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By Michael V. Wolski, Ryan O. McCarter, Kenneth A. Johnson

"The Central Subway is Phase 2 of the San Francisco Municipal Transportation Agency’s (SFMTA) Third Street Light Rail project and will extend the existing Phase 1 initial operating segment from its current connection to the Embarcadero line at Fourth and King streets along Fourth Street to Market Street, under the Bay Area Rapid Transit (BART) and Muni Metro tunnels and then north beneath Stockton Street to Chinatown (Fig. 1).Total new track to be constructed as part of the Phase 2 work consists of approximately 734 m (2,410 ft) of surface track and 2,636 m (8,650 ft) of tunnels. The tunnels were constructed as twin, singletrack bores by two tunnel boring machines (TBMs) (Johnson, 2014) moving north from the southern end of the launch box under the I 80 freeway between Bryant and Harrison streets. North of Chinatown Station the TBMs continued another approximately 683 m (2,240 ft) to a retrieval shaft near Columbus Ave. at Washington Square. The project also includes five cross passages to connect the two tunnels, and three underground stations (the Yerba Buena/ Moscone Station, Union Square/Market Street Station and Chinatown Station.)Excavation of the twin tunnels was performed with two TBMs, with both TBMs driving northward from the launch box. TBM excavation was performed such that the location of the machines was staggered to separate the active excavation faces by a minimum of 91 m (300 ft) between headings. This minimum separation was maintained until the first TBM arrived at the retrieval shaft plug, at which time the separation requirement was relaxed.Excavation began with the “southbound” (SB) tunnel which will ultimately accommodate the southbound TBM light rail trains followed by the second TBM in the “northbound” (NB) tunnel. With the completion of the drives in June 2014, cross passage excavation then began and was completed in April 2015. Overall, construction of the Central Subway tunnels was a success considering the nature and complexity of the project. Additional details of the completion of the Central Subway tunnels are presented in another paper from the RETC 2015 conference (Leong et al., 2015)."

Jan 1, 2015

By H. H. Hughes, J. G. Dunn, P. G. Fernandez, H. G. Linge

Dissolved Arsenic (As) is stabilised primarily as As(III) and As(V) and enters ground water streams from sources such as the increasing metallurgical processing of As - containing ores [1]. As(III) is more toxic than As(V) and is less effectively removed from solution by oxide precipitation. Even for dilute As(III) solutions, skin contact or ingestion can cause dermatitis or cancer and there are stringent effluent control standards in place for As containing effluent from mining operations [2]. Chemtronics (Perth, Australia) has manufactured a compact digital voltamme­ter, based on anodic stripping voltammetry (ASV) and suitable for use in the laboratory or field. In this paper we demonstrate the utility of this equipment for measuring As(III) concentration with a detection limit of ca. 10 ppb.

Jan 1, 1995

Over 800 mines have closed in Australia in the past 25 years. This paper summarizes the data obtained from those closures and includes all Australian States and Territories and all commodities, including metalliferous, coal and industrial minerals. Twenty five percent of the mines closed due to resource exhaustion or depletion; 24% due to high costs, price drops, or declining grades; 8% due to open pit resource depletion (but with underground reserves remaining) or underground reserves depleted (but plans to open cut remainder) and 7% due to receivership or voluntary administration. The environmental, social and economic impacts of these closures are also significant and include acid mine drainage and impact on mine employees. An understanding of the causes of premature mine closure will better equip mining companies and governments to better manage future mine closures, wherever in the world the mines are operating.

Jan 1, 2007

A knowledge of airway friction factor (K-factor) is necessary to designing mine ventilation systems for least cost and optimum effectiveness. The friction factor used must be accurate and reliable to estimate correctly roadway resistances and pressure sources for required flows. Though the resistance to flow offered by mine airways has been an object of study over the last half century, no accurate relation has yet been established from which the prediction of the resistance of a projected airway can be made. In Kentucky, only limited and incomplete data on local K-factors are available. Therefore, there is a need for field investigations to determine these values in-situ for existing mining conditions. The author describes a study concerning K-factor that was carried out in ten coal mines, located in eastern and western Kentucky. The results of these investigations are presented in both tabular and graphical form.

Jan 1, 1991

By Lawrence Lien

The reduced need for traditionally trained and educated personnel in the mining industry is systemic to the changing mining industry. Universities and other training institutions are meeting the traditional skill needs required by the industry, but are the skill needs going to be the same in the near future? The answer may be no. Mining is changing because of increased liabilities and costs of environmental and safety is-sues; lower grades of minerals in traditional mining activities and the advent of new bio-chemical processes and robotic equipment. More productive and economic alternatives, and larger, more sophisticated and automatic equipment, are also changing the industry. Engineering is more specific, accurate, precise and expensive. Measurement is more thorough and timely of progress, production, costs and productivity. And, the industry will likely be engaging in more undersea mining, possibly space-based processing, less human interaction and more remote control of events than was previously thought possible.

Jan 1, 2011

By C. Waddell

PDMI mines five different grades of ore. Shovel operators were experiencing problems differentiating one material type from another. In 1997 PDMI decided to try GPS ore control to aid operators in identifying material boundaries. Computer generated ore control maps and GPS data defining the shovels' position is fed to a computer on board the shovel. A monitor, located near the shovel operator, displays material types, their boundaries, and the shovels' position and movement in relation to the mining face. This information has reduced errors in material identification by 50%.

Jan 1, 1998

By Peter G. Chamberlain

The Bureau of Mines is conducting research to boost domestic production of manganese. Virtually no mining exists in the low grade and/or small deposits that occur in this Country. One large, low-grade manganese deposit located in westcentral Arizona--The Artillery Peak district--was extensively studied and sporadically mined during the 1940's and 1950's. Although manganese mining in the district has been long dormant, recent studies indicate that the deposits may be amenable to economical production by heap and/or in situ leaching methods. A conceptual design for an in situ leaching system features undercutting and blasting a block of ore, leaching with SO2, and extracting the manganese as a sulfate or oxide. Possible applications to other manganese deposits depend upon formation permeability and specific manganese mineralogy.

Jan 1, 1981

By A. L. Anderson, J. T. Rybock

Lime, soda ash and similar precipitants have been the industry standard for treatment of acid rock drainage (ARD) because of their proven ability and low per-gallon operational cost. However, these methods carry serious environmental drawbacks and high life-cycle costs. KEECO’s Silica Micro Encapsulation (SME) technology has all the positive characteristics of conventional ARD-treatment systems but none of the drawbacks. SME achieves highly effective treatment in a single step, provides options for ARD prevention and recovery of metals, requires lower capital expenditures, generates smaller volumes of higher-density sludge, consistently passes leach tests, and eliminates long-term liabilities associated with potential metal remobilization and hazardous waste landfilling.

Jan 1, 2000

By M. J. Gula, S. S. Xue, E. P. Horwitz

A study has been conducted to remove iron from sulfate solutions using Eichrom's Dipexo® extractant, P,P'-di(2ethylhexyl) methanediphosponic acid (H2DEH[MDP]). It is found that this extractant can effectively and selectively extract ferric ion from highly acidic solutions. Ninety-nine percent of the iron was extracted from a simulated feed solution in a single stage. The separation factor, Fe/Zn, was 106. Over 90% of the iron in a loaded organic can be recovered in an aqueous solution by reductive stripping. This paper presents the experimental results. A new process for iron removal using Dipex extractant is described and discussed.

Jan 1, 1999

By C. A. F. Pinto

In the present work compared flotation kinetics of apatite with four different collectors was established. Sodium oleate and rice bra~ oil were used to represent conventional collectors. The new collectors included a sulfosuccinate and a sulfosuccinamate. It was observed that the collection ability of each reagent was very dependent upon the mineral size ranges. The results-were analyzed in terms of size-by-size recovery curves. Flotation rates were also very dependent on size ranges of the mineral particles. One of the new collectors displayed higher flotation rates for coarser particles than the other reagents tested. Synergetic effects were also apparent when a conventional collector was mixed to a new collector.

Jan 1, 1991

By Jan Krason

Introduction The South African Witwatersrand is the world's largest gold-bearing province and gold producing district. But the production capacity of the very big mines (Vaal Reef, Driefontein Cons., Western Holdings, Western Deep Levels, and others) is not as large as that of the Soviet Union's Muruntau gold mine. The Muruntau gold-bearing ore body was discovered in 1956-57, and has been in operation since that time. In the early 1970s, this mine produced 70 to 80 t/a (2.3 to 2.6 million oz per year) of gold. Within the last few years it has become the world's largest producing gold mine. Russian authors do not publish ore reserve or rate of production data. But it is very likely that the Muruntau mining complex, which involves several ore bodies, is currently producing about 143 t/a (4.6 million oz per year) of gold. The author has confirmed this by personal information from several knowledgeable Russian geologists. This amounts to one-half of

Jan 11, 1984

In 1991, Placer Dome Venezuela established a 70% stake in Minera Las Cristinas, to mine the Las Cristinas gold deposits in Bolivar. This case study examines the multi-sectoral partnership arrangement that was developed to improve health services near the proposed Las Cristinas gold mine. The investment climate in Venezuela is uncertain and the socio-economic circumstances are potentially hostile. Despite that, the partnership between the mining company, local communities, government agencies and an international health nongovernmental organization (NGO) collectively leveraged nearly $2.5 million to build and operate a community health center.

Jan 1, 2002

By D. W. Mitchell

Never increase, reduce, or remove ventilation without unquestionable, compelling reasons. This rule applies every day as well as when fighting fire, attempting to find survivors, or recovering the mine. Right now in some mine a miner is adjusting a regulator in one place to get more air into another. The chances are the desired result will be achieved. Has the miner done a good thing? NO! Solving the immediate problem reinforces the belief he or she can do it again. That "again" might be, to give but one of many examples, the explosion in Greenwich No. 1 Mine. Robbing the proverbial Peter can be the prelude to disaster in a mine. Reducing the airflow is a common practice when fighting a mine fire. In fact, some people have been taught to do that at MSHA's academy. People who believe that to be proper must be people who never experienced a fire. To fight most fires you have to scramble to get enough air. An explosion demands totally different "thinking". If people are soon to go into the mine, DON'T adjust the ventilation. If teams are in the mine, each affected area must be explored or sealed before making any ventilation change.

Jan 1, 1993

By William G. Pariseau

Few departments of mining, metallurgical or petroleum engineering in the United States have critical mass. Cost per student credit hour (SCH) in departments across the country are usually the highest among engineering departments, which are the highest on campus. Almost all departments are operating at fixed costs and enrollments could easily double without incurring much additional cost. However, the cost per SCH would remain unacceptably high and the probability of doubling enrollment is nil. Declining enrollment is a more likely future. The pressure to reduce SCH from university administration is unrelenting. And it has the potential for doing serious damage to program quality when standards and requirements are lowered in attempts to maintain enrollments and increase retention.

Jan 1, 2002

By D. Royston

Gold ores containing antimony suffer from poor recoveries of gold in cyanidation due to the impact of antimony on the cyanidation process. Techniques such as lowering the pH for cyanidation can improve gold recovery, nevertheless a limit can be reached where high cyanide consumption makes traditional processing uneconomic. The paper outlines a process for the pre-treatment of gold-antimony concentrates to remove the antimony resulting in a low-antimony content gold-bearing residue suitable for efficient treatment for gold recovery through cyanidation. This hydrometallurgical process produces a by-product credit of commercial grade antimony trioxide as Senarmontite that can significantly offset the cost of the pre-treatment.

Jan 1, 2007

By J. A. Botín

Identifying, quantifying and minimizing technical risks associated to investment decisions is a key challenge for the minerals industry decision takers and investors. However, risk analysis in most bankable mine feasibility studies are based on stochastic modelling of project NPV which, in most cases, fail to provide decision makers with a truly comprehensive analysis of risks associated to technical and management uncertainty and, as the result, are of little use for risk management and project optimization. This paper presents a value-chain risk management approach where project risk is evaluated for each step of the project lifecycle, from exploration to mine closure, and risk management is performed as part of a stepwise value added optimization process.

Jan 1, 2011

By Richard F. Hammen

Mineral extraction from sulfide ore deposits usually leads to the combined action of oxygen and water on the newly exposed ore. The result is acid mine drainage, a low pH solution of various metal sulfate salts and sulfuric acid. Paradoxically, the valuable metals dissolved in acid mine water are a liability because they are too toxic for discharge but too dilute to recover economically. The expense of compliance with water quality release standards has reduced the profitability of many mining operations. Solid phase extraction (SPE) columns have been developed to extract metals from acid mine water. These columns are designed to remove the toxic elements from water and recover the metals as purified fractions. This article describes the results of a Phase 1 bench-scale project to test the performance of the SPE columns. The tests were conducted with water collected from the abandoned Berkeley Pit copper mine in Butte, MT.

Jan 1, 1993

By Charles K. Presley

This paper deals with drilling large diameter shafts for the mining and construction industry with diameters in excess of 3 feet to more than 20 feet in diameter. It discusses appropriate applications of the rotary drill method, linings for large diameter shafts, circulation systems,, and the limitations of the method. Each specific rotary drill method is determined by the geology of the area, the depth to be drilled and the formation fluids encountered. Shaft lining or casing must be improved to result in lighter weight, higher strength and lower cost. All phases of rotary drilling equipment must be improved to drill shafts in excess of 10 feet in diameter. As these goals are reached, more shafts of large diameter will be drilled by the rotary method for the mining and construction industry.

Jan 1, 1967

Steady increases in longwall production have required operators to apply greater quantities of ventilating air in an effort to control and dilute respirable dust. Significant increases in shearer speeds necessitate that longwall supports also be advanced at a faster rate. Both of these factors may contribute to overall respirable dust levels on the longwall face because as supports are lowered and advanced, broken material falling from the top of the canopy is entrained directly into the air stream. To address this issue, the Pittsburgh Research Laboratory collected respirable dust samples from four longwall faces to characterize shield-generated dust. This paper investigates the influence of air velocity and shield advance rates on respirable dust levels. Also discussed are engineering controls currently used to reduce shield dust and alternative controls being investigated by the National Institute for Occupational Safety and Health (NIOSH).

Jan 1, 2009

By J. R. Batista

Leachates from gold heap-leaching mines contain selenium concentrations as high as 2 mg/L. Previous studies report satisfactory selenium adsorption by activated alumina when using relatively "clean" drinking waters. However, the findings of these studies cannot be directly applied to the treatment of mine leachate where other ions compete for the alumina adsorption sites. This study evaluated the adsorption of selenium from a mine leachate to develop design parameters for full-scale activated alumina processes. The study revealed that 68% of the selenium in the leachate could be removed by alumina at pH > 5.0. Silica adversely affected the selenium adsorption capacity. At pH values < 4, silica was poorly adsorbed by alumina and selenium adsorption was improved.

Jan 1, 1994