Figure 4

Simplified subseafloor structure of the Hakurei Site, Izena Hole. The subseafloor sulphide body underlies the pumiceous underwater debris flow deposit within hemipelagic sediment and contains at least two hemipelagic sediment layers. The footwall of the sulphide body consists of hydrothermally altered clay with alteration minerals dominated by chlorite + illite ± K-feldspar. A layer of hydrothermally altered clay 10–15 m below the sulphide body contains pyrrhotite-cubanite veins. A deeper cap layer in Hole C9026A appears to confine hot (> 200 °C) hydrothermal fluid. Not to scale. See Supplementary Fig. S11 for more details. Cbn cubanite, Po pyrrhotite.