The additional cost of transporting ore from PB to AN will be...

The additional cost of transporting ore from PB to AN will be somewhere between 10c and 20c per Lb.
With the copper price as low as it is, from a financial view point, it makes no sense to transport ore 60km to 70km. It's not that PB is going to earn AVB any extra dollars while they wait for an upturn in the copper price. In fact PB will be taking some production off AN.

Every Lb of copper taken out of PB to go to AN is one less Lb that could be making more money when the copper price is higher and AVB has a plant at PB.

Apart from the if and when, more importantly we don't know for how long they intend to cart from PB to AN if the copper price stays low or what if the copper price goes higher or lower than it is now.

Sure, this prelim work will give AVB a head start on PB when the decision to build a mine plant is made but can't they instead start the mining while the plant takes 18 months or more to build?

Sorry for the down ramp but no one here seems to be considering pros and cons of this latest idea.