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By Richard H. T. Garnett

In 1900, placer gold was discovered on the beach of Nome, AK on the southern coastline of Alaska's Seward Peninsula (Garnett, 1991). The site is about 800 km (500 miles) from Anchorage. Nome is connected to Anchorage only by air (daily) and by sea (summer). Total onshore placer gold production from Nome's immediate vicinity was more than 155.5 t (5 million oz). Alaska Gold Co, has continued to produce gold onshore with, until recently, two bucketladder dredges, each of 255-L (9-cu ft) bucket capacity. Small-scale marine dredging for gold has been at- tempted several times this century (Garnett, 1991). Western Gold Exploration and Mining Co. Ltd. Partnership (WestGold) is the only company to have been successful in achieving a significant offshore production. The Nome bucketladder-dredging operation from 1986 to 1990 constituted a unique marine-mining experience in the United States. \Inspiration Gold Inc., WestGold's predecessor, acquired six offshore leases in 1985. The total lease area of 87 km2 (21,551 acres) extended from the coastline to the 4.8-km (3-mile) offshore limit (Fig. 1). Those leases al- ready had been partially explored. Drilling was conducted off the shorefast winter sea ice. Therefore, it was rarely more than 1.6 km (1 mile) from the shore or in water deeper than about 9 m (30 ft). In 1985, estimated reserves comprised of a 5-m (17-ft) vertical thickness of sediments below 6.3 m (20 ft) of water. This meant a mean digging depth below the mean sea level (msl) of 11.3 m (37 ft). It was thought that the offshore Nome deposit possessed a feature that is common with many terrestrial gold placers - the secret of profitable exploitation of the marine deposit lay in maximizing the dredge throughput to minimize the unit costs. The inability of the project to withstand the prohibitively high cost of a new dredge was recognized. So Inspiration Gold purchased a used unit. This was the world's largest ocean- going bucketladder dredge (Fig. 2). Binzn was an 850-L (30 cu ft) bucket capacity dredge that was lying idle in Singapore. Originally constructed in the Jurong shipyard of Singapore in 1979, Bima was designed by Mining and Transport Engineering, a subsidiary of IHC Holland. Billiton Marine used the dredge for tin production at Pulau Tujuh in Indonesia (Dieperink, 1978) before it was laid up in mid-1985. Bima underwent a nine-week refit before departing Singapore on June 4,1986, with 800-t (880-st ) of deck cargo. It was dry-towed for 32 days to Alaska. A slower, less expensive, wet-tow at the authorized 5.5 kmthr (3 knots/hour) would have delayed the dredge's arrival in Alaska untl almost the onset of winter. The 13,000-km (8,100-mile) voyage was made on the deck of Smit Lloyd's "Giant-4" submersible barge towed by its 7.8- MW (10,500-hp) tugboat. The first season's dredging revealed several major shortcomings in Bima. Further repairs and modifications were undertaken at Tacoma, WA. The dredge returned to Nome for the June start of the 1987 summer dredging season. The refitted Bima worked offshore at Nome from 1987 to 1990. It produced 3.67 t (118,078 oz) of gold at an average recovered grade of 824 mg/m3 (0.0204 oz/cu yd). In 1991, the dredge was dismantled and sold.

Jan 1, 1997

By Dale C. Matthews

Pressure oxidation of refractory gold ores is becoming more popular in what has become an environmentally sensitive society. This article discusses some specific process problems and solutions involved with starting up and operating an autoclave circuit. The Getchell gold deposit is located about 72 km (45 miles) northeast of Winnemucca, NV. The deposit was discovered in 1934 and first production came about in 1938. The oxide portion of the ore body was mined and milled from about 1936 through 1950. Refractory arsenic-bearing sulfide ores had long been known to exist in the Getchell deposit. These ores had been mined concurrently with the oxides since 1938.

Jan 1, 1991

By C. A. Fleming, R. G. Williamson

Process development for Eskay Creek began in early 1990 at Lakefield Research, and was initially focused on producing a high-grade/high-recovery concentrate for sale. Owing to the significant base metal sulphide (Cu, Zn, Pb) content of the ore, such a product would have made an attractive feed to a copper smelter, while a gravity and/or flotation flowsheet would have circumvented many of the environmental permitting problems that were anticipated. In the event, it was found that neither gravity nor flotation (nor even a combination of the two) was able to produce a discardable tailing and, in late 1990, attention shifted to the development of a hydrometallurgical flowsheet.

Jan 1, 1995

By Roy J. Leonard

Two small diameter sewer tunnel projects being hand dug under major highways in the Greater Kansas City area encountered problems which were unforeseen from the geotechnical engineering information supplied with the contract documents. Both tunnels were being excavated by experienced crews using steel liner plates. One required the use of compressed air for completion, while the other required poling boards. Both contractors overran their budgets and filed changed condition claims, and this promoted further geotechnical engineering investigations. Fissured clays beneath a water table were encountered at both sites, but the character of these clays differed; however, both were inadequately described in the original geotechnical engineering reports.

Jan 1, 1987

By S. L. Jung, T. L. Nichols, K. Prisbrey

The problem was to evaluate the on-line detection of rock properties through acoustic emission sensors. Acoustic emission sensors, when attached to crushers, grinders, and roof bolters, are robust, economical, and relatively maintenance free. Our objective was to relate acoustic emissions to rock fracture mechanisms, including micropore closures, linear elastic deformations, and crack propagation. We evaluated acoustic emissions from steel jacketed rock cores during indentation tests. In addition we attached sensors to the rotating shaft of a rock bolter drill. A back propagation neural network "learned" rock fracture characteristics and rock type with 99% classification accuracy. A neural network's calibration and computational abilities suggest better acoustic emission sensor capabilities.

Jan 1, 1993

By Hidehiko Nakazaki, Sakuro Murayama, Mitsuo Miura, Masaaki Endo, Yoshiaki Hurukawa

This is a detailed report of construction experience of a tunnel built by a shield of rectangular cross section with reinforced concrete segments. In case of tunneling by a rectangular shield, there were the following problems to be overcom by technical developments; (1) structural joints between segments, (2) complexity in erector handling, (3) exact steering operation of shield and perfect filling of tail void left around the lining erected. Such rectangular shape of cross section has various advantages comparing the conventional circular shape as follows; (1) effective utilization of excavated space, (2) greater overburden depth, (3) stability of lining against unbalanced earth pressure caused by neighbouring construction.

Jan 1, 1979

By William F. Kane, Eric C. Drumm

Rock slope failures in the Great Smoky Mountains of Tennessee are a continuing problem. A study of the geotechnical factors affecting such slopes was conducted in this geologically complex region. Seven rock slopes, five of which had undergone failure, were identified and mapped. Other parameters were mapped in addition to the standard geologic and geometric parameters. These were joint frequencies across and down the slope, and surface hardness from Schmidt hammer tests. Regression analysis on the various data revealed that Schmidt hammer hardness correlates very well with joint cohesion back-calculated from failure geometries. This approach suggests an alternative means for estimating joint strength.

Jan 1, 1986

By Steven W. Hunt, J. Patrick Powers, Roger C. Ilsley

Artificial groundwater recharge has been used successfully to mitigate water level drawdown in upper alluvial deposits during construction of the Milwaukee deep rock tunnels. Recharge wells in rock as well as soil were used. The effort reduced settlements from consolidation of compressible estuarine deposits, and has minimized damage to existing structures. The paper describes the geology that presented the consolidation problem, and the hydrogeologic conditions that caused the drawdowns. Also presented are the details of recharge well design, construction, operation and performance in an urban environment. The project design calls for grouting and lining of the tunnels to control groundwater in the long term.

Jan 1, 1991

By J. A. Rose, A. S. Atkins

Environmental awareness has become a paramount consideration in the issue of planning and licensing arrangements for the disposal of wastes associated with mining operations. In this con- text the disposal of liquid tailings is a difficult and controversial problem with regard to environmental surface disposal. The paper outlines the use of Information Systems for decision support in the safe and environmental disposal of liquid tailings linked to conventional coarse refuse operations. This offers both an economic and an aesthetic approach to a historical perception of waste tipping in the underground coal extraction industry. The paper will demonstrate a prototype system that incorporates multimedia facilities which include data such as; voice comments, site photography, site plans and fluid flow circuits.

Jan 1, 1996

By J. L. Goodier

The paper points up the hesitance of private capital to pursue development of offshore mineral mining endeavors due to the deterrent effect of the clouded legal status of such endeavors. Some states have no laws or regulations to protect the potential exploiter. Others have regulations which give no proprietary rights of exploration to mineral discoveries. The above factors and others are discussed and analyzed in some detail, covering, in turn, summations of the federal regulations and of each of the coastal states. Some comparative analyses are provided, and some recommendations for encouragement to capital investors are made.

Jan 1, 1968

By I. Dumitrescu

Since 1990, the entire Romanian mining industry has suffered a major restructuring, i.e. technical and economic. The large majority of the remaining active mines are these with a chance for economic comeback. This is also the case for the mines that belong to MINVEST Deva Company; most of the mines are closed, and are waiting to be reclaimed. The authors present the closing procedures of the former copper mining perimeters managed by MINVEST. It is well known that pollutants of concern for the environment must be monitored to obtain reliable information on the quality of ambient conditions and to minimize their impact on the environment. Consequently, the monitoring problems during the closing procedures will be presented.

Jan 1, 2008

By William H. Mount

INTRODUCTION Effective mine ventilation is required to maintain a healthy underground environment for humans. Without effective ventilation, the environment can become unhealthy or hazardous as a result of the depletion of oxygen, contamination with toxic gases, or the buildup of an excessive amount of particulate matter (dust). Each contaminant has an upper limit of concentration that should not be exceeded within an 8-hr period. This is known as the threshold limit value (TLV). The TLV represents an acceptable level of exposure that should produce no ill effects. Unfortunately, more than one contaminant may be present at any one time and the effects of the individual contaminants may be additive, i.e., the effects of each contaminant must be considered simultaneously to determine the potential danger to miners. Possibly the greatest threat to mine-air quality is the uncontrolled underground use of the diesel engine. The diesel engine was invented in 1892 by Rudolf Diesel. His intention was to develop a power source that could burn coal dust as a fuel, but he was unsuccessful in that attempt and had to resort to liquid petroleum fuels (Johnson, 1975). In 1898, the diesel engine was intro¬duced into the United States by Adolphus Busch, who anticipated using it as a prime mover in factories and generating plants. At that time, the diesel engine was a very large and very heavy engine, designed for fixed installations. By 1919, lighter engines were being developed, and by 1931, Caterpillar was marketing a diesel-powered, track-type tractor (Henderson, 1975). Since 1931, the diesel engine has evolved into an extremely popular prime mover in medium and heavy-duty applications. Efficiencies now are on the order of 40% and improvements such as turbocharging and aftercooling have produced engines capable of generating power at a ratio of 0.3 kW/kg (1.0 hp per 5.0 lb) of engine weight. Although the diesel engine is relatively efficient as a mobile power plant, it is far from efficient in terms of the energy produced from the energy potential of the fuel. About 60% of the heat value of the fuel leaves the engine as wasted heat, with about 50% of that heat being emitted through the exhaust pipe and the other 50% being emitted through the radiator or cooling fins. Perfect combustion in an engine would produce only water vapor (H_0), carbon dioxide (CO_), and nitro¬gen (N2) as the byproducts. Since the diesel is not a perfect engine, each pound of fuel burned generates 5.6 m° (200 cu ft) of exhaust gas, containing about 0.009 m3 (0.33 cu ft) of carbon monoxide (CO), 0.009 m' (0.33 cu ft) of nitrogen oxides (NO, NO2, and NOD), and 0.57 m3 (20 cu ft) of carbon dioxide. The balance of the exhaust emission consists of free nitrogen and water vapor (Hurn, 1975). Contrary to popular belief, the diesel is not inherently dirty. Under normal operating conditions, a well-maintained engine neither smokes nor smells. However, the same well-maintained engine can and does produce toxic emissions. A diesel engine is not inherently safe and constitutes a distinct hazard to personnel. This chapter is devoted to a description of the various toxic substances that may be generated by a diesel engine. Although some of these substances may also be produced by blasting or natural causes, the focus of this chapter is on the relationship between the internal- combustion compression-ignition engine (the diesel) and the quality of the mine air. CARBON MONOXIDE Combustion Process During the combustion process (burning) of organic fuels, each atom of carbon combines with two atoms of oxygen, provided that a surplus of oxygen atoms is available. Thus, the carbon is oxidized to carbon dioxide. Most open flames, such as trash fires, camp fires, gas ranges, etc., produce carbon dioxide. However, with insufficient oxygen, incomplete combustion results as the carbon atoms each combine with one atom of oxygen to produce toxic carbon monoxide. Burning charcoal briquettes produce carbon monoxide because the combustion takes place inside the briquettes where sufficient oxygen is not available to the combustion process. Internal-combustion engines, whether burning gasoline or diesel fuel, also produce carbon monoxide. The only oxygen available to the combustion process is that trapped within the cylinder. If the amount of fuel delivered to the cylinder is excessive, there is insufficient oxygen for complete combustion and carbon monoxide production results. In a normally aspirated (nonturbocharged) diesel engine, the amount of air "sucked" into a cylinder is the same on every intake stroke, resulting in complete combustion only at low levels of engine loading, when small amounts of fuel are injected. Higher levels of engine loading cause larger amounts of fuel to be injected into the same volume of air in the cylinder. Unless the volume of air is increased, the combustion process becomes progressively less complete as the amount of fuel increases. Turbocharged engines are able to compensate some¬what for increased loading and increased fuel consumption. The turbocharger acts as a compressor for the intake air, forcing a larger volume of air into the cylinders as the engine speed increases. Hence the turbocharged engine burns cleaner than a naturally aspirated engine and produces slightly less carbon monoxide (Marshall and Fleming, 1971). Much of the underground equipment used today is powered by turbocharged indirect-injection diesel engines. Although these engines emit fewer toxic contaminants than naturally aspirated engines, they do not eliminate the problem. Since the turbocharger is driven by the exhaust gases, rapid accelerations can cause temporary overfueling of the engine until the turbocharger attains a speed sufficient to restore the correct air-to-fuel ratio. During this "turbocharger lag," the combustion cylinders contain insufficient oxygen, causing severe smoking and an increased output of carbon monoxide.

Jan 1, 1982

By Jeffrey M. Listak, Gregory J. Chekan

The U.S. Bureau of Mines, in an effort to improve coal conservation and utilization is currently investigating longwall panel layouts to maximize coal recovery and minimize interactive problems in multiple-seam operations. When longwalling coalbeds in descending order, the transfer of stress from overlying gate roads is a major design constraint affecting pillar stability in the lower mine. The lower mine gate road pillars must be properly designed to withstand the additional load transfer if gate roads are superpositioned in successive seams. The Bureau's MULSIM/NL model was used to analyze load transfer mechanics for superpositioned gate road pillars. Analysis of Longwall Pillar Stability (ALPS), which is an empirically based design method for longwall gate road pillars, was used to calibrate model input parameters. The attributes of both the MULSIM/NL model and ALPS were combined to develop a modified method for estimating pillar stress for multiple-seam cases. The modified method uses a multiple-seam (MS) factor to estimate the stress on the lower mine gate road pillars when superpositioning is practiced. Numerical analysis shows that the MS factor is dependent upon the interburden thickness and pillar width and is presented in a series of graphs relating these two parameters. Several examples are included to illustrate the use of the MS factor for estimating lower mine pillar stress and resulting stability factors.

Jan 1, 1992

By L. C. Atkinson, E. A. Azrag, T. M. Hanna

The results of using a simple analytical solution and a relatively complex numerical model to estimate ground water inflow to an open pit mine are compared. The analytical solution assumes lateral, radial flow to a fully penetrating pit in an idealized confined aquifer, whereas the numerical model simulates fully three-dimensional flow to a partially penetrating pit from a water table aquifer. The latter is a more realistic simulation of the problem, but the former method is significantly easier to use. Comparison of the results obtained with the two methods for some typical hydrogeologic conditions encountered in mining yields ratios between them in the range of 0.2 to 0.6. These values can be used as a coefficient in the Pit Flow analytical solution to produce reasonable estimates of in-flow even when there are significant differences from the idealized conditions implicit in its application.

Jan 1, 1995

By André G. Journel

As opposed to graphics applications in medical sciences and mechanical engineering, computer imaging of the subsurface faces a severe problem of data shortage. Most graphics softwares include an interpolation algorithm aimed at producing slick graphic output, irrespective of the attribute being interpolated, the quantity and quality of the data available, and what the map is intended for. It is suggested that the power of modern computers be also used in providing representations of the subsurface that accurately reflect actual spatial variability and the large variety of soft information available beyond hard data. Since any subsurface representation is uncertain, a measure of that uncertainty should be provided which can be used for risk analysis.

Jan 1, 1992

By E. A. Metz

It has been approximately four years since the International Agency for Research on Cancer (IARC) reclassified crystalline silica as a "group one" substance. Since then, crystalline silica has been considered a human carcinogen. Silicosis is a preventable disease, and several aggressive campaigns have been developed to increase awareness of silica-dust-related problems in the industrial environment. New analytical techniques are now being developed to determine quantitatively the amount of crystalline silica in materials. Yet, still much is to be learned about the surface properties of silica and the way in which the disease progresses into full-blown silicosis. This paper discusses the interaction of free radicals generated by the mineral particles and lung tissue. It is the cell injury and DNA damage that progresses to fibrogenesis. Freshly fractured surfaces of silica contain free radicals. These free radicals play an important role in the stimulation of the alveolar macrophage and the development of the inflammatory reactions leading to the fibrotic response caused by silica. Engineers, scientists and physicians need to discuss the mineralogy of silica and the technical issues concerning the development of silicosis.

Jan 1, 2000

By William T. Griswold

Few metals or industrial minerals can boast a better growth record over the past fifteen years than the borates. This period of growth occurred before the influence of any large-scale use in plastics or high-energy fuels. These new developments not only provide expanding markets, but the programs related to their development are generating research information that will lead to many other new uses. The most dynamic growth areas for refined products of boron or borates are in the acid, the oxide and the reduced forms, such as the metal and the hydrides. Expanding requirements for these products will modify the emphasis on the use of naturally occurring sodium borates. Any borate from which boron can be economically extracted will become a potentially important ore. This is particularly true of the calcium borate, colemanite. Only one large deposit in the Western World has ever been developed where the principal economic minerals are sodium borates, This factor alone would discourage any exploration program directed solely toward the discovery of these ores; on the other hand, ample exploration opportunities for calcium borates exist in the desert regions of California and Nevada. It is therefore reasonable to restrict a program to this region, in spite of geologically favorable areas in foreign countries such as Turkey, Argentina and Chile.

Jan 1, 1959

By W. F. Hahnert, P. A. S. Ralston

In off-line training of a rule-based controller, the significant measure of successful training is the quality of control provided by the generated rule set. In an adaptive or on-line control environment, performance is also measured by the ability to accurately maintain a satisfactory rule set, but within constraints on speed and/or resource availability. Very small population genetic algorithms, or microGAs, have been proposed as a means of capitalizing on the hill climbing characteristics of faster local optimization techniques while requiring less memory and retaining much of the robustness of traditional, larger population genetic search. A traditional genetic algorithm and a similar microGA are developed and applied to two control problems. The performance of these algorithms is analyzed with respect to (1) the quality of the rules learned, (2) the rate at which learning occurs, and (3) the memory resources required during learning.

Jan 1, 1993

By S. Hartman

The Escalante Silver Mine in Southwest Utah produces an average of 71.000 kg (2.3 million troy ounces) of silver dore annually. Precipitates from a cyanide leach circuit are treated by either acid leaching prior to fusion or a direct fusion with nitre. Process development, plant experience, and a comparison of both methods will be discussed. Plant experience from the custom treatment of a gold/silver precipitate containing matte producing elements will also be covered.

Jan 1, 1989

By O. A. Bascur

The problem of setting the proper control objectives and/or having several objectives to be met in the implementation of grinding control strategies can be resolved. The design and implementation of a distributed control system for safe operation of a grinding circuit while maximizing profit is presented. An optimal recovery through- put target for a desired grind is accomplished by advanced control strategies at the DCS level. A mill load constraint control technique provides stable operation with a substantial increase in throughput, while the desired grind index is maintained by an inferential grind control technique without using a particle size analyzer. The integration of crushing/grinding and flotation in the overall design was the key to the success of the project. This synergistic effect was obtained by implementing a computer plant management system in the concentrator. The overall/philosophy was to keep the implementation simple while using new technology creatively.

Jan 1, 1991