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By R. V. Ramani

Control is a vital management function by which operations are brought into compliance with predetermined standards to achieve the goals of an enterprise. Events that are characterized by a low degree of expectation, avoidability, and intent necessarily have a low degree of control. Such events are difficult not only to predict but to control as well. Fortunately, very few industrial situations fall into that category of events. It is an axiom of control technology that in order to control, one must first measure; further to measure, one must know the characteristics of the subject (or environment) upon which the measurement must be made. Finally, if measurements are to be made reliably, the influences that affect the measurement must be known and, if possible, understood. The complete control cycle therefore consists of the following: (1) defining the objective, (2) planning to achieve the objective, (3) putting the plan into practice with appropriate instructions, (4) measuring variables or parameters of interest, (5) transmitting and transforming the measurements to analyze the system's status and to predict the future outcome, (6) comparing these with the defined objective, and (7) determining and taking corrective actions to bring the actual results closer to the objective. The management principle underlying the control cycle is the principle of management by exception. The application of the principle and the frequency with which corrective actions are taken vary according to the purposes of the review and control. For example, the control of a machine operation (e.g., truck on a haul road) may require adjustments and therefore data, analysis, and decisions, in intervals of seconds whereas the review for ore-grade control may take several hours. Reviews, on the other hand, for cost control may be done in intervals of weeks or months. In any case, three specific purposes of the control cycle are: (1) to correct the operation so that it follows the accepted plan closely, (2) to evaluate the operation and predict future outcomes in light of changes in the environment or of more experience, and (3) to review the objectives and modify these to be reasonable and realistic.

Jan 1, 1979

By Roger Holmberg

INTRODUCTION The driving of drifts is a very important aspect of underground mining. It is not unusual for the percent¬age of rock broken during development in a mine using sublevel caving, for example, to be as much as 25% of the total. If one also considers the amount broken for transport, ventilation, and exploration drifts, one can easily understand that the planning and excavation of drifts play a major part in the total economics of the mine (Fig. 1). Increasing mechanization in mining demands larger tunnel areas for transport and mining equipment. With modern machines the hard work involved in using hand¬held pushers is gone, and a better environment is achieved. More rational methods could be used, but much of the experience the working man acquired by working close to the rock face (such as utilizing the natural weak planes in the rock when he placed the drill¬ing holes) has unfortunately been lost. By having sepa¬rate shifts for drilling, loading, and hauling, more atten¬tion has to be placed upon a well-designed drilling pattern. Some reduction in the number of holes required can be achieved with mechanized drilling because of the larger holes that can be produced. On the other hand, it is probably not possible to achieve the same precision as with pneumatic pushers, and it is difficult to utilize the larger holes because these cause more damage to the re¬maining rock. Recently, however, the precision has be¬come very good with the parallel booms and automatic devices for setting the lookout angle (Fig. 2). A larger arch of the drift roof requires a more carefully executed blasting procedure than before in order to prevent rock fall and to insure a sufficiently long stand-up time. In this chapter, empirical relationships that can be used to design an economic and optimal drift blasting design will be presented. The principles of the calcula¬tion method are based upon the earlier work of Langefors and Kihlström (1963) and Gustafsson (1973). COMPARISON OF EXPLOSIVES To provide for the use of various explosives it is necessary to have a basis of comparison. Several meth¬ods have been developed to characterize the strength of an explosive. Some examples are comparison of values given by (1) calculated explosion energies; (2) the ballistic mortar test; (3) the Trauzl lead block test; (4) the brisance test; (5) the weight strength concept; and (6) the underwater test. However, most of these meth¬ods should be used carefully when stating the breaking

Jan 1, 1982

By Robert D. Hansen, Basil S. Fee, Richard R. Klimpel

Despite the importance of froth flotation to the mineral industries as a means of separating various minerals, the commercial flotation reagents used have varied little in the last twenty years. Numerous articles and books are available describing existing flotation chemistry and its application, e.g., Fuerstenau (1962), Fuerstenau (1976), Aplan (1980), Somasundaran (1980), King (1982), Leja (1982), Ackerman, et. al. (1984), Crozier (1984), Hansen and Klimpel (1985). There are many reasons for this lack of significant new reagent development including the general utility and relative cheapness of collectors, such as xanthates, and frothers, such as methyl isobutyl carbinol and the glycol ethers. Another important reason is the inherent complexity of the flotation process itself coupled with highly variable and difficult to standardize feed materials which make reliable reagent comparisons difficult and seriously limit the use of theoretically based studies to "predict" new or optimal reagents. In addition, the higher cost of "specialty flotation reagents demands that their performance attributes be significantly greater than existing general all- purpose commercial reagents – something often difficult to prove in practice. Faced with this situation, a detailed applications research pro- gram [Klimpel (1980 ab, 1982, 1984 ab), Klimpel, et. al. (1982)] was organized from 1979-1985 on mineral flotation with the following goals: 1) the development of appropriate batch laboratory flotation testing techniques sensitive enough and statistically reliable enough to identify small differences in performance between different flotation tests (i.e., between various reagents, even those with relatively minor chemical structural changes); 2) the identification of mathematical models with appropriate numbers and types of parameters that have maximum statistical power to statistically distinguish between various time-recovery profiles; 3) the generation of laboratory and corresponding plant scale data in sufficient quantity and consistency so that the highly interactive nature of the "flotation system9' of chemistry/ equipment/operating conditions could be quantified; and 4) the invention and development of really new and unique reagents for giving improved flotation performance. The goal #1 was achieved [Klimpel (1980b. 1984b), Meyer and Klimpel (1984)l by basically using a simple automated paddle device for consistent

Jan 1, 1986

By E. Lefeuvre

Precambien in age, the phospate deposit under study which outcrops to the south forms a synclinal consisting of only one mineralized horizon. The synclinal strikes SSW/NNE, dips from 30 to 60 NNE and is about 5 km wide. The deposit has been explored by : - trenches and pits about 50 m apart in the outcropping area ; - core drill holes forming lines perpendicular to the outcrop. These lines are about 100 m apart. On each line, the drill holes are about 50 m apart The phosphate layer is clearly visible and has then been defined from the geologicia1 description of drill hole logs. The layer has been divided into two parts : a very rich, altered part at the hanging wall and a poor part displaying opposite physical characteristics, i.e. a fresh and hard rock. With open pit mining in view, the deposit has been divided into a 3-dimension network of blocks, each block measuring 50 X 50 X 100 m. The tonnages of rich and poor ore, PO25, MgO, Si02, CaO and R2O3 grades and the tonnages of barren waste at the hanging wall and the footwall have been calculated for each block. Given the dip of the phosphate layer ranging from 30 to 60° and its relative thickness (between 10 and 15 m), it was impossible or inappropriate to carry out direct calculation by 3-dimension kriging : too many neighboring blocks to obtain sufficient date and impossibility to draw up the morphology of the layer.

Jan 1, 1986

By Aurel Goodwin, Diann Kraft, V. S. Znamensky

This chapter deals with the Mine Safety and Health Administrations's (MSHA] concern and obligations with regard to asbestiform minerals. Asbestiform minerals are defined as the magical group of hydrated, silicate minerals that possess a fiberlike structure capable of being woven into cloth. Their unique combination of properties, such as resistance to heat and chemical attack, high tensile strength, and flexibility was recognized centuries before Christ. Pausanias, the early Greek geographer, speaks of golden lamps, made about 430 BC, with in- combustible wicks of Carpathian flax. The Ro- mans used asbestos as cremation clothes to con- serve the ashes of deceased persons of rank. Charlemagne had an asbestos table cloth that he used to pass through fire to clean (Lanza, 19381. Early recognition of the health hazards associated with exposure to asbestos was documented in the first century by Pliny the Elder, a Roman naturalist, and Strabo, a Greek geographer. Both wrote of slaves with sickness of the lungs, whose occupation was that of weaving asbestos into cloth. This concern for the health of asbestos workers disappeared over the ages. Today, with the use of modern technology, asbestos products have been greatly exploited. The asbestos output has increased over a hundredfold in the past 70 years. World production has jumped from 454 t/y (500 stpy) in 1900 to 4.5 Mt/y (5 million stpy) in 1978. An increase in health problems for asbestos workers accompanied this increased usage. However, it was not until the modern era that the association of asbestos with chronic respiratory disease was rediscovered. Reports were published at the turn of the century documenting the effects of asbestos exposure on textile workers. One such report in 1907 by H.M. Montague Murray described the post mortem findings on a 34-year- old carding machine operator. Murray de- scribed the lungs as showing extensive diffuse pulmonary fibrosis spicules of asbestos. Subsequently, more reports of pulmonary fibrosis following inhalation of asbestos were published, including an epidemiological study of asbestos miners in 1930 (Merewether and Price, 1930), at Thetford, Que., Canada. This study took place at the mine 52 years after large-scale mining of asbestos had begun. But, the cancer- producing potential of asbestos was not established until 1949 when a report by Merewether in England described an excess of cancer of the lung and pleura [the lining of the lungs) among individuals dying from asbestosis (Merewether, 1949). In the past decade much attention has been focused on asbestosis, mesothelioma, and bronchogenic carcinoma, as the three major biological effects associated with asbestos ex- posure. Parenchymal and pleural asbestosis is a fibrosis in the substance of the lung with thickening and often calcification of the membranes lining the thoracic cavity. Mesothelioma is a malignant tumor of the membranes lining the thoracic or abdominal cavities, and bronchogenic carcinoma is a cancer of the lung tissue itself. These diseases occur in various degrees and combinations. The severity and occurrence of these biological effects are directly influenced by conditions such as dose response relationships, intensity of exposure, duration of exposure, lapse of time since initial exposure, and cigarette smoking. Numerous studies indicate that the relationship between these conditions and the incidence of disease is proportional. Congress has recently concluded (Congressional Record, 1979) that, "exposure to asbestos fibers has been identified as significantly in- creasing the incidence of cancer and other severe or fatal diseases such as abestosis." Congress conveys its concerns for the safety and health of the nation's miners through the Federal Mine Safety and Health Act of 1977 in which it gave MSHA the authority to set safe

Jan 1, 1986

By William G. Doepken

GENERAL DESCRIPTION The Henderson mine utilizes a highly mechanized, continuous panel-caving system to extract ore from a deep, massive, molybdenum deposit. The mine site, lo¬cated 80.5 km (50 miles) west of Denver, is situated at 3170 m (10,400 ft) above sea level in a steep valley on the eastern side of the Continental Divide. The mill site, located on the western side of the divide, is linked to the mine via a 15.5-km (9.6-mile) railroad tunnel. Mine production is scheduled to reach 27 215 t/ d (30,000 stpd) from the uppermost production level. This pro¬duction rate will have been reached within the four years following an intensive ten-year preproduction development program. A second production level, due to come on stream in later years, will expand production capabilities to 31 751 t/d (35,000 stpd). The mine, which employs approximately 2000, has blocked-out ore reserves of 220 Mt (242 million st) at an average grade of 0.42% MoS2. Geology The Henderson deposit is composed of two partially overlapping ore bodies that lie 1080 m (3600 ft) beneath the peak of Red Mountain. The ore bodies are entirely within a Tertiary rhyolite porphyry intrusive complex that has intruded Precambrian granite. The de¬posit is elliptical in plan with overall dimensions of 670 x 910 m (2200 x 3000 ft). In section it is arcuate with an average thickness of 185 m (600 ft). The top of the deposit is at an elevation of 2610 m (8700 ft) while the lower limits range from 2340 m (7800 ft) on the west to below 2100 m (7000 ft) on the east. The mineralization is relatively continuous in the ore bodies and consists of molybdenite and quartz in random to subrandom, intersecting, closely spaced veinlets. Cavability RQD (rock quality designation) * values measured from Henderson drill core and compared with the RQD values from the Climax and Urad block-cave mines in¬dicated that the Henderson ore would cave but with difficulty and that a high percentage of the cave ma¬terial would be blocky. Initial caving experience shows the Henderson ore caves easier and with greater frag¬mentation than was indicated by the RQD values. Pos¬sible reasons for this are: 1) The greater lithostatic load at the Henderson has a greater effect on caving and fragmentation than anticipated. 2) The relief of confining pressure due to caving action and brittleness of the rock is enhancing breakage. Mine Layout The Henderson mine layout was designed from its inception for a large-scale, rubber-tired, continuous panel-caving mining system. The ore body is vertically divided into three major mine levels (Fig. 1). The top¬most level (8100 level), which is 2469 m (8100 ft) above sea level, is the current mine production level. The intermediate or 7700 level, which is in the initial

Jan 1, 1982

By J. H. Jennekens

INTRODUCTION "Most people would probably agree that some degree of government control and regulation is essential in modern society, and it will likely continue as an important part of our social organization for the foreseeable future. But most of us tend to be ambivalent about it. In one situation or another we are likely to see government commitment to social benefit programs or regulatory devices either as an expanding encroachment on the freedom of the individual or as an undue interference with private enterprise or with the rules of the market place. But even where there is agreement as to the desirability of government initiatives, either in general or in a particular context, it by no means follows that there will be approval of the mechanisms or procedures used or the means of carrying them out." The above statement is taken from a 1980 Working Paper of the Law Reform Commission of Canada prepared in connection with its study of the exercise of administrative law in Canada and the practices and procedures of administrative tribunals. The Atomic Energy Control Board (AECB) is one such administrative tribunal, and as the federal nuclear regulatory authority, it is responsible for licensing the production, possession and use of nuclear materials, equipment and facilities and enforcing compliance with licence conditions governing the health, safety, security and environmental aspects of the activities involved. Although the AECB was established 35 years ago with the passage in August 1946 of the Atomic Energy Control Act, like many administrative tribunals its role and functions and the regulatory process which it applies have evolved significantly during this period. The changes which have taken place over the years reflect not only the vast scientific and technological developments which have occurred but also the marked differences between contemporary society and the social milieu of the mid-1940s. However, the basic philosophy of nuclear regulation in Canada and the underlying principles of the regulatory process have changed very little. Certainly, the process is far more open in terms of the general public, it has become appreciably more comprehensive and systematic in terms of the depth and extent of both the pre- and post-licensing technical evaluations which are conducted and the ensuing compliance program. Furthermore, it now applies to the whole of the nuclear fuel cycle as well as the industrial, agricultural and medical applications of radionuclides. Nevertheless the following fundamental principles remain unchanged: a. primary responsibility for achieving high standards of nuclear safety and environmental protection in the design, construction, commissioning and operation of nuclear facilities resides with the licensee; b. the credibility of the nuclear regulatory process depends not only upon its technical correctness and practicability, but also upon acceptance by the public-at-large of its perceived effectiveness and efficiency; c. regulatory criteria and principles should be concise, clearly stated and understandable; d. regulatory decision-making should be based upon stated criteria and principles taking into account pertinent scientific and technical facts only; e. fairness and impartiality must characterize all regulatory decision-making; f. the regulatory process should be subject to a comprehensive periodic review and evaluation to ensure that it continues to produce the desired results at justified costs. EXPLANATORY NOTES The mere statement of a set of principles is a relatively simple task. Far more difficult is the explanation of what these principles mean in practical terms. To stipulate that a licensee bears the primary responsibility for achieving and maintaining high standards of nuclear safety and environmental protection may be regarded by some as an attempt by the regulatory agency to evade the responsibilities assigned to it. However, this is not the case. It is unrealistic for anyone to claim that a licensee only complies with accepted norms of public and occupational health and safety and of environmental protection because of the fear of prosecution. The vast majority of citizens conduct their affairs in a proper manner not because there

Jan 1, 1981

By Jinrong (Patrick) Zhang

Improvement of conventional flotation efficiency, separation of carbonates from apatite, recovery of phosphate values from phosphatic clay and other ways of utilizing the clay, disposal of clay slurries and subsequent reclamation of the settling areas, and conservation of resources and energy remain major challenges in the beneficiation area for the phosphate industry. These problems have been actively investigated by the industry, government agencies, and research organizations for decades with modest success. However, some recent research activities have generated promising results and possible new technologies. The dominant position of the Crago process in phosphate beneficiation is being challenged by some of the single stage processing schemes. Heavy media separation enables one producer to process a portion of high carbonate ores. Separation of dolomite from apatite by reverse flotation of carbonates with phosphate depressants showed potential for industrial application. Consolidation of phosphatic clays in mine cuts using a modified "sandwich" process is being tested. Beneficiation in the acidulation plant or grinding at the mines may be considered in the future.

Jan 1, 1993

By Jean-Luc Cornet

As modern conveyors are increasing in size and complexity, their control requirements are becoming more and more critical. In addition to the safety and equipment protection requirements, control systems are now called to implement intelligent drive controls derived from dynamic analysis modelling, as well as to provide fast and accurate diagnostics while keeping operator controls simple. These requirements led to the development of a new and innovative approach to control system development. This paper describes the control philosophy used by Conveyor Dynamics, Inc. (CDI) and some of the key features of our approach to the architecture of control systems.

Jan 1, 1993

By V. T. Vacariu, P. D. Georgescu, N. Tomus

To assess the potential for radioactive pollution unique to the environmental conditions of the Bacau phosphogypsum waste dump, surface samples were taken, drillings were performed on the entire waste dump's height, and the Ra226 distribution on the height and surface considered to contain a medium content of the radium of 0.57 Bq/gr was studied. Thus, the waste dump's radioactive potential was estimated at 30-40 Ci in equivalent Ra226. Also analyzed was the granulometric composition of the phosphogypsum and the distribution of Ra226 on granulometric orders, which indicated that the radium was concentrated in the very fine fractions. Parameters were set up for the classification by hydrocycloning to obtain a fine class (less than 41 microns) having a radium content of more than 0.9 Bq/gr and a coarse class having less than 0.37 Bq/gr. A chemical process was devised for removal of the radium from the phosphogypsum with the possibility for recovering the contained sulfur.

Jan 1, 1999

By Kostas Fytas, Pierre Bousquet, Bill Evanelou

Acid mine drainage (AMD) is a serious environmental problem that preoccupies the Canadian Mining Industry. Considerable amounts of money are spent every year in an effort to prevent or reduce the acid mine drainage phenomenon. AMD occurs when sulphide minerals (ex. pyrite) contained in rock are exposed to air and water and subsequently oxidise to produce low pH water. This acid effluent has the potential to mobilise any heavy metals contained in the rock. Coating the sulphide minerals with silicates is a new promising technology to reduce AMD. Pynte is treated with a solution containing H2O2, sodium silicate and a buffering agent. H2O2 oxidises a small part of pyrite producing ferric iron (Fe3+) ions. These ions subsequently react with the silicate ions to produce ferric hydroxide-silica that precipitates on the pyrite surface producing a passive coating. This silicate coating can protect the grains of pyrite from oxidation. This paper presents a series of experiments that confirm that silicate coating can considerably reduce AMD.

Jan 1, 2000

By L. Sandbak

A geomechanical rock mass classification or RMR is currently being used for the evaluation of an LHD mechanized mining system versus the conventional block caving method. The successes and failures of a Panel lS-19 LHD test block on the 2315 level can be attributed to the geologic and geomechanical zonation present. Trench blasting, caving procedures, and sequencing are other factors that were also considered. Lessons learned from the P.lS-19 test block have been used to alter the design for future LHD production blocks on the 2615 level. These modifications are designed to maximize the pillar and insure an adequate draw connection.

Jan 1, 1988

By Robert A. Jankowski, Charles A. Babbitt, Natesa I. Jayaraman

The U. S. Bureau of Mines, through a contract research program with Foster-Miller, Inc., has identified guidelines for the selection of the most effective water spray system and water flow rates for use on continuous mining machines. Specifically, these parameters were modified to obtain maximum dust control with regard to quartz dust exposure and more stringent respirable dust standards due to quartz. A novel water spray system, consisting of flat fan spray nozzles, mounted across the top of the mining machine, along with high flow, flat fan and higher pressure hollow cone nozzles mounted under the boom has been identified and tested. The anti-rollback/underboom spray system minimizes dust rollback while increasing dust knockdown by its unique positioning of spray manifolds and orientation of spray nozzles. Respirable dust suppression characteristics of the system acted in three ways: - by wetting the surface of the broken coal material to prevent dust from becoming airborne; - by controlling the airflow pattern at and near the face to minimize dust rollback to the operator Is control location; and - by dust knockdown, i.e., airborne capture, or scrubbing of airborne dust from the air. During underground trials, the anti-rollback/ underboom spray system reduced dust levels at the operator's position and in the immediate return by 55 and 15 pct, respectively, when compared to a conventional spray system. Quartz dust levels at the operator '8 position were essentially eliminated, while quartz dust levels in the immediate return were reduced by 57 pct. Applying the concepts of this technique throughout the mining industry should reduce the health hazard associated with excessive exposure to respirable quartz dust, as well as allow coal mine operators to comply with the associated, more stringent, respirable dust standards.

Jan 1, 1987

By D. Park, V. Gall

The three-dimensional finite element technique combined with a progressive failure approach were used to simulate stress distributions in a complete mine section that occur in response to a longwall mining operation. Due to the availability of a Cray supercomputer, a large-scale, three-dimensional, finite-element model was developed for the analysis. The Hoek-Brown failure criterion, which describes a realistic behavior of rock masses, was used for the simulation of progressive failure. A comparison of calculated and monitored stresses in the mine has shown that the model gives a good representation of stresses in the mine structure.

Jan 1, 1992

By T. J. Harvey, W. van der Merwe, J. Joubert

GeoBiotics, LLC and Kumba Resources (Pty) Ltd are jointly developing the GEOCOAT® heap bioleaching technology and downstream processing technology for recovery of zinc from tailings at the Rosh Pinah Mine in Namibia. This paper outlines the development of a computer simulation for the bioleaching of sphalerite and the downstream processing. Computer modeling has shortened the product development cycle by allowing many flowsheet scenarios to be analyzed negating much of the expensive and time consuming laboratory testing. A model was developed using the Limn® system which is an Excel® Add-In flowsheet drawing and solution engine. Given that most engineers are familiar with Excel® this software is extremely easy to use and has less hidden calculations making model verification much easier.

Jan 1, 2003

By Sotiris Psomas, Colin M. Eddie

"Steel Fibre Reinforced Concrete (SFRC) Segmental Tunnel Linings have successfully been used for over 20 years in the UK and have been adopted in a number of high profile projects such as High Speed 1, Crossrail, Thames Tideway, as well as High Speed 2. Tunnel linings and especially SFRC design are not covered in the Eurocodes. This shortage of SFRC tunnel design rules seems to be partially addressed by several international publications. However, in the UK, the ‘design-assisted by testing’ (DAT) approach has also been adopted. The Paper discusses the UK’s best design practice and focuses on the DAT methodology as applied in the case of the 6.9km (4.3miles), 7.8m (25.6 feet) ID Lining for the £635million Lee Tunnel Project. The design approach, the full scale testing at the Building Research Establishment (BRE), and the construction innovations are presented. This experience will be transferred to the £4billion Thames Tideway Tunnel.INTRODUCTIONSteel Fibre Reinforced Concrete (SFRC) has been used for Tunnel segments for more than 20 years. The first application of SFRC in the UK was for the Heathrow Baggage tunnel (1994). Since then significant size tunnels have been designed and constructed, such as the Jubilee Line (1999) High Speed 1 (CTRL, 2006), Crossrail (2014), Lee Tunnel (2014) and the scheduled 25km Thames Tideway (‘Super Sewer’) and High Speed 2 rail tunnels. However one the main obstacles in achieving streamlined design and improving efficiency are the lack of appropriate design guidelines for SFRC tunnel segments. This issue will – to some extent – be addressed by a number of current documents on tunnel FRC design either being produced by BSi (PAS8810, expected 2016), ACI (544.R) and ITAtech (Design Guideline PCFRC, 2015) in an effort to advance the design of SFRC and take into consideration the recent developments in Steel and Macro-Synthetic FRC technology."

Jan 1, 2016

By W. R. Reed

NIOSH continues to conduct respirable dust control research for surface mine blasthole drilling operations. Research areas have included testing variables (shroud leakage area, drill deck cross-sectional area, shroud height, collector-to-bailing airflow ratio, etc.) that have the most impact on respirable dust control, development of a dust collector inlet hood, development of a dust collector dump point shroud, and testing of a small diameter water separating sub. This paper summarizes the results of the aforementioned research that has been completed. Additionally, past dust control research for drilling operations of both underground and surface mines completed by the U.S. Bureau of Mines, created in 1910 and incorporated into NIOSH in 1997, is reviewed.

Jan 1, 2008

By P. L. Dunn, G. T. Adel, E. B. Cruz

Automatic control of fine-coal cleaning circuits has traditionally been limited by a lack of adequate sensors. Although several nuclear-based analyzers are available, none have seen widespread acceptance. In this investigation, image analysis is used for the on-line determination of ash contents in fine-coal slurries. The ash content of a flotation tailings stream is correlated to the mean gray level of the slurry. Based on a 90% prediction interval, an analysis of sensor performance indicates an accuracy of 73[±] 4% ash over a range of from 65% to 90% ash. While the results are comparable, the video-based system costs only a fraction of what a nuclear-based analyzer costs. The sensor is now installed at the Middle Fork preparation plant, which is owned by Pittston Coal Co.

Jan 1, 1999

By G. W. Johnston

INTRODUCTION For many years mining at the Stobie mine of the Inco Metals Co. consisted mainly of fill-type mining for higher grade ores and block caving or blasthole open stope mining for lower grade ores. Open stope mining, although quite favorable in the initial stoping phase, has always presented problems in the pillar recovery phase, especially at depth. In 1966, sublevel caving was introduced. This method is ideally suited for low-grade ore and can be applied very successfully to intermediate or higher grade ores providing proper controls are enforced. Sublevel caving has three distinct advantages: it is highly adaptable to mechanization; it recovers the ore in one operation; and it provides adequate ground sup¬port and safety regardless of mining depth. This method does, however, make extra demands, particularly for new types of supporting services. The constant presence of rock makes quality control of the grade of the ore being extracted essential. Increased de¬velopment, different types of ventilation, roadways, and maintenance are only a few of the many changes re¬quired. The care and maintenance of the fleets of diesel equipment and the modification of equipment is a con¬stant challenge. CHOICE OF SUBLEVEL CAVING The question arises, why mine by sublevel caving? Fig. 1 shows a typical problem encountered by the open stope or blasthole mining method. Near the surface there is little or no ground support problem. As mining progresses to an intermediate depth, however, ground failure starts to occur in the supporting pillars. If open mining is carried beyond this point, the critical depth is soon reached, accompanied by hanging wall caving, ex¬tensive pillar failure, and the danger of losing control of the mining cycle. The rock caved from the hanging wall mixes with and dilutes the ore being extracted from the blasthole stopes. Ore losses occur when pillar failure pre¬vents drilling and development of part of the ore. The interruption to the mining cycle causes serious curtail¬ment in production until ground failure is controlled and the mining method changed to adapt to the new conditions. Having recognized the limitations of open stope min¬ing, alternatives were sought. The first alternative (Fig. 2) was to fill the open stopes with sand fill be¬fore extensive pillar deterioration occurred, recover the pillar ore by fill mining, and then convert to total fill mining below. If the ore grade is high enough it can support the costly fill method. Recovery will be at a much slower rate and will therefore extend over a longer period of time. On the other hand, sublevel caving gives complete primary mining recovery in a short time and is very adaptable to mechanization, which is now a necessity to combat spiralling labor costs and give greater produc¬tivity per man. Sublevel caving is ideally suited as a mining method for low-grade ore bodies which eventually reach a criti¬cal depth for open stope mining. DEVELOPMENT The development phase comes first and of course its main purpose is to gain access to the ore and provide a route for ore removal from the mine. Initially a 20% inclined service ramp is driven in the footwall rock (Figs. 3, 4, and 5). It is preferable to start at the top of a mining block and drive the ramp down¬ grade so gravity can assist in mucking the blasted de¬velopment round, and also access can be gained more quickly to the initial production area. The ramp nor¬mally turns at 3.1 rad (180°) about every 152.4 m (500 ft) to keep it reasonably close to the rock disposal

Jan 1, 1982

By Glen L. Black

Choosing a mining method for an underground orebody is a complicated and often iterative process. Advances in technology have given design teams an array of possibilities for methods and equip¬ment. Hecla Mining's discovery of the deep Gold Hunter ore body challenged the staff at the Lucky Friday Mine to determine the optimum mining method. Taking an ore body from prospect to production requires traditional resource characterization. This includes drilling, delineating and modeling. Developing the mining plan is an evolving process, changing with each new piece of in¬formation as the project progresses through exploration and development. The Gold Hunter deposit is a steeply dipping vein system in the Wallace Formation of Idaho's Coeur d'Alene mining district. Gold Hunter is a misleading name for the ore body. The vein is a silver-rich, lead-zinc deposit with only traces of gold. The Gold Hunter ore body is located about 1.6 km (1 mile) north to northeast of Mullan, ID. The ore body is mined from the Lucky Friday Mine, located 0.4 km (0.25 miles) east of Mullan. Mining began on the vein from an access drift driven from the Lucky Friday Mine's 4900 level. Production from the ore zone is projected to be 771 t/d (850 stpd). The Gold Hunter ore is combined with Lucky Friday ore and milled in the Lucky Friday mill. The combined ore boosted Lucky Friday's 1998 silver production from 62.2 t/a (2 million oz/year) to more than 124.4 t/a (4 million oz/year).

Jan 1, 1999