Miguel,
You have a small Creole knife, (Cuchillo Criollo) made by the late “La Movediza” factory in Tandil (Prv Buenos Aires) Argentina. The sheath and handle are made from German silver (Alpaca), a cheap substitute for real silver.
Cutlery was imported into Argentina up to WWII, but during the hostilities they were forced to make their own and La Movediza, named after a locally famous rock, was such an enterprise, but which lamentably ceased production in 1963. As such, these blades acquired desirability as collectables, though the famous European brands imported earlier, remain the most sought after.
Cheers
Chris
PS For the rock, see
https://en.wikipedia.org/wiki/Piedra_Movediza