roh, you have to look at WHY the AUD is tumbling. It is because the mining boom is over, and there will be/is less demand for commodities, and thus less demand for AUD with which to buy them.
Which is one reason why M&G are getting out of all their miners.
I'm sure you are aware of the two year copper chart, with Cu falling from US$4.40/lb to US$3.1, or the six month chart form US$3.80. Sure, a weakening AUD helps to offset the drops, but the trend of the metal is firmly downward.
CDU Price at posting:
$1.64 Sentiment: Sell Disclosure: Not Held