The commonly seen Argentine Mauser Model 1891 is marked:
'Mauser Modelo Argentino 1891 / Manufactura Loewe, Berlin' in 2 lines on the left recv'r wall.

Argentine Nat'l Crest on the top of the front ring,,often the crest is ground off on import milsurp rifles. This practice even goes back to the good old days of Milsurp imports . Not just anything recent.

The 7.65 Argentine and 7.65 Belgian Mauser cartridges are the same round as far as reloading and commercial ammo is concerned. Likely differences in the countries loading for their forces of course.

The odd Mauser is the Belgian Model 1889 Mauser mfg'd in the 1915/1916 period in the USA by 'Hopkins and Allen/Norwich, Conn'. That is what is proudly roll marked on the front ring.
They made a carbine version as well but fell short of their contract for the Belgian Gov't and H&A went bankrupt.
Very hard to find collectible rifle.
The Belgian Model 1889 looks like the Argentine 1891 with it's 5rd extended straight feed magazine. But the 1889 retains a sheet metal bbl jacket like the older GEW88 Commission rifle had.
All of the rest of the Belgian Model 1889 Mausers were made in Belgium. None were made by Loewe or any other German contractor.
Some will be found marked with a front top ring marking of Birmingham Etat Belge (sp?) Birmingham-Belgian State.
These are rebuilt rifles done during WW1 in England/Birmingham gun district in an area set aside for the Belgian Govt to do this work and with Belgian civilian workers.