In an area of about 1000x600 m east-northeast of Kusk Lake feldspathic sandstones and greywackes of the Mississagi Formation (Huronian Supergroup) are fenitized. Various stages of brecciation, disappearance of quartz, and development of aegirine, riebeckite and alkali feldspar have been recognized and mapped. The most highly evolved rocks are essentially syenitic. Associated igneous rocks do not appear to crop out at the surface. Rock analyses, including trace elements, and microprobe analyses of K-feldspar and magnesioriebeckite have been published.