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By S Hapugoda, J R. Manuel, M J. Peterson, A Poliakov, E Donskoi

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Aug 12, 2013

By Shining Z

The strength and deformation of more than two hundred coal samples have been tested in the condition of triaxial compression. The regression equation showing the relationship between coal strength and pressure in the pores, as well as confining pressure, was obtained. The appropriate calculation for stress-strain curve was carried out. Further, an analysis shows the variation of coal strength and its modulus of elasticity in methane medium.

Jan 1, 1992

By D Hillier, A Giblett, K Parker, V Ramsell

Kalgoorlie Consolidation Gold Mines (KCGM) operates the Kalgoorlie Super Pit open cut, Mt Charlotte underground mine, Fimiston process plant and Gidji Roaster facility for joint venture partners Newmont Mining Corporation and Barrick Gold. In 2004, the Fimiston plant was upgraded by the addition of gravity concentration to the Fimiston and Mt Charlotte grinding circuits, including the installation of a central intensive cyanidation reactor to process the gravity concentrates. The gravity project was justified after detailed analysis demonstrating an expected increase in overall gold recovery of approximately one per cent, in addition to reduced elution costs and reduced gold inventory in flotation concentrate stockpiles. The gravity circuits were commissioned in August 2004, and have since consistently recovered 10 to 20 per cent of the gold present in the KCGM ore, delivering a reduction in coarse gold losses equivalent to 0.45 per cent additional metal recovery and contributing to improved metal accountability.CITATION:Giblett, A, Hillier, D, Parker, K and Ramsell, V, 2012. The impact of gravity gold recovery at Kalgoorlie Consolidated Gold Mines, in Proceedings 11th AusIMM Mill OperatorsÆ Conference, pp 199-206 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Oct 29, 2012

By Lewis J. W

The mineral sand orebodies of the east coast of Australia occupy approximately three per cent of the dune-heath-wetland coastal environment. They are associated with coastal plant communities ranging from Holocene high dunes carrying mature Eucalypt forests to low- lying heaths on Pleistocene deposits. Commonly, 0.25 to 1.5 per cent of the sand volume mined is removed from the site. Therefore, the volume change is insignificant. The equipment and techniques in use are flexible and the land can be returned in a manner suited to its subsequent use for grazing, subdivision or recreation. Landforms similar to the pre-existing are created in two case studies given. Sophisticated revegetation techniques are practised and are discussed in two case studies. Pre-mining vegetation surveys and post-mining monitoring are used to guide the management of the ecosystem.

Jan 1, 1976

By M Fitzgerald

Fimiston Open Pit is operated by Kalgoorlie Consolidated Gold Mines (KCGM) as a joint venture between Barrick Gold and Newmont Mining. Over 110 years of underground mining resulted in the development of nearly 3500 km of underground workings including backfilled and open stopes up to half a million tonnes in size. These voids significantly complicate blasting processes at KCGM, influencing blast movement direction and magnitude. Blast movement monitoring to improve mine reconciliations was identified as an improvement project in the business plan for the geology team in 2008. Following successful trials in 2008 to 2009, blast monitoring and translation of ore blocks were implemented as a permanent grade control program from late 2009 and is now part of the Management Operating System (MOS) of the mine. This paper presents a summary of results from the Blast Movement Monitoring (BMM®) data collected to date. Ore blocks at KCGM are translated primarily using BMM® data. This data is obtained from the BMM® system which measures the movement of a radio transmitter installed in a blast pattern from a preblast position to a post-blast position. The application of the data collected by the BMM® tends to be both mine site and blast specific. At KCGM, an average distance obtained from the BMM® data within a given shot is the primary method used for translation. In the case that BMM® data is unavailable, a theoretical movement vector established from Orica Shotplus with distances gained from the historical BMM® database is used. Data is presented in an ore loss and dilution exercise for a bench undertaken at KCGM to understand the potential effects on reconciliations. Improvements that have flowed from implementing blast monitoring include improved reconciliations when combined with other grade control improvement projects. The increase in liaison between the geology and blast personnel at KCGM has been a significant improvement gained from the implementation of the blast monitoring program. This has allowed a better understanding of blast movement and the effects on ore dilution and ore loss by the mine geology team. In addition, the discussion of blasting tie-in plans between geology and blasting personnel has been improved which leads to more favourable blasting practices that take ore movement into account.

Aug 22, 2011

By S C. Dominy

Gravity amenable gold ores are those that after comminution produce liberated particles, composites and/or carriers that can be recovered by gravity separation means. Recovery depends upon mineralisation type and the comminution and concentration method used. Any in situ ore with more than 20 per cent of gold greater than 100 µm in size is likely to have a strong gravity recoverable component. A less traditional approach is where the gold is sulfide-locked and the gold carrier plus any liberated gold is recovered via continuous gravity recovery following fine crushing. Specific tests are undertaken to determine the level of gravity amenable gold within a deposit. The principal methodology is the gravity recoverable gold (GRG) test, which consists of three sequential liberation and recovery stages. For continuous gravity recovery (CGR), the sample is fed over a laboratory Wilfley table to simulate continuous recovery of the gold. Tails from the feed can be progressively re-ground and re-tabled to develop a grade-recovery curve. Primary geology and gold particle size-distribution have a strong effect on the mass of sample required to provide representative results for both tests. Where low-grade ore contains very coarse gold, substantially larger sample masses are required. Experience has shown that GRG and CGR values can vary throughout an orebody, particularly within different geological-grade domains. A testing regime must consider sample frequency and support.

Sep 5, 2011

Biologically-mediated phenomena are involved in many of the natural processes by which mineral deposits are formed and ore bodies transformed and degraded. They may facilitate the environmentally-damaging effects of mining and mineral-processing operat- ions. Under contrived and controlled conditions, however, these phenomena can form the basis for economically- attractive processes for the recovery of metals from low-grade deposits by dump, heap or in situ leaching. They have application also in processes for the regeneration of leaching reagents and some potential for'-the recovery of metals from dilute solution. The micro- organisms concerned are potential sources for the production of novel flotation and solvent-extraction reag- ents. Perhaps the greatest opportunity for biotechnological processes in min- ing and metallurgy lies in the possib- ility of the evolving of novel proced- ures for the substantially complete recovery of metals from process tail- ings by the unlocking of recalcitrant and complex mineral assemblages, and for the beneficiation of some mineral materi,hls.

Jan 1, 1982

North Eastern Russia encompasses the northern part of the Circum Pacific. The region comprises various tectonostratigraphic terranes, including cratonic blocks, fragments of volcanic arcs, accretionary wedge terranes, oceanic crust and passive continental margins. The terranes have been accreted to the eastern margin of the Siberian Craton in the Late Mesozoic. The prominent structures of the region are extended zones of the Mesozoic flysch and turbidites. Another important structure is the 3000 km long Okhotsk-Chukotka volcanic arc which marks the Cretaceous active continental margin of northern Eurasia. The youngest structure of the region is the 2000 km long Late Cainozoic Kamchatka-Kuril island arc system. North Eastern Russia is the main gold producing region of the Russian Federation. Since the beginning of recorded gold production in 1932 until 1995 the region has produced 2575 t (83M oz) of gold. Most of it, 2439.5 t, has been produced from placers. Owing to depletion of alluvial gold resources, exploration and mining emphasis is currently switching to the development of the lode deposits. At least five distinct types of the gold mineralisation are reported in North Eastern Russia - mesothermal gold mineralisation in the Mesozoic fold belts, Paleozoic epithermal gold mineralisation occurring within Omolon block, epithermal gold mineralisation related to the Mesozoic volcanics, Cainozoic epithermal gold mineralisation, gold-bearing Cu-porphyry deposits. The current paper introduces the metallogeny of lode-gold deposits of North Eastern Russia. It provides the review of the regional geology, the selected gold provinces and representative deposits with an emphasis on the mineralisation styles and distribution control.

Jan 1, 1999

By P F. Knights, P Boniwell

This paper investigates the causes of low effective utilisation of the production drill fleet at the Telfer Underground Gold Mine, as measured by the percussion hours per shift. The first part of this paper focuses on a site time and motion study conducted to accurately identify shift time allocation and optimal drilling parameters (manual versus automatic, and suitable flushing mediums for varying ground conditions) as well as quantifying the business potential for automated or remotely operated production drilling. The second part of the paper focuses on the rate of successful hole completion for automated production drilling during shift changes. Two main areas of drill optimisation were identified. Firstly, a site-specific drilling procedure was established so as to ensure that all operators were drilling using optimal parameters. Total production metres per rig increased by 10.7 per cent as a result of the implementation of this standard. It was observed that a 25 per cent faster overall drill cycle was achieved using air mist flushing, and that manual drilling achieves a 19 per cent faster overall drilling cycle in comparison to automated drilling. Secondly, routine provision to the maintenance department of automation reliability reports that outlined the principal causes of unsuccessful hole completion led to an increase in production metres of a further 4.1 per cent, measured between January 2007 and August 2007. First hole automation reliability increased from 39 per cent to over 77 per cent over the same time period. Second hole automation completion was increased to 74 per cent, leading to a higher proportion of production achieved through automated technologies.

Jan 1, 2008

By W Mahoney, F Clement, E Saraiva

Prefabricated waterproofing sheet membranes are extremely complicated to install in underground sections with complex geometries and, despite being already subjected to quality tests in the factory, the installed membrane often exhibits leakages due to different reasons. Main sources of leaks are the required high amount of welding seams and damages caused during installation of reinforcement, as well as overstretching and poorly installed secondary concrete linings. Also the design of the tunnel lining is strongly influenced and limited by the use of prefabricated waterproofing sheet membranes. The use of sprayed waterproofing membranes for more than a decade has contributed to durability and serviceability, as well as to increasing sustainability of tunnel linings. The presented sprayed waterproofing membrane MasterSeal 345 is an advantageous alternative to prefabricated waterproofing sheet membranes under typical tunnelling conditions, especially in geometrically complex areas, such as in lay-by niches, cross passages and crossover caverns, where installation of conventional waterproofing membranes is inherently difficult, and locating leaks is challenging. This membrane has been successfully used in underground projects with different waterproofing design concepts and under diverse hydro-geological and environmental conditions for over a decade. It provides tunnel designers with different options and optimisation for the design of the tunnel concrete lining. Additional advantages to owners, contractors and designers from the use of the sprayed membrane include flexibility in the design, increased productivity and flexibility in working programming, as well as improved logistics, resulting in significant program and cost savings and reduced long-term maintenance costs. This paper describes the key features of this sprayed waterproofing membrane, its application range and limitations, the waterproofing concept, design options and related benefits. Further, guidance for membrane application and quality control and a summary of two recent project references in the United Kingdom and in Switzerland are provided.CITATION:Saraiva, E, Clement, F and Mahoney, W, 2014. The use of sprayable waterproofing membranes in underground structures – concept, design options, benefits and limitations, in Proceedings 15th Australasian Tunnelling Conference 2014 , pp 323–332 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 17, 2014

By M Hawkins

The Clem Jones Tunnel (formally known as the North-South Bypass Tunnel), a A$2.88 billion road tunnel project in Brisbane, Queensland, was successfully completed almost seven months ahead of schedule. The project included two parallel 4.7 km long road tunnels, 740 m of intermediate roadway access ramps and two auxiliary ventilation tunnels. The tunnels incorporate intelligent tunnel systems, best practice fire and life safety standards and typical civil tunnel elements.Over the duration of the project the Parsons Brinckerhoff (PB) and AECOM (formally Maunsell) design joint venture (MPB) were Lead Designers to the Leighton Contractors and Baulderstone Bilfinger Berger Joint Venture (LBBJV). Construction of the toll road commenced in September 2006 and was completed in March 2010, with the tunnel opening then. Contributing to the success of this project was the continued support the lead designers gave throughout the construction period.This paper will focus on some of the structural elements that contributed to the success of the project – in particular the cable tunnel structure, a small precast, culvert shaped element under the pavement of the mainline tunnel, and the fit-out of the Gibbon Street shaft which were designed to be constructed in a combination of precast and in situ concrete.The cable tunnel was incorporated early in the design phase and runs the length of much of the tunnel. This paper will outline the challenges faced by the designers with implementing this system which provided significant construction advantages, among which were being able to install a separate ventilation duct during construction and to start fitting out the mechanical and electrical conduits and drainage system while tunnelling was still underway.The Gibbon Street shaft had a length and width of 20 m by 40 m and an overall depth of 38 m. A 20 m high structure of precast and in situ concrete was constructed in the base to accommodate mechanical and electrical equipment and provide a take-off access for the southern ventilation tunnel. The construction purpose for this structure was to provide a junction between the tunnel boring machine (TBM) and the roadheader-style tunnels, a staging platform for commencing the roadheader tunnelling, and a platform where the TBMs could be dismantled and removed.The design was assessed and reviewed many times throughout the construction process to address the needs of each of these stages. Innovative use of precast concrete was used to minimise construction time.Additionally, the designers provided support to the construction team from the time of design completion through to the tunnel opening. This meant that the changes to the design and adjustment of construction loadings could also be assessed. The fi nal outcome resulted in an efficient construction sequence and a project that has provided an excellent outcome for the client, stakeholders and community.

Mar 8, 2011

By H Fukaya T Miki, J Gamutan

Molybdenum disilicide (MoSi2) is a promising material for thermal applications due to its excellent heat and oxidation resistance. It can operate at temperatures of up to 1800°C as furnace heating elements and protect refractory metals such as molybdenum from rapidly reacting with air to form volatile molybdenum oxides at elevated temperature. In this work, the feasibility of forming MoSi2 on a molybdenum substrate by hot dipping in a silicon-saturated molten metal bath was investigated. This method is simple, predictable and can be used to coat large components and complex parts. It was found that tetragonal MoSi2 can be successfully synthesised on the surface of the substrate after dipping for 15 mins at 1000°C using molten tin (Sn), bismuth (Bi) and copper (Cu) baths. The growth of the MoSi2 layer was fast within the first 15 mins and then gradually slowed down with time. After dipping for 60 mins at 1000°C, the thickness of the MoSi2 layer were measured as 441.5, 19.5 and 13.1 μm for the copper, tin, and bismuth baths, respectively. The MoSi2 coating synthesised in this study provided oxidation resistance at 1150°C by forming a protective SiO2 layer on the surface. The SiO2 layer prevented the sample from rapidly oxidising by inhibiting direct contact between the molybdenum substrate and oxygen in the atmosphere. Compared to conventional methods, the proposed hot dipping method produces a MoSi2 layer more rapidly and at much lower operating temperatures. This makes it a more attractive option for coating large and complex components, with the potential to enable the use of MoSi2 in a wider range of applications.

Jun 19, 2024

By E Williams

The role and importance of a well designed test work program during the development of an orebody is often underestimated. A test work program should be tailored to deliver very specific answers to relevant questions. With a clear purpose, the results from the test work program will enhance the outcome of the feasibility study and provide the information required to meet the requirements of all stakeholders. With regard to test work programs there are three main areas that should be considered: orebody characterisation and definition, process flow sheet development and engineering design information.Orebody definition relies on reliable analytical methods to characterise and assess the economic minerals present in the ground. In mineral sands, the physical processing characteristics of the minerals play a significant role in the definition of an orebody. The analytical method therefore has to be customised using a combination of laboratory techniques. These techniques can include heavy liquid separation, gravity separation and magnetic separation and are usually combined with chemical and mineralogical analyses to create a picture of the orebody. During the definition phase of test work programs, an appropriate analytical technique has to be developed to evaluate drilling samples, but also to support the information collected during flow sheet development.Process flow sheet development is usually done once there is a reasonable understanding of the size and variability of the orebody. Selecting the best sample for test work is critical, as any flow sheet design is tied to the specific characteristics of the sample used for development. There are other factors that can improve the outcomes of flow sheet development test work, including the skills and knowledge of the operator and allowing sufficient time to process and analyse the results. Very often this work is conducted under pressure with limited time and resources, only to result in a suboptimal flow sheet. During this phase of flow sheet test work, iterative testing will provide the information required to develop an optimal metallurgical flow sheet. The data collected will provide indicative recoveries and yields that are required for feasibility studies.Equipment specification is often included as part of process flow sheet development. This includes comparative test work between different equipment suppliers, assessment of operating conditions such as the loading to determine the number of processing units required, as well as other design information required such as particle size distributions, density and operating temperatures.While restricting the time and costs expended on test work programs may seem to meet a short term need to meet investor requirements, neglecting to develop a proper framework of the requirements that has to be met in the long-term can lead to significant long-term cost overruns. This is mainly due to a need to repeat test work, or do confirmation test work, as insufficient information was collected during the initial program.

Oct 5, 2011

By K J. Davey, J T. Woodcock

Australian steelmakers produce up to 30 000 t/yr of electric arc furnace (EAF) dust. Current disposal techniques include sending EAF dust to landfill, stockpiling, and paying zinc smelters or registered waste removalists/processors to take the dust. Many of the complex overseas pyrometallurgical and hydrometallurgical treatment routes cited in the literature are not considered economic. Governmental, environmental and social pressures on producers to consider more sustainable disposal options are mounting, and there is now a strong push to consider recovering potentially valuable or recyclable components, such as zinc and iron units, from EAF dust. As well, there remain strong economic drivers for producers to find lower cost disposal solutions. Characterisation studies undertaken at CSIRO Minerals have revealed important physical differences in the nature of the zinc- and iron-bearing phases contained in domestic EAF dusts. These differences have been exploited using simple and cheap mineral processing techniques such as water washing, wet cycloning and wet magnetic separation. This has allowed a significant upgrade in the zinc content of EAF dust to be achieved, together with a reduction in the levels of key smelter penalty elements, such as chlorides and fluorides. The zinc-rich portion of the dust is now a more attractive smelter feed while the iron-rich part of the dust could potentially be briquetted or pelletised with a reductant and recycled to recover iron, and thus close the loop on dust processing. The basis of the separations tested together with laboratory results from several Australian dust samples are presented and discussed in this paper.

Jan 1, 2006

By C Li

Removal of gangue minerals from ilmenite concentrates can be accomplished by relatively low temperature roasting in controlled gas atmospheres to selectively enhance the magnetic separation characteristics of the ilmenite. At roasting temperatures below 800¦C the magnetising reactions are often not consistent with phase equilibria considerations. Metastable phases can nucleate and control the roasting products. In weathered ilmenites the phase assemblages and microstructures in the altered ilmenite grains can influence the roasting reactions. In this paper we give an overview of the phase chemistry of chemically weathered ilmenites and of metastable phases formed by low temperature roasting. We also report the results of roast experiments conducted in a neutral gas atmosphere. Major increases in magnetic properties after short roasting times at low temperatures were obtained for a range of ilmenite concentrates. For example heating a secondary ilmenite concentrate from Western Australia for 15 minutes in nitrogen at 600¦C gave an increase in the three kilogauss magnetic fraction from three to 92 wt per cent. The solid state phase changes accompanying the inert atmosphere roasts were characterised by combining elemental analyses with quantitative phase analyses of the ilmenite concentrates and their roast products. It was found that the phase reaction that is principally responsible for the increase in the magnetic properties of weathered ilmenites involves a transformation of disordered ferrous-containing pseudorutile to an ordered ilmenite-hematite solid solution containing typically ten to 35 mole per cent of the hematite component. Examples are given of the application of the inert atmosphere roast to effect separations of ilmenite from gangue minerals.

Jan 1, 2001

Subsurface development requires some geotechnical conditions and challenges. Most of then are related to the compatibility between tunnelling system and surrounded ground conditions, and design criteria. Design criteria usually involve lining pressure and ground control of displacements. In order to fulfil these requirements, geotechnical parameters have to be obtained as well as construction aspects have to be taken into account for predicting the tunnel behaviour. The Brasilia Metro is presented as a case history illustrating the geotechnical conditions and challenges for its implementation. It is 42 km long, including tunnels excavated in collapsible porous soils by the New Austrian Tunnelling Method. The Brasilia porous clay presents some characteristics, which may lead to large deformations due to structural collapse. Empirical methods were calibrated for collapsible porous soils and then applied to predict tunnelling-induced settlements. Settlements due to soil structural collapse modify completely the expected settlement profile, increasing their values from the tunnel crown to the ground surface. Consequently, surface settlement trough volumes were also greater than the ground losses around the tunnel. In this case history, structural collapse of porous soils played an important role and must have been taken into account to predict correctly the settlement trough and profile. Numerical simulation has shown that settlement magnitudes due to structural collapse are strongly dependent on the soil stiffness reduction after collapse and the extent of the collapsible zone.

Jan 1, 1999

By A N. Parry, G van Wyk

"Sensor based automatic ore sorting technologies are used in the minerals industries to efficiently remove waste and submarginal grade material from crushed and screened run-of-mine (ROM) ore, producing a coarse (typically >10 mm) upgraded preconcentrate at an early stage in the mineral processing circuit. This avoids additional energy intensive downstream processing of this rejected component of the ROM feed, leading to lower unit operating costs and reduced tailings disposal volumes.Test work on bulk low-grade gold ore stockpile samples from Central Norseman Gold Proprietary Limited has been conducted, indicating high gold recoveries as well as high material rejection rates. A financial model, based on these results, evaluates grade sensitivity and identifies a minimum stockpile grade for adequate financial returns. The base case modelling estimates that the ex-stockpile grade (including the fines bypassed fraction) can be more than doubled through ore sorting and that the project will be highly viable with strong cash flow generation at stockpile grades as low as 0.7 g/t gold. The modelling will enable the company to benchmark ore sorting options against stockpile reclaim and screening operations currently employed. Citation:Parry, A N and van Wyk, G, 2016. Upgrading Low-grade Gold Ore Stockpiles by Preconcentration Using Ore Sorting - an Assessment of the Economic Impact and Viability, in Proceedings 13th AusIMM Mill Operators’ Conference 2016, pp 179–190 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Oct 10, 2016

By J H. Kyle

Cyanide is a significant cost in gold processing, as well as an environmentally sensitive issue. It has been suggested that precipitation of cyanide from leach liquors as copper-iron-cyanide compounds such as Cu2Fe(CN)6 may account for part of the total cyanide consumption. This may be especially true for ores that are rich in both copper and iron minerals. Ammonia addition has been shown to decrease the cyanide consumption by copper. Cu2Fe(CN)6.xNH3 precipitates have also been postulated to form during conventional cyanide detoxification processes, using oxidants such as SO2/air, with ammonia arising as a breakdown product from the oxidation of free cyanide. The present work has examined the conditions under which such precipitates may form, particularly in gold plant process and detoxification liquors. Ammonia and pH were found to have a large effect on the extent of precipitation. The compounds that were formed were found to comprise mainly Cu2Fe(CN)6.7H2O, as well as a range of NH3-bearing variants. The stabilities of the various precipitates are important from an environmental perspective. The long-term stability of copper ferrocyanide precipitates in tailings dams may be a problem under alkaline conditions and when some free cyanide is present, elevating the measured total cyanide in solution significantly. Case studies including data from actual plants are also considered, and the importance of these effects is reaffirmed from these results.

Jan 1, 2000

By Sataev IS, Malinovskaja ND, Otrozdenova LA, Knodov NV, Maximov II, Kuznetzou OK

The technology of flotation recovery of silver from the residue of a zinc plant is described. The peculiarity of this technology is a preliminary pulp conditioning in sodium chloride solution in the presence of aluminum metal under high temperature. In this process the silver is converted to the metallic phase and then floated with the usual sulphydryl collectors. A variant using a combined technology is also described, in which before flotation is performed about 50 per cent of silver is leached. The total silver recovery with the combined technology comes up to 90 - 94 per cent.

Jan 1, 1993

By J Andrina, D Richar, R Smart, A Neale

The Grasberg is a large copper and gold open pit mine operated by PT Freeport Indonesia and located in the high equatorial mountains of Papua Province, Indonesia. The climate is alpine/sub-alpine with little seasonal variation in temperature and rainfall. The annual precipitation varies from about 3000 to 5000 mm over short distances around the Grasberg, but in general, an average daily precipitation of 10 mm per day applies and leaching of the overburden is continuous throughout the year. Mining commenced in 1988, and almost all of the overburden mined up to 2003 was potentially acid forming. From 2003 to the end of the Grasberg pit operation in 2014, approximately 70 per cent of the overburden will be potentially acid forming and 30 per cent limestone. A major focus of the investigations is developing strategies to maximise the beneficial use of the limestone that will be mined. Laboratory columns and field test pad investigations have been ongoing for six years examining limestone blends. Trial dumps utilising truck placement and conveyor/stacker placement and blending of limestone and acid generating rock have recently been constructed. In addition, based on initial results, investigations aimed at further evaluating the performance of limestone covers in this high rainfall environment have commenced. A significant finding has been the identification of strong armouring layers on sulfide surfaces within well-blended material and under limestone covers. These layers effectively isolate sulfides and thus progressively slow the oxidation rate to a level where the alkalinity load from the limestone exceeds the rate of acid generating. ARD is controlled and neutral low metal drainage results. The results have demonstrated that although limestone blending is effective, it is necessary to ensure that all size fractions within the blend receive adequate acid neutralising capacity to buffer the potential acidity. Because the sulfur content generally increases and the acid neutralising capacity decreases with decreasing particle size in limestone blends, the amount of limestone required greatly exceeds the stoichiometric requirement. This paper describes the development of limestone blending specifications for potentially acid forming overburden and presents the results of the ongoing limestone cover trials at the Grasberg mine.

Jan 1, 2003