minerals Article Medieval Pb (Cu-Ag) Smelting in the Colline Metallifere District (Tuscany, Italy): Slag Heterogeneity as a Tracer of Ore Provenance and Technological Process Laura Chiarantini 1,* , Marco Benvenuti 2 , Giovanna Bianchi 3, Luisa Dallai 3, Vanessa Volpi 3,4 and Rosarosa Manca 2 1 Centro di Microscopia Elettronica e Microanalisi, Università di Firenze, Via. G. Capponi 3r, 50121 Florence, Italy 2 Dipartimento di Scienze della Terra, Università di Firenze, Via G. La Pira 4, 50121 Firenze, Italy; m.benvenuti@unifi.it (M.B.); rosarosa.manca@unifi.it (R.M.) 3 Dipartimento di Scienze Storiche e dei Beni Culturali, Università di Siena, Via Roma 56, 53100 Siena, Italy;
[email protected] (G.B.);
[email protected] (L.D.);
[email protected] (V.V.) 4 Dipartimento di Biotecnologie, Chimica e Farmacia, Università di Siena, Via A. Moro 2, 53100 Siena, Italy * Correspondence: laura.chiarantini@unifi.it; Tel.: +39-055-2757792 Abstract: Archaeological investigations of the Colline Metallifere district (Southern Tuscany, Italy) have highlighted several Medieval sites located close to the main Cu-Pb-Fe (Ag) ore occurrences. This study is focused on the investigation of late-medieval slags from Cugnano and Montieri sites using both geochemical and mineralogical methods to understand slag heterogeneities as result of ore differences and technological processes. Matte-rich slags present in both sites (with abundant matte ± speiss and frequent relict phases) represent waste products related to primary sulphide ore smelting to obtain a raw lead bullion. The distribution of slags between the Ca-rich or Fe-rich dominant composition, and the consequent mineralogy, are tracers of the different ore–gangue Citation: Chiarantini, L.; Benvenuti, M.; Bianchi, G.; Dallai, L.; Volpi, V.; association that occurred in the two sites.