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By J Tickner, Y Van Haarlem, G Roach, D Abernethy, M Smith, J OÆDwyer

The development of novel technologies capable of real-time, high-accuracy, automated analysis of gold, other precious metals and mineralogy, both in ore samples and directly on process streams is reported.X-ray fluorescence (XRF) analysis is widely used for process stream monitoring of base metals. However, detection limits are generally a few parts-per-million (ppm) or larger, precluding the use of this method for monitoring precious metals. Complex interferences with other elements also limit accuracy. An XRF slurry analyser that uses advanced data-analysis techniques to resolve overlapping fluorescence lines, achieving detection limits in the parts-per-billion (ppb) range has been developed. This allows feed, concentrate and tailings streams in precious metal applications to be monitored in real-time. An extended trial of our technology in a platinum group element concentrator and laboratory tests on gold process slurries in the 0.1 - 2.0 ppm concentration range is discussed.Analysis of process stream mineralogy can provide useful information to supplement conventional elemental data. An on-stream X-ray diffraction analysis technique that provide real-time mineral and elemental measurement of process slurry streams has been developed. Both X-ray techniques can be combined into a single on-stream analyser to provide simultaneous elemental and mineralogical information. The successful trial of a combined XRDF (X-ray diffraction and fluorescence) slurry analyser is also reported.It is widely recognised that rapid, accurate analysis of grade is an essential prerequisite for optimising the efficiency of exploration, mining and processing of metals ores. The low grades of precious metals ores, such as gold and the platinum group elements, have led to fire assay becoming the predominant analysis technique. Significant drawbacks of fire assay include long turn-around times, limited absolute accuracy, high costs and requirement for skilled operating staff. For rapid measurement of gold samples, a technique that allows the gold content of large samples to be determined absolutely with high accuracy in less than two minutes using activation with high-energy X-rays has been developed. The method is non-destructive, has detection limits in the low ppb range, is capable of measuring slurries, ground or crushed solids with minimal preparation and can be made fully automatic. Initial results from laboratory trials are presented.CITATION:Roach, G, Abernethy, D, OÆDwyer, J, Smith, M, Tickner, J and Van Haarlem, Y, 2013. Advanced instrumentation for analysis of exploration, mining and process materials, in Proceedings World Gold 2013 , pp 277-282 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 26, 2013

By M C. Ackland

The Grande Côte Mineral Sands Deposit (GCMSP) is located on a coastal mobile dune system in Senegal on the west coast of Africa. Senegal is a stable, democratic republic, having gained its independence from France in 1960. It has a population of about 12.5 million people. The dunes begin about 25 km north-east of Dakar, the capital city of Senegal, and extend northwards for more than 140 km. The mineralised dune system averages about 2 km wide with some areas extending to up to 4.5 km wide.Mineral Deposits limited (MDL), a Melbourne-based company with over 60 years operational experience in mineral sand mining in Australia, holds, through its Senegalese subsidiary MDL Senegal SARL (MDLS), a 25-year Mining Concession covering the deposits. The main heavy mineral (HM) areas identified to date are, from south to north, Mboro, Fass Boye, Diogo and Lompoul. Within the Mining Concession there is potential to identify additional resources beyond the limits of present drilling. The dunes are mobile or semi fixed, pale yellow in colour and overlie older white marine sands. The dunes range between 5 m and 30 m in height and the mineralised zones, which are essentially flat-lying, average around 15 m in thickness. The mineralisation consists, principally of ilmenite with accessory zircon, rutile and leucoxene. Zircon and ilmenite are the main commodities of interest.Independent consultants AMC estimated mineral resources for the four main deposits in 2006 of 1330 Mt of sand averaging 2.0 per cent HM at a cut-off grade of 1.5 per cent HM. At a cut-off grade of one per cent the resources were 3200 Mt averaging 1.5 per cent HM. All of the estimate was classified as Inferred Resources under the 2004 Australasian Code for Reporting of Exploration Results, Mineral Resources and Ore Reserves (JORC, 2004).Subsequent completion of infill drilling, sampling and assaying of the initial mining area, centred at Diogo, was completed in 2008, enabling a final dredge path to be designed and ore reserves estimated, based on a JORC compliant Measured and Indicated Mineral Resource. Infill drilling is continuing in the Lompoul and the results of this campaign will be included in the JORC compliant data base by AMC in April 2010 to enable the 15 per cent year dredge path and mine plan to be finalised.Development studies have shown that the project can be optimised as a dredging operation, with mineralised sand being treated in a conventional floating spiral preconcentrator, wet concentrator and dry mineral separation plant. Engineering work now substantially completed by Ausenco Limited (Ausenco) has developed the combination of some existing plant from MDL’s past operations, and new plant for the complete process from dredging to final product separation and grading. Testwork on a series of bulk samples has determined that the project can yield a high quality zircon product and an ilmenite product along with minor rutile and leucoxene.Work to date indicates a likely output of around 80 000 t of zircon in various quality streams (Primary, Secondary, Standard and Foundry Grades), around 550 000 t of ilmenite plus around 15000 t of rutile and around 12 000 t of leucoxene/secondary ilmenite. Planned zircon output would represent around 7per cent of the total world production, which would make the GCZ&IP a significant producer on a world scale.The studies have indicated capital costs to be in the range of US$400 M total operating cost (after completion of ramp-up) of around US$50 M - $55 M/a. Revenue is expected to be in the range $127 M - $157 M/a.

Oct 5, 2011

New Celebration Gold Mine is located 35 km SE of Kalgoorlie, Western Australia, in the Archaean Kalgoorlie-St Ives Greenstone belt. The leases total 119 sq kms and arepart of a joint venture between Newmont Australia Ltd (as manager) and Mt Martin Gold Mines N.L. Mining commenced in August, 1986 and is now producing over 115,000 ounces of gold per annum. A variety of gold mineralisation styles with a total resource of 23.5 million tonnes at 2.19g/t are associated with shear zones at New Celebration. Gold production is co-ordinated from 7 open pits with others planned to com- mence soon. A large scale underground trial mining operation has com- menced with a decline on the hanging wall of the main producing orebody, Hampton Boulder. Millfeed produced is classified on the stockpile according to grade and metallurgical performance and blended tomaximise throughput while main- taining grade through a CIL treatment plant currently operating at 1.7 million tonnes per year.

Jan 1, 1991

By J Nortier, J Dray

There is no single factor that determines the appropriate capacity for a mining project. It is driven by the size of the resource, the capacity of the market, the availability of capital, the availability of power, the availability of water, and a myriad of other considerations. There is also no single solution to the question of how big the project should be. However, to develop a project, the study team needs to select the configuration options that it regards as the best for the project. To be able to make this selection, the study team should consider the range of available options and do so at a level of detail that gives it confidence in the conclusion but does not lead to multiple detailed design exercises. Having considered the range of options, and with a clear definition of the project owner’s objectives and constraints, the work to be carried into feasibility studies can be focused appropriately. This paper discusses the process of completing strategic mine planning to identify project configuration options to assist in the selection of the processing plant throughput rate (Capacity Study) for a large greenfield open pit mine. The processes described in this paper allow for the basis of design to be set for subsequent studies that meets the objectives at a risk profile acceptable to the owner.

Jun 22, 2022

By A Yame, P J. Pollard, E Atase, J Garu, M Tangwari, D R. Hastings, R W. Smillie

"An EXTENDED ABSTRACT is available for download. A full-length paper was not prepared for this presentation. The Townsville prospect is situated approximately 4 km north of the Ok Tedi copper-gold mine in Western Province, Papua New Guinea. Drilling in the 1990s delineated a resource of >1 Moz of gold within shallow, skarn breccia-hosted mineralisation associated with quartz-carbonate infill, together with pyrite, chalcopyrite, pyrrhotite, sphalerite, galena, tennantite-tetrahedrite, arsenopyrite, marcasite, and a variety of Au-, Ag- and Bi-telluride minerals. The deepest of these historical holes (TVL034) also intersected copper-gold-silver mineralisation more than 100 m below the gold-rich zone that is associated with calc-silicate skarn breccia. Although copper-gold-silver mineralisation in DDHTVL034 is associated with clinopyroxene-rich skarn, it was also noted that garnet in the skarn breccia became progressively darker in colour with depth, ranging from green at shallow levels to dark red-brown at depth. This indicated that the skarn breccia is zoned, with more proximal garnet skarn at depth possibly indicating an association with porphyry-style copper-gold mineralisation.Based on this skarn zonation model, recent drilling at the Titan prospect, located approximately 500 m south of TVL034, was targeted at potential copper-gold silver mineralisation beneath shallow skarn breccia-hosted gold mineralisation. DDHTVL 081 intersected 46 m at 6.36 g/t Au from 68 m and 80.7 m and 1.67 per cent Cu, 1.27 g/t Au and 20.32 g/t Ag from 184 m. Exploration is now attempting to define the extent of copper-gold-silver mineralisation by defining structural controls on the skarn breccia together with paragenetic and mineral zoning data.CITATION:Smillie, R W, Pollard, P J, Hastings, D R, Yame, A, Tangwari, M, Garu, J and Atase, E, 2015. Exploration of the Townsville Cu-Au-Ag skarn, western province, Papua New Guinea – preliminary observations of paragenesis and zoning, in Proceedings PACRIM 2015 Congress, pp 593–600 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Mar 18, 2015

By E S. Weiss, S P. Harteis

The Pittsburgh Research Laboratory (PRL) of the National Institute for Occupational Safety and Health (NIOSH) has conducted full-scale explosion experiments, to evaluate the strength characteristics of various seal designs, used for safely isolating worked-out areas in underground coal mines. Large-scale explosion tests conducted within the multiple entry section of PRLÆs Lake Lynn Experimental Mine (LLEM) is currently the only accepted test method used by the Mine Safety and Health Administration (MSHA), for deeming a seal design suitable for use in American mines. These explosion tests are labour intensive, expensive to conduct, and can interfere with other critical underground safety and health research programs conducted by NIOSH. The PRL has developed an alternative seal evaluation method, based on a hydrostatic pressure loading concept, that can facilitate the in situ testing of seals in an operating mine. Two chambers within LLEM and one within PRLÆs Safety Research Coal Mine (SRCM) were used for hydrostatic pressure loading various seal designs. The results from these chamber tests compare favourably with those from the large-scale explosion tests in the multiple entries. In addition to testing seal designs at the required 20 psi static pressure level, the chamber test approach also allows for the determination of the sealÆs ultimate design strength. Size-scaling relationships for predicting the strength of seal designs as a function of entry size are also presented.

Jan 1, 2005

The hoisting system at the Newcrest Telfer mine is designed for a final duty of 7.35 million tonnes per annum at a hoisting distance of 1450 m. In terms of hoisting capacity (t/h) times hoisting distance it is one of the largest friction hoist installations. Initially, the hoist will be equipped for hoisting 6.5 Mtpa from 1100 m depth. This new drive technology is now well proven by ABB for mine hoist applications with the first installation in commercial operation since July 2001. To date 17 systems for medium voltage drives and another five for low voltage drives have been purchased from ABB for mine hoists. This paper will also deal with skip design and powerful data loggers with diagnostics for local and remote monitoring that are installed in the Telfer mine hoist.

Jan 1, 2005

By M Lovitt, T Hewitt

The extraction of drawbells in Lift #2 at Northparkes Mines E26 orebody was achieved by single shot blasting, enabled through the use of electronic detonators. This paper discusses the designs considered at the time of the feasibility study and the various changes made to these designs prior to and during the construction phase of the Lift #2 block cave. Operational issues encountered are highlighted, as are ways in which these were overcome. The amount of personnel utilised to mine the drawbells is also covered. Lists of design and operational considerations to be used for drawbell extractions have been included.

Jan 1, 2005

The QSL continuous lead smelting process incorporates two basically different pyro- metallurgical operations: roast-reaction, smelting of galena concentrate, followed by carbothermic reduction of some by-product lead oxide slag. Both steps are performed simultaneously in separate compartments of a long horizontal cylindrical reactor, which is lined with fused chrome-magnesite bricks. This converter-type reactor contains a liquid bath consisting of a shallow layer of lead bullion with a superimposed layer of slag, the lead content of which is gradually reduced from about 50% to discardible levels. Metal relative to slag, and slag relative to the gas phase are in continuous countercurrent motion. A lead well is arranged at the flue end of the reactor, and an overflow tap for slag at the opposite end. Tonnage oxygen for oxidation and smelting of the charge, and sub- stoichiometric mixtures of pulverized coal and oxygen for reduction and heating of the slag, are directly blown into the bath using fluid-protected Savard-Lee injectors. High gas-liquid momentum transfer ensures intensive local mixing, and enables rapid mass and heat transfer.

Jan 1, 1984

Reverse circulation (R.C.) drilling or the dual tube method as it is quite commonly known, has a unique place in conventional mineral drilling. It can be classified half-way between open hole drilling at the lower end of the scale and diamond drilling at the upper end. The system basically consists of two tubes, one inside the other, with compressed air flowing between the inner and outer tubes. Sample cuttings return up the inner tube through the head of the rig and via a hose to a cyclone where the sample is collected. This system means that the cuttings are free of contamination as they are at no time in contact with the outside formation of the hole.Reverse circulation drilling is divided into two areas: R.C. Roller and Blade for softer formations; and R.C. Percussion for harder formations.

Jan 1, 1986

By E P. O’Dwyer

Segment and gasket lining in tunnel boring machine (TBM) tunnels; and sheet membrane lining systems in driven tunnels are robust waterproofing systems each with a proven history of performance in Australia and further afield. Where an interface between these two systems occurs, the potential for costly failures is vastly increased and additional attention to detail is required in design, planning and construction. TBM cross-passages represent the most common occurrence of this interface, with steel compression flanges and neoprene gaskets being the typical means of connecting the waterproofing systems. There is a large variance in both detailing these flanges and associated outcomes, which makes this an area where there is room for improvement within the industry.The paper will look to tease out the various issues associated with this interface and how they can be dealt with efficiently with appropriate design measures, robust planning and carefully controlled construction methods.The paper will also look to review the new technologies and systems currently being put forward as potential alternatives, including an epoxy tape system, which has recently been successfully trialled on a project in Europe under high-pressure head.CITATION:O’Dwyer, E P, 2014. The challenge of waterproofing cross passages in segmentally lined tunnel boring machine tunnels, in Proceedings 15th Australasian Tunnelling Conference 2014 , pp 315–322 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

By C M. Stewart, P Bowen

McArthur River Mine, in the Gulf Country of the Northern Territory, exploits one of worldÆs largest deposits of zinc, lead and silver. It was officially opened in September 1995, 40 years after its discovery in 1955. This paper describes the geological, engineering and metallurgical assessments which made up the feasibility study. It then relates how these study components compare with the first two years of operation. The challenges that had to be overcome before the McArthur River Mine became economically viable included the metallurgical problems associated with extremely fine grained ore and the development of an effective mining process.

Jan 1, 1998

By E Garbarino, P Molina, V Badino

Given the ever increasing quantity of construction and demolition waste (C&DW), one of the most challenging issues presently facing policymakers and public administrators in Italy concerns how to organise and manage collection and recycling and to understand whether and to what extent recycled aggregate can complement natural building aggregates in a sustainable supply mix (SSM). The paper presents the results of a research aimed at analysing energy and environmental implications of the C&DW recycling chain in the administrative territory of Provincia di Torino in northern Italy. In respect of a population of about 2.25 million inhabitants, the annual production of C&DW in the area under study is 1.8 Mt. A combined geographical information system (GIS) and Life Cycle Assessment (LCA) model was developed, paying attention to the geographical location, land use, transportation network and avoided landfill: crucial issues for sustainable planning and management. Around 90 recycling plants were classified according to the size, typology (stationary, semi-mobile and mobile) and physical- mechanical characteristics of the recycled aggregate. Under different assumptions relevant to the delivery distance, and considering the typology and grade of recycled aggregate, as well as local availability of natural aggregates, it was possible to evaluate the geographical coverage of aggregates demand and to use LCA in order to identify and quantify energy and environmental indicators.

Jan 1, 2009

By A Moreira, A B. De Souza, S Latchireddi, E Faria

Material transport plays a significant role in the efficiency of horizontal grinding mills - autogenous (AG)/semi-autogenous (SAG)/ball mills. The magnitude of benefits that can be achieved with efficient material transport in AG/SAG mills has been demonstrated in a greenfield milling operation at Mirabela MineratpoÆs SantaRita Nickel operation located in north eastern Bahia in Brazil. This grinding circuit was commissioned in October 2009, was designed as a typical SABC circuit to grind 4.6 Mt/a (575 t/h) to produce a P80 of 125 ¦m with ten to 12 per cent ball charge in the SAG mill. However, it has been operating as an ABC circuit without any grinding media in SAG mill. The nameplate design capacity was achieved in few days and was gradually increased to an average of +800 t/h, still operating in ABC mode. The Santa Rita grinding circuit consists of one 30 ft + 15.4 ft 8.5 MW SAG mill fitted with Outotec patented Turbo Pulp Lifters (TPLÖ) in closed circuit with a HP400 short head pebble crusher and one 20 ft + 28.4 ft 5.5 MW Ball Mill in closed circuit with a Warman cyclone cluster fitted with 10 + 26 in CAVEX cyclones. This paper examines the comminution design process, operating philosophies, experiences, post commissioning optimisation and future development works. Evaluation of the milling circuit performance relative to the design criteria is also discussed.CITATION:De Souza, A B, Latchireddi, S, Moreira, A and Faria, E, 2012. Application of turbo pulp lifter in greenfield operation - Mirabela SantaRita nickel operation, in Proceedings 11th AusIMM Mill OperatorsÆ Conference, pp 53-58 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Oct 29, 2012

By H Zhang, A Lawrence

To accommodate the fast growing need for services in Singapore’s Marina Bay downtown area, Marina South, the construction of a common services tunnel (CST) was required. The CST includes various services such as telecom cables, power lines and water pipes. A deep excavation and temporary earth retaining system (TERS) was required to facilitate the construction of the tunnels. Marina Bay is reclaimed land over thick soft marine clay which is likely to be still consolidating. The deep soft marine clay poses a big challenge for deep excavations in downtown areas where highways and sensitive structures are close by. This paper presents a case study of part of the CST Phase 1B and 2 at Marina South, in particular a 26 m deep excavation supported by a 46 m diameter temporary caisson. The construction started in late 2006 and the basic structure was completed in early 2011. The caisson was formed by 1.0 m thick overlapping diaphragm wall panels with a capping beam and three ring beams at different depths. Two-dimensional finite element analyses were conducted to predict the ground settlement, lateral displacement, bending moment and hoop stresses in the diaphragm wall and ring beams during different excavation stages. A comprehensive instrumentation and monitoring scheme was established to verify the design predictions, control excavation safety and trigger the contingency plan to protect public safety. The impact of construction activity, unbalanced temporary stockpiles and adjacent deep excavation for a mole removal will be discussed.CITATION:Zhang, H and Lawrence, A, 2014. A case history of a deep excavation in a big circular shaft in Singapore marine clay, in Proceedings 15th Australasian Tunnelling Conference 2014, pp 581–588 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

By D Zielinski-Nicolson

The emergence of affordable, portable and versatile wireless devices has enabled a new frontier in mine safety equipment. Existing solutions provide methods for tracking personnel and assets in underground mines but are not designed to optimally integrate into existing and emerging systems. Mine management are often required to coordinate primarily independent emergency, personal protective equipment (PPE), tracking and collision avoidance systems from multiple vendors. These systems involve a variety of wireless technologies that require separate integration projects that discourage adopting new services and policies.

May 5, 2022

By M Yadav, K Clode, S Daykin

The mining industry faces numerous challenges related to sustainability and circular economy principles, necessitating strategic approaches to innovation and resource management. As demands for mineral resources continue to rise, mining companies are under increasing pressure to address environmental impacts, minimise waste generation, and optimise resource utilisation. These challenges underscore the importance of Research and Development (R&D) roadmaps as strategic tools for guiding innovation and sustainability efforts within the sector (Jochen Berbner, 2022). A design-led methodology offers a structured approach to R&D roadmap development, emphasising stakeholder engagement, collaboration, and alignment with industry objectives. By leveraging design principles, mining companies can ensure that their R&D initiatives are responsive to evolving challenges and opportunities, fostering a culture of innovation and continuous improvement. Against this backdrop, the project aims to address the pressing challenges associated with sustainability and circular economy in the mining industry. Through the development of R&D roadmaps and the application of a design-led methodology, the project seeks to identify innovative solutions for enhancing resource efficiency, minimising environmental impacts, and promoting sustainable practices within mining operations. This paper highlights the collaborative efforts among Isle, the mining industry, and water utilities, which have yielded tangible benefits. The study demonstrates how the outcomes from the roadmaps outlined below effectively align research with strategic objectives, fostering innovation to address pressing challenges.

Sep 1, 2024

By D Thornton, R Hodson, D Sprott

Blast fragmentation size distribution and thus blast design have been found to have a direct impact on the load and haul cycle through excavator dig time and bucket payload. Previous studies have demonstrated that by reducing the excavator dig time and increasing bucket payload, significant improvements can be made in both productivity and unit cost. Simulation work reported in the literature indicates that a 20 per cent improvement in dig time may result in only a three per cent improvement in load and haul productivity and unit cost. At the same time, a ten per cent improvement in bucket payload will directly translate to a ten per cent improvement in load and haul productivity and unit cost. Based upon these findings, extensive laboratory and field work have been undertaken in the past to correlate blast fragmentation distribution to bucket payload. In contrast, the literature reports limited studies quantifying the impact of blast fragmentation on excavator dig time. Field work was conducted at Placer Dome Asia PacificÆs Granny Smith Mine (Wallaby Pit) in Western Australia, concentrating on quantifying the impact of blast fragmentation on the dig time of a Liebherr 994 hydraulic excavator (shovel attachment with 14 m3 bucket). Fragmentation was assessed for each truck load of material using the Split Desktop system, while the excavator cycle analysis was conducted manually. Measured fragmentation P80 (fragment size at which 80 per cent of material passes) values ranged from 200 mm to 1200 mm. The field study investigated the impact of various fragmentation parameters (P20, P50, P80, cumulative per cent passing 250 mm size fraction, and uniformity index) on the average and total dig times. The results indicate that the fragmentation P80 provides the best correlation to average dig time (total dig time divided by the number of bucket passes to load a truck). The total dig time was found to be dependant upon the fragmentation P80 and the number of bucket passes to fill a truck. Monte Carlo simulation results, based upon these relationships, indicate a 26 per cent improvement in average dig time and a 12 per cent to 46 per cent improvement in total dig time (bucket passes ranging from 4 to 8), with a change in fragmentation P80 from 600 mm to 200 mm.

Jan 1, 2003

By Stevenson BG

The relevance of ore-dressing mineralogical investigations to developing and improving metallurgical flow-sheets is discussed and examples are given of the application of such studies to various types of ores and mill products (Au, Cu-Sn, Ni and Sn). The mineralogical investigations described illustrate (a) assessment of the feasibility of ore pre-concentration by heavy-media cyclone separation, (b) evaluation of the potential applicability of various metallurgical treatment processes to an ore, and (c) characterization of mill products to assess circuit efficiency and to guide circuit modifications.

Jan 1, 1978

By N K. DavT, A Coggan

The performance of in situ, shallow water covers in controlling acid generation was evaluated at four recently decommissioned pyritic uranium tailings sites at Elliot Lake, Ontario, Canada. The tailings are acid generating, having a pyrite content of approximately five to ten per cent and a very low to non-existent alkaline buffering capacity. Adverse market conditions led to the closure of all operating uranium mines in the early- to mid-1990s, followed by rehabilitation and decommissioning of mine and waste management facilities. In order to control acidic drainage, all new and active tailings areas at Denison, Quirke, Panel, Spanish-American and Stanleigh mine sites were re-engineered to provide in situ submersion of these tailings under shallow water covers. The tailings impoundment dams were upgraded and reinforced or in some cases reconstructed, to minimise seepages and provide a minimum 1 m depth of water cover. With the exception of Stanleigh mine, which was closed in 1996 and rehabilitated during the late-1990s, the water covered Tailings Management Areas (TMAs) at other sites have been in operation for a period of six to nine years. The surface water quality at these sites is maintained at near neutral pH conditions by periodic addition of lime slurry to the established water covers. Additional treatment of effluent is provided as required to meet the discharge water quality standards. The performance of the established water covers at the sites was evaluated by analysing the annual equivalent limestone consumption data. The results were compared with the performance of an older, decommissioned Nordic TMA, which was rehabilitated using revegetation techniques. The water covers at these sites are performing as designed and acid generation has been reduced to low levels. Based on the total amount of yearly equivalent limestone required to maintain water quality in the water cover and at the effluent treatment plant, it is concluded that acid generation rate at the Denison TMA has reduced to less than 0.15 per cent of its pre-water cover conditions during normal operation and rehabilitation periods. In comparison to the revegetated Nordic TMA, the acid generation rates at Denison and Panel TMAs have decreased to less than 1.6 per cent of that at the Nordic TMA. The acid generation rate at the Quirke TMA was comparable or only slightly lower than that at the Nordic TMA because of its unique terraced cell configuration, having tailings in five hydraulically interconnected cells at different elevations. Historic acidity and oxidation reaction products, accumulated during normal operating and pre-water cover periods, are flushing from upstream locations to downstream cells, thus requiring much higher equivalent limestone additions for acid neutralisation and effluent treatment.

Jan 1, 2003