Managing closure risks by integrating acid and metalliferous drainage assessments with mine scheduling – real world applications

Pearce, Steven; Beavis, Fern; Winchester, Stuart; Thompson, Hugh B.

doi:10.36487/acg_rep/1208_66_pearce

Cited by 4 publications

(9 citation statements)

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“…To reliably implement selective waste placement within the TSF embankment based on the criteria in Table 3, it is necessary to develop and plan around a waste rock schedule. The use of the waste rock schedule to inform planning decisions has been demonstrated by the author in previous publications (Pearce et al 2012).…”

Section: Waste Rock Schedulementioning

confidence: 98%

Progressive rehabilitation — Martabe Gold Mine as a case study

Pearce¹,

Orr²,

Grohs³

et al. 2016

Proceedings of the International Conference on Mine Closure

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Progressive rehabilitation has been recognised by the mining industry as a key strategy for minimising mine closure costs and environmental risk, with the rehabilitation of potentially acid-forming waste rock being of particular interest due to the very large liabilities associated with sites where this risk has not been properly addressed. When properly implemented as an engineered solution, progressive rehabilitation of potentially acid-forming waste rock can provide an inherently more robust and lower risk rehabilitation strategy compared with the commonly-implemented alternative of an end-of-life waste dump covers. A case study is presented herein where progressive rehabilitation of potentially acid-forming waste rock has been successfully integrated with ongoing construction of the embankment of a tailings storage facility (TSF). The mine site in question, the Martabe Gold Mine in Indonesia, is thought to be unique in that construction of the TSF embankment at the site will require utilisation of almost all of the waste rock to be produced life-of-mine. The TSF embankment is therefore a fully integrated and engineered structure addressing both tailings and waste rock disposal requirements for the site. This approach offers a number of key benefits, including minimisation of both waste rock rehabilitation and tailings storage costs, and minimising the risk of long-term acid mine drainage. The progressive mine waste rehabilitation strategy adopted by G-Resources at the Martabe Gold Mine was designed taking into account the inherent properties of the waste rock materials, the run-of-mine waste rock schedule, and the engineering constraints required in order to construct a TSF embankment to exacting geotechnical standards. The strategy has required systematic implementation of outcomes reflective of industry leading practice, including:  Detailed waste characterisation studies.  Development of waste characterisation criteria.  Production of a life-of-mine waste schedule.  Selection of a waste sealing specification based on oxidation modelling.  Progressive implementation of selective waste placement and sealing.  Performance measurement to validate design and implementation. All key technical teams at the Martabe Gold Mine, including exploration, mine geology, mine planning, TSF construction and environment, have played an integral role in the implementation of this strategy, which can be described as an integrated waste management solution in which minimisation of mine closure risk is process that is carried out across the life of the mine.

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Section: Waste Rock Schedulementioning

confidence: 98%

Progressive rehabilitation — Martabe Gold Mine as a case study

Pearce¹,

Orr²,

Grohs³

et al. 2016

Proceedings of the International Conference on Mine Closure

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“…Typically, waste characterisation classification systems used as part of long-term mine planning based on industry best practice geochemistry methods (Garbarino et al 2018;Price 2009) are translated into mine planning and operations by the utilisation of block models (Pearce et al 2012). The majority of waste characterisation classification systems used as part of long-term mine planning utilise block models that define waste based on discrete grade-weighted cutoff grades (COGs).…”

Section: Study Rationalementioning

confidence: 99%

“…The majority of waste characterisation classification systems used as part of long-term mine planning utilise block models that define waste based on discrete grade-weighted cutoff grades (COGs). The COG is used to differentiate between waste and ore zones, and wastes of different geochemical or physical properties (Pearce et al 2012). The use of a COG approach reflects an underlying assumption that waste rock properties can be defined and treated in block models as having static and bulk characteristics in the same manner as ore. That is to say that, once mined, the waste material block has the same intrinsic property as defined from the averaged value obtained from the block model.…”

Section: Study Rationalementioning

confidence: 99%

“…To differentiate between ore and waste in mine plans and block models, a numeric COG is often utilised that is applied throughout the model domain (in the case of an open pit mine, the pit shell) by the use of model estimation parameters. In many cases, ore zones may be further split into low-grade and high-grade designations and waste zones may be split into a number of classes based on AMD risk (Pearce et al 2012). Figure 1 shows a generic sliding scale to highlight the simplistic relationship between COG and material designation.…”

Section: Cutoff Grade Assessmentmentioning

confidence: 99%

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Optimising waste management assessment using fragmentation analysis technology

Pearce¹,

Brookshaw²,

Mueller³

et al. 2019

Proceedings of the International Conference on Mine Closure

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The blasting and excavation of rock at mine sites generates a heterogeneous waste/ore product with a wide range of particle sizes. The study of the particle size profile generated as a result of mining is typically termed 'fragmentation analysis'. Although the potential for material geochemical properties to vary with grain size as a result of the mining process has long been known, the concept is not commonly subject to detailed analysis. As a result, it is typical at the mine planning stage for both waste and ore materials to be represented within mine block models and schedules as comprising monolithic blocks with respect to geochemical properties. However, significant changes to material properties that do occur as a result of fragmentation have the potential to significantly alter both the environmental risk profile and economics of the proposed mine plan. This paper discusses the application of modern fragmentation analysis techniques to the characterisation, management and long-term planning of waste rock. Detailed laboratory-based heterogeneity testing including geochemical, compositional and quantitative mineralogical analysis has been twinned with fragmentation data to assess properties of as-mined waste at two operational sites. The results presented herein highlight the importance of incorporating fragmentation analysis into the process of setting and validating cutoff grades for ore and waste, and in particular the management of low-grade ore. Opportunities are identified for recovery of resources that would otherwise have been discarded and removal of high-risk material from the waste rock stream. The results indicate that, at a high level, the use of a grade-weighted cutoff grade approach to waste modelling requires careful consideration before being relied upon to estimate environmental risks from mining. Further, the study indicates the benefits of the integration of a robust validation program into waste characterisation and grade control systems to both manage risk and optimise project economics.

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“…Many successful engineered cover designs have been implemented so the reliance on the cover system cannot be seen as a significant risk in all instances; however, the fact remains that the most common failure point on a WRD is at the surface. As a result, many cover systems have an inherently low factor of safety (FS) in design compared to alternatives such as truly engineered containment systems (Pearce et al 2012).…”

Section: Introductionmentioning

confidence: 99%

Waste material placement options during construction and closure risk reduction — quantifying the how, the why and the how much

Pearce¹,

Lehane²,

Pearce³

2016

Proceedings of the International Conference on Mine Closure

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Technical aspects of waste rock characterisation and assessment have been the focus of considerable research over the past decade, with many guidance documents being published on the subject internationally and within Australia. While these documents provide detailed information on how to characterise waste rock, there is not a great amount of guidance on how the placement of waste rock can be optimised to account for the results of the characterisation studies. In this respect it could be reasonably concluded that the science has progressed to a more advanced stage for waste classification in comparison to how to manage it. This has lead in many cases to site specific waste characterisations being followed up with generic waste management solutions such as widespread adoption of the ubiquitous potential acid forming cell as a management solution. The net result of this mismatch is that although acid and metalliferous drainage (AMD) assessments are undoubtedly being carried out to a higher level of detail than in the past, there is not a definitive correlation with site management practices and, therefore, effective closure risk reduction over this time. The net effect of this trend has been that site operators are being given better information on AMD risks, but not better solutions on how to manage these risks. That is to say site operators are being told why they should manage risks but not how to achieve this, and by how much risks can effectively be managed (if at all). Questions that site engineers and operators may ask about the relative benefit of one placement solution over another have for the most not been adequately addressed by research. Examples include assessment of the quantitative benefit of paddock dumping vs end tipping, determining the optimal tip head height for waste placement in a storage facility, and how sulphide grade control should be carried out. A detailed risk-based investigation of the influence of factors common to waste placement is presented herein and has been completed as part of a wider research initiative to investigate the technical aspects of developing a quantitative assessment tool. Applying a numerical modelling approach to assessment of the different waste material placement strategies allows for the graphical presentation and communication of the variation in risk through risk matrices and histograms.

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Managing closure risks by integrating acid and metalliferous drainage assessments with mine scheduling – real world applications

Cited by 4 publications

References 0 publications

Progressive rehabilitation — Martabe Gold Mine as a case study

Progressive rehabilitation — Martabe Gold Mine as a case study

Optimising waste management assessment using fragmentation analysis technology

Waste material placement options during construction and closure risk reduction — quantifying the how, the why and the how much

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