Topic
Integrated Mine Planning to Minimise AMD and Improve Mine Closure Outcomes
Presenters
Dr. Greg Maddocks
Principal Hydrogeochemist, RGS Environmental Consultants Pty Ltd.
greg@rgsenv.com
Ainsley Ferrier
Technical Product Manager Enviro Tools, Deswik Mining Consultants (Australia) Pty Ltd.
Matt Landers
Principal Geochemist, RGS Environmental Consultants Pty Ltd.
André Stengl
Principal Mining Consultant, Deswik Mining Consultants (Australia)
Nick Anderson
Product Manager, Deswik Mining Consultants (Australia)
Amanda Forbes
Senior Mining Consultant, Deswik Mining Consultants (Australia)
Objectives
The objectives of the short course are to familiarize participants with current leading developments and practices in integrated mine planning and designing for closure that aim in part reduce the risk of AMD and improve mine closure outcomes for rehabilitation.
Description
The purpose of the course is to provide participants with a clear understanding of how the mining industry now has the tools to couple geochemical, physical, hydraulic and soil fertility data with a GBM and integrate these within mine planning reduce the long-term risk of AMD and improve both operational and mine closure outcomes.
The course will be presented in two sessions by RGS/Deswik/Geosystems personnel who have introduced and applied these tools at mine sites mining various commodities around the world.
The course provides a strategic analysis of what integrated mine planning and designing for closure is at a corporate level, and what this means to the people working on smaller discrete technical packages of work that occur multiple time horizons.
The course will describe mine material characterisation techniques and detail how the geochemical, physical, hydraulic and erosion properties of mine materials are acquired, interpreted and used to develop criteria for incorporation into geoenvironmental block models (GBM).
Four case studies will be presented to demonstrate how integrated planning and designing for closure can be applied to provide better technical, social, financial and closure outcomes.
Integrated mine planning and designing for closure – strategic analysis – focal points on waste rock management
1.1 (RGS: Greg Maddocks): Industry standards and guidelines (30 minutes)
- What is integrated mine closure planning and designing for closure, what is in the toolkit, and is good practice guidance (INAP 2019, ICMM 2019) being implemented to minimise AMD production?
- Are beneficial outcomes being achieved for mine waste management from integrated mine closure planning and designing for closure, how do poor design outcomes impact water (MCA, 2014, ICMM, 2021), and are risks to water considered significant to the sector (EY, 2021).
- If successful outcomes are not being achieved where are the flaws in these processes and what can we do to improve environmental and social governance?
1.2 (RGS: Matt Landers): Mine material properties (30 Minutes) – what materials do you have and how can they be utilised for rehabilitation and closure?
- Deleterious (e.g. PAF) and beneficial (e.g. NAF, regolith, top soil) mine materials.
- NAF materials include unconsolidated topsoil and subsoil through to competent rock all of which may have specific purpose for closure and rehabilitation.
- Soil fertility, geochemical and physicochemical attributes for each mine material are characterised according to specific tests discussed in this presentation.
- Case study – Mount Isa Mines Glencore Copper
1.3 (Deswik: Nick Anderson): A technical toolkit – geoenvironmental block models (30 minutes)
- Understanding the characterisation of ore and waste in a mine during production is essential for Ore Control process to make the most profitable decisions at dig time. Material characterization for waste and landform construction is critical in building landforms that consider the optimal geochemical, soil fertility and physical characteristics.
- Building a geo-environmental block model that characterizes ore, low grade ore and waste that have soil fertility, geochemical and physical attributes appended to each block in the block model. Dig blocks are then designed that incorporate the desired characterization and account for practical mining constraints, such as mining direction and minimum mining widths. Characterization dig blocks are then used to determine where the material will be moved to.
- The data can be used to verify a WRD is built to design Ernest Henry Mine case study_Evolution Mining.
1.4 (Deswik: Ainsley Ferrier): A social engagement toolkit – landform haulage schedules and the social license (30 minutes)
- As part of the 2017 Environmental Impact Statement, Glencore’s McArthur River Mine (MRM) constructed an integrated LoA model depicting the mining sequence and all subsequent closure activities.
- The model included quarry and borrow pit mining to achieve closure designs, the complex WRSF sequencing, in-pit dumping, stockpile sizing and reclamation as well as the TSF construction during operations, reprocessing of tailings and the final placement of tailings in-pit. The simulation was released to the public to convey the projected mining and closure sequence as well as the final landform surface. McArthur River Mine case study_Glencore Zinc
1.5 (Deswik: Andre Stengl): A financial toolkit – the financial upside of mine waste) (30 minutes)
- Pulling a holistic mine and closure plan together should be supported with a detailed economic model using variable costs rather than fixed unit costs. As a mine moves toward the closure phase, real costs rather than NPV should be used to evaluate the impact of final mining and dumping without discounting closure costs.
- Understanding waste rock types as a commodity and placing a value on their suitability for mine planning can drive strategy and remove risk by improving operational performance as well as satisfying closure requirements. Placing a value on waste means identifying its potential application(s), then prioritizing or constraining it during scheduling.
- Building an inclusive plan challenges assumptions, breaks down planning silos, engages co-reliant departments and often reveals hidden opportunities.
Case Study – Pan-American Silver
- The study was designed to consider variable mining & closure costs to confirm high-level assumptions from the co-reliant strategy:
- Construction of new leach pad facility on steep terrain to process additional ore.
- Mined open pit waste to be used to build a large rock structure (base pad).
- Reshaping of base bad before leach ore stacking (geotechnical constraint).
- The study concluded that the additional haulage cost to build the base pad cancelled out the revenue from the marginal ore that would be processed at the end of mine life. The optimisation of ore feed processing revealed that the leach pad crusher would not send marginal ore to the base pad based on the result being cost neutral (base pad was built for no reason!).
- A secondary finding was that the reduced waste inventory in the pit (result of upgrading waste to ore) slowed the rate of waste delivery to build the base pad (dynamic landform haulage modeling) and this resulted in delays for commissioning the base pad and therefore a risk to continual processing.
- Finally the geotechnical constraint for reshaping the base pad early brought forward closure costs that contributed to a higher operating cost and therefore a higher cut-off grade than originally assumed.
1.6 (Deswik: Amanda Forbes): A closure planning toolkit – optimising rehabilitation for MIM TSF) (30 minutes)
- The integrated planning and designing for closure allowed MIM to develop a comprehensive rehabilitation plan for the TSF and provided assurance that the proposed cover system design would be effective when constructed using the identified borrow materials. Soil fertility, geochemical and physical analysis work conducted by RGS Environmental (RGS) was integrated into an overburden model which was used in an integrated landform and haulage model.
- The modelling immediately identified a topsoil deficit and the need to potentially dilute the available topsoil with underlying subsoil.
- The model also showed that previous assumptions significantly underestimated the equipment requirements and the time required to construct the TSF cover. The equipment requirements were also highly sensitive to both the dumping strategy and the selected borrow pit locations due to the spatial extents of the TSF.
- Unsaturated zone modelling on the final landform surface showed that cover will shed runoff when constructed using the available borrow material.
- By confirming the material properties of the available soil regolith and rock units and running schedules of the placement work, MIM have ensured that their solution has longevity and will provide a cost effective and environmentally effective outcome. Mount Isa Mines case study_Glencore Copper
1.7 (RGS: Matt Landers): Mine water modelling (30 Minutes)
- Hydrogeochemical modelling to assess the performance of the final landforms.
- Case studies using reactive transport modelling and development of pit lake water balance/ water quality models (Hazelwood Coal Mine).
1.8 (RGS: Greg Maddocks): Integrated planning toolkit – bringing it all together (30 minutes)
- At the domain level, integrated planning and designing for closure to the authors means:
- keeping the ICMM big picture outcomes in the back of mind so we do not get caught in a technical, environmental, financial or social (bubble)
- communicating these broader outcomes to technically focused staff in technical silos
- working across the technical silos to find the people who have information we need
- talking to those people and explaining what we are trying to achieve
- asking the right kind of questions to find data and information we need
- sharing what we have found, as they would probably find what we have uncovered from other silos to be useful to them
- presenting and progressively updating what we have done to the group so the bigger integrated mine closure planning picture is always in their collective minds and keeps them moving in the same direction down the funnel the successful (ICMM) outcome that society is seeking.
Live Questions and Answers (1.5 hour)