Provenancing variscite beads: Pico Centeno (Encinasola, Spain) outcrop case study

Abstract

In this study we discuss the exploitation and exchange of variscite at Pico Centeno mining district during the Copper Age. X-ray fluorescence and diffraction (XRF and XRD, respectively) and Fourier transform infrared spectroscopy (FTIR) analyses of the mineral recovered at Pico Centeno mining district provides a baseline mineral signature, which was then compared to other Iberian sources and beads from SW Iberian megalithic tombs. We found that the concentrations of trace elements don not allow establishing provenance of the beads, as traditionally claimed. Instead we found that different proportions of phosphate species, which results in P/Al ratios higher than 1, arose during the genesis of the variscite deposits, modifying the concentrations of PO4 3–, H2PO4 – and HPO4 2–. Thus, the P/Al atomic ratio should be an indication of provenance as it is established during mineral genesis.