The region is underlain by the Coast Plutonic Complex, consist- ing of pre- to post-kinematic quartz diorite to granodiorite batho- liths intruded into Paleozoic to Mesozoic metasedimentary and meta- volcanic rocks. Younger supracrustal assemblages overlying deformed rocks include the (?)Cretaceous Gambier Group and Tertiary Bella Bella Formation volcanic rocks.

Metamorphism of the region ranges from chlorite to sillimanite grade. Sillimanite bearing rocks occur in a broad northwesterly trending zone, more or less parallel to the trend of the Coast Plutonic Complex. The Roscoe Inlet kyanite showing occurs in the sillimanite zone within an enclave of metasedimentary rocks in foliated diorite and granodiorite. Although kyanite is not reported to coexist with sillimanite, the presence of garnet within this zone plus sillimanite suggests high pressure and temperature conditions of metamorphism.