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By Jim Johnson

The purpose of this paper is to summarize and discuss a variety of site specific conditions which are typically evaluated as part of the engineering design process for heap leach pads, solution control ponds, and associated facilities. The following sections will focus primarily on the topographic, climatologic, hydrologic, and geotechnical evaluations critical to selection of heap leach sites, and selection of a preferred heap leach configuration or method. Other important considerations in the design of a heap leach project, including evaluation of ore properties and leachability, pregnant solution processing requirements, spent ore neutralization/disposal requirements, and other anticipated reclamation requirements are beyond the scope of this paper are not addressed in any detail.

Jan 1, 1998

By A E Reschke

The high-shear colloidal mixer is generally recognised as the most efficient method of mixing cement based grouts. Only recently however has this technology been applied to the production of cemented rockfill (CRF) for use in underground mines in North America. Traditionally, paddle type mixers have been used to produce the cement based slurries required for the preparation of CRF. While considerable success has been achieved with these mixers, tremendous advantages are attained with the colloidal mixer. The combined effect of the highly efficient mixing action and the ability to mix low water/solids ratios, allows for reductions in the cement content for a given strength requirement. Cement can also be replaced by cheaper fillers such as flyash, resulting in further cost savings. Although large-scale dedicated CRF hatching plants are typical, there is a growing need for mobile plants capable of operating anywhere underground. The compact size and rapid hatching speed of high-shear colloidal mixers has allowed them to be incorporated into skid mounted systems capable of producing and discharging cement based slurries onto rockfill aggregate for the production of CRF. In many cases run-of-mine development waste can be used as CRF aggregate with these slurry plants thereby reducing the cost of waste rock removal. These relatively low cost portable plants have now allowed several mines to economically rccmer isolated pillars and realise positive returns on their investment.

Jan 1, 1998

By D M R Stone

Failings di,posal presents many challenges at metal mines in Peru where the extreme relief yields very little useable land area. These challenges are amplified by other hazards such as the high seismic environment, high rainfall, and frequent debris torrents down the steep hillsides. As a result many mining operations have resorted to in-river disposal of mill tailings. This paper presents a case history of one underground metal mine located in the high Andes mountains of Peru where in-river disposal of tailings has been used for some 30 years. The paper outlines a comprehensive engineering study that was aimed at increasing the utilisation of tailings disposal underground. The scope of this study included modifications to the grinding and flotation circuits to produce a high sulphide and low sulphide tailings for underground and surface disposal respectively: mapping and cataloguing of abandoned stopes for hackfilling: modifications to the existing backfill system to improve icliahility and throughput, and a preliminary evaluation of alternatives Such as silicated and paste fills.

Jan 1, 1998

By A G McLean

This paper will first discuss the fundamental requirements for reliable discharge of backfill by gravity alone at high per cent solids. This discussion will include brief mention of the underlying principles of saturated solids flow contrasted to that of stirred tank or dilute discharge systems. Here the need to possess full knowledge of the flow properties of the stored material will be highlighted. In regard to attainment of reliable discharge it will he revealed flow from a backfill silo will only occur provided: ò the flowing material in the converging channel is yielding throughout; ò slip is occurring along the walls; ò an arched stress field is present in the vicinity of the outlet; ò the flowing backfill must be dilating to flow in response to the dilating stress field; ò sufficient dilation water is injected, in the hopper, to eliminate the formation of adverse interstitial pressure gradients; ò sufficient dilution water is injected, downstream from the hopper outlet, to generate a pumpable slurry of maximum per cent solids; ò the silo level must be sufficient to prevent the pump suction forming a rathole; ò the system must be configured and operated to generate stable discharge density; and ò the system must be configured and operated to minimise damage to the pump liners. In addition proper account must be made of the silo overflow weir and settling capacity to match plant throughput. Here opportunity will be taken to highlight the complexity of this multi-phase flow situation as well as the general yet paramount requirements for reliable solids flow. It will be shown that by proper attention to the multi-phase considerations gravity discharge of slurries as a consolidated bed with minimal water content is possible. Such high solids discharge results in greatly reduced demand for process water. In addition pumping costs are reduced as is the delay time associated with the mine drainage operation. Confirmation of successful applications will be highlighted by reference to several recent case studies. In the concluding phase mention will be made of the key yet very simple and effective operation techniques which enhance reliable Discharge.

Jan 1, 1998

By S. Partney

Waste clay ponds are a necessary part of the phosphate rock beneficiation process. They are large, averaging a square mile in size; unsightly, in that they protrude 20 to 50 feet (6 -15 meters) above natural grade; stabilization and reclamation is slow; and they have had a history of catastrophic failure. The State of Florida has never published a specific rule regarding the configuration or height of these ponds, but has enforced numerous policies along these lines. The current rules are given and interpreted, along with the reasoning for current policy. In addition, an overview of the history of the policies, and an attempt at explaining the reasons for the changes that have occurred is given. The industry has been forced to make major monetary decisions, having effect for decades on mine economics, in a constantly changing regulatory environment. The Bureau of Mine Reclamation is confident that a direction of regulation has been solidified, but changes are still to be anticipated.

Jan 1, 1998

By Leslie Thompson, Randy Hiebert, Marietta Canty

A paper is presented in which an innovative biological process is described for the treatment of cyanide-, metals-, and nitrate-contaminated mine process water. The technology is capable of detoxifying cyanide and nitrate and immobilizing metals in wastewater from agitation cyanide leaching as well as heap leaching. A pilot-scale demonstration is described in which a pilot plant was constructed to detoxify cyanide and immobilize several metals from a mine process wastestream at a mine in Nevada. The demonstration was performed jointly under the Mine Waste Technology Program (MWTP), which is funded by the U.S. Environmental Protection Agency (EPA) and is jointly administered by the U.S. Department of Energy's (DOE) Western Environmental Technology Office (WETO) and the Superfund Innovative Technology Evaluation (SITE) Demonstration Program under Interagency Agreement Number DW89938513-01-0. MSE Technology Applications, Inc. (MSE) located in Butte, Montana, was the contractor responsible for conducting the project, and Pintail Systems Inc. of Aurora, Colorado, was the technology provider. The pilot-scale unit was field tested at the Echo Bay McCoy/Cove Mine southwest of Battle Mountain, Nevada. The biotreatment process was con­sidered to be very successful in detoxifying cyanide from the mine process water. The process was also determined to be very effective in removing metals. The pH was consistently neutral­ized and nitrates were successfully removed in the mine process water. As a result of conducting these pilot-scale tests, the biotreatment process was concluded to offer an innovative, cost­effective alternative for the treatment of mining wastewaters.

Jan 1, 1998

By R. E. Mclaughlin, R. J. McLaughlin, A. H. Danzberger

Acid mine drainage (AMD) can occur as a natural phenome­non through oxidation of sulfide minerals. Oxidation by air and water can be exacerbated by mining. Because AMD can exhib­it low pH, it is capable of extracting heavy metals from mineral deposits. The result is highly acidic drainage with elevated heavy metal concentrations - the combination of which can cause extensive environmental damage. Because of the importance of these factors, this paper is focused on sulfate based AMD. Due to widespread mining, the occurrence of AMD is ubiqui­tous. As a result, several approaches to treatment have been developed. Chemical treatment using alkali is most commonly employed to treat AMD. There are alternative methods of treat­ment, as well as alternative ways of handling treatment sludges or concentrates. Dewatering of sludge or concentrates is beyond the scope of this paper. Within the family of chemical treatment processes, there are three principal recognized methods, namely, "Conventional," "High Density Sludge" (HDS) and "Heavy Metals Removal Process" (HMRP). All three are now employed or specified for treating AMO at mining sites which are being reclaimed under Superfund. Only limited data are available for more specialized chemical treatment processes such as "ferrate", borohydride membrane and electrochemical methods. Therefore, these data are not included here. Performance data for these three processes are presented in this paper and comparison among them is made. Comparisons include consideration of water quality, sludge characteristics, and operational ease. Capital and operational cost comparisons of these processes were addressed in a previous paper by the authors (see bibliography). The results presented here are impo1tant not only to metals mining, but are also applicable to other industries experiencing metals-laden acidic wastes including: coal mining and prepara­tion, metal plating, and electronics circuit board manufacturing. The acceptance of any process should be based on bench scale demonstration before implementation is contemplated. The three processes included herein are discussed in relation to the particular sites at which they are in use, or their use is planned. The sites selected were representative of the various types of processes and the wastewater parameters.

Jan 1, 1998

By Kevin Bell

The TRAC™ Program was developed to provide our clients with a mechanism that allows them to better manage site remedia­tion and closure costs. This program provides a fixed-price contract for site remediation and case closure and is well suited for large pro­jects with multiple PRPs, such as Superfund sites. Because Kvaerner is a large engineering/construction firm and not a consult­ing firm, we can offer this type of contracting mechanism that envi­ronmental consulting firms are hesitant or unable to provide. With TRAC™, Kvaerner assumes financial and technical responsibilities for carrying a site through the closure process for a fixed price. Liabilities carried on our client's balance sheet for site closure can be removed when they sign up forTRAC™. In many instances, a profit can be realized as the liability on the balance sheet may exceed our TRAC™ fixed-price cost to close the site. Bonds and other sureties securing the site can be released and set­tlement with other involved parties can be quickly reached. For a project to be considered for this program, it typically meets the following criteria: 1) The project site should be physically separated from other contaminated sites 2) A reasonable quantity of site investigation data must be avail­able including site-usage history with or without a projected fea­sibility study(ies) and/or remediation design 3) Access to perform all necessary work must be available. After a review of all site data, K vaerner develops a "risk menu" to manage financial risks. In this "menu", each compo­nent of the project is assigned a level of probability that the costs will occur. Then the base cost of each activity is "weighted" by multiplying the potential cost growth by the probability. This analysis assures that the financial risks are appropriately defined, weighted, and mitigated and a realistic fixed price is developed. Upon acceptance of our proposal and conclusion of contract negotiations, Kvaerner takes over future responsibility for clos­ing your site. This allows the client to: 4) Release reserves obligated on financial statements for the site (and potentially realize a profit if the TRAC™ fixed-price cost is less than our client's booked obligation) 5) Finalize cost settlement with other responsible parties, insur­ers, etc. 6) Redirect resources involved in the environmental manage­ment of the site 7) Cap legal and administrative costs In addition to performing the site cleanup and closure work, at our client's request we are able to: 8) conclude lease obligations for property 9) dispose of equipment and buildings

Jan 1, 1998

By Gary E. Geiger

laboratory studies were performed to assess the calcium carbonate inhibition performance of phsophonates and polymeric dispersants at high hardness and high pH conditions. Based on the results of these studies, a new calcium carbonate treatment program was developed that shows excellent Inhibition characteristics and Is not sensitive to calcium hardness.

Jan 1, 1998

By J. Libaude

The Changement mine in French Guyana has, since 1983, processed gold ore by classical gravity methods. A large part of the gold is in the form of very small, free or enclosed grains. Recovery by gravity methods is thus limited (25-30%) and the present plant produces about 40,000 t annually of auriferous waste assaying about 6 git. The company therefore decided to retreat the waste by heap cyanidation. After laboratory tests which showed the feasibility of the method, a pilot test was set up on site. An experimental 3000 t heap, composed of waste of 0-8 mm grain size, was laid out by bucket loader on an impermeable pad covered by PVC and geotextile cloth. The upper layer of the heap was reworked by mechanical shovel to break up the area that had been compacted by the passage of the loader so as to restore adequate permeability.

Jan 1, 1998

By R. Bruce Thorndycraft

Heap leaching should not be chosen for development of a property solely on the basis of paper studies. Management should be made to understand where the risks are in heap leaching, and management should be alerted to the variability of costs in heap leaching, many of which are based upon company philosophy. These concepts are complex, but easily illustrated with guided tours of existing heap leach facilities.

Jan 1, 1998

By Vink L, Johnson N. W, Mackenzie J, Young M. F, Johnston M, Landmark V

The influence of ore textures on metallurgical behaviour is poorly understood for most ores. An alternative method for characterising ore textures and for determining the resulting implications on ore processing has been developed for the Geor

Jan 1, 1998

The green field site is one that has no history of mining and as such it presents the designer with a blank canvas, on which any number of drill and blasting options can be drafted. No matter which mining method is selected all technology and experience will need to be acquired from outside sources, applied quickly and produce the right results. North Limited, in joint venture with the Sumitomo Group (20 per cent), have developed AustraliaÆs first block cave mine at Northparkes in New South Wales, Australia. This innovative and large scale mining project was taken from a green field site in November 1993 to a fully commissioned block cave mine in December 1997. NorthparkesÆ Endeavour 26 mine is now producing at a rate of 3.9Mt per annum from a 27Mt ore block. Prior to 1993 no history of mining activity existed at Northparkes. The rock had never been blasted and many questions were raised about how it would behave. While it was clear that the Endeavour 26 (E26) orebody contained geotechnical properties appropriate to block caving, the blasting methods required to establish a block cave mine had never been used in Australia and no designs were available. The joint venture partners had no prior experience with block caving and it was immediately apparent that this blasting technology would have to be acquired from foreign sources and applied to the unique local conditions. Conceptual designs for the block cave drill and blast were first drafted in 1994, first issued for drilling in December 1995 and first blasted in January 1996. 470 km of drill metres and four million tonnes of rock were blasted to complete the undercutting project by September 1997. This paper will provide those developing new drill and blast projects with an inside view of how one small technical team solved many design challenges to successfully construct AustraliaÆs first block cave mine under strict quality controls and ambitious time constraints.

Jan 1, 1998

HW Process Technologies, Inc. (HWPT) has developed a patented membrane-based ion fractionation system, which specifically separates copper from gold and silver species in a cyanide matrix. This Engineered Membrane Separation (EMS?) system was pilot demonstrated on the 82,000 liters of pregnant leach solution' (PLS) generated from tailings, via thin layer leaching, at a mine site in Durango State, Mexico. The EMS? recovered ~90% of the gold-silver cyano-complex to a 90% volume permeate (based upon an EMS? feed stream of 100% volume) while rejecting -90% of the copper cyano-complex to a \0% (by volume) concentrate. The EMS? technology combines pore-size specific electro-statically charged membranes with engineered materials of construction and application-specific operational design that reject multi-valent, ionically charged species to the concentrate and transmit mono-valent species through the membrane to the permeate. The 850 ppm Cu PLS contained approximately 0.8 gil free NaCN with, the copper cyano-omplex principally in the CU(CN)3 and CU(CN)4 forms. The gold grade of the PLS was -2 ppm Au. The ~LS calcium concentration at -700 ppm Ca was reduced to ISO ppm.Ca (± 50 ppm) by sodium cycle ion exchange pre-treatrnent prior to EMS? processing.

Jan 1, 1998

By Adrian Fleming

Adrian Fleming is Executive Vice President of Exploration for Golden Star Resources Ltd., Denver. Adrian is an Australian who graduated in 1973 with an honors degree in geology from Newcastle University, New South Wales. His extensive international experience has spanned exploration, project development, and operations for both large and small companies in Australasia, Southeast Asia, North and South America, and Africa. Adrian has been with the Golden Star group of companies for four years and he is responsible for all exploration activity. ABSTRACT Golden Star acquired the rights to the Omai prospect in 1985 at a time when the country of Guyana was out of favor with the exploration fraternity. Subsequently in the late 1980s and early 1990s, Golden Star acquired exploration properties in Suriname and French Guiana well ahead of its competitors. Golden Star's strategy entailed identifying windows of opportunity and aggressively pursuing them. We also recognized that the Guiana Shield hosted a significant area of highly prospective greenstones which were comparable in metallogenic potential to similar terrains in eastern Canada, western Australia and west Africa. The geological skills Golden Star developed and the exploration techniques employed to explore deeply weathered rocks are described. The paper highlights the key elements of Golden Star's strategy and illustrates how some of the milestones reached by the company led Golden Star to establish an enviable portfolio of gold and diamond properties in the Guiana Shield.

Jan 1, 1998

By Lon Santis, Scott Deitchman, John A. Decker

This report describes three cases of carbon monoxide (CO) poisoning in a manhole, including one fatality, from CO migrating through soil after nearby use of explosives. A municipal sewer project involved installation of new pipes and manholes. Work of the general construction contractor was interrupted when a subcontractor detonated 265 pounds of nitroglycerin-based explosive 40-60 feet south of the manhole to break up underlying rock. A construction worker who descended into the manhole 45 minutes after the explosion collapsed within minutes, and two co-workers descended into the manhole to rescue him. One rescuer retrieved the unconscious worker, and the other rescuer died in the manhole. All workers had elevated carboxyhemoglobin levels. In the subsequent NIOSH investigation, air monitoring was conducted with real-time instruments, and air samples were collected in Tedlar bags. Laboratory analyses of the bag samples collected near the bottom showed 1905 parts per million (ppm) CO, 19.5% oxygen, and 3% carbon dioxide. Direct reading instruments showed progressively higher concentrations as the sensor was lowered into the manhole. Subsequent chamber tests on sample explosive yielded 27 liters CO per kilogram detonated. Based on this value, the surface blast at the construction site may have produced about 3,250 liters (114.8 cubic feet) CO. The CO in this incident most likely was released from the nearby explosion and migrated through soil and fractured rock into the manhole. The blasting and construction industries should be made aware of this previously unrecognized CO exposure hazard associated with surface blasting. The extent of CO exposure from explosives used in construction is not known, and additional information on the extent of CO exposure must be collected. In addition, confined space entry procedures (including monitoring confined space atmospheres before entry) should be observed; CO monitoring of confined spaces in the presence of blasting can prevent future incidents such as this one.

Oct 30, 1997

By Robert F. Randolph

Research on improving haulage truck safety, started by the U.S. Bureau of Mines, is being continued by its successors. This two-part article reports the orientation of the renewed research efforts, beginning with an update on accident data analysis, the role of multiple causes in these accidents, and the search for practical methods for addressing the most important causes. Fatal haulage accidents most often involve loss of control or collisions caused by a variety of factors. Lost-time injuries most often involve sprains or strains to the back or multiple body areas, which can often be attributed to rough roads and the shocks of loading and unloading. Part II will describe research to reduce these accidents, including improved warning systems, shock isolation for drivers, encouraging seatbelt usage, and general improvements to system and task design.

Jun 1, 1997

By N. Paas

Diesel powered equipment has been operated in underground coal fir mare than 50 years. According to the Mine Safety and Health Administration (MSHA), there are approximately 3,000 diesel units operating in underground coal mines in the United States. This number is expected to reach 5,000 diesel units in 250 coal mines by the year 2000. Also, there are approximately 5,000 diesel units operating in metal/nonmetal mines such as trine, potash and salt mines: and more than 3,000 diesel units operating in Canada. This increased popularity of diesel powered equipment over trolley wire, electric trailing cable or battery powered equipment is because of improved safety, greater mobility, higher productivity and increased power of diesel equipment. The operation if diesel powered equipment is not without challenges. Diesel engines generate exhaust emissions, in particular carbon monoxide, oxides of nitrogen, sulfur dioxide, unburned hydrocarbons, and diesel particulate matter that must be maintained at safe levels. The chief method to control ambient exposure has been dilution by ventilation. A new concept to ensure continued safe ambient emissions levels from diesel equipment in underground mines is the EMISSIONS MANAGEMENT PROGRAM™. The program encompasses all factors that will influence diesel emissions. By ESTABLISHING low tailpipe emissions through technology, such as clean engines, clean fuel selection, exhaust aftertreatment devices and filtration of the exhaust gases via the Dry System ™, this program ensures that the baseline emissions are at their lowest technically feasible concentrations. The DST Dry System™ exhaust conditioner reduces DPM by over 98%, as demonstrated through laboratory research at the West Virginia University. Carbon monoxide and hydrocarbon emissions and odor are similarly reduced. MAINTAINING these low emissions requires an expanded training program for operators and mechanics, onboard feed-back devices and a maintenance program with special focus on events and faults that can alter emissions. Finally, an on-board emissions sampling system allows the mechanic to VERIFY emissions levels and help diagnose engine faults. If the tailpipe emissions fall outside an established limit for a particular equipment, corrective actions will be initiated.

Feb 24, 1997

By Anthony B. Szwilski, Dalip Sarin, Richard D. Begley

This paper will present the results of an analysis of several abandoned coal mine projects and includes field data for over a dozen different reclamation projects recently completed in the state of West Virginia. The analysis was performed with the objective of summarizing and or classification of the environmental consequences with reference to the characteristics of the mining facilities (surface, underground, etc.). The analysis also addressed the itemized cost of remediation with respect to procedures, environmental concerns and time. The results of the analysis are that each abandoned coal mine site in West Virginia have/had many unique features and in most cases include a combination of environmental concerns that complicate comparisons. The study also revealed that the abandoned mine land program for mines abandoned prior to 1977, that is being financed by a tax on the production of coal, has produced many benefits for the state of West Virginia. This grant program administered by the Office of Surface Mining, has resulted in a high quality methodology of remediation that has been successful for many years in greatly minimizing and/or eliminating environmental concerns from abandoned coal mines.

Feb 24, 1997

By J. J. Gusek

Several final pits in the Seneca No. 1 Surface Coal Mine were abandoned in the 1960's without king reclaimed. In addition, a progressive landslide aggravated by the abandoned mine land conditions was threatening a county mad and private property. An AML-funded project to stabilize the landslide and reclaim the final pits was completed in 1986 for the Colorado Division of Mines and Geology (formerly Colorado Mine Land Reclamation Division). The site was visited after ten growing seasons. The land is stable and the vegetation re-establishment is strong. Volunteer native plant species are now invading the reclaimed sites.

Feb 24, 1997