title: Flow and geochemical modeling of drainage from Tomitaka mine, Miyazaki, Japan.
abstract: The chemistry and flow of water in the abandoned Tomitaka mine of Miyazaki, western Japan were investigated. This mine is located in a non-ferrous metal deposit and acid mine drainage issues from it. The study was undertaken to estimate the quantities of mine drainage that needs to be treated in order to avoid acidification of local rivers, taking into account seasonal variations in rainfall. Numerical models aimed to reproduce observed water levels and fluxes and chemical variations of groundwater and mine drainage. Rock-water interactions that may explain the observed variations in water chemistry are proposed. The results show that: (1) rain water infiltrates into the deeper bedrock through a highly permeable zone formed largely by stopes that are partially filled with spoil from excavations (ore minerals and host rocks); (2) the water becomes acidic (pH from 3 to 4) as dissolved oxygen oxidizes pyrite; (3) along the flow path through the rocks, the redox potential of the water becomes reducing, such that pyrite becomes stable and pH of the mine drainage becomes neutral; and (4) upon leaving the mine, the drainage becomes acidic again due to oxidation of pyrite in the rocks. The present numerical model with considering of the geochemical characteristics can simulate the main variations in groundwater flow and water levels in and around the Tomitaka mine, and apply to the future treatment of the mine drainage.
authors.affiliation: Mitsubishi Materials Corporation, 1-297 Kitabukuro, Omiya, Saitama 330-0835, Japan. Electronic address: kyama@mmc.co.jp.
authors.forename: Kohei
authors.initials: K
authors.lastname: Yamaguchi
authors.affiliation: Mitsubishi Materials Techno Corporation, 1-14-16 Kudankita, Chiyoda-ku, Tokyo 102-8205, Japan; Faculty of Systems Engineering, Wakayama University, 930 Sakaedani, Wakayama 113-0033, Japan.
authors.forename: Shingo
authors.initials: S
authors.lastname: Tomiyama
authors.affiliation: Japan Oil, Gas and Metals National Corporation, 2-10-1 Toranomon, Tokyo 105-0001, Japan.
authors.forename: Hideya
authors.initials: H
authors.lastname: Metugi
authors.affiliation: Faculty of Systems Engineering, Wakayama University, 930 Sakaedani, Wakayama 113-0033, Japan.
authors.forename: Hiroyuki
authors.initials: H
authors.lastname: Ii
authors.affiliation: Graduate School Division of Science and Engineering, University of Toyama, 3190 Gofuku, Toyama 930-8555, Japan.
authors.forename: Akira
authors.initials: A
authors.lastname: Ueda
mesh_terms: D004784:Environmental Monitoring; D060587:Groundwater / Q000032:analysis*; D007564:Japan; D007700:Kinetics; D008906:Mining; D008956:Models, Chemical; D011891:Rain; D014872:Water Movements; D014874:Water Pollutants, Chemical / Q000032:analysis*
chemical_list: D014874:Water Pollutants, Chemical
keywords: Hydrogen isotope; Mine drainage; Oxygen isotope; Rock–water interaction; Water movement