Figure 3. Pb isotope composition of sulfide, sediment, and basalt samples for Escanaba Trough and Middle Valley. Escanaba Trough sulfide composition indicates a large contribution of sediment-derived lead to the hydrothermal deposit whereas the Middle Valley sulfides are intermediate between basalt - and sediment-derived fields. Isotopic data are from Zierenberg et al. (1993) and Goodfellow and Franklin (1993).