Excellent question Ike.... rule of thumb is that wages and other A$ consumables is about 30-40%..... some costs are priced in A$ but are influenced by the U$....ie: fuel.
In real terms the difference between a 10% movement in the AUD:USD exchange rate is around 3-4% in operating costs....therefore if the US$ moved against you by 10% it would cost you about 6% in profit margin....roughly.
Conversely if the A$ dropped against the US$ there would be a like benefit...again roughly.
If you are doing back of envelopes for the australian mining industry I have found that about 40% of costs are not influenecd by the exchange rate... all else is.
Hope this helps,
Regards, Tony.
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