The gold necklace, made nearly 4,000 years ago, was found in a burial site near Lake Titicaca, researchers report in Tuesday's issue of Proceedings of the National Academy of Sciences.
The discovery "was a complete shock," said Mark Aldenderfer, an anthropologist at the University of Arizona.
"It was not expected in the least," he said in a telephone interview. "It's always fun to find something and go, 'Wow, what is that doing here?"'
In the past, it had been assumed that a society needed to be settled to produce agricultural surpluses that can support activities such as making ornamental objects, he explained.
But the people living in this region at the time were still primarily hunter-gatherers, he said. "They were on their way to becoming settled peoples, but they were not quite there yet."
Someone, though, had the time and knowledge to make this ornament, which he speculates is a sign of importance.
"These folks are obtaining this by their effort, accumulating more wealth and using objects for prestige," Aldenderfer said. It says: "Pay attention to me, I'm successful."
There is no evidence at the site that shows how it was made, he said. But it looks like a nugget of native raw gold, which occurs near the area, was pounded flat in a stone mortar and pestle.
Then the gold was probably wrapped around a piece of wood and pounded until it was folded into a tube, he said.
The researchers restrung the necklace, alternating nine small gold tubes with a series of round stones, identified as either greenstone or turquoise, with holes in them that were found in the same grave.
The next oldest gold ornaments found in this hemisphere, also located in Peru but farther north, date to about 600 years later than this necklace, Aldenderfer said.
Scott Raymond, an archaeologist at the University of Calgary, Canada, said the date of the necklace is "remarkably early for that region to have something of that order."
He said he had not previously seen any substantial evidence from that period of the kind of ceremonialism that developed later.
The oldest previously known worked gold was found in highland Peru and dated to about 3,500 years ago, said Raymond, who was not part of the research team.
Heather Lechtman of the Massachusetts Institute of Technology called the design "very interesting for such a very early piece of jewelry."
Lechtman, who was not part of the research team, said it was not surprising that early people used gold because it is available in that area and easy to work.
The research was funded by the U.S. National Science Foundation and the University of Missouri.