The country rocks near this prospect consist mainly of andesitic and basaltic metavolcanic rocks and subordinate flyschlike metasedimentary rocks that are intruded by Cretaceous stocks, sills, and dikes of feldspar-porphyritic granodiorite (Berg and others, 1988). There also are scattered, small, fault-bounded outcrops of Cretaceous ultramafic rocks. The strata were regionally metamorphosed to greenschist-grade phyllite and semischist in Late Cretaceous time, and, near some of the granodiorite contacts, subsequently contact metamorphosed to hornblende hornfels (Brew, 1996, p. 27; Berg and others, 1988, p. 17). The premetamorphic age range of the strata is unknown. Berg and others (1988, p. 17) note that they closely resemble Upper Jurassic to mid-Cretaceous marine flysch and volcanic rocks nearby on Gravina Island.