Dilution in Prism Frameworks
In underground stope design, dilution refers to the extraction of material that lies outside the economic ore zone. This material adds tonnage without adding value and can significantly reduce the overall profitability of a stope.
In the Prism framework, dilution is not an error – it is a design trade-off that may be accepted where increased recovery or improved stope geometry outweighs the cost of additional waste.
Prism optimisation evaluates predefined 3D stope shapes and may modify them to improve economic outcomes. Dilution can be introduced when the optimiser is allowed to extend stope geometry beyond the nominal ore envelope.
The Dilution screen (the version for Prism frameworks) controls how much non-ore material may be included in a prism stope during optimisation. These settings help balance ore recovery against dilution by limiting how far the optimiser can extend stope geometry beyond the ore envelope.
Common sources of dilution include:
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Crown side annealing, where the stope crown is adjusted upward (convex refinement).
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Trough overcut, which allows extraction above the planned stope back.
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Trough undercut, which allows extraction below the planned stope floor.
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Variable stope height, where stope height changes to capture additional material.
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Irregular ore geometry, where simple prism shapes cannot perfectly match contacts.
In a Prism framework, as with other frameworks, you can define the maximum waste percentage allowed.
Dilution & Recovery
Reducing dilution often means leaving some ore behind. Increasing recovery may require accepting additional waste. Prism optimisation balances these outcomes using the economic parameters supplied by the user.
For this reason:
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Low dilution does not automatically mean a better stope.
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Higher dilution may be acceptable where grades are strong or continuity is uncertain.
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Controlling dilution.
Several Prism settings directly influence dilution behaviour:
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Concave Distance limits inward crown adjustment, helping reduce crown dilution. See Define Crown Side Annealing.
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Convex Distance controls how far the crown may extend upward
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Trough overcut / undercut enable or restrict extraction beyond the stope envelope. See Define Prism Framework Troughs.
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Sub-level definition influences how closely stope shapes align vertically with ore zones. See Define Sub-Levels (Prism Framework).
Careful adjustment of these parameters allows users to explore the trade-off between recovery and dilution in a controlled way.
Note: Whilst the principle of dilution are the same for all frameworks, the Slice framework has its own Dilution screen. See Dilution in Slice Frameworks.
Summary
This part of the MSO workflow is used to:
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Define maximum waste and crown dilution settings for Prism frameworks.
