Unfortunately I do not have a good estimate for mining costs, my model uses past numbers and the estimates (say guesstimates) have assumed that mining cocts going forward are proportional to the volume of ore input to BHP's processing operations. But there are probably other operational efficiencies that come with size. We'll know a lot more once we see the latest financials, though they always seem to be ramping up something. FNX's cash operating cost per tonne mined is $105 which at a 2 % grade would amount to about $2.31 a pound of nickel and that is for deep underground mining. One would hope that BMC could eventually get down to $2 or less but then we have to add all kinds of other corporate expenses and depreciation and amortization.
As for the 58 %, yes it seems low but remember it is for both concentrating and refining and imbedded in that is some assumed recovery. Many operations have their own concentrators and simply pay for refining.