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By E J. Coyle, L A. Millington

Tailings storage facilities are geotechnically complicated structures that develop heterogeneous strength profiles and varied porewater conditions. The monitoring of porewater pressures is one of the only direct measurements that can be performed to monitor the performance of a facility throughout its life and is of particular importance in upstream facilities. Foundation underdrainage, continuous and staged tailings deposition, climate inputs (rain, snow, humidity, evaporation, etc), and stratified tailings permeabilities can complicate this critical measurement that introduces uncertainty to stability analyses. These difficult conditions manifest in vibrating wire piezometer measurements as very low or negative pressure readings, both of which are within the instrument’s range of accuracy. However, the data can be difficult to interpret, and a range of interpretations are adopted from optimistic low phreatic surfaces to conservative fully saturated tailings. Where tailings are potentially liquefiable, these very low readings introduce further uncertainty regarding the pore space saturation ratio and liquefaction potential above the estimated phreatic surface. This area of uncertainty is the vadose zone, and its affect on tailings behaviour is not well understood. The two facilities analysed in this paper are upstream, raised embankments with tailings classified as clayey, sandy silt that have been found to be potentially liquefiable. The vibrating wire piezometers (VWP) at both sites show very low or negative readings when they are initially installed near the surface and then go through cycles of re-saturation and de-saturation. Eventually the readings settle as the VWPs are buried deeper within the tailings. The instrumented sections within the tailings column do not show consistent readings that would be indicative of a hydrostatic phreatic surface at either site. Rather, they are highly variable and can be interpreted as either representing a high phreatic surface within the tailings or as a ‘perched’ phreatic zone within the tailings layers. How the VWP data is interpreted has a significant impact on how the facilities are raised and operated. The design outcome for Site 1, which adopts a lower phreatic surface, results in an embankment that meets factor of safety (FoS) requirements under residual strength conditions without any buttressing. Conversely, a conservative (high) phreatic surface has been adopted for Site 2 and has resulted in the facility requiring a significant buttress to meet FoS under residual strength conditions.

Jul 1, 2021

By T O&apos, Sullivan

Reconciliation of metal production from a sublevel cave (SLC) mining operation is a complicated process. SLC reconciliation is unlike reconciliation for open stope operations, where a tonnage of extracted ore can be assigned to an exact volume of in situ ore, and a direct comparison made between the estimation of contained metal and actual metal production. In SLC operations the ore extracted from a particular SLC drawpoint will be composed in part from the parcel of freshly blasted in situ material, in part from varying components of ore material (from cave stocks) flowing down from other previously mined areas vertically above the current draw position and in part from external dilution. This leads to difficulties in reconciling production grades against estimated grades. The problem is that we know how much metal we have produced but we can not precisely say where it has come from. Metal production reconciliation is fundamental in assessing ore reserve estimation accuracy and performance and in determining a draw management strategy for SLC mining. In terms of contained metal, differences in extracted metal compared to in situ metal represent changes to cave stocks. To generate local estimates of the cave stocks, differences in metal for each ring are treated as additions to or subtractions from a series of vertical columns of stocks extending throughout the height of the cave. The sum of metal differences (extracted versus in situ) for each vertical column results in a residual metal map at any particular mining level. The metal maps show areas where the metal production has been greater than or less than expected. The maps also highlight areas in the cave where residual metal is located, areas where targeted overdraw can reduce cave stocks.

Jan 1, 2006

By M Nehring, M Kizil, P Knights, A Mousavi, F Sotoudeh

A cut-off grade is used to distinguish an economically viable block of ore from non-economical ones in mining operations. In order to obtain a high Net Present Value (NPV), a strategic and precise determination of cut-off grades (mill feed/marginal, marginal/waste) is required. In recent years, the significant depletion of feed grades and increasing mining operating costs have affected the viability of new and existing mining operations. Hence, the introduction of a pre-concentration system to process ore before sending it the main processing plant has gained increasing attention for its potential improvements in resource exploitation processes, mineral processing, energy consumption and environmental impacts. The primary potential advantage of implementing a pre-concentration system is the improvement of resource utilisation and increased reserves as a result of a reduction in cut-off grade. The objective of this paper is to present a new cut-off grade method, which can be used in the presence of a pre-concentration system for underground metalliferous mining operations. The results of this study illustrate the potential economic benefits of using a pre-concertation system prior to a mineral processing operation as a result of the reduced cut-off grade and increased NPV.

Nov 10, 2020

By B Stump

Reliable particle size analysis in minerals processing plants is a critical factor to the economic return of a plant. As recovery of valuable minerals is compromised for particles outside the optimal size range, effective and reliable particle size analysis is more crucial than ever, particularly in the current upswing of the global commodities market. Inefficient particle size analysis can lead to excessive over-grinding, thereby significantly increasing energy consumption and reagent costs, whilst negatively affecting process operation, thickening capacity, water recovery and tailings disposal.Australia’s first installation of a particle size analyser in Iron Ore has been monitored with great interest by the industry. Previously, manual size sampling at Rio Tinto’s Paraburdoo fines processing plant involved off-site sample analysis, with a turnaround measured in days. The Outotec PSI® 500 particle size indicator, commissioned in July 2009, takes approximately three minutes per line at site.The paper will include details on the following:• plant description,• sampling design,• PSI® 500 analyser functionality description, and• key learnings from site.

Jul 11, 2011

By M Gasparon, J Harris, T Baumgartl, D J. Williams, M Edraki, P A. Kirsch, D Rowe

RISKGATE, an Australian Coal Association Research Program-funded (ACARP) initiative, has been designed to assist the Australian coal mining industry in improving minimum standards for safety performance, efficiency, operating practice and training. The online system is innovative in that it is built upon a foundation of industry expert knowledge gathered through action research workshops, which is further supported by a broad array of industry, academic and technical resources. In operation, RISKGATE offers a continuum for knowledge transfer and communication of current practice in risk identification, assessment and management in the coal mining industry. The primary mission of RISKGATE is to focus industry attention on prioritising control management as a way to achieve acceptable risk.A Coal Mine Tailings Dam Module has recently been added to the RISKGATE suite. The key risk, or initiating event, associated with coalmine tailings dams is catastrophic failure of the dam, leading to the release of tailings and water. This can occur due to geotechnical instability of the dam itself or of its foundation, overtopping and erosion of the dam, and piping failure of the dam itself or of its foundation. Coalmine tailings dams are also prone to seepage into the foundation and through the dam, particularly during operation when large volumes of water are discharged with the tailings. The most significant risk associated with seepage is the release of potentially contaminated water to the environment. Contamination can take the form of elevated salinity, acidity and dissolved metals. Run-off from coalmine tailings can cause erosion and can also potentially contain contaminants. Desiccation of the tailings surface can result in dust generation and dispersion.The paper presents the background and context of the RISKGATE project, the need for the addition of the RISKGATE Coal Mine Tailings Dam Module, and a description of the developed module, including the five initiating events considered, their causes and associated preventive controls, and their consequences and associated mitigating controls. This paper concludes with a discussion of the ways in which Australia’s coal mining companies are starting to apply the RISKGATE body of knowledge at their sites, which will flow onto the management of their tailings dams.CITATION:Williams, D J, Kirsch, P A, Gasparon, M, Baumgartl, T, Edraki, M, Rowe, D and Harris, J, ?2014. Application of RISKGATE to coal mine tailings dams, in Proceedings Life-of-Mine 2014 , pp 219–230 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 16, 2014

By Marwick PL

As part of its operations Hamersley Iron operates a heavy medium Concentrator to upgrade low grade, unsaleable iron ore to produce saleable lump and fines products. Firstly, the attempts at delivering a blended feed in both chemical and physical characteristics are presented. Improvements in blending controls are shown to have given process performance improvements. Secondly, improvements to the feed preparation section are detailed. These alterations are providing a much cleaner feed to the subsequent processing stages.

Jan 1, 1987

The problems of the as-built water supply system are discussed. Recent modifications to the collection dams and the water cleaning station using wedge wire screens to resolve these problems are outlined.

Jan 1, 1978

One of the responsibilities of the Melbourne and Metropolitan Board of Works is to provide a sewerage system for the metropolis of Melbourne which now contains over 2.5 million people. In providing this sewerage system it was necessary for the Board to embark on a large tunnelling programme some 20 years ago. As a result of this extensive tunnel construction programme, tunnel boring machines and shaft sinking methods have been developed to cope with the soft ground and soft to medium rock found in the southern and eastern areas of Melbourne where the majority of the recent tunnelling has been carried out. While in the last few years radical changes in construction methods have not been made, development has continued and improvements have been made, which have enabled the Board to extend the limits of the ground conditions in which it can efficiently construct shafts and also tunnels with boring Machines.

Jan 1, 1976

By S Pigram, G J. Jameson

This paper is concerned with the tracking of particles in the froth phase of an aerated water/glycerol mixture. Experiments have been carried out in a specially designed laboratory flotation cell that allows formation of a deep froth. Phosphorescent tracer particles of various sizes were injected into the centre of a froth column where they were excited by ultraviolet lights, positioned at the back and front of the column. The motion of particles was captured on a digital camera with a green filter. The images from the digital camera were then transferred to a computer and an image analysis program was used to convert the colour intensity to the concentration of particles at each location within the froth. The tracer technique was used to determine the dispersion of hydrophilic particles and the variation of the concentration of solids with axial and radial positions.

Jan 1, 2005

By A Roshal

It is anticipated that many future uranium mines in Australia will be using the in situ leaching mining process. It is fair to say that close to one third of uranium production will be generated by this method, whilst the other two thirds will fall on the uranium generated from hard rock mining and other mining methods, such as traditional open cut mining. For other types of deposits the in situ leaching mining method will remain the best technological, commercial and environmental alternative. It is important to identify and prevent all risks involved in uranium mining. The expertise in this subject is limited. Over the years there was only one mine using the in situ leaching process for uranium extraction in Australia. Computer simulation of propagation of leachate during and after the uranium in situ leaching is a crucial factor, not only for addressing the environmental concerns, but also for the most efficient recovery of the deposit. The decontamination can be modelled for a period of up to 100 years, with the acid neutralisation forecast for a period of up to 400 years. The results of the modelling are paramount for definition of the reserves, efficiency of the mining method and the environmental impact statement. The accuracy of the hydrogeological modelling and carefully selected environmental management program enables a mining company to quantify and minimise the impact of the mining activities on the regional aquifer and to prevent environmental disasters. In the study, the completed hydrogeological model allowed the client, the authorities and the community to make an informed decision about the environmental impact of the in situ leaching of uranium. In particular, the model proved that neither during the mining, nor during the neutralisation the toxic elements would interact with the local catchment area.

Jan 1, 2008

By P Gomez, R Baumgartner, G Escobar

"The Cerro Corona mine consists of a Cu-Au porphyry deposit located in the Andes of northern Peru. The deposit comprises a typical Cu-Au multiphase porphyry mineralisation that has been overprinted by an epithermal event. This has generated a complex pattern of argillic alteration facies, which was accompanied by a locally structural-controlled Au-Cu mineralisation with the presence of gold and limited Cu sulfides and sulfosalts. These features, along with the porphyry-style mineralisation, produced a multifaceted occurrence of gold.Since the beginning of operations at Cerro Corona in 2008 there has been a continuous improvement of the geological and mineralogical knowledge. All mineralogical studies have mainly focused on host rock types and, to a lesser extent, alteration minerals, but little work has been done on the mineralisation itself. As a consequence, limited mineralogical information was available for use in the process optimisation initiatives.In the last two years, a series of mineralogical characterisation studies were undertaken with two main goals. First, to gain an understanding of the mineralisation genesis and second, to obtain a detailed characterisation of copper and gold minerals to support ongoing process optimisation. The first goal was achieved by conventional optical microscopy while the second required electronic microscopy and other microanalyses due to the necessity of quantifying several minerals of interest for the processing.The results were used to refine pre-existing geometallurgical domains, explain copper and gold losses in the flotation process and to some extent, improve copper and gold recoveries. The mineralogical characterisation is an ongoing work. Mineralogy provides the basis for any optimisation exercise since it looks in detail at the material to be treated and therefore, should be part of all geometallurgical programs.CITATION:Baumgartner, R, Gomez, P and Escobar, G, 2016. Comprehensive Mineralogical Characterisation at the Cerro Corona Cu-Au Porphyry Mine – the Fundamental Key for Geometallurgical Applications, in Proceedings The Third AusIMM International Geometallurgy Conference (GeoMet) 2016, pp 221–230 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Jun 15, 2016

By T Schrimpf, I Bryan

The life cycle of a mining project begins with initial regional exploration and ends with mine closure and rehabilitation. Between resource definition and the commencement of mine construction is the study phase. In this phase technical concepts and processes are defined, evaluated and assessed with the aim of establishing whether the deposit is economically feasible. The study phase usually involves various steps from a concept/scoping study to prefeasibility and ultimately definitive feasibility study. The complete study phase can take several years. Although the costs for studies are low in comparison to actual construction and operating costs of a mining project, they are significant especially for junior exploration and mining companies advancing projects to the point of being funded.The studies aim to determine selected parameters for the project, eg mining and processing methods, operating strategy, etc and provide a roadmap for project development ahead. Although mining studies are of the utmost importance for the mining project and the project owner, they are usually carried out using a conventional engineering approach: the consultant or design engineer works to a defined scope of work. The resulting design might be based on good engineering, but might often also fail to provide the solution for the project owner that delivers the best shareholder value. An alternative to this more traditional approach to project evaluation is what we have termed a value engineering approach. Value engineering is a creative, organised effort, which in the case of a mining study analyses the requirements of the study for the purpose of achieving the essential outcomes with the highest shareholder value. The outcome of a study is a concept that delivers the highest achievable value of the resource project and shows the way ahead to realise this value. Through a group investigation by experienced, multi-disciplinary teams the value of the resource is improved through the study of alternative options, methods and processes. The scope of the study is not limited to a narrowly defined engineering scope, but to the creation of value.The study commences with the identification of key value drivers and risks, based on the available information (drill data, geotechnical data, metallurgical test work, etc). This enables the quantification of key uncertainties, risks and value adding opportunities. Study efforts concentrate on key value drivers and are not unnecessarily spent on side issues. This approach can significantly reduce the time frame and costs for the study phase.This paper describes in more detail RMDSTEMÆs value engineering approach to mining studies and illustrates it with examples and case studies.CITATION:Schrimpf, T and Bryan, I, 2012. The application of value engineering principles to mining studies, in Proceedings Project Evaluation 2012 , pp 163-170 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 24, 2012

By G Hancock, A Kemp, I Taylor

The mine site is situated south east of Port Hedland in the Pilbara region of Western Australia. A detailed engineering design was undertaken for six irregularly shaped waste rock dumps at the site. The design was undertaken to ensure long-term stability of the dumps and optimise material movements for closure construction. The Watershed Erosion Prediction Program (WEPP) and SIBERIA landscape evolution modelling was undertaken for the landforms using regional and site-specific material characteristics to provide an indication of the maximum allowable slopes and corresponding slope lengths for long-term stability.The majority of the waste materials present in the waste rock dumps are considered likely to be subgrade banded iron formation (BIF) and chert, which is generally competent material. The presence of a large number of dolerite dyke swarms indicates appreciable volumes of dolerite were produced as waste from the pits. Geological records also indicate that the dolerite is logged as being heavily kaolinised in the geological logging, hence kaolinite is very likely to be present within the waste dumps on-site. This material has an elevated risk of being highly erodible/dispersive. Clays and shales are also likely to be present in the dumps and are considered to be less competent material (relative to the BIF/chert).The final design configuration of the largest existing ‘unplanned’ waste rock stockpile is compared to a hypothetical continuous ten degree outer embankment alternative. This paper will present a brief description of the alternatives for closure of three waste dumps in close proximity to each other and how the detailed design based on site-specific materials and conditions compare to an alternative approach blankly assuming that most materials will be erosionally stable at less than ten degrees.CITATION:Kemp, A, Taylor, I?and Hancock,?G,?2014. Landform design for Pilbara mine site – why plan and design waste rock dumps for closure based on site-specific conditions?, in Proceedings Life-of-Mine 2014 , pp 47–54 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 16, 2014

By Carter A. J, Miller D. M, Holder N. H M, Van Aswegen P C

The Harbour Lights Mine situated at Leonora in Western Australia, mines a refractory sulphidic gold ore. The main sulphide minerals are pyrite and arsenopyrite. Due to the association of gold with the pyrite and arsenopyrite, gold recovery is not amenable to the normal cyanidation process.A pyrite/arsenopyrite flotation concentrate is produced at Harbour Lights. This concentrate has been stockpiled for the past two years.A bio-oxidation process (BIOX«)* to treat refractory gold flotation concentrates has been developed by GENMIN in South Africa. Harbour Lights acquired the technology from CRL BIOX« Pty Limited in Brisbane, to treat the refractory gold concentrates.

Jan 1, 1992

Banks' focus in using cash flow methods can differ markedly from that of equity investors. This paper attempts to explain and describe bankers' approach by: ò outlining the fundamental difference between banks' and investors' risk / return profiles. ò describing lenders' consequent use of cash flow methods in mineral valuation. areas. explaining lenders' specific treatment of key risk Fundamental to understanding banks' appraisal of mineral projects is the appreciation that lenders have a basically different risk profile and outlook from those familiar to equity investors. Lenders do not normally participate in any project upside. The economics of lending dictate that banks can only accommodate a low probability of loan default and consequently banks' principal focus in mineral ""valuation"" is ensuring an acceptably comfortable probability of debt repayment. A simple conceptual explanation of lenders' risk / return position is outlined.

Jan 1, 1994

By R Berry, S G. Walters, J A. Hunt, D Collett

The texture of an ore type is fundamental in understanding the metallurgical behaviour of an ore. This study will show examples of how quantified textural attributes (mineral shape, grain size and mineral association) can be obtained from automated and scanning electron microscope (SEM)-based microscopy and utilised using advanced image processing techniques. Examples will be shown of integrating quantified and semi-quantified meso- and macro-scale textural attributes as well as how they relate to texture-based visual logging systems. The implications of texture for processing behaviours such as comminution, liberation and recovery will be discussed. This research is part of a major collaborative geometallurgical project undertaken at the Centre of Excellence in Ore Deposits (CODES, University of Tasmania) and the Julius Kruttschnitt Mineral Research Centre (JKMRC, University of Queensland). The authors wish to acknowledge financial support and permission to publish from the sponsors of the AMIRA P843 GEMIII project.

Jan 1, 2008

By A Scott, I Onederra

Most iron ores occur in mine benches as complex mixtures of lithologies and ore types. This significantly complicates their characterisation for both blast design and fragmentation modelling. A great deal of technical and research effort has been applied to the development of models to predict fragmentation from rock blasting. A number of quite useful engineering models are currently available to blasting engineers and consultants, and more sophisticated approaches using mechanistic descriptions of rock breakage continue to be developed and applied by researchers and explosives companies.The engineering or empirical models that are in more general use within the industry, such as the Kuz-Ram model, require appropriate data if they are to generate useful fragmentation predictions. Some of these models have reached significant sophistication and have made very useful contributions to both routine blasting operations and the exploration of new blasting paradigms. However, these models struggle to adequately deal with rock that is as complex as iron ore. This paper reviews the characteristics of the most successful blast fragmentation models available to the industry and discusses approaches to the derivation of suitable rock mass properties to adequately describe blast fragmentation in a range of iron ores.CITATION:Scott, A and Onederra, I, 2015. Characterising the blasting properties of iron ore, in Proceedings Iron Ore 2015, pp 481–490 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 13, 2015

Just as geophysics, in the form of 3D seismic and wireline logging, plays a key role in petroleum reservoir management, so too will geophysics play an important role in mining of coal, metals, and minerals in the 21 st century. The commercial and social imperatives driving greater use of geophysics are reduced costs, increased revenues, and enhanced safety. In short, superior utilisation of capital and management of risks. In relatively undeformed sedimentary environments it is possible to adapt petroleum-style 3D reflection seismic to image mines. This has been demonstrated most impressively in the Witwatersrand. Anglo-American, for example, completed a $1 million 3D seismic survey at Western Deeps in order to site a new $300 million shaft with confidence. Likewise, 3D seismic has gained rapid acceptance at Australian coal mines in recent years. Encouraged by these successes, metalliferous mining companies are supporting research in Canada and Australia, as well as South Africa, to adapt 3D seismic for more highly structured, metamorphic terranes. Because the mining industry is far more diverse than the petroleum industry in terms of commodities and geological environments, 3D seismic is not always cost-effective. A plethora of other geophysical techniques can be applied, many of which are employed in mineral exploration. Mine applications of geophysics differ from traditional exploration applications in two main ways: time scales and length scales are shorter, and boreholes are more plentiful. Borehole geophysical techniques therefore play a more significant role, both for logging and imaging. Logging systems detail the variations of in situ physical properties down the borehole at scales measured in centimetres, while geophysical imaging techniques can map features located tens or even hundreds of metres from the sensors. While geologists tend to think of boreholes in terms of chips and core, geophysicists perceive them first and foremost as access paths for instruments. Borehole logging has been employed at iron and coal mines for decades, mainly to accurately define ore boundaries in delineation holes. In base metal mines, Outokumpu implemented logging widely for orebody delineation in percussion holes in the 1980s. The benefit was a direct cost-saving, arising from substitution of core drilling with percussion drilling plus borehole logging. The practice has since spread to other companies. INCO, for example, defines nickel boundaries in blast holes at Sudbury using conductivity logs. The benefits are in the form of reduced dilution and enhanced ore recovery, flowing from a more accurate mine model. Density, natural gamma radiation, magnetic susceptibility, and conductivity are the principal metalliferous mine logging parameters because they can be recorded in both dry and water-filled holes. Sonic velocity is the premier geotechnical logging parameter, given its sensitivity to rock strength, stress, porosity, and degree of fracturing. Sonic is recorded routinely in exploration and geotechnical holes at coal mines. With the advent of slimline dipmeter, full waveform sonic, and optical and acoustic scanner tools, the role of borehole logging in geotechnical evaluations is expanding. Monitoring of strain and micro-seismic activity enhances safety during mine production. While qualitative interpretation of logs is adequate for stratigraphic identification or definition of boundaries, a wealth of quantitative information, eg density, can be derived from properly calibrated, repeatable geophysical logs. Moreover, geophysical logs can sometimes serve as surrogates for geochemical assays, and not only for magnetite and uranium. At OutokumpuÆs Kemi chromite mine, for example, gamma-gamma logging provides the basis for grade control. By reducing reliance on assaying, three benefits can be realised: reduced reliance on core drilling; lower core handling and assaying costs; and shorter turn-around times. Conventional downhole EM and borehole magnetics are used for near-mine exploration, and for ground sterilisation. Inco has enjoyed considerable success with borehole UTEM in the Sudbury Basin, for example, and Geopeko has applied three-component borehole magnetics successfully in the Tennant Creek area. Electrical techniques such as applied potential and magnetometric resistivity (MMR) are also finding application at mines. For higher resolution, borehole seismic, radio imaging, and radar have been invoked, with varying degrees of success, to delineate orebodies and map structures, or to geotechnically characterise the rock mass and identify hazards. Success mapping nickel sulphide shoots with borehole radar has been reported by WMC at Kambalda. There are no universal geophysical panaceas, and each mine imposes different geological, logistical, and economic constraints. Geophysics will not always be cost-effective. However, the greatest single impediment to expanded use of geophysics at mines has been the low level of awareness of geophysics on the part of most mine geologists, engineers, and managers and, equally, the limited understanding of mine geology and engineering exhibited by the majority of geophysicists. This myopia will be remembered as a 20th century affliction! Blue Sky areas for mine geophysics in the next ten years include integration of geophysical data acquisition with drilling, enhanced grade estimation and rock mass characterisation, and the incorporation of geophysical information into mine models using geostatistical techniques. All these advances will be predicated on an expansion of petrophysical knowledge.

Jan 1, 2000

By Ibrahim AR

The experimental phosphate mine of abu Tartur has been recently placed into production. Some problems'have been encountered in maintai- ning grade control due to the differences between early block estimates and actual produ- ction grade. An area of 100 km2 is evaluated by using four methods of evaluation , namely polygonal, inverse distance , inverse distance squared and geostatistical methods. The results of calculations are compared statistically with the control values of grade and thickness. The comparison showed that the. kriging technique gave better estimations for the relative ore reserved, while for grades or thickness any of these techniques except the polygonal can be Used.

Jan 1, 1986

By A Grice

AMC has completed a number of backfill options studies, including several in recent years for large, three-dimensional orebodies involving total extraction by longhole open stoping with backfill. This has led to the development of a thorough review methodology that assists in the selection of the most appropriate backfill system and the most economic mixes to achieve the required performance. A recently developed design tool has simplified the calculation of backfill strengths for various exposure dimensions and automatically determines strengths incrementally over the height of a stope. Using a generic orebody with a plan dimension of 120 m wide by 360 m long, several different stoping layouts have been analysed to determine the effect of stope dimensions and sequencing on backfill strength requirements. This has been done for stope heights from 50 m to 300 m, in 50 m increments. The required strengths have been calculated in slices and summarised for each stope in four equal layers. The average strength requirement for each layout at each stope height has been compared graphically. For all stope heights, a panel stope layout that minimises the proportion of primary stopes results in a lower average strength requirement than grid layouts on a checkerboard pattern. However, for very high stopes, smaller plan dimensions become more economic. The increase in required strength with stope height is non-linear, making taller stopes potentially more attractive. The main cost factor in most backfills is the rate of binder addition, which is closely related to the strength required. By choosing a layout that minimises the backfill strength requirement, significant savings in binder addition rates and overall costs can be achieved. These must, of course, be weighed against other factors to determine the optimum stoping layout and backfill system.

Jan 1, 2000