• Binns, Ray
• Grice, Kliti

Abstract

Hydrothermal chimneys are widespread on the seafloor along the mid-ocean ridges and back-arc basins (German et al., 2016) and provide habitat for diverse microbes where early life has been suggested to begin (Holden et al., 2012; Takai et al., 2009). It has been widely recognised that microorganisms play an important role in the formation of minerals and the cycling of metals (Holden et al., 2012; Jennifer Lin et al., 2014; Ver Eecke et al., 2009). Microbial organisms can contribute actively to mineralization when utilising trace elements as energy sources or inactively by releasing trace element as metabolic byproducts that are attached to the cell surface (Holden et al., 2012; Templeton and Knowles, 2009). Most previous studies focus on microbial interaction with common metals, such as Fe and Mn (Ver Eecke et al., 2009) on the surface of chimneys. However, the interaction between microbes and some other toxic elements, like As and Pb, or reaction during chimney growth is poorly understood. This study examines the microbe and trace element distribution in hydrothermal chimneys based on petrographic and SEM observations. Chimney samples were collected from seafloor of PACMANUS area in MANUS basin. Microbial colonisation that consists of nano-scale filaments were observed to have been mineralised to dufrenoysite (Pb2As2S5) (Figure 1), which is the first observation ever, to our knowledge. Pb-rich filaments also occur within sphalerite that contains pyrite and chalcopyrite zonation as an indication of pulses of hydrothermal fluids during the chimney growth (Figure 2). Filaments around chalcopyrite zoning are characterised as galena (PbS) with minor As, which transform to dufrenoysite with the same morphology at the edge of sphalerite or cluster as dendritic structure outside of sphalerite (Figure 3). Two explanations are proposed. All the filaments may be results of microbial activities, which are associated with Pb mineralization, and are produced during pulses of hot hydrothermal fluids during the growth of this chimney. Alternatively, galena is deposited as a result of rapid cooling down of hydrothermal fluids along with the precipitation of sphalerite and chalcopyrite, and then is utilised by microbes to precipitate dufrenoysite at the edge of sphalerite. This study provides a new understanding of the chimney growth process, and documents a remarkable example of extremophile life associated with high-toxicity elements.

Topics

• impedance spectroscopy
• mineral
• surface
• cluster
• scanning electron microscopy
• precipitate
• precipitation
• toxicity
• trace element