<p> Stable isotope analysis of thirty-five samples from the Northwestern Coast Mountains indicates a complex fluid history related to terrane accretion, metamorphism, and magmatism. The greenschist to amphibolite facies metasedimentary rocks from the Western Metamorphic Belt have variable &delta;D and &delta;¹⁸O values that appear to be in isotopic equilibrium with metamorphic fluids at low water-rock ratio conditions. Carbon isotope values indicate organic rich protoliths. Stable isotope values from the Coast Shear Zone indicate the involvement of both magmatic and meteoric-hydrothermal fluids during deformation, in contrast to meteoric-free fluid systems related to Au-mineralization along strike to the north (Goldfarb et al., 1988). The Coast Mountain Batholith and Central Gneiss Complex have homogeneous &delta;D and &delta;¹⁸O values that indicate magmatic fluids at low water-rock ratio (Magaritz and Taylor, 1976). Further to the east, large amounts of meteoric-hydrothermal fluids circulated through a network of ductile-to-brittle normal faults (Andronicos et al., 2003; Heah, 1990).</p>