Search Documents

By R O’Sullivan, D Taylor, J G. McLellan, B Miller

The Mount Isa copper deposit is located adjacent to the city of Mount Isa, Queensland, and lies within a series of Palaeoproterozoic to Mesoproterozoic Superbasins. The deposit is hosted almost entirely within the Urquhart Shale (US), a unit of the Mount Isa Group sediments and part of the Isa Superbasin. The copper mineralisation is separated into two distinct orebodies: the X41 mine (1100 and 1900 orebodies) and the Enterprise mine (3000 and 3500 orebodies). The orebodies are situated in the hanging wall of the major controlling structures, the Paroo Fault, which has juxtaposed older basement Eastern Creek Volcanics against the younger Mount Isa Group sediments cf 1655 ± 4 Ma. Conjecture remains over the exact timing of this thrust event. However, it is clear that inflections on the Paroo Fault have a close association with the orebodies and are an important structural feature in the mineralisation of the Mount Isa copper deposit.The life-of-mine is reducing steadily and new geomechanical modelling techniques were employed to target structurally controlled mineralised zones in three dimensions. Following a structural review of the mine using underground mapping, structural data and core shed observations, a conceptual 3D mine model was constructed utilising existing data modelled in MineSight®. This conceptual model included all the main lithological units and structures. The conceptual model aimed to test the effects of deformation on the main lithological and structural components of the system and attempted to highlight areas of anomalous stress and strain that may indicate a higher likelihood of fluid focusing and mineralisation potential. This project was focused on testing the latter stages of a D3 event (NE–SW compression) and D4 event (SE–NW compression), which are considered to be responsible for the current location of the mineralisation.The fully coupled 3D finite element analysis models resulted in highlighting anomalous patterns of stress and strain and subsequent fluid flow as a result of the two deformation events. The NE–SW D3 simulation provided the best correlation with the known distribution of mineralisation. This event also indicated several areas on the Paroo Fault and within the US that have potential to host further areas of mineralisation. The SE–NW D4 simulation provided less of a correlation with known mineralised zones. However, this event may have been responsible for post mineralisation re-mobilisation of copper on a relatively small scale. Areas of maximum shear strain, shear stress, volumetric strain and fluid flow correlated well with areas of minimum principal stress and provided the best overall match with known mineralised zones. Furthermore, several additional highlighted areas provide a high potential for further discovery of copper mineralisation. Recent exploration drilling north of the Enterprise mine 3000 orebody, utilising geomechanical modelling as part of the targeting criteria, intersected copper mineralisation, providing further validation of the modelling results.CITATION:McLellan, J G, O’Sullivan, R, Miller, B and Taylor, D, 2014. Geomechanical modelling of the Mount Isa copper deposit – predicting mineralisation, in Proceedings Ninth International Mining Geology Conference 2014 , pp 197–206 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 18, 2014

By H Kundapen, B R. Bolton, H Davies

The Ok Tedi porphyry copper-gold mine is located in the Star Mountains of Western Province, Papua New Guinea. Open-cut mine commenced in 1984 and is due to cease around 2010. The mine produces a total of 88 Mt of waste annually including 58 Mt overburden and 30 Mt tailings, which are discharged directly in to the Ok Tedi River. Mine derived wastes are transported downstream and deposited within the river channel in a variety of bar forms. The prevailing hydrogeological conditions including, velocity, competency, capacity, gradient, grain size and specific gravity, control the deposition and segregation of these sediments. Periodic exposure of the reactive sulfides to oxygen during fluctuations in the river discharge may result in oxidation, localised acid generation and liberation of metals into solution. To evaluate the significance of this issue, Ok Tedi Mining Limited initiated an investigation of the sediments deposited in the upper Ok Tedi River as part of its overall ARD Management Program. The specific objectives were to: evaluate the acid-forming characteristics of identified high sulfide river deposited sediments; characterise geochemically the waters in contact with sulfide-bearing river deposited sediments; map and monitor exposure areas and oxidation depth of deposited potentially acid forming (PAF) sediments; determine the depositional processes controlling sulfide distribution; and assess lag period, oxidation and metal release rates for the sediments. This work included the analysis of sediment and water samples collected on a 50 + 50 metre grid at six gravel/sand bars. The sediment samples were analysed for total sulfur, ANC, NAG, total sulfur and total copper. Water samples were tested for general water quality parameters, sulfate and a suite of dissolved metals including; Al, Ca, Cd, Cu, Fe-sol, K, Mg, Mn, Na, S and Zn. This paper presents the results of these investigations with particular emphasis on the geochemistry of the river sediments and associated contact waters.

Jan 1, 2003

By A Dal-Corobbo

Traditional acid and metalliferous drainage (AMD) wastewater treatment focuses on the iron co-precipitation/adsorption process as this is a very effective method of reducing heavy metals, including copper, lead, zinc, arsenic, etc, to parts per billion (ppb) levels in AMD wastewater streams. One of the drawbacks to this method however is the large volume of sludge produced and subsequent disposal costs for the mine site concerned.A proprietary metals treatment system called high density sludge (denoted HDS) which significantly reduces the quantity of waste generated is described in this paper. This process generates a dewatered sludge that contains in the order of 50 to 55 per cent solids. This sludge is denser than conventionally dewatered sludge, which typically contains only 20 to 30 per cent solids. This advanced process has a wide range of applications and can be easily retrofitted into existing AMD treatment systems. It has been successfully installed at several mine sites to treat AMD wastewaters. This paper discusses the high density sludge process, its benefits and provides data and operating results from pilot test installations.CITATION:Dal-Corobbo, A, 2013. High-density sludge process for treating metal bearing acid and metalliferous drainage wastewaters, in Proceedings Water in Mining 2013 , pp 217-220 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Nov 26, 2013

By P Ottenio, B CarrT

In the last 40 years, the froth flotation process widely spread in the paper industry becoming the dominant technology for ink removal from recovered paper slurries and cellulose fibres recovery. Most of current models used to describe the flotation deinking process are based on hydrodynamic and statistical theories of ink particles collision/attachment to air bubbles. The complexity of these theoretical models, together with the variability of the recovered papers composition, does not allow to define a set of æeasy to handleÆ equations to be used for modelling industrial flotation cells. This main limiting aspect makes that, in several deinking process modelling tools, basic parameters used to characterise the flotation unit, ie yield, ink removal efficiency, water loss, are constant parameters. Although in some process simulation tools the flotation yield/efficiency is adapted to process control parameters (air ratio, pulp flow, pulp consistency), physicochemical variables (namely the pulp frothing aptitude, the pulp surface tension and the ink adhesion energy to air bubbles) are not taken into account to adjust the flotation yield/efficiency. Data collected during recent laboratory and pilot plant experiments focusing on the role of surface active substances on the flotation efficiency were therefore interpreted and used to identify general trends that could be described with simple semi-empirical models. A set of model equations using surface tension and froth removal height as main variables was then defined in order to describe the behaviour of a pilot flotation cell. Trends obtained during the dynamic simulation of the deinking pilot plant were in good agreement with experimental data obtained under similar experimental conditions, thus indicating that developed equations can forecast with good approximation the behaviour of a flotation deinking unit.

Jan 1, 2005

At the Waikato North Head Ironsand operation, NZ Steel Mining Ltd is using a Bucket Wheel Excavator û shiftable conveyor mining system to excavate Titanomagnetite bearing sand and clay. The system utilises two Bucket Wheel Excavators with a two level shiftable bench conveyor and common trunk conveyor to deliver the material to a processing plant. The system was commissioned in November 1984 and has proved itself to be a high capacity, low cost method of excavating. Techniques of handling high sand faces have been developed and the conveyor layouts are going through a process of change to cope with the variable geo technical conditions and remain within: the characteristics of the excavators. The safety requirements for operating the system have been of a high standard and the experience has increased the confidence of the Company and the Mines Department Inspector's, for the first Bucket Wheel Excavator Mining system in New Zealand.

Jan 1, 1986

By N Pirouznia, F Rashidi Nejad, S Naraghi

Sungun Copper Mine, which is the second largest copper mining operation in Iran has a large tailings storage facility with a seepage control dam located downstream of the main dam. Surface and groundwater in surrounding area of the tailings storage facility has been monitored for ten years. This paper will discuss the results of the surface and groundwater monitoring and seepage control at the Sungun Copper Mine. The results of the study show that if the tailings storage facility influence the water quality of the rivers, this effect is not significant, so that the prevailing parameters of the measured parameters were within the permissible standard of drinking water in Iran.CITATION:Rashidi Nejad, F, Naraghi, S and Pirouznia, N, 2018. Surface and groundwater monitoring and seepage control at the Sungun Copper Mine, in Proceedings Mine Waste and Tailings Stewardship Conference 2018, pp 439–453 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 23, 2018

By C DahnTr-Lindqvist

The Kiruna mine produced about 19 Mt processed iron ore in 1999 using sublevel caving. General failure in the hangingwall has been widely studied and its mechanism is rather well understood. Failure in the footwall is more recent and not perfectly explained. Plane shear failure and Hoek and BrayÆs circular failure charts were successfully used to match the first surveyed failure surfaces. The footwall is not free yet but covered by a caved waste rock abutment whose exact behaviour is poorly known. Based on new field data and numerical models (FLAC), the following paper presents recent improvements in understanding the Kiruna mineÆs footwall failure process.

Jan 1, 2000

By R Ahola, M D. Henschel, M A. McParland

With the introduction in recent years of third-generation interferometric synthetic aperture radar (InSAR) techniques, monitoring of mine slopes, benches and surrounding areas has benefitted from increased accuracy and coverage. Fundamental research into point and distributed scattering techniques has pushed the use of InSAR to provide higher spatial and height resolution. In this paper we discuss the operationalisation of third-generation InSAR techniques and show its application to active mining operations.This paper will discuss the use of multiple independent measurements of ground movement obtained from operationally-derived InSAR products over a wide variety of deformation areas within an active open pit mining operation (ie pit slopes, dewatering depressions, tailings containment and waste dumps). A technique that shortens the time between observations (increased observation frequency) and provides ongoing estimates of measurement accuracy will be described. The methodology exploits available satellite data by using multiple satellites and multiple beams. The paper will also examine factors in the design of a mine survey with third-generation InSAR and illustrate some of the necessary engineering trade-offs to efficiently monitor a mine from space.Overall, this paper aims to demonstrate the capabilities and advantages of operational third-generation InSAR techniques for ground movement monitoring of mining operations and provide a framework for proper design of a mine InSAR survey.CITATION:Henschel, M D, Sato, S, Ahola, R and McParland, M A, 2014. Designing interferometric synthetic aperture radar surveys for mine monitoring with accuracy assessment, in Proceedings AusRock 2014: Third Australasian Ground Control in Mining Conference , pp 233–238 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Nov 5, 2014

The An Shan iron ore deposit is the biggest low-grade oxidised iron deposit in China. Over the past ten years, about 120 SLon verticalring-pulsating high gradient magnetic separators units have been installed in An Shan to process oxidised iron ore. This paper describes how several plants have upgraded their old technologies to new technologies with SLon magnetic separators as the key equipment for controlling tails grades, including using reverse flotation as the key technology for iron concentrate cleaning, These plants have been modernised with beneficial results at low cost.

Jan 1, 2009

By A Creighton, C McKenzie

Blasting is a critical task in the development of an open pit. The formation of stable slopes is also essential to the safe and economic extraction of ore. The objectives of a mine blasting department are often considered to be in direct conflict with those of the geotechnical department. This should not be the case. Personnel in the various mining departments need to understand that their goals are the same û to optimise safety and cost-effectiveness of the operation. Blasting has the potential to damage rock that is to remain in situ by generating either excess vibration, and/or pressure. These damage mechanisms are described and guidelines with respect to blast design to minimise the potential for damage are given. A rock mass could be expected to be subjected to varying degrees of damage by blasting, including both intensity of damage and also the extent of damage. These issues have potential to impact significantly on geotechnical design considerations. It is therefore important for the practitioner to define what constitutes damage. In the context of mining, it is recognised that there is a need to balance the requirements for efficient excavation with those of forming stable and cost-effective pit walls. It is therefore important to have a set of key performance indicators (KPIs) against which the performance can be bench marked. These would include cost and time, both of which may be influenced by very diverse factors such as drilling, explosives and their performance, fragmentation, excavator and haul truck performance, requirements for batter clean-up and safe working practices. KPIs are identified and discussed in this paper.

Jan 1, 2003

By H M. Parker, G Verly, T Postolski

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

Nov 24, 2014

By R Varden

Friction rock stabilisers, commonly termed ‘Split Sets’, friction rock bolts, or continuous friction coupled bolts are the most widely used rock bolt in the Australian underground metalliferous industry. Historically, they were used for temporary reinforcement, mainly within ore development. However, their use as primary reinforcement has grown with the demand for higher development rates at lower costs. The introduction of galvanisation has increased their longevity and pattern bolting in conjunction with weld mesh, specifically made for use in development headings, has allowed the use of friction rock stabilisers to increase rapidly with development jumbo’s undertaking the installation. The installation of friction rock stabilisers appears to be deceptively simple, particularly when compared to resin encapsulated bolts. The friction rock stabilisers capacity is a function of the borehole parameters, rock mass quality/strength, the bolt dimensions and steel quality, and lastly and perhaps the most important the operator skill levels. However, as in industry we are still seeing common occurrences of friction rock stabilisers not reaching their design pull test capacity. Pull testing the friction rock stabilisers is used to verify the installation of the design capacity. It involves loading the collar of the bolt with a hydraulic ram until the design load is reached or the bolt slips. Pull tests often show failure rates of 20 per cent or higher. This is despite over 40 years of use and with millions of units installed annually. Such high failure rates would suggest there remain issues with the quality of installation. Ground support quality assurance and quality control (QAQC) programs are needed in combination with operator training to ensure that pull test failure rates are kept as low as practical. However, there are times when despite the QAQC being completed the pull test failure rates increase quite suddenly. When this occurs, it is important to conduct a thorough investigation. These investigations often show there are several factors that are not obvious to personnel installing the bolts. To complete a useful investigation, it must also be done methodically, working through the entire process that includes less obvious factors such as steel quality and the calibration of the hydraulic pull test kit. The aim of the paper is to give mine practitioners an understanding of the complexities of friction rock stabilisers, what QAQC requirements they should be doing on-site, what can go wrong during installation and, if necessary, a process of how to conduct investigations into high friction rock stabiliser pull test failure rates.

Mar 29, 2023

By R Jones

OneSteel Whyalla’s grate-kiln-cooler pelletising plant was commissioned in 1968 processing haematite feed from the local South Middleback Ranges mining area. The existence of a magnetite resource beneath the haematite ore at Iron Duke had been known for some time. In 2004, a decision was made to covert the primary iron source for the Whyalla steelworks from haematite to magnetite – known as project magnet. The intent of the project was to convert the feed to the steelworks from haematite to magnetite and to free up the remaining haematite resource for export. The pelletising plant was cut over to a magnetite feed in 2007.The thermochemical differences of magnetite compared to haematite are threefold:1. the introduction of an exothermic reaction during conversion of magnetite to haematite,2. the absence of bound water which existed within the haematite, and3. lower gangue content requiring lower fluxing levels and therefore lower calcination energy demand.The combination of these differences results in a significantly different induration requirement for magnetite as compared to haematite. The change therefore required extensive research and test work to design modifications to the furnace and to ensure appropriate risk mitigation for the Whyalla steelworks.Preliminary pot-grate test work was performed to define the pellet chemistry and confirm the suitability of the magnetite to produce pellets suitable for the OneSteel blast furnace. A heating curve was developed by use of computer-based heat and mass balance modelling. Extensive pilot scale grate-kiln-cooler test work was then performed to confirm the heating curve and to verify and fine-tune the pellet properties. Computation fluid dynamics was used to design the physical changes to the furnace required to achieve the proposed heating curve.Following installation of an additional preheat zone, including a wall and dilution air fans, into the preheating furnace, and installation of an additional wall into the cooler, the modified furnace was commissioning in December 2007. The plant performed as expected during commissioning with the actual heating curve matching the proposed curve and the produced pellets within blast furnace specifications.

Jul 11, 2011

By Y Gu, R Fandrich

Traditionally, characterisation of the mineralogy and textures of ore and rock samples were based on observations of hand specimens and thin sections using an optical microscope. The extent of the data collection was limited by the available tools and thus variations in mineralogy and texture were generally not described by quantitative data. These qualitative to semi-quantitative approaches, even though well established over the years, resulted in variable observations and data sets. The data were unlikely to be representative of a sample and limited statistical validity meant the results could not be reliably used in modern digital mining design and planning. With recently developed SEM based quantitative mineralogy tools and the corresponding methodologies, ore textures can be quantified and compared numerically. The numerical data can not only enhance the understanding of an orebody in geological terms, but can also be used in the creation of metallurgical models for mine and mineral processing design and simulation. These capabilities provide valuable inputs to risk assessment studies and the evaluation of mineral projects.

Jan 1, 2007

By D Atheis, S Williams, A Dance, D Taplin

"Resurrected from its former life at the Big Bell operation, the grinding circuit at Evolution Mining’s Edna May operation in Western Australia has many a story to tell. The task of optimising a plant designed for another orebody provides as many challenges as opportunities. Initially faced with a blend of primary and oxide ore, the circuit achieved in excess of 320 t/h until the oxide was depleted, leaving only the much harder primary feed.The 2.0 MW semi-autogenous grinding (SAG) mill and 3.7 MW ball mill were assisted by a 150 kW pebble crusher, but the power limitation of the SAG mill resulted in a drop in throughput. Edna May personnel have been involved in a number of progressive improvements to restore the design capacity of the concentrator and work towards 3 Mt/a or even higher ahead of the gravity and leach recovery circuits.These improvements include: a crush forward configuration of the SAG mill scats partial to full secondary crushing variable speed drive upgrade of the SAG mill lifter and grate design changes ball mill circuit grinding efficiency.This paper summarises the chronology of events that has resulted in significant improvements in throughput by conventional (and in some cases, novel) methods of reconfiguring the existing grinding mills. Lessons learned and hindsight perspectives will be summarised, sharing this educational experience with other operations in a similar situation.CITATION:Dance, A, Atheis, D, Williams, S and Taplin, D, 2014. Grinding circuit improvements at Evolution Mining’s Edna May operation, in Proceedings 12th AusIMM Mill Operators’ Conference 2014, pp 63–70 (The Australasian Institute of Mining and Metallurgy: Melbourne)."

Sep 1, 2014

By A Grigg, L Hackett

Alcoa operates two bauxite mines at Huntly and Willowdale, located within the jarrah forest south-east of Perth in Western Australia. Ore reserves are shallow but extensive, and mining pits averaging around 20 ha in size are distributed across a mining region in a mosaic pattern, linked to a centrally-located crusher by a radiating network of haulroads. A mining or crusher region is defined partly in terms of economic haul distances, and new regions are opened once the current regions’ reserves have been mined. Since commencing in 1973, the Huntly mine has constructed and progressively closed three previous mining regions and is presently in a transition from the fourth and current region of McCoy to the new region of Myara. At present rates of production, approximately 450 ha is cleared, mined and rehabilitated each year.The value of topsoil in returning a diverse mix of native jarrah forest plant species and supplying nutrients, organic matter and soil biota to rehabilitated areas has long been recognised. Managing the topsoil resource is therefore a critical element in the success of rehabilitation outcomes, but the distribution and dynamic nature of mining operations pose significant planning and logistical challenges. The regionalised approach to mining at Huntly also presents a range of issues for what are, in effect, soil management plans for episodic mine closure. The nature of mining and rehabilitation operations are described, together with the planning processes that Alcoa follows to quantify, track and report on soil movement. A case study of the Huntly mine demonstrates that an integrated operational and life-of-mine planning process is essential for successful and cost-effective mine rehabilitation.CITATION:Hackett, L and Grigg, A, 2014. Topsoil management for long-term mine operation and closure – a case study from Alcoa's bauxite mining operations in south-west Australia, in Proceedings Life-of-Mine 2014 , pp 609–614 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 16, 2014

By K Rees

In the ideal world of an underground mining engineer, all narrow vein orebodies would be perfectly straight and continuous, thus would be a dream to mine. However, this is usually not the case. Narrow vein orebodies generally occur in association with shear zones and while shear zones do form linear trends, they most commonly preserve undulating expressions that need to be closely monitored, particularly when overprinted by post-formed structures. The surge in mines using fibrecrete as a primary form of ground support effectively reduces the time available for geological interpretation down to a 30 minute window between bogging and shotcreting. Thus, if the quality of the data collected is not up to scratch, then there is only a limited ability to reassess using 2D face photographs. To negate this, Xstrata Nickel AustralasiaÆs Cosmos mine has upgraded its data collection procedure. Geological information is now collected using photogrammetry survey, producing 3D images of the drive. Once created, the digital image of the drive is loaded into Vulcan, thus enabling geological interpretation to be carried out along entire drives, between levels and in association with all other data (eg drill holes, seismic data, etc). In addition to this, the 3D image can be used to accurately model the location of the ore, enabling stoping panels to be confidently positioned to maximise grade and minimise dilution. However, with the focus at Cosmos changing from narrow vein mining, to bulk mining methods in a more geotechnically complex terrain, the use of the 3D images has become paramount in understanding the structural geometry. Continual interpretation of the data has enabled drive profiles to be maintained through the increased use of ground support in poor ground and the redesign of development to enable optimal intersection of structures. Nevertheless, while the collection of quality data is important, it is only the effective use of the data, which enables significant gains in understanding.CITATION:Rees, K, 2012. The benefits of using photogrammetry in the geological interpretation of the Cosmos nickel mine, in Proceedings Narrow Vein Mining 2012 , pp 145-148 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Mar 26, 2012

Limnological processes are often overlooked when trying to assess the long-term water quality of pit lakes. It is essential to deal with these aspects, since they determine the geochemical and redox conditions around the submerged reactive rocks. Underground mining at East Sullivan (northwestern Quebec, Canada) stopped in 1966. Two adjacent stopes, 91 and 106 m deep, were left open to the surface, with roughly circular apertures of about 7700 and 18 000 m2. Water filling of the two glory holes went on over three decades and overflow began in 1999. Surface water pHs values were near neutrality as late as 1994 (6.3 - 7.0) but had become acidic by 1999 (2.6 - 3.5). Limnological processes were investigated in late-1999 and early-2000, with temperature measurements at 1 m intervals and sampling of the water columns before and after the late fall density inversions. A strong chemocline-thermocline was observed at 15 m. Above the chemocline, the water had low pH (3.2), no alkalinity, and low Na, Ca and sulfate. Below the chemocline, the concentrations of these parameters and the pH increased, with pH at 5.5 - 6. Consistent with the low pH values present in the upper 15 m, the concentrations of Al, Cd, Cu, and Zn were high near surface, and decreased below the chemocline. Dissolved oxygen concentrations as well as Eh decreased with increasing depth. Alkalinity integrated over the entire water column below the chemocline was at least six times larger than the acidity inferred from Fe2+ and Fe3+ concentrations. The temperature survey showed that seasonal density inversions do occur in the water column. The inversions do not involve the entire water body, since the surface to depth ratio is too small for a complete overturn. Oxygen from surface waters is carried to the bottom where it oxidises sulfides, until its depletion. Residual Fe2+, stable under anoxic conditions, is displaced upward by the next dense water incursion. It eventually reaches the thermocline, but only after many successive incursions. There, its oxidation to Fe3+ allows hydrolysis, which consumes dissolved and wall-rock alkalinity. It is only in 1999 that alkalinity was finally exhausted and that the pH shifts to acid values. The low pHs in the surface waters allow a build up of Fe3+ and Al3+, and desorption of metals from colloids. Buffering is assumed to be controlled by wall-rock oxyhydroxides in surface waters, and by carbonate minerals in the bottom waters. Because the seasonal overturns are far from being complete, the large amounts of alkalinity acquired from the wall-rock in the bottom waters cannot balance the acidity of near surface waters. Hence the surface water is acidic.

Jan 1, 2003

People in economically developed societies demonstrate inherent human care for Earth and want to stop pollution. Yet efforts to clean Earth seem bogged in confusion from wildly contradictory and alarmist predictions of æclimate crisisÆ. Supposed experts openly disagree yet weÆre told thereÆs universal agreement humans are causing æthe end of life as we know itÆ. The turmoil combines with peopleÆs feelings of fear, guilt, anger, hopelessness and even resignation and apathy to trigger æclimate alarmÆ. The paper enables people to rediscover clarity, hope and support for Earth by understanding how climate alarm and confusion were created and how they actually increase pollution. Many people seem to think global warming is as serious as pollution and worry that questioning alarm will enable pollution. Yet theyÆre different. We need be even more concerned about climate alarm because history shows repeatedly that when buried by ignorance and panic real problems grow overwhelming. Environmental credibility is endangered by confused politicians and sensationalist media. When weÆre willing to re-evaluate what weÆve been told we replace fear and confusion with facts and freedom to identify opportunities. Combining this with practical understanding of human behaviour and leadership enables opportunities to be identified and action taken. The paper shows how confident, informed leadership leads and supports higher productivity and effective care for the natural environment.

Jan 1, 2009

By V Ser, R Crosbie

To date, Anglo American Research Laboratories (AARL) has carried out several projects, based on the techniques developed in AMIRA International LimitedÆs (the mineral industries research association) AMIRA P9 project, to develop models for several Anglo Base Metals flotation plants. Further detailed analysis of the data which was generated has realised additional benefits: the various hydrodynamic measurements were useful in comparing cell operating parameters to literature sources, while the laboratory batch tests give an indication of plant recovery potential. A detailed cell by cell mass balance, which is a critical feature of the modelling process, is in its own right a valuable diagnostic tool. Several examples of how this can be used to highlight potential improvement areas in the plants are presented. The added understanding gained from sampling each cell is clear and this is shown to more than compensate for any necessary modifications needed to allow sampling to take place. The model fitting process generates an ore floatability distribution, which is used in the JK SimFloat simulation package to assess the effect of possible changes to each of the circuits. An example of an actual circuit change as a result of this approach is presented. The current limitations of and the potential improvements to the modelling process are also briefly discussed. Future models will be extended to include enhanced size and mineralogical information where the basic models suggest this has potential to improve understanding.

Jan 1, 2005