The effects of sulphide oxidation on the preservation of hydrothermal chimneys from the endeavour segment, Juan de Fuca Ridge

Abstract

Inactive seafloor hydrothermal vents on the seafloor are continuously exposed to oxygen-rich seawater and subjected to oxidative processes. These processes result in mineral breakdown, structural instability, and eventual collapse of the vents. Rates and timing of these processes are largely unconstrained, despite laboratory experiments using combinations of oxidizing agents, environmental conditions, and reacting mineral species. Here, sixteen sulfide- and oxyhydr(oxide)-rich samples were collected from inactive hydrothermal vents along the Endeavour Segment of the Juan de Fuca Ridge to document natural oxidative processes. Petrographic observations indicate preferential oxidation of low rest potential minerals due to the formation of galvanic cells between polymetallic sulfide minerals. Under ambient seawater conditions, sulphide-rich samples demonstrate dual production of iron oxide and oxyhydroxide precipitates produced by abiotic oxidation of sulfide minerals or microbially-mediated precipitation of Fe-oxyhydr(oxide) on exterior surfaces. The results suggest that dissolution of minerals hosting valuable metals like Cu and Zn will occur more rapidly than Fe-bearing minerals. Radiometric ²²⁶Ra/Ba ages were determined from a subset of the collected samples. This subset increases in age with distance from the current spreading center, supporting previous results indicating progressive aging of hydrothermal vents from the axial spreading center.