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By T. C. Rao, N. Suresh, M. Vanangamudi

Experiments have been conducted on a 76¬mm water-only cyclone treating cowl below 2 mm size having different proportion of -0.075 mm fines. The effect of cone angle of the cyclone (compound cone) has been analyzed on water split, separation of -0.075 mm fines, separation of coarse solids, and on separation behavior of individual size ructions of the feed. It has been noted from the results that there exists a linear relationship between the flow rate of water in the feed and flow rate of water reporting to overflow stream. This relationship is independent of the cone angle and, with changes in the fines content in the feed, only the intercept of the straight varies, keeping the slope constant. Further, it has also been found that the percentage of fines below 0.075 mm reporting to the overflow is directly proportional to the percentage of feed wafer reporting to the overflow. This relationship is found to be independent of the cone angle and the fines in the feed. The performance of the water-only cyclone has been analyzed by plotting partition curves for different experimental conditions. In addition to this, the Rosin-Rammler equation has been fitted to the partition curves of the hulk feed and individual size-fractions. Tile analysis of the results has revealed that the specific gravity of separation increases with increase in the cone angle of the cyclone while it decreases with increase in percent fines present in the feed. Mathematical relationships have been developed to relate the variation in SG50 with cone angle and percent fines in the feed.

Jan 1, 1990

By S. J. Parkin, P. Shead

Extraction of coal at Harworth Colliery is undertaken in the Deep Soft seam at roughly 1000m depth where the strata temperature is 42 "C. Production employs the longwall retreating method using high powered mechanised methods to extract coal at a rate of approximately 40,000 tonnes per week from a single face. This paper describes the climatic conditions encountered on a typical district , 6's district, where the initial ventilation set-up was as a typical U-type district which was antitropally ventilated. Under this initial set-up climatic conditions in the intake typically exceeded 30 "C effective whilst in the face area and in the return airway effective temperatures in excess of 32 "C and 33 "C were common . The paper then proceeds to describe the methods employed to attempt to improve the climatic conditions on the district, especially with regard to the coal face and return airways and describes in detail the effects of reversing the district airflow direction, employing homotropal ventilation, on the climatic conditions. The results of this reversal have been dramatic and have resulted in a substantial improvement in the climatic conditions experienced , however problems have been encountered with the control of methane gas since the changeover. The final part of the paper describes the results of computer simulations to analyse the effect of various ventilation designs on the predicted climate for future production districts in order to de- fine a district layout which will produce acceptable climatic conditions in the working zone without the need to use refrigeration techniques and which will improve methane gas control .

Jan 1, 1997

By Wenhua Li, Tsuyoshi Adachi

Resource nationalism is essentially mandatory government intervention in natural resources businesses by political or economic means in order to benefit the nation and the people. It is attacking the mining industry more and more rampantly by all kinds of means since the twenty-first century. Poor countries who count on a resource-led economic growth usually find themselves trapped into “resource curse”. The harmfulness of resource nationalism for investors is that one event can quickly escalate and lead to a chain of events which make projects commercially unavailable. In spite of historical and theoretical social investigations in the causes of resource nationalism, rare studies engaged in quantification of dominant parameters of it. The objective of this study is to find significant factors that dominate the occurrence of resource nationalism for important metal and energy resources producing countries and quantify their marginal effects. The study applies binary choice logit model for panel data using pooled method. One feature of the research is that binary data set of occurrence of resource nationalism are sorted out by authors referencing U.S. Geological Survey’s reports. The results indicate that high-technology export (% manufactured export), ores and metals exports (% merchandise exports), rule of law (world governance indicator), trade (% GDP), and natural resource rent except forest (% GDP ) dominant the occurrence of resource nationalism for high and upper middle income group countries; government effectiveness (world governance indicator), policy perception index (The Fraser Institute), high-technology export (% manufactured export), and mineral rent (% GDP) dominant the occurrence of resource nationalism for lower middle and low income countries. According to our model, probability of occurrence of resource nationalism in 90 countries are predicted. Top 10 risky countries in 2012 are estimated to be North Korea, India, Honduras, Indonesia, Kazakhstan, Burkina Faso, Mongolia, Cuba, Bolivia, and Peru. The study is a primary trial of researching on resource nationalism and provides some insights for theoretical building and simulation on the issue.

Jan 1, 2017

By A. W. Khair

This paper presents an analysis of surface subsidence characteristics in room and pillar mining using physical models and laser holographic interferometry (holometry). The analysis included the effect of various geometric parameters and different overburden materials (sand and gelatin) and resulted in the formulation of a more realistic model material for laboratory simulation of typical geologic overburden. Previous work using this technique involved the use of sand to model over- burden and detailed results are presented elsewhere (1). The main emphasis of this work was to develop a gelatin based mixture which would provide a better model. Initial work during the development of this model included testing various ingredients and monitoring the time dependent characteristics of the model, such as the surface penetration resistance. This value indicated changing deformability/ridgidity of the model with time. Once several models had been developed, holometry techniques were applied. Initial tests showed that the stiffness of gelatin created a bridging effect over the mine models, thus restricting deformation. At this point, a 0.5 inch (1.27 cm.) layer of sand was placed directly over the mine model with the gelatin mixture on top. The approach was to model different zones of overburden movement that exist as an extraction occurs (2). The sand would represent the caved and fractured zones which occur above the excavated area. The gelatin models the continuously deformed zone which occurs between the fractured zone and the surface. Holometry techniques applied to this model yielded successful results.

Jan 1, 1986

By G. L. Bloomsburg, E. G. Zahl

INTRODUCTION During the past decade, disposal of mine and mill waste material has become an increasingly important issue. Problems of structural stability and seepage effects on stability have been well addressed, and significant technological advances have been achieved [(1-4)]. The primary problem currently facing industry in the waste disposal area is environmental protection. The greatest environmental concern is over the amount of seepage or leachate entering the ground or surface water systems. Methods to determine the quantity of water seeping from a tailings pond have also been covered in the literature [(5-23)]. However, much further work is necessary to fully implement these techniques to evaluate tailings pond performance and accurately predict the various influences of disposal management on seepage from mill tailings. This study is an effort to develop those necessary techniques. The partially saturated method of analysis which is discussed here is applicable to most situations involving seepage from waste piles. In a conventional type of tailings pond, a slime layer is ordinarily built up under the ponded area. This material will consolidate slowly from capillary pressures and the weight of material deposited above it. In situations where this consolidation results in a slime layer of lower permeability than the native foundation soil, a partially saturated flow condition will usually exist in the native soil. This will result in a smaller quantity of water entering the ground-water system than would be predicted by saturated flow analysis. The finite-element program used in this study was originally developed by Neuman [(17)] and is called UNSAT2. The program will analyze problems of saturated or unsaturated, steady or nonsteady flow and can be used with a variety of boundary conditions such as constant flux, constant pressure, maximum flux, minimum pressure, and with infiltration, evaporation, and seepage surfaces. The maximum conditions are controlled by exterior factors such as atmospheric conditions; but the actual flow in the porous media is determined by properties of the porous media. In this test, the computer code was used

Jan 1, 1980

By George A. Desborough, David L. Fey, Stanley E. Church

About 100 mine-waste dumps from past metal exploration and mining in Colorado and Montana were sampled using surficial-sampling methods for laboratory studies of the minus-2-mm fraction. In the laboratory, the composite samples were split into l00g samples that were leached to assess their acid-generation potential and associated release of potentially toxic metals that may degrade water quality in the headwaters of the Animas River watershed in Colorado and the Boulder River watershed in Montana. Two leach methods were studied: a passive leach using de-ionized water, and a more aggressive leach following the EPA-1312 method. The resulting pH values of the leachates using both methods are comparable. The concentrations of sulfate and several, but not all, dissolved or water-soluble metals are higher in the EPA-1312 leachates than in the passive leachates; however, the overall trends of the data are very similar. The passive leach method is less labor intensive and may be more representative of the natural weathering process occurring on the mine-waste dumps, simulating the natural precipitation and snowmelt. Three chemical characteristics of mine wastes studied here provide a relative ranking of mine-waste dumps for the purpose of determining priority for removal or remediation. These characteristics are: net acid production (NAP), sum of dissolved toxic metals (?As+Cd+Cu+Pb+Zn), and dissolved iron in leachates. Ranking can be done evaluating plots of NAP versus the sum of dissolved toxic metals, and NAP versus dissolved iron. These two plots serve as a basis for relative ranking of polymetallic-vein and acid-sulfate mine wastes studied. This ranking scheme may apply to mine wastes from production of other deposit types in other watersheds.

Jan 1, 2000

By Bruce K. Cantrell

As part of a continuing study of diesel exhaust aerosol characteristics, the Bureau of Mines has applied Chemical Mass Balance (CMB) model source apportionment analysis to evaluate a size selective sampling method for determining the separate diesel exhaust and coal dust aerosol concentrations in a diesel equipped coal mine. Size selective sampling was used under the premise that diesel exhaust aerosol dominates the submicrometer aerosol size range, while most of the mineral dust aerosol is greater than 1 m. A micro-orifice, uniform deposit impactor (MOUDI) was used as the size selective sampling method. Concurrent samples of mine aerosol were collected using a dichotomous, respirable aerosol sampler. This sampler separated the fine and coarse size portions of its sample at 0.7 m. Trace element concentrations for in-mine aerosol sources and the dichotomous samples used by the CMB model were measured using Instrumental Neutron Activation Analysis. The CMB analysis, applied to both the fine and coarse fractions of the respirable mine aerosol, yielded the mass concentration contributed to each by diesel exhaust and mineral dust aerosol sources. The MOUDI size distribution data were analyzed using nonlinear regression to parameterize the fine and coarse fractions of the sampled aerosol and to estimate the contributions to each fraction from both coal dust and diesel aero- sol sources. For the diesel mine visited, analysis of the MOUDI samples yielded a value for the fraction of the fine aerosol attributable to coal dust of 15[]7% fine fraction coal from analysis of the MOUDI samples versus 25[]4% from the CMB analysis. The remainder of the fine aerosol in the mine was diesel exhaust aerosol. CMB analysis confirms the original premise for such sampling. After correcting for the presence of coal dust in the fine aerosol fraction, analysis of the MOUDI size distributions yielded estimates of respirable mineral and diesel exhaust aerosol concentrations that were accurate to with-in 10% of values determined by the CMB apportionment.

Jan 1, 1987

By Stephen H. E. Phillips

Geological and hydrological conditions in the strata overlying the Salado Formation vary considerably in the Carlsbad, New Mexico area. The first four shafts sunk at international Minerals and Chemical Corporation's property have been located in competent and essentially dry conditions, while other shafts on adjacent properties have had such adverse conditions that ground freezing has been chosen as the water and ground control technique for shaft sinking. At the location of the IMC No. 5 Shaft there has been extensive-erosion and salt dissolution in the Rustler Formation which has led to collapse of some zones of the strata. Both ground freezing and pregrouting were considered as alternative methods of stabilizing the extremely poor ground conditions and controlling the potentially very heavy water inflows it was decided that pregrouting the shaft was feasible and would offer substantial cost and time saving over a ground freezing technique. This paper describes the pregrouting techniques used and illustrates the requirement for flexibility in a grouting program so that it can be codified to reflect any new or additional information which is obtained during the progress of the grouting.

Jan 1, 1984

By M. Imazu, Ö. Aydan

"A new rock classification, Rock Mass Quality Rating (RMQR) proposed by the authors is briefly explained and its application for the design of tunnels and large underground openings support systems is described in this paper. RMQR is an index to evaluate the state of rock mass. The preliminary support design may be based on the concept to prevent structurally controlled failures of rock mass. RMQR can also evaluate the yielding characteristics of rock masses so that it is possible to design a support system to prevent or control the deformation of surrounding rock through the utilization of the proposed rock mass classification and some analytical and numerical techniques.INTRODUCTIONThe first three authors proposed a new rock classification system named Rock Mass Quality Rating (RMQR) (Aydan et al. 2014). RMQR quantifies the rock mass state, and using the classification system together with intrinsic geo-mechanical properties of intact rock, possible geo-mechanical properties of rock masses can be estimated. The instability modes of underground openings can be structurally controlled because of the orientation of discontinuities in rock mass and the in-situ stress induced (Aydan 1989; Aydan et al. 1993, 1996; Aydan and Genis, 2010). The authors (Aydan and Ulusay, 2013; Aydan, 2016) have also tried to apply this system to the design of a tunnel support system. The authors presented initial guidelines for the RMQR classification system earlier (Aydan and Ulusay, 2013).In this paper, the authors provide further guidelines and establish some criteria for support system design that considers loading conditions and types of underground structure according to RMQR. Guidelines are alsos proposed for selecting the proper size of rockbolts, rock anchors, shotcrete, steel ribs and concrete liner. These guidelines are based on past experiences with various underground structures, theoretical understanding and the anticipated behavior of rock mass under given in-situ stress conditions and excavation techniques. The authors also utilized some databases developed for large underground caverns and tunnels excavated in squeezing or rock-bursting ground conditions."

Jan 1, 2016

A general form of pore pressure in a saturated porous medium, which is subject to external forces it has the pressurization of a borehole in hydraulic fracturing, is derived. The pore pressure consists of two parts: the preexisting initial pore pressure and the pressure induced by fluid flow due to the pressure difference caused by pressurizing the borehole The initial pore pressure associates with the effective stresses in the stress, fields of crustal stresses and a thick hollow cylinder subjected to internal and external pressures. The pure pressure weaned by fluid flow is implied in Biot's (1941) constitutive equation for three-dimensional consolidation and proved to be the exact effective pore pressure (Nur and Byerlee, 1971). Using this general form of pore pressure, a general poroelastic model for hydraulic-fracturing breakdown (fracture-initiation) pressure was derived. This model was validated by laboratory experimental results on Indiana limestone. Three sets of tests were conducted under the conditions of preexisting pore pressures of 6, 21 and 28 MPa, respectively. The equal horizontal (confining) pressures applied in the tests ranged from 6 to 60 MPa. Hainison and Fairhurst's (1967) model appear to be applicable to rocks having microcracks or flows. Experimental results of fracture reopening pressures on Indiana limestone supported this assertion. The test results also demonstrated that, when the pressure difference between the confining and the initial pore pressure grows larger than 14 to 21 MPa, the breakdown pressures agree well with the general poroelastic model developed in this paper. This indicates that the developed model will be superior when hydrofacturing stress measurements are conducted at great depth.

Jan 1, 1997

By Jorge Lanza

SUMMARY La Granja copper deposit, in terms of volume, is among the five largest deposits in the world and represents reserves of three thousand million tones. The field consists of a 40 m. thick layer of copper lying over the secondary ore and further down the primary copper. The flotation process has indicated a recovery rate of 88 to 90 percent and concentrates of 27 to 32 percent of copper. The acid leaching process of low grade ore produces financially acceptable results. To carry out the project, it is necessary to build long distance pipelines and a port. Both the Feasibility Study and the Environmental Impact Study on the project have been approved by the Peruvian government. INTRODUCTION La Granja is located in the district of Querecoto, province of Chota, in the department of Cajamarca, in the Northwest of the country (Figure 1). Geographically it is situated on the eastern slopes of the Andean mountains at an altitude of 2,000 to 2,700 m.a.s.1. (Figure 1). The site is an 8 hour car ride from the city of Chiclayo, capital of the department. The first 60 km. are over a paved road and the remaining distance is over a narrow hard dirt road. The copper porphyry of La Granja was discovered between 1969 to 1971 during some geochemical prospecting activities carried out by the State mining institution, Ingeomin (currently Ingemmet). From 1978 to 1982, Ingemmet continued with its geochemical and geophysical studies supported by a German technical assistance program. A total of 19 bore- holes were drilled (5,814 m.) and a 90 m. long tunnel made. This study calculated reserves of 175 million MT. In 1993, Minero Peru drew up a technical-financial study based on the above studies and proposed a 12 year extraction operating program: 20,000 MT daily using the leaching process, followed by 13 years of operation using the flotation process with the same daily volumes. In 1994, Cambior Inc. won an international auction in order to carry on further exploration work and to have a purchasing option. Since that date the company

Jan 1, 1998

By A. F. Alsobrook

Specialty silica materials, as defined in this chapter, are rocks that consist predominantly of silica (SiO2) and are produced as chunks, round pebbles, and sawed or trimmed blocks and other shapes for nonconstruction applications. The rock types include quartzite, sandstone, novaculite, flint, chert, and vein quartz. Other terms used commercially include jasper, silex, lascas, and rock crystal. In its publication, Minerals Yearbook, the US Bureau of Mines (USBM) reports the production and consumption of some specialty silica materials under several headings. Quartzite, sandstone, and novaculite used in abrasive applications are addressed by the USBM under Abrasive Materials. Lascas, a type of vein quartz used in growing synthetic quartz crystals and in fusing applications, is discussed under Quartz Crystal. Silica gravel used in manufacturing silicon metal and ferrosilicon, as metallurgical fluxstone, and as a filtration medium is covered under Industrial Sand and Gravel. Information on

Jan 1, 1994

By T. Ruff, J. Steele

The lack of visibility near earthmoving equipment results in an average of five fatalities in U.S. surface mines each year. These accidents occur when a piece of equipment either strikes another vehicle or worker, or travels over the edge of an embankment. Researchers at the National Institute for Occupational Safety and Health have evaluated off-the-shelf proximity warning systems that sense obstacles near the equipment and provide an alarm to the operator. Limitations of existing systems have necessitated the development of new systems designed specifically for mining equipment, including a GPS-based proximity warning system and a computer-assisted stereovision system.

Jan 1, 2004

By W. Rocher

The Minera Ojos Del Salado (?MINOSAL?) concentrator is located 20 kilometers southeast of Copiapo, Chile and processes copper ore provided by its Santos and Resguardo mines at a capacity of 4,200 tip (4,620 stpd). Phelps Dodge acquired the majority interest in MINOSAL in 1982. The principal incentive for this purchase was the exploration potential of the property. At that time, the concentrator plant was a small, antiquated installation with a capacity of 674 t/d (740 stpd). In 1982, the majority of the ore was produced from the Santos and Resguardo mines, but custom ores of copper, silver, and gold were also treated. The acquisition occurred at a crucial time in the copper business, since the price had fallen to nearly $0.50 per pound. In 1985, Phelps Dodge purchased the outstanding interest in MINOSAL and acquired 100% of the property. Today, after numerous improvements and two expansion projects, the concentrator is an interesting combination of old and new equipment. The regrind mills, for example, have been in service for about 50 years, while the ceramic concentrate filter represents the latest technology.

Jan 1, 1993

By T. H. Jones

Fall of ground is a leading source of worker injury and fatality indicating a persistent need for ground monitoring technology. The HRTMM is an experimental convergence monitor utilizing a digital camera and custom software to track the position of one or more lasers across the target. Apparent laser movement is proportional to target convergence. The HRTMM was installed in an underground mine near active operations to test its response to the mining environment. This included intense blasting vibration and mine fog. Results and potential of the new monitoring technology will be discussed.

Jan 1, 2008

By Bern Klein, Rafael Fernandes de Mesquita, Fatima Regina Ney Matos, Andre Xavier

"193 United Nations members are signatories of the 17 Sustainable Development Goals (SDGs). Even though it does not make it legally binding to the country members, the SDGs establishment incites national and managerial frameworks to achieve the SDGs. The mining industry inserts itself in this context by its global presence and frequent location within ecologically sensitive and less developed areas. This paper aims to consolidate the state of academic research on mining, sustainability and sustainable development, by organizing the results of previous studies within a systematic review on the SDGs set. To do so, the ISI Web of ScienceTM Core Collection database was chosen as a database of record, as it is one of the most widespread databases of academic journals. We have used all years available in the ISI database, from 1945 to 2016 (for complete years). The systematic review process comprised of five steps: (i) to search terms [(“sustainability” or “sustainable development”) and mining] on the database and to apply filters of criteria; (ii) organizing papers; (iii) metrics and relations between papers and authors; (iv) classification of the results through content analysis techniques; and (v) synthesis. The results were divided in two groups: the highly cited and the most recent papers, to include papers that have academic impact and those which show the newest contributions to the field. The results showed that, in spite of a growing amount of publications in the past years that relates to mining and sustainability, the main focus of these publications are still on the environmental dimensions of the UN goals. This suggests that more practical and academic work in the mining sector are required to fill in the blank spaces regarding the other set of goals that compose the SDGs framework.Introduction A total of 193 United Nations members are signatories of the 17 Sustainable Development Goals (SDGs). Even though it does not make it legally binding to the country members, the SDGs establishment incites national and managerial frameworks to achieve the SDGs. The mining industry inserts itself in this context by its global presence and frequent location within ecologically sensitive and less developed areas (Atlas 2016). The goals are important because they add common targets for different countries and easily establish discernible criteria for it (Costanza et al 2016). A forward-looking approach like the SDGs would be able to attach the sustainable development framework with profitable activities taken by the mining companies (Starke 2016). This paper aims to consolidate the state of academic research on mining, sustainability and sustainable development, by organizing the results of high impact previous studies and recent publications, within a systematic review, on the SDGs set. By doing so, the results can portray the actual concern and the lacks that the academic field had on this subject in comparison to the UN contemporary agenda."

Jan 1, 2017

By C. O. Brawner

Geotechnical theory is reasonably well developed to evaluate the stability of rock slopes for surface mining projects. It is recognized widely that structural geology, groundwater pressures and seepage, and blasting are key factors that influence the stability of such slopes. However, our capabilities to model the structural geology, to determine rock strength along discontinuities and to model groundwater pressures and profiles are still very approximate. Plus, practical experience of the rock mechanics engineer is one of the most important inputs to the design of open pit mine slopes. To emphasize the use of practical experience, a number of case examples are reviewed here to illustrate key factors that must be evaluated. These case examples comprise a continuation of other examples presented in the Jackling lecture to the SME in 1986 by the author (Brawner, 1986). Example no. 1 In situations where the orientation of geologic discontinuities will not influence rock slope stability, extremely steep slopes can be developed, providing blasting and groundwater are controlled adequately. An excellent example of this condition is the Republic Pit of Cleveland Cliffs in Michigan. The rock slope in Fig. 1 isover400fthigh with a face angle of approximately 80". The rock is hard and massive, and blasting was carefully controlled. The original design of this slope was at45", a standard design angle at that time. The competency of the rock and the lack of critical geologic structure subsequently was recognized, and the much steeper slope angle was developed successfully. The rock proved to be so competent and the slope sufficiently stable that an underground crusher station was developed with entrance and exit tunnels excavated at the toe of the steep wall.

Jan 1, 1991

By R. R. Fernández

The Newmont roasting plant in Carlin, Nevada, commenced operating in December 1994. Over the years, refractory ores and pyrite concentrates from different gold deposits constituted the feed to the facilities. Historical plant performance indicated that the roasting temperature was the main variable affecting the structural characteristics of the calcine, which in turn affected the recovery of gold by cyanidation. Gold recovery as a function of roaster temperature has been closely monitored since October 2000. The original design temperature was 550° C. Lower roaster temperatures of around 500° C resulted in a gold recovery increase of more than six percent. This increase was directly related to an increase of the surface area of the calcine. The implementation of an ?intelligent? process control system helped significantly in achieving steady low roasting temperatures, thus obtaining high gold recoveries of 92 to 93 percent. Under these conditions, several roasting campaigns with high-arsenic-containing ores were conducted, which resulted in a significant decrease in gold recovery. The reduced gold recovery was caused by the loss of surface area (e.g., porosity) of the calcine as the arsenic content of the roaster feed increased.

Jan 1, 2010

By Dale W. Norris, John A. L. Campbell

INTRODUCTION Optimization, as measured by productivity gains, is being achieved in our nation's preparation plants principally by automation, economy of scale, and reducing maintenance. Increased tonnage per unit of investment, a1 so a measure of optimization, is being achieved by breaking with tradition and increasing plant utilization, while simultaneously improving on equipment re1iabi1ity. Improved qua1ity, another measure of optimization, is being attained through technical innovation. This review will concentrate on state-of-the- art unit operations and processes, and will not discuss emerging new technologies which are covered in detail in other presentations of this symposium. It is recognized that much of what will be discussed in this paper is not unique to the fine coal circuit, but is equally applicable to the entire preparation plant. However, the areas reviewed are the principal means being used today to optimize an existing preparation plant's fine coal circuit. Prior to designing and optimizing a fine coal cleaning circuit, the question that must first be answered is, "Do we even want a fine coal circuit? This is a much more complex question than is readily apparent, as most of you recognize. It can be argued either way. In the final analysis the "bottom line" will hold (Blackmore, 1982). If your sales contract a1 lows it, and the selling price can justify it, you most assuredly want to build a fine coal circuit into your preparation plant. In general today, most new preparation plants do have fine coal cleaning circuits. The purpose of fine coal cleaning has changed with time. Some of the early applications of fine coal cleaning were to prevent stream pollution rather than to prepare a product for market (Merrill a Pennington, 1962). During the 50's, 60's and into the 70's the principal thrust of fine coal cleaning was in metallurgical coal preparation. More recently, the emphasis of the 80's is on steam coal processing. There is no consensus on what is fine coal. Traditionally, fine coal would be anything below 1/4" in size. Because of the advances being made in intermediate coal cleaning processes, i.e. heavy media cyclones and jig cleaning, this discussion will define fine coal as -28 mesh (Aplan, 1987). Figure 1 is a plot of the size ranges of a large number of U.S. bituminous coals. In general the -28 mesh fraction of a bituminous coal will be between 7% and 18% of the ROM feed with reported ranges of 5% to 40% (Aplan, 1987). Consequently, traditional fine coal cleaning is general 1 y involved with a re1 actively mi nor portion of the coal feed. Every effort is taken both in terms of mining and preparation to keep it that way because of the high cost of cleaning fines. The move away from this posture, namely, the techniques to fine grind coal to liberate pyrite is probably the biggest challenge facing fine coal processing today.

Jan 1, 1988

By G. Le Bel

Discussion by G. Le Bel The paper proposes three methods to determine optimum lifetime of a mining project 1. The conclusion is that the three methods arrive at the same optimum production rate (by coincidence). It is also stated that: "The stochastic and option pricing models, in addition to providing a more realistic optimum mine life than the traditional NPV (net present value) calculation, showed that the example project has the potential for substantially higher return. By explicitly considering a project's potential risks, the stochastic or option pricing techniques can more accurately describe its probable investment performance." This discussion is intended to demonstrate that: •It is no coincidence that the three methods arrive at the same optimum production rate. • The stochastic and option pricing models do not provide a more realistic optimum mine life than the traditional NPV calculation. •The potential for a substantially higher return is misrepresented. First, a review of investment decision theory in mining is needed. Net present value is the preferred performance measure because of the flexibility offered when comparing various alternatives. However, it presents the following disadvantages: • The discount rate selection is not straightforward. • The NPV obtained represents a deterministic characterization of the variables included in the cash flow calculations, i.e. a single-point estimate. Discount rate selection The opportunity cost of capital represents the rate of return that would be obtained if the capital was instead invested in other opportunities considered to exist. Such opportunities must be bypassed if the available capital is invested in the project studied 2. If these other opportunities carry risk similar to the project under analysis (for example, if they are other mining projects), there is no need to add incremental [ ] risk factors. On the other hand, if these opportunities are represented by the acquisition of government bonds yielding 7%, a risk premium factor must be included. The types of risks associated with a mining venture are shown in Table 1. Together they represent the "business risk" of being a mining company. The individual project risk is important to investors if it differs substantially from the business risk of the company and that of the other investments in mining ventures that we must pass up to invest in this particular project. A risk premium or discount would then be required. This can be illustrated by the following example. Consider that a company has two investment alternatives: one is the Cavender hypothetical project located in Nevada, and the other is the same project located in a civil war zone of central Europe. The second project requires a risk premium factor on the discount rate. Conversely, a project showing highly uncertain returns that are negatively correlated with the returns of the firm's other assets may decrease the company's corporate risk. Deterministic character of NPV calculation The cash flows used in NPV calculations are obtained from a set of variables. These variables are estimated using one parameter obtained from the engineering studies. Each parameter is thus a single value that is often termed a "realistic" or "best estimate" as opposed to "optimistic" or "pessimistic." However, considering that each variable can assume a range of values between the

Jan 1, 1994