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Closure plan: a tool for mine management and cost savings
A.M. Pulino Golder Associates, BrazilE. Chapadeiro Golder Associates, BrazilA.A.S. Pena Golder Associates, BrazilA.P.M. Saliba Golder Associates, Brazil
Summary
• Introduction
• Methodology
– Mine Closure Plan
– Identification of Critical Closure Costs
– Assessment of alternative closure approaches
• Results - Case Study
– Mine Closure Plan and Critical Costs
– Alternative closure approaches and potential savings
• Conclusion
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Introduction
• Mining should be managed using a life cycle approach the way you conceive and operate the mine has huge impact on closure (costs)!
• Mining is a dynamic activity Mine closure planning must be a dynamic process.
• Knowing closure costs in advance is crucial.
• Mine Closure Plans can be a powerful tool for mine planning and management.
• Decisions made in the early stages of mine planning can significantly impact closure costs.
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Introduction
• Objective: to demonstrate how the mine closure plan can be used as a tool for mine management.
• Focus of presentation:
– Methodology for identifying critical closure costs Planning and financing closure.
• Technical aspects of closure solutions proposed on the case study are not the focus.
• Social aspects of mine closure are not the focus also.
• Case study presented to exemplify the methodology.
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Methodology
Conceptual mine closure
plan
Identification of critical
closure costs
Assessment of alternative
closure approaches
Simple but powerful
Dynamic process
Focus on main issues
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Methodology• Mine Closure Plan Guidelines:
– Must be prepared as early as possible;
– Updated throughout the mine life cycle;
– Level of information increase uncertainties and risks decrease
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Methodology
• Conceptual mine closure plan:
– Define life of mine: ROM, waste rock and tailings production schedule;
– Define domains (ex: open pit, waste pile, tailings dam, process plant);
– Describe future condition of each domain (physical and chemical characterization) propose closure concept estimate cost (quantities x unit costs) risk assessment;
– Put all domains together in the closure plan prepare physical-financial closure schedule;
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Methodology
• Identification of critical closure costs:
– Find out what are the costs that contribute the most to the overall closure costs.
– Critical closure costs can be of two kinds:
• Domains ; and
• Activities.
– Critical Domains: direct comparison.
– Critical Activities: add up costs of similar activities for all domains and compare.
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Methodology
• Assessment of alternative closure approaches:
– Why is it a critical cost (quantity or unit costs)?
– Quantity:• Large structures
• Usually hard to reduce
– Unit costs: • The more complex the closure concept, the higher costs
– Is it possible to reduce these costs? How?• Alternative closure approaches
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Case Study - Mine Description
• Open pit mine with both oxide and sulphide ore types.
• Process includes crushing, milling, flotation and acid leaching.
• Mine domains: open pit, waste rock pile (sulphide material), two dams for the flotation tailings and ponds for the leaching tailings.
• Confidentiality:
– Site name, owner and values will not be disclosed.
– Closure costs and potential savings will be disclosed as percentages only.
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Case Study - Closure PlanDomain Closure Measures Closure Cost
GeneralAdditional studies, decommissioning management, socioeconomicactions, water quality monitoring for the whole site.
8%
Open PitPump water to accelerate lake formation, cover exposed sulphideareas, treat pit lake water until it reaches a stable geochemicalcondition.
4%
Waste PileCover with soil layer (mine overburden), implement surfacedrainage system and revegetate.
14%
Process Plant Complete demolition and removal. Revegetate the whole area. 3%
Flotation Tailings Dam AImplement multilayer cover over the whole dam reservoir:trafficability layer (soil), capillary break (crushed rock), store andrelease (soil). Revegetate the whole area.
28%
Flotation Tailings Dam B
Keep a lake on the upstream part of the dam reservoir; implementmultilayer cover over exposed tailings beaches: trafficability layer(soil), capillary break (crushed rock), store and release (soil).Revegetate the covered area.
32%
Leaching Tailings PondsImplement multilayer cover over the whole area: trafficability layer(soil), capillary break (crushed rock), HDPE membrane, store andrelease (soil). Revegetate the whole area.
11%
TOTAL 100%
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Case Study - Critical Costs
• Soil covers will use all mine overburden material mass balance to ensure there will be enough cover material
• Critical Domains: – Waste Pile (14%), Tailings Dam A (28%) and B (32%) 74% of total
closure costs.
• Critical activities:– Excavation of cover material: 14% of total closure costs.
– Transport of cover material: 29% of total closure costs.
– Crushed rock for covers (capillary breaks): 15% of total closure costs.
– Together those activities represent 58% of total closure costs.
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Case Study - Alternatives
• Waste Pile:– Cover: 80% of domain cost
– Quantity issue: Large volumes of cover material
– Recommendation: optimize cover design (modest savings)
• Alternative: – Reduce unit costs by using mine equipment
– Cost of third party equipment is 5 times higher than mine costs
– Recommendation use a progressive rehabilitation approach to reclaim the pile with large mine equipment
– Potential savings: 57% of domain closure costs
– Issues: change the pile design (allow traffic of large equipment) + integrate pile reclamation with mine planning
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Case Study - Alternatives
• Flotation tailings dam A:– Receives oxide + sulphide tailings complex cover to avoid ARD
– Cover: 91% of domain cost
– Quantity issue: Large volumes of cover material
– Unit Cost issue: crushed rock (capillary break) cost
• Alternative: – Make a “cover” with oxide tailings during operation (enough material
to dispose a 4 m thick oxide tailing top layer) minimize ARD risk
– Change to a simple soil cover (reduce unit costs)
– Potential savings: 60% of domain closure costs
– Issue: change mine operation and production schedule
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Case Study - Alternatives
• Flotation tailings dam B:– Will receive sulphide tailings only complex cover to avoid ARD
– Cover: 90% of domain cost
– Quantity issue: Large volumes of cover material
– Unit Cost issue: crushed rock (capillary break) cost
• Alternative: – Improve flotation recovery desulphurization minimize ARD risk
– Desulphurization plat is currently under feasibility study focus on process recovery, not closure
– Potential savings: 64% of domain closure costs
– Dam closure cost great impact on desulphurization plant feasibility
– Design for closure approach
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Case Study - Alternatives
• Soil Covers:– Critical costs activities are all related to cover construction.
– Most part of this material is overburden that will come from the mine
– Alternative: improve overburden management allow direct hauling from the mine to the other areas
– Issue: timing overburden is mined before waste rock need to identify areas that can be covered throughout the mine life
– Requires integration between mine planning and closure planning.
• Crushed Rock (capillary break layers):– Segregate oxide and sulphide waste rock
– Reduce unit costs of crushed rock in 80%
– Requires waste rock management changes mine operation
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Case Study - Alternatives
DomainClosure Cost –
Base Case
Alternative Closure
Approach
Potential Saving Closure Cost –Alternative
Scenario
General 8% None - 8%
Open Pit 4% None - 4%
Waste Rock Pile 14%Progressive
rehabilitation57% 6%
Process Plant 3% None - 3%
Dam A 28%Oxide Tailing
Cover60% 11%
Dam B 32% Desulphurization 64% 12%
Leaching Tailings Ponds
11% None - 11%
TOTAL 100% 55%
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Conclusion
• Methodology for assessing critical closure costs was shown to be simple but very useful allowed focusing on the key issues in order to improve the economic effectiveness of closure solutions.
• Alternative closure approaches identified directions to further studies rather than final closure solutions additional engineering design will be necessary to assess technical and economical feasibility.
• Alternative closure solutions proposed will require changes on mine design, planning and operation, but might result in a great reduction of closure costs.
• Need to integrate mine closure on mine planning mine closure plan can be an important tool for mine management and cost savings.
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