlite aggregate into industrial markets caused the term to be applied as well to the lightweight, cellular aggregate that is produced through the rapid thermal expansion of milled perlite ore. Perlite is distinguished petrologically from other natural glasses by a silicic or rhyolitic composition by the presence of 2 to 5 wt% total chemical water held within the glass structure and often by the presence of pearly luster and onionskin-like perlitic fractures. Worldwide, occurrences are associated with Tertiary through early to middle Quaternary volcanics and with the glassy portions of silicic domes and flows, with vitric tephra, with the glassy chill margins of dikes and sills, and with the glassy portions of welded ash flow tuffs. Less commonly, perlite is reported in association with the glassy portions of volcanic plugs and lacco¬liths. The perlite carapaces that partially or fully comprise extru¬sive domes and flows are often thick and areally extensive, and thus provide commercially attractive targets for low cost open pit mining. Perlite tuffs and tephras are also important commercial sources. Mining costs are minimized by open pit quarrying and by either bulldozer ripping or blasting. Crushing and sizing facilities are generally close to the pits. Due to the low weight and large volume of expanded perlite, unexpanded perlite that has been crushed and sized is usually shipped nationwide directly to local markets where it is expanded and processed for distribution to end users. The vast majority of international trade is in unexpanded perlite. In the United States, the evolution of the expanded perlite industry can be traced to the late 1930s and early 1940s when expanded perlite aggregate was introduced into gypsum plaster and concrete markets as a substitute for vermiculite (Schundler, Jr., oral communication, 1991) and was promoted for use in a much broader spectrum of products (Howell, 1974). By the early 1950s, end user markets were well established and small expanders were numerous east of the Mississippi River. Today, mining and expan¬sion is undertaken throughout the world. Worldwide production of perlite is dominated by the former Soviet republics, the United States, and Greece. Total worldwide production of processed perlite during 1990 is estimated at roughly 1 778 000 tons (Davis, 1991). The physical properties of expanded perlite that give this prod¬uct unique commercial value include: low bulk density, chemical inertness, high insulating ability, nonflammability and fire resis¬tance, and its ability to retain water. These and other physical properties give expanded perlite value in such uses as: lightweight acoustical and thermal insulating aggregate; component in plaster, insulating cements and lightweight concrete; loose fill insulation; as aggregate in horticultural applications; and in milled form as filter aid. In the United States and Europe, the largest end use is within building construction products.

Jan 1, 1994

By Thorvald Wetlesen

Computer controlled drilling is now proven technology. It was first introduced by the development of the Furuholmen system for a prototype three boom tunneling jumbo in Norway in 1978. Now, 13 rigs with this concept are in operation in Europe, 3. in mining in England and. 10 in tunneling elsewhere in Europe. The system is also adapted to roadheader guidance. Practical experience has shown that the computer control system makes it possible to drive tunnels with a more accurate contour thus reducing the total amount of rock excavated, and where a full concrete lining is required a reduction in concrete volume is achieved. The total tunneling economy is improved. In the future we expect to see a wider range of instrumentation on jumbos, from the simple direction instruments to computer guidance systems for monitoring only, as well as fully automatic drilling to a programmed drilling pattern. More compact and reliable electronics will be available. Systems with low power consumption will fit easily into flameproof applications. Cabling complexity will be reduced by connection of sensors to serial signal lines.

Jan 1, 1989

By W. M. Ma, Daniel W. H. Su, K. Centofanti, Yi Luo, W. L. Zhong, Syd S. Peng

4.1 INTRODUCTION There have been numerous methods developed for predicting the final subsidence and final displacement profiles (Voight and Pariseau, 1970; Brauner, 1973a; Kratzsch, 1983). But for discus- sion purposes, they can be classified into six categories: theoretical, profile function, influence function, graphical, physical, and numerical modeling. The theoretical method employs mainly continuum mechanics theories and attempts to explain the mechanisms that lead to sur- face subsidence. Many models using nearly all kinds of material behavior have been developed. These include elastic (Salmon, 1963; Berry, 1964), plastic (Pariseau, 1968), viscoelastic (Iman, 1965), and elastoplastic (Dahl, 1969). The Profile Function Method is essentially a method of curve-fitting against the measured subsidence profiles in a particular mine or region. There are more than 20 profile functions developed empirically for nearly all major coalfields in the world. These include, to name just a few representative ones: Hungary (Martos, 1958), Japan (Hiramatsu and Oka, 1968), Russia (Avershin, 1947), United Kingdom (Wardell, 1965), and USA (Peng and Chen, 1981; Karmis et al., 1984). The NCB's graphical method in the subsidence Engineers' Handbook (1975) also belongs to the profile function method. The influence function method was first proposed by Bals (1931/1932). It was further developed in various periods and stages by Knothe (1957), Liu and Liao (1965), Brauner (1973a) and Marr (1975). This method is now widely used in various parts of the world. The physical models include sand (Litwiniszyn, 1959; Pariseau and Dahl, 1968) and gelatin (King and Whetton, 1958; Khair et al., 1986). They are used mainly to study the parameters that control subsidence behavior. The most popular numerical method is the finite element technique. It can simulate nearly every conceivable material behavior, inhomogeneity, bedding planes, anisotropy, and various boundary conditions. This versatility is absolutely necessary considering the ever-changing geologic and mining conditions encountered. In the following sections, only those methods that have been applied to US coalfields will be discussed. Furthermore, the methods for prediction of several key parameters such as maximum subsidence, maximum possible subsidence, and maximum displacement are discussed first, because they are the key parameters to be used in the profile function, influence function, and graphical methods.

Jan 1, 1992