Search Documents

By H. M. Conger

I'm really very pleased to be talking with you today about the environmental impacts of gold ore processing as part of this symposium on emerging process technologies for a cleaner environment. But before I talk about some of the newer developments that are coming, I would like to set the stage by reviewing some of the recent past. Over the last decade or so the U.S. gold mining industry has experienced remarkable growth, primarily in heap leaching operations, and not surprisingly there has been parallel growth of environmental regulations. At Homestake, we have had the excitement of bringing on-line a new mine embodying state-of-the-art technology and environmental planning, and during the same period the flagship of our company, the Homestake mine, has been brought into modern day compliance through the application of innovative environmental technology. This has been a learning process; in both cases we found that we had to develop new ways to meet our objectives. At our McLaughlin mine in California a major achievement was pioneering the use of pressure oxidation, or autoclaves, for refractory gold ores, and at the Homestake it was the development of a unique bio-treatment plant for wastewater. These projects were developed balancing operational goals, environmental concerns and costs, and I would submit that being cost-effective is our greatest challenge in the development of new, environmentally sound, process technology. In meeting that challenge, our job has not been made any easier by the myriad environmental laws and regulations that directly affect the design and operation of our facilities. Most of these constraints have evolved through the political process more or less independently, but in their application there often are over-lapping provisions. Adding to this complexity is the fact that action takes place in both state and federal arenas. As a result, state and federal roles sometimes become intertwined, and a good case in point is provided by various cyanide issues faced by gold producers. The vast majority of U.S. gold mining takes place in the so-called "mineral States," the western States that come under the Mining Law of 1872 as amended. This is the basic statute that provides for access and tenure to develop mineral resources on federal lands in those states. There is gold mining outside the defined mineral States, and there is also gold mining in the mineral States on private lands. Our own Homestake mine in South Dakota is one of the best examples of the latter category: located entirely on private land, it is nevertheless subject to at least 13 federal environmental statutes and some 29 federal regulatory requirements. There are also nine significant state statutory and regulatory requirements that apply. On federal lands in the mineral States there are numerous federal statutes and regulations which affect mining, over and above the current Mining Law. These, which are in addition to the laws applying to private land, include the National Environmental Protection Act and the Federal Land Policy and Management Act, among others. Still, those who advocate radical changes in the basic Mining Law would have us believe that sweeping environmental protection and reclamation provisions, not to mention new land use restrictions, are needed. Such changes could effectively prohibit mining on the federal public lands. Strict enforcement of our current Mining Law would have presented most of the abuses cited by the critics but if the Law is to be changed at all, I believe that, at a minimum, the principles of self-initiation and security of tenure embodied in the present statute should be maintained. These are critically important concepts, but there are other statutory and regulatory issues constantly before us as gold miners. Let me cite a few examples: Reauthorization of RCRA There are several bills being considered by Congress to amend the Resource Conservation and Recovery Act (RCRA) that have as their theme

Jan 1, 1992

By Randall D. Peterson

Economic operation of a mine ventilation system must include some means by which operating costs can be quantified and evaluated periodically. Current practice at most mines relies upon the best judgement of foremen, engineers and managers to identify high cost or problem areas in the system and to estimate potential costs and benefits of work proposed to reduce inefficiencies. The problem with this is that significant savings can be overlooked or sub-economic projects may be undertaken when sufficient attention is not paid to the interrelationship between airflow characteristics and corporate financial criteria. In order to accurately determine costs and benefits it is necessary to view the solution of each potential ventilation problem as a separate economic opportunity.

Jan 1, 1993

By Romeo Jurani, Ralph Dresel, Fred Kissell, Charles Parker

This report describes actions taken to control silica dust at the Yucca Mountain Exploratory Studies Facility (ESF), a tunnel located in Southern Nevada that is part of a scientific program to determine site suitability for a potential nuclear waste repository. The rock is a volcanic tuff containing significant percentages of both quartz and cristobalite. Water use for dust control was limited because of scientific test requirements. A major dust reduction was achieved with an intermediate air cleaning station located on a rear deck of the TBM trailing gear.

Jan 1, 1999

By M. Cimini

The main objective of this paper is to propose a new sustainability parameter, called Visibility Indicator (VI), to describe the influence of mining operations on the visibility of the open works in the site from the surrounding land. A further goal is to point out a procedure for Visual Impact Analysis and Assessment (VIAA) of mining and quarrying operations in the phases of elaborating and evaluating of the project and depleting the resources. The Visibility Indicator has been computed taking into consideration the evolution of the area involved in the exploitation activity.

Jan 1, 2003

By C. J. Pritchard, R. E. Gundersen

I commend the authors on examining an interesting method of shaft lining and attempting to improve safety in a dangerous environment by remotely installing the shaft lining. It is important, though, to not trade off shaft lining safety for long-term mine safety by lining an intake shaft with combustible material. In many operations, the mine utilities are installed next to the lining of the intake shaft, supplying a possible ignition source if damaged or overloaded. Although the polyurethane studied in the paper is of relatively high density, no mention is made of the flame retardency of the samples. When exposed to heat, small amounts of polyurethane will melt and bum but are extinguished when the heat source is removed. If large surface areas of combustible polyurethane - a tunnel or mine shaft- are exposed to ignition heat sources that are not removed or extinguished early, an uncontrollable, fuel rich fire may result with high carbon monoxide levels, low oxygen concentrations, and greatly increased burning rates that can have devastating effects on the ventilation system and miners' safety. Although these heavy polyurethanes lend themselves to a "pouring" application around the annulus of the shaft liners and is a continuous process, past experience with atomizing and frothing polyurethane spray systems indicates a high degree of maintenance and operator attention to the nozzle1 delivery system. This may require more miner's time to be spent in the shaft maintaining the foam system, negating some of the safety advantages of the system. If polyurethane foams are to be used in mines, they must be of the highest quality available in terms of flame spread, heat emitted while curing, and contaminants emitted while curing and spraying. In addition, employees must be given adequate training and be thoroughly informed in all aspects of polyurethane foam safety procedures. As witnessed by our fellow miners in South Africa, we can accept no less.

Jan 1, 1991

By George Munro

New Zealand is a small, almost pristinely pure country environmentally speaking. It is blessed with an abundance of clear waterways, lush green vegetation and fresh clean air. It is a country in which agriculture and forestry predominate, and mining developments have to be introduced prepared to answer in considerable detail the question "How will this proposal affect the New Zealand environment as we know it today". Those who make the legislation have the difficult problem of establishing standards at a level which will maintain as far as possible the status quo without unduly inhibiting the developments currently approaching the starting line. We have been fortunate in some sense in that since the demise of the early gold rush days by the 1920's, little mineralisation of a complex nature has been uncovered in New Zealand. Coal fields have been developed in the central North Island, and on the West Coast and Southland regions of the South Island. A ban on large scale open cast mines in the Coromandel area has restricted mining in that highly prospective area, although three large gold prospects have got underway elsewhere in the last three years. There is no other ore processing being undertaken at present. Some recent proposals involving lead, gold and silver in complex arseno­ sulphides have failed to get the necessary approvals and have been discarded. Our ore processing problems are therefore straightforward ones, and confine themselves to acid drainage, mercury handling and disposal, and cyanide.

Jan 1, 1991

By J. M. Keane, C. K. Chase

Critical to successful dump and heap leaching of copper is an adequate evaluation of applicable parameters. This paper deals with methods to establish optimum conditions for dump and heap leaching copper so that commercial operations can proceed. Discussion is also offered of ore occurrences and preparations for dump or heap leaching.

Jan 1, 1988

By Stephen Leslie

A multimedia tutorial illustrating the geology and mineral resources of Gulf Coast salt domes has been developed as a pilot project for a course on Texas geology and resources at the University of Texas at Austin. The principal objective of the tutorial is to educate students with limited background in geological sciences about a major local geologic feature and its geologic and economic significance. The content of the tutorial represents materials generally covered in 4 hours of lecture and laboratory instruction. These materials are presented using a flattened hierarchy of topics, each accessible from a central menu, including salt-dome history, salt tectonics, anhydrite and calcite cap rocks, mineral resources, and geophysical character. Information concerning salt-dome geology is communicated using interactive software; sound and animation are used throughout to reinforce key concepts. Visual aspects include field views, hand specimens, and photomicrographs that were digitized from slides. Illustrations were created using a graphics program or scanned from available archives. Each visual element has an accompanying explanation, which in many cases is linked to other parts of the tutorial. Navigation is accomplished using hyper-links or a set of unobtrusive buttons. The program includes a glossary of the major minerals associated with salt domes available as a pull-down menu and digitized video footage of the Gulf of Mexico sea floor to illustrate the active environment of the formation of the salt-dome cap rock. In addition, a group of interactive questions is presented to assess the level of mastery. Technical aspects were accomplished using a Power Macintosh ? 7100AV and a variety of commercial software. Actual linking of information was done with Authorware? 3.0 Educational, an icon-based, multimedia authoring program. Graphic illustration was done with Adobe Illustrator ?; image processing was accomplished using Adobe Photoshop?; video was cap¬tured, edited, and compressed using Adobe Premiere ?. The interactive nature of the project was designed with regard to future means of dissemination, especially on the World Wide Web. This tutorial serves as a template to build additional modules covering the entire course. A modular approach to the coding of the project and extensive self-documentation should ensure the viabil¬ity of the project by allowing other workers with moder¬ate computer skills to complete other lessons within the curriculum framework.

Jan 1, 1999

By Wallace W. Roepke, James C. Church

Introduction The history of mining machine development has been and is one of "bigger is better." While this may not always be true, it is currently the only approach open to machine designers without specific in situ cutting force information. The US Bureau of Mines has tried to modify this approach by supporting research, both in the laboratory and in field tests, that demonstrates that bigger is only better if the equipment is used correctly. In-house research has shown conclusively that deeper cutting reduces both dust and energy (Roepke, Lindroth, and Myren, 1976). This approach has been applied to a large Lee-Norse (LN456) continuous mining machine, which confirmed that slow deep cutting is beneficial and does not have a negative effect on production (Black and Rounds, 1977; Black et al., 1978). Specific in situ engineering data needed on coal cutting forces have not, however, been obtained by field tests with the LN456. Although the machine was instrumented to obtain data on one seam, it would be impractical to move the machine from mine to mine. It became apparent that a portable, easy to use device was needed for obtaining coal cutting forces in situ. Such a device could provide the engineering data needed by manufacturers, the site-specific cutting information needed by operators, and a field research tool to establish correlation with laboratory cutting tests. Design and Development According to a set of design guidelines established by the Bureau, the proposed device should be able to measure cutting forces directly with standard coal cutting bits, be transportable by two miners, and be self-contained. These guidelines were given to Ingersoll-Rand Research Inc. (IRRI). The contractor performed a rigorous review of 16 existing in situ portable tester designs, none of which could use a standard coal cutting bit to measure cutting force directly. These included a wide range of devices, all of which are discussed in the final report (Banerjee and Wisner, 1982). A series of design tradeoffs were established to satisfy initial design guidelines. The final deci¬sion was heavily weighted by an industry survey to determine the preferred concept from four man¬ufacturers and four operators. To assure ease of use with maximum information, all respondents wanted a linear cutting device that could work in seams down to 1 m (40 in.). The final design choice was between a linear and a rotary tester. The rotary tester would cut on an arc in the same manner as a rotary drum machine. It had several faults, however, that could not be resolved within the scope of this contract. The worst was related to arc cutting (Roepke, Lindroth, and Myren, 1976). Since any bit cutting on arc enters the coal at zero depth, goes to maximum depth only at the horizontal centerline, and exits at zero, maximum cutting force is obtained only at the instant the bit crosses the horizontal centerline. This centerline peak response would require that many replications be made with an arc-type cutter to get reliable force information. The arc-type tester would require extensive face preparation to establish the cutting path and extensive wasted clearing cuts to advance the device for additional layers of cuts. The linear tester could be mounted directly on any face or rib with only minor preparation. By its nature, a linear cut at a constant depth provides multiple peak force data over the length of the cut, thus reducing the required number of replications. The final review of these two major design concepts plus indus-

Jan 9, 1983

By Homer S. Anderson

To clarify what r mean about this long title, I would like to define the term technology. A standard definition of the word "technology" is "a technical method of achieving a practical purpose". Incidently, another definition of the term is merely "technical language". The same dictionary defines the word "technology" as "having a special, usually practical, knowledge of mechanical or scientific subject." Naturally, the practical purpose of the subject with which we are concerned is solving of problems we encounter in the mining industry. I might further describe the subject of this discourse by defining the term "manager". An old definition, "one who dispenses the duties of his position with care and economy." In line with the above definition most of the technology with which we in the mining industry are confronted with deals with some form of cost reduction. This may be related to the speed of doing an operation or to saving of labor or supply costs. These can be improvements of an existing method or the result of new processes or inventions, such as new machinery.

Jan 1, 1974

By Brad C. Lewis

The coal mining industry has experienced a general trend toward longwall operations. An increasing percentage of underground coal is being mined by longwalls. And productivity in longwalls is likewise increasing. Operators of longwalls, however, have not yet reached a state of mining euphoria. Competitiveness within the industry and from alternate fuel sources is forcing continued pursuit of higher productivities and lower costs. [Figures 1, 2 and 3] present trends in the industry. Longwall mines, as defined here, are those reportedly having longwall installations in each of the respective years. Production from both the continuous miner and longwall units is included in the longwall mines. Nonlongwall mines are all other underground mines. Productivity calculations are based on total employee-hours associated with the operation. Annual percent increases in productivity appear to have peaked in the 1985-1987 time frame. This was due, in part, to implementation of technological advancements and improvements in management-labor relations. The results shown in [Fig. 3] aroused the author's curiosity. The first question was "Have technological advancements to increase productivity peaked?" It does not appear so.

Jan 1, 1990

By D. R. East

Recent experiences within certain sectors of the international mining industry suggest an underestimation of the environmental risk associated with the design of mine waste management facilities. These experiences show that the technical and managerial challenge of responsible mine waste management is not always fully appreciated. Unfortunately, the image of the mining industry's environmental performance is negatively impacted by a relatively few number of failures. This negative view overrides the many positive contributions made by the majority of mining companies. The fact that these failures continue to occur to this day in both developed and developing countries is indeed remarkable, and indicates a degree of risk-taking approaching unacceptable levels. The design requirements for tailing storage facilities are, in many cases, more demanding than those of conventional water dams, because seepage of fluids which contain dissolved metals may pose a greater threat than the mere loss of water.

Jan 1, 1999

By David R. Reid, Lawrence W. Talbot

INTRODUCTION In the mining industry, timing in land acquisitions can be of the essence. In order to secure promising lands, deals are often negoti- ated quickly and evidenced by letters of intent containing what the parties feel are the essential terms of the deal. In some cases, a company is willing to acquire land only if it can lock up a number of promising properties, and so a "non-binding" letter of intent is used to formalize the essential terms, while leaving the company without legal liability. Later, the letters of intent will be sent to a lawyer to prepare a formal acquisition agreement. Many times, how- ever, especially in a land acquisition rush, another company will attempt to better the deal prior to the execution of that formal agreement, and the first company will be forced to rely on the initial letter of intent, only to find out to its chagrin that it has no deal In other cases, the company holding the desired property is another mining company, and the negotiation of an option or joint venture is the only way the first company can acquire an interest in the desired land. In order to make its offer more attractive, it may have to reveal confidential or proprietary information about the property or the surrounding lands. Here, too, letters of intent are often used to formalize the essential points of the agreement. Once again, however, prior to the execution of a formal joint venture agreement, the transaction may collapse and the letter of intent prove to be only that. In this paper, the authors examine the dangers associated with the use of letters of intent and the specific provisions courts look for to find a binding contract, and consider how to increase the

Jan 1, 1988

By Frank T. Wheby, Edward M. Cikanek

A computer performs all logic and computations customarily done by hand in preparation of engineers' estimates or contractors' bids on tunnel-shaft systems. The program described is based on construction methods, work forces and equipment selections corresponding to the current state-of-the-art of rock, soft ground and cut-and-cover tunneling. The program contains logic to permit estimates of cost of complicated tunnel-shaft systems; it is not necessary to input quantities, as the program calculates those from the tunnel design that is internally generated. In any estimate, the program bases its cost computation on user-input requirements and site conditions, such as tunnel shape and size, shaft depth, ground characteristics, construction methods, and other factors. To provide great flexibility, the user of the program is provided with options for accepting designs built into the program or overriding these designs by his own inputs. An illustrative example is presented.

Jan 1, 1974

By Sean E. Armstrong, Deepak Malhotra

The current trend in gold ore processing is the development of lower grade or highly refractory deposits. The perplexity of treating low grade oxidized ores has been adequately addressed by heap leach technology. However, refractory gold ores are very difficult to positively characterize the gold association within the mineral matrix. Gold accompanied with refractory sulfitlc or carbonaceous mineralization can often be sub­micron In size and occur interstitially. Mineralogical examination of these ores Is difficult, expensive, and occasionally Inconclusive. Hence, the metallurgist Is given little information for the selection of processing alternatives. The purpose of this paper Is to demonstrate the use of diagnostic leach procedures to assist the metallurgist' s decision-making process to solve some of these problems. By sequentially liberating and/or leaching gold associated with specific minerals, the amount of recoverable gold in each stage can be determined. Through careful interpretation of the results obtained by diagnostic leaching, the metallurgist can devise a flowsheet for treating the ore or solve a problem at an existing plant

Jan 1, 1992

By Rex C. Bryan

An application of geostatistics to financial decision analysis is the linking of reserve parameters estimation precisions to a mine economics computer program calculating profitability. The estimates of economic reserve parameters are obtained by the kriging method, while precision are calculated by a technique more akin to the polygon method. To indicate the effect of the variables probability distribution on a distribution of profitability, their values are sampled by a Monte Carlo technique and entered into a mine economics modelling program developed by T. R. Ellis. The distribution of profitability calculations are in essence, a superior method of sensitivity analysis. The method is applied to a roll-front uranium deposit in the Powder River Basin, Wyoming.

Jan 1, 1982

By F. -U. Schneider, F. Wellenkamp

Based on previous investigations of ultrafine comminution in planetary ball mills, a new centrifugal mill has been developed which permits similar high stress conditions. Because this new type of mill is equipped with an immobile chamber, devices for measuring energy, for cooling the milling vessel, as well as, in continuous operation, for material feed and discharge can be more easily attached than to planetary ball mills. Observations of particle behaviour have shown that, in the case of dry grinding, most of the material is found on the mill walls even after short grinding times. Due to the fact that energy dissipation takes place mainly in the zone near the wall, a grinding system which reduces the amount of ball filling required is at an advantage.

Jan 1, 1995

By Anthony J. Peach

With the new generation of so called "Super TBM", we would all expect to witness the implied super-performance. In some instances this is occurring, but one must ask why is it not occurring in the majority of applications? For hard rock TBM related projects, we are observing a decrease in the volume of projects in the previously traditional areas such as North America and Western Europe and an increase in Asia (Hong Kong, Indonesia, China, Korea etc). As a consequence less experienced contractors are acquiring the latest ultra high power equipment, without the knowledge necessary to achieve optimum performance. The interdependence of TBM and muck removal systems has been assessed with emphasis on the emergence of the continuously extending conveyor technology, as a means of achieving dramatic productivity increases. The Australian system assessed here at the time of drafting this paper holds the world record tunnel excavation production of 2,166 metres. A little considered aspect of the adoption of conveyors is the associated improvement in safety.

Jan 1, 1995

By Frank Hagar, George M. L. Robinson

NTRODUCTION The Resource Conservation and Recovery Act and CERCLA (SUPERFUND), in many instances, has had an adverse economic impact on the hardrock mining industry. Over the last few years, many abandoned and active mining operations have been added to the Environmental Protection Agency (EPA) National Priority List (NPL) . When the property is placed on the NPL the operator or EPA is required to conduct extensive environmental assessments to determine if historical mining practices have degraded the existing environmental. If degradation has or will continue, the responsible party is required to implement appropriate remedial action plans. If a responsible party is not identified, the EPA implements a cleanup program. Experience has demonstrated abandoned and active mining operations are subject to RCRA, and possibly Super- fund, if the mine has not adopted appropriate hazardous waste disposal management procedures. If off-site contamination has occurred, the operator will be required to mitigate the impacts and will be required to adopt additional procedures to minimize future impacts. Since the passage of RCRA and Super- fund, many mining operators are adopting management procedures to monitor and inventory hazardous sub- stances and wastes generated, stored and disposed on site. Many operators are in a difficult position because ore, waste rock, process chemicals or other solid waste, in many instances, can be classified as hazardous waste. If the process or other solid waste is deemed to have the characteristics of a hazardous waste, the operator can inventory and adopt appropriate, in- expensive management procedures. However, if the ore or waste rock has hazardous waste characteristics, in- expensive control technologies are impossible to implement. Since existing statutes and regulations require hazardous waste control, the operator will be required to inventory, characterize and monitor all aspects of the mining operations including but not limited to exploration, mining, ore processing and waste disposal. During this process, geological, geotechnical, geochemical, waste and ore volumes, and process materials must be tracked throughout the mining process. To accomplish this task, the most cost effective method to maintain documented and accurate records, is through the implementation of an integrated database management system. The database management system can be used to model and simulate the entire mining operation and if necessary, used to predict whether the operation is in compliance with existing regulations. The developed database can also be used to operating optimize mining and disposal costs.

Jan 1, 1987

By B. R. Reddy, Y. V. Swamy, B. V. R. Murthy

Chromitiferous overburden containing nickel in oxide form is reduced with CO-CO2-N2 gas mixtures. This converts the nickel oxide to metallic nickel and restricts the iron oxide to the magnetite state to extract the nickel. Reduction experiments were carried out on 500-g samples in a bench-scale vertical reactor. The tests were run to establish the process parameters, including the optimum partial pressure of CO, the reducing gas flow rate, granule size and roasting time. The reduced calcine is then subjected to an ammonia-ammoniacal carbonate leach to extract nickel selectively as its amine complex. More than 90% of the nickel could be extracted with a volumetric CO/(CO+CO2) ratio of 0.57 at 750°C and a roasting time of 90 min. The addition of 2.5% (by weight) charcoal to the granules improved nickel extraction by 11 % to 19%. Nickel leaching efficiency with ammoniacal solution is compared to the bromine-methanol method.

Jan 1, 2000