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Laboratory and pilot plant investigations aimed at recovering gold as an electroformed sheet from gold eluate and gold leach solutions and slurries are discussed. The electrolytic test work undertaken makes use of high surface area electrodes, in particular nickel-chrome foam metal and activated carbon, as well as ultrasonic activation. The process involves initial gold electrowinning (or adsorption onto activated carbon), followed by gold electroforming, both operations being carried out in a specially designed reactor. The pilot plant work mainly involved the treatment of gold eluate solutions from a South African gold mine containing 600 mg/L Au: some tests were also carried out on gold leach solutions containing 6 mg/L Au. In the former case, very efficient gold extraction onto the foam metal cathode was achieved using electrolysis combined with ultrasonics. The polarity of the gold-loaded cathode was then reversed and, using a replacement electroforming electrolyte, gold was electroformed in situ onto a polished stainless steel mandrel, from which gold sheet was subsequently removed. In the case of leach solutions, pilot plant tests confirmed laboratory findings that in the presence of calcium (resulting from the lime used during the leaching process) no electrowinning is possible. Laboratory tests showed, however, that when sodium (in the form of NaOH or Na2CO3) is added to the leach solution, electrowinning can indeed take place. Alternatively, if a special activated carbon electrode is used (without current), the non-ionic calcium aurocyanide complex is adsorbed on to the activated carbon. When a gold-loaded activated carbon electrode is made anodic in a gold electroforming electrolyte, gold electroforming is feasible, although the efficiency is very low. The possible implications of these developments for gold recovery are further examined.

Jan 1, 2007

By R L. Brathwaite, R Carver

The REGCHEM (Regional Exploration Geochemistry) database of open file mining company data, managed by GNS Science, has recently been upgraded with the compilation of additional data, especially for the Otago region (see http://maps.gns.cri.nz/website/minmap). In June 2007, data compiled for the Otago region included more than 2000 stream sediment samples from 19 surveys, more than 800 BLEG (bulk leach extractible gold) samples from 12 surveys and a few pan concentrate samples. The stream sediment samples were typically analysed for Au and As, and in many cases for other elements including Cu, Pb, Zn, Sb, W and Mo. The BLEG samples were analysed for Au and in some cases also for As. The main exploration target was mesothermal gold deposits in the Otago Schist, although one survey of the Otago Peninsula targeted potential gold deposits associated with the Dunedin volcanic complex. Geochemically, the mesothermal gold deposits are characterised by anomalous As and Au, with some also characterised by anomalous W and Sb, and these four elements are the best pathfinders in stream sediment geochemical surveys. The introduction of lower detection limits in Au analyses in the more recent stream sediment surveys and in the BLEG surveys enables the use of this element as the primary pathfinder for mesothermal gold deposits.

Jan 1, 2007

Ladies and gentlemen, distinguished guests and fellow members of The AusIMM, good morning.   Thank you for the opportunity to address you all today, Crown Minerals are very pleased to be associated with the conference again this year, and I commend the committee on their organisation and delivery of this yearÆs event.   As you can see from the topic of my discussion, I would like to broach the subject of collaboration between ourselves û Crown Minerals û and you our clients, and convince you that we are on the right track but can each do more.

Jan 1, 2007

Project evaluation is completed through individual studies covering technical and financial aspects of the mine to market. These studies are completed at various levels of detail depending on where the project evaluation is in the projectÆs life cycle. The competency of the studies varies in relation to the quality of data, level of the skills employed, control, management and reporting structure. The focus of this paper is managing elements of the study, looking at the cost of opportunity to influence the project, against the value added. Selection of the study manager and study teams is central to getting an integrated project evaluation addressing the correct issues completed on time. Retention of key personnel can reduce rework which, in turn, can reduce time and cost impacts. It is important to have a work breakdown structure at the outset so that the study teams have a common numbering and naming system that will integrate areas, equipment, budgets estimates and accounts. Having set up the evaluation groups and provided training in the study procedures, understanding the scope and schedule are vital elements in producing a project evaluation that addresses the opportunities and the risks of the final project. Arriving at an accurate capital budget requires integration of the research controlled through common systems. Project evaluation process must also address how the project is to be delivered.

Jan 1, 2007

By J S. Moema, R Paton, J Zimba

Today, most organisations are familiar with the pressure to increase their effectiveness and efficiency, regardless of the nature of their business. Cost cutting and increased productivity are the main themes of many initiatives to ensure the profitability of operations and, ultimately, shareholder satisfaction. It is well known that the cost of comminution to liberate minerals such as gold from their respective ores is a major expense for mines. Comminution costs consist predominantly of grinding balls and electricity. However, there are no national or international standard specifications for grinding balls û on which a single mine may spend several million dollars per month. In addition, in the past mines generally did not specify the minimum requirements when purchasing grinding balls from suppliers. The result is that every supplier has its own grinding ball recipe (regarding chemistry and heat treatment), and is under no pressure to implement a quality assurance plan to ensure that a consistent product is delivered. The resulting variation in the quality of grinding balls leads to increased steel consumption rates and hence increased milling costs. A more stringent quality plan will generally not be welcomed by suppliers since this may entail further investments and/or reduce the production rate. In a sense, suppliers benefit from poor quality grinding balls as this leads to increased sales. Perhaps the main problem is a lack of understanding of the factors that influence grinding ball performance. This paper will describe the factors that influence the wear rate of grinding balls from both a microstructural perspective and a mill perspective. In addition, some insights are provided on the different grinding balls available and ways that users can verify their quality.

Jan 1, 2007

By E S. Souza, H Delboni Jr, M F. Calixto

This paper aims at presenting the results of laboratory, pilot plant and simulation studies for the design of the grinding circuit for the beneficiation of compact itabirites from the Conceitpo mine. Two alternatives were investigated, both utilising the current crushing circuit up to tertiary crushing. Under alternative #1, quaternary crushing was considered to produce the feed of the ball mill; under alternative #2, high pressure grinding rolls were selected to prepare the ball mill circuit feed. Pilot scale studies pointed towards the use of high pressure grinding rolls (HPGR). The circuit design was based on a throughput of 720 t/h, representing a nominal solids flow rate of 600 t/h, considering a design factor of 1.2, and P80 of 95 ¦m.

Jan 1, 2007

By B S. S Rao, S Chandra

IndiaÆs iron ore mining industry is growing rapidly in order to augment the capacity to meet the unprecedented demand for the iron ore. Traditionally, much of Indian iron ore production came from exploitation of high-grade haematite ores, with the exception of Kudremukh which beneficiates lean grade Banded Magnetite Quartz ore. Now with the changed scenario of demand and supply, keeping long term sustainability in mind, it is imperative to develop suitable processing technology for exploitation of banded haematite quartz (BHQ) ore available abundantly and not utilised so far. In this direction detailed characterisation and beneficiation studies were conducted with BHQ iron ore from the Bellary-Hospet region of India, assaying 36.5 per cent Fe. The mineralogical studies with the image analyser system revealed the presence of maghemite and haematite as iron-bearing minerals. The gangue mineral associations were siliceous, ferro-magnesian and carbonate minerals. Higher degrees of liberation were observed in the size range of 75 - 212 microns. Liberation grind tests were performed by grinding the ore to different top sizes in a closed circuit laboratory ball mill with the ground samples subjected to Davis tube tests. The yield, grade and recovery were used as parameters to plan a two-stage wet drum magnetic separation based on grinding the primary magnetic concentrate. After subjecting the final magnetic concentrate to flotation to remove residual silica a concentrate assaying more than 68 per cent was obtained. The non-magnetic product from the primary magnetic separation was deslimed, ground, blended with secondary magnetic tails and was subjected to a two pass wet high intensity magnetic separation (WHIMS). The WHIMS concentrate was further subjected to two-stage flotation to remove residual silica to obtain concentrates assaying 64 - 66 per cent Fe. The final combined concentrate from wet drum magnet and WHIMS after flotation could yield a blast furnace (BF) grade pellet feed concentrate assaying more than 65 per cent Fe with a yield about 39 per cent and iron recovery about 70 per cent. A direct reduction (DR) grade pellet feed concentrate assaying 67 per cent Fe with a yield of about 28 - 31 per cent and iron recovery about 53 - 57 per cent could also be produced. Based on the test work, a process flow sheet was developed to beneficiate the BHQ ore for production of BF/DR grade pellet feed concentrate. In this paper methodology adopted for selection of individual process, various diagnostic tests performed to rule out other beneficiation processes and the final process flow sheet development is presented and discussed in detail.

Jan 1, 2007

By J Manuel, L Lu

Increasing bed depth is one of the main options sinter plants consider to increase production, since it is an incremental improvement and less expensive compared with a new plant. To maximise the benefits of increased bed depth, correct blend design and plant operation is critical. This paper discusses test work conducted to show the effects of ore type and bed depth on sintering performance and the adjustments required in both fuel rate and lime addition depending on ore type. The differences in sinter plug macro and microstructure were also examined to show the effect of bed depth on ore assimilation and matrix formation. Finally, the benefits of blending ores to achieve the best sintering performance as bed depth increases is discussed.

Jan 1, 2007

Gold mining in Australia and globally has a long and variable history. In recent years, due to ongoing public concern over long-term environmental impacts, the mining industry globally has been moving towards a more sustainable framework, presented as the æMining, Minerals and Sustainable DevelopmentÆ (MMSD) framework at the Johannesburg Earth Summit in 2002. There are a number of fundamental issues and concerns with assessing the sustainability of mining. Firstly, long-term trends show that ore grades for almost all metals and minerals will continue to decline (some rapidly so), increasing waste rock is being produced due to the trend towards large-scale open cut mining and more complex ores are now commonly being developed. The impact of these trends on the resource intensity, or unit cost, of gold production is of major concern as it could lead to an increase in energy, water and reagent consumption and greenhouse emissions per unit gold produced. A detailed compilation of these fundamental sustainability indices for gold mining has been undertaken, and is presented with respect to indices over time, ore grade and ore throughput. A clear observation is that the resource intensity of gold mining is extremely sensitive to the ore grade, with energy, water and cyanide consumption and greenhouse emissions rising significantly as ore grade decreases. Based on the gold ore resources at operating mines and other known gold deposits, it is most likely that the average gold ore grade will continue to decline, leading to increased resource intensity and consequent environmental impacts (assuming no breakthrough new technologies occur). These findings are of major importance to understanding the sustainability of gold mining. The final judgement of the sustainability of gold mining therefore must take into account the sensitivity of the ore grade in the resource intensity of gold production.

Jan 1, 2007

By P Lotz

With the recent increase in environmental awareness, gold mining companies are fast becoming signatories of the International Cyanide Management Code (ICMI, 2007). The objective of the Code is to improve the management of cyanide used in gold mining and to assist in the protection of human health and the reduction of environmental impacts associated with the use of cyanide. In particular the code specifies the following cyanide concentration limits: 50 ppm WAD cyanide in a tailings storage facility, 0.5 ppm WAD cyanide for effluents, and 0.022 ppm free cyanide or 0.022 ppm WAD cyanide as surrogate in the post mixing zone of river discharge. Weak acid dissociable (WAD) cyanide refers to those cyanide species liberated at a moderate pH of 4.5, such as HCN(aq) and CN-, and the majority of Zn, Cd, Cu, Ni and Ag complexes with low dissociation constants. It is potentially toxic to humans and animals. Gold plants using cyanide should ideally measure WAD cyanide online and destroy WAD cyanide in excess of the applicable limits to ensure compliance with the Code. Mintek has recently developed an online WAD cyanide analyser (WAD Cynoprobe). The WAD cyanide analysis technique is based on the use of a ligand exchange reagent that liberates WAD cyanide bound to metals such as Zn, Cd, Cu, Ni and Ag. The ligand exchange reaction is represented by the following chemical equation: Metal(CN)X + yLigand ↔ Metal(Ligand)y + xCN- The plant filtrate is treated with a ligand exchange reagent, to liberate WAD cyanide, before measuring the free cyanide concentration via amperometry. The WAD Cynoprobe measures both free and WAD cyanide concentration. Its fast analysis time, approximately five minutes, makes it suitable for use in the control and optimisation of the cyanide destruction and recovery process. The instrument has proven accurate and reliable in the analysis of synthetic copper, nickel and zinc cyanide solutions made up in the laboratory as well as under industrial gold plant conditions during various trials. The WAD Cynoprobe has gained widespread commercial acceptance and is currently implemented on nine gold plants around the world.

Jan 1, 2007

By S Brunt

A new elution process has been developed for the recovery of gold thiosulfate from ion exchange resins. This is a synergistic system which utilises a base eluent, such as nitrate or trithionate, along with an additive that improves the elution of gold. The use of the additive enables lower eluent concentrations to be adopted, as well as weaker eluents such as chloride. With the chloride + additive system, complete gold elution can be achieved within 12 BV when utilising an eluent flow of 5 BV/h. When the eluent flow is reduced to 2 BV/h, complete elution is achieved within 8 BV. Similar results are obtained when using nitrate or trithionate as the base eluent. A copper pre-elution process has also been developed, whereby the majority of copper can be stripped within 5 BV prior to gold elution. This method is a significant improvement on the ammonia + oxygen pre-elution previously suggested. The development of a new analytical procedure based on ion chromatography with UV detection is also described for the quantification of polythionates in leach solutions and loaded on resins. This enables analysis to be carried out for resin-in- leach type processes where the polythionates are being formed in solution and simultaneously adsorbed onto the resin.

Jan 1, 2007

Gold mines produce unique water treatment requirements. This paper focuses on case studies of innovative processes used for treatment of water resulting from gold mining and processing. The case studies include treatment of mine dewatering water for beneficial application from an Australian gold mine, Bendigo Mining, as well as treatment for arsenic removal of tailings water from mining and processing at Goldcorp mines in Canada. Gold mining can often require dewatering to prevent groundwater seeping into and flooding the mine workings. Gold mining and processing often accumulate wastewaters in a tailings dam. The mine water can contain contaminants such as dissolved salts, iron, arsenic, manganese, heavy metals and odorous sulfates. Environmental discharge requirements as well as community needs for water drive mine operators to consider the most appropriate water treatment process. Treatment of gold mine water can require processes including oxidation, pH adjustment, coagulation, flocculation, clarification, further oxidation/adsorption of specific metals such as manganese, filtration, salt reduction utilising reverse osmosis, brine minimisation and other innovative technologies. These processes are discussed through the case studies with examination of the specific treatment process that is required. This paper uses real case studies of gold water treatment processes to explain and examine the technology and the reasons for designing specific processes. The focus is toward explaining innovative processes where the water is used for sustainable environmental discharge or treatment to a quality that can be beneficially used by the local community.

Jan 1, 2007

By B Ilich, M Brad, R Brandli, E MarT

The Wirtgen surface miner was investigated for application to the Cloud Break iron ore deposit since it can selectively mine thin seams and there is no requirement for drilling and blasting or primary crushing as the surface miner cuts and breaks the rock to secondary cone crusher feed size. A physical metallurgical study of the surface miner run-of-mine (ROM) from Cloud Break was conducted to better understand the product size distribution, amount of -31.5 +6.3 mm lump produced, lump stability and physical metallurgical quality compared to conventional drill and blast techniques. Since the Cloud Break mine was not in production, the lump product from crushing and screening of surface miner ROM was compared with product simulations using traditional premining physical metallurgical processing techniques including drop testing of PQ diamond core. Drop test conditioning is widely used in the iron ore industry to simulate blasting, crushing and screening at the mine and subsequent product degradation during handling from mine to port to predict both the amount of lump product on ship and the size distribution of the fines and lump. The size distributions of surface miner ROM for hard, medium and friable ore types show very tight size distributions with very little above 100 - 150 mm, about 60 per cent of the distribution between 75 and 6.3 mm, with less below 1 mm compared to conventional drill and blast ROM. Crushing, screening and drop test conditioning of the surface miner ROM produced more lump in equivalent ore types compared to drill and blast techniques or their breakage simulation using PQ diamond core. The higher lump yield from the surface miner was also confirmed by pilot scale crushing of some 7400 t of surface miner ROM from the Cloud Break trial pit. The lump produced from surface miner ROM was quite stable and showed similar low degradation characteristics to lump simulated from drill and blasting techniques. Product size distribution simulations using conditioned crushed lump from 1 m diameter Bauer hole samples were found to compare well with processed PQ core samples and surface miner product from trial mining at Cloud Break. The Bauer sample method is therefore considered to be a very useful close simulation to actual lump production, although the lump yield is lower.

Jan 1, 2007

By J G. Webster-Brown

The Tui Mine is located near Te Aroha at the base of the Coromandel Peninsula. It was a lead-zinc mine, which closed in 1973 due to declining concentrate prices, high overheads, and high mercury levels in the ore. The site was abandoned, leaving behind an acid rock drainage generating system, including a sulfide-rich tailings dam which has since caused pollution of Tui Stream, as well as open adits and waste piles which drain predominantly into the neighbouring Tunakohoia Stream. At the AusIMM conference in 2003, Harvey and Webster-Brown presented water quality results from the Tui mine site and lower stream catchments in 2002. In April 2006, Environment Waikato undertook remediation works to stabilise the dam and reduce acid drainage entering Tui Stream. In this study, water quality results from the Tui mine site and lower stream catchments are again being determined, in order to compare with the pre-remediation results. Preliminary data collected for summer indicate a minor but consistent improvement in water quality in the lower stream catchments, although lower Tui Stream continues to exceed ANZECC (2000) aquatic life guidelines for Cd, Cu, Pb and Zn. This slight improvement may be due to a decrease in the flow of ARD into Tui Stream, as there does not appear to have been an improvement in quality of the contributing ARD waters.

Jan 1, 2007

The Beaconsfield gold mine processing plant is a complex operation and utilises crushing, grinding, gravity gold concentration, sulfide flotation, bacterial oxidation, cyanidation and zinc cementation to recover gold from the partially refractory ore. This paper discusses the challenges, developments and advancements throughout the processing plant since start up, which have culminated in a 25 per cent increase in the mill throughput over the nameplate design and a concomitant gold recovery increase from 75 to 92 per cent. The improvements have been attained via advancements in mechanical integrity, metallurgical review, process control and operator training, resulting in the current operation producing over 630 000 ounces of gold to date.

Jan 1, 2007

Its two years since we have presented at this conference and since that time we have made significant progress with our coal developments in New Zealand. In 2005 we held the Whareatea West exploration permit and had just completed the purchase of the Cascade mine. Today, in addition to Cascade and Whareatea we now have the Takitimu Mine, Eastern Coal Supplies, our coal blending and distribution facility in Timaru, prospecting permits at Ohai and Orepuki and an established customer base underpinned by the contract to supply FonterraÆs Clandeboye plant commencing in September 08. For this presentation I would like to take you through our purchase and development of the Takitimu mine.

Jan 1, 2007

The profitability of gold placer mining operations is determined by more factors than many placer miners recognise until too late. This study is based upon field trips to examine the efficiency of mining and transportation of gravels to a wash plant by bulldozer and truck. At the examined open pit mining operations gravels were washed using water canons, derockers or scrubber trommels. The objective of this study was to determine the relationship between unit costs and power requirements for gravel mining and processing. The author conducted a number of time and motion studies at four open pit gold mines, including the Maly Patom Creek, the Nizhny Patom, the Taimendra Creek and the Kadali-Makit in the Bodaibo District, Irkutsk Region and collected and processed field data. As a part of the study significant correlations were determined and empiric regression equations derived between: power requirements (Ep) and unit cost (Cp) for gravel processing; and total power requirements (Et) and total unit cost (Ct) for gravel mining, transportation and processing. Based on the results of the study it was proposed to modify the current mining procedure methods and to replace water cannons at the Maly Patom Creek with a PPM-5 derocker. Introduction of the proposed technology resulted in 2004 in US$385 000 mining cost reduction at the Maly Patom Creek over a short-time Siberian mining season.

Jan 1, 2007

Knelson concentrators are commonly used to recover fine liberated gold in gold processing plants. The decision to employ a gravity gold circuit consisting of centrifugal devices such as Knelsons is primarily taken on the results of GRG tests, among other considerations. While the GRG test is considered a material characterisation test, which is useful in the design stages, its use in evaluating the performance of an existing unit is questionable. The problem is exacerbated by the fact that it is time consuming and costly. This paper examines the validity of the GRG test for performance evaluation and discusses alternative test work that can be performed to evaluate the performance characteristics of an operating machine. Principles that are useful in selecting optimal operating parameters, such as optimal fluidising water flow rate for a given ore/machine combination, are also discussed and illustrated with laboratory and plant data.

Jan 1, 2007

By D Macfarlane, T McMorran

  This paper describes the design and construction of the upper section of the Pike River Mine Access Road. The road extends 11 km from Logburn Road alongside Big River on the West Coast of the South Island of New Zealand up Pike Stream to the new mine portal on White Knight Stream (Figure 1). This new road starts on alluvial terraces, then partially follows an old logging road before entering virgin bush and traversing the true left bank of a steep sided gorge on Pike Stream some 50 - 100 m above the stream before dropping down to the mine entrance. Its development has been an extended process from route selection, consenting through to design and construction.   The paper focuses on the 1 km section of road between the Amenities Area (Figure 1) and the portal. This section of road is a steep section through the gorge, principally on Conservation estate, and has presented the most challenges and required the greatest effort to obtain the regulatory approvals, prepare the design and to construct. This paper outlines the history of the challenges faced and how the road was successfully developed.

Jan 1, 2007

By N J. Welham

This paper reports on an innovative professional development program for school science teachers run collaboratively between the Centre for Sustainable Resource Processing and Murdoch University. Ultimately the initiative aims at increasing the pool of school students with strong science and mathematics backgrounds while highlighting the challenging careers available in the mineral resource sector including the gold industry. The program is unique in that it seeks to develop a network of science teachers who may participate in a series of workshops, short courses and tours over several years. The objective is to raise secondary school studentsÆ awareness of potential careers within the minerals sector by exposing teachers to a real life, hands-on look into the mining and minerals resource industry. Though the program includes the breadth of the resource processing sector, the potential value to gold processing is in developing a greater pool of potential employees. The initiative allows teachers to develop a better insight into the practical applications of the theoretical sciences they are required to teach. The evolution of the program from the first trials with Western Australian teachers to the introduction of the initiative to Queensland teachers are reported on. Additionally, the results of a pilot study involving 40 participating teachers are described. This study used a questionnaire and follow-up interviews to gain quantitative and qualitative feedback from teachers. There is evidence that the professional development program has resulted in teachers acquiring a new found appreciation for the application of the fundamental chemistry and physics they teach within the school curriculum. Also reported are associations between teacher participation in this professional development program and changing attitudes towards the industry in a positive way. Finally, there is some indication that these positive teacher attitudes may result in their students developing a better understanding of the diversity and availability of career paths within this industry.

Jan 1, 2007