Soft Boundary Grade Estimation in Micromine

In many deposits, geological contacts are not sharp. Grade often transitions gradually across lithological, alteration, or domain boundaries. Using hard boundaries imposes an artificial cutoff that can cause underestimation of grades near the higher-grade side or over-smoothing when grades actually diffuse across domains.

In Micromine, there is a traditional workflow which involves creating a distance field describing how far each sample lies from a contact surface. That distance can then be used to control sample weights, apply distance-based tolerances, or create grade reduction near boundaries.

To compute the distance to a wireframe, navigate to the Wireframe tab, select Calculation, and then choose ‘Distance from Points to Wireframe.’ Select your composite or assay file and the wireframe(s) you are interested in. This distance field can then be used to adjust influence.

Now we can apply the distance field in several ways. You can use the distance field to control which samples are allowed in each search pass by setting distance limits for Pass 1, Pass 2, and Pass 3. Samples closer to the boundary are included early, while samples farther away are only used in later passes or excluded entirely, creating a smooth soft-boundary effect. You can also use the distance field to adjust each sample’s weight so that nearby samples contribute strongly, while samples farther from the boundary are automatically downweighted. You can use distance to define an “influence halo,” where samples are allowed to cross the boundary only up to a specific distance. Within that halo they contribute normally, but beyond it they are completely ignored, giving you controlled soft influence without fully mixing domains.

The second, and likely the best, way to handle soft boundaries is the newly introduced Soft Boundary option within the Grade Estimator. This feature has quickly become a successful enhancement. It makes dealing with gradual boundary transitions across the deposit much easier, more convenient, and far more consistent.

The new option allows Micromine to automatically detect the distance from samples to the domain boundary. It lets you control how the influence of samples gradually decreases as they move farther across the contact. This creates a controlled and realistic soft-boundary transition without needing to manually calculate distance fields or build custom weighting rules.

Compared to the traditional distance-based workflow, the new Soft Boundary option is far simpler and more efficient. It removes the need for manual distance calculations, extra fields, and custom expressions, replacing them with built-in smoothing controls. Instead of scripting or fine-tuning complex rules.

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