There are two ways to look at Schaft Creek:
1. A mine with 7.1B lbs of copper (M+I) and operating costs of $1.15 / lb.
2. A mine with 14B lbs of copper equivalent (M+I) and operating costs of $2.09 / lb.
If you choose to look at the project using Option 2 then you need to use the higher operating costs. A mine with an operating cost of $2.09 / lb will not get built. Therefore, you must look at the project using Option 1 in order for it to be a viable project. The other metals are going towards reducing the operating costs to an economic number. The other metals are not a bonus, they are essential to keeping this project economical.
To make the Las Bambas project comparable to Schaft Creek, you have to look at the buyout as a $2.7B buyout. If I sell a $50K car with $200K in cash in the front seat, this does not mean the car is worth $250K. Similarly, if I sell a $2.7B mine with $3.3B in sunk costs, it does not mean I am getting a $6B mine. You need to account for the sunk capex when you compare the buyout value to Schaft Creek.