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By Dan B. Kivari

A key operation of any milling circuit is grinding. Over the last two decades, large diameter semiautogenous grinding (SAG) mills have become the preferred primary grinding mills. The drive systems became more complex as the size of the mills became larger, during which time operating and design experience for SAG mill accumulated. Considerable reliance is now placed in power electronics to provide flexibility in SAG mill operation to meet the demands of lower operating costs. Most earlier SAG mills were designed to operate at fixed speeds. Present day SAG mills can operate at a fixed speed or variable speed through the use of an ac synchronous motor or dc motor. This flexibility, however, comes with an increase in capital and operating costs. Since the capital and operating costs of a project directly affect the project's rate of return, the selection of a SAG mill and its drive system should depend, in part, on the impact that the extra cost makes on the project. This impact can be measured by performing an economic analysis based on net present cost (NPC) calculations. Although the NPC calculation is an important factor in the grinding mill selection, other factors, such as reliability of mill drives and power source, are important elements in the decision making process. This article examines how the NPC calculation, plus reliability and power source, influence SAG mill selection.

Jan 1, 1992

By Thomas D. Kaufmann

Whether pursuing hedging or speculative strategies, gold miners can increase sales revenues 1 % to 6% by constantly pricing production forward. Unlike other commodities, gold futures prices are consistently higher than spot prices. A Colorado School of Mines study showed theoretically and empirically that in the 15 years since the price of gold was released from government control, the forward price for gold has been higher than the current price almost 100% of the time. The reason why Metal traders know that holders of metal earn a bonus selling forward when the metal is in "contango." "Contango" is a mysterious word that crept into the trading vocabulary a century ago. It designates a situation when the price of a metal on the futures markets is higher than the price in the immediate or spot market. If the spectrum of spot and futures prices remains static over time, the forward seller who has contracted at a higher than spot price can make a profit equal to the contango by redeeming his commitment at the lower spot price when the contract matures. Consequently, when a seller in a contango market hedges, he makes a profit on the transaction in addition to avoiding a price change risk. On the other hand, buyers of the metal who hedge in a contango situation will sustain a loss equal to the contango. Producers of gold, however, are sellers of gold. For most metals and oil, there is no inherent reason why futures prices should be higher than present prices. Buyers and sellers decide that the price of the commodity will be lower or higher than present values for a variety of reasons.

Jan 1, 1991

By Gunther Riedmuller, Johann Golser, Peter Schubert

The paper deals with the experience of the authors to cope with tunnel projects in heterogenous and weak rocks. The procedures applied to the investigation of such areas, the geotechnical assessment, the choice of tunnelling methods, the preparation of contract documents and the main features of NATM tunnelling to adapt to these conditions are outlined.

Jan 1, 1993

By R. A. Speirer, T. C. Bettinger, L. P. Richardson

INTRODUCTION The Bureau of Mines (The Bureau) remote sensing researchers at the Denver (CO) Research Center, have been investigating computerized methods to detect and map surface linear features called "lineaments" for ground hazard assessment in mines. Many of these lineaments at the test mine site were found to correlate to subsurface geologic discontinuities such as faults, fractures, and joints that intersect coal seams at depth. These features adverse1 y affect the roof and rib integrity in underground mines, thus contributing to rock failures that may result in injuries to mine workers and loss of production. Advance knowledge of the existence of such hazardous geologic features can aid in mine planning and development. Lineaments may be observed in a variety of images of the earth's surface. Linear features that can be observed using Landsat mu1ti spectral scanner data (MSS) images range from regional (greater than 3 miles in length) to an intermediate length of from 1 to 3 miles. These images are recorded in discrete radiation bands in the green, red, and near-infrared portions of the el ectromaynetic spectrum. These data are acquired from the EROS Data Center of the U.S Geological Survey, Sioux Falls, SD, in digital format on magnetic tapes that are suitable for processing on certain minicomputers. Shorter lineaments length (less than 1 mile) can be observed in high- to low-a1titude aerial photography, radar, and infrared images with image scale ratios of 1:1,000,000 or less. These linear features can correlate to smaller dimensioned faults, and to fracture and joint sets at the local geologic scale. Other informational sources can help substantiate 1ineament analyses, such as well logs, mine naps, topographic data, and geophysical data acquired over the study site. These data must be in a digital format to process on the "DEC PDP 11/23 minicomputer system1". Data can be acquired in

Jan 1, 1986

By Rob Dorey

The disposal of mine waste continues to be one of the main controlling factors in the economics and feasibility of project development. Particular to gold and precious metal mining, waste disposal is further complicated by the environmental and political implications of the use of cyanide. Regulatory compliance criteria have partially dictated and can be anticipated to further dictate the approach and methods of tailings disposal. To develop practical, economic, and environmentally acceptable tailings disposal systems within these criteria requires the use of common sense approaches and the application of available technology. Waste disposal is typically considered during the pre-feasibility stages of project evaluation. At this time, the main emphasis is on the economics and practicality of extracting the metal values from the ore. Frequently, the result of this is that the nature of the tailings and the ability to dispose of the tailings is prejudged. It is also frequently the case, however, that during the feasibility stage and project permitting, the requirements for tailings disposal become paramount.

Jan 1, 1998

By Thomas R. Kuesel

All engineering designs are based on assumptions regarding the behavior of the structure or facility being designed. These assumptions may be based more or less heavily on theory, but are credible only if verified by observations of field performance. Dr. Peck's "State-of-the-Art" paper has described the semi -empirical process of soft ground tunnel design, emphasizing the importance of records of field performance of actual projects constructed under a variety of conditions. This paper will present the principal results obtained from measurements made during construction of the soft ground tunnels for the San Francisco Bay Area Rapid Transit System. SCOPE The BART System comprises 75 route miles, including 14 miles of soft ground tunnelled subways in San Francisco, Oakland, and Berkeley. All tunnels are single-track sections, approximately 18 feet in diameter. Usually there are two parallel tunnels at the same level, but under Market Street in San Francisco there are four tunnels (two over two), and there is also a three-track section (two over one) in Broadway, Oakland.

Jan 1, 1997

By Richard Lovat

INTRODUCTION Soft ground tunnels may be above the ground water table or they may be subaqueous. The ground may be clays, silts, sands, gravels, glacial deposits, boulder tills, and any of these in any combination. Because of the relatively low strength and deformability of soils, difficulties often arise in soft ground tunnelling. These soil characteristics and resultant tunnelling difficulties, have had a direct influence on the development of "Lovat" Tunnel Boring Machines. We have been required to recognize and adapt to unusual ground conditions and to follow through with design, fabrication, and field maintenance to ensure dependable, trouble-free operation. The basic "Lovat" machine is a fully shielded, wheel-type with the cuttinghead driven by a monorace type bearing with gear drive incorporated in the bearing. Mechanical innovations have been added to the basic machine which complement the resources of manpower, equipment, and materials available to the contractor for a specific operation. FULL FACE SUPPORT The installation of hydraulically operated closure doors or flood control doors, at the cuttinghead, is one of the early "Lovat" technical innovations. Flood control doors provide full face support in running or flowing ground. In water bearing sands and silts the excavated material can

Jan 1, 1981

By Andreas Rubo, Stephen Gos

Over the past couple of decades several endeavours have been made to develop lixiviants with the intention of replacing cyanide in gold leaching. In 1980s these endeavours were largely economically driven, due to cyanide shortages at that time. In more recent times, the driving force has shifted to occupational health and environmental considerations. It is often argued that the high acute toxicity of cyanide alone makes it worthwhile considering to replace it completely by less toxic alternative lixiviants. This has led to having to consider more criteria in the choice of any alternative lixiviants, which have often not been taken into account in the past. The intention of this paper is to review these alternative lixiviants and also review the criteria, which have ultimately led to most of these lixiviants never having found any large scale application, if they passed laboratory stage at all. It is also intended to show, that by handling and treating cyanide in a proper manner, the overall profile for the use of cyanide compared to these alternative lixiviants is very favourable. The question to really be answered is whether there is actually any chemical or process applicable to gold leaching that does not show the high toxicity potential of cyanide and that is still favourable with regard to looking at a broader spectrum of criteria and not only acute toxicity.

Jan 1, 2000

By J. J. Scott, G. H. Bennett

INTRODUCTION Friction Rock Stabilizers, commonly called Split Sets,tm* have been under development since early 1973. Five years of intensive laboratory and field testing led to their introduction to the metal mines in the United States in the fall of 1976. Actual sales started in February of 1977 and, to date, over five million units have been marketed to metal mines. The present rate of useage is near 3 1/2 million units per year which is approximately 50 per cent of all roof fixtures used in the United States metal mining industry. Mr. Richard Hoppe, Senior Editor of Engineering & Mining Journal, in an article of the February, 1979, issue, entitled "Winning the Battle Against Bad Ground", said, "In hardrock mining operations in the western U.S., particularly underground uranium mines where exceedingly difficult ground is common, no roof support system has been accepted more quickly than the Split Set friction bolt invented by Dr. James J. Scott and developed by Ingersoll-Rand Co." This paper describes how Friction Rock Stabilizers function and presents technical data to show the uniqueness of the Friction Stabilizer system. SPLIT SET STABILIZERS The Split Set System is a revolutionary development in the field of ground control. The system produces an interior reinforcement to a rock mass which: *Trade Mark of Ingersoll-Rand Co.

Jan 1, 1979

By Peter A. Spencer

Much criticism has been levelled at bacterial oxidation over the quantities of air required for successful operation. Examination of the oxidation reactions and the assumptions concerning oxygen transfer made in the literature (1) indicate that the aeration requirements can be much less than those beirig suggested. Observations made on a large scale pilot test have confirmed reasonable aeration levels in extended site operation over a six month period. These aeration levels have implications for the engineering design and the power needed for aeration and agitation. Thus, these parameters effect both capital and operating costs as well as influencing the complexity of the design and normal operation. A number of companies have developed bacterial oxidation cultures intended for commercial ·expl oi tat.ion ( 2, 3, 4). Most of these cultures have been based on Thiobacillus and operate at temperatures between 30°c and 40°c. This temperature range limits their application in hotter regions unless means for both heating and cooling are provided in the design. Thiobacil!us cultures are also reported as not able to oxidize arsenic (III), which may limit the application of these cultures to successfully treat arsenopyritic ores and concentrates (5). BacTech (Australia) Pty Ltd has developed a culture which operates at temperatures above 4o0 c and which has been tested in a large site based continuous pilot plant at up to 55°c over a six month period. The culture showed resistance to high levels of soluble arsenic, allowing the arsenic to be retained in solution for control led precipitation and disposal. Data for. the arsenic precipitates indicated that these waste solids were relatively stable and, under the correct circumstances, were suitable for disposal into tailings dams without causing environmental problems.

Jan 1, 1990

By Bruce D. Hansen

The complexity of large geographically diverse or multicommodity mining companies requires a corporate structure, which provides the maximum long-term effectiveness. Structure models exist along the spectrum of centralization to decentralization. This paper examines the trade-offs of flexibility, cost, decision making, consistent strategies, and corporate control associated with different structural models as applied to mining companies. The mining industry typically lends itself to a business unit model. However, the degree of decentralization depends on size, proximal operations, technical complexity, product mix, geographic spread, mining methods employed, and the inherent capabilities of an organization.

Jan 1, 2001

By Abdullah Arik

The resource classification methodologies have always been a topic of research and debate. There are both traditional and Geostatistical methods used in practice. Because of the uniqueness of each ore deposit, it seems almost impossible to have a single industry-accepted norm for resource classification. Therefore, some practitioners have adapted the methodologies to suit the deposits they are working on, but many simply use the methods they are comfortable with. Another reason for the existence of varying classification methodologies is the lack of an easy and established way to measure the confidence in the estimates. Therefore, their classification becomes a subject of debate. In this paper, a new approach is offered to classify the resources using a "Resource Classification Index." The approach using this index takes into account the local variation, the spatial data configuration around the block being estimated, as well as the traditional distance measures. A case study for a gold deposit is presented to demonstrate how this new index can be used to classify the resources. The results from this approach are compared to those from two popular classification methodologies.

Jan 1, 2002

By Edward J. Zeigler, John T. Miller

INTRODUCTION Construction of Phase I, Section A, of the Baltimore Region Rapid Transit System required that six underground stations be built using a cut and cover excavation technique. For five of these stations, soldier piles, used as support of excavation, were installed with tip elevations well below the bottom of the excavation. However, in the case of the sixth subway station, the Mondawmin Station, soldier piles were installed only through soil and decomposed rock, with the tips of the piles being stopped well above the bottom of the excavation in partially decomposed rock. Below the tips of the soldier piles, and below a cut slope where piles were not installed, the sides of the excavation consisted of partially weathered and fresh rock and were supported by a combination of rock bolts, wire mesh and shotcrete. An extensive installation of geotechnical instrumentation permitted detailed monitoring of horizontal and vertical movements of the soldier piles and the walls of the excavation. Preliminary studies indicated that the excavation support system selected for the Mondawmin Station would have several advantages over a conventional system consisting of soldier piles extending to the bottom of the excavation, braced with prestressed struts. These advantages included lower cost of installation, a decreased time required for installation, and a more open excavation for the contractor during construction of the station. The Mondawmin Station is situated in the northwestern quadrant of Baltimore City, approximately 6.4 km (4 miles) from the center of the City. The station lies midway in a project 12.9 km (8 miles) long identified as Phase I, Section A, of the Baltimore Region Rapid Transit

Jan 1, 1981

By James F. Fraser

Construction of a major linear project in any environment is difficult, at best. Construction of a major linear project which includes major subway elements, both cut and cover and tunneling, in the center of an urban environment, approaches the impossible. I believe such a project would be impossible for a private company or a privately owned utility for a variety of reasons. The major two reasons are the funding necessary for such massive projects and the myriad of individual interests associated with private ownership of land. Such projects are possible in the public sector only because the need for the project... as is the case with mass transportation in Atlanta. . .overrides the profit motive. Without the profit motive, private companies, whether utilities or not, are precluded from practical interest in the development of any project. While it is safe to conclude that a profit-oriented business would have no practical interest in developing such massive projects as may include major tunnels, it would be useful, I think, to compare some of the significant differences between private profit-oriented businesses, and an agency, or Authority, such as MARTA, in building a major linear project. SLIDE 1. Comparison of a Private Company and a Public Agency [Item Private Company Public Agency Simplified To make a profit To provide a pre Purpose scribed service]

Jan 1, 1979

By Gus Van Weert, Roy van Lier

It has been demonstrated for two totally different silver bearing and cyanide refactory concentrates that the formation of silver jarosite can be prevented through the addition of iodide to the autoclave feed. A molar ratio of r/ Ag+ of no more than 1 was sufficient to raise silver extractions in a subsequent cyanide leach from 4% after autoclaving without iodide addition to 98% for the sulpho-salt concentrate and from 15% to 97% for the pyritic acanthite concentrate. Flowsheet proposals will be discussed to prevent loss of the iodide additive. The use of chloride instead of iodide will also be reviewed.

Jan 1, 2000

By Elisa Comis, David Chastka, Miriam Piemontese, Maria Chastka

The Lower Olentangy Tunnel (LOT) Project involves the construction of a 17,000 ft (5,200 m) long, 12 ft (3.65 m) internal diameter Combined Sewer Overflow (CSO) tunnel. The tunnel is excavated by using an Earth Pressure Balance (EPB) machine designed to cope with soft ground, weak rocks and water pressure. The project is located in the city of Columbus, Ohio and the main geotechnical hazards are related to the heterogenous soils and the low overburden in an urban environment. This paper focuses on the performance of the EPB first drive and the comparison between the design assumptions and the actual TBM performance during construction.

Jun 23, 2024

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

Today, approximately 31% of underground coal mining operations have designated occupations or areas with more stringent (below 2.0 mg/m3) respirable dust standards in place. Many U.S. coal mines have been able to maintain compliance with very low dust levels, and the Bureau of Mines, in an effort to identify those factors contributing to low dust levels, completed a survey of twelve continuous miner sections which were able to maintain their dust levels at or below 0.5 mg/m3. The quantity and quality of face ventilation appeared to be the most important factor in controlling dust exposure. The results directed Bureau research towards identifying improved face ventilation techniques for reducing quartz dust levels on continuous mining operations. This research has involved the evaluation of a half-curtain face ventilation technique which reduces the cross-sectional area of the entry, thus increasing the air velocity over the operator. The Bureau has also conducted extensive laboratory studies to compare tubing versus brattice, including an evaluation of both systems in a crosscut turn. In an effort to improve ventilation and reduce dust exposures of roof bolter operators working downwind of the continuous mining machine, the Bureau has evaluated two novel face ventilation systems. The first system consists of a fan discharge tubing technique which routes dusty air away from the return entry being bolted. In a technique similar to the fan/tubing concept, exhaust air from the upwind continuous miner face can be scrubbed using a dust collector to capture a portion of the dusty air, clean it, and supply it to the bolter operators as a split of clean intake air. A better understanding of face ventilation techniques should lead to solutions to the problem of more stringent dust standards due to quartz.

Jan 1, 1989

By Marc E. Orman, Todd V. Ramey, Mark E. Smith

Heap leaching in certain parts of the world, such as Chile's Atacama Desert, brings unique design problems in the form of possible large differential settlements of the foundation soils due to the dissolution of salts. In northern Chile the soils often c?ntain very high concentrations of soluble salts (nitrates, potas­smm, magnesium, and common sodium). When a leak in the liner occurs, the escaping solution dissolves these salts and trig­gers differential settlement. If the settlement is great enough, the geomembrane tears, the leakage increases, triggering more dif­ferential settlement. The nitrate plants have experienced many occurrences of this phenomenon where a brine pond will under­go a sudden and complete loss of the impounded liquors. The authors present a simplified technique to quantify the differential settlement resulting from dissolution and provide a method which can be used to select a geomembrane with suit­able flexibility under axi-symmetric (multi-axial) load condi­tions to tolerate the predicted settlement.

Jan 1, 1996

By E. Topuz

Mining equipment, like all other equipment, is subject to failure. Since most failures occur at random and are unexpected, corrective maintenance is usually more expensive and causes more down-time than preventive maintenance. In order to reduce the number of failures and thereby increase the availability of an equipment or system, preventive maintenance can be scheduled at predetermined points of time. The preventive maintenance scheduling policies presented in this paper utilize reliability and probability theories. They can be applied to various production bottlenecks where high cost equipment precludes having sufficient quantities of stand-by units.

Jan 1, 1982

By C. L. Barron, M. L. Smith, K. A. Prisbrey

SAG mill throughput is often a bottleneck to increasing plant productivity. Improved size distribution control in the mill feed can be used to increase mill production. This can be accomplished by controlling blast fragmentation as a function of energy input and rock characteristics. Such an approach requires the integration of rock fragmentation and comminution modeling. The optimal mill feed size distribution is determined by adapting a population balance comminution model to a measure of rock hardness or fragility, which is also related to the rock fragmentation that is achieved by blasting. The relationship between the size distribution and fragility of the feed and the mill's product and the critical size in a SAG mill is examined.

Jan 1, 1994