What Are These Spots Caused By...?

Those lumps on the surface are caused by pitting in the face of the die.
Which begs the next question:
'How did the die come to be pitted?'

I can guess two causes:
1.) rust spots on the dieface,
2.) hard contaminant particles sticking to the die face, causing damage before being disloged.

Can anybody else come up with other possible causes, and perhaps give reasons?

Could there be a possible problem with the the planchet that has caused blistering after being struck? (I think this one is a long shot).

DBM: I know that the Royal Australian Mint chrome plates their dies to extend die life. I can't see a date on the coin from the picture. For how many years has the RCM been plating it's dies for?

(Date noted as 2002.)

I think secoinedchance is correct. There is all kinds of green corrision on the coin which suggest water damage.