RE: News - Silvertip NI 43-101 Bold notes
Glad they have it right this time, doesn't instill confidence in the past work though
Grades were lowered, and contained metals moved from indicated to inferred. Someone should have been fired for this blunder...
Lower Zone: Comparing the 2011 resource estimates in the Silvertip 2011 Technical Report with the Silvertip 2012 Technical Report have the following results: contained metals in the Indicated category were lowered by 15% for silver, 18% for lead and 37% for zinc, and estimated grades were lower by 8% for silver, 10% for lead and 31% for zinc. Contained metals in the Inferred category increased by 146% for silver, 126% for lead and 88% for zinc in comparison to the 2011 resource estimates, however estimated grades were lower by 18% for silver, 24% for lead and 40% for zinc.
The larger overall resource at lower metal grades calculated by Golder is attributed to the many modeling enhancements summarized below: the 2012 estimate may be more conservative than previously reported estimates but is more robust. Actual mining tonnage and grade may be higher than the 2012 estimate if a high level of extraction selectivity can be achieved during the mining process.
Some of the specific differences between the 2011 and 2012 estimates include the following:
- The mineral envelopes were changed from a highly constrained interpretation to a less constrained mineral envelope with a much larger volume that captures many more mineralized samples.
- The LZ domain was changed from multiple lenses to one large geological domain, and does not include the small zone formerly reported in the 2011 Technical Report, as Discovery North.
- The new models used the Datamine UNFOLD process to unfold samples and estimate block grades in unfold space, which automatically adjusts for changes in the orientation of mineralization.
- The block size was increased from 5m x 5m x 1m (X,Y,Z) to 5m x 5m x 3m (X,Y,Z).
- The grade interpolation method was changed from Inverse Distance Squared to Multiple Indicator Kriging (LZ) and Ordinary Kriging (UZ).
- A more robust set of search criteria was defined based on an octant search and a higher minimum and maximum number of samples.
- Samples in the 2012 LZ model were weighted by specific gravity.
- The classified resources were based on continuous areas of drill spacing that are less than (Indicated) or greater than (Inferred) 20m.
Metal prices have increased over the 2011 model and new reporting cut-offs were chosen to better account for mining costs.
Upper Zone: In comparison to the 2011 resource estimates in the 2011 Technical Report, contained metals in the 2012 Indicated Resource in the Silvertip 2012 Technical Report was reduced to zero, while contained metals in the 2012 Inferred Resource decreased by 34% for silver, 47% for lead and 14% for zinc. Estimated grades were lower by 85% for silver, 88% for lead and 81% for zinc. Reasons for changes to the Upper Zone are similar to the Lower Zone as stated above.