It's hard to tell without a picture, but the "Mission" word might mean it was made to honor, or close to the region of the spanish catholic missions that existed in southern Brazil and easter/northern Argentina.
The gaucho style knife is in fact a mediterranean dirk with large propotions (most of the time) that was somehow redesigned to make a better choil, usualy shaped as an "S" in Brazil and with a number of diferent shapes in Argentina. That was made to keep your fingers from being cut by the blade, because those knives were heavily used in the field as camp knives.
The Gaucho people were cowboys mostly and it was a region of constant border conflicts between the Brazilians and Argentines untill the late 1800's. The Argentine gaucho and the Brazilian gaucho have some cultural diferences.
Here what's an Argentine gaucho should look like:
And this is how they wear their knives:
The sash like belt is called "guaiaca" and it's got pockets for money and things to help on the daily work and of course to look good.
Argentine gauchos tend to like larger hats and they also like silverwear (sheaths and coins stitched to their belts for instance) than the Brazilian gauchos.
If I had to guess I would say your knife was forged from spring steel and made by an old countryside blacksmith in a semi-productions fashion. But it can be a nice custom work made by a good craftsman as well, it's hard to tell without an image.
Just as an illustration:
This is a modern made gaucho style knife, all in damascus blade with integral bolster. Sheath and pommel are also damascus. It was made an year ago by Brazilian bladesmith Luciano Dorneles.
Hope all this info help a little.
Jeff Velasco