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By A Kurniawan, A Sjadat and M Akhasyah

PT Freeport Indonesia’s Deep Ore Zone (DOZ) is a block cave mining operation that has been in production for 15 years. DOZ is located approximately 900 m below surface and has an average production rate of more than 5000 t/d. The footprint of the extraction level will ultimately be 900 m long and average more than 200 m wide. The undercut level is located 20 m above the extraction level.While developing Panel 1K on the northern portion of the extraction level, a major geotechnical problem was encountered when there was a change in lithology and an associated fault intersection. A large collapse of the hanging wall of the extraction level drifts occurred in the area of the fault intersection between February and March 2011. This was followed by a collapse of one of the undercut level drifts directly above the extraction level in May 2011.It was suggested that the best approach to mitigate risk during rehabilitation was to systematically open up the failed area under the protection of a steel set support system. To achieve this, approximately 60 t of grout was injected from the undercut level to fill the voids created when the rock mass between the two levels failed. A ground penetrating radar system was used to survey the condition of the rock mass between the two levels before and after the injection of grout. After the grout injection phase was completed to a satisfactory level of confidence, rehabilitation activities started on the extraction level by taking out the now consolidated material from inside the drift in 2 m advances from under steel sets initially constructed in secured ground.Controlled blasting was the key aspect to the success of the initiative to open up just enough of the drift to systematically support the rock mass before the next set was installed. The systematic support consisted of in-cycle shotcrete sprayed over mesh pinned to the exposed rock, as effectively as possible, with splitsets before spiling the next advance’s protection canopy with rebar. Once secure, a combination of steel set and pumped concrete was installed as the final support. This final support provided a safe platform to repeat the process until the failed zone was safely traversed.CITATION:Kurniawan, A, Sjadat, A and Akhasyah, M, 2016. Rehabilitation of the collapsed panel 1K north in the Deep Ore Zone block cave mine, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 763–768 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By A T. Yuniar, C A. Brannon, N D. Pascoe, H H. Firdausi

This paper describes the key components of the Grasberg Block Cave (GBC) mine design and the development and construction status of the mine. Drawpoint production from GBC will be initiated in 2018 following the closure of the Grasberg open pit. Full production of 160 000 t/d is planned for 2024, which will make it a 20-year time period between initial access development in 2004 and full production.Diluted ore reserves are about 1 Bt at a grade of 1.0 per cent Cu and 0.78 g/t Au. The mine plans some 2400 drawpoints on a 20 m × 30 m drawbell spacing in a 700 000 m2 footprint using the El Teniente layout. The drawpoint opening sequence includes five production blocks, the first two of which are scheduled to be undercut simultaneously in 2018. Ore is transported using diesel-powered load-haul-dumps to a series of orepasses and then delivered via loading chutes to a rail haulage system, which delivers the ore to a three gyratory crusher complex. Crushed ore is transported to the mill stockpiles via dual inclined conveyors.Development and construction of the substantial fixed facilities are now well underway. Primary access for personnel and materials is via the 6 km Ali Boediardjo (AB) adits. A service shaft will hoist personnel and materials from the AB adits level to the various operating levels. Shaft commissioning is scheduled for late 2015. The rail haulage system installation and construction is in progress and is due to be commissioned in 2017, which is timed to coincide with the commissioning of the ore handling system. Ventilation is provided through a series of large intake and exhaust drifts, and two of the four main fans have been commissioned. A 1600 L/s pumping system will manage drainage from the mine.Other key facilities include separate shops for rail and rubber-tired equipment, warehousing, a powder magazine, a main control centre and an underground concrete batch plant.CITATION:Brannon, C A, Firdausi, H H, Pascoe, N D and Yuniar, A T, 2016. Development and construction update of the Grasberg block cave mine, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 625–634 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By A Gustafson, D Johansson, K Jonsson

The underground mining process, from in situ characteristics of the unmined rock mass to the final mill product with fully liberated minerals, consists of a chain of unit operations. Some of them influence fragmentation while fragmentation impacts others. From a production point of view, fragmentation is a key parameter for the proper functioning of many unit operations and affects total production; it influences the ability to load, haul and crush the rock later in the process. Fragmentation varies because of rock mass strength, the presence of joints, the chosen explosive, specific charge (kg/m3) and quality of drill holes. The efficiency and result of unit operations such as drilling, blasting, loading and crushing depend on the rock properties, which vary throughout a mine. Generally speaking, operations are not well adapted to the actual rock properties, leading to a non-optimised flow in production. This paper presents the initial part of a project that will build knowledge on the impact of fragmentation on each step of the production chain in an underground mine. It identifies the key parameters of fragmentation, which influence the overall energy consumption and productivity in a mining operation through interviews, mine visits and a literature review. In the subsequent stages of the project, a number of field tests in the case study mine will address important segments of the production process where fragmentation is a major obstacle to improvements. Optimising the entire process, rather than isolated unit operations, will lead to increased productivity, decreased amount of interruptions and lower energy consumption.CITATION:Gustafson, A, Jonsson, K, Johansson, D and Schunnesson, H, 2016. From face to surface – a fragmentation study, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 555–562 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By K A. Bunker, A D. Campbell, E Ah Mu, A R. Penney

The Ernest Henry mine is a transverse sublevel cave (SLC), which is relatively unique due to the 45 degree inclination of the orebody. To economically recover ore, each sublevel is horizontally offset from the previous level by around 25 m, depending on the orebody geometry. Mine development, slotting and initial production within this zone occurs in a high stress abutment that increases in magnitude at depth. These areas are seismically active and close to the hanging wall where cave propagation is yet to initiate. High stress conditions and the close proximity to the cave seismogenic zone results in challenging geotechnical conditions in the step out zone of each level and requires management of hazards including stress driven rockfalls, rock bursts and pillar failure.This paper outlines how these hazards were forecast using numerical modelling and geotechnical monitoring. Risk management techniques included dynamic ground support design, development of a new mine layout and extraction sequence as well as delayed re-entry into seismically active areas. Ongoing monitoring, instrumentation measurements and field observations were used to track the effectiveness of the controls.Future production levels are forecast to experience increasing stress and seismicity, which will increase demand on excavations and installed ground support. Ensuring the techniques and controls for monitoring, measuring and mitigating stress and seismic hazards are enforced is essential for continued safe production.CITATION:Campbell, A D, Bunker, K A, Ah Mu, E and Penney, A R, 2016. Managing stress and seismicity in an inclined sublevel cave, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 319–328 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By A Gustafson, G Shekhar, P Boeg-Jensen

The amount of material extracted from each blasted ring in sublevel caving mines is vital when deciding the overall mine production target. The orientation of the production drifts is normally perpendicular to the strike of the orebody, and rings are blasted from the hanging wall side to the footwall side in a retreating manner. For an inclined orebody, a given ring will contain different amounts of material based on its relative position along the production drift. This layout creates a distinctive problem with respect to the extraction ratio optimisation along the axis of the production drift. This paper describes the current drawpoint control strategy practiced at LKAB and presents the variation of drawpoint performance parameters along the production drifts. It uses automatically generated data from a bucket weighing system that measures tonnage drawn per bucket, and it classifies the blasted rings into four zones based on their relative position along the production drift. It considers the loading procedure for blasted rings at Kiirunavaara mine and analyses the variations in drawpoint performance along the production drift. The paper finds that although the current draw control strategy is sensitive to ring position along the drift, it could be modified to optimise the final extraction ratio.CITATION:Shekhar, G, Gustafson, A, Boeg-Jensen, P and Schunnesson, H, 2016. Draw control optimisation along the production drift in sublevel caving mines, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 241–250 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By E Ah Mu and C R Lilley, A D. Campbell

Cave propagation is a complex process due to interacting variables such as mine geometry, rock mass heterogeneity and complex structural networks and stress fields. The Ernest Henry sublevel cave (SLC) is directly below an open pit, which provided an opportunity to observe and measure rock mass failure as the cave initiated and propagated through the pit wall. This paper describes interaction between the open pit and SLC as well as rock mass failure mechanisms observed from the start of the SLC to surface breakthrough.Cave propagation and slope failure mechanisms were found to be governed by intermediate structures, while the cave shape was largely controlled by cave-scale faults. The open pit, production-level geometry and production draw strategy were also important factors for cave and subsidence growth. Cave propagation was episodic and asymmetric in shape due to the orientation and relative position of geological structures, combined with the effects of the increasing SLC geometry and drawdown from the underlying production levels. The precursors and failure mechanism of a 2.5 Mt wall collapse are also reviewed in detail.Cave growth was simulated using a 3D, non-linear, discontinuum finite element model coupled with Newtonian Cellular Automata. Model results are compared to field observations and monitoring data to determine the accuracy of forecasts and compared models versus actual rock mass response during cave propagation.CITATION:Campbell, A D, Ah Mu, E and Lilley, C R, 2016. Cave propagation and open pit interaction at the Ernest Henry Mine, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 311–318 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By B Mobilio, M Secheny, J Rachocki, G B. Sharrock, A Jäger, J L. Lett, I Brunton, G W. Capes

Establishment of the Cadia East Panel Cave Stage One (PC1S1) commenced with the firing of the first bell in early 2011. Production began with the completion of the undercut in May 2014. PC1S1 used a post-undercut composed of 114 drawbells covering a footprint area of 73 438 m². The extraction level is located at a depth of 1200 m below the surface and is based on a 32 × 20 m El Teniente layout. Cave establishment required the construction of multiple conveyor drifts, a large-capacity jaw-gyratory crusher and ancillary ventilation and pumping infrastructure. Preconditioning via hydraulic fracturing and blasting was implemented at various locations of the cave block height. This paper presents an overview of the key learnings from the commencement of undercutting to surface breakthrough, including rock mass classification and modelling, stress measurements, preconditioning, numerical modelling and cave monitoring.CITATION:Lett, J L, Brunton, I, Capes, G W, Jäger, A, Mobilio, B, Rachocki, J, Sharrock, G B and Secheny, M, 2016. Undercutting to surface breakthrough – Cadia East panel cave (stage 1), in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 65–82 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By L Olivier, R J. Lowther, J L. Lett, I Brunton

Hydraulic fracturing to precondition the orebody to enhance rock mass cavability is gaining acceptance in underground cave mining applications. Assisting cavability is becoming important as an increasing number of cave mines are being implemented in hard, deep and competent rock masses where clamping stresses are higher and cave column heights may be in excess of 1000 m. Propagating large caves to surface in such conditions can be challenging as risks such as slowed propagation and air gaps can develop during the process.Underground-based hydraulic fracturing is routinely used at Cadia East as a means of preconditioning the orebody to assist in cave propagation, fragmentation and seismicity reduction. This paper presents a summary of a surface-based hydraulic fracture program that was successfully implemented to assist in the propagation of the Cadia East Panel Cave 1 (CE-PC1) cave to surface through competent overlying rock masses. In this case study, the propagation of the CE-PC1 cave slowed as the cave grew past 750 m in height, initiating a Trigger Action Response Plan regarding the cave propagation rate. Surface-based hydraulic fracturing was subsequently used to stimulate the cave to propagate through the final 450 m to surface. The paper details the equipment, strategy, implementation and risk management involved in the program as well as the key learnings.CITATION:Lowther, R J, Olivier, L, Lett, J L and Brunton, I, 2016. Implementation of a surface-based hydraulic fracturing program to successfully propagate a large cave through hard, competent near-surface rock masses to achieve breakthrough, in Proceedings Seventh International Conference and Exhibition on Mass Mining (MassMin 2016), pp 83–96 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 9, 2016

By J. A. Ober

"In 2015, the estimated value of nonfuel mineral production in the United States decreased by 3 percent from that in 2014 (Table 1), mainly as a result of decreased metal and metallic mineral prices, especially iron ore, copper and precious metals. Lower metal prices were attributed to decreased consumption, especially in China and increased global inventories. Several U.S. metal mines were idled in 2015, including the only U.S. rare earths mine at Mountain Pass, CA. Downstream processors also were affected, with smelters and refiners either shutting down or idling production lines. Increases, however, took place in the value and quantity of production of industrial minerals, especially those used in the construction sector, including cement, construction sand and gravel and crushed stone. Trends in mineral-related sectors of the domestic economy, except for iron and steel manufacturing, aluminum manufacturing, coal mining and metals mining, all experienced growth (Table 2).Discussion of mine production is frequently segmented according to the type of materials produced within the broad categories of metals and industrial minerals (also known as nonmetallic minerals). Industrial minerals can be further subdivided as construction aggregates and other industrial minerals. Metals tend to have higher unit values but very low production quantities compared with those of industrial minerals, which have higher production quantities but are lower-valued materials, such as crushed stone or construction sand and gravel. Therefore, for discussion and analysis of the performance of the nonfuel minerals industry, the value of production is used rather than the tonnage produced. Tonnages of construction aggregates are orders of magnitude larger than those for most other mineral commodities thus making direct comparisons based on weight meaningless (Fig. 1).Mineral industry performanceThe estimated value of domestic nonfuel mineral production, including metals ($26.6 billion) and industrial minerals ($51.7 billion), in 2015 declined to a total of $78.3 billion, from $80.8 billion in 2014 (Table 1). However, as shown in Fig. 2, minerals remained fundamental to the United States economy, contributing to the real gross domestic product at several levels, including mining, processing and manufacturing finished products. Net exports of mineral raw materials and old scrap were $14.4 billion. Domestic raw materials, along with domestically recycled materials, were used to produce mineral materials worth $630 billion. These mineral materials, including aluminum, brick, copper, fertilizers and steel, and net imports of processed materials (worth about $32 billion) were, in turn, consumed by downstream industries with a value added to the gross domestic product estimated to be $2,490 billion."

May 1, 2016

By J. Kemeny, J. Lyons-Baral

"Point cloud technology is now an indispensable tool in geological and geotechnical data collection, interpretation and analysis. Open-pit and underground mines of all sizes are regularly collecting point cloud data as laser scanning (LiDAR) and photogrammetry surveying devices have become affordable and the workflows fast and efficient. Past challenges of large data processing and manipulation are gone with recent technological advancements in computer hardware and software. These innovations reduce file sizes, ease rendering requirements and allow for the implementation of real-time 3D viewers and surface meshing tools. With its ability to remotely and safely, rapidly and accurately extract large quantities of georeferenced and 3D-oriented data, point cloud technology provides numerous applications to the geomechanical field. The list of uses is continuously growing. This article specifically focuses on digital outcrop modeling and digital terrain engineering. Point clouds. The high-resolution and increasing availability of point cloud technology is rapidly improving open-pit and underground mines’ investigation, interpretation and characterization of site geology and rock mass properties (Kemeny et al., 2015; Lyons-Baral, 2012). LiDAR and photogrammetry are common remote sensing methods employed to measure the coordinates of surfaces in three dimensions (3D), providing the X, Y and Z locations and typically the reflective intensity and/or the visible three-band color of each point (Fig. 1).LiDAR uses either a time-of-flight or phase-shift measurement of a laser beam reflected off targeted surfaces and received back into the device.Photogrammetry generates point clouds by merging multiple overlapping photographs and uses stereographic plotting to define the locations of object points in 3D space. These methods can be deployed from airplanes, unpiloted aerial systems (UAS or drones), tripods, land vehicles and even in a mobile backpack shown in Fig. 2. RADAR, Total Station-Prism and other remote sensing systems also offer very precise “point clouds,” but this article does not address these due to their higher cost and lower versatility and mobility."

May 1, 2016

By Alberto Ríos Carranza

El presente texto describe la evolución de la cuenca Lancones (Piura) y sus estilos de mineralización en la búsqueda de yacimientos vulcogénicos de sulfuros masivos. Dada las características de la cuenca es considerada el principal objetivo en la prospección de yacimientos vulcagénicos de sulfuros masivos. Así también se revisa el contexto geotécnico, geológico, metalogenia, depósitos magmáticos - hidrometales, tipo Skarn, y vetiformes, estratigrafía y modelo metalogénico.

May 1, 2016

"In the conceptual stages of engineering, benchmarking and empirical ratios are commonly the only references for estimating the production rate of greenfield projects. For underground mining projects, the lack of similar cases often makes the comparison difficult due to each project’s unique geology, rock quality or other singular characteristic. This paper discusses an analytical alternative for determining the maximum achievable production rate for underground stoping mining by modeling production as a continuous process. The results show that long-term maximum capacity depends exclusively on the achievable development rate and the development intensity of the design. In operations constrained by backfill, the development rate could be limited by the backfilling rate. Extraction rate and stope size only have impacts on capacity estimates during the ramp-up period.These findings allow shaping of the maximum capacity profile of a project. They can be used as a tool for quick assessment of conceptual capacities, and sensitivities of mining rates. Benchmarking tests compared favorably with projects, mines in operation and scheduling exercises. IntroductionA key consideration in the value proposition of a mining project is its capacity or production rate (Tatman, 2001). At a conceptual level, it is common practice to refer to empirical references (Taylor, 1986; Long, 2009), rules of thumb (de la Vergne, 2014), benchmark ing studies or consultant experience to estimate or validate a target value. There is, however, a lack of analytical methodology to guide an early estimate of the maximum capacity.Araneda and Gaete (2004) presented an interesting mathematical approach to estimate the capacity of panel caving mines. Using a continuous model, they confirmed that the mine capacity is essentially determined by the rate of area incorporation, in terms of area per period, and ore column height. This simple relationship has been confirmed by multiple detailed scheduling works"

May 1, 2016

By Georgene Renner, Chee Theng, William Gleason

"More than 6,300 people attended SME’s 2016 Annual Conference & Expo in Phoenix, AZ and many of them made the trip to the conference to take part in the excellent technical sessions that are presented on a yearly basis by the Society.Holding true to form, this year’s conference was full of options. In fact, this year there were 121 technical sessions and 751 presentations to chose from. The following is a sample of some of the technical sessions as seen through the eyes of the editors of Mining Engineering and SME technical papers.SME Sections Sharing Success: Changing thePublic Perception of MiningThis session was a workshop on how several local sections were effective in getting the message out to their communities and schools about the value of the extractive minerals industry. Several sections shared their outreach successes, including the Mining in Society merit badge activities by the Minnesota Section by Julie Lucas and SME’s participation in the World Scout Jamboree in Japan by Frank McAllister.Dan Alexander highlighted activities by the Pittsburgh Section, such as preparing minerals kits and pamphlets for elementary school classes and regional science fairs. The West Virginia University Student Chapter used the kits as handouts at their local gem and mineral show. School speakers in full mining gear were especially interesting to the young children.Other speakers were Michael Linn, Paradise Valley Unified School District — Business and School Partnerships; and Greg Kruse, Central Wyoming Section of SME — What makes a successful section?Engineering Competency ModelAmerican Association of Engineering Societies and the U.S. Department of Labor, with a grant from the United Engineering Foundation, developed a guide to the set of skills necessary for success in the engineering community -- Knowledge – Skills – Abilities — needed for all disciplines.Various engineering societies are now writing the Tier 5 occupation-specific requirements. The Competency Committee is charged to write concise and discipline-specific mining engineering, mineral processing engineering, geological engineering, and geophysical engineering by Sept. 30, 2017."

May 1, 2016

By T. R. Ellis

"In August 2013, the Appraisal Practices Board of the U.S. Appraisal Foundation issued its “APB Valuation Advisory #4 - Identifying Comparable Properties,” which contains analysis and examples that may suggest a broader meaning of the term “comparable properties” than is current convention in real property value appraisal in the United States and internationally. The advisory is directed at the appraisal of real property of all kinds, including interests in mineral properties, as indicated by the inclusion of two mineral property appraisal papers in the appendix that lists suggestions for further reading.This paper firstly reviews as background the historical meaning of a comparable property, with its perceived constraints, against real-world examples of transacted mineral properties that are adjusted to subject properties to provide market value indications. The advisory’s findings are then examined and evaluated as to whether they may influence and benefit the work of mineral property appraisers, particularly in situations where their sales comparison analyses may be challenged. The conclusion is that the combination of constraints that the advisory’s findings specify for use of the term “comparable” will for mineral properties be met infrequently or rarely. As a result, mineral property appraisers are advised to avoid using the terms comparable or “comp” when referring to transactions of mineral properties that they analyze to derive data for appraising the value of their subject mineral properties. IntroductionA mineral property appraiser rarely finds a sale of a mineral property that meets the literal meaning of the term “comparable sale,” by being directly comparable to the subject property of the appraisal in all factors of significance in the determination of the value of the property interest being appraised. Real estate appraisers have long used a more liberal interpretation of the meaning of comparable sale and its commonly used abbreviation, “comp.” Real estate appraisers compare sales to their subject property on the basis of price per hectare or acre of land and price per square meter or square foot of building floor area. Adjustments totaling to within the range of +30 to -30 percent from the sale property to the subject, before factoring in the property area, have generally been viewed as appropriate for the sale to be considered a comparable sale."

May 1, 2016

By Levi Guzmán

"La molienda representa la etapa donde suceden los principales costos en la operación y de una planta concentradora (energía y medios de molienda). Por ello, los esfuerzos en la optimización de esta repercutirán en los resultados financieros de la empresa. En ese sentido, el presente texto señala la optimización el efecto del collar de bolas como elemento importante de la molienda donde a través de una metodología de caracterización se puede determinar la función selección específica para cada collar de bolas y así establecer, en base a los parámetros de las funciones selección y fractura y las simulaciones, el collar óptimo de bolas a emplear. Así también, se presentan los beneficios obtenidos en el proceso producto de la optimización del collar de bolas."

Apr 1, 2016

By Julio Bonelli Arenas

"El presente artículo señala una metodología de caracterización de minerales de plata que busca separar las fases mineralógicas predominantes de una muestra e identificar las especies minerales en dichas subfases. Luego se necesita completar el balance y la distribución de plata para conocer su comportamiento cinético de respuesta, a diferentes sistemas lixiviantes, de forma que se puede obtener una respuesta integrada de la muestra original al sistema hidrometalúrgico. De otro lado, se comparan las tecnologías innovadas que constituyen el estado del arte en la recuperación de plata, a fin de beneficiar minerales refractarios, residuos de lixiviación y otros materiales mineros donde esté presente la plata metálica y otras especies mineralógicas de este mineral. "

Apr 1, 2016

By P. B. Moran, J. W. Rozelle, J. Forbort

"The Mount Todd gold mine is located approximately 50 km (31 miles) north of the town of Katherine in the Northern Territory (NT) of Australia just off the Stewart Highway, and was operated in the 1990s until 2000 (Fig. 1). After cessation of mining operations, meteoric precipitation and acid rock drainage (ARD) associated with surface water runoff continued to report to the retention ponds across the mine site. In 2000, the mine site entered receivership and the NT government became responsible for the care and maintenance program. In 2006, Vista Gold Corp. (as Vista Gold Australia) acquired the rights to resume exploration on the mine site without the financial responsibility of the environmental liability. In January 2007, Vista Gold assumed the care and maintenance activities on behalf of the NT government, with the environmental liability remaining with the NT government, with the goal of reinitiating mining operations. A critical path component of the planned upgrades to the existing mine/milling facilities and infrastructure was the development of a cost effective treatment and dewatering program for the approximately 11 GL (2,900 million gal) of ARD stored in the Batman Pit (RP3), which has a maximum capacity of approximately 12 GL (3,200 million gal). The Batman Pit must be dewatered in order for Vista Gold to restart mining activities. The Batman Pit Lake had reached a maximum water depth of 104 m (341 ft) when Vista Gold initiated water level monitoring. It is important to note that the ARD water in the Batman Pit has been pumped into it from 2000 to 2012 under an NT government-approved environmental control program.The Batman Pit has virtually no connection to the local ground water regime due to the intensive silicification that accompanied the mineralizing event. In October 2012, just prior to treatment, the pit lake profile was characterized by uniform acidic pH (approximately pH 3.2) and oxic conditions (dissolved oxygen greater than 7 mg/L with depth (Fig. 2). The temperature decreased by approximately 4 °C (39 °F) between the lake surface and approximately 20 m (66 ft) deep, and remained near constant with increasing depth. This temperature difference is believed to be associated with an existing shallow mine bench at approximately 20 m (66 ft) deep around the perimeter of the pit. Similarly, electrical conductivity, an estimate of total dissolved solids, decreased by about 85 microSiemens per centimeter (µS/cm) from 2,800 to 2,715 µS/cm between 10 and 20 m (33 and 66 ft)."

Apr 1, 2016

By Howard Lum, Sergio Valles, John Bednarski, Gordon Enas, Jay Arabshahi

"Water drawn from the Sacramento-San Joaquin Delta provides water supply to 66 percent of California’s population and supports the state’s agriculture industry. The existing through-Delta water system is outdated and unreliable with environmental risk to some fish and wildlife species. The Bay-Delta Conservation Plan (BDCP) has been established to environmentally retrofit and modernize California’s water delivery system through the Delta by restoring habitats, constructing new diversion points in the north Delta and providing a means to transport water supplies under the Delta, rather than through sensitive natural channels.Under BDCP, the Delta Habitat Conservation and Conveyance Program (DHCCP) has developed several alternatives to convey water from the Sacramento River in the north to the existing pumping facilities in the south Delta through an isolated conveyance system. The new conveyance system would become an integral part of the State Water Project (SWP) and the federal Central Valley Project (CVP) by transporting water to the export pumping plants for each of these projects. The DHCCP is managed by the California Department of Water Resources (DWR), while state and federal water contractors provide technical support to the program.The initial conceptual study efforts on the overall program commenced in 2007 and examined various options for the proposed conveyance system. Several conveyance alternatives were analyzed at that time. The Conceptual Engineering Report published on Oct. 1, 2013 identified the modified pipeline/tunnel option (MPTO) as the preferred alternative to be included in the BDCP environmental documents. MPTO includes three river intakes and pump stations along the Sacramento River, various sizes of pipelines and tunnels, junction structures and two forebays that are capable of delivering up to 4 million gpm (9,000 cfs) from the Sacramento River to the SWP and CVP. The river intakes are located near Hood in Sacramento County approximately 64 km (40 miles) from Clifton Court Forebay (CCF) in Contra Costa County. This route would cross portions of Sacramento, San Joaquin and Contra Costa counties. Figure 1 depicts the configuration of the MPTO alternative."

Apr 1, 2016

By Todd Schrauf, James Scott, Mark Smith

"Cyanide heap leaching of gold ores in areas with extremely low winter temperatures requires special considerations to prevent freezing of the leach solution. Factors that impact the solution temperature include ore temperature at the time of stacking and during operation, burial of drip irrigation lines, use of geomembrane covers and heating of the leach solution. Thermodynamic modeling was performed to simulate expected ore and solution temperatures under different operating strategies for Kaminak Gold’s Coffee gold project in the Yukon Territory. Mean monthly temperatures at the site ranged from a low of -22.5 °C (-8.5 °F) to a high of 13.6 °C (56.4 °F), while in situ ore temperatures ranged from -0.5° to about -1.5 °C (31 ° to 29 °F). The modeling results were used to optimize the operational parameters and indicated that a combination of drip line burial and heating of the leach solution during the winter months was required to maintain solution temperatures above freezing during the initial years of stacking, although as the size of the heap increased, heating was no longer necessary.Modeling objectivesThe successful operation of a cyanide heap leach under extremely cold winter temperatures requires the implementation of operational strategies to prevent freezing of the leach solution and the ore within the heap. Thermodynamic modeling of the heap provides the means to quantify the effectiveness of these different operational parameters on maintaining the required operating temperatures to avoid freezing within the heap. The operational parameters that were evaluated with the model included:"

Apr 1, 2016

By N Cusworth, W R. Mackenzie

"In 2007, the authors presented a framework for the conduct of resource project feasibility studies and provided guidance on minimum standards and best practice (Mackenzie and Cusworth, 2007).This paper will present the authors’ observations in relation to feasibility studies undertaken to support investments made during the unprecedented period of resource project capital investment since 2007. It will also provide comments on general trends in the mining industry’s approach to project assessment and update recommendations on best practice.CITATION:Mackenzie, W R and Cusworth, N, 2016. The use and abuse of feasibility studies – has anything changed?, in Proceedings Project Evaluation 2016, pp 133–148 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Mar 8, 2016