New insights on chimney growth model and native gold enrichment in modern seafloor hydrothermal chimneys

Summary

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 appreciation of detailed mineralogy and chimney growth histories. This study reports the mineralogy and microstructures of chalcopyrite-lined conduit wall of a multi-conduit hydrothermal chimney from the PACMANUS hydrothermal field (eastern Manus basin, Papua New Guinea). New observations revealed that the conduits are dominated by thick chalcopyrite walls with bi-directional growth (towards and away from the conduit) which are bounded by a thin layer dominated by fine-grained sphalerite. Clustered pyrite grows outwards from the sphalerite substrate. The mineralogy records the early growth stage 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 been reported before. Native gold is interpreted to have precipitated by various mechanisms. This study bears important potential for searching for native gold in fossil hydrothermal chimneys.

• hydrothermal chimneys
• sulphides
• growth history
• native gold enrichment