I was visiting my aunt out of town many years ago, and started reading a library book one of my cousins had checked out. We went back home, so I never got to finish the book. I read it in the late 60's to early 70's, it could have been written some time before that.

It was about an archaeologist/scientist that was studying pre-Columbus Native Americans like the Incas, Aztecs, or a similar tribe. There was at least one young person with him, a young woman or older girl (college student?). They were looking for a sacrificial well where gold was sacrificed (possibly people too). I think they were looking for it on small uninhabited islands.

There was also a greedy bad guy looking for it because of the gold. The girl found a well in a cave she thought was the one they were looking for. No one had found it before because they were all looking above ground. The bad guy showed up (maybe with goons?), captured them, and threatened to hurt/kill them if they didn't tell him where the well was. I think it was before the girl even mentioned the well she found to the scientist. I had to quit reading around that point.

I have no idea of the author or title, if anybody knows, I would be grateful for any help with this.