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By Norbert Patzelt, Johann Knecht, Wolfgang Baum

High pressure roll grinding (HPGR) is a mature but still expanding comminution technology. In the metals mining industry, HPGR is slowly gaining acceptance as a cost-efficient, high-throughput alternative for plant optimization. The increasing need to treat ores with progressively lower grades, complex mineralogies, refractory metal occurrence and variable rock types requires an energy-efficient comminution technology that reduces metallurgical problems inherent in conventional crushing and grinding, while stabilizing leach and flotation circuits and increasing metals extraction. This paper will summarize our latest HPGR pilot test results for gold and copper projects in the United States and South America and their confirmation through the first HPGR operation in copper mining. This paper will also stress the use of the high pressure grinding roll as a metallurgical tool. The application of HPGR for the treatment of heap leach SX-EW ores, semi-refractory gold ores, waste rock material and concentrator feeds will be illustrated.

Jan 1, 1998

By A. C. Noble, D. E. Ranta, J. W. Mustard

Skarn deposits present many unique problems in estimating ore reserves, including difficulties arising from the complex character of the mineralization and intricate ore body shapes resulting from structural complexity. Mineralization within skarns occurs in metasomatically altered carbonate horizons produced by magmatic hydrothermal fluids emanating from intrusive stocks. Deposit formation is controlled by both the presence of favorable host rocks and by proximity of these host rocks to a mineralizing intrusion. Ore controls must be defined to account for abrupt changes in grade that occur between miner- alized and unmineralized horizons. Gradational grade changes within the mineralized zones must also be defined in terms of skarn type and included barren rock to assist in reserve estimation. Defining mineralized limits can be further complicated by faulted, rotated, or folded strata affecting the morphology of an ore body. The MacTung copper-tungsten exoskarn deposit, located along the Yukon-Northwest Territories border in Northwestern Canada exhibits a number of unique properties that preclude a simple mathematical approach to ore re- serve estimation. This deposit is used to demonstrate methods for modeling geologic controls and geostatistical properties for a skarn deposit.

Jan 1, 1992

By Roland Heersink, Charles H. Wells

This paper discusses how a mill uses off-site data hosting approach to effectively utilize an entire suite of advanced applications to optimize daily operations, without incurring the overhead of on-site systems, staff and support. Details of the solution are provided, together with a live view of actual plant operations. Security and authentication mechanisms are also outlined so that users may gain an appreciation of the actual security of the remotely hosted data. A number of Web-hosted software applications provide direct connectivity to the database offering rapid and deterministic response times to clients. A 24x7 help-desk is available to authorized users from any Internet connected device. The paper shows how mill management advantageously use wireless PDA's to view what is going on at anytime and from anywhere. It concludes with a summary of how the approach is being used to speed decision-making and capture spot market opportunities.

Jan 1, 2002

By Donald S. Skufca

This chapter focuses attention on major factors pertaining to plant design and general arrangement of equipment. Considered are efficiency of operations, coordination of maintenance and repairs, plant testing of reagents and possible future plant expansions. The design and general arrangement of equipment considers accessibility for maintenance and isolation for repairs, minimum personnel for operations and cleanup, safe working conditions with minimum interruptions to operations. The constant introduction of new reagents requires eventual plant testing and the manner of isolating a “line” or part of the facilities to allow comparisons in the testing of new reagents is discussed. As technology improves and process changes occur, additional equipment or plant expansions are inevitable. Space for these eventualities must be considered while the general arrangement drawings are in the development stages.

Jan 1, 1986

By K. K. Haramy, J. McDonnel

INTRODUCTION Primarily because of mining at greater depth, an increasing number of coal mines in the United States experience floor heave problems. In many instances, the floor heaves at a slow rate without causing health and safety related problems; only additional roadway maintenance and coal handling equipment are required. However, when rapid, massive heaving occurs, the safety of mine personnel in the vicinity is jeopardized. Extensive floor heave causes a redistribution of stress around the mine opening and can cause additional ground control problems. This paper presents an analysis of rapid floor heave in a deep western coal mine. The analysis is based on field measurements, laboratory data, and beam design theory. Factors affecting floor heave, such as mining-induced stress, mine opening size, entry orientation, mine geology, rock physical properties, and gas pressure, are considered. Examination of floor heave in the mine indicates that heaving is primarily caused by deformation of a soft floor member that is subjected to high mining-induced stress. Theoretical analysis of in situ floor stresses resulting from overburden loading indicates that floor failure will occur. The analysis is confirmed by visual observations of floor heave in the mine. Recommendations for mine layout and opening design to control rapid, massive floor heave under these conditions are also presented. MINE-FLOOR-FOUNDATION THEORY The floor stratum in a coal mine acts as a foundation to support coal pillars and artificial supports, thereby providing support to the mine roof. The overburden load, transferred through pillars and other supports, applies tremendous stress to the floor. Soil mechanics theories provide solutions for foundation design problems that apply to the mine floor. Based on foundation theory, vertical load on pillars causes high shear stress zones in the floor. If the floor is relatively weak, it may fail and dislocate upward into the mine opening. Strong roof strata that do not readily fail transmit most of the overburden load through pillars to the floor. Heaving may result, depending on the thickness and physical properties of the floor

Jan 1, 1986

By M. C. Williams, T. P. Meloy

With the increasing power of computers to simulate and control processes in the mineral industry, predicting the potential use of computers in the minerals field is not a hazardous enterprise, but predicting the timing of their use is. Like the railroad industry, technology invades the mineral industry, rather than being an industry like electronics that creates technology. Because of this invasive nature of computer technology in the minerals field, this paper predicts what will be possible to do effectively and economically with computers in the mineral industry. Moreover, this paper explores the problems of using the emerging computer technology in the mineral industry. For example, if not now, it soon will be possible to control the output of a mineral processing circuit - high grade, high flow or a mixture of it - to meet the daily market conditions and to sell each day that daily "mill" output as "mill" futures on the commodity market. Finally, suggestions are made which may be done to prepare the industry for the computer revolution in the mineral industry.

Jan 1, 1993

By J. F. T. Agapito, R. R. Goodrich

Yield pillars have been used for many years to help reduce stresses near mine openings and improve roof and floor stability. A yield pillar is often defined as a pillar that fails but retains residual strength. Stress transfer occurs through the roof and floor after the peak strength of the pillar is reached. High stresses are transferred from around the openings onto abutments that can be barrier pillars or unmined ground. This mechanism, often referred to as pressure arching, is possible as long as the width of yield pillar mining (panel width) is less than the critical width above which stresses cannot be carried by the overburden. Significant stress transfer also can occur due to small amounts of pillar and/or floor yielding before the peak strength is reached. This is accomplished in a quasi-elastic manner with little or no visible roof and pillar fracturing or floor heave. Long-term stability may be achieved when stresses and mechanical properties are favorable to prefailure yielding. This paper gives practical examples where improvements in stability and resource recovery were achieved with this mechanism. Yielding was assessed by comparing measured and calculated vertical pillar stresses. Results indicated that calculated stresses in the pillars were 25% to 40% higher than the measured stresses, demonstrating significant arching load transfer to the abutments. Prefailure yielding is probably often present but unintentional in both development and production areas. Better recognition and use of this mechanism should lead to design improvements, as mines become deeper.

Jan 1, 2003

By Michael Michaylov, Elana Vlasseva

This paper presents a method for three-phase foam preparation recipe optimization. The pressurized foam is injected into porous media of gob area for prevention and fighting of SPONCOM fires. The method includes laboratory experiments for main foam properties as well as mathematical optimization procedure. Optimization criteria are formulated reflecting foam application purposes. The influence of solid phase on foam heat stability is shown. Results from optimization procedure for four foam agents by varying fly ash consistency of foam are presented. Theoretical basis for original construction of foam generator, specially constructed for of three-phase foam generation, is set u

Jan 1, 1997

By B. Cavender

The operating lifetime, or production rate, selected for a mining project is among the most important factors influencing the project's design and ultimate economic success. Incorrectly-determined lifetimes can lead to the erroneous rejection of projects as uneconomic as well as the suboptimal exploitation of producing properties. This paper examines the optimal lifetime calculation using traditional discounted cash flow and recently-proposed option pricing techniques. Using each method, the production rate is determined as that rate at which the project's net present value is maximized.

Jan 1, 1993

Researchers at National Institute for Occupational Safety and Health (NIOSH) are investigating how fiber-reinforced shotcrete mix designs can be extrapolated from proven designs employing wire mesh. This paper explains the results of round determinate panel tests and relates the flexural strength and toughness of fiber-reinforced shotcrete to known energy absorbing properties of wire mesh. The energy absorbed with central deflection is strongly influenced by the amount of fibres. The higher the energy absorption the more load cracked shotcrete can support. Two types of fiber-reinforced shotcrete were investigated, one with steel fiber and another with polyfiber. The residual load supported in Round Determinate Panel Tests can be matched with the strength of wire mesh, thus providing equivalent bag strength values for fiber reinforced shotcrete panels. There is also evidence of a panel crack width comparison to the load holding capabilities of the fiber in the shotcrete mixes. In practice, this provides designers with a method for comparing the ground support provided by fiber-reinforced shotcrete with that supplied by wire mesh.

Jan 1, 2010

By A. Maréchal

It has been shown since a few years that the problem of estimating recoverable reserves should be solved by using specialized statistical techniques : whenever the selected blocks are chosen without any other constraint than a cut-off grade criterion, the problem of estimating the corresponding tonnage-grade curve is resolved by estimating the local histogram of block grades. Two major statistical techniques are currently used by geostatisticians to estimate local histograms : the "average conditional distribution" technique (Parker, Journel, Dixon 1979) and the disjunctive kriging technique. (Matheron, 1976, Jackson, Maréchal, 1979). Both have proved to be applicable in practice, with their pros and conconcerning their practibility and versatility.

Jan 1, 1982

By John Rushton

Surface mining, from ore extraction to processing, requires many types of equipment to obtain the final product. Mine equipment often includes shovels, drills and haul trucks. Ore processing equipment, including plants, mills and concentrators, are also part of surface mining operations. Surface mining operations emphasize production. Production is where the bills are paid and fortunes are made. However, there must be support to keep the equipment operational. To most production people, equipment maintenance is a necessary evil. Maintenance is not glamorous work. It is often neglected when praise is being passed around. It is easy to recognize higher production, greater capacities, faster cycle times or more loads hauled. But who cares if an engine is replaced in 12 hours instead of 48? The answer is, everyone should - from the hourly miner to the mine manager. Surface mining equipment needs constant maintenance work. It must be lubricated, components replaced, electrical problems repaired and other problems addressed. Repair work for any surface equipment takes time away from production. It costs money. Maintenance costs cannot be avoided. However, they can be minimized. Minewide communication should include operations cooperating with maintenance. Traditionally, operations resist surrendering equipment to maintenance if it can continue to produce. The rationale is, every load that can be hauled today is money in the bank. If the unit is taken down, the money is lost. This thinking is prevalent in many surface mining areas, including the mill. "Not on my shift," the operator thinks. "Let the next crew worry about it. The problem with this thinking is in probability and statistics. The longer equipment goes without maintenance work, the higher the probability of equipment failure. When the failure does occur, it is certain to cause the equipment to remain down longer than if the maintenance department had been allowed to take it down. Many mining operations have closed early in their lives because of poor maintenance practices. This has become the industry standard because substandard levels of performance are acceptable. Management believes it gets five to six hours of work from maintenance people during an eight-hour shift. Actually, the industry average is less than two hours of work per shift. Real productivity levels of less than one hour are not unusual. There are few exceptions. However, a daily work schedule (DWS) will increase productivity at many properties by 50% to 100%. A 200% improvement is not unusual. The DWS will work. Maintenance people are among the most intelligent and motivated people on the property. They deserve the chance to be productive. [ ] In preparing a DWS, management needs to understand two productivity principles - the productivity spread and the real maintenance workday.

Jan 1, 1997

By Helen Leung, Colin R. Phillips

The performance of personal alpha dosimeters in mixed radon daughter and thoron daughter atmospheres in Ontario uranium mines is described together with monitoring developments which enable the radon daughter working level to be determined separately. The theoretical bases for continuous and integrated working level measurements based on individual and gross counts are presented in terms of the weighting factor for combining the thoron daughter working level with the radon daughter working level, and in terms of the in-growth time of the air. Implications for the determination of working level in the presence of thoron daughters are discussed.

Jan 1, 1981

A chartered bus with about 30 attendees of the just completed 1998 SME Annual Meeting headed toward Green Cove Springs, FL, which the author had been told was located somewhere south of Jacksonville, FL. In conjunction with the meeting in Orlando, RGC (USA) Mineral Sands provided a tour of its facility. The author had worked with heavy minerals on a laboratory scale, performing the usual gravity and magnetic separations, but had never been to a heavy mineral mine and processing facility. Years ago as a metallurgist, the author once applied for a job in a heavy mineral operation in Florida -it may have been the same operation. After turning north on to Highway 95, the endless billboards promoting beach-front retirement communities proved the Atlantic ocean was just a few miles away (although the author never caught a glimpse of it). After another hour, the bus suddenly turned west and continued inland for about 65 km (40 miles). The thought occurred, "We are talking about beach sands, what are we doing heading away from the ocean?" As the bus continued inland, the author was struck by the flatness of the land and by the lakes, rivers and wetlands. He was also impressed by the many fine stands of pine and hardwoods. The office of RGC (USA) Mineral Sands is located about 16 km (10 miles) south of Green Cove Springs. Upon leaving the bus, members of the tour were greeted by Graeme Sloan, general manager, and Elliot Mallard, manager of mining. They provided some general information about the operation, including a slide show. RGC's Florida operation produces four concentrates: zircon (ZrSiO,), rutile (TiO,), ilmenite (FeTiO,) and leucoxene (an alteration product of ilmenite containing 67% to 70% TiO,). With a work force of about 170, the annual production of the above products is about 23,27, 45 and 14 kt (25,000 30,000 50,000 and 15,000 st), respectively. RGC also has other mineral sand operations, in addition to gold and base metal mines, mostly in Australia.

Jan 1, 1998

By Richard S. Mateer

The percent ash in a coal blend is equal to the weighted average of the ash contents of the component coals. If the raw coals differ in washability characteristics, the total yield may be maximized by washing the component coals to different quality levels. A mathematical basis for blend maximization is developed and a computer program is described The program determines the component weights that maximize the yield, while meeting an individual coal-quality specification. The procedure is directly applicable to linear parameters of grade quality such as percent ash, percent sulfur and the calorific value. A transformation of variables permits program execution to meet a sulfur-compliance specification. Blends may consist of any number of component coals.

Jan 1, 1997

By A. P. Cook

Methane drainage on a mine-wide scale is a relatively new technology to South African coal mines. Shallow seams and apparently low methane contents have been assumed to result in less methane problems than experienced in other countries. The introduction of deeper mines however, has now resulted in methane drainage taking on a higher priority. Methane contents in the region of 12 m3\t have resulted in one colliery introducing drainage as a ventilation support. Although a low seam permeability initially indicated reduced potential for drainage, early borehole flows of 90 m3\m\year have since increased to 450 m3\m\year. Rapid inflow of methane into goafs and sealed areas from seams surrounding the main production seam at another colliery have warranted extensive evaluation of the methane properties of these seams with the projected introduction of predrainage from surface. Methane pressures in excess of 1000 kPa and contents in the region of 10 m3\t again give methane volumes suitable for drainage. Coal seam drainage ahead of mining is becoming more significant and is likely to see an increase in the near future. INTRODUCTION Methane gas is an everpresent hazard associated with underground coal mining. Safe working levels of methane in the mine atmosphere are normally maintained by ventilation practises, ensuring sufficient dilution of the gas. However in some cases the ventilation must be assisted by methane drainage, either from the mined seam, or from adjacent seams and strata, or from goafed areas. South African collieries have practised only limited methane drainage until now. Relatively shallow mining depths, and apparently low in-seam methane contents have been assumed to result in fewer problems with methane than are the normal for other countries. This is now being shown to not necessarily be the situation. Work carried out by the Coal Mining division of COMRO (Cook and Erwee, 1991) indicates South African production coal seams have very similar methane retention properties to those of coals in other countries, with seam gas contents of up to 12 m3/t. This awareness, as well as greater mining depths, and higher degrees of mechanisation, has resulted in higher priority being given to methane emission problems throughout the industry. Increased levels of safety, as well as possible commercial applications, are the main reasons for the interest now being shown in methane drainage. Not only is there possible applications in the present production coalfields, but South Africa has vast areas of coal reserves which are presently non-mineable, now being seen as possible alternative energy sources. Limited methane drainage is practised within the industry, but only on collieries that have identified specific methane problems that can be alleviated by drainage. Historically this has been restricted to surface drainage of longwall goafs, reducing emissions onto the faces. More recently, horizontal in-seam holes have been drilled, until now for bord and pillar sections, but the results are being evaluated for later application to shortwall faces. Adjacent seams pose problems at some sites and vertical and cross measure boreholes are now being considered.

Jan 1, 1993

By José Salim, T. V. Subrahmanyan

The occurence of primary stratiform and vein gold deposits in the Precambrian rocks of Northeastern Brazil is discussed. The stratiform deposits are related to clastic sediments (quartzites and conglomerates). The veins are associated with quartz and sulfides and are structurally controlled by shear zones. The gold was recovered for a long time by small miners. Developmental programmes for large scale mining are now envisaged. The recovery problems and gold economics are also discussed.

Jan 1, 1988

By L. Shevenell

Nevada now has, or will have, 35 pit lakes resulting from open-pit mining below the water table. State regulators are requiring that the ultimate pit lake water quality be predicted as part of the permit application process. Water balances/pit lake filling rates must be esti¬mated in support of the geochemical modeling. In Nevada, analytical and numerical methods have been employed for the study of pit lakes. In the current work, analytical solutions are investigated for one pit lake, the Getchell south pit lake, which previously filled be¬tween 1968 and 1982 during a hiatus in mining. Water levels vs. time are available for this lake and these data have been fitted with a hyperbolic curve. This water-level-vs.-time curve was used in simple water-balance computations to find the net inflow rates by forcing computed water levels and volumes to match those of the known water levels and volumes through time. The model described here provides realistic volume fluxes into and out of the lake on a monthly basis as the pit lake filled.

Jan 1, 2000

The design of solvent extraction plants has been generally based on the assumption of steady operating conditions in both the settler and the mixer units. However, recent experience in both large and small plants has shown this not to be the case. Mixer transients include start up aqueous locking and partial phase separation in secondary mixers, which both lead to reduced plant capacity or overflow of upstream mixers. Analysis of the hydraulic pressure profiles has generated new design methods to eliminate the effects of the partial or complete phase separation. Changes to the method of specification and selection of primary and secondary mixers have been made to eliminate the onset of partial separation during operation. The observation of settler operation has shown that it is also a dynamic process, even under "steady-state" conditions. Four transient phenomena have been identified that lead to internal circulating flows, poor disengagement of fine secondary haze and erratic and high entrainment levels in the discharges. A, first approximation analysis has shown that there are significant pressure differentials within settlers, and these change along the length and with the phase separation rates. A technique to control the effects of these transients was developed that allows plant performance to be improved beyond "standard" expectations. The design and selection of the settler internals is described. Key words: Solvent extraction, Mixer-settlers, Phase separation, Entrainment, Mixer transients

Jan 1, 2003

By Laurence B. James

The California Department of Water Resources is concerned with the development, distribution, and protection of the State's water resources. Geologic activities of the Department relate to planning, construction, and operation of water projects, supervision of the safety of over 900 dams under state jurisdiction, and investigation and control of ground water supply. The Department is engineering oriented, and the role of the geologist is to assist with the solution of engineering problems. Some of these problems require the integration of many talents, including not only those of geologists and engineers, but also those of economists, lawyers, seismologists, chemists, geophysicists, and hydrologists, Frequently, a task force of several disciplines will attack a problem as a team.

Jan 1, 1965