• Quadir, Zakaria
• Binns, Ray
• Schoneveld, Louise

Abstract

Seafloor hydrothermal chimneys from back-arc basins are important hosts for metals, e.g. Cu, Zn, Pb, Ag and Au, and bear potential for deep-sea mining. A solid understanding of the distribution of metals requires an appreciation of detailed mineralogy and chimney growth histories. This study reports the first submicron scale investigation of mineralogy and microstructures of a chalcopyrite-lined conduit wall of a multi-conduit hydrothermal chimney from the PACMANUS hydrothermal field (eastern Manus basin, Papua New Guinea). New observations reveal that the conduits are dominated by thick chalcopyrite walls with bi-directional growth (towards and away from the conduit) which is bounded by a thin layer dominated by fine-grained (< 1 μm) sphalerite. Clustered pyrite grows outwards from the sphalerite substrate. The mineralogy reflects a detailed process of the early growth of chimneys during the initial mixing between hydrothermal fluids and seawater. Late-stage sphalerite and barite then overgrew the conduits at the waning stage. Four types of native gold are observed within the conduit walls, three of which are associated with the sphalerite-rich layer and have not previously been reported. Native gold is interpreted to have precipitated from various mechanisms. This study bears important potential for searching for native gold in fossil hydrothermal chimneys.

Topics

• impedance spectroscopy
• microstructure
• gold