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By Ulf Marklund, Manfred Lindvall

Fighting the challenge of diminishing ore grades, low base metal prices and a changing pattern of ore supply, Boliden has now taken the second generation of the fully­autogenous grinding concept on stream, Using new design and a highly-developed process control system the benefits of conventional two stage autogenous grinding technology are obtained with a wide range of ore types. The APC grinding system has been developed further. A new design of the Boliden Pebble Extractor together with an advanced control strategy make the performance of the APC concept superior to all other grinding systems with any ore quality. The capacity and simplicity of the autogenous grinding concept is equivalent to the best SAG installations but the operational costs are up to 25 % lower than for SAG or other primary ball or rod mill systems. The concept is as flexible as conventional crushing and rod mill installations but investment and operating costs are of the order of 25 % lower. Also, from the metallurgical point of view, the different types of autogenous grinding system outperform all other comminution systems including SAG. From 1989 to 1991 four fully autogenous grinding sections have been installed at various concentrators at the Boliden company. Old crushing plants and rod and pebble grinding circuits have finally been replaced by highly productive and cost-efficient autogenous grinding equipment. Significant savings in operational costs have already been reported. Power consumption and maintenance costs have been reduced significantly. Productivity expressed as milled tonnes per operator has been improved. Metallurgical results have developed favourably.

Jan 1, 1992

By E. Topuz

Productivity is the most important determinant in the economics of underground coal mining operations. Lower labor productivity increases labor requirements per ton. This, in turn, increases the unit cost of production. Intensive labor requirements may also affect miner injuries and fatalities by increasing man-hours of exposure necessary to produce a given amount of coal.

Jan 1, 1988

By Thomas R. Kuesel

In simpler times, construction was a cooperative undertaking. The frontier tradition of barn-raising is the construction equivalent of the academic ideal of a single student seated on a log with Horace Greeley. In a more complex world, ideals become more elusive. Still, it was only a generation ago that toll revenue bond financed projects generally involved a team composed of investment bankers, engineers, and construction contractors, who all shared a common objective -- to create something useful, at minimum cost and in minimum time, with fair compensation to all involved. In an increasingly contentious public climate, the team has too frequently been splintered into separate camps of owners, engineers, and contractors, who have lost the old objective of creation and have, under the guidance and control of the lawyers, substituted two new primary objectives: 1. To protect one's own skin. 2. To detect and punish culpable negligence of one of the other parties. This process has become so ludicrous that a number of thoughtful observers from all of the camps (including even some lawyers) have come to recognize that there must be a better way to undertake construction works than to use them as wrestling arenas. The road to improved contracting methods starts with mutual understanding of each other's problems and viewpoints. To this end, discussions such as this RETC session make a useful contribution. To

Jan 1, 1983

By Sammie D. Guy

This paper discusses the subject of "Improving Contracting Methods" from the owners point of view, particularly the public. An overview is given of the work of the U.S. National Committee on Tunneling Technology and some apparent results of the implementation of these recommendations or lack thereof. Selected recommendations that are not being implemented are discussed as to the the desirability and the possible impact of their implementation. Impediments to acceptance of the recommendations are identified and solutions proposed. The difference in the flexibility, attitudes and approaches of owners, public, quasi-public and private, toward improving contracting methods are discussed. Particular emphasis is given to the fact that the onus to improve is on the owner because they usually develop the contractual language or at least have the final decision on its content and are or should be an equal party to the contract during its administration.

Jan 1, 1983

By R. Shields

"Hard rock mines move large volumes of material. But the conveyors essential to this movement suffer lots of problems, including carryback, spillage, dust, and belt wander. Many of these issues are created at the transfer points where the belts are loaded. This presentation will start with an overview of the latest transfer point systems that incorporate safety and serviceability by design. It will then report on recent projects. One project is the Conveyor B Transfer at the Coeur Rochester silver mine near Lovelock, Nevada. Here performance was improved with the installation of belt support cradles, engineered chute walls with external wear liner, and a compact dust collector. A second project is the improvement of belt support idlers and skirtboard sealing in a long loading zone of a conveyor under the concentrator at an Arizona copper mine. THE IMPORTANCE OF TRANSFER POINTS Conveyors are essential in mine material handling. Their performance will often make the difference in mine productivity and profitability. A key to conveyor performance are the transfer points where the conveyor belt is loaded and discharges. At these transfer points, many of the problems encountered with the conveyor system are created. The problems that arise at the transfer stations include off-center and segregated loading, mistracking, blockages and plugging. And there are a variety of problems originating with fugitive material—cargo released in the form of carryback, spillage, or airborne dust—that are created or exacerbated in the transfer points. These fugitive materials turn into other conveyor-related problems, including shortened component life, unplanned outages for conveyor maintenance, unexpectedly high labor costs for maintenance and cleanup, worker health and safety problems, and issues with community relations. As estimate attributed to the U.S. Mine Safety and Health Administration (MSHA) notes that 85 percent of conveyor maintenance is a result of fugitive material at conveyor transfer points. TECHNOLOGIES TO IMPROVE TRANSFER POINTS A number of techniques to improve the performance of conveyor transfer points have been developed. They include: • Absorbing impact, to prevent damage to belt, belt support systems, and conveyor structure, and reduce spillage caused by the impact energy arising from long material drops or large lumps of material loaded onto the receiving belt. • Stabilizing the belt line, to eliminate sag that allows spillage and encourages material entrapment that can damage the belt. • Protecting the skirtboard seals, by sheltering the sealing strips from the mass of cargo pushing material toward the edges of the belt. • Using self-adjusting, multiple-barrier edge seals, to keep material on the belt by providing long-lived seal efficiency with minimum maintenance requirements. • Controlling and centering the belt’s path, to eliminate belt wander and the spillage and damage it can cause. • Allowing dust to settle, through the incorporation of chutework that provides expanded stilling zone and the use of dust curtains at the points where the belt enters and exits the transfer. • Adding supplemental dust control systems, through the installation of systems for passive dust gathering, water-based dust suppression, and/or active dust collection."

Jan 1, 2017

By R. Shields

"Hard rock mines move large volumes of material, which can cause the conveyors that are essential to this movement to suffer lots of problems, including carryback, spillage, dust and belt wander. Many of these issues are created at the transfer points where the belts are loaded.This article provides an overview of the latest transfer point systems that incorporate safety and serviceability by design as well as a report on recent projects. One project is the Conveyor B Transfer at the Coeur Rochester silver mine near Lovelock, NV. Here, performance was improved with the installation of belt support cradles, engineered chute walls with external wear liner, and a compact dust collector. A second project is the improvement of belt support idlers and skirtboard sealing in a long loading zone of a conveyor under the concentrator at an Arizona copper mine.The importance of transfer pointsConveyors are essential in mine material handling. Their performance will often make the difference in mine productivity and profitability. A key to conveyor performance is the transfer points where the conveyor belt is loaded and discharges. At these transfer points, many of the problems encountered with the conveyor system are created.The problems that arise at the transfer stations include off-center and segregated loading, mistracking, blockages and plugging. And there are a variety of problems originating with fugitive material — cargo released in the form of carryback, spillage or airborne dust — that are created or exacerbated in the transfer points. These fugitive materials turn into other conveyor-related problems, including shortened component life, unplanned outages for conveyor maintenance, unexpectedly high labor costs for maintenance and cleanup, worker health and safety problems and issues with community relations. The U.S. Mine Safety and Health Administration estimates that 85 percent of conveyor maintenance is a result of fugitive material at conveyor transfer points.Technologies to improve transfer pointsA number of techniques to improve the performance of conveyor transfer points have been developed. They include:"

Jan 11, 2017

By R. L. Miller

"Why should we care about diesel quality amidst the complexity of mining for minerals? Mining companies use a large amount of diesel fuel in their worldwide operations, both for moving ore from the mine to the processing mills or transportation hubs, and to generate power for onsite processing. This creates a large carbon footprint and poses both environmental risk with the production of emissions, and public perception of how those companies do their business as stewards of the environment while incurring a huge fuel expenditure. To improve diesel quality and create incremental value and greater environmental stewardship, the opportunity is broken down into several segments: 1. Mining industry diesel consumption 2. Fuel quality issues 3. Impacts on operations, economics, and emissions 4. Potential solutions 5. How improved fuel quality saves fuel expenditures 6. Economics of improved fuel quality 7. Recommended testing process 8. Fuel quality analysis checklist MINING INDUSTRY DIESEL CONSUMPTION The average grade of mined Australian ore bodies has halved, while the waste removed to access the minerals has more than doubled over the last 30 years, thus increasing energy consumption by 70%, (http://eex.gov.au/industry-sectors/mining/). Energy consumption and intensity in mining and mineral processing is rising at around 6% per annum. The mining industry is a huge consumer of diesel fuel worldwide, and the SRS Rocco Report of 4 August 2014 gives a better picture of recent trends. To better understand the reasons to reduce both fuel costs and consumption, we need to compare metrics on the amount of diesel consumed per each ounce of gold produced over the last decade. The rate of diesel consumption in gallons per each ounce of gold produced for the top five worldwide gold producers has doubled in the last 8 years from 12.7 gallons per ounce in 2005 to 25.8 in 2013 as shown in Figure 1 below.This is caused by 1) lower ore grades requiring more hauls to get same amount of finished gold product, and 2) haul trucks moving ore from deeper sources in open pit and underground mines. For one large multi-national gold mining company, the 2005 waste rock / production ratio was 52 metric tons/gold ounce; by 2013 that ratio had grown to 113 metric tons/gold ounce per the same SRSrocco 4 August 2014 report. Using the metrics above, the top 5 gold miners used over 591 million gallons of diesel fuel in 2013. The cost of diesel in dollars per ounce of gold has increased from $30.48 in 2005 to $101.14 in 2013, an annual appreciation of 16.2% as shown in Figure 2 below."

Jan 1, 2017

By R. A. Pimentel

Many longwall operators experience difficulty complying with the federal regulation limiting average dust exposure. Others are currently in compliance, but the dust exposure limit keeps then from increasing their production. Spray water is a major means of dust control. Excess water can cause problems in the transportation system and the cleaning plant, and reduces the Btu value of the run of mine coal. Thus, the dust exposure reduction per unit of water sprayed must be maximized. This paper discusses underground tests recently completed as part of a Bureau of Mines research program to determine the effects of variations in spray water flow rate, pressure, proportioning and spray orientation on longwall shearers.

Jan 1, 1984

By H. Walqui

The Empire concentrator was built in four stages, with the latest stage accounting for 50% of the overall plant capacity. Over the past 5 years, the average throughput of the three grinding lines has decreased by 50 LTPH (15%) without significant changes in ore characteristics and despite the addition of secondary grinding capacity to supplement the existing pebble mills that are the constraint of the grinding circuit. This paper discusses the different areas under study that are aimed at optimizing grinding circuit utilization which includes improving system logic, pebble crushing operation and pebble mills operation.

Jan 1, 2009

By K. A. Lewandowski

Leach heaps are plagued with problems due to fine material migrating downwards, clogging the spaces between the coarser ore particles, resulting in decreased metal recovery rates. The use of a binder in agglomeration would allow the fine material to be immobilized, increasing the availability for the solution to come in contact with all the ore. As much as 1.64*1012 BTU per year would be able to be saved if a 25% increase in copper recovery was experienced, assuming that 70% of heap leaching units converted to using agglomeration technology. This is equivalent to approximately 18% of the energy currently being used in leaching heaps.

Jan 1, 2008

By S. J. Page

The personal dust monitor (PDM) is a combined tapered element oscillating microbalance (TEOM) respirable dust monitor and cap lamp, configured to have dimensions and weight similar to those of a lead-acid miner’s cap lamp battery. The Higgins-Dewell (HD) cyclone design operated at 2.2 L min-1 airflow has previously been reported to have low bias relative to the International Organization for Standardization (ISO) convention. Previous reports have described the PDM as meeting the NIOSH Accuracy Criterion. In order to avoid certain analysis anomalies encountered during these evaluations, a different method of establishing the PDM relative standard deviation was employed. Re-analysis of laboratory data for both the early prototype and precommercial PDMs indicates that the PDM still meets the NIOSH accuracy criterion, and that the precommercial PDMs are more accurate than previously reported.

Jan 1, 2011

By B. A. Filas

Stabilizing fine coal refuse ponds for reclamation at Monterey Coal Company's No. 1 Mine has been difficult. Entrained water in the stored refuse causes liquefaction as reclamation caps are placed, resulting in additional material requirements than originally projected to stabilize the pond surface. Laboratory results indicate that in-place refuse densities may be substantially improved at No. I Mine by converting from a single-point to a managed slurry distribution system. Increased densities result in improved storage efficiency, less entrained moisture and a more stable refuse mass, thereby providing an improved working surface for reclamation and improved post-closure cover stability.

Jan 1, 1993

By Peter J. Suardini

Over the last few years, researcher have been working on improving procedures for fine-coal (minus 150 microns) washability analyses. The effort was stimulated by past difficulties in obtaining accurate and reproducible results from the various commercial laboratories providing fined washability services. This paper contains the results from fine-coal washability testing, performed by Process Technology, Inc. (PTI), as part of a U.S. Department of Energy (DOE)-sponsored project. The testing focused on comparing the performance of a number of media options (i.e., aqueous solutions and organic solvents), as well as evaluating the impact of a number of procedural steps on separation performance. The paper summarizes PTI's recommended washability procedures for various size fractions and ranks of coal, and makes recommendations for future studies of certain phenomenon, such as void penetration and particle density changes, which are not well understood.

Jan 1, 1995

By Charles D. Litton

Introduction The successful performance of a mine-wide fire detection system depends upon its ability to detect the presence of a fire rapidly and reliably. It should be sufficiently rapid so that there remains enough time to either safely evacuate a mine or successfully extinguish and control the fire or both. It should be reliable so that false alarms are minimized without sacrificing sensitivity or time response. Systems should also be durable enough to withstand the mine environment over long periods of time while maintaining a high degree of re1iability. Maintenance and calibration of the system should be simp1 e and not require the expenditure of excessive time and manpower to keep it operational. Sensitivity, reliability, and durability of mine fire sensors and their electronic support systems have been the subject of significant Bureau research within recent years. The bulk of this type of information, along with the reports from which the remainder of this paper is derived, can be found in the Bibliography. It suffices to say that there exist commercially available systems for use in mines. This paper addresses a strategy for the use of such sensors and systems. Many factors influence the design of a mine-wide fire detection system, such as the potential sources and modes of ignition, the types of combustibles involved and the quantities avai1able for fire growth and flame spread. Mine air ventilation influences the growth and spread of a fire and also serves to transport the products-of-combustion to other areas of a mine remote from the fire. Fire sensor alarm thresholds place limits on the sizes of fires that can be detected. The time to respond to a detected fire, either in terms of evacuation or control and extinguishment, place additional time constraints on the design of fire detection systems. These factors interact with each other, often in complex ways, and it is the definition and understanding of these factors and their interactions that hold the key to the design of adequate and re1iable fire detection systems. Our level of understanding of the problem has increased dramatically within recent years and it is the intent of this paper to discuss the progress that has been made and how the information can best be used to improve the level of fire detection in underground mines.

Jan 1, 1986

By Steven J. Schatzel, James Addis, K. Vaibhav Raj, Berk Tulu

The National Institute for Occupational Safety and Health (NIOSH) is conducting research to enhance methane control and mine ventilation practices at coal mines, as a method to mitigate hazardous work conditions. NIOSH researchers conducted case studies to investigate the effectiveness of existing systems and improve performance to decrease the potential for unplanned or excessive methane emissions. At one mine, drainage was influenced by hydrofracking inefficiencies where two of the six wells showed good frack development. Methane content was variable, from 300 ft3/t to 600 ft3/t. This paper also summarizes overburden movement during undermining and the estimated quantities of gas transported to the mine using FLAC3D and CFD modeling. The findings from this research effort highlight considerations based on specific mine conditions that may also be applicable to most longwall mines utilizing methane control systems.

Feb 1, 2025

By Jeffery S. Thompson, Harry Hinds

Recent advances in the development and application of the DuPont Activator Technology are discussed. Activators are catalysts of gold dissolution in cyanide solution. Plant testing of this technology in the vat leach circuit of the Homestake mine in Lead, South Dakota, showed increased gold recoveries ofup to 5%. Homestake has licensed the technology for this application and is in the process of full commercialization. Results from testing additional ores on a laboratory scale are also presented. These results indicate this technology will also increase leaching at much lower cyanide concentrations while achieving the same gold recovery.

Jan 1, 1997

By Robert R. Dorfler

AMPS[. has completed a rationed grinding ball test in a 2.93 m x 2.93 m ball mill at Climax Molybdenum Company. The test consisted of purging the ball distribution formed by charging 100%, 76 mm carbon steel balls with a distribution formed by charging 50% 76 mm and 20% 51 mm alloy steel balls. The resulting change in ball surface area yielded improvements in both tons ground and fineness of grind with a significant reduction in total ball consumption. This paper summarizes preliminary studies leading to the plant test, grinding efficiency results, and future plans to optimize the ball charge.

Jan 1, 1981

By Levent Ozdemir, Russell Miller, Fun-Den Wang

The full utilization of tunnel boring machines for excavation in medium hard and hard rock has been limited by insufficient knowledge of rock behavior under the action of mechanical cutters. An understanding of factors affecting the rock removal process will permit: (1) the more efficient design of tunneling machines, (2) the prediction of boring performance from geologic data and cores taken from the proposed tunnel alignment, and (3) an improved excavation rate, thus a lower tunneling cost.. The Colorado School of Mines, under the sponsorship of the National Science Foundation, is studying the effects of a number of parameters in regard to tunnel boring using both full and small scale laboratory tests, analyzing field boring performance and comparing the laboratory and field data. Results indicate: (1) the field boring performance can be reproduced in the laboratory, (2) the optimum spacing of cutters or optimum spacing to penetration ratios may be found in laboratory testing, (3) it is promising to use small core samples and laboratory testing to predict field machine performance and (4) effect of joints on boring rate is significant and should be included in predicting tunnel boreability.

Jan 1, 1974

By A. E. Stewart

Slope design in an open pit mine includes determining bench height, bench face angle and berm width. Case histories are presented of two highwall slopes (160 and 220 m or 525 and 720 ft high) excavated in dipping strata in an op¬erating coal mine. These examples illustrate the influence that bench face angle can have on the stability of an entire slope. The two highwall slopes, the lower of which experienced significant instability, were excavated in approximately the same lithologic and structural environment. The main differences between the slopes were the angle at which the bench faces were excavated and the excavating methods that were used. Relevent aspects are also described of the engineering geology, slope design and excavation procedures.

Jan 1, 1998

By J. M. Ekenes

New approaches that increase hydrometallurgical recovery from refractory minerals in below-mill-cut-off-grade sulfide copper ore can add significant value, improve profitability and increase ore reserves. This paper describes the development and implementation of an engineered heap (EH) approach to leaching low-grade, chalcopyrite-bearing ore at Freeport-McMoRan?s mine in Morenci, Arizona. The technical evolution of the engineered heap concept is described together with the challenges and benefits following implementation.

Jan 1, 2012