Search Documents

By M J. Pejovic, S BoÜevski, I Miljanovic, M Hudej, A Milutinovic, A Petrovski

The paper deals with the problem of managing the supplies of consumables (energy resources, lubricants, explosives, explosive supplies, tires, spare parts, etc) in mines. After the introductory remarks and comments, a general stochastic model of supply, relating in general to the dynamic programming method is presented. A selection of stochastic supply model for experiments and research by the authors of this paper is not a coincidence, based on of their long experience, showing that this type of model is the most suitable to provide support for decision-making and management of supplies of consumables in mines.In order for the problem?of?consumables?supply?management to be reviewed, in whole and objectively from the aspect of risk, experimental tests of the stochastic model in real conditions were performed at the limestone open pit mine æZelenikovecÆ near Skopje, the capital of Macedonia. The scope of the experimental research enabled reliable analysis. The results obtained confirm the efficiency and reliability of the stochastic model and two separate manipulative-operational positions regarding its application, which may have an important influence on the optimisation of supplies.

Sep 26, 2011

The Australian gold industry has in recent years experienced a tremendous growth period, though not to levels prevailing at the turn of the century. There are, however, a number of dynamic factors at play which collectively indicate that it would be unwise to assume that this growth will be maintained; indeed the future discovery of viable new deposits may be insufficient to prevent an industry decline in Australia.The higher gold prices of the 1980's together with technological advances, made previously worked mining centres areas of excellent prospectivity. These resources, signposted for us by the oldtimers, are being rapidly depleted. Whilst there can be no doubt that these resources can be replaced the real question is whether it is economic to explore for new deposits when it is likely that:The cost of future exploration will increase as exploration must focus on grassroot areas with few signposts. Almost by definition this primary exploration effort will be subject to a lower success ratio.The cost of future exploration will increase as new deposits will be located in more remote areas and at depth.

Jan 1, 1986

By J Rutter, S Dunham

Technological advances in sensor and material handling technology has enabled a step change in mine operations performance. Sensors capable of monitoring the grade of broken rock mass can be mounted on shovels, truck loading units or conveyors allowing highly precise ore/waste decisions to be made on small parcels of rock, increasing selectivity. This increased selectivity has the potential to remove sub-economic material from the product stream prior to incurring ore treatment costs. Bulk ore sorting is capable of intervening at <10t “pods” on Run Of Mine conveyors, or alternatively at per bucket loading (5-100t) or truck scale (30-350t) parcels of ore. This Grade Engineering technique being developed by CRCORE (Rutter, 2017) can improve mill feed grade, remove deleterious materials and ensure that the high capital intensity ore treatment facility is presented with the best ore feed strategy. While this technology can improve mine economics, estimating the performance of a bulk ore sorting system is challenging. Traditional resource estimation practices such as Ordinary Kriging and Inverse distance weighting (IDW) are based on weighted averages, a process that smooths the grade profile, reducing modelled variance and dispersion. Its purpose is to generate a globally unbiased result but is less suited to generating a model of adequate granularity to enable confidence in local grade heterogeneity. This is an essential component for bulk ore sorting success. Estimating ore sorting performance requires knowledge of the grade-tonnage curve at the scale of the sensor diversion unit (SDU). Evaluation based on an estimator that smooths the SDU distribution will not correctly predict ore/waste separation or economic performance. Alternatives to traditional linear geostatistics have been tested on a variety of mineralisation styles. Additionally, a number of heterogeneity metrics have been developed to assist with evaluation and assessment. The difference between estimation for grade (metal) and modelling for traditional mining block models, versus methods used for predicting heterogeneity and variability are explored.

Nov 10, 2020

By J Boshoff

The management and operation of tailings storage facilities (TSFs) are often neglected until the process plant has to shut down as a result of this negligence or as a result of a catastrophic failure as was the case during the recent TSF failure in North America.TSFs are often regarded as non-assets and do not receive the attention they deserve in terms of technical expertise and financial provision. A TSF is not a simple structure but a complex and dynamic structure that changes throughout its operational life. The operational life of a TSF is the period in which there is the greatest opportunity for risks to occur. The failure of a TSF is normally not as a result of a single event but as a result of a consequence of events. These events are often not recognised in time due to a number of factors.Process plants and slurry pumping systems are operated at suboptimal conditions in order to maintain throughput. At the same time, the tailings properties are compromised in terms of slurry density and particle size distribution amongst other things. Tailings deposition cycles and drying cycles are not well understood and the tailings management strategy is not well tuned in terms of maximising consolidation and improving in situ densities. Pond control is also neglected. These are aspects that form the keystone to the effective utilisation of available deposition area as well as the frequency and cost of future embankment raises.Apart from operational issues, forward planning in terms of budget requirements, increases in tailings throughput, embankment raises, pipe replacements, etc are normally put on the back burner. Available deposition space at the time seems to render this planning obsolete.The bottom line is that responsible tailings management and proper forward planning can limit liability and reduce the bottom line in terms of cents per ton if correctly implemented by suitably qualified tailings managers and engineers.The aspects that need to be considered as part of responsible tailings management are highlighted in this paper.CITATION:Boshoff, J, 2015. Responsible tailings management, in Proceedings Tailings and Mine Waste Management for the 21st Century , pp 317–322 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 27, 2015

By D Carroll

Mining of the zinc, lead and silver deposit at the Broken Hill Southern Operations site has been occurring for over 100 years. As a result of this, a significant amount of high-grade ore is now taken from narrow remnant pillars left between old stopes and zones of previously mined ground. Stopes have been filled with either hydraulic fill (also known as ‘sandfill’), cemented hydraulic fill (cemented sandfill), waste rock backfill or a mixture of these fill types.In the last ten years, there has been considerable success mining through narrow pillars where sandfill is exposed in the development face and/or walls using a ‘shell’ support regime, wherein a layer of bolted mesh is sandwiched between two layers of sprayed fibrecrete (25 mm fibrecrete, then mesh and bolt, followed by a final 50 mm layer of fibrecrete). Shell support is also used in very poor, broken, relaxed ground conditions and in areas filled with cemented fill (sandfill with a minimum four per cent cement content).The next stage of innovation has been to develop a technique for mining through old stope voids filled with uncemented sandfill, known locally as ‘contours’ (old cut-and-fill working), an activity where unconsolidated sandfill can run at the face and from the backs. The challenge is to prevent exposed sandfill in the face and the backs from failing before it can be supported.To achieve this, the Southern Operations mine has implemented a technique in which 6 m long spiling bars are used to strengthen and stabilise the sandfill in front of the face. The hollow steel bars are driven in around the heading perimeter in a closely spaced pattern then pumped full of grout. The bars and the grout stabilise the sandfill in front of the face, preventing it from failing into the drive during excavation and prior to further support being installed.A final support system consisting of shotcrete, mesh, bolts and steel girders is installed as excavation progresses. Both the initial and final support systems are essentially passive support systems designed for a low-stress environment (as the stress originates mostly from the mass of unconsolidated sandfill).This process is slow and labour intensive. Fifteen separate cycles of people/machinery are needed to progress one equivalent heading cut (compared to six for a standard fibrecrete- and bolt pattern-supported rock face heading). This slow pace introduces scheduling challenges, but the process opens up parts of the orebody that were previously uneconomical to mine.CITATION:Carroll, D, 2014. Mining through sandfill using spiling bars, in Proceedings AusRock 2014: Third Australasian Ground Control in Mining Conference , pp 95–100 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Nov 5, 2014

Mother Nature controls, technical professionals model and miners decide. Decisions to explore, mine and mill. Mine decisions, mine design, planning and scheduling are subject to the quality of models û geological models, geotechnical models, resource models, density models. The closer these models are to reality, the more accurate the predicted outcome. So why is it we delegate the modelling tasks to the most junior and least experienced people? If we insist on this, we need to support them û to provide them with æexperience acceleratorsÆ. Technical mentoring is the most effective way to provide the right information at the right time. When this information (read skills) is supplied at the right time we can inject experience into the quality of our modelling and into our decision- making processes. The objective of this paper is to share those behaviours and manners that foster relationships and create frameworks for skills and experience transfer. Central to this is an understanding of how adults learn, an understanding of the basic rules of mentoring etiquette, and the three keys to building meaningful mentoring relationships. An understanding of adult learning processes and styles provides a structure within which a mentor can understand the learnerÆs perspective. Understanding the world from the learnerÆs point is critical to selecting the right language to engage, teach and transfer skills. Basic rules of mentoring etiquette like timeliness, respect and trust need to be brought into the consciousness so they can be agreed on and monitored to prevent conflicts in cultural and generational norms between the mentor and the learner.Meaningful relationships hinge on the three behaviours: truly listening, rather than just hearing; understanding the technical issues within the WIIFM (whatÆs in it for me?) question; and facilitative behaviour. Stronger and more meaningful technical mentoring relationships within our industry will bridge the generational gap and ensure we can capture and capitalise on the wealth of grey hair experience and develop an informed group of young decision-makers.

Jan 1, 2006

The borehole televiewer is a downhole geophysical logging device that produces continuous, oriented, 360¦ images of the drill hole wall. Two types of borehole images are currently being generated at the BHP Billiton Mount Whaleback deposit. The optical televiewer (OTV) tool captures a ærealÆ image of the borehole wall whereas an acoustic televiewer (ATV) generates an image through variations in physical borehole size, scattering the energy from an acoustic beam. Orientation of the resulting ævirtual coreÆ is derived through magnetometers and accelerometers, providing values within one degree for both inclination and azimuth. Downhole structures such as fractures, joints, foliations and bedding planes are selected directly off the borehole image, recorded and displayed in a 3D modelling package along side adjacent drill holes. Measurements are corrected from apparent to true dip and magnetic to true north. Strata-bound magnetic anomalies are identified and corresponding measurements excluded. The importance of borehole imaging increases substantially with its ability to integrate the OTV and/or ATV data with other forms of lithological and structural data. At Mount Whaleback, the borehole televiewer has been implemented to provide information for geotechnical exploration including structural analysis, lithological characterisation and rock-mass conditions. Within the large area in and around Mount Whaleback, drilling may intersect a number of different geological formations with various rock types and conditions. With the application of the borehole televiewer, reverse circulation drilling can provide information traditionally obtained by diamond drilling.

Jan 1, 2007

Detailed underground mine design and optimisation studies undertaken by the author over the past few years have clearly demonstrated that additional value can be created by varying the cut-off grade (COG) spatially throughout a deposit as well as over time. This additional value can be particularly significant for marginal operations. This paper, by way of worked examples, illustrates the conceptual and practical considerations of applying a differential cut-off policy for an underground mine to both maximise value and manage risks associated with production and metal price volatility. Consideration is given to both the design stage of a new mine and to the strategic and practical application of a differential cut-off policy in an operating mine.

Jan 1, 2005

In May 2000, Kanowna Belle Gold Mines (KBGM) carried out a detailed Truck versus Shaft Haulage Study. The study showed that whilst the shaft option had many operating cost benefits the capital costs were too high, therefore the truck option was selected. In May 2001, the concept of achieving æshaft typeÆ benefits without the capital costs was floated. This is achieved by separating the hoisting of ore from other mining activities. The general concept is that material from underground is transported to a central location and then transported to the surface by a special truck fleet, thus removing the dependency between trucks and loaders, providing the mine with surge capacity and decreasing operating costs. At KBGM these advantages have been gained by installing an ore pass system with a plate feeder at its base that directly loads trucks. This provides the mine with a haulage system with enough surge capacity to remove the interdependency between trucks and loaders. The plate feeder is situated just off the decline which creates the opportunity to use larger more reliable, lower cost trucks. A number of truck types were considered for the truck loop including Elphinstone AD55Æs which are the truck type being used on site prior to the truck loop, CAT 775EÆs and power trailer road trains. This paper covers the philosophy behind the truck loop, the truck selection process, project installation and commissioning, people issues and the benefits expected by the operation. As of May 2002, the project is nearing completion, with decline haulage expected to commence in July 2002.

Jan 1, 2002

By J Rowland

"Ventilation models are invaluable tools for both prediction of routine daily ventilation changesin an operating mine to circuit performance expectations at the mine in 20 yearsÆ time. Arguably ventilation offi cers are becoming increasingly reliant on maintaining an accurate ventilation model with which to do their work. This paper relates to the practical assessment of the accuracy and thus ability of a mine site ventilation model to be reliably utilised on such varied tasks. The author&apos;s experience shows that in some cases the incumbent model is found to be in a state of tune that demonstrates a mine wide detailed assessment of branch resistances is simply not required. The money spent on a detailed mine wide ventilation survey that is not required would be far bett er served purchasing much needed monitoring equipment, rather than fixing something that is possibly not even broken. The term ænot rocket scienceÆ has been incorporated into the title of this paper because it appears that many practitioners believe that circuit validation is diffi cult. As long as clear att ention to detail is paid to the actual data collection process then drawing an accuracy comparison between the circuit performance and the model performance at any particular point in time, is really very simple. This paper will show a manner in which a circuit can be analysed to determine its actual state of health by using various diagnostic tools and tips. It will help ensure that subsequent work scopes to address any highlighted model defi ciencies can be more effi ciently scoped and targeted. It will hopefully remind operational people that such self assessments can easily be done æin houseÆ if the appropriate steps are followed."

Jun 1, 2012

By C Smith, J Cilliers, K Hadler

Unstable flotation froths, that burst before they overflow, produce no concentrate. Increasing the froth stability to improve recovery is therefore an obvious control strategy. Froth stability can be measured readily as the fraction of air entering the flotation cell that overflows as froth, rather than bursting on the surface; the ‘air recovery.’ Air rate is one of the most significant variables affecting froth stability. It is interesting that froth stability (air recovery) is maximised at a specific air rate, above or below which it decreases. It is important for metallurgists to realise that this maximum froth stability also produces the maximum mineral recovery, without compromising concentrate grade. Flotation cells must be operated at the air rate that produces the highest air recovery. The peak air recovery (PAR) to maximum mineral recovery relationship was first demonstrated by Hadler and Cilliers in 2009. Since then, the relationship between PAR and flotation performance has been widely explored; varying air rate, froth depth and particle size. Industrially, reducing the flotation bank air rate to achieve PAR yielded better mineral recoveries than other down-the-bank air rate profiles. In this paper, we present an overview of these key developments and findings in flotation optimisation based on PAR. Furthermore, using new industrial data, we show that PAR is not just applicable to rougher-scavenger cells, but also to flotation columns. Finally, we consider the future application of such an optimising control concept. CITATION:Smith, C, Hadler, K and Cilliers, J, 2018. Flotation control using froth stability: past, present and future, in Proceedings 14th AusIMM Mill Operators&#39; Conference 2018, pp 441–454 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 29, 2018

The restructuring of the minerals industry has created new challenges for the design and delivery of professional development, and difficult decisions for potential participants. New technologies offer some new methods of delivery, but fall short in providing all of the benefits of face-to-face participation. This paper is intended to be a catalyst for discussion of the issues involved in delivery and participation in cost-effective, relevant and timely professional development.

Jan 1, 2000

By M J. Sale

The Epithermal and Mesothermal Gold Prospectivity Modelling Projects recently completed by Crown Minerals provided explorers in New Zealand with a new compilation of historical exploration data combined with new geological information from the GNS QMap 1:250 000 scale mapping project. These data were used to produce predictive mineral potential maps for gold mineralisation in New Zealand. The aim of these projects, which was to stimulate mineral exploration and investment in exploration, has been successful with new companies acquiring new tenements and committing significant exploration expenditure to exploring in New Zealand in the coming years. The projects were undertaken at a national scale and consequently not all exploration data were compiled into the prospectivity models. HPD New Zealand Ltd recognised the value of the prospectivity modeling work and committed exploration funds to continue the modelling process started by the projects. They recognised the need to compile the remaining data and run the models again to allow detailed exploration targeting.

Jan 1, 2004

By P Duuring

Late-Archean banded iron formation (BIF)-hosted deposits in the Yilgarn Craton of Western Australia are less well understood compared to the larger Paleoproterozoic, Superior-type BIFhosted deposits of the Hamersley Province. The Weld Range greenstone belt, in the Murchison Domain of the Yilgarn Craton, hosts two Archean, high-grade deposits, Madoonga (68 Mt resource at 57.7 wt per cent Fe) and Beebyn (62 Mt resource at 59.6 wt per cent Fe, ASX announcement 2008). Five main types of high-grade (&gt;55 wt per cent Fe) iron mineralisation at Weld Range each display characteristic grades, tonnage, and contaminant levels, which affect exploration strategies and beneficiation methods:1. ‘Residual’ ore formed as a result of two generations of hypogene alteration of BIF. The first alteration phase replaced silica-rich bands with siderite and/or Fe-rich dolomite; the second phase involved the removal of carbonate gangue minerals and the concentration of residual Fe oxide-rich bands in the BIF via volume reduction. The product is a high-grade, high-tonnage Fe orebody, with minor contaminants.2. Magnetite-bearing shear and fault zones cut BIF along lithological contacts. These zones of secondary magnetite formed as a result of the addition of hypogene magnetite via the circulation of Fe-rich, hypogene hydrothermal fluids through BIF. This type of mineralisation produces narrow (low-tonnage), high-grade magnetite-rich ore zones with high levels of contaminants (eg SiO2, Al2O3) due to the difficulty in mining these zones.3. Specular haematite ± quartz-bearing shear and fault zones cut residual orebodies and magnetite bearing structures. They share similar characteristics to magnetite-bearing structures.4. Goethite-haematite supergene ore zones are controlled by brittle faults that cut BIF. These faults promoted the flow of supergene fluids through BIF and resulted in large ore zones with variable Fe grades and contaminants.5. Detrital deposits comprise transported BIF fragments and are intensely goethite-haematite supergene-altered. These orebodies are locally extensive, with moderate Fe grades.

Jul 11, 2011

This paper reviews the geochemistry of weathered nickeliferous sulphidic and lateritic profiles, the supergene behaviour of nickel and ore-associated elements, and their implications for exploration in an attempt to distinguish between barren and mineralised nickeliferous profiles. Nickel is an abundant accessory element in ultramafic rocks with background concentrations in some units up to 0.25 weight per cent. Ore-grades in fresh rock are mostly associated with massive and disseminated sulphide zones within magnesium-rich layered ultramafic sequences. In lateritic weathered terrain, nickel is also concentrated in the regolith profile. This process not only upgrades nickel in the gossanous weathered product of sulphidic deposits, but for sub-economic sulphide zones and some ultramafic rocks, is sufficient to result in a supergene resource. Ore-grade accumulations of nickel in regolith after sulphide-poor ultramafic rocks are referred to as lateritic deposits. Nickel sulphide zones and their ferruginous weathering products are collectively referred to as sulphidic deposits and are the major source of nickel in Western Australia. Mineral exploration in the Yilgam Block is hampered by deep lateritic weathered profiles (eg Butt and Sheppy, 1975; Smith, 1977; 1982). During the nickel boom of 1967 - 1972, most discoveries resulted from the location of outcropping nickeliferous gossan and ironstone. Exposed ultramafic terrain with nickel sulphide potential were explored intensively, mostly by gossan and soil sampling. However, up to 85 per cent of the area of the Yilgarn Block is buried by transported regolith. In these covered areas, barren and mineralised rock responses at the surface are similar and soil sampling produced unreliable results due to many false anomalies. A statistical, multi-element approach to regional geochemical exploration has evolved. Potential trace element indicators investigated, include Co, Cr, Cu, Ir, Mn, Pb, Pd, Pt, Sc, Se, and Zn. In recent years, trace element ratios have also been tested with varying degrees of Success.

Jan 1, 1996

By Collins AR, Meares RMD, Graham JM

Exploration programs for both alluvial (placer) and hardrock platinum group metal deposits are being conducted in Papua New Guinea by a joint venture between Degussa AG and Pancontinental Mining Limited. Prospective areas were defined on the basis of ultramafic/ophiolitic source rocks shedding detrital platinoid grains. Field sampling techniques including churn drilling, together with appropriate laboratory analytical and mineralogical techniques, were developed and are contributing to the success of the exploration programs.

Jan 1, 1987

Sishen uses a state-of-the-art tracking system to track material from its position in blast blocks through various stockpiles and crushers. Qualities are blended directly to the crusher as opposed to blending from stockpiles. This poses an interesting challenge to the planning department to simulate these conditions. The software used in these simulations are Whittle 4X and Maximiser for long-term planning, Xpac for medium-term planning and Mine Works Planner for short-term planning. Geological models and mine design layouts utilise Surpac. Sishen introduced Xpac a number of years ago; the system has developed and changed over the years. With the Sishen Expansion Project (SEP), which aims to utilise low-grade material, major changes to the planning process have to occur. SEP requires that the mine have two different plants, which utilise two different ROM feeds and have different beneficiation curves. Xpac is used to produce a rolling 18-month plan, which is as close to actual operations as possible. In order to do this, the simulations have to take into account the plants beneficiation curves, stockpile movements, hauling distance and equipment needs. On top of this, the schedule has to continually consider specifications for Fe and the contaminants. Plant yields also have to be kept within a certain bandwidth. Xpac is used to simulate the above parameters, as well as generate the raw data required to produce a mine budget. The paper will also show how the 18-month planning process and subsequent planning processes are measured and aligned. Xpac has proved to be an excellent tool to achieve these goals.

Jan 1, 2005

An image analysis system has been built which automatically digitizes camera input of rock fragments, analyses the digitised data to determine the sizes and shapes of the rock fragments, and outputs the analysed data to a printer in the form of a histogram or a scatter chart. The high speed of such a system allows for direct collection of data from material thrown into the air by blasting, material travelling on a conveyor belt, and material free-falling on to a stock-pile or into or out of a rock-crusher. Data on the blasted, un-crushed material provides information on changes in the lithology and structure of the rock face as it is quarried or mined: flatter fragments may represent approach to a brittle, unstable shear zone, or a change from sandstone to shale; so that the informa- tion reflects the effect on the sizes and shapes of the fragments by the blasting process and/or by the rock structure. The size and shape distributions of rock fragments produced during blasting and during processing may now be continuously monitored. Such detailed analysis of the results of fragmentation is labour-intensive and expensive when the size and shape distributions are obtained manually, but is cheap and efficient when using this image analysis system. Such a system will enable the results of blasting, quarrying, mining and crushing to be cheaply analysed and correlated with current and changing indus- trial practice so leading the way to increased productivity.

Jan 1, 1988

By Caivin JS, Freeman CJ

The Fairbanks Mining District in central Alaska was discovered in 1902 and since then approximately 7.5 million troy oz of placer gold, 250,000 troy oz of lode gold, and several thousand short tons of antimony and tungsten hap been produced from an area of about 1000 km . Historic lode production was from high grade gold-quartz veins that averaged 1.3 OPT free milling gold. Five main types of mineral deposits&apos; are recognized in the district. I. Conformable, stratabound volcanogenic zinc, antimony, lead, and copper sulfides in places containing gold, silver and tungsten in bimodal metavoleanics (Cleary Sequence). II. Complex precious metal-bearing lead sulfosalt-quartz veins in Cretaceous granitic intrusives. III. Tungsten skarns adjacent to granitic intrusives. IV. Gold-bearing polymetallic sulfide-quartz veins crosscutting metavolcanics and metasedimentary units of the Cleary Sequence. V. Antimony-bearing gash veins along axial plane shears in various lithologies of the Cleary Sequence. Type I and Type IV mineral occurrences are currently being evaluated as low. grade bulk tonnage (target model 16-20 &apos;million tons of 0.05 to 0.15 OPT)&apos;and high grade moderate tonnage (target model 0.5 to 2.5 million tons of 0.5 OPT) gold deposits. The host rocks for Type I mineralization occur over a 30 km strike length and are at least 300 meters thick. Stratigraphic, structural, fluid inclusion, and isotopic data suggest that the Type IV mineralization is related to remobilization of Type I

Jan 1, 1987

The Pilbara region, located in the north-west of Western Australia, is significant as the second-largest source of iron ore on the planet. Iron ore mines owned and operated by Pilbara Iron are located within the Hamersley Basin. This paper refers to the Greater Paraburdoo mines, the 4WEST and 4EAST pits, located on the southern margin of the Hamersley Basin. The groundwater model refers to ephemeral watercourses: Seven Mile and Pirraburdoo creeks, which are adjacent to the two pits, and Ratty Springs, located upstream from 4WEST and within Pirraburdoo creek. The spring and creeks hold cultural heritage significance for local Aboriginal communities. Two of these, the Gobawarrah Minduarra Yinhawanga (GMY) and Innawonga native title claim groups, initiated hydrological work on the two creeks and Ratty Springs, with the aim of determining the affects of dewatering on the natural water flows of these systems. The numerical model used to simulate drawdown in the Pirraburdoo and Seven Mile Creeks was derived from PMWIN Pro software and covered an area of 77 km2. The modelling period was from January 1998 to December 2004, and the prediction period was from January 2005 to December 2015. The model has four layers and incorporated effects caused by mining voids, 4WEST and 4EAST pits, creek bed material, weathered bedrock below creeks and surrounding banded iron formations (BIF). The model has been calibrated using the trial-and-error method set down by Middelmis et al (2001). The current dewatering schedule (12 ML/day) in the 4WEST and 4EAST mining areas does not affect the water table levels in the adjacent creeks significantly or for any considerable periods of time. However, changes to mine plans may occur, for example, in response to changed commodity price and may lead to significant increase in rates of vertical advancement. This, in turn, affects dewatering schedules, as greater vertical advancement requires increased dewatering effort. When an accelerated mine plan is applied to the model and dewatering rates increased to 18 ML/day, drawdowns in the creeks are more noticeable. The model has therefore helped to indicate the extent to which increased dewatering rates may be acceptable, especially in terms of immediate and longer-term damage to riparian species, ie Melaleuca and Eucalypt. Predictions from the model may also allow mine planners to schedule decreased rates of vertical advancement, where these are required to meet environmental constraints.

Jan 1, 2006