I think you'll find the reference to costs in USD to allow a...

I think you'll find the reference to costs in USD to allow a direct relationship with the spot/term price. I/O companies do the same thing (generally).

Although you would expect that the mine costs (C1) should be positively affected by a falling AUD and result in a lower cost base.

I haven't read the PFS for a while but there should be a note in there somewhere about what they assumed the AUD would be as it obviously impacts the costs. If you can find that note then you'll know if the current economics have improved or not. If memory serves the AUD was significantly higher at the time, possibly over 90c.

I'll try and find some time to have a look later.