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By D. R. Cook

This paper is a case history of an exploration venture for base metals, begun by the Rocky Mountain District of Bear Creek Mining Company in 1952 and completed in 1954. The project was based on the idea of W. S. Burbank, U. S. Geological Survey, that commercial deposits of base metals might occur in Paleozoic sediments beneath hydrothermally altered volcanic rocks in the Southern Bonanza mining district, Colorado. Here, an area of andesitic rocks, four square miles in extent, has been argillized, pyritized, chloritized and silicified. Geological, geophysical and geochemical studies were followed by the diamond drilling of three holes totalling 6,220 feet. Further alteration ang geochemical studies were made on the cores from these holes. A brief review of the alteration and geologic mapping, colored aerial photograph interpretation, geochemical soil and rock sampling, magnetic, gravity and radio-metric surveys are presented together with some conclusions regarding this work. This paper is a case history of an exploration venture for base metals, begun by the Rocky Mountain District of Bear Creek Mining Company in 1952 and completed in 1954. Important contributions were made to the project by personnel of the Rocky Mountain District and the Geophysics Division. Individual acknowledgements to these people are made at the end of the paper. BASIS FOR THE PROJECT The project was based on the idea of W. S. Burbank (1947, p. 444) that commercial deposits of base metals might occur in Paleozoic sediments beneath hydrothermally altered volcanic rocks in the Southern Bonanza mining district, Colorado. Paleozoic sedimentary rocks, including the favorable Leadville limestone, are exposed three miles south of the altered area, and reason exists to believe that they might underlie it within a reasonable depth. Alteration of pre-mineral volcanic rocks has been used successfully as a guide to concealed orebodies in the Main Tintic and East Tin tic mining districts, Utah (Bill-ingsley, 1933, p. 120-122; Lovering et al, 1949; Howd, 1957, p. 124-134; Cook, 1957, p. 73) and could be a useful guide here. GENERAL GEOLOGY AND STRUCTURE The Northern and Southern Bonanza mining districts are northwest of the San Luis Valley in southern Colorado, just within the northeastern edge of the San Juan volcanic province. The districts are1ocated on the southern extension of the Sawatch uplift, a prorninent northwest-trending structural high. The highly productive mining camp. of Leadville, Gilman and Aspen are on the northeastern and northwestern flanks of this uplift where Paleozoic limestones have

Jan 1, 1961

By W. Barnett

The Limpopo Metamorphic Belt is a complex geological terrane with at least three major deformational events. Tectonically juxtaposed lithology, open to isoclinal folding, crosscutting and re-activated shear zones and metamorphic gneisses and schists make pit slope design and maintenance a risky business. Venetia diamond mine?s Cut 3 is planned to reach 360 m by 2011. The difficult rockmass created problems in the original pit and a new more comprehensive slope design was necessary. Nearly 9 km of geotechnical drilling were undertaken to produce a new geological model and provide geotechnical information near the final Cut 3 face. All existing data from the pit were brought together into a database. SRK Consulting were brought into the project to audit the process and provide most of the manpower for the data analysis. Existing failures were back-analysed and the geotechnical domains identified. Analyses of only the southern domains are discussed in this paper. Geotechnical engineers can design slopes at any angle, but it is up to the managers at the mine to decide what risk they are willing to accept in a slope design. Once the issue of risk was discussed and settled in respect of the consequences of failure, each of the main geotechnical domains were analysed to produce a slope design at5% probability of failure with 15% above the first ramp. A risk assessment of the design was then undertaken to determine what risk the design placed on the equipment, personnel and the profitability of the overall mining operation. The risk assessment indicated minimal risk to the operation. One of the main assumptions of the final design is that the pit slopes will be dewatered. A project was immediately put in place to determine a groundwater model for the mine and to thereby determine the best dewatering procedure. However, it should be obvious that it is practically impossible to prevent benches from getting briefly saturated with water during storm conditions. It was therefore necessary to look specifically at supporting the crests of the ramps in the problematic southern domains to guard against the possibility of crest failure during heavy rains. The data available were re-analysed toward this objective. Spiles were recommended as the most cost-effective support system, and a probabilistic approach was used in the design. The final design has a 5% probability of failure, and the analyses indicate a strong sensitivity of the required spile spacing to the strength of the reinforcement material that will eventually be used. The pit slope parameters derived as per the discussion in this paper have just begun to be implemented at Venetia Mine.

Jan 1, 2001

The key aspects of process metallurgy that distinguish platinum group metal (PGM) concentrate smelting from that of other base metal sulphide concentrates are presented. These differences include considerably higher input chrome and magnesia contents that directly raise the slag liquidus temperature and have the potential to increase accumulations of refractory spinels. Most importantly, the higher processing temperature required for PGM smelting and the resulting very high matte superheat lead to considerably more onerous smelting conditions than those typical of other smelting operations. This has presented challenges to furnace design and integrity, especially when coupled with the progressive intensification of smelting, involving doubling, and then redoubling, of furnace power inputs over the past 20 years. These power increases have been enabled by increasingly more advanced furnace cooling and structural technologies. Key technologies include strong constant-force spring-loaded bindings acting in three dimensions to minimize infiltration of superheated matte into brick joints, and robust well-cooled tapholes for reliably tapping the superheated matte. The result has been substantially improved productivity, and reduced smelting capital cost outlay per unit of production. A significant challenge, which was not anticipated, presented itself in the form of insidious corrosion of the furnace lining, and especially high-intensity copper cooling elements. Investigation of corrosion in related industries eventually identified chloride-accelerated sulphidation', and this term has been retained as it generically describes the most pertinent aspects of the accelerated low-temperature wear of copper coolers observed in PGM smelting. In addition to discussing the corrosion mechanism, this paper describes a number of solutions that were developed jointly by Anglo American Platinum and Hatch to address the copper corrosion problem. First, new monitoring technologies allowed furnaces to be operated more safely for a longer period of time. Second, a system for replacing corroded coolers from outside the furnace during a fast 'hot' shutdown minimized the impact on furnace operating factor and hearth life. Finally, a corrosion-resistant graphite-protected cooler design significantly improved furnace campaign life, and heralds a more lasting solution to cooler corrosion in PGM furnaces.

Jan 1, 2013

By D. E. Wolfson

As part of its overall program of coal carbonization, the Bureau of Mines is studying the coking properties of coals that may be used for metallurgical purposes. The objectives of this study were given in detail in a previous report.2/ The suitability of coal for metallurgical use depends primarily on (1) chemical composition, (2) preparation characteristics, and (3) carbonization behavior. The first two factors, as well as the available reserves, are considered in selecting coals for carbonization tests. According to the estimate of reserves by Dowd,3/ the recoverable coal in Raleigh County in beds 28 inches or more thick, in thousand tons, is: [ ]

Jan 1, 1957

By Greaves M. C

X-ray fluorescence spectroscopy used for the analysis of mill samples results in improved control of flotation concentrators.Techniques and equipment for sampling pulp streams, filtration and drying, grinding, briquetting and X-ray fluorescence analysis of samples have been developed.The current methods in use permit the analysis for lead and zinc in six pulp samples within 30 min total elapsed from the start of sampling. The X-ray method gives a precision at least equal to the former routine wet-way assay methods.The equipment is used also for pilot plant control, as a means of solving complicated analytical problems and in the rapid qualitative analysis of exploration samples.INTRODUCTIONIn milling and concentrating operations, classical methods for the assay of lead and zinc have been mainly of use for accounting purposes and for the post-mortem examination of plant operations, but have been of little value for rapid mill control. Where attempts have been made to apply these methods to control assaying, it has been necessary to modify the procedures and introduce short cuts which have tended to reduce their reliability.Even with these shortened procedures, the time taken to obtain a limited amount of information rendered them of little value for the control of milling operations where sudden, large fluctuations can occur. In recent years, a number of new and rapid analytical techniques, based on physical rather than chemical principles, have been introduced.These include direct reading emission spectroscopy, x-ray fluorescence spectroscopy and atomic absorptionspectroscopy.

Jan 1, 1964

The Ediacara mineral field is classified as a Mississippi Valley type deposit with stratiform mineralization near the base of the Cambrian beds. Mineral deposition was contemporaneous with sedmentation and reerystallization, and mobilization took place after lithification of the sediments. Several mechanisms of deposition were possible.INTRODUCTIONThe Ediacara mineral field is located in the Mt. James Range approximately 300 miles north of Adelaide, about 12 miles west of Beltana railway siding and 10 miles east of Lake Torrens. It is isolated geographically from similar deposits of equivalent age and environment in the Flinders Range Province (Fig. 1). The climate may be described as semi arid with high summer temperatures and frequent dust storms. Occasional thunder storms are the main source of rain in the summer months.The exact date of discovery is unknown, but is believed to be about middle of the last century. Ulrich (1872) was the first geologist to report on the field. At that time only the southern portion of the field had been prospected (and abandoned). Although the prospects did not appear encouraging Ulrich advised prospecting of the shales and testing beneath the limestone.In 1888, Rosewarne, an Inspector of Mines, visited the Southern Workings and queried whether they were connected with some lode at deeper level or were merely bedded deposits. The first geological map with sections was drawn by H.Y.L. Brown (Brown 1892).Brown recognized three principal rock formations as dolomitic sandstone, kaolinised shales and sandstone, and quartzites and sandstone in descending order. These three basic units are still recognized. He recognized also the stratiform nature of the mineralization in the shales as a...

Jan 1, 1963

By T. M. Williams, P. M. Green

Paper presented at Mineralisation in the Caledonides, the Mike Gallagher memorial meeting held in Edinburgh, 27-28 June 1996. The sediment geochemistry of streams draining Southern Uplands and Lake District turbidites was compared with lithogeochemical data for the source greywackes, using stratigraphically defined catchments. Several systematic trends in element abundance variation between source and stream sediment can probably be applied more widely to interpretation of drainage geochemistry. Pb and Zr increase markedly from source rock to sediment, by adsorption on clay and zircon grain concentration. Variation of feldspar-related elements Rb, Sr, K and Ba appears to be controlled by source grain size and compositional maturity. Ni shows surprisingly little change and Fe and Co are only slightly raised. Cr is particularly useful, with variations superimposed in anomalously high regional levels. Abrupt changes in Cr distribution in stream sediment coincide with stratigraphical boundaries, allowing drainage data to be used as a surrogate for whole-rock values

Jun 19, 1905

When the Mining Bill came before the Victorian Legislature not so many months ago, the question arose whether mining managers required education, and to what extent. Some members of the House expressed themselves in a way which appeared to leave the impression that mining managers would be all the better if they were not brought up in a scientific school.To try and prove what we owe to science I will give a short history of colonial mining from the earlier period to the present time and compare results.I believe I am right in saying that South Australia is the pioneer colony in mining and to her belongs the credit of not dnly being the first mining colony, but also that her beginning turned out so successful, as the history of the Burra Burra copper mine will testify. At about the same time a little galena mining was carried on nearer to Adelaide, but as this did not prove a success and was only worked by tributing parties, little notice was taken of it.

By S. Okubo, K. Fukui

Empirical equations established for estimating the rock strength of the working face based on the cutting forces of a tunnel boring machines (TBM) are further examined and discussed with respect to the dominant factors affecting TBM performance. Constants in the equations are related to TBM-specific parameters such as excavation (tunnel) diameter, cutter diameter, and cutter distance. The relationship between the constants and the TBM specifications is examined in this study on the basis of data collected at ten tunnels, and it is found that the constants are most strongly influenced by the cutter diameter and tunnel diameter. Zur Schätzung der Gesteinsfestigkeit an der Arbeitsfläche ermittelte empirische Gleichungen, die auf den Schneidekräften von Tunnelbohrmaschinen (TBM) beruhen, wurden weiter im Hinblick auf die vorherrschenden, die Leistung der TBM beeinflussenden Faktoren hin untersucht und diskutiert. In der Gleichung enthaltene Konstanten werden zu den TBM-spezifischen Parametern wie Auschachtungs- (Tunnel) Durchmesser, Schneidendurchmesser und Schachtlänge in Beziehung gesetzt. Die Beziehung zwischen diesen Konstanten und den technischen Daten der TBM wird in dieser Studie auf der Basis der bei 10 Tunnelbauten gesammelten Daten untersucht. Dabei wurde gefunden, dass diese Konstanten am stärksten von den Durchmessern der Schneiden und der Tunnel beeinflusst werden. Cette étude examine et discute les équations empiriques permettant d'estimer la résistance de la roche attaquée aux forces de coupe des tunneliers dans le cadre de l'étude des facteurs dominants affectant les performances des tunneliers. Les constantes de ces équations concernent les paramètres spécifiques des tunneliers comme le diamètre d'excavation (du tunnel), le diamètre du couteau et la distance de coupe. Cette étude examine le rapport entre ces constantes et les caractéristiques techniques des tunneliers d'après des données collectées dans dix tunnels et elle conclut que ces constantes sont principalement influencées par le diamètre du couteau et le diamètre du tunnel.

Jan 1, 2003

By Pat C. Hautala, J. R. Hoskins

This is a new era for the minerals industry. Never before has there been more need for effective communication. So said Robert Anderson, chairman and chief executive officer of Hanna Mining Co. He was speaking to the American Mining Congress's Communication Workshop. The question is whether there is enough industry concern to meet the challenge. Anderson observed that increased workshop attendance, in continuing tough times, reflects the industry's concern for communication. But, why were students, faculty, engineers, supervisors, and managers not at the conference? Communication applies to every manager, Anderson said. But he was the only operating manager present. And only one company sent operating supervisors. The remaining conference participants were public relations personnel, generally with nonmining backgrounds. And the program dealt mostly with public relations issues. Role of Communication in the Minerals Industry. It is well known that the minerals industry faces economic, political, and social problems. Economic shifts and foreign competition have created an international minerals industry and an international marketplace. This, in turn, calls for worldwide communication. Other factors effecting communication are: • Governmental protectionism as well as regulatory reforms call for increased interaction with governing officials. • Changing social values have created environmental issues and anti-industry attitudes. This intensifies the need for improved public relations. • Traditional work values are shifting towards self-actualization and humanistic movements. The work force is better educated and more informed. Employees demand more satisfaction, equality, and job autonomy. • The mining industry's task of managing its human resources is complicated by layoffs, job uncertainties, and bleak outlooks concerning employee morale and motivation. Technology and Information for a New Era As noted, this is a new communications era, one propelled by technology and information. Technology has led to reduced demand for raw materials by developing substitutes. Copper demand, for example, will never fully recover. Copper cables are replaced by fiberoptics; copper transmission lines, with aluminum. Technology has shifted the US from traditional to high tech and service industries. The speed, frequency, and scope of information transmission have greatly increased. But the most significant characteristic of this information is not the pace of advancing technology. It is the dramatic increase in the importance and frequency of our personal transactions. Knowledge has replaced raw materials and capital as the strategic resource. Information has replaced energy as the transforming resource. And the game against nature has become an interpersonal game (D. Bell, Post-industrial society, Physics Today, '76). In Megatrends, John Naisbitt says that information will soon double every 20 months. So, professionals will become "information workers." And communication will be the life channel of the information age. Thomas Wolfe said you can't go home again. Hanna Anderson said we are, indeed, facing a new day. It will never again be "business as usual." We must move into the information age with the rest of society. We cannot trust that the world will continue to rely on our products. Nor can we place the responsibility and control for problems and solutions outside the minerals industry. Improved communication is not a panacea. But, Anderson said, it is critical to the minerals industry. What is Communication? The word communication is overused. It is applied to every aspect of our lives. Satirist Tom Lehrer got sick of hearing about the need to communicate. He said, "It seems to me that if someone is having all that trouble communicating, the very least he can do is shut up!" Obviously, we cannot follow that advice (though we might wish that some others would do so). Communication is always going on. It is inevitable. Yet we have many misconceptions about com-

Jan 1, 1985

By G. R. Corbett

The introduction of roof bolts to Phalen Colliery in the Sydney Coalfield, Nova Scotia (annual output of 2Mt) has been successfully implemented in maingate and tailgate entries over the last four years. Monitoring of the roof bolted areas continues to be an integral part of the quality control program as the results are utilized to maintain safety and to aid in long-term design strategies. Although all gateroads in the Phalen Colliery have converted to roof bolts as their primary means of support, the majority of intersections which intersect the main slopes remain supported by large steel structures. Several intersections within the Phalen Colliery were monitored as they were created by the mining process. A comparison is made between intersections supported with only traditional 6.4 to 6.7 m steel structure and intersections supported by 2.44 m fully resin encapsulated roof bolts in conjunction with 7.6 m fully cement grouted cable bolts. Detailed monitoring was conducted using CA NM ET's intrinsically safe sonic probe extensometer datalogger which has the ability to read up to sixteen probes simultaneously at programmed intervals. The density of the data from the datalogger has allowed a better understanding of the deformation of cable bolted intersections than was possible with manual monitoring. Test results have helped mine operators to design safer cable bolted intersections.

Jan 1, 1995

In preparing this paper, the writer hopes to achieve two main objects. Firstly, an indication of the desirable features of coke from the viewpoint of a blast furnace operator should be of assistance and value to those connected with coal and coke research, coal mining, the manufacture of coke and the production of iron. Secondly, it is hoped that the conclusions and opinions expressed herein, which are known to be of a controversial nature, will promote some discussion and thought. In this way, other workers may see fit to contribute and enlarge our general knowledge of Australian coke and its behaviour in blast furnaces.Those properties of coke that are considered to be of importance to blast furnace operation will be examined. Although broadly speaking, the composition and characteristics of coke are inherent in the coals used, any special features of coal preparation and carbonization that affect the resultant coke will be discussed. An attempt will also be made to indicate the effect on blast furnace operation of significant irregularities in these properties.THE FUNCTION OF COKE IN A BLAST FURNACECoke has four important functions in a blast furnace:1. To reduce the oxides of iron and other elements to metal and to provide the carbon absorbed by the iron.2. To supply the necessary heat for the process.3. To provide an open supporting structure in which the descending ore and limestone lie exposed to the action of the ascending gas.4. To provide voidage in the bottom of the furnace, so that iron and slag can accumulate in the hearth.

Jan 1, 1957

By Walter S. Bergholz, Michael L. Schreder

"Since Escondida began operations in fiscal 1991, a series of aggressive expansion projects have enabled market share to be increased and ever larger profits to be realized. This was possible due to the very large size of the ore body and its high grade - averaging 2.7% copper from startup through fiscal 1997. The situation has now changed: ore grade is falling rapidly and is projected to be only 1.55% by 2003. Since revenue is directly proportional to ore grade, while costs are proportional to quantity of ore processed, profits will begin to fall dramatically. The Phase IV Expansion Project is intended to forestall this drop in profits by increasing ore processing capacity by over 85%.The Phase IV concentrator is designed for a nominal capacity of 110,000 MTPD and the key to achieving this value is through the proper design of the grinding circuit. This paper presents the general design criteria for the grinding circuit, as well as a description of the facility.INTRODUCTIONThe Phase IV Expansion Project consists of a new copper concentrator located 8.5 km south of the existing operations, a new tailings disposal and water reclaim system, a new concentrate slurry pipeline to the coast, and added concentrate handling capacity at the port of Coloso. The new concentrator has a nominal capacity of 110,000 tonnes per day (MTPD), compared to the existing concentrator’s capacity of 127,500 MTPD. The Laguna Seca concentrator is based on using the largest and most efficient ore grinding mills now available.The concentrator has been designed for a 110,000 MTPD nominal capacity. The process design criteria for the Phase IV project were established from in-house operating information and from test work. Unlike a green field project, Escondida already had an operating plant and it processes ore from the same pit that feeds the Phase IV plant. It is expected that the current mineralization will be similar for the first 6 years of operation of the new project. Therefore, some of the current plant operating conditions were incorporated directly into the design criteria."

Jan 1, 2004

By H. K. Lin

Residual cyanide in cyanidation tailings can be detoxified by its oxidation to cyanate, as in the Inco and Degussa processes. However, cyanate, the product of detoxification and other oxidation processes, may be reduced to cyanide in reducing environments, e.g., deepwater discharge of cyanidation tailings. This study shows that the reduc-tion of cyanate to cyanide occurs and that the reduction rate increases with decreasing solution redox potential. Solutions with lower pH favor the reduction rate. No significant difference was observed between the results of tests prepared with distilled water and seawater, and the presence of cyanidation solid tailings does not show an effect on the reduction. Because cyanate can be reduced to toxic cyanide, causing environmental concerns, the deepwater discharges of cyanidation tailings must be handled carefully.

Jan 1, 2008

By J. J. Wallace

This report describes the initial phase of Bureau of Mines research in the hydraulic mining of bituminous coal. The mining site and equipment are described, and the test procedures and results obtained with a bar-mounted monitor are given. Tests showed that hard Pittsburgh-bed coal can be mined hydraulically from a solid face at water pressures of 4,000 pounds per square inch.4 Coal was penetrated to a depth of 4 feet in 20 seconds with 225 gallons of water per minute coming from a 3/8-inch nozzle at 4,000 pounds per square inch pressure. Some difficulty was encountered in cutting the binders occurring in the coal; it was not possible Lu penetrate directly the overlying draw slate.

Jan 1, 1961

By J. R. Lucas, R. L. Frantz

Mine sealing programs for the alleviation of acid mine drainage were begun by the Federal Government in the '30's. As part of an acid mine research project to The Ohio State University, a field test was undertaken to determine the effectiveness of mine seals for reducing mine acid. Details of the tests made at the McDaniels mine show the feasibility of air-sealing and flooding an acid-producing drift coal mine. Work by the University continues. The Federal Government undertook in the early thirties an extensive mine sealing program for the alleviation of acid mine drainage. In the states of West Virginia, Ohio, and Pennsylvania many general summaries have been made on this program but no critical evaluation with supporting data has been found on the effectiveness of mine seals for reducing mine acid. Because of this it was decided to undertake a field testing program as part of an acid mine research project of the Engineering Experiment Station, The Ohio State University. The objective of this phase of the project was to develop and install a field research laboratory for acid mine drainage studies. Specifications for such a mine laboratory were developed and resulted from the following considerations: 1) Size and preservation—the test mine shou1d be of limited size to permit frequent and detailed examinations; it should be in a reasonably sound condition to permit safe entry. 2) Isolation—the mine should be physically separated from all other mines. 3) Openings—a minimum number would be desirable to reduce the sealing problem. 4) Structure—the mine especially near the openings should be structurally sound. 5) Acid production—the mine should be producing significant quantities of acid. After considerable searching, the McDaniels mine was selected in the Hocking coal field in Vinton County just above Lake Hope State Park in southeastern Ohio. The small drift mine in the middle Kittaning coal consisted of two small rooms with one mine opening about 6 ft above a seasonal stream bed. Before it was finally decided to seal the mine, a short study was made of the acid drainage over several months. Fig. 1 shows a plot of acidity (milligrams per liter), flow (gallons per minute), and acid production (pounds per day) vs time over the sampling period. Because the coal was overlain with a porous sandstone, the mine drainage was consistent the year around even though the mine was

Jan 1, 1961

From a vast army of workers to gargantuan machines to immense volumes of material being moved, almost everything about the Port of Miami Tunnel (POMT) project points to tunneling on a massive scale. Almost.The star of this underground and underwater show is a Herrenknecht tunnel boring machine (TBM,) nicknamed ?Harriet? by a local Girl Scout troop. With her 12.9-m- (42.3-ft-) diameter cutting head and a total length of 139 m (457 ft), Harriet is boring through thousands of cubic meters of clay, dirt and sand, which is often mixed with coral and other materials, to create two 1,280-m (4,200-ft) traf?c tunnels connecting Watson Island and the Port of Miami (Dodge Island) beneath Biscayne Bay, FL. But in the midst of all of the oversized equipment and machines, a strong contender for the best supporting nod goes to a relatively tiny machine: the Brokk 400. Bouygues Civil Works Florida crews are using the compact, remote-controlled and electric-powered machine to excavate five cross passages between the twin traffic tunnels. The pas-sages will be essential to the safety of people who drive their vehicles under the bay every day.

Sep 1, 2013

By D. Grobbelaar, A. Cichowicz, D. J. Birch

The Q-coda method for estimating the quality factor Q(f)= Qo(f)n was used to characterize seismic wave attenuation in a region of the Kaapvaal Craton that includes the mining areas of the Bushveld Complex and Witwatersrand Basin. Seismic waveform data, collected by locally distant stations of the South African National Seismograph Network (SANSN), consisted of mining-related events with magnitudes ranging from ML 1.8 to ML 4. Q was calculated for nine different source-receiver pairs spanning the study region. A weighted average Q based on the number of available data gave an estimated attenuation relation for the study region of Q(f) = 327 f 0.81.

Jan 1, 2015

Jan 1, 1994

By Barry C. Slocombe

The development of new ports, extensions of existing facilities and reclamation of former docks will involve consideration of a variety of geotechnical problems. This paper presents data including instrumentation of structures from three UK projects involving vibro techniques to provide economic engineering solution.

Jan 1, 2008