The American Southwest, including Arizona and New Mexico, is chock-full of ancient turquoise mines. Mesoamerica, including southern Mexico and Central America, however, have few if any. So researchers long believed that the Aztec empire and Mixtec cultures must have traded with peoples of the Southwest for the culturally important blue-green mineral. But Nicholas St. Fleur at The New York Times reveals a new study now questions that bedrock assumption.

According to the paper, published in the journal Science Advances, between the 1970s and 1990s, archaeologists had put their assumptions to the test though chemical analysis of the Aztec turquoise, which revealed that the turquoise came from the northern mines. In the new study, however, researchers decided to take another look using more modern techniques, analyzing the lead and strontium isotopes in turquoise mosaics from both the Aztec Temple of Mayor in Mexico City as well as Mixteca tiles held by the Smithsonian’s National Museum of the American Indian.

After shaving the edges of the tiles, the researchers dissolved them in acid, then looked for the isotopic ratios, which act as a geographic fingerprint. What they found is that the chemical signatures of the turquoise matched the geology of Mesoamerica, not the Southwest. That suggested that the Aztec and Mixtec got their supplies of the blue-green rock locally, not from distant mines.

Lead author Alyson Thibodeau from Dickinson College in Pennsylvania tells St. Fleur she was working late one night when she got the results. “I saw the number pop up and I’m pretty sure I did a dance around the lab,” she says. “Not only do they have isotopic signatures that are absolutely consistent with the geology of Mesoamerica, but they are completely different from the isotopic signatures of the Southwestern turquoise deposits and artifacts that we have seen so far.”

According to the study, just because archaeologists have not found many turquoise mines in Mesoamerica doesn’t mean they don’t exist. Turquoise often appears near the surface of large copper deposits, created when aluminum in groundwater percolates through the copper. The smaller, shallow, turquoise deposits are easy to mine out, meaning Mesoamerican mines could have been mined into oblivion. Or maybe they just haven’t been found. The samples give the researchers a sense of where the minerals came from even if they can’t pinpoint the mines.

Whatever the case, the finding is a blow to the idea that the Southwest had a strong trading link to Mesoamerican cultures. “The evidence increasingly suggests there was no organized contact between Mesoamericans and the American Southwest,” co-author David Killick, University of Arizona anthropologist, tells St. Fleur.

That doesn’t mean there was no trade, just that it wasn’t as robust as previously thought. “Although the presence of cacao, macaws, etc. in the Southwest provides undeniable evidence of long-distance interaction, the volume of Mesoamerican items in the Southwest is not so great as to require the existence of large-scale exchange networks moving large quantities of materials between the two regions,” Thibodeau tells Kiona N. Smith at Ars Technica. “Although perishable materials like cotton could have been traded south, it is also possible that there was no major flow of trade items from the Southwest to Mesoamerica.”

Next, Thibodeau hopes to study turquoise from the Toltec, Maya and Tarascan cultures to understand more about the Mesoamerican trade in the mineral.