Hi, I'm from Argentina. I'd like to help you but it's really very few data. Very hard years to research. Do you think he died in Salta city, or Salta province? which was his job? that could help.
I don't think you'll find obituary, but not imposible. It's possible to ask for a certificate to the province government, but they ask for precisions and in fact it seems the procedure is for locals only.
There are also a couple of companies that can research for you, not free but unexpensive. They are quite good, I used them a couple of times.