Thanks for the input. I think we may be getting somewhere on this. I hadn't thought about postal stationery (mostly because the perforations through me off that trail...).
Looking closer though, the 'stamp' is perforated 12X12 (not a common gauge for Argentine stamps).
The paper isn't really thick so it wouldn't be from a postal card but a postal envelope is entirely possible.
It is one layer of paper.
A couple of the perforations look too elongated (they should be half circles at the most but some of them appear like ovals) so it is very possible that the perforations were fabricated.
So, now to confirm that this is a 'perforated stamp' fabricated from a postal stationery envelope, I just need to find the appropriate piece of postal stationery. A quick google and eBay
search of Argentine postal stationery didn't pull up anything that matches. Anyone have a Higgins and Gage (or other catalogue) that would identify Argentinian postal envelopes from the 1940s?