Note: with the virtual crash of the Rial, Islamic Iran's currency, claiming that sanctions are the cause for this is very premature.
Iran moved hundreds of tons of gold out of other countries and back home to prevent it being frozen and inaccessible.
Buying their needs with gold and oil "barter" instead of an almost worthless Rial currency - where they have lots of both barter items and do not have to set gold or oil's value internationally makes good sense.
The time may come when sanctions cause severe difficulties for Iran but for the moment they are using good business sense and yes, by-pass sanction restrictions. Every country needs oil and "unofficial" transactions, as well as in "faceless" gold leavs llittle or no trail for penalties on the barterers.