Title:

The development of a new geometrical blast fragmentation model and its application to Grade Engineering®

 Category:

Blast Modelling

Author:

David La Rosa

Affiliations:

CRC ORE

Abstract text:

The ability to accurately predict run of mine (ROM) fragmentation is a well-documented, invaluable tool for blast optimisation. In the emerging field of Grade Engineering®, grade by size metal deportment can be induced by differential blasting. It is equally important to know the size distribution of the blasted ore in order to quantify the value of upgrading concentrator feed by screening.

Generally, fragmentation models can be grouped into empirical and mechanistic categories. Empirical models include the common Kuz-Ram model variants, and can be easily implemented in a spreadsheet. Mechanistic models are usually developed by research consortia or explosive companies, requiring significant computing power to deal with the complexities of the explosive detonation processes and rock mass descriptors. Each approach has advantages and disadvantages.

The author has used a modified Kuz-Ram model for some time in mine to mill projects. While the results of the model can usually be calibrated to measurements of the actual ROM particle size distribution, there are limitations to its application, especially in finely structured rock masses. In addition, the output of the model, applies to the entire blast and doesn’t allow for the size distribution of a particular region of a blast to be interrogated. A new fragmentation model has been developed that combines coarse fragments created by radial cracks fracturing a 2D representation of the rock mass structure with fines created around the blast hole to determine the final ROM size distribution.

Conclusions
The new fragmentation model was able to be calibrated against a number of previously audited blasts. The approach allowed for spatially dependent results to be obtained throughout the blast volume which were able to be varied with the strength, structure and grade parameters found in the mines’ block models. Once this confidence was attained, a differential blast study was conducted on an ore body with well understood and characterised grade by size deportment behaviour. The outcomes of this analysis were used to quantify the value proposition that exploiting induced grade deportment would bring.

Recommendations
The outcomes of the study did show significant benefits could be derived by upgrading the ROM using induced deportment. As the mill feed was screened to separate the high grade ore, increased mill throughputs could also be achieved. Further validation work will be required to ensure that the modelling approach is robust enough to be applied to a wide range of scenarios. In addition, the use of standard comminution parameters to estimate the fines size distribution around each blast hole will be incorporated into the modelling framework.

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Cooperative Research Centre Optimising Resource Extraction (CRC ORE)