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By G F. Brent, S Hawke, M Rothery, P Dare-Bryan

Mine-to-mill studies have previously demonstrated downstream productivity benefits from relatively modest increases in blast energy, or powder factor. These increases have up to now been limited by safety and environmental constraints, since excessive blast energy can result in flyrock, unacceptable vibration, airblast and wall damage.Here, a new blasting method that overcomes these constraints is presented. For the first time it is possible to employ powder factors that are several fold higher than conventional blasting. Independent modelling has shown that such powder factors can potentially increase mill throughput by 20 to 40 per cent. The economic implications are substantial, both in terms of increasing production in existing operations and in consideration of capital and plant requirements for greenfield sites. In addition, mill electricity and grinding media consumption and their associated costs and energy and emissions penalties can be reduced.This method represents a step-change in blasting practices. It involves a novel design utilising dual blast layers within a single blast event, all initiated with state-of-the art electronic blasting systems. The energies in the lower layer can be as high as five times the standard energies, providing for intense fragmentation of the ore. Results from blast models have been confirmed in field trials of the method.Open cut gold mining, in particular, stands to benefit from this method. As gold grades decline, milling costs and throughput increasingly become constraints on production that can be alleviated with this new method. Additionally, it opens possibilities for improved recovery. Blast modelling studies show that dilution of gold ore within the blast can be managed with the new method. Furthermore, it has been shown that vibration from the new method is actually lower than from conventional blasting, allowing the use of the technique in proximity to mine highwalls and other key infrastructure such as underground orepasses.It is concluded that this new method could substantially increase gold mine production and profitability while reducing overall energy consumption and associated emissions.CITATION:Brent, G F, Dare-Bryan, P, Hawke, S and Rothery, M, 2013. Ultra-high-intensity blasting - a new paradigm in mining, in Proceedings World Gold 2013 , pp 395-400 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By W T. C Kendall, H D. Ngo

Garden Well is a shear-hosted Archaean orogenic gold deposit located 100 km north of Laverton, Western Australia. The Garden Well processing plant is designed for a nominal 491 t/h milling rate and annual capacity of 4 Mt. The plant has three key innovations:1. a scrubbing circuit, expected to reduce grinding power consumption by up to 20 per cent2. a secondary cycloning/gravity circuit, providing a second opportunity for gravity gold recovery (additionally, the circuit effectively increases the leach residence time of the coarse gold bearing fraction of the leach feed by approximately 60 per cent, without any additional tankage)3. the use of mid-stream oxygenation to enhance gold recovery.The Garden Well deposit is free-milling with overall laboratory gravity/leach gold recoveries exceeding 95 per cent at a P80 grind size of 150 ¦m. Three mineralogical domains have been identified: oxide, transition and fresh, with the fresh domain having subdomains of fresh ultramafic and fresh shale. There is a high component of gravity recoverable gold in all three domains.This paper will discuss these innovations and the design challenges and the risk mitigation strategies that were adopted to ameliorate the prototyping risk. The performance of the plant since commissioning together with lessons for the future will also be presented.CITATION:Smith, R J, Kendall, W T C and Ngo, H D, 2013. Treatment plant innovation at Garden Well, in Proceedings World Gold 2013 , pp 315-324 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By J Savage, A Crawford, M Doyle, N McNaughton, T G. Blenkinsop

Area selection criteria for gold exploration have historically highlighted the low prospectivity of high-metamorphic grade terranes relative to regions with lower metamorphic grades. The Tropicana gold project, Western Australia, is a rare example of a major greenfields gold discovery in Archean mid-amphibolite to granulite-facies gneissic rocks that have experienced widespread recrystallisation and partial melting.The project, located on the tectonically reworked eastern margin of the Yilgarn Craton, is part of the Tropicana Joint Venture, which is 70 per cent owned by AngloGold Ashanti Australia (manager) and 30 per cent by Independence Group NL. Construction of the mine commenced in the June quarter of 2011 and first gold pour from open pit mining is anticipated in the December quarter of 2013. The approved project will have a ten-year mine life and in the first three years of operation, gold production will be between 470 000 - 490 000 oz/a at a cash cost of A$590 - A$630/oz.Reserves as at 31 December 2011 total 56.4 Mt grading 2.16 g/t for 3.91 Moz of gold. The mineral resource, as of 30 December 2012, has grown to 7.89 Moz of contained gold, including Inferred Resources of 11.9 Mt at 2.83 g/t for 1.08 Moz.Economic gold mineralisation post-dates peak metamorphism and is interpreted as younger in age (ca. 2500 Ma) than other gold deposits in the Yilgarn Craton on the basis of structural and geochronological constraints. Mineralisation is genetically related to an imbricate thrust stack that records a prolonged history of reactivation during the Proterozoic era. Gold mineralisation formed from higher temperature (>350¦C) silica-undersaturated fluids that preferentially migrated though a favourable intensely potassium metasomatised zone. Permeability created during brittle fragmentation was accompanied by replacement of mafic metamorphic minerals, and synchronous partitioning of strain into pervasively biotite-sericite-pyrite-altered stylolites and shear planes that bound more competent lithons.CITATION:Doyle, M, Savage, J, Blenkinsop, T G, Crawford, A and McNaughton, N, 2013. Tropicana - unravelling the complexity of a +6 million ounce gold deposit hosted in granulite facies metamorphic rocks, in Proceedings World Gold 2013 , pp 87-94 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By R J. Beazley, M C. Woods

"The International Cyanide Management Code (the Code) is a voluntary industry program for gold miners and associated cyanide transporters and cyanide producers. By becoming a signatory, a company commits to follow the CodeÆs principles and implement its standards of practice.Signatories are required to undergo an initial certification audit within three years and a recertification audit every subsequent three years. Recertification audits evaluate compliance over the preceding three-year period. This approach presents a number of challenges. Golder Associates has undertaken in excess of 75 initial certification audits and 25 recertification audits; more than any other audit firm. This paper outlines some of the challenges identified and lessons learnt from the recertification audit process. Central to the process is the challenge for organisations to maintain commitment to compliance over the full three-year period and effectively address deficiencies or non-conformances that may have occurred during that period in a prompt manner.The International Cyanide Management Institute (ICMI) provides guidance in evaluating deficiencies or non-conformances, which requires consideration of the æcauseÆ, ædurationÆ and æongoing compliance effortsÆ and an assessment of the concept of ægood faithÆ in response actions. Golder AssociatesÆ experience with the recertification process highlights some common deficiencies with Code compliance programs, such as: system breakdowns (leading to ineffective communication between departments or loss of information) exceedance of discharge limits inadequate inspections, maintenance activities and associated record-keeping.Such deficiencies can be attributed to: personnel changes organisational changes or structures management systems (eg integrated or standalone) awareness and interpretation of Code requirements transparency of management decisions with Code implications.We have identified that ongoing programed assessment is an effective strategy in maintaining Code compliance.CITATION:Beazley, R J and Woods, M C, 2013. Cyanide code recertification - the three-year challenge, in Proceedings World Gold 2013, pp 247-254 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Sep 26, 2013

By J Tiihonen, J OÆCallaghan, T Haakana

Outotec is today capable of providing technologies, process equipment and engineering for the construction of pressure oxidation leaching (POX) plants in any location in the world. Outotec works with customers from mine to pure metal, participating in plant design from the process development phase (including test work execution/supervision) to plant commissioning and operations. Either key equipment technology packages with basic engineering or entire POX plants can be supplied.The addition of pressure oxidation equipment to OutotecÆs product portfolio adds to and complements already existing significant experience in general hydrometallurgical process and proprietary equipment design and supply.In addition to providing key pressure vessels, piping and valves to a POX plant, Outotec can offer an enhanced and proven autoclave agitation system that maximises oxygen mass transfer and utilisation. Novel energy and water recovery technology can also be tailored to a customerÆs specific needs. Importantly Outotec owns and operates extensive test work facilities and can provide test work to ensure the optimum POX flow sheet and materials of construction. Outotec ensures that best available technology (BAT) concepts are used in POX design to improve the availability of the process and minimise unpredicted shutdowns.CITATION:Tiihonen, J, Haakana, T and OÆCallaghan, J, 2013. Outotec pressure oxidation - more out of sulfide ore, in Proceedings World Gold 2013 , pp 197-206 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By P Breuer, X Dai, A Bergamin, D Hewitt

"Copper-ammonia-thiosulfate?leaching of gold has been researched for several decades as a potential alternative to cyanidation. However, this technology has not yet been applied commercially due to many challenges such as complex solution chemistry, reagent degradation and losses, system instability with losses of precious metals and difficulties in gold recovery from the leachate. Progress has been made at CSIRO in tackling some of these challenges including:better understanding and control of the leach conditions to minimise reagent losses whilst maximising gold recovery use of strong base ion exchange resins to recover the gold strategies to deal with polythionates that adsorb competitively with gold on ion exchange resins development and evaluation of process flow sheets.As a result there has been increased interest from the gold industry and renewed activities to develop thiosulfate based processes for gold recovery. One application area, which has been developed to the point of piloting, is the treatment of gravity gold concentrates using a copper-ammonia-thiosulfate leach with ion exchange recovery of the gold thiosulfate. This paper describes some of the advancements in the development of a potential process flow sheet for this application.CITATION:Dai, X, Breuer, P, Hewitt, D and Bergamin, A, 2013. Thiosulfate process for treating gold concentrates, in Proceedings World Gold 2013, pp 61-70 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Sep 26, 2013

By L Lorenzen, H Muller, L Bernard

Australian companies and consultants are becoming ever more involved in projects in African, South American, East European and Middle Eastern countries. However, significant differences in culture and approach to projects sometimes make these projects challenging for reasons that are not purely technical. Often the challenges are rather related to how the project owner and local authorities perceive the reality. These perceptions and sometimes unrealistic expectations regarding project costs and potential outcomes need to be addressed by the æWesternÆ project developer and consultant.This paper will discuss the specific experience of Snowden in studies commissioned by companies from such countries for the development of very large, low-grade gold deposits in some of the most inhospitable areas in the world. The paper will further review similar projects undertaken in other ænew worldÆ countries and compare these to the initial Snowden experience.As the process operating costs of operations in many of these countries are extremely competitive when compared to the typical Australian operating costs, the paper will review the operating costs and the factors which may be pertinent to a large project of this nature, both in the Australian and the ænew worldÆ context. Will Australian-based operations be able to compete in the global gold market when the gold price softens again, as it will do at some stage in the possibly not-so-distant future?CITATION:Muller, H, Lorenzen, L and Bernard, L, 2013. Challenges of developing low-grade deposits in ænew worldÆ countries from a mining consultantÆs perspective, in Proceedings World Gold 2013 , pp 307-314 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By D Capstick, M B. Ebell

This paper describes the test work, process design, commissioning and operation of a processing system at the Ergo gold operation that improves the extraction efficiency from gold tailings material. The improvement in recovery is derived from the separation of the gold contained within the sulfides of the tailings material and a dedicated process stream to recover that gold.The sulfides are separated by means of a flotation circuit and that resulting concentrate is subjected to a regrind of below 20 ¦m to enable a greater liberation of the gold. The ultra-fine material is then subjected to a dedicated leach circuit to recover the now exposed gold particles.The case study is an example of the challenges of introducing new technology and methodologies to a well-established operation and thereby attaining improved efficiencies and tangible business benefits.CITATION:Ebell, M B and Capstick, D, 2013. Improving extraction efficiency from Witwatersrand gold tailings using flotation and ultra-fine grinding of concentrates, in Proceedings World Gold 2013 , pp 301-306 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By T Bookless, J Pownell, D Meadows

The ever increasing trend of the gold price has meant that ore deposits that were previously considered too complex, or unattractive by virtue of their low gold grade, are now being investigated more closely. These ore deposits present a greater risk of failure than previously was the case. To ensure that the risk of project failure is reduced and the maximum value is derived from the deposit, its mineralogy, as well as other characteristics, should be well understood such that the optimum process can be designed.Quite often the flow sheet design is assembled using individual process components, from various sources, and without consideration of the complete system. Test work programs require careful planning and an open viewpoint in terms of comminution circuit design particularly with respect to ever increasing power costs across the globe. As an example, high pressure grinding roll (HPGR) technology in many cases offers better mineral liberation than the more traditional comminution devices and it does so at a reduced energy input, and yet HPGR test work is often restricted in its scope due to the perceived novelty of the technology and the resultant lack of generally agreed and accepted test work routes.In this paper the authors outline a typical HPGR test work process route driven by the needs of different ore types and illustrate that to optimise the project value, any test work program should start from the premise that thorough understanding of the ore is vital.CITATION:Bookless, T, Meadows, D and Pownell, J, 2013. Enhancing project value through a designed high pressure grinding roll test work program, in Proceedings World Gold 2013 , pp 291-300 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By S T. L Harrison, J-P Franzidis, M Becker, N Dyantyi, J L. Broadhurst

Gold mining is a major contributor to the South African economy, but is associated with several environmental issues such as acid rock drainage (ARD). ARD is due to the oxidation of sulfides in gold tailings and is characterised by low pH, high sulfate content and elevated concentrations of heavy metals that contaminates scarce water resources and subsequently limits the use of such waters without treatment. Treatment strategies can only be implemented if the acid-generating potential of mine wastes is effectively predicted using common static and kinetic acid prediction tests. The choice of test performed is usually a trade-off between the number of samples, speed of the test, cost of the analysis and level of information obtained. Often the results of these various tests are not consistent with one another. This study uses mineralogy to analyse biokinetic test results of a Witwatersrand gold sample in order to improve the understanding of behaviour of mine wastes under different ARD prediction test conditions.All ARD prediction testing methods investigated in this study showed that the gold sample is considered to be potentially acid forming with net acid generation (NAG) pH of 2.5 and net acid producing potential (NAPP) of 36 kg H2SO4/t. Results of biokinetic test showed that ANC was consumed within four days confirming acid producing potential of the sample with low neutralising potential as observed from acid base accounting (ABA) (4.7 kg H2SO4/t) and mineralogy (4.9 kg H2SO4/t). Results generated in this study demonstrated importance of mineralogy in both understanding the controlling reaction mechanisms playing key role in ARD formation and its capability as a prediction technique. Future work will focus on the application of mineralogy in interpreting the behaviour of mine waste under different static test conditions with a view to assessing their applicability and reliability in estimating potential acid generating characteristics of gold tailings.CITATION:Dyantyi, N, Becker, M, Broadhurst, J L, Harrison, S T L and Franzidis, J-P, 2013. Use of mineralogy to interpret laboratory-scale acid rock drainage prediction tests - a gold case study, in Proceedings World Gold 2013, pp 519-526 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By R Dunne, J Dodd, J Snyder, F Roberto

Energy costs are steadily increasing worldwide while the availability and quality of water are becoming contentious issues between the users (municipalities/households, agriculture, manufacturing and mining). Refractory gold ore treatment - pressure oxidation, biological oxidation and roasting (ultra-fine grinding, or UFG, will not be discussed here as this process only reduces the particle size of the feed prior to cyanidation) - requires substantially more energy and water quantity and quality are vastly different compared to the standard and simple flow sheets used for treating non-refractory ores This paper will provide an overview of the energy and water requirements for treating refractory gold ores, a topic which does not appear to have been considered previously in the literature.CITATION:Roberto, F, Snyder, J, Dodd, J and Dunne, R, 2013. Energy and water requirements in the treatment of refractory gold ores, in Proceedings World Gold 2013 , pp 527-532 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By M G. Aylmore, L W. de Klerk

Roasting of refractory gold ores has been a commercial process for many years. Improvements in design of fluidised bed roasting technologies and low capital and operating costs compared with other refractory treatment processes can potentially make roasting a viable option.However, gold extraction from roasted ores carried out on laboratory scale equipment often invariably yields lower recoveries than other processes such as bio-oxidation or pressure oxidation. Non-optimal laboratory roasting conditions can incorrectly write roasting off as a process option.Low gold recoveries from the cyanidation of calcine products from roasting can often be attributed to roasting conditions not favouring gold liberation and agglomeration processes, particularly if lockups of elements such as arsenic are being pursued for environmental reasons.This paper reviews the conditions favoured for gold agglomeration and accessibility of gold to cyanide, test conditions to achieve gold liberation and agglomeration on laboratory scale and designs that incorporate staged decomposition and roasting to make roasting a more commercial option.CITATION:Aylmore, M G and de Klerk, L W, 2013. Conditions and design considerations for maximising recoverable gold in roasting of refractory gold ores, in Proceedings World Gold 2013 , pp 375-388 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By J Langhans, Y Choi, Q Wang, J Y. Baron, P Kondos

Barrick has successfully developed the thiosulfate leaching process to treat sulfidic high preg-robbing ores. The process was developed through rigorous bench test programs and proved in pilot campaigns and demo plant operations. The process uses calcium thiosulfate as a leaching reagent, resin for gold recovery with sulfite/trithionate elution and reverse osmosis as a mean of reagent recovery. The thiosulfate leaching plant is under construction as a brownfield project and the start-up is planned in 2014 at Goldstrike, Nevada, USA, one of BarrickÆs operations.CITATION:Choi, Y, Baron, J Y, Wang, Q, Langhans, J and Kondos, P, 2013. Thiosulfate processing - from lab curiosity to commercial application, in Proceedings World Gold 2013 , pp 45-50 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By K Afewu, R Dunne, W P. Staunton

The treatment of preg-robbing gold ores has always been a technical challenge in the gold industry. Early solutions included removal of preg-robbing carbonaceous material by flotation, the addition of kerosene to æblindÆ/passivate the surface of the preg-robbing component, and the most effective of all options, roasting the ore. Unfortunately gold ores have become more complex and roasting has environmental challenges, so other methods of treatment have had to be found. This paper will review methods of characterising preg-robbing gold ores, method of treatment and cite examples of actual application in the industry.CITATION:Dunne, R, Staunton, W P and Afewu, K, 2013. A historical review of the treatment of preg-robbing gold ores - what has worked and changed, in Proceedings World Gold 2013 , pp 99-110 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By G Lumley

Gold miners have been underperforming the price of gold for a number of years. So why has the æmarketÆ undervalued our gold miners relative to what they have been mining? The low valuation ascribed to gold mining companies is largely attributable to their profit performance. In the period since 2006 the price of gold in A$ has risen about $900/oz, but the real cash margin (operating cash costs + cost of finding and/or acquiring deposits + the cost of bringing them into production) has only risen about A$100. Rising operating costs are a major part of this reduction in real margin. Energy and labour costs have risen more than the inflation rates across a number of countries as have taxes, royalties, etc. There are however, more significant contributors to the rising cost base. Firstly, in 2006 the average gold grade was 2.0 g/t; today it is 1.3 g/t. Secondly, strip ratios (for surface mines) have increased by 19 per cent during this time. Open cut mining equipment unit output across the world has dropped by 26 per cent during 2006 - 2012. Finally, costs have risen by 55 per cent during this time period. Consequently, there is now 3.8 times more mining cost required to produce an ounce of gold from surface mines compared with 2006. The decline in gold grade looks to be a permanent trend as does increasing strip ratio if output is to be maintained. Costs will continue to rise although cost control will be necessary. Reversing the decline in equipment performance and closing the gap between median and best practice provides the hope for a sustainable reversal of cost increases. The current gap between best practice and median performance has grown to 112 per cent for mining trucks, 168 per cent for excavators and 169 per cent for front end loaders. Closing this gap is the potential for a more profitable future. For most gold mining companies improving mining efficiency is not an option; it is an imperative.CITATION:Lumley, G, 2013. How many gold mines will inefficiency kill?, in Proceedings World Gold 2013 , pp 267-276 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By D Preedy, J K. Claflin, S R. J La Brooy

This paper summarises the lessons learned during a recent carbon reactivation kiln upgrade project at the Sukari Gold Mine in Egypt. The kiln is being replaced to ensure that the plant achieves full value from the current throughput expansion from 5 to 10 Mt/a.The suitability of the original engineering design criteria for kiln selection and the adequacy of the original kiln are reviewed in the light of the carbon chemistry, operating experience and a site inspection of the kiln. Particular aspects of the reactivation facility are discussed including: predrying, preheating, feeding, gas seals, kiln heat transfer, steam injection, counter-current sweep gas flow, carbon cooling, fines minimisation and removal.Design criteria for a carbon predryer, reactivation kiln and cooler combination for carbon heavily fouled by high molecular weight frothers and collectors are discussed and the abridged Ausenco datasheet for the combination is presented.Responses to a request for a budget price sent to most of the worldÆs suppliers of carbon regeneration kilns are summarised.CITATION:Claflin, J K, La Brooy, S R J and Preedy, D, 2013. Ausenco carbon reactivation design criteria, in Proceedings World Gold 2013 , pp 401-410 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By P de Caritat, A Davidson, A Mann

Top outlet sediments from the National Geochemical Survey of Australia have been extracted by a partial extraction method for over 50 elements including gold. The partial extraction results from this low-density survey show discrete coherent anomalies for Au in the vicinity of many of AustraliaÆs known goldfields, and in the vicinity of some minor gold occurrences. In several instances catchment outlet anomalies for Au have been recorded from areas not known to contain significant economic gold. Several large economic goldfields are shown to not produce anomalies in catchment outlet samples. A survey of overbank samples in the Swan Avon catchment of Western Australia at double the sampling density shows that low level anomalies (>1 ppb) can be traced back to source using overbank sediments. Follow-up of one of the Au anomalies at Kent River in previously regarded non-auriferous terrain (western Albany-Fraser Belt) indicates a non-economic, but perhaps geochemically significant, Au anomaly with associated pathfinders including palladium. This may indicate that further exploration of the western part of Albany Fraser Belt for Au is warranted. The combination of catchment overbank samples and partial analysis technique has been shown to be effective at locating the source of gold anomalies from initial low-density continental and regional surveys.CITATION:Mann, A, Davidson, A and de Caritat, P, 2013. High resolution soil geochemistry for gold exploration at the continental, regional and prospect scale, in Proceedings World Gold 2013 , pp 167-174 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By A Hall, D Kratochvil, P Littlejohn

Economic recovery of gold from complex gold ores, including poly-metallic deposits, is impacted by the presence of cyanide-soluble base metals. These base metals can create both a metallurgical challenge plus waste handling and disposal challenges. Base metals such as Cu and Zn compete for the cyanide reagent and often increase the total cyanide consumption to the point of making precious metals recovery uneconomic. In addition, the accumulation of base metals in cyanide solutions represent a challenge for cyanide detoxification and waste water treatment as these metals report to waste sludge. Such sludge requires safe handling and disposal, with possible long-term liabilities.Base metal interference can be removed with sulfidisation-acidification-recycling-thickening (SART) process technology. SART liberates the base metal from the cyanide complex and precipitates the metal as an insoluble sulfide product that can be recovered as a commercial grade concentrate. With the base metal precipitated, the cyanide can be regenerated as free cyanide and recycled to the gold extraction circuit.BioteQ completed laboratory testing for two projects, one employing cyanide leaching of copper-gold sulfide flotation concentrate and one employing a Merrill Crowe process, to determine the effectiveness of SART to remove and recover Cu and Zn in high-grade sulfide concentrates and to reduce the impact of cyanide-soluble metals on gold recovery and cyanide consumption. This paper will provide an overview of the testing methodology and results along with a review of the potential for SART to be applied to complex gold ores with poly-metallic deposits to improve project economics, operability and waste management.CITATION:Littlejohn, P, Kratochvil, D and Hall, A, 2013. Sulfidisation-acidification-recycling-thickening (SART) for complex gold ores, in Proceedings World Gold 2013 , pp 149-156 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By B Twidle, D Bertoldi, J Meikle, R Dunne

The Waihi Gold Mine is situated in a high rainfall area (annual average of over 2 m) on the North Island of New Zealand. Water treatment and discharge at the mine has been ongoing for the last 25 years. The first water treatment plant consisted of a æstandardÆ water treatment facility (ferric chloride precipitation) and cyanide detoxification. With time the project has expanded and the volumes of water increased requiring additional treatment methods (reverse osmosis) to meet the water quality for discharge. This paper will provide information on the historical development of the water treatment flow sheets, performance data and operating costs.CITATION:Bertoldi, D, Dunne, R, Twidle, B and Meikle, J, 2013. Water treatment at the Waihi Gold Mine, in Proceedings World Gold 2013 , pp 503-508 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By G Corbett

Epithermal Au-Ag deposits form in the upper 1 km of the crust and are therefore best preserved in the less eroded Pacific rim arcs, although also recognised elsewhere. Two profoundly different ore fluid types give rise to low and high-sulfidation styles apparent as variations in ore and gangue mineralogy as well as characteristic zoned wall rock alteration. Low sulfidation epithermal Au deposits are derived from near neutral composite magmatic-meteoric fluids and divided into a group with a stronger intrusion association within arcs grading in time and space from: quartz-sulfide Au + Cu, to carbonate-base metal Au, and the epithermal quartz Au + Ag, whereas in strongly extensional settings the influx of meteoric waters promotes the development of chalcedony-ginguro banded Au-Ag epithermal veins. In the presence of continental crust particularly in Latin America polymetallic Ag-Au veins represent a Ag-rich equivalent of carbonate-base metal Au and passes upwards to chalcedony-ginguro Au-Ag style. By contrast high-sulfidation epithermal deposits are deposited from an acidic magmatic fluid which provided characteristic hydrothermal alteration by reaction with wall rocks grading outwards as mineral assemblages dominated by: vughy silica, alunite, pyrophyllite-diaspore, dickite-kaolin and then illite-smectite neutral clays. Au mineralisation is commonly refractory with enargite deposited dominantly later within the silica zone.Exploration for epithermal Au deposits benefits from an understanding of the controls to mineralisation which commonly give rise to the development of ore shoots with widest and highest Au grade ore zones. In low-sulfidation systems a combination of competent host rocks, dilatant structures, higher grade styles of mineralisation and efficient mechanism of Au deposition, contribute towards ore shoot formation. High-sulfidation epithermal Au systems occur in permeable volcanic and breccia host rocks which are linked by major structures to the magmatic source.CITATION:Corbett, G, 2013. Pacific Rim epithermal Au-Ag, in Proceedings World Gold 2013 , pp 5-14 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013