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By John W. Rold

These encompass all adverse effects of oil shale mining, processing, and ancillary developments on the environment. Specific problems concern: land, vegetation, wildlife, water, air, population growth, aesthetics and public emotion; and fall into four categories of: land, water, air and emotion. Land includes excavations, spent shale disposal, loss of vegetation and impact on wildlife and domestic grazing, plant sites, buildings and roads, necessary urbanization and the total aesthetic or visual Impact. Water considerations are: requirements for Industrial and domestic supplies, adverse effect of underground water on mining, avoidance of pollution or adverse effect on surface or near-surface water, and the utilization or safe disposal of liquids. Air problems include dust, smoke and stack gas, Public emotional problems include reaction to the above problems, and misconceptions of oil shale country and an oil shale Industry. Government and industry are aware of the problems, and are seeking solutions. Last year, the three affected states studied oil shale environmental problems and solution costs. Colorado estimated environmental costs would add approximately 7% to construction and 7% to operation. The report suggested research in: (1) Water availability and impact; (2) Disturbed lands revegetation and rehabilitation, including spent shale; (3) Environmental inventory and impact; and (4) Regional development and land use planning. Governor Love appointed a 47-person committee representing Industry, government and environmentalists to attack the problems. Research pro-posals were prepared to focus on each problem. $715,000 state, federal and industry money is being committed. Results should provide data for industrial solutions and equitable agency administration.

Jan 1, 1972

By E. Karampinos, P. Morissette

"INTRODUCTION Ground support is a critical element in maintaining the stability of mining drives in deep and high stress mines. In challenging ground conditions, it is necessary to continuously explore ground support strategies that can control the resulting large deformations. It is an objective of mining operations to optimize the ground support by selecting both appropriate systems and the time of installation of each reinforcement element. A successful ground support strategy will result in the use of a system that ensures both the structural and operational integrity of the excavations and mitigates the need for rehabilitation. Preliminary ground support design is often based on empirical observations and methods. Once a design is implemented, field trials, observations and in situ pull tests are used to fine tune or improve the design. Although not often employed during this process, numerical modelling can provide helpful insights on the impact of different ground support strategies. In this respect, it is possible to explore the use of multiple options before selecting the most promising ground support system for implementation in field trials. The challenges associated with the numerical modelling of rock support for mines have been described by Lorig and Varona (2013) and Potvin (2017). The employed numerical models should capture all potential failure modes of reinforcement over the mining sequence of the excavation. In particular, it is important to emulate the observed in situ ground support performance, as well as the influence of the installation sequence of the support. However, the time and expertise required for this type of modelling of ground support is not often available at mine sites. Even when the expertise is available it requires a major time and commitment of resources to set up, run and calibrate the sophisticated models capable of explicitly capturing the behavior of ground support. Rock reinforcement is an integral part of all ground support systems used in underground mines. Long flexible tendons can reinforce the rock mass deeper into the walls and create a thicker reinforced shell around the underground excavation. This paper focuses on the optimization of the cable bolting strategy in squeezing conditions at the LaRonde Mine by integrating the 3D distinct element method (DEM) in the design process. A calibrated numerical model is used to investigate a series of cable bolt configurations and provide recommendations for the ground support design."

Jan 1, 2018

By Lawrence A. Roe

This paper describes research and development efforts leading to a wet process for the beneficiation of Western talc ores in which the values are primarily present as soft, platy talc mineral. The mineralogy of the ore, as it relates to the logic of utilizing an uncomplicated, attrition-scrubbing sedimentation process is described. Bench-scale laboratory testwork and a pilot-plant test program are described. The pilot-plant program included production of several tons of products. The thickened talc slurries were very difficult to dewater prior to the drying step. Dewatering difficulties were overcome by use of a high-speed centrifuge. The centrifuge cake was dried either by tray, flash or spray drying. The successful use of one high-grade talc product as titanium dioxide extender in paper is discussed. The talc product has extremely low abrasion values, an important characteristic for minerals used in paper manufacture. It is concluded that this wet process for soft talc ores is capable of producing high-purity talc products for paint, paper, cosmetics and other industrial uses re-quiring very pure soft talc.

Jan 1, 1972

By C. B. Manula

The application of computers to materials handling problems has recently been investigated by various mining groups. This approach has been found, especially useful where a large amount of alternatives must be investigated prior to arriving at a final decision. These alternatives may be expressed in terms of man hours, units and types of equipment such as trucks or conveyors, or the allocation and operation of proposed or existing haulage facilities. The decision problem becomes especially evident when we consider the mechanical revolution which has flooded the mining industry in recent years. The industry has become highly competitive, with the need to keep low profit materials away from high cost production faces ever increasing. The capital investment required for the highly sophisticated equipment that is necessary to perform this function is generally great, and management is faced with decisions which must all too often be made without sufficient data.

Jan 1, 1967

By Christopher J. Bise

Traditionally, mine drainage systems have not received the high level of emphasis on careful engineering design which has been rendered to many of the other auxillary operations. This may be due, in part, to the situation-response approach toward dealing with an influx of water. When the installed system becomes inadequate, costly alterations to the pump, such as staging or speed increases, are considered expedient solutions. In order to rectify this situation, computer-aided solutions to mine drainage problems could represent an efficient alternative to the methods presently used. This paper will consider the application of microcomputer technology to mine drainage problems and will show how the relative economy and convenience of microcomputers can make them become valuable analytic tools at any mine site.

Jan 1, 1983

By A. F. MacDonald

The rugged foothills of the Allegheny Mountains in Washington County, Southwestern Pennsylvania, lend their terrain very well to the use of aerial tram systems to carry refuse from Bethlehem Mines' two preparation plants to disposal areas some distance from the plant site. Bethlehem Nines Corporation has three deep mines in this area, all of which are mining the Pittsburgh Coal Seam, The raw coal is prepared for metallurgical use in a preparation plant at each mine, Trio of these preparation plants, Mine No, 51, Ellsworth and Mine No. 58 Marianna, use aerial tram systems to dispose of reject material.

Jan 1, 1966

By R. D. Hutchinson

I consider it an honour to be the opening speaker in this afternoon's session on "Canadian Exploration". I also think it most appropriate that this joint meeting of the MMIJ and AIME should consider this subject, because Canada is a major exporter of mineral products and Japan and the United States are our two largest customers. Clearly, therefore, both countries have a valid interest in developments on the Canadian minerals scene. I represent the Mineral Development Sector of the Canadian Department of Energy, Mines and Resources. I will therefore speak from the point of view of the Federal Government. At this point I would like to acknowledge the help and constructive criticism I have received from several of my colleagues in Mineral Development Sector in the preparation of this paper. In any discussion of exploration in Canada, it is essential to emphasize at the outset that Canada has a federal system of government, with powers shared between Ottawa and the provinces. Under our constitution, the federal government has jurisdiction over the north, and over offshore areas, while the provinces own the natural resources within their boundaries. They control the systems of land acquisition for exploration and the terns under which mining titles are issued, and are therefore able to determine the rate and conditions of exploration and development of these resources. It follows that the Federal Government can influence the exploration and development of the provincial resources only indirectly by consultation with provincial authorities. However, once the resources are developed and begin to flow to market, the Federal Government can exert a much stronger influence because of its constitutional right to control both inter-provincial and international trade, as well as through its general fiscal and tax powers.

Jan 1, 1976

By Richard J. Leary

At the 1976 Annual Meeting of AIDE, Alan Merson reminded his audience that economic' success comes to those who understand things as they are, rather than as they have been or what ideology says they should be (1). He went on to say that, measured by this standard, the mining industry is in trouble. The mining firms had recognized long ago the importance of effective lobbying in Washington and the state capitals. But, he pointed out, those methods are nearly worthless anymore in coping with many land use problems because the critical decisions are likely to be made at the local level. There the tactics are far different as are the relations of the decisionmakers to the parties before then. Furthermore, in his estimation the trend is to leave land use regulation largely to the local level of government. All who are concerned for access to land for mineral development will be benefited by reading Professor Merson's paper lie is speaking effectively about the context of decisionmaking for specific cases, the shape of things in the here and now. There is, however, a longer-tern set of considerations that if pursued will be likely to foster the creation of public support for mining developments. At that sane meeting I spoke on two foundations of the long-term relationships: namely, the growth in requirements for minerals implied by projections of increasing consumption; and a rationale for fostering mineral exploration and development. I mentioned in passing the social decisionmaking process for public uses of land (2). This paper is intended as a complement. The growth of requirements for Minerals and the rationale for development based on the Entropy Law will be only mentioned. The main concern will be on the process of social decisionmaking in the context of access to land for mineral development.

Jan 1, 1976

By J. P. P. Silva

Sodium silicate (water glass) is a modifier reagent widely used in flotation with the function of a depressant or dispersant. The interaction between sodium silicate and mineral surfaces is still not well understood. This investigation aimed to illuminate the sodium silicate action mechanism as a depressant in the flotation of the minerals quartz and calcite. The experiments were done with high-purity mineral samples in the particle size range below 147 µm. The microflotation tests in a modified Hallimond tube showed that, in all systems tested, the efficiency of sodium silicate increased with the concentration. At concentrations above 1,500 g/t, almost total depression (96% for calcite and 97% for quartz) was achieved. The variation of sodium silicate modulus did not alter the quartz flotation performance in the presence of amine (150 g/t). The most efficient depression pH range was observed between 5 and 8. Above pH 10, the depressant action of sodium silicate was negligible. The infrared spectra obtained at pH 7 after silicate contact showed the presence of the groups OH and Si-OH, both suggesting that the adsorption of the neutral species Si(OH)4, as well as siloxane groups (Si-O-Si), attributed to adsorption of polymeric species. Sharing electron pairs is the proposed adsorption mechanism between Si(OH)4 and polymeric species and the surface sites (Si-O on quartz and Ca-O on calcite). At pH 11, the electrostatic repulsion prevents the species adsorption, impairing the sodium silicate action.

By C. N. Bailey

Let's review the economic factors in mill design. Talking about engineering economics in mill design reminds me of an old' saying "There are several ways to handle women but nobody knows what they are." I'm sure that the same economic factors do not apply to each of our mill designs, but for the sake of emphasis, it is well to review a few of them. They are so simple that we are apt to feel they are not important. Other speakers today are talking about the engineering factors of mill design, but I'm asking the question "Have we checked the economic factors involved in these designs? Have we checked the obvious? Many great discoveries have resulted from analysis of the things that appeared to be obvious all the time. What are some of these economic factors? Perhaps the most basic one is simply the value of minerals in place if minerals have value in the ground, they have value only because many important and different considerations add up to the probability that the minerals can be mined, beneficiated and disposed of profitably. The size formation and quality of the ore body, the distance from market, and the transportation available to the market area, depreciation rates, taxes, and the ownership interests involved are but some of the factors that must dovetail into the answer of profit, an answer prerequisite to hoped-for financing.

Jan 1, 1961

By Amoussou Coffi Adoko, Shevaune Zeng, Sebastian D’Hyon, Gareth Kennedy, Eleonora Widzyk-Capehart

Inertization of coal dust with stone dust is a common control implemented within underground coal mines to mitigate the hazard of a coal dust explosion. To achieve adequate inertization, the total incombustible content (TIC) of the coal/stone dust mixture is required to meet certain percentages depending on the risk and relevant legislation. Current methods for determining the TIC of a mixture involves laboratory analysis, colorimetric comparison, or the use of portable instruments. This paper provides preliminary analysis of determination of a sample’s TIC in real-time with chemometric modelling, using portable instruments employing near-infrared (NIR).

Feb 1, 2024

By G. B. J. Leon, M. Karmis, C. Newman

"The prediction of surface deformations due to underground mining operations has been a long recognized practice with case studies documented as far back as 1556 in Georgius Agricola's De Re Metallica (Latin for On the Nature of Minerals). There is currently increased public awareness and regulatory scrutiny on the potential impacts of underground longwall and second mining operations, but this time the focus is placed on environmental impacts to overlaying bodies of water such as streams, rivers, wetlands, lakes, etc. (Karmis and Agioutantis, 2015). Community residents and environmental groups, as well as federal and state regulatory agencies, have often cited adverse stream impacts and demanded stronger measures and scrutiny in issuing mining and reclamation permits (Booth, 2006). Mining companies are required to focus on the protection of sensitive bodies of water through the monitoring of stream flow and water quality, management and rehabilitation techniques, as well as the adoption of ""no mining zones,"" which potentially sterilize large portions of minable coal reserves. This paper examines the use of an empirical modeling approach for the protection of surface streams based on evaluation of ground strain magnitudes. Utilizing enhanced features of the Surface Deformation Prediction Software (SDPS), ground movements can be predicted accurately in the vicinity of surface bodies of water. The modeling of ground movements can aid in establishing optimum extraction sequences, while the magnitudes of anticipated subsidence can be used in the evaluation of mitigation plans when undermining surface bodies of water. INTRODUCTION When utilizing high recovery underground mining methods, such as longwall or room-and-pillar mining, the movement and deformation of the overburden propagates toward the surface and may affect the integrity of overlying surface streams (Peng et al, 1996). Published studies cite three major mechanisms of subsidence as most likely to impact streams: displacement, slope, and strain. While subsidence-induced vertical displacement cause little structural damage to the stream bed, it may create adverse drainage and stream flow issues as the subsidence trough allows for ponding (Dawkins, 2003). Subsidence initiated changes to the slope, or tilt, of a stream may have adverse effects on water flow. As the stream enters the subsidence trough, the gradient increases providing potential erosion control problems. When exiting the subsidence trough, a reduction of the gradient may inhibit stream flow, causing localized ponding (Peng, 2008). While vertical displacement and tilt both may have detrimental effects to surface streams, subsidence induced strains have been documented as being the most damaging to surface streams and structures causing distortion, fractures, or failure (Singh, 1992). When stream beds are subjected to high tensile strain, tensile cracks may form at the surface level allowing for the direct loss of stream flow through fissures. When stream beds are located in areas of high compressive strain, rock layers forming the stream bed can fail as the stream bed, ""ruptures,"" upward blocking stream flow or having the stream diverted into the facture zone at the base (Iannacchione, et. al., 2010)"

Jan 1, 2016

By E Marambio, R Brändle, G Fischer, G von Rickenbach, L Burgos, R Luis Fonseca

Ground support systems must provide safe and effective designs for underground excavations under high stress conditions. These systems must be capable to resist dynamic impacts and yielding during the loading process. In this context dynamic testing of the reinforcement and retaining elements that compose the ground support system are required to study and improve the behaviour of these elements under dynamic load events. During the last years, Geobrugg has been working on the improvement of retaining products by testing them in a large-scale impact test facility located at Walenstadt, Switzerland. The test facility is composed of a double level platform with a square-shaped pyramidal trunk geometry, in the upper level housing a loading mass that drop from a height up to 5m. The loading mass is guided by one central steel pipe, and the impact occurs in the sample to be tested located at the lower level in a slab with an area of 3.6m × 3.6m where the ground support system is installed. During the last years, this innovative facility has been used to test several configurations of ground support systems. The results of these tests have enabled to improve the understating of the behaviour of ground support systems under dynamic loads. In this manuscript, the arrangement, measurement, results, and the preliminary analysis of a single impact dynamic test performed during 2021 of a ground support system with a high-tensile steel wire mesh MINAX 80-4.6 is presented.

Apr 26, 2022

By H. L. Monroe

Meramec Mining Company, owned 50% by St. Joseph Lead Company and 50% by Bethlehem Steel Corporation,- is engaged in the mining, concentrating and pelletizing of iron ore from the Pea Ridge Mine which is located in the rugged, wooded Missouri Ozarks about 15 miles from the town of Sullivan or 75 miles southwest of St. Louis. The orebody was delineated in the middle 1950's by the St. Joseph Lead Company during the Company's intensive exploration program to discover new lead orebodies to replace the declining reserves of the famous Southeast Missouri Lead Belt. An airborne magnetometer survey was run by the U.S. Geological Survey, the Missouri Survey and several mining companies, (of which St. Joseph Lead Company was the principal supporter). The survey was published in 1950 and disclosed an anomaly in the vicinity of Pea Ridge. In 1950 test drill holes disclosed that under some 1300 feet of sediments there did exist an iron deposit of probable commercial significance. No further action was taken until 1956 when additional drill holes confirmed beyond reasonable-doubt-that this was a major iron ore discovery.

Jan 1, 1965

By R. T. Swinderman

This paper discusses how many of the common practices in conveyor specification and design are out of date compared to the current expectations of users for safe, serviceable, reliable, and fugitive material-free conveyance of bulk solids. Ten of the most common mistakes made in the specification and design stages related to user expectations are reviewed along with the cost vs. price implications of those decisions. A general specification and design hierarchy that designers can use to improve conveyor design is included.

Jan 1, 2010

By William G. Davenport, Eric H. Partelpoeg

Direct smelting of copper in a single vessel has long been the extractive metallurgist's dream. Such a process offers the important advantages of (i) maximum use of the energy available from oxidizing the sulphur and iron of the concentrate; (ii) restriction of SO2 emissions to a single constant-strength source; (iii) minimum materials handling and (iv) elimination of at least one process step. Extensive developmental work was carried out in the 1960's and 1970's to implement such single-step processes. Some of the processes reached the prototype stage and it appeared that copper smelting technology was on the threshold of a new, efficient, minimum-pollution era. Since that time, however, the forward thrust has slowed and single-step smelting is still a process of the future. The paper describes in detail the potential advantages of single-step smelting; its history and current status; and the reasons why it has not been adopted industrially. It concludes that the potential benefits of single-step smelting are powerful and that many of the difficulties encountered in the 1970's will be overcome in the 1980's.

Jan 1, 1985

By Edwin H. Bentzen, Immo H. Redeker

Important industrial minerals are separated and concentrated by froth flotation by industry today. The following descriptions are presented as an overview of the methods employed to separate and recover a few of these industrial minerals. The minerals described in this section of the book are not, by any means, the only important minerals treated by froth flotation. Other minerals, such as calcite, kaolin, wollastonite, rare earths and vermiculite were not included, primarily due to the confidential nature of the information held by the Minerals Research Laboratory and the Colorado School of Mines Research Institute. Flotation of nonmetallic minerals is sometimes viewed as alchemy. However, the art is, in reality, based on sound chemistry, experience and a little luck in the treatment of new ores. In the flotation of nonmetallic minerals, as opposed to base metal sulfides, highly specific treatment conditions are required to accomplish separations. The presentation of the treatment of each of the minerals described was outlined as follows: DEPOSITS PROCESSING SPECIFICATIONS FLOWSHEETS (in some cases) A presentation of the factors, often critical, which must be carefully investigated to accomplish successful flotation of nonmetallic minerals is presented in the section on Sulfonate Collectors, elsewhere in this volume.

Jan 1, 1986

By M. Visnjic

Open Pit Mine Production scheduling under commodity price uncertainty suffers from an exponentially increasing problem size as simulations and real options flexibility are used to generate and evaluate multiple production schedules. Robustness evaluation techniques attempt to evaluate a production schedule that is generated on a single set of economic parameters against several varying prices and sources of uncertainty. This approach is invalid as the corresponding optimal LOM mine plan will change for each set of evaluation parameters. Using commodity market futures and treasury bonds as production schedule economic input parameters provides fully price and time-value-of-money risked scheduling parameters that maintain a deterministic problem size. This paper will provide comparative analysis of project NPV’s coming from traditional price uncertainty evaluation based on a single fixed LOM mine plan using varying prices versus evaluation based on varying LOM plans that are both generated and evaluated using varying prices. When cross evaluating constant price mine plans against simulations, the upside potential and downside risk of a project are significantly misrepresented. INTRODUCTION The life of mine (LOM) production scheduling problem seeks to answer the question of from where and when to extract a given block within the ultimate pit limit as well as where and when to process it. Solving this problem takes into account the constraints of extracting any particular block while seeking to maximize the net present value (NPV) of the mineral asset as a whole. A direct driver of the value of a block, and there for the entire asset, is the market price of the commodity in question. Complications arise when an optimal production schedule is attempted to be solved under price uncertainty. Many solution methodologies have been proposed in an attempt to optimize under this criterion, yet there are three salient aspects that are overlooked during this process. They are: • Generating a single production schedule and evaluating it against many simulated price paths. • Failing to understand the mechanism describing particular commodity price behavior • Inappropriate risk adjustment In an effort to address these aspects of production scheduling under commodity price uncertainty, we propose a methodology to define the economic parameters as input that is applicable to most if not all production scheduling approaches. This methodology will not only simplify the production scheduling process in terms of establishing block value but utilizes the risk adjustment of real options valuation to avoid the arbitrary blanket risk adjustment of traditional discounted cash flow valuation. Our findings conclude that attempting to optimize around individual price paths is futile and using a market risk adjusted single price forecast provides a justified economic basis for production scheduling while maintaining the same problem size as a deterministic production scheduling problem.

Jan 1, 2019

By F. Kitzinger

The possibility of increasing the efficiency of mineral processing plants by means of computer control has prompted metallurgists to examine their flowsheets more critically in order to develop practical control strategies. Control schemes in use to date generally rely on the automation of traditional and previously manually regulated control loops, for instance the addition of reagents to maintain a constant assay or a constant pH. This approach is predicated on the availability of well-established primary sensors such as pH electrodes or on-stream analyzers. Noranda Research Centre, in cooperation with Noranda Group concentrators, has developed a froth level monitor and a pulp density meter susceptible of application in this type of control. Although some of the basic principles on which they are based have been known for some time, their incorporation into the design of reliable, direct-reading instruments which can be interfaced with a computer, is be-lieved to be novel*.

Jan 1, 1977

By A. L. Wilder, S. N. Dixon

Introduction Coeur d'Alene Mines Corp.'s largest precious metals property is located in the historic Rochester Mining District 40 km (25 miles) northeast of Lovelock, NV. The property encountered cold weather operational problems soon after its fall start-up in 1986 due to its elevation of over 1830 m (6000 ft). The problem of ice buildup on the heaps because of sprayed solution application was faced immediately. It was felt that allowing ice to build up all winter long until a spring thaw was impractical due to the large area under leach. Further, the operating cost and delivery schedule for a solution heating system was unacceptable. The development and installation of a leach solution distribution system using drip emitters made efficient, cost-effective winter operation possible. Other benefits of this system have also been observed and are discussed here. General process description 15,422 kt/day (17,000 stpd) of - 1.27-cm (-1 /2-in) crushed ore from the three-stage crushing plant are delivered to the leach pad using 77.1 t (85 st) rear dump haul trucks. The ore is drifted into place with a D-9 bulldozer. Leach panels are contiguous and are approximately 8861 m'(90,000 square ft) in area built in 6-m (20-ft) lifts. New panels are built on top of older areas to a final height of 61 m (200 ft). Each panel is ripped and cross-ripped prior to leaching. Barren solution is distributed to the heap using drip emitters at rates of 0.02 to 0.41 L/min/m2 (0.0005 to 0.01 gpm per sq ft), depending on the age of the panels. The pH of the leach solution is 10.7 with a cyanide concentration of 0.75 kg/t (1.5 lb per st). Approximately 50% of the silver and 80% of the gold are finally recovered. Pregnant solution percolates though the heap and flows by gravity into one of two 9.46 ML (2.5 million gal) pregnant solution ponds. The solution is then pumped to a conventional Merrill-Crowe process plant. Clarification takes place in three 9464 L/min (2,500 gpm) capacity filters. The solution is then pumped to a packed vacuum deareation tower for the removal of dissolved oxygen. Typical deareated solution contains 0.7 parts per million dissolved oxygen. Precipitation of gold and silver is accomplished by adding a zinc dust slurry to the deareated solution at the suction of the filter press feed pump. Precipitated gold and silver are recovered in three recessed plate and frame filter presses. Barren solution is discharged into a 11.7 ML (3.1 million gal) pond where cyanide makeup occurs. This solution is pumped back to the heap for further leaching. The precipitate filter cake, containing approximately 75% dore (Ag + Au), is then fluxed with anhydrous borax, soda ash, sodium nitrate and fluorspar to yield a neutral, bisilicate slag. The fluxed precipitate is then charged into a propane-fired melting furnace and heated to 1150° C (2100° F) for 3 1/2 hours. Slag and dore bullion are poured into conical cast iron pots yielding buttons of 800 to 1000 troy oz. The dore typically contains 98.5% silver and 1 % gold. Slag is crushed and tabled to recover the trapped dore blebs and beads. Concentrate from the table is returned to the furnace. Table tails are sent to the crushing circuit and out to the leach pad. Solution application The area kept under leach at Rochester is approximately 130 000 m2 (1.4 million sq ft). Barren solution is delivered to the pad at 21.2 kL/min (5600 gpm) for a resultant application rate of 0.16 L/min/m2 (0.004 gpm per sq ft). A traditional solution sprinkling system using No. 12 Senninger Wobblers with individual pressure regulators was installed at the onset of leaching activities. The Wobblers were placed at 9.1-m (30¬ft) staggered centers and were fed off of a gridwork of Yellowmine plastic piping. Solution flow rates were moni¬tored to each panel. The onset of cold weather with an average nighttime temperature of -12° C (10° F) made it apparent that continual operation would not be possible with the sprinklers. A significant amount of ice was built up on top of the heap, making maintenance and pipe removal dangerous, if not impossible. Leach solution application was restricted to daylight hours to inhibit ice formation. Process plant flow rates were reduced to maintain steady-state operating conditions. However, as daylight temperatures dropped below freezing, ice continued to accumulate due to the sprays. Besides the obvious operating hazards brought on by the growing icefield, there was also the potential environmental hazard associated with an early thaw melting the ice too rapidly for the solution containment facilities. One other option for preventing ice formation was heating of the barren solution prior to spraying. Initial plant design allowed for expansion of the propane storage and distribution system as well as modification of the barren piping for a solution heater. This option was not exercised because the operating costs for an adequate system would have been prohibitive, and timely delivery of a system was not available. An investigation was conducted on the various drip irriga¬tion products available, since subsurface solution applicators would eliminate ice formation altogether. Systems utilizing external flow emitters were ruled out because of their ten¬dency to clog when buried. Emitter systems using perforated tubing were also eliminated from consideration due to their inability to adequately control flow over required lengths of tubing. An in-line emitter system was finally selected which demonstrated clog resistance and adequate flow control, enabling direct burial.

Jan 1, 1990