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By A. Zorychta, T. Cyrul, Z. Kleczek

INTRODUCTION Underground mining causes disturbances of the primary state of stresses. Resulting from those disturbances a loss of stability of rocks that surround excavation may occur interrupting the production and creating life danger for the personnel. One of the manifestations of such an instability is a rock burst phenomenon which mainly occurs at great depths. From the mechanical mint of view the rock burst is a loss of stability /Filcek et a1.,1984; Pietuchow and Linkow, 1976/ due to : - quasi-static stress changes in the surrounding rocks; we will call it s seam burst , - dynamic stress changes in the surrounding rocks caused by rock shocks ; we will call it roof burst. Possibility of the rock burst occurrence Is uniquely determined by the state of stresses existing in the rock mass. In the following sections of the paper we will consider different aspects of this question. Moreover distributions of displacements and failure criteria for a coal seam at longwall mining will be defined. STATEMENT OF THE PROBLEM Determination of the vertical stresses and displacements resulting from longwail mining will be based on the Budryk’s idea of a stress wave /Salustowicz, 1955/. The idea originates from the analysis of a roof plate /beam/ resting on the deformable foundation /Sean/ and subjected to the cylindrical bending. Equation of the bending lice uniquely defines vertical stresses and displacements which are induced in the seam. The equation will account only the shear force effect. Elimination of the bending moment has been shown and discussed by Zorychta and Bcrecki /Zorychta, 1985; Borecki and

Jan 1, 1986

By Benjamin K. Pocock

When considering alternative equipment choices in mill or process flowsheets, it is important to determine both capital and operating costs of such equipment as well as other possible savings related to downstream operations. This paper presents a few case studies and shows cursory guidelines for the selection of equipment for new installations or in the retrofitting of existing plants. Based upon recent plant experience, suggestions are given to improve the operation of clarifiers, thickeners and vacuum filters.

Jan 1, 1986

By D. S. Cronan

Based on analogy with the Clarion-Clipperton zone, three main factors appear to influence the occurrence of potentially economic nodules in the study area, (i) elevated biological productivity, mainly above 50gCm-2y-l, (ii.) sea floor depth near or below the CCD, (iii) an absence of turbidite sedimentation. These conditions are fulfilled in parts of the following basins, where available data indicate that high grade and sometimes abundant nodules occur. i) The East Central Pacific Basin west of the Line Islands extending to the East Central Pacific Basin north and east of the Phoenix Islands ii) The West Central Pacific Basin west and northwest of the Phoenix Islands iii) The North Penrhyn Basin north of Penrhyn Island Notwithstanding the similarities between the environmental conditions under which potentially economic nodules occur in the Clarion-Clipperton zone and in the areas listed above, such similarities may relate only to present day conditions. During the possibly long periods of nodule formation, environmental conditions may have varied, and the deposits formed under conditions different from those prevailing at the present day. However, the fact that both present day conditions and the deposits in the two areas do show similarities suggests that applying the same genetic model to them has some validity. Possibly, any changes in environmental conditions during the period of formation of the deposits has been similar in both areas. Such uncertainties can only be resolved by a much fuller evaluation of the evolution of nodule deposits in both areas throughout recent geological time.

Jan 1, 1986

By D. A. Stanley

The Bureau of Mines is investigating a method of dewatering flocculated fine-particle waste that involves treating the waste with a high molecular-weight polymer such as polyethylene oxide (PED) followed by dewatering on a static screen and/or in a trommel. Dilution of the polymer solution used for dewatering and use of the ion-exchanged form of the montmorillonite clay were found to be major factors determining the amount of polymer required to dewater clay-containing slurries. The amount of polymer, A, required to dewater ion-exchanged montmorillonite can be described by the equation, An = kC + b where n, k, and b are empirical constants and C is the concentration of the polymer solution used for dewatering. Clays that require large amounts of polymer for dewatering also dewater to a lower solids content. The concentration of the polymer solution is important because it affects the radius of the polymer coil in solution and hence its ease of transfer to a bridging configuration by shear. The constant, n, a function of the charge to hydrated radius of the exchange ion, relates to the strength of the bond between the polymer and the surface of the clay through a water bridge. The constant k is related to the hydrated radi-us for sodium or to the unhydrated radius for the other exchange ions.

Jan 1, 1986

By K. R. Price, M. Gauna

Jim Walter Resources No. 4 mine produces coal through retreat longwall mining at 610 to 670 m (2000 to 2200 ft) of depth. A three entry, total yield pillar, longwall development experimental region was established for three adjacent longwall panels utilizing 6.1 m (20 ft) wide gate section pillars. Presently, the first longwall panel is completed with roadway deformational behavior monitored for a ground control assessment of the mining system. Data illustrate that the total yield pillar gate section design at No. 4 mine is presently comparable to gate section designs having large equal size chain pillars. Ground conditions will continue to be monitored during the mining of subsequent longwall panels in order to determine the ground control implications from multiple panel extraction.

Jan 1, 1986

By Andrew B. Cecala, Edward D. Thimons

"The Bureau of Mines has recorded a number of different background dust sources that significantly contaminated the air breathed by bag machine operators. These background sources, observed at five different plants over the past 2 years, can expose bag machine operators to more significant dust concentrations than the filling process itself. To keep bag operator exposure within acceptable dust levels established by the Mine Safety and Health Administration, U.S. Department of Labor, the significance of these background sources must be realized, and the sources must be identified and controlled. The purpose of this work is to identify common background dust sources and show the significant effects that they have on the bag operator's overall dust exposure. INTRODUCTIONThe purpose of this report is to identify some common background dust sources in and around the bag-filling area. Although these background dust sources are of ten unrecognized, they can be more significant sources of contamination than the dust generated from the bagging process.The bagging of mineral products into 50- and 100-lb paper bags is common throughout the entire mineral processing industry. Bagging is performed by a bag operator who sits in front of a two- or four-station fill machine. The bagger's function is to attach empty bags to the fill nozzles as filled bags are ejected from the machine. If the product being bagged is extremely fine (smaller than 200 mesh), the bag operator's dust exposure is usually one of the highest in the plant.The bag operator is exposed to two primary dust sources. The first is product blowback during the bag-filling cycle. This occurs as excess pressure is released from around the fill nozzle during filling. As the excess air forces its way out of the bag, product is forced out with it. This blowback of product leaving the bag creates a considerable amount of dust. The second major source is the ""rooster tail"" of product thrown from the bag valve and fill nozzle as the bag is ejected from the fill machine. Since the bag is pressurized as it leaves the machine, product spews out of the valve for a few seconds."

Jan 1, 1986

By K. J. Stratford

The selection of a suitable mathematical function for the modelling of the partition curve for dense medium cyclones is discussed. Five alternative functional forms (based on three basic functions) are compared using data obtained in the course of an extensive experimental study of a 610mm dense medium cyclone. It is shown that, for adequately sampled tests, any of the functions may be used, although a function based on the Weibull distribution is shown to be most suitable. Where data are poor, all functional forms exhibit disadvantages, notably in terms of a reduction in precision of parameter estimation. This problem can be exacerbated by the complex numerical techniques required to estimate the parameters of a particular function. A set of ideal requirements for a performance function are presented.

Jan 1, 1986

By Edward Finch, William F. Riggs

Selectivity and recovery of many industrial minerals can be directly affected by the carbon length, degree of unsaturation, and melt point of fatty acids used as collectors. Examples of several modifications are provided based on actual experiences of commercial applications. A review of recent history indicates that fatty acid collectors are applicable from C9'C18 in carbon length, however, not for all minerals. The mesh size, density, and surface characteristics of the particular mineral, as well as other related operating conditions, are important in selecting the correct fatty acid configuration. A review of some past programs are submitted as a guideline in the selection of fatty acids and supported by isolated, successful examples demonstrating the effect of carbon length and unsaturation.

Jan 1, 1986

The impact of computers on the mining industry has increased for the past twenty years in most parts of the world. The application of computers in the mining industry has been demonstrated in areas such as geological data analysis, ore reserve estimation, mine planning, and manpower training. There is also a general concern in this country regarding the computing background of graduating mining engineers from the Australian higher institutions of learning. This paper describes specific steps which have been taken at the Department of Civil and Mining Engineering, The University of Wollongong to provide adequate computing background to mining engineering graduates. Specific topics discussed include hardware and software available to students and how "computers" have been integrated into the mining engineering course.

Jan 1, 1986

By Michael A. Poling

Ladies and gentlemen, I appreciate this opportunity to be with you, and to share my outlook on the future of Federal coal leasing. I'm told that you wanted the best speaker on this subject in the world. Perhaps it's a reflection of these trying financial times, but I'm glad you finally agreed to settle for the best speaker your budget would afford. I have been asked to give you some insight on the status of Federal coal leasing, and how the budget problems facing the Department will affect the coal program. So I've polished up my crystal ball, and I'll try to give you a peek at the future. Before I do that, however, let me first go back in time - to when this Administration took office in 1981. We had a coal program then, after a hiatus of ten years. But that program was untested and - for reasons well known to all of you - did not work well in practice once we began operating the program. We went back to the drawing board and redesigned the program so that it can do what it is intended to do. We've made the program more predictable. That means that when future lease sales are scheduled, those sales will be reflective and reactive to the need to lease coal. On February 26, Secretary Hodel unveiled a framework for resumption of Federal leasing program activities, ending a more than two-year suspension of regional coal sales. The new program will provide the opportunity to satisfy market demand for acquiring and developing new leases, assure the government of fair market value for its coal reserves, and provide a stable supply of coal for this country's energy needs. The new program grew out of the Department's response to recommendations of the Linowes Commission and the Office of Technology Assessment, coupled with a supplemental environmental study. The Linowes Report, issued in 1984, contained 36 recommendations and three Judgments on leasing levels, tract selection, sale procedures, appraisal methods, key statutory and related factors, and organization and management of the leasing program. Major changes in the new leasing program reflect these concerns. We have developed a definition for captive tracts and devised procedures to appraise their value to the adjacent coal or mine owner. Other steps include a coal lease appraisal guide which describes our appraisal methodology and is available to the public. Improvements have also been made in the gathering of lease assignment information to help in estimating the value of potential lease tracts. To improve market analysis, a three-tiered system will be used to ensure that steps of the lease sale decision process are undertaken in the context of coal supply and demand. Regional Coal Teams will thus have the advantage of long range, regional and tract specific market studies to help them determine whether sufficient demand is expected first to warrant the initiation of activity planning, then to set regional leasing levels, and finally to actually offer specific tracts for lease sale. Sale procedures will also be improved in many ways to encourage competition, improve the chances for receiving adequate bids, and to evaluate whether bids represent fair market value. We made additional modifications to the program in response to the OTA recommendations. Regional Coal Teams have been given a larger role in recommending key decisions concerning the amounts of coal to be studied and the actual selection and scheduling of tracts for lease sale. These recommendations will be accepted unless the Secretary can cite an overriding national interest factor, or a governor's request to modify the recommendations. Smaller, more frequent sales will be held, to better judge market conditions and prevent over- or under-leasing. Public participation guidelines have been written, to document all opportunities for the public to comment at various stages in the planning process. We also decided that resource management plans prepared after the passage of FLPMA in 1976 must be completed, in order for a new round of lease sale planning to begin. The BLM will also beef up its procedures for consulting with affected Federal agencies during the planning process, to assure that the purposes and values of those agencies are considered and factored into land use decisions. To assure consistent use of an adequate data base in coal lease decision-making, Regional Coal Teams will develop standards and guidelines for data adequacy, and document the use of these standards. These procedures will also be applied to the unsuitability criteria screening process. Thus, the new leasing system announced by Secretary Hodel: is fully responsive to recommendations made by the Linowes Commission and the Office of Technology Assessment for improving environmental planning and fair market value procedures; gives the regional coal teams a major say in determining leasing levels, and on the timing,

Jan 1, 1986

Introduction The Homestake Mining Co. has always been big on gold. After 108 years in the business, the company and its principal product are almost synonymous. The relationship continues. On Sept. 28, 1985, Homestake held formal dedication ceremonies for its newest gold mine - McLaughlin. The McLaughlin open-pit operation is located in northern California, some 113 km (70 miles) northeast of San Francisco. It lies near the boundaries of three counties - Napa, Yolo, and Lake - and a portion of its facilities are located in each. McLaughlin was originally the site of the Manhattan mercury mine that produced nearly 80,000 flasks of the quicksilver from the 1860s to 1978. At the September dedication, Homestake renamed the mine in honor of the late Donald H. McLaughlin. McLaughlin was with Homestake for nearly 60 years. He rose from exploration geologist to his ultimate positions of chief executive officer, director, chairman of the board of directors, chairman emeritus, and chairman of the executive committee. The discovery of the McLaughlin deposit occurred in 1978, the last year of operation for the Manhattan mine. Homestake geologists used a newly developed model and found surface gold at the mine site. That same year, Homestake signed an agreement with the property owner and began a two-and-a-half year exploration program. An initial discovery announcement of 31.1 t (1 million oz) of gold was made in 1980. In 1981, this was revised to 93.3 t (3 million oz), or 18 Mt (20 million st) of ore grading 5.2 g/t (0.152 oz per st). Expected mine life is 20 years. Construction began in September 1983, following the issuance of stage one permits. Start-up of operations took place in early 1985 and the first gold-silver dore bar was poured on March 4. Since then, more than 540 kt (600,000 st) of ore has been milled, producing about 1.6 t (50,000 oz) of gold. Of special interest at McLaughlin is the use of three autoclaves for gold extraction. According to Homestake, this is a first. The autoclaves are designed for a 90% gold recovery rate. Early results have proven yields at this rate and higher. Geology The McLaughlin deposit is about 1.5 km (5000 ft) long. It occurs as a wedge-shape, narrowing to a verti-

Jan 1, 1986

By R. E. Sundell, S. M. Correa

"A mathematical model is developed for the fluid flow in tungsten-inert gas weld pools. The fluid is taken to be incompressible, viscous, electrically conducting, and confined within a pool of specified shape. The flow is driven by surface-tension gradient (thermocapillary), electromagnetic, and buoyancy forces generally in this order of importance. Analysis indicates that the electromagnetic field may be calculated a priori and so decoupled from the nonlinear fluid mechanics and heat-transfer problem. The resulting set of equations is solved numerically by a line relaxation process. Computational errors caused by truncation in finite-difference schemes and by inadequate grid distributions are considered. The model is used to study several cases of differing heat and current input to the pool with and without surfactant-induced thermocapillary forces. The principal conclusions are that the thermocapillary flow, when present, is dominant with surface velocities on the order of 1 m/s. The heat transfer, as deduced from isotherms within the pool, is crucially dependent on the flow. Also, flow velocities and weld-pool surface temperatures were measuredand agree well with the model.2. IntroductionThe requirements of improved control and of automation in the TIG (tungsten-inert gas) welding process have led to the development of mathematical models for the heat transfer to the workpiece. It is now widely recognized that the fluid flow in weld pools sufficiently distorts the conduction heat transfer pattern to warrant inclusion in a process model. The experiments of Woods and Milner (1), among others, demonstrated that TIG weld pools could be driven by the electromagnetic J x B body forces present, J being the current distribution and B the induced magnetic field. Atthey (2) calculated that in typical pools the buoyancy force was about an order of magnitude less important - despite the large temperature gradients present - and neglected it in a computational study of the magnetohydrodynamic (MHD) flow. This work also reviewed many earlier studies of MHD flow caused by a source of current at a fluid surface, including analytical studies by Shercliffe (3), Sozou (4), and Sozou and Pickering (5), and a numerical study by Andrews and Craine (6). These works establish the importance of the electromagnetic force in the weld-pool flow."

Jan 1, 1986

By Bob Newbery, Kenneth W. P. Eng. Kolthammer

SUMMARY Reference is made to the reasons for drying and the equipment is described that is available from which the engineer can make a selection. The factors affecting this decision are described. In the case of drying, design and sizing are ultimately developed empirically and no theoretical approach has been advanced.

Jan 1, 1986

By Robert H. Peters

Several significant problems associated with employee turnover among underground miners are described in this Bureau of Mines report. Although a vast amount of research has been conducted on turnover among employees in nonmining industries, there has never been an attempt to empirically investigate the causes of turnover among underground miners. This report presents the results of empirical research on employee turnover in other industries and describes and critiques the research methods that have been used to investigate turnover. Using the findings on employee turnover in other industries and known data about miners and the mining industry, a conceptual model of the factors that cause turnover among miners was generated. This model, which is expected to provide a basis for later empirical studies, is presented. Several recommendations for controlling miner turnover are also presented.

Jan 1, 1986

By Theodore Triplett

To assess the value of various subsidence mitigation techniques, twelve linear foundations were constructed above a longwall mine. The structures were monitored during and after undermining, and footing curvatures at the time of cracking were compared with predicted values. An unreinforced concrete footing sustained substantial damage. Other footings received varying degrees of damage, with inclusion of a sand layer significantly affecting performance. A post-tensioned concrete foundation suffered minimal cracking. Also, a technique developed by the Bureau of Mines is presented for determining the subsidence, slope, curvature and strain of the ground surface.

Jan 1, 1986

By D. F. Symonds

INTRODUCTION Dense medium processes have been used to separate coal and ores for over a hundred years. In fact Sir Henry Bessemer first patented a process in 1858. In recent years, their importance relative to other gravity dependent processes has increased. This is particularly true in the coal industry where over 60% of all preparation plants operating in 1984 in North America (1) contained either dense medium vessel or cyclone circuits. In addition, the stringent product quality demands of the consumer, together with increases in mining costs, dictate that the cleaning circuits be both predictable and efficient. Dense medium systems are the most predictable and efficient of all gravity- dependent processes. The majority of the text of this chapter will be concerned with dense medium applications as they relate to the coal industry. However, the techniques and calculation procedures can be applied, in general, to all non-coal minerals (such as diamonds, marginal iron and lead-zinc ores and gravel) which take advantage of a difference in specific gravity between the saleable product and the reject. The object in dense medium cleaning is to produce a liquid whose effective specific gravity is between that of the concentrate and the reject. In which case the lighter product will float to the surface and the heavier product will sink to the bottom. Unfortunately, this simple process becomes complicated by the following practical necessities: (a) collecting and removing the float and sink products from the medium without disturbing the free settling effects; (b) maintaining and controlling the specific gravity of the medium; (c) separating and reclaiming the medium once the products have left the separating vessel; and (d) separating finer sized particles which take longer to fall through the dense, and often viscous, medium. As a result of the last issue (item d) two main types of dense medium separators have evolved: dense medium vessels and dense medium cyclones. Dense medium vessels are essentially large baths through which the dense medium flows at a relatively slow velocity. The lighter products float to the surface and are carried out of the vessel by the medium flow. The heavier products sink to the bottom of the vessel and are physically transported out either by means of a conveyor (usually a chain conveyor) or a rotating, lifting arrangement (Figure 1). They generally

Jan 1, 1986

By Brown DJ, Croghan JA, Denby B

The paper describes the development and analysis of an instability database to establish a new method of slope stability assessment for U.K. surface coal mines. The concept is based upon a Stability Index, which relates to the probability of failure of a slope. This forms the basis for a geotechnical planning software package to be incorporated into a computer aided mine design system , which is currently under development.

Jan 1, 1986

Ore deposit modelling is becoming an increasingly accepted tool in mineral exploration. Successful models have already been proposed for several ore deposits of base metals and gold, but tin has so far received comparatively little attention, perhaps because of an excessive preoccupatioi with alluvial operations. This situation is rapidly changing and some of the world's most profitable and newly commissioned tin mines are large, primary tin deposits. Some basic principles of ore deposit modelling are briefly reviewed and the fallacy of an excessive reliance on grade tonnage diagrams based on the tin industry worldwide is discussed. The four proposed models and submodels of large, hard-rock, tin deposits focus on basic concepts such as the spatial relationship with "tin granites", depth of emplacement and the level of erosion. General concepts are drawn. The modelling of large primary tin deposits is reviewed not only in its geological and exploration aspects but also in its mining and economic implications.

Jan 1, 1986

By B. Pesic

Manganese is about twelfth in the list of the most abundant elements in the earth's crust (Reidies, 1981). More than 150 known minerals contain manganese as an essential constituent (Mellor, 1932). In general, ores containing at least 35%Mn are classified as manganese ores, ores with 10-35%Mn are called ferroginous manganese ores, and ores containing 5-10%Mn are known as manganiferrous ores. One very important class of manganiferrous ores are manganiferrous-silver ores. They occur in the oxidized portions of the silver deposits of the Western United States. Silver is very often associated with manganese oxides which in some ore deposits are dispersed through calcite, causing the black color of the host rock, which is known as black calcite. Black calcites can occur in carbonate rocks (10-1500oz Ag/ton) and in volcanic rocks (less than 1.0oz Ag/ton).

Jan 1, 1986

By Dennis Z. Mraz, Maurice B. Dusseault

INTRODUCTION In 1982 and 1983, as part of the mine design program for a New Brunswick potash mine, series of laboratory tests were conducted on potash and salt samples obtained during the mine exploration program. Concurrently, two rock mechanics monitoring programs were initiated in-situ the short term test at site A, and the long term test at site B (figures 1 and 2). SHORT TERM TEST (FIGURE 1) The purpose of this test was to obtain a quick confirmation of laboratory data and comparison of the rock response to excavation with the data available from Saskatchewan potash mines. Instrumentation in the main drift was installed on Day 4 after excavation, and the pressure cells were pressurized on Day 33. The packer type cells in the east crosscut were pressurized on Day 25. Excavation of the west cross-cut was begun on Day 71. This "mine by" test has provided important information required for calibration of laboratory tests, as will be shown later. The test data recorded are shown in a series of diagrams: a. initial room closures, main drift-figure 3; b. convergence graphs, main drift-figure 4; c. stresses recorded, main drift-figures 5 to 8 and, d. stresses recorded, east crosscut - figure15 Three types of instruments were used in this test. In the main drift. Saskatchewan Research Council water type hydraulic inclusions. encapsulated in potash, were used to measure lateral and vertical stresses. In the east crosscut a home-made packer type hydraulic inclusion was used to record radial stresses. The convergence stations consisted of end-grouted bars of reinforcing steel. LONG TERM TEST (FIGURE 2) The purpose of the long term test was to study the steady-state behaviour of a single opening in potash. Site B was placed in a remote area of the mine, well away from any anticipated early mining activities. To assure homogeneity of rock mass, the site was placed within a 30 meter thick vertical limb of a syncline-shaped ore body contained within a 360 metre thick vertical section of salt rocks. It was excavated mechanically as close as possible to the designed square cross-section for the entire length of the room. The square cross- section was chosen in order to achieve a comparable geometry in vertical and horizontal directions; that is, to eliminate any undesired effects of geometry interaction with lithostratigraphy which might have generated non-homogeneous behaviour. The site was extensively instrumented. As in site A, the convergence stations consisted of end-grouted bars of reinforcing steel. However, in order to avoid any measurement inaccuracies which would be associated with the brittle yield zone in the opening walls, bars were placed to the same depth in opposite sides of the opening. This allowed the convergence measurement to be obtained as the absolute convergence between two points, rather than the convergence of a single point with respect to a potentially unstable reference. For stress measurements the Saskatchewan Research Council cells were placed vertically, laterally and radially. Unfortunately, due to cost considerations, it was decided to use a compacted sand, rather than grout, to encapsulate the cells in the boreholes. Due to the extremely small strain rates, only radial ly placed cells could be adequately pressurized. The rest of the cells did not perform adequately, and are currently being replaced.

Jan 1, 1986