Was Aztec and Mixtec turquoise mined in the American Southwest?

Archaeologists have long suggested that prehispanic states in Mesoamerica acquired turquoise through long-distance exchange with groups living in what is now the American Southwest and adjacent parts of northern Mexico. To test this hypothesis, we use lead and strontium isotopic ratios to investigate the geologic provenance of 43 Mesoamerican turquoise artifacts, including 38 mosaic tiles from offerings within the Sacred Precinct of Tenochtitlan (the Mexica or Aztec capital) and 5 tiles associated with Mixteca-style mosaics currently held by the Smithsonian's National Museum of the American Indian. Most of these artifacts have isotopic signatures that differ from turquoise deposits in the American Southwest, but closely match copper deposits and crustal rocks in Mesoamerica. We thus conclude that turquoise used by the Aztecs and Mixtecs likely derives from Mesoamerican sources and was not acquired through long-distance exchange with the Southwest.