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 l ead since at least Renaissance times. Detailed field work has led to the re cognition of several mine dumps which differ in size, age, and types (rock waste dumps; jigging and handpicking wastes). In the dumps, the primary sul fides are sphalerite, galena, and pyrite +/- variable amounts of chalcopyri te, pyrrhotite, arsenopyrite, and a wealth of other sulfides and sulfosalts . These minerals are associated with gangue quartz, white micas, chlorite, and carbonates, mostly of the siderite-magnesite and dolomite-ankerite seri es, whereas calcite is scarce. Supergene alteration led to the development of secondary minerals such as goethite, lepidocrocite, pyrolusite, cerussit e, and clay minerals (kaolinite, montmorillonite, and vermiculite). Two mai n types of supergene effects have been observed: (a) development in situ of pseudomorphic replacement of primary minerals, and (b) leaching and dissol ution. Acid generation and metal release are mainly produced by the replace ment of pyrrhotite by iron hydroxides, the partial dissolution of siderite- magnesite carbonates, and the extensive dissolution/replacement of galena a nd sphalerite. Given the scarcity of calcite in the primary assemblage, the most effective attenuators of acidity seem to have been dolomite-ankerite and siderite-magnesite. The mainly unpolluted character of the Bottino wate rs may be explained by a number of concurring factors, including the modera te volume of wastes, their overall coarse sain size, the low abundance of a cid-producing phases (pyrite and pyrrhotite) relative to acid-consuming pha ses such as dolomite-ankerite, and the steep topography.