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By Todd Minoski, KRISTIN FLOYD, Michael Murphy, VASU GANGRADE, Gamal Rashed, DYKE MARK VAN, Brent Slaker

Underground stone mines frequently operate on multiple mining horizons or are required to undermine or overmine old workings. In these situations, the effects of pillar columnization and interburden thickness on the stresses surrounding mine workings are poorly understood. Many old workings were not designed to consider the effect on future undermining or overmining and, as a result, are laid out on irregular patterns and with pillar sizes that are difficult or impossible to replicate on adjacent levels. Additionally, as depth increases, even a consistent gridded mine layout may result in poor columnization due to the need to increase pillar sizes. Rules of thumb and past practice for designing multiple levels may often be effective. This paper explores the effect that multiple-level stone mining has on stress redistribution through the discussion of two case-study mines and associated numerical modeling to provide additional insight into situations which may cause concern.

By Yuexin Han, Mu. Yufan, Yanjun Li, Peng Gao, Yongsheng Sun

"The objective of this study was to evaluate the effect of reduction temperature, reduction time and binary basicity on the size of metallic iron particles in coal-based reduction products of an oolitic iron ore. The particle size distribution behavior (i.e., cumulative passing percentage and mean size of metallic iron particles) during reduction was investigated in detail. Results showed that the particle size distribution of metallic iron particles was strongly influenced by reduction temperature, reduction time and binary basicity. The cumulative passing percentage and mean size significantly increased with reduction temperature and time in the entire range of the experiments. All curves of cumulative passing percentage versus particle size under different conditions demonstrated a similar trend (continuous increase). The size distribution parameters and mean size slightly increased with increasing binary basicity and significantly decreased when the binary basicity exceeded 1.0. The size of metallic iron particles could be controlled by adjusting the reduction conditions during coal-based reduction.IntroductionThe increasing demand for iron ore coupled with diminishing high-grade iron ore reserves has resulted in the urgent need for innovative technologies in order to use refractory iron ores. Oolitic iron ore is a typical refractory iron ore with tremendous abundance globally. Based on published literature, oolitic iron ore reserves are approximately 140 million tons in Europe, 10 billion tons in China and 66 million tons in Pakistan (Kazmi and Abbas, 2001; Wu et al., 2011; Yu and Qi, 2011; Sun et al., 2013a). Therefore, the efficient exploration and use of oolitic iron ore resources can play a significant role in easing the mineral resource crisis in the iron and steel industry. However, oolitic iron ore cannot be effectively upgraded by traditional beneficiation methods due to its mineralogical characteristics (e.g., low grade of iron, poor liberation of iron minerals and high phosphorus content) (Li et al., 2011b; Sun et al., 2013b).Researchers recently proposed coal-based reduction followed by magnetic separation to recover iron from refractory iron ores (especially oolitic iron ore) and a certain degree of breakthrough was achieved in both theory and practice. In this technology, iron minerals in the ore are directly reduced by coal to metallic iron, which grows into particles of different sizes. After comminution and liberation, metallic iron is concentrated by magnetic separation (Srivastava and Kawatra, 2009; Sun et al., 2013a; Li et al., 2011b; Sun et al., 2013b; Li et al., 2011c; Gao et al., 2013). Sun et al. and Gao et al. used this technology to examine the recovery of iron from oolitic and Bayan Obo iron ores, respectively (Sun et al., 2013a; Li et al., 2011b; Li et al., 2011c). Metallic iron powder with more than 90% iron content was obtained as the final product, which could be used directly in steel production."

Jan 1, 2015

By Galyn Rippentropp, Finn Erik Overlie

INTRODUCTION The wet shotcreting system utilizing steelfiber microsilica shotcrete with remote controlled equipment (The Robocon System) was developed in Norway 7-8 years ago. Norway was the natural origin for this system due to several factors. Almost 30% of all underground hydro-power stations in the world are located here. These projects created a need for high productivity shotcreting rigs for the rock support work in the caverns and in the connecting tunnels. During the period of 1976-1980, more than 1000 miles of tunnels were completed in Norway. Secondly, the utilization of microsilica in concrete was also developed in Norway due to a concentration of the world's ferroalloy p ants there. Robocon has presently placed approximately 110,000 m (150,000 cu. yds.) of this superior shotcrete, and has consequently an extensive experience in the shotcreting method. During a relatively short period of time (1975-1980), Robocon had a change from hand-operated, dry-process shotcrete to remote-controlled, wet-process shotcreting, because of improved productivity, reduced rebound, safer and cleaner working conditions. The introduction of microsilica and water-reducing admixture made it possible to produce wet-process shotcrete of high strength.

Jan 1, 1987

By Marco D. Boscardin, Paul A. Roy, Kevin J. DiRocco, Andy J. Miller

The North Shore Connector Project for the Port Authority of Allegheny County involves TBM mining a pair of subway tunnels through soil and rock under the Allegheny River and a narrow city street. Along the tunnel alignment are a historic building on shallow foundations and modern buildings on deep foundations, one constructed directly over the alignment during the latter phases of design. This paper provides an overview of the general site conditions, and technical basis for excavation support and tunneling decisions. Deformation limits, ground improvement, monitoring and mitigation plans, geotechnical baseline report development, and risk management will also be discussed.

Jan 1, 2007

By Bauer, Steve, Colin Goodwin, Gerald, Randy Dempsey, Courtland

"The City of Ottawa’s Combined Sewage Storage Tunnel consists of two interconnected tunnels totaling 6.2 km with a diameter of 3m including access shafts and hydraulic structures which connect to the City’s most critical sewers. This tunnel will be built 15m to 30m below ground in the downtown core adjacent to, and crossing below, the Light Rail Tunnel, which introduces additional considerations in terms of sequencing and risk mitigation. The City embarked on a unique Procurement Process to address the risks involved with a large tunnel project and those associated with tunneling below downtown, underneath and adjacent to UNESCO World Heritage Sites, and connecting to live critical sewers. This paper describes the unique procurement approach employed and the contractual risk mitigation measures developed to provide the best value while minimizing risk. Specific features include Market Sounding, using a Fairness Commissioner, Contractor Prequalification and Risk Mitigation Measures in the Tender documents. INTRODUCTION This paper describes how the City of Ottawa (the City) and the project design team developed a strategic Procurement Process and Tender that incorporated industry best practices for technical and contractual risk management for the Combined Sewage Storage Tunnel (CSST) project. The process was unique in that, while it employed a systematic review of project risks, it also solicited input from industry, stakeholders and provincial and federal partners to develop the request for Tender for this traditional design-bid-build project. Key drivers for this approach were initiated from the City’s concerns for cost control, cost certainty and overall project risk mitigation. To address these concerns, the City implemented the risk review and mitigation process right from the project design team selection. It was critical that the project design team embraced this risk management philosophy and carried it through each phase of the project. This paper serves as an excellent resource for municipalities or other owners embarking on a similar tunnel project, on how to properly apply industry best practices and the benefits of using them."

Jan 1, 2016

By R. J. Reuss

The ore at this new underground operation is a massive sulfide breccia with high copper values. A major highway and electric transmission line pass directly over the near-surface orebodv. The mining method being used is undercut and fill. A continuous miner together with a single boom, hydraulic jumbo is used for the mining. Backfill is a weakly cemented sand-gravel mixture that is pneumatically placed. The ore is treated by conventional crushing, milling and flotation.

Jan 1, 1992

This study was conducted to evaluate the effects of a diesel particulate filter (DPF) regeneration process on the concentrations and size distributions of aerosols in an underground mine. Two active regeneration strategies were examined for an electrically regenerated sintered metal fiber filtration system, and the effects were compared with those observed for a muffler and the same system operated in a passive configuration. The effects were assessed for three steady-state engine operating conditions. The number and mass concentrations and size distributions of aerosols in mine air were found to be strongly affected by the exhaust configuration, engine operating conditions and the regeneration process. When the system was operated in active configurations, the concentrations exhibited a transient and cyclic nature. At light load conditions, the distributions of aerosols in mine air were dominated by accumulation mode aerosols for all exhaust configurations and regeneration strategies. High concentrations of nucleation aerosols were observed when the DPF system was used and the engine was operated at high load conditions. A positive correlation between accumulation of particulate matter in the filter and the efficiency of the filter in removing accumulation mode aerosols was observed for all conditions. In the case of high engine load, reductions in accumulation mode aerosol concentrations were linked to a substantial increase in number concentrations of nucleation mode aerosol. Overall, the filtration system was found to be very effective in reducing total aerosol mass and elemental carbon concentrations for all engine operating conditions. However, the system was substantially more effective in passive than in active regeneration configurations.

Jan 1, 2012

By António Fiúza, Anthony Danko, Patrícia Leitão, Aurora Futuro, Cristina Vila, Lurdes Dinis

The average global recovery rates for processing scheelite ores by physical methods are normally in the range 50 to 70%, and it is problematic to attain a minimum grade of 60% WO3 in the concentrates without penalizing further this yield. Direct hydrometallurgical processing of low-grade concentrates or medium- to high-grade ores may become an interesting global economic alternative as it allows increasing the recovery rate, avoiding major penalizations due to the grade of the concentrate and increasing the added value of the final product. Leaching of scheelite by sodium carbonate presents several advantages such as its selectivity regarding the dissolution of troubling metals like iron and aluminium, allowing for a simple and flexible process diagram. However, it has the disadvantage that it is performed at high temperature and pressure with a high consumption of reagents. The feasibility of leaching is appraised by the extraction yield and selectivity, but also by the operating cost. Considering these aspects, a relevant objective of the research was to transform alkaline pressure leaching into a feasible processing alternative directly applicable to both medium- and high-grade ores and simultaneously to low- and high-grade concentrates produced by physical methods. The research used ore samples and low-grade concentrates from a typical skarn orebody as well as high-grade concentrates from a chalcopyrite-scheelite orebody. Different operating conditions were tested. Temperature, pressure and reagent concentration showed to be fundamental, but not exclusive, in determining the leaching behaviour. The operating conditions are milder than the ones generally proposed in the literature or currently in use in industry, but with higher carbonate consumptions. The research was oriented towards potential industrial implementation allowing for the application of optimization methods and straight scale-up to pilot-plan design and project.

By F. V. Antonio, R. S. Pizarro

Masbate Gold Mines, dormant since WWI I, are now back in operation. The ore treatment plant incorporates carbon-in-pulp processing, utilized because of the ready availability of coconut shell charcoal in the Philippines and the high clay content of the ore. A detailed description of the plant, including the surprisingly fast and efficient alcohol stripping facility is presented. Operating data for the plant is provided together with an interesting performance evaluation of mechanical versus air- lift agitated leach tanks.

Jan 1, 1981

By S. J. Schatzel, V. Gangrade

A ventilation research study was conducted by the National Institute for Occupational Safety and Health and a cooperating trona mine in the Green River basin of Wyoming, USA. The mine operation uses the longwall mining method in trona bed 17, a commonly mined unit in the region. The longwall face length is 228 m (750 ft), and caving on the face occurred up to the back of the longwall shields. The mine is ventilated using a main blowing fan and a bleeder shaft. For this study, sulfur hexafluoride (SF6) tracer gas was released in two separate monitoring experiments. For the first experiment, tracer gas was released on the face, this test focused on airflow along the longwall face of the active panel. Face test showed the airflow patterns to be more complex than just head-to-tail flow in the main ventilation air stream on the active panel. For the second experiment, tracer gas was released 2 crosscuts inby the face on the headgate side, this test focused on gas transport in the mined-out portion of the same active panel. Gob test showed a pathway of movement through the front of the active panel gob that moved outby from the tailgate corner. The primary pathway of tracer gas movement in the active panel gob was towards the headgate and tailgate bleeders and out of a bleeder shaft. The rate of movement towards the back of the gob was measured to be 0.19 m/s (37 fpm).

By S. Al-Thyabat

Conditioning of flotation feed is an important prerequisite for efficient flotation. This process depends on parameters such as conditioning time, slurry concentration and slurry pH. The objective of this paper is to optimize the conditioning process for the flotation feed. This was achieved by first conducting preliminary experiments at constant slurry pH to determine the significant ranges of slurry concentration and conditioning time. Then, factorial experimental design (32 experiments) was used to investigate the significance of the above parameters and their interactions on flotation recovery and grade. Statistical analyses using ANOVA approach showed that flotation recovery (R) and concentrate grade (g) were affected by feed conditioning. It was found that concentrate grade was linearly proportional to the slurry concentration and conditioning time, while flotation recovery was exponentially proportional to the conditioning parameters. A contour plot of the flotation response (recovery and grade) against conditioning parameters showed that the optimum operating parameters for flotation feed conditioning was a conditioning time of 1.5 to 2 minutes and a slurry conentration of 55% to 60%.

Jan 1, 2008

By L. Ou

This paper reports on research on leaching pyrite in a germ-free system. The effects of mineral particle size, pulp potential and various oxidation agents on pyrite leaching were studied. The results indicated that a smaller mineral particle size leads to a higher leaching rate of pyrite. The optimum results were obtained with a mineral particle size of -0.037 mm. The pulp potential reflected the leaching process and an increasing pulp potential improved pyrite leaching. The leaching rate rapidly increased with the addition of oxidation agents such as Fe3+ and H2O2. However, the precipitate generated by ferric ion coated the surface of the pyrite and prevented further leaching.

Jan 1, 2007

By H. J. Sutherland

This paper reviews the results of the subsidence research prop ram at Sandia National Laboratories. The manuscript highlights the following: the application of empirical methods (profile functions) to the subsidence above longwall panels in the U.S.; the use of the "rubble model" to describe the behavior of broken strata as it distends when it falls to the Mine floor (or top of the rubble pile) and then is subsequently compacted as it is loaded by overlying elements of strata; and, the application of physical modeling techniques (centrifuge simulations) and numerical techniques to study the failure mechanisms in highly structured stratigraphy. The capabilities of the latter two are illustrated ')y comparing their predictions to the results of a field case that has complicated stratigraphy.

Jan 1, 1982

By H. L. Barwood

Luminescence excited by electron bombardment, or cathodoluminescence (CL), is a very useful tool in petrographic examination of rocks, minerals and ores. Differences in luminescence colors and intensities allow detection and delineation of mineral species and composition zones difficult to separate visually by normal polarized light microscopy. The cold cathode CL chamber at Indiana University is used with a binocular microscope that has interchangeable attachments for a normal film camera, a digital camera and a fiber optic spectrometer. This allows imaging of the specimens as well as limited spectrographic analysis of the emitted luminescence. The chamber on this CL unit is large enough to accommodate several thin sections, polished mounts, grain mounts or rock slices at one time. Luminescence petrographic techniques were used to study alkali syenites and carbonatites from the Arkansas. Alkali feldspars in the syenites reveal a history of growth, fenitization and replacement through color and intensity differences. Primary orthoclase luminesces bright blue and is often zoned with a duller blue overgrowth of microcline. Fenitization of the feldspars is demonstrated by dull to bright red luminescence and replacement veins of albite often have a bright yellow green luminescence. Late microcline and perthites from the syenite pegmatites have a dull yellow to orange luminescence. Easily visible on this background of feldspars are grains of apatite (yellow), fluorite (violet), zircon (greenish), sodalite (orange) and mosandrite (green). Complex pseudoleucite syenites from Magnet Cove, Arkansas show similar minerals but also include xenolithic quartz (violet), manganwollastonite (bright orange), benitoite (intense blue) and lorenzenite (green). Carbonatites from Arkansas contain a wide variety of calcite textures and intensities of luminescence. Grains of carbonatite in well cuttings are easily distinguished from sedimentary calcites by their complex “flame” luminescence and the frequent presence of euhedral apatite grains (yellow). Apatite crystals separated from the Arkansas River Valley carbonatites by acid digestion show complex zoning. The cores of these apatites are yellow luminescing due to CL activation by Mn enrichment while the rims are violet luminescing due to REE enrichment. Complex zonation between the cores and rims is easily visible using CL.

Jan 1, 2001

By Steven C. Borell

For more than a decade, changes have occurred each year that have improved the regulatory and business climate for mining in Alaska. These changes have taken place during Republican and Democratic governorships as well as when the state House of Representatives and Senate were controlled by either party. During some years, the changes have been relatively minor. In others, including the 2003 legislative session, the changes could only be characterized as massive. These improvements have encouraged exploration. This, in turn, has resulted in some major new discoveries. But Alaska is essentially unexplored and tremendous opportunities remain.

Jan 1, 2004

By Bengt L. Stillborg

INTRODUCTION This paper summarizes the result of a two and a half year research program. The objective of the research was to develop a fundamental understanding of the Rib-in-Roc method. Through the development of a new model technology, namely three-dimensional physical models which powerfully exploit the results of dimensional analysis Stillborg, Stephansson and Swan (1), it has been possible to establish the contribution to both permanent and immediate stabilization of a large underground opening pre-reinforced by the Rib-in-Roc method. Using the results from these physical models and earlier work by Stillborg and Stephansson (2) and Åkesson (3), a conceptual synthesis is given in this paper so demonstrating the Rib-in-Roc method to be a practical working system of pre-reinforcement. DESCRIPTION OF THE RIB-IN-ROC METHOD To give the reader an idea of how this method of pre-reinforcement is performed, a short description will be given, Figure 1. Before any full-scale excavation takes place an entry is made in the host rock and rib raises are driven around the proposed opening. These raises are made at a spacing that is dependent upon rock quality; an opening in poor rock needs more ribs per length of opening. As the ribs are driven they are used as a site from which very competent rock bolting can be done. As a rib is excavated it is filled with reinforced concrete. Finally after having in this way reinforced the zone around the proposed opening, (a reinforced arch is formed) the displacements are automatically controlled as the opening is being excavated. Using this method openings with a span of 50-60 meters (160-200 ft) and a height of 60-80 meters (200-260 ft) are likely to be realised.

Jan 1, 1979

By William R. Yernberg

The Cripple Creek & Victor Gold Mining Co.(CC&V) celebrated completion of a two-year, $168.5-million expansion and capital improvement program. An open house celebration was held in the historic mining town of Victor, CO on Oct. 4, 2002. Hundreds of townspeople, the press and other invited guests from the mining industry joined the employees of CC&V in the celebration. The event included mine tours, company displays and a barbecue picnic, complete with a country and western band. The Cresson Mine is located about 40 km (25miles) west of Colorado Springs, CO between the towns of Cripple Creek and Victor. The mine is the only large-scale gold mining operation in Colorado and now employs about 300 (ME, October 2001, pp.21-28). The operation is a joint venture between Anglo-Gold (Colorado) (67%), based in Greenwood Village, CO, and Golden Cycle Gold (33%), based in Colorado Springs. CC&V is managed by AngloGold North America. AngloGold North America is the U.S. subsidiary of AngloGold, the world’s second largest gold mining producer. AngloGold is based in Johannesburg, South Africa.

Jan 1, 2002

By Nick Karl, David Wilburn

"The mission of the U.S. Geological Survey (USGS) National Minerals Information Center (NMIC) is to collect, analyze and disseminate information on the domestic and international supply of and demand for minerals and mineral materials essential to the U.S. economy and national security. Understanding mineral exploration activities and trends assists government policy makers, minerals industry decision makers and research entities in identifying where future sources of mineral supply are likely to be discovered, the amount and type of these resources and factors that may affect exploration and development.This review summarizes significant exploration trends related to active sites and budgets, mineral commodities and regional factors for the years 2001-2015. Data were compiled by specialists in the USGS-NMIC, and reported annually in the USGS-NMIC Minerals Yearbook series and in the May issue of Mining Engineering magazine. External data for these analyses were derived from industry sources, published literature, and SNL Metals & Mining, an offering of S&P Global Market Intelligence (New York, NY).The USGS-NMIC compiled exploration site data for more than 80 mineral commodities, focusing on base metals, diamond and precious metals. More than $138 billion constant U.S. dollars were budgeted by the minerals industry from 2001 through 2015 to explore more than 16,000 mineral deposits globally (SNL Metals & Mining, 2016a). Annual analyses identified where mineral exploration took place by principal commodity target, ranked the magnitude of activity in each region, identified the factors that most affected changes in exploration activity and highlighted developments that led to changes in global supply or increased diversity of supply to the United States. Geographic classifications noted in this report were Africa, Australia, Canada, China, Latin America, Pacific, Russia, United States and Rest of the World."

Apr 1, 2017

By Doug Harding

The Niagara Tunnel Project (NTP) is a 10.4 km (6.5 mi) long, 14.4 m (47.5 ft)bored tunnel that will run under the City of Niagara Falls from the Upper Niagara River to the Sir Adam Beck Power Station. The completed project will enhance the capacity of the Sir Adam Beck Power Station by adding 500 m3 (17,657 ft3) of water per second through the tunnel. The paper describes the project in which the world’s largest hard rock TBM at14.4 m (47.5 ft) in diameter is being used to excavate the tunnel. Features of the project include the use of a High Performance (HP) Main Beam TBM, state-of-the-art ground support and tunnel logistics systems. A continuous conveyor is used for muck transport from the TBM to the disposal area. The paper will also discuss the optimization of the TBM system as the tunnel advances through the varying geology. In June 2004 the Ontario Government announced that Ontario Power Generation(OPG) had been given approval to proceed with the third tunnel under the city of Niagara Falls—the first two tunnels were constructed in the 1950s using drill and blast techniques. The third tunnel, appropriately named The Niagara Tunnel Project (NTP), consists of a 10.4 km (6.5 mi) long TBM-bored, concrete-lined tunnel with a finished diameter of 12.5 m (41.1 ft). In August 2005, OPG announced the selection of Strabag AG of Austria, one of the largest construction companies in Europe, as the contractor to build the NTP Project at a price of CAN $600 million. In September 2005, Strabag A.G. selected The Robbins Company of Solon, Ohio to design, manufacture and deliver a new 14.4 m (47.5 ft) diameter High Performance state-of-the-art Main Beam Hard Rock TBM to be used in the excavation of the tunnel. In order to meet the aggressive construction schedule as requested by OPG/Strabag, the TBM needed to be supplied as “ready to bore” within a 12 month period after the contract was awarded to Robbins.

Jan 1, 2007

By M. Nehdi

Deficient surface disposal systems of sulfidic mine waste often cause severe contamination of surface streams and groundwater reservoirs due to the oxidation of sulfide phases. The subsequent generation of leachates characterized by high acidity and elevated concentrations of toxic elements (commonly known as acid mine drainage) jeopardize the health of contiguous ecosystem. Stabilization/solidification (S/S) is recognized as a promising solution for treating such wastes. S/S processes generally mobilize alkaline and/or cementing materials/additives that act as neutralizing and/or binding agents. In the present research, industrial byproducts, namely, cement kiln dust (CKD) and Class C fly ash (FAC) have been used as candidate materials along with the partial addition of sulfate-resistant cement (SRC) in the S/S of polymetallic sulfidic mine tailings (MT). The effectiveness of S/S was assessed by comparing laboratory experimental values obtained from unconfined compressive strength, hydraulic conductivity and leaching propensity tests of S/S samples with regulatory standards for safe surface disposal of such wastes. Despite general regulatory compliance of compressive strength and hydraulic conductivity, some solidified/stabilized-cured matrices were found unable to provide the required immobilization of pollutants. Solidified/stabilized and 90-day cured mine tailings specimens made with composite binders containing (10% CKD + 10% FAC), (5% SRC + 15% FAC) and (5% SRC + 5% CKD + 10% FAC) significantly impaired the solubility of all contaminants investigated and proved successful in fixing metals within the matrix, in addition to achieving adequate unconfined compressive strength and hydraulic conductivity values, thus satisfying U.S. EPA regulations. Laboratory investigations revealed that, for polymetallic mining waste, leachate concentrations are the most critical factor in assessing the effectiveness of S/S technology.

Jan 1, 2008