December: Comparing new drillhole assay data with an old block model
QUESTION:
I am working on a project which includes a block model and a drillhole database; the drillhole database includes holes (with assays data) that were drilled after the block model was created.
I would like to compare the new drillholes’ assay data with the grades of the block model where the drillhole samples intercept the block model. Can a set of ‘pseudo assay’ results (based on the block model data and with the same sample lengths as in the new drillholes’ assays) be created for holes that did not contribute to the creation of the block model?
The purpose of this exercise would be to see how well the block model has predicted the ore grade and width. Can someone please let me know what tool/function/procedure, if any, I should be using?
ANSWER:
There are a few different ways to approach this question. First, there is a fast approach under Modelling | Block Model Tools | Assign. It is enough to have X Y Z for your assay file and create a new BlockModel_Grade Column to be populated with the Block Model grades.
BM grades will be assigned straight to your interval centroids and you can compare them easily with the assayed grades. Second, you could use either Modelling | 3D Block Estimate | Statistical or use IDW as a nearest neighbor back into the assay interval.
The statistical estimation option averages xyz points within user defined block extents. So no data that is physically outside the block will be averaged. This is a common option for blast holes to block (grades) comparison. One annoyance is you will have to merge based on the xyz centroid from the previous model, I don’t believe you can use an existing model for this function.
Using Modelling | 3D Block Estimate | Inverse Distance Weighting, you could do a nearest neighbor (set max samples to 1, not explicit nearest neighbor option). Hang ups for this approach is that the search size isn’t the same shape as the original block extents (may be a minor concern). You may want to bench composite to make a more reasonable comparison. You will need to generate xyz centroids of assays, then add dummy “_xyz columns so they can be used to be estimated into a pseudo block model. Depending on your block model, using it as source data can take some time to process (if very large), so some sort of filtering or subsetting of the model is recommended to be used it as the composites. One note, this is a favorite aspect of Micromine with users – using block models as composites or assays as blocks. This is another major differentiating factor between Micromine and other mining software solutions, where Micromine has far more flexibility when it comes to this work.
Third, if you have the Wireframing module, then try the following steps: Use Generate Trace to create a string file to represent the hole trace with points at each interval boundary. Use Wireframe | Centreline to Solid, with a circular profile (say 1m in diameter), to create a wireframe for each downhole interval Use Wireframe | Report | Grade Tonnage to calculate grades, from the block model, for each “wireframe” interval. Merge the report file (from Step 3) back into the interval file to compare the results.
Please contact support at nasupport@micromine.com for additional details.
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