Sorry I must be slow this evening.
Say they produce 10,000 pounds of nickel. Under my method they get 10,000 pounds x ($12 x .58) or $69,600. Under your method (if I understand you correctly) BMC gets .58 x 10,000 pounds or 5,800 pounds of nickel and BHP gets the rest. BMC can then sell the 5,800 pounds of nickel at $12 a pound for 5,800 x $12 = $69,600. Same amount. And you are quite correct that the margin they receive per pound of nickel produced if the costs are $6 a pound would be about $1. Now $6 a pound for costs is probably a bit high for the original mine but definitely high for Winner and Deacon with their higher grades (the higher the grade the lower the operating costs per tonne).