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By A Litwinowicz, M Laxman, A Fourie, A L. Li

This paper presents a design approach and analytical methods that were used for assessing the potential of static liquefaction and developing the mitigation measures for a tailings dams. The rigour of the design and analysis approach represented leading practise in the industry to address static liquefaction, which contributed to a robust design with high confidence and certainty. The salient features of our approach to static liquefaction included geotechnical investigation and tailings characterisation, static liquefaction screening assessment, static liquefaction triggering analysis, limit equilibrium analyses and numerical modelling of static liquefaction using the NorSand model, which was amongst the first tailings dam projects involving numerical modelling of static liquefaction using these methods.

Jul 1, 2021

By J-T Zhu, Q-Y Tu, S-L Kong, L Wang, Y-P Cheng, H-Y Liu, Q-L Yang

China is the largest coal-producing country in the world, while the geological conditions of deep coal mining are extremely complicated with high ground stress, high gas pressure and low permeability, which results in the difficulty of gas drainage and aggravation of gas explosion and coal and gas outburst disasters. Co-extraction of coal and gas is an effective method to eliminate coalmine gas disasters and realise the safe exploitation of coal and efficient gas drainage at the same time. This concept is widely accepted by the main coal-producing countries around the world, while the concrete definition of co-extraction is vague and not unified, and there is little accurate theoretical support for co-extraction of coal and gas, which makes it hard to determine efficient gas drainage methods correspondingly according to the features of coal seams in a comprehensive and systematic way. Based on theoretical analysis, laboratory test and field observations, basic thoughts and specific definition of co-extraction of coal and gas were put forward after analysing the occurrence characteristics of coal seams in China. We obtained the mechanism of mining-enhanced permeability and established the corresponding theoretical model, which is the process of fracture network formation through opening recovery of the original fractures and new fractures produced by unloading damage. Based on the core idea of ‘mining-enhanced permeability’, engineering approaches of ‘unloading by boreholes drilling’ for the single coal seam and ‘unloading by protective seam mining’ for the coal seam group were proposed to realise safe and efficient co-extraction of coal and gas. Meanwhile, combined with engineering practice, we put forward the construction principle of coal exploitation and gas drainage system in different coal seam occurrence conditions. The above methods were applied successfully in the Tunlan coalmine in Shanxi Province and the Panyi coalmine in Anhui Province, which had established the ‘underground-surface united’ spatial gas drainage modes, and could ensure safe and efficient co-extraction of coal and gas in the outburst coalmines.CITATION:Cheng, Y-P, Wang, L, Liu, H-Y, Kong, S-L, Yang, Q-L, Zhu, J-T and Tu, Q-Y, 2015. Theory of safe and efficient co-extraction of coal and gas and its applications, in Proceedings The Australian Mine Ventilation Conference, pp 79–92 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Aug 31, 2015

By D Tuazon, M Powell, M Ziemski, G D. Corder

Although mining companies have made broad corporate-level commitments to adopt sustainability, there continue to be problems when attempts are made to adopt higher-level sustainability aspirations and translate them into appropriate targets and methods at the more-specific operational level. The integration of sustainability principles into minerals processing operational decision-making processes has unique challenges that are not addressed adequately by current tools and methodologies, yet impacts from operational decisions can have longer-term effects realised at closure and rehabilitation.This paper describes a proposed methodology to achieve the integration of sustainability at the operational level through a systematic and rigorous process of identifying and qualifying sustainability issues and opportunities in an operation. The methodology, starting from a sustainability point of view rather than an operational one, guides the identification of process issues and opportunities by examining the operation, unit-by-unit, similar to a Hazard and Operability (HAZOP) process. Each issue or opportunity is qualified according to its measurability, scopes of impact and consequences so that it may be understood fully and the correct engineering problems are formed. Through improved decision-making to account for broader sustainability factors, operations can better address environmental and social expectations and pressures (both corporate and community, as well as immediate and in the longer-term), whilst still delivering on operational and business goals.The methodology has been tested with two case studies at minerals processing operations. At one site, the methodology identified a dust issue which had considerable business risks (loss of valuable product) compared to conventional engineering analysis processes. The other site also benefited from using the methodology as an opportunity to improve the operation of the milling and flotation circuits was identified. The opportunity not only showed a potential to improve operational efficiency, but also potential improvements in water and energy efficiency and a resulting increased resilience against water and energy supply risks. It was important to utilise the holistic approach of the methodology in the identification of opportunities at this site; the goals of the operation showed a strong coupling between water and energy issues which would be difficult to overcome using the operationÆs current organisational model, which deals with such issues separately of each other.CITATION:Tuazon, D, Corder, G D, Powell, M and Ziemski, M, 2012. A practical and rigorous approach for integrating sustainability principles into decision-making processes at minerals processing operations, in Proceedings Life-of-Mine 2012 , pp 233-242 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 10, 2012

By G M. Jones, J Rademan

Debswana, owned by the Government of the Republic of Botswana (GRB) and De Beers in a 50:50 joint venture partnership, operates the Jwaneng diamond mine in Botswana - the most valuable diamond mine in the world. The mine provides between 60 - 70 per cent of DebswanaÆs earnings, and about 30 - 40 per cent of the GRBÆs income. In 2008, the company embarked on the Cut 8 Project - an open pit waste cut-back to expose more diamond bearing ore to sustain mine life by another six to seven years. This undertaking was much larger than previous cut-backs; it increased the waste stripping ratio threefold, increasing significantly the waste handling fleet of trucks, shovels and infrastructure, and impacted a large part of the materials handling plant which required replacement with new facilities. The project coincided with the beginning of the Global Financial Crisis (GFC) and a slowdown in the economy. Its $4 billion total life cost was billed as æthe largest private investment project in BotswanaÆ which produced heightened expectations amongst stakeholders that it would redress some of the issues brought about by the GFC and leave behind a legacy of jobs, increased opportunities for citizen owned business and improved social infrastructure.Most of the big project challenges were non-technical and ranged from dealing with various stakeholders?at?all levels, a 25 per cent currency depreciation of the Botswana Pula against the South African Rand, obtaining work permits for non-citizens in a job starved environment, managing construction to world class safety standards, managing the low productivity of construction workers and producing a viable legacy program that satisfied the GRB and stakeholders. Whilst most of these risks were identified in front end studies, the magnitudes were in many instances underestimated. Managing this uncertainty on Cut 8 can provide valuable lessons to other projects in a similar environment, or at least provide the information to indicate that these factors should be adequately provided for in the financial evaluation of a project in the form of budget, schedule, contingency or risk mitigation.CITATION:Jones, G M and J Rademan, 2012. Reliability of expert judgements and uncertainty assessments, in Proceedings Project Evaluation 2012 , pp 109-116 (The Australasian Institute of Mining and Metallurgy: Melbourne).

May 24, 2012

Organisations are starting to develop processes for achieving sustainability principles they have defined for their organisation. The foundation for these principles is now well accepted. The definition of a sustainability framework is a good starting point for any project. The delivery of the framework requires the organisation to think differently about how project objectives can be met. New tools are becoming available to help achieve the sustainability outcomes for the projects. This paper will examine the project building blocks that are necessary to ensure the sustainability framework can be achieved for the project. These include new approaches to decision-making processes and evaluation tools and when to apply them. An integrated approach with shared expertise to project delivery, which is applicable to the whole supply chain, will be discussed. This will cover sustainability procurement, integrated waste management, cleaner production and eco-efficiency, sustainable products and disposal. A project toolkit will be presented and some key project tools identified. The need for management support in undertaking these new approaches is critical, as is the need to develop partnerships and cooperative management to facilitate delivery.

Jan 1, 2004

By S C. Dominy

The gravity recoverable gold (GRG) parameter reflects liberated gold or gold-dominated composite particles that can be recovered by gravity separation. Recoveries depend upon mineralogy, in situ particle size and the comminution and extraction method used. Any ore bearing >15 per cent of gold greater than 50 ¦m in size is likely to have a GRG component. The principal characterisation methodology applied is the three-stage GRG (3GRG) test, based on a 40 kg to 100 kg sample. An alternative is the single-stage GRG test (SGRG), which is generally based on a 20 kg sample. Experience has shown that GRG values can vary throughout an orebody, particularly within different grade and/or mineralogical domains. Test programs must consider sample frequency and mass. This study demonstrates the variability of GRG results based on different sample masses. Consecutive underground faces on a coarse-gold dominated quartz vein were sampled taking five different masses from each. Each sample was processed using a SGRG approach. Subsequently, each development round was batched through a small gravity production plant. The results show that the small samples understate the plant GRG and show inter-sample variability. Large samples show less variability and a SGRG closer to the plant GRG. A high SGRG broadly correlates to higher gold grades, more coarse gold and larger gold particles. These results are intuitively correct, but indicate the likely challenges of sampling for gold recovery in heterogeneous systems.CITATION:Dominy, S C, 2013. Variability of gravity recoverable gold values in relation to test sample size, in Proceedings The Second AusIMM International Geometallurgy Conference (GeoMet) 2013 , pp 293-302 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Sep 29, 2013

By R Norris, M Dunne

Mining and mineral processing is expected by society and obliged by law to operate in an environmentally friendly fashion, minimising the impact on and avoiding damage to the environment. Substantial efforts by the industry, as well as by process and equipment designers have resulted in many innovative developments, which show that operating in an environmentally responsible manner can be achieved in a cost-effective way. This paper showcases five emerging equipment best practices in industry including installation examples. Flip-flow screening machines are proven worldwide in the dry classification of coal and other minerals, reducing the size of beneficiation plants whilst reducing energy, water demand and media consumption. They also allow the screening of wet/sticky materials not able to be sized using conventional screens. The belt press filter is a small fraction of the operating and capital cost of alternative dry tailings technologies. This gives operators who must dry their tailings a competitive advantage and makes such ægreenÆ operations much more sustainable. The filtercake is disposed with other plant rejects, eliminating the need for tailings dams to be constructed and thus also often increasing mine reserves. Mining applications include coal tailings, sand tailings, sinter plant waste and power station fly ash. Screen-scroll and vibrating centrifuges are widely used in the coal, potash and salt industries to dewater the product to low surface moistures. Inclined plate Lamella separators are used for toxic water clarification and/or sludge thickening in many downstream metal industries with the underflow often dewatered in a belt filter press. Such low cost, high capacity thickeners could also be used instead of conventional thickeners at smaller mines. The simple and reliable continuous washing upward flow (CWUF) sand filters have been used for treatment of waste water from coal preparation plants and steel works as well as in the worldwide production of potable water. The filtered waste water from mining processes can then either be reused or discharged from site. Other installations include cleaning mine water to prevent the blocking of dust suppression spray nozzles.

Jan 1, 2006

Outline of situations when valuations required - from capital raisings and takeovers, stamp duty, rates and capital gains tax, to probate and litigation between joint venture parties. Definition of types of exploration and mining properties as background to discussion on what methodologies to use (from grass roots to operating mine). Discussion on nature of alluvial deposits in New Zealand and how their characteristics and tonnage/grade uncertainties affect choice of methodology. Assessment of risk factors in New Zealand û technical, financial and socio-political (legislation, access, Maori land rights, environmental). Discussion of appropriate methodologies.

Jan 1, 1992

By C Ausa, Nyunt Htay, A, L Deiparine

The main tectonic elements in Myanmar are a late Mesozoic and Cenozoic magmatic arc system in the west, repeated in northern Myanmar by more than 300 km of dextral movement on the Sagaing Fault, and the back-arc continental region affected by early and late Mesozoic orogenies, in the east. Historically most lode gold production has been from latest Cretaceous high-grade mesothermal veins and derived placers in the Wuntho and Tagaung-Myitkyina segments of the magmatic arc. Placer deposits in the Ayerwaddy River north of Myitkyina are currently worked by more than 100-bucket dredges. South of Wuntho, the magmatic arc and Pegu Yoma fold belt host epithermal gold with associated As, Sb and Zn in mid-Tertiary marine sediments. MyanmarÆs most productive lode gold deposit, the Kyaukpahto mine, lies within a north-trending district east of the magmatic arc and north of Mandalay. Here mineralisation and associated jasperoidal silica occur in Eocene sandstones and Permian and Triassic carbonates. Possibly this district continues southeastwards, across the Sagaing Fault, as sediment-hosted Sb Au and locally skarn Au mineralisation within a 1100 km long fold-thrust belt. Also present in the back-arc region are sandstone-hosted Au Cu in a Palaeozoic slate belt, and gold and stratabound gold-base metal mineralisation in the medial metamorphic belt. While untested targets remain in the magmatic arc, particularly for high sulphidation Au, the best potential is clearly within the back-arc slate and fold-thrust belts in the western part of the Shan Plateau and in northeastern-most Myanmar.

Jan 1, 1999

By B Clements, G Lane

The operations and project environments are very different, but overlap in many areas. The development of mineral processing projects is goal oriented, is schedule focused and is a contractual environment. The operating environment for a mineral processing plant is oriented around longer-term commitments, focused on delivery against budget expectations, and an environment heavily influenced by long-term personal relationships, community relationships, and people issues.Further contrast is evident in the way expenditure is managed. Projects commit large amounts of money quickly to meet schedule-based objectives. Operations manage expenditure to minimise operating costs and are able to, or are forced to delay decisions on large expenditures. However, these two environments need to come together in many ways, ranging from greenfields plant handover to a new operations and maintenance crew, to day to day interaction and management of brownfields projects, often in close proximity.This paper considers the different perspectives people bring to projects and early operations, including the advantages and disadvantages of æoperationsÆ input to a project and models for managing value adding during project development, implementation and debottlenecking.CITATION:Lane, G and Clements, B, 2012. Operations versus projects - How do people think and what are the implications?, in Proceedings 11th AusIMM Mill OperatorsÆ Conference , pp 11-16 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Oct 29, 2012

By D Kilkenny

Underground contractors in the mining industry must be prepared to take a position at the forefront of innovation of equipment and work methods in order to maintain a competitive advantage over in-house operations and remain relevant. Innovative concepts such as split-feed development jumbos, high capacity trucks and loader guidance systems were implemented by contractors to stay ahead of ‘the pack’. All of these are now common across the industry.The demands of regular participation in competitive tendering coupled with aggressive fleet depreciation, means contractors tend to have more communication and opportunities to work with equipment suppliers than mine owners. Therefore, they are more likely to influence equipment design and product directions. They also have a unique opportunity to assist in trialling new concepts and technologies across a wide variety of operating conditions rather than being restricted to one mine.In addition, as a ‘guest’ on a mine site, mining contractors do not have the luxury of creating the environment for their preferred systems, rather they must have the capacity to adapt their technology to suit the offered environment at a particular mine. This leads to a pursuit of adaptive technologies that can be implemented selectively and seamlessly without excessive disturbance rather than ‘all-of-mine’ systems. These incremental innovations then become available for use across the mining industry where they can add value as ‘bolt-on systems’ to existing operations.Mining contractors, therefore, act as the bellwether for industry practices and equipment. However, in order to maintain their position they must engage industry stakeholders to deliver practical, innovative and cost-effective technologies that add value and result in an improved bottom line for all. This paper uses case study material to illustrate how the Byrnecut Group has approached innovation and how the theory of Disruptive Technology applies to underground mining innovation.CITATION:Kilkenny, D, 2017. Innovation in mining – a contractor’s role, in Proceedings 13th AusIMM Underground Operators’ Conference 2017, pp 59–68 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Oct 16, 2017

Olympic Dam Operation is located in the Stuart Shelf Geological Province approximately 520 km north-north-west of Adelaide in South Australia. It is estimated to be one of the worldÆs top five copper orebodies by size and the biggest single occurrence of uranium. The deposit was discovered by Western Mining Corporation in 1975. Exploration was based on a conceptual model for the formation of sediment hosted copper deposits together with gravity and magnetic anomalies.The capital cost of the current expansion is estimated to be A$ 1.64 billion. The underground expansion includes a total of 36 km of lateral development, a railway haulage system delivering ore from a series of ore passes to a new crusher station and a significant increase in ventilation capacity and mine services.In the current underground expansion the mining method will essentially remain unchanged. The ore handling system will incorporate some recent advances in technology, improving efficiency and safety standards.Major infrastructure excavations are designed by a team of engineers attached to the Olympic Dam Expansion Project and a number of consulting groups. Once the expansion is fully completed it is expected to increase the current annual underground production level from 3.4 Mt to 9.0 Mt of ore by the year 2000. Mine design engineers working for the Olympic Dam Operation have recently completed a three year final design plan to achieve this target.Access to the existing mine is through the decline and Whenan shaft. The Whenan shaft was originally sunk as an exploration access and later upgraded for hoisting. The 4 km long service decline connecting to the Whenan shaft was later constructed to accommodate the increase in service demand. The Robinson and Sir Lindsay Clark shafts were developed at later stages to cater for the hoisting during and following the expansion lead up.

Jan 1, 1999

By E Deucker, A White

Gold Fields Australia (Gold Fields) has identified that improving productivity through more detailed shift planning and operational control of mining activities is a key driver to the success of their business. The Hamlet mine was chosen as a pilot site to trial a system that would allow production engineers and shift bosses to align the execution of short-term activities with the longer-term goals of the organisation.Gold Fields partnered with Deswik to introduce an on-site, collaborative, web-based system to allow mine planners to quickly build-up a detailed, activity-based, shift schedule for the coming week from the 13-week plan. Multiple stakeholders could then review and alter the plan, and then track and manage the execution of the activities.The system is designed to be integrated with production data capture systems to allow tracking of progress towards completion for each activity, as well as to plan and monitor the equipment operating in the mine. Integration of systems allowed engineers to use the large quantities of production data being captured to make informed decisions in the operations environment.The system replaced a complex set of spreadsheets that required expert users in Gold Fields to maintain. By capturing the data in a central database, the planning process is transparent and historic data from the execution of activities is available for analysis to improve productivity in the future.The system has ensured that the highest priority and critical path activities for the business are completed at the right time, improving the efficiency of operations.CITATION:Deucker, E and White, A, 2017. Productivity improvement through collaborative shift planning and tracking, in Proceedings 13th AusIMM Underground Operators’ Conference 2017, pp 225–234 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Oct 16, 2017

Diversity; what a wonderful topic. Diversity; the condition or quality of being diverse, different, varied to the point that the very word diversity means different things to different people. As one example of diversity the American Science Magazine (April, 1994) contained a light-hearted interview with Dr Noitall who was pushing his case for diversity.

Jan 1, 1996

By B D. Burford

High intensity stirred milling using the IsaMill has been the enabling technology for many projects by transforming the economics of fine grinding and simplifying circuit design. IsaMill grinding technology was originally developed for large-scale grinding to P80 sizings of 7 ¦m. The IsaMill is a high throughput, high efficiency mill that produces sharp product size distributions in open circuit configuration. The ability to grind in an inert environment, using a wide variety of media types, can give further metallurgical and economic benefits. The high energy intensity results in a small footprint that enhances the ability to distribute grinding power throughout the circuit, applying grinding energy to the minerals that need it. Recent scale up developments in IsaMill technology have enabled the benefits to be extended to large-scale conventional grind sizes, until now the domain of ball and tower mills. This paper will examine the crossover of IsaMill technology from ultrafine applications into the more conventional grinding area (P80 20 - 150 ¦m). Scale-up developments in IsaMill technology that have enabled this are reviewed. The upcoming commissioning of a 3.0 MW M10,000 IsaMill, the most powerful to date, grinding to P80 55 ¦m at PPL in South Africa will be discussed, as will the recent commissioning of a 2.6 MW M10,000 IsaMill at Kumtor. Recent testwork at McArthur River, where an IsaMill is being considered as an addition to the primary grinding circuit to replace the current tower mill will be reviewed. The potential combination of HPGR and IsaMill to transform concentrator grinding economics will also be discussed. Large-scale IsaMill technology has the ability to transform circuit design and energy efficiency for both coarse and fine grinding.

Jan 1, 2006

By A Hamanaka

EGAT Mae Moh Lignite Mine in Thailand produces about 16 Mt of lignite annually from open-cut mining. The coal is used to generate 2400 MW of electricity. In the near future, however, the coal must be extracted from underground at 400 - 500 m deep from the surface. The problem is the thickness of the coal seams. There are two coal seams that are about 25 m thick with 20 - 25 m of interburden between them.In order to investigate thick seam mining systems and propose a new mining system in ultra-thick coal seams in Thailand, a joint research group was established by Japanese and Thai researchers and mining engineers in early 2009. This paper describes conventional underground mining systems and underground coal gasification for thick coal seams and discusses the applicable coal mining systems to this mine. Then, this paper proposes an innovative underground coal mining system for thick coal seam, ‘eco-friendly underground coal mining system which consists of the utilisation of flyash and CO2 storage’.

Nov 22, 2011

By S McEachern, J Lowe

An important issue currently facing the mining industry in Australia is the management and cost to the industry and other stakeholders of entry into and exit from towns and their communities. These costs can be environmental, social, economic, political or reputational. The ability of companies to engage the trust of stakeholders, including: communities, governments and investors, is critical, and corporate reputation plays a significant role in this. For the industry to secure a long-term and sustainable future, it must have the technical, business and reputation assets to proceed in a cost-effective, environmentally acceptable and socially supportive way. This research assesses reputation as a critical competitive issue for mining companies, as technology and information make mining more predictable; the physical and human assets of mining companies are less likely to be the critical resource in a Resource Based View model of competitive advantage. The proposition is that in mining today, reputation as it facilitates day-to-day operations, regulatory zeal and access to new mine sites will become the rare, inimitable and valuable resource for mining companies. This paper reports on an ongoing research program to evaluate the impact a mining companyÆs reputation(s), with its various stakeholder groups, has on a companyÆs ability to sustain competitive advantage. Integral to this study is to develop an understanding of the relationships between mining companies and their stakeholders, and the importance of corporate citizenship polices to reputation and hence to corporate sustainability. Through the identification of the drivers of reputation for the various stakeholder groups, a model of reputation formation will be developed and also reputation measures for the mining industry in Australia. The preliminary findings of this research, the results of an industry focus group conducted with representatives from regional mining operations, are reported. The industry focus group was designed to enable a better understanding of who are the main stakeholder groups and how they regard mining companies and to inform the second stage of the research project a Delphi Study of the drivers of reputation by stakeholder groups. The aim of this research is to further the understanding of the relationship between corporate citizenship, reputation and performance in the mining industry, thus assisting companies to strategically manage their corporate citizenship investments.

Jan 1, 2006

By A Cheatle

GoldcorpÆs Musselwhite mine in north-western Ontario, Canada has in recent years become a world-class deposit. Initially discovered in the early 1960s by Alan and Harold Musselwhite, the then marginal mine eventually started production in 1997 and has to date produced 2.6 Moz of gold. Two million ounces of gold are currently classified as Mineral Reserve and a further 1.2 Moz of gold are classified in the Mineral Resource category for a total gold inventory approaching 6 Moz. Growth of the mineral inventory has been achieved through the successful implementation of strategic planning that sought to extend the mine life through discovery of additional economic zones and increased mined tonnages. Accelerated exploration activity commenced in 2001, at a time when gold price was at its lowest in decades. Focus was placed on building, developing and retaining a highly skilled geological team, maintaining purpose, conducting external reviews and developing a new geological model through research partnerships. Ongoing collaborative research between Lakehead University and Musselwhite mine has seen the development of new structural and geological models through post-graduate and academic studies. Research has included lithogeochemical, stable isotope and structural and metamorphic studies and has led to the evolution of a new mineralisation model (for the mine) and the recognition of brittle and ductile deformation regimes within the mineralised horizons. Exploration drilling continues to provide support for the new geologic model. Gold discoveries have extended known mineralisation 2.3 km along strike from mineral reserves and laterally into parallel zones. The exploration potential to further increase production rates, Mineral Reserves and Resources remains very positive and increases in overall gold inventory are likely. Musselwhite mine has significantly exceeded initial projections for a ten year life-of-mine and a marginal existence.

Jan 1, 2009

By B Ganesia, H Sahupala

PT Freeport Indonesia is a copper-gold mine operation located in West Papua, Indonesia about 3500 km east of Jakarta. Current ore production is about 270 000 tpd, of which 30 000 tpd comes from underground. In the future, the production from underground will be gradually increased to reach a maximum of 115 000 tpd, as the Grasberg open pit production decreases. The current and future challenge for PT Freeport Indonesia is to fill the quota of underground miners, as Indonesia does not have a long culture of underground work. At present, there are only three active underground mines in Indonesia. The lack of underground skilled labour incited the company to develop its own skilled workforce. In the mean time, to overcome the shortage of personnel, the underground management had to find a way to improve the productivity. Since 21 May 1998, PT Freeport Indonesia Underground Mine has operated with the new roster of two rotating shifts a day, 11 hours per shift. The previous schedule consisted of three nine-hour shifts per day, six days a week, for a total of 26 working days in a month. This change was intended to increase the productivity of the miners. With the previous roster, studies determined that the effective working time was only seven hours per shift. The new roster produces an improvement of effective working hours to about nine hours per shift. As a result, total production has increased by 33 per cent and the utilisation of production equipment has increased by 16.5 per cent. This paper describes the background of the decision to change the work schedule, the study carried out to evaluate the benefits and drawbacks of the new shift roster, the challenges, and then compares the results for various parameters between the old schedule and the new one.

Jan 1, 2002

By McLennan T, Howells E, Zastawny H, Watt J. S

Nuclear techniques have been used to determine the solids weight fraction (W) and ash content of (fine) coal in slurries independent of voidage variations. The method is based on the correlation between W and the hydrogen concentration Hsl (wt/wt) of the slurry. Hsl is determined by combining measurements of neutron moderation and ?-ray transmission. Both Wand ash content are determined by combining the above measurements with the ash-sensitive measurement of X-ray backscatter compensated by a measurement of iron K X-ray intensity.The nuclear analysis system, called the SIRO coal slurry gauge, has been proved in a six-week plant trial at the BHP Steelworks washery at Newcastle, NSW. Several probes, each containing a radioisotope source and scintillation detector, were immersed directly into the coal slurry in the feed box upstream from the bank of flotation cells. For 140 samples W, ash and voidage varied in the ranges of 0 to 13 wt percent, 26 to 41 wt per cent and 0 to 4 vol. per cent, respectively. The r.m.s. difference in solids weight fraction, determined by probe measurements and conventional assay, was 0·52 wt per cent. Ash was determined with an r.m.s. difference of 2·0 wt percent in the coal. Better sampling techniques were used in the last half of the plant trial, and r.m.s. differences were 0.35 wt per cent solids and 1·5 wt per cent ash.

Jan 1, 1986