What is the mechanism for the oxidation of Cu(I) by ammonium nitrate?

I can't seem to find any resource online that describes the arrow pushing mechanism behind the oxidation of Cu(I) by ammonium nitrate in acid.


Does a radical oxygen form? Or does it require both copper atoms simultaneously? I've drawn out a few possible mechanisms, but all seem plausible...


Here is the mechanistic formula: 


$$\ce{2Cu(I) + 2H+ + NH4NO3 -> 2Cu(II) + H2O + NH4NO2 -> 2Cu(II) + N2 + 3H2O}$$


