Accuracy of a bulk sample - is actually the point
Yes...that is the whole point of the math exercise I completed and shared yesterday with the BB
Aggregate all the samples together using the assay results.
The total samples of 258 (149 from drilling and 109 from trenching) aggregate to a bulk sample of 498.06 kg
That bulk sample assays at 3.694 g/t (details posted yesterday). this is the correct math for those 258 samples whether you like it or not.
That bulk sample is 0.0135% of the approximate first stockpile size (my estimate 36,900 t or 36,900,000 kg at a ton being 1000kg approx.). At 0.014%, this aggregate bulk sample is still very small, and I concur with the company on the add of the word "anticipated" as 0.014% is not large enough to be representative.
The company clearly identified that the bulk sample they performed was from the previously completed sampling, and was an aggregate of samples (ie. They did not pull up a 5, 10, 20, or 40 ton truck and take a massively large bulk sample - as this type of bulk sample is very expensive to process in a controlled fashion)
As for 'the nugget effect". The stockpile is previously milled material, and by the assay information provided is "course to very course", and yes, also would include 'nugget effect' throughout the pile....
So, yes there are large g/t values included in my calculations. 8 samples of the 258 grade over 10 g/t. these 8 results equal 2.6% by weight and 3.1% by number of samples (8/258).
The % weight is low (2.6% versus 3.1%) as one of those 8 was a mere 0.51kg grading 18.7 g/t. At 0.51 kg it is significantly smaller than both the mean and median and thus dropped the % by a small amount.
Conclusions
I used all of the assay results provided by the company for both trenching and drilling
this aggregation results in a bulk sample of 498.06kg grading 3.394 g/t gold
2.6% of the samples by weight of this 'aggregate bulk sample' grade higher than 10 g/t
At 498.06 kg, this bulk sample is only 0.0135% of the entire estimated size of the first stockpile, and is IMO, not large enough to be 'representative', but would be correct as 'anticipated'.
I have included the 'outliers', or 'nugget effect' samples, as I believe in aggregate, the stockpile includes nugget effect sporadically throughout - as it is previously milled material from a mine, and with the by weight and by number of samples being at 2.6%-3.1% of the stockpile, I believe that is reasonable nugget effect for previously milled material.
The original stamp mill likely would have had a recovery rate of 60% from the raw ore a century ago, leaving the remainder unrecovered in the stockpile. It would also likely have included milled material from waste, or near waste rock - which is the primary reason we also see low values in assays as well.
The original mine was reportedly producing over an ounce of gold per ton. At 40% unrecovered.
If the mine was producing 34 g/t - or 1.1 o/t @ 40% unrecovered = 0.44oz unrecovered = 13.6g/t gold remaining in the previously milled ore.
You will note that the above 'matches' the company information for the 'anticipated' high grade - thus validating that there is previously milled material in the stockpile.
Hope this helps folks - I know it did for me - especially as I was able to validate the 13.78 g/t and 1.47 g/t recovery rates provided by the company and provided through news release on 'anticipated' values.
It's Friday - enjoy your day and weekend