What you have is a mate straw. Mate is an infusion of stimulant herbs, including caffeine in a mixture called (collectively) yerba mate. Yessir, this is a big beverage for folks in South America, namely Argentina, Paraguay and neighboring countries.
Mate is served with a metal straw from a shared hollow calabash gourd. The straw is called a "bombilla" and the gourd a "bomba". The straw is traditionally made of silver or contemporarily, nickel silver. Hope this helps.
Well, I had to look it it up, and looks like Cordilleran hit the nail on the head on this one. Never heard of a yerba mate straw. Never had nothing that fancy down here, you just passed the jug . After all, the alcohol in the shine was gonna kill all the germs anyway.[][][]
Many years back I dug a brass plated one, it looked exactly like yours. I thought it was an ice tea spoon. Sold it many moons ago. It's cool to see one again and now I know what it was for. Yerba matte is kinda like tea, so I was close on my guess.