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Monday, April 25, 2016

Making the grade

Exploration companies love to 'expand' the widths of mineralization in their drill-holes.

Here is an example from Royal Nickel’s Beta Hunt “Hand of Faith" (link) where they have released the following results:


Wow, 3.4m at 3.5 ounces/tonne, it looks like it is a very wide, very high grade vein, but if we look closer, we can see that they intersected:

  • 3.4m grading 107.5 g/t Au,
  • Including a narrower zone of 0.8m that returned 455.9 g/t Au

So what the rest of the 2.6m wide zone grade? We can calculate that quite easily. Personally, I prefer to use the Drill Interval calculator (link)
  • width of high grade interval / width of structure
    • 0.8 / 3.4 = 0.235 or the grade multiplication factor
  • average grade of structure - (grade of high grade zone x grade multiplication factor)
    • 107.5 - (455.9 x 0.235) = 0.22 g/t

So we can see that virtually all (99.8%!) of the gold is found within the 80cm wide structure. They have even included a nice photo of the structure.

Here we have a photo of the Hand of Faith zone that was drilled and returned bonanza gold grades. You can clearly see that only a small portion of the structure is mineralized, and the rest of the rock is essentially barren, but that hasn't stopped the company from presenting and advertising the Hand of Faith zone as being a 3.4m wide bonanza vein, whereas in reality it is a very narrow zone, with gold (in areas a lot of gold) found only in a very small part of it.

Unfortunately, this type of reporting is typical among exploration companies, I wish it would stop.