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By M. Laliberte

"Gold-mine effluents are often characterized by high concentrations of copper, ammonia and cyanide derivatives (mostly cyanates and thiocyanates). While not acutely toxic to birds, this water can be acutely toxic to fishes and invertebrates. In many jurisdictions, the effluent requires further treatment in order to pass a mandatory requirement to be nonlethal to species like the rainbow trout (Oncorhynchus mykiss) or Daphnia magna. Using actual mine water, it has been demonstrated that aerated moving bed biofilm reactors will biodegrade the ammonia, cyanides, cyanates and thiocyanates, thereby removing the toxicity associated with these components. By removing copper by precipitation the water can be made to pass acute toxicity tests. Tests have demonstrated that the process is stable between 4 and 25°C, with no significant changes in the treated water composition. Once the biomass is acclimatized, the process is resistant to upsets and requires very little inputs except for phosphorus and air. Furthermore, it has been demonstrated that an anoxic reactor can be added downstream of the aerated reactors to remove nitrates if required.IntroductionThis paper will demonstrate that gold-mine effluents, which are toxic to fishes and invertebrates, can be made nontoxic by using a combination of chemical precipitation and biological oxidation.The typical composition of gold-mine effluents will first be described. The applicable legislation will then be introduced, with its requirement that the treated effluent be nontoxic. The toxicity of a typical untreated effluent will then be confirmed, and the sources of the toxicity identified. After that, a number of toxicity reduction treatment methods will be presented, and the selected method will be described.The lab tests that confirmed the efficiency of the treatment method will be presented, with three phases of testing as the understanding of the process gradually improved. Toxicity test results showing that the water is nontoxic after treatment through the temperature range will be presented."

Jan 1, 2015

By C. O’Hara, S. Roy, K. Swedburg, J. Katchen

"New Gold Inc.’s New Afton concentrator commenced operation in June 2012, producing a copper-gold-silver concentrate. During the first two years of operation, various optimization efforts have improved mill throughput, recoveries and concentrate grade. Daily mill throughput has increased 20% above the design rate. This was achieved through more consistent instantaneous feed rate and size distribution from the mine reclaim stockpile, higher pebble crusher reliability, changes to the SAG and ball mill grinding media sizes, larger SAG grate openings, reduced SAG discharge screen-deck aperture size and an increase in the maximum ball mill power draw limit. Metal recoveries at New Afton are primarily limited by liberation in the coarser size fractions; therefore, improving the grind size at a given mill throughput has been the main means of improving recovery. The average rougher flotation feed F80 size was reduced from 175µm in Q1 2013 to 165µm in Q1 2014, while the average operating mill throughput increased by 25%. Other flotation circuit changes focusing on recovery improvement include the addition of froth crowders to the rougher cells and the use of a stronger frother. The average concentrate grade increased from 22% Cu in Q1 2013 to 25% Cu in Q1 2014. This was achieved by redirecting the flash flotation concentrate stream to the regrind circuit and by the addition of lime to the cleaner circuit.This paper describes the above improvements made at the New Afton mill. The paper describes the objectives, timing and end result of each area of improvement.IntroductionThe New Afton Mine is situated approximately 10km west of Kamloops, British Columbia, 340km north-east of Vancouver. The mine has a moderate climate, access to transportation and electrical infrastructure, nearby fresh water supply, and close proximity to industrial and mining service businesses. The population of Kamloops is around 90,000 with most mine employees living in or around the city."

Jan 1, 2015

By William Gleason

"The Colorado School of Mines has used the Edgar Mine in Idaho Springs as an experimental mine to teach students since 1921. Since the school acquired the former gold, silver, lead and zinc mine, countless students have received hands-on engineering lessons on their way to earning mining engineering degrees. On Dec. 14, the House Subcommittee on Energy and Mineral Resources held a historic field hearing about the future of mining education in the United States in a classroom about 300 m (1,000 ft) inside the Edgar Mine. Representatives Doug Lamborn (R-CO), Rob Bishop (R-UT), Cresent Hardy (R-NV) and Ed Perlmutter (D-CO) were on hand for the first ever congressional hearing held in a mine where they heard testimony supporting the Mining School Enhancement Act, which was introduced to Congress by Hardy and Perlmutter on Oct. 9, 2015. The act, which is part of a larger mining development and reclamation reform package, seeks to address the absence of a viable pipeline necessary to replenish current faculty vacancies in United States Mining Schools. “What better place to hold a hearing to discuss the need for future mining engineering experts,” Subcommittee Chair Lamborn said in his opening statement. “It is a need felt by industry, states, the federal government as well as nonprofits.” The Mining School Enhancement Act would redirect millions of dollars in fees that are being collected from active mining operations to fund the research and educational programs at engineering schools with mining programs. Those fees now are being used in the form of grants awarded by the Surface Mining Control and Reclamation Act of 1977 (SMRCA)."

Jan 1, 2015

By A. O. Sfriso

"Numerical modelling is becoming universal in rock engineering practice. Most applications focus on the prediction of failure loads of 2D problems, where the numerical models are useful extensions to analytical methods and experience-based design criteria. For 3D problems and problems where the assessment of serviceability indicators – displacements, ground-structure response, etc. – are of importance, the selection of the constitutive models themselves and the implications of the selection of material parameters may have a very heavy impact on the reliability of the model outcome and its predictive capability.This paper overviews basic common aspects of constitutive equations used in practical rock engineering and summarizes some challenges that are frequently observed when reviewing numerical models performed for routine problems in rock engineering. INTRODUCTIONNumerical methodsFrom a philosophical perspective models, either analytical or numerical, are idealizations of a perceived reality. For us engineers, models are just tools we use to guide our judgement and understanding of the problem in hand. When dealing with problems in rock engineering, we resort to a wide range of techniques:1. Closed form solutions like confinement-convergence methods for circular tunnels: these methods satisfy equilibrium and compatibility requirements at the cost of a crude simplification of the material behavior and geometry;2. Limit analysis methods, like bearing capacity formulas: lower bound methods satisfy equilibrium but sacrifice compatibility, and upper bound methods do the opposite. Material behavior must be simple, geometry admits limited freedom;3. Limit equilibrium methods, like method of slices for slope stability: they satisfy restricted forms of equilibrium, do not satisfy compatibility requirements, require simple material behavior but have a much greater flexibility on geometry;4. Numerical methods, where a mesh is employed to discretize the problem geometry: when properly formulated, these methods satisfy equilibrium and compatibility requirements and give reasonable approximations to the behavior of very complex geometries and construction sequences. Very little restrictions remain on geometry and material behavior, but the cost of calibrating the material parameters can be very high."

Jan 1, 2015

By Syd Peng

"As the International Conference on Ground Control in Mining (ICGCM) enters its 35th year in 2015, it is time to look back and identify the areas that need to be emphasized and to look forward to see what areas need to be researched in the future. In the past three decades, ground control has made a tremendous advancement, and many case studies published in the 36 volumes of proceedings have demonstrated its important role in the daily mining operations. However, there is still plenty of room for improvements. This paper discusses the research needs in 12 subject areas, including mine geology, rock property, zones of disturbance in overburden, computer modeling, underground stress measurements, research method, roof bolting, coal pillars, failures, subsidence, shield supports, and coal bumps.INTRODUCTIONThe International Conference on Ground Control in Mining (ICGCM) was founded in 1981. Since then, 1,546 papers have been published in the 36 conference proceedings, including the three surface subsidence workshops held in the 1981, 1986, and 1992. All types of topical areas regarding mining, from geotechnical core loggings in the exploration phase through backfilling after mining to finally spoil piles stability on the surface, have been addressed. A review of these papers, and other related literature as well, indicate that ground control has developed to become an inseparable part of mine design and a problem-solving tool for safe production.After 34 years, it is time to look back and identify the areas that need to be emphasized and to look forward to see what areas need to be researched in the future. There is no doubt that the conference series has achieved the goal for which it was originally designed: to provide an annual forum for the exchange of information among the researchers, government regulators, equipment manufacturers, consultants, service providers, and—above all—mine operators. There have been many papers addressing the application of ground control techniques for successful mine design and safe production, and, without these papers, many projects would have failed. In fact, the conference emphasis on application types of papers may have steered too far toward the application side. A review of the conference papers shows that papers have been leaning mostly toward the applied side, leaving most, if not all, fundamental issues behind in nearly every topical area. This paper addresses research needs in 12 topical areas: mine geology, rock property, zones of disturbance in overburden, computer modeling, underground stress measurements, research method, roof bolting, coal pillars, failures, subsidence, shield supports, and coal bumps."

Jan 1, 2015

By Dale Ramsey

As someone who has enjoyed photography as a hobby for many years, aerial photography to me has always been an exciting way to give a different perspective to my images. Our industry is always in search of new technology for bet­ter and more cost effective methods to improve our trade and aerial photography is a great tool to improve project planning or document its progress. It has typically involved conventional aircraft both fixed wing and helicopters but neither method is always available or cost effective. The lat­est innovation since digital imaging is the development of Unmanned Aerial Vehicles (UAVs) or drones. But there is a lot of uncertainty with this amazing new technology’s fu­ture in the U.S. as the Federal Aviation Administration (FAA) is under review and development of UAV regulations for commercial use which are slated to be completed in 2015.

Jan 1, 2015

By A. J. Martin, M. J. Peoples, D. J. Adams, A. Opara

"The weathering of coal mine waste rock releases iron, calcium, sulfate and associated trace elements like selenium (Se). Nitrogen species are also found in association with coal-mining drainages mainly due to the leaching of residual blasting compounds. Elevated concentrations of Se are a ubiquitous occurrence in coal-mining environments in British Columbia. A major concern with waterborne Se in British Columbia is the potential for its bioaccumulation in aquatic food chains.Treatment to remove Se from coal-mining waste waters has proven to be challenging for conventional water-treatment technologies. Compounding this challenge, many streams are characterized by high flows and low selenium concentrations. Conventional membrane and ion exchange treatments produce concentrated brine streams that are difficult to treat or require disposal. Conventional biotreatment systems use excess nutrients to provide the required electrons to compensate for inefficient and variable electron availability, as well as to adjust reactor chemistry.This paper's electro-biochemical reactor (EBR) technology provides a controllable and consistent supply of useable electrons to the microbes directly at a low voltage potential (1-3 V) and low current. In this manner, the EBR technology overcomes the shortcomings found in conventional systems, as it reduces the required nutrient addition and provides a more controllable, efficient, economical and robust biotreatment system. Additionally, the EBR process does not produce excess solids or biomass; therefore, solids management post-treatment is not required.Laboratory EBR bench-scale and on-site pilot-scale systems were used to treat five British Columbia coal-mine waste waters; influent Se concentrations ranged from 35 µg/L to 531 µg/L. Se treatment targets for the tested waters ranged from 5 to 10 µg/L. Mean Se concentrations in EBR effluents ranged from 0.5 µg/L to 1.4 µg/L, while reducing sulfate concentrations. The test data demonstrate that the EBR technology is an effective Se removal option for British Columbia’s coal-mining waste waters.IntroductionSelenium in Mining. Selenium (Se) is a naturally occurring trace element, which is an essential nutrient in small amounts (Thompson and Robinson, 1980; Brown and Arthur, 2001). However, it is also toxic to aquatic life, birds, and humans at very low concentrations. A major concern with waterborne Se is the potential for its bioaccumulation in aquatic food chains, resulting in acute and/or chronic toxicity to fish, water birds and amphibians (Besser et al., 1996; Conley et al., 2009)."

Jan 1, 2015

By H. Huang, R. N. Gow

"The reactivity of an enargite mineral electrode was investigated spectroelectrochemically under conditions typically found in alkaline sulfide leach solutions, with pH 11-13 and Na2S additions of 50 and 250 gL-1. A bulk enargite electrode was cycled between 0 and -1,000 mV for each set of solution conditions. Raman spectroscopy was used to determine and compare surface formations against species in mass-balanced EH-pH diagrams generated using STABCAL. Previously, it was determined that arsenic could be selectively leached under alkaline conditions at an average solution potential of -300mV, across the pH range 11-13. Operating under such conditions allowed for the selective leaching of arsenic with elemental sulfur formation. From several of the voltammograms obtained during this current testing, the formation of elemental sulfur appeared at increasingly reducing conditions with increasing sulfide concentration. At high concentrations, copper started to dissolve, possibly as a bisulfide complex, reducing the selectivity of the leach, unlike previous studies. However, the presence of the higher sulfide concentration is also anticipated to prevent passivation by consuming any surface formation of elemental sulfur. This study provides insight into the operating parameters of alkaline sulfide leaching in regards to the selectivity of arsenic leaching, as well as guidance for control of reagents and solution potential and, of course, the need for water treatment afterwards.IntroductionEnvironmental limitations on the pyrometallurgical processing of arsenic-bearing concentrates have forced operations to consider other solutions. Attempts to hydrometallurgically process enargite (Cu3AsS4) fall into two categories: the co-dissolution of arsenic and copper under acidic conditions, and the selective leaching of arsenic under basic conditions. The authors believe that the selective leaching of arsenic is more amenable because it produces a solid copper phase, preferably chalcocite (Cu2S) or covellite (CuS) that could then be processed using conventional methods already in place in the copper and gold industries. Potential leaching methods include alkaline sulfide leaching (Achimovicovica et al., 1999; Anderson and Twidwell, 2008a,b; Tongamp et al., 2009 and 2010), hypochlorite leaching (Vinals et al., 2003; Curreli et al., 2005; Mihaljovic et al., 2007), ammoniacal leaching (Gajam and Raghavan, 1983), and acid leaching (Gow et al., 2014b) with or without fine grinding to mechanically activate the enargite surface and increase normally slow leach reaction kinetics (Achimovicova et al., 1999; Balaz et al., 2000; Balaz and Achimovicova, 2006). In this study, the reactivity of enargite under alkaline sulfide leach conditions was examined."

Jan 1, 2015

By A. E. M. Warner, P. J. Mackey

"In 1988, two of the present authors Warner and Vahed [1] were amongst several co-authors on a seminal paper reviewing nickel pyrometallurgical operations of the era. Given that significant changes in the nickel industry have occurred since that time, including the overall political landscape, technology, the overall world energy picture, the countries sourcing nickel and finally the nickel market itself, the present authors considered it timely to provide a 2015 update. In 1988, total world nickel production from sulphide and laterite sources, including production in the former "Centrally Planned Economies"- was about 0.86 million tonnes/a, while in 2014 total world nickel production reached an all-time high of almost 2 million tonnes/a - some 230% higher. On the other hand, while in 1988, about 94% of world nickel was produced pyrometallurgically and of the order of 33% via laterites, today, about 88% of nickel is by pyrometallurgy, with some 41% from laterites, thus showing that more nickel is now sourced from laterites, a trend which is expected to continue.During the period under review, new processing technologies were developed and introduced, along with substantial improvements in both the technologies employed and the scale of operations. Significant productivity gains have been achieved in sulphide pyrometallurgy in part through more efficient mineral processing, particularly in pyrrhotite rejection, and the use of ever larger-scale process equipment. This made it possible to treat lower grade and more complex ores. The significant game-changer from a production perspective was the introduction in the early 2000s of nickel pig iron (NPI) in China via modified iron blast furnace smelting, an old technology long ago cast aside by other nickel producing countries. With the exception of the emergence of this new NPI capacity in China, in the laterite industry modernization and expansion of existing operations has been employed to gain productivity, to cut costs and/or offset the effect of declining ore grades. The NPI technology development has become a game changer in the traditional global supply and demand relationship, opening up a new frontier to supply nickel to low grade utility steel producers. One other key nickel development was the Indonesian ban on nickel ore exports effective in January 2014, thus effectively curtailing NPI production at existing Chinese plants, but on the other hand, potentially prompting new smelting facilities in Indonesia. This paper reviews and updates major pyrometallurgical sulphide and laterite operations worldwide, including changes in nickel extractive metallurgy. It also provides a brief review of new developments in pyrometallurgical operations, with special focus on the NPI process and presents an outlook of the potential future direction of the industry."

Jan 1, 2015

By T. G. Carter

"Tremendous progress has been made in recent years towards developing computational tools that allow ready solution of most common rock engineering problems, with amongst the most advanced of the tools focusing on evaluating engineered openings within Synthetic Rock Masses. These new codes have the potential to allow much more realistic design, but they must not be used without careful calibration – prior to – during and – post completion of any modelling. This paper explores some of the pitfalls of inadequate data collection and suggests more emphasis be given to calibration. Guidelines for minimum levels of parameter data are suggested for improving application of basic to sophisticated modelling codes.INTRODUCTION & BACKGROUNDTremendous progress has been made in recent years towards developing computational tools that allow ready solution of most common rock engineering problems. The degree of sophistication now possible with some of the available codes allows one to tackle extremely complex problems that were not thought tractable even a decade ago. Indeed, generation of synthetic numerical rock masses, based on discrete fracture network representations that closely mimic actual rock mass conditions, such as are shown in Figure 1, is today relatively straightforward, and not as user-challenging as employing state-of-the-art codes of even a few decades ago. This is largely because major improvements in computer graphics and in availability of ready-made user-friendly input-output interfaces have paralleled development of these new codes, now in some cases outpacing actual new analytical/procedure developments. This is something of a reversal from the first few decades of DOS-based rock engineering computational experience, when only rudimentary graphics were available and user-friendly input-output interfaces were virtually non-existent."

Jan 1, 2015

By P. L. Yorio, D. R. Willmer

"The current paper presents the results of a study designed to explore the types of practices that are fundamentally important to developing and maintaining comprehensive risk-based health and safety management systems (HSMS) in mining organizations. Eighteen practicing health and safety (H&S) executives, managers, and professionals from a variety of mining commodities were asked to assess the fundamental importance of 20 distinct elements and 133 different practices assembled from a review of several HSMS consensus standards. The research approach assumes that developing and maintaining a robust HSMS requires unwavering attention to activities designed to either: 1) directly contribute to a risk management system’s plan-do-check-act cycle; or 2) build an organization’s internal infrastructure without which the cycle cannot be sustained. The results of this study suggest that the following areas require consistent focus and attention: Leadership Development; Accountability; Knowledge, Skills, and Abilities Development; System Coordination; Culture Enhancement; Behavior Optimization; and Risk Management Studies. Each element and its corresponding top-ranked and top-rated practices are discussed.INTRODUCTION Since the time of the Industrial Revolution, occupational health and safety (H&S) management has been a topic of practitioner thought and academic inquiry (1). In the U.S., decades of regulation and research have resulted in a surplus of prescriptive information (techniques, tools, approaches, standards, programs, practices, policies, etc.). With an abundance of such information, a simple H&S solution to address a problem in the U.S. mining industry may seem straightforward. Counter to this assertion, however, some evidence suggests that the abundance of information may create complexity and cause confusion in the minds of organizational leaders and H&S managers, ultimately discouraging the voluntary pursuit of a sound approach (2). In line with this perspective, in 2006 the U.S. National Mining Association (NMA) formed an independent commission to examine H&S management issues within the mining industry. The findings of the commission called for the mining industry to adopt a risk-based management paradigm. In the presentation of its findings, the commission stated that “…every mine should employ a sound risk-analysis process, should conduct a risk analysis, and should develop a management plan to address significant hazards identified by the analysis” (3). Grounded in the well-known plan-do-check-act cycle, the recommended risk management system allows for mines to ground strategic management choices in their mine-specific hazards and risk profiles"

Jan 1, 2015

By Darin Cotton, Tim Burgess, Tim Martin

"As the leading US supplier of roof control drills, J. H. Fletcher and Company® has encountered an extensive set of roof strata challenges and has overcome various drilling issues by varying machine parameters and working with customers and tool manufacturers to develop solutions. Every mine wants to drill and install roof bolts as fast as possible with maximum safety at the lowest possible installation cost for their conditions. In most circumstances, the intuitive method of higher speeds and pressures can actually have a detrimental effect on the roof drill safety and performance.This paper will outline recent tests carried out at several different coal mines in the Eastern United States. The tests focused on optimizing the drilling parameters of feed pressure, feed rate, rotation speed, and drill torque.The drill feed, rotation speed, and rotation torque, as well as the type of bit selected, have a definite impact on the performance of the roof drill including drilling speed, safety, and tool life. The drilling process can be improved while also improving operator safety and reducing bolt installation costs by maintaining the appropriate roof drill settings for the specific strata conditions.The advantages of improving the drilling process includes increased bit life, increased drill steel life, reduced hanging drill steels, reduced clogging of the vacuum system, decreased whipping drill steel potential, reduced noise generation, and increased cutting size which reduces fine dust generation and dust collection system servicing.INTRODUCTIONIn recent times, the economic pressures that coal producers are facing have created an increased emphasis on controlling operating costs. Several coal operators have pointed out their dissatisfaction with low bit life, and there is a renewed interest in improving tool life and machine performance as part of an overall cost control strategy. Operators are looking for ways to reduce tooling cost, maintenance costs, and drill downtime without decreasing drill performance. This renewed interest in reducing operating costs, along with the ongoing desire to improve safety, created a perfect environment to take a fresh look at the existing fleet of machines to see what could be accomplished. The goal was to take a practical approach to reviewing machine parameters to determine what changes could be made. The emphasis was on changes that would be feasible to roll out to an entire fleet of machines in a short period of time with minimal capital expenditure. The thought process was that significant improvements could be made by simply tuning up the machine parameters to provide a more efficient and safer bolting process."

Jan 1, 2015

By Randy Settgast, Daniel Moos, Hyunil Jo, Ghazal Izadi, Christine Baba

"Analyses of production logs of multiply fractured horizontal wells in unconventional plays show that only a small percent (~30%) of perforation clusters contribute to production. We present in this paper one possible approach to mitigating this problem, based on use of a fully 3-D numerical model of fracture propagation through a heterogeneous medium, by studying the influence both of spacing and of perforation friction on the initiation and propagation of simultaneous hydraulic fractures from a horizontal wellbore. The results indicate that while limited-entry perforating can help to equalize the lengths of fractures simultaneously growing from multiple clusters, it cannot equalize their widths. Both fracture width and fracture length can be equilibrated by combining non-even cluster spacing with limited-entry perforating. This has obvious benefits as it allows equalized placement of proppant across the entire series of perforation clusters, resulting in similar fracture widths and conductivities which enhances the likelihood that all clusters will contribute equally to production.INTRODUCTIONThere is substantial evidence from production logs and other information that during the hydraulic stimulation of horizontal wells, not all perforation clusters within a given stage will produce. One possible cause is the interaction between the hydraulic fractures emanating from each perforation cluster. Typically fractures created at the outer perforation clusters create “stress shadows”, i.e. increases in compressive stress in the minimum principal stress direction, which limit the growth of fractures growing from interior clusters; this is confirmed by modelling [1, 2, 3]. An example of this can be seen in Figure 1 which shows the final configuration of simultaneously propagating fractures from multiple, evenly spaced clusters when there is no perforation friction. The inner fractures are substantially shorter, reproducing the results by Bunger and Peirce [3]. The inner fractures also have substantially smaller widths.One approach to equalize the growth of simultaneously propagating fractures from a horizontal wellbore is by using limited-entry perforating as a method to equilibrate the flow rates into each of the different perforation clusters. Perforation friction is caused by the finite diameter of the entry points into the formation, and leads to a pressure drop across each perforation which is proportional to the flow rate squared. Fractures that take more fluid have a higher fluid velocity through the perforations than fractures receiving less fluid. This causes a larger pressure drop between the wellbore and more rapidly growing fractures, compared to the same pressure drop between the wellbore and the fractures that grow more slowly. Because pressure within the wellbore is approximately the same at each entry point, the larger pressure drop leads to less pressure being delivered to rapidly growing fractures, thereby decreasing their ability to propagate and reducing the amount of fluid they are able to receive. Because the mass rate of injection into the wellbore is constant, this forces more fluid into the fractures that were propagating more slowly, increasing their growth rate. It also increases the pressure required to drive fluid injection. The balance of these effects makes the system largely self-regulating and delivers more balanced fracture growth. While this effect is well known, it is often neglected in current numerical models."

Jan 1, 2015

By V. S. Gischig, G. Preisig

Hydraulic stimulation of deep reservoirs is an essential procedure for developing engineered/enhanced geothermal systems (EGS), but also in other Geo-energy contexts. The goal is enhancing permeability to such a degree that fluid flow rates within the reservoir are sufficiently high for an economically productive reservoir. Two fracture stimulation mechanisms are distinguished that may occur concurrently during the hydraulic treatment: 1) During hydro-fracturing (HF) new tensile fractures are propagated from the borehole by means of a fluid pressure overcoming the minimal principle stress d3 plus the tensile strength T0 of intact rock. In case of a pre-existing fracture oriented normal to d 3 , the fracture can be opened by exceeding d 3 only. Fluid injection is performed via small packed intervals for creating a stack of hydraulic fractures. 2) During hydro-shearing (HS), over-pressure induces slip along pre-existing fractures that are favourably oriented in the stress field for reactivation in shear. Such stimulation is usually performed in a large packed interval or in an open borehole. Which mechanism occurs predominantly during stimulation depends on the rock mass structure and in-situ stress field, but also on the orientation of discontinuities intersecting the open-hole section and thus being pressurized. Both mechanisms also differ in how they affect fracture permeability. While permeability gained by HS is mostly irreversible due to rearrangement of asperity contacts accompanied with shear dilation, permeability enhanced during HF reduces nearly reversible after pressurization unless proppant is used to ensure permanent apertures. In this contribution, we critically discuss the pros and cons of both mechanisms regarding efficiency of enhancing permeability and the associated hazard of induced earthquakes based on literature review and numerical modelling. We review literature that reports on how much permeability required for productive EGS reservoirs and how much permanent permeability can be gained by stimulation. We also compile information regarding the degree of seismicity induced during HFor HS-dominated stimulation procedures, together with conceptual studies that reveal characteristics of seismicity associated with the two mechanisms. Many observations and models indicate that HF may have a higher tendency of being aseismic, while felt seismic events are usually associated with HS. Further, we present a hydro-mechanically coupled fracture flow model that investigates, if and to what degree the stimulation strategy can be designed such that one of the two mechanisms is evoked and dominates over the other. It shows that HS may dominate in presence of larger persistent fractures nearly optimallyoriented in the stress field, even if HF is attempted in short packed intervals. The model further demonstrates that stress transfer during HS promotes the development of permeability across an anisotropic layer of the stimulated rock instead of a large volume. Hence, the study sheds light onto the feasibility of creating productive EGS reservoirs in crystalline rock at several kilometres depths.

Jan 1, 2015

By R. E. Vivas, J. Garcia

"INTRODUCTION Freeport-McMoRan is a leading international natural resources company that operates large, long-lived, geographically diverse assets with significant proven and probable reserves of copper, gold, molybdenum, cobalt, oil and natural gas. Freeport-McMoRan is the world’s largest publicly traded copper producer and largest producer of molybdenum. The Sierrita mine is an open pit truck and shovel operation from which copper and molybdenum are produced. An important key to Sierrita’s success lies in their ability to realize their plans in the field. In certain circumstances, the mine plans are not achieved, and the operation fails to meet its targets which is an issue revealed in reconciliation reports. This technical session discusses the methodologies and procedures used at Sierrita to monitor the implementation of the mine plans, measure the performance of the operation and reduce the variance between plan and actual. Ensuring the operation stays on target is vital so mine productivity and profitability can attain its maximum potential. PROJECT OVERVIEW The Sierrita mining complex is located in Pima County, approximately 20 miles southwest of Tucson, Arizona as shown in Figure 1. The first mining claims at Sierrita date back to the late 1800s while underground mining activities started in the early 1900s. However, open pit development of Sierrita began more than 50 years ago to become the modern mining complex it is today. In 2009, Freeport-McMoRan purchased the adjacent Twin Buttes copper mine, providing significant synergies in the Sierrita minerals district. This venture included the potential for expanded mining activities, operations growth for mining copper and molybdenum, and reclamation activity. It should be noted that in addition to copper and molybdenum, the Sierrita mine produces rhenium which is a rare and highly value metal. The ore deposit contains oxide and sulfide mineralization. The oxide ore is delivered to the leach process while the sulfide ore is routed to the crusher and mill circuit 4,700 jobs on Arizona’s economy Freeport-McMoRan partners with the communities near Sierrita to provide programs that contribute to their sustainability"

Jan 1, 2015

By Panagiotis (Takis) Katsabanis, Lyall Workman, Jack Eloranta

The reduction of metallic ores to concentrate consumes a great deal of electrical energy. In the past two decades, a number of case studies have demonstrated a beneficial relationship between powder factor and grindability. However, changes in mill performance cannot be attributed to changes in feed size alone. Blasting energy and the distribution of that energy appears to affect subsequent comminution beyond crushing. This experience has prompted researchers to attempt to duplicate and quantify the mechanisms involved. To date, published reports indicate a measure of success. However, the blast engineer and the mill engineer still lack the tools and basic understanding necessary for full drill to mill optimization.

Jan 1, 2015

By Bob Drew, Goran Vukovic, Bojan Zivanovic, Klaus Gamweger

Reaction bath temperature is a major factor in processing liquid metals and in many applications where a balance between process duration and temperature has to be found to run a procedure efficiently. Also extremes of temperature can decrease the output of a process if too cold or even make it impossible, conversely overheating can be detrimental to both the product and furnace integrity. With the help of the new online temperature measurement system very accurate monitoring of the process is possible in contrast to the current routine practice where the temperature is measured periodically with dip thermocouples. The system works with a digital, fiber optic pyrometer, which is embedded in a refractory housing. Installation in the lining is possible below liquid level as nitrogen is blown to keep the system open and to ensure continuous sight from the optical head of the pyrometer to the molten metal through the tuyere. This permanent temperature measurement gives optimal process control with the potential of taking appropriate actions at an early stage enabling proactive process control. Therefore energy savings and even process endpoint detections can be realized.

Jan 1, 2015

By Arthur Barnes, Mika Muinonen, M. J. Lavigne

"The carbothermic reduction of chromite ore to produce high carbon ferrochromium is among the most energy intensive metal extraction processes performed, due not only to the highly endothermic nature of the reduction reactions but also the very high operating temperatures required for the smelting operation to separate the chrome-containing alloy from the discard slag.KWG Resources and XPS have collaborated over the last 3 years in developing a patented (Winter) processing alternative to the traditional smelting operation in which all processing takes place in the solid state at temperatures many hundreds of degrees lower than those required for liquid processing. Amongst the attractions of the process are much lower capital costs, as well as reduced operating costs, particularly of energy.A techno-economic study on the new process identifies a reduction in overall energy consumption of 70% against conventional processing and approximately 40% lower than the current best practice. By utilising more natural gas than coal based energy sources, the KWG process is able to show an overall 50% reduction in greenhouse gas emissions compared with the most energy efficient current practice. The impact of the new process on future processing is therefore regarded as highly significant, with global energy reductions equivalent to the effect of completely eliminating energy demand from a country the size of Italy.The study concluded that the potential for this process to completely revolutionise the global ferrochrome industry should not be underestimated. Its impact reaches far beyond exploitation of a regional natural resource."

Jan 1, 2015

By Russell J. Denny

"A 25m deep cut-off wall is required for environmental remediation of a Former Chlor-Alkali Plant. Extensive trials were conducted to verify the effectiveness of the mixes proposed, with the requirements of the cut-off wall to include limiting criteria for hydraulic permeability, vapour permeability and strength, over a 100 year design life. A limited number of field CSM trial panels were installed on a nearby site with similar stratigraphy, and a variety of mixes and mixing methodologies were used, together with the extraction of deep wet grabbed samples from the panels, which were tested for strength, hydraulic permeability and gas permeability. Test results obtained from these trials revealed a trend which allowed the construction methodology to be decided. Further to this, the mix design needed to be resolved, together with sensitivity analysis on the variations in the mix which might occur during construction, as a result of normal unavoidable variations in construction technique. Laboratory sampling would be used at lesser expense, to resolve the final mix design and analyse the sensitivity of the possible mix variations. An initial series of laboratory mixed samples were prepared using soil samples and groundwater obtained from the site, and testing carried out. However the test results in this initial series of laboratory tests could not match the results which had been achieved in the field trials. Closer scrutiny and investigation and rounds of sampling and testing, then revealed laboratory techniques for mixing and sampling which provided a logical way to match the actual field test results. CSM Construction is due to commence soon and will provide more extensive results which can be compared back to the laboratory trials. This project provides a valuable opportunity to resolve methods of laboratory sampling so that they compare well with results from in-situ deep mixing.INTRODUCTIONThe former chlor-alkali plant at Botany, NSW, which operated from 1945 until 2002, used mercury cell technology and brine solution to manufacture chlorine, caustic soda, hydrochloric acid, sodium hypochlorite and ferric chloride. Mercury contamination is present in the permeable alluvial soil profile beneath the site. The mercury is present in the form of elemental and inorganic mercury, together with dissolved methyl mercury in the groundwater and soil profile beneath the site and also down-gradient of the site, to depths of up to 25m. Residual clay and sandstone bedrock at approximately 25m depth are relatively impermeable and limit the contamination plume. A cap and contain approach has been recommended by consultants Golder Associates, and this involved a subsurface containment wall, or cutoff wall, to restrict groundwater ingress and egress, and lateral subsurface vapour migration. The cut-off wall is situated on the perimeter of the site, with a total length of 430m and passing through alluvial Botany Sands, with a nominal key into the underlying residual clay or sand stone at 20 to 25m depth. An HDPE liner insert was proposed for the upper 7m of wall above the water table, to further limit gas permeability."

Jan 1, 2015

By T. Banerjee, D. Felsher, G. Leavoy

"Lake Shore Gold is engaged in commercial gold production at both the Timmins West and Bell Creek mines, located in Timmins, Ontario. Run of mine ore is processed at the Bell Creek mill which consists of a conventional gold mill flow sheet involving crushing, grinding, gravity concentration and carbon-in-leach (CIL) for gold recovery. Since 2009, the operating capacity of the mill has been upgraded from 2000 tpd tonnes per day (tpd) to over 3,000 tpd. The most recent expansion involved the installation of a low aspect ratio SAG mill to replace the secondary crusher. Without operational data on the low aspect mill, combined with a site team that was new to SAG milling, there were many challenges in achieving the target throughput from the circuit. Through the implementation of AwaRE advanced controllers, running in closed loop with PRC fragmentation cameras as well as embedded PARC modules within the Allen Bradley PLC, the site was able to rapidly develop a best operating practise and has been successful in creating a stable and consistent operational environment. The process, lessons learned and eventual solution will be reviewed in this paper.INTRODUCTIONLake Shore Gold is engaged in commercial gold production at both the Timmins West and Bell Creek mines, located in Timmins, Ontario. Run of mine ore is processed at the Bell Creek mill which consists of a conventional gold mill flow sheet involving crushing, grinding, gravity concentration and carbon-in-leach (CIL) for gold recovery. Since 2009, the operating capacity of the mill has been upgraded from 2,000 tpd tonnes per day (tpd) to 3,150 tpd. The most recent expansion involved the installation of a low aspect ratio SAG mill to replace the secondary crusher. This endeavor was split into two phases: the expansion of the back-end (Phase 1) and the front-end (Phase 2) of the mill. Phase 1 of the expansion was completed at the end of 2012 and involved enhancements and capacity addition to the leaching and adsorption circuits, which increased the mill’s capacity to 2,500 tpd. Phase 2 of the expansion commenced at the end of July 2013 and involved the expansion of the crushing and grinding circuits. The expanded front-end of the mill now has a capacity of 5,500 tpd, and processes ore from both Bell Creek and Timmins West mines. The updated flow-sheet, as shown in Figure 1, illustrates the replacement of the two-stage crushing and ball milling circuit with a single stage crusher and a low aspect ratio SAG mill."

Jan 1, 2015