I decided to crunch some numbers after reading through the feasibility study.

The 171M tonnes of waste rock is enough to feed the mill for 3.6 years (assuming it's mineralized). To be conservative, I'm going to round this down to 3 years.

The waste rock is worth $25.13/tonne after recovery. The mine has an operating cost of $13.33/tonne to process ore. However, since this ore has already been mined at a cost of $2.26/tonne, I'm going to use this as a credit to the operating cost and reduce it to $11.07/tonne. Therefore, processing this waste rock at 130,000 tpd will generate $658M in cash flow. To be conservative, I'm going to round this down to $600M per year.

The mine is scheduled is to process the highest grade ore first. It looks like the waste rock should fit into the schedule around Year 10 (assuming it's been mined by this point). Therefore, adding 3 years into the schedule at Year 10 to process the waste rock impacts the economics like so:

NPV 5% improves from $1694M to $2400M

NPV 8% improves from $513M to $927M

NPV 10% improves from $25M to $304M

NPV 12% is still negative at -$137M

IRR improves from 10.1% to 11.3%