As his last (?) project, Heyerdahl was in the Andes somewhere, investigating a known but obscure site with a bunch of pyramids. Heyerdahl's excavations on Easter Island in the 1950s turned up a statue (shown in "Aku-Aku" I think) that was an early ancestor to the famous statues of that place, and also has affinities to art of Tiahuanaco.
There was a claim that the plaza at Tiahuanaco was built to align with (I think) the sunrise at the equinox, but that the alignment was only valid about 17,000 years ago. That is very poor methodology, obviously, since there is no inscription or carved illustration showing that intent. That's my usual complaint for most archaeoastronomical claims. The site is obviously not 17,000 years old.
Surviving stonework was set without mortar (a common technique in PreColumbian America), but there are also carved channels to bridge across the tops of many of the stones; metal joiners were either pounded in to the holes, or molten metal poured in to fill the channels. The same technique was used here and there in pharaonic Egypt.
I'm pretty sure it was poured. What was the metal, bronze?