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By M N. Mian

The Cayeli volcanogenic massive sulphide deposit is located in Black Sea region of Turkey. Cayeli Bakir Isletmeleri (CBI) was formed as a joint venture between Inmet (Canada) and Eti Holding (Turkey). CBI is processing complex copper/zinc sulphide ores. The Cayeli concentrator was commissioned in 1994, with a design capacity of 600 000 tonnes/year. The grinding circuit was a classical rod mill/ball mill combination. The rod mill was converted to a primary ball mill in May 1997. The reasons for conversion were to use mill power more efficiently and eliminate feed interruptions during rod charging. The grinding circuit now has a primary ball mill in open circuit, and a secondary ball mill in closed circuit with hydrocyclones. Classification was originally done in two stages with hydrocyclones. Both mill discharges were combined and pumped to a primary cyclopack having two, 500 mm diameter cyclones. Primary cyclone overflow was pumped to a secondary cyclopack for further classification. The secondary cyclopack had ten, 200 mm cyclones. Both unit underflows were fed to a secondary ball mill by gravity. The secondary cyclone overflow, typically 62-64 per cent passing 36 ¦m, at around 42 per cent solids (w/w) was fed to flotation circuit. In order to increase circuit capacity to 1 000 000 tonnes/year and to improve control over the grinding circuit, it was decided to convert the classification circuit from two stage to one stage. For this purpose, six Warman Cavex cyclones having 400 mm diameter were installed. Now, the combined primary and secondary ball mill discharge was classified in single stage with the Warman cyclones in closed circuit with the secondary ball mill. The cyclone overflow goes directly to the copper rougher circuit as flotation feed. The grinding circuit is producing a flotation feed of 70 per cent passing 36 ¦m. The change over to single stage classification at Cayeli was successful. A mill throughput of 1 000 000 tonne/year is being achieved with better control over classification, and improved grind size. Results and comparison between the two classification circuits are presented in the paper.

Jan 1, 2003

By S Servant

In the mine of this study, cemented hydraulic backfill is placed under the form of a slurry at a percentage of solid by weight varying from 50 to 65 per cent. This slurry settles and cures in the stope. During this process an important amount of water must be drained from the stope. Field observations in the case studied here show that the geometry of the drains system has a significant impact on the drainage of the stopes. The mode of filling produces a backfill showing an evident stratification typical of a sedimentation process. In situ observations on this material show that this stratification translates into a very strong heterogeneity in the physical properties of the cemented backfill. This heterogeneity should affect the hydraulic conductivity of the backfill in the stope. In order to study this aspect, finite element simulations were performed. This paper presents the results of these simulations, where the impact of this stratification on hydraulic conductivity is related to the performance of the backfill drainage system for various geometry. This preliminary study is aimed at providing a better understanding of the role of the drains in the dewatering process of the backfilled stope in the case of this mine.

Jan 1, 1998

By P N. Duan, Z G. Liu, M S. Chu, X X. Xue, B Liu, G J. Cheng, T Jiang, J X. Liu

High-chromium vanadium-titanium magnetite has not been exploited and made full use of on a large scale so far due to the immature utilisation technology and the reality that the utilisation efficiency of valuable metals still urgently needs to be improved. In the present paper, the isothermal reduction kinetics and mechanism of high-chromium vanadium-titanium pellets were studied at 800–1100°C. The mineral composition transformation of pellets before and after reduction was analysed by means of X-ray diffraction (XRD), and the microstructures were examined by scanning electron microscope (SEM) equipped with energy dispersive X-ray (EDX) to reveal the elemental distributions. The effect of reduction temperature on the volumetric swelling degree and cold crushing strength was also studied. It was found that reduction temperature has a large effect on the reduction rate of pellets, and the increase in reduction rate is more obvious in the range 1000–1100°C than 800–1000°C. The volumetric swelling degree of pellets increased with increasing reduction temperature, while the cold crushing strength decreased. The transformation of mineral species can be expressed as Fe2O3 ? Fe3O4 ? FeO ? Fe, Fe2O3·3TiO2 ? Fe3O4· (2FeO·TiO2 ) ? 2FeO· TiO2 ? FeO·TiO2, (Fe0.6Cr0.4)2O3 ? FeO· Cr2O3 ? Cr2O3 , and Fe2O3· VO/V2O3 ? VO. The apparent activation energy of the reduction reaction was calculated to be 44.3 kJ/mol, and the reduction rate is controlled by the combined effect of interfacial chemical reaction and gas diffusion through the porous product layer. The rate controlling steps were further studied by calculating the resistance percentages. The interfacial chemical reaction was found to be predominant in the initial reduction stage, with the percentage effect of gas diffusion through the porous product layer gradually increasing during reduction.CITATION:Cheng, G J, Xue, X X, Liu, J X, Liu, Z G, Chu, M S, Jiang, T, Liu, B and Duan, P N, 2015. Reduction kinetics and mechanism of pellets prepared from high-chromium vanadium-titanium magnetite concentrate, in Proceedings Iron Ore 2015, pp 349–358 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 13, 2015

By M Berndt

Four siltite-argillite rock samples were characterised (particle size, chemistry, mineralogy) and subjected to laboratory dissolution testing for 36 to 298 weeks. In two samples sulfur (0.99, 1.69 wt per cent) occurred largely as pyrite, and in the other two samples sulfur (0.96, 1.93 wt per cent) occurred predominately as potassium jarosite. The observed rate of sulfate release from the pyritic samples was one to two orders of magnitude greater than that from samples containing potassium jarosite. Drainage pH values from the pyritic samples were one to two units lower and acidities were ten to 70 times higher than associated values from the potassium jarosite samples. Geochemical modelling supported the hypothesis that pH and concentrations of sulfate and potassium in drainage from the potassium jarosite samples were controlled by the limited solubility of potassium jarosite. This dissolution produced an iron-dominated mineral phase, but iron concentrations in the drainage were well below those predicted by ferrihydrite solubility.

Jan 1, 2003

By P Bartlett, K Naidoo

Premier Diamond Mine is planning a new, mechanised, block cave, with a production level approximately 1000 m below surface. A high degree of tunnel damage is expected, due to stress and the relatively low in situ strength of kimberlite. An evaluation of the timing of tunnel excavation, tunnel size and spacing has been carried out to define critical parameters for planning layouts and development schedules. Extensive use has been made of three-dimensional FLAC3D numerical models, calibrated against known rock mass behaviour at 650 m depth, to examine the influence of undercut advance on production level excavations. These were able to represent the effect of stress rotation on tunnels during undercut advance and the effect of an inclined undercut. The analysis has provided guidelines that are possibly applicable to any deep block cave layout. The choice of drawpoint layout is of considerably less significance than the proportion of ground extracted on the production level elevation prior to advancing the undercut. The analysis shows that damage to production development will be potentially severe if it is all excavated prior to advancing the undercut, or is mined directly beneath the undercut face. The development of the main production tunnels alone ahead of the undercut may be feasible, but no breakaways should be put in as they appear to trigger a rapid increase in the severity of damage. The optimal sequence is when all production tunnels are developed at least 10 m in plan behind the undercut, where the induced peak field stress is less than 20 MPa and a maximum support pressure of 100 to 500 kN/m2 is require to contain movement. The assessment showed that the conditions are not significantly improved by increasing drawpoint spacing from 15 m to 18 m. The vertical spacing between the undercut and production level beneath is investigated. Provided production level development is carried out beneath the undercut, there would appear to be little benefit in increasing the vertical spacing between the undercut and production level beyond the current 15 m to 18 m.

Jan 1, 2000

By S Matos Camacho, K G. van den Boogaart, R Tolosana Delgado, U Mueller

"The precise formulation of a geometallurgical optimisation problem is by necessity a simplification of reality. It includes implicit choices such as data availability or mining block geometry. Additional data can be orebody data, production data or market data. Often these choices are predetermined by the software, the workflow or the corporate culture, and as such are not even queried. There are several aspects that might play a role in the optimisation. They include not only the spatial model on which the selection of mining blocks and the potential mining sequence are based, but also the complexity of the processing model, the way in which uncertainty is treated, the scope of responsibility and the complexity of the model. In addition the timing of the optimisation and the availability (or lack thereof) of information will influence the outcome of any optimisation.We show that different modelling choices and different model formulations for the same mine can lead to very different processing choices, substantially different net present values (NPV), opposite investment decisions and so to overall different values for the entire operation. The selection of adequate simplifications and corresponding formulations for the optimisation problem is thus an important task in itself.For this purpose we introduce a method for quantifying the impact of certain simplifications prior to the optimisation. For example, the effect of mining block choices depends mainly on the spatial structure and the structure of the processing gain function. Both can be quantified beforehand. Based on the outcome, appropriate simplifications can be selected for the geometallurgical optimisation.CITATION:van den Boogaart, K G, Tolosana Delgado, R, Mueller, U and Matos Camacho, S, 2016. How Details of the Geometallurgical Optimisation Influence Overall Value, in Proceedings The Third AusIMM International Geometallurgy Conference (GeoMet) 2016, pp 303–312 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Jun 15, 2016

By K Evtiminova, G Jobson, M Nolte, S Meik

Chelopech Mining EAD (CMEAD) is a wholly owned subsidiary of Dundee Precious Metals Inc (DPM) and operates the Chelopech underground mine and processing facility located in Bulgaria. The final product sold is a flotation concentrate containing copper minerals with associated gold and silver. The increase in production from 0.6 to 1.0 Mt/a by 2009 occurred with the original (1975) secondary/tertiary crushing, and primary/secondary ball mill circuits. As part of the mine/mill upgrade project to 2.0 Mt/a, a new single stage semi-autogenous (SAG) mill and ancillary equipment was installed, replacing the original circuits, with commissioning occurring during the first half of 2011. Aspects of the design, commissioning and operation of the new comminution facility are the subjects of this paper.An extensive program of comminution characterisation test work was completed in 2004/2005, which indicated moderate hardness and competency characteristics. The characteristics were considered suitable for a range of comminution approaches which were assessed with respect to power requirements and capital and operating costs. Retention of the existing primary crushing facility, and installation of a new single stage SAG mill located within the existing mill building, was selected as the design for the expansion.An extended ramp-up schedule for the overall concentrator upgrade turned out to be necessary as the comminution and flotation circuits were completed prior to several downstream unit processes (concentrate filtration and tailings thickening), which were required to reach the design mill feed throughput rate on a sustainable basis. This resulted in the opportunity to gradually increase the SAG mill ball charge as necessary, to obtain the throughput corresponding to the various downstream processing constraints.A relatively fine cyclone overflow stream particle size distribution is a feature of the Chelopech comminution circuit that has not been fully overcome with increasing ball charge conditions. However, design throughput has been met even under the finer product size conditions and will be consistently achieved following the commissioning of two further process improvement projects scheduled for late 2012.CITATION:Jobson, G, Nolte, M, Evtiminova, K and Meik, S, 2012. The modernisation and upgrade of concentrator operations at the Chelopech Mine, Bulgaria - Design, installation and operation of the 250 tonnes per hour comminution circuit, in Proceedings 11th AusIMM Mill OperatorsÆ Conference, pp 325-332 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Oct 29, 2012

By N Haque

Base metal ores contain low levels of toxic/hazardous elements such as arsenic, antimony, bismuth, cadmium, lead and mercury. Given the large tonnage of base metal ores mined and processed each year globally, the accumulated mass of minor elements introduced into the biosphere is large and could be expected to have a significant environmental impact. Life cycle analysis (LCA) is a methodology that has been developed to assess the environmental impacts of material supply chains over their entire life cycle. Assessing the toxicity impacts of metallic wastes and incorporating these impacts into LCA methodology is not a simple task given the complexity of the issue. However, research and methodology development is in progress internationally to address this. Despite limitations concerning the lack of a coherent framework for characterising the toxicity impacts of metals, including issues such as bioavailability, a study was carried out to give first estimates of the relative toxicity impacts of various waste streams from metal production processes. The wastes considered were: red mud; sulfide tailings (copper, nickel, lead/zinc); lead/zinc slags; synthetic rutile residue; iron oxide residue; and copper slags and anode slimes. These toxicity estimates can be considered the æworst caseÆ scenario for these wastes, where all the metals present are bioavailable. Combining estimates of the amounts of the various waste streams produced in Australia each year with the toxicity results showed that despite their relatively low human toxicity impact per unit mass compared to some other waste streams, red mud and the various sulphide tailings had the highest annual human toxicity load on the environment, along with copper smelting slag and dust. Data from the pH dependent leaching test reported in the literature were assumed to represent first approximations of metal bioavailability and used to compare the two approaches to estimating the toxicity impacts of red mud.

Jan 1, 2009

By J W. Dong, Y M. Li, J L. Tian, Z H. Jiang

Electroslag remelting is widely used to produce various special steels, mainly because of its ability to provide high cleanliness and excellent homogeneity of ingot. Undoubtedly an optimal slag plays a key role in removing inclusions and enhancing the mechanical properties of a specific special steel. In order to improve the metallurgical performance of the slag in electroslag refining of die steel, a variety of slags have already been developed using traditional trial-and-error methods. Nonetheless, these slags may not be inherently optimal for the specific requirements of actual die steel refining processes. In this work, we have designed a CaF2-CaO-Al2O3-SiO2-MgO quinary slag system using genetic algorithms method aiming to remove the existing large size inclusions (D and Ds type) in high quality die steel. The comprehensive effects of five components (CaF2, CaO, Al2O3, SiO2 and MgO) were studied based on existing fundamental theory. The slag composition was screened considering the parameters such as melting point, electrical conductivity, calcium ion concentration, and appropriate viscosity etc. Furthermore, the candidate optimal slag was applied in the industrial production of die steel by electroslag remelting method. The detection results indicate that majority large inclusions (D and Ds type) have been successfully removed, showing significant advantage to traditional slags. This result has demonstrated the genetic method to be efficient and reliable. In addition, depending on the personalised demand of other steel and alloys, this method allows for the adjustment of the screening frameworks and processes to develop the candidate optimal slags. This method has not been reported previously in the field of electroslag composition design, and compared with the traditional trial-and-error method, the new method will save a lot of time and experimental costs.

Jun 19, 2024

By A R. McKinnon

The recently opened Hera Au-Pb-Zn-Ag mine in central New South Wales has provided an ideal opportunity to demonstrate the calculation of sulfide ore mineralogy using normative methods. Normative mineralogy applies a set of sequential rules based on the species likely to be present to assign the chemical components of a sample to their respective mineral components. The dominant sulfide mineral assemblage present at Hera is galena, iron-bearing sphalerite, chalcopyrite, pyrrhotite and pyrite. A normative technique for estimating the relative abundance of each of these species from drill hole, grade control and metallurgical assay data sets has been developed. This includes a process for deriving a gangue iron value and differentiating pyrrhotite from pyrite using sulfur/iron ratios. A calculated total sulfide volume value has been utilised at the mine to improve interpretation of lode boundaries. Normative drill hole values have also been used for domaining within the orebody, with large scale mineralogical trends evident. Dry bulk density (BD) values calculated using a normative species-weighted method show good correlation with measured BD values (R2 = 0.895) and are a significant improvement on the Pb+Zn+Cu regression method (R2 = 0.646) previously used. Application of these calculations to identify errors in assay databases is demonstrated, with specific reference to the data set for the nearby Nymagee copper deposit. Validation of block model grades is also explored and a method to improve resource estimates using direct normative mineral interpolation is proposed. The integration of the normative data into the production and metallurgical data sets at Hera is described and the relationship of the normative minerals to other economic elements such as gold and silver is discussed.CITATION:McKinnon, A R, 2017. Application of normative ore mineralogy to geological and metallurgical data sets at the Hera Au-Pb-Zn-Ag mine, New South Wales, Australia, in Proceedings Tenth International Mining Geology Conference 2017, pp 63–74 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 20, 2017

Any Australian who knows of the poverty of the early settlers in the first few years following the arrival of Captain Arthur Phillip with his "first fleet" at Botany Bay must feel proud of the progress that has been made in the 174 years that have elapsed since that momentous occasionGFor all its attractive appearance as reported by Captain Cook and Sir Joseph Banks, the shores of Botany Bay and of Port Jackson proved most ,inhospitable, and the accessible country surrounding them anything but suitable for sustaining the life of the small settlement. It is well known that during the first 15 or 20 years the hardy colonists and un-tfortunate convicts were close to starvation on several occasions and were only saved by the arrival of supply ships, which were dependent on the vagaries of wind and current, and the hazards of the uncharted seas they had to -navigate-.When Australia was little more than a miserable penal settlement, Great Britain was one of the great-powers of the world, and the U,.S.A. was an independent nation with a growing degree of prosperity that even then gave promise of its mighty awakening to become, as it has, a e.olossus of industry and commerce,-and the. leader in living standards of the world to-day.Australia, from such a shaky, and comparatively recent start, has risen to a position in which its living standards rank very high in comparison with those of most of the nations of Europe and America. Exact com-parisons are hard to fix because of the wide variety of factors involved .but the Institute of Pab?Lic Affairs .(Victoria) places Australia fifthin the world, excelled only by the U.S.A., Canada, Sweden and Switzerland. The next best after Australia are the United Kingdom, West Germany and France.How we achieved such a high standard of living is a vast subject for study but some of the economic aspects of our climb from abject poverty to a position of near affluence can readily be identified.

Jan 1, 1962

By H M. Parker, G Verly, T Postolski

Assessing the uncertainty and risk in mineral resource estimation is required for best practice and is implied by the public reporting codes in the categorisation of mineral resources and reserves. One industry best practice is quantifying the risk on future production for a given period, which can be done using two geostatistical approaches: conditional simulation and drill hole spacing studies based on estimation variances. Conditional simulation can provide a more complete and flexible answer to the problem, but it takes a fair amount of time to complete. Drill hole spacing studies are simpler, faster and can provide reasonable assessments of mineral resource uncertainty.This paper is a presentation of the principles, theory and practice of drill hole spacing studies. Various types of risk assessment are considered. Difficulties encountered in practice are discussed, and solutions are proposed. The important parameters impacting the results are reviewed. Examples of results and sensitivities are shown.CITATION:Verly, G, Postolski, T and Parker, H M, 2014. Assessing uncertainty with drill hole spacing studies – applications to mineral resources, in Proceedings Orebody Modelling and Strategic Mine Planning Symposium 2014, pp 109–118 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Nov 24, 2014

By C Katonga

Mindola mine is currently the deepest mine in the Zambian copper belt. Stoping is currently active to 1330 m below surface with long range plans indicating future production from 1590 m level. The orebody is tabular and dips between 55o to vertical. The thickness varies from 8 to 14 m. The vertical crater retreat method of mining was first introduced at Mindola mine in the late-1980s following several trials that helped define the design criteria for its application. Over the last ten years the method has been continually modified to improve safety and maximise ore production. For example, due to the weakness of some rock units within the orebody formation and the instability of the hanging wall, the last VCR slices are usually between 8 - 10 m thick, and efforts are being made to strictly apply shrinkage method in order to reduce dilution. Recent advances in mining technology in the areas of equipment, blasting techniques, rock mechanics and materials handling have been employed to increase the overall productivity of the mine. Large down-the-hole machines capable of drilling 165 mm diameter blast holes, up to 80 m long are used in stoping. Each stope produces up to 20 000 tonnes of ore per month and can last for three months. Heavy systematic ground support of VCR development has significantly enhanced safety for mining crews and equipment. Crater mining has not only improved productivity and enhanced safety, but also overcome various problems associated with conventional sublevel open stoping previously employed at the mine. This paper discusses the technical and operational aspects of vertical crater retreat mining at Mindola mine during the last ten years. The changes in mining method are often accompanied by changes in mine design, blast design, mining equipment, ground support and operating practices.

Jan 1, 2000

By B Manda, K L. Sandvik, K Musiwa

Mining and processing of pyrite ore at Iron Duke Mine, north east of Zimbabwe, generates large quantities of acidic mine water as a result of the oxidation of iron sulfides on exposure to air and water used in the drilling and blasting operations. The acid mine drainage (AMD) contains elevated levels of dissolved Fe, Al, Mn and sulfate and has characteristic pH values ranging from about 0.50 to 3.00. Handling and disposal of such a drainage places significant impacts on the economics of the mining operation due to the corrosive nature of the drainage on infrastructure, the limitations placed on water reuse and discharge to the environment under a new law governing effluent discharge. Treated sludge at Iron Duke is chemically unstable, changing pH from ~7 to ~3 within four days after deposition in the evaporation ponds. The effluent does not meet the permitted level of neutral pH, 500 mg/l sulfate and less than 2000 mg/l total dissolved solids. Excessive acid seepage from the evaporation ponds has resulted in contamination of the ground water below the ponds area, which shows high mean annual levels of iron (368.67 mg/l), sulfate (1702.89 mg/l) and low pH (2.86) in addition to other pollutants. This poor quality seepage infiltrates into the nearby Yellow Jacket River, contaminating the public water source. Furthermore, a deterioration of the land area and vegetation adjacent to the tailings dump is also observed. Understanding the controls on the neutralisation of acidic drainage and long-term sludge stability after placement in evaporation ponds is essential to minimise costs of closure requirements and for the protection of environment and human health. This study examined the effects of the master variables pH, redox potential, acidity and alkalinity on acid neutralisation. The results indicate that ferrous hydroxides are not as stable as ferric hydroxides and that proper oxidation of iron also leads to better sludge stability, higher treatment efficiency and a manageable sludge viscosity. Metal hydrolysis and secondary mineral formation at the evaporation ponds under a wide range of pH and redox conditions is responsible for equilibrium shifts in metal reactions, resulting in high potential for metal leaching and mobility. Mechanisms of metal attenuation are also discussed.

Jan 1, 2006

By L E. Krause

This paper discusses the considerations for optimum maintenance of critical ore handling infrastructure in order to minimise the cost to the business of maintenance periods. As maintenance periods are a direct interruption to production, time is of the essence and careful management of shutdown periods is essential. The ore pass systems currently in use at Xstrata Copper û Mount Isa Copper Operations are up to 30 years old and have had significant wear over the years. The maintenance of these passes and their brows and chutes in a production situation is a challenge as it can potentially expose personnel to high risk situations in addition to the production interruptions. Some alternatives for mitigating the risk of working in ore passes including plugging and ballooning are described. Criteria are included for selecting a method for the safe entry into a given ore pass. Experience in adapting the method of ore pass plugs and some lessons learnt in the process are also discussed.

Jan 1, 2005

By G W. Scott, R C. Johnson

Hypogene alteration zones have been described as a precursor to high-grade haematite deposits in Australia, Brazil and elsewhere. This alteration is described as being below or distal and is typically magnetite-carbonate-silicates reflecting Mg - Fe metasomatism. This paper describes, without genetic implication, the mineral zonation and possible structural control on mineralogic variation within the Tilden Mine, a concentrating grade haematite deposit in Michigan, USA. In contrast to the high-grade deposits, these variations are not peripheral to the orebodies but are the ore. The deposit occurs within the Negaunee Iron Formation, along the southern margin of the Paleoproterozoic Marquette Range Supergroup basin. The regional structure is a fault-bounded west plunging syncline within the crustal scale Great Lakes Tectonic Zone, which forms the boundary between Archean granite-greenstone and gneissic terranes. Local structure consists of second-order anticlines and synclines with variable northwest and southwest plunges. The interaction of sedimentation and diagenesis within growth fault controlled basins, along with a possible metamorphic and/or hydrothermal overprint has resulted in a complex series of ore types. For modelling purposes, the deposit is divided into geologic domains based on both lithology and metallurgical response in the laboratory and in the plant. Mineralogic variation is recognised within individual mineral grains; at blast pattern (10 - 15 m) and development drill hole (100 m) scales.

Jan 1, 2007

Resue or split face firing has the potential to separate ore and waste rock into separate muck piles within a stope. Thus split face firing has the potential to reduce dilution of the ore stream to be transported to the surface for subsequent processing. It also potentially reduces the total amount of broken rock needing to be transported out of the mine as the waste material is physically separated from the ore as part of the blasting process. Waste can therefore be used directly from the stope to backfi ll other mining areas. This paper reports on the results of split face firing trials at the Hillgrove mine in NSW and analyses the results of these blasts.

Aug 1, 2010

By G E. Holt

Active EM subsurface imaging is a proprietary technique developed by Marschall Acoustics Instruments Pty Limited (MAI) to image subsurface features at depths useful for the mining industry. Similar in field operations to high resolution seismic surveying, the Active EM technique employs electromagnetic energy rather than elastic wave energy. Received backscattered energy in the Active EM technique is thus due to differences and contrasts in electromagnetic permeability and permittivity in the subsurface, analogous to LamTÆs constants in elastic wave imaging. Carrying the analogy to seismic imaging even further, the Active EM method employs high power transmissions of very wide-band coded signals of a controlled polarisation. Likewise, the array pattern and polarisation of the receiving transducers is also tightly controlled. Thus, in a certain mathematical sense, Active EM is the electromagnetic equivalent of high power high resolution vibroseis seismic surveying. An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation.

Jan 1, 2008

By Gillies A. D S

The active history of foreign investment in the mining industry has resulted in Australia emerging as a major world producer of a range of mineral commodities. The current contribution to the national economy represented by mineral production and export revenues would not have occurred without both capital and expertise provided by foreign investors in the past. The initial foreign investment has led to the formation of Australian majority owned and controlled multi-national mining groups such as BHP Limited, CRA Limited and MIM Holdings Limited. These Australian companies, and others, are playing a significant part as foreign investors in the mining industries of Papua New Guinea (PNG) and Indonesia. The study examines issues of importance in foreign investment in each of the countries. It concludes that in Indonesia, the nationalisation of the Dutch mining industry in 1957 did much to deter foreign investment. The remarkable degree of policy stability brought about by the Contract of Works system since 1967 has gone a long way to restoring that confidence. The level of investment in the Indonesian mining sector is steadily increasing. Its attraction to Australian investors is a combination of policy stability, favourable fiscal terms, geological prospectivity for a range of commodities and proximity to Asian markets to the north. PNG has a stable policy regime which until recently has been free from political interference at the administrative level. As such, investors were developing confidence in the system and investment was progressively increasing as evidenced by growing exploration expenditures up to 1988. The 1989 Bougainville revolution caused a re-assessment of PNG's investment and country risk. The recent Mt Kare incident has further raised concerns over the government's ability to guarantee internal security. Foreign investors are faced with weighing concerns with the risks of operation in PNG against the undoubted geological prospectivity of the country. The fiscal regimes of Australia, Indonesia and PNG were compared by means of a simulated open pit gold mine in each country. The effect of taxation is examined by reference to the relative change in project internal rates of return (IRR). The comparison of the relative differences between pre-tax and post-tax IRRs provides a measure of the relative attractiveness of each fiscal regime.

Jan 1, 1994

"Recognising that the mining industry is wedded to the break-even cut-off grade rather than a cut-off grade that optimises value, the author examines some perils and pitfalls in the use of break-even grades that lead to what the author calls ‘negatively geared ore reserves’.Negatively geared ore reserves occur when a portion of the ore reserves actually has a negative value and is effectively being subsidised by the more profitable portion of the ore reserves. This situation is generally difficult to detect with the level of information available to the public investor. The ore reserves can still be quite profitable in total, but now possess a level of risk that may not be appreciated.The risk profile (financial risk) of a negatively geared ore reserve is far greater than for a non-negatively geared ore reserve. Like a negatively geared investment property in a falling property market (for readers familiar with the Australian tax minimisation investment strategy), when the price of a commodity falls, a company that possesses a negatively geared ore reserve loses value at a magnified rate relative to a company that has a neutral or positively geared ore reserve. In the extreme case of a major commodity price reduction, as happened with the gold price in mid-2013, the negatively geared ore reserve can easily become negative value in total, not just in part.The negatively geared ore reserve is sometimes intentional – for instance in order to increase published ore reserve tonnages and meet the CEO’s key performance indicators – but is also often unintentional, resulting from various errors in the break-even calculation. Common errors in calculating a break-even grade include using fixed metallurgical recoveries, not including allowances for ideal laboratory versus real plant results, ignoring available operational data and using modal rather than mean parameter values in cost and performance calculations.This paper examines a common value distribution profile in many ore reserves and the effect of common break-even grade errors on this profile.CITATION:Poniewierski, J, 2016. Negatively geared ore reserves – a major peril of the break-even cut-off grade, in Proceedings Project Evaluation 2016, pp 236–247 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Mar 8, 2016