The block model provides a three-dimensional, spatial interpretation of the ore body that is fundamental to the mine planning process. Typically, the block model will include the following information:
- Centroid position and block dimensions,
- Interpolated geology, estimation and/or processing domains and rock types,
- Estimated grade and density of the block,
- Geotechnical estimates for mine design, and
- Geometallurgical estimates for processing throughputs and recoveries.
Additional parameters are required for the Grade Engineering block model including:
- The interpolated natural deportment response ranking (required for GE-screening assessments),
- Estimated heterogeneity of blocks or panels at relevant SMUs (required for induced deportment and bulk ore sorting assessments),
- Estimated screening and particle sorting response, and
- Estimated gravity separation response.
These Grade Engineering parameters are combined with blast fragmentation models and selected GE plant settings (screening aperture, ore sorting cut-off grades) to populate the Grade Engineering block model with the proportion of mass and metal reporting to upgrade and downgrade products of GE options. Process modelling and simulations are required to estimate changes to plant throughput for GE-screening options, that alter the PSD of material sent to processing, and estimate changes to processing recoveries based on the increased grade of GE products to the plant. A trade-off exists between the number of GE-options assessed and the computation time required for scheduling and cut-off optimisation. The complexities of GE options for the evaluation of natural and induced deportment and bulk ore sorting are depicted in the image below.
The Grade Engineering block model is combined with GE cost models and economic and financial assumptions to calculate the value of each block if processed via all treatment and storage options. The resultant Grade Engineering economic block model forms the basis for defining the ultimate pit or underground mining shapes. An example of treatment and storage options for a GE operation with a processing plant and heap leach are presented in the picture below. Please note that high-value and barren material mined may bypass Grade Engineering and be sent directly to a treatment or storage destination to yield the greatest possible value for the block.