NI 43-101 Technical report, Surface diamond drilling ... - Iamgold

R a r e E a r t h E l e m e n t E x p l o r a t i o n P r o g r a m M a r c h - 2 0 1 3
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19.1.5 Grade Interpolation
Grade estimation was done using an ordinary kriging method in Gems 6.3.1 software. The
method was applied with a numerical digitation of the 3 x 3 x 3 blocks. The interpolation
threatened a data base of 5 metres equal length composites obtained from the original assays.
The ordinary kriging was completed using a sample search approach as summarized below:
• The first interpolation for each block is calculated with a minimum of 6 and a
maximum of 12 composites within the search ellipse. The ellipse dimension is
limited to 100m x 100m x 100m (Figure 28). There is no maximum number of
samples per drill hole.
• Then, a second interpolation is calculated with a minimum of 2 and a maximum of 12
composites within the search ellipse. The ellipse is less restrictive and has a
dimension of 150m x 150m x150m (Figure 29). Once again, there is no maximum
number of samples per drill hole.
A top value capping is used in both cases. A value of 10% TREO was used for this purpose.
In addition, Gems allow reducing the range of influence of high grade values. A high grade
cut-over of 5% TREO was used. The high grade values are used in the interpolation up to
10% with a range half of the rest of the data. This way, if a cluster of high grade value is
intersected, Gems will generate a high grade zone in the block model. Otherwise, an isolated
high grade value will be discounted more heavily.
The TREO value was the only one interpolated in 2012. It perfectly reflects the global
distribution and the economic value of the REE zone. Each 14 rare earth elements could be
interpolated individually for comparison or other specific purpose. These elements could be
estimated using the same methodology as described for TREO.
Table 24 shows the complete search parametres, Appendix 1 the main section view and plan
view of the 2012 block model TREO grade interpolation.
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