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Seafloor hydrothermal chimneys from back-arc basins are important hosts for metals such as Cu, Zn, Pb, Ag, and Au. Although the general growth history of chimneys has been well documented, recent studies have revealed that the fine-scale mineralogy can be highly complex and reflects variable physicochemical conditions of formation. This study utilized a novel combination of scanning electron microscopy (SEM)-based electron backscattered difraction (EBSD) and synchrotron X‑ray fluorescence microscopy (SXFM) to uncover the detailed growth processes of multiple chalcopyrite-lined conduits within a modern chalcopyrite-sphalerite chimney from Manus Basin and to assess the controls on native gold precipitation. On the basis of previous studies, the chimney conduit was thought to develop from an initial sulfate-dominated wall, which was subsequently dissolved and replaced by sphalerite and chalcopyrite during gradual mixing of hydrothermal fluids and seawater. During this process, sphalerite was epitaxially overgrown by chalcopyrite. Accretionary growth of chalcopyrite onto this early formed substrate thickened the chimney walls by bi-directional growth inward and outward from the original tube wall, also enclosing the outgrown pyrite cluster. A group of similar conduits with slightly diferent mineral assemblages continued to form in the vicinity of the main conduit during the further fluid mixing process. Four types of distinct native gold-sulfide/ sulfosalt associations were developed during the varying mixing of hydrothermal fluids and seawater. Previously unobserved chains of gold nanoparticles occur at the boundary of early sphalerite and chalcopyrite, distinct from gold observed in massive sphalerite as identified in other studies. These observations provide baseline data in a well-preserved modern system for studies of enrichment mechanisms of native gold in hydrothermal chimneys. Furthermore, native gold is relatively rarely observed in chalcopyrite-lined conduit walls. Our observations imply that: (1) native gold is closely associated with various sulfides/sulfosalts in chalcopyrite-lined conduit walls rather than limited to the association with tennantite, Bi-rich minerals, and bornite as reported previously; and (2) the broad spectrum of gold occurrence in chalcopyrite-line conduits is likely to be determined by the various mixing process between hot hydrothermal fluids with surrounding fluids or seawater. Quantitative modeling of fluid mixing processes is recommended in the future to probe the precise gold deposition stages to eficiently locate gold in modern hydrothermal chimneys. [ABSTRACT FROM AUTHOR]

Unravelling complex microbial activity in modern hydrothermal vents can provide crucial insights into the evolution of ancient life on Earth. It is well established that microorganisms in hydrothermal vents have a significant impact on the cycling of metals and mineral formation. However, the detailed roles played by microorganisms in driving sulfide deposition and cycling of toxic metals, like arsenic (As) and lead (Pb), in high-temperature deep-sea hydrothermal vents remain unknown. The understanding of these mechanisms in extreme environments is of particular importance as As has been postulated as a driver of microbial activities on the early Earth. Here, we present the first geologic evidence of Pb As rich microbial filamentous clusters observed in a modern high-temperature black smoker from the Manus back-arc basin, Papua New Guinea. The clusters occur as net-like structures on the surface of barite and sulfides and are composed of multiple filaments and fine-grained Pb As sulfosalt. Each of the filaments includes an As-Pb-rich sulfosalt core and organic-rich shell structure with elevated carbon, nitrogen and phosphorus. Further synchrotron X-ray absorption near edge structure analysis shows that the clusters contain a mixture of As (II) and As (III). Additionally, those filaments show a close association with realgar (As 4 S 4), by penetrating and dissolving this As-sulfide mineral. We interpret the filaments to be a result of As-related microbial activity in As- and Pb-enriched hydrothermal environments. The findings show possible processes through which extremophiles live in Pb and As-rich environments during chimney growth. In addition, as hydrothermal vents are regarded as modern analogs of ancient volcanogenic massive sulfide deposits, the observed biominerals present the potential to be used as proxies to trace the signatures of early life in ancient geological systems. • Clusters of Pb As sulfosalt-mineralized filaments are found in a modern high temperature hydrothermal vent. • Individual filaments exhibit a unique structure, i.e. a sulfosalt core and an organic-rich shell. • The clusters contain a mixture of As (II) and As (III) and individual filaments penetrate into and dissolve realgar. • Filaments are interpreted to result from As-related microbial activities in As- and Pb-enriched hydrothermal environments. • The observations can be important biosignatures used for tracing early life on Earth. [ABSTRACT FROM AUTHOR]