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.

The Lagoon Bay perlite showing occurs in an area mapped as dominantly foliated granodiorite and paragneiss. On the west side of Fisher Channel, west of the showing, is an area underlain by andesitic volcanic rocks of the Bella Bella Formation. While no volcanic rocks have been mapped in the area of the showing, it is likely that Bella Bella volcanics have been deposited here and that the perlite is derived from these rocks.