Hello,
I was hoping advice could be given on the following problem. We store nickel (eg 0.40 Ni %) and mill recovery (55.45%) in our mine model. From this we calculate a mill recovered nickel (eg 0.22 RecNi %) and store this in the model. All 3 model items are stored to two decimal places. The rounding is to three decimal places (i.e. +/-0.005).
We create ore-cuts based on the tonnes-weighted average of the Mill Recovered Nickel (using an Ore-material classification scheme based off Mill Recovered Nickel).
My problem is given below and highlighted in green. I have assumed tonnage weighting in each row is 1.
Nickel Mill Recovered
Head Recovery Nickel
Grade % (Ni %)
0.53 60 0.3180
0.65 62 0.4030
0.32 20 0.0640
0.8 70 0.5600
0.56 63 0.3528
0.45 55 0.2475
0.58 68 0.3944
Average 0.555714286 56.85714286 0.3342
Average Nickel Head Grade
divided by Average Mill Recovery ====> 0.315963265
It would appear that the averaging of the recovered nickel (0.3342) gives a different result to dividing the average Nickel Head Grade by the Average Mill Recovery (0.315963265). These averages are generated in Microsoft Excel so it doesn't seem to be a rounding error. We believe the first average is wrong and it would appear that the greater the variability of the data set, the greater the difference between the two calculation averages. If possible, would anyone know what is happening here and which is the correct approach.
Thank-you in appreciation.
Craig Allison
MKO Resource Evaluation Geologist
