I. Mascaro

Environmental mineralogy and geochemistry of waste dumps at the Pb(Zn)-Ag Bottino mine, Apuane Alps, Italy

The Bottino mine (Apuane Alps, Tuscany) had been exploited for silver and lead since at least Renaissance times. Detailed field work has led to the recognition of several mine dumps which differ in size, age, and types (rock waste dumps; jigging and handpicking wastes). In the dumps, the primary sulfides are sphalerite, galena, and pyrite ± variable amounts of chalcopyrite, pyrrhotite, arsenopyrite, and a wealth of other sulfides and sulfosalts. These mine- rals are associated with gangue quartz, white micas, chlorite, and carbonates, mostly of the siderite-magnesite and dolomite-ankerite series, whereas calcite is scarce. Supergene alteration led to the development of secondary mine- rals such as goethite, lepidocrocite, pyrolusite, cerussite, and clay minerals (kaolinite, montmorillonite, and vermi- culite). Two main types of supergene effects have been observed: (a) development in situ of pseudomorphic replacement of primary minerals, and (b) leaching and dissolution. Acid generation and metal release are mainly pro- duced by the replacement of pyrrhotite by iron hydroxides, the partial dissolution of siderite-magnesite carbonates, and the extensive dissolution/replacement of galena and sphalerite. Given the scarcity of calcite in the primary assem- blage, the most effective attenuators of acidity seem to have been dolomite-ankerite and siderite-magnesite. The mainly unpolluted character of the Bottino waters may be explained by a number of concurring factors, including the moderate volume of wastes, their overall coarse grain size, the low abundance of acid-producing phases (pyrite and pyrrhotite) relative to acid-consuming phases such as dolomite-ankerite, and the steep topography.

Pb-isotope 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 ( 206 Pb/ 204 Pb = 17.88-18.71, 208 Pb/ 204 Pb = 38.01-38.86, 207 Pb/ 204 Pb = 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.