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By A Densten, C Gimber

Surface water management and drainage is a key aspect of mine rehabilitation and closure planning. In the authors’ experience, drainage related problems are amongst the most common forms of failure in mined landscapes. The appropriate design of surface water infrastructure is therefore a key focus of practitioners. While there is currently a trend towards distributed drainage networks and avoiding hard engineered structures, in many situations (especially for existing landforms) engineered drainage structures cannot be avoided. CITATION:Gimber, C and Densten, A, 2018. A risk-based approach to drainage design standard selection for mine rehabilitation and relinquishment, in Proceedings Life-of-Mine 2018, pp 116–118 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By T Baumgartl, R Akesseh, M Edraki, B Usher, M Shaygan

With the continuing demand for industrialisation and urbanisation, the rate of mining and processing lower grade ores will also increase, producing large quantities of waste. As extreme weather events associated with global climatic changes are to be expected, the risk from mine tailings management will also increase (Edraki et al., 2014). In sulfide rich tailings, weathering within the critical zone controls the fate and distribution of the contaminants such as copper, zinc, and lead in the environment (Hayes et al., 2014). Tailings evolve geochemically and physically with time as they age under the influence of complex interacting factors. Understanding of the complex interactions between these controlling factors is important for predicting and mitigating the potential risks associated with sulfide tailings such as generation of acid mine drainage (Lindsay et al., 2015). Wetting and drying initiates weathering processes, influencing the hydrological, geochemical and geomechanical properties of the tailings. In semi-arid climates where evaporation exceeds precipitation, salts may precipitate within the pore system as well as on the tailings surface. These salts become the temporal sink of heavy metals until the next episodic rainfall (Nordstrom, 2011, Grover et al., 2016). Therefore, using kinetic and static test to describe the trajectory of these material evolutions without considering the complex interactions could potentially lead to erroneous prediction. In order to understand these relations, the effect of drying and wetting cycles on the hydrological, geochemical and geomechanical properties of ageing tailings was studied to draw conclusions for advanced tailings site rehabilitation and mine closureCITATION:Akesseh, R, Shaygan, M, Usher, B, Edraki, M and Baumgartl, T, 2018. Wetting and drying cycles as a means to determine the effect and consequences of tailings ageing, in Proceedings Life-of-Mine 2018, pp 24–27 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By C Nucifora, M Landers, J Jones, G Maddocks, K Mandaran, A Forbes, W Wilson, S Newman

Glencore’s Mount Isa Mines Limited (MIM) operates the Mount Isa open cut and underground copper (Cu) and zinc-lead (Zn/Pb) mines near Mount Isa in Queensland, Australia. Tailings from processed Cu and Zn-Pb ore is contained in a 1,315 ha shallow (< 35 m deep) multi-cell valley fill tailings storage facility (TSF). Static geochemical testing conducted by MIM over the life of mine (LoM) verifies that the Cu, and Zn-Pb tailings has a wide range in sulfide content and diverse mineralogy with significant acid neutralising capacity (ANC) in some samples. The tailings are predominantly classified as potentially acid forming (PAF) using static analytical methods. Kinetic leach testing using free draining columns and humidity cell tests simulating tailings placed on the surface of the TSF suggest that the tailings samples are likely to remain non-acid forming (NAF) for 10 to 40 years under aerial exposure, and much longer than this under saturated conditions within the TSF. During this period of weathering, as ANC is depleted, the neutral pH drainage may contain elevated concentrations of some elements including sulfate, manganese and zinc. Only when the ANC is depleted would the tailings then begin to produce acid drainage. CITATION:Mandaran, K, Jones, J, Nucifora, C, Maddocks, G, Landers, M, Forbes, A, Wilson, W and Newman, S, 2018. Mount Isa Mines Rehabilitation Materials Sampling and Analysis program for closure planning, in Proceedings Life-of-Mine 2018, pp 138–140 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By A Remes, A Dennis, M Talikka, T Kotiranta, S Horn

A mine project combines vast amounts of information from various disciplines including but not limited to geology, mining, metallurgy, technology, environment and economics. In many cases, all relevant information is not fully shared between all disciplines. Thus, project performance (technical, economical and sustainability) may be evaluated on basis of insufficient information resulting in non-optimal decisions, project execution and risk management. Advances in computing power and simulation software enable various data sets to be incorporated in a single digital platform enabling more efficient and transparent data sharing. In addition, linked data sets and simulation can support assessment and optimization of the project as a whole rather than focusing on optimization of individual events. CITATION:Horn, S, Remes, A, Kotiranta, T, Talikka, M and Dennis, A, 2018. Evaluation of sustainability of copper production value chain from ore to metal using advanced simulation, in Proceedings Life-of-Mine 2018, pp 87–89 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By R Barritt

Remedial options for a waste rock dump (WRD) were considered as part of closure planning studies at an active mine in Western Australia. To minimise the impact of any seepage from the landform it was determined that placement cover system utilising the moisture ‘store-and-release’ concept was appropriate. The purpose of the cover system was to:•Reduce net infiltration of meteoric water to attenuate peak concentrations for contaminants of concern in natural receptors to levels that can be assimilated without adverse impact to the surrounding ecosystem; •Provide a growth medium for establishment of a sustainable vegetation canopy; and •Improve current quality of surface water runoff from waste storage areas.The project comprised several phases of work: materials characterisation, numerical soil-plant-atmosphere (SPA) modelling and finally cover system construction and monitoring equipment installation.CITATION:Barritt, R, 2018. Conclusions from long-term cover system performance monitoring – a case study, in Proceedings Life-of-Mine 2018, pp 101–105 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By L Dawson, S Carr-Cornish, N Boughen, K Moffat, S Masterson

The risk and consequences of community rejection and loss of a social licence to operate is well articulated (Moffat et al 2018), however, the means for systematically managing this risk are less established. At the local scale, a mining operation is said to have a social licence to operate (SLO) when it achieves ongoing acceptance or approval from the local community and other stakeholders who can affect its profitability (Graafland, 2002). Without this social acceptance, it is very difficult for a business to operate effectively or profitably. It is well understood that social (or community) acceptance of a mine and its associated operations is a reflection of the quality of the relationship a company has with their host community (Thomson & Boutilier, 2011; Lacey & Lamont, 2014; Parsons et al., 2014; Moffat et al., 2015). Community relations are an integral part of successful mining operations and where these interactions are effective, they tend to foster mutual understanding, trust and support between a company and the host community (Kemp et al., 2006; Holley & Mitcham, 2016). Research further demonstrates that where such interactions are perceived to be procedurally fair, the increased trust created in these company-community interactions tends to lead to higher levels of acceptance of mining operations (Moffat & Zhang, 2014; Lacey et al., 2017).The challenge, however, is how to listen systematically to communities that mining and associated operations; communities that are often located across vast geographic areas and with diverse demographics. To date, traditional methods deployed to both guide and evaluate community engagement and social investment activities have been challenged to reflect the nature of the phenomenon they seek to observe, the voice of community. For example, detailed baseline surveys of community attitudes every three years by companies, as is the requirement within the policy frameworks of most large miners, provide rich insights but do not reflect the dynamic, temporal nature of the relationships that underpins their SLO. These processes typically are largely opaque to communities and distinct from the company’s engagement activities. The CSIRO Local Voices project was developed with Rio Tinto to go some way towards meeting this challenge of how to listen to the voice of community systematically. CITATION:Moffat, K, Dawson, L, Carr-Cornish, S, Boughen, N and Masterson, S, 2018. Listening to Local Voices – a systematic approach for understanding what a social licence to operate means for Rio Tinto in the Pilbara, in Proceedings Life-of-Mine 2018, pp 8–11 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By D Bradshaw, E Forbes, M Edraki, M Tayebi-Khorami, E Manlapig

There is an increasing trend in the extraction and development of copper resources from complex deposits. These deposits pose mineral processing challenges, as they often contain low grade disseminated copper ore with high levels of impurities particularly arsenic. Although arsenic is a naturally occurring element, the concentrations of arsenic can be magnified by mining and mineral processing activities. Therefore, while arsenic has no significant market value, its presence in the ore deposit will have production, environmental and human health implications. The mining industry’s approach to life-of-mine planning has improved significantly in recent decades and managing arsenic is not an exception.CITATION:Tayebi-Khorami, M, Edraki, M, Manlapig, E, Forbes, E and Bradshaw, D, 2018. Arsenic pathways in copper mining – sustainability issues and potential solutions, in Proceedings Life-of-Mine 2018, pp 60–63 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By J J. Jiang, B G. Bow

Atlas Iron Limited’s (Atlas) Abydos Mine has developed its Scarborough open pit proximal to a rock shelter that has been assessed as a significant Aboriginal heritage site by the Traditional Owners of the land. The rock shelter, named Yurlu Kankala, is located to the north-west of the pit with a stand-off distance of 35 m. Within Atlas’ Native Title Agreement with the Traditional Owners, and approvals from the Western Australian Department of Aboriginal Affairs, commitments have been made to conduct mining in a way that avoids or at least minimises disturbance and damage to the rock shelter. This complies with the Aboriginal Heritage Act 1972 (WA) and respects the heritage and culture of the Traditional Owners.CITATION:Bow, B G and Jiang, J J, 2018. Iron ore mining in proximity to a significant Aboriginal heritage rock shelter, Pilbara Region, Western Australia, in Proceedings Life-of-Mine 2018, pp 2–5 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By K Cochrane

Time and time again history shows us that mine closures are sustainability failures. Mine operators do not know how to turn the mine closure into an asset and communities around the mine do not know how to plan or what to implement to be sustainable when the mine needs to close. If we want to achieve sustainability when we close a mine, we generally need to consider what economic activity we will have to create leading up to the mine closure to ensure that the communities remaining in the area are not worse off after mining than before. There is not one silver bullet solution to mine closure, as all mines are affected by different environmental and socio-economic conditions. That is one of the reasons why mine closure is so difficult.Effective stakeholder engagement is the nucleus around which sustainability is built. Achieving sustainability as part of mine closure means not only a self-sufficient community, but also could lead to transformation of that asset.A key issue is that neighbouring communities become completely reliant on the mine. The mine has influenced the economic, environmental and social aspects of the community and with no alternative economic sources. The community and municipality will struggle with capacity to maintain infrastructure, services and jobs. This not only impacts the mine workers and their families but also other businesses and people in the town that make a living by servicing the needs of the workers and their families. Social problems associated with a mining operations and closures need to be considered. The misuse of alcohol, domestic violence, breakdown in law and order, economic and health issues all have a severe influence. Families often need to relocate from the mining town to find work. This further perpetuates the impact of the mine closure to the economic viability of the town. CITATION:Cochrane, K, 2018. Is your mine closure a sustainability failure? Transform your asset and create a self supporting neighbouring community. It’s as easy as ABCD!, in Proceedings Life-of-Mine 2018, pp 38–42 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By A Querzoli, B Williams

In late 2014 the Flinders Power Management Team was executing business improvement plans to ensure continued electricity generation until 2028 and beyond. Six months later, in June 2015, the Board announced the closure of the Flinders Power South Australian business, including the Leigh Creek Coal Mine, the Northern and Playford Power Stations located at Port Augusta and the 250km railway line. The announcement was preceded by a brief period of internal planning. A date was soon set for ceasing coal mining operations, being November 2015. The mine is unique in many ways. Located approximately 550km north of Adelaide the site has over 100 years of history and was formerly operated by the South Australian Government. Privatisation in 2000 saw the mine continue operation under Perpetual Leases from the South Australian Government. The leases included exemptions from multiple sections of the Mining Act 1971, obliging primary regulation under the Mines and Works Inspection Act 1920. The coal, being a low rank sub-bituminous brown coal, is prone to self-heating and spontaneous combustion. The mine and company town Leigh Creek were the economic and cultural heartbeat of the community. Facilities at the mine were shared by the community and vice versa. While many mines across Australia and the world enter periods of care and maintenance, few have been actively closed to the point of relinquishment (Bennett and Lacy, 2016). A swift decision to close, followed by a short mining operations shutdown period, presented significant technical and regulatory challenges for both the mine operator and for Regulators. The subsequent joint risk mapping process employed by Flinders Power and South Australian Mining Regulators was a unique real-world example of collaborative mine closure planning and execution. Lessons learnt are valuable for all mines, production facilities and for Regulators, even for those who may wrongly assume that closure is many years away. CITATION:Williams, B and Querzoli, A, 2018. Risk management for minesite closure planning and execution – start now! Lessons from the closure of the Leigh Creek Coalfield, South Australia, in Proceedings Life-of-Mine 2018, pp 68–72 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By P J. Bangerter, G D. Corder

With the societal desire and drive towards low carbon energy sources, there is a growing awareness of the important role that minerals and metals will play with renewable energy technologies. Copper is an essential metal for technologies that generate energy from renewable sources, in particular for wind and solar photovoltaic energy systems. A recent report (Arrobas et al., 2017) estimated that the median increase in copper demand through to 2050 for wind technologies and for solar photovoltaics would need to be 250% and 300% respectively to meet the goal of a 2°C global temperature increase scenario compared with a 6°C global increase, which is largely an extension of current trends (IEA, 2018). The aim of this extended abstract is to demonstrate with the necessary increase in copper production for renewable energy technologies that sound sustainability performance across the global copper value chain is to the benefit of government, society and industry.CITATION:Corder, G D and Bangerter, P J, 2018. Balancing the benefits and impacts of future copper demand – climate change and arsenic, in Proceedings Life-of-Mine 2018, pp 17–19 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By G R. Hancock, M J. Saynor, J B. C Lowry, K G. Evans, M Narayan

Tools such as landform evolution models (LEMs) provide a means of predicting how a landform may evolve over extended periods of time. Here, we utilise the CAESAR-Lisflood LEM to assess a proposed rehabilitated landform of the Ranger Uranium Mine in the Northern Territory of Australia (Figure 1). The environmental requirements for the closure of the mine state that the final landform must be able to physically isolate tailings material from the environment for a period of at least 10,000 years (Australian Government, 1999). However, uncertainty exists as to the reliability of model predictions representing thousands of years.In this study, we use model predictions from an undisturbed pre-mine landform to calibrate the parameters used in model simulations of a post-mining rehabilitated landform over a simulated period of 1,000 years. Specifically, we vary environmental conditions such as rainfall, presence/absence of vegetation and surface particle size characteristics in a series of model simulations to determine their impact on the respective landforms, to revise model input parameters as required. A simulated period of 1,000 years was used as it represents a period in which long term landform evolution patterns and trends may be established and identified. CITATION:Lowry, J B C, Narayan, M, Evans, K G, Saynor, M J and Hancock, G R, 2018. Using an undisturbed landform to calibrate long-term predictions of the evolution of a rehabilitated landform, in Proceedings Life-of-Mine 2018, pp 133–137 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By J L. Merritt

Contour banks and waterways are standard soil conservation measures to assist farmers reduce the impact of gully erosion on sloping cropping land by reducing the slope length to the interval between the banks. The Universal Soil Loss Equation (USLE) developed by the USA Department of Agriculture Soil Conservation Service in 1930s predicts the long-term average annual soil loss (A).The equation is the product of the rainfall erosivity factor (R), the soil erodibility factor (K), the topographic factors of slope length and angle (L and S) and the cropping management factors (C and P). Contour banks reduce the slope length (L) only.Contour banks are a constructed earth embankment, incorporating a channel on the upslope side, typically traversing a slope on or close to the contour to control and/or prevent the erosion of that slope. The banks are also referred to as graded banks, terraces, or bunds (DSITI 2015). Contour banks are either broad based or narrow based. Broad based banks allow the passage of the machinery over the banks whilst narrow based bank batters are too steep preventing the passage of machinery. Waterways are a stable, longitudinally sloping water disposal area of sufficient capacity used to discharge surplus runoff from the contour bank and to allow it to flow to a lower level without causing erosion (DSITI 2015).The mining industry must decide what the role for contour banks and waterways is in each operation’s rehabilitation and closure plan.CITATION:Merritt, J L, 2018. Contour banks in spoil rehabilitation – a matter of timing, in Proceedings Life-of-Mine 2018, pp 147–149 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By E Thomas, L McCallum, G Dale, J Bennett, K Reardon-Smith, S Raine

Sustainable closure of coal mines in Australia to a safe, stable, non-polluting condition remains one of the industry’s biggest environmental and social challenges. A significant proportion of mines in the Bowen Basin of Queensland have dispersive spoil. Based on an estimated area of 20,000ha and a rehabilitation cost of AUD$100,000 to AUD$150,000/ha, the instantaneous rehabilitation liability for the Bowen Basin alone is estimated at AUD$2 to $3 billion.Dispersive spoils present problems in post-mining rehabilitated landforms due to increased potential for surface and tunnel erosion, compromising the ability to achieve fundamental mine closure objectives of a safe, stable, non-polluting and self-sustaining post-mining landform (Minserve, 2004). Dispersion results in clay particles being mobilised and transported in water, even at low flow velocities (So et al., 1998; Minserve, 2004), and blocking of soil pores, resulting in surface sealing, crusting and reduced permeability (DNR, 1997; Vacher et al., 2004) which, in turn, further increases runoff (Dang et al., 2018).CITATION:Dale, G, Reardon-Smith, K, Thomas, E, Bennett, J, McCallum, L and Raine, S, 2018. A process-based approach to mine rehabilitation decision making using Bayesian modelling and risk-based principles for dispersive spoil rehabilitation, in Proceedings Life-of-Mine 2018, pp 106–109 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By D C. Verdon-Kidd, G R. Hancock, M J. Saynor, J B. C Lowry, T J. Coulthard

Designing post-mining landscapes requires quantifying the short and long-term risks. In recent years, computer based landscape evolution models (LEMs) have been used to provide insight into both erosion rates and processes (i.e. sheetwash, rill, gully erosion). An important requirement of these models is high quality model input parameter data, which includes both the surface material (i.e. soil and waste rock) and climate information. However, in many cases such data is limited and in the case of climate information, the data is often short and incomplete. Here we develop climate scenarios and examine different surface material properties using a case study at the ERA Ranger mine located in the Northern Territory, Australia Firstly we develop scenarios that represent the range of future climates that may be experienced at the site. Secondly we develop a series of plausible particle size distributions based on a large sampling exercise of the waste rock material. We then test the sensitivity of different rainfall sequences and surface materials on sediment output using a well-tested landscape evolution and sediment transport model (Hancock et al., 2017). CITATION:Hancock, G R, Verdon-Kidd, D C, Coulthard, T J, Lowry, J B C and Saynor, M J, 2018. Quantifying the effect of climate and surface materials on post-mining landscape erosion – a risk approach using landscape evolution models, in Proceedings Life-of-Mine 2018, pp 122–124 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By M J. Saynor, J B. C Lowry

The Ranger Uranium Mine is located in the wet-dry monsoonal tropics approximately 250 km east of Darwin in the Northern Territory of Australia (Figure 1). Mining of open-cut ore bodies commenced in 1980 (Pit 1) and ceased in 2012 (Pit 3) and milling and production are scheduled to cease by 2021. At the conclusion of mining and milling operations, mine tailings will be returned to the mined out pits 1 and 3, which must then be physically isolated from the environment for at least 10,000 years (Australian Government 1999). The final landform also needs to have sufficient mitigation measures in place to ensure that areas downstream are not impacted by erosion products from the mine site. The proposed post-mining rehabilitated landform will cover approximately 847 hectares (8.5 km2) which represents an area that has the potential to supply sediment to catchments and streams downstream. One method of reducing runoff and associated sediment is the construction of rip lines along the contour to slow down the runoff velocity and to also trap fine sediment and nutrients in the depressions to assist vegetation growth.CITATION:Saynor, M J and Lowry, J B C, 2018. The impact of rip lines on erosion at the Ranger Mine Site, in Proceedings Life-of-Mine 2018, pp 150–154 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By H J. J Boshoff

Pit lakes, as a final void after completing open cut mining, are in most cases unavoidable. Initial mine designs and approvals require consideration and assessment of closure objectives, legislation and stakeholder acceptance to ensure suitable understanding of the closure liability. Mining companies undertake studies and engineering during the planning, operational and closure stages of mining to identify closure options for the final voids, which would be sustainable. Without adequate planning prior to and during the life of the mine, options during the closure stage become limited resulting in costly closure works or long-term liabilities. Engineering consultants provide a specialist service in the assessment of long-term pit lake water levels and characteristics. Ongoing advances in mining methodology and technology, coupled with improved data collection and data management aid in a better understanding of the complexities in estimating long-term pit lake water levels and characteristics. Closure objectives developed during the planning stage sets the requirements for long-term pit lake water levels, which could require maintaining a water level and pit water or discharge water quality. A variety of approaches could be used to assess these closure scenarios each requiring specific data and methodologies. Typically, limited data is available during the planning stage, which results in assumptions based on past experience and relevant case studies. Closure assessments are revisited during the life of mine and leading up to the closure stage, during which additional site-specific data is available improving the accuracy of the assessments.CITATION:Boshoff, H J J, 2018. Assessment of approaches, data requirements and methodologies for estimating long-term pit lake water levels, in Proceedings Life-of-Mine 2018, pp 28–31 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 25, 2018

By N Jamson, T K. Rohde

The Mine is an underground zinc (Zn), lead (Pb) and silver (Ag) operation in central New South Wales (NSW). Broadly speaking the Mine has two domains that require rehabilitation, the mine industrial area (MIA) and the tailings storage facility (TSF). The MIA has been used for the handling and processing of ore and contains elevated sulfate, sulfide and metals (Pb, Zn). The TSF receives the by-products of processing, that is, potentially acid forming (PAF) tailings which also contain elevate sulfate, sulfide and metals. Typically, the rehabilitation of a TSF involves two controls. Firstly, controlling the potential for PAF tailings to form acid rock drainage (ARD) by limiting interaction with oxygen. Secondly, once the tailings are unsaturated, limiting interaction with water (usually as rainfall) to reduce the potential for ARD to be transported to the receiving environment. These two controls are often employed in the form of a cover.In semi-arid environments there are many Australian examples of covers that have been built to limit interactions of mine by-products with oxygen and water. Typically, the covers contain one or more layers and are built from soil and rock which may include run-of-mine rock. The Mine however has limited supplies of stockpiled soil; and run-of-mine rock is not generated in large volumes because it is used as backfill underground. A cover design strategy was developed to cater for these limiting factors. The strategy identified soil, ore and rock accretion (the accretion) below the MIA could be a potential source of borrow material for the cover. The purpose of this paper is to describe the cover design process, the method and results of large (2 m tall) column trials that were used as a cost-effective way to trial three cover options and finally, the paper describes the water balance that was developed from the column trial results and subsequent modelling using SVFlux.CITATION:Rohde, T K and Jamson, N, 2018. Making use of potentially contaminating mine waste in cover design, in Proceedings Mine Waste and Tailings Stewardship Conference 2018, pp 285–298 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 23, 2018

By T Rohde, P Defferrard

In 2010 a store and release cover (the cover) was constructed on the south waste rock dump (SWRD) at Century mine. This also included aerial seeding of province native trees and shrub seeds. The purpose of the cover is to reduce percolation into the potentially acid-forming (PAF) waste rock by maintaining a compacted reduced permeability layer (RPL) at near-saturated conditions. This is achieved by overlaying the RPL with a 1.5 to 2 m thickness of soil-mulch. The soil-mulch has a hummocky final surface that captures rainfall, so it does not runoff, allowing it in part to infiltrate, with excess water removed by evaporation and transpiration. The RPL is the trafficked surface of the SWRD.The unsaturated behaviour of the cover is being monitored by instrumentation including volumetric water content and matric suction sensors and a weather station capable of estimating evapotranspiration. The instrumentation allows for direct measurement of infiltration into the cover, storage of rainfall, percolation through the base of the cover and in situ soil water characteristic curves (SWCC).The key functions used to describe the unsaturated behaviour of the cover materials is the SWCC and the unsaturated hydraulic conductivity function. The SWCC is a plot of soil water versus soil suction. It provides the loci of moisture states of a soil from the saturated to the dry state.The paper presents the results of five years of monitoring. It shows that total infiltration into the top of the SWRD was about 1.6 – 3.7% of cumulative rainfall over five years, with most of the infiltration going into storage within the cover. Runoff from the top of the dump is not allowed therefore, the remaining 95% of the total rainfall was lost to evaporation or as lateral flow when infiltration reached the RPL. The paper presents some simple analyses of the wetting by rainfall infiltration of the cover, leading to breakthrough at the base. Field data are used to support the analyses.Presentation of the SWRD water balance is also included in the paper using SVFLUX™GE which is a finite element model that simulates water transport through a saturated or unsaturated medium.CITATION:Defferrard, P and Rohde, T, 2018. Five years of cover performance monitoring and modelling for a store and release cover at Century Mine, in Proceedings Mine Waste and Tailings Stewardship Conference 2018, pp 179–189 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 23, 2018

By L P. Trout, D G. Reid

PanAust Limited (PanAust) has successfully constructed and commissioned two mining operations in Lao PDR over the past decade and undertaken major studies for three new mine developments. The management of potentially acid generating mine waste and tailings in close proximity of local communities sensitive to water discharge quality have been recurring themes that have confronted PanAust’s project study, development and operational teams. Further compounding challenges, such as the effects of intense annual tropical monsoonal conditions, staging of embankment raises and regular lifting of spillway structures, integrating mine waste and tailings management into production plans and ensuring the long term stability of structures, have been addressed by implementing leading practice management solutions.A recognition of the criticality of managing the substantial business risks associated with these crucial activities led to the early establishment of a governance structure to ensure that the highest standards are embraced for planning and execution. Importantly, these are guided and monitored by a panel of highly experienced and qualified international specialists reporting directly to PanAust’s Managing Director – the Tailings Independent Review Panel. The stewardship process has been effective in identifying potential shortcomings in management systems and has led to enhanced executive commitment to risk informed designs, assurance and overall process rigour.CITATION:Trout, L P and Reid, D G, 2018. PanAust Limited’s approach to mine waste and tailings stewardship, in Proceedings Mine Waste and Tailings Stewardship Conference 2018, pp 135–155 (The Australasian Institute of Mining and Metallurgy: Melbourne).

Jul 23, 2018