Going back through the released information, looks like you misinterpreted the following from the August 7 presentation:
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4,445/5,692 = 78% ( closest number I could find to 75% and I'm assuming here you misinterpreted this as quality, whereas it really is just 0.78 carats per tonne recovery )
Gem Quality "rubies" is actually a key distinction from corundum which tends to be in primary deposits.
https://en.wikipedia.org/wiki/Corundum
( although some of the better corundum can be good enough to be "commercial" quality ruby but it will be heavily included and may need heat or other treatment )
This "Gem Quality" is very important for us and it can cover a range of grades (see below), where we will have issues is if we have significant volumes of material below 1.5ct rough size. If the material below these sizes it is harder to achieve a sufficient reserve price for rough.
Note - prices below are 2016 wholesale prices for cut rubies and sourced from the Q3 2016 Mustang quarterly, I have added the blue annotations for indicative rough sizes for associated cut size. I also interpret the green box as "High" quality and the orange as "medium" in the absence of specific definitions. Mustang are developing their own "rough ruby" grading system and we don't have that information available so the below is a convenient alternative supported by pricing.
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