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By George A. Roche

Since our firm was established by Mr. Price in 1937, we have followed an investment philosophy which is based on the belief that investment in growth stocks is the most assured way of achieving superior, long term investment accomplishment. There are many criteria that we use to select growth companies but the most important is a combination of superior management operating in an industry with above average growth potential. This growth stock approach is the cornerstone of our investment strategy for two of the three mutual funds sponsored by the Price organization and for our private clients. However, during the past 5 years we have seen inflation accelerate due to a variety of factors including the inability of our government to meet seemingly unlimited needs with limited revenue sources. While there might be temporary periods of price stability, we believe that inflation will still continue to be the investor's greatest problem in future years. Our conviction that inflation would increase combined with the acceleration of inflation in the late 1960s stimulated an intensive investment research effort, on our part, to identify those companies with strong natural resource bases -- who own or control large, secure, and low cost tangible assets. Over the longer term and in an environment of a depreciating dollar some of these firms should be able to develop and sell these assets at higher prices. While we still believe that investing in growth companies is a sound investment strategy to offset inflation, we also believe that certain natural resource companies will show well above average investment performance. In the newest Price mutual fund, The Rowe Price New Era Fund, we have, as a matter of policy, placed a large portion of the portfolio in natural resource companies.

Jan 1, 1972

By Chee Theng

"Keep calm and carry on mining. That has long been the conventional wisdom in the mining industry, a largely cyclical one that has weathered roller-coaster booms and busts. But in the years from 2002 to 2016, an unprecedented steep rise in commodities prices that lasted a decade and then took a sharp turn downward had made it hard for gold and silver miners to stay the course.“The last 15 years highlighted some of the structural and inherent challenges that our industry has, from product price uncertainty to long lead times to the capital intensity of our business,” said Mitchell Krebs, president and chief executive officer of Coeur Mining, who was the luncheon speaker at the American Exploration & Mining Association’s 122nd Annual Meeting held Dec. 5-9, 2016, in Reno, NV.Looking back, Krebs said, “We were given this enormous gift of a commodities super cycle, and the industry kind of blew the opportunity.” While gold prices rose 319 percent and silver prices rose more than 200 percent over the 2002 to 2016 period, the XAU index of 30 gold and silver mining companies’ stock prices went up by only 20 percent.Entering 2016, precious-metals prices have made a comeback, with gold rallying strongly from a six-year low at the start of the year. This time, the industry is ready. Companies are leaner and meaner, with lower costs, reduced debt and an increased focus on higher grades and quality ounces. Although opportunities were missed in the past, the industry has got its act together and is now well positioned to take advantage of a price upswing and even to show profits when prices fall, as they did in August 2016, pushed down by a strong dollar."

Feb 1, 2017

By J. C. Irvine

Meramec Mining Company is a joint venture by Bethlehem Steel Corp. and St. Joe Minerals Corp. which mines and pelletizes iron ore at the Pea Ridge Mine. The Pea Ridge property is located near Sullivan, Missouri, about 70 miles southwest of St. Louis. The orebody was delineated in the mid-1950's by St. Joe during a lead exploration program. The first test holes drilled on the Pea Ridge magnetic anomaly revealed the presence of a large magnetite deposit; further drilling in 1956 and 1957 confirmed that the orebody was mineable, Meramec Mining Co. was incorporated in 1957 and shaft sinking began late in the year. Production commenced in April 1964. The orebody is overlain by about 1300 feet of flat-bedded sediments. It is tabular, about 2600 feet long and up to 600 feet thick. It dips about 80° and is of unknown depth. The ore is mainly high grade magnetite with small zones of specular hematite. The wall rock is a Precambrian rhyolite porphyry. The mine was initially started with five major levels on 150 foot intervals. Crosscuts were driven across the orebody on 190 foot centers. Banks of scopes were mined between the crosscuts by a modified shrinkage stoping method. This was done by undercutting a 40 foot wide by 150 foot long block and blasting horizontal "lifts" drilled on 5 foot intervals. A 65 foot still was left between levels which contained the slushing drift, fingers, crown pillar, and adequate thickness for support. By 1971 a ?lattice? of pillars had been left and mining had progressed to the point that an orderly pillar recovery program was necessary.

Jan 1, 1976

By D. Yokom, T. Katsabanis, E. Tremblay

"The mining industry has always faced the problems of replacing retired mining professionals, retaining their knowledge, continuously developing the skills of local talent and employing under-represented groups. In expansionary scenarios the industry faces the additional challenge of increasing available talent. New talent has traditionally come from current mining programs; however, these programs have been declining in numbers, and those that remain face challenges such as fluctuating enrollments, and reduced budgets. Queen’s University and Northern College have partnered to develop an innovative new program that offers online mining education to engineering technologists seeking to upgrade their skills and obtain a Bachelor’s degree. The high quality, flexible curriculum, offered online, includes a wide range of learning activities that promote interaction (student-to-student, student-to-instructor, and student-to-content), and is enabled by modern learning technologies (an integrated learning platform, as well as a variety of types of purpose-built video, web conferencing, and simulation software). The program issues block transfer credit to college graduates, and consequently reduces the time to completion when compared to other Bachelor’s degrees in Mining. The curriculum has been carefully designed to enhance a balance of technical, managerial, and societal skills for students. The program also includes short summer field school sessions, where students gain practical application skills under the direct supervision of engineering experts. THE NEEDS OF INDUSTRY Canada is the world’s largest exporter of minerals, and the contribution of this sector to Canada’s gross national product is more than three times that of the automotive industry, representing approximately 4% of Canadian GDP (MiHR, 2015)1. According to a recent report by the Canadian Mining Industry Resources Council (MiHR, 2016)2, despite the recent downturn in commodity prices, the industry will continuously need to attract new engineers to replace talent retirements and prepare for the possibility of expansion when the industry recovers. As past experience indicates, the challenges during expansion times are severe and the effects on education counter-productive. For example, during the prolonged expansion cycle of 2006-2012, several new programs were started worldwide, and mining became the profession of choice for many young students. During the subsequent downturn in the industry, many of these programs face dwindling enrollments, placing their sustainability in question. However, there is a continual need by industry to retain employees, as well as attract and train local talent, while providing educational opportunities to its employees. High potential college graduates can find themselves reaching a ceiling in their advancement due to their lack of a University degree. Furthermore, there exists an under representation of women, immigrants, and Aboriginal peoples in the labour force, and engineering fields in general1,2. Traditional mining engineering programs have tried to respond to the needs of industry, as well as meet the needs of students seeking diverse and successful employment careers. These programs tend to cater to the educational needs and aspirations of a general population, and their ability to grow and respond to changing industry needs is constrained by the number of students they can attract, as well as the resources available to them in a steady-state scenario."

Jan 1, 2017

By G. V. Sullivan, B. E. Davis, T. O. Liewellyn

A technique was devised by the US Bureau of Mines to recover coarse [+1.2-mm (14- mesh)] North Carolina phosphate now discarded as waste. Concentration utilizes the difference in particle sphericity between the relatively flat calcite and the rounded phosphate pebbles. Sizing, treatment in a continuous hydraulic classification system, and grinding upgraded a 17% P,O5 reject to 4.5% P,05 with a phosphate recovery of 63%. The CaO: P2O5 ratio was reduced from 2.49 to 1.66.

Jan 1, 1987

By K. Rüter

Sustainable investment is a global growth market. Companies that can reconcile economic, environmental and social objectives not only minimise risks, but also realise significant potentials of added value. This particularly applies to the metals & mining industry, as it is an attractive sector for investors and, at the same time, faces major challenges in the field of sustainable development. oekom research AG is an independent rating agency specialised in the analysis and evaluation of the environmental and social performance of companies, sectors and countries for institutional investors and financial service providers in the socially responsible investment (SRI) sector. oekom research has been active in the sustainable investment field since 1993 and its research is currently being used by managers of more than 60 bond and share funds with a volume of assets totalling more than 4.5 billion Euro. The company?s research and its central instrument, the Corporate Responsibility Rating (CRR), are based on the world's most comprehensive set of criteria for the ethical assessment of companies. With the support of an independent scientific advisory board, these universal and industry-specific sustainability criteria are being constantly updated reflecting the dynamics of global challenges in sustainable development. Increasingly, the rating results and benchmark reports of oekom research are also being recognised by the companies as a valuable tool to identify best practices, areas for improvement, and potential risks. This paper will outline the methodology of oekom research, the identification of key sustainability issues in the metals & mining industry, the development of industry-specific sustainability criteria (indicators) for the assessment of the metals & mining industry and key findings of the recently completed CRR of twenty major metals & mining companies.

Jan 1, 2007

By Joseph C. Hirschi

Mine engineers have been interested in building models that simulate mining operations since computers were introduced to the industry in the 1960s. Computer models enable operational scenarios to be evaluated without the need for actual field experimentation. Virginia Tech’s FACESIM and CONSIM, Penn State’s UGMHS, and KETRON’s CPMINE are perhaps the best known early models. Recently, SIUC has modified a Microsoft® Excel version of Virginia Tech’s Mathematical Model, calling it the SSP Model. It is used to quantify the significance of various controllable parameters. Productivity increases approaching twenty percent may be achieved where recommendations suggested by the model are applied.

Jan 1, 2005

The National Mining Hall of Fame and Museum (NMHFM) in Leadville, CO will induct the class of 2011 on Sept. 10, 2011. Representing the coal, metallurgical/processing, research and development, marble and lead industries, this year?s inductees cover a diverse crosssection of the mining industry. William Francis Diamond, Wayne Hazen, Redfield Proctor and Jeffrey Zelms will join 210 other mining industry pioneers when they are formally inducted into the National Mining Hall of Fame at the 24th Annual Induction Banquet and Ceremony. The members of this year?s class were selected for being visionaries, leaders and ambassadors both within their own sectors and across the industry at large. Diamond had an illustrious engineering and managerial career that spanned four decades with Island Creek Coal Co. During that time, he was responsible for the engineering and construction of the deepest coal mines producing in North America at the time.

Jan 1, 2011

By William Gleason

"Sometimes it’s the smallest things that make the biggest difference. In the world of mining, erosion can lead to small cracks, which can then lead to bigger problems that, over time, can eventually lead to a catastrophic event. However, when managed correctly, as in the case of the Manefey Slide at the Bingham Canyon Mine in Utah, the damage can be minimized.Numerous industry conferences, technical papers, studies and resources are dedicated to these issues each year, but what is sometimes overlooked is how the erosion of personal ethics can also have life-changing effects.At the 2019 SME Minnesota Conference, April 15-17 in Duluth, MN, two inmates serving their respective prison sentences at the U.S. Federal Prison Camp in Duluth spoke to the conference about how small cracks in their ethical foundations grew over time, eventually leading each man to his new address at the minimum-security facility.The men’s full names were not released and they were introduced as Jeff and Tony. Other than the matching green uniforms, both middle-aged men could have fit in with the rest of the crowd. They are well-educated and articulate whose career paths eroded thanks to greed and careless decisions.Tony, a licensed professional engineer, enjoyed a successful career working in contract oversight for the U.S. Department of Defense. Jeff is a former senior vice president of investments who ran a well-respected investment management team. Both spoke openly about the mistakes they made and emphasized that their crimes were not flagrant violations of the black and white rules but grew from ethical violations that live in the gray area between black and white, and right and wrong.Working in contract oversight for the U.S. Department of Defense (DOD), Tony said he was befriended by a wealthy man who was generous with his money. As Tony told it, a few meals with this man led to a few trips to casinos and eventually to gifts of money. The donor did not ask for anything in return, and at the time, Tony said he did not think that he was doing anything wrong. He admits now that the perception of a high-ranking officer in the DOD accepting gifts is not a good one, as it could be construed as the donor might have been trying to gain favor for future contracts; which is how it was presented in court by the prosecution team."

Jun 1, 2019

By J. van Wijk

"Vertical material transport is one of the major challenges for the successful implementation of deep sea mining projects. The EU research project „Blue Mining” is focusing on sustainable solutions for deep sea mining operations, with one major goal being the advancement of Vertical Transport Systems (VTS). To investigate flow effects under realistic conditions, especially clogging effects, a 136 m high test facility for flow analysis in vertical transport has been constructed using available mining infrastructure. Tests are run in a closed circuit, using a system of downfall and riser pipelines connected to a compact sediment injection- and separation unit as well as the centrifugal pump. The riser is equipped with pressure sensors, as well as temperature sensors, flow meter, concentration meter and high speed camera to allow comprehensive analyses of the flow regime and behavior of transported material within the flow. Additional mobile measurement devices allow wear and tear analyses of pipe material. This paper focuses on the determining factors of the tests leading to the design as well as the installation and trial of the test facility itself and explains the used components and work principles. INTRODUCTION Since the 1970s several research projects had been conducted investigating in the possibility of deep sea mining. In recent times projects for deep sea mining operations have started again, considering the rising demand on natural resources, especially raw earth elements. Yet projects like the Nautilus project on the deposit Solwara 1 [1], or Japanese projects focusing on the region of Okinawa [2] and Chinese projects [3] planning on depths of “only” about 2,500 up to 3,000 m. Until now no economical deep sea mining project was realized, due to the enormous difficulties of deep sea environments. Vertical material transport is one of the major challenges for the successful implementation of deep sea mining projects, considering transportation heights up to 5 km. The EU research project „Blue Mining” is focusing on sustainable solutions for deep sea mining operations, with one major goal being the advancement of Vertical Transport Systems or VTS [4]. Critical parts of the system would be identified and investigated to deliver solutions and higher the technology readiness level to a level were planning of a pilot project can be considered. At first case examples for mining projects of seafloor massive sulfides (SMS, 1,600 m water depth) and manganese nodules (MnN, 5,000 m water depth) had been calculated on basis of economical frame conditions, such as planned production rates to be efficient. As depicted in Figure 1 two major possible systems had been used for comparison, airlift system and pump system, considering multiple pump stations or single pumps. Based on the results and comparisons for the calculated vertical transport systems critical components and flow effects had been identified."

Jan 1, 2018

By Robert A. Jankowski, Charles A. Babbitt, Natesa I. Jayaraman

Today, approximately 31% of underground coal mining operations have designated occupations or areas with more stringent (below 2.0 mg/m3) respirable dust standards in place. Many U.S. coal mines have been able to maintain compliance with very low dust levels, and the Bureau of Mines, in an effort to identify those factors contributing to low dust levels, completed a survey of twelve continuous miner sections which were able to maintain their dust levels at or below 0.5 mg/m3. The quantity and quality of face ventilation appeared to be the most important factor in controlling dust exposure. The results directed Bureau research towards identifying improved face ventilation techniques for reducing quartz dust levels on continuous mining operations. This research has involved the evaluation of a half-curtain face ventilation technique which reduces the cross-sectional area of the entry, thus increasing the air velocity over the operator. The Bureau has also conducted extensive laboratory studies to compare tubing versus brattice, including an evaluation of both systems in a crosscut turn. In an effort to improve ventilation and reduce dust exposures of roof bolter operators working downwind of the continuous mining machine, the Bureau has evaluated two novel face ventilation systems. The first system consists of a fan discharge tubing technique which routes dusty air away from the return entry being bolted. In a technique similar to the fan/tubing concept, exhaust air from the upwind continuous miner face can be scrubbed using a dust collector to capture a portion of the dusty air, clean it, and supply it to the bolter operators as a split of clean intake air. A better understanding of face ventilation techniques should lead to solutions to the problem of more stringent dust standards due to quartz.

Jan 1, 1989

By S. B. Bhagwat

The United States has abundant coal resources that could last at least another century. and probably longer at present consumption rates. Geographically, the coal resources are distributed over the entire nation including Alaska, although there are no coal deposits in the highly populated areas on the two coasts. This allows free access to the coal, but makes transportation more expensive. Not all coals can be utilized equally because they differ vastly in quality. The sulfur content of coals, considered as the most detrimental acid rain-causing element, varies from as low as 0.3 percent in some areas of the western U.S. to 5 percent or more in parts of the Midwest. The chlorine content, which causes corrosion of plant hardware, also varies regionally. The 1990 amendments of the Clean Air Act of 1963 (CAA) require that emissions of sulfur be restricted and rolled back in two stages by the year 2000. There have been a number of reports expressing concern about the future of the industry in the states where high sulfur coal is produced. The remedies devised by the federal government and many coal-producing states in the past to "se-cure" the future of the regional coal industries have focused on the physical task of removing sulfur rather than the economic challenge of doing so at a cost that will enable high-sulfur coals to survive and compete. The past remedies, generally, were not specific enough to account for the characteristics of regional coal deposits and did not look at the coal market as an integrated national and international entity. The State of Illinois has, in recent years, taken a more comprehensive approach to the solution of the problem.

Jan 1, 1992

By Richard Switalski, Thomas Scotese, James Morrison, Randall Essex

OVERVIEW Like many older metropolitan areas across the U.S., the Greater Cleveland area is served by a combination of separate sanitary sewers and combined sanitary-stormwater sewers. In 1966, a Master Plan was implemented by the Northeast Ohio Regional Sewer District (District) to minimize pollutant overflows into adjoining Lake Erie and its tributary rivers and streams, that would occur during wet weather events. One component of the Master Plan was to reduce the load on combined sewers by constructing new conveyances to intercept separate sanitary flows and convey them to upgraded regional waste water treatment plants for priority treatment. As part of a 15-year program to construct 74 km (46 miles) of new interceptors, the West Leg Interceptor (WLI) Project intercepts flows from four decommissioned waste water treatment plants (WWTPs), and conveys those flows to the new Southwest Interceptor (SWI), which conveys the flows to the Southerly Treatment Plant, a tertiary level treatment facility. The WLI Project was built in sections to permit decommissioning of the WWTPs as each segment of the interceptor system was completed and put into service. Flows from the first of the four WWTPs was converted to the WLI in November, 1992; the final connection was achieved in July 1994. The WLI comprises 9.1 km (5.7 miles) of 21 to 29 m (70 to 95 ft) deep mainline interceptor tunnel, four vortex drop structures, approximately 2 km (1.3 miles) of shallow tunneled connector sewer to the mainline, approximately 2.9 km (1.8 miles) of open cut connector sewers, five construction work shafts (not including one work shaft constructed under SWI Contract 6 at the north end of the WLI), and 15 access shafts.

Jan 1, 1995

By W. R. Reed, G. J. Joy, B. Kendall, A. Bailey

"Testing of the roof bolter canopy air curtain (CAC) designed by the U.S. National Institute for Occupational Safety and Health (NIOSH) has gone through many iterations, demonstrating successful dust control performance under controlled laboratory conditions. J.H. Fletcher & Co., an original equipment manufacturer of mining equipment, further developed the concept by incorporating it into the design of its roof bolting machines. In the present work, laboratory testing was conducted, showing dust control efficiencies ranging from 17.2 to 24.5 percent. Subsequent computational fluid dynamics (CFD) analysis revealed limitations in the design, and a potential improvement was analyzed and recommended. As a result, a new CAC design is being developed, incorporating the results of the testing and CFD analysis.IntroductionExposure to respirable coal mine dust can cause coal workers’ pneumo-coniosis (CWP), also known as black lung. If silica is present in the dust, the miner may develop silicosis in addition to CWP. CWP and silicosis are occupational respiratory diseases that are ultimately fatal and have no cure. The only method of prevention is to eliminate exposure to respirable coal mine dust and crystalline silica, or quartz. The occupational exposure limit on a Mining Research Establishment (MRE) basis for respirable coal mine dust had been 2 mg/m3 during each shift that a miner is exposed in the active workings of the mine or in mine facilities. Under recently enacted legislation, this standard was changed in August 2016 to 1.5 mg/m3 for a full working shift (The Office of the Federal Register, 30 CFR 70.100, 2015). When respirable quartz is present, the mine must maintain its average concentration at or below 0.1 mg/m3. If the mine exceeds the 0.1 mg/m3 respirable quartz dust concentration, then the applicable respirable dust standard is reduced, calculated as 10 divided by the percentage of quartz present (The Office of the Federal Register, 30 CFR 70.101, 2015).The sources of exposure to respirable coal mine dust for roof bolting occupations include infrequent maintenance and cleaning of the vacuum dust collection system and operating the bolter downwind — in the return air — of the continuous miner (Good-man and Organiscak, 2003). Recent studies have demonstrated that vacu-um dust collection systems are effective in capturing bolter-generated dust if maintained and operated correctly and if proper face ventilation techniques are used. However, most expo-sure to respirable coal mine dust for a roof bolter occurs when the roof bolter machine is operated downwind of the continuous miner (Potts, Reed and Colinet, 2011; Colinet, Reed and Potts, 2013). Because of this higher exposure downwind of the continuous miner, the roof bolter is often limited to working downwind of the miner only once during a production shift."

Jan 1, 2017

By Ralbern H. Murray

Typical First Year Selling Price Strip Mined Western Sub-Bituminous Coal Based [Fixed Capital (1) $600 MM Construction Loan Interest $100 Working Capital $ 30 Start-up Costs $ 30 Total Capital Requirement $760 MM Annual Costs (First Year) $M/Year Coal (2) 443,550 Operating Costs(3) 53,000 Depreciation(4) 36,500 Interest(5) 45,220 After Tax Profit(6) 34, 200 Federal Income Tax (48% Rate) 31, 570 Gross Revenue Required 245,040 (Less) By-Product Sales (18, 000) Net Revenue Required 227, 040]

Jan 1, 1975

By R. H. Bartlett

Hydrometallurgical processes for copper flotation concentrates avoid the S02 emission problems associated with smelting, but they require oxidation of copper to obtain solubilization during leaching. The resulting copper ions must be reduced to metal, which normally requires large amounts of energy or energy equivalent reagents such as hydrogen or iron. The conventional reduction method is electrowinning which is labor intensive and involves 35 to 40% of both the en-tire operating and capital cost of the better hydrometallurgical processes. Smeltermen are correct in criticizing the available hydrometallurgical processes for being more energy intensive than modern smelting processes. Clearly, there is considerable incentive to reduce the cost and energy required for reducing copper ions from solution. Furthermore, it is thermodynamically possible to do this using sulfur contained in the concentrate itself. In fact, the thermodynamic potential of oxidizing sulfur from S+4 to the S+6 state is greater than required to reduce cupric ion to metallic copper. (1) Realization of this potential in a practical process would significantly reduce the cost of hydrometallurgical processing of sulfide concentrates because sulfur would become a cost-free reducing agent. An apparently practical method is to use SO3 and HSO3 ions, obtained by ammonia scrubbing of SO2 from a concentrate roaster gas, to reduce leached copper to metal in an autoclave. This reduction step is the Jumau 1907 patent. (2) A series of steps including sulfite reduction constituting a crude flowsheet was suggested by Parker in 1976(3), but apparently little development work has been done by him, since he has been interested in new routes of refining the resulting copper powder. The purposes of the present paper are to elaborate on the Jumau-Parker thrust. Describe a detailed complete sulfite process flowsheet based on materials and energy balances, discuss the chemistry, and discuss further work that is required to develop this process. The results of the present paper are largely based on a synthesis of the steps using handbook chemistry. Process materials, utilities costs, and energy requirements are projected to be unusually low.

Jan 1, 1978

By William Gleason

"The city of Denver, CO has experienced extreme growth in the past decade, with the population of the city topping more than 700,000 people in 2018. The current storm water drainage system was put in place in the early 1900s and has not been able to keep up with the growth of the city.When it rains north and east of the city, the runoff goes toward the South Platte River. With the dense population and sometimes severe thunderstorms in the summer, the city has experienced significant flooding that not only endangers lives of residents, but some of the storms have caused millions of dollars of property damage.The Platte to Park Hill Project is a $298-million nearterm, four-phase solution to the flooding that includes the Globeville landing outfall; an open drainage project in the Cole neighborhood in north Denver; an area for temporary water detention and another temporary water detention in Park Hill.The largest and most complex phase of the project is the Globeville landing outfall — a $70-million box culvert project that includes a pair of 157-m (515-ft) long, 243-cm (96-in.) diameter storm water tunnels that pass beneath a busy rail yard with 17 tracks for the Union Pacific Railroad (UPRR) and two Regional Transportation District (RTD) commuter rail tracks. The tunnels, which were installed parallel to a pair of existing 243-cm (96-in.) tunnels, were designed by Brierley & Associates as a client of Merrick & Company for the City & County of Denver, and Bradshaw Construction constructed the one-pass tunnels.From the start, it was evident that the tunneling portion of the project would be the most challenging because of the rail yards.“It’s a little bit more complicated because the railroads have such tight restrictions for settlement,” said Rebecca Brock, Brierley’s project manager. “We had a lot of meetings with Union Pacific and RTD to figure out what are prescribed versus tolerable settlements.”“The portion extending beyond the UPRR under the RTD rails was challenging, as RTD is new to tunnel installations under its tracks,” said Lester Bradshaw, president of Bradshaw Construction. “The RTD tracks employed a unique foundation of continuous concrete with integral raised concrete ties on rubber bushings. Minimizing settlement to these tracks was a critical requirement.”"

Jan 9, 2018

By LeEtta M. Shaffner, John R. Marks

INTRODUCTION In the last twelve years, underground stoping methods at the Homestake Gold Mine have evolved from open cut-and-fill with jacklegs, cribbed raises and electric slushers to ramp-based mechanized cut-and-fill (MCF) and vertical crater retreat (VCR) with dieselpowered loaders, trucks and drill jumbos. The evolution was swift. Unfortunately, ventilation practices have had trouble keeping pace. Stope ventilation is still too dependent on auxiliary fans and coolers. A single large MCF stope might contain up to eight headings, each of which requires significant ventilation resources when a diesel loader is present. Air is shortcircuited all too frequently through mined-out VCR panels. These factors and the recent rapid decent of the center of mining prompted a study to improve ventilation practices and to more accurately project future requirements. BACKGROUND In 1992, the underground portion of the Homestake Gold Mine produced 8336 kg of gold from 1407 ktons of ore (268,000 oz from 1,551,000 st). The ore is hosted in low to medium grade meta-sediments. Stoping took place from 420 to 2347 m below the surface (1400 to 7700-ft levels). The weighted center of mining was 1662 m deep (5450-ft level) in 1990 and is projected to be 1890 m (6200-ft) in 1993. The deepest level is 2440 m (8000-ft) where the virgin rock temperature (VRT) is 56.1°C (133F). The mine is ventilated by 504 m3/s (1,069,000 cfm) measured at mid-exhaust-circuit density. The air-conditioning system includes an 8.1 MWR (2300 ton) controlled recirculation plant, a 2.0 MWR (580 ton) chilled water plant, a 1.0 MWR (290 ton) exploration drift refrigeration plant, 28 spot-coolers totaling 3.4 MWR (960 tons) and 35 spray coolers totaling 1.5 MWR (420 tons). The mine employs 117 diesel units with a total nameplate rating of 7961 kW (10,672 hp). These units include twenty-four 1.5m3 (2-yd) loaders, twenty-six 2.7m3 (3.5-yd) loaders, fourteen 3.8m3 (5-yd) and two 7.6m3 (10-yd) trucks, and assorted utility vehicles and drill jumbos. THE STUDY In April 1991, the University of Nevada-Reno (Mackay School of Mines) and the South Dakota School of Mines and Technology cooperated with Homestake on an MCF study. Mackay instrumented a stope with thermocouples, air velocity meters and hygrometers (Duckworth, 1992). South Dakota Tech conducted a finite-elements computer analysis of a back-filled MCF stope with/without light-weight shotcrete insulation on the sidewalls and back (Chellam, 1992). Homestake conducted an empirical analysis of deep-level MCF stoping. This paper describes the Homestake study. Twenty-three of the forty MCF stopes deeper than 1800 m were surveyed at least once during the last quarter of 1992. The stopes not included were being cable-bolted or back-filled. Figure 1 shows the complexity of one of the ramp-based stoping areas included in the survey. This particular stope has six separate production headings. A baseline wallrock heat load was derived for each stope or heading from psychrometric calculations. Broken ore, waste rock fill and fissure water were noted when present and the effects included in the baseline heat load. Other heat sources often mentioned in the literature such as metabolic heat from workers, heat from explosives and small electric loads were neglected. Fan heat was considered part of the ramp & crosscut heat load and thus not included in the study. Diesel heat was addressed separately. RESULTS Survey results, plotted as the heat flux against VRT, are shown in Figure 2. The equation for the regression line is: W/m2 = 2.1236*VRT - 75.405 The 0.31 correlation coefficient is poor which implies that the results should be used cautiously. Previous experience strongly suggests that differences in productivity are most likely responsible for the scatter in data points. A rapidly advancing stope will have a

Jan 1, 1993

By T. McWaters

In 1911, Miami Copper Co. began a block caving operation at its Miami, AZ property. A gravity mill was used to separate copper minerals from the Pinal Schist host rock. Until 1932, the mill tailings were deposited by the upstream method using perimeter launders and spigot valves in six canyons adjacent to the mill. In 1928, the larger and more distant Solitude tailing pile was developed. By 1932, it was receiving all tailings. In 1925, Miami Copper converted the gravity mill to flotation with sulfide copper recoveries. From 1934 to 1943, Miami, Copper ran a leach-precipitate float (LPF) circuit on mined ore and, in 1943, began sulfuric acid in-place leaching of a portion of the caved area formed by block caving. The pregnant solutions were collected underground and pumped to the LPF precipitating drums to harvest copper. In 1954, the company started mining low-grade ore. This led to the running an old LPF plant on select mill tailings from April 1957 to March 1959. In 1959, block-cave mining ceased. Solution mining became the only source of production using a launder precipitation plant. In the mid-1960s, Miami Copper merged with the Tennessee Corp. In the latter part of the decade, Cities Service Co. bought the combined properties. In 1976, Cities Service commissioned a 15-t/d (16.5-stpd) solvent extraction electrowinning(SX-EW) facility at its Miami copper property to replace the precipitation plant. In 1982, Occidental Petroleum Co. bought Cities Service. In 1983, the Miami operations were sold to Newmont Mining Corp. and set up as a subsidiary company, Pinto Valley Copper Corp. Finally, in 1987, Newmont Mining spun off a combined Pinto Valley and San Manuel unit as Magma Copper Co.

Jan 1, 1990

By R. Kalra

The current paper looks at evaluating the merits of large geared mills versus gearless driven mills by evaluating the following factors: The capability of currently available systems in terms of power and mill diameter Efficiency in terms of overall electrical power consumed vs mechanical output power Capital cost Running costs Cooling requirements in terms of air versus water cooling Installation and delivery time World?s largest geared drive ? 2x8500kW ? Wushan, China (operating) Among the many reasons that geared drives on large SAG mills are not favoured, is due to not having an efficient variable speed drive option (60 to 80% critical speed), which is required for process reasons. As technological advances have occurred quite rapidly in recent years, this paper uses the latest data in applying these comparisons and attempts to dispel some of the myths regarding Slip Energy Recovery (SER) and variable frequency drive technology on twin pinion drive systems. Early attempts to provide load sharing on twin pinion drives used primitive electronics which have since been developed to eliminate the problems encountered in earlier attempts. In particular, torque pulsations between the twin motors have been overcome using a higher number of devices (pulses) and better electronics. With successful operation of 2 x 6.5MW (Phu Kham, Laos) and three 2 x 7MW units under manufacture (Pascu Lama) and a further 40 projects worldwide, energy efficient Hyper Synchronous SER drives are now mature and ready for use on 2 X 10MW dual drive mills. Speed variation required is in the range of +/- 15% of synchronous motor speeds. VVVF drive packages from ABB and Siemens are also available for 2 x 10MW in low and high speed options. Dual hydraulic inching drives provide a much safer and convenient operation with the added advantage of locked charge detection.

Feb 27, 2013