I didn't think I would see this one again. The Mawson Huts Expedition of 2011/12 was cancelled so when I saw this in my mail box I was a bit puzzled. And more so by the "First Day of Issue" postmarks.
A little bit of internet searching revealed that a team did manage to get through to Cape Denison as part of the AAE Centenary. They came aboard the Aurora Australis and traveled the last 20km by helicopter on 14 Jan 2012. One of the people flown in that day was the postmaster which explains the 14 Jan 2012 postmark on my cover. More to read about the event here.
Why the first day postmark? The iceberg stamps were issued 7 June 2011 and the Cape Denison post office is closed most of the year so 14 Jan 2012 was the earliest this post office could have cancelled these stamps. Hence the first day of issue postmark.