James, your calculation is correct except it should be...

James, your calculation is correct except it should be 12,859x$855 - the average cost you are using includes Kangaroo Flat production

Yes, I am sure the costs are higher because of lower grade, the question is what grade is sustainable and what average costs are sustainable. The ore reserve is at 6.9g/t which corresponds to the low cost May production so hopefully costs will revert to around $700-750 on average.

Just my opinion
Monty