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By B Young

Variable bench heights, interaction with underground workings and a steeply dipping orebody are challenges faced daily by geologists at Xstrata Zinc’s Black Star Open Cut (BSOC) Zinc/Lead/Silver mine in Mount Isa, Queensland.BSOC has been in operation since late 2004 and was developed to extract the surface extents of the Zn/Pb/Ag mineralisation mined in the underground lead mine. To date many large scale stopes and extensive development drives have been intersected and successfully mined. The stratigraphically hosted orebodies strike in a north-north westerly direction, dipping ~75° west. Ore production from the pit is currently at 4.5 Mt/a.Historically, sampling was conducted using a multiple spear technique from blasthole cuttings. This method proved to be relatively reliable when blasting benches at a consistent height, but a requirement to vary bench heights to safely collapse and then mine through underground workings reduced sample representivity to unacceptable levels.The purchase and commissioning of a production rig which had been converted for reverse circulation (RC) has allowed for the flexibility of a small rig, with the capacity to easily drill 48 m holes while ensuring sample quality. Sample quality is not the only benefit of introducing RC grade control. By collecting grade control data well in advance, informed decisions can be made by planning, drill and blast and mining departments weeks beforehand, rather than hours before firing. Additionally, seeking operational value to offset higher drilling costs has proved positive with benefits including increased confidence in orebody wireframes, accurate tonnage and grade for proceeding five benches along with the ability to representatively test metallurgical response on a tight grid spacing.

Aug 22, 2011

By P Collier

From 1972 until 1989 when operations were suspended Bougainville Copper Limited (BCL, owned 53.58 per cent by Rio Tinto Limited) operated a large open pit mine and processing facility at Panguna on Bougainville Island, Papua New Guinea producing copper concentrate containing significant quantities of gold and silver.BCL has a stated vision of recommencing operations at Panguna. In 2008, Rio Tinto, on behalf of BCL, conducted a multi-disciplinary study to assess the technical and financial viability of redeveloping the Panguna operation. One of the key outputs of the study was a Joint Ore Reserves Committee (JORC) Code compliant mineral resource statement based on the existing block model and fundamental data, archived since mine closure. Historical data (including the resource block model and drill hole data) was recovered from computer archives by a former Panguna mine employee familiar with the various obsolete data formats, thus maintaining an unbroken chain of custody of the data by Rio Tinto since operations were suspended. No additional data were collected as part of this study.The extensive data and documentation archive facilitated a sufficiently detailed evaluation of the fundamental data and model to support an updated resource statement. Table 1 of the JORC Code was used to guide the model validation process.Reconciliation of blasthole and metallurgical plant data with the reserve model, indicated that the copper and gold drill hole composite database was significantly biased towards underestimation in several key domains due to a combination of the following: mineralisation loss during core loss, core loss (minor), vertical drill holes failing to intersect sufficient subvertical mineralised fractures and veins, drill hole spacing too wide, and variable diamond drill hole core size. The resource model evaluation was based on three material types (all previously mined at Panguna), that were defined based on cut-off grade and rock type parameters: direct feed ore – material for delivery directly to the plant, preconcentration and screening ore – subeconomic material beneficiated to produce fines of economic grade, and waste. Three pit shells and designs were generated based on three separate sets of economic parameters. These economic parameters were also used to assign material types to the block model. The three resulting models were then evaluated against the corresponding pit shells.Classification of the resource was approached conservatively due to the inherent bias in the drill hole data. Consequently only Indicated and Inferred resources were tabulated.The study highlighted the importance of maintaining detailed documentation pertaining to resource estimates and operational history, particularly reconciliation, and the value that can be added by a simple, low-cost data compilation exercise.

Aug 22, 2011

By V Pere

A geotechnical data management system has been developed to manage drillhole and mapping data generated from in house and consultant administered field programs. This system comprises a data collection interface with integrated validation, processing and reporting functionality. Development of the database required careful consideration of how and what geotechnical information is gathered in the field, a clear understanding of the interdependency of the parameters, and the outputs required to support geotechnical design.The acQuire Geoscientific Information Management System was selected as the preferred software to support the process because of its ability to easily manage data from capture in the field through to quality reviews and ultimately into reports. Initially only geotechnical logging of diamond core was considered, subsequently the system has been expanded to support additional geotechnical data sources such as laboratory test results, traverse and window mapping data. This paper focuses on the core logging data acquisition, validation, analysis and presentation of data.The acQuire Geoscientific Information Management System has proven to be a robust platform for the capture, interrogation, and reporting of geotechnical data. Data entry objects have been created to manage seven different areas of geotechnical data collection ranging from core logging to mapping to automated reports for falls of ground.

Aug 22, 2011

By S Juras

The terms measured resources and proven reserves denote the highest level of estimation confidence in all of the major classification schemes. But what do they really bring to today’s project or mine with respect to production planning and expectations? Initial reserve declaration does not need measured resources, just indicated resources. Economic viability of a project is assessed on total reserves with nary a bonus for the amount of proven reserves. Production plans are based on grade and tonnage goals that may only coincidently correspond to proven reserves. So are the measured and proven categories still relevant? Historically, and almost exclusively in underground mines, companies only allowed mining in areas of proven reserves. Some companies still follow that philosophy. But many others will mine a mixture of probable and proven reserves without hesitation. Also what of the undeveloped project in a new district – what is to be made of their declared measured resources and proven reserves? Measured resources are commonly set either by some type of proximity to data scheme or a matter of ‘feel’ based on the qualified person’s experience. The parameters for reserve conversion focus on the project as a whole and then a portion becomes classified as proven reserves almost solely based on whether the resource category is measured. So should the mining industry continue to use these categories of resource and reserve classification? This paper will present arguments about making these categories once again more relevant. A more disciplined usage of these categories may re-introduce their relevancy in public disclosures of resources and reserves. As well a more consistent usage in operations may lead to increased confidence in managing production targets and costs.

Aug 22, 2011

By S C. Dominy

Grade control programs aim to deliver economic tonnes to the mill via accurate definition of ore and waste. The foundation of a successful program is high quality sampling supported by geology and a suitable data management and modelling system. Underground sampling methods include chip, channel and panel samples; grab/muck pile samples; and drill-based samples. Grade control strategy is related to mining method and orebody type. Sampling protocols must be designed to suit the style of mineralisation in question. Holistic studies focussing on ore mineralogy and gold particle deportment, size and distribution are required for sample collection and preparation protocol optimisation through ‘Theory of Sampling’ application. Where possible, such programs should be undertaken early in the life of a project. Appropriate assaying procedures are also required. Program implementation will require suitably skilled individuals to train and mentor staff, with ongoing Quality Assurance/Quality Control (QA/QC) monitoring and review will allow protocols and staff to be updated as required.

Aug 22, 2011

By G Kirk

Definition and delineation of in-pit ore and waste material are the most significant tasks for an open pit production geologist; adding or destroying value in the mining value chain. Anglo American’s Mogalakwena Platinum mine, an open pit operation in South Africa moving 100 Mt/a, has recognised the value of improved material definition and is in the process of changing from blasthole to reverse circulation (RC) sampling for in-pit grade control. This is aimed at obtaining more representative samples, which are required to maximise ore recovery, minimise waste dilution and to increase the accuracy and confidence of production forecasts. Early in the project, it was realised that the key risks for implementing RC grade control were related to change management processes, rather than failure of technology. Recognising the importance of this issue, Mogalakwena chose an integrated implementation approach that incorporates all stakeholders of the mining cycle in order to develop a process that delivers maximum value and is sustainable within an active mining environment. The following core goals were addressed over five phases of project implementation: extensive definition and design of integrated project implementation, comprising: project buy-in and ownership from all key stakeholders, including survey, geology, mine planning, drill and blast, load and haul, maintenance, supply chain and finance; and detailed analysis of all potential issues and possible solutions, allocated to stakeholders as part of the scoping process; optimising hole patterns and drilling procedures, focusing on delivering maximum value for minimum cost using multiple scenario analysis from borehole data and operational sequencing requirements; and evaluation of lessons learnt during project implementation in order to optimise the technical solution and operational efficiencies. Although this project is not yet finalised, Mogalakwena Platinum Mine is already providing a blueprint for the effective development, implementation and optimisation of sustainable in-pit grade control RC drilling for other open pit mines within Anglo American plc.

Aug 22, 2011

By A Fowler

The unpredictability of the location, grade and width of narrow-vein deposits presents difficulties for mine geologists and engineers attempting to estimate, schedule, forecast and mine their deposit profitably. This unpredictability stems not only from the grade distribution within a vein, but also the irregularity of vein geometry in three-dimensional (3D) space. Traditional deterministic methods of modelling vein geometry do not account for the inherent variability of the veins, resulting in significant errors when using limited drill hole information. This paper presents a probabilistic method of modelling narrow-vein deposits using sequential gaussian simulation (SGS), which can quantify this variability and improve production forecasts. Vein geometry, thickness and grade are simulated to provide a number of different equi-probable realisations that each honour the drill hole and face sample input statistics. An example is presented from the Augusta narrow-vein Au-Sb mine in central Victoria, where the simulation results are validated against the input data and survey pick-ups of the veins along ore drives.

Aug 22, 2011

By T N. Little

The aim of any rock breaking activity is to achieve success by developing designs that are blasting objective-specific and geology-specific, and then implementing such designs. This paper targets mining geologists with the aim of extending their knowledge of the rock fragmentation processes and providing insights to the significant relationships between geology and blasting. There are two main relationships, and if mining geologists appreciate both these relationships, then they can play a key role in optimising production. The business risk continuum is introduced to support this understanding. The first relationship is between geology and potential blasting hazards, and the operational complexity required to manage those risks. The risks associated with eight different ground types are discussed in terms of ground conditions, hazards and controls. These types are: reactive ground, hot ground, geothermal ground, fibrous ground, cavernous ground, combustible ground, pyritic ground and conductive ground.The second relationship is between the bench geology and blasting results. The blasting results discussed include: muckpile characteristics, remaining rock faces and blasting emissions. In this regard, some detailed insights and graphical examples are given for the influence of geology on blasting emissions, in particular, vibration, airblast and flyrock.A detailed description of the geological materials themselves can convey much useful information for blasting operators provided they are able to utilise this knowledge. Geologists are ideally suited to provide this description more effectively if they are familiar with the blasting process and the rock mass properties that influence blasting hazards and blasting results. It is also important to have clear statements of blasting objectives and associated operational targets, and this will maximise the likelihood of achieving the desired outcomes. The main aim of the paper is to highlight that geology is currently not fully utilised in the blasting process. In this regard, geologists are often not entirely aware of the blasting process and how they can contribute. The two significant relationships discussed above are integral parts of this process, and thus they are discussed as separate issues in the main body of this investigation.

Aug 22, 2011

By B Reynolds

The process design for green- or brown-fields metallurgical plants typically starts with two fundamental elements: the detailed mass and energy balance and the plant flow availability. The detailed mass and energy balance is generally developed using process flow-sheet simulation software and represents the steady-state operation of the plant at normal operating conditions. The plant flow availability, also known as a range of other industry-specific terms such as ‘flow availability’ and ‘operating factor’, describes the ratio of plant production to the steady-state mass balance. These elements are then used together as the basis for equipment selection and design.Plant flow availability takes into account a myriad of production loss factors including planned and breakdown maintenance, feed availability and composition changes, variability in operational performance and the interaction of batch and continuous unit operations. The combined impact of these loss factors are complex and as such plant flow availability is usually derived using a top-down approach such as comparison to an existing operation, a group of similar operations or to an anecdotal ‘industry leading’ benchmark. These top-down approaches are fraught with risk however, as they cannot factor in changes to equipment selection, flow-sheet or plant operating philosophy, and can result in over-expenditure of scarce capital or shortfalls in plant production.The use of dynamic simulation to provide a bottom-up alternative to quantifying the plant flow availability in metallurgical plant design has been growing rapidly in recent years. It provides a technique to quantify the combined impact of the loss factors described here and a tool to support process design and equipment selection by facilitating a range of sensitivity and what-if analyses. This paper presents a case study of how dynamic simulation has recently been used to support the

Aug 8, 2011

By D Connelly

As the resources sector becomes tougher with rising costs and cyclical metal prices, mining companies need to continue to reduce their costs and do more with less. Many new resource projects fail to come in under or on budget based on Feasibility Studies. Particularly, capital expenditure (CAPEX) proves difficult to achieve for resource projects. A number of resource projects have failed because of aggressive plant CAPEX cost cutting resulting in projects with no surge capacity and are unable to achieve design throughput. In addition, the plants are not operable because of the omissions. In recent times many businesses have also experienced the "costs" of simply implementing aggressive operating "cost cutting” measures as a strategy for solving business performance problems. This paper looks at technology driven, employment related, luxury cuts, department cuts and restructuring cuts. In the past companies used an incremental approach based on the use of past budget information as an integral part of the budget construction process going forward. The use of performance reports and Management Information Systems (MIS) is examined along with the role of continuous improvement in achieving sensible cost cutting.

Aug 8, 2011

By J Canterford

Although we have access to a wide range of sophisticated process design and improvement tools in combination with a significant range of case studies, the mineral resource industry still manages to be plagued by the negative publicity surrounding operating plant failures because they were neither smart nor safe, together with proposed projects that fail at the first or second hurdle. The general public and the finance industry are generally totally uniformed about projects that ramp-up to name plate capacity on time and on budget and even more so when ahead of schedule and under budget. As the saying goes, good news does not cut the mustard.The following is a summary of the author’s sometimes jaundiced view about why metallurgical plants do not live up to their technical and commercial expectations. In no way should the summary be construed as a negative reflection on the skills of the metallurgical profession. Rather, it is to be taken as a positive acknowledgement of those skills and is intended to highlight some of the major considerations that need to be assessed as a potential project transforms into a sustainable technical and commercial reality.While a considerable portion of the summary is directed at developing hydrometallurgical flowsheets, the general principles are equally important to all aspects of extractive metallurgy.For convenience, the summary covers the following five basic discussion points – project, people, process, patents and politicians.

Aug 8, 2011

By R Bearman

The importance of crushers in the mining industry declined with the introduction and resultant dominance of AG and SAG based circuits, but the recent move to consider more energy efficient circuits has caused the industry to re-consider the role of crushers.Different types of comminution equipment have different efficiency in the way the energy is applied in the size reduction process. Because of the general trend towards more sustainable production processes and emission of carbon dioxide, energy use has become more important. To fully understand how crushers can contribute to optimising the energy application in comminution circuits, detailed models of process performance are required. Such models need to take into account the mechanical design factors and how the crusher performance changes in response to feed conditions, the control strategy utilised and the wear of the crusher liners.It is also critical to analyse the total circuit, not just the individual crushers. To fully understand the performance of the entire circuit, dynamic simulation should be applied. Without the holistic understanding of the total circuit and the incorporation of transient effects, the full circuit performance cannot be adequately determined and the true energy picture will not be quantified.Based on detailed mechanistic modelling of crushers by the authors and the application of dynamic simulation, the opportunities to optimise the use of crushers for energy efficiency are examined.

Aug 8, 2011

By M Griffiths

This paper outlines an approach to high solids slurry pipeline design with data generated from a closed pipe-loop test system. The pressure and flow rate data generated is used to develop a pseudo-shear diagram for the purposes of system design. Following this approach enables the design of a full pipe flow system maximising system life and reliability. The alternative free fall system is explained and the disadvantages highlighted.Environmental and social considerations are discussed; mainly water and land use, and how designing for high solids slurry pipeline systems can be used improve these aspects of a mining project.Also discussed is how the use of high solids slurry pipeline systems can help to mitigate the risk associated with surface tailings storage facility failure, with the Bulyanhulu project used as a positive example.

Aug 8, 2011

By A Bird

Gravity gold circuits have an important part in reducing operating costs and maximising recovery in modern gold plants where coarse gold is present in the ore body. The design and selection of equipment has a vital part in the overall effectiveness of the gravity gold circuit. There are a number of associated factors that need to be taken into consideration when selecting the most suitable equipment for gravity gold circuits including occupational health and safety, security and labour requirements. This paper is a case study that outlines the validation behind the design, selection of equipment and subsequent benefits of the recent upgrade of the gravity circuit at the Marvel Loch gold mine with the main component to the upgrade being the installation of a Consep Acacia Reactor. Since the upgrade there has been a significant increase in gravity recovery, which has reduced the amount of gold reporting to the leaching circuit therefore reducing reagent consumption and overall operating costs. There has been an increase in overall gold recovery and therefore increased gold production. The benefits to occupational health and safety include the removal of toxic gases being released in the gold room during the previous practice of gold concentrate calcination and the removal of the arsenic and nickel from the gold doré, which poses a risk during refining. Manual handling and security has improved as there is no physical contact with gold concentrates during the automated process using the Acacia reactor. The total time for gold room personnel working in the gold room has also reduced from around six hours per day to less than one hour per day.With the continuing development of low grade gold deposits, there will be an increase in demand for low capital, high recovery gravity gold circuits that can significantly increase overall production while reducing operating costs.

Aug 8, 2011

By T Arena

To maintain copper recoveries and maximise production at the Sepon Copper Operation it is crucial to control the amount of copper entering the leaching circuit. This requires close control of blending of the multiple ROM stockpiles to achieve the desired head grade. Grade variability in the ROM stockpiles can lead to significant variation in the processing plant copper feed grade.Head grade sampling from the milling circuit at Sepon is complicated due to milling in leach solution to preserve the water balance. Copper is present in both liquid and solid forms and copper in the added milling solution has to be accounted for. This leads to difficulties in manual head sampling which also introduces delays due to sample preparation and assay turnaround. On-stream analysis is complex because of the solution and solid copper and the need to account for recycled copper solution.This paper describes the complexity of feed grade management at Sepon and the application of on-belt analyser technology to assist in the control of copper metal throughput.

Aug 8, 2011

By J Wheeler

The objective of this paper is to examine the operation of high frequency screens in closed circuit grinding, where the outcomes achieved indicate favourable economic gains at the comminution stage and downstream processes, including flotation, dewatering, and filtration operations. The classification process in grinding circuits has been slowly evolving within the last century. The history of classification devices brings to mind rake classifiers and spiral classifiers, which although having higher efficiencies compared to hydrocyclones, were not able to keep pace with the evolution of concentrator equipment treating higher tonnages. This higher tonnage throughput has tended to drive the concept of utilising hydrocyclones as the classification stage in closed grinding circuits. The comminution process is commonly the most energy intensive stage of mineral processing. Researchers have determined that the classification stage in the comminution process has the greatest potential for improvement. This paper is intended to inform mineral process engineers of the benefits that high frequency screens offer over hydrocyclones. This will be done by reviewing the purpose for the evolution of classification in the comminution process, documenting past and recent studies, and explaining the modern technology that is currently available.

Aug 8, 2011

By P McCarthy

The relatively new field of geo-metallurgy promises to improve the predictability of mill feed quality and enhance processing outcomes. However, it is subject to the same limitations as the prediction of grade using geostatistics and has additional limitations due to the spatial distribution of the variations being measured and the sample sizes required. Schedules based on geo-metallurgical models will, in turn, be subject to variations arising from geological control and practical mining constraints.This paper discusses the key drivers of variations in mill feed quality and quantity from a mining perspective. It concludes that geo-metallurgical modelling addresses only one aspect of the problem. A case study is provided to illustrate poor predictability of metallurgical performance even with very detailed geological data.

Aug 8, 2011

By P Toor

Due to the high energy consumption of milling, it is desirable to improve the efficiency of this process. One alternative to reduce energy and material consumption while optimising production yield in mill operation is through balanced design and selection of liners. Over-design of liners leads to increased life but at a cost to grinding performance, a relationship which to date has not been studied closely. This paper provides a description of this process of liner life cycle optimization and presents initial results from the first of two life cycles being studied for a 32 foot (ft) SAG mill. The use of commercially proven high resolution laser scanning based liner shape information provided by the MillMapper® software correlated with well controlled site surveys at various points in the liner life was used as the basis for comparison. The survey data was modelled in JKSimMet to provide direct comparisons of mill performance. This potentially provides a methodology for the design of liners that maintain a favourable shape for the majority of liner life, yielding desirable production parameters such as lower specific energy consumption and higher throughput, while at the same time maintaining practical liner life cycles.

Aug 8, 2011

By P Bartsch

Uranium solvent extraction, USX has been applied commercially for recovery and concentration for over 50 years. Uranium in acidic liquor, which is prepared following ore leaching, solid/liquid separation and clarification, can be treated through a sequence of operations; extraction-scrubbing-stripping, to obtain purified liquor. USX has dominated the primary uranium industry as the preferred technological route to converter grade yellowcake. The practices of design and operation of USX facilities has found renewed interest as new mines are developed following decades of industry dormancy. This article seeks to outline principles of design and operation from the practitioner’s perspective. The discussion also reviews historical developments of USX applications and highlights recent innovations. This review is hoped to provide guidance for technical personnel who wish to learn more about good practices that leads to reliable USX performance.

Aug 8, 2011

By M A. Wells

The various mechanisms by which phosphorus (P) occurs and is distributed within banded iron formations (BIF)-derived iron ore are examined. In unenriched, precursor BIF P occurs predominantly as discrete grains of primary apatite. In high-grade ores hosted mainly by the Brockman Iron Formation, P occurs in three main forms:1. as secondary apatite;2. other submicron, P-rich phases (eg Rare earth containing minerals (REE), vivianite, strengite,wavellite) present in pore networks; and3. as P occurring with iron oxides, in particular, goethite.However, the presence of secondary P-bearing phases does not contribute signifi cantly to the total P level in iron ore, and it is P associated mainly with goethite, which represents the most common occurrence of P in these ores.No direct evidence for the replacement of Fe by P within the structure of synthetic goethite has been demonstrated. Therefore, it is most likely that in iron ores P associates with goethite in occluded form as adsorbed PO4 3- species or as discrete P-bearing minerals, such as strengite, wavellite or vivianite, in ultra-fine, micro-pores or within intra-domain regions of multi-domainic goethite. Such occluded P is not easily extracted with commonly used lixiviants, such as weakly alkaline leachates. Recent development of a low temperature-alkalie/water leach extraction method has been successful in reducing not only the P content, but also amounts of Si and Al inthe initial ore. Refi nement of such a method to commercial application will have enormous benefit in realising the economic potential of large tonnages of high-P (ie >0.07 wt per cent P) bearing iron ore.

Jul 11, 2011