Ann: Media Interview - New High Grade Copper at Bawdwin, page-20

I'm not sure as to the rigor underpinning the 'suck your finger and hold it in the air' model for deciding a 50% discount is the correct factor to apply to your otherwise rigorous evaluation method. I guess they're required to come up with a target, but spending a long time being absolutely meticulous about an evaluation and then plonking an arbitrary 50% over it seems a bit whimsical.
As suggested, when it gets to the pointy end I expect a lot of that discount will disappear.