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By D. J. Wood

BHP Copper has grown, in just over six years, from a minor participant to the world's largest privately owned copper producer. BHP Copper's major asset is the world's largest copper mine -Escondida in Northern Chile. Ten years ago investing in Chile was considered high risk. Today, Escondida represents an investment of approximately US$2 billion. Reward is the result of managed risk and Escondida is a clear demonstration of both. The Ok Tedi copper and gold mine in Papua New Guinea represents a Rubicon of risk and a retrospective on reward in a developing country on the doorstep of a developed one. The story of these two mines encapsulates risk in the mining industry.

Jan 1, 1998

By M. J. Oliver, A. J. Nugent

Hydrogen Peroxide and Caro's Acid (H2so5) were used to treat cyanide containjng effluents. Significant reagent savings were achieved by using Caro's Acid. Weak Acid Dissociable (W.A.D.) cyanides were removed at near stoichiometric levels of Caro's Acid. Hydrogen Peroxide showed poorer efficiency in the presence of W.A.D. cyanide complexes, resulting in higher consumption rates. By using Caro's Acid, reaction catalyst requirements ar(! el.iminatnd, react.ion I.imes significant.I y rnduced and capita] costs for an effluent lreal.ment facility are minimal. The Efflox* Process ut ilisc�s this more efficienl oxidising reagent in a treatment system exhibiting a simple non proprietary control system with minimal peroxygen consumptions.

Jan 1, 1991

By K. A. Prisbrey

Mineral carbonation is the reaction of carbon dioxide with mineral silicates to form solid, carbonate compounds. The carbonate ion holds carbon in a low energy state – lower than in carbon dioxide. Thus the reaction of carbon dioxide to produce mineral carbonates captures the carbon in a stable, solid form. The University of Utah is investigating the carbonation of silicate minerals by mechanochemical processing, which has the potential of being much less expensive than other methods. Tests to date have shown that a marked change takes place in the lizardite variety of serpentine after 15 to 20 minutes of intense grinding in the presence of gaseous CO2. Further testing is in progress.

Jan 1, 2004

By J. L. Post

A near-surface body of readily available Na-montmorillonite is located about 24 km (15 miles) southeast of Fallon, NV. The clay, which forms an irregular deposit about 4.8 km (3 miles) long, lies in altered rhyolite within a fault zone. The clay is similar to Wyoming bentonite but is less uniform in composition and contains less MgO and more Fe2O3 in its crystal structure. The clay interlayer cation population can be estimated by using a modified DTA procedure. With selective mining, the industrial properties of the Nevada clay are adequate for use as drilling mud, in foundry applications and as a sealant for hazardous wastes and canals.

Jan 1, 1997

By J. Vaino Huhta

An exploration program which covered an area of about 17 000 km2(6564 sq miles), was carried out between 1966 and 1969 by the United Nations project named "Mineral Survey of the Azuero Area." The target became Cerro Petaquilla, Province of Colon, Panama. See Fig. 1. Regional exploration led to discoveries of many geochemical anomalies and minor mineralization, but it was only toward the end of the project that a promising target was indicated by a large zone of comer and molybdenum anomalies in stream sediments in a remote 1, area between the Cordillera and the Caribbean coast. Follow-up surveys established the presence of porphyry-type copper mineralization in the area now known as Cerro Petaquilla.

Jan 1, 1991

By R M. Whyte, D McArthur, A Macintosh

In designing a gold extraction circuit utilising carbon­in-pulp (CIP) technology a number of process options can be considered. These include various combinations of leach or pre-leach, CIP or carbon-in-leach (CIL) and conventional counter-current or carousel CIP (or CIL) circuits. Factors affecting the process selection include the project's sensitivity to capital and working costs, the project life, and the mineralogy and head grade. Each process option has it's own advantages and disadvantages. This paper compares both the financial and technical aspects of the flow sheet options. The flow sheet, design aspects and operating performance of Anglogold's West Wits No. 2 and 3 Plants which are leach, pump-cell circuits are described.

Jan 1, 2000

By Shawn Orser, Jennifer Waddell, Mike Sierakowski, Tom Barrett

Production evaluations were conducted at Daisy Gold Mine (Glamis Gold, formerly Rayrock), between August, 1997 and August, 1998 to quantify the effect of 3M fluorochemical surfactants (fluorosurfactants) on extraction kinetics and gold recovery in gold heap leach mining operations. Ore was treated at a level of 7-10 grams surfactant per ton of ore using 3M Pluorad TM Leach Mining Additive PC-GOLD. Kinetics and gold recovery were determined by solution assay for each of the tests. Both tests indicated improved kinetics, and data from Test 2 was used for determination of a quantitative increase in gold recovery resulting from PC-GOLD addition. A discussion of test results including methods used to determine gold recovery is provided.

Jan 1, 2000

By Edward C. Spalding

The mineral estate of Arizona's State Trust lands, which are administered by the State Land Department for the benefit of the common schools and 14 other beneficiaries, totals more than 10.5 million acres, or almost 15 percent of the State's entire area. Trust lands exist in all 15 of the State's counties, with the most and least acreage found in Yavapai and Gila Counties, respectively. Revenues derived from the Trust mineral estate include royalties, rentals, and fees. In Fiscal Year 1983-84, these revenues amounted to $4.2 million, or 13.5 percent of all income received by the Trust during this period. Industrial minerals, led by sand and gravel, contributed $1.1 million from 82 active properties.

Jan 1, 1987

By Edward (Ted) M. Dowey

Shaft 26B of New York City’s Third Water Tunnel was constructed by Frontier-Kemper Constructors, Inc. of Evansville, Indiana. The 176.8 m (580 ft) deep shaft will serve as the construction shaft for the Manhattan spur of Water Tunnel No. 3. Twelve m (40 ft) of over-burden was supported by a rectangular cofferdam. This shaft was excavated in 13 months, through 164.6 m (540 ft) of rock, using 24,040 kg (26.5 tons) of explosives. Concrete lining cycles included the installation of stainless steel pipes embedded in the lining as the shaft advanced. A total of 635 m (2,084 linear feet) of stainless steel pipe was installed.

Jan 1, 1997

By James Barker, Jacques Renault, Chris McKee

Previous XRD work by us (McKee, Renault, Barker; 199Oa, 1990b) showed that by using pressed powder briquettes and a peak deconvolution technique, quartz in perlite can be routinely determined at <0.1 wt. %. In the present report, we discuss two additional methods of standardization: 1) chemical determination of quartz in silicate standards and 2) addition of a large amount of quartz to an unknown mixture. The first method applies the concept of mass balance and is sensitive to the analysis of silica and a monitor element. The second minimizes mixing errors; its equation is non-linear and is derived from the two component case with unequal mass absorption coefficients treated by Klug and Alexander (1974).

Jan 1, 1991

By Warren W. Frech

11.1-FRAGMENTATION PRINCIPLES WARREN W. KRECH Energy must be supplied to rock by direct or indirect means to fragment that rock. The amount is dependent upon the properties of the rock and the type of loading system. Fragmentation energy is consumed by three main mechanisms: (1) creation of new surface area (fracture energy), (2) friction (plasticity) and (3) elastic wave energy dispersion. The loading method determines the relative proportions and the amount of energy consumed in fragmenting a given rock type. Unconfined tensile failure consumes the least energy, with an increasing amount of energy required as the rock is more highly confined within a compressive stress field during fragmentation. The way energy is applied by tools to cause rock or mineral fragmentation is important in determining fragmentation efficiency. Rock-tool interaction should always be controlled to the fullest extent possible to optimize the combination of rate of energy input and fragmentation energy requirements. While the direct cost of energy, (dollars per horsepower-hour) may at first glance appear low relative to other hourly costs, there is a tie between power consumption and other cost factors, such as maintenance and wear. A high rate of energy application utilizing a rock-tool interaction producing only unconfined tensile failure would provide the most efficient fragmentation. No tool that produces a combination of high energy input rate and a loading system that produces failure under only conditions of unconfined tensile load now exists. Present mining methods and tools produce failure under conditions of high compressive confinement, high dispersive energy loss and high frictional energy requirements. Thus, while generally applying energy at high rates, they are highly inefficient with respect to energy consumed in fragmenting rock. To best design fragmentation tools and optimize fragmentation systems it would be desirable to know how rock properties influence breakage. At present, rock properties directly- related to fragmentation are undefined. Although present testing technology- does not permit rigorous definition of in-situ rock fragmentation behavior, several properties (mechanical and physical) commonly are used to indicate the relative case with which rock breaks. The more common test is for uniaxial compressive or tensile strength of cylindrical cores taken from intact portions of the in-situ rock (testing details are provided ill Sec. 6.2, Rock Mechanics). The strength of rock is influenced by the environmental conditions imposed on the rock. Those of most importance in rock are (1) confining pressure. (2) pore fluid pressure, (3) temperature and (4) rate of load application. Increase in confining pressure, as with increasing depth beneath the earth&apos;s surface or under the action of a fragmentation tool, causes an increase in rock strength. Increases from atmospheric pressure to 10.000 psi commonly cause up to n fourfold increase in the compressive strength of crystalline rock. Apparent rock strength decreases as pore fluid pressure increases, since it decreases the effect of confining pressure. The effective stress concept of soil mechanics generally applies to rock. Although chemical effects of pore fluids influence rock strength, they geologically are small compared to the confining pressure effect, except for a small minority of rock types. Increase in rock temperature causes a decrease in rock strength. This effect

Jan 1, 1973

By R. J. Lee

Asbestos analysis is conceptually simple. The objective, in most environmental analyses, is to determine the number of asbestos fibers per unit area or volume in a sample. The sample may be a consumer product, an ambient air sample, or a water sample. This determination is complicated by several factors: (1) sample collection and preparation, (2) counting techniques, and (3) operational definitions of asbestos in use. Three different definitions have been used in the study of environmental samples and are summarized in Table 1. The analytical procedure and detail required in the analysis vary with the definition of asbestos. Accordingly, this may be the only type of environmental analysis where the definition of a substance dictates the choice of analytical methods, and the rigor demanded of the analysis. Lead, arsenic, or beryllium are sub- stances having a constant definition and the method of analysis chosen depends on the concentration and precision required. However, the meaning of the term asbestos fiber is dependent on the eye of the beholder. Macroscopically, asbestos has certain physical properties that make it highly useful. Rockforming minerals do not display similar characteristics. Now, the question arises as to how three definitions of asbestos came into being. This is a result of two factors: (1) the definition of asbestos on any scale intrinsically involves the morphology or shape of the material, and (2) the advent of the transmission electron microscope permits detection of asbestos fibers and other mineral fragments in a size range where the physical properties of asbestos such as tensile strength, flexibility, or thermal resistance are difficult, if not impossible, to measure. There is a good deal of controversy about which definition is most appropriate for regulatory purposes because of a lack of appropriate health effects data (Cooper, 1978). Most differences of opinion center on the questions surrounding the following: 11 Morphology-Is a 3:l aspect ratio an appropriate medical or physical lower limit for the definition of an asbestos fiber? 2) Length-Are asbestos fibers shorter than some arbitrary length (5 pm) as hazardous as longer fibers? 3) Mineralogy-Is the mineralogical distinction between asbestos and nonasbestos minerals medically significant? While these questions are directly resolvable only with the biological and health effects data, ultimately such data reflects the ability of analytical procedures to fully characterize the materials used in health effects studies on animal models, and to monitor the exposure to particulates with different physical attributes in the workplace or community (Cooper, 1978). The following sections outline the analytical problems involved in distinguishing the asbestos and nonasbestos varieties of the same mineral; the analytical procedures available for identifying asbestos and measuring its concentration in environmental samples; the ability of these methods to distinguish asbestos fibers from nonasbestos particles; and their precision and reproducibility. Finally, we suggest some future directions in terms of definition and procedure that would greatly improve the quality of such analyses. ASBESTOS VS. NONASBESTOS Asbestos that is mined commercially belongs to two mineral families; amphibole and serpentine (Zoltai, 1978, Wylie, and Steel, 1978). The

Jan 1, 1986

By L. Yuan, R. A. Thomas

"Atmospheric monitoring systems (AMS) have been widely used in underground coal mines in the U.S. for the detection of fire in the belt entry and monitoring of other ventilation-related parameters such as airflow velocity and methane concentration in specific mine locations. In addition to an AMS being able to detect a mine fire, the AMS data has the potential to provide fire characteristic information such as fire growth (heat release rate) and exact fire location. This information is critical in making decisions regarding fire-fighting strategies, underground personnel evacuation, and optimal escape routes. In this study, a methodology was developed to calculate the fire heat release rate using AMS sensor data for carbon monoxide (CO), carbon dioxide (CO2), and airflow velocity based on the theory of heat and species transfer in ventilation airflow. Full-scale mine fire experiments were then conducted in the Pittsburgh Mining Research Division (PMRD) Safety Research Coal Mine using an AMS with different fire sources. Sensor data collected from the experiments were used to calculate the heat release rates of the fires using this methodology. The calculated heat release rate was compared with the value determined from the mass loss rate of the combustible material using a digital load cell. The experimental results show that the heat release rate of a mine fire can be calculated using AMS sensor data with reasonable accuracy. INTRODUCTION Fires at different stages generate different gases and smoke toxicity hazards. When fires occur in underground mines, a significant amount of toxic gases and smoke enter the mine ventilation system and are carried throughout the mine ventilation network, increasing the hazard potential for personnel even if far away from the actual fire. Although fires that develop to the point of rapid flame spread pose imminent hazards, fires in their smoldering, pre-flaming stages can also contaminate the mine atmosphere with debilitating levels of smoke and toxic gases. The most important parameter for evaluating the fire hazard in mines is the heat release rate (HRR), which is directly related to the rate at which heat, smoke, and toxic gases are produced and transported by the ventilation system, and provides an indication of the time available for escape or firefighting [1]. The HRR is also an important input parameter to mine fire simulation models. Measuring the HRR of an actual fire can be a difficult task. Early experimental measurement of HRR focused on the heat output as represented by the temperature of the product gases. In ASTM E1321 (LIFT test), an array of thermocouples was positioned in a duct which captured all gaseous combustion products to measure their average temperature. This approach assumed the flow is adiabatic, which is never a reality. Significant progress on measuring HRR was made when Huggett showed that, for most common materials containing C, H, O, and N, the average heat release per unit mass of oxygen is 13.1 MJ/kg O2 [2]. Thus, the oxygen deficit is a measure of the HRR in the flow that the duct captures. This approach is termed oxygen consumption calorimetry (or the oxygen consumption method), and is widely used in the fire protection community."

Jan 1, 2017

By N. S. Aouad

"Gaseous explosions are one of the most hazardous incidents in process and mining industries. Experimental research in this area is shown to be high risk and expensive. Computational Fluid Dynamics (CFD) techniques are reasonable alternatives to experiments; specifically when testing large scale gaseous explosions such as methane explosion in underground mines. The dimensions of a confined space where explosions could occur vary significantly. Thus, the scaling effect on explosion parameters is worth to be investigated using CFD tools. In this research paper, the impact of scaling on the explosion overpressures is investigated by employing two scaling factors. These two factors are the Gas-fill Length scaling factor (FLSF) and the Hydraulic Diameter scaling factor (HDSF). The combinations of eight HDSFs (1, 2, 4, 8, 16, 32, 64, and 100) and five HDSFs (0.5, 1, 2, 4, and 8) will cover a wide range of space dimensions where flammable gas could accumulate. Experiments were conducted to evaluate the selected premixed combustion and turbulence models. Large Eddy Simulation (LES) turbulence model was used because it shows accuracy compared to the widely used Reynolds’ averaged models for the scenarios investigated in the experiments. Researchers also simulated methane explosions in both deflagration and detonation regimes using different numerical schemes. Three major conclusions can be drawn from the simulation results. (1) The overpressure increases with both FLSF and HDSF within the deflagration regime; (2) in an explosion duct with length to diameter ratio greater than 54, detonation is more likely to be triggered for stoichiometric methane/air mixture; (3) overpressure increases as an increment hydraulic diameter of a geometry within deflagration regime. INTRODUCTION The most typical category of gaseous explosion accidents is methane explosion accidents in the mining industry. It normally leads to significant economic loss and massive amount of casualties (McPherson, 1993). It could occur in unconfined spaces, such as combustion due to flammable gas leakage, as well as confined spaces, such as inner-combustion in process equipment and methane explosions in airways of underground mines. Gaseous explosions in confined spaces are more intensive compared to unconfined spaces provided that the total energy of explosives is the same. In addition, explosion characteristics are also affected by the geometry of a selected confined space. The size of confined spaces commonly encountered in process and mining industries could differ as much as an order of four (Catlin & Johnson, 1992). A better understanding of the scaling effect on gaseous explosions could contribute to explosion mitigation and prevent operation activities within high risk regions. This research paper has investigated this scaling effect and its impact on explosion propagation. The approach to investigate explosions is either experimental or numerical. Large scale explosion experiments are often costly and dangerous (Catlin, 1991; Zhang, Pang, & Zhang, 2011). Lab scale experiments and numerical methods are common alternatives. However, it is not yet clear if the findings in lab scale experiments can be used to represent the explosion characteristics or not. On the other hand, CFD modeling has been used to simulate chemical combustions and, thus, can be used to evaluate the scaling effects in methane explosions."

Jan 1, 2015

By Stephen H. Partney

Waste clay ponds are a necessary part of phosphate rock beneficiation. They are large, averaging 2.6 km2 (1 sq mile). They are unsightly in that they protrude 6 to 15 m (20 to 50 ft) above natural grade. Stabilization and reclamation is slow and they have had a history of catastrophic failure. Florida has never published a specific rule regarding the configuration or height of these ponds. But it has enforced several policies along these lines. The phosphate industry has been forced to make major monetary decisions that affect mine economics for decades. The Florida Bureau of Mine Reclamation believes that the direction of regulation has been solidified but changes are still anticipated. Phosphate rock has been mined in Florida since 1890 (Fig. 1). Three notable technological changes occurred in the industry that led to major shifts in mining technique and volume. By about 1915, hydraulic mining had been replaced by centralized washers. Hydraulic mines usually started at an outcrop in or adjacent to a stream of the pebble zone. Water was pumped out of the stream through high-pressure monitors and sand and clay were washed away from the pebble. Mobile grizzlies and screens were used in conjunction with animal and human labor to concentrate the pebble and haul it away. Populations were sparse and the clays washed into the stream were considered an acceptable price for the commerce. The clays were not voluminous because the pebble zone typically contained relatively small amounts of them. Machines largely replaced animals by 1910 and provided greater efficiency of production. Centralized washers replaced mobile trommels. They allowed greater ease of access to shipping routes by rail. Some clays were placed in mine cuts from 1915 to 1930. Some were dammed off to increase the capacity of a given site. Some of these also failed, leading to clay plumes that were visible all the way to the Gulf of Mexico. By concentrating the waste clays (slimes) in impoundments, the solids concentration had increased, making plumes persistent for long distances. There were complaints. But there was no litigation against the companies during that time. In 1930, flotation technology allowed the recovery of the phosphate from deeper zones. This was because the "concentrate" size phosphate rock was in the sand-size range and could not be screened out. Centralized beneficiation plants grew into a three-step process - washing and screening, feed preparation and flotation (Fig. 2). Reagent storage, safety and the flotation cell complex made the plants into large capital installations. Larger draglines were required to dig deeper into the matrix. These had dramatically larger production capacities, which were then figured into the overall material balance for a given plant. The number of operators shrank and the production per operator grew. Larger areas were being bermed off for waste clay storage. An economic incentive became apparent for storing as much waste clay as possible in each settling area. At the same time, the population was steadily growing and more eyes were watching the activities of the phosphate mines. Phosphate mining, focused on production and profit, was earning a bad name from its neighbors. When the subject of phosphate mining

Jan 1, 1998

By A. Ballester, F. Gonzalez, M. L. Blázquez

Pyrometallurgical process are usually used to recover valuable metals from metal sulphide concentrates. However, their use is diminishing as the cost of energy rises and pollution controls become strictes. An alternative method of treatment sulphides could be bacterial leaching due its simplicity and negligible contamination (1-2). This process is presently used commercially to re cover metals such as Cu and U from low grade ore concentrates. In spite of numerous researchs during recent years (3-5) there exists very little kinetic data concerning the speed of bioleaching process. The kinetic analysis of bacterial activity is related with the metabolism and growth of microox ganisms . This fundamental information permits ma- king the best utilization of bacterial oxidation and to suggest techniques which might increase the production of the products desired. However, bio- kinetic models are especially complicated due to the existence of many metabolic routes and parallel reactions which are important for the life of the bacteria. Microbiological oxidation of a mineral substrate is influenced by its own inicial concentration: This influence can be determined by means of a kinetic study. In a medium with sufficient concentration of nutrients (nitrogen, phosphorous and potassium) and an adequate supply of 0, and CO2, as the only & L source of carbon for the biochemical synthesis, the substrate concentration would remain the only limitation in the rate of leaching. In this case the Michaelis-Menten model could be applied (6). The model is based on an association of the enzyme (El with the substrate (S) with consequent decomposition of the latter into enzyme and products [ ] The rate of dissolution is defined by the equation : [ ] Were V is the rate of metal extraction (mg 1-1 1 h-1 ) ; S is the pulp density Mn is the maximum rate for metal extraction (mg 1-1 h-1) and K is the constant of Michaelis (concentration of substrate that yields Vm/2). This method is applicable only when the rate of bacterial growth is similar to the rate of metal extraction. It would therefore be sufficient to control the concentration of metal in the medium over the period of time. In the present work a systematic study of the kinetics of ZnS and CuFeS bioleaching in sphalerite and complex ore concengrates was carried out. The rate of dissolution of the Zn and Cu as function of the pulp density and temperature was determined. However, most oxidations of sulphide dissolution take place with a very slow kinetic; but, this can be accelerated considerably by the addition to the solution of suitable catalytic ions, as was Suggested many years ago by Bjorling (7). Such ions can exercise an important influence on the rate of the oxidation-reduction reactions, both homogenous and heterogenous, which take place during the leaching of sulphides; they also affect the nature of the reaction products. The action of catalytic ions has been fully developed in aqueous systems, but in the absence of bacteria (8 - 11) although the actual machanisms is not totally known. The mechanisms proposed as hypotheses in the literature (8) indicate that, in the case of ZnS, the catalyst ion act through an electrochemical mechanism according to the reactions: [ ]

Jan 1, 1989

By M. K. Mohanty

Over the years, screen bowl centrifuges have been widely used for dewatering fine coal in coal preparation plants in the United States and elsewhere. Its popularity is attributed to its relatively low cost, its high capacity of providing low moisture content product and its relative ease of operation and maintenance. It is generally recognized in the engineering and scientific communities that screen bowl centrifuges provide some degree of particle size separation while dewatering fine coal in a common application. However, the extent of differential partitioning of coarse and fine particles achievable by a screen bowl centrifuge has not been systematically studied in the past. The present investigation was aimed at conducting a parametric study using a statistically designed experimental program to better understand and optimize the size classification performance of a screen bowl centrifuge. A continuously operating screen bowl centrifuge having a bowl diameter of 0.5 m was used for this study at the Illinois Coal Development Park. Three key operating parameters, i.e., feed flow rate, feed solid content and pool depth, were varied to conduct a total of 17 experiments using a three-level factorial test matrix. Some of the best size separation performances achieved in this study may be described as having an imperfection value of 0.13 at an effective separation size (d50c) of 38 µm and an imperfection value of 0.27 at an effective separation size (d50c) of 2.8 µm. Due to an effective separation of ultrafine high ash materials, the ash content of the screen bowl feed was reduced from 22.3% to a minimum of 8.84% with a combustible recovery of 84.1% and an ash rejection of 71.6%. A higher combustible recovery of 92.1% was achieved at a product ash content of 12.5% with a d50c of 2.8 µm and imperfection of 0.27.

Jan 1, 2008

By D. Dunbar

Flooding of open pits now receives considerable attention from the mining industry as an option that may minimize environmental impacts, particularly when anoxia in pit lake deep waters can effectively eliminate oxidation of pit-wall sulphides. A state-of-the-art, coupled physical-geochemical pit lake model is used to verify that a cost-effective, environmentally responsible closure strategy for the open pit at the Kori Kollo gold mine, southeast of La Paz, Bolivia is to adopt a controlled, two-stage infilling of the open pit upon cessation of operations. By filling the pit initially with highly saline waters from evaporation/infiltration basins and naturally saline deep groundwater, followed by capping with fresh river water, a very stable and strongly stratified pit lake will be developed. In addition, the stratification will result in the isolation of metal-rich saline bottom waters from surface waters of good quality. Results of this model provide defensible predictions of the physical stability and evolution of water quality in the Kori Kollo pit lake over time. The model results indicate that anoxic conditions will develop below the fresh-saline water boundary within 1 to 2 years, followed by the rapid onset of sulphate reducing conditions in the bottom waters. Hydrogen sulphide produced by sulphate reduction will readily react with dissolved metals to form highly insoluble metal sulphides. The process results in the gradual removal of metals from the water column and the concomitant improvement of water quality over time. A notable benefit of this strategy is that it can be fully integrated with other mine site closure options as well as future environmental management strategies. The proposed plan allows for: 1) safe storage of saline evaporation basin waters; 2) the potential for passive treatment in anoxic bottom waters of ARD seepages from other mine site operations should they arise; and 3) a repository for future reactive wastes that could be effectively isolated in a physically and chemically stable environment.

Jan 1, 2001

By Jason Morrison

The Norwegian Lake Tap Method was successfully used to tap into the side of Lake Dorothy 36.5 m (120&apos;) below the lake surface. The lake tap allows water to flowinto an access tunnel from the lake lowering the water elevation below its natural out-fall. When the lake reaches a predetermined elevation below the outfall, a 1.5 m (60?) valve in the tunnel will be shut and discharge from Lake Dorothy will stop temporarily allowing construction of a dam located 2.9 km (1.8 miles) downstream at Bart Lake. The lake tap and tunnel were one phase of the $64 million Lake Dorothy Hydroelectric Project, owned and operated by Alaska Electric Light & Power Company (AEL&P), a private utility located in Juneau, AK. The Lake Dorothy portal site and tunnel are located approximately 25.7 km (16 miles) southeast of Juneau, AK, in the remote Tongass National Forest at an elevation of 701 m (2,300&apos;) above sea level in the mountains above the Taku Inlet. Thirty degree snow covered mountainsides and limited access by helicopter were just two of the many factors which challenged this unique project. The lake tap and tunnel development consisted of 250 m (820&apos;) of horizontal tun-nel, averaging 3.6 m x 3.6 m (12&apos; × 12&apos;), excavated using conventional drill and blast methods in highly competent Granodiorite and Tonalite rock, placement of one 3.9 m (13&apos;) long concrete plug, or bulkhead, located at the tunnel midpoint, and one 3 m (10&apos;) diameter lake tap into the side of Lake Dorothy. This paper will provide an analysis of the logistical and engineering challenges involved in the development of one of only a handful of lake taps in North America. AEL&P and contractor J. S. Redpath Corporation worked together to complete this critical project phase safely and on schedule, in a location accessible only by helicopter and plagued by constantly changing, harsh weather conditions. A strict schedule had to be maintained to ensure the timely operation of the downstream dam and power plant.

By A. E. Ketler

Conventional Atmospheric Monitoring System (AMS) installations for monitoring CO, CH4, O2 and air-velocity throughout underground mines are usually relegated to a modest 3-5 mile extent and with data communication speeds confined to a ponderous 1-5K baud range. New US-MSHA and state regulations require fast reporting of unsafe conditions, and the old 20-30 minute updates are no longer acceptable. To communicate farther and faster has always been a problem, because data reliability degenerates with excessive distances and high speeds. Because of this, very large mines often resort to costly optical-fiber media, using expensive OF cables and repeaters to obtain the necessary coverage. This entails high initial cost, as well as high maintenance and downtime costs to repair or replace broken optical fibers. Rel-Tek has pioneered with its DX-Bus communication data highway, which uses inexpensive twisted-pair telemetry cables, which can now communicate well into the 20-mile extent of the largest mines -- normally a brick wall for low-tech AMS systems. This extended range, enables the use of twisted-pair cables and provides a low cost alternative to OF systems. This paper discusses the DX-Bus, and its latest accomplishment, the ?B-LINK,? a unique high-speed communication repeater that maintains the 19.2K-Baud data rate. On-going innovations to our workhorse Millennia-DX computer software have kept pace with this extra speed/distance phenomenon, resulting in a dually-optimized AMS package: both hardware and software. Cost savings are substantial, and at no sacrifice of reliability ? nearly always at 100%. Sensor updates are measured in seconds, not minutes and hours. Twisted pair copper cable is cheap to purchase and install and a breeze to maintain. Rel-Tek uses the B-LINK&apos;s wide branching capabilities to enable the AMS to extend 20-miles both far and wide. Actual experience in large US coal mines -- both longwall and continuous mining operations -- confirms the large mine performance. The ventilation and safety benefits to the mining industry are immeasurable.

Jan 1, 2009