Just an excellent breakdown of values 'if' core values can be applied to bulk of ore body. Guess it depends on the type of ore body and the kind of fluctuations to be expected. Since it's all we can know until mining starts we'll have to go with it.
Almost certainly $400 a tonne is very conservative for what Noront has found, even when discounting from current metal values to values that might be expected in 4 or 5 years time. (I think you'll find that even Gold miners when calculating return in future use a per ounce figure way below the current market, ($450 to tops $500 I believe.)
Noront is drilling as fast as they can to prove up tonnage because tonnage will make a mine even if no one else up there finds another deposit. All we can really do is wait.