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By M. S. Safarzadeh

Over the last fifty years, the treatment of enargite concentrates has not received much attention primarily because of the availability of other clean concentrates suitable for processing with existing smelting and/or leaching technologies. As traditional copper ores have become scarcer, copper-arsenic ore deposits have garnered more interest. Arsenic release is a significant concern during the treatment of enargite by pyro or hydrometallurgical methods. Enargite is also very refractive in standard leaching procedures. Thus, economical treatment options for enargite concentrates are needed. Preliminary experiments have shown that the acid-bake leach process could be adapted and used for the treatment of enargite concentrates. In this study, low-temperature (100-400 ºC) sulfuric acid baking of an enargite concentrate followed by water-leaching has been evaluated. The results indicate the thermal transformation of enargite to copper sulfate during sulfuric acid baking, with most of the arsenic being released from the concentrate into the gas phase for baking at 400 ºC. The condition for maximum copper extraction (~100%) from the concentrate was found to be 400 ºC, sulfuric acid amount of 0.5 mL/g of concentrate, and 2 h baking time. Part of the arsenic was captured in the form of arsenopyrite (FeAsS). XRD analysis proved the presence of some arsenic in the form of claudetite (As2O3) in the baked concentrate. Acid baking of pure enargite behaved in similar fashion.

Jan 1, 2012

By Rodney K. Morrison

MARTA, The Metropolitan Atlanta Rapid Transit Authority, is building a 53 mile heavy rail transit system to serve the City of Atlanta. Phase A of the Rail System, consisting of approximately 14 miles of at-grade, aerial and subway construction is underway. Metropolitan Atlanta lies in the Piedmont Geologic province of Georgia and is underlain by rocks of essentially granitic and gneissic nature. The soils encountered are primarily silty sands which are in-place weathering products of the parent rock and exhibit their relic structure. In general, these materials have presented no unique construction problems other than those created-by proximity of manmade structures, local availability of ground water, and top of rock elevation. The subway sections of primary interest in this paper consist of hardrock and soft ground tunnels and extensive cut-and-cover sections. The cut-and-cover construction includes excavations as deep as 80 feet. Temporary support systems in these deep excavations consist of soldier pile-timber-lagging or soldier pile-tremie concrete (SPTC) walls with internal bracing or tiebacks. In shallow cut-and-cover sections, where right-of-way economics permitted, slopes were laid back partially or fully to reduce or eliminate the need for bracing systems. Dewatering systems were required in most open cut excavations. Due to the close proximity of utilities and existing structures to the MARTA

Jan 1, 1979

By J. E. Urosek

Decisions made during a response to a mine fire or an explosion greatly affect the final outcome. The safety of miners should be the primary concern with accounting for all of the miners the first issue for resolution. If miners have not safely evacuated from the mine, the last known location of the miners at the time of the event and anticipated travel routes are primary exploration areas. After the mine is evacuated, there are many very important decisions that must be made quickly and often under great stress. It is critical that the mine operator establish an orderly method to direct the mine emergency response. Designation of a Command Center, staffed with personnel charged with developing plans, is a common method of establishing control. Scheduling of key mine managers will be critical, since decisions must be made 24 hours a day and people working for extended periods with little or no sleep do not always make clear or cognizant decisions. Internal communications, passing information on to subsequent shifts, and external communications with families and media must be accurate and timely. Assembling resources for responding to the mine emergency is critical for an effective response, and pre-planning can pave the way to a successful recovery. Sampling mine gasses and accurately determining the composition of gas mixtures is a common tool used to develop response plans in all fires and explosions. It is essential that preparations for emergency situations are made well in advance of a disaster. Effective communications are essential for mine management to successfully respond to a mine emergency. This paper discusses some considerations which need to be addressed in directing a response to a mine fire or explosion.

Jan 1, 2009

Market confidence is on the rise and industry leaders turning toward the vast and diverse region of Latin America are faced with abundant, yet daunting, opportunity. From the iron orebodies of Brazil to the renowned copper mines of northern Chile, drilling teams in Latin America are often faced with abrasive, broken ground. These types of ground conditions tear up coring bits rapidly, making it extremely difficult for even the most seasoned drilling teams to maintain effective productivity. The drilling challenges faced in this rich and opportune region are being met today by advanced coring technology, bringing with it the potential for increased productivity in Latin American mineral exploration.

Jan 3, 2010

By Jafar Khademi Hamidi

The Zagros long tunnel is one of the main components of Sirvan water transfer project in western Iran. It is approximately 48 km in length and consisted of two lots. The second 26 km lot of this tunnel is under construction by a 6.73 m diameter double shield (DS) TBM. The tunnel passes through several formations with wide range rock mass qualities. During the tunnel alignment, changes in rock quality were highly frequent from poor to very good. The encountered geological conditions required TBM operation to change frequently from hard rock to soft, dry to flowing, sticky to nonsticky ground (and vice versa), more often than expected. In the course of tunneling, the machine has encountered nearly many adverse geologic conditions. The most important problems have been sudden high volume water inflow into the tunnel, sticky ground, and gas seepage, all of which resulted in reduced TBM advance rates. This study will high-light two difficult ground conditions including large water ingress and sticky ground and also the related problems encountered by the TBM along 8 km of excavated tunnel. In sticky grounds, cleaning of the clogged cutter head caused many delays and contributed to additional downtime. Application of some operational modifications, including decreased TBM thrust showed satisfactory results in such cases. While reduced thrust resulted in reduced penetration rate, but the overall TBM advance was greatly improved by the increase utilization rate and elimination of down time related to cleaning of the head. To cope with high water inflow, application of preventive measures such as pre-grouting has proved to be a more efficientsolution. The sealing of ground water inflow also decreased seepage of dangerous H2S gas and other chemicals such as hydrocarbons accompanying the groundwater.

By J. T. Hollow

The Fort Knox Mine is located in Alaska?s interior, where the average ambient air temperatures range from -24°C (-11°F) in January to 16°C (61°F) in July. The mill processes a free-milling gold ore utilizing both a gravity recovery circuit and conventional cyanide leach/carbon-in-pulp circuits. Mathematical models have been developed to accurately predict the impact of leach circuit slurry temperature on gold leaching, carbon adsorption and cyanide destruction kinetics. Additionally, an energy-balance approach has been used to model the seasonal variations in slurry temperatures throughout the Fort Knox mill. The energy-balance model, combined with the kinetics models previously developed to predict plant performance, was used to justify a tailing thickener installation at the Fort Knox Mine. This paper describes the development of the energy-balance model and its prediction of plant performance assuming a tailings wash thickener to reduce heat loss from the mill. Also presented is an analysis of the post-project plant performance that validates the model and shows that the mine produced an additional 596 kg (19,155 oz) of gold while reducing mill reagent costs by $6,302,000 during the first 38 months of operation.

Jan 1, 2007

Mine Terex articulated dump trucks are working on a large restoration project of an abandoned open cast coal site in Blacklaw, central Scotland. The project is part of the construction of a 42-turbine wind farm complex. During the scheduled 18-month duration of the project, three 28-t(31-st) Generation 7 TA30 dump trucks and the six 36.5-t (40-st) TA40articulated trucks are estimated to move about 1Mm3 (1.3 million cu yd)of material. The trucks are working12-hour shifts, 5.5days a week.

Jan 1, 2005

By Morris T. Worley

Editor’s note: Mining companies doing business in Central Asia, and parts of the developing world, should look for ways to promote community development through the introduction of appropriate technology. This article should be of interest to SME members. It shows sustainable development type projects need not be massive or expensive. Smaller, utilitarian projects are equally valuable to developing communities as they seek to develop their own economic and social infrastructures. Joint Development Associates International (JDA) began humanitarian relief and community development in Central Asia in 1992, following the collapse of the former Soviet Union. Appropriate technology has played an important role in the company’s efforts to assist those segments of society that are most vulnerable to poverty and disease.

Jan 1, 2005

By G. Gaidajis, K. Angelakoglou

The development of a tool for assessing the environmental sustainability of mining facilities is described in this study. The tool is based on the analysis of basic components of the examined system, i.e., the quantities of the incoming materials and outgoing wastes, their hazardousness and scarcity, the utilization of water and energy resources, and the biodiversity. The developed tool provides both qualitative and quantitative assessment of the environmental performance of a mining facility in a broad time scales (past-present-future) and is easily applicable from non environmental experts. Moreover, relative software is developed to further support the application of the methodology. The implementation of the tool is expected to lead to an improved understanding of the environmental performance of a mining facility and more importantly identify the areas of significant environmental concern. However, based on feedback from industries, a number of shortcomings of the approach have been identified so far and are presented, indicating further actions for the advancement of the proposed tool.

Jan 1, 2011

By S. Frimpong

The cable shovel excavator is used for primary production in many surface mining operations. A major problem in shovel excavation is the variability of material diggability, resulting in varying mechanical energy input and stress loading of shovel dipper-and-tooth assembly across the working bench. This variability has a huge impact on the shovel dipper and tooth assembly in hard formations. In addition, the geometrical constraints within the working environment impose production limitations resulting in low production efficiency and high operating costs. A potential solution to the above problems is the application of an intelligent cable shovel excavation(ICSE) technology. In this paper, dynamic models of the cable shovel excavator are developed with numerical examples. These models form the basis for developing dynamic shovel simulators for an intelligent shovel excavation technology. The dynamic equations are developed using the Newton-Euler techniques. The path trajectories for efficient excavation, dynamic velocity and acceleration profiles, and dimensioned parameters for optimum feed force, torques and momentum of shovel boom-bucket assembly are modeled and used for efficient excavation. The optimum digging forces and resistances for the cable shovel excavator are modeled and used to predict optimum excavation performance.

Jan 1, 2003

By Christopher J. Bise

INTRODUCTION Perhaps no other area reflects the art as well as the science of mining-engineering design quite as obviously as strata control. This is due to the fact that the design of mining structures is difficult because rock rarely behaves as a homogeneous medium. Further, the original state of stress and the mechanical proper- ties of the in situ rock are somewhat difficult to deter- mine. However, those aspects that are hard to treat mathematically can and have been successfully approached by model studies and in situ measurements. This chapter will review the fundamentals of strata- control design and will provide examples of applications to typical problems. STRESSES AROUND MINE OPENINGS A close examination of Fig. 1 reveals that, prior to mining, stresses exerted in the overburden can be in both the horizontal and vertical directions. In the example problems of Chapter 1, it was shown that the maximum compressive stress (uv) at any depth (D) below the surface can be approximated as follows: [ ] Further, the lateral stress (oh) is related to the maxi- mum compressive stress by utilizing Poisson's ratio (µ): [ ] As soon as a heading is driven, such as the one in the coal seam shown in Fig. 2, the stresses shift to the sides, or abutments, of the opening. Clearly, these compressive stresses around the opening exceed the pre-mining conditions. The problem of designing an underground opening, therefore, is to determine the maximum stresses and to note if they exceed the ultimate strength of the rock. Table 1 lists several rocks with their corresponding strengths. Figs. 3 to 5 depict the boundary stress concentrations around circular, ovaloidal, and rectangular openings. M is the ratio of the horizontal stress to the vertical stress, or as defined above, p/(l-p). This text will concentrate on the state of stress represented by M = 0.33, which corresponds to the condition of no lateral deformation in a rock having a Poisson's ratio of 0.25. For an ovaloid with an opening width-to-height ratio of 2.0 (Fig. 4), the boundary stress concentrations are at their maximum values at the comers of the opening, with values in excess of 3.0. If the depth of overburden is 500 ft, then the maximum boundary tangential stress ([ ] ) of the ovaloid is: [ ]

Jan 1, 1986

By Andrew K. hg` Officer, A. L. Griffiths, J. Andrew Hindmarch, Gert Wittneben

Durban Harbour in South Africa is one of the continent’s busiest ports however the harbor entrance is currently too small for the new generation of container ships. There-fore it is to be deepened and widened by the National Ports Authority in the near future. An existing immersed tube tunnel carrying major sewer, water and other utilities under the harbor first needs to be removed and replaced by a deeper 4.4 m ID ser-vices tunnel. Construction of the deeper tunnel saw the first use of a slurry machine in South Africa and was required to negotiate grades up to 20%.

Jan 1, 2007

By Ray Brainard

The Jollyville Transmission Main will be a 10.5-km- (6.5-mile)-long, 213-cm (84-in.) diameter rock tunnel. The tunnel will pass beneath the Balcones Canyonlands Preserve, which was established to protect two endangered bird species, six endangered cave invertebrates and a threatened salamander. To address the sensitive habitat that the transmission main is to pass through, the city of Austin developed an environmental commissioning (EC) process that brought together environmental engineers and scientists, the city?s project management team and the designer team to work collaboratively to meet the city?s goals of producing a cost-effective design while also protecting the environment. This paper describes the environmental commissioning process and the benefits it brought to the project and environment through some unique environmental mitigation measures to protect this sensitive area.

Jan 1, 2012

By Michael J. Rinker, P. A. Tibble, M. Wiseman, R. V. Nicholson

Tailings, from an active copper-zinc operation, containing about 10% sulphur were investigated to assess the onset of acid production and potential lime requirements for treatment of drainage. Oxygen consumption rates were measured over two years to verify spatial and seasonal variations in sulphide oxidation rates. Shallow cores were collected to assess the quality of tailings porewater and to characterize solids that had been subjected to oxidation and depletion of neutralization potential (NP) for several years. Oxygen consumption data were used to quantify rates of NP depletion and onset of acid drainage from the near- surface tailings. Based on measured oxygen consumption rates and identification of NP remaining in the tailings, future lime use in the treatment plant was expected to rise significantly without mitigation. Geochemical modeling calculations were calibrated with observed oxygen consumption rates and the model results agreed well with actual lime use in the waste water treatment plant during operations. The modeling also demonstrated the benefits of lower lime demands and treatment costs after closure as a result of construction a soil cover on the acid generating tailings.

Jan 1, 2000

By C. -G. Zhang

This paper presents the results of a study on cellular acclimation of Acidithiobacillus ferrooxidans to sulfur biooxidation in terms of cells growth and changes in surface properties and morphologies of both cells and sulfur particles. The results showed that A. ferrooxidans cells were grown faster and demonstrated higher concentration in the soluble thiosulfate substrate than in nonsoluble hydrophobic S0 substrate. The results showed that A. ferrooxidans cells acclimated to the sulfur biooxidation by actively expressing some extracellular polymers substance and maybe some outer membrane proteins that modified the surface properties of both sulfur particles and the cells themselves. In addition, the results showed that the A. ferrooxidans cells were able to dynamically adsorb to or desorb from the surface of sulfur particles. The cells aggregating onto the S0 surface enhanced the use of S0 substrate by the bacteria cells. This mode may be one of the most important characteristics for the better growth and propagation of the cells in solid sulfur-containing media.

Jan 1, 2009

By K. Lang

A case study is provided that highlights the successful use of high efficiency electrical submersible pumps (ESPs) adapted from the oil and gas industry for a large scale, open pit mine dewatering operation. In this case, the mine is Goldcorp?s Peñasquito Mine, Peñasco and Chile Colorado open pit development areas in Zacatecas, Mexico. At the time of publication (July 2012), there were 18 vertical bedrock dewatering wells producing an average flow rate of 350 liters per second (lps) from the Peñasco and Chile Colorado development areas. Average pumping rate per well was 18 lps, with a maximum of 44 lps. The depth of wells varies from 330 m to 500m, and includes both in-pit and perimeter (ex-pit) pumping centers. A network of 50 piezometers was used to monitor the response of groundwater levels to pumping. Since dewatering operations were initiated in 2007, groundwater elevations decreased overall, from approximately 1950 m above sea level (masl) to around 1625 masl, for a total of 340 m of drawdown. The pit floor elevation was approximately 1655 masl. All of the producing wells were constructed with 16-inch boreholes, completed with 10-inch diameter blank casing and louvered screen sections and equipped with ESPs. The application of ESPs has proven to be highly effective in the case of Peñasquito?s dewatering operations. Noted advantages include the following: ? Small diameter pump allows use of smaller diameter boreholes (16 inches) and casing / screens (10 inches) reducing well drilling and construction costs ? Greater application range for flow rate and total dynamic head ? Variable speed drive systems for greater energy efficiency and flow rate optimization ? Integration of downhole instrumentation into the motor and pump assembly The advantages and benefits of using high efficiency ESPs revolutionized the dewatering program at Peñasquito open pit mine as evidenced by the number of deep vertical well installations and high dewatering flow rates and total dynamic head requirements.

Feb 27, 2013

By M. L. Harris

In underground mines, coal dust explosions are prevented by the addition of rock dust sufficient to render the coal dust inert. The National Institute for Occupational Safety and Health (NIOSH) developed a hand-held instrument that uses optical reflectance to measure the explosibility of a rock dust and coal dust mixture. This instrument is called the Coal Dust Explosibility Meter (CDEM). In this study, NIOSH personnel accompanied Mine Safety and Health Administration (MSHA) inspectors on their routine band surveys in five underground coal mines in MSHA District 2 (Pennsylvania) and three underground coal mines in MSHA District 11 (Alabama). While underground, NIOSH personnel and MSHA inspectors used the CDEM to assess the explosibilities of the dust samples. The values of percent incombustible content (percent IC) determined by the CDEM agreed well with those obtained later by low-temperature ashing (LTA) in both MSHA and NIOSH laboratories. Further, the meter identified some samples as potentially explosible that LTA analysis had found to possess sufficient rock dust for inerting. The CDEM provides more information on the hazards in the mine. Rapid identification of areas with explosible dust mixtures using the CDEM allows for immediate intervention rather than a wait of several weeks for laboratory analysis.

Jan 1, 2008

By John J. Murray, Michael T. McRae, Michael A. Krulc, Kathy L. Schuler

The San Vicente Pipeline Tunnel Project involves the construction of an 8.5-foot-diameter water pipeline in an 11 mile tunnel in San Diego, California. The tunnel is located in extremely variable geologic conditions of strong granitic and volcanic rocks, weak sedimentary rocks, abrasive conglomerates, and mixed face conditions. One reach of the tunnel is a 5,200-foot mixed face reach that includes Friars Formation Conglomerate overlying granitic rock. Due to the variable ground conditions in this reach, the use of a TBM was deemed too risky and the contract documents required drill-and-blast and hand mining methods. Although it was not required, the contractor elected to construct this reach using NATM methods. This paper describes the geology of the 5,200-foot mixed-face reach, the design evaluation, and the construction challenges faced on this project.

Jan 1, 2007

By Steve Kral

For a state whose roots are in mining, most Colorado residents probably do not realize that the industry still contributes heavily to the state’s economy. In 2005, the industry contributed, directly and indirectly, about $8 billion to the state’s economy, according to the Colorado Mining Association (CMA). It employed nearly 10,000 people at mines and support businesses. And the mining industry in Colorado is one of the highest paying occupations in the state, averaging about $80,000 a year in wages and benefits. The state’s coal mining industry produced nearly 36 Mt (40 million st) of coal in 2005, valued at $800 million, the CMA said. That was seventh in the nation. And Colorado’s only major gold mine produced 10.2 t (329,000 oz) last year, valued at $124 million. That was third in the nation. And Phelps Dodge’s Henderson Mine produced about 12.7 kt (28 million lbs) of molybdenum, valued at $350 million. Colorado is the largest molybdenum producing state in the nation.

Jan 1, 2006

By Jaidev Sankar

The dream of constructing the new Second Avenue Subway in New York has finally become reality as the first construction contract package is currently underway. This first contract requires the construction a TBM Launch Box in the middle of Second Avenue from which a Tunnel Boring Machine (TBM) will bore two tunnels south to 63rd Street. This paper will discuss the design of this contract and how construction has progressed including preparation, site constraints, utility construction and com-munity impacts while highlighting the challenges of working in an urban environment. It will also discuss moving forward on this major project outlining the remaining contract packages including their scope and status.