The question of the need to declare movements of gold/silver in/out of Australia (as well on domestic flights) pops up frequently, most recently on silverstackers. I left the following comment to that forum thread below.
I think we need to distinguish between the security screening and customs functions (international flights only), which have different purposes.
Domestically there are no customs - something to do with the Australian Constitution i think :) So the screening is just for security reasons so I see no reasons why you can't carry as much as you want on a flight within Australia unless the security people think you are going to clobber someone over the head with your PMs.
There possibly is some thing for the security people about looking out for potential criminal activity but I suspect they are just trained to look for anything out of the ordinary, which would account for the request to check what those discs or blobs of metal are in your luggage.
For international flights/customs, there isn't anything in the Migration Act 1958 about gold. In Division 3.1 (Information to be given by arriving persons) of the Migration Regulations 1994 there is nothing about the interpretation of the wording on the passenger card, which says:
"AUD$10,000 or more in Australian or foreign currency equivalent? Note: If a customs or police officer asks, you must report travellers cheques, cheques, money orders or other bearer negotiable instruments of any amount."
Same wording on outgoing declaration:
"Are you taking out of Australia AUD$10,000 or more in Australian or foreign currency equivalent? If answered ‘Yes’ you must complete a Cross Border Movement – Physical Cash (AUD$10,000 or more) Report to present with this card. Note: If a customs or police officer asks, you must report travellers cheques, cheques, money orders or other bearer negotiable instruments of any amount."
The above requirements come from the AUSTRAC Act 2006, Section 53:
"53 Reports about movements of physical currency into or out of Australia
(1) A person commits an offence if:
(i) the person moves physical currency into Australia; or
(ii) the person moves physical currency out of Australia; and
(b) the total amount of the physical currency is not less than $10,000; and
(c) a report in respect of the movement has not been given in accordance with this section."
The definitions section in the AUSTRAC Act 2006 defines physical currency such:
"physical currency means the coin and printed money (whether of Australia or of a foreign country) that: (a) is designated as legal tender; and (b) circulates as, and is customarily used and accepted as, a medium of exchange in the country of issue."
would seem to exclude Perth Mint coins and bars as they don't circulate as money. That is, precious metals are not reportable at all, and face value has no bearing. To back up this view, see this interesting article by the Australian Institute of Criminology where the whole focus is on cash money laundering (includes great examples of how people try to smuggle cash and stats on the number of cash reports). I just don't think money laundering in/out of the country via bullion is a big risk that AUSTRAC are interested in - I mean, it is going to show up on the security scanners so can't actually be smuggled. See the AUSTRAC Typologies page where I can't find anything relating to gold.
FYI, note that moving cash in/out of the country is allowed, you just have to report it, see this Customs PR release:
"A 44-year-old Stirling man was detained for allegedly attempting to export over AUD$182,000 cash out of Australia via Perth International Airport. ... On his Outgoing Passenger Card the man had declared he was not taking over AUD$10,000 in cash out of Australia. ... There is no limit to the amount of currency you can bring in or out of Australia, however, under the Anti-Money Laundering and Counter-Terrorism Financing Act 2006 you must declare amounts of AUD$10,000 or more in Australian currency or foreign equivalent."
However, note that in the article it says that "Customs officers subsequently referred the matter to the Australian Federal Police (AFP) and the large amount of cash has been seized by AFP officers and investigations are continuing." While there is no law against such cash movements (just on not reporting it), keep in mind that the police can seize it if they think something dodgy is going on (proceeds of crime etc).
End result is, in my humble and non-legal advice opinion, while you don't need to report bullion, it will get picked up in the scanners and on the basis that such activity is not normal. Questions will be asked, so good to have proof of ownership so the AFP doesn't have cause to think it is proceeds of crime and want to "investigate" it further.