Thresholds
On the Thresholds tab of the form, select the Enable Grade Thresholds check box to enable the configuration of sample grade thresholds.
Select a Method from the drop down and then use the grid to set parameters to apply different sample grade thresholds.
Grade thresholds are useful in the estimation of deposits which contain extreme value outliers in the sample distribution (typically gold and other precious metal deposits) and allow for the separate treatment of those outlier grades, without the application of a top cut, by restricting the estimation range of samples above a nominated threshold to a user-specified proportion of the total data search.
This parameter depends on a combination of grade and distance to the centre of the search neighbourhood. The idea is to adjust the grade value while using the search neighbourhood to limit its spatial reach so that it does not extend too far from its origin.
Method
Choose how high values will be constrained at a specified distance threshold. If sample points lie beyond the Distance and their values exceed the specified Threshold value, they will be clamped or ignored depending on the method chosen:
|
Method |
Description |
|---|---|
|
CLAMP |
Reduce the high value to the Top Cut value for sample points outside the specified Distance. |
|
IGNORE |
Ignore sample points outside the specified Distance. |
Fields
On each row of the grid, select the Grade Field to create a threshold for, specify the Threshold value, and a Distance value. Multiple thresholds for the same attribute or different attributes may be specified.
The Threshold column is used to enter the threshold value for the element in the selected method.
The Distance (%) column is used to indicate the distance from which trimming will be applied - as a percentage of the centroid of the search form. 100% is the full distance from the centroid to the border of the search form.
As an example, a threshold of 3 and a distance (%) of 64, for the CLAMP Method, means that for samples or composites further than 64% (in this case, 64m) from the centroid of the sphere that have a value greater than 3, will be cut when evaluating the content in the block.
Selecting IGNORE from the Method drop down means that the samples will not be included in the evaluation of the block if their value exceeds the specified threshold.
Use the buttons on the local toolbar to Manage the rows in the list.
Grade threshold values and Distance are plotted on a graph to the right of the grid list:
