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By James A. Bloom

To operate the Morris Fork Preparation Plant with a closed water circuit has been an elusive goal for Union Carbide. The benefits of a closed circuit have never been questioned. The removal of fine solids from washery water makes possible the recirculation and reuse of the water. Heavy media drag tanks and other separating machines perform better and more consistently with washery essentially free of fine solids. Finally, the production of a clarified effluent makes unnecessary the sludge ponds usually associated with a coal preparation plant. Why then do I say elusive? Because, since plant design was completed in 1970 we have been in hot pursuit of an ever-growing fine solids problem. In four years the minus 28 mesh material in the plant feed has nearly doubled. The replacement of conventional sections with continuous mining machines has led to a lowering in size and quality of product from the mine. In addition, increasing emphasis underground on roadway clean-up has contributed to the fines problem.

Jan 1, 1975

By A. Casuge, D. Lee, J. A. Finch, C. C. Sui

The adsorption of copper and lead und their subsequent xanthate uptake were compared at pH 3.0, 6.0 and 9.2 on both fresh and oxidized sphalerite. The extent of adsorption and the rate of adsorption were strongly dependent on pH, with the highest adsorption of Cu and Pb being at pH 9.2. In the presence of both Cu and Pb, Cu adsorption was enhanced and Pb adsorption was suppressed. The adsorption kinetics of Cu and Pb were characterized by two- and three-stage adsorption processes, respectively. The exchange ratio of Cu to Zn was about one and that of Ph to Zn was greater than one and varied with pH. The uptake of xarlthate on "activated" sphalerite was dependent on pH. The rnaximum uptake was found to be at pH 6.0 for Cu-activated sphalerite artd at pH 9.2 for Pb-activated sphalerite. A measure of "activation strength" based on inetal ion adsorption and xanthate uptake was introduced. The activation strength of Cu to Pb was about one at acidic pH, but it was higher at neutral (pH -6) and alkaline (pH -3) conditions. The oxidation of sphalerite decreased Pb and, especially, Cu adsorption and decreased xanthate uptake.

Jan 1, 2000

By John W. Nebgen

Surface water quality is determined by complicated interactions between water and land. Runoff--the flow of waters in surface streams and rivers-¬represents the total amount of water collected in a drainage basin or watershed that appears at the outlet of the basin. As the water flows through the basin, it is in contact with land and can pick up impurities from the land. Thus, surface waters are not pure--they contain impurities, or "pollutants," in vary¬ing concentrations determined by the nature of the land which they drain. The composition of surface waters thus tends to represent a steady state equilibrium between interactions of water and land. However, when man utilizes the land in the drainage basin or watershed, the natural equilibrium between water in the runoff and the land is disturbed. Such disturbances usually effect adverse changes in surface water quality, as new equilibrium conditions between land and water are established. These adverse changes in surface water quality can be thought of as "nonpoint pollution." Esti¬mation of nonpoint pollutant loads thus ultimately reduces to determining the magnitude of the differences between water qualities before and after man's disturbance of land within a watershed. The important key in making such an estimation lies in the determination of water quality in the natural or "back¬ground" condition of the watershed. In subsequent discussion in this paper, tools for making an estimation of background water quality will be described.

Jan 1, 1975

By T. I. Martinovic

A major investigative' program was conducted on the development of an acceptable substitute organic binder for bentonite for the pelletizing of the Iron Ore Company of Canada's Carol concentrate. The first phase of the program covered an evaluation of several organic binders in laboratory tire balling in order to identify the most promising potential organic binders. Based on the green ball quality obtained, Peridur C-10, Alchem 8C26 and peat moss were selected for full scale pot-grate testwork. The selected binders were tested with various pelletizing mixes (acid, dolomite, limestone and fully fluxed). The pot-grate test results showed that an acceptable pellet quality can be produced with the use of Peridur C-10.

Jan 1, 1989

By J. W. Walkiewicz

The U.S. Bureau of Mines has conducted studies using microwave energy to stress-crack iron ores. In a microwave chamber which simulates a continuous throughput operation, the Bond grindability of a taconite sample was improved by 13 pct at a bulk temperature of 197? C. To further improve the economics of microwave fracturing, higher powers up to 16 kW were used to rapidly heat samples to relatively low temperatures in a continuous belt-fed applicator. A significant enhancement of grindability was obtained with a minus 1.9-cm taconite rod mill feed. At a sample temperature of 130? C, the grindability was improved a maximum of 26.1 pct over the non-microwaved sample.

Jan 1, 1993

By Martha McJunkin, Lawrence Pietrzak

This paper describes and demonstrates the application of systems analysis and mathematical modeling techniques in the planning of actual tunnel projects and research and development to improve tunneling techniques. A recently completed tunnel project located in Utah is used as an example. Although cost estimating computer programs are used in tunnel project planning, the introduction of performance modeling, simulating the time to excavate, has added advantages that are explored here. The performance/cost tunneling model (TM) described herein mathematically simulates on a high-speed digital computer the important activities of a number of tunneling techniques accounting for activity interactions, variable external environments, mechanical failure, and other uncertainties. A cost accounting segment is included to facilitate cost-effectiveness comparisons. It is shown that, when combined with informed judgment and appreciation of limitations, the TM can be a useful tool that may help improve tunneling operations and cost estimation, for example, by achieving more balanced system designs or bounding the performance/cost implications of geologic and other uncertainties. Ultimately, this might lead to more competitive bids and greater profits. The need for systems analysis and modeling in tunneling research and development (R&D) is well recognized and documented.(1-5) In R&D one must seek broadly useful solutions to the basic problems of face fragmentation, materials handling, ground support, and environmental control. These solutions must take account of the interdependence of these elements and, for a variety of ground conditions, the limitations or constraints that any innovation in one element may impose on total system performance and cost. In this regard the structure and logic of the TM has been kept as simple and modular as possible so

Jan 1, 1974

By Danforth R. Hale

The pressure of military use of quartz resonators led to efforts to Grow high, grade quartz crystals in Germany and in Great Britain during 19)3-25, and was responsible for a series of U.S.A. Signal Corps contracts beginning in 1946 with the Clevite Corporation (as the former Brush Development Company), Bell Telephone Laboratories, Antich College, and others. The technique of growing crystals from the melt, such as KI, NaBr, was already commercially inuse Quartz could not be so grown, since its utility depends on the form stable below 573°C, and, even if it could be grown from an extraordinarily viscous melt, the higher form passing through this transition becomes twinned. Again, several crystals were being grown commercially from water solutions; quartz, however, is listed in the common literature as being insoluble in water. Fused quartz, or vitreous silica, was chosen as raw mater¬ial by the European experimenters because of its thermodynamically lesser stability than quartz, and various alkaline solutions were tried for the purpose of enhancing the solubility.

Jan 1, 1964

By E. Milosavljevic, C. H. Bucknam, K. L. Gabby, T. C. Eisele

"Since mercury is chemically similar to silver, it tends to dissolve along with the silver and gold during cyanide leaching. Ultimately, mercury is recovered along with the silver as mercury/silver/gold amalgam, which requires retorting to remove the mercury prior to refining the silver and gold. A possible approach to separating mercury from silver and gold in cyanide leach solutions is to take advantage of the replacement reaction between [Hg(CN)4]2- and Ag2S, which results in precipitation of mercury as HgS while dissolving silver as [Ag(CN)2]-. Results are presented demonstrating that mercury can be removed from cyanide solutions with high effectiveness while, at the same time, recovering additional silver in solution. Initial experiments with static flasks in the laboratory showed a high degree of mercury removal could be achieved. Results using actual metallurgical plant products in bottle roll tests indicate the process works on a larger scale, but also results in significant gold losses if the solution being treated has high gold levels, such as carbon stripping pregnant eluent solution. IntroductionThe dissolution of mercury along with precious metals during cyanide leaching is a long-standing problem, which can result in significant mercury toxicity issues (Washburn, 2003). Mercury is first dissolved by the cyanide solution, and then, since it has a great deal of chemical similarity to silver, it follows silver throughout the concentration and recovery processes, ultimately being recovered as a silver/ mercury amalgam when the metal is precipitated by either the Merrill-Crowe process or by electrowinning.While it would be desirable to either prevent mercury dissolution entirely while still allowing silver dissolution, or to selectively capture mercury before the precious-metals recovery step, there is not yet an effective and economically practical approach to doing this (Grosse, 2003; Ravichandran, 2004; Misra, 1998; Pai, 2000). There are a few processes that have been proposed, such as differential adsorption. While activated carbon, as used in the carbon-in-pulp process, is not highly selective between mercury and silver (Washburn, 2003), it may be possible to achieve some separation by selective elution of the carbon to produce high-mercury and low-mercury eluates (Bunney et al., 2010). Certain synthetic resins were shown to be selective for gold but are more expensive than carbon, requiring special equipment, and have not yet been shown to be selective for mercury (Grosse, 2003). There may be potential for differential dissolution approaches, as thiosulfate leaching does not dissolve mercury sulfides as readily as it dissolves gold (Oraby et al., 2010), and it is possible that it may be similarly more selective for dissolving silver relative to mercury. Some work has also been done with selective precipitants, such as sodium polythiocarbonates (Bucknam, 2007), and 1,3-benzenediamidoethanethiol (Matlock, 2002). Common problems with these approaches include introduction of a solid:liquid separation step, reagent costs, the need to measure the mercury concentration for process control for minimizing silver losses, and regulatory requirements to retort otherwise stable mercury concentrates."

Jan 1, 2015

By William E. Bonini

Gravitational field anomalies have been observed over many igneous intrusives of medium (4000 km2) to small (100 km2) size in outcrop area. These studies give good results because the residual anomalies can be separated from larger scale crustal anomalies and density contrasts usually are present. Although unique solutions are not possible, the analysis of the gravity anomalies can put limits upon the geologic interpretation of such bodies. Three examples in Montana, U. S. A. are discussed: (1) the Boulder Batholith, a late Cretaceous quartz monzonite series of intrusives of 4000 km2 outcrop area; (2) the Little Rocky Mountains, an up-domed area, in which an Eocene porphyry (130 km2) has intruded the Precambrian crystallines and lower Cambrian sediments; and (3) the Crazy Mountains, an Eocene diorite (100 km2), which has intruded the Paleozoic and Mesozoic sediments. In both the Boulder Batholith and the Little Rocky Mountains, intrusive rocks are less dense than the surrounding rocks and negative anomalies are found (40 and 28 mgal, resp.). In the Crazy Mountains, the intrusive is more dense than the surrounding sediments and a sharp positive residual anomaly of 42 mgal is observed. The analyses of the gravity anomalies predict that: (1) the thickness of the Boulder Batholith is on the order of 10 to 15 kms and is concave upward; (2) the Little Rocky Mountain syenite is not a simple laccolith, but is T-shaped and extends in depth to about 16 kms; (3) the Crazy Mountain diorite is not a simple small scale series of stocks, but a large connected body extending in depth 5 kms to the basement (although nothing can be said of it within the basement because there is little density contrast). The analyses of the anomalies place important limits on both the areal and depth extent of the intrusive bodies. Of all possible geophysical techniques, gravity studies offer the most promise in the determination of the shape in depth of intrusive bodies.

Jan 1, 1969

By J. A. Marts, R. C. Gilmore, Jr. Bogin, S. A. Saki, J. F. Brune, J. W. Grubb

"Colorado School of MinesResearchers at Colorado School of Mines (CSM) have developed computational fluid dynamic (CFD) models to study gas distributions and explosion and fire hazards in longwall gobs. In underground coal mines, methane continuously emitted from surrounding strata mixes with air from active mine workings and may form explosive gas zones (EGZs). Some western United States coal mines are also prone to spontaneous combustion (spon com). Insight into oxygen concentrations within the gob is crucial for assessing spon com hazards and mitigation strategies. Nitrogen injection used in conjunction with progressive gob sealing can reduce EGZs and spon com hazards by forming a dynamic seal that separates the methane in the gob from the air that ingresses from the face. This paper describes CFD modeling simulations studying the formation of such dynamic seals by optimizing the nitrogen injection locations. The impact of nitrogen on oxygen ingress and formation of EGZs is discussed. Optimum nitrogen injection quantities and injection locations were determined. Dynamic seal formation is most effective if the headgate nitrogen injection locations are split between the first crosscut inby the face and a second location about 300 m (1,000 ft) further inby. INTRODUCTION Underground longwall coal mine ventilation systems are designed to dilute hazardous gases and to provide breathable air to miners working in the area. Methane gas is liberated as the mining process extracts the coal and disturbs the surrounding strata. Methane mixes with the ventilation air and often produces explosive gas zones (EGZs) within longwall gobs (Brune 2013). Past CFD modeling research of underground coal mine ventilation systems has shown the effects of face air quantity on EGZs (Worrall 2012) and nitrogen injection to control spon com (Balusu et al. 2005; Ren et al. 2012; Ren et al. 2011; Smith and Yuan, 2008; Yuan and Smith, 2014). Other modeling approaches include network ventilation models of oxygen ingress (Dziurzynski and Wasilewski, 2012), and coupled Linear Network CFD algorithms (Wedding 2014). In a project sponsored by the National Institute for Occupational Safety and Health (NIOSH), CSM researchers are using Fluent®, a CFD software package by ANSYS, Inc., to model gas compositions and flows in underground longwall gobs. Figure 1 shows a progressively sealed gob with a U-type ventilation system in a three entry development. As the longwall advances, seals are constructed along the headgate in the crosscuts between the center entry and the gob. Additional gob isolation seals are built to block off the headgate entries inby the face. Nitrogen is injected through the seals in the first two crosscuts on the headgate side and at the first crosscut inby the face on the tailgate side, as shown in Figure 1."

Jan 1, 2015

By V. A. Temeng, M. Owusu-Tweneboah, K. Awuah-Offei

The mining industry has long recognized the value of dispatch systems in open pit mines as they reduce load and haul costs. Over the years, researchers have proposed many dispatch systems with various limitations and advantages. The simplest dispatch algorithms are the so called 1-truck-for-N-shovels dispatch strategy. These algorithms are limited by the fact that their objective functions do not consider all the objectives of a mine and cannot be applied to all possible truck-shovel configurations. They are also myopic in nature. However, they are simple and computationally efficient and do not require occasional updates of the upper stage problem as required in multi-stage dispatch algorithms. In this work, an agent-based truck dispatch algorithm that conceptualizes trucks as intelligent agents that make autonomous dispatching decisions to maximize their utility is proposed. The advantages of this algorithm includes utility functions that encapsulate all of management’s objectives and agent’s with broad situational awareness. They are also more suitable for autonomous trucks. We evaluate the new algorithm against a simple 1-truck-for-N-shovels dispatch strategies using discrete event simulation. The simulation results show that the new utility function has significant advantages over 1-truck-for-N-shovels inspired utility functions. Future work will incorporate adaptive behavior into the model via reinforcement learning algorithm. INTRODUCTION In an attempt to optimize truck shovel operations in open pit mines in order to reduce the cost of haulage operation, which according to (Alarie and Gamache, 2002) is estimated to be about 50-60% of the total cost of mining, several effective and efficient strategies have been developed. Optimizing truck haulage systems in an open pit mine is one of the greatest challenges of mining engineering and has been the subject of many research projects. It is important that haulage systems are designed to be efficient, in order to minimise haulage cost, improve profitability and increase the total mine value. Although optimizing the number of trucks required in the operation of open pit mines can help reduce the cost, an effective and efficient truck dispatching system add value by ensuring that the available trucks are used efficiently. With truck dispatching systems, the trucks are normally dispatched between the crusher and dumping station (e.g. waste dumps and stockpiles), and the shovels in order to maximize the total output, obtain grades targets, reduce fuel consumptions and other objectives. Truck dispatching, which can have one or more objectives, is typically subjected to certain operational constraints such as truck and shovel capacities, empty and loaded trucks speed, among others. The problems associated with truck dispatching was first mentioned by Dantzig and Ramser (1959) after they made an attempt to determine the optimum routes of a fleet of delivery trucks between bulk terminals and a service stations. The problem occurs in several industrial systems besides mining (Alarie and Gamache, 2002; Gendreau et al., 2006; Rego and Roucariol, 1995). The dispatching problem, also referred in literature as the vehicle routing problem, has seen a number of modifications and extensions with Bertsimas and Ryzin (1991) presenting a dynamic and stochastic vehicle routing problem, and Ralphs et al. (2003) also adding to the original concept, the concept of vehicle capacity routing.

Jan 1, 2019

By Robert L. Gamble

The world's largest fluidized bed steam generator located at Rivesville, West Virginia is currently undergoing initial operation. This unit is designed to generate 3708 kg/s (300,000 Ib/hr) equivalent to 30 MWe of superheated steam while firing coal in a fluidized bed of limestone. Coal was first fired in this unit in December, 1976 and start up operation is progressing.

Jan 1, 1977

By S. L. Bessinger

In the design and specification of a ventilation system for an underground mine, it is necessary to make reasonably accurate estimates of the pressure losses in the various airways of the mine. These estimates can be made with little difficulty for open airways with simple geometric cross-sections, such as those cut by continuous miners or tunnel-boring machines. The situation is much different on a longwall face, where the airway's complex geometric cross-section and the presence in the airway of obstructing equipment having a variety of shapes make it difficult, if not impossible, to estimate pressure loss using traditional methods of calculation. Headlosses in mine entries are calculated using Atkinson's Equation (1). [H = (English) H = (SI) (1)] where H = pressure ,loss, in. of H20 (Pa) K = friction factor, lbf min2/ft"4(Kg/m3) P = perimeter, ft. (m) L = airway length, ft (m) Q = airflow quantity, ft3/min (m3/sec) A = flow cross sectional area, ft2 (m2)

Jan 1, 1987

By Muhammad I. Kabir

A new minitest of in situ uranium leaching processes at reservoir conditions is proposed. The test which consists of a single observation/ production well and two observation wells is designed to permit the evaluation of both restoration and leaching parameters. It is shown that by using a straight forward history matching procedure, sometimes called a type curve analysis, both the rate of leaching and the ultimate uranium recovery can be evaluated based on the results of the test. Type curves are presented for the case in which the reaction rate is kinetically controlled and there are no other minerals competing for oxidant. Other situations can be approached using the same techniques as those presented here.

Jan 1, 1981

By Jerry Dolph

In September 1855, 55-year-old Noah Spencer Kellogg and his $3 jackass named Bill discovered what was known at the time as a “blow out” of high-grade lead and silver ore. The deposit was located on the side of a North Idaho mountain high above the South Fork of the Coeur d’Alene River. The ore was later assayed at 41,141 g/t (1,200 oz/st) silver. Kellogg named his discovery the Bunker Hill Lode, after the June 17, 1775 Revolutionary War battle of Bunker Hill. A thriving pioneer settlement sprang into existence around the resulting mine’s workings and was eventually— and appropriately — named Kellogg. The peak rising hundreds of feet above the mine’s adit was named “Jack-ass Peak” after Noah Kellogg’s hairy companion.

Jan 1, 1996

By M. Hepokoski, M. Klein, D. S. Yantek, L. Yan

Research by the U.S. National Institute for Occupational Safety and Health (NIOSH) has shown that heat/humidity buildup is a major concern within coal mine refuge alternatives. High temperature and humidity levels inside a refuge alternative may expose occupants to heat stress. Due to the safety risks associated with testing using human subjects, NIOSH partnered with ThermoAnalytics Inc. to create detailed thermal simulation models of refuge alternatives with human occupants. The objective of this effort was to predict a miner’s core temperature response and moisture loss in environments that may be encountered in a coal mine refuge alternative. These parameters were studied across a range of temperatures and relative humidity values to determine if the current 35 °C (95 °F) apparent temperature limit for refuge alternatives is reasonable. The results indicate that the apparent temperature limit is protective, provided that miners are supplied with sufficient water. The results also indicate that the body core temperature does not reach dangerous levels even at an apparent temperature of 54 °C (130 °F). However, the results show that moisture loss increases with apparent temperature. Therefore, if the apparent temperature limit were raised, the water provided in a refuge alternative would have to be increased to offset moisture loss.

Jan 1, 2017

By M. Hepokoski, M. Klein, D. S. Yantek, L. Yan

Research by the U.S. National Institute for Occupational Safety and Health (NIOSH) has shown that heat/humidity buildup is a major concern within coal mine refuge alternatives. High temperature and humidity levels inside a refuge alternative may expose occupants to heat stress. Due to the safety risks associated with testing using human subjects, NIOSH partnered with ThermoAnalytics Inc. to create detailed thermal simulation models of refuge alternatives with human occupants. The objective of this effort was to predict a miner’s core temperature response and moisture loss in environments that may be encountered in a coal mine refuge alternative. These parameters were studied across a range of temperatures and relative humidity values to determine if the current 35 °C (95 °F) apparent temperature limit for refuge alternatives is reasonable. The results indicate that the apparent temperature limit is protective, provided that miners are supplied with sufficient water. The results also indicate that the body core temperature does not reach dangerous levels even at an apparent temperature of 54 °C (130 °F). However, the results show that moisture loss increases with apparent temperature. Therefore, if the apparent temperature limit were raised, the water provided in a refuge alternative would have to be increased to offset moisture loss.

Jan 1, 2018

By Albert Hofstra, Joel Leventhal

The gray, dark gray and black colors of the sediments and the presence of pyrite in the Carlin, Jerritt Canyon, Horse Canyon, Betze, and Gold Acres sediment-hosted disseminated gold (SHDG) deposits indicate that these rocks are not oxidized with respect to carbon and iron sulfide. Both ore and non-ore host rocks generally are dark colored. Analyses for noncarbonate carbon (usually called organic carbon) in samples from SHDG deposits and related unmineralized rocks indicate that these rocks contain from a few tenths to a few percent carbon. We use the term noncarbonate carbon because, strictly speaking, organic carbon denotes carbon that is bound to hydrogen. However, the carbon present in SHDG deposits and related rocks has very little hydrogen chemically bound to it. Rocks with less than 2% organic carbon are usually gray in color. The dark colors in our samples are due to the relatively high temperatures that these rocks have experienced relative to organic matter maturation. We confirm the results of Nelson et al. (1982) that previous reports (for example, Radtke and Scheiner, 1970) were incorrect in reporting significant amounts of humic acids, extractable hydrocarbons (bitumen) or "carbonaceous" material. We believe these reports had problems with contamination or misdirected emphasis. Our samples consisted of unweathered rocks, collected mainly from mine cuts (benches, trenches, cores) and put into glass containers or wrapped in aluminum foil to avoid contamination. Only a few samples were collected from natural outcrops. We were careful to avoid samples in proximity to blast holes that were packed with ammonium nitrate and diesel fuel ("ANFO"). Contamination by ANFO may explain some of the previous reports of hydrocarbons, pyrobitumens, humic acids and anomalous nitrogen. When we were collecting samples, it was apparent that in addition to lithologic and color differences, the surface appearance of the rocks was distinguishable: "preg robbing" material that had a sooty surface; "graphitic" rock with a shiny surface; and more ordinary rocks that had a flat gray or black appearance. [Preg robbing is a term for ores that adsorb gold from the milling circuit; the graphitic material had not been x-rayed to actually identify graphite.] We hoped that laboratory study of these samples would show some fundamental differences that we could relate to ore genesis. Even though these sample types appeared different in the field, we could not distinguish any differences in thermal maturity (see below). Normal petroleum/organic geochemical laboratory procedures (solvent extraction, Rock-eval, pyrolysis-gas chromatography) failed to yield much information because the carbon was over-mature relative to oil and gas generation. Rock-eval results show less than 20 (± 20) mg of pyrolizable hydrocarbons per gram organic carbon (and an indeterminate Tmax) indicating that the organic matter in these deposits is burned-out relative to petroleum generation [with an H/C (atomic) ratio of less than 0.41. Because of the non-definitive results from standard organic geochemical methods, x-ray diffraction (XRD) and Raman spectroscopy were used to characterize the carbon. Prior to XRD, samples were treated with HCl and HF acids (1) to remove quartz that has a peak near 26° [20] at the position of the 002 peak of graphite and (2) to concentrate the carbon to a level detectable by XRD. The residue was put on a colodion mount and analyzed by XRD. The XRD analyses yielded a broad peak at 26° [20]. The shape of this peak indicates that the carbon is more thermally mature than anthracite rank coal but less mature than crystallized graphite. Based on XRD results from the literature (Landis, 1971) that are calibrated to metamorphic facies, results from our samples correspond to pumpellyite-actinolite to lowermost greenschist facies conditions, probably

Jan 1, 1990

By Robin J. Hickson

El Abra is one of the world’s premier copper de-posits. The project is located in northern Chile, 140 km (87 miles) inland from the Pacific coast. It has the same geologic age and structural setting as the world-class Chuquicamata copper mine located 42 km (26 miles) to the south. The current development plan for El Abra extracts798 Mt (879 million st) of high-quality oxide ore. This will require building a solvent extraction/electrowinning(SX/EW) facility that can produce 225 kt/a (248,000stpy) of cathode copper. This will make El Abra the largest SX/EW copper operation in the world, and the world’s seventh-largest copper producer.

Jan 1, 1996

By W. M. Ma, Daniel W. H. Su, K. Centofanti, Yi Luo, W. L. Zhong, Syd S. Peng

10.1 I~RODUC1'ION In order to understand the effects of surface subsidence due to underground mining on the ground water hydrology, a brief introduction to the rate, direction, and general pattern of ground water movement in aquifers is necessary. Ground water movement in an aquifer is controlled by aquifer lithology, structure, permeability, water levels, topographic set¬ting, and pumping patterns (Sgambat et al., 1980). Fig. 10.1 shows an idealized flow pattern of ground water in a hilly terrain (Coe and Stowe, 1984). The hill is made up of a series of interbedded permeable aquifers (mostly sandstone) and confining units (mostly shale). Since sandstone is porous and permeable, ground water moves through it downward and laterally until it reaches the interbeddings of the confining unit immediately below. The ground water then moves laterally along the interbeddings, be¬cause the confining unit is less permeable, and comes out as springs on the surface at the intersection of the aquifer and the confining unit. If there is a ground water table in each aquifer, it is a perched water table (e.g., right side of Fig 10.1). On the other hand, if the ground water recharge is larger than can be drained out, the interbedded permeable aquifers and confining units will be filled with water and a ground water table will exist only at the uppermost permeable aquifer. This is the semi-perched water table (e.g., left side of Fig. 10.1). There are three ground water flow systems: shallow, interme¬diate, and deep. Shallow flow systems occur near the land surface and the surface drainage system. The flow depth ranges from a few to several hundreds of feet with a resident time of a few weeks to a few years after entry, depending on the permeability of the rock strata. In a shallow flow system, the drainage coincides with sur¬face run-off water divides. Intermediate flow systems occur in minor hills some distance away from surface drainage. The travel distance ranges from several hundreds to several thousands of feet, the travel time from several months to tens of years. These systems are less dependent on seasonal recharge or discharge. In deep flow systems, the ground water travels from thousands of feet to miles, and transfers between surface basins. The travel time ranges from several tens to several hundreds of years. The systems generally receive recharge over a large area on major mountains and dis¬charge into major stream systems. 10.2 CASE STUDIES There are two ways of monitoring water wells for studying the effects of dewatering due to underground mining, i.e., water level and piezometric level. The water level is the water elevation in a water well that has penetrated two or more aquifers. Thus it indi¬cates the combined flow of all the aquifers that the water well intersects during the time of measurement. The piezometric level is the level to which water rises in a piezometer cased to a specific aquifer, and coincides with the pressure level of water in that aquifer. Therefore piezometric level reflects the water condition in that particular aquifer to which it is confined, while the water level represents the total yield of a water well without regard to the source of water. For instance, if a water well intersects two aqui¬fers, and if the lower aquifer is affected by undermining and goes dry while the upper aquifer does not, the water level in the well will drop, but may never go dry. Under this condition, the data obtained by monitoring the water level do not indicate the true behavior of the individual aquifers, especially if they are located at widely separated heights. 10.2.1 WATER LEVEL EFFECTS The effects of underground mining on ground water flow have been the subject of many investigations (Booth, 1984; Coe and Stowe, 1984; Owili-Eger, 1983; Rauch et al., 1984). However, the problems are very complicated, as have been exemplified by the conflicting conclusions reached by various investigators in var¬ious case studies. The most dramatic examples were described by Coe and Stowe (1984). In the first case (Fig. 10.2), the coal seam was 5 ft thick with cover from 400 to 800 ft deep. The majority of water supplies came from a sandstone aquifer in most ridge tops. When the face of the Panel No. 3 passed under it, dug well WW-1, which was approximately 670 ft above the coal, went dry, while the water level in Borehole B- 1, which was located at the center of Panel No. 4 with the bottom reaching the coal seam, also dropped about 160 ft. In Panel No. 5, the developed spring DS-2, which originated from the surface of the sandstone/shale contact and was approximately 750 ft above the coal seam, stopped when the face passed under it. The water level in the dug well W-2, which was dug into the shale about 700 ft above the coal seam dropped about 22 ft, but the well did not go dry. Therefore, nearly every spring or well located above or near the active panels was affected by longwall mining. In the second mine (Fig. 10.3), the seam was 5 ft thick with cover from 200 to 400 ft thick. Dug well DW-2, the bottom of which was 35 ft deep and approximately 330 ft above the coal seam in a perched sandstone aquifer, went dry right after the longwall passed under it. Drilled well W-3, in the sandstone aquifer, about 220 ft above the coal seam, experienced a 75-ft drop in water level when the face was under it, but showed some re¬covery after the face had passed under it. Ponds P- I and P-2 were developed in shale bedrock and were spring fed. They were not affected by longwall mining. Pond P-3 was developed in the sand¬stone aquifer, and its water table showed some decline when the face passed under it. Spring ST-1, which originated from Pond P-1 and was fed from several tributary valleys, was affected by longwall mining, probably because it passed across the panel edges where tension cracks drained off the water. Although the overbur¬den in case 2 was about half of that in case 1, the majority of water resources were not affected by longwall mining. Coe and Stowe (1984) attributed this discrepancy to: (1) a higher percentage of clays, shales, and claystones, resulting in a lesser degree of inter¬connected fracturing, and (2) a less rugged topography resulting in a less localized ground water flow system. Therefore, in order to assess the effects of underground mining, the premining ground water flow patterns, topographical, lithological, and meterological conditions must be known. Booth (1984) also monitored the ground water effects of a longwall mine (Fig. 10.4) in a seam 5 ft thick and 300 to 800 ft deep. There were three major aquifers: Morgantown sandstone approximately 30 ft thick and 630 ft above the coal; Saltsburg sandstone of up to 50 ft in thickness and 520 ft above the coal; and

Jan 1, 1992