Pb - isotopes signatures of Italian alabasters: possible application to provenance studies of works of art

Gypsum alabaster is being used to realise works of art since ancient times. In Italy, a number of quarries exploiting Messinian outcrops (in particular in Sicily and Tuscany) are known since the Etruscan period, and the Opificio delle Pietre Dure of Firenze posed the question to geochemically characterise these in order to recognise the provenance area of raw materials. In this paper, a discrimination was attempted using Pb isotopes because of 1) the low residence time of this element in seawater, and 2) the supposed interaction between Tuscan alabasters and hydrothermal fluids of known Pb-isotope composition. Textures indicate that de- and re-hydration reactions after deposition actually affected alabaster involving fluids circulation. Pb-isotope data are scattered (206Pb/204Pb = 17.88-18.71, 208Pb/204Pb = 38.01-38.86, 207Pb/204Pb = 15.58-15.76) suggesting that: 1) fluids did not drive any compositional homogenisation; 2) the isotopic signature is inherited from the evaporitic sedimentary environment and reflects a complex hydrology of the Messinian evaporitic basins; 3) Pb isotopes are an unreliable marker because of the compositional overlap between Tuscan and Sicilian samples. However, at odds with the general trend of their large scattering, the collected data suggest a relative homogeneity at the local scale