Onboard experiment investigating metal leaching of fresh hydrothermal sulfide cores into seawater

• Main Authors: Shigeshi Fuchida, Jun-ichiro Ishibashi, Kazuhiko Shimada, Tatsuo Nozaki, Hidenori Kumagai, Masanobu Kawachi, Yoshitaka Matsushita, Hiroshi Koshikawa
• Format: Article
• Language: English
• Published: BMC 2018-12-01
• Series: Geochemical Transactions
• Subjects: Onboard leaching experiment; Hydrothermal sulfides; Metal contamination; SMS-mining; Marine environmental impacts assessment
• Online Access: http://link.springer.com/article/10.1186/s12932-018-0060-9

Abstract We observed the initial release rate of metals from four fresh (i.e., without long time exposure to the atmosphere) hydrothermal sulfide cores into artificial seawater. The sulfide samples were collected by seafloor drilling from the Okinawa Trough by D/V Chikyu, powdered under inert gas, and immediately subjected to onboard metal-leaching experiments at different temperatures (5 °C and 20 °C), and under different redox conditions (oxic and anoxic), for 1–30 h. Zinc and Pb were preferentially released from sulfide samples containing various metals (i.e., Mn, Fe, Cu, Zn, Cd, and Pb) into seawater. Under oxic experimental conditions, Zn and Pb dissolution rates from two sulfide samples composed mainly of iron disulfide minerals (pyrite and marcasite) were higher than those from two other sulfide samples with abundant sphalerite, galena, and/or silicate minerals. Scanning electron microscopy confirmed that the high metal-releasing sample contained several galvanic couples of iron disulfide with other sulfide minerals, whereas the low metal-releasing sample contained fewer galvanic couples or were coated by a silicate mineral. The experiments overall confirmed that the galvanic effects with iron disulfide minerals greatly induce the initial release of Zn and Pb from hydrothermal sulfides into seawater, especially under warm oxic conditions.