A new approach to determining the geological provenance of turquoise artifacts using hydrogen and copper stable isotopes

The procurement and exchange of turquoise was an important part of pre-Columbian American Southwest and Mesoamerican cultures. For decades, archaeologists have sought to chemically characterize turquoise deposits. However, these studies have met with limited success due to intrinsic limitations of trace element analyses of compositionally complex minerals such as turquoise. Here, we show how isotopic ratios of hydrogen (2H/1H) and copper (65Cu/63Cu), measured by a secondary ion mass spectrometer, can be used to characterize turquoise deposits, thus allowing us to link turquoise artifacts to prehistoric mines hundreds of kilometers from archaeological sites. Twelve turquoise mines were analyzed and the technique was successful in defining 10 turquoise provenance regions with the clustering of three mines from one mining district. We also analyzed a number of samples from the Sleeping Beauty turquoise mine to determine the variation in H and Cu isotope ratios at the deposit-scale. Our results show that the Cu and H isotopic composition within this mine are relatively homogenous. Thirteen of 17 artifacts analyzed from several sites in northwestern New Mexico fell into several distribution patterns of characterized source regions, suggesting that turquoise was obtained from several source areas and moved over long distances.