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By C. V. Deutsch, D. A. Silva

The geologic modeling of multiple domains is required for the prediction of mineral resources and reserves. In general, explicit methods have wide acceptance among modelers due to the ability to manually add deemed important trends and geological features into the models. As an alternative, implicit geologic modeling techniques are increasingly adopted to reduce professional time requirements. These methods aim for objective, repeatable and flexible models by replacing the manual time-consuming interpretation of sections with the interpolation of signed distance values. These techniques, however, have been developed for the binary case of two domains at a time. The current paper presents an algorithm that extends the binary case to multiple domains. The method is able to transfer large-scale geological features from data to geologic models. A case study illustrates the benefits of the algorithm and practical implementation considerations.

Jan 1, 2016

By W. H. Stahl

The continuous vacuum filtration is the solid-liquid separation process that is nowadays most frequently used in the beneficiation industry all over the world. After a development time of several decades, the various filter types such as drum filter, disk filter, plate filter and belt filter can be consideres as a sound functional design ensuring a trouble-free operation. Nevertheless, the vacuum filtration does no longer meet the present and future technological requirements. The moisture content of filter cakes is too high. Their thermal secondary drying is too expensive (coal, ores) and may bring about undesirable material changes and the filter cake conditioning with water-binding substances for dumping purposes is too costly.

Jan 1, 1983

By M. C. Williams

The solution of the dynamic population balance model (PBM) of a closed grinding network consisting of a mill, sump, and cyclone is problematic. The fact that the dynamic PBM model equation solution to the Inverse Problem for grinding systems is degenerate or underspecified is demonstrated. Two numerical solution approaches to the Inverse Problem are used. These are: 1) providing additional constraints on breakage selection functions or 2) performing the Arbiter-Bhrany (or other) normalization of the selection functions. Actual experimental anthracite batch grinding data is used to demonstrate the non-unique functionality of the batch dynamic mill selection and breakage functions for a real physical system. The Levenberg-Marquardt algorithm for systems of constrained non-linear equations is used to solve the batch dynamic PBM grinding equations to obtain the grinding selection and breakage rate functions. Different solutions to the same PBM transport equations are provided. The mill, sump and hydrocyclone were modeled as a CSTR operating at various retention times. Batch dynamic PBM data was used to provide the mill kinetic and breakage selection function data. Two different solutions were obtained depending on the numerical solution approach. The severity of the non-uniqueness problem for dynamic grinding is demonstrated. Each solution approach to a dynamic PBM with transport, while giving the same prediction for a single batch grinding time, gives different solutions or predictions for mill composition for other grinding times. This fact makes dynamic nodal analysis and control problematic. The fact that the constraint solution approach gives a solution may suggest that normalization for closed networks is not necessary. Differences in solutions to the PBM cannot be excused away by inaccuracies in the data used to model the grinding phenomenon.

Jan 1, 1995

By E. T. Tuzcu

Microscale information about single particle fracture can be incorporated into the macroscale model of the whole size reduction process in the mill. The ultrafast load cell (UFLC) device provides a substantial amount of information about fracture characteristics of a particle under impact loading. UFLC captures high-resolution compressive force signals during particle breakage. The measurement of the compressive force at the instant of fracture of the particle allows computation of a number of comminution-related particle properties, as well as the energy absorbed during fracture. In the current study, limestone particles 50 mm in size were fractured to obtain specific fracture energies. Then, based on the experimental data, two models were proposed to quantify the fracture process. The specific fracture energy distribution of the particles in the range of 6 to 50 mm was defined by the well-known Weibull distribution. The other model is a probabilistic fracture model. This model is a link between energy events occurring in a grinding mill and the breakage rates of particles. The impact energy spectra or energy events occurring in a grinding mill can be obtained with a discrete element method (DEM) simulation. One can model the breakage rates of the mill material by combining the energy spectra with the probabilistic fracture model. This novel approach for the modeling of breakage rates via DEM and UFLC is shown here.

Nov 1, 2011

By A. A. El-Midany, R. M. Farag, A. M. Salem, S. E. El-Mofty

Bentonite is one of the main players in the stability of drilling mud. Its particle size and particle size distribution significantly affect drilling mud’s rheological properties. Although the Specifications for Drilling Fluids Materials report on Oil Companies Material Association (OCMA)-grade bentonite states that the API recommended powder having 2.5 percent mass fraction as the maximum value of residue of diameter greater than 75 μm, there is no other information on the specific size distribution for API bentonite. It was found that API bentonite has a specific size distribution with specific mixing weights. It is important to investigate why that mixture represents the optimum properties of drilling mud and how each individual size fraction has a specific function in the mixture. To clarify the effect of individual size as well as the collective effect of the size distribution, API bentonite was classified into different size fractions, with each tested separately for controlling properties such as filtration loss, plastic viscosity, gel strength, cake thickness and packing density.

By Emmanuel V. Manlapig

The variables involved in a complex process like flotation can be classified as follows: a. Disturbance variables - which are undesired properties of the process input which affect the value of the process output but which are not subject to adjustment. They are the result of changes in the properties of the feed, like changes in head grade, flow rate, fineness of grind, etc. b. Manipulated variables (sometimes referred to as process variables or control variables) -which are those that are adjusted - reagent addition, aeration, pulp level - in order to compensate for the disturbances in the properties of feed. c. Performance variables (sometimes referred to as controlled variables) -which are those whose values measure the performance of the process. They are properties of the process output such as grade and recovery. The function of a control system is to maintain the process performance equal to the control objective in spite of the disturbances by adjusting the manipulated variables. Attempts at developing automatic control systems for mineral processing operations date back to the thirties and in many of these attempts the results were not surprisingly poor and un-stable. The poor results brought indifference and suspicion towards automatic control on the part of operators and management. The reasons for the apparent failure of these attempts were two-fold: a. the lack of adequate understanding of the behavioural responses of the process from the control point of view, and b. the lack of reliable control instrumentation which could withstand the harsh environment in mineral dressing plants. Many operators had accepted the fact that control of mineral dressing could be best conducted manually. In the case of flotation circuits, control had been virtually based on the skill and experience of operators particularly their ability to identify and rectify poor flotation performance aided by results from the laboratory (chemical) analysis of regularly collected samples from strategic points in the circuit which are at best, hourly collected samples.

Jan 1, 1978

By Chun K. Ip, Simon T. Johnson, Robert J. Fowell

Laboratory conducted cutting tests at traverse speeds up to 1 m/s have been undertaken with high pressure water jets assisting the cutting action of drag tools. Four sandstones and one limestone have been investigated, which represents a wide range of compressive strength. Variables investigated include water jet pressure, nozzle diameter, depth of cut, traverse speed, jet position, and tool bluntness. The test programme has allowed a model to be developed which describes the action of water jet assistance for three conditions dependent on the ability of the jet to penetrate the rock: where no significant penetration occurs, where penetration is greater than 50% of the tool depth, and an optimum condition around 30% of tool depth.

Jan 1, 1986

By S. Lu, J. P. Barta, T. W. Meikle

Three nutrient amendments and a biological seed inoculant were evaluated for use in establishing vegetative cover on waste rock substrates. Randomized blocks were placed on three substrates. Treatments included two types of organic fertilizer, mineral fertilizer, Azospirillum bacterial inoculant, plus controls. The seed mix consisted of native grass species adapted to low nutrient conditions. Canopy cover has been monitored for three growing seasons. Results indicate : 1) two of three substrates support plant growth following amendment with organic fertilizers; 2) organic fertilizers increase cover substantially over mineral fertilizer; and 3)Azospirillum had no effect on canopy cover.

Jan 1, 1999

By J. A. Procarione

Introduction Ventilation engineers have always felt somewhat uneasy when, in the normal course of their work, they are forced to consider the flow in any mine entry as "wholly rough." Under such conditions in pipes, friction factor is no longer a function of Reynolds' number. This assumption serves to simplify the problem and overcome an evident lack of information concerning the variability of K-factors. During the summer of 1985, a unique opportunity to investigate the reaction of friction factor to changing flow rates presented itself. A Utah coal mine was temporarily directing a substantial airflow through a single entry. By regulating the quantity, it would be possible to obtain a wide range of Reynolds' numbers in an entry composed of two distinct coal thicknesses. This paper describes the conducted study. The theory covering basic fluid flows in pipes that led to the questioning of constant K-factor is presented first. Experimental procedures are then described, including the use of a view camera in determining entry area and perimeter. Finally, a discussion of the observed variations in friction factor versus Reynolds' number is given. Changes of 34% and 45% in K-factor were seen in this study for the two entry heights. The implications of ignoring the relationship in this case and a call for an expanded research effort are also presented. Theory Since a gas is a fluid, the general principles of fluid mechanics are equally applicable to airflow in a mine entry as they are to the flow of water in a pipe. The Darcy equation is, therefore, equally applicable to pressure drop calculations in both situations. This famous formula was originally derived for use in circular cross sections and may be modified for any other shape by the use of hydraulic radius (defined as the area divided by the "wetted" perimeter). The Darcy equation relates the physical parameters of the pipe (diameter, length, and resistance to flow) and fluid velocity to the energy needed to create the flow. A study by Nikuradse (1933) brought to light the suspected dependency of the friction factor term in the Darcy equation upon Reynolds' number. By performing a large number of laboratory experiments, he established some basic concepts upon which other researchers built. Chief among these contributors was Colebrook (1939). Using commercial-grade pipe, he established an empirical relationship between Darcy's friction factor and Reynolds' number that is still in use today. If Colebrook's system of equations is plotted on log-log paper (as was done by Moody, 1944), the curves have some very distinct features. Of importance to the subject at hand is the relative response of friction factor to Reynolds' number at a given relative roughness. Simply stated, a pipe can appear to be either smooth or rough, depending on the flow conditions. As the Reynolds' number increases, the friction factor decreases at a decreasing rate until it becomes nearly a constant value. At this point, the flow is said to be "wholly rough." It is upon this condition that many traditional ventilation solution methods depend. For calculating pressure drops in a mine entry, Atkinson's equation is much more popular than the Darcy equation. Both of these formulas describe the same phenomenon and so have similar forms and functions. The K-factor in the Atkinson equation is equivalent to the Darcy friction factor and can be related by simply changing units, equating the pressure drops, and canceling like terms. A generalized form of this relationship is presented below as equation 1. K = yf/28,800g = [q]f/28,800 (1) where K is Atkinson's friction factor in kg/m3 (lb - min2/ft4), Y is the specific volume in Nt/m3 (lb per cu ft), p is the fluid density in kg/m3 (slugs per cu ft), g is the acceleration due to gravity (9.8 m/s2 or 32.2 fpsz), and f is Darcy's friction factor, which is unitless. The objective behind Eq. 1 is to show the strong correlation between K and f. Since these two quantities differ only by a constant (q]/28,000), the assumed independence of K-factor and Reynolds' number is suspect in light of the known response of f. Unfortunately, the formulation does not provide information concerning the actual relationship, as entry geometry likely plays a major role in the response curve. Only an indirect indication that such a relationship might exist is provided. Previous work on this subject was performed by Thomas Falkie (1958). The study involved a laboratory model composed of sections of straight, steel duct and a range of Reynolds' numbers from 15,610 to 137,200. Results from this work show a variation in friction factor with Reynolds' number in much the same way as it was found to vary in pipes. Over the range of velocities examined, a decrease of approximately 38% in K-factor was observed. This previous experience provides additional incentives to investigate the phenomenon under field conditions. Past model studies done at the University of Utah by Ozukurt (1945), Biron (1944), and Greenhalgh (1942) present similar evidence of this variability. More recently, Kharkar's (1974) study of coal mine friction factors contains similar indications that K-factor is not constant in all situations. Taken together, the data

Jan 1, 1988

By Bryan Ulrich

On March 15, 2012, about 24 attendees from several western states attended Roundtable 2012, hosted by Knight Piésold and Co. at the Red Lion Hotel and Casino in Elko, NV. The focus of this year?s discussion was ?Acid Rock Drainage for Engineers and Environmental Scientists.? Other names may have been more suitable for the event, perhaps combining geochemistry, with air and water quality and their long-term effects on soil and rock mechanics. Bryan Ulrich (senior vice president, Knight Piésold?s Nevada operations) and Steve Lange (senior geochemist, Knight Piésold, Denver, CO), helped facilitate the discussion. Attendees included personnel from a dozen mining properties, various corporate offices and academia. There were also attendees from a geochemical testing laboratory to help respond to specific questions pertaining to testing protocol and procedures.

Jan 1, 2012

By J. A. Restrepo, K. D. Luxbacher

"The U.S. underground coal mining industry has recently seen the occurrences of several multifatality events that have interrupted an otherwise steadily improving safety record. These events transpired even with an unprecedented level of government regulations and safety technologies. These events may indicate that current safety practices have reached a level of diminishing returns. Risk management, a safety approach that has been successfully applied in numerous industries including mining, may provide a means to overcome this plateau. Riskgate is an Australian mining risk management program that may be successfully applied in the United States. However, fundamental differences between the Australian and U.S. coal mining industries prevent direct implementation. This paper discusses aspects of the Riskgate body of knowledge that require adaptation for its application in the United States. IntroductionThe underground coal mining industry in the United States has recently seen the occurrences of several high profile, multifatality events. These events transpired in the midst of an unprecedented level of government regulations and modern safety technologies. The recent increase in fatal events in conjunction with minimal declines in fatal and nonfatal injuries over the past decade may signify that current safety practices have reached a level of diminishing returns. In order to surpass this plateau, a modification to the manner in which the mining industry approaches worker safety may be warranted.The implementation of a risk-management- based approach may potentially provide a means for not only surmounting the current safety stagnation but also for achieving the long-desired objective of zero harm.Riskgate is an Australian risk-management- based body of knowledge that shows great potential for application in the United States. This paper discusses aspects of the Riskgate body of knowledge that require adaptation for the U.S. mining industry. The proposed adaptations are based on differences in operating practices and government regulations. This discussion will focus on the three major U.S. risk areas of explosion prevention, ground control and moving equipment."

Jan 1, 2015

By Jr. Freed

Basic design features, details of the face ventilation system, roof support and Operator protection system, certified lighting, and in-mine evaluation plans are presented for an Automated Extraction System (AES) that has been designed to fill needs which are present in the Mining Industry. The philosophy of design and proposed operation of the machine, as well as the relationships between these factors, are reviewed. The AES is designed to help overcome production problems resulting from the regulation of roof control, clean-up, ventilation, dust suppression, and operator protection required by the Federal Coal Mine Health and Safety Act of 1969. The design permits more continuous operation and greatly improves operator safety. The machine is a full-face drum-type continuous miner which includes self-advancing, continuous temporary roof support and permanent roof support equipment. Onboard self-advancing face ventilation, dust suppression, and air scrubbing equipment are also included in the design. A further improvement over existing equipment is the incorporation of an automatic programmed cutting cycle control system. All mining functions including movements of the roof support system are handled by this automatic system.

Jan 1, 1978

By Neil and Associates

Seismic tomography is one of several additions to the suite of geotechnical engineering tools for use in various underground rock and mineral geologic structures. Seismic tomography is a method for reconstructing a cross section of an object based on attributes of seismic energy that have been transmitted through the object. The in-seam seismic tomogram provides a dataset that can be graphically portrayed in a color-coded format that is then used to infer relative stress concentration (Fig. 1). During the past several years, the US Bureau of Mines (USBM) at its Denver, CO and Twin Cities Research Centers in Minnesota funded several innovative hardware and software developments. These were directed toward use of in-seam seismic tomography for underground geologic strata evaluations. These preliminary investigations have matured into well-defined and field-proven technical advances for improving ground-control decision making in the mining industry.

Jan 1, 1996

By ERIK CHARRIER, HUGH MILLER, JOSEF BOURGEOIS

In this study, a unique excavation system was characterized using waterjet technology as the primary tool for material removal during rehabilitation of reinforced concrete and shotcrete structural liners. Through empirical testing, this research seeks to validate the hypothesis that waterjet removal of these support systems will result in less unintended damage than conventional removal methods. The intent is to develop a viable technology that will reduce the collateral damage caused to surrounding liners during excavation, improve the adhesion between shotcrete and the substrate for longer lasting ground support, and improve overall safety for workers in underground environments. An analysis on the fracture mechanisms and operating parameters of each method was completed. Instrumented shotcrete panels were physically tested and examined through visual inspection and ground penetrating radar (GPR) to compare substrate damage according to each testing method. After testing was completed, the data strongly indicate that waterjet cutting causes less collateral damage to the surrounding intact liner and substrate than conventional impact hammers. This research is intended to provide a scientific basis for additional applied research in the rapid excavation and repair of shotcrete support systems.

By Jeffrey A. Yonkey, Timothy J. Lutz, Jacob L. Carr, Christopher C. Jobes

"Since 1984, there have been 39 fatalities involving striking and pinning of the operator and other workers by the continuous mining machine (CMM). In January 2015, the U.S. Mine Safety and Health Administration (MSHA) finalized a regulation to require proximity detection systems on all continuous mining machines except full-face machines (MSHA, 2015). Proximity detection systems are designed to stop machine motion to protect miners from striking/pinning hazards. Several MSHAapproved proximity detection systems are commercially available.NIOSH researchers have been involved in the development and testing of proximity detection technology since creating the HASARD system (Schiffbauer, 2002) and have recently conducted research intended to develop more advanced proximity detection technology for CMMs (DuCarme et al. 2013; Jobes et al. 2012; Carr, DuCarme et al. 2013 and Carr, Li et al. 2013). In addition, NIOSH has also conducted research investigating how the signals of a proximity detection system propagate (Li, Carr et al. 2013 and Li, Jobes et al. 2012) and have developed a novel method for determining the location of a personal wearable device (PWD) relative to the magnetic field generators (Carr et al. 2010 and Jobes, et al. 2012).To evaluate the performance of proximity detection systems implemented in industry, NIOSH researchers conducted tests in 2013 on three systems installed on CMMs at three underground mines in Illinois and West Virginia. The results of these tests indicated that, while generally consistent performance was observed, there were opportunities for improving performance. These results were presented at the 2014 SME Annual Meeting (Carr, Lutz, et al. 2014). Since that time, second-generation systems have become available to the industry and are becoming more commonly used.Beginning in early 2014, NIOSH researchers conducted underground testing of these secondgeneration proximity detection systems installed on CMMs. Five tests were conducted on four installations of second-generation proximity detection systems, with one installation being tested twice. The tests were conducted at mines located in Illinois, Virginia and Kentucky with seam heights ranging from 137 cm (54 in.) to 213 cm (84 in.). These tests were conducted using the same test protocol used during first-generation testing, which is summarized in the following section."

Jan 1, 2014

By R. W. Culbertson

During the 1920's, approximately 11,000 small gasifiers were in operation in the United States. They converted about 15 million tons of coal per year into low Btu gas. In some cases, hot raw gas was used for applications such as firing open hearth furnaces or brick kilns. In other cases the gases produced in the gasifiers were cooled, cleaned and desulfurized for various utility and industrial purposes. The steel industry was by far the largest user. The most important fact was that the conversion of coal to a usable fuel gas was demonstrated to be commercial. During the late 1940's and early 1950's, this form of energy was largely replaced by natural gas as the pipeline net work was expanded. Producer gas was no longer economically competitive. Over the past twenty-five (25) years, government controls on the interstate price of natural gas have maintained this situation. At present only three commercial small coal gasifier plants are still in operation in the United States. These facilities are operated by the Glen-Gery Corporation which is located in eastern Pennsylvania; the National Lime and Stone Company which is located at Carey Ohio; and Holston Defense Corporation which is located at Kingsport, Tennessee. There are, however, numerous operating gasifiers in other parts of the world. Recent events indicate that this situation is changing. The quantity of domestic natural gas available to the interstate market has been declining at the same time that demand for all forms of energy has been increasing. The current potential market for gas with a heating value ranging from 100 to 500 Btu per cubic feet has been estimated at sixteen (16) quads (16 x 1015 Btu) per year. This is expected to grow to twenty (20) quads by the year 2000.

Jan 1, 1978

By C. K. Skokan

Various geophysical tools have been tested over the last eight years to evaluate their usefulness in defining damaged rock zones in an underground facility at the WIPP site in New Mexico. These tools include direct current and frequency domain electrical methods and seismic tomography. The electrical measurements show a "drying rind" to exist around older excavations. Seismic tomography confirms that a rind of lower velocity has developed along walls. In combining these tools, a monitoring program has been proposed to observe long-term changes in bedded salt. Results from the monitoring of electrical data over a 2-year time period illustrate the applicability of the technique in an underground environment.

Jan 1, 1993

By C. Heath

US coal consumption reached new heights in 1985, but production was constrained by excess consumer inventories. Domestic consumption of coal reached a record 742 Mt (818 million st) during the year. This is a 3.4% gain over the previous consumption high 718 Mt (791 million st) in 1984. An additional 84 Mt (92.7 million st) of US coal were shipped abroad in 1985, up 13.7% from exports a year earlier. Coal production in 1985 totaled 804 Mt (886 million st), 1.1% below the record 813 Mt (896 million st) produced in 1984. The slight decline in coal output is attributed primarily to a 13% drawdown of large consumer stockpiles built up in 1984 in anticipation of a miners strike that never occurred. Coal demand, and hence production, were also restrained by slower economic growth in 1985 and additional gains in nuclear generation of electricity. Domestic market requirements for coal in 1985 were mixed. Electric utility consumption rose 4.4%; coke plants consumed 6.7% less coal; coal requirements in the other industrial sector expanded by 2.1% and consumption in the residential and commercial sector fell 14.8%. The 2.2% increase in electric power generation in 1985 resulted in a 4.4% rise in utility coal consumption, totaling 630 Mt (694 million st) for the year. Twenty-nine of 45 states where coal-fired electric power plants were operating shared in the 26.7 Mt (29.5 million st) increase in 1985. Coal receipts at utilities fell by 16 Mt (18 million st) as these facilities worked off 21 Mt (23.4 million st) from stockpiles during the year. Electricity generation at coal-fired power plants similarly climbed 4.4% to 1.4 trillion kWh in 1985. This gave coal a 56.8% share of electricity generated from all energy sources compared with 55.5% in 1984. The average price of coal delivered to these facilities remained essentially unchanged during the year. It declined on 1.5% from $38.26/t ($34.71 per st) during the fourth quarter of 1984 to $37.70/t ($34.20 per st) in the fourth quarter of 1985. Coal consumption at coke plants continue to reflect a depressed steel industry. After rebounding 18.9% in 1984 for the first time in five years, coal consumption at coke plants again declined 6.7% to 37 Mt (41.1 million st) in 1985. Coke consumption 26.5 Mt (29.3 million st) exceeded production, 26 Mt (28.7 million st), in 1985. This resulted in a 1-Mt (1.2-million st) decline in coke stocks at producer and distributor levels during the year. The average price of coal delivered to coke plants decreased 7.6% from $64.30/t ($58.34 per st) during the final quarter of 1984 to $59.42/t (53.91 per st) in the last quarter of 1985. Coal consumption in other industries, including all manufacturing and industrial consumers except coke plants, totaled 68.3 Mt (75.3 million st) in 1985. This was the highest level attained in more than a decade. But the lower percentage rise last year (2.1% compared to 11.8% in 1984) reflected slower growth in the nation's economy in 1985. The average price of coal delivered to industrial firms declined 4.5% from $42.32/t ($38.39 per st) in the fourth quarter of 1984 to $40.39/t ($36.65 per st) in the last quarter of 1985. Coal-producing states in Appalachia mined 9.8 Mt (10.8 million st) tons less in 1985 than in 1984 for a 2.4% loss. The largest contributors to the region's production decrease to 393 Mt (433 million st) were Pennsylvania, down 14.7% to 60 Mt (66 million st); Ohio, down 8.3% to 32.6 Mt (36 million st); and West Virginia, down 2.9% to 115 Mt (127 million st). Conversely, eastern Kentucky production was up 4.8% to 111 Mt (122.8 million st) in 1985, while production in Tennessee climbed 9.7% to 40 Mt (44 million st). No coal was mined in Georgia last year. Coal production in the interior region in 1985 declined 3.9% to 173 Mt (190.4 million st). Substantial production losses occurred in Indiana, down 8% to 31 Mt (34.5 million st); and in western Kentucky, down 7.9% to 36 Mt (40 million st). Coal production in Texas rose 5.7% to 39 Mt (43.5 million st) in 1985. Louisiana began mining lignite 140 kt (151,000 st) during the year. Production in the western region increased 3.4% to 238 Mt (262.5 million st) in 1985. Wyoming, up 5.3% to 125 Mt (140 million st); and North Dakota, up 16.5% to 23.5 Mt (26 million st) contributing the largest amounts. Production gains were also shown in Washington, Utah and, notably, in Alaska where coal output climbed 72.9% to 1.3 Mt (1.5 million st) in 1985. Most of the additional coal produced in Alaska last year was shipped abroad. Coal stocks held by consumers totaled 154 Mt (170 million st) at the end of the year. This was 27 Mt (30 million st), or 13.7% below the inventory level at the end of 1984. Stocks held by producers and distributors declined by 868 kt (957,000 st), or 2.8% in 1985 to 30 Mt (33 million st). A drawdown in stockpiles occurred in each consumer sector during 1985. Stocks held by electric utilities totaled 142 Mt (156 million st) at the year's end, 13% lower than stock levels at the end of 1984.

Jan 5, 1986

By E. W. Sawyer

Gelling-grade attapulgite and sepiolite clays are employed as thickening agents for the preparation of ionically contaminated drilling fluids where the use of fresh water clays are unfeasible or impossible. Attapulgite and sepiolite are nonswelling clays that can be dispersed and reflocculated by mechanical and chemical means to increase the viscosity of fresh water, salt containing waters, gypsum contaminated waters and fluids containing cement. Such gelled systems are quite stable in viscosity properties and can be further treated with other necessary additives such as thinners, water loss reducers, weighting agents, surfactants, etc. Many of the oil well drilling fluid practices have influenced such technologies as water well drilling, foundation drilling and waste disposal. The use of salt water gelling clays in these fields will be described and compared to oil well drilling.

Jan 1, 1986

Over 800 mines have closed in Australia in the past 25 years. This paper summarizes the data obtained from those closures and includes all Australian States and Territories and all commodities, including metalliferous, coal and industrial minerals. Twenty five percent of the mines closed due to resource exhaustion or depletion; 24% due to high costs, price drops, or declining grades; 8% due to open pit resource depletion (but with underground reserves remaining) or underground reserves depleted (but plans to open cut remainder) and 7% due to receivership or voluntary administration. The environmental, social and economic impacts of these closures are also significant and include acid mine drainage and impact on mine employees. An understanding of the causes of premature mine closure will better equip mining companies and governments to better manage future mine closures, wherever in the world the mines are operating.

Jan 1, 2007