Proton-induced x-ray emission analysis of turquoise artefacts from Salado platform Mound sites in the Tonto Basin of central Arizona

During the Classic period (AD 1280-1450), prehistoric native Americans used turquoise for adornment, pigment and rituals at the Salado Platform Mound communities of the Tonto Basin in central Arizona. These rare, but valued, artefacts were obtained through social and trade connections to settlements and resource zones in adjoining and distant areas. We systematically examine the chemical signatures of turquoise artefacts to assess differences in access to turquoise sources between two large, competing Platform Mound communities (Cline Terrace Mound and Schoolhouse Point Mound) and determine whether they shared the same trade network. PIXE (proton-induced x-ray emission) is used to non-destructively characterize the chemical signatures of the turquoise artefacts; x-ray diffraction is used on a subset of artefacts to precisely identify mineralogical variability within copper-based blue-green minerals. Examples of multiple and mixed phases are further examined. These controlled chemical and mineralogical studies are used to guide the PIXE analysis of the larger dataset and to assess differences in source accessibility between the Cline Terrace and Schoolhouse Point Platform Mounds. Results indicate differential access to turquoise sources, similar to obsidian and decorated ceramics, and further delineate the regional social networks of this prehistoric culture.