What do Iso values in Leapfrog represent:
The indicator interpolant is a useful tool for understanding the distribution of a variable (e.g. grade), when we don't have a clear understanding of the geological parameters driving it. The indicator RBF interpolants allow you to specify a cut-off grade, then assigns either a "0" (for grades below the cut-off) or "1" (for grades above the cut-off) to each sample point within the interpolant model boundary.
Based on the user-defined Iso value, which must be specified between 0 and 1, an isosurface is created around the "1" values, resulting in the generation of Inside and Outside volumes. Small, uneconomic volumes generated by this process can be automatically removed using a volume filter, and a Statistics tab provides detailed statistics on how the model overlaps with other data in the project.
Once the volume has been created, it can be used as a boundary or domain within which further processing can be carried out. In addition to the use cases mentioned in the introduction, the indicator RBF interpolant can be a very useful tool to temper the effects of extreme high-grade samples combined with sparse drilling. Because all of the samples are transformed into 0s or 1s, the resulting solid that is produced tends to be more conservative, with fewer 'blow-outs'.
What does the Iso value represent?
Iso values for indicator RBF interpolants are probability values that are restricted to between 0 and 1.
An iso value shell of 0.3 represents the volume for which:
- There is a ≥ 0.3 (=30%) probability that any point (of composite support) inside the resulting modelled volume will be ≥ the specified cut-off value.
-
There is a > 0.7 (=70%) probability that any point (of composite support) outside of the resulting modelled volume will be < the specified cut-off value.
An iso value shell of 0.5 represents the volume for which: -
There is a ≥ 0.5 (=50%) probability that any point (of composite support) inside the resulting modelled volume will be ≥ the specified cut-off value.
-
There is a > 0.5 (=50%) probability that any point (of composite support) outside of the resulting modelled volume will be < the specified cut-off value.
An iso value shell of 0.7 represents the volume for which:
There is a ≥ 0.7 (=70%) probability that any point (of composite support) inside the resulting modelled volume will be ≥ the specified cut-off value.
- There is a > 0.3 (=30%) probability that any point (of composite support) outside of the resulting modelled volume will be < the specified cut-off value. A low iso value (0.1-0.3) will create a more “inflated” shell, whereas a higher iso value (0.7-0.9) will create a tighter, more restricted shell. Using a low iso value can be used to prioritise the tonnage included in the volume, whereas a high iso value will prioritise metal (or other physical properties). The choices made here should generally reflect the proposed mining method - bulk mining methods will be more suited to tonnage prioritisation, while selective mining methods are more suited to prioritising grade. Remember: The interpolant function is continuous and can be evaluated at any point. The iso-surface shell represents this underlying continuous function, but is depended on the surfacing parameters chosen, eg. changing the surface resolution alters the resulting model volumes (Inside and Outside), which, by extension, affects the sample grouping categorisation of the points (at composite support).