Block modelling in the CIS and alignment with the GKZ

The CIS countries inherited the resource estimate code from the Soviet era that was originally created and is still updated by the Geological Commission for Reserves or GKZ. The official method of the resource estimation is still based on sections and plans.

Now the GKZ body in Russia plans to implement the block modelling approach; however, it faces serious methodological differences.

The main problem is this: the GKZ approach requires an estimate within a hard boundary based on an economic cut-off that excludes any material below the stated cut-off grade. If the boundary includes lower-grade material, the resource figures should be corrected, using the ore-waste coefficient, to exclude any possible dilution in the estimate. In contrast, the international approach uses the mineralisation boundary to define the zone of estimate.

This block modelling approach allows for some dilution, depending on the style of mineralisation, geostatistical characteristics and block size. Comparing the results of the two estimates, using a cut-off grade, reveals this difference: the GKZ approach excludes any possible dilution below the stated cut-off grade, while block modelling allows some dilution in the model.

The current GKZ requires the estimate to be made strictly according to the existing code, using hard boundaries. If block modelling is used, it should compare closely to the polygonal estimate results, but it is seldom possible to achieve results comparable to the sections method. Therefore, to use block modelling following international standards, some GKZ requirements need to be changed.

SRK is part of the group currently working on adopting the block modelling approach in GKZ. The group is trying to explain the main difference in the two methods and to propose the possible solutions and changes required to adopt the block modelling technique. SRK is trying to prevent the usage of a mixed approach when the block model is only used to honor the polygonal method, since this could not provide a reliable and unbiased estimate according to the international approach.

Liubov Egorova: egoroval@srk.ru.com

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